Machine requirements

Electric injection molding machines require high-speed, finely tuned closed-loop control of the velocities, positions, and pressures of all machine axes involved in the process. Moreover, the temperatures of the heating strips on the cylinder, the injection screw on the injection nozzle, and the mold temperature must all be precisely controlled.

The typical process sequence of an injection molding machine is as follows:

• Mold closure:
  The mold is closed, and the clamping pressure builds up. This enables the mold to remain closed while the liquified plastic is being injected. During this process, the mold protection function continually monitors the clamping pressure, thus preventing the mold from being damaged during closure in the event that material remains in the mold.
• Injection unit forward:
  For injection to take place, the injection nozzle must be seated in the mold. In this step of the process, the nozzle is seated in the mold at a defined nozzle contact pressure.
• Injection:
  The plasticated material located in the tab of the injection screw is injected at high pressure into the mold until the mold is filled. The material is injected using velocity profiles that are adjusted for the mold.
• Hold:
  To compensate for material loss during the cooling phase, pressure is reapplied. This hold-pressure phase requires closed-loop pressure control.
• Decompression:
  To discharge the melted material, the screw can be retracted before and after recovery.
• Injection unit retracted:
  To prevent cooled molds from affecting the temperature of the heated injection cylinder, the entire injection unit is retracted, thus removing the heated nozzle from the mold.
• Mold open:
  When the cooling period is complete, the mold is reopened. The mold contains the finished, cooled part.
• Ejector:
  The produced part is ejected from the mold, falls from the machine or is removed by the gripper of a retrieving device, and is then fed to additional production steps (such as imprinting).
• Recovery
  The granulate is melted (plasticated) by the rotation (shear warmth) and heating of the screw. The plasticated material is transported to the retention chamber by the rotation and simultaneous retraction (performed using pressure control, for example) of the screw.