penn state capstone project investigating part warpage in qc 10 vs steel

Investigation into Part Warpage Differences

Between Aluminum and Steel Tooling

Laird Samuel Raybuck Jr

Chad Matthew Shumaker

09/28/2010 – 05/01/2010

Investigation into Part Warpage Differences Between Aluminum and Steel Tooling

Laird Samuel Raybuck Jr, Chad Matthew Shumaker

Abstract

A study was performed to compare the results of

cooling properties, the reduction of overall cooling time

and warpage of parts produced with Aluminum and P20

Steel inserts. Four different materials were used to achieve

this, PE, Nylon, ABS, and PC. Cooling water

temperatures used in the experiment were kept consistent

for the materials when switching between the inserts.

Results showed an average of 10 °C in mold temperature

which resulted in an average of 1mm in warpage in parts

ran in the aluminum inserts when compared to steel.

Introduction

Warpage has always been an issue in the plastics

industry due to part design and various processing

parameters to produce parts with in tolerances. Aluminum

is expected to cool the molded parts quicker and more

efficiently than the steel insert because aluminum is

approximately four times as thermally conductive as steel.

Although there has never been any published data backing

up aluminums excellent thermal properties by comparing it

to steel, this study will publish numbers that prove

aluminums excellence to be true in regards to it being a

sufficient molding compound. Being more thermally

conductive allows the aluminum to cool the parts quicker

than the less thermally conductive steel which is a common

mold material. The negative aspect of aluminum is its

wear characteristics. Aluminum being less tough than steel

ultimately has manufactures expecting a decreased life

expectancy. Aluminum has relatively low cost, due to its

ease of machining, and thermal conductivity making it a

first choice in most applications.

With faster cycle times and decreased tooling

cost, aluminum tooling can give any company the

competitive edge that they need in the plastics industry.

With aluminum tooling, developed manufactures can keep

cycle time down which in turn reduces cost. Not only

making the manufacture more efficient, but also could

potentially decrease the use of energy and help the

environment. The differences between steel and aluminum

inserts are decreased cooling time increased cooling rate,

warpage, and the rate at which the mold material wears

under high pressures, and multiple cycles. This study needs

to be performed to optimally prove how thermally

conductive aluminum is and how beneficial it can be to any

manufacturer that wants to be competitive in their market.

As more and more companies try to decrease costs they

will turn to aluminum to satisfy these needs to produce

parts faster while still holding dimensions.

Aluminum tooling will decrease cooling time due

to its higher thermal conductivity but will cost more over

time due to wear and replacing the mold. So, immediately

the aluminum tooling will cost less but over time could

prove more costly when examining mold expenses. The

study performed was an (OFAT), One Factor At a Time,

type of experiment. An (OFAT) experiment changes one

factor at a time to make sure that none of the factors have

an effect on each other.

The parameters that needed to be changed from

one mold material to the next and one resin material to the

next were based upon the best two stage injection molding

process that could be optimized. Cooling time was the

parameter that was changed during the study. The study

measured changes in warpage and the temperature of the

insert both core and cavity, as well as their respected parts

and how they were associated with the changing

parameter. The two semi crystalline materials that were

used are High Density Polyethylene (HDPE) and

Polypropelene (PP) and the two amorphous materials are

Polycarbonate (PC) and, Acrylonitrile Butadiene

Styrene(ABS).

Statement of Theory and Definitions

The main focus of the experiment is the difference

between the P-20 steel inserts and the T-79 aluminum

inserts in regards of thermal properties, mainly cooling

rate, cooling time, and part warpage. Recent developments

have produced two new aluminum alloys which maintain

traditional aluminum’s high thermal conductivity, and have

significantly higher yield strength and hardness than earlier

aluminum alloys QE-7 and QC-9. These new aluminum

alloys have thermal conductivities four times greater than

the industry tool steels, and have significantly increased

strength and hardness compared to traditional aluminum

materials. As part wall thickness increases the polymer

properties began to limit the effectiveness of aluminum

alloy usage [1]. The thicker wall decreases the efficency

of the aluminums cooling.

