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THE UNIVERSITY OF QUEENSLAND
Affordable Tooling for Mid-Volume Manufacturing
Student Name: Marlunn Eric ODUCAYEN Course Code: MECH4501 Supervisor: Dr. Gui WANG Document Name: FINAL Report Submission date: 1 JUNE 2018
i
ACKNOWLDEGMENTS
I would like to acknowledge the following people who helped me along with the project:
First and foremost to Dr Gui Wang for giving me the opportunity to work on this thesis topic,
for helping me shape the project and allowing me to enjoy working on CAD software.
And to the UQ Faculty Workshop Group, especially towards Mr Blair Knight, the faculty’s
toolmaker, who helped share his deep and wide knowledge of toolmaking to me.
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THESIS: FINAL REPORT Marlunn Oducayen
TOPIC:
Affordable Tooling for Mid-Volume Manufacturing
Abstract Permanent mold casting is a manufacturing technique used for high production runs where
its mold can last up to 100,000 plus castings. Making molds to be used for permanent mold
casting, via traditional tooling methods, is a labor intensive and expensive process (because
of the long machining hours) and is only economical if they are to be used for production
volumes that range from 10,000 to 100,000 castings, which make them unsuitable for mid-
volume production runs, which are in the range of 1000 to 10,000 castings. Additive
manufacturing such as 3D printing technology offers a great alternative to traditional tooling
methods as it may offer a faster, less labor intensive and affordable solution for creating
molds. This study compares conventional tooling methods against a proposed alternative
solution - machining near net shape casts of molds made from 3D printed sand molds to -
check which method will be cost effective in making molds for mid-volume production runs.
Tooling path simulations will be used to help determine this.
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TABLE OF CONTENTS
ACKNOWLDEGMENTS ................................................................................................. i
Abstract........................................................................................................................... ii
TABLE OF CONTENTS ................................................................................................. iii
LIST OF TABLES ........................................................................................................... vi
LIST OF FIGURES ........................................................................................................ vi
LIST OF EQUATIONS .................................................................................................. vii
1.0 TOPIC INTRODUCTION ..................................................................................... 1
2.0 GOALS OF THE PROJECT .................................................................................. 1
3.0 LITERATURE REVIEW ....................................................................................... 1
3.1 Permanent Mold Casting Process and Tool Steels: Background ................................ 1
3.2 Permanent Mold Casting background ..................................................................... 2
3.2.1 Permanent mold casting process ......................................................................... 2
3.2.2 Tool Steels: Background ...................................................................................... 3
3.2.3 Hot-Working group (H-Group) ........................................................................... 4
3.2.4 Conventional Mold Materials for Permanent mold casting ................................ 5
3.2.4.1 Typical mold manufacturing from tool steel .................................................... 5
3.3 Manufacturing with sand ............................................................................................ 6
3.3.1 Sand Casting Process: A background .................................................................. 6
3.3.2 Sand Casting Process ........................................................................................... 6
3.3.3 Sand Cast molds ................................................................................................... 7
3.3.3.1 Making the Sand Mold ..................................................................................... 7
3.3.3.2 Sand types ..................................................................................................... 8
3.4 Mid-Volume Manufacturing – An Alternative ............................................................ 9
3.4.1 Additive manufacturing ....................................................................................... 9
3.4.1.1 Three-dimensional printing: Voxeljet’s Sand Printer – VX1000 .................. 10
3.4.1.1.1 Technology Overview ................................................................................ 10
3.4.1.1.2 Applications to casting: Process in making molds .................................... 11
3.5 Mold Manufacturing: Costing principles .................................................................. 12
3.5.1 Costing and Economics ...................................................................................... 12
3.5.1.1 Terms ............................................................................................................. 12
3.6 Machining: Background ............................................................................................ 13
3.6.1 CNC Machining: Milling .................................................................................... 13
3.6.2 Tooling: Tools used in CNC Milling ................................................................... 13
3.6.2.1 Tool Materials ................................................................................................ 13
3.6.2.2 Tool Geometry: End Mill Types.................................................................. 14
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3.6.2.3 Tool Geometry: Flutes ................................................................................ 14
3.6.3 Tool Parameters ................................................................................................. 15
3.6.3.1 Cutting Speed ................................................................................................. 15
3.6.3.2 Spindle Speed ............................................................................................. 16
3.6.3.3 Feed rate and Feed per Tooth (Chipload) .................................................. 16
3.6.3.4 Recommended Speeds and Feeds for HSS and Carbide Tools .................. 17
4.0 KNOWLEDGE GAP ........................................................................................... 18
4.1 Work relating to knowledge gap ............................................................................... 18
5.0 METHODOLOGY ............................................................................................... 18
5.1 Method: Conducting the Project ............................................................................... 18
5.2 Project Scope and Assumptions and Note ................................................................20
5.3 Generic Cost Model ................................................................................................... 21
5.3.1 Scope, assumptions and limitations .................................................................. 21
5.3.2 Parameters Used ................................................................................................ 21
5.3.2.1 Labor Costs ..................................................................................................... 22
5.3.2.1.1 General Labor: Toolmaker Role ............................................................... 22
5.3.2.2 Raw Material Characteristics ..................................................................... 23
5.3.2.3 Manufacturing Tooling ............................................................................... 23
5.3.3 Parameter Relations in the Spreadsheet ........................................................... 24
5.4 Parts evaluated for the project .................................................................................. 25
5.4.1 Part description.................................................................................................. 25
5.4.1.1 Grate and Grate Mold Components ............................................................... 26
5.4.1.2 Leg and Leg Mold Components ..................................................................... 28
5.4.1.2.1 Sand Molds to be printed in Voxeljet 3D Sand printer ............................ 29
5.5 CAD/CAM Approach: Tooling path generation ........................................................ 32
5.5.1 Grate Mold: CAM Workspace ............................................................................ 32
5.5.2 Leg Mold: CAM Workspace ............................................................................... 35
5.5.2.1 Conventional Manufacturing for Leg Mold components ............................... 35
5.5.2.2 Tool Path files for Leg Mold components casted from printed sand molds .. 37
5.5.2.3 Note on Leg sliders ........................................................................................ 40
5.6 Raw Material Costs .................................................................................................. 40
6.0 RESULTS ............................................................................................................ 41
6.1 Tool Parameters for machining path simulation ...................................................... 41
6.1.1 Tool Parameters for H13 tool Steel ....................................................................... 41
6.1.2 Tool Parameter for Cast Iron ............................................................................. 42
6.2 Output of Tool Path setups ....................................................................................... 42
6.2.1 Expected Machining times................................................................................. 42
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6.2.1.1 Grate Mold Components: Expected machining times ................................... 43
6.2.1.2 Leg Mold Components: Expected machining times ...................................... 44
6.2.1.2.1 Conventional Mold Manufacturing method ............................................ 44
6.2.1.2.2 Machining time via machining Mold components from Sand molds ..... 44
6.2.2 Estimated Machine Hire Costs vs Tool Material ............................................... 45
6.3 COST ESTIMATES .................................................................................................... 45
6.3.1 Part Cost Estimates ............................................................................................ 45
6.3.2 Grate Mold Components .................................................................................... 46
6.3.3 Leg Mold Components ....................................................................................... 47
6.4 Production Run Cost Estimates ................................................................................ 49
6.4.1 Grate Mold Components .................................................................................... 49
6.4.2 Leg Mold Components ....................................................................................... 52
7.0 DISCUSSION ..................................................................................................... 54
7.1 Tool Parameters calculated in 6.1.1 and 6.1.2 ........................................................... 54
7.2 Expected Machining times calculated in 6.2 ............................................................ 54
7.2.1 Expected machining times for Grate Mold components ................................... 54
7.2.2 Expected machining times for Leg Mold components ...................................... 55
7.2.2.1 Expected machining time from conventional mold manufacturing technique
55
7.2.2.2 Expected machining time from near net shape casts from sand molds ........ 55
7.3 Machining cost estimates versus tool material (Figure 27) ...................................... 56
7.4 Part cost estimates (Table 23) ................................................................................... 56
7.5 Mold Cost Estimates ................................................................................................. 56
7.5.1 Grate Mold Components .................................................................................... 56
7.5.2 Leg Mold components ....................................................................................... 57
7.6 Production run cost estimates .................................................................................. 57
7.6.1 Grate part and mold components (Figure 31) ................................................... 57
7.6.2 Leg part and mold components (Figure 32) ...................................................... 58
8.0 CONCLUSIONS AND RECOMMENDATIONS ................................................. 58
8.1 Conclusions ............................................................................................................... 58
8.2 Recommendations .................................................................................................... 59
REFERENCES ..............................................................................................................60
APPENDIX ................................................................................................................... 64
A1: COST MODEL SPREADSHEET USED IN PROJECT ................................................... 64
A2: CAM TOOL PATH CUTTING SIMULATION OUTPUT ................................................ 71
A3: PERMANENT MOLD CASTING .................................................................................. 80
A4: SAND CASTING ............................................................................................................ 81
A5: VOXELJET VX1000 SAND PRINTER SETUP ............................................................. 82
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LIST OF TABLES
Table 1: Tool steel codes and their composition attributes ....................................................... 4 Table 2: Alloying Constituents of H13 tool steel ........................................................................ 5 Table 3: Family of H-Grade tool steel and composition type .................................................... 5 Table 4: HSS - FEED PER TOOTH (ROUGHING AND FINISHING). Courtesy of Conical
Cutting tools (2017). (Surface Feet per Minute is SFM) .......................................................... 17 Table 5: Carbide - Recommended Feeds and Speeds. Courtesy of Morse Cutting Tools (2011)
.................................................................................................................................................. 17 Table 6: Description of relations between parameters and cost inputs .................................. 24 Table 7: Grate Specifications ................................................................................................... 26 Table 8: Specifications for the Fixed and Moving Die from Figure 9 ...................................... 27 Table 9: Leg Specifications ...................................................................................................... 28 Table 10: Specifications for Fixed and Moving Die and Sliders of Leg mold .......................... 29 Table 11: Total milling operations for the Fixed Die ................................................................ 34 Table 12: Total milling operations for the Moving Die ............................................................ 35 Table 13: Total milling operations for the Fixed Die ............................................................... 36 Table 14: Total milling operations for the Moving Die ............................................................ 37 Table 15: Total milling operations for the Fixed Die (Machining from near net shape) ......... 38 Table 16: Total milling operations for the Moving Die (Machining form near net shape) ..... 39 Table 17: Price per kg of Raw materials for components used in project. Courtesy of (CES
EduPack 2018) ........................................................................................................................ 40 Table 18: Tool Parameters for HSS and Carbide tools for machining H13 Tool Steel ............ 41 Table 19: Tool parameters for HSS and Carbide tools for machining Cast Iron ..................... 42 Table 20: Expected machining times for the Grate Mold. Varying tool material and mold
material. ................................................................................................................................... 43 Table 21: Expected machining times for the Leg Mold. Varying mold material. .................... 44 Table 22:Expected CNC mill machining times for the Leg Mold components casted from
sand molds. .............................................................................................................................. 44 Table 23: Cost estimates for casting Grate and Leg parts for each cast .................................. 45
LIST OF FIGURES
Figure 1: Diagram of components of sand mold ........................................................................ 8 Figure 2: Layer of powdered material spread on powder bed. (Voxeljet, 2016) ..................... 10 Figure 3: Binder printed on layer of powdered material. Binder prints the part geometry.
(Voxeljet, 2016) ......................................................................................................................... 11 Figure 4: Diagram of flutes on an end mill. Photo Courtesy: (Harvey Performance, 2017) ... 15 Figure 5: Increasing cutting speeds based on general workpiece hardness, Courtesy of
(Visarak, n.d.) .......................................................................................................................... 15 Figure 6: Increasing cutting speed based on tool material hardness. Courtesy of (Visarak,
n.d.) .......................................................................................................................................... 16 Figure 7: Grate and Leg Assembly ........................................................................................... 25 Figure 8: Provided CAD Geometry of Grate (Rendered) ......................................................... 26 Figure 9: Mold Geometry as shown. (a) is called the Fixed Die, (b) is called the Moving Die 26 Figure 10: (a) Exploded view of mold assembly with mesh (bottom view), (b) Exploded view
of mold assembly (top view), (c) Mold assembly enclosed ...................................................... 27 Figure 11: Provided Leg part CAD geometry ........................................................................... 28 Figure 12: Mold Geometry for Leg. (a) is the Moving Die (b) is the Fixed Die and (c) is called
the Slider. A pair of Sliders are present for the mold for the legs. .......................................... 28
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Figure 13: Leg Mold assembly ................................................................................................. 29 Figure 14: Assembly of Cope and Drag of 3D Printed sand molds ..........................................30 Figure 15: Exploded View of Sand Molds showing Drag Pattern ............................................30 Figure 16: Exploded View of Sand molds showing Cope Pattern ............................................30 Figure 17: Assembly of Cope and Drag of 3D Printed sand molds .......................................... 31 Figure 18: Exploded View of Sand molds showing Drag Pattern ............................................ 31 Figure 19: Exploded View of Sand molds showing Cope Pattern ............................................ 31 Figure 20: Section view showing a sample of offset present in the sand molds ..................... 32 Figure 21: Workspace illustrating the milling operations done for the Fixed Die. (a) the
workspace for the 1st set of operations on the mold cavity, (b) workspace for second set of
machining operations for the side of the Fixed Die ................................................................. 33 Figure 22: Workspace illustrating the milling operations for the Moving Die ....................... 34 Figure 23: Workspace illustrating the milling operations for the Fixed Die ........................... 35 Figure 24: Workspace illustrating the milling operations for the Moving Die ....................... 36 Figure 25: Workspace illustrating the milling operations for the Fixed Die ........................... 38 Figure 26: Workspace illustrating the milling operations for the Moving Die ....................... 39 Figure 27: Plot comparing Machining cost estimates versus tool material for grate mold ..... 45 Figure 28: Comparing cost estimates for manufacturing Grate mold components between
H13 Tool Steel and Cast Iron blocks ........................................................................................ 46 Figure 29: Comparing cost estimates for manufacturing Leg Mold components between H13
Tool Steel and Cast Iron blocks ............................................................................................... 47 Figure 30: Cost comparisons for Leg Mold components - Conventional machining from tool
steel and cast iron blocks versus machining from near net shape via sand molds ................. 48 Figure 31: Production run cost comparisons for Grate Mold components. Comparing cost per
unit between manufacturing mold components from H13 tool steel and cast iron blocks ..... 50 Figure 32:Production run cost comparisons for Leg Mold components. Comparing cost per
unit between manufacturing mold components from H13 tool steel, cast iron blocks and
machining from a near net shape cast from 3D printed sand molds ...................................... 52
LIST OF EQUATIONS
Equation 1: Total costs equation .............................................................................................. 12 Equation 2: Spindle speed equation ........................................................................................ 16 Equation 3: Feed rate equation ............................................................................................... 16
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1.0 TOPIC INTRODUCTION
The context of the thesis topic is described below:
Permanent mold casting is a metal casting process that employs reusable molds (also known
as permanent molds) usually made from tool steel or cast iron. It is often an economical
option for producing 10,000 to 100,000 parts due to economies of scale, in which the high
tooling costs are spread out over more parts. On the other hand, these high tooling costs are
a major limitation for production runs ranging from 1,000 to 10,000 parts, which is
normally the number required for military vehicle production. The high tooling costs are
attributed to the intense labor required for casting the mold block and long machine hours to
make the mold cavities. Additive manufacturing such as 3D printing technology offers a
great alternative to the traditional tooling methods as it may offer a faster, more affordable
and less labor-intensive tool manufacturing process.
