To compensate the shrinkage, it is necessary to inject more material after 100% filling of the part.
The length of packing time (green line in the time-pressure diagram below ) must be selected in such a way that the gate freeze time is reached.
A short packing time leads to a higher risk of sink marks and voids.
Similar things will happen, if there is still molten material within the part but the gate is already frozen.
In the plastic industry, different materials (components) are used frequently to create parts with more functionality.
For example:
Components with a different material (e.g. metal) are inserted into the mold before injection molding.
This is done manually or with a robot.
It is important to hold the insert in the correct position until the plastic flows around and fixes the part.
The encapsulation allows a strong connection between insert and part, and both will be ejected as one.
Related topics:
A process in which fine powdered material with high melting point (>1.000°C) is mixed with thermoplastic based binders to a moldable compound is called powder injection molding.
The powdered material comes preferred wise in globular shape and corn sizes of 15 µm – 20 µm. The binder is incapsulating the powdered corn.
Volumetric share: Binder > 20 % / powdered material
This term refers to an auxiliary substance used in plastics processing to prevent a molded part from adhering to the surface of the mold. By applying this substance to the mold surfaces, the demolding of plastic parts becomes easier and the risk of damage or surface defects is reduced. Such agents are particularly used in processes such as injection molding, compression molding, or laminating. They can be applied as a spray, liquid, or solid coating and form a thin separating layer between the mold and the plastic material. This supports a reliable and consistent demolding process.
Related topics:
The injection mold is usually temperated during the complete cycle.
The time from the end of packing phase until ejection is called residual cooling time (blue line in the time-pressure diagram below).
During this time the cooling of the part takes place solely.
