1. Forming Process of Plastic Molding
Chapter III
Forming Process of Plastic Molding
3.1 Injection molding process
3.2 Compression molding process
3.3 Transfer molding process
3.4 Extrusion molding process

2. 3.1.1 Principles of Injection Molding
Clamping device
Injection device
right angle connected set
Demolding mechanism
Rod
Cylinder
Heater
Screw
funnel
Motor
Prevent reflux valve
Injection molding, Mainly used for the molding of thermoplastics
Particles, powdered plastic
Injection machine barrel
Melt
injection
Cooling curing
Plastic parts

3. 3.1.2 Injection Molding Equipment
Clamping unit
Injection unit
1. Main function of injection molding machine
Eject
Mold clamping action
holding pressure and feeding
Injection Plastic fluid into the cavity under certain pressure and speed
Melt plastic to fluid state

4. 3.1.2 Injection Molding Equipment
2. Classification of injection molding machine
Plasticizing: the process that putting the plastic into the barrel heated to flow state and having a good plasticity
Can be classified as horizontal, vertical and angle injection molding machine according to their shape
Injection molding machine can be classified as: plunger type and screw type injection molding machine according to the plasticizing way

5. 3.1.2 Injection Molding Equipment
2. Classification of injection molding machine

6. 注射成型设备
Horizontal-type
Vertical-type
Angle-type

7. 3.1.2 Injection Molding Equipment
3.Plunger type injection molding machine
funnel
Heater
nozzle
Plunger
Heating barrel
shunt
Cooling water

8. 3.1.2 Injection Molding Equipment
Large part of the pressure used in the compaction of solid plastic and overcome the plastic barrel friction
② maximum injection volume is limited:
The maximum injection volume depends on the plasticizing capacity of the barrel (related to the area with plastic heat) and the piston diameter and stroke
① the plasticizing uneven:
Plastic shuttle heat transfer depend on the barrel wall and the shunt, the plunger to promote plastic mixing, easy to result in the plasticizing uneven phenomenon
3. Plunger type injection molding machine
③ injection pressure loss:
Shortcomings of the plunger-type injection machine:

9. 3.1.2 Injection Molding Equipment
3.plunger type injection molding machine
Shortcomings of the plunger type injection machine:
④ injection speed is uneven:
From the plunger into contact with plastic to compaction plastic, injection speed is gradually increased
⑤ easy to produce a laminar flow phenomenon and the barrel difficult to clean

10. 3.1.2 Injection Molding Equipment
4 screw injection molding machine

11. Screw injection machine molding cycle
3.1.2 Injection Molding Equipment
4. screw injection molding machine
Screw injection machine molding cycle
Clamping
Injection
holding
pressure
cooling
Mold
opening
eject
Screw rotating
The advantages of screw injection molding machine:
With the rotary motion of the screw, the material within the heat evenly plasticizing capacity.

12. 3.1.2 Injection Molding Equipment
4 screw injection molding machine
advantages of screw injection molding machine:
Less dwell time and decomposition reduced
Lower heat loss, lower injection pressure molding
Short cycle times, high efficiency, production process can be automated
Can form complex shapes require high dimensional accuracy and inserts available

13. 3.1.2 Injection Molding Equipment
Screw compared with the rotating action of the piston, resulting in contributing (Ft), allows materials in the spiral groove between the mixing role, increasing the plasticizing capacity.
Screw injection machine and plunger-type injection molding machine
plunger - type
screw - type

14. Testing of raw materials,
Injection Molding Process
Injection process
Post-processing
Pre-processing
Testing of raw materials,
dyeing and dry
Mold cleaning
Insert preheating
Barrel clean-up
Annealing
Humidity

15. 3.1.3 Injection Molding Process
1. Pre-processing
Testing of raw materials
Dyeing of raw material
Raw material drying
Mass Volume
Mobility
Moisture and volatile matter content
Shrinkage
Oven drying
Infrared drying
Hot-plate dry
Frequency drying

16. 3.1.3 Injection Molding Process
2 injection process
Testing of raw
materials
Pretreatment
Clamping
Injection
Putting into
the funnel
Packing
Demolding
Load
embedded
parts
Clean-up barrel
Clean up mold
Coating release
agent
Embedded pieces of clean-up,
warm-up
Pre-plasticizing
Post-processing of plastic parts
Cooling

