international journal of mechanical engineering and...

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –

6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 6, November - December (2013) © IAEME

227

OPTIMIZING INJECTION MOULDING TOOL COST BY USING VIRTUAL

SOFTWARE TECHNIQUES

Sri. P V S M VARMA, Sri. P N E NAVEEN

Mechanical Engineering Department, Godavari Institute of Engineering & Technology, E.G.Dt. A.P.

ABSTRACT

Now a day’s Die design is the major part in product development. Die design will cause of

the increase in component cost, machining complexity. For avoiding these problems we are taking

virtual software support.

In this thesis paper I am working on injection moulding die design optimizing. To provide an

initial design of the mould assembly for customers prior to receiving the final product CAD data is a

preliminary work of any final plastic injection mould design. Traditionally and even up till now, this

initial design is always created using 2D CAD packages. The information used for the initial design

is based on the technical discussion checklist, in which most mould makers have their own standards.

This technical discussion checklist is also being used as a quotation. This paper presents a

methodology of rapid realization of the initial design in 3Dsolid based on the technical discussion

checklist, which takes the role of the overall standard template. Information are extracted from

databases and coupled with the basic information from customer, these information are input into the

technical discussion checklist. Rules and heuristics are also being used in the initial mould design. A

case study is provided to illustrate the use of the standard template and to exhibit its real application

of rapid realization of the initial design for plastic injection moulds.

In this paper we are avoiding the all the problems involved in die design and how to make

standard template for the die design.

INTRODUCTION

BASICS OF INJECTION MOLDING DESIGN Designing plastic parts is a complex task involving many factors that address a list of

requirements of the application. “How is the part to be used?” “How does it fit to other parts in the

assembly?” “What loads will it experience in use?” In addition to functional and structural issues,

processing issues play a large role in the design of an injection molded plastic part. How the molten

INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING

AND TECHNOLOGY (IJMET)

ISSN 0976 – 6340 (Print)

ISSN 0976 – 6359 (Online)

Volume 4, Issue 6, November - December (2013), pp. 227-240

© IAEME: www.iaeme.com/ijmet.asp

Journal Impact Factor (2013): 5.7731 (Calculated by GISI)

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IJMET

© I A E M E



228

plastic enters, fills, and cools within the cavity to form the part largely drives what form the features

in that part must take. Adhering to some basic rules of injection molded part design will result in a

part that, in addition to being easier to manufacture and assemble, will typically be much stronger in

service. Dividing a part into basic groups will help you to build your part in a logical manner while

minimizing molding problems. As a part is developed, always keep in mind how the part is molded

and what you can do to minimize stress.

APPLICATIONS

Plastic injection molding is the preferred process for manufacturing plastic parts. Injection

molding is used to create many things such as electronic housings, containers, bottle caps,

automotive interiors, combs, and most other plastic products available today. It is ideal for producing

high volumes of plastic parts due to the fact that several parts can be produced in each cycle by using

multi-cavity injection molds. Some advantages of injection molding are high tolerance precision,

repeatability, large material selection, low labor cost, minimal scrap losses, and little need to finish

parts after molding. Some disadvantages of this process are expensive upfront tooling investment and

process limitations.

POLYMERS BEST SUITED FOR INJECTION MOLDING

Most polymers may be used, including all thermoplastics, some thermosets, and some

elastomers. There are tens of thousands of different materials available for injection molding. The

available materials mixed with alloys or blends of previously developed materials means that product

designers can choose from a vast selection of materials to find the one that has exactly the right

properties. Materials are chosen based on the strength and function required for the final part; but

also each material has different parameters for molding that must be considered. Common polymers

like Epoxy and phenolic are examples of thermosetting plastics while nylon, polyethylene, and

polystyrene are thermoplastic.

MAIN AIM OF THE THESIS

The most established method for producing plastic parts in large quantities is plastic injection

moulding. This is a highly cost-effective, precise and competent manufacturing method, which can

be automated. However, costly tooling and machinery are needed in this manufacturing process. The

design of a plastic injection mould is an integral part of plastic injection moulding as the quality of

the final plastic part is greatly reliant on the injection mould. A plastic injection mould is a high

precision tooling that is being used to mass produce plastic parts and is by itself an assembly of

cavities, mould base and standard components etc.

