30120130406024

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 6, November - December (2013) © IAEME

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)
www.jifactor.com

IJMET
©IAEME

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
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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
Blister

Burn marks

Color streaks
(US)

Delamination

Flash
Embedded
contaminates

Flow marks

Jetting
Polymer
degradation
Sink marks
Short shot
Splay marks

Voids

Weld line

Warping

Alternative
Name

Descriptions

Causes

Raised or layered zone on Tool or material is too hot, often caused by a lack of
surface of the Plastic part cooling around the tool or a faulty heater
Black or brown burnt
Air Burn/Gas areas on the plastic part
Tool lacks venting, injection speed is too high
Burn
located at furthest points
from gate
Plastic material and colorant isn't mixing properly, or
Localized change of color the material has run out and it's starting to come
through as natural only
Contamination of the material e.g. PP mixed with
ABS, very dangerous if the part is being used for a
Thin mica like layers
safety critical application as the material has very
formed in part wall
little strength when delaminated as the materials
cannot bond
Excess material in thin
Tool damage, too much injection speed/material
Burrs
layer exceeding normal injected, clamping force too low. Can also be caused
part geometry
by dirt and contaminants around tooling surfaces.
Foreign particle (burnt
Particles on the tool surface, contaminated material
Embedded
material or other)
or foreign debris in the barrel, or too much shear heat
particulates
burning the material prior to injection
embedded in the part
Injection speeds too slow (the plastic has cooled
Directionally "off tone" down too much during injection, injection speeds
Flow lines
wavy lines or patterns
must be set as fast as you can get away with at all
times)
Deformed part by
Poor tool design, gate position or runner. Injection
turbulent flow of material speed set too high.
polymer breakdown from Excess water in the granules, excessive temperatures
oxidation, etc.
in barrel
Holding time/pressure too low, cooling time too
Localized depression
short, with sprueless hot runners this can also be
(In thicker zones)
caused by the gate temperature being set too high
Non-Fill/Short
Partial part
Lack of material, injection speed or pressure too low
Mold
Splash
Circular pattern around Moisture in the material, usually when resins are
Mark/Silver
gate caused by hot gas
dried improperly
Streaks
Lack of holding pressure (holding pressure is used to
pack out the part during the holding time). Also mold
Empty space within part
may be out of registration (when the two halves don't
(Air pocket)
center properly and part walls are not the same
thickness).
Knit
Discolored line where
Mold/material temperatures set too low (the material
Line/Meld
two flow fronts meet
is cold when they meet, so they don't bond)
Line
Cooling is too short, material is too hot, lack of
cooling around the tool, incorrect water temperatures
Twisting Part Distorted part
(the parts bow inwards towards the hot side of the
tool)
Blistering

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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.

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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.

232


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
Max
General
operating
operating
operating
temperature
Pressure
pressure is
less than
Rotational
260°c
20 Mpa
1.5 Mpa
molding
Transfer
320°c
76 Mpa
20 Mpa
molding
Compressio
260°c
55 Mpa
20 Mpa
n molding
Injection
371°c
250 Mpa
100Mpa
molding

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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.
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PREPARING QUOTATION
Based on the rough assembly prepare quotation.
S.No

Part name

1
2
3

Cavity plate
Core plate
Core back plate

Raw material
size(mm)
1380*620*420
1380*620*400
1380*620*120

4

Spacer(2Nos)

620*120*350

5

Back plate
Ejector guide
(8Nos)
Ejector &
Retainer
plate(2Nos)
Guide
pillar(4Nos)
Guide
bush(4Nos)
Ejector
pins(25Nos)
Retainer
pins(6Nos)
Other materials

1380*620*120

Weight
Kg
2800
2700
134
210*2=
420
800

350*100Dia

6
7
8
9
10
11
12

EN31(120)
EN31(120)
EN8(60)

Cost
Rs
336000
324000
8040

M2
(Rs/Kg)
C45 (70)
C45 (70)
M.S (50)

Cost
Rs
196000
189000
6700

M.S(50)

21000

M.S(50)

21000

M.S(50)

40050

M.S(50)

40050

200

M.S(50)

10000

M.S(50)

10000

1160*620*45

510

M.S(50)

25500

M.S(50)

25500

350*100Dia

100

EN31(130)

13000

C45 (80)

8000

400*90

120

EN31(130)

15600

C45 (80)

9600

400*12

OHNS

8750

OHNS

8750

400*16

EN31

1200

EN31

1200

M1(Rs/kg)

30000
Total material
cost

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 533000/237

30000

833140/-

545800/-


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
833140/-

238

30000
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/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

239


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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