Injection Molding Simulation Analysis

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I n j e c t i o n M o l d i n g S i m u l a t i o n A n a l y s i s

o f C a r R i m U s i n g S o l i d W o r ks P l a s t i cs

Muhammad Sheharyar

Department of Polymer & Process Engineering,

University of Engineering & Technology Lahore, Pakistan.

Abstract

In this project the main purpose is to study the injection molding parameters of a car rim using

injection molding simulation software SolidWorks

Plastics. The material used for simulation

was PEEK(Polyether ether ketone) with an addition of 30% carbon fibre. The investigations

were carried out on flowing, packing, cooling and costing of injection moulded car rim. At the

end of analysis the most feasible design can be selected for further stress or other analysis.

1. Introduction

In the past years, injection molding has

become very popular in designing the parts

of complex geometry. This technique is very

much efficient in decreasing labor cost and

to design the discrete parts. Now-a-days

more than one third of polymer products are

manufactured by injection molding.

Injection molding is a process in which

polymer in the form of powder or pellets is

injected into a mold cavity. Mold unit cools

down the polymer & heat is removed from

the polymer so that it becomes rigid. In an

injection molding process there are certain

parameters which ensure the efficient

molding process. These parameters are melt

temperature, mold temperature, injection

pressure, cooling rate & shear rate. The

insert material in an injection molding

process is made of polymer. Different insert

parts have variable effects on the injection

molding process. [AVRAAM, 1987] In this

project an analysis had been made to

analyze the different parameters of the

injection molded part. In this project the

study of car rim simulation had been carried

out using SolidWorks Plastics. The study

of injection molding simulation analysis

requires proper knowledge about its

parameters and thermal properties of

material. Simulation technique is very

important tool for the analysis and the

testing of the product before implementing

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in the real systems. Due to computer, as

more powerful, problems can be solved

before manufacturing it. [DOMINICK,

2000] Before going towards simulation by

SolidWorks

Plastics the part was first

designed in SolidWorks

Premium and then

imported in SolidWorks Plastics for

simulation. There are many other important

injection molding simulation softwares like

Autodesk

Moldflow.

2. Part Selection

The car rim was selected as the desgin part

to study the injection molding simulation

analysis. The rim has great importance in

car. It is the outer part of the wheel on which

tyre is mounted. Basically, it provides the

base to tyre for mounting. It also provides

strength to the tyre and holds the car tyre

together. A car cannot operate without rims.

They come in different materials and sizes

to meet the specifications of cars. [JERRY,

2013] SolidWorks Premium was used to to

draw car rim geometrical layout as well as

SolidWorks Plastics software was used for

injection molding simulation analysis. The

design of car rim is shown in Figure 1.

Figure 1: Design of Car Rim

The major dimensions are 215.53mm x

450.49mm x 446.71mm After making part

the simulation of injection molded part was

carried out.

3. Material Selection

Many types of materials are used to

manufacture the car rim. The most popular

and common materials are metal alloys and

polymer based composits. Out of these

materials polymers play an important role in

the energy saving design of car rim. In this

project the simulation was carried out using

PEEK(Polyether ether ketone) polymer with

30% addition of carbon fibre. The heat

transfer property of polymers helps to

decrese the heat losses in the tyre due to

road friction. The reason of selecting

PEEK+30% carbon fibre was that it has very

high modulus and is high impact polymer. It

provides excellent strength to the tyre and is

light weight. Due to light weight it provides

good acceleration and handeling to the car

[JERRY, 2013]. The material information is

shown in Table 1.

Table 1: Material Information

Melt Temperature 385C

Glass Transition

Temperature

145C

Thermal

Conductivity

13.5x 104 W/m.K

Youngs Modulus 24.5x 1010

Pa

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4. Results & Discussion

The processing parameters mold & melt

temperature, cooling time, packing pressure,

packing time, injection location, diameter of

gate have direct effect on volumetric

shrinkage, frozen layer, sink marks, weld

lines, residual stress. The simulation was

done using SolidWorks Plastics by varying

above parameters to study this model.

4.1 Number of Gates

Number of gates have major influence on

weld lines. Also by locating more gates

decrease the fill time. The gate should not be

located at sensitive location of part.

4.1.2 Effect of Number of

Gates on Weld Lines

Weld lines are formed when two or more

plastic melt flow fronts come together and

they can be caused by mold shut-off

surfaces, mold core features, multiple

injection locations or wall thickness

variations that cause flow front promotion or

hesitation. Weld lines are typically weaker

than areas without weld lines and they often

result in cosmetic defects. They can also act

as stress concentrators in the molded part.

Weld lines weaken the mechanical

properties [SHOEMAKER, 2006]. Weld

lines increase when greater number of gates

are used. In the first simulation single gate

was used while other processing parameters

were fixed. Table 2 shows the parameters to

study effect of number of gates on weld

lines when single gate was used.

Table 2: Parameters when single gate was used


Mold Temperature 190C

Injection Pressure

Limit

100 MPa

Gate Diameter 5 mm

Number of Gates 1

Figure 2 shows the weld lines when single

gate was used.

Figure 2: Weld Lines when single gate was used

Table 3 shows the parameters to study effect

of number of gates on weld lines when two

gates were used.

Table 3: Parameters when two gates were used


Mold Temperature 190C

Injection Pressure 100 MPa

Gate Diameter 5 mm

Number of Gates 2

Figure 3 shows the weld lines when two

gates were used.