Over the years, much research work using computer-aided techniques had been done from

studyingthe very specific areas of mould design to studying mould design as a whole integrated

system. Many commercial mould design software packages such as IMOLD, PRO/ENGINEER, UG

MoldWizard, R&B MoldWorks, etc are also available today in the market for mould makers.

However, the systems and software packages mentioned above did not consider the initial design

prior to actual mould design. These software packages assist in the preparation of the detailed mould

design that includes the core/cavity creation, cooling and ejection design. As a result, mould

designers hardly used the mould design software packages when they are doing their initial design

because the software does not catered for such a design process.



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Molding

Defects

Alternative

Name Descriptions Causes

Blister Blistering Raised or layered zone on

surface of the Plastic part

Tool or material is too hot, often caused by a lack of

cooling around the tool or a faulty heater

Burn marks Air Burn/Gas

Burn

Black or brown burnt

areas on the plastic part

located at furthest points

from gate

Tool lacks venting, injection speed is too high

Color streaks

(US) Localized change of color

Plastic material and colorant isn't mixing properly, or

the material has run out and it's starting to come

through as natural only

Delamination Thin mica like layers

formed in part wall

Contamination of the material e.g. PP mixed with

ABS, very dangerous if the part is being used for a

safety critical application as the material has very

little strength when delaminated as the materials

cannot bond

Flash Burrs

Excess material in thin

layer exceeding normal

part geometry

Tool damage, too much injection speed/material

injected, clamping force too low. Can also be caused

by dirt and contaminants around tooling surfaces.

Embedded

contaminates

Embedded

particulates

Foreign particle (burnt

material or other)

embedded in the part

Particles on the tool surface, contaminated material

or foreign debris in the barrel, or too much shear heat

burning the material prior to injection

Flow marks Flow lines Directionally "off tone"

wavy lines or patterns

Injection speeds too slow (the plastic has cooled

down too much during injection, injection speeds

must be set as fast as you can get away with at all

times)

Jetting Deformed part by

turbulent flow of material

Poor tool design, gate position or runner. Injection

speed set too high.

Polymer

degradation

polymer breakdown from

oxidation, etc.

Excess water in the granules, excessive temperatures

in barrel

Sink marks Localized depression

(In thicker zones)

Holding time/pressure too low, cooling time too

short, with sprueless hot runners this can also be

caused by the gate temperature being set too high

Short shot Non-Fill/Short

Mold Partial part Lack of material, injection speed or pressure too low

Splay marks

Splash

Mark/Silver

Streaks

Circular pattern around

gate caused by hot gas

Moisture in the material, usually when resins are

dried improperly

Voids Empty space within part

(Air pocket)

Lack of holding pressure (holding pressure is used to

pack out the part during the holding time). Also mold

may be out of registration (when the two halves don't

center properly and part walls are not the same

thickness).

Weld line

Knit

Line/Meld

Line

Discolored line where

two flow fronts meet

Mold/material temperatures set too low (the material

is cold when they meet, so they don't bond)

Warping Twisting Part Distorted part

Cooling is too short, material is too hot, lack of

cooling around the tool, incorrect water temperatures

(the parts bow inwards towards the hot side of the

tool)



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In this thesis emphasis is done on injection moulding die design optimizing. To provide an

initial design of the mould assembly for customers prior to receiving the final product CAD data is a

preliminary work of any final plastic injection mould design. A case study is provided to illustrate

the use of the standard template and to exhibit its real application of rapid realization of the initial

design for plastic injection moulds. In this thesis all the problems involved in die design are avoided

and a standard template for the die design is made.

STEPS INVOLVED IN THIS PROJECT

1. Study customer requirement

2. Preparing model by CAD software

3. Inspecting CAD Component

4. Adding Material Properties

5. Extracting Core and Cavity

6. Preparing rough assembly for die

7. Preparing Quotation

8. Technical and cost discussion with customer

9. Prepare Final Assembly of die

10. Prepare Raw material required quantity

11. Planning for machining and prepare total approximate machining time

12. Planning for die assembly

13. Planning for trial and dispatch

STUDY CUSTOMER REQUIREMENT

In this project we are working for Piaggo Automotive Company. Their requirement is making

front driver cabin interior component.

� Initially the company has given outer dimensions of the component and other components

that need to be assembled on that component. Also they have given strength requirement and

no. of components to produce and maximum weight of the component.

