This document discusses plastic injection molding. It begins with an abstract that develops a steady state model to describe fluid behavior during the filling stage of injection molding. It then discusses factors that affect part quality and different approaches that have been used to determine optimal process parameters, including mathematical models, Taguchi methods, neural networks, and more. The rest of the document provides details on an experiment conducted to analyze how independent variables like temperature, pressure, and flow rate affect the dependent variable of part weight. It summarizes the injection molding process and concludes that pressure and flow rate had the biggest impact on part weight.

1. 1
Plastic
Injection
Molding
Abstract:
This paper is concerned with the injection
moulding process, in which hot molten
plastic is injected under high pressure into a
thin cold mould. Assuming that the velocity
and temperature profiles across the mould
maintain their shape, a simple steady state
model to describe the behaviour of a
Newtonian fluid during the filling stage is
developed. Various phenomena of the
process are examined, including the
formation of a layer of solid plastic along
the walls of the mould, and the relationship
between the flux of liquid plastic through
the mould and the average pressure gradient
along the mould. In any given situation, it is
shown that there is a range of pressures and
injection temperatures which will give
satisfactory results.
Injection molding has been a challenging
process for many manufacturers and
researchers to produce products meeting
requirements at the lowest cost. Faced with
global competition in injection molding
industry, using the trialand- error approach
to determine the process parameters for
injection molding is no longer good enough.
Factors thataffect the quality of a molded
part can be classified into four categories:
part design, mold design, machine
performance and processing conditions. The
part and mold design are assumed as
established and fixed. During production,
quality characteristics may deviate due to
drifting or shifting of processing conditions
caused by machine wear, environmental
change or operator fatigue. Determining
optimal process parameter settings critically
influences productivity, quality, and cost of
production inthe plastic injection molding
(PIM) industry. Previously, production
engineers used either trial-and-error method
or Taguchi’s parameter design method to
determine optimal process parameter
settings for PIM. However, these methods
are unsuitable in present PIM because of the
increasing complexity of product design and
the requirementof multi-response quality
characteristics. This article aims to review
the recent research in designing and
determining process parameters of injection
molding. A number of research works based
on various approaches have been performed
in the domain of theparameter setting for
injection molding. These approaches,
including mathematical models, Taguchi

2. 2
method, Artificial Neural Networks
(ANN),Fuzzy logic, Case Based Reasoning
(CBR), Genetic Algorithms (GA), Finite
Element Method(FEM),Non Linear
Modeling, Response Surface Methodology,
Linear Regression Analysis ,Grey Rational
Analysis and Principle Component Analysis
(PCA) are described in this article. The
strength and the weakness of individual
approaches are discussed. It is then followed
by conclusions and discussions of the
potential research in determining process
parameters for injection molding.
Introduction:
This project takes a look at a half factorial
experiment on plastic injection molding and
how independent variables affect the
dependent variables. These independent
variables include Barrel Temperature,
Nozzle Temperature, Dwell Time, Injection
Pressure, and Flow Rate. This independent
variable will be tested to see what affects
they have on the final part weight
(dependent variable). The range of the half
factorial and 3 replication will help give a
broad range of data to further understand
what affects have the most impact on the
final outcome.
Theory:
The first plastic injection molding machine
was introduced in 1872 by John Wesley
Hyatt and his brother Isaiah. When World
War II hit in the 1940's the industry boomed
and mass production plastic injection came
about. Today's industry supplies a wide
variety of injection plastics ranging from
bottle caps to automotive dash boards and
hair combs. Plastic injection can be very
cost efficient to run with high production
rates, high tolerance repeatability, low scrap
and little finishing needed. Most injected
polymers are either thermoplastics,
thermosets or some elastomers. They range
in a wide variety of alloys and blends from
epoxy, phenolic, nylon, polyethylene, and
polystyrene.
The plastic injection machine consists of a
heating and injecting unit to make the plastic
injection. A heated barrel with a screw type
feeder or ram feeds the material into the
machine to be heated before injection. By
means of pressure and the ram the material
is fed into the heater to melt the plastic
pellets. With more pressure and force of the
ram the plastic flows into the nozzle as a
liquid and into the mold where it fills the
mold and cools until it is hardened. The
mold is place near the nozzle of the plastic
injection machine and clamped into place
with a large force to keep the mold firmly in
place during injection. This helps to reduce
flash from the mold. After cooling the part
can be ejected from the mold and the sprue
can be moved as well.
Many factors play into the final outcome of
the injected plastic part. Temperature of the
barrel and nozzle play a vital role in how
viscous the plastic is when it is being
injected. Pressure and flow rate aid in the
injection rate and flow, too high and jetting
can occur from turbulence in the flow. Flow
marks can also occur is the speed is to slow
for injecting. Mold design is critical to make
sure that the mold fills with material and that
it can be ejected from the mold. Draft angles
and fillets or chamfers can help reduce voids