With this context description, the project’s aim is to perform a benchmark study on the
viability in which molds are made. This benchmark study looks to compare an alternative
technique from the additive manufacturing field (using a 3D sand printer) to manufacture
molds, against conventional mold manufacturing techniques to see which will have better
costs for mid-volume production runs. Thus, factors such as machining time, tooling and
labor costs are important parameters that will be used for comparing all mold manufacturing
processes. The mold manufacturing techniques that are being investigated and compared for
the project are machining down blocks of H13 tool steel and sand cast steel (conventional
techniques) versus using 3D printed sand molds that achieve a near net shape cast for the die
blocks.
To note, this thesis topic is a part of an industry project.
2.0 GOALS OF THE PROJECT
The goals for the project are:
- To generate a generic cost model that can be used to compare all mold manufacturing
technologies investigated for the project. This cost model will contain a breakdown of
important parameters, where the price of each parameter serves as the input to the
model.
- To show that the alternative mold manufacturing techniques – using additive
manufacturing via sand printing molds – can be a cost-effective solution for making
molds for part production runs of mid volumes (i.e. part productions in the ranges of
1,000-10,000’s).
3.0 LITERATURE REVIEW
3.1 Permanent Mold Casting Process and Tool Steels:
Background
This section provides a background to the Permanent Mold Casting process which is the
manufacturing technique the molds evaluated in this project will be applied to. It also
provides a background to Tool Steels, as this category of steels generally constitute the molds
for this manufacturing technique.
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3.2 Permanent Mold Casting background
For permanent mold casting, liquid metal is typically poured into a metal mold where it then
solidifies. It comes behind die casting as a popular method to produce aluminum castings
(Campbell, 2012). Due to high tooling costs, permanent mold casting is mainly reserved for
high volume production runs (AFS, 2017). Typical production runs using a permanent mold
can go up to 120,000 castings (Wetzel, 2014). Parts made using this process are relatively
small, more uniform, have more dimensional tolerances compared to sand casting, and
enable great service finishes – from 3.2 to 6.4 μm (CustomPart.net, 2017). Permanent mold
castings also have good mechanical properties because of the fast solidification rates as
compared to sand casting (Campbell, 2012).
Permanent mold casting produces parts for a wide range of applications, from the
automotive and electrical industry to the architectural industry (China Savvy, 2017).
Components casted via this process include, but are not limited to, engine components,
gears, wheels, valve bodies for the electrical industry and electrical housing units (China
Savvy, 2017).
There are several materials that can be casted with permanent mold casting, mainly
aluminum, copper and magnesium (China Savvy, 2017). Other metals can also be used, but
the selection is generally limited to zinc and lead alloys, tin, iron and steel (China Savvy,
2017). Because aluminum alloys are the popular choice for this process, aluminum 300
series are used as they can be work hardened and are alloyed with manganese (China Savvy,
2017). See APPENDIX A3 for list of aluminum alloys popular with permanent mold
casting.
Magnesium alloys can also be made using permanent mold casting. If the magnesium alloy is
suitable for sand casting, then it can be used for permanent mold casting (China Savvy,
2017). A shortlist of magnesium alloys that can use this process includes AM100A, AZ81A,
AZ91C and AZ92A (China Savvy, 2017). What these alloys have in common is that they have
a high composition of aluminum, where the typical composition range is from 7.60% to 10%
(China Savvy, 2017).
Copper alloys are only used, however, to a limited extent. A few copper alloys under yellow
brasses, high conductivity coppers, and engineering alloys can use the permanent mold
casting process (China Savvy, 2017).
3.2.1 Permanent mold casting process
Permanent mold casting is also known as gravity die casting. The name for this process
derives from the normal process in which liquid metal is poured into the mold halves, which
are clamped together, with no external force other than gravity (China Savvy, 2017).
The steps to make parts using Permanent mold casting process are:
1) Mold preparation
The mold is pre-heated up to about 150-260oC (Custompart.net, 2017). Preheating
allows the metal to flow better and reduce defects. A ceramic is applied onto the
cavity (geometric features) to help with part removal and increase the mold’s lifespan
(Custompart.net, 2017). Coatings are inert to avoid reactions to the liquid metal
(Campbell, 2012)
2) Mold Assembly
Molds normally consist of two halves which contain a “negative” of the part’s
geometric features (also called mold cavity). Also, the mold assembly can contain
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cores and can be either reusable if made from steel or iron, or expendable if made
form sand (Custompart.net, 2017). For this step, the cores are placed, and the molds
are clamped shut (Custompart.net, 2017).
3) Pouring
The liquid metal is then poured at a controlled rate from a ladle and into the mold
through the sprue at the top of the mold (CustomPart.net, 2017). This liquid metal
then flows through the runner system to enter the mold cavity (Custompart.net,
2017)
4) Cooling
The metal then cools and solidifies within the mold.
5) Mold opening
After the solidification of the cast, the mold halves are opened and are removed.
6) Trimming
Excess material formed through the runner system and sprue is then cut away.
(Custompart.net, 2017)
See APPENDIX A3 to see the typical setup of permanent mold casting.
3.2.2 Tool Steels: Background
Tool steels are a type of carbon alloy steel (Metal Supermarkets, 2015). They also contain
varying amounts of tungsten, cobalt, vanadium and molybdenum to improve durability and
heat resistance (Metal Supermarkets, 2015). Tool steels are well suited to be made into tools
because of their hardness, abrasion resistance, deflection performance under loads and
ability to keep a cutting edge (maintain shape in the case of molds or dies) at elevated
temperatures (Otai Special Steel, 2016).
Tool steels are categorized into 6 groups (also called grades or classes):
1) Water-hardening
2) Cold-work
3) Shock-resisting
4) High speed
5) Hot-working
6) Special Purpose
(Metal Supermarkets, 2015 and Otai Special Steel, 2016)
Choosing tool steels among these 6 groups depends on a few main factors, namely cost,
working temperatures, surface hardness requirements, shock resistance and required
toughness (Metal Supermarkets, 2017). If there are higher performance requirements, such
as extreme temperatures, high abrasive resistance or excessive loading, then tool steels of
higher alloy content may be required (Metal Supermarkets, 2017). Table 1 provided by
Metal Supermarkets shows the Tool steel code of each group and their corresponding
attributes.
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Table 1: Tool steel codes and their composition attributes
Tool Steel Code
Class Attributes
W Water hardening O Cold worked Oil hardening A Cold worked Air hardening D Cold worked High Carbon, High Chromium S Shock resisting H Hot worked H1 to H19 are Chromium based H Hot worked H20 to H39 are Tungsten based H Hot worked H40 to H59 are Molybdenum based M High Speed Molybdenum based T High Speed Tungsten based Tool Steel Code
Class Attributes
P Plastic mold L Special Purpose Low Alloy F Special Purpose Carbon / Tungsten based
(Table: Metal Supermarkets, 2017)
3.2.3 Hot-Working group (H-Group)
H-Group tool steels were made to maintain their strength and hardness while exposed to
elevated temperatures for a prolonged duration (Otai Special Steel, 2016). This category of
tool steels has low carbon content and moderately high alloys (Metal Supermarkets, 2017).
Important characteristics for H-group tool steels are good hardness under hot environments,
toughness, and have fair wear resistance due to the considerable amount of carbide present
within them (Otai Special Steel, 2016). Other desirable properties include its abrasion
resistance and ability to hold up against high pressures (Metal Supermarkets, 2017).
Because of its properties, the main applications for H-Group tool steels include Die casting,
zinc and aluminum cores, along with hot forging and hot extrusions for aluminum and
magnesium (Metal Supermarkets, 2017).
A common H-Group steel is H13 tool steel. H13 has a mixture of alloys consisting of
chromium, molybdenum and vanadium (Metal Supermarkets, 2017). These alloying
constituents, namely molybdenum and vanadium, provide the tool steel with high
hardenability and excellent toughness properties (Metal Supermarkets, 2017). Molybdenum
and vanadium are known strengthening agents (Metal Supermarkets, 2017). The chromium
within the material prevents it from softening during high temperature exposure (Metal
Supermarkets, 2017). H13 has a good combination of shock and abrasion resistance, is
described to have good red hardness, and can counter the effects of rapid cooling (Metal
Supermarkets, 2017). Lastly, this tool steel has good weldability and ductility, along with
good machinability at 50% as compared to 1% carbon steel (Metal Supermarkets, 2017).
5
The typical alloying constituents of H13 steel is illustrated in the following Table 2:
Table 2: Alloying Constituents of H13 tool steel
Alloying Element
Percentage Composition (%)
Carbon 0.32 – 0.45 Molybdenum 1.10 – 1.75 Phosphorus 0.03 Sulfur 0.03 MAX Silicon 0.80 – 1.20 Magnesium 0.20 – 0.50 Vanadium 0.80 – 1.20
(Table: Metal Supermarkets, 2017)
Table 3 provides the other H-Grade tool steels within the H-Group, along with their name
designations and main alloying compositions:
Table 3: Family of H-Grade tool steel and composition type
AISI Code AISI Designation Tool Steel Type H H10 – H13 Chromium, Molybdenum AISI Code AISI Designation Tool Steel Type H H14, H16, H19, H23 Chromium, Tungsten
H20- H22, H24 – H26 Tungsten
H15, H41 – H43 Molybdenum
(Table: Otai Special Steel, 2016)
3.2.4 Conventional Mold Materials for Permanent mold
casting
Molds for Permanent mold castings are conventionally made from grey cast iron, H11 and
H13 (Campbell, 2012). For this project, grey cast iron and H13 Tool steel were selected as the
two materials to be compared (price, machining and production wise) for use with
permanent mold casting for the parts needed to be manufactured by the project’s industry
partner. These two materials were chosen simply because of their popularity in the
permanent mold casting process (Campbell, 2013).
3.2.4.1 Typical mold manufacturing from tool steel
Generally, to manufacture molds from tool steel, the following steps are taken:
1) Tool steel bars are cut from a supplier;
2) Milling machines wear down the cut steel into a mold base;
3) A grinding step is introduced to smoothen all surfaces;
4) A CNC machine and possibly an Electrical Discharge machine is then used to create
the mold cavities (part geometry negative) on both halves of the mold;
5) Cooling holes are drilled into the mold;
6) Mating surfaces and cavity surfaces are polished to ensure smooth casting.
(Steps are featured in courtesy of How It’s Made, Episode 2, Season 4, 2004)
From interviewing Blair Knight from UQ’s Faculty Workshop Group (UQFWG), the above
steps are generally consistent throughout the toolmaking industry. Mr Knight added that
manufacturing molds also involve a lot of manual processing. For example, when tool steel
blocks (also called bars) are cut in step 1, each face of the block is more than likely mislaid.
To align and ensure that all faces are perpendicular to each other, a lot of manual work (done
by a toolmaker) is done via milling, grinding, squaring, etc before the block is placed onto
6
milling machines (automated). This is to make certain that datums are easily identifiable by
the automated CNC machines. Other points of manual processing work include lots of
surface grinding and polishing to achieve the tolerances needed for the mold geometries
(Blair Knight, personal communication, May 16, 2018).
3.3 Manufacturing with sand
This section provides a background to the sand casting process. Although not used to
manufacture the industry partner’s components, it has still been included because it provides
a basis for manufacturing the industry partner’s components via the proposed alternative
solution: 3D Sand printing.
3.3.1 Sand Casting Process: A background
Sand casting is a process where liquid metal is poured into a sand mold in which it
subsequently solidifies. However, unlike permanent mold casting, the sand mold is
destroyed after the cast has solidified (Poli, 2001). This casting process is the most widely
used as it forms complex geometries made from almost any alloy (CustomPart.net, 2017).
One of the big reasons why sand casting is very popular is that it can produce large parts,
much larger than what permanent mold casting is capable of (Poli, 2001). Other advantages
for the sand casting process are low tooling and equipment costs (CustomPart.net, 2017).
Some disadvantages of this process include poor surface finish, as most of the cast’s surface
result in a grainy surface requiring some finishing machine operations (Poli, 2001). High
porosity through the sand mold can also occur which decreases material strength and
increase labor costs (CustomPart.net, 2017). Typical production runs go up to 1,000 castings
(CustomPart.net, 2017).
Because of the versatility of sand casting, it produces parts for a wide array of applications.
Examples of parts made via sand casting include, but are not limited to, engine blocks,
manifolds, machine bases, gears and pulleys (CustomPart.net, 2017).
Lastly, the type of materials that sand casting can cast include metals such as alloy steel,
carbon steel, cast iron, stainless steel, aluminum, copper, magnesium and nickel
(CustomPart.net, 2017).
3.3.2 Sand Casting Process
The process for sand casting components is not too different from permanent mold casting
(whose process is described under section 2.1.2) and can be broken down into six main
stage:
1) Mold making
Since sand casting is an expendable process, a mold must be produced from a pattern
of the desired part. This includes packing the sand onto each half of the mold (for
sand casting, the bottom half of the mold is called a Drag, and the other half the
Cope) and goes around the pattern (CustomPart.net, 2017). If internal features are
required, cores are placed. After the sand is packed, lubricant is applied to the mold
cavity to aid with removing the cast from the mold (CustomPart.net, 2017). See
APPENDIX A4 for sand casting mold setup.
2) Clamping
Once the mold halves are made, they are correctly positioned with the cores in
between them, and are then pressed together and closed by clamping
(CustomPart.net, 2017). Clamping both the Cope and the Drag securely and tightly
ensures no material loss (CustomPart.net, 2017)
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3) Pouring
After the furnace sets the temperature for the molten metal, it is then poured into the
mold (CustomPart.net, 2017). The molten metal must fill all channels and cavities
within the mold to precent shrinkage, but pouring must also be kept to a minimum as
to prevent early solidification at any one section of the casted component
(CustomPart.net, 2017)
4) Cooling
The component is then allowed to cool and solidify. Cooling time and rates depend on
a few main factors such as size and wall thickness (CustomPart.net, 2017)
5) Removal (also known as shakeout)
Once the component is cooled, the sand mold can then be broken. Normally,
vibration is employed to remove the sand mold (CustomPart.net). It is not
uncommon to have sand and oxide layers stick to the surface of the cast, so a process
called shot blasting is used to remove any remaining sand to external and internal
faces to reduce surface roughness (CustomPart.net, 2017)
6) Trimming
Excess material such as the leftover metal from the runner system, vents and sprues
are then cut off from the main component (CusotmPart.net, 2017)
3.3.3 Sand Cast molds
This section is used to illustrate how a conventional sand mold is made and provides a
background for the alternative 3D Sand printing solution.
3.3.3.1 Making the Sand Mold
The sand mold is the central piece of equipment in the sand casting process. The mold used
is usually made in two halves, just like in permanent mold casting – the cope (upper half)
and drag (lower half), with their meeting point is known as the parting line (CustomPart.net,
2017). Both halves are contained within a box (called a flask) which provides the outer walls
for the side of the sand mold (CustomPart.net, 2017).