� Our design team prepared models according to their requirement and shown to customer.

� Then models are changed by design team according to their requirement. And that component

model is sent to the companies design department, production department.

� Finally the component model is approved according to the company requirement.

This is the first step for any component manufacturing before going to die design because if

the component shape has irregular shape it increases manufacturing cost as well as component cost.

In this process I am involved in doing component modeling.



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2D DRAWING OF THE COMPONENT GIVEN BY THE COMPANY

SAMPLE 3D MODEL DESIGNED FROM 2D DRAWING

PREPARING FINAL COMPONENT MODEL BY CAD SOFTWARE

Our design team prepared models according to their requirement and shown to customer.

Then models are changed by design team according to their requirement. And that component model

is sent to the companies design department, production department.

This is important stage of the product development because by using the software we can change our

model according to customer requirement, manufacturing requirement at any stage before going to

die design. It decreases the designing time and also increases quality of the product. In most of the

cases, designers do mistake without knowing manufacturing knowledge while doing modeling of the

component, that’s why I am prescribing that while doing component design, consult with

manufacturing and quality departments. This approach is called as Concurrent Engineering. By this

approach, we can reduce mistakes in the manufacturing in the design stage itself. Most of the die

makers not following this theory, that’s why manufacturing lead time is increased.



232

MODIFIED MODEL ACCORDING TO THE CUTOMER REQUIREMENT

2D DRAWING OF THE FINAL MODEL

INSPECTING CAD COMPONENT

After modeling CAD component, it needs to be inspected according to die design

requirements. With my knowledge, the following check list needs to be prepared for any plastic

component.

a. Maintaining maximum uniform thickness for reducing material flowing problems while injecting

material in to the die.



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b. Avoiding sharp corners due to which material flow struck at the sharp corners. It causes decrease

in component strength and also increases stresses in corner. It causes failure of component. In our

component we have avoided all sharp corners.

c. Maintaining draft angle in die opening and closing direction. It the draft angle is not maintained

the component struck in production. The providing of draft angle depends on type of plastic material,

size of component and thickness of component.

Allow at least minimum draft of ½ Deg to 1 Deg to facilitate removal of parts from the mould.

d. Avoiding long flat surfaces. Due to the long flat surfaces, the component will bend and more

warpage will come. For avoiding this, the design needs to be modeled with some curved surfaces or

ribs are needed to be provided on flat surfaces.

e. Allow for shrinkage after moulding.

Before Shrinkage After Shrinkage

f. Specify only dimensional tolerance as close as actually necessary. A tolerance closer than 0.005

inch, the usual commercial limit, generally increases costs.



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g. Avoid undercuts which requires cores or split-cavity moulds

h. Locate the mould parting in one plane, if possible

i. Locate holes at right angles to part surfaces, Oblique holes add to mould costs.

j. Avoid long cored holes

k. Design projections in order to have circular sections. Irregularly shaped holes are generally more

expensive to obtain in the mould

l. Locate all holes and projections in the direction of mould opening & closing, if possible.

Otherwise, holes must be formed by the use of retractable core pins

m. Locate lettering to be embossed or debossed on surfaces perpendicular to the mould closed

n. Arrange ejector pin locations so that marks will occur on concealed surfaces

o. Design toward uniform section thickness and uniform distribution of mass for optimum flow of

the plastic in moulding.

p. Design corners with ample radii or fillets. This makes possible a more durable mould and

improves the flow of the plastic during moulding

q. Use ribs to add strength and rigidity, to minimize distortion from warping and to improve the flow

of the plastic during moulding

r. Restrict the rib height to not more than twice the thickness of the rib section. Otherwise, “sink”

marks will obtained on the flat surfaces opposite the ribs

s. Break up large flat surfaces with beads, steps or other geometric Designs to increase rigidity.

Improved appearance too can be obtained.

We have to check all of the above points before going to extract core and cavity. If we have

done any mistake while checking the model it affects the final product. Again we have to do

rework which will cause of increasing die cost and die manufacturing time.



