Pattern Manufacture / Mold

Assembly

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Process Flow ChartPattern Manufacture/Mold Assembly

Wax injection Assembly

Shell build Dewax

Wax

cool

Dimensional

inspection

Visual

inspection

Patterns

OK?

Patterns

OK?

Mold

inspection

Mold

OK?Mold preheat

Mold repair

Cast Mold

CleanKnockout Cutoff GrindVisual

inspection

Yields,

defects, etc.

Final dry

Mold cool

Y Y

Y

N N

N

Wax Injection Tooling

3

• Tooling features drive pattern and/or

casting costs and quality.

• Trade offs exist among tooling designs

/ costs and pattern costs.

Why is the Tool Design so

Important?

Materials for Tooling

Construction

• Aluminum – Excellent thermal

conductivity.

• Brass - Good resistance to galling

• Hardened steel – Length of life.

• Epoxy, soft metal, additive

manufacturing - Used for short run

prototypes.

General Types of Tooling

• Automatic Tool

• Manual Tool

• Semi-Automatic Tool

7

Tooling Examples

Pattern Manufacture Materials

• Many materials can and are used to

create patterns used in Investment

Casting

• In this chapter we are going to discuss

most commonly used material: wax

Investment Casting Waxes

Different Types of Waxes used

in Investment Casting

• Pattern Waxes

– Non-Filled

– Filled

• Gating

• Specialty Waxes

• Reclaimed Waxes

Hollow Pattern Manufacturing

• Cavity formation

– By Tooling

– By Soluble Cores

– By Ceramic Cores

Water Soluble Cores

Ceramic Cores

Ceramic Cores do the

same thing as soluble

wax cores but became

part of the shell and are

removed after the

casting is “knocked out”

14

Ceramic Cores

Used to form voids in

castings

Dimensional accuracy

is very high

15

Ceramic Cores

Very complex shapes

can be formed

More expensive than

water soluble cores

Wax Equipment & Process Control

in the Wax Room

Wax Equipment & Process

Control in the Wax Room

• Wax Melting

• Wax Injection

• Pattern Assembly

Wax Melting and Preparation

• The method in which pattern wax is

melted, conditioned, and loaded into

wax injectors will directly effect the

quality of wax patterns produced by

the wax injector.

Wax Melting

• Many different methods

• Separate melting and transferring to

machines

• Melting as integral part of injection

machine

Wax Injection Equipment

• There are different types of wax

injectors with different press designs.

• Semi Automatic

• Fully Automatic

• C-Frame design

• 4 Post or guide column design

Injection Machine BasicsWhat does the wax injection machine do?

Stirs wax

Holds

wax

Die

Connects the injection

system to the die

Wax Pressure

Forces the wax in

the die

Clamps die

Controls

wax

temperature

Wax Flow

Controls the

speed of wax

Wax Injection Presses

Wax Injection Process

• Wax Injection is the process of filling a

wax die (mold) with wax.

Liquid Injection

• A wax in a liquid state should be used to inject large

thin section parts with a lot of detail.

– A liquid wax has lower viscosities and lower surface

tensions, so it can inject under lower pressure.

– Liquid injected patterns are more prone to air entrapment,

caused by turbulence during injection.

– Therefore it is important to control the speed of the wax

during injection for ideal mold filling.

– Liquid injected patterns have higher volumetric shrinkage.

Common injection system

consist of:

• Wax Reservoir

• Injection Unit

• Injection Nozzle

• Wax Die

Injection System has a

uniform Temperature of

65ºC

Machine produces quality

repeatable patterns

After continuous injections

the level of wax drops in

the wax reservoir

Liquid Wax Injection Machine Stable and ready for operation

Liquid Wax Injection MachineTypical Operating Cycle

Close wax valve & clamp

wax die

Open nozzle valve

Inject

Close nozzle valve

Open wax die

Open the wax valve &

remove wax pattern

Refill injection unit

Cycle complete

Wax reservoir 50% full

Liquid Wax Reservoir

Manual Wax Refill

Reservoir refilled with 170ºF

wax

20ºF Increase in temperature

After mixing, temperature of

wax in the reservoir becomes

an average temperature of

160ºF

This is an increase in

temperature of 10ºF

Higher Temperature wax is

passed through the entire

wax system.