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Figure 3: Weld Lines when two gates were used

So, it is clear from the figures that when one

gate was located, lesser number of weld

lines were formed and when two gates were

located, greater number of weld lines were

formed which is not a good thing for the part

as they decrease mechanical properties of

part.

4.2 Melt Temperature

Melt temperature is one of the most

important parameter that disturbed the

properties of end product. Shrinkage

increased at high melt temperature.

Shrinkage can be defined as an extreme

decreased in the dimensions of a molded

part after it had cooled to room temperature.

If the melt temperature is too high, the resin

absorbed an excessive amount of heat and

this in-creased the size of the voided area

between the plastic molecules. Upon

cooling, the skin of the material solidifies

first and the remaining resin closed up the

excessively large molecules and voids as it

cooled, pulling the solidified skin with it.

[FISCHER, 2013]

4.2.1 Effect of Melt

Temperature on Volumetric

Shrinkage

The volumetric shrinkage occurs in the thick

portions of the part. It means polymer

contracts when temperature is decreased

from high melt temperature to normal

cooling temperature. Also the high melt

temperature means that the part can be

packed with more pressure and part weight

is reduced as large increase in volumetric

shrinkage. [SHOEMAKER, 2006]

Three simulations were carried out at three

different melt temperatures that were 385C,

420C and 450C when single gate was used

while other processing parameters were

fixed. Figure 4 shows the shrinkage in the

part at melt temperature of 385C.

Figure 4: Volumetric Shrinkage at Melt

Temperature 385C

Figure 5 shows the shrinkage in the part at

melt temperature of 420C.

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Temperature 420C

Figure 6 shows the shrinkage in the part at

melt temperature of 450C.


Temperature 450C

Table 4: Effect of Melt Temperature on Shrinkage

Sr.No Melt

Temperature

Mold

Temperature

Injection

Pressure

Shrinkage

1 385C 190C 100 MPa 11.1535%

2 420C 190C 100 MPa 12.4804%

3 450C 190C 100 MPa 13.6471%

4.3 Mold Temperature

Mold temperature had more effects on final

properties. Higher mold temperatures

produced lower levels of molded in stress

and consequently better impact resistance,

stress crack resistance and fatigue

performance. The mold temperature was the

dominant factor; however, the best results

were obtained when higher mold

temperatures were combined with lower

melt temperature. This behavior is

characteristic of all polymers. In general

optimal performance is produced by

combining low melt temperature and high

mold temperature. [SHEN, 2010]

4.3.1 Effect of Mold

Temperature on Frozen

Layer

When plastic melt makes contact with the

mold wall, a thin layer of the melt instantly

freezes along the cavity wall. This layer of

solidified plastic is called the frozen layer.

This frozen layer depends upon the

difference between melt temperature and

mold temperature. Frozen layer also depends

upon filling time because by giving more

filling there is a possiblity of freezing of

material in mold cavity. But the factor of

geometry of part is also important because if

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we give less time to part of complex

geometry then there will not be equal

distribution of material in mold which leads

the formation of more weld lines. [SHEN,

2010]

The three simulations were carried out at

three different mold temperature when

single gate was used while other processing

parameters were fixed.

Figure 7 shows the frozen layer in part at

mold temperature of 190C.

Figure 7: Frozen Layer at Mold Temperature

190C




210C




230C

It is clear from the figures that when the

difference between mold temperature and

melt temperature was decreased the frozen

layer also decreased. In other words when

mold temperature was increased the frozen

layer formed was decreased. Generally, a

hot mold will allow a material to stay molten

longer than a cold mold and cause the

molecules to flow farther before they

solidify. If the mold was too cold, the

molecules solidify before they were packed

and the weld lines will be more evident. So,

the solution is that Increase the mold

temperature to the point that the material has

the proper flow and packs out the mold with

maximum weld line strength. If the mold is

not cooling the plastic the molecules will

have varying cooling and shrinking

characteristics and this causes warpage.

[FISCHER,2013]

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Table 5: Effect of Mold Temperature on Frozen Layer

Sr.No Melt

Temperature

Mold

Temperature

Injection

Pressure

Frozen Layer

1 385C 190C 100 MPa 0.2500

2 385C 210C 100 MPa 0.2358

3 385C 230C 100 MPa 0.2279

Conclusions

This study shows that by changing the

different parameters in the SolidWorks

Plastics, defects which are produced in the

product can be easily detected and by

adopting suitable parameters for the product,

these defects can be easily removed before

using the product for the practical

applications.

Acknowledgements

First of all, the author wants to say thanks to

Almighty Allah then thanks to Dr. Shafiq

Irfan and also the group members Umer and

Khizar for their guidance and advices on

injection molding simulation analysis.

References

AVRAAM, I. 1987. Injection and

Compression Molding Fundamentals, New

York, NY, USA, Marcel Dekker, Inc.

DOMINICK, R. 2000. Injection Molding

Handbook, Massachusetts, USA, Kluwer

Academic Publishers.

FISCHER, J. 2013. Handbook of Molded

Part, Warpage and Shrinkage. Intermediate

Technology Publication, UK

JERRY, F. 2013. Handbook of Molded Part

Shrinkage and Warpage, Oxford, UK,

Elsevier Publishers.

SHEN, J. 2010. Design and Molding

Simulation of the Plastic Part. John Wiley

and Sons Publications, USA

SHOEMAKER, J. 2006. Moldflow Design

Guide, Massachusetts, USA, Hanser

Publishers.

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Injection Molding Simulation Analysis