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ADDING MATERIAL PROPERTIES AND ADDING SHRINKAGE

File – Properties – Material – Change – Select or Create Material – Enter properties – Save to Model

– Ok – Ok

Injection molding vs. other process

Process Max

operating

temperature

Max

operating

Pressure

General

operating

pressure is

less than

Rotational

molding

260°c 20 Mpa 1.5 Mpa

Transfer

molding

320°c 76 Mpa 20 Mpa

Compressio

n molding

260°c 55 Mpa 20 Mpa

Injection

molding

371°c 250 Mpa 100Mpa



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ADVANTAGES OF INJECTION MOLDING OVER THE OTHER MOLDING PROCESSES

• The manufactured object generally requires no further machining.

• Rate of production is high.

• Hot mold is used in some special cases only.

• Waste of material is negligible.

CAVITY

CORE

In this step extracting core and cavity is done in Pro/Engineer. By extracting core and cavity

in software we will get exact component from model.

PREPARING ROUGH ASSEMBLY FOR DIE

In this stage we have to prepare rough assembly of die of the total mould base for knowing

how much material required and the manufacturing processes required to prepare the quotation for

the die design.



237

PREPARING QUOTATION

Based on the rough assembly prepare quotation.

S.No Part name Raw material

size(mm)

Weight

Kg M1(Rs/kg)

Cost

Rs

M2

(Rs/Kg)

Cost

Rs

1 Cavity plate 1380*620*420 2800 EN31(120) 336000 C45 (70) 196000

2 Core plate 1380*620*400 2700 EN31(120) 324000 C45 (70) 189000

3 Core back plate 1380*620*120 134 EN8(60) 8040 M.S (50) 6700

4 Spacer(2Nos) 620*120*350 210*2=

420 M.S(50) 21000 M.S(50) 21000

5 Back plate 1380*620*120 800 M.S(50) 40050 M.S(50) 40050

6 Ejector guide

(8Nos) 350*100Dia 200 M.S(50) 10000 M.S(50) 10000

7

Ejector &

Retainer

plate(2Nos)

1160*620*45 510 M.S(50) 25500 M.S(50) 25500

8 Guide

pillar(4Nos) 350*100Dia 100 EN31(130) 13000 C45 (80) 8000

9 Guide

bush(4Nos) 400*90 120 EN31(130) 15600 C45 (80) 9600

10 Ejector

pins(25Nos) 400*12 OHNS 8750 OHNS 8750

11 Retainer

pins(6Nos) 400*16 EN31 1200 EN31 1200

12 Other materials 30000 30000

Total material

cost 833140/- 545800/-

CNC machining cost= Rs.400000/-

Jig boring cost=Rs.10000/-

Drilling & tapping cost=Rs. 15000/-

Cooling holes cost=Rs 8000/-

Polishing =Rs 30000/-

Transportation=Rs10000/-

Other machining=Rs60000/-

Total machining amount=Rs 533000/-



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TOTAL DIE COST IF WE USE FIRST MATERIALS M1 FOR DIE COMPONENTS

Total material & machining cost for first material=Rs13,66,140/-

Profit+ Risk factor=Rs 2,73,860/-

Total die cost with first material=Rs16,40,000/- TOTAL DIE COST IF WE USE FIRST MATERIALS M2 FOR DIE COMPONENTS

Total machining amount=Rs533000/-

Total material & machining g cost for second material=Rs1078800/-

Profit+ risk factor=Rs1,67,820/-

Total die cost with second material=Rs1246620/-

TECHNICAL AND COST DISCUSSION WITH CUSTOMER

In this stage, we have to explain technical points involved and cost to the customer.

Basically following points have to be discussed with the customer.

a. Material used for component production. Specify 2 to 3 materials to the customer and explain

strength and cost of each material.

b. Material used for die design for various components in mould base die.

� Example material used for core, cavity, core and cavity plates, ejector and retainer plates,

guide pillars, ejector pins, retainer pins, guide bushes, spacers, back plate

c. Finally prepare quotation for the component based on customer specification.

From the above quotation, if the materials specified in M2 are used, the total die cost is reduced

almost by 3,90,380/-.