3. 3
in molds and help with ejection from the
mold.
Experimental Procedure:
Variables: By varying the independent
variables stated down below will conclude
the interactions between them and show if
there is significant cause of that variable.
Also interactions of combinations of
variables will be taken into account as well.
Independent Variables: Barrel Temperature,
Nozzle temperature, Dwell Time, Injection
Pressure, Flow Rate
Dependent Variable: Part Weight
Equipment Used:
Safety Goggles
Plastic Injection Machine
Air Compressor
Injections Die Molds
Polyethylene
Gloves
Cutting Snips
Weight Scale
Procedure:
Preliminary:
Turn on the plastic injection machine
and let it warm up to proper
operating temperature.
Put clean Die Mold into alignment
bolts.
make sure the table clamp holds the
mold securely. Clamp should click
into place insuring proper mold
clamping. (between 7 and 10 Tons)
if necessary use allen wrench to
adjust clamp pressure.
Check to following:
o Barrel Temperature
o Nozzle Temperature
o Tooling Temperature
o Clamp Pressure
o Injection Pressure
o Flow Rate
Injection pressure control is
controlled by a T screw at air line.
Flow rate is controlled in the back by
turning the adjustment knob.
Double check all settings before
continuing.
Injection Procedure:
Place Die Mold into alignment bolts.
Clear nozzle drool with aluminum
scraper.
Lower table guard.
Push Clamp Valve to raise bottom
platen (check to hear click of the
clamp)
Use aluminum scrapper to cylinder
hopper.
Double check settings.
Push injection control valve to inject
plastic.
Wait specified time by experiment.
Pull the injection control valve to
retract ram. (check hopper to make
sure ram is fully retracted)
Pull clamp valve out to lower bottom
platen.
Raise table guard.
Remove Die Mold.
Open mold, grasp plastic part and
remove part with twist method.

4. 4
Remove sprue with push pull method
from Die Mold.
Check to make sure Die Mold is
clean or excess plastic and debris.
Snip part of excess plastic
consistently.
Weigh part.
Shut Down Instruction
Check the Clamp Valve is the out
position.
Lower table guard.
Turn off main power switch on side
of temperature control.
Remove both 110V power plugs.
Turn off air supply.
Bleed air lines out.
Discussion:
Plastic injection molding consists of two
main components: injecting and clamping.
Starting with the clamping end of the
process, a mold must be made for the plastic
injector to push hot liquid plastic into. The
mold is usually made of a machine-able
metal, usually aluminum or steel. The mold
consists of a closed cavity for the material to
flow into. A sprue is a hollow tube leading
up from the mold for the material to flow
into and into the mold. A well is located at
the bottom of the sprue to build up material
and push it into the mold. Another important
part of the mold cavity is the vents; these
help push ambient air in the mold so the
mold can be completely filled. The injection
part of the process includes a hopper for raw
plastic material to be fed into. This is
usually fed into the barrel by a screw
pushing the material towards the nozzle. The
barrel heats up the material till it is soft and
turned into a liquid. The nozzle pushes the
material through down into the mold by

5. 5
pressure. The barrel and nozzle temperatures
can be controlled separately. These
temperatures control the viscosity of the
material. The pressure of the injector
controls the rate of flow of the injection into
the die cavity.
Polyethylene is a synthetic fiber used
in making various products like beverage
and containers. It is a good barrier against
gas, moisture, alcohol, and solvents. The
chemical composition for polyethylene is
(C10H8O4) and is a thermoplastic. Has a
crystalline density of 1.455 g/cm3
, a tensile
strength of 55-75 MPa, a Young’s Modulus
(E) of 2800-3100 MPa, and a melting
temperature of 260o
C. It is strong and
impact resistant. It has a semi-crystalline
structure and is transparent or opaque
depending on the structure and particle size.
Polyethylene is commonly referred to as
polyester for packaging materials. Before
the material can be processed it must be
dried to bring down its moisture content as
far as possible. Polyethylene can be formed
through plastic molding injection or blow
molding. After a product has reached its end
of life cycle the polyethylene can be
recycled back into the system and used
again once it has been process and chipped
back up to be used again in molding.
Polypropylene (PP) is a
thermoplastic polymer with whose mer
chemical formula is C3H6. PP’s density
ranges from 0.855 g/cm3
to 0.946 g/cm3
. Its
melting point ranges from 130 to 171
degrees Celsius, however in most
application it is assumed to be 160 degrees
Celsius. PP is commonly used to produce
both fiber and molding. Therefore, the two
main manufacturing processes are extrusion,
and injection molding, respectively for fiber
and plastic molds. PP is commonly used for
Tupperware due to its higher melting point,
which allows it to heat foods without
melting. It is also highly resistive to fatigue
and stress, allowing it to be used in high
wear application. Its main weakness is
degradation due to UV radiation.

6. 6
Conclusion
In conclusion this project was useful in
exploring and understanding how different
control factors have different effects on a
desired characteristic for a part. Through the
use of design expert it was shown how some
control variables have a strong effect on a
specified characteristic, while others have
little to no effect. Through design expert it
was found that the variables affecting the
final weight of the plastic mold injected part
the most, were pressure and flow weight.
Each of these factors had a larger impact
than the nozzle temperature, barrel
temperature and dwell time combined. Even
though this experiment was a half factorial,
a lot of useful data was collected about the
different factors and how they interact with
each other.
Finally we conclude that plastic
injection molding is very helpful in making
all necessary basic goods like tumblers,
body of the brush etc which attract people
with snazzy colours as well as shining and
their smoothness.
REFERENCES
1.Mathivanan D. ; Parthasarathy, N. S.
(2009) .Prediction of sink depths using
nonlinear modeling of injection molding
variables,International Journal of Advanced
Manufacturing Technology, vol. 43 pp.654–
663.
2.Protyusha Das Neogi (2009) , Comparing
the Predictive Ability of T-Method and
Linear Regression Method , Proceedings of
the IndustrialEngineering Research
Conference.
3. Raviwongse ,Rawin; Allada., Venkat;
(1997) Artificial Neural Network Based
Model for Computation of Injection Mould
ComplexityInternational Journal of
Advanced Manufacturing Technology , 13,
pp. 577-586
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