Smart Manufacturing

(ME505)

Injection Molding

By
Dr Vishal Jagota
vishal.jagota@chitkara.edu.in
+91 8683038218
Injection Molding
• Injection molding is one of the most popular manufacturing processes used to mass-
produce plastic parts. Many industries use this method because of the various benefits it
offers such as accuracy and repeatability.

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Injection Molding

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Injection Molding

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Injection Molding

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Injection Molding

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Injection Molding

• Injection molding is a manufacturing process that allows for parts to be produced in

large volumes.

• It works by injecting molten materials into a mould / mold.

• It is typically used as a mass production process to manufacture thousands of

identical items.

• Injection molding materials include metals, glasses, and polymers.

• It is most commonly used with thermoplastic and thermosetting polymers.

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Injection Molding

• Injection molding is a forming process that produces parts by injecting their molten
form into molds.

• After cooling and hardening, this gives a final product that takes the shape of the
mold.

• Injection molding is used in the mass production of parts where product consistency is
a major concern.

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Injection Molding

Melting Stage

• The first step is to melt the plastic pellets;

• Then, place the pellets into the machine’s hopper;

• This goes to the barrel, where the rotating screw liquefies the plastic using heat and
friction.

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Injection Molding

Injecting Stage

• This is the most important step;

any mistake may affect the final
part’s quality. Here, inject the
molten plastic into a mold under
high pressure and at a uniform
speed.

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Injection Molding

Cooling Stage

• Once in the mold, the

plastic resin sets and cools.
Because plastics are
generally poor conductors
of heat, this cooling phase
may be time-consuming.

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Injection Molding

Ejection Stage

• After sufficient cooling, open

the mold and remove the
plastic part using the mold’s
built-in ejector pins. At this
stage, close the mold and
repeat the process to make
other identical parts if need be.

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Injection Molding

Post-treatment

• This final step involves

twisting or cutting any
physical defects and
applying various surface
finish options to make the
part glossier as needed.

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Injection Molding

Wall Thickness

• Design should meet/exceed the nominal wall thickness requirements to create an

appropriate balance of pressure and flow during manufacturing.

• Ensure even cooling of your part due to consistent wall thickness in the design.

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Injection Molding
Corners:

• Radii of any corners been set appropriately to

avoid shrink marks, warpage, shearing, and/or
breakage during manufacturing?

• Are all corners appropriately shaped to allow

sufficient material to flow in during the molding
process, and to maintain consistent wall
thickness?
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Injection Molding Materials

Polyethylene (PE)

• Polyethylene is the most common plastic used in manufacturing industries.

• Based on density, it comes in two forms (High-density polyethylene and low-density

polyethylene).

• High-density polyethylene is more suitable for injection molding because the heating
and cooling process does not alter its physical and chemical characteristics.

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Injection Molding Materials

Polypropylene (PP)

• This is the second most used plastic in injection molding applications known for its
lightweight and high melting point.

• Though easy to mold, polypropylene is highly flammable, and it is difficult to paint

the molded part.

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Injection Molding Materials

Nylon (Polyamide, PA)

• Nylon comes in different grades and can conveniently replace metals for vehicle parts.

• However, it may be tricky to mold nylons. This is because nylon shrinks fast, so the
mold may not be filled properly.

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Injection Molding Materials

Acrylonitrile Butadiene Styrene (ABS)

• Of all injection molding materials, ABS is the most versatile.

• Its low melting point makes it suitable for processing by injection molding.

• However, ABS molded parts degrade in contact with UV and sun rays, limiting
outdoor application.

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Injection Molding Materials

Polyoxymethylene (POM, Acetal)

• POM is a semi-crystalline polymer used to make large precision parts.

• Generally, this plastic has good moldability properties.

• Also, its excellent dimensional stability and high tensile strength of POM molded
products make it suitable for the automotive and electronics industry.

