Basics of injection moulding

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PROCESS KNOWLEDGE / MOULDING / SL1
Moulding Pressing Welding Forging Machining
Casting
Basics of Moulding

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Brief agenda
Process knowledge on Moulding – SL1 ( Module pilot )
1.
2.
3.
Pre-test on basics of Moulding process
Module presentation with exercises
Post-test

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After completing this training program on Moulding process
you will be able to explain
different types of Moulding process
key process controls
key terminologies
manufacturing facilities
and Choose
appropriate process for a part with given data

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What do you think when you hear plastic products ?
PET bottles and plastic bags,
contact lenses and spectacles
frames we use daily, tableware,
optical discs such as CD and DVD,
refrigerator and TV cabinets,
housings of portable telephones
and personal computers, and so
on -- a great variety of goods.
Plastic is used for a wide variety
of things ranging daily
necessities such as packaging
materials,various parts of
household appliances,
construction materials, and
automotive parts, exteriors, and
interiors, to those that are used
in hidden places.

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Lets take our house

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Can you imagine the living room with out plastic resins ?

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Can you imagine the kitchen with out plastic resins ?

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Can you imagine the bath room with out plastic resins ?

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The usage of plastics for various applications is
increasing from house hold items to high performance
aeronautical applications.
These plastics are getting shaped by Moulding process

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What is Process ?
It is the sequence of part operations necessary for the
complete manufacture of a part
Input
material
Melting Pouring Cooling Fettling Final
casting
For example, in a casting process
Process

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General manufacturing process in TVS-M
Casting process
Moulding process
Forging process
Machining process
Heat treatment process
Pressing process
Welding process
Painting process
Plating process

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Moulding

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Moulding process
Definition of Moulding process
A plastic / rubber object obtained by allowing polymer to shape in the
mould
General Moulding process flow – Injection type
Input
material-
Granules
Melting of
plastic
granules
Injection
of melt
Cooling De-
flashing
Final part
Few types of Moulding process
Extrusion
Moulding
Blow
Moulding
Injection
Moulding
Vacuum
forming
Compressio
n Moulding
Transfer
Moulding

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Why Plastics & Moulding process ?
Production of complex shapes
with close tolerances.
Little or no machining is required.
Integrated fastening elements,
such as bosses and studs.
Aesthetically superior and good
weather resistance
Light weight

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Major types of Moulding process
Moulding
process
Extrusion
Moulding
Blow
Moulding
Injection
Moulding
Vacuum
forming
Compression
Moulding
Rotational
Moulding

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Injection
Moulding

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What is Injection Moulding ?
A powder or pellet is liqueﬁed, injected into a mold, cooled under
pressure, and ejected.
Injection Moulding

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Injection Moulding Animation

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Injection Moulding process ﬂow
Raw material
(Granules)
Transfer to
hopper
Melting in
injection unit
Clamp
pressure
applied
Injection of
melt into
mould
Hold on
phase
Cooling Mould
opening
De-gating &
De-ﬂashing
Final
Inspection
Part ejection
Mould
closing

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Application of Injection Moulded parts
Automobile parts
Fenders
Covers
Air cleaner assembly
Dash boards etc.,
Toys
Other industrial parts
Best option for high productivity and production quantity and part accuracy

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Blow
Moulding

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What is Blow Moulding ?
The process of forming hollow articles by expanding a hot plastic
element called a parison against the internal surfaces of a mold.
Extrusion blow Moulding Injection blow Moulding
Injection stretch Moulding

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Blow Moulding process ﬂow
Raw material
(Granules)
Transfer to
hopper
Melting in
injection unit
Injection of
melt into
parison
Parison passed
through mould
Mould closes Parison is cut Mould opens Part is
removed
Air is blown

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Blow Moulding process

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Blow Moulding process

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Application of Blow Moulded parts
Automotive fuel tanks
Bottles and containers
Best option for hollow parts - both symmetric / asymmetric parts

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Compression
Moulding

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What is Compression Moulding ?
Slug is placed in mould and heated under pressure in the Mould cavity.
When reaction is complete, product is cooled and ejected.
Mould
heating
Hydraulic press
operation
Compression to
mould shape
Placing the
slug

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Application of compression moulded items
Rubber grommets,cushions
Electrical switch and fuse boxes
Domestic electrical equipment
Microwave containers
Tableware
Business machine housings
Gas and electricity meter housing
Dish aerials
Original process for 'Bakelite'. Slow process and wasteful for 'ﬂash'.

