This document provides information about plastic injection molding processes. It begins with an overview of plastic products and mold types, including injection, blow, rotational, and extrusion molding. It then covers the product development process for injection molding, including mold design, machining, materials, defects, and design considerations. The document discusses the main components of injection molding machines and their functions. It also explains cooling systems, gate types, and ejection systems for molds. In summary, the document outlines the key steps and factors involved in plastic injection molding from design to production.

1. Plastic!What comes in your mind?
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.
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2. Plastic
Good or Bad ? • Global Plastic Problems and Why is it ?
What are Single-use
Plastic ?
• Pet Bottles
• Wrappers
• Polyethene bags
50 %
Single –Use Waste
Plastic
Reuse
Recycle
Reduce

3. PLASTIC PRODUCTS
Kathmandu University, Nepal
Design and Production
Presentation on
Presented By:
Anamika Pokharel
Nirajan Ghimire
Injection Molding

4. Raw Materials
Product and
Mold Design
Mold
Manufacturing
Machines
Markets
Plastic Products
Components
1

5. Plastic Product types of Mold ?
Injection
Molding
Rotational
Molding
Blow
Molding
Extrusion
Molding
2

6. Product Development Steps
Injection Molding
Machines
Mold
Raw Materials
Products
3

7. Product Development Steps
Blow Molding
4

8. Injection Molding : Plastic Products
• Mold Design
• Mold Machining
• Injection Molding Machine
• Molding Defects
• Plastic Raw Materials
Injection Unit
Clamping Unit
Product Design
Core and Cavity
Sprue, Runner and Gate
Ejection and Cooling Unit
Topic Covered
Materials
EDM, CNC& Milling
Blister, Flash Burnout
Wrapping & Weld Lines
Voids & Color stress
Circular and flow marks
Types & Properties
5

9. 6
13%
47%
14%
8%
11%
7%
Plastic Products Market Share
White goods, construction
Packaging
Auomotive parts
technical parts
Electronics and telecommunicaions
Medical, pharmacuitical and optical product
In North America and Europe,
Injection molding is used to
process > 10million
tons(10billion KG ) of polymers
per year
Packaging
Injection Molding : Plastic Products
Advantages
• Parts can be produced at high production rates
• Large volume production is possible
• Relatively low labor cost per unit is obtainable
• Parts require little or no finishing
• Many different surfaces, colors, and finishes
are available, Good decoration is possible
• For many shapes this process is the most
economical way to fabricate
• Process permits the manufacture of very small
parts which are almost impossible to fabricate
in quantities by other methods
• Parts can be molded with metallic and non-
metallic inserts

10. Injection Molding
Pressure should be constant till the material is hardened
and is ready to be removed from the mold
7
Injection molding (IM) technology
consists of:
• Heating thermoplastic material from the
machine component called the hopper to a
heated chamber in order to melt
• Forcing this melted plastic into a steel mold
by screw, where it cools and solidifies
• Polymers that are capable of being brought
to a state of fluidity can be injection-
molded.
• Polymers can be divided into two
categories:
1. Thermoplastic
2. Thermosetting

11. Injection Molding Raw Materials
• ABS
• HDPE
• Polypropylene(PP)
• LDPE
• Polyethylene (PE)
• Polycarbonate
• Polyamide (Nylon)
8

12. Injection Molding Raw Materials
Heat deflection temperature:
• Temperature at which a thermoplastic
can be operated under load
• This is the temperature at which a
simply supported beam specimen of the
material, with a centrally applied load,
reaches a predefined deflection
Raw materials :
PP + LDPE (color) +
Master batch (strength)
9

13. Injection Molding Raw Materials 10
Additive Function Examples
Filler increase bulk density calcium carbonate, talc,
limestone
Plasticizer improve processability, reduce
product brittleness
phthalate esters,
phosphate esters
Antioxidant prevent polymer oxidation phenols, aromatic
amines
Colorant provide desired part application
color
oil-soluble dyes, organic
pigments
Flame retardant reduce polymer flammability antimony trioxide
Stabilizer stabilize polymer against heat or
UV light
carbon black,
hydroxybenzophenone
Reinforcement improve strength E-glass, S-glass, carbon,
Kevlar fibers