Aluminum compared to steel inserts have better

thermal conductivity, cost less, and are easier to machine

due to aluminum’s increased density which decreases the

overall hardness of aluminum. Cooling system design and

layout is important for making injection molding tools that

have short cycle times and produce high quality parts that

need to be stress and warp free. Guidelines for waterline

placement vary widely and don’t satisfy most

requirements. With aluminum’s better thermal

conductivity there is less chance for the part to warp when

compared to P20 steel. Although aluminum has better

thermal properties than P20 steel, aluminum tooling will

wear more, it is also easier to damage tooling, and will

decrease the total amount of cycles that the insert does

produce.

Previously the placement of waterlines has been

over looked and was one of the last things to be

considered. The distance between the center of the water

line of the plastic metal interface and center to center of

each water lines distance should be considered [2].

The two most common styles of water line layouts

are conventional, and conformal. Both steel and aluminum

inserts used conventional cooling line layouts in this

sturdy. The benefit of conventional cooling lines is the

decreased cost to produce the layout. The benefit of

conformal cooling lines are their increased cooling ability

due to the cooling line channels being cut to contour and

flow with the geometry of the specified part. The

disadvantage of a conformal layout is the increased time

and machining cost that is associated with the increased

cooling abilities.

Due to aluminum’s soft nature it is often not a

desirable choice but, because of its ease of machining

when more complex geometries and sizes it is often times

considered. Aluminum is the most widely utilized

cavity/core for prototyping due to its softness. Aluminum

is a desirable material because it is easy to cut and machine

and possesses a high thermal conductivity. It is also light

weight which makes it easier and cheaper to transport and

ship. Aluminum is also very easy to polish if a greater

surface appearance is required. When aluminum is

machined compared to tool steel, aluminum can be

machined 2-4 times quicker than steel [3].

As soon as the plastic resin touches the mold

walls the cooling cycle begins. Once the flow of the

plastic stops the plastic resin is conductively cooled

through the plastic to the mold walls. To achieve uniform

cooling the following should be considered when molding,

uniform part temperature prior to the start of the cooling

cycle, uniform part thickness, and uniform mold wall

temperature at the start of the molding process and when

the part begins to cool to the ejection temperature [4].

Cooling has a direct effect on part warpage and shrinkage

as do the material the part is molded out of. Molders still

continue to struggle with the warpage of fiber-filled resins

[5].

When a fiber-filled material shrinks it shrinks

less in the direction of flow due to the fiber orientation.

When differential cooling occurs in a molded part one side

of the part will cool faster compared to the other. The

cooler side of the part will freeze sooner and shrink less

than the hotter side of the part. When this differential

cooling occurs a bending moment is created causing the

warpage of the part [5]. Cooling can also affect molded in

stresses of injection molded parts.

Cooling rate is the rate at which the heat is

removed from the part geometry from conduction into the

molding material and finally into the cooling water. The

cooling time is the amount of time allotted for the material

to shrink to core locking in the residual stresses while

being held under pressure to obtain the dimensions of the

insert.

Increased cooling rate inhibits crystal growth

there fore decreasing the density and the over all warpage

of a semi-crystalline material. An amorphous material

being less dense aids in the ability of the polymer chains to

orient under high pressures such as experienced during fill

velocity. It is natural for an amorphous material to attempt

to return to its natural un-oriented state when it is above it

glass transition temperature. When a semi-crystalline

material is above its glass transition temperature it

increases the number of crystals that are formed.

A cold mold will lock in more of the orientation

and the resultant stresses. This will affect the stresses

through out the thickness of the part. As a warmer mold

will reduce polymer orientation and the resultant stresses

[5]. Meaning cooling time and rate have a direct

relationship with shrinkage and warpage.

The three processing variables that appear to

cause warpage by themselves are cooling time, cooling

temperature, and cooling distribution in the mold. More

stress relaxation occurs when a shorter cooling time of a

part in a warm mold occurs during the shrinkage process.

A longer cooling time at a given mold temperature allows

the part to become more rigid which resists warpage more

efficiently [5].

Cooling lines should be developed and placed

efficiently to maximize cooling. If a Reynold’s number of

10,000 or greater is achieved optimal cooling is developed

and heat transfer is maximized [5]. Turbulent flow is

developed at a Reynold’s number of about 2300-4000.

The turbulent mixing of the water pulls more heat from the

surface of the cooling channel vigorously mixing it back

into the center of the channel and then circulating it

through out the mold and eventually back into the

thermolator.

