Three Plate

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UNIVERSITI I

- v l l

EKNIKAL MALAY SIA MELAK A

Analysis of Plastic low inside the Three Plate

Mould

Thesis submitted in accordance with the partial requirements of the

Universiti Telcnikal Malaysia Melaka for the

Bachelor of Manufacturing Engineering Manufacturing Design)

Nurul Syarafina bt Sholahuddin

Faculty of Manufacturing Engineering

May 2007



ABSTRACT

The purpose of this project is to analyze the behavior of the plastic flow inside the three

plate mould by using Moldex software. This research project was done by calculating

the optimum size of feeding systems including sprue runner and gate. Besides that the

research focused on identifling the suitable location of gate runner system and sprue

system. Other than that this research was to understand the parameters involved in flow

simulation typ of the plastic material typ of mould and typ of injection moulding

machine. In order to complete this research hand phone housing for Nokia 2210 model

was chosen as the D model. The D modeling of hand phone housing was prepared

using Solidwork software. Then transferred to Rhinocerous software. After the D

modeling was exported Rhinocerous software was used to do the meshing process on

the part surface and then continue to design the runner gate and sprue. fter that plastic

flow analysis of Nokia 221 0 mould was done using Moldex software. As result various

defects have been identified on Nokia 221 0 such as short shot weld line and air trap.



Kajian projek ini bertujuan untuk mengkaji kelakuan aliran plastik di d l m acuan tiga

plat dengan menggunakan perisian Moldex. Kajian ini dilakukan dengan mengira s iz

yang optimum terhadap spru pelari dan get. Lokasi b gi sistem get sistem pelari dan

sistem spru juga dikenalpasti. Seterusnya kajian ini diteruskan dengan memahami

semua parameter yang terlibat d l m simulasi aliran jenis bahan plastik berkenaan

dengan acuan dan jenis pengacuan suntikan. Untuk menyempurnakan kajian ini

perumah telefon bimbit Nokia siri 2210 dipilih sebagai model 3D. Penyelidikan ini

h u l a dengan melukis model 3D perurnah telefon bimbit yang dipilih dengan

menggunakan perisian Solidwork. Dari perisian Solidwork lukisan model dipindahkan

ke perisian Rhinocerus untuk proses seterusnya. Dengan menggunakan perisian

Rhinocerus proses penjaringan pada permukaan model dilakukan seterusnya rekabentuk

pelari get dan spru dihasilkan dengan mengambilkira s iz d n kedudukan yang sesu i

dengan acuan tiga plat. Setelah semua proses merekabentuk sistem p d acuan selesai

fail dipindahkan ke perisian yang seterusnya iaitu perisian Moldex. Dalam perisian

Moldex pemilihan bahan plastik yang sesuai dilakukan cl n parameter-parameter yang

tertentu ditentukan sehingga mencapai tahap optimum. Setelah analisa dijalankan

keputusan mendapati terdapat beberapa kerosakan dikenalpasti seperti plastik tidak

lengkap garis kimpal d nair yang terperangkap.



CHAPTER 1

1 0 INTRODUCTION

1 1 ackground

Plastic materials are the most important material in the world. The history of plastics

goes back more than 100 years. However compared to other materials plastics are

relatively modern. Their usage over the past century has enabled society to make huge

technological advances to take us towards the new Millennium. Plastics are usually used

in agriculture appliances clothing construction electronics furniture packaging

transportation and numerous other areas. Almost in every human life activity directly or

indirectly involves in the products that made from plastics materials. [I7]

There are many process can be used to produce the plastic product such as injection

moulding process extrusion process blow moulding process compression and rotating

process. The most popular process is injection moulding process. In the past many

people do not have any detail information about plastic injection technology. It was

known by only a handfbl of expert. This process can produce high mass production and

complicated shape of product. Injection moulding is the process of forcing melted plastic

in to a mould cavity. Once the plastic has cooled the part can be ejected. It is usefbl

when the parts are too complex or cost prohibitive to machine. With this process many

parts can be made at the same time out of the same mould. In injection process mould

is needed which it can be attached to the injection machine to produce plastic part. [I ]



Mould is a tool to produce plastic part. To get one mould involves various stages from

design stage where the mould needs to be designed using Computer Aided Design

Software and then machine the raw materials to become mould parts and finallyassemble the mould parts to become one complete set of mould.

It is very important to get good appearance such as no welding line sink mark accurate

dimension flatness and the most important capable to assemble to other parts. Some

plastic parts are produced using injection machine have various problems such s

welding line sink mark and etc. due to various factors such as wrong gate location

wrong size of gate wrong size of runner wrong length of runner wrong location of

water hole and other factors that effect the quality of plastic parts [101

In the past few years many mould makers have used trial and error method to produce

mould where they were usually very high skill people to assist on design stages.