To make the actual sand mold, the sand is packed into the cope and drag respectively. At the
same time, the pattern – which is in the shape of the desired part – is added and more sand
is packed around it (CustomPart.net, 2017). The pattern is split into two parts, the lower half
goes to the drag and upper half goes to the cope. Sand packing can be done by hand or
machine compacted. Machine compacted is the favourable option because it ensures that the
sand has been packed evenly and requires less time (CustomPart.net, 2017). Once the sand
has been compacted tightly, the patterns are removed ready for the cope and drag to be
clamped together (CustomPart.net, 2017). The patterns used in the creation of the sand
molds only produces the external features of the cast (Poli, 2001). In order to produce
internal features, cores are placed between the cope and the drag (CustomPart.net, 2017).
Depending on its location, the core can be supported using what is known as a chaplet
(CustomPart.net, 2017).
8
Lastly, due to the issues of shrinkage and porosity in sand molds, a vital feature that must be
incorporated is the riser. Risers allow the cast to have additional metal during the
solidification stage (CustomPart.net, 2017). Figure 1 below shows the structure of a sand
mold:
Unlike permanent mold casting, creating sand molds does not require much, if any,
machining to generate the mold cavities. However, production labor costs are high
(CustomPart.net, 2017).
3.3.3.2 Sand types
The molds are normally composed of mainly of silica sand (SiO2) and is mixed with a binder
which helps maintain the shape of the mold cavity (CustomPart.net, 2017). Sand is an
inexpensive material that has very high heat resistance, thereby allowing metals with high
melting points to be casted with this method (CustomPart.net, 2017). This sand has different
preparation methods which can be used in the casting process:
7) Greensand Mold
This preparation method uses a mixture of sand, water and clay or binder. The
composition is typically 90% sand, 3% water and 7% clay or binder (CustomPart.net,
2017). This type of mold is used widely as it is the least expensive to make
(CustomPart.net, 2017).
8) Skin-dried mold
This method is similar to the greensand mold except for the usage of more bonding
material is used. The mold cavity surfaces are dried via a torch or heating lamp in
order to increase the strength of the mold (CustomPart.net, 2017). Skin-dried molds
tend to be more expensive as they require more time to be made (CustomPart.net,
2017).
Figure 1: Diagram of components of sand mold
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9) Dry sand mold
Also known as a cold-box mold, it is composed of sand with an organic binder. The
mold is then baked in order to strengthen it (CustomPart.net, 2017). Despite
increasing its dimensional accuracy, this mold is costly (CustomPart.net, 2017).
10) No-bake mold
To prepare this mold, sand is mixed with a liquid resin and left to harden at room
temperature (CustomPart.net, 2017)
3.4 Mid-Volume Manufacturing – An Alternative
This section highlights the significance of the project. As noted, permanent mold casting and
sand casting can typically be used for up to 120,000 castings and 1,000 casting, respectively
(CustomPart.net, 2017), thereby classifying the former as a high-volume production method
and the latter as a low volume production method. In this project, the sand casting process is
not considered as the industry partner utilises molds for components associated mainly with
the permanent mold casting process. The conventional way for making molds for this
manufacturing process is heavy machining of steel blocks as described in Section 1.0 and
Section 3.1.5.1. The argument contained in this project is to determine the viability of
circumventing all heavy machining and labor, to create the final mold product using the
concept of near net shape manufacturing. The alternative solution involves making a near
net shape of the mold and then use machining and labor to take off excess material (i.e.
millimetre offset from the required tolerance), which should be less expensive than starting
the machining from blocks.
This section provides a background to additive manufacturing and the proposed alternative
solution for making molds for mid-volume manufacturing: the Voxeljet VX1000 3D Sand
Printer.
For the context of this project, mid-volume production is classified as production runs of
100-10,000 parts. Additionally, this project will look at the viability (in terms of costs) of
every manufacturing technique explored in making these production runs.
3.4.1 Additive manufacturing
Processes used in additive manufacturing involve creating 3D objects based on CAD or
computer files by sequentially depositing material layer by layer on a substrate normally
called a build plate (Greenemeier, 2013). Additive manufacturing is a growing field and is
quickly becoming mainstream in the manufacturing industry (Kang and Ma, 2017). There
are several methods used in additive manufacturing, mainly:
11) Fused deposition modelling (FDM)
This technology builds parts layer by layer and heating and extruding thermoplastic
filament (Kang and Ma, 2017).
12) Lamination object manufacturing (LOM)
This process involves stacking, bonding and cutting layers of adhesive coated sheet
material on top of the previous layer (CustomPart.net, 2017)
13) Stereo lithography (SLA)
This process involves solidifying liquid resin layer by layer via laser or ultra violet
light (Kang and Ma, 2017).
14) Selective laser sintering (SLS)
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Making metal parts via this method is known as Direct Metal Laser Sintering. This
involves using lasers to burn wax, resin and powdered materials together layer by
layer (Kang and Ma, 2017).
15) Three-dimensional printing (3DP)
This process is based off an inkjet system and is generally used to deposit a binder
onto powdered material layer by layer (Kang and Ma, 2017). As the binder is dried,
excess powdered material is removed (Kang and Ma, 2017).
From these main additive manufacturing techniques, the technology being investigated in
this project is a 3D Sand printer that employs the three-dimensional printing method,
specifically the technology provided by Voxeljet1. This technology will be used in the
benchmark study, with the assumption that casts for molds can be printed via this method.
The other additive manufacturing techniques were not chosen as they are primarily used for
plastics (Kang and Ma, 2017).
3.4.1.1 Three-dimensional printing: Voxeljet’s Sand
Printer – VX1000
CSIRO’s additive manufacturing research center, Lab22, employs the Voxeljet VX1000
(CSIRO, 2017).
The VX1000 is dubbed as the “3D Printer for Industrial Applications” (Voxeljet, 2018). The
build area for the VX1000 is 1000x600x500 mm and was meant for prototyping and
producing medium-sized molds and cores (Voxeljet, 2018).
3.4.1.1.1 Technology Overview
The way that the Voxeljet VX1000 3D prints components is as follows:
1)
The first printhead passes over a powder bed, spreads a layer of powdered (sand)
material and with infrared radiation, hardens the binder on the previous layer as shown
in Figure 2 below:
1 ExOne is also another company that offers 3D sand printing services and machines.
Powdered Material Printhead
Figure 2: Layer of powdered material spread on powder bed. (Voxeljet, 2016)
11
2) The second printhead (Binder Printhead) then passes over and deposits the binder
onto the powdered material as shown in Figure 3 below.
3) The bed is then lowered in preparation for the next layer of powdered material.
4) Steps 1 – 3 are repeated until the net shape of the component is completed
(Voxeljet, 2016)
5) Once the bind and print are completed, a technician removes the part and blows off
any excess material and can proceed to use the part as there is minimal post
processing required (Maxey, 2015)
See APPENDIX A5 for the setup of the Voxeljet VX1000 sand printer.
The company’s sand printers have a wide range of applications, most notably their
involvement in casting processes. Sand molds are normally made via these sand printers to
provide a cost-effective and time saving alternative versus conventional methods in creating
molds just as in sand casting (Voxeljet, 2018). This is because they can create and replicate
complex geometries quickly as compared to toolmakers.
Voxeljet printers such as the VX1000 employ phenolic resins to bind each layer of the sand
mold (Voxeljet, 2018). The process in which they employ this binding resin is called Phenol-
Direct-Binding (PDB). The PDB process is illustrated by Figures 2 and 3 above. Phenolic
Binders are used mainly for printing sand molds and cores because of their resistance to
temperature (ExOne, 2018). Other advantages include binding strength, recyclability (100%
of the printed sand mold can be recycled and reused for a later job) and reduced gas
consumption.
3.4.1.1.2 Applications to casting: Process in making
molds
One of the profound aspects of 3D sand printers is their applications with creating molds for
casting processes. The biggest reason that this particular additive manufacturing technique
was considered as the alternative to mid-volume manufacturing is because this project
checks to see if manufacturing sand molds to create metal molds (the supplied parts for sand
molds are shown starting in section 5.4.1.2.1) would be more cost effective to be used for
the permanent mold casting process. This would be done by minimizing the high labor costs
associated with constructing the geometries of the mold. Instead of using labor throughout
the entire mold making process, applying 3D sand printers would relegate labor costs to
Binder (Brown) Binder Printhead
Figure 3: Binder printed on layer of powdered material. Binder prints the part geometry. (Voxeljet, 2016)
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post-processes that bring the mold within required tolerances. This is because the 3D sand
printer would already print the geometries, regardless of complexity, to a near net shape of
the required part.
3D Sand printers like those of Voxeljet are ideally used for foundries and industrial users
and, by nature of their technology, can be applied to making molds (Nectar3d, 2017).
3.5 Mold Manufacturing: Costing principles
A cost model will be formulated for this project, which leans towards manufacturing and cost
engineering fields. As such, providing a context of the core cost principles to be used in the
cost model spreadsheet is beneficial.
This section is provided because the project’s scope is exploring manufacturing techniques
that are viable for mid-volume manufacturing and will therefore be using these costing
principles to justify that a certain manufacturing technique could be used.
3.5.1 Costing and Economics
3.5.1.1 Terms
Some terms that are related to this project include:
1) Economies of scale
Economies of scale are factors which cause a drop in production costs as output
volume increases (The Economist, 2008).
This term will be used to describe how costs are affected in response to variations in
number of parts required for all the manufacturing techniques covered in this
project.
2) Variable Costs
Variable costs describe costs that change with the volume of activity (Dobrescu,
Faravelli, McWhinnie, 2016). In this project’s context, the variable costs in a
manufacturing technique increase with the number of parts produced. Variable costs
in the context of the project may include:
a. Direct (or raw) materials
b. Direct labor (based on the hourly rate of the work to complete a unit)
3) Fixed Costs
Fixed costs are costs that do not change even if the output is decreased or increased
(activity (Dobrescu, Faravelli, McWhinnie, 2016). Examples of fixed costs associated
with the manufacturing techniques covered in this project may include:
a. Machine costs
b. Total Mold costs
4) Total Costs
Total cost is the combined value of variable and fixed costs (Dobrescu, Faravelli,
McWhinnie, 2016). Total cost is calculated by:
Equation 1: Total costs equation
(fixed cost + variable cost) × Number of units = Total cost
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3.6 Machining: Background
Machining is used within the mold-making process to generate the rather complex
geometries on the mold. Simulating the machining paths for the provided mold components
via CAM software is part of the investigation done for the project. Hence, it is worthwhile to
provide a background to machining principles used to set up the machining simulation files.
3.6.1 CNC Machining: Milling
Computer Numeric Controlled (CNC) Machining is a term for machines that uses a computer
to automatically control the motion of one or more axes of the tool of a machine (Abcon,
2018). For the project, the CNC Machine used to simulate the conventional method of
manufacturing molds and refining the near net shape of the cast mold is the 3-axis CNC Mill.
A 3-axis machine is used mainly due to access limitations to a software capable of simulating
higher-order axis control, along with the fact that it is one of the widely used machines for
generating geometries.
3 Axis CNC milling machines typically controls tool lateral movements in the X-Y Plane and
depth through the Z-Plane (Abcon, 2018).
CNC Milling requires CAD/CAM software to program a toolpath using the correct
parameters (e.g. tool cut depth, feed and cutting rates, etc) to enable the stock material
(workpiece) to be machined to the desired finished product (as modelled by the CAD file)
(Abcon, 2018).
3.6.2 Tooling: Tools used in CNC Milling
3.6.2.1 Tool Materials
The component which interacts with the stock material for machining is the tool (Total
Tooling, 2017). Choosing appropriate tool materials for CNC milling is an important
consideration as it contributes to the machining time length, tool parameters, dimensional
accuracy and surface finish (Prasad & Chakraborty, 2016). Some common tool materials for
end mills (also called cutters) include Carbide, High Speed Steel (HSS), HSSCoM42 (HSS
with added Molybdenum and Cobalt content), HSSCoPM (a Powdered metal variant of HSS
which has added Cobalt content), Ceramic and Diamond (Prasad & Chakraborty, 2016). For
this project however, the choice for tool materials are narrowed down to two – HSS and
Carbide.
Main characteristics of the chosen tool steels are highlighted below:
1) Carbide
Carbide cutters are extremely hard, which allows them to operate at faster speeds
with little tool wear (MSC, 2018). Compared to other materials such as HSS, it also
has high wear resistance and resistance to high cutting temperatures (Prasad &
Chakraborty, 2016). Carbide tools offer better rigidity, which enables the
performance of machining operations that require high dimensional accuracy and
superior surface finish, thereby making them adept for finishing applications (MSC,
2018). It should be noted that Carbide’s hardness comes at the expense of toughness,
which makes carbide tools brittle and creates a higher tendency for them to chip
rather than wear when it is not run in ideal conditions (MCS, 2018).
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2) HSS
Although HSS tools do not have high wear resistance as Carbide, it is a very popular
tool because it is very cheap compared to Cobalt or Carbide end mills (Prasad &
Chakraborty, 2016). HSS tools are used mostly for general purpose milling of ferrous
and non-ferrous materials (MSC, 2018). Lastly, HSS tools are tough and are adept for
interrupted cutting (Prasad & Chakraborty, 2016).
The choice for narrowing down the machining path files to simulate Carbide and HSS tools is
mainly because these two tool materials offer insight in comparing their effects on machining
time and if it is worth using one over the other. It also provides a comparison because the
rule of thumb is that HSS tools should be used to machine softer materials whereas Carbide
tools should be used for the harder and more abrasive materials (Machining News, 2016).
HSS tools are cheaper then Carbide, but dull and wear out quicker. Carbide, although
relatively expensive, can be run 2-2.5x faster than HSS which can increase production and
decrease changeover times (Machining News, 2016). From typical tool material charts (such
as with speed and feed charts) provided by tool manufacturers such as Morse Cutting Tools
(n.d.) show that HSS tools can still machine down tool steels such as H13 just like Carbide.
The purpose for comparing the two tool materials in the machining path simulations is to see
how much HSS tools affect machining time, and in turn machining costs and to see if it
would be beneficial to use them.
3.6.2.2 Tool Geometry: End Mill Types
End mills (Cutters) come in two main categories: Finishing End Mills and Roughing End
Mills. The difference between these categories is that the former is used for general
machining and the latter is used as “sacrificial” cutters as they generally do not last long
because they are used to remove more material by taking heavier cuts in a set amount of time
while minimizing vibration (MSC, 2018).
End mill types that come under Finishing End Mills include Square End, Ball End, Corner
Radius and Tapered. Roughing End Mill types include Coarse Profile and Fine Profile (MSC,
2018).
For the machining path files in the project, the Square End mill type is used because it is
applied for general milling operations (MSC, 2018). The reason only one end mill type from
the Finishing End mill category is used is because there will still be post-processing steps
involved (such as grinding and polishing by the toolmaker) after the tool steel is run through
the CNC machine, i.e. the CNC machining step is a general milling application.