14. Injection Moulding Machine Types
• Hand Injection Moulding M/C
• Plunger type Injection
Moulding M/C
• Reciprocating Screw Type
Injection Moulding M/C
11
Important components
• Clamping Unit
• Ejection Unit
• Hopper
• Screw

15. Injection Molding Machine
Clamping
Unit
Mold
Control
System
Output
Product
Hopper
Screw
Ejection
System
12

16. Injection Molding Machine Size
• Injection units are usually rated with two
numbers:
1. First rating No.: Shot capacity
2. Second rating number: plasticizing rate
• Shot capacity: max volume of polymer
that can be displaced by one forward
stroke of injection plunger or screw.
• recommended shot sizes: 20 to 80% of
rated capacity.
Plasticizing rate: amount of material that can be softened into a molten
form by heating in the cylinder of machine in a given time.
• It is usually expressed as No. of pounds of polystyrene material that
the equipment can heat to molding temperature in one hour
13

17. Reciprocating Screw
• The feeding zone
• The compressing (or
transition) zone
• The metering zone
Injection Molding Machine 14

18. Injection
• Plasticizes the material by reciprocating
Screw
• Injects the molten material to a closed
mold via a channel system of gates and
runners.
• Cools the Mold
• Refills the material for the next cycle
• Ejects the Product
• Closes the Mold for further cycle
Injection Molding Process 15
How plastic product
were developed?
How Injection Molding
Process Works?

19. Machine operation sequence
The mould closes and the screw
begins moving forward for injection
The cavity fills as the reciprocating
screw moves forward, as a plunger
Injection Molding
1
2
16

20. Machine operation sequence
The cavity is packed as the screw
continuously moves forward
The cavity cools as the gate
freezes off and the screw begins
to retract to plasticize material for
the next shot
Injection Molding
3
4
17

21. Machine operation sequence
The mold opens for part ejection
The mold closes and the next
cycle begins
Injection Molding
5
6
18

22. Injection Molding Cycle
Stages of injection molding:
1. Injection or filling
2. Cooling
3. Ejection and Resetting
19

23. Injection or Filling Stage
• Forward stroke of plunger to facilitate flow of molten material from the heating
cylinder through nozzle and into mold.
• Gradual increase in pressure.
• As soon as cavity is filled, pressure increases rapidly, and packing occurs.
• During packing part, flow of material continues, at a slower rate, to account for
any loss in volume of material due to partial solidification and shrinkage.
• After packing, injection plunger is withdrawn and pressure in mold cavity begins
to drop.
• At this stage, next charge of material is fed into the heating cylinder in preparation
for next shot.
Injection Molding Cycle 20

24. Cooling Stage
• Cooling starts from 1st rapid filling of cavity and continues during packing and then following
withdrawal of the plunger, with the resulting removal of pressure from the mold and nozzle area.
• Upon pressure removal, gate of mold may still be relatively fluid.
• Because of pressure drop, there is a chance for reverse flow of material from mold until material
adjacent to the gate solidifies and the sealing point is reached.
• Reverse flow is minimized by proper design of gates such that quicker sealing action takes place
upon plunger withdrawal.
• Following the sealing point, there is a continuous drop in pressure as material in cavity continues to
cool and solidifies in readiness for ejection.
• Length of sealed cooling stage depends on:
1.wall thickness of part
2.material used
3.mold temperature
• Because of low thermal conductivity of polymers, cooling time is usually the longest period in the
molding cycle.
Injection Molding Cycle 21

