With its reliable, high-quality performance, injection moulding is one of the most common manufacturing processes used to produce plastic components. Indeed, the compound annual growth rate (CAGR) of the global injection moulded plastics market is expected to increase by 4.6% up to 2028. Yet, despite its ability to produce high numbers of plastic components quickly, the injection moulding process must be tightly controlled to maintain the quality of the final parts. Our visual guide explains the steps involved in the injection moulding process from the injection of plastic at high speed and pressure into a mould to cooling to form the final part. To find out more about plastic injection moulding, read our guide - https://www.essentracomponents.com/en-gb/news/manufacturing/injection-moulding/what-is-plastic-injection-moulding-and-how-does-it-work

1. How does the injection
moulding process work?
APRIL 2020

2. “At Essentra
Components, we have
over 65 years of
experience in injection
moulding. This enables
us to supply our
customers with high
quality, accurate
components that meet
their needs.”
Chris Butler, Divisional
Process Development
Manager, 2020
Injection moulding is a manufacturing process, which is
commonly used to create plastic components.
Its ability to produce thousands of complex parts quickly
makes it the perfect process for the mass production of
plastic parts. Essentially, the process involves the injection
of plastic at high speed and pressure into a mould, which is
clamped under pressure and cooled to form the final part.
What is the injection
moulding process?
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Within the process of injection moulding, there are lots of
parameters that need to be tightly controlled. This ensures
that the component produced is consistently high quality.
If one of these parameters isn’t quite right, then the parts
produced from the process may have faults or not meet the
correct specifications. It’s important to get the process right
to make sure each of the components produced within an
injection moulding cycle is accurate and high quality.
Why is it important to
get the process right?

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Materialselection
Toolingselection
Temperatures
Pressures
Before the injection moulding
process begins, there are
several aspects that need to
be considered by a
manufacturer.
Preparing for the injection
moulding process
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2
3
4
Materialselection
Toolingselection
Temperatures
Pressures
Preparing for the injection
moulding process
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1 Material selection – different types
of thermoplastics can handle
different temperatures and pressures
and have the right properties for
specific part applications.

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2
3
4
Materialselection
Toolingselection
Temperatures
Pressures
Preparing for the injection
moulding process
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2 Tooling selection – the size of the
tool, number and complexity of the
cavities within the tool will affect the
temperature and injection pressure
of the thermoplastic being used.

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2
3
4
Materialselection
Toolingselection
Temperatures
Pressures
Preparing for the injection
moulding process
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3 Temperatures – as well as considering
the temperature the plastic needs to
be heated to, the heat caused by the
friction of the machine processes also
needs to be considered to avoid
overheating the plastic.

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2
3
4
Materialselection
Toolingselection
Temperatures
Pressures
Preparing for the injection
moulding process
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4 Pressures – the pressure at which
the plastic is injected into the mould
and the clamp pressure of the
mould need to be set correctly to
keep parts consistent.

9. Once the thermoplastic (or combination of
thermoplastics) has been selected, it is fed into the
machine in its pellet form into the hopper at the top
of the machine.
The pellets pass through the machine and into a
temperature-controlled cylinder called the machine
barrel. Here the plastic pellets are heated until the
thermoplastic is molten.
The temperature of the barrel and the plastic needs to
be carefully monitored to make sure the thermoplastic
doesn’t overheat and cause faults in the final part.
FEEDING & HEATING
THE PLASTIC
Step 1
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10. Before the molten plastic is injected, the tool, which
is usually made up of a fixed half called the cavity
and a moving half called the core, closes.
When closed, a clamp applies pressure to the tool,
ready for the injection of the plastic.
The screw within the barrel of the machine also screws
back to its set point so the plastic can enter the barrel,
ready to be injected.
PRE-INJECTION
PROCESS
Step 2
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THE TOOL
THE CORE THE CAVITY

11. Once the clamp pressure is at an optimum level, the
plastic is injected by the screw at high speed and
pressure into the cavity. A gate inside the tool helps to
control the flow of the plastic.
To make sure that there’s no damage done to the final
components, it’s important that a manufacturer monitors the
pressure at which the plastic is injected and that they have the
expertise to maintain and use the mould tools correctly.
This ensures that the they are creating high-quality and
consistent parts from their injection moulding process.
PLASTIC
INJECTION
Step 3
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12. When the tool cavity is mostly full of liquid, a holding
phase begins where the part in held under high pressure
so it can start to take its final form.
After a set holding time, the screw will screw back to its set
point. This happens at the same time as the cooling phase of
the cycle, this allows the thermoplastic to set in its final form.
Once the set cooling time has passed, the mould opens and
ejector pins or plates push the new part out of the tool. These
fall on to a conveyor belt ready to be finished and packed.
FORMING
THE PART
Step 4
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13. Dependent on the final application of the part,
the moulded component may require some
finishing, including dyeing, polishing, or removing
of excess material.
These processes are unique to each part and are completed
before they’re packed and distributed to customers.
By picking and checking products by hand, as well
as performing regular quality checks, experienced
manufacturers can make sure that they’re producing
consistent, high-quality parts for their customers.
PART
FINISHING
Step 5
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At Essentra Components, we reprocess
any excess plastic to be used again in
future processes, helping to reduce waste
and environmental impact.

14. Step 5
Depending on the
final application
of the part, it will
be finished and
packed ready for
distribution.
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Step 4
Hold pressure is
applied to the part
and a cooling
phase begins to
help the final part
form in the tool.
Step 3
The screw injects
the molten
thermoplastic at
high pressure and
speed into the
moulding tool.
Step 2
The mould tool
closes and clamp
pressure is
applied. The
screw moves back
to its set point
ready to inject.
Step 1
The selected
thermoplastics are
fed into the injection
moulding machine
and heated until
they’re molten.
THE INJECTION
MOULDING PROCESS
Overview

15. During the injection moulding process, an
experienced manufacturer will be able to
help you with:
Pre-injection decisions – selecting the right
mould tool and thermoplastic for the
application of the final component.
Monitoring the process – controlling the
parameters of the injection moulding process,
such as pressure and temperature.
Create a consistent process – apply controls
to get optimum performance from the mould
tool and thermoplastic.
Optimise performance – maintain tools and
machinery so they perform flawlessly.
High-quality and consistent parts – finish,
pack and distribute parts to best suit a
customer’s needs.
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Get the process right
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16. THANK YOU
For further information about the
injection moulding process, head
to our article by clicking here.