Compression molding

Material used

  • Polyester
  • Polyimide (PI)
  • Polyamide-imide (PAI)
  • Polyphenylene sulfide (PPS)
  • Fiber-reinforced plastics
  • Melamine formaldehyde
  • Preheating up to temp 70-80dc to remove moisture
  • Pressure of 150 to 211kg/cm2 maintained (3000psi)
  • Temp of mold cavity held up to 150-200dc


  • Satellite antenna dishes
  • Architectural lighting components,
  • Electric motor parts,
  • Engine components
  • Electrical components
  • Electric power transmission parts,
  • Fuel cell components,


  • Low initial setup costs and fast setup time
  • Heavy plastic parts can be molded
  • Complex intricate parts can be made
  • The Good surface finish of the molded parts
  • decay almost seldom element as to with other processes
  • The molding process is cheaper as compared to injection molding


  • Creation quickness is not up to injection molding specification

Transfer molding

Step 1

The powdered plastic is placed into a portion of the mold called the pot. The plunger on the top-most part of the mold fits into the pot.

Step 2

The mold is closed up and under hydraulic pressure, the plastic is forced through the small hole into the cavity. The mold is held while the plastic cures.

Step 3

The plunger is raised up.

Step 4

Mold is not closed and the section can be ejected. The gate may need to be trimmed.

Material used

  • Generally, thermoset plastic(such as epoxy-polyester phenol-formaldehyde vinyl ester silicon)


  • Integrated circuits,
  • Plugs, connectors, pins, coils, and studs.
  • Radio and television cabinets
  • Car bodyshells


  • Fast setup time and lower setup costs
  • Low maintenance cost
  • Plastic parts with metal inserts can be made
  • Design flexibility
  • Dimensionally stable
  • Uniform thickness of the part
  • Large production rate


  • The transfer molds are more complex and more costly to build
  • Loss of material as scrap
  • Air can be trapped in the mold
Plastic materialShrinkage




A,B,S0.4 to 0.60.004 to 0.006
Polystyrene(PS)0.5 to 0.60.005 to 0.006
Nylon(PA)1.0 to 2.50.01 to 0.025
Acrylic(PMMA)0.4 to 0.80.004 to 0.008
Polycarbonate(PC)0.6 to 0.80.006 to 0.008
Polyacetal(POM)1.5 to 2.50.015 to 0.025
Polypropylene(PP)1.0 to 2.00.015 to 0.020
Polyethylene(LDPE)1.5 to 3.00.015 to0.030
Polyethylene(HDPE)1.5 to 3.00.015 to0.030
Poly vinyl chloride(PVC)0.1 to 0.20.001 to 0.002


Plastic injection molding summary

Plastic injection molding process

  • The molding tool
  • Clamping
  • Injection
  • Step by step process

Plastic types and applications

  • ABS
  • POM
  • PA6&PA66
  • PC
  • PP
  • PBT
  • PMMA

Common molding defects

  • Sink marks
  • Voids
  • Weld lines
  • Short shots
  • Burn marks
  • Flash
  • Flow lines
  • Warping
  • Mold stick

Molding inspection guide

  • Tool design
  • Ejector pins
  • Machine set-up
  • Inspection equipment
  • Sample report


  • Plastic injection molding


  • Compression and transfer molding