25. Ejection and Resetting Stage
• During this stage:
1.mold is opened
2.part is ejected,
3.mold is then closed again in readiness for next cycle to begin.
• Rapid movements may cause:
1.undue strain on the equipment
2.damage the edges of the cavities
• Adequate time must be allowed for mold ejection.
• This time depends on part dimensions
• For parts to be molded with metal inserts, resetting involves reloading of inserts
into mold. After resetting, mold is closed and locked, thus completing one cycle.
Injection Molding Cycle 22

26. • Clamp unit has three functions:
1. open and close mold halves
2. eject the part
3. hold mold closed with sufficient force to resist melt pressure inside mold as it
is filled
• Required holding force: 30 to70 MN/m2 of projected area of part
• Magnitude of initial opening force required depends on:
1. packing pressure
2. Material
3. part geometry (depth and draft)
• is approximately equal to 10 to 20% of nominal clamp force.
Injection Molding Machine
Clamp Unit
23

27. Injection Molding Machine
Clamp Unit
Two common types of clamp designs:
1. Linkage or toggle clamp:
• very fast closing and opening actions
• lower in cost than alternative systems
• clamp force is not precisely controlled
2. Hydraulic clamp units:
• long term reliability
• precise control of clamp force
• relatively slow and expensive compared to toggle
clamp systems.
• Force required to eject the part depends on:
1. Material
2. part geometry
3. packing pressure
• less than 1% of nominal clamp force
24

28. Calm down
We are half way out

29. Injection Mold
25

30. Dr. Mohammad Abuhaiba
Injection Mold
1. Fixed Clamping Plate
2. Runner Stripper Plate
3. Cavity plate
4. Movable Cavity Plate or
Cavity plate
5. Back up Plate
6. Spacer Block
7. Ejector retainer plate
8. Ejector Plate
9. Movable Clamping Plate
Components
26

31. • Mold basically consists of two parts:
1. a stationary half (cavity plate)
2. a moving half (core plate)
• Parting line: separating line between the
two mold halves
• The injected material is transferred
through a central feed channel, called the
sprue.
• In multi-cavity molds, sprue feeds
polymer melt to a runner system.
Injection Mold
Most common Types of molds:
1. Two-plate molds
2. Three-plate molds
3. Side-action molds
4. Unscrewing molds
27

32. • Core plate holds the main core.
• Purpose of main core is to establish the inside configuration of
the part.
• The core plate has a backup plate.
• Backup plate in turn is supported by pillars against the U
shaped structure known as the ejector housing, which consists
of the rear clamping plate and spacer blocks.
• The U-shaped structure, which is bolted to core plate, provides
the space for the ejection stroke.
Injection Mold Design 28

33. Injection Mold Design
Cavity ? Core ?
Injection Mold is an assembly of parts
containing within it an impression into
which plastic material is injected and
cooled
Impression is defined as the part of mold
which imparts shape to the molding
Impression consist of:
• Cavity
• Core
Cavity: Hollow portion of the Mold, gives
the molding its external form
Core: Projected portion of Mold, forms
the internal shape of molding
Cavity
Core
29

34. Injection Mold Design Cavity ? Core ?
Simple Concept: Mold
Cavity
Core
Cavity Core
30

35. Injection Mold Design
Core Plate and
Cavity Plate
Core Plate: Plate or assembly
which contains the core
Cavity Plate: Plate or assembly
which contains the cavity
31

36. Injection Mold Sprue 32

37. Injection Mold Sprue
33

38. Sprue Bush
During the injection process, plastic materials is
delivered to the nozzle of the machine as a
melt; it is then transferred to the impression
through passage
This passage is tapered hole within a bush. The
material in this passage is termed as sprue and
the bush is called sprue bush
Feed System for single impression mold
34

39. Sprue Bush
• Is a connection member between the machine nozzle
and the mold face, and provides a suitable aperture
through which the material can travel on its way to
the impression or to the start of the runner system.
• Sprue bushes are made from 1.5% Nickel Chrome
steel and should always be hardened.
• The internal aperture of the sprue bush has between 2
to 4° included taper, which facilitates the removal of
the sprue from the mold at the end of the molding
cycle
Spherical seating
Flat seatingTypes of Sprue Bush
• Spherical seating
• Flat seating
35

