1

Project On

Quality Improvement of Plastic Injection Mould Design

using Mould Flow Analysis

Submitted in partial fulfillment of the requirements for the award of the degree

BACHELOR OF TECHNOLOGY

IN

MECHANICAL ENGINEERING

Submitted by

Jatinder Singh (0816232)

Bhupender Sharma (0816233)

Under the guidance of

Sh. PUNEET KATYAL

Assistant Professor

DEPARTMENT OF MECHANICAL ENGINEERING

GURU JAMBHESHWAR UNIVERSITY OF SCIENCE & TECHNOLOGY

HISAR

(May, 2012)

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CONTENTS

Title Page No.

Certificate i

Candidate’s Declaration ii

Acknowledgement iii

Abstract iv

List of figures v

CHAPTER-1

Introduction 1

Introduction to Plastics 2

Injection Mould Design 3

Polymer Selection 5

Types of Gates 8

Feed System 10

Ejection System 13

Cooling System 12

Mould Design & their Considerations 14

CHAPTER-2

Product Drawings 17

CHAPTER-3

Analysis Report 20

CHAPTER-4

Conclusion 27

REFERENCES 28

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ABSTRACT

The main objective of the project is to improve the Quality of Plastic Injection Mould Design using Mould

Flow Process. In this project, an attempt has been made to design & development of the automatic

injection molded product for “GLASS”. The work started with concept generation of a mould glass using

brainstorming approach. Design concepts were developed on CATIA and best design was selected based

on analysis results achieved on Plastic Advisor/Pro-E. The results revealed the quality of mould design. In

doing so, Concurrent Engineering and Computer Aided Engineering made Mould Design process quick

and simpler. The main consideration of this project work is the product & mould design of the existing

product and do its quality improvement using mould flow analysis.

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INTRODUCTION

A tool is required for converting plastic into a product. The tool is called to be mould. In our life

we need so many types of components to fulfill our requirements. All these components cannot

be made in single method and from a single material. So depending upon the components shape

and material used for manufacture we need different types of moulds. For larger production,

automatic moulds are used where as a hand mould uses where the cost rate is primarily

considered and produced them is given least importance. Automatic injection moulds are

generally used for small to large components with any complicated shapes. Keeping the above

things is mould this project report covers theoretical input into of plastic property, processing

techniques and tooling considerations.

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INTRODUCTION TO PLASTICS

PLASTICS:

A polymer which is shaped into a hard and tough utility article by the application of heat and

pressure by using suitable techniques. All plastics are polymer but all polymers are not plastics.

Plastics are classified in to two types:

Thermoplastics

Thermosets

Thermoplastics:

The material, which can be soften when heated and solidify on cooling, is known as

“thermoplastic”. These materials can be recycled and can be processed through injection

molding process, extrusion process, Blow Molding etc.

Ex: - PP, ABS, PE etc.

Thermosets:

It is the hardest form of plastics which cannot be reduced once processed. These materials are

processed through compression molding.

Ex:- UF, MF, Epoxy resin etc.

According to source point of view:

Natural Plastics : which are readily available in nature

Synthetic : Which do not occur in nature but have prepared artificially.

Application : plastic industry is passing through different phases

1st Phase : Replacement of Non- Metallic material by simple plastic

2nd Phase : Number of engineering and high performance plastics have been

Introduced which are capable of exhibiting higher performance

characteristics

3rd Phase : Substitution of metallic parts by use of advanced fiber

Composites using carbon or other high performance fiber

Reinforced which need not be the final stage.

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INJECTION MOULD DESIGN

Injection molding is one of the most versatile processing methods by means for manufacturing

small clips to large industrial crates.

In mold design, there are some rules which must be paid attention. The rules are:

(1) Use uniform wall thicknesses throughout the part. This will minimize sinking, warping,

residual stresses, and improve mold fill and cycle times.

(2) Use generous radius at all corners. The inside corner radius should be a minimum of one

material thickness.