The steel insert was used as a base line for the

experiment optimizing the process. With that the process

parameter that was changed by using the aluminum insert

was cooling time, These are based upon performing a two

stage setup and were perceived based upon the advantages

of a optimized two stage robust injection molding process

having the injection velocity, hold time, and pack pressure

optimally found.

Part testing will be done on each part using the

optical scope once the parts have been able to cool for a

minimum of 48 hours.

Description of Equipment and Processes

The injection molding process of the contoured,

center bottom side gated box, while not optimal, provides

an adequate base to study warpage seen on similar part

geometries. The mold base used in the experiment was the

mold base used in a previous rapid tooling experiment.

The same mold base will be utilized during all runs with

the P20 inserts as well as the T-79 aluminum inserts. Both

the P20 steel mold and T-79 aluminum inserts have the

same conventional cooling line layout. Mold flow was

used to determine and compare some optional outcomes

prior to molding as well as supported our results. As the

mold cycles it gradually increases in temperature. To keep

the warp and deformation experiment accurate and

repetitive a thermolator was utilized to keep temperatures

in check while molding on the Husky 90 metric ton

hydroelectric injection molding press with a 32mm screw

and the Arburg Allrounder 470, 170 metric ton, with a

40mm screw. Due to the size of the mold the Husky

injection molding press was the optimal choice for the

experiment. The same mold base was used for every run

of the experiment while the inserts were changed.

Aluminum and P20 steel inserts were used in the mold

base for the experiment to compare the cooling

characteristics of the two mold materials. The cooling

characteristics directly relate to the warpage of the parts.

To concentrate on localized heating of the cavity, core, and

parts A Flir A-20 digital infrared thermal camera was used

to take the pictures of the of the cavity, core, and the

produced parts.

Application of Equipment and Processes

An optimized two- stage robust injection molding

process was created to sufficiently produce the parts with

the P20 inserts in the same mold base as the aluminum

inserts were ran. Once an optimized two stage process was

achieved with the P20 steel inserts as a base line, the

cooling time was set to 90 seconds. With a cooling time of

90 seconds three pictures were taken of the core, the cavity

At a cooling time of 5 and 20 seconds pictures were taken

of three parts at each time per material per mold insert both

core and cavity side of the part. After all the pictures were

obtained; the cooling time was then decreased to 60

seconds. The process was cycled for ten minutes to let any

temperatures or other parameters equalize to reduce error

and to keep the experiment accurate, and repetitive. The

same experiment was performed then with a 45, 30, 25, 20,

15, 10, and lastly a 5 second cooling time. Once all the

parts were made with the four materials at the designated

cooling times the aluminum inserts were inserted into the

same mold base and the process was cycled to reach

equilibrium. The parts were made using the same two

stage process that produced the parts with the P20 steel

insert using the same cooling times. After all the parts

were molded they were measured after being stored in a

controlled environment for at least 48 hours. The same

experiment with the P20 steel insert and the aluminum

insert was executed one material at a time for four

materials those materials being high density polyethylene,

acrylonitrile butadiene styrene, nylon and polycarbonate.

The cooling water was held constant for both the

aluminum and steel inserts. How ever the cooling water

temperature did change with the resins. A cooling water

temperature of 32°C was used for the PP and PE. A

cooling water temperature of 60°C was used for the ABS

and 70°C for the PC.

The steel insert was used as a base line for the

experiment optimizing the process. With that the process

parameter that was changed by using the aluminum insert

was cooling time. These are based upon performing a two

stage setup and were perceived based upon the advantages

listed above.

The parts were measured at a minimum of 48

hours after being molded with the Avant 400 CFOV serial

number AV4001266. The 48 hour minimum time frame

assures that the parts are fully cooled and the polymer

chains are in there frozen state given enough time to stress

relax.

The measurements taken of the molded parts

where in the X-Direction and Y-Direction in comparison to

the hard dimensions of the cavity side insert. Shown in

illustrations 1 and 2 below.

Illustration 1 – Y-Direction measurement

method in core half of insert.

Illustration 2 – X-Direction measurement

method in core half of insert.

Presentation of Data and Results

Figure 1 - PP Aluminum Cavity at Five Second Cooling

Time

The above Figure 1 is of the Aluminum Cavity at

a 5 second cooling time shows the temperature to be

between 25-35 °C.

