May 29, 2019
The sequential process during the injection of the melt into the cavity until the part is cooled down, is called mold filling phase.
After the volumetric filling of the cavity (95% to 98% of the cavities volume), (A) there is a switch-over from injection to packing.
During this phase the material is packed and pressed to the mold wall (B).
After the switch over point the complete filling (100%) of the cavity takes place.
During the packing phase (C) the material will be compressed is in good contact with the mold wall.
The plastic shrinks while it is cooling down (approximately 0,2 – 2,0 %).
Shrinkage is compensated in the packing phase due to a material delivery through the melting core. This is important to ensure the dimensions of the part itself.
After the packing phase, cooling phase will start (D). Here the part will be cooled down to a point, where the dimensional stability can be ensured (to ejection temperature) and ejection can be done without deformations on the part.
Jan 28, 2019
If an integration of electronic, optical and mechanical functions is realized in one part, the part is called MID part.
MID is short for the term Molded Interconnected Device. In a newer description, MID is also referred to Mechatronic Integrated Device.
When it comes to injection molding, a part is produced using a thermoplast with additives. