penn state capstone project investigating part warpage in qc 10 vs steel
DESCRIPTION
Penn State Senior Capstone Project -Investigation into Part Warpage Differences between Aluminum and Steel ToolingTRANSCRIPT
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
second cooling time shows the temperature to be between
40-50 °C.
Figure 6 - PP Aluminum Cavity at 20 Second Cooling
Time
The above Figure 6 is of the Aluminum Cavity at
a 20 second cooling time shows the temperature to be
between 25-35 °C.
Figure 7 - PP Aluminum Core at 20 Second Cooling time
The above Figure 7 is of the Aluminum Core at a
20 second cooling time shows the temperature to be
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
The above Figure 9 is of the Steel Cavity at a 20
second cooling time shows the temperature to be between
35-45 °C.
Figure 10 - PP Steel Core at 20 Second Cooling Time
The above Figure 10 is of the Steel Core at a 20
second cooling time shows the temperature to be between
35-45 °C.
Figure 11 - PE Aluminum Cavity at Five Second Cooling
Time
The above Figure 11 is of the Aluminum Cavity at
a 5 second cooling time shows the temperature to be
between 20-30 °C.
Figure 12 - PE Aluminum Core at Five Second Cooling
Time
The above Figure 12 is of the Aluminum Core at a
5 second cooling time shows the temperature to be
between 20-35 °C.
Figure 13 - PE Aluminum Insert Cavity Side of Part at
Five Second Cooling Time
The above Figure 13 is of the Aluminum insert
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
The above Figure 14 is of the Steel Cavity at a 5
second cooling time shows the temperature to be between
40-50 °C.
Figure 15 - PE Steel Core at Five Second Cooling Time
The above Figure 15 is of the Steel Core at a 5
second cooling time shows the temperature to be between
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
temperature to be between 55-65 °C.
Figure 17 - PE Aluminum Cavity at 20 Second Cooling
Time
The above Figure 17 is of the Aluminum Cavity at
a 20 second cooling time shows the temperature to be
between 20-30 °C.
Figure 18 - PE Aluminum Core at 20 Second Cooling
Time
The above Figure 18 is of the Aluminum Core at a
20 second cooling time shows the temperature to be
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
cavity side of the part at a 20 second cooling time shows
the temperature to be between 30-40 °C.
Figure 20 - PE Steel Cavity at 20 Second Cooling Time
The above Figure20 is of the Steel Cavity at a 20
second cooling time shows the temperature to be between
35-45 °C.
Figure 21 - PE Steel Core at 20 Second Cooling Time
The above Figure 21 is of the Steel Cavity at a 20
second cooling time shows the temperature to be between
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
temperature to be between 45-55 °C.
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
The above Figure 24 is of the Aluminum Core at a
5 second cooling time shows the temperature to be
between 25-35 °C.
Figure 25- ABS Aluminum Cavity Side of Part at Five
Second Cooling Time
The above Figure 25 is of the Aluminum insert
cavity side of the part at a 5 second cooling time shows the
temperature to be between 50-65 °C.
Figure 26 - ABS Steel Cavity at Five Second Cooling
Time
The above Figure 26 is of the Steel Cavity at a 5
second cooling time shows the temperature to be between
40-55 °C.
Figure 27 - ABS Steel Core at Five Second Cooling Time
The above Figure27 is of the Steel Core at a 5
second cooling time shows the temperature to be between
40-55 °C.
Figure 28 - ABS Aluminum Cavity at 20 Second Cooling
Time
The above Figure 28 is of the Aluminum Cavity
at a 20 second cooling time shows the temperature to be
between 25-35 °C.
Figure 29 - ABS Aluminum Core at 20 Second Cooling
Time
The above Figure 29 is of the Aluminum Core at a
20 second cooling time shows the temperature to be
between 25-35 °C.
Figure 30 - ABS Aluminum Cavity Side of Part at 20
Second Cooling Time
The above Figure 30 is of the Aluminum insert
cavity side of the part at a 20 second cooling time shows
the temperature to be between 35-45 °C.
Figure 31 - ABS Steel Cavity at 20 Second Cooling Time
The above Figure 31 is of the Steel Cavity at a 20
second cooling time shows the temperature to be between
40-55 °C.
