Injection molding process is basically a process that raw material being melted, being injected and molded as a part, the equipment set could produce from one to hundreds of parts each shot/cycle depending on mold design. Since the cycle time is relatively less and the quality is keep improving, more and more parts are made by plastic and this process nowadays.

Here discuss how the molding equipment works in a molding process cycle, in which we study most are:

• Injection: IMM injects most plastic into mold cavity area, and the injection unit controls screw by speed.
• Holding: IMM will have mold cavity area filled completely and keep the plastic inside cavity area, injection unit controls the screw movement by pressure.

• Injection
  • This is the first step of an injection molding process, and it starts right after the mold closing and clamping force implementation. The screw moves forward to push the plastic out of injection unit/ into mold till the cavity area is almost (<100%) filled.
  • Most of the cavity area shall be filled at a feasible/minimum period of time since plastic begins to cool down after leaving injection unit. (it could be hot runner system if the mold equips the same.)
  • Injection time stands for the time spent by screw moving from metering volume position to switchover position, it represents that how the plastic being injected, and it could be defined by approach discussed in establish molding process.

• Switchover
  • Switchover is the end of injection, IMM change the control of screw movement from speed to pressure. A good switchover position could reduce internal stress of part and lead to stable end position, furthermore, a more stable molding process.

• Holding
  • The purpose of holding is to keep the required amount of plastic inside cavity area by certain amount of pressure (e.g. keep the required amount of plastic inside cavity area by certain amount of pressure) before gate freeze.
  • Part is suggested to be filled completely during start holding.
  • The in-mold pressure is provided by screw; therefore, the movement of screw is controlled by pressure. It defines how the cavity/part is filled completely and it could be defined by approach discussed in establish molding process.

• Cooling
  • The purpose of cooling is to wait until the temperature of plastic at cavity area lower then HDT (see more detail in properties of plastic) to minimize the part deformation after mold open.

• Re-filling
  • After holding, screw stops moving forward. During cooling, screw starts to rotate and retract to let raw material for next cycle to fill the barrel.

• Mold open
  • Clamping unit of IMM moves the moving side to open the mold.

• Ejection
  • IMM push the eject system of mold to have part ready for leaving mold.

• Part Removal
  • Part being taken out of mold by manual/robot…etc. Sometimes part leaves mold automatically depending on mold design.

• Mold close
  • Clamping unit of IMM moves the moving side to close the mold. The clamping force from IMM is so big (several dozen to thousands of tons), it is very important to ensure that there is no unexpected particle (such as part, plastic, stringiness…etc.) between fixed and moving side before mold closed in order to prevent mold damage. The safety setting in IMM shall always be activated, it is a function if IMM detect unexpected resistance when mold is closing, IMM stops closing mold. It could protect mold from unnecessary damage.