40. Sprue Design 36

41. Injection Mold Design
Runner and Gate
• Runner is a channel machined into the mold
plate to connect the sprue with the gate to the
impression
• Gate is a channel or orifice connecting the
runner with the impression
• Feed system is a flow way which connect the
nozzle of the injection molding to each
impression
Feed system for multi impression mold
37

42. Unbalance Sprue Material Design 38

43. Unbalance Sprue Material Design 39

44. Balance Sprue Material Design
Balance Sprue Material Design
40

45. Balance Sprue Material Design 41

46. Types of Gate
42
• Sprue gate – this gate is suitable for single
chamber parts and thick sections because it can
hold pressure well. The disadvantage of this gate
is that a mark is left on top.
• Pin gate – for parts that have multiple cavities or
chambers. It is usually located at the top.
• Tunnel gates – also known as submarine gates, it can
be placed at the side or movable parts of the mold. It
is automatically cut as the mold opens.

47. Types of Gate
43
• Sub gate is used for 2 plates molds, the gate point is very
small and location of the gate is choose to be on uncritical
area, the gate can be easily trimmed off along with the action
of injection mold opening, this type of gate is widely
employed for automatically plastic products production.
• Fan gate – commonly used for large or flat
plate parts. It is placed at the sides and
manually cut by a cutter.
• Direct gate. Commonly used for single cavity molds, it
required less injection pressure and feeding time is short,
but the disadvantage of this type gate is difficult to remove
and there would be big gate marks left. This gate type is
common to see in house appliance and consumer product,
such as bins, printers, washing machine, TV etc.

48. Injection Mold Cooling
One fundamental principle of Injection Molding is
that hot material enters the mold, where it cools
rapidly to a temperature at which it solidifies
sufficiently to retain the shape of the impression
Factors deciding operating temperature of mold:
• Type and grade of material to be molded
• Length of within the impression
• Wall section of the molding
• Length of the feed system. Etc.
It is often found advantageous
to use a slightly higher
temperature than is required
just to fill the impression, as
this tends to improve the
surface finish of the molding
by minimizing weld lines, flow
marks and other blemishes
44

49. Injection Mold Cooling
• To maintain the required temperature differential
between the mold and plastic material, water or
other fluid is circulated through holes or
channels within the mold.
• The holes or channels are termed flow ways or
water ways and
• The complete system of flow ways is termed the
circuit or cooling circuit
Cooling Circuit
45

50. Injection Mold Cooling
Cooling Integer type mold plates
• Cooling Integer type cavity plate
• Cooling Integer type core plate
Cooling Insert – Bolster Assembly
• Cooling Bolster
• Cooling Insert
o Cooling Cavity Inserts
o Cooling Core Inserts
Cooling Circuit Classifications Different types of cooling Integer type cavity
plate are;
1. Simple circuit
2. U-Circuit
3. U-Circuit with interconnecting milled
channel
4. U-Circuit with interconnecting milled
channel
5. Rectangular circuit
6. Z – Circuit
46

51. Injection Mold Cooling
1. Simple Circuit 2. Rectangular Circuit
47

52. Injection Mold Cooling
3. U-circuit with interconnection milled
channel 4. Z-Circuit
48

53. Injection Mold Cooling
5. Angle hole System 6. Baffled straight hole system
49

54. Injection Mold Ejection System 50
• Pin Ejection
o Cylindrical pins are used for ejection purpose, in case of square and
rectangular components minimum fore pins
o a the four corners are required and in case of cylindrical component
minimum
o three pins at 120° apart is required based on the component profile,
size and area of ejection the number of pins to be increased.
o visible ejection marks will be there on component
•
• Sleeve Ejection
o This type of ejection is preferred for only to cylindrical cores and core
has to be fixed in bottom plate.
o ejection is limited to cylindrical core due to manufacturing constrains,
when ejection assembly is moved the sleeve will slide over the core
and eject the component.
o No visible ejection marks will be there on component

55. Injection Mold Ejection System 51
• Stripper Plate ejection
o This ejection is preferred for component with larger area, an
additional plate (stripper) will be provided in between core plate
and cavity plate.
o In order to avoid flash the stripper plate will be in contact with
cavity plate and gap is maintained between cavity and core plate.
o No visible ejection marks will be there on component
• Air Ejection
o This method is used to actuating the ejection pin fitted in
core using compressed air.
o Retraction of ejection pin in core is by spring.