3.6.2.3 Tool Geometry: Flutes
Each tool has what is known as flutes. Flute is the term used for the available cutting edge of
a tooth (Prasad & Chakraborty, 2016). The number of flutes present on an end mill can vary,
tools can have one flute or more. The significance of the flute on an end mill is the number
present in it (Machining News, 2016). This is because of the number of flutes affect the
cutting characteristics of the tool called the chipload. Normally, single and two flute end
mills give the tool more chip carrying and material removal capacity (MSC, 2018). Increasing
the number of flutes provides better finish but chip removal starts to become an issue.
However, because a tool with higher flute numbers are stronger, the feed rates can be
increased which may decrease machining time (Harvey Performance, 2017). See Figure 4
for flute illustration.
15
Because this project simulates machining from H13 tool steel and Cast Iron (both being
ferrous materials), all simulations involve the use of a 4-flute tool as a 4-flute tool is widely
accepted as the option to machine ferrous materials (Harvey Performance, 2017).
3.6.3 Tool Parameters
Tool Parameters form an important aspect in the project. In order to have machining path
files that simulate closely what the tools would do and to obtain a more precise time on how
long it would take for the tool to machine the provided components used in the project, these
parameters must be understood. Therefore, the most important parameters for CNC Milling
that are used for the machining path files are covered.
3.6.3.1 Cutting Speed
Cutting speed is defined as the speed at the outside edge of the tool as it is cutting (Virasak,
n.d.). This is parameter is also called surface speed and is measured in surface feet per
minute or meters per minute (Virasak, n.d.). Surface cutting speed is proportional to the
dimeter of the tool when keeping revolutions per minute (RPM) constant (Virasak, n.d.).
Cutting speed is determined by two things (Virasak, n.d.):
1) The material of the work material, also called workpiece (i.e. the cast iron and H13
tool steel blocks chosen for the project)
2) The tool of the material
Normally, cutting speed is a parameter that is provided by the tool manufacturer in their
Speed and Feed Recommendations charts. The general principle for cutting speeds is that
the harder the work material, the slower the cutting speed and vice versa (Virasak, n.d.).
Figure 5 below shows the increasing cutting speed based on general work material
hardness:
Figure 4: Diagram of flutes on an end mill. Photo Courtesy: (Harvey Performance, 2017)
Figure 5: Increasing cutting speeds based on general workpiece hardness, Courtesy of (Visarak, n.d.)
16
The second general rule is that the harder the tool material, the faster the cutting speed and
vice versa, as illustrated in Figure 6 below:
3.6.3.2 Spindle Speed
Spindle speed is determined by two other parameters – Cutting Speed and tool diameter.
This parameter is defined as the speed in revolutions per minute that the tool spins at
(Virasak, n.d.). Once the cutting speed (in m/min-1) is determined or found, it is calculated
by:
Equation 2: Spindle speed equation
Spindle Speed (𝑛) =1000 × 𝑉𝑐
𝜋𝐷
- where 𝑉𝑐 is the cutting speed and D is the tool diameter (NS Tool, 2018).
3.6.3.3 Feed rate and Feed per Tooth (Chipload)
Based on speed and feed charts provided by Morse Cutting Tools (2011) for example, feed
per tooth is usually a given value by the tool manufacturer. From there, the Feed rate is
determined by the formula:
Equation 3: Feed rate equation
𝑉𝑓 = 𝑛 × 𝑓𝑧 × 𝑍
- where 𝑉𝑓 is the Feed rate, n is the spindle speed, 𝑓𝑧 is the Feed per Tooth and Z is the
number of flutes of the tool (NS Tool, 2018).
Feed per Tooth is also called Chipload and is measured by mm/tooth and represents the
amount of material removed by each flute of the cutter as it advances through the work
material (Virasak, n.d.). Chipload is dependent on three things: the tool material, workpiece
material and tool diameter. Since chip load is a given parameter by the tool manufacturer, it
is a matter of selecting the corresponding chip load to match the tool diameter and
workpiece material from charts given by the tool manufacturer.
Feed Rate, measured in mm/min represents the distance the workpiece advances into the
end mill (Virasak, n.d.). Even though the Feed rate is highly dependent on the feed per tooth,
it is also affected by other factors such as (Virasak, n.d.):
- Depth and width of cut
- Cutter material and type
- Sharpness of end mill
- Workpiece material (H13 tool steel and cast-iron blocks as per the project)
- Strength and uniformity of the workpiece
Figure 6: Increasing cutting speed based on tool material hardness. Courtesy of (Visarak, n.d.)
17
- Required surface finish
- Required accuracy
- CNC Machine power and rigidity
From these tool parameters, the machining files will incorporate them to provide a precise
evaluation on machining times.
3.6.3.4 Recommended Speeds and Feeds for HSS and
Carbide Tools
For the project, Cutting speed and Feeds for the tools used in the tool path simulations were
determined from Speeds and Feeds tables provided by Conical Cutting tools (2017) for the
HSS tools and Morse Cutting tools (2011), and Tools Today (n.d.) for the Carbide tools. The
speeds and feeds table is normally presented in imperial units, so an extra step to convert
into metric units was conducted.
Table 4 below shows the recommended speeds and feeds for HSS tools to machine H13 and
Cast-iron tool steels (in inches) as provided by Conical Cutting tools (2017):
Table 4: HSS - FEED PER TOOTH (ROUGHING AND FINISHING). Courtesy of Conical Cutting tools (2017). (Surface Feet per Minute is SFM)
Material SFM 3/32 – 1/8
5/32 – 3/16
7/32 – 1/4
5/16 – 3/8
7/16 – 1/2
9/16 – 5/8
11/16 – 3/4
7/8 – 1’’
Cast Iron 100 0.0003 0.0004 0.0007 0.0013 0.0025 0.003 0.004 0.005 Tool Steel H13
80 0.0002 0.0003 0.0004 0.0006 0.0015 0.002 0.0025 0.003
Table 5 below shows the recommended speeds and feeds for Carbide tools to machine H13
and Cast-iron tool steels (in inches) as provided by Morse Cutting tools (2011) and cross
referenced by Tools Today (n.d.).
Table 5: Carbide - Recommended Feeds and Speeds. Courtesy of Morse Cutting Tools (2011)
Material SFM 1/8 1/4 1/2 3/4 1’’ Cast Iron 300 0.0005 0.0010 0.0020 0.0030 0.0040 Tool Steel H13 250 0.0006 0.0012 0.0025 0.0037 0.0050
The cut and feed charts are based on recommended values, especially for the chip loads. For
an experienced machinist, these values serve as a starting point and these parameters can
either be increased or decreased by the them depending on the conditions of the tool and
workpiece.
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4.0 KNOWLEDGE GAP
Based on the literature review done, it is now known that the conventional manufacturing
technique to produce molds for the permanent mold casting process involves a lot of
machining and labor work to obtain the required surface finishes and dimensional accuracies
from working with tool steel and cast-iron blocks. From this, the costs for making the molds
will be high especially for a production run whose target is up to 10,000 parts. By proposing
to use the Voxeljet VX1000 used by CSIRO’s Lab22, the desire is to 3D print a sand mold
that achieves the near net shape of the mold, and, instead of machining from blocks of steel
and cast iron, the mold with the near net shape gets a finishing step via machining. The
intended outcome is that labor costs can be reduced from the pattern generation stage (while
leaving the labor costs in the finishing stages) which in turn reduces the costs for making a
mold to use for a mid-volume production run. The knowledge gap that this thesis aims to
investigate is if it is more cost-effective to introduce the 3D sand printing stage for mold
pattern generation against conventional machining techniques.
4.1 Work relating to knowledge gap
The work that will be done to address this knowledge gap is to investigate the methods
currently being employed in creating molds for the manufacturing techniques, and to
discover the costs associated with them in order to create a cost model spreadsheet to
compare which of these techniques are most suitable for mid volume production runs.
5.0 METHODOLOGY
This section illustrates the overall methodology that was employed to obtain benchmark data
for the project.
5.1 Method: Conducting the Project
This project is, by nature, more research-based rather than experimentally based. As such,
the methodology is more focused on finding the data and prior art required for an evaluation
to meet the goals stated of the study stated in Section 2.0.
The overall method that was used to conduct the project is outlined as follows:
1) Collect information regarding the manufacturing techniques used for the benchmark
study:
▪ Machining down steel blocks for permanent mold casting applications – This
technique is the conventional way of manufacturing molds.
▪ Additive Manufacturing technique – This is the primary technique that will be
explored, especially as the proposed solution for making molds for mid-
volume production is the technology used by CSIRO’s Lab22 – Voxeljet
VX1000.
2) Create a generic cost model spreadsheet that will be used to compare the cost
estimates for the mold productions for each manufacturing technique explored in the
project.
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This generic cost model incorporates important parameters and values such as
machining time, material costs and labor costs to provide the direct cost estimates for
mold production.
3) Obtain CAD files for the parts, mold components (Cope and Drag) along with any
part files associated with the 3D sand printer.
For this project, the two components that will be provided are referred to as Grate
and Legs. Their respective mold CAD files will be provided alongside the parts and
Sand printer molds.
4) From the provided components used in the project, use CAD software such as Creo to
create tool path files for the mold components of the Grate and Leg. This is done to
obtain the machining time that will then be used as an input for the generic cost
model spreadsheet.
Due to the structure of the project, the tool path files that are generated will simulate
machining down blocks of steel (normally done for mold manufacturing) and
machining off excess material from a mold that possesses geometries in a “near net
shape” form made possible by using the 3D Sand Printer.
Therefore:
a) For the machining paths simulating conventional mold manufacturing,
program the machining files to simulate machining the mold down from
blocks of steel (H13 and Cast-Iron blocks). Machining paths for this
technique will be programmed for all mold components of the Grate and
Leg parts.
b) For the near net shape machining paths, the machining files will simulate
machining the mold as more of a finishing step. Since the 3D Sand printer
can print the complex patterns and geometries contained within the mold,
the tool paths are programmed to simulate the removal of excess material
from the mold. i.e. the mold has its rough shape after being casted from
the sand molds. Thus, the machining step refines the mold geometry.
Machining paths for this technique are only applied to the molds of the
Leg as their mold components have been proposed to be made via 3D
Sand printing.
c) Once the machine files have been set up, calculate the proper tool
parameters for them (tool parameters are dependent on tool and mold
material) and place these tool parameters for each tool step to obtain the
most precise machining time.
To note: a comparison was made between tool materials to check whether the cost
effectiveness of using Carbide tools against HSS tools for the project.
5) From the provided mold components, consult with tool makers and machine experts
about the processes, labor costs and overall time estimates for constructing molds for
the part. This will involve showing the geometry to enable the provision of feedback
20
on these parameters. This step is done to obtain the labor cost estimates which will
then be used for the cost model spreadsheet.
6) Find the other labor costs associated with making molds, (i.e. labor costs – hourly
rates for machinist, engineer, etc., material costs and machine costs) to use as inputs
for the cost model spreadsheet
7) Use CES Edu package to find raw material costs for the components and their molds.
8) From the input parameters obtained via steps 3 – 7,
▪ a plot of total cost (and cost breakdown consisting of labor, raw materials and
machine hire costs) vs mold material was produced for the conventional
manufacturing technique for the components of the Grate and Leg. This was
used to recommend a material for the mold of the Grate and Leg parts.
▪ A plot of Total cost (mold costs plus unit part cost) vs part quantity was made
for each manufacturing process considered in the project to compare if
making molds via the 3D Sand printer would be more viable than the
conventional method.
5.2 Project Scope and Assumptions and Note
The scope of the project is:
1) To find the total costs for manufacturing the Grate molds using the conventional
method of machining down from steel blocks. The costs comparisons will be done
between machining from H13 tool steel and Cast iron (material wise) and these total
costs will be based on the labor, raw material and machining time costs. A quick
comparison will be made between what tool material to recommend for the project as
this will also affect the machining time
2) To find the total costs for manufacturing the Leg molds using the conventional
method of machining down from steel blocks (again, comparing machining between
H13 tool steel and cast iron) and machining off excess material from a near net shape
formed from casting the mold components from sand molds. Only the Leg molds do
the comparison between the conventional mold making technique and using 3D
printed sand molds as they were the mold components that were proposed to try out
this technique. Also, sand molds were designed only for the Leg components for the
Fixed and Moving Die
For the project, certain assumptions were made, and these were:
1) The assumption that creating the mold components for the Grate and Leg is
successful in one run, i.e. no re-doing the manufacturing from the start
2) All manufacturing takes place in Australia, specifically by UQ’s Faculty Workshop
Group (UQFWG) as they served as consultants to the project, unless otherwise stated
21
One thing to take note of for the project is that all the cost figures are estimates. No actual,
set costs are made because of additional assumptions which were made for the cost model
that can affect the actual costs for making the mold components, with a big factor being the
estimation of lead times. Cost estimates for manufacturing the mold components, either
through the conventional or proposed alternative technique, are based on the direct work
done on the raw materials.
5.3 Generic Cost Model
To be able to make cost estimates when comparing the different manufacturing processes for
the Grate and Leg molds, a cost spreadsheet was made. It has a mostly generic layout
because the intent is to be able to fill in important common parameters with ease. The cost
model spreadsheet contains a sheet template – to fill in for the cost estimates of the mold.
To note: The Cost model specifies the manufacturing technique that is being See
APPENDIX A1 for the cost spreadsheet layout and the actual cost spreadsheet used for the
results in Section 6.0.
5.3.1 Scope, assumptions and limitations
As with all tools, the generic cost model spreadsheet has its scopes, assumptions and
limitations.
The scope of the cost spreadsheet is:
1) To provide the total unit cost of manufacturing a mold versus manufacturing
technique
2) To use it as a tool to check and record the total production costs to manufacture parts
from a mold made with a certain manufacturing technique, i.e. total costs in dollar
versus part production volume
3) To provide data points of these total costs for comparing manufacturing techniques
via a plot with the x-axis labelled as part and y axis labelled as cost
Assumptions made for the generic cost model are:
- Capital costs exists to create and pay for the price of the parts given by
the cost spread sheet
- Any costs relating to shipping material, machines, tools and parts are
not considered for the direct costs of making the molds and parts.
- All costs are measured in Australian dollars
- No defective units
A Limitation of the generic cost model is as follows:
1) Only the direct costs associated with making a mold are considered, i.e. it will only
consider:
▪ Costs of the machines used in the manufacturing processes
▪ Material costs that come strictly from material type, weight, dimensions, etc.
▪ Direct labor input, i.e. only the costs of skilled labor such as engineers,
machinists, etc who contributed in the process of making the mold and part
5.3.2 Parameters Used
The model takes in a number of parameters that would significantly influence the cost of a
manufacturing process. The way that the cost model has been constructed makes it such that
22
costs are associated with three main categories: Labor, Material Characteristics and
Manufacturing technique.
5.3.2.1 Labor Costs
The main labor costs considered for the cost spreadsheet were:
1) Engineer Hire
This is part of the labor costs as an engineer must be used to validate the part, which
in this context, a mold, before it is sent off to be made. Validation includes ensuring
the tool path files run correctly and tool parameters are correct. For the project,
according to PayScale (2018), the median hourly rate for an Engineer (Mechanical) is
$31.23AUD per hour, which is the value used in the Cost spreadsheet.