(3) Use the least thickness compliant with the process, material, or product design requirements.

Using the least wall thickness for the process ensures rapid cooling, short cycle times, and

minimum shot weight. All these result in the least possible part cost.

(4) Design parts to facilitate easy withdrawal from the mold by providing draft (taper) in the

direction of mold opening or closing.

(5) Use ribs or gussets to improve part stiffness in bending. This avoids the use of thick section

to achieve the same, thereby saving on part weight, material costs, and cycle time costs.

Concerning radius, Sharp corners greatly increase the stress concentration. This high amount of

stress concentration can often lead to failure of plastic parts.

In these operation plastics granules are feed into the cylinder through a hopper, where it is

plasticized and then forced out to other end of cylinder through a nozzle in to a relatively cool

mould held closed under pressure. Here melt cools and hardened until fully setup and then opens

and the molded part is removed.

Classification of injection mould based on the design feature and manner of operation:

The type of gating and means of de- gating

The type of ejection.

The presence or absence of external and internal undercuts on the products.

The manner in which the product is released from the mould.

Types of injection moulds:

Two plate mould

Three plate mould

Split mould

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Mould for threaded components

Hot runner moulds

Two plate mould:

The basic mould consists of two parts namely a fixed half and a moving half. When these two

parts are opened the molding can be extracted. Such an assembly is some times referred to, as a

single day light mould because when the mould is open there is only one space as it is normally

termed day light, between the two mould halves.

Advantages:

Large components can be molded easily

Economical

Simple mould construction

Disadvantages:

Manual attention is needed

Automatic degrading is not possible

Number of impression is limited.

Three plate mould:

When the mould is opened there are two day- lights. This design permits a particular feed

technique known as underfeeding and double day light is necessary in this case to permit the feed

sustem to floating cavity plate.

Advantages:

Small components with inner cross section can be molded easily

Less manual attention

Automatic degating is possible

Number of impressions can be mote when compared to two- plate mould.

Disadvantages:

Cost of mould construction is more

Split mould:

A mould which has a recess or projection is termed as undercut molding. The design for this type

of component is initially more complex than for the inline of draw component as it necessitates

the removal of that part of the impression which forms the conduct prior to rejection. For such

molded parts with undercuts i.e. articles that cannot be released in the direction of the mould

opening, requires moulds with more than one opening for such articles. Various methods have

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been developed that may be operated Manually, Mechanically, Hydraulically, Pneumatically or

electromechanical.

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POLYMER SELECTION

In choosing the “right material to do a job, we may find several products that will meet the

requirement but in any case they present a choice. One should first list the condition then list all

of materials that provide need to meet criteria.

Material selected:

As our component is “Glass” right material will be “PP” (Poly Propylene)

About the material:

PP is a soft thermoplastic co-polymer

Amorphous in nature

Manufacture:

Styrene and acrylonitrile monomers are added to polybutadiene latex and the mixture is warmed

to 50 c to allow absorption of monomers

A water soluble initiator such as potassiumper sulphate is the added to polymerize styrene and

acrylonitrile.

Characteristics:

Good tensile strength

High glass transition temperature

High melting point

Excellent chemical resistance

Very good fatigue resistance

Less tendency to Stress

Low ultraviolet resistance

Properties Value

Specific gravity (density) 0.903 g/cc

Tensile strength, Mpa 35.5

Elongation at break % 35

Hardness R100

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Melting Point (celcius) 164

Impact-strength, izod, J/M 134-120

Glass transition temperature 5

Mould shrinkage,% 1 – 2.5

Processed by:

Injection molding

Extrusion molding

Rotational molding

Blow molding

Application:

Automotive – Bumpers, Steering cover, Seat covers, Door covers, Acceleration pedal etc.

Electrical & Electronics – Radio, Transformer housing, Switch gears, Table & Wire

coating etc.

House Hold – Hair dryers, Microwave ovens trays, Glasses, Chairs etc.