56. Injection Mold Ejection System 52
Blade Ejection
o This type of ejection is preferred for thin rectangular cross
sections
o rectangular blades will inserted in cylindrical
pins or cylindrical pins will be machined to rectangular
cross section till ejection length
o for easy accommodation of ejection pin head in counter
bore provided in ejection plates
By Rotation of Core (Internal Threaded Components)
o This method of ejection is required for threaded
components
o component is automatically ejected by rotating the
core insert

57. Calm down
Almost Done!

58. Mold Types – three-plate mold
• Consists of:
1. Stationary or runner plate, which
contains sprue and half of runner
2. Middle or cavity plate, which contains
other half of runner, gates, and cavities
and is allowed to float when mold is
open
3. Movable or core plate, which contains
cores and ejector system.
• Facilitates separation of runner system and
part when mold opens
Injection Mold 53

59. • Three main plates
• Runner is contained completely in the fixed plate,
which is heated and insulated from the rest of the
cooled mold.
• Runner section of the mold is not opened during
molding cycle.
• There are no side products (gates, runner, or sprues)
to be disposed of or reused
• There is no need for separation of gate from part
Injection Mold
Mold Types – Hot runner system
54

60. • Used in molding components with external
depressions or holes parallel to the parting plane.
• Undercuts prevent molded parts from being
removed from cavity in axial direction.
• The usual way of providing the side action
needed to release the part is with side cores
mounted on slides.
• These are activated by angle pins, or by air or
hydraulic cylinders that pull the side cores
outward during opening of the mold.
• As the two halves of the mold move apart during
mold opening, the slide, which is mounted on the
moving plate, is forced to move sideways by the
angle of the pin.
Injection Mold
Mold Types – Side-acting Molds
55

61. Injection Mold
Parting Lines
56
• “parting line” refers to a line on the part that is created
where the two halves of the mold come together.
• results is a faint, sometimes unnoticeable line on the part.
• This line usually doesn’t affect the overall shape or
dimensions of the part, but can be visually noticeable to
varying degrees, depending on mold finish, material type,
material color and processing parameters.
• The parting line will usually be determined by the geometry
of the part.
• The mold designer’s goal is to choose a location for the
parting line that will create the most robust tooling design,
while at the same time making it less noticeable.

62. Injection Mold Manufacturing
How to make Mold ?
Machining
• Milling
• CNC
• EDM
• Polishing
• Mold material
57

63. Injection Mold Manufacturing
Selection Criteria Selection Criteria
• Type of Mold Type of Mold
• Mold life i.e. Number of accepted Mold life
• i.e. Number of accepted components produced over its
components produced over its working life working life
• Ability to take mirror finish (High Ability to take mirror finish (High
degree of polishibility) degree of polishibility)
• Good machinability
• Good hardenability Good hardenability
• Low distortion during Heat Low distortion during Heat treatment
treatment
• Corrosion resistant Corrosion resistant
• High compressive strength High compressive strength
• High toughness
59

64. Injection Mold Manufacturing
Mould Design Requirements Role and responsibility of
a Mould Designer
• Ensures that the mould is fabricated as easily and as
economical as possible by the mould maker
• Specifies best mould steels with optimum hardness required for
different optimum mould parts
• Selection of standard parts such as such as guide pillars, Guide
bushes, ejector pins etc, standard mould bases reduces time and
cost
• Helps in better planning, prompt mould delivery as well as
minimizing initial machining cost and material losses
60