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Vacuum
forming

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What is Vacuum forming?
The process involves heating a plastic sheet until soft and then
draping it over a mould. A vacuum is applied sucking the sheet into
the mould. The sheet is then ejected from the mould
Mould
Plastic
sheet
Vacuum
creation
Vacuum Forming

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Application of Vacuum formed parts

Main body of a land yacht
Wheel guard and control cover
Domestic bath & wash basin
Truck Dash Board
Battery Cover
Inner Wheel Arch
Machine Cover
Electric golf trolley body
Low tooling cost & best option for Proto-typing & low volume large parts

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Rotational
Moulding

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What is Rotational Moulding?
Resin loaded in the mould it is heated. Simultaneously the mould is
rotated and the melted resin fuses into inner surface of the moulds.
The mould is cooled and the solidiﬁed part is taken out.

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Rotational Moulding Animation

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Application of Rotational Moulded parts
Oil recovery bank
Oil storage tanks
Steering wheel
Modular play equipment
Emergency evacuation stretcher
Diesel tanks
Rain water tanks
Seamless ,Stress free components. Economical for large hollow components

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Extrusion
Moulding

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What is Extrusion Moulding?
Molten plastic is forced through a die, which contains a hole whose
shape corresponds to that of the required article. The extrusion will
then be cut into lengths

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Extrusion Moulding process
Pipe extrusion
Sheet extrusion

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Application of Extrusion Moulded parts
Pipes & hoses (continues process)
Insulate coating wires
Windows and door beadings (PVC)
Flat plastic sheets
Low tooling cost for large components and continuous process

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Key process controls

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S # Parameter Definition Why To Control Application
Details
1 Melt
Temperature
Temperature of
melt at the time
of injection
Significant impact on
Mould filling
Sink mark
Flow marks
•
•
•
Injection
Moulding
2. Mould
Temperature
Mean
temperature of
the Mould core &
cavity halves
during production.
Shrinkage
Flow of plastic
Warpage
•
•
•
Injection
Moulding,
Compression
Moulding,
Blow
Moulding
3. Pre-heating
(Plastic
granules)
Heating the
plastic granules
before processing
To remove moisture content.
Moisture content causes
significant reduction in
Physical Properties.It also
produces silver streaks on
the part.
Injection
Moulding,
Blow
Moulding
(Nylon, PC,
ABS)
~ 180-240° c
~ 60-100° c

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S.No. Parameter Definition Why To Control Application
Details
4. Filling Time The time required to
fill the complete
cavity with plastic
melt.
Shrinkage
Moulding filling
Short Moulding
•
•
•
Injection
Moulding
5. Hold Time The time for which
the holding /
packing pressure is
retained after filling
phase
Shrinkage
•
Injection
Moulding
6 Cooling
time
The time for which
the part is allowed
to cool inside the
mould
To avoid
Warpage
•
Injection
Moulding,
Blow Moulding,
Compression
Moulding

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Summary
Blow Moulding process is opted for making bottles, containers and
other hollow parts like fuel tank, boxes etc.,

General types of Moulding
Injection Moulding, Blow Moulding, Rotational Moulding, Vacuum forming,
Compression Moulding, Extrusion Moulding etc.,
Plastics & Moulding process is selected for parts with complicated shapes,
to reduce weight, to improve aesthetics and for integrating different
function like fastening, bosses etc.,`
Injection Moulding is the most common process used in automobile
industry

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Summary
Rotational Moulding is used producing big barrels. In this process the
entire mould is rotated to make the plastic melt to fuse along the mould
Vacuum forming generally used for prototyping and for small volume
large parts.
Compression Moulding is generally used for rubber parts,plates and
other small bushes

Key process controls in a Moulding process are
Melt temperature, Mould temperature, Filling time, injection pressure, hold
time etc.,

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Moulding terminologies

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General Moulding process terminologies
Mould related
Core,
Cavity
Ejector plates
Back plates
Cooling channels
Machine related
Clamp & Clamp force
Platen
Tie bars
Hopper
Shot capacity
Part related
Runner & Sprue
Gate
Draft
Parting line
Plant terminology – Leaf, stem, root, seed etc.,

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Moulding process terminologies – Mould related
Core
One of the two halves which form
the required hollow shape to
produce part.

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Cavity
The blocks containing the cavity,
runners and sprue

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Sprue
Sprue is the channel / passage created in the mould which transport
melt from entrance of the mould to runners.