Packaging – Packing of goods, contact lens cases, buttons etc.

Appliances – Drain tables, Door Handles etc.

Medical – Disposable syringes.

Other application - Ropes.

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TYPES OF GATES

1. Sprues:

Sprues are generally used when the parts have relatively thick walls or when highly viscous

melts require gentle processing. The spme has to be removed mechanically from the molded part

after ejection. Appropriate spme bushes are available as standard units in various versions, for

example, with twist locks, temperature control, etc., see also IS0 10072. Due to their large flow

diameters, conventional spmes exhibit minimal pressure loss. However, it must be taken into

consideration that a too-large spme can determine the cycle time. Thus maximum diameter ought

not to exceed part wall-thickness plus approx. 1.5 mm. If temperature-controlled (cooled) spme

bushes are used, this value may be exceeded. Conventional spmes offer optimum holding time in

the injection molding process. To prevent sink marks or non-uniform gloss, sufficient (separate)

cooling power should be provided at a distance from the gate.

Fig: 1.1

2. Pinpoint gate

In contrast to the spme, the pinpoint gate is generally separated from the molded part

automatically. If gate vestige presents a problem, the gate dl can be located in a lens-shaped

depression on the surface of the molded part. Commercially available pneumatic nozzles are also

used for automatic ejection of a runner with pinpoint gate. Pinpoint gating has been especially

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successful in applications for small and/or thin-walled molded parts. At separation, however,

drool has been a problem with certain polymers and premature solidification of the pin gate may

make it diffcult to optimize holding time.

Fig: 1.2

3. Diaphragm gate

The diaphragm is useful for producing, for instance, bearing bushings with the highest possible

degree of concentricity and avoidance of weld lines. Having to remove the gate by means of

subsequent machining is a disadvantage, as is one-sided support for the core. The diaphragm,

Fig. 1.3, encourages jetting which, however, can be controlled by varying the injection rate so as

to create a swelling material flow. Weld lines can be avoided with this type of gating.

Fig: 1.3

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FEED SYSTEM

Design of runner:

Shape of the cross section of the runner.

This is simple two-plate mold, having flat paring surface so we use the fully round runner.

A circular cross section provides the largest flow area for the less mass. On the other hand, it is

more expensive to produce because the runner must be cut in to two parts. Hence machining is

more expensive.

Runner efficiency =cross-section area/Periphery of the runner = 0.25D

(Higher the value, grater the efficiency)

Fig: 1.4

Runner Size:

When deciding the size if the runner the designer must consider the following factors:

The wall section and volume of the molding.

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The distance of impression from the main runner or sprue.

Runner cooling consideration.

The range of mould maker’s cutter available.

The plastics material to be used

D= (√W * 4√L)/3.7

Where

D= runner diameter (mm)

W= weight of molding (mm)

L= length of runner (mm)

Design of Gate:

Agate is a channel or orifice connecting the runner with the impression. It is the thinnest part of a

feed system.

The optimum size of a gate will depends upon a number of factors including:

The flow characteristics of the plastics material.

The wall section of the molding.

The volume or weight of the molding.

The molding temperature.

The mould temperature.

Positioning of gate:

The position of gate should be such that there is an even flow of melt in all the impression so that

it fills all the impression uniformly at the same time.

Selection of gate:

A channel or orifice connecting the runner to impression is called as the gate .it is one of the

thinnest parts of feed system.

Types of gate:

For two plate mould:

1. Direct sprue gate

2. Edge gate

3. Fan gate

For three plate mould:

1. Pinpoint gate

2. Subsurface gate

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3. Submarine gate

Gate used for our Glass model is Sprue Gate.

Sprue Gate:

Fig: 1.5

This type is particularly desirable for use with material give differential shrinkage characteristics

and it often used as an alternatively to film gating. This type of gate often used for multi-point

feeding and for single off centre feeding.

