Exp Extrusion Injection Molding Testing

8/6/2019 Exp Extrusion Injection Molding Testing

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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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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


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


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


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


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


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


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.


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.

Exp Extrusion Injection Molding Testing

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