Figure 2 - PP Aluminum Core at Five Second Cooling

Time

The above Figure 2 is of the Aluminum Core at a

5 second cooling time shows the temperature to be

between 25-35 °C.

Figure 3 - PP Aluminum Insert Cavity Side of Part at Five

Second Cooling Time

The above Figure 3 illustrates the temperature of

the cavity side of the part at a range of 50-60 °C.

Figure 4 - PP Steel Cavity at Five Second Cooling Time

The above Figure 4 is of the Steel Cavity at a 5

second cooling time shows the temperature to be between

40-50 °C.

Figure 5 - PP Steel Core at Five Second Cooling Time

The above Figure 5 is of the Steel Core at a 5


40-50 °C.

Figure 6 - PP Aluminum Cavity at 20 Second Cooling

Time



between 25-35 °C.

Figure 7 - PP Aluminum Core at 20 Second Cooling time



between 25-35 °C.

Figure 8 - PP Aluminum Insert Cavity Side of Part at 20

Second Cooling Time

The above Figure 8 is of the Aluminum insert

cavity side of the part at a 20 second cooling time shows

the temperature to be between 20-30 °C.

Figure9 - PP Steel Cavity at 20 Second Cooling Time



35-45 °C.

Figure 10 - PP Steel Core at 20 Second Cooling Time



35-45 °C.

Figure 11 - PE Aluminum Cavity at Five Second Cooling

Time



between 20-30 °C.

Figure 12 - PE Aluminum Core at Five Second Cooling

Time



between 20-35 °C.

Figure 13 - PE Aluminum Insert Cavity Side of Part at

Five Second Cooling Time


cavity side of the part at a 5 second cooling time shows the

temperature to be between 50-65 °C.

Figure 14 - PE Steel Cavity at Five Second Cooling Time



40-50 °C.

Figure 15 - PE Steel Core at Five Second Cooling Time



40-50 °C.

Figure 16 - PE Steel Insert Cavity Side of Part at Five

Second Cooling Time

The above Figure 16 is of the Steel insert cavity side

of the part at a 5 second cooling time shows the


Figure 17 - PE Aluminum Cavity at 20 Second Cooling

Time



between 20-30 °C.

Figure 18 - PE Aluminum Core at 20 Second Cooling

Time



between 25-35 °C.

Figure 19 - PE Aluminum Cavity Side of Part at 20

Second Cooling Time

The above Figure19 is of the Aluminum insert



Figure 20 - PE Steel Cavity at 20 Second Cooling Time

The above Figure20 is of the Steel Cavity at a 20


35-45 °C.

Figure 21 - PE Steel Core at 20 Second Cooling Time



35-45 °C.

Figure 22 - PE Steel Insert Cavity Side of Part at 20

Second Cooling Time

The above Figure 22 is of the Steel insert cavity

side of the part at a 20 second cooling time shows the


Figure 23 - ABS Aluminum Cavity at Five Second

Cooling Time

The above Figure 23 is of the Aluminum Cavity

at a 5 second cooling time shows the temperature to be

between 25-35 °C.

Figure 24 - ABS Aluminum Core at Five Second Cooling

Time



between 25-35 °C.

Figure 25- ABS Aluminum Cavity Side of Part at Five

Second Cooling Time




Figure 26 - ABS Steel Cavity at Five Second Cooling

Time



40-55 °C.

Figure 27 - ABS Steel Core at Five Second Cooling Time

The above Figure27 is of the Steel Core at a 5


40-55 °C.

Figure 28 - ABS Aluminum Cavity at 20 Second Cooling

Time



between 25-35 °C.

Figure 29 - ABS Aluminum Core at 20 Second Cooling

Time



between 25-35 °C.

Figure 30 - ABS Aluminum Cavity Side of Part at 20

Second Cooling Time




Figure 31 - ABS Steel Cavity at 20 Second Cooling Time



40-55 °C.

Figure 32 - ABS Steel Core at 20 Second Cooling Time



40-55 °C.

Figure 33 - PC Aluminum Cavity at Five Second Cooling

Time



between 25-35 °C.

Figure 34 - PC Aluminum Core at Five Second Cooling

Time



between 25-35 °C.

Figure 35 - PC Aluminum Insert Cavity Side of Part at

Five Second Cooling Time




Figure 36 - PC Steel Cavity at Five Second Cooling Time

The above Figure 36 of the Steel Cavity at a 5


40-55 °C.