To prevent gate fracturing the area of molding adjacent to the gate particularly with more brittle

materials, it is desirable to taper the gate so that the gate is caused to break at the junction with

the secondary sprue.

Land length L= 0.75-1 mm suitable

Gate diameter d= nC4√A

Where n= material constant in mm.

A= surface area of the cavity (mm^2)

C= function of wall section thickness (t)

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EJECTION SYSTEM

Ejection Used For Glass Model:

All the thermoplastics material contracts as they solidify, which means that the molding will

shrink on to the core, which forms it. This shrinkage makes the molding difficult to remove.

So, it is advisable, it possible, to use a type of ejection mechanism which doesn’t have any marks

on the molded part.

Various types of ejection are there but for this component (Glass Model) pin ejection is used.

Pin Ejection:

In this system molding is ejected by the application of a force by a circular steel rod called an

ejector pin.

The ejector pin is headed to facilitate its attachments to the ejector plate assembly. When

actuator of machine actuates the ejector rod which is attached with the ejector plate assembly the

molding is ejected with the help of pin.

Different shapes of ejector pin may be used based on the size and shape of the molding i.e. D-

shaped pin, part pin, circular pin etc.

Fig: 1.6

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COOLING SYSTEM

All the injection moulds are generally provided with cooling in order to solidify the hot plastics

material, which is injected inside the cavity during molding process. Cooling is accomplished by

a continuous circulation of chilled water, hot oil flowing through the channel which is drilled

into various portion of the molding order to control the mould temperature depends upon the

types of plastics material to be used. For many commodity plastics cooling water supply is in the

order of 4-60~c at pressure of at 4-5 kg/cm^2.

Cooling used for Glass Model:

Rectangular circuit:

In this system we have to drill two flow ways on either side of the cavity and further drill is done

in other two sides to ensure that the flow ways are closed to all four ways of the cavity allowing

a more even temperature control.

It is rectangular in shape so it is called as rectangular circuit cooling.

Straight hole drilled channel:

This type of cooling is achieved by drilling straight holes. The two ends of the holes are

connected by hose nipple. On one end water is inset and by the other end the water is out let.

According to the size of the pate the number of drilled holes would be provided.

Fig: 1.7

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MOULD DESIGN & THEIR CONSICERATION

The following design concepts are followed while designing plastics products:

Parting line

Bosses

Ribs

Radii, filets, gussets

Draft angle

Parting line:

The parting line may be described as those lines made by the juncture of male and female mould

half and loose mould section. It should be around the section of the part having the large cross

section area.

Bosses:

Bosses are defined as protruding studs on a part that assist in the assembly of the plastics part

with the other piece. Special attention should be paid to the design of bosses in contact with

exterior surfaces avoid any heavy sections to prevent voids or external sink marks.

Ribs:

Ribs may be defined as long protrusions on the part which may be used to decorate or strengthen

the part of if properly placed to help prevent it from warp age, radii, fillets, gussets:

Fillets and radii are used at the ribs or bosses to facilitate the flow of plastics material and to

eliminate sharp corners thus reducing stress concentration in the molded article. The overall

advantages of fillets and radii are:

Eliminates cracking and increase impact strength

Reduce cycle time

Uniform density of the molded parts

Draft angle:

Article produced by the molding processors must have or draft on all surface perpendicular to the

parting lines of the mould. Plastics materials tend to shrink around cores. In order to remove the

mould parts, adequate taper must be provided.

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MOLD MATERIAL & THEIR APPLICATION

SL NO. ISI BS APPLICATION

01 T35CrMo1 V30 BH 11 Cavities, core, ejector pins, guides wear pads of

molds.