FINAL QUOTATION AS APPROVED BY THE CUSTOMER

S.No Part name Raw material

size(mm)

Weight

Kg

Cost

Rs

M2

(Rs/Kg)

Cost

Rs

1 Cavity plate 1380*620*420 2800 336000 C45 (70) 196000

2 Core plate 1380*620*400 2700 324000 C45 (70) 189000

3 Core back plate 1380*620*120 134 8040 M.S (50) 6700

4 Spacer(2Nos) 620*120*350 210*2=420 21000 M.S(50) 21000

5 Back plate 1380*620*120 800 40050 M.S(50) 40050

6 Ejector guide

(8Nos) 350*100Dia 200 10000 M.S(50) 10000

7 Ejector & Retainer

plate(2Nos) 1160*620*45 510 25500 M.S(50) 25500

8 Guide pillar(4Nos) 350*100Dia 100 13000 C45 (80) 8000

9 Guide bush(4Nos) 400*90 120 15600 C45 (80) 9600

10 Ejector

pins(25Nos) 400*12 8750 OHNS 8750

11 Retainer

pins(6Nos) 400*16 1200 EN31 1200

12 Other materials 30000 30000

833140/- 545800/-



239

CNC machining cost= Rs.400000/-

Jig boring cost=Rs.10000/-

Drilling & tapping cost=Rs. 15000/-

Cooling holes cost=Rs 8000/-

Polishing =Rs 30000/-

Transportation=Rs10000/-

Other machining=Rs60000/-

Total machining amount=Rs 533000/-

TOTAL DIE COST IF WE USE FIRST MATERIALS M2 FOR DIE COMPONENTS

Total machining amount=Rs533000/-

Total material & machining g cost for second material=Rs1078800/-

Profit+ risk factor=Rs1,67,820/-

Total die cost with second material=Rs1246620/-

In this step we explained about the die cost to the customer. Also explain both merits and demerits of

the die manufacturing with two materials. We have taken approval from the customer in cost point of

view and productivity point of view. Then we can start our die work without any objections.

Otherwise if we didn’t explain all these to the customer after starting of die if customer changes his

design, there will be lot of lose to us. Here we can reduce total lead time and cost by explaining

about the die to the customer.

FINAL ASSEMBLY OF DIE

After all the technical discussions and cost discussions with the customer, the final quotation

is prepared and submitted to the customer. Now the total complete die required should be prepared.

Total Die components and their drawings are given below.

TOTAL DIE ASSEMBLY



240

PLANNING FOR MACHINING AND PREPARE TOTAL APPROXIMATE MACHINING

TIME

• CNC milling- 400hours, 17 days but we have to put tolerance put 25days +5 weekly half total

no of days for CNC are 30 days.

• Time taken for jig boring is 7days

• Time taken for drilling are 7 days

• Time taken for turning operation is 7 days.

• Time taken for heat treatment 4 days

• Total time taken for machining are 55 days

• Time taken for assembling 7days

• Time taken for part modeling and die design in software 7days.

• Time taken for trail 2days

• Time taken for total die manufacturing is 65 days.

By knowing time taken for manufacturing we can give die delivery time to the customer.

If we prepared our plane we can reduce total lead time of die manufacturing. We can explain

about the die to the customer by technically and cost point of view. We can have clear

permeation from the customer. Customer also satisfies with our work.

• In this project we can save 10 days time and lead time cost of 2, 52,300/-.

CONCLUSION

In product development die design will plays major roll. If we didn’t don die design with

proper planning. It will cause of increasing total lead time and cost of the die.

In this project I rectified above problems by giving proper planning for developing die. In this

project I rectified the major problem faced by most of the die makers. I taken virtual software

support in all steps. In model developing, shrinkage allowance adding, quotation preparation, output

drawings, machining cost, machining time, final assembly preparation. In all aspects of the die

design and manufacturing we taken software support, I saved 10 days time and 2,52,500/- cost. Also

we can manufacture die with out mistakes.

FUTURE SCOPE

By following above steps in plastic component die design and manufacturing to any

component we can save time and amount.

REFERENCES

1. 3D RAPID REALIZATION OF INITIAL DESIGN FOR PLASTIC INJECTION MOULDS

by Maria L.H. Low1 and K.S. Lee2.

2. Case study on Injection Moulding tool cost at JDP TOOLS.

3. G. Boothroyd et al., "Design for Injection Molding.

4. Robert A. Malloy, Plastic Part Design for Injection Molding. Cincinnati, OH: Hanser/

Gardener Publication, Inc.,

5. Robert G. Launsby and Daniel L. Weese, Straight Talk on Designing.

6. Experiments. Colorado Springs, CO: Launsby Consulting.

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