2) Machine Operator
The machine operator is defined as the individual who interfaces with the particular
machine used in the manufacturing process and thus serves as an integral component
in the process. Machine operators ensure that the machine is building the component
as per required. According to PayScale (2018), the median salary for a CNC machine
operator is $26.26AUD per hour. As for the machine operator for the 3D Sand
Printer, it is $200AUD per hour according to Gary Savage (2016). Both these hourly
rates are used in the spreadsheet.
3) General Labor
This was included in the cost spreadsheet as not all manufacturing processes
necessarily use a machine. This parameter is an input as it provides a cost for
processes that have manual work such as fabricators, welders, etc.
Labor costs are the rates of hire, i.e. cost per hour or ($$/hr).
Also, within the spreadsheet, it is possible to add multiple laborers to provide a breakdown
of costs.
5.3.2.1.1 General Labor: Toolmaker Role
Toolmakers construct tools, dies, jigs and other precision parts and equipment for machine
tools and other machinery (WorkReady, 2018). From interviewing Blair Knight of UQFWG,
for the project, a toolmaker would be hired and be held responsible for making molds – i.e.
the Grate and Leg molds used in the project. Toolmakers would also be hired to work
throughout the manufacturing of the molds (Blair Knight, personal communication, May16,
2018).
In the cost spreadsheet, toolmakers come under general labor. In the actual cost
spreadsheets used in the project (See APPENDIX A1), a new field entry for toolmaker
hours is introduced to hold the total hours that the toolmaker will be potentially working on
making the Grate and Leg molds. According to PayScale, toolmakers earn a median
$26.27AUD per hour which is the hire rate used in the cost spreadsheet (PayScale, 2018).
23
5.3.2.2 Raw Material Characteristics
This category was included as the characteristics of materials affect their upfront purchasing
costs and the tool parameters needed to work on them. The main costs associated with the
material being worked on were:
1) Overall Dimensions
This is an important parameter as the size and volume of the part (mold) being made
can greatly influence cost, i.e. it will generally cost more to work with more material
than with little material.
This parameter is measured in meters for each dimension of length, width and
height. This parameter was provided in the case that the volume needed to be
calculated.
2) Material
Another important parameter, this forms part of the upfront costs as, from the
literature review done in Section 3.0, material has its associated costs. Additionally,
different materials may need different manufacturing techniques to work with which
contributes to the cost of manufacturing. Multiple materials may be added as can be
seen in the spreadsheet used for the project in APPENDIX A1.
This parameter is measured in kilograms.
In the spreadsheet, the total weights of the material used in the conventional mold
manufacturing technique and 3D sand printed molds were used.
5.3.2.3 Manufacturing Tooling
Different manufacturing techniques have different processes and because of that, their costs
can differ. The parameters considered under this category include:
1) Machine Setup (Initializing, Tool setup, etc.)
This parameter includes how long it takes to initialize the machine associated with a
particular manufacturing process. It also includes setting up of the tool bits,
essentially any steps or workflows needed to start or clean up the machine from
previous jobs to manufacturing the mold components.
This parameter is measured in hours.
From interviewing Blair Knight from UQFWG, CNC setup, maintenance and cleanup
time is estimated at 2 hours for each job (Blair Knight, personal communication, May
16, 2018).
For the Voxeljet VX1000, it takes 15-30 mins to load the CAD model into the machine
and about 4 hours to clean up the machine and prepare it for the next print job
according to Dr Gui Wang (Gui Wang, email communication, April 29, 2018).
2) Tooling Costs
This parameter is associated with the upfront costs of any tooling bits needed to be
installed on the machine. This is an optional field included if tools are not included in
the costs for hiring a machine.
24
This parameter is measured in currency.
3) Maintenance
Maintenance forms part of the overall costs to run the manufacturing technique. This
is an optional field included in the spreadsheet in the case that maintenance fees are
included on top of the machine hire.
This parameter is measured in cost per hour, i.e. $$/hr.
4) Machine Hire Rate
This parameter looks at the cost per hour that the machine must run to produce a
single part. This value is multiplied by the number of parts for that particular
manufacturing process.
This parameter is measured in cost per hour, i.e. $$/hr
From personally interviewing Blair Knight from UQFWG, UQFWG charges $77AUD
per hour to hire out the workshop’s CNC machine for external projects. This machine
hire rate is used in the cost spreadsheet.
5) Machine Hire Time
This parameter looks at the total time the machine must operate to produce the
specified components. The value for this parameter is from the expected machining
time that is calculated from the tool path simulation files for the Grate and Leg mold
components.
This parameter is measured in hours.
5.3.3 Parameter Relations in the Spreadsheet
This subsection provides insight to how parameters described under all subsections of
5.3.2 relate and contribute towards the production costs of the parts and mold.
Table 4 outlines the basic relations between the parameters and cost inputs of the
spreadsheet, i.e. the calculations to get the total costs of production.
Table 6: Description of relations between parameters and cost inputs
Parameters (Input)
Calculated Cost Output
Relations or Comments
- Engineer Hire (Rates)
- Hours logged
- Total Engineer Cost
The multiplication of cost per hour rate and hours logged provides the total cost of engineering labor. As can be seen in the spreadsheet, the total cost can be applied if multiple engineers are hired. This is considered as a fixed cost as Engineer hire will mainly be for validation before the part and tool path files go into production.
- Machine Operator (rates)
- Hours Logged
- Total Machinist Cost
The relation between the inputs works the same as with the Engineer hire. However, the “Hours logged” input is based strictly on the Machine set up time. This is considered as a direct variable cost as a machine operator is hired to help produce each individual part.
25
- General Labor (rates)
- Hours logged
- Total General Labor Cost
General labor (rates) is multiplied by Hours logged to obtain Total Cost. This is considered as a direct variable cost with the same reasoning for machine operator Total Cost.
- Material (weight)
- Material Cost
- Total Raw Material cost
Material weight is multiplied with material cost (material cost should usually come in $/kg). This will be considered as direct variable cost as raw material is needed for each individual part
- Machine Hire Time
- Machine Hire Rate
- Machine Costs The hire time and hire rate are multiplied together. This will be considered as a fixed cost as the machine hire time is the total time the machine is on to produce the specified quantity of parts.
N/A - Mold Costs This is the cost calculated from the “Mold Costs” Spreadsheet. The thing to note about this input cost is that it is considered as a fixed cost for permanent mold casting and the 3D print solution as the mold is reusable. It is then considered as a direct variable cost as a new sand mold must be made for each individual part.
N/A - Maintenance This is a parameter that have fixed costs associated with them. These are fixed costs as they are consistent costs N/A - Tool Costs
5.4 Parts evaluated for the project
5.4.1 Part description
The parts belong to an industry partner and for this project, are called the Grate and Leg that
are assembled is shown in Figure 7:
Permanent mold casting was the method that would be used to create these parts with a
limited production run. The Molds for these components were designed and provided by Dr
Gui Wang for the cost evaluation for the molds. Also, the sand mold CAD files to be printed
in the 3D sand printer were provided.
This section gives a description of the parts that were evaluated for machining.
Figure 7: Grate and Leg Assembly
Grate
2x Leg
26
5.4.1.1 Grate and Grate Mold Components
Figure 8 below shows the Grate part to be casted:
The specifications of the part are provided in Table 7 below:
Table 7: Grate Specifications
Weight (kg) 1.16 Overall Dimensions (in m) 0.4255 x 0.182 x 0.04055
The grate is to be made from Aluminum AC603 which is also AA Grade 357.0 and ASTIM
B108 Grade 357.0 (Matmatch, 2018). To cast this part using permanent mold casting, mold
geometry were created and are shown in Figure 9 below:
To note, the Fixed Die is the name given to the mold component that stays fixed on the jig
where the casting is made, whereas, the Moving Die is the mold component that is removed
and re-placed to eject the part from the mold.
Top View Bottom View
Figure 8: Provided CAD Geometry of Grate (Rendered)
Figure 9: Mold Geometry as shown. (a) is called the Fixed Die, (b) is called the Moving Die
(b) (a)
27
The specifications of each mold are provided in Table 8 below:
Table 8: Specifications for the Fixed and Moving Die from Figure 9
Fixed Die Moving Die Weight (kg) Material Weight (kg) Material
101.52 H13 Tool Steel 55.73 H13 Tool Steel 93.00 Cast Iron 51.05 Cast Iron
Overall Dimensions
(m)
0.5255 x 0.3350 x 0.0805 Overall Dimensions
(m)
0.5255 x 0.3350 x 0.0400
To note, Table 8 shows the two steels that are being compared for the mold components to
be made out of.
Figure 10 below shows the exploded view and assembly views of the molds and the mesh
put together:
(a)
(c)
(b)
Figure 10: (a) Exploded view of mold assembly with mesh (bottom view), (b) Exploded view of mold assembly (top view), (c) Mold assembly enclosed
28
5.4.1.2 Leg and Leg Mold Components
Figure 11 below shows the Leg part to be casted:
The specifications of the part is provided in Table 9 below:
Table 9: Leg Specifications
Just like with the Grate, the Leg is to be casted from Aluminum AC603. From there, Figure
12 shows the Mold components for the leg:
To note, there is a pair of Legs in the Grate and Leg assembly. The mold components aim to
produce each leg pair in one casting. From Figure 12, another component called the Sliders
are present because no draft angle is present where they assemble into the mold assembly
Weight (kg) 0.85 Overall Dimensions (in m) 0.484 x 0.051 x 0.126
(b) (a)
Figure 12: Mold Geometry for Leg. (a) is the Moving Die (b) is the Fixed Die and (c) is called the Slider. A pair of Sliders are present for the mold for the legs.
(c)
Figure 11: Provided Leg part CAD geometry
29
and it allows the hole geometries to be made which are perpendicular to the flow of the cast
metal. Two sliders are present.
Table 10 below shows the specifications for each mold component:
Table 10: Specifications for Fixed and Moving Die and Sliders of Leg mold
Figure 13 below shows the assembly of the Leg Molds:
5.4.1.2.1 Sand Molds to be printed in Voxeljet 3D
Sand printer
This section shows the sand molds that are to be made from the 3D Sand printer. These sand
molds will be used to cast the Mold components, specifically the Fixed and Moving die of the
Legs.
Figures 14, 15 and 16 below shows the assembly of the sand molds for the Fixed Die of
the Leg mold:
Fixed Die Moving Die Sliders (1x Slider) Weight (kg) Material Weight (kg) Material Weight Material
390.24 H13 Tool Steel
324.64 H13 Tool Steel
11.40 H13 Tool Steel
357.48 Cast Iron 297.38 Cast Iron 10.46 Cast Iron
Overall Dimensions
(m)
0.680 x 0.700 x 0.120
Overall Dimensions
(m)
0.680 x 0.700 x 160.27
Overall Dimensions
(m)
0.194 x 0.195 x 0.041
Figure 13: Leg Mold assembly
30
Figures 17, 18 and 19 below shows the assembly of the sand molds for the Moving Die of
the Leg mold:
Cope Drag
(a) Top View (b) Bottom View
Sprue
Figure 14: Assembly of Cope and Drag of 3D Printed sand molds
Drag
Cope
Fixed Die
Figure 15: Exploded View of Sand Molds showing Drag Pattern
Drag
Cope
Fixed Die
Figure 16: Exploded View of Sand molds showing Cope Pattern
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Drag
Cope
Moving Die
Figure 19: Exploded View of Sand molds showing Cope Pattern
Drag
Cope
Moving Die
Drag
Figure 18: Exploded View of Sand molds showing Drag Pattern
Drag
Cope
Figure 17: Assembly of Cope and Drag of 3D Printed sand molds
Sprue
32
From Figures 16 to 20, it can be seen that the Copes and Drags for the sand molds of the
Fixed and Moving Die are split into two. This is mainly because the widths of the Cope and
Drag exceed the 600mm width of the job box of the Voxeljet. Thus, the way they have been
designed by Dr Gui Wang, the copes and drags will be printed into two parts and will be
assembled via guide hole geometries that have been modelled in them.
To note, Figure 20 below is a section view for the assembly of the sand molds for the
Moving Die. The Moving Die (beige) is placed in the assembly and it can be seen that there
are gaps in around the area of the pattern geometry. This represents the extra material that
will be present after the Moving Die is casted. This extra material is a small offset from the
true geometry – in this view the offset is in the range of 4 to 6mm - and thus, machining path
files made for the near net shape approach will simulate removing these extra material. The
same goes for the Fixed Die which has the same range of extra material offset from its faces
on its geometries.
5.5 CAD/CAM Approach: Tooling path generation
To be able to get the expected machining time for the molds, tooling path files were made via
the NC Assembly feature in Creo and also through SolidCAM in Solidworks. For tooling path
files, as long as the tool parameters are the same and consistent between both software
programs, the expected machining times will be correct. NC Assembly was used mainly for
the Fixed and Moving Dies of the Grate mold for the Leg Mold. SolidCAM was used for the
tool path files of the Fixed and Moving Dies of the Leg mold and the tool path files of the
Fixed and Moving Dies that simulate machining down the near net shape forms made from
the 3D Sand molds.
5.5.1 Grate Mold: CAM Workspace
Tool paths were made which simulated machining the components of the Grate mold from
tool steel blocks (conventional method for manufacturing molds). This tool path generation
simulates the Grate mold components to be machined for the Permanent mold casting
process.
Figure 20: Section view showing a sample of offset present in the sand molds
33
Figure 21 below shows the workspace on Creo and the milling operations for the Fixed Die:
(a)
(b)
Figure 21: Workspace illustrating the milling operations done for the Fixed Die. (a) the workspace for the 1st set of operations on the mold cavity, (b) workspace for second set of
machining operations for the side of the Fixed Die
34
The total operations for the Fixed Die is shown in Table 11 below:
Table 11: Total milling operations for the Fixed Die
Machining Face Operation Number and Mill Operation
Comments
Mold Features for part
1 – Face Mill Machines part of the runner system that leads the molten metal to the mold cavity (4mm diameter tool)
2 – Profile Mill Machines the guide pin holes, the riser and well (8mm diameter tool)
3 – Profile Mill Additional machining to the runner system that leads molten metal to mold cavity and rise (3mm diameter tool)
4 – Profile Mill Additional machining for the guide pin holes (5mm diameter tool)
5 – Profile Mill Machines the runner system (where molten is poured in)
6 – Profile Mill Additional machining to the well (3mm diameter tool)
7 – Face Mill Machines the perimeter of the mold cavity (4mm diameter tool)
8 – Face Mill Machines the mold cavity patterns (4mm diameter tool)
9 – Profile Mill These steps machine the rest of the mold cavity patterns. They were broken down into 3 mill steps to ensure the program is stable with calculating the tooling path (3mm diameter tool)
10 – Profile Mill 11 – Profile Mill
Mold Side
1 – Profile Mill Machines both clamp holes (8mm diameter tool)
2 – Profile Mill Additional machining to both clamp holes (3mm diameter tool)
Figure 22 below shows the workspace and milling operations for the Moving Die:
Figure 22: Workspace illustrating the milling operations for the Moving Die
35
The total operations for the Moving Die is shown in Table 12 below:
Table 12: Total milling operations for the Moving Die
Machining Face Operation Number and Mill Operation
Comments
Mold Features for part
1 – Face Mill Machines all the features of the mold cavity (12mm tool diameter)
2 – Profile Mill Additional machining for all features of the mold cavity (4mm tool diameter)
5.5.2 Leg Mold: CAM Workspace
The following two subsections show the workspace for the tool path files for the Leg Mold
components.