17. 3.1.3 Injection Molding Process
3 post-treatment
Infrared or circulating hot air oven or liquid medium (mineral oil, paraffin) , on a certain temperature for some time, and then slowly cooled
Put molded plastic parts into hot water ( ℃), isolated from the air, to achieve moisture balance. Humidity slow cooling to room temperature.
Annealing:
Humidity:
Annealing temperature: above the use temperature of 10 ~ ℃ below the phase transition temperature of 10 ~ 20 ℃

18. 3.1.4 Injection Molding Process parameters
Temperature
Pressure
Time
(Molding cycle)

19. 3.1.4 Injection Molding Process parameters
1 Temperature
① barrel temperature
② Nozzle temperature
③ mold temperature
—— high internal stress, easy to cracking, poor surface quality
Temperature too high
Temperature too low
Slightly lower than the barrel temperature: to prevent “salivation phenomenon”; not too low.
When the scope of Tf (Tm) ~ Td is narrow, the barrel temperature should take lower values
Barrel back temperature is the lowest, the front is the highest
Tf (Tm) ~ Td, to ensure the normal flow of plastic melt, no deterioration or decomposition
—— long Molding cycle, warpage after ejection, affect dimensional accuracy.

20. 4. Product Internal stress 5. Product finishing 6. cooling time
1.Plastic flowability
2. Filling pressure
3. Productivity
4. Product Internal stress
5. Product finishing
6. cooling time
7. Product density or crystallinity
8. Mold shrinkage rate
9. Product deflection
Effect of Mold temperature for molding parts
tc<Tg为骤冷；
tc≈Tg中速冷却；
Tc>Tg很多为缓冷。
Usually, the majority of mechanical strength of molding product increased with the mold temperature, but the elongation and impact strength decreased.

21. 3.1.4 Injection Molding Process parameters
Determination of mold temperature
(1) mold temperature is usually below Tg or are unlikely to cause the temperature of the workpiece deformation, demolding temperature slightly higher than mold temperature.
(2) High viscosity (such as polycarbonate, polysulfone) should choose high mold temperature.
Low viscosity (such as PE, PA) should choose lower mold temperature
(3) consider the mold temperature influence for molecular orientation, crystallization, internal stress and physical properties.
Lower Mold temperature: more obvious orientation effects, high internal stress, not easy to crystallization
Higher mold temperature: easy to crystallization

22. ① plasticization pressure
Injection Molding Process parameters
2 Pressure
① plasticization pressure
Also known as back pressure (The pressure exerted on the melt of the head Screw when the screw rotation), can be adjusted by relief valve
② injection pressure
Exerted by plunger or screw head on plastic melt, generally from 40 ~ 130MPa, can overcome melt flow resistance and ensure filling rate
Injection pressure is determined by: plastic type, type of injection machine, gating system, wall thickness, flow length, etc.

23. 3.1.4 Injection Molding Process parameters
2 Pressure
③ Packing pressure
To continue exert pressure after the plastic melt filling into the mold cavity. The role is to make the melt curing under pressure, feeding shrinkage
generally less than or equal to the injection pressure
High packing pressure is easy to produce flash and internal stress, while low packing pressure cause inadequate filling

24. 3.1.4 Injection Molding Process parameters
—— Completed the time required for injection molding process.
3 Molding time
Molding cycle or the total cycle
Molding cycle
Filling time
Injection time
Closed mold cooling time
Other times
Dwell time

25. Injection Molding process window
Chalking
Decomposition
flashing
Material temperature
Short shot
Bad surface
Forming difficult
Injection pressure

26. 3.2 Compression Molding Process

27. 3.2.1 Compression Molding Principle
Melt forming
Compression mold
Compression molding press
Compression molding products

28. 3.2.1 Compression Molding Principle
1. molding method
——Also known as compression molding or suppress. Mainly used for the molding of thermosetting plastics, thermoplastics can also be used for molding.
Compression
molding
Powder, granular or fiber material
Placed in cavity of the molding temperature
Clamping pressure
Forming curing

