this file is useful for industrial and manufacturing & also for mechanical engineers & usefull for the industrial point of view This file is about injection molding for plastics best of luck

1. Plastic Forming

2. Types of Plastics
• Any synthetic organic material that can be molded under heat
and pressure into a shape that is retained after the heat and
pressures are removed is called plastic.
• Plastics are of following two types:
(1) Thermoplastics
(2) Thermosets.

3. Types of Plastics
• Thermoplastics are the plastics which can be molded into any shape
on application of heat and harden on cooling.
• They can be retransformed into thermoplastics by reheating.
• The thermoplastics are those that do not undergo a curing process
during heating and shaping.
• Thermoplastics are more important type commercially comprising
more than 80% of total plastics.
• For example
– Polythene
– Polypropylene
– Polyvinyl Chloride
– Nylon
– Acrylics
– polystyrene

4. Types of Plastics
• Thermosets are those plastics which can be molded into any shape
by application of heat, and harden on cooling.
• But once hardened they can not be transformed back to thermosets
by application of heat.
• The thermosets are those that undergo a curing process during
heating and shaping, which causes a permanent chemical change in
their molecular structure.
• For example
– Phenol formaldehyde (Bakelite)
– Urea formaldehyde
– Melamine formaldehyde
– Polyester resin

5. Identifying Plastics
• Plastics are impossible to identify by simply their appearance,
as incase of wood or other materials.
• So, there are some tests which are used to identify some of the
plastics.
Procedure:
• The plastic is held in flame and the fumes are fanned towards
the nose by hand to catch their smell.
• This is done as direct smelling can be hazardous to health.
• Moreover test must be performed in properly ventilated room.

6. Identifying Plastics
• Thermoplastics:
TEST 1: Drop the sample into soapy water.
It floats.
TEST 2: Hold the sample to flame.
Smell Colour of flame Conclusion
Marigold (Tropical
plants)
Smoky Expanded polystyrene (EPS)
Burning Candle Yellow and blue Polypropylene (PP)
Burning Candle Blue If on burning drips like wax: High Density polyethylene(HDPE)
If on burning doesn’t drip like wax: Low Density polyethylene
(LDPE)
TEST 1: Drop the sample into soapy water.
It sinks.
TEST 2: Hold the sample to flame.
Smell Colour of flame Conclusion
Marigold (Tropical
plants)
Yellow + black dots Polystyrene (PS)
Vinegar Dark Yellow Cellulose Acetate
Acrid (sharp) Yellow If it burns easily: Plasticised PVC
If it doesn’t burn easily: Unplasticized PVC (uPVC)
Floral / fruity Yellow Acrylic
Rubber Orange yellow Acrylonitryl-Butadiene-Styrene (ABS)
Burning hair Blue Nylon

7. Identifying Plastics
• Thermosets:
TEST 2: Hold the sample to flame. TEST 2: Scratch the
sample.
Conclusion.
Does it burn
easily?
Smell Visible Scratch marks
Yes Carbolic (Antiseptic) Phenol
formaldehyde (PF)
Yes Fishy smell Yes Urea formaldehyde
Yes Fishy smell No Melamine
formaldehyde
No Acrid (sharp) Epoxide
No Floral / fruity Polyester resin

8. Types of Processes
• Injection molding
• Extrusion molding
• Blow molding
• Vacuum forming
• Compression molding
• Rotational molding

9. Injection molding
Fig:

10. Injection molding
• Injection molding is a manufacturing process for producing
parts from both thermoplastics and thermosetting plastic
materials.
• Injection molding is a manufacturing process for producing
parts by pouring the molten metal into a mold having internal
cavity or cavities and allows it to solidify to get the required
casting.
• 50% plastic products are made by this process.

11. Injection molding
• The injection molding process requires the use of an
– Injection molding machine
– Raw plastic material (Granular form)
– Die (Mold)
• The plastic is melted in the injection molding machine and
then injected into the mold, where it cools and solidifies into
the final part.

12. Parts of Injection molding machine
Injection Unit
Die Assembly
Clamping unit

13. Injection Unit
This unit or section melts the polymer resin and
injects the polymer melt into the mold. The
unit may be ram fed or screw fed. It has 3
zones: feed zone, transition zone and metering
zone.

14. Injection Unit

15. The whole unit has the following parts:
• Feed Hopper
Conical shaped feed hopper is used for feeding the raw material or plastic
to be molded into the barrel, the next part of the machine.
• The Barrel
The barrel is the intermediate part between the hopper and the nozzle that
has screw in it and heaters around it. The feed goes to the barrel from
hopper.
• Reciprocating Screw
It is used to push the material through the barrel and nozzle to the mold.
The rotational motion of the screw fills the barrel’s front part with the
molten material and then rotation stops and through reciprocating
movement of screw the material is injected to the mold through nozzle.
• The Heaters
Heaters are provided in the barrel section to melt the material. These may
be electric or gas heater. Electric heaters are more safe ones.
• The Nozzle
The molten material is injected to the mold through the nozzle from the
barrel. The nozzle opens during the reciprocating movement of the screw
when screw pushes the molten material. Different types of nozzles are used
in the process.