5.5.2.1 Conventional Manufacturing for Leg Mold
components
This section shows the tool path files that were generated to simulate machining down the
Leg Mold components from steel blocks.
Figure 23 below shows the workspace and milling operations for the Fixed Die:
To note, since the tool paths for the Fixed and Moving Dies for the Leg mold were done in
SolidCAM, there will be difference to the names of the Mill operations as compared to Table
11 and 12.
The total operations for the Fixed Die is shown in Table 13 below:
Figure 23: Workspace illustrating the milling operations for the Fixed Die
36
Table 13: Total milling operations for the Fixed Die
Machining Face
Operation Number and Mill Operation
Comments
Mold Features for part
1 – P_contour14 Machines the opening tip of the Sprue (8mm tool diameter)
2 – P_contour15 Machines the rest of the opening tip of the Sprue and machines the tip of the mold geometry (10mm tool diameter)
3 – 3DR_model Machines the crevices of the feed system (the crests and trough geometry) of the mold. (8mm tool diameter)
4 – 3DR_model1 Machines the crevices needed for the Leg geometry of the mold. (12mm tool diameter)
5 – P_Contour Machines the pockets where the sliders will be put into for the mold. (10m tool diameter)
6 – P_contour1 Machining of Mold geometry for Slider guide holes. (8mm tool diameter)
7 – 3DR_target Additional machining on Pocket area for sliders. (4mm tool diameter)
8 – 3DR_target_2 Additional machining on Pocket are of sliders (4mm tool diameter)
9 – 3DM_target Finishing step for guide holes for sliders. (3mm tool diameter)
10 – 3DR_target_1 Additional finishing step for Poket area for sliders. (6mm Tapered tool diameter)
11 – P_contour2 Machining of mold cavity geometry (6mm tool diameter)
12 – P_contour3 Machining of remaining cavity geometry (6mm tool diameter)
Figure 24 below shows the workspace and milling operations for the moving die:
Figure 24: Workspace illustrating the milling operations for the Moving Die
37
The total operations for the Moving Die is shown in Table 14 below:
Table 14: Total milling operations for the Moving Die
Machining Face
Operation Number and Mill Operation
Comments
Mold Features for part
1 – P_contour3 Face machining on right and left side of geometry. (40mm tool diameter)
2 – P_contour4 Face machining on central portion of the mold (in between the leg geometry) (40mm tool diameter)
3 – 3DM_target Machining of Sprue and runner of mold. (12mm tool diameter)
4 – 3DM_target_1 Additional machining of runner of mold. (6mm tool diameter)
5 – 3DR_target Machining of Riser of mold (6mm tool diameter)
6 – 3DR_target_1 Machining of remaining Riser geometry of mold (4mm tool diameter)
7 – 3DR_target_2 Machining of Leg geometry – For slider holes (12mm tool diameter)
8 – 3DR_target_3 Additional machining of Leg geometry – For slider holes (4mm tool diameter)
9 – 3DR_target_4 Machining of mold geometry responsible for making the pattern of Leg component (12mm tool diameter)
10 – 3DR_target_5 Additional machining of mold geometry responsible for making pattern for Leg component (4mm tool diameter)
5.5.2.2 Tool Path files for Leg Mold components casted
from printed sand molds
This section shows the tool path files that were generated to simulate the machining of the
Leg Mold components from their near net shape that was casted from the sand molds.
To note, for the Fixed and Moving Dies, workpieces were modelled and overlayed on top of
the provided CAD to simulate the extra material brought about by casting these mold
components from the sand printer. The transparency of the overlayed workpiece on the mold
component have been turned transparent in the images provided.
Figure 25 below shows the workspace and milling operations for the fixed die (grey) with
the workpiece overlayed (transparent):
38
The total operations for the Fixed Die is shown in Table 15 below:
Table 15: Total milling operations for the Fixed Die (Machining from near net shape)
Machining Face Operation Number and Mill Operation
Comments
Mold Features for part
1 - FM_facemill1 Facemill to remove excess material on main surface of mold geometry (40mm tool diameter)
2 – P_contour Machines to remove excess material on main surface (8mm tool diameter)
3 – P_contour2 Additional machining to remove excess material on main surface (8mm tool diameter)
4 – F_contour3 Machines to remove strips of excess material on face where Sliders are placed (6mm tool diameter)
5 – F_contour4 6 – F_contour5 7 – F_contour6 8 – 3DR_target Machines to remove remaining excess
material on left and right-hand side pockets of Slider insertion area (12mm tool diameter)
9 – 3DR_target_1 Machines to remove remaining excess material for guide hole areas for Sliders (10mm and 4mm tool diameters)
10 – 3DR_target_2 11 – 3DR_target_3 12 – 3DR_target_4 Machines to remove excess material of
Leg geometry (8mm tool diameter) 13 – P_contour7 Machines the Sprue are of the leg
geometry (8mm tool diameter) 14 – P_contour8 15 – 3DR_target_5 Removal of remaining material for Leg
geometry of mold. (10mm tool diameter) 16 – 3DR_target_6 Machines tapered cylindrical protrusion
around the Slider area. (6mm tapered tool diameter)
Figure 25: Workspace illustrating the milling operations for the Fixed Die
39
Figure 26 shows the workspace and milling operations for the moving die (grey) and its
workpiece overlayed (transparent):
The total operations for the Moving Die is shown in Table 16 below:
Table 16: Total milling operations for the Moving Die (Machining form near net shape)
Machining Face Operation Number and Mill Operation
Comments
Mold Features for part
1 – F_contour2 Machine operation that removes a strip of material of the mold geometry responsible for making the Leg part features. (10mm tool diameter)
2 – F_contour3
3 – P_contour5 Facemill to remove excess material on main surface of mold geometry (40mm tool diameter)
4 – P_contour6 Facemill to remove excess material on area between the Leg mold geometry.
5 – 3DR_target Machines off geometry for slider guide holes (40mm tool diameter)
6 – 3DR_target_1 Additional Machining to remove remaining excess material from slider guide holes (6mm tool diameter)
7 – 3DR_target_2 Finishing step for Guide holes for Sliders (4mm tool diameter)
8 – 3DR_target_3 Machines down the Riser system (10mm tool diameter)
9 – 3DR_target_4 Additional machining to remove remaining excess material on riser system (4mm tool diameter)
10 – 3DR_target_5 Machines off the Sprue and runner system of mold (10mm tool diameter)
11 – 3DR_target_6 Additional machining for sprue and runner system. (4mm tool diameter)
Figure 26: Workspace illustrating the milling operations for the Moving Die
40
12 – 3DR_target_7 Machines the geometries responsible for the Leg shape (12mm tool diameter)
13 – 3DR_target_8 Additional machining to machine remaining material off the mold feature responsible for the Leg parts shape
5.5.2.3 Note on Leg sliders
From Figure 12, it can be seen that the Leg Mold components consist of one Fixed and
Moving Die and two sliders. However, from sections 5.5.2.1 to 5.5.2.2, no machining path
files were made for the sliders. This is because Blair Knight of UQFWG emphasized that with
the size of the sliders (as seen in Table 10), it would be made manually by a toolmaker,
which is why no machining files exists for the sliders. However, the making of the sliders will
be tallied against the hours of the toolmaker (Blair Knight, personal communication, May 16,
2018).
5.6 Raw Material Costs
From Section 5.1, it was mentioned that CES EduPack, a materials selection database
program, would be used to find the raw material costs for the materials used in the project.
CES EduPack was chosen because it contains a vast library of materials and their
specifications. At the same time, because of its materials selections applications, it contains
material prices. From using the CES EduPack library, the costs for raw materials are shown
in Table 17:
Table 17: Price per kg of Raw materials for components used in project. Courtesy of (CES EduPack 2018)
Material Price ($AUD/kg) Component Lower Upper
H13 3.73 4.02 Grate and Leg Mold Components – for comparison Cast Iron 0.381 0.394
AC603 or AA Grade 357.0 2.53 2.73 Grate and Leg Parts SG 400 – 15 Cast Iron 0.381 0.394 Leg Mold components (casted
from sand molds)
On top of the steel raw materials, sand costs are also present for the 3D sand printer route.
According to Gary Savage of CSIRO (2016), sand costs are at $2.00 per kg and the activating
agent (Phenolic binders) cost $0.63 per kg.
41
6.0 RESULTS
6.1 Tool Parameters for machining path simulation
6.1.1 Tool Parameters for H13 tool Steel
Table 18 below shows the recommended tool parameters needed to machine H13 Tool steel
using HSS or Carbide tools.
Table 18: Tool Parameters for HSS and Carbide tools for machining H13 Tool Steel
Tool Type Tool Size (mm)
Cutting Speed (m/min)
Spindle Speed (rpm)
Feed Rate (mm/min)
HSS
3
24.38
2587.22 52.57 4 1940.42 59.14 5 1552.33 63.09 6 1293.61 52.57 8 970.21 59.14 10 776.17 47.32 12 646.81 98.57 40 194.04 79.95
Carbide
3
76.20
8085.07 492.87 4 6063.80 739.30 5 4851.04 591.44 6 4042.54 492.87 8 3031.90 770.10 10 2425.52 616.08 12 2021.27 513.40 40 606.38 249.83
As mentioned in Section 3.6.3, cutting speeds and chipload values are given. From there,
calculating the recommended spindle speed of the tool and the feed rate in which the
workpiece is fed into the tool can be done using Equation 2 and 3 respectively. To note, in
Table 4, there is one chipload value given for a range of tool diameters, which means if the
tool diameter falls within that range, that will be the chipload value to be used for that tool
diameter. A sample calculation will be shown below using the HSS 3mm tool:
1) From Table 4, the 3mm tool falls within the 3/32 – 1/8’’ range, hence the Cutting
Speed is 24.38 m/min (after converting 80 ft/min) and the chipload value, 𝑓𝑧, is
0.0051 mm/tooth (after converting from in/tooth).
2) Using Equation 2, the spindle speed is calculated:
Spindle Speed (𝑛) =1000 × 𝑉𝑐
𝜋𝐷=
1000 × 24.38
𝜋 × 3= 2587.22 𝑅𝑃𝑀
3) And then using Equation 3 and recalling from Section 3.6.2.3 that the number of
flutes Z, was chosen to be 4 for all tool in the tool path simulations, the federate is
calculated:
𝑉𝑓 = 𝑛 × 𝑓𝑧 × 𝑍 = 2597.22 × 0.0051 × 4 = 52.57 𝑚𝑚/𝑚𝑖𝑛
42
These steps were repeated for the rest of the HSS tool diameters, and the same goes for the
Carbide tools, but using the chipload values from Table 5.
6.1.2 Tool Parameter for Cast Iron
Table 19 below shows the recommended tool parameters needed to machine Cast iron using
HSS and Carbide tools:
Table 19: Tool parameters for HSS and Carbide tools for machining Cast Iron
Tool Type Tool Size (mm)
Cutting Speed (m/min)
Spindle Speed (rpm)
Feed Rate (mm/min)
HSS
3
30.48
3234.03 98.57 4 2425.52 98.57 5 1940.42 138.00 6 1617.01 115.00 8 1212.76 160.18 10 970.21 128.15 12 808.51 205.36 40 242.55 99.93
Carbide
3
91.44
9702.09 492.87 4 7276.56 739.30 5 5821.25 591.44 6 4851.04 492.87 8 3638.28 739.30 10 2910.63 591.44 12 2425.52 492.87 40 727.66 299.79
The steps to calculate the Spindle Speed and Feed Rates were the same as described in
Section 6.1.1.
6.2 Output of Tool Path setups
This section shows the results obtained from the machining tool path simulations.
6.2.1 Expected Machining times
Expected machining times were obtained from the machining tool path simulations from the
following:
1) Fixed and Moving Dies of the Grate molds
a. 2x tool path simulation if both components were machined down from H13
tool steel. One simulation set was for machining with HSS tools and the other
was for machining with Carbide tools.
b. 2x tool path simulation for both components but this time if they were
machined down from cast iron blocks. One set was for machining HSS tools
and the other was for machining Carbide tools.
2) Fixed and Moving Dies of the leg molds
a. 1x tool path simulations if both components were machined down from H13
tool steel blocks
43
b. 1x tool path simulations for both components if they were machined down
from Cast Iron blocks
c. 1x tool path simulations for both components when machining their near net
shapes casted from the sand molds. The material these Dies are casted from is
SG400-15 cast iron
In total, 7 simulation sets were run for both the Fixed and Moving Dies.
6.2.1.1 Grate Mold Components: Expected machining
times
Table 20 below shows the expected machining times obtained from the tool path
simulations of the Fixed and Moving Dies of the Grate Mold:
Table 20: Expected machining times for the Grate Mold. Varying tool material and mold material.
TOOL PARAMETERS TOOL MATERIAL CARBIDE HSS CARBIDE HSS
MOLD MATERIAL H13 TOOL
STEEL H13 TOOL
STEEL CAST IRON
CAST IRON
MOLD COMPONENT
OPERATION NAME
EXPECTED MACHINING TIMES (MINS)
FIXED DIE
SIDE OPERATION (TOTAL)
51.12 480.62 18.97 292.98
PATERN OPERATION (MOLD GEOMETRY)
340.66 3830.51 37.94 2266.24
MOVING DIE PATTERN OPERATION (MOLD GEOMETRY)
524.75 2793.65 545.46 1366.82
TOTAL 916.53 7104.78 900.53 3926.04 TOTAL (HOURS) 15.28 118.41 15.01 65.43
See APPENDIX A2 for the output of the tool path simulation files.
44
6.2.1.2 Leg Mold Components: Expected machining
times
6.2.1.2.1 Conventional Mold Manufacturing method
Table 21 below shows the expected machining times obtained from the tool path
simulations of the Fixed and Moving Dies of the Leg Molds:
Table 21: Expected machining times for the Leg Mold. Varying mold material.
TOOL PARAMETERS TOOL MATERIAL CARBIDE CARBIDE MOLD MATERIAL H13 TOOL STEEL CAST IRON
MOLD COMPONENT
OPERATION NAME EXPECTED MACHINING
TIMES (HOURS)
FIXED DIE PATERN OPERATION (MOLD GEOMETRY)
30.98 31.80
MOVING DIE PATTERN OPERATION (MOLD GEOMETRY)
71.20 69.92
TOTAL (HOURS) 102.18 101.72
See APPENDIX A2 for the output of the tool path simulation files.
6.2.1.2.2 Machining time via machining Mold
components from Sand molds
Table 22 below shows the expected CNC mill machining time obtained from the tool path
simulations of the Fixed and Moving Dies of the Leg Molds, however, these machining times
are from the Fixed and Moving Dies that were casted from the sand molds.
Table 22:Expected CNC mill machining times for the Leg Mold components casted from sand molds.