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Injection Molding Materials

Polystyrene (PS)

• Polystyrene is strong, rigid, and transparent that is resistant to degradation that comes
with sterilization.

• As a result, it is highly applicable in the dental and optical industries.

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Injection Molding Materials

Acrylic (PMMA)

• Acrylic is transparent and lightweight, so it is a great alternative to glass.

• This plastic has low mold shrinkage but can self-ignite at extreme temperatures.

• Because of its resistance to UV rays and moisture, one can use it for anything from
solar panels to spray paints.

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Injection Molding Materials

Thermoplastic Elastomer (TPE)

• TPE is a mixture of rubber and plastic. So, it exhibits properties of both.

• This plastic material is expensive compared to others.

• TPE can withstand extreme temperatures associated with injection molding and does
not require vulcanization. As a result, you can use TPE in medical supplies like masks
and breathing tubes.

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Design Considerations Injection Molding

• Having uniform wall thickness

prevents warping and other
injection molding defects.

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Design Considerations Injection Molding

Causes:

(1) Mold structure: pouring, cooling system and ejection system

(2) Product structure: plastic parts wall thickness changes, with curved or asymmetrical
geometry, ribs and BOSS column design is not reasonable

(3) Production process: the plastic parts are not fully cooled, and the injection and pressure
holding curves are unreasonable

(4) Plastic materials: plastic materials have, no added fillers, and the size of the shrinkage is.

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Design Considerations Injection Molding

Remedies:

(1) The mold temperature is unstable. Provide cooling/heating balanced mold

(2) Irregular section thickness Redesigned product shape and size according to resin
characteristics

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Design Considerations Injection Molding

• Draft angles lessen the possibility of flaws and make sure the part is ejected from the
mold with ease.

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Design Considerations Injection Molding

• Short Shot:

Material selection before production is a crucial process. the shrinkage rate and flow rate
define each material.

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Design Considerations Injection Molding

Causes:
(1) Die temperature, material temperature, or injection pressure
and speed are too low
(2) Uneven plasticization of raw materials
(3) Poor exhaust
(4) Insufficient liquidity of raw materials
(5) The part is too thin or the gate size is too small
(6) Polymer melt is prematurely cured due to unreasonable
structural design

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Design Considerations Injection Molding
Remedies:

• Material:
Use more fluid materials

• Mold design:
(1) Fill the thick wall before filling the thin wall to avoid the retention
phenomenon.
(2) Appropriately increase the number of gates and runner size to
reduce the process ratio and flow resistance
(3) The position and size of the exhaust port should be properly set to
avoid the phenomenon of poor exhaust.

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Design Considerations Injection Molding
• Overheating the plastic material can cause burn spots on the surface of the plastic part.
Caused by overhigh melt temperature; overcast screw speed; improper design of the
runner system.
• Add an exhaust system to a place where
the exhaust gas is easily generated
• Increase the size of the runner system
• Reduce the injection pressure and speed
• Reduce the barrel temperature
• Check if the heater and thermocouple are
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Types of Injection Molding Machines
Plunger Type Injection Molding Machine
• The plunger injection molding machine uses the plunger to push the plastic in the barrel
forward, make it pass through the diverter shuttle, and then inject it into the mold through the
nozzle.

• Due to its simple structure, convenient operation, and low technical requirements, this
plunger-type machine can meet the molding of general small parts or parts with fewer
precision requirements.

• It’s a simple method and used in small-scale industries for some small products, now it’s very
rare.
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Types of Injection Molding Machines
Plunger Type Injection Molding Machine

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Types of Injection Molding Machines
Screw Plunger Type Injection Molding

• In screw plunger type injection molding machine there are two chambers.

• One chamber is to plasticize the raw material and another chamber is used for
injecting the material inside the mold.

• Upper section consists of plasticizing chamber in which the hopper is attached the
material which is inside the hopper is transmitted in the plasticizing chamber and then the
plasticized material will be transmitted to the injection plunger area.