Machine will take several

hours return to a stable

condition.

Liquid wax reservoirs do not

have the ability to cool

Dimensional change to

patterns

Sink

Flow lines

Air in pattern

Variable injection

requirements

Direct Melting: Melting Plates

Melting Plate Mounted to a

Wax Reservoir

Direct melting

Automatic operation

Need to match the

reservoir’s conditioning

rate

Liquid Wax Reservoir

With Direct Melting

Liquid Wax Reservoir

With AutoFill

27-4 Wax at 71 ºC (160ºF) 27-4 Wax at 74 ºC (165ºF)

Liquid Wax Injection

Paste (Semi-Solid) Wax

• A wax is defined as being in a Paste State

when it is at a higher viscosity than a liquid

wax. Over 10,000 cP, and as high as

400,000 cP.

• The temperature of the wax in a paste state

depends on the wax formula. Paste

temperatures are generally below 140°F.

Wax Conditioning ReservoirPaste Wax Reservoir

With AutoFill

27-4 Wax at 60 ºC (140ºF) 27-4 Wax at 63 ºC (145ºF)

Paste Wax Injection

Wax Injection Process

• Pattern quality depends on how well

you replace the air in a die with wax.

• If you remove 100 % of the air from

the die and replace it with wax you will

achieve a quality wax pattern.

Wax Injection Machine Control

Variables

• Wax Temperature

• Die Temperature

• Wax Flow

• Wax Pressure

• Injection Time

• Hold Time

Selecting the Correct Injection

Parameters

• Selecting the correct injection

parameters generally starts with some

experience from your wax room.

• Select a wax injection procedure sheet

for a part that is similar in size and

features as your new part (i.e. similar

overall dimensions and wall thickness).

160 ºF, 50 PSI, Flow 3.5 140 ºF, 50 PSI, Flow 3.5

Injection Parameter ExampleTemperature Variation

180ºF with Flow of 3.5 turns 140ºF with Flow of 3.5 turns

Injection Parameter ExampleTemperature Variation

180ºF with Flow of 3.5 turns 140ºF with Flow of 3.5 turns

Pattern Assembly

• The attachment of wax patterns to the wax runner

• The complexity of the assembly is driven by the gating and runner systems that are required for proper metal pour to make a sound casting

• Requires skill and care to insure good wax welds or wax seals

• Poor wax welds will result in broken patterns and metal inclusions

HORIZONTAL SURFACE

Requires the pattern gate

to be smaller then the

surface of the runner…

Requires surface area

around the pattern gate to

form a fillet weld…

This is true regardless of

the welding method being

used.

Wax Weld – Pattern to Sprue

VERTICAL SURFACE

Welding a pattern gate to

a vertical surface of the

runner…

Causes wax running and

or dripping...

Requires rework…

This is true regardless of

the welding method being

used.

Wax Weld – Pattern to Sprue

Typical Assembly

Pattern Assembly

Wax Mold Assembly &

Inspection (Video)

Injected Assembly

47

Pattern Defects

• There are many types and causes of

pattern defects and the ICI has a very

good Atlas of Wax Pattern Defects.

• Typical examples include flow lines,

knit lines and air bubbles.

• Atlas and other reference materials are

located on the ICI website.

48

Pattern Defects

Non-Fill Causes

• Flow Rate too low

• Low Injection Pressure

• Wax to cold

• Die to cold

49

Pattern Defects

Non-Fill Causes

• Flow rate to high

• Wax to hot

• Trapped air due

to improper die

Venting

• Excessive die

release

Additive/Subtractive

Manufacturing

• Investment casting patterns made

without using tooling

– 3D printing

– Machining pattern/core shape

• Details will be discussed later

Pattern Manufacture / Mold

Assembly

Thank you.

Any Question?