TOOL PARAMETERS TOOL MATERIAL CARBIDE MOLD MATERIAL (CAST IRON) SG400-15
MOLD COMPONENT OPERATION NAME
EXPECTED MACHINING TIMES
(HOURS)
FIXED DIE PATERN OPERATION (MOLD GEOMETRY)
29.33
MOVING DIE PATTERN OPERATION (MOLD GEOMETRY)
22.00
TOTAL (HOURS) 51.33
See APPENDIX A2 for the output of the tool path simulation files
45
6.2.2 Estimated Machine Hire Costs vs Tool Material
Figure 27 below compares the estimated machining costs versus tool material. This is a
sample comparison and the Grate mold components used. This plot was created by getting
the total expected machining time for each mold and tool material configuration in Table
20 and multiplying that by the CNC machine hire rate of $77AUD as per UQFWG mentioned
in Section 5.3.2.3.
Figure 27: Plot comparing Machining cost estimates versus tool material for grate mold
6.3 COST ESTIMATES
6.3.1 Part Cost Estimates
Table 23 shows the cost estimates to cast one Grate (Figure 8) and a pair of Legs (Figure
11) in their respective molds. They are to be casted from Aluminum Grade AC603 (or AA
Grade 357.0) with their price per kg shown in Table 17. To note, for the Leg part, in Table
23, the mass per cast is 1.70kg (0.85kg in Table 9 is for one Leg) to represent the pair of
legs that are casted in their mold.
Table 23: Cost estimates for casting Grate and Leg parts for each cast
Grate Leg Mass per cast (kg)
Price ($AUD)
Mass per cast (kg)
Price ($AUD)
1.16 3.18 1.70 4.64
$1,176.56
$9,117.57
$1,155.77
$5,038.11
$0.00
$1,000.00
$2,000.00
$3,000.00
$4,000.00
$5,000.00
$6,000.00
$7,000.00
$8,000.00
$9,000.00
$10,000.00
H13 - CARBIDE H13 - HSS CAST IRON - CARBIDE CAST IRON - HSS
CO
ST
S (
$A
UD
)
TOOL MATERIAL USED FOR MACHINING MOLD MATERIAL
MACHINING COST ESTIMATES VERSUS TOOL MATERIAL
46
6.3.2 Grate Mold Components
Figure 28 below is a plot comparing of cost estimates for manufacturing the Grate mold
components out of H13 Tool Steel or Cast Iron blocks:
In regards to the results generated in Figure 28, Blair Knight from UQFWG explained that
the lead time estimated to make all mold components for the Grate is 3 to 6 months in total.
Labor cost estimates uses the assumption that the average lead time would be 4.5 months
(average between 3 to 6 months), which is inclusive of hiring out a CNC machine. Mr Knight
also mentioned that the toolmaker would be working full working days (8 hours) in those
months to manufacture all mold components, with any CNC machining being included in
that timeframe. Part of the assumption of labor cost estimates are that the CNC machinist
will be present throughout the CNC machining process; therefore, the machinist is paid for
the hours (expected machining time in this context) that the CNC machine is running (Blair
Knight, personal communication, May 16, 2018). Lastly, Engineer hire costs assumes
inspecting, creating drawings and programming tool path simulations for both the Fixed and
Moving Dies would take 8 hours each.
Another note about the results generated in Figure 28 is that the material cost estimates
are based on the total weight of all leg mold components for the Grate.
$1,176.56$632.15
$17,102.15
$18,910.85
$1,155.77$56.76
$17,102.15
$18,314.68
$0.00
$2,000.00
$4,000.00
$6,000.00
$8,000.00
$10,000.00
$12,000.00
$14,000.00
$16,000.00
$18,000.00
$20,000.00
Manufacturing Material(Mold)
Labor Total Manufacturing Material(Mold)
Labor Total
H13 CAST IRON
GRATE MOLD
CONVENTIONAL MACHINING
To
tal
Co
sts
($A
UD
)
Manufacturing Type
GRATE COST BREAKDOWN - H13 VS CAST IRON
Figure 28: Comparing cost estimates for manufacturing Grate mold components between H13 Tool Steel and Cast Iron blocks
47
6.3.3 Leg Mold Components
Figure 29 below is a plot comparing cost estimates for manufacturing the Leg mold
components out of H3 Tool Steel of Cast Iron blocks:
The results generated in Figure 29 come about from the same notes as mentioned under
Section 6.3.2. The only difference is that an extra 2 hours is added to accommodate for the
inspection and creating drawings for the sliders for the Engineer hire costs. Even though
they do not get machined in the CNC mill, they do need documentation such as 2D drawings
for the toolmaker to make.
$7,867.86
$2,965.67
$17,163.74
$27,997.27
$7,832.44
$266.26
$17,163.74
$25,262.44
$0.00
$5,000.00
$10,000.00
$15,000.00
$20,000.00
$25,000.00
$30,000.00
Manufacturing Material(Mold)
Labor Total Manufacturing Material(Mold)
Labor Total
H13 CAST IRON
LEG MOLD
CONVENTIONAL MACHINING
To
tal
Co
sts
($A
UD
)
Manufacturing Type
LEG COST BREAKDOWN - H13 VS CAST IRON
Figure 29: Comparing cost estimates for manufacturing Leg Mold components between H13 Tool Steel and Cast Iron blocks
48
Figure 30 below shows the comparisons of the cost estimates between manufacturing the Leg mold components with the conventional method
(machining down from H13 tool steel and Cast iron blocks) and manufacturing them via machining off from a near net shape casted from 3D
printed sand molds
Figure 30: Cost comparisons for Leg Mold components - Conventional machining from tool steel and cast iron blocks versus machining from near net shape via sand molds
$9,232.41
$4,838.70
$7,054.27
$21,125.37
$7,832.44
$266.26
$17,163.74
$25,262.44
$7,867.86
$2,965.67
$17,163.74
$27,997.27
$0.00
$5,000.00
$10,000.00
$15,000.00
$20,000.00
$25,000.00
$30,000.00
Ma
nu
fact
uri
ng
Ma
teri
al
(Mo
ld)
La
bo
r
To
tal
Ma
nu
fact
uri
ng
Ma
teri
al
(Mo
ld)
La
bo
r
To
tal
Ma
nu
fact
uri
ng
Ma
teri
al
(Mo
ld)
La
bo
r
To
tal
NEAR NET SHAPE MANUFACTURING (VIA SANDPRINTER)
CONVENTIONAL MACHINING - CAST IRON BLOCK CONVENTIONAL MACHINING -H13 IRONBLOCK
CO
ST
S (
$A
UD
)
MANUFACTURING METHOD
COST COMPARISONS FOR LEG MOLD - VIA SAND PRINTING VS CONVENTIONAL MACHINING
49
To note about the results generated in Figure 30, especially for the near net shape
manufacturing via casting the Leg molds from the sand molds:
- From an email interview with Dr Gui Wang about the Voxeljet VX1000
sand printer, the printer set up and clean up times total 4.5 hours for
each print job (mentioned in Section 5.3.2.3). From the sand mold
assemblies seen in Section 5.4.1.2.1, there are 4 sand molds for each
of the Fixed and Moving Die (Gui Wang, email communication, May 16,
2018). Cope and Drag halves are printed together in pairs, and thus, the
3D sand printer is set up and cleaned 4 times. Therefore, the total
hours of setting up and cleaning the sand printer is 18 hours.
- From a personal interview with Dr Gui Wang regarding the Voxeljet
sand printer, the average print time (time taken for the sand printer to
fill the entire content of the job box) is 12 hours (Gui Wang, personal
communication, May 9, 2018). With 4 print jobs in total, the total
machine hire time for the 3D Sand printer should be approximately 48
hours which is added onto the CNC machine hire time
- In terms of raw materials, the amount of sand binders equals the mass
of the sand molds which total to about 1139.82 kg (found through CAD
models) for all 4 3D printed copes and drags.
- Unlike the conventional mold making techniques, the lead time to
manufacture the Grate and Leg molds would be about 1 month. This is
based off the interview with Blair Knight in which he mentioned that
preparing a Die to be square takes a month (Blair Knight, personal
communication, May 16, 2018).
6.4 Production Run Cost Estimates
6.4.1 Grate Mold Components
Figure 31 below shows the plot comparing cost estimates for production runs with Grate
mold components being made either from H13 tool steel or Cast iron:
50
500 1000 2000 5000 10000 25000 50000 100000
GRATE MOLD: H13 TOOL STEEL BLOCK $41.00 $22.09 $12.64 $6.96 $5.07 $3.94 $3.56 $3.37
GRATE MOLD: CAST IRON BLOCK $39.81 $21.49 $12.34 $6.84 $5.01 $3.91 $3.55 $3.36
$0.00
$5.00
$10.00
$15.00
$20.00
$25.00
$30.00
$35.00
$40.00
$45.00T
OT
AL
CO
ST
PE
R U
NIT
($
AU
D)
NUMBER OF PARTS
PRODUCTION RUN COST COMPARISONS: GRATE MOLD
Figure 31: Production run cost comparisons for Grate Mold components. Comparing cost per unit between manufacturing mold components from H13 tool steel and cast iron blocks
51
The plot generated in Figure 31 makes use of Section 3.5.1. The plot illustrates the effect
of economies of scale on the costs to make the Grate using the Grate mold components.
From the plot, it shows that there is not much difference in terms of cost per unit of the grate
if its mold was made from either machining down H13 tool steel or Cast-iron blocks. It can
be seen that starting at a production run of at least 5000 grate parts, the total cost per unit is
almost identical.
Te plot was generated using Equation 1 to find the total cost per unit and is expressed as:
𝑇𝑜𝑡𝑎𝑙 𝐶𝑜𝑠𝑡
𝑢𝑛𝑖𝑡=
𝐹𝑖𝑥𝑒𝑑 𝐶𝑜𝑠𝑡
𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑟𝑢𝑛+
𝑉𝑎𝑟𝑖𝑎𝑏𝑙𝑒 𝑐𝑜𝑠𝑡
𝑢𝑛𝑖𝑡
Where:
▪ Total cost/unit represents the unit cost of the Grate part at the particular production
run volume
▪ Fixed cost is the total cost of the mold components of the Grate
▪ Variable cost is the price of the Grate material to be casted (and is already in a per
unit term)
A sample calculation is demonstrated for a production run for 500 parts if the Grate molds
are to be made from H13 tool steel:
- Total Cost of all of all Grate mold components (Fixed cost) =
$18,910.85 (from Figure 28).
- Variable cost per unit = $3.18 (from Table 23 – this is the cost of the
aluminum material for every cast to make the Grate)
- Production run = 500 units of the Grate
𝑇𝑜𝑡𝑎𝑙 𝐶𝑜𝑠𝑡
𝑢𝑛𝑖𝑡=
𝐹𝑖𝑥𝑒𝑑 𝐶𝑜𝑠𝑡
𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑟𝑢𝑛+
𝑉𝑎𝑟𝑖𝑎𝑏𝑙𝑒 𝑐𝑜𝑠𝑡
𝑢𝑛𝑖𝑡
𝑇𝑜𝑡𝑎𝑙 𝐶𝑜𝑠𝑡
𝑢𝑛𝑖𝑡=
$18910.85
500+ $3.18 = $41.00
52
6.4.2 Leg Mold Components Figure 32 below shows the plot comparing cost estimates for production runs with Leg mold components being made conventionally
(machining down from H13 tool steel and cast iron blocks) and via the proposed solution (machining from near net shape casts made from sand
molds):
Figure 32:Production run cost comparisons for Leg Mold components. Comparing cost per unit between manufacturing mold components from H13 tool steel, cast iron blocks and machining from a near net shape cast from 3D printed sand molds
500 1000 2000 5000 10000 25000 50000 100000
LEG MOLD: H13 TOOL STEEL BLOCK $60.63 $32.64 $18.64 $10.24 $7.44 $5.76 $5.20 $4.92
LEG MOLD: CAST IRON BLOCK $55.16 $29.90 $17.27 $9.69 $7.17 $5.65 $5.14 $4.89
LEG MOLD: SAND PRINTING MOLD $46.89 $25.76 $15.20 $8.86 $6.75 $5.48 $5.06 $4.85
$0.00
$10.00
$20.00
$30.00
$40.00
$50.00
$60.00
$70.00
TO
TA
L U
NIT
CO
ST
S (
$A
UD
)
NUMBER OF PARTS
PRODUCTION COSTS COMPARISONS: LEG MOLD
53
The plot generated in Figure 32 makes use of Section 3.5.1 just like with Figure 31. The
plot in Figure 32 illustrates the effect of economies of scale on the costs to make the Legs
using the Leg mold components. From the plot, it shows that there is not much difference in
terms of cost per unit of the Leg if its mold was made from either machining down H13 tool
steel or Cast-iron blocks. It can be seen that starting at a production run of at least 5000 Leg
parts, the total cost per unit is almost identical. However, the alternative solution of
manufacturing the Leg molds via machining down from the casts made from the sand molds
is significantly cheaper in all volumes of production compared against the conventional mold
making technique.
To note, the plot was generated using Equation 1 to find the total cost per unit of the Legs
and is expressed as:
𝑇𝑜𝑡𝑎𝑙 𝐶𝑜𝑠𝑡
𝑢𝑛𝑖𝑡=
𝐹𝑖𝑥𝑒𝑑 𝐶𝑜𝑠𝑡
𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑟𝑢𝑛+
𝑉𝑎𝑟𝑖𝑎𝑏𝑙𝑒 𝑐𝑜𝑠𝑡
𝑢𝑛𝑖𝑡
Where:
▪ Total cost/unit represents the unit cost of the Leg parts at the particular production
run volume
▪ Fixed cost is the total cost of the mold components of the Legs
▪ Variable cost is the price of the Leg material to be casted (and is already in a per unit
term)
A sample calculation is demonstrated for a production run for 1000 parts if the Leg molds
are to be made via the 3D Sand printer:
- Total Cost of all of all Grate mold components (Fixed cost) = $21125.37
(from Figure 30).
- Variable cost per unit = $4.64 (from Table 23 – this is the cost of the
aluminum material for every cast to make the Legs)
- Production run = 1000 units of the Grate
𝑇𝑜𝑡𝑎𝑙 𝐶𝑜𝑠𝑡
𝑢𝑛𝑖𝑡=
𝐹𝑖𝑥𝑒𝑑 𝐶𝑜𝑠𝑡
𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 𝑟𝑢𝑛+
𝑉𝑎𝑟𝑖𝑎𝑏𝑙𝑒 𝑐𝑜𝑠𝑡
𝑢𝑛𝑖𝑡
𝑇𝑜𝑡𝑎𝑙 𝐶𝑜𝑠𝑡
𝑢𝑛𝑖𝑡=
$21125.37
1000+ $4.64 = $25.76
54
7.0 DISCUSSION
This section discusses the results generated in Section 6.0.
7.1 Tool Parameters calculated in 6.1.1 and 6.1.2
For the Cut speeds shown in Tables 18 and 19, it can be seen that the harder Carbide tools,
have a higher cutting speed than HSS. Additionally, the Cutting speeds are faster for HSS
and Carbide tools when machining a relatively soft material, i.e. cast iron in Table 19.
For both Tables 18 and 19, it can be seen that the spindle speeds decrease with increasing
tool diameter, which is to be expected as the cutting speed is kept constant for the mold
material. Therefore, in order to keep the cutting speed constant of the tool constant, the
spindle speed must decrease.
In Tables 18 and 19, the feed rates do not show a uniform trend with increasing tool
diameter. This may be caused by factoring the chipload value for the tool size. However, it
can be seen that the feed rates for the Carbide tools are faster than the HSS tools which agree
mostly with what was mentioned in Section 3.6.2.1.
