Mar 11, 2019
In the CAD-System, a geometry of the part is generated.
This can be done in different ways:
One way is to use simple 3D-volumes (cylinder, cuboids, etc.) to build directly a more complex 3D-object.
The other way is to create single surfaces to build a 3D-object.
Independent of the selected way to generate the CAD model, the result is called volume model, if all surfaces build a closed skin with a clearly defined inside and outside surface.
Simulation: Volume model of a ship.
Related topics:
This glossary of plastic industry is provided by PLEXPERT Canada Inc.
Dec 19, 2018
The reduction of the specific volume of the part is called volumetric shrinkage.
It takes place inside the mold between injection and ejection.
The thermal contraction is the main reason for the volumetric shrinkage.
For semi crystalline polymers the crystallization is another cause.
High differences in wall thickness and inadequate packing lead to a high volumetric shrinkage.
This results in a high warpage, sink marks and voids.
Dec 11, 2018
After approximately 95-98% of part filling the switch between filling and packing phase is made.
This point is called VP-Switch (red arrow).
It is the change from the flowrate controlled filling to the pressure controlled packing phase.
The right time for the switch can be found with the help of the cavity pressure.
Jan 11, 2019
A geometrical difference between target and actual geometry is called warpage.
In the plastic industry this is caused by the developing stresses during the process.
Stresses arise due to the different shrinkage degrees in the part.
Varying Cooling rates, Orientation of the molecules, in-mold constraints (limitations for the shrinkage), uneven wall thickness/packing pressure are responsible for the differences.
These effects can cancel each other out or enhance one another.
Nov 18, 2021
To process plastic, an injection mold must be brought to a certain temperature.
The thermal energy introduced by the melt must be dissipated to ensure that the temperature in the mold is as uniform as possible.
These tasks are performed by the temperature control system installed in the mold.
This is usually formed by bores, some of which are provided with plugs to guide the coolant (usually water).
The tightness of the individual channels in the cooling system is ideally carried out before the mold is set up.
For this purpose, water is pumped into a circuit via a pump and kept under pressure for a certain time.
If water does not leak at any point, the leak test of the sewer is complete and the next sewer can be tested.