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Types of Sprue
Cold sprue and runners remain attached to the part
and required to be removed as a post moulding
operation called degating
In case of hot sprue, the sprue always remains in the
molten condition inside the mould.This reduces the
wastages thereby increasing the raw material
utilisation.
Clampingring Adjustingring Heaterelement Spruetip Spruebush Thermocouple
Injection
point
Injection
point
Cold sprue
Hot sprue

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Moulding process terminologies – Part related
Runners
Channels cut interior to the mold
which transport the melt from the
entrance to the mold to the
entrance to the cavity.
Gate
The narrowed link between the
runner and the cavity.
The melt enters the cavity at the
gate.
Part
Sprue
Gate
Runner
Part

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Moulding cycle

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Parting line
A line generated by the butting of
core and cavity halves of the mould.
Parting line

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Moulding Direction
The direction in which the mould
opens and closes.
Also, called ejection direction as
the component is ejected from the
mould in same direction.
Moulding
direction

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Draft
The taper given to the mould in
order to facilitate easy removal of
part

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Ejector plates
Plate carrying ejector pins used to
eject the component after
moulding.
Ejector plate moves forward to
eject the component.

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Back plates
The plates supporting the core and cavity.
Used to mount the mould onto the machine.
Back plate
Back plate

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Cooling Channels
The channels are drilled in the core and cavity.
The water is circulated through these channels to cool the part
and maintain the mould temperature.

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Moulding process terminologies – Machine related
Platen
The structural part of the machine on which the mould is mounted.
Tie bars
Four tie bars guide the movable platen during opening and closing
of mould.
Platen -
Stationary
Platen -
Movable
Force

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Clamp force
The clamping force is exerted to prevent the opening of mould
during injection phase.
Clamping force should always be more than the seperating force
created during injection.
Force

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Shot capacity
Express in terms of grams is maximum amount of melt that can be
injected by the machine.
Melt

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Hopper
Mounted above the injection unit
and stores the granules for feeding
into injection unit.

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General Moulding Problems
Sink mark
Weld / Meld lines
Flash
Air traps
Voids
Flow marks
Scoring marks
Silver streaks
Warpage
Short Moulding

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Sink mark
An indentation on the surface of the
part as a result of signiﬁcant local
change in wall section. The mark
will occur in the thicker area.
General Moulding problems
Causes
The thickness of ribs or boss is more
Injection pressure too low
Short of shot capacity
Mould temperature too high
Gate too small,melt too hot

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Weld lines
The intersection of two confronting
ﬂow fronts creating areas of local
weakness. Weld lines should be
positioned in the least sensitive areas.
Causes
Wrong part and gate design
Injection pressure and/or speed too low
Insufﬁcient venting
Mould and/or melt too cold
Distance from gate too excessive

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Meld lines
The juncture of two ﬂow fronts moving
in the same direction rather than in
opposite directions. Meld lines should
be positioned in least sensitive areas.
Causes
Wrong part and gate design
Injection pressure and/or speed too
low
Mould and/or melt too cold
Distance from gate too excessive

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Flash
Excess material retained by the part
along the parting line.
Causes
Clamping force (machine tonnage)
too low
Injection pressure too high
Melt too hot,viscosity too low
Damaged mould surface at parting
line

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Air traps
Small air or gas ﬁlled hollows in the
moulding
Causes
Trapped gases in the mould
Mould temperature too low
Thin to thick transition

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Voids
An unﬁlled space within a solid
material.
Causes
Part wall too thick
Melt temperature too high
Injection speed too high
Injection pressure too low

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Flow marks
Causes
Mould too cold
Melt temperature too low
MFI of material very low
Wrong gate location
This occurs due to restriction to ﬂow of
melt resulting in cloudy appearance on
the part surface

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Scoring marks
This scratch marks observed on the part due to rubbing of part against
mould wall during ejection.
Causes
The draft angle is inadequate
Poor surface ﬁnish of the cavity

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Streaks
Appearance of large,dull and lamellar
areas on the moulding
Causes
Moisture content in the granules
Material contamination by other resin

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Short moulding
Resulting from incomplete ﬁlling of
mould.All parts of moulding are not
formed
Causes
Injection pressure and speed too low
Melt temperature too low
Melt Viscosity too high
Poor mould venting
Wrong gate design

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Warpage
A dimensional deformation of the
moulding resulting from frozen-in
stress
Causes
Wrong part design
Part too heavy
Insufﬁcient cooling
Wrong gate location
Wrong material choice

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Summary
General terminologies used in Moulding process
Mould related
Core,
Cavity
Ejector plates
Back plates
Machine related
Clamp & Clamp force
Platen
Tie bars
Hopper
Shot capacity
Part related
Runner & Sprue
Gate

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Summary
General problems / defects in Moulding
Sink mark
Weld / Meld lines
Flash
Air traps
Voids
Flow marks
Scoring marks
Silver streaks
Warpage
Short Moulding

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Exercise
Identify the problems in the
given Moulding parts ?