Figure 37 - PC Steel Core at Five Second Cooling Time



45-55 °C.

Figure 38 - PC Steel Insert Cavity Side of Part at Five

Second Cooling Time



temperature to be between 70-80°C.

Figure 39 - PC Aluminum Cavity at 20 Second Cooling

Time



between 25-35 °C.

Figure 40 - PC Aluminum Core at 20 Second Cooling

Time



between 25-35 °C.

Figure 41 - PC Aluminum Insert Cavity Side of Part at 20

Second Cooling Time



the temperature to be between 40-50°C.

Figure 42 - PC Steel Cavity at 20 Second Cooling Time



45-55 °C.

Figure 43 - PC Steel Core at 20 Second Cooling Time



45-55 °C.

Figure 44 - PC Steel Insert Cavity Side of Part at 20

Second Cooling Time



temperature to be between 60-70°C.

Figure 45 - ABS Warpage In the X-Direction Vs. Cooling

Time

The above figure illustrates the Warpage in the X-

Direction vs. Cooling Time. The figure shows that the

warpage of the aluminum insert is less than that of the steel

insert in the X-Direction. The warpage decreased as the

cooling time increased in regards to the steel insert. The

warpage of the aluminum insert parts stayed constant

through out the cooling time study. There was an average

difference of 0.2 mm of warpage between the steel and

aluminum parts.

Figure 46 - ABS Warpage In the Y-Direction Vs. Cooling

Time

The above figure illustrates the Warpage In the Y-



insert in the Y-Direction. The warpage decreased as the


warpage of the aluminum insert parts stayed relatively

constant through out the cooling time study. There was an

average difference of 0.4 mm of warpage between the steel

and aluminum parts.

Figure 47 - PE Warpage In the X-Direction Vs. Cooling

Time

The above figure illustrates the Warpage In the X-



insert in the X-Direction. The warpage decreased then

increased as the cooling time increased in regards to the

steel insert. The warpage of the aluminum insert parts

stayed relatively constant through out the cooling time

study. There was an average difference of 0.5 mm of

warpage between the steel and aluminum parts.

0

0.5

1

10 15 20 25 30 45 60

Warpage(mm.)

Cooling Time (sec.)

ABS (X-Direction)

0

0.5

1

1.5

10 15 20 25 30 45 60

Warpage(mm.)

Cooling Time (sec.)

ABS (Y-Direction)

0

0.5

1

1.5

2

2.5

3

10 15 20 25 30 45 60

Warpage(mm.)

Cooling Time (sec.)

PE (X-Direction)

Figure 48 - PE Warpage In the Y-Direction Vs. Cooling

Time









and aluminum parts.

Figure 49 - PC Warpage In the X-Direction Vs. Cooling

Time

The above figure illustrates the Warpage In the X-



insert in the X-Direction. The warpage decreased as the





and aluminum parts.

Figure 50 - PC Warpage In the Y-Direction Vs. Cooling

Time




insert in the Y-Direction. The warpage stayed relatively

the same as the cooling time increased in regards to the

steel insert. The warpage of the aluminum insert parts

stayed relatively constant through out the cooling time

study. There was an average difference of 0.2 mm of

warpage between the steel and aluminum parts.

Figure 51 - PP Warpage In the X-Direction Vs. Cooling

Time

The above figure illustrates the Warpage In

the X-Direction vs. Cooling Time. The figure shows that

the warpage of the aluminum insert is less than that of the

steel insert in the X-Direction. The warpage stayed

relatively constant as the cooling time increased in regards

to the steel insert. The warpage of the aluminum insert

parts varied as the cooling time was increased through out

the cooling time study. There was an average difference of

0.3 mm of warpage between the steel and aluminum parts.

0

1

2

3

10 15 20 25 30 45 60

Warpage (mm.)

Cooling Time (sec.)

PE (Y-Direction)

0

0.5

1

1.5

10 15 20 25 30 45 60

Warpage(mm.)

Cooling Time (sec.)

PC (X-Direction)

0

0.5

1

1.5

10 15 20 25 30 45 60

Warpage(mm.)

Cooling Time (sec.)

PC (Y-Direction)

00.51

1.52

10 15 20 25 30 45 60

Warpage(mm.)

Cooling Time (sec.)