Figure 32 - ABS Steel Core at 20 Second Cooling Time
The above Figure 32 is of the Steel Core at a 20
second cooling time shows the temperature to be between
40-55 °C.
Figure 33 - PC Aluminum Cavity at Five Second Cooling
Time
The above Figure 33 is of the Aluminum Cavity
at a 5 second cooling time shows the temperature to be
between 25-35 °C.
Figure 34 - PC Aluminum Core at Five Second Cooling
Time
The above Figure 34 is of the Aluminum Core at a
5 second cooling time shows the temperature to be
between 25-35 °C.
Figure 35 - PC Aluminum Insert Cavity Side of Part at
Five Second Cooling Time
The above Figure 35 is of the Aluminum insert
cavity side of the part at a 5 second cooling time shows the
temperature to be between 50-65 °C.
Figure 36 - PC Steel Cavity at Five Second Cooling Time
The above Figure 36 of the Steel Cavity at a 5
second cooling time shows the temperature to be between
40-55 °C.
Figure 37 - PC Steel Core at Five Second Cooling Time
The above Figure 37 is of the Steel Core at a 5
second cooling time shows the temperature to be between
45-55 °C.
Figure 38 - PC Steel Insert Cavity Side of Part at Five
Second Cooling Time
The above Figure 38 is of the Steel insert cavity
side of the part at a 5 second cooling time shows the
temperature to be between 70-80°C.
Figure 39 - PC Aluminum Cavity at 20 Second Cooling
Time
The above Figure 39 is of the Aluminum Cavity
at a 20 second cooling time shows the temperature to be
between 25-35 °C.
Figure 40 - PC Aluminum Core at 20 Second Cooling
Time
The above Figure 40 is of the Aluminum Core at a
20 second cooling time shows the temperature to be
between 25-35 °C.
Figure 41 - PC Aluminum Insert Cavity Side of Part at 20
Second Cooling Time
The above Figure 41 is of the Aluminum insert
cavity side of the part at a 20 second cooling time shows
the temperature to be between 40-50°C.
Figure 42 - PC Steel Cavity at 20 Second Cooling Time
The above Figure 42 is of the Steel Cavity at a 20
second cooling time shows the temperature to be between
45-55 °C.
Figure 43 - PC Steel Core at 20 Second Cooling Time
The above Figure 43 is of the Steel Core at a 20
second cooling time shows the temperature to be between
45-55 °C.
Figure 44 - PC Steel Insert Cavity Side of Part at 20
Second Cooling Time
The above Figure 44 is of the Steel insert cavity
side of the part at a 20 second cooling time shows the
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-
Direction vs. Cooling Time. The figure shows that the
warpage of the aluminum insert is less than that of the steel
insert in the Y-Direction. The warpage decreased 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 0.4 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-
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 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
The above figure illustrates the Warpage In the Y-
Direction vs. Cooling Time. The figure shows that the
warpage of the aluminum insert is less than that of the steel
insert in the Y-Direction. The warpage decreased 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 2.1 mm of warpage between the steel
and aluminum parts.
Figure 49 - PC 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 relatively
constant through out the cooling time study. There was an
average difference of 0.3 mm of warpage between the steel
and aluminum parts.
Figure 50 - PC Warpage In the Y-Direction Vs. Cooling
Time
The above figure illustrates the Warpage In the Y-
Direction vs. Cooling Time. The figure shows that the
warpage of the aluminum insert is less than that of the steel
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
The above figure illustrates the Warpage In the Y-
Direction vs. Cooling Time. The figure shows that the
warpage of the aluminum insert is less than that of the steel
insert in the Y-Direction. The warpage decreased as the
cooling time increased in regards to the steel insert. The
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
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 0.4mm
in the Y-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 (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
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 0.5mm
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
0
1
2
3
10 15 20 25 30 45 60
Warpage(mm.)
Cooling Time (sec.)
PP (Y-Direction)
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 PE 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 1.9mm
in the Y-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 (Figures 33,34,35) 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 36,37,38) at a five second cooling time when
molded with PC.
In (Figures 39,40,41) 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 42,43,44) at a 20 second cooling time when
molded with PC.
In the PC 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 0.5mm
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 (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).