17. Injection molding
Injection:
• The raw plastic material, usually in the form of granulers, is fed into
the injection molding machine, and advanced towards the mold by
the injection unit.
• During this process, the material is melted by heat and pressure.
• The molten plastic is then injected into the mold very quickly and
the buildup of pressure packs and holds the material.
• The amount of material that is injected is referred to as the shot.
• The injection time is difficult to calculate accurately due to the
complex and changing flow of the molten plastic into the mold.
• However, the injection time can be estimated by the shot volume,
injection pressure, and injection power.
Shot:
• The amount of material that is injected or poured into a mold.
• The shot volume includes the volume of all part cavities, as well as
the feed system which delivers the material.

18. Mold
It is the solid mass of suitable material having internal cavity or
cavities & vertical passage for pouring of molten plastic.
1- Impression:
The injection mould is an assembly of parts containing within it an
“impression” into which plastic material is injected and cooled. It is the
impression which gives the molding its form. The impression may,
therefore, be defined as “that part of the mould which imparts shape to the
molding”.
The impression is formed by two mould members:
• The cavity, which is the female portion of the mould, gives the molding its
external form.
• The core, which is the male portion of the mould, forms the internal shape
of the molding.

19. Product

20. Impression

21. 2- Sprue Bush:
The passage for the molten material in the impression or cavity is
called sprue. And the bush used for that passage is called the
sprue bush.

22. 3- Runner And Gate System:
The material may be directly injected into the
impression through the sprue bush or for
molds containing several impressions; it may
pass from the sprue bush hole through a runner
and gate system before entering the
impression. The cross sections of gates are
made smaller as the product has to be removed
after solidification of the

24. 4- Guide Pillars and Bushes:
To mold an even-walled article it is necessary to ensure that the
cavity and core are kept in alignment. This is done by
incorporating guide pillars on one mold plate which then enter
corresponding guide bushes in the other mold plate as the mold
closes.

25. Injection molding
(Process)
Process:
• Clamping
• Injection
• Cooling
• Ejection

26. Clamping Unit
• Clamping unit or section holds the mold together. Mold opens
and product is removed then mold closes by this unit. It makes
the mold open and close automatically. Therefore ejects the
finished part. Mechanism used for this movement may be
 Mechanical
 Hydraulic
 Hydro mechanical
• The movement of moveable platen of the mold is controlled
through this unit. Mostly toggle mechanism is used for
clamping as shown in figure below on left side, while on the
right side simple piston cylinder mechanism is shown as.

28. Injection molding
(Process)
Clamping:
• Prior to the injection of the material into the die, the two halves of
the die must first be securely closed by the clamping unit.
• Each half of the die is attached to the injection molding machine and
one half is allowed to slide.
• The hydraulically powered clamping unit pushes the die halves
together and exerts sufficient force to keep the mold securely closed
while the material is injected.
• The time required to close and clamp the mold is dependent upon
the machine - larger machines (those with greater clamping forces)
will require more time.

29. Injection molding
(Process)
Clamping:
Clamp force:
• The force that is applied to a mold by the molding machine in order
to keep it securely closed while the material is injected.
• The clamp force is typically some factor of safety greater than the
separating force, which is the outward force exerted on the mold
halves by the injected material.

30. Injection molding

31. Injection molding
Cooling:
• The molten plastic that is inside the mold begins to cool as soon as it
makes contact with the interior mold surfaces.
• As the plastic cools, it will solidify into the shape of the desired part.
• However, during cooling some shrinkage of the part may occur.
• The mold can not be opened until the required cooling time has
elapsed.
• Water is used as the primary cooling agent. To cool the mold, water can be
channeled through the mold to account for quick cooling times
• The cooling time can be estimated from several
– Thermodynamic properties of the plastic and
– The thickness of the part.

32. Ejection System
 Facilities are provided on the injection machine for automatic actuation of
an ejector system, and this is situated behind the moving platen.
 After sufficient time has passed, the cooled part may be ejected from the
mold by the ejection system, which is attached to the rear half of the mold.
 When the mold is opened, a mechanism is used to push the part out of the
mold.
 Force must be applied to eject the part because during cooling the part
shrinks and adheres to the mold.
 In order to facilitate the ejection of the part, a mold release agent can be
sprayed onto the surfaces of the mold cavity prior to injection of the
material.
 Most ejection plates are found on the moving half of the tool, but they can
be placed on the fixed half.