PP (X-Direction)

Figure 52 - PP Warpage In the Y-Direction Vs. Cooling

Time






warpage of the aluminum insert decreased as the cooling

time increased. There was an average difference of 2.1

mm of warpage between the steel and aluminum parts.

Interpretation of Data and Results

In (Figures 23,24) the temperature of the cavity

and core insert are shown to be 10-15°C less than that of

the steel cavity and core insert in (Figures 26,27) at a five

second cooling time when molded with ABS.

In (Figures 28,29) the temperature of the cavity

and core insert are shown to be 10-15°C less than that of

the steel cavity and core insert in (Figures 31,32) at a 20

second cooling time when molded with ABS.

In the ABS molded with the aluminum insert

warped less than the parts molded with steel insert.

Aluminum being up to four times as thermally conductive

as steel inhibited the parts molded with the aluminum

insert to warp as much as the parts molded with the steel

insert because the increased cooling rate locked the

polymer chains in their current state. The overall average

warpage of the aluminum inserts molded parts was 0.2mm

in the X-Direction less than that of the parts molded with

the steel insert. As the Cooling Time increased the amount

of warpage the steel inserts produced in their

corresponding parts decreased because the longer cooling

time relieved stresses while holding the part to the core

making it more dimensionally stable. The aluminum

inserts molded parts warpage was relatively constant as the

cooling time increased. The increased cooling rate of the

aluminum removed heat more efficiently when compared

to the steel locking the polymer chains in their orientation

at a lower cooling time making them warp less once

ejected from the core.

In the ABS molded with the aluminum insert








in the Y-Direction less than that of the parts molded with












In (Figures 11,12,13) the temperature of the

cavity and core insert, as well as the parts molded with the

aluminum insert are shown to be 10-15°C less than that of

the steel cavity and core insert, and its produced parts in

(Figures 14,15,16) at a five second cooling time when

molded with PE. In (Figures 17,18,19) the temperature of

the cavity and core insert, as well as the parts molded with

the aluminum insert are shown to be 10-15°C less than

that of the steel cavity and core insert, and its produced

parts in (Figures 20,21,22) at a 20 second cooling time

when molded with PE.

In the PE molded with the aluminum insert











0

1

2

3

10 15 20 25 30 45 60

Warpage(mm.)

Cooling Time (sec.)

PP (Y-Direction)










In the PE molded with the aluminum insert








in the Y-Direction less than that of the parts molded with
















(Figures 36,37,38) at a five second cooling time when

molded with PC.





(Figures 42,43,44) at a 20 second cooling time when

molded with PC.

In the PC molded with the aluminum insert




















In (Figure 50) the PC molded with the aluminum

insert warped more than the parts molded with steel insert.

The overall average warpage of the Steel inserts molded

parts was 0.4mm in the Y-Direction less than that of the

parts molded with the Aluminum insert. While molded in

stresses cause more warpage in PC. The increased

temperature of the cooling water increased the temperature

of the steel therefore relieving more of the molded in

stresses. This created less warpage of the parts molded

with the steel insert when compared to the aluminum

insert. The aluminum inserts molded parts warpage was

still held relatively constant as the cooling time increased.

The increased cooling rate of the aluminum removed heat

more efficiently when compared to the steel locking the

polymer chains in their orientation at a lower cooling time

making them warp less once ejected from the core.

In (Figures 6,7) the temperature of the cavity and

core insert are shown to be 10-15°C less than that of the

steel cavity and core insert in (Figures 9,10) at a 20 second

cooling time when molded with PP.

In (Figures 1,2) the temperature of the cavity and

core insert are shown to be 10-15°C less than that of the

steel cavity and core insert in (Figures 4,5) at a five second

cooling time when molded with PP.

In the PP parts molded with the aluminum insert

warped more than the parts molded with steel insert by an

average of 0.4mm in the X-Direction. This difference was

a direct cause of the time in between part production and

the measurements taken. The PP steel insert parts were

measured four months after molding. The aluminum insert

parts were measured two days after molding. The four

month time period the steel insert molded parts had

relieved molded-in stresses causing the warpage to

decrease when compared to the aluminum insert parts that

had only two days to relieve molded-in stresses which

greatly influence their warpage.