To note about tool parameters found in Tables 18 and 19, these parameters are inserted
into the machining tool path file simulations and are set when the simulation is run.On the
other hand, in practice, these tool parameters are a starting point for a machinist as they can
be increased or decreased depending on how the cutting conditions of the tool and workpiece
are. This assertion is made because these parameters were calculated based on
manufacturer’s recommendations. However, just like with the charts provided by a
manufacturer such Tools Today (n.d.), they mention changing them slightly is possible. This
may affect the actual machining time, but as long as the parameters are close to what is used
in the tool path simulations in the CAM workspace, the output for the machining time in the
simulation should be approximately close to the actual machining time.
7.2 Expected Machining times calculated in 6.2
The term expected is used because the tool path simulations are based strictly on the value of
the tool parameters calculated in Tables 18 and 19. The CAM software is not flexible in
changing these parameter values for a specific tool while it is in the middle of a cutting
operation like a CNC machinist can, therefore, all machining times are estimated or expected
based on the tool parameter values assigned for each tool operation in the tool path files.
7.2.1 Expected machining times for Grate Mold
components
Table 20 summarizes the expected machining times calculated by the CAM software for the
Grate Molds when manufacturing the molds from tool steel and cast iron blocks. For the
Grate mold tool path files, four simulations were run and this was done to compare the
expected machining times if HSS tools were used versus Carbide tools. The four simulations
that were run were:
1) Tool Material: Carbide, Mold Material: H13 tool steel
2) Tool Material: HSS, Mold material H13 tool steel
55
3) Tool Material: Carbide, Mold material: Cast Iron
4) Tool Material: HSS, Mold material: Cast Iron
Between the four simulations, the ones with the longest expected machining times were the
simulations which uses HSS as the tool material, with the longest expected machining time
being the simulation with HSS as the tool material and Mold material as H3 tool steel.
Between the simulations that uses Carbide as the tool material, machining down from cast
iron blocks is relatively quick at 15.01 hours, as compared to 15.28 hours with H13 tool steel.
However, the time difference between these two simulations is 16 minutes.
This expected machining times calculated by the simulations are based on the tool
parameters calculated in Tables 18 and 19 and the time to machine reflect what was
mentioned in Section 3.6.3.
7.2.2 Expected machining times for Leg Mold
components
For the leg mold, three simulations were run, two of them being from the conventional
method for making molds (machining down from tool steel and cast iron blocks) and the
other from machining down a near net shape cast of the Leg molds from the 3D printed sand
molds.
7.2.2.1 Expected machining time from conventional
mold manufacturing technique
Table 21 summarizes the expected machining times calculated by the CAM software for the
Leg molds using the conventional method. From Table 21, it is observed that the
simulations only use Carbide tools. That is because, based on the simulations involving HSS
tools in Table 20, the expected machining times are too long with HSS tools. As a result,
carbide tools are only considered and the comparison now looks at what type of material the
mold should be made out of (H13 or Cast iron) based on the expected machining times. From
Table 21, it can be seen that the total expected machining times for both the Fixed and
Moving Dies are 102.18 hours for simulating machining down H13 tool steel and 101.72
hours for simulating machining down Cast iron blocks. The time difference between the two
simulations is about 28 minutes.
The expected machining times are close to each other, but it may be caused by the fact that
even if the cutting speed for carbide tools is faster for the Cast iron (Table 19) than H13 tool
steel (Table 20), the feed rates calculated for the carbide tools for machining H13 tool steel
and Cast iron (Table 19 and 20) are close to each other.
7.2.2.2 Expected machining time from near net shape
casts from sand molds
Table 22 shows the expected machining time from the tool path files which simulate
machining down the near net shapes of the Fixed and Moving dies that were casted from the
3D printed sand molds. The expected machining time was calculated to be 51.33 hours,
significantly less than the expected machining times shown in Table 21 for the conventional
mold making technique. This is because the machining step for the Mold components casted
from the sand molds are mainly a finishing step rather than the main step in the
56
manufacturing method. Even if that is the case, the reduced machining time using the
printed sand mold method is a positive sign.
7.3 Machining cost estimates versus tool material (Figure
27)
The purpose for this plot was to compare the estimated price to hire a CNC mill machine
based on the tool material. Figure 27 shows that the costs to hire the CNC machine will be
very expensive if HSS tools are used, rather than Carbide tools. Machining from Carbide
tools, from Table 20, shows that they achieve the lowest expected machining times and
based on Figure 27, to hire a CNC machine and using Carbide tools to machine H13 tool
steels represents an estimated AUD$7,941 savings and a AUD$3,882 savings if machining
cast iron blocks. These price differences illustrated in Figure 27 explains why HSS tools are
not considered for simulating for the Leg mold components because of how big the job is
(the Leg mold components are larger than the Grate mold components) because of the
expense.
7.4 Part cost estimates (Table 23)
Table 23 shows the cost estimate for the material (Aluminum AC603) that will be poured
into the mold for casting the Grate and Leg parts. It was included because these are the
values that were used to help plot out the total cost per unit of the parts for the production
run cost curves seen in Figures 31 and 32.
7.5 Mold Cost Estimates
7.5.1 Grate Mold Components
From Figure 28, it can be seen that the total estimated costs to manufacture the mold out of
H13 tool steel would be about AUD$18,910.85 while it would be about $18,314.68 if it was to
be made out of Cast iron.
The total Labor costs works out to be the same because in the breakdown, the Engineering
hire stays constant (8 hours to work on each mold component for a total of 16 hours). The
Machinist hire time is almost the same because of the expected machining times being close
to each other, with the same going to the Toolmaker hours. (The toolmaker hours was
calculated by getting the total hours of the assumed lead time and subtract the expected
machining time from that).
The machining cost estimates are almost the same because the expected machining times
summarized in Table 20 are 15.01 and 15.28 hours for the simulations looking at making
the mold components out od H13 tool steel and cast iron respectively.
The main price difference comes from the total material costs because H13 tool steel is
relatively more expensive. The total costs for the H13 tool steel to make the Grate molds is at
$632.15 comparing to $56.76 total for the cast iron.
57
7.5.2 Leg Mold components
The total costs of the mold components, illustrated in Figure 29, are AUD$27,997.27 (if
made from H13 tool steel) and AUD$25,262.44 (if made from Cast iron).
The labor costs in Figure 29 are the same because the hire rates and times stay constant for
the Engineer. Also, because the expected machining times from Table 21 are almost the
same, the hire times for the CNC machinist and toolmaker is roughly the same.
What creates the price difference in the estimated total costs in Figure 29 between the
conventional mold making methods is the total price of the mold material. Figure 29 shows
that the total material cost for H13 tool steel is $2965.67, whereas it is only $266.26 for Cast
iron.
Figure 30 shows the estimated cost breakdown for both the conventional mold
manufacturing technique versus the proposed alternative of using 3D printed sand molds.
This was done to compare each mold making technique cost-wise. What can be seen is that,
compared to the conventional mold making method (whether the mold components are to be
made from H13 tool steel or cast iron), the labor costs for making molds using the 3D printed
sand molds dramatically decrease by approximately AUD$10,000. Even if the costs of
manufacturing increases by about AUD$1,365 (against the conventional methods), material
costs increase by about $4,570 (as compared to machining down from cast iron blocks), and
$1,870 (as compared to machining down from H13 tool steel blocks), because the 3D Sand
printer decreases the total labor hours of the CNC machinist and toolmaker, the total cost
estimate for making the Leg molds via the sand printer is reduced to AUD$21,125.37. By
using the sand printer to manufacture the Leg mold components (specifically the Fixed and
Moving dies), the cost reduction in the total price to manufacture the Leg molds is 16%
compared against machining from Cast iron blocks and 25% compared against machining
from H13 tool steel blocks.
7.6 Production run cost estimates
Production run cost estimates were done to check which manufacturing technique provides
the best total cost per unit for the Grate and Legs for mid-volume production runs. Finding
the manufacturing method that achieves a lower the total cost per unit is desired because it
provides a possibility for larger sales margins or competitive selling prices for the company.
The total cost per unit represents the price to manufacture one unit of Grate or Leg
components in the particular production quantity.
7.6.1 Grate part and mold components (Figure 31)
From Figure 31, the effect of economies of scale can be seen as the total cost per unit
decreases with the production volume for both manufacturing techniques.
For a production volume of 2,000 castings, Figure 31 shows that the mold components
made from machining down Cast iron blocks is slightly cheaper than machining down from
H13 tool steel blocks, however, as the production volume increases to 10,000 casts, the total
cost per unit starts to reach the same value.
58
7.6.2 Leg part and mold components (Figure 32)
The effect of economies of scale are also displayed in Figure 32 as total cost per unit price
decreases with the production volume for all manufacturing techniques.
Comparing all the manufacturing methods in Figure 32 shows that , between machining
from H13 tool steel and Cast iron blocks, mold components made from the Cast iron blocks
have a cheaper total cost per unit for a production run of up to 10,000 casts. However, when
incorporating the manufacturing method of using 3D printed sand molds in Figure 32
(Grey line), the total cost per unit is cheaper than the conventional techniques for a
production volume of up to 10,000 castings.
8.0 CONCLUSIONS AND RECOMMENDATIONS
8.1 Conclusions
This project was undertaken with the intent to investigate how molds are made, how they
apply to the permanent mold casting process and to compare which mold manufacturing
techniques would be best suited to make molds for a mid-volume production run (up to
10,000 parts).
Based on the literature review done in accordance with the scope of the project set out by Dr
Gui Wang, the manufacturing techniques explored the areas were machining blocks of H13
tool steel and Cast iron blocks down to the desired shape (which was labelled as the
conventional mold making technique as normal mold making techniques involved heavy use
of CNC-based machining and toolmaker labor skills) using a 3D Sand printer offered by
CSIRO’s Lab22 facility to print sand molds which generate a near net shape cast of the mold
components that would be machined down into the required tolerance and specifications
(which was the alternative solution).
In order to figure out the most cost-effective solution for making molds for a mid-volume
production run, goals for the project were set to generate a generic cost spreadsheet that
could be easily used to compare the costs of different mold manufacturing techniques, and to
show that using the 3D Sand printer to make near net shape casts of molds (the alternative
solution) would be a more cost effective solution to make molds.
Based off the results produced in Section 6.0 and the discussions made in Section 7.0:
1) A generic cost spreadsheet was successfully made and it aided in the cost comparison
of the different mold making techniques. APPENDIX A1 shows the spreadsheet that
was used and build up from the template
2) Based on Figure 30 and its related discussions in Section 7.5 and 7.6, it can be
seen that the alternative solution of using the 3D Sand printer to make sand molds in
order to cast near net shapes of mold components is cost effective, and, because it is
cheaper, it provides a lower total cost per unit value to cast leg pairs for a mid-volume
production run as seen in Figure 32.
59
8.2 Recommendations
Based on the results generated Section 6.0 and discussions in Section 7.0, some
recommendations are as follows:
1) From Figure 27, even if harder tools such as Carbide have a higher upfront cost, it is
recommended to use them as they may provide faster machining times because of
their ability to take faster speeds and feeds
2) From Figure 28, if costs are the utmost priority in making the Grate Molds, i.e.
make them as cheap as possible, then it is recommended to make the Grate Molds out
of Cast Iron blocks.
3) From Figure 30, it can be seen that using the near net shape approach via the 3D
sand molds (alternative solution) has the cheapest total costs versus the conventional
mold making methods by about AUD$10,000. Therefore, the alternative solution can
be used to make the Leg mold components and with the Leg mold components bring
casted from Cast Iron SG400-15.
From conducting this project, below are some recommendations that can help enhance this
project going further:
1) Try apply the alternative solution to the Grate mold components, i.e. check to see if it
is also cost-effective to 3D print sand molds that achieve a near net shape of the Grate
mold components and machine them down to required specifications;
2) Gain access to CAM software that allows programming machining path files for a 5-
axis CNC machine and see if it:
a. Is suitable to make molds components using it; and
b. Can reduce the expected machining times of the mold components;
3) Consult other manufacturers. All costs especially for machining processes and lead
times were estimated from consulting UQFWG and UQFWG’s toolmaker, Blair
Knight;
4) Attempt to build the components and compare with the actual cost figures especially
for the conventional solutions.
60
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APPENDIX
A1: COST MODEL SPREADSHEET USED IN PROJECT (Input Parameters for Grate and Leg mold Sheet)
65
(Grate mold cost estimates) (Leg Mold cost estimates)
66
(Input Parameters for Leg Mold – Sheet used for cost estimate using 3D sand printer)
67
(Leg mold cost estimates using the 3D sand printer)
68
(Grate and Leg parts cost – This sheet was used to calculate the mass of these parts that will be casted into their respective molds)
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(Production Costs calculation sheet)
70
Generic cost spreadsheet template – Before spreadsheet was filled in, the template looked like this:
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A2: CAM TOOL PATH CUTTING SIMULATION OUTPUT The following images are the outputs of each tool path simulations.
1) GRATE MOLD COMPONENTS
a. Mold Material: H13 Tool Steel, Tool Material: Carbide
Fixed Die – Machining face geometry
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Fixed Die – Side Operation (since both sides the same, expected machining time is
multiplied by 2)
Moving Die – Machining face geometry
73
b. Mold Material: Cast Iron, Tool Material: Carbide
Fixed Die – Maching face geometry
Fixed Die – Side operation (same for both sides)
74
Fixed Moving – Maching face geometry
c. Mold Material H13 Tool Steel, Tool Material: HSS
Fixed Die -Machining face geometry
75
Fixed Die – Side Operation
Moving Die-Machining face geoemetry
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d. Mold Material: Cast Iron, Tool Material: HSS
Fixed Die – Machining face geometry from Cast Iron block
Fixed Die – Side Operation – machining pocket from Cast Iron block
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Moving Die – Machining face geometry from Cast Iron block
2) LEG MOLD COMPONENTS
(Tool Path outputs from Conventional Mold manufacturing technique)
a) Mold Material: Cast Iron, Tool Material: Carbide
Die Fixed – Machining face geometry from Cast Iron block
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Die Moving – Machining face geometry from Cast Iron block
b) Mold Material: H13 Tool Steel, Tool Material: Carbide
Die Fixed – Machining face geometry from Tool Steel Block
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Die Moving – Machining face geometry from Tool Steel Block
(Tool Path outputs from Machining Fixed and Moving Dies that were casted from sand
mold)
Die Fixed – Machining off excess material from near net shape Mold component
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Die Moving – Machining off excess material from near net shape Mold component
A3: PERMANENT MOLD CASTING - The image below shows the general setup of the permanent mold
casting process
Courtesy of: http://www.custompartnet.com/wu/permanent-mold-casting
- The table below shows the Aluminum alloy 300 series that is popular to
use with the permanent mold casting process
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A4: SAND CASTING The typical setup for sand casting:
Courtesy of http://www.custompartnet.com/wu/SandCasting#capabilities
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A5: VOXELJET VX1000 SAND PRINTER SETUP The Typical setup of a Voxeljet VX1000 3D Sand Printer
Courtesy of Voxeljet (https://www.voxeljet.com/3d-drucksysteme/vx1000/)
Job Area