02 T35CrMo1 W1 V30 BH 11 Die casting dies & plastic molds.

03 40N112CrMo28 EN 24 Cavities, core ejector pins guides, wear pads for

moulds

04 T35Cr5Mo1 V1 - High tensile load applications, Max strength

05 13Ni3Cr80 - Cavity & Core

*06 T10 5Cr1 EN31 Used for guide pillars

**07 T103 BW 18 Used as wear plate, backing plate

***08 C10 & C14 EN 2A Bolster, support, block, plates, backing plates,

holder plate

09 C35Mn75 EN 8 Moulds with shorter run and owes non accurate

cavities

10 40Cr1 EN 18 Pillar, brush, sprue brush, locating ring, bigger

diameter ejector pins

11 50Cr1 V23 EN 47 Bright steel, used for ejector pins

12 T55Ni2Cr65Mo30 - Core, Cavity

* Bearing Steel

** Carbon Tool Steel

*** Mild Steel

(A) 1% Chromium Steel

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PRODUCT DRAWINGS

1. GLASS MODEL

Fig: 2.1

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Fig: 2.2

2. MOULDING MACHIME ASSEMBLY

FRONT VIEW

3-D VIEW

Fig: 2.3

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Fig: 2.4

Fig: 2.5

SIDE VIEW

ISOMETRIC VIEW

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ANALYSIS REPORT

MOLDFLOW PLASTICS ADVISERS REPORT

Prepared By:

Prepared for: Date: 01/May/2012

INTRODUCTION

SUMMARY

Release Level: 7.0

Glass

Part Name: Glass

Part Revision: 4

Material Supplier: Generic Default

Material Grade: Generic PP

Max Injection Pressure: 180.00 MPa

Mold Temperature: 40.00 deg.C

Melt Temperature: 240.00 deg.C

Model Suitability: Part model was highly suitable for analysis.

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Filling Analysis Glass

Moldability:

Your part can be easily filled but part quality may be

unacceptable.

View the Quality plot and use the Dynamic Adviser to

get help on how to improve the quality of the part.

Confidence: Medium

Injection Time: 0.67 sec

Injection Pressure: 47.64 MPa

Weld Lines: Yes

Air Traps: Yes

Shot Volume : 24.21 cu.cm

Filling Clamp Force: 23.94 tonne

Packing Clamp Force Estimate @20%:

( 9.53 )MPa 13.12 tonne

Packing Clamp Force Estimate @80%:

( 38.11 )MPa 52.48 tonne

Packing Clamp Force Estimate @120%:

( 57.17 )MPa 78.72 tonne

Clamp Force Area: 135.03 sq.cm

Cycle Time: 7.91 sec

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GLASS MODEL

Fig: 3.1

SOLID MODEL

Fig: 3.2

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PLASTIC FLOW

Fig: 3.3

FILL TIME

Fig: 3.4

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CONFIDENCE OF FILL

Fig: 3.5

INJECTION PRESSURE

Fig: 3.6

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PRESSURE DROP

Fig: 3.7

FLOW FRONT TEMP.

Fig: 3.8

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QUALITY PREDICTION

Fig: 3.9

SKIN ORIENTATION

Fig: 3.10

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CONCLUSION

The result of this study using 3D design tools in conjunction with Mold-Flow analysis produced

an accurate representation of plastic part.

In summary, the results of this paper have shown the following

• Cycle time is the most critical factor affecting quality control.

• There are three contributors of warpage, the shrinkage due to differential cooling shrinkage,

differential shrinkage and orientation shrinkage. In most cases, the differential cooling shrinkage

and differential shrinkage cannot be avoided.

It has been shown in this study that the Mold-Flow analysis can have a significant positive

impact in the design and manufacturing processes. The using of Mold-Flow could help shorten

development time.

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REFERENCES

1. American Foundrymen’s Society, 2000, “Basic Principles of Gating”, American

Foundrymen’s Society, Inc., Illinois.

2. American Foundry Society, 2001, “Aluminum Permanent Mold Handbook”, American

Foundry Society, Illinois.

3. Strong, A. Brent, 2000, “Plastics Materials and Processing”, 2nd ed., Prentice Hall, New

Jersey.

4. Thomas, B.G., 2002, “Casting Process Simulation and Visualization: A JOM-e Perspective”,