Sometime to produce one set of mould had taken long time due to the modification and

repairing at mould to get good plastic part

The defects of plastic part c n be reduced by flow analysis on the plastic part at the

design stage which plastics parts will be analyzed using flow analysis software. This

analysis usually looks at the various parameter such as flow front flow rate temperature

different shrinkage distribution air trap optimum window condition and etc. lo]



1 2 Objectives

The objectives of this project are:

1. To analyze the behaviors of plastic flow inside the 3-plate mould.

2 To calculate the optimum size of sprue runner and gate.

3. To identi@ the suitable location of gate runner and sprue.

4. To understand the parameters involved in flow simulation.

5. To understand the type of plastics material mould and injection machine.

1 3 Scope

In this study the typ of 3-plate mould is used to analyze the flow behaviors of plastic

using Moldex software. The 3D product will be drawn using solid work software. In

order to analyze the plastic behavior the optimum sizes of feeding systems were

calculated and the location of the feeding systems was identified. fter that the 3D

product will be transferred to Rhinoceros software as post processor. Moldex software

will be used to analyze the flow of plastic. Data fiom the result will be compiled and

study the result.



1 4 roblem Statem ents

At the present time mould makers are still using try and error method to locate the

location of feeding system such as gate runner and sprue inside the plastic injection

mould. They need experienced people who capable to decide the size and location

of feeding system especially in plate mould.

With simulation software the behaviors of flow of plastic inside the cavity mould

can be predicted. In 3-plate mould the feeding system can be decided using different

approach such s centre gate offcentre gate and multiple gate systems. The size

and location of gate runner and sprue play importance role for producing good

quality plastic product. If wrong method used when choose the feeding system size

and location it will affect the product quality such swelding line air trap and etc.

The Moldex software as a simulation software is used to ensure the best choice

location and size of feeding system such as gate runner and sprue. This because of

the defect of plastic product can be eliminated before fabrication actual mould.



CH PTER

2 0 LITER TURE REVIEW

2 1 Introduction

This section discussed about analysis plastic flow inside the 3-plate mould. In this

chapter, the theory in the field of plastics technology is described. In the re of plastic

technology, studies focuses on a few different aspects namely are three-plate mould,

plastic materials, injection flow rate and etc.

2 2 Plastic material

plastic is a material that can change its shape; so many things can be made of plastic.

The head of the Monsanto Plastics Research says that, Plastics are materials that, while

being processed, can be pushed into almost any desired shape and then retain that shape.

171

There are many types of plastic. Some can be shaped only when they are freshly made;

then they become hard afterwards. Others can be changed by heating them up or even by

melting them.



Most plastics re man-made; they do not occur in nature. They are often made fiom oil

that comes out of the ground. The process of making plastics is usually quite

complicated

The term plastics encompasses organic materials, such as the elements carbon (C),

hydrogen (H), nitrogen (N), chlorine (Cl) and sulfur (S), which has properties similar to

those naturally grown in organic materials such as wood, horn and rosin. Organic

materials are based on polymers, which are produced by the conversion of natural

products or by syththesis from primary chemicals coming fiom oil, natural gas or coal.

[I7

It designs in many different formulas for different purpose including for moulding.

Approximately 18000 different materials re available for moulding. Majority of

available materials are blends of previously developed material. Malaysia exports of

plastics and plastics product were valued at RM9.38 (US$ 2.47 billion in 2003, the

bulk of which went to the key markets of some country like Singapore, China and Hong

on^. ^]

2 2 1 hermoplastics

Basically, plastic materials re divided generally into two groups namely thermoplastic

and thermoset, based on their characteristic after the processing stage. The behavior of

thermoplastics depends on other variables as well as their structure and their

composition18] Thermoplastic materials is softened by the application of heat, hardened

when cooled and fixed the shape of the moulding which may be quite rigid or flexible

according to the type of plastic used. It can remould again and can recycle. This is

because, there re no chemical changes takes places.



2.2.2 Types o f thermoplastic Materials

2.2.2.1 Acrylonitrile Butad iene Styrene AB S

Tough and good resistance to chemicals, oils etc., and has excellent outdoor properties.

Applications are used where are smooth and glossy finish wit strength is required, such

as piping for chemical and gas installations, safety helmets, typewriter and telephone

cases, tables, chairs luggage, torch and vacuum body cases. Trade names are BASF-

Terluran, Bayer Novudor, Mosanto Lustran r2 1as shown in Figure 2 1

Figure 2 1:Characteristics of ABS

2.2.2.2 Polymethyl M ethacrylate acrylic) PM MA

It has good weather properties and resistance to most acids and oils. Available from

through glass clear and full range of translucent semi-transparent) and opaque colours.

