A lecture delivered by our group project on Injection Moulding. If there are any contents that has violated any intellectual rights, please let me know and I will try my best to correct it wherever I can.

1. Injection Moulding

2. Aims
1. History of Injection Moulding
2. Business context
3. Process
4. Mould design
5. Comparison to other alternative processes
6. Q&A

3. History of Injection Moulding

4. John Wesley Hyatt
Patented 1878

5. 1930s
• Polystyrene
• PVC
• Polyolefins
• Nylon (for moulds)
• WW2 – huge boost in production

6. 1946 – James Watson Hendry
Extrusion screw injection machine
• 1945-55 huge fall in cost
polystyrene and polyethylene

7. 1956 – W H Willert
Reciprocating Screw
From mid 50s: high density polyethylenes and
polypropylene

8. 1970s – James Watson Hendry (again)
• Gas assisted injection process

9. 1970s – large scale use of added fibres

10. • 1979 - Plastic production overtakes steel
production by value
• 1985 - First all electric injection moulding
machine developed in Japan
• 1990 - Aluminium moulds widely used for
the first time
• 2000 - 2 stage IMMs have surpassed
reciprocating screw machines in popularity

11. Today
• Co-injecting machines
• Piezoelectric sensors
• 5 axis machines

12. Business context
• Mould tool: 5-12 weeks, £3000 - £20000
• Production costs – low
• Cost of plant – quite low – machines for under $50,000
• Last decade – huge move to China
• UK plastics sector 2002 - £18 billion, 2014 £3.5 billion
• China plastics sector 2015 - £194 billion (9.6% annual
growth in revenue)

13. Injection Process –
Reciprocating screw
• Solid granules are fed through the
hopper into the barrel
• Rotation of the screw, powered by
an electric or hydraulic motor,
drives the granules forward.
• 3 stage screw:
 Feed zone 50%
 Melt zone 25% (decreasing flight
depth)
 Metering zone 25%
• Plastic heated. Pressure increase
and volume decrease hence
friction. ‘Drag flow’.

14. • Plastic melts and is forced through
a one way valve
• Resulting pressure forces valve and
screw backwards forming a
chamber of plastic
• When enough plastic builds up,
screw is pulled back to decompress
• Screw pushed forward by hydraulic
press and one way valve closed
• Molten plastic pushed through the
nozzle and into the mould
Injection Process –
Reciprocating screw (cont.)

15. https://www.youtube.com/watch?v=YPXCeY24Mjs

16. Injection Process – Two Stage
• Two separate barrels, screw and plunger.
• Solid granules initially go through the
same process as in the single stage
machine.
• Once melted it is fed to a chamber or
‘accumulator’.
• Screw then shut off (as shown) and
plastic forced through the nozzle by the
plunger.

17. http://www.plustech-inc.com/plasticizing.htm

18. • Two stage can provide comparable size shot from a
smaller machine
• Reciprocating screw machine normally bigger so greater
production costs
• Two stage system provides 100% of the shot volume
unlike the reciprocating IMM
• Reciprocating IMM more suited to larger shots,
hydraulic power advantage
Injection Process – Comparisons

19. Design of mould
• Design is crucial.
• Able to produce in some cases
over a million products,
• Made of two halves, Injector and
Ejector mould.
• Vents, guide pins and ejector
pins, coolant holes.

20. Design of mould (cont.)
• Typical moulds are made out of hardened steel,
Aluminium or beryllium-copper alloy
• Modern Aluminium alloys can produce hundreds of
thousands of products.
• 3D printing photopolymers
• Only when the melting point of the material being
injected is lower than that of the photo polymer.
• As a general rule the higher the upfront cost the longer
the lifespan of the mould.

21. Design of mould (cont.)
• If not cooled properly, distortion and stress occur in product.

22. Clamping
• The two halves of the mould are clamped
together by hydraulic presses.
• Forces exerted are between 4 and 9000
tonnes.
• The ejector mould is forced against the
injector mould by a hydraulic press.

23. Design considerations/Ejection.
• Draft angles.
• Typical draft angle: 1° to 2°
• Avoid sharp corners.
• There can be no parallel
overhang.

25. Machining of mould
• High speed milling
• Controlled by CNCs.
• Materials softened by
annealing.
• High quality surface finish
• Followed by heat treatment to
harden the mould.

26. •Electrical Discharge
Machining (EDM)

27. Comparisons with other
processes
• Injection moulding has wide range
of properties making it suitable for
wide-scale applications in the
industry.
• Factors including…
Flexible dimensions
Good Finishing
Cost requirements
• …influence vastly on decisions to
whether adapt injection moulding,
as the desired process.

28. Comparisons with other
processes (cont.)
oLow initial cost due to
simpler mould design.
oBig dimensions possible.
oSingle-sided mould restricts
complexity of the product,
as opposed to a full mould
in IM.
oIn longer run and increased
quantities, thermoforming
has poorer advantage in
economies of scale.
oPoor surface finish and
require further trimming.
Thermoforming compared to injection moulding

29. Comparisons with other
processes (cont.)
oLow initial cost.
oHigh product rate similar
to injection moulding.
oDifficult to control
thickness and finishing.
oHigh defect rate.
oPoorer dimensional
accuracy.
Blow moulding compared to injection moulding

30. Comparisons with other
processes (cont.)
oPrecise control prevent
excess use of expensive
materials.
oPermits the product of
intricate and good surface
finish parts.
oFewer knit lines in the
product.
oHeat and pressure is
consistent.
oMedium production rate.
oCycle time of 2 minutes, as
opposed to injection
moulding can be counted in
seconds.
Compression moulding compared to injection moulding

31. Comparisons with other
processes (cont.)
oPre-heated materials
smoothens production
cycle, hence it has high
product rate (= injection
moulding)
oFaster and cheaper set
up.
oWaste cannot be reused,
due to its thermosetting
nature.
Transfer moulding compared to injection moulding

32. Comparisons with other
processes (cont.)
oRapid and cheap for initial
set ups.
oLow product cost.
oSimilar production
duration (per unit).
oLimited to only rod- or
tube-like products.
oProducts has to be cooled
evenly or mechanical
properties jeopardised.
Injection moulding is
‘batched’ so it can be
cooled evenly.
Extrusion moulding compared to injection moulding

33. Any questions?
I want my lunch, now! Hell no!
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