29. 3.2.1 Compression Molding Principle
2. compression molding characteristics
⑴Plastic added directly into the cavity, the feeding chamber is an extension of the cavity
⑵ Mold is fully closed when plastic parts are final shape
⑶ pressure punch directly to the plastic
Difficult to obtain accurate dimensional, especially high-precision plastic parts
Not suitable for plastic parts with fine, easy-off inserts and more embedded pieces of plastic parts
Easy to forming polymer with more fiber filler

30. 3.2.1 Compression Molding Principle
2. compression molding characteristics
⑷ simple operation, and simple mold structure
No gating system, less material consumption
Can suppress the large flat plastic parts or a suppression of multiple plastic parts
Less parts shrinkage, small deformation, to the performance of uniform and high strength.
(5) production cycle is long and inefficient
Multi cavities

31. 3.2.2 Compression Molding Equipment
1. Molding equipment effect
2. Types of molding equipment
By Transmission
Mechanical press：Spiral press
Hydraulic press：Hydraulic press and hydraulic press
Provide necessary pressure
Mold top piece
Clamping
Some cases to pass heat required 　
为了保证压缩模塑的正常进行，应选用适当的压机，并校核模具与压机的关系

32. 3.2.3 Compression Molding Process
Compression molding circulation
Pre-processing
Molding process
post-processing
Preheat and dry
Preload
Inserts placed
Clamping
Venting
Mold cleaning
Stress Relieving
Modified polishing
Special treatment
demolding
Packing and curing
Feeding

33. 3. 2.3 Compression Molding Process
To facilitate operations and improve the quality of plastic parts，first pre-molded powder, fibrous plastic powder in the pre-press, pressed into a certain weight, the shape of the same ingot
1. Preparation before molding
⑴Preload
①Preloading method
②Advantages of using pre-ingot
Feeding fast and accurate
Reduce compression ratio, reducing the size of cavity, less air content for better heat transfer and little bubbles

34. 3.2.3 Compression Molding Process
Complex production process, not used often
1. Preparation before molding
② advantages of using pre-ingot
Avoid feeding process dust emissions and improve working conditions
Preheating temperature can be increased and shorten the preheating and curing time
ease of forming complex or with a small insert plastic parts

35. 3.2.3 Compression Molding Process
1. Preparation before molding
③Compression molding powder
④Preload conditions
The best particle size
Compression ratio (plastic / ingot) should be about 3.0
Containing lubricants
Pressure:Pressure range of 40 ~ 200MPa
Temperature : Room temperature or 50 ~ 90 ℃ preload
Principles:The density of ingot up to 80% of the maximum density of plastic parts

36. 3.2.3 Compression Molding Process
Preparation before molding
⑵Preheat and dry
purpose of heating before Plastic molding :
Plastic molding before heating:
High-frequency heating
Infrared preheating
Oven preheating
Hot plate to preheat.
Provide hot plastic
Remove moisture and volatile matter
Dry
Warm-up

37. 3. 2.3 Compression Molding Process
As the conductive part of the plastic parts or plastic parts and other parts connected to parts.
1. Preparation before molding
⑶ Inserts placed
Inserts placed requirements in the correct position, smooth
Inserts---
Commonly used insert bushings, screws, nuts, terminal, etc.
Large inserts in the mold mounted on the press after the first warm-up

38. 3.2.3 Compression Molding Process
⑴ Feeding
① the key of feeding is the feedstock
② The quantitative methods:
③ reasonable stacking plastic, Stowage of powder or pellets to be high in the middle surrounded by low, to facilitate gas emissions.
Volumetric method: Convenient but not very accurate
Gravimetric method: Accurate, trouble
Piece-rate method: Pre-ingot, counting

39. 3.2.3 Compression Molding Process
② punch touches the plastic: slow down the mold speed (venting)
① Before punch touches the plastic: to speed up the clamping speed (reduce cycle time, avoid plastic premature curing)
clamping after Feeding, the clamping time ranging generally from a few seconds to tens of seconds.
The clamping process is divided into two parts:

40. 3.2.3 Compression Molding Process
Clamping pressure to a certain pressure, immediate relief, punch up slightly, 1-3 times
2. Molding process
⑶ exhaust
Exclusion of moisture and volatiles into a gas and chemical reaction by-products, so as not to affect the performance and surface quality of plastic parts
good flowability Plastic use late pressure method, the pause of 15 to 30s from the punch and plastic come into contact with the die completely closed process
Plastic parts with a small metal inserts are not using the exhaust operation, in order to avoid displacement or damage
Methods:
Objective:

41. 3.2.3 Compression Molding Process
Cross-linking reaction to the extent required to maintain a certain time, under the molding pressure and temperature.
Time from closed pressurized to demolding
2. Molding process
Packing and curing
undercuring
overcuring
Inadequate
Over
Pressure the length of time is based on the plastic type, preheating of the impact of plastic parts shape and degree of compression.
Dwell time:
Curing phase of the request:
Degree of cure

42. 3.2.3 Compression Molding Process
(5) demolding
Complex plastic parts under pressure, cooled to a certain temperature after demolding
Plastic parts mold release method:
Manually demolding outside of mold
automatically demolding

43. 3.2.3 Compression Molding Process
3 Molded post-processing
Copper shovel or compressed air to clean up, so as not to damage the mold appearance
⑴ mold cleaning
⑵ plastic to stress
Cooling in a plastic mold
After ejection put into a certain temperature, the oil pool or in the oven slowly cooled or annealed
Large, thick-walled parts
Easily deformable thin-walled

44. 3.2.3 Compression Molding Process
3. post processing
⑶ modified polishing
⑷ special treatment
Secondary processing: moisture and decorating (electroplating, spraying)
Go to flash, burrs, surface finish

45. Compression Molding Circulation
Check plastic
quality
Preload, preheating
drying
weighting
material
Cleaning inserts,
insert preheating
Cleaning pressure mode
Coating off the mold agent
embedded
parts
Plus
materials
Clamping Heat
and pressure
Exhaust
Heating relief
Curing
Pressure and
temperature
packing
Mold Relief
demolding
Plastic pieces of
the whole shape
Stress handling
Plastic parts sent
to the next process

46. 3.2.4 Compression Molding Process parameters
Molding pressure (molding pressure)
Molding temperature (molding temperature)
Molding time
To produce high-quality plastic parts, in addition to the mold structure, but also the correct choice of Process parameters. 46

47. 3.2.4 Compression Molding Process parameters
1. Molding pressure
Definition: Punch unit projected area of ​​the parting surface pressure of plastic melt and solidification while compression of plastic parts.
To exert molding pressure for the purpose of:
The mold is closed, to prevent flash
Overcome the force of the plastic molding process for a variety of top mold
The viscous flow state material is solidified under a certain pressure
Plastic filled with cavity 47

48. p = 3.2.4 Compression Molding Process parameters 1. molding pressure
A - punch contact with the plastic part in the projected area of the parting surface (mm)
The formula is:
p =
The formula:
p - molding pressure (MPa)
pb - press from cylinder pressure (MPa)
D - press the master cylinder piston diameter (m)
Molding pressure and the types of plastics, plastic structure, mold temperature and other factors 48

49. 3.2.4 Compression Molding Process parameters
2. Molding temperature
Refers to the compression required for the mold temperature, the quality of the plastic parts, molded in
Thermosetting plastic mold temperature is higher than the mold temperature
Slow hardening, long cycle, lack of hardening; plastic matte finish; physical, poor mechanical properties
Mold temperature
Too high
Resin, the decomposition of organic matter; the outer layer of plastic parts before hardening
High
Short cycle times, increase in productivity
Too low 49

50. 3.2.4 Compression Molding Process parameters
3 Molding time
Plastic in the closed mold curing to harden the required time. With plastic variety, moisture content, plastic parts molding temperature of the shape and size, and compression mold structure, pre-pressure warm-up, molding pressure and other factors.
worse performance
Molding time
Short
Lack of hardening, appearance and mechanical properties, easy to deform
Too long
Under the premise of ensuring the quality of the plastic parts should be sought to shorten the molding time 50

51. 3.3 Transfer Molding Process
3.3.1 Transfer molding principle
Developed in the compression molding of a thermosetting plastic molding method, also known as transfer molding, plastic extrusion molding.
Transfer molding 51