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Types of Injection Molding Machines
Screw Plunger Type Injection Molding

• Screw which is rotating and along with a screw, the barrel consists of some band
heaters along with screw, they both helps in plasticizing the raw material.

• The melted raw material move toward another chamber which is called the injection
chamber, in that injection chamber, there is a plunger which moves forward and the raw
material which is in melted form is being injected inside the mold.

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Types of Injection Molding Machines
Screw Plunger Type Injection Molding

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Types of Injection Molding Machines
Plunger-Plunger Type Injection Molding

• The function for the plunger-plunger type injection molding machine is the same, instead
of a screw which is in the plasticizing chamber, there is a plunger and heaters used for
plasticizing.

• The functions of both the plunger type injection molding machine and a screw plunger
type injection molding machine are quite similar, but the result and efficiency of a screw
plunger type machine are more efficient than plunger type injection molding.

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Types of Injection Molding Machines

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Types of Injection Molding Machines
Reciprocating Screw Injection Molding
• The heating elements are attached to the barrel, inside the barrel, there is a reciprocating screw,
that’s why the name of the machine is called reciprocating screw type injection molding.

• The reciprocating screw is divided into three zones, which are feed zone, transition zone, and
metering zone.

• In the feed zone, the material is transferred from the hopper to the barrel, transition zone also
known as compression zone, the material is being compressed, the third is the metering zone in
front of that screw there is an NRV which prevents backflow of material that it does not return
back inside the barrel at the time of injection.
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Types of Injection Molding Machines
Reciprocating Screw Injection Molding

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Types of Injection Molding Machines
• Manually operated Injection Molding Machine

• Semi Automatic operated Injection Molding

• Automatically operated Injection Molding

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Types of Injection Molding Machines
Manually operated Injection Molding Machine:
• In a manually operated injection molding machine, the operator is
responsible for many critical tasks in the injection molding process.

• The operator manually loads the mold with the raw material
(usually plastic pellets) and activates the machine.

• They must also monitor and control the temperature, pressure, and
timing throughout the molding cycle.

• Once the part is formed, the operator manually removes it from

the mold.
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Types of Injection Molding Machines

Semi-Automatic Operated Injection Molding Machine:

• Semi-automatic machines introduce some automation into the process while still
requiring operator intervention.

• The machine may automatically perform some functions, such as closing and
clamping the mold, injecting the material, and opening the mold once the part is ready.

• However, the operator often needs to load the raw material, remove finished parts, and
monitor the process for quality and consistency.

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Types of Injection Molding Machines

Automatically Operated Injection Molding Machine:

• In a fully automatic injection molding machine, the entire process is automated and
requires minimal human intervention.

• The machine loads the raw material, closes the mold, injects the material, cools the part,
and ejects it without direct operator involvement.

• These machines often have advanced control systems to ensure precise and consistent
results.

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Advantages of Injection Molding

Shapes and Geometries

• Injection molding gives the freedom to make custom parts. With this manufacturing
process, one can make parts with different shapes and designs.

Product Consistency

• In injection molding, it is possible to reuse the mold over and over before changing
them. So, the next part is identical to the previous one. This increases the overall
speed of production.

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Advantages of Injection Molding

Low Cost Per Part

• Although the setup investment is high, the cost to produce a single part is relatively
low. Also, this process eliminates the need for some surface finish options. So, it
produces high-quality parts while saving injection molding costs.

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Disadvantages of Injection Molding

High Tooling Costs

• Injection molding needs high capital investment, leading to a stringent, expensive,

and time-consuming mold design and prototyping stage.

• There is a need to test and retest the mold before production runs begin. However,
for large-scale production, the cost reduces.

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Disadvantages of Injection Molding

Small Batch Production is Expensive

• It is advisable to use injection molding in the mass production of parts. This is

because you use the same mold for them.

• However, producing in small quantities means one needs to design molds for different
parts. This increases cost and the time spent.

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