Applications such as fish tanks, watch glass, sink and bath tap tops, machine guards,

goggles, lighting optical lenses. Trade names are Altulor Altulite, Du Pont Lucite,

ICI Diacon, and Rohrn GMBH Plexiglas. 12 1



Resist most chemicals oil and is touch with exceptionally good flexing properties.

Applications are for milk bottle crates packing trays and containers cooling fans and

electrical connectors on motorcars moulded toys shoe heels chairs luggage and

instrument cases. Trade names are BASF Novolen ICI Propathene Shell Shell PP

12 1as shown in Figure 2 2

Form acronym recycle code characteristics common uses

hard flexible containers

polypropylene PP translucent dry appliances

feel toys plumbing

Figure 2 2: Characteristics of PP



2 2 2 4 olyethylene P

Polyethylenes are divided into two groups, which are Low Density Polyethylene,

LDPE) and High Density Polyethylene HDP E) 12 1 s shown in Figure 2 3

Form acronym recycle code characteristics comm on uses

hard to semi- fertiliser bags, carhigh

HDPE flexible, waxy petrol tanks, gasdensity

surface, opaque pipe, tanks and rope

Figure 2 3: Characteristics of PE



2.2.2.4.1 High Density Polyethylene HDPE)

HDPE has higher level crystalline th n LDPE. These give plastics which have a higher

density, rigidity, tensile strength, hardness, heat distortion temperature, chemical

resistance, viscosity resistance to permeability; however the impact strength is lower.

The material has a density less than water 0.94g/cm3 0.965g/cm3. The shrinkage value

up to 0.05 inlin possible for thick sectioned moulding. Application for this material re

using for milk-bottle crates, containers used for refrigeration, fish boxes, shipping pails

for paint and adhesive. This material is strong and stiff, even at low temperature. For this

reasons it is used to produce components which must have reasonable impact strength at

low temperature. Trade names are BASF Lupolen HD, BP Rigidex, Dow Dow

polyethylene. i201

2.2.2.4.2 Low Density Polypropylene LDPE)

LDPE is crystalline thermoplastic material and is such it is not available in transparent

grades. Its natural colour is a milky white and it has a soft wax-like feel. The material

has a density less than water 0.9 g/cm3- 0.925 g..cm3.LDPE is an easy flow material and

at 200°C a material with a melt flow index (MFI) of 2 will have a higher viscosity than

PS. The shrinkage of LDPE is about 2 . The melting point is approximately 105OC. By

refer to density and melting point determinations, LDPE canbe

distinguished fromHDPE and PP. injection pressure for injection machine up to 13000 bars equal to 13

h4hJm2equal to 11600 psi. The applications for this materials re using for toys, caps and

lids for containers, bowls, beakers, pipe coupling, pots, bins etc. trade names are BASF

- Lupolen, u Pont-Alathon, ICI-Alkathene and Shell-Cartona.12 1



2.3 Characteristic of Low Density Polyethylene LDPE)

2.3.1 Common Name

Low Density Polyethylene

2.3.2 Abbreviation

PE

2.3.3 Systematic chemical name

Low density po y methylene)

2.3.4 Suppliers and trade names

There are some suppliers and trade name listed in Table 2 1



Table 2.1 Suppliers and trade names

2 3 5 Material properties

L PE s a crystalline thermoplastic and as such it is not available in transparent grades.

Its natural colour is a milky white and it has a soft wax-like feel. The material has a

density less than water (0.92 g cm ), is tough but only has moderate tensile strength.

The chemical resistance and electrical insulation properties (over a wide range of

temperatures) are excellent.



2 3 6 Ease flow

LDPE is an easy flow material. Ease of flow is rated by the melt flow index (MFI), the

lower the number, the stiffer is the flow. However, low MFI materials have better stress-

crack resistance and exhibit higher impact strength (Due to higher molecular weight).

2 3 7 Shrinkage

When the density is 0.910 0.925 g cm 3 the shrinkage is approximately 0.020-0.050

idin (type I-low). When the density is 0.926 0.940 g cm type 11- medium) the

shrinkage is about 0.015 0.04idin. For typ 111, or HDPE, it can have very high

shrinkage. The shrinkage for LDPE is about 2%

2 3 8 Resistance to the following

There is no solvent at room temperature. Not chemically attacked by non oxidizing

acids, alkalis and many aqueous solutions. Low water absorption even after long

immersion times, addition of carbon black (to improve weathering) will increase water

absorption. Absorption of other liquid (e.g acetone and benzene) will be greater for

LDPE than for HDPE.



