Rapid injection moulding

RAPID INJECTION
MOULDING
P R E S E N T E D B Y:

A N I L VA R G H E S E
G U P TA G A N E S H
SANDEEP KURIAKOSE
PRADEEP KUMAR

D E PA R T M E N T O F M E C H A N I C A L E N G I N E E R I N G
S P E C I A L I Z AT I O N : D E S I G N A N D M A N U FA C T U R I N G
N AT I O N A L I N S T I T U T E O F T E C H N O L O G Y, S I L C H A R

Introduction
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 Rapid Injection Moulding is the process of making injection moulds

and manufacturing using them for the small production run parts in less
time and at a reduced cost than full production moulds.
 The injection moulds typically made for prolonged production runs are
very expensive and time consuming.
 Rapid injection moulding techniques can produce moulds better suited
to low volume production runs.

Design & Manufacturing

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Injection Moulding
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 It is a manufacturing process for producing parts by injecting material

into a mould.
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Injection moulding can be performed with a host of
materials, including metals, glasses, elastomers and most
commonly thermoplastic and thermosetting polymers.
 It is the commonly used process for thermoplastics and thermosetting
plastic.
Fig 1: An Injection moulding machine


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 Thermoplastics are prevalent due to characteristics which make them

highly suitable for injection moulding, such as the ease with which they
may be recycled, their ability to soften and flow upon heating and it is
safer.
 There two types of mould: Single and Multiple moulds.
 In multiple cavity moulds, each cavity can be identical or different.
 Moulds are generally made from steel or aluminium.


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Injection Moulding Process
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 When thermoplastics are moulded, raw material is fed through a hopper
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into a heated barrel with a reciprocating screw.
Upon entrance to the barrel the thermal energy increases and the Van
der Waals forces that resist relative flow of individual chains are
weakened. This reduces its viscosity, which enables the polymer to
flow.
The screw delivers the raw material forward through a check valve and
collects at the front of the screw into a volume known as a shot.
Shot is the volume of material which is used to fill the mould
cavity, compensate for shrinkage, and provide a cushion to transfer
pressure from the screw to the mould cavity.
When enough material has gathered, the material is forced at high
pressure and velocity into the part forming cavity. Often injection times
are well under 1 second.


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 The packing pressure is applied until the gate (cavity entrance)
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solidifies.
Once the gate solidifies, no more material can enter the cavity;
accordingly, the screw reciprocates and acquires material for the next
cycle while the material within the mould cools so that it can be
ejected.
This cooling duration is dramatically reduced by the use of cooling
lines circulating water or oil.
Once the required temperature has been achieved, the mould opens and
an array of pins, sleeves, strippers, etc. are driven forward to demold
the article.
Then mould closes and the process is repeated.


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Injection Moulding Process
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Fig 2: Schematic of thermoplastic Injection molding machine

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Rapid Injection Moulding.
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 Rapid injection moulds are usually produced from aluminium and

sometimes plastic.
 It uses techniques such as plaster moulding, rapid prototyping and
CNC machining to create moulds which allows for very quick
production times.
 Although these moulds generally lack the life span or qualities of a
final production set, they can produce thousands of parts, are suitable
for most materials and colours, and may even be textured.
 Modern machining techniques also means that rapid injection
moulding can produce ever increasing levels of complexity and size
differences which further expands the list of possible benefits the
process offers.

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Mould Making Techniques
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The major mould making method used for rapid injection moulding are
as follows:
1. Plaster Moulding.
2. Rapid Prototyping.
3. CNC Machining.


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1. Plaster Moulding
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 Plaster mould casting is a metalworking casting process similar to sand

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casting except the moulding material is plaster of Paris instead of sand
it can only be used with non-ferrous materials
The plaster is not pure plaster of Paris, but rather has additives to
improve green strength, dry strength, permeability, and cast ability
First, the plaster is mixed and the pattern is sprayed with a thin film of
parting compound to prevent the plaster from sticking to the pattern.
The plaster is then poured over the pattern and the unit shaken so that
the plaster fills any small features. The plaster sets, usually in about 15
minutes, and the pattern is removed.
The mould is then baked to remove any excess water.
The dried mould is then assembled.


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2.Rapid Prototype Moulding
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 Rapid Prototyping Technology is a group of manufacturing processes

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that enable the direct physical realization of 3D computer models.
This technology build parts on a layer-by-layer basis.
First, a CAD model of the mould is designed.
Then the model is sliced into layers using dedicated software for this
purpose.
The To perform a print, the machine reads the design and lays down
successive layers of liquid, powder, paper or sheet material to build the
model from a series of cross sections.
These layers, which correspond to the virtual cross sections from the
CAD model, are joined or automatically fused to create the final shape.


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3.CNC Machine Moulding
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 CNC technology is changing rapidly, and the changes are helping to

improve the productivity of machine tools used in the mould industry.

Fig 3: A mould made using CNC machine

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 Here are some of the CNC features fundamental to many mould
1.

2.
3.

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machining processes today:
NURBS Interpolation:- This technology for interpolating along curves
instead of dividing curves into short, straight line segments that deliver
improved surface finish, smoother motor performance, faster cutting
rates and smaller part program size.
Finer command unit:- Some CNCs today offer a command unit of 1
nanometer to machine axes , providing for improved accuracy.
Bell-shaped acceleration/deceleration:- Bell-shaped acceleration /
deceleration allows a machine tool to accelerate faster than linear
acceleration/deceleration. It also provides less position error than
various acceleration/deceleration types including linear and
exponential.
Digital servo control:- Digital servo technology has improved
significantly .These advances have combined to allow CNCs to control
the servo loops more tightly and thus control the machine better.


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Fig 4 : CNC Vertical Machining Center, Heavy
Duty Mould Making Machine


Fig 5 : Mould making using CNC machine

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When do we require Rapid Injection Moulding?
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 Injection moulding is a production method that delivers low unit costs during

production.
 Moulds made for extended production may take several months to produce.
 This is not always feasible where small numbers of parts are required as
prototypes for function and fit testing or marketing tests.
 In these cases, moulds identical to the full production examples regarding
design and dimension can be made, although they lack the longevity of the
final moulds.


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Fig 6: Rapid v/s Conventional Injection Moulding

References
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 http:// www.elsevier.com/locate/mee
 http://www.sciencedirect.com/science/article/pii/S0167931709006832

 http://www.protomold.com/ProtomoldProcess.aspx
 http://www.wisegeek.com/what-is-rapid-injection-molding.htm
 http://en.wikipedia.org/wiki/Injection_molding
 http://blog.stratasys.com/2013/08/21/3d-printed-injection-molds-rapid-

manufacturing/
 http://www.mmsonline.com/articles/cnc-technology-for-mold-applications


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Questions ???
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Rapid injection moulding

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