52. 3.3.2 Transfer Molding Characteristics
1. Before feeding, mold closed
4. mold structure is relatively complex, higher manufacturing costs, the molding pressure and complicated to operate, feed consumption more than the compression modulus.
2. Plastic parts flying side of the thin, accurate size, uniform performance and higher quality.
3. Can be molded deep hole complex shape, with a fine or fragile inserts plastic parts.
5. gas is difficult to rule out the exhaust ducts must be set up in the mold. 52

53. 3.3.2 Transfer Molding Characteristics
Or compression molding of powder pre-ingot
Clamping
Squeeze plastic
Curing
Mold
Off mode
Manufactured articles
Pre-heat
Heating
Increase pressure
Paul temperature
Packing
Unloading pressure
Clear mode
And compression molding difference is:
Compression: feeding - Clamping
Pressure Note: Clamping feeding

54. 3.3.3 Transfer Molding Process parameters and Equipment
Less than compression molding method
① mold temperature
Lower 15 ~ 30 ℃ than Compression molding, usually between130 ~ 190 ℃. The feeding chamber and the lower mold temperature is below the temperature of the box
② molding pressure
Loss of pressure by the gating system, to ensure cavity filled with plastic in s.
③ packing time

55. 3.3.3 Transfer Molding Process parameters and Equipment
(2) molding equipment
3.3.4 plastic requirements for transfer molding
a. With good flowability before curing
b. With good curing speed
Such as: phenolic, melamine formaldehyde, epoxy resin, etc.
Ordinary hydraulic press
Special hydraulic machine (dual pressure hydraulic machine)

56. 3.4 Extrusion molding process

57. 3.4.1 Extrusion Molding Process
Feeding port
Thrust bearing
Gear box
Barrel and screw
Heater
Head connector
Drive motor
Base
Cooling system
Extruder

58. 3.4.2 Extrusion Equipment
Control system
Extruder
Extrusion systems, drive system, heating and cooling system, machine body
Head, sizing devices, cooling devices, drawing devices, cutting devices, take-up device
Auxiliary:
Extruder:
Shaping device
Plastic pipe
Head die
Cutting device
drawing device
Extruder
Cooling tank

59. 3.4.3 Extrusion Process Plasticizing Forming Setting
(1) Preparation of raw materials
Dry, purify
(2) Extrusion
preheating-- feeding plastic - melting plasticizing - extrusion
(3) Plastic parts of the setting and cooling
Pipe sizing methods: sizing, sizing ring, sizing plate, etc.

60. 3.4.3 Extrusion Process 3.塑件的定型与冷却 setting way
Plastic parts setting and cooling
Setting plate
Product
Simple sliding setting device
Cooling water inlet
Cooling water outlet
vacuum section
Cooling section
Profile
Vacuum shaping device
The sliding of the co-shaping device
setting way

61. 3.4.4 Extrusion Process parameters
(4) plastic parts of the drawing, coiling and cutting
3.4.4 Extrusion Process parameters
Temperature
Pressure
Extrusion speed
drawing speed
Drawing at different speeds for different plastic parts
Drawing speed is slightly higher than extrusion speed
Cooling the same time, continuous and uniformly lead plastic

62. 3.4.4 Extrusion Process parameters
(1) Temperature
(2) Pressure
Reasonable control of the screw speed, keep the accurate control of the temperature, which can reduce pressure fluctuations
The die temperature should be lower than head temperature, while keep the flowability of plastic
Head temperature should be controlled to prevent plastic thermal decomposition
feed section temperature should not be too high

63. 3.4.4 Extrusion Process parameters
—— drawing speed and extrusion speed ratio, its value is equal to or greater than 1.
(3) Extrusion speed
(4) drawing speed
The amount of material plasticizing per unit time, showing the working ability of a extrusion machine
drawing speed and extrusion rate is equivalent, slightly larger than extrusion speed.
drawing rate

64. Thinking and Practice
Fill in the injection molding process flow diagram
Different characteristics of the screw plunger injection machine
What's the difference of transfer molding and compression molding
What are the extrusion molding Process parameters 64