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INTRODUCTION
Extrusion Machine
Extrusion molding is a manufacturing process to make pipes, hoses, fibers and
curtain tracks. The machine used to extrude material out and is very similar to an injectionmolding machine.
Figure 1: Extrusion machine
Thermoplastic will be put inside the hopper and drop through feed throat into the
screw section. A motor turns a screw which feeds pellet of material through a heater. The
pellets melt into a liquid which is forced through a die, forming a long tube like shape. The
shape of the die determines the shape of the tube. The extrusion is then cooled with water or
some other cooling element and will form a solid shape. Then will be cut into specific
dimensions and be stored before being s hipped or be used.
Most thermoplastic can be used for extrusion molding, the most preferably materials
are with high strength in the molten state because they are easy to form and better maintain
in the intended shape. Other factors of determine the mater ial selection are heat and UV
stability, flame and chemical resistance and strength and flexibility. Common plastic used in
extrusion molding are:
y Polycarbonate (PC) y Polyethylene (PE)
y Polypropylene (PP) y Polyester
y Polystyrene (PS) y Polyvinylchloride (PVC)
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Injection Molding Machine
Injection molding is process for producing parts from thermoplastic and thermoset
materials. Injection molding is used to produce many things such as wire spools, packaging,
bottle caps, automotive dashboards, pocket combs, small table and many more. It is a very
efficient machine in terms of producing high quantity in short time and it low labor cost may
give high return to the company.
Figure 2: Injection molding machine
Polymer material is fed into the hopper and goes into the barrels and screw will rotate
and move the material into the heating sections until it reach the melting temperature. Screw
will then used force to inject the melted material into the mold and being cool to allow the
material to solidify and be cool to be touch. The mold plates are held together by hydraulic or
mechanical force. The clamping force is defined as the injection pressure multiplied by the
total cavity projected area. Once it solidifies, mold will be open and ejector will push the
material out form the mold.
Universal Testing Machine
Universal tester is used to test the tensile stress and compressive strength of
materials. It named UTS because it can perform many standard tensile and compression
tests on materials, components and structures . To use UTM, user have to refer to a test
method which normally published by a standard organization. Normally, for testing purpose
material will be shape into dog -bone shape. Then it will be attached to the grips and
extensometer will record the change in the gauge length. The machine itself will record the
displacement between its cross heads on which the specimens is held. This method will also
record other extending or elastic components of the testing machine and its drive systems
including any slipp ing of the specimen in the grips.
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Figure 3: Universal testing machine
When the load is increase, software will record the load and the extension or
compression of the specimen and present it in graph format. The machine ranges from very
small table top systems to one with over 53 MN capacities.
PROBLEM STATEMENT
Extrusion and injection molding are the manufacturing process for producing parts from
both thermoplastic and thermosetting plastic materials. The machines which are used in
these processes are commonly used in the industries nowadays. The properties of the
material produced can be tested by using the universal testing machine to test the tensile
stress of the material . However, the results will be different depending on the type of plastic
used.
OBJECTIVES
1. To understand the manufacturing process by using the extrusion and injection molding
machine.
2. To understand the principles of tensile testing using universal testing machine.
3. To determine the stress -strain relationships for the given material.
4. To obtain approximate values from stress -strain curve.
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. Once the mold is sufficiently cooled, the mold opened and the part is ejected.
Ex eriment 3 Universal Testing Machine
1. Length and thickness of the specimen is measured and recorded in the software.
2. The specimen is now placed in the UTM.
3. Extensometer is adjusted so that the laser beam is located along the specimen. Stand
clear of the UTM as the extensometer is ver y sensitive towards any vibrations or
movements.
4. Once the machine is initialized, the test is beginning. The hydraulic ramp slowly pulled the
sample. Load and corresponding displacement is recorded.
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5. Once the sample reached its maximum load, necking will be come apparent in the
sample.
. After the sample is fractured, test is stopped. The specimen is then removed from theUTM.
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RESULT
Ex eriment Extrusion Machine
Two materials of polymer, polypropylene (PP 1 4oC) and low density polyethylene
(LDPE 120
o
C) in the pellets form are mixed together in the hopper, then been melted. Themolten polymers then been pressed through a shaped die, that give the shape of a long -
continuous wire cable. It is cooled in water tank and become solidified, before been cut into
pellets form to be used in other plastic -forming processes, such as injection molding.