2 3 9 Not resistance

LDPE has no resistance to Ultra-violet light, oxygen at elevated temperatures and strong

nitric acids. It will dissolve in benzene at 60°C. Aromatic and chlorinated hydrocarbons

will cause swelling. Certain materials, e.g detergents, may cause stress cracking of

grades with a MFI greater than 0.4 HDPE is also more prone stress cracking. I

2 3 10 Material detection or identification

LDPE floats in water and cuts easily with a knife. It is insoluble in most common

solvents but soluble in hot benzene or toluene. Ignites easily when placed in a flame and

bums rapidly. Burning drops usually fall and there is an odour of burning wax or

p in, the flame is blue but tipped with yellow. The melting point is approximately

105°C. It can be distinguished from HDPE and PP by density and melting point

determinations. LDPE is an inert material which does not dissolve in common

chemicals.

2 3 11 Colouring

ry colouring is used for noncritical applications but master batching is the preferred

system where accurate and consistence colour matching is required. Compounded

material is more expensive and is not so widely used as good colouring can be achieved

with master batches. Liquid colour is under active development, e.g. to overcome

problems such as poor feeding.



2 3 12 Material and component handling

Predrying is not usually necessary unless hygroscopic additives are present. When

necessary, 3h at 65OC is usually sufficient.[5

2 3 13 Mould and gate consideration

As the MFI increases the smaller the feed system of the mould needs to be. However,

the runner sizes should not be reduced too much as it necessary to supply a reasonable

amount of dwell pressure in order to compensate for shrinkage. A wide range of gates

types is used. There is now considerable interest in the use of hot runners and insulated

hot tip runners, such systems reduce scrap production and components are ejected from

the mould already finished.

2 3 14 Flow path

This material is a very easy flow material. At mm wall thickness, the maximum flow

path, wall thickness ratio would be higher.

2 3 15 Projected area

The clamping pressure required is of the order of 1 2 tsi 15-30 N m-2 .[



2.3.16 Cylinder equipment

To prevent material weeping from the nozzle it is usual to fit a value in the nozzle (e.g

spring loaded), to minimize material flowing back down the screw a valve is also fitted

to the screw. Decompression (suck-back) is used as n alternative to nozzle valves, e.g

in conjunction with hot-runner moulds.

2.3.17 Screw cushion

From 2 to 6 r r

2.3.18 Shot capacity

Because of the material's good heat stability as little as 10% of the cylinders rated

capacity may be used, the maximum possible will be about 95%.

23 19 Melt temperature as measured in the nozzle or by n air-shot technique: 180-

280°Cas shown in Table 2.2.

Table 2.2: Melt temperature

Type

Low (Type I)

Medium (Type 11)

High (Type 111)

Melt temperature

180 -280°C 356 -536°F)

165 -220°C 330 -428°F)

205 -260°C (400 -500°F)



2 3 20 Barrel residence tim

If the material is overheated oxidation occurs and there is a serious loss of electrical

insulation ability, it is therefore necessary to incorporate antioxidants, e.g di-Q-naphthyl-

p-phenyl-enediamine, so s to minimize change. It is good practice not to allow the

material to cook in the barrel.

2 3 21 Temperature settings

Table 2.3 shows that the stages of the temperature on the various part of injection

moulding machine.

Table 2.3: Temperature settings

Zone

No.

1

2

3

4

5

Location

Barrel rear

(near the hopper)

Barrel middle

Barrel middle

Barrel front

Nozzle

Mould

Temperatures C

From

120

160

180

200

210

10

Temperatures F

To

200

230

260

280

270

60

From

248

320

356

392

410

50

To

392

446

500

536

518

140



2.3.22 Injection speed-mould filling speed

To get fast injection speeds, high pressure are not required.

2.3.23 Injection pressure

The machine should be capable of giving the following: First Stage: up to 1300 bars;

130MN m2 18800 psi. Second Stage (dwell or follow-up pressure): up to 800 bars; 80

MN m-2 1600 psi. Careful control over both dwell time and pressure is needed in order

to avoid over packing of the mould and yet still be able to compensate for shrinkage.

2.3.24 Screw rotational speed rpm)

The screw rotational can be very high High screw speeds can, however, result in melt

temperature variations; therefore adjust the speed to suit the cooling time.

2.3.25 Back pressure

Up to 200 bars; 20MN mm2 900 psi.

2.3.26 Shutting down

No need to purge with another material.