33. Ejection Method
 Different types of techniques can be used for ejection of mold when
cooled like:
• Pin ejection
• Sleeve ejection
• Bar ejection
• Blade ejection
• Air ejection
• Stripper plate ejection
 But the most commonly used method is pin ejection in which the
ejector plate assembly to which the ejector pin is attached is moved
forward relative to mold plate. Thus the ejector pin pushes the
molding from the cavity.

34. Injection Molding Cycle
The sequence of events during the injection mold of
a plastic part is called the injection molding cycle.
The cycle begins when the mold closes, followed
by the injection of the polymer into the mold
cavity. Once the cavity is filled, a holding
pressure is maintained to compensate for material
shrinkage. In the next step, the screw turns,
feeding the next shot to the front screw. This
causes the screw to retract as the next shot is
prepared. Once the part is sufficiently cool, the
mold opens and the part is ejected.

35. Time Function
The time it takes to make a product using injection molding can be calculated by
adding:
Twice the Mold Open/Close Time (2M)
+
Injection Time (T)
+
Cooling Time (C)
+
Ejection Time (E)
Where T is found by dividing:
Mold Size (S) / Flow Rate (F)
Total time = 2M + T + C + E
T = V/R
V = Mold cavity size R = Material flow rate

36. Injection molding
(Defects)
Flash:
• The occurrence of molten material seeping out of the mold
cavity and solidifying.
• Once the part is ejected, a thin layer of material will have
formed attached to the part along the parting line.
Causes:
• Injection pressure is too high.
• Clamp force is too low.

37. Injection molding
(Defects)
Warping:
• The permanent bending of a part that occurs when certain section of
the part shrink faster than others, as result of a non-uniform cooling
rate.
Causes:
• Non-uniform cooling rate

38. Injection molding
(Defects)
Bubbles:
• Balloon shaped cavities.
Causes:
• Injection temperature too high
• Too much moisture in material
• Non-uniform cooling rate

39. Injection molding
(Defects)
Unfilled sections:
• Incomplete parts
Causes:
• Insufficient shot volume
• Flow rate of material too low

40. Injection molding
(Defects)
Sink marks:
• When molten material is injected into a mold, voids can occur if
certain sections solidify first.
• The remaining material will fill these voids as it continues to cool
and shrink.
• This shrinkage causes marks on the part where the material sunk
into the void.

41. Injection molding
(Defects)
Sink marks:
Causes:
• Injection pressure too low
• Non-uniform cooling rate/Non-uniform wall thickness

42. MOLDING DEFECTS
Molding Defects Alternative name Descriptions Causes
Burn Marks
Air Burn/ Gas
Burn
Localized burnt zone
(often in the
yellow/brown tones)
Tool lacks venting, injection speed
is too high
Flash Burrs
Excess material in thin
layer exceeding
normal part geometry
Tool damage, too much injection
speed/material injected
Color Streaks Localized change of color
Master batch isn't mixing properly,
or the material has run out and
it's starting to come through as
natural only
Flow marks
Directionally "off tone"
wavy lines or patterns
Injection speeds too slow (the
plastic has cooled down too
much during injection,
injection speeds must be set as
fast as you can get away with
at all times)
Short shot
Non-Fill / Short
mold
Partial part
Lack of material, injection speeds
too slow

43. Polypropylene (PP)
Properties:
Dull, semi-rigid, translucent, good chemical
resistance, tough, good fatigue resistance, integral
hinge property and good heat resistance.
Applications:
Flexible and rigid packaging, automotive Bumpers,
and exterior trim, consumer products, and
industrial uses. PP fiber is used in tape and
strapping, chairs, tables, safety helmets, washing
machine body, fan body

44. Nylon
Properties:
Nylon is a generic designation for a family of synthetic
polymers known generically as polyamides. Variation of
luster: nylon has the ability to be very lustrous, semi
lustrous or dull, high elongation. Excellent abrasion
resistance. High resistance to insects, fungi and animals
molds, mildew, many chemicals
Applications:
Due to its high tenacity fibers are used for seatbelts, tire
cords, ballistic cloth, tooth brush, comb and other uses.
It is used in carpets and nylon stockings and in many
military applications

45. Acrylonitrile Butadiene Styrene(ABS)
Properties:
The advantage of ABS is that this material combines the
strength and rigidity of the acrylonitrile and styrene
polymers with the toughness of the polybutadiene rubber.
The most important mechanical properties of ABS are
resistance and toughness. It has a shining format.
Applications:
Used to make light, rigid, molded products such as piping (for
example Plastic Pressure Pipe Systems), musical
instruments, golf club heads , automotive body parts,
wheel covers, enclosures, protective head gear, toys, TV
casing, telephone casing, car bodies.

46. Injection Molding
(Applications)

47. Injection Molding
(Applications)

48. Injection Molding
(Applications)