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Moulds and Equipments
Moulds and Equipments
of Moulding process
of Moulding process

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Moulds used for Moulding process
Moulds are made in two halves called the core and cavity.
The core and cavity ﬁt together to form the required cavity which
ﬁlls with melt.
The mould are made of alloy tool steels. These tool steels have the
strength, wear resistance, and thermal shock resistance to
withstand thousands of melt injections.

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Types of Moulds used for Moulding process
Single cavity
mould
Multi cavity
mould
Family Mould
Moulds

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Types of dies used for Moulding process
Single cavity mould
Single cavity to
produce one
component
Multiple cavity
to produce a
number of
identical parts
Multi cavity mould
Family mould
Family mould to
produce different
parts at one time

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Types of machines used for Moulding
Injection Moulding machine
Blow Moulding machine
Vacuum forming machine
Compression Moulding machine
Extrusion Moulding machine

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Injection Moulding machine – Key speciﬁcations





Clamping force in tonnes
Shot capacity
Injection pressure & speed
Screw diameter
Tie bar distance

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


Max. product volume in litres
Locking pressure
Max. blowing pressure

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



Pressing capacity in tonnes
Stroke length
Heating platen size
Platen temperature

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Vacuum Forming machine




Sheet size max.
Max. form size
Max. form depth
Max. sheet thickness

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Rotational Moulding machine



Max. volume of part
No. of arms
No. of stations

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



Extrusion capacity
Screw diameter
Screw speed
No. of screws

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Summary






General types of Moulding machines
Injection Moulding machine
Vacuum forming machine
Rotational Moulding machine



General types of dies used for Moulding process
Single cavity mould
Multi cavity mould
Family mould

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Supplier

selection
Manufacturing
process
selection
Performanc
e
requiremen
t
Type of raw
material
Size
Shape
Thickness
Tolerance
Surface
ﬁnish
Operational
cost
Manufactur
ing cost
cost
Tooling
cost
Quantity
required
Developme
nt lead-
time
Raw
material &
its
properties
Dimensional
requirement
Economic
consideratio
ns
Environmen
t & safety
Workplace
hazard
Pollution –
Air,water,
noise
Raw
material &
its
properties
Factors considered for Mfg. process selection

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Inﬂuencing factor : Performance requirement
Process selection based on Raw material

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Process selection based on RM & its properties

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






Properties:
Semi-rigid
Translucent
Good chemical resistance
Tough
Good fatigue resistance
Integral hinge property
Good heat resistance
Raw material properties & applications
Poly Propylene (PP)



Limitations:
Poor Dimensional Stability
Poor Paintabililty
Cannot withstand higher temperature




Applications in Two Wheelers:
Rear Fender
Seat Base
Air Cleaner Housing
Mud Flaps

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







Properties:
Rigid
Glossy
Tough
Good low temperature properties
Good dimensional stability
Excellent Paintability
Easily Electroplated
Low creep
Acrylonitrile Butadiene Styrene (ABS)


Limitations:
Low Heat Distortion Temperature
High Cost
Raw material properties & applications



Applications in Two Wheelers:
Cover Frames
Tail Covers
Body Panels

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Moulding process selection based on
Quality aspects
Cost aspects
Delivery aspects

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Moulding process selection – Quality aspects
Best option, Probable option, Not feasible
Mention the thickness in mm
Mention the thickness in mm
Wide range, Medium range, Narrow range
High, Medium, Low

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Moulding process selection – Cost aspects
High, Medium, Low
High, Medium, Low
High, Medium, Low
Very high, High, Medium, Low, very low
Very high, High, Medium, Low, very low

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Moulding process selection – Delivery aspects
Long, Medium, Short
High, Medium, Low
Preference : High, Medium, Low volumes

103
Moulding process selection – Quality aspects

104
Moulding process selection – Cost aspects

105
Moulding process selection – Delivery aspects

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Moulding process selection – in conclusion
Select Injection Moulding, for
Higher volumes per annum
Excellent consistency in the part
Excellent product quality
Less rejections and wastages
Lower cycle times

107
Moulding process selection – in conclusion
Select Blow Moulding, for
Hollow parts
Select compression moulding, for
Medium production per annum
Lesser development time
Medium tooling investment

108
Summary
Mainly the part geometry and complexity decide the manufacturing process
selection





The manufacturing process selection is done considering the following main
factors
Part complexity
Raw material & its properties
Dimensional requirement
Economic considerations
Environment & Safety aspects
Other factors like Quality, Cost and Delivery requirement will further
decide the selection of manufacturing process

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1.
2.
3.
4.
Please take up the post test questionnaire
The objective of the test is to evaluate the
effectiveness of the module
The duration of the test is 15 minutes
Please do not discuss during the test

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Thank you

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Basics of injection moulding

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