2 3 27 Reprocessing

Up to 100 regrind may e used; ensure that the scrap is kept clean and dry. If the

regrind is mixed with virgin polymer then the material can be re-used more than other

plastics.

2 3 28 Finishing

Difficult to deflash because of the flexibility of the material. Hands scalpels cropping

etc. may be used to remove the feed system. Better to design the mould so that the

degating is achieved during mould opening. Decoration of mouldings is not very

common.

2 4 Mould

An injection mould normally consists of two basic sets of component.. One is cavities

and cores; the second is the base in which the cavities and cores are mounted as shown

in Figure 2.4. The combination of these two components is a result of standardization in

the mouldmaking industry.



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Figure 2.4: Elements of injection mould

2 4 1 ould base

The exploded view in Figure 2.5 shows parts of a mould base. The locating ring

surrounds the sprue bushing and is used for locating the mould in the press-platen

concentrically with the machine nozzle. The opening into which the ring fits is made to a

tolerance of -0.000 and 0.002. The ring itself is made 0.010 smaller than the opening

providing a clearance of 0.005 per side. The sprue bushing on the locating ring end has a

spherical radius of L z or % in. to fit the machine nozzle radius.

The sprue bushing goes through the front clamping plate or backup plate and front

cavity plate, thus extending to the parting line. The parting line is formed by cavity

plates A and B. Cavity plate A, as the name implies, retains the cavity inserts and

supports the leader pins, which maintain the alignment of cavity halves during operation.

Leader pins are made 0.001 below nominal and to a tolerance of 0.0000 and -0.0005.



Occasionally, there are instances where the core protrudes a considerable amount, thus

requiring precise guidance of mould halves before cavity and core touch each other. In

such an event, the leader pins must be long enough to perform the job of guiding prior to

contact of the mating halves.

Mating with plate is B plate, which holds opposite half of the cavity or the core and

contains the leader pin bushings for guiding the leader pins. B plate has its own backup

or support plate. It also frequently supported by pillars against the U-shaped structure

known as the ejector housing. The U-shaped structure consisting of the rear clamping

plate and spacer blocks are bolted to the B plate either as separate parts or as a welded

unit. The U-shaped structure provides the space for the moving ejector plate or ejection

stroke also known as stripper stroke. The ejector plate, ejector retainer, and pins are

supported by the returns pins.

The stripper plates provide clearance holes around the supporting pillars. The rear

clamping plate of the U-shaped structure usually has openings for stripper rods, which

actuate the ejector plate. The ejection plates retain the heads of knockout pins as well s

return pins. All the mould plates excluding the ejector parts) and spacer blocks are

ground to a thickness tolerance of +-0.001. A combination of tolerance could

conceivability build up to cause an unevenness at the four corners. It is advisable to

check the uniformity of all four comers prior to preparing the base to receive cavities.



Figure 2 5: Exploded view of mould base and Cross section of mould base

2 4 2 avity nd core

Figure 2.6 shows a cross section and top view of the part drawn to actual size. A

fieehand outline of cavity core is made using as a guide the fact that the outside of the

part will form the cavity and the inside of the part the core. This establishes the parting

line and the gate location. An analysis is made of whether with this arrangement the

part will stay on the core during mould opening. The depth of the ribs and the binding

between them s a result of shrinkage should overcome any tendency of sticking in the

cavity. The finish in the slots for the ribs would be smooth as machined or s electric-

discharge-machined EDM) but would not have a directional polish.



Figure 2 6:Parting line cavity and core outline

The part is designed without the ribs and that the center ring has tapers in the direction

of withdrawal as illustrated in Figure 2 7 With this the part would definitely stick in the

wrong side. Ejection pins are placed as indicated in Figure 2 7 Even a slight ring scratch

of 0.001 depths in the middle of the flange could aid in the retention of the part. If it

were permissible to have the ejection-pin impressions on the outside then the

arrangement in figure 2 6 could prevail except that the half that was stationary would

become the ejection half and would incorporate the ejecting pins. Not all parts lend

themselves to this kind of treatment. For example a /4 in.-diameter rod 2 in. long. The

part is symmetrical and there are no means of making it stick to the ejection side.

Should the end opposite to the gate tend to adhere to the stationary half it could be

provided with a dummy gate to retain it on the correct side.



Figure 2.7: Parting line cavity and core outline

2.5 haracteristic of plastic injection moulding

Each types of mould has same characteristic which can be known such s sprue runner

gate and air vent s shown in Figure 2.8.

Mold

spwt oFt ojedionn w

: . -:I .I .a * r : r - - n . .

Figure 2.8: Sprue runner and gate

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