Process	Push-pull injection moulding
	Suitable for achieving long thin parts with high stiffness in the longitudinal direction. The molecular structure of the parts is very uniform and internal welding lines are reduced. It is a relatively new variant of injection moulding which improves strength. Unlike injection moulding, two injection units are used for injection of plastic. While one unit is pushing plastic into the mould, the other one is pulling. First the cavity is filled by the first unit, then pressure and new molten plastic is injected from the second unit to keep the material in motion while it cools down. The process is then reversed.
Danish Name	Push-pull sprøjtestøbning
Category	Mass conserving processes, Shaping plastics
Materials	HDPE PA ABS PC PE PP
Typical products	Window frame for airplane
Competing processes	Injection moulding Air injection moulding Extrusion Pultrusion
Additional info	Possible to achieve good dimensional accuracy and surface finish.
Photo	Thomas Nissen (Computer graphics)
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