In the PP parts molded with the aluminum insert

warped less than the parts molded with steel insert by an

average of 2.0mm in the Y-Direction. Although the parts

were still measured four months after being molded and

the difference was a direct cause of the time in between

part production and the measurements taken. The

aluminum insert parts were measured two days after

molding. The four month time period the steel insert

molded parts had relieved molded-in stresses causing the

warpage to decrease when compared to the aluminum

insert parts that had only two days to relieve molded-in

stresses which greatly influence their warpage. The trend

in the Y-Direction is a direct correlation of the warpage in

the X-Direction was less than the warpage in the Y-

Direction due to less material being present; the modulus

can not resist the warpage.

There were many possible reasons that the study

performed could have varied and the variables that were

expected to have a major effect did not. The reflections in

the thermal images were very noticeable in the steel

inserts. This caused it to be difficult to measure the exact

temperature of the steel. An average temperature was taken

to try to eliminate this variable. Time between measuring

and molding was another factor that skewed the results of

the study. This cause one of the materials to show

improper results. This is the only factor that could have

skewed the results due the results shown in the other

materials. The PP was the only material that there was a

difference in the time after molding and before measuring.

The storage of parts could have caused the warpage to

increase in all of the parts. Since there was not a

standardized process for the storage of the parts, some

parts at the bottom of the bag could have had more force

applied to them in storage. This would cause a false

warpage in the parts. Reproducing a standardized process

in two different machines is difficult to do. Running parts

in both the Husky and Arburg could have caused the

injection molding process to be off. Although a robust

process was found, differences in injection, packing and

holding pressure would have huge effects on the warpage

of a part.

Conclusion

The industry there is a high demand to cut costs in

production and increase a company’s bottom line and still

continue to make quality parts. The study concluded that

this could be done in industry by using aluminum inserts

for injection molding.

In the warpage study, the parts made in the

aluminum insert warped between 0.2 to 2 mm. less than

that of the parts made in the steel. This is due to the fact

that the aluminum is more thermally conductive than that

of the steel. This allows more heat to be removed from the

part and then passed into the water lines and removed from

the mold. As thinner parts are cooled faster it will decrease

the amount of warpage that occurs. This is due to the fact

that polymer orientation is frozen into place and not

allowed to relax.

The decrease in warpage is made possible because

of the higher thermally conductivity of the aluminum. This

is made apparent in the thermal images taken throughout

the molding. The aluminum inserts have between a 5 to 15

°C decrease in temperature when compared to steel. This

would not only decrease warpage in some parts but cause

for a faster cooling time. It takes the steel inserts 15

seconds longer to reach the same water temperature in that

of the aluminum at the same cooling water temperature.

This would decrease the overall cycle time of any process

causing production time to become shorter.

Future Work

For the future work of this study there are a

couple of things that would be beneficial to do. The first

would be to measure the tooling wear in the aluminum

insert versus that of the wear in the steel insert in a

production type run. This would allow a further

investigation into how beneficial aluminum could be to the

industry. This would give a more accurate reading and

show where hot spots on the mold are. Also have a

standardized process would greatly improve the study. This

would eliminate many outside variables narrowing the

study.

References

[1] Nerone, Jim and Iyer, Ramani, “Exploration of the Use

of Advanced Aluminum Alloys for improved Productivity

in Plastic Injection Molding,” Journal of Injection Molding

Technology, (Sept. 2000). [Online]. Available: 4spe.org.

[Accessed Nov. 9, 2010].

[2] Shoemaker, Jay and Hayden, Engelmann, Miller,

“Designing the Cooling System: What’s the relationship

between Mold material Selection, Water Line Spacing and

Mold Surface Temperature Variation,” ANTEC papers,

(2004). [Online]. Available: 4spe.org. [Accessed Nov. 9,

2010].

[3] Paradis, Robert, “A Comparison of the Conventional

Machined Aluminum and Rapid Epoxy Shell Prototype

Mold Building Processes,” Journal of injection Molding

Technology, (1998). [Online]. Available: 4spe.org.

[Accessed Nov. 9, 2010].

[4] Beaumont, John, Runner and Gating Design Handbook,

Edition 2. Cincinnati: Hanser Gardner Publications, Inc.,

pages 33-34, (2007).

[5] Beaumont, John and Nagel, Sherman, Successful

Injection Molding, Cincinnati: Hanser Gardner

Publications, Inc., Pages 64-65,187, (2002).

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