65. Injection Mold Manufacturing
Some of the commonly used
steels are:
• Pre hardened Mould Steels
• Through hardened mould steels
• Corrosion resistant mould steels
• Plain carbon Steels
61
Carbon Steel Carbon Content
Low Carbon Steel 0.1 – 0.3 % 0.1 – 0.3 %
Medium Carbon Steel 0.3 – 0.7 % 0.3 – 0.7 %
High Carbon Steel 0.6 – 1.5 %
ALLOY STEELS
More stronger, tougher and resistant than carbon steel
Sufficient formability, ductility and weld ability
Corrosion and abrasion resistant
Typical application are
Structural applications
• HIGH CARBON HIGH CHROMIUM STEEL
• STAINLESS STEEL

66. Injection Mold Manufacturing
Machining/ Milling / CNC / EDM
62

67. Moulding Faults & Remedies
• Sink
• Jetting
• Splay Marks (Silver Streaking, Splash Marks)
• Burn Marks
• Blush
• Poor Weld Lines (Knit Lines)
• Short shot
• Flash
• Cracking
• Blister
• Brittleness
• Black specks
• Warpage
63

68. Sink Marks
Depression in a moulded part caused by shrinking or
collapsing of the resin during cooling.
Moulding Faults & Remedies
Resin feed inadequate
Improper mould design.
Parts cool too rapidly
Rib section in part too wide.
Temperature of mould surface opposite rib too hot.
Entrapped gas.
Nozzle too restrictive,
land length too long.
Sink Marks Problems • Pressure too low.
• Mould temperature too low or high
• Stock temperature too high
• Gate too small
• Improper gate location
• Nozzle and metering zone temperatures too high.
• Excessive cooling time in mould
• Unbalanced flow pattern.
• Bad check valve.
64

69. Jetting
Turbulence in the resin melt flow caused by undersized
gate, abrupt change in cavity volume, or too high
injection pressure.
Moulding Faults & Remedies
Jetting Problems
• Excessive injection speed.
• Melt temperature too high.
• Melt temperature too low.
• mould Temperature too low.
• Nozzle opening too small.
• Gate and length too long.
• Sprue, runner, and/or gate size too small.
• Nozzle heating band malfunction.
• Inefficient gate location.
65

70. Splay Marks (Silver Streaking, Splash
Marks)
• Marks or droplet type imperfections formed on the
surface of a finished part.
Moulding Faults & Remedies
• Obstruction in nozzle.
• Screw rpm too high.
• Back pressure too low.
• Melt temperature too high.
• Nozzle too hot.
• Nozzle too small.
• Gates too small.
• Sprue too small.
• Insufficient venting.
Problems • Burr in runner or gate.
• Cracked mould.
• Trapped volatiles.
• Excessive moisture.
• Resin contaminated.
• mould cavity contamination.
• Excessive shot size.
66

71. Burn Marks
Black marks or scorch marks
on surface moulded part;
usually on the side of the part
opposite the gate or in a deep
cavity.
Moulding Faults & Remedies
Blush
Discoloration generally
appearing at gates, around
inserts, or other obstructions
along the flow path. Usually
indicates weak points.
Poor Weld Lines
(Knit Lines)
Inability of two melt fronts
to knit together in a
homogeneous fashion
during the moulding
process, resulting in weak
areas in the part of varying
severity.
67

72. Plastic Products Markets
Injection molding products: 19.3%
68
Plastic Raw materials tax: 10%
Machine tax: 15%
Plastic product tax: 56%
No. of Plastic industries in Nepal: 250+
Major product: PVC pipe, PET bottles,
Household utensils, polyethene bag,
hardware accessories
Make your Plastic product and Sell

73. Thank You!
You are amazing listeners

74. Any
Questions
?
.
.
.
.
.
Sprue, Runner, Gate
Ejection System
Cooling system
Screw
Defects
Core, CavitiesProduct design
Material (ABS)