These are the temperature at different section in the machine:
Set (oC) Actual (
oC)
Barrel Z.1 180 1 0
Barrel Z.2 180 180
Barrel Z.3 170 170
Barrel Z.4 170 170
Barrel Z.5 170 170
Barrel Z. 170 170
Barrel Z.7 170 170
Flange 1 0 1 0
Die 1 0 1 0
Figure 4: Mixture of PP and LDPE before put
into the machine
Figure 5: The product after been extruded by
the machine
Figure : Materials after been cooled and solidified, then cut -off into pellets form
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Ex eriment Injection Molding Machine
The pellets polymers that been produced from previous experiment are been used.
They are fed to the machine through the hopper and heated to the appropriate melting
temperature. The melted solution is injected into the mold through nozzle, sprue, runner and
gate to get the shape. For this experiment, the machine is produced the dogbone shape, as
will be used for next experiment.
Figure 7: Injection molding machine
Figure 8: The materials that been produced (Dogbone shape)
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Ex eriment 3 Universal Testing Machine
The dogbone that been produced by injection molding machine used for this tensile
test. The holder will start move upward and pull the dogbone slowly. Then, the necking will
be happen until it ruptures.
Figure 9: Universal testing machine
Figure 10: The process for tensile test (Second picture - necking, and last picture - rupture)
The experiment had been done for three times, with three different dogbones. The
specification of the dogbones:
auge length: 50 mm Area: 40 mm2
Width: 10 mm Speed: 50 mm/min
Thickness: 4 mm
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Test 1
Stiffness: 139 7.038 N/m
Youngs Modulus: 174.583797 MPa
Load at maximum: 770.1981417 N
Extension at maximum: 15.72109073 mm
Tensile strength: 19.25495354 MPa
Percentage strain at maximum: 31.44218145%
Work to maximum: 9.300238884 J
Load at yield: 770.1981417 N
Extension at yield: 15.72109073 mm
Stress at yield: 19.25495354 MPa
Percentage strain at yield: 31.44218145%
Work to yield: 9.300238884 J
Load at offset yield: 371.0 9 032 N
Extension at offset yield: 2.75 815857 mm
Stress at offset yield: 9.27 740079 MPa
Percentage strain at offset yield: 5.513 31715%
Work to offset yield: 0.549705217 J
Load
N
00
100
200
300
400
500
00
700
800
Extension
efore
om
ensation
mm
0 10 20 30 40 50
0 70 80 90 100
Yield and Maximum
ffset Yield
reatest Slo e
Tensile Setu
50.0 mm
10.0 mm
4.00 mm
ld
e
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Test 2
Stiffness: 145505.9402 N/m
Youngs Modulus: 181.8824253 MPa
Load at maximum: 818. 234877 N
Extension at maximum: 14.04033037 mm
Tensile strength: 20.4 558719 MPa
Percentage strain at maximum: 28.080 074%
Work to maximum: 8.59485 872 J
Load at yield: 818. 234877 N
Extension at yield: 14.04033037 mm
Stress at yield: 20.4 558719 MPa
Percentage strain at yield: 28.080 074%
Work to yield: 8.59485 872 J
Load at offset yield: 408.8 05798 N
Extension at offset yield: 2.909923 33 mm
Stress at offset yield: 10.22151449 MPa
Percentage strain at offset yield: 5.8198472 7 %
Work to offset yield: 0. 9 07 34 J
Load
N
00
100
200
300
400
500
00
700
800
900
Extension
efore
om
ensation
mm
0 10 20 30 40 50
0 70 80 90 100
Lo er Yield
Yield and Maximum
ffset Yield
!
reatest Slo"
e
Tensile Setu#
50.0 mm
10.0 mm
4.00 mm
# #
$
ld#
e
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Test 3
Stiffness: 158758.2878 N/m
Youngs Modulus: 1 98.4478597 MPa
Load at maximum: 893.78993 1 N
Extension at maximum: 13.81733984 mm
Tensile strength: 22.3447484 MPa
Percentage strain at maximum: 2 7. 34 79 9%
Work to maximum: 9.18 24271 J
Load at yield: 893.78993 1 N
Extension at yield: 13.81733984 mm
Stress at yield: 22.3447484 MPa
Percentage strain at yield: 2 7. 34 79 9%
Work to yield: 9.18 24271 J
Load at offset yield: 44 .4897007 N
Extension at offset yield: 2.91238 738 mm
Stress at offset yield: 11.1 224252 MPa
Percentage strain at offset yield: 5.82477347 %
Work to offset yield: 0.752281307 J
Load%
N&
00
100
200
300
400
500
(
00
700
800
900
Extension)
efore0
om1
ensation%
mm&
0 10 20 30 40 50(
0 70 80 90
Yield and Maximum
2
ffset Yield
3
reatest Slo4
e
Tensile Setu5
50.0 mm
10.0 mm
4.00 mm
5 5 6 ld 5 e
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DISCUSSION
Ex eriment Extrusion Machine
For experiment 1 which is the extrusion process using the extrusion machine, the
parameters that are to be focused on are the extrusion temperature, friction and speed. Thisis to prevent the surface of an extrusion from splitting which will eventually lea d to surface
cracking. At lower temperatures the extruded product could temporarily stick to the die which
will also lead to surface cracking. Due to high friction or cooling of the outer regions of the
billet, a flow pattern may occur. This flow pattern draws the surface oxides and impurities to
the centre of the product which is called pipe. In this process, internal cracking may also
start to occur when the centre of the extrusion develops cracks or voids. These cracks are
attributed to a state of hydro static tensile stress at the centerline in the deformation zone in
the die. This is somewhat similar to the necked region or necking in a tensile stress
specimen. The quality of the die production and also maintenance of the die is important in
preventing surface lines of the extruded profile. This is because some residues of the
material extruded can stick to the die surface and produce the embossed lines.
Ex eriment Injection Molding Machine
For experiment 2 which is the injection molding process usi ng the pellets polymer
produced from the extrusion machine, handling cavity pressure level is important to switch
over from the injection phase to the holding phase. This is to ensure constant filling rate in
the cavity. A stable production window is essen tial and they can be maintained by focusing
on:
1. Optimizing the injection speed by ensuring an optimum pressure drop between the
pressure measured in the nozzle and the pressure measured in the cavity. Melted
material with a higher viscosity has more pressu re loss from nozzle to cavity than material
with a lower viscosity. Shear rate changes as injection speed is varied. Higher speed
gives a higher shear rate and lower viscosity. The viscosity and shear rate will decrease
as the mold and melting temperature are increased.
2. Optimizing the metering phase by varying screws turns per minute and back pressure.
The variation of time needed to reload the screw indicates the stability of this phase.
3. Cooling time which starts once the injection phase is finished. The c ooling time is longer if
the melted plastics are hotter and of the parts produced are thicker.
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4. ate seal which prevent sink marks and geometrical faults. The height and duration of
applied holding pressure based on cavity pressure curves should be optimize d. The
holding pressure should be applied longer for thicker parts.
Some of the defects of injection moldings could be blister due to lack of cooling of too
hot tool or material or a faulty heater, burn marks as the tool lacks venting and injection
speed is too high and jetting which may be caused by poor tool design, gate position or
runner or the injection speed is set too high. The possible solutions may be decreasing the
peak cavity pressure and fill rate and use profile injection for the burn marks an d for the
jetting, the cavity pressure an melting or mold temperature should be increased.
Ex eriment 3 Universal Testing Machine
For the last succession which is experiment 3, a tensile test was done on the product
of the injection molding machine which is in the form of a dog bone using the universal
testing machine (UTM). The typical points of interest when testing a material include,
ultimate tensile strength (UTS) or peak stress, offset yield strength (OYS) which represent a
point just beyond the ons et of permanent deformation and the rupture or fracture point where
the specimen separates into pieces. During the handling of UTM, there are three main
parameters to focused on which are force capacity, speed, as well as precision and
accuracy. Force capacity means that the machine must be able to generate enough force to
fracture the specimen. The machine should also be able to accurately and precisely
measure the gage length and forces applied. For example, a large machine that is designed
to measure long elongations may not work with a brittle material that experiences short
elongations prior to fracturing. The alignment of the dog bone is important because if it is
misaligned, the machine will exert a bending force on the specimen. This situation can b e
reduced by using spherical seats or U-joints between the grips and the test machines. A
misalignment is indicated when running the test if he initial portion of the stress -strain curve
is curved and not linear.
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CONCLUSION
From the three experiments that had been done, we learned that in prod ucing one
product, it may take three machines. To mix up two or more polymer materials, extrusion
machine is used till we get the pellets. Then, to get the shape as required, injection molding
machine is used and we get the dogbone shape. Finally we conduct a test by using universal
testing machine to measure its stiffness, tensile strength and the maximum load before the
dogbone starts the plastic deformation. The experiments will give us the amount of
composition of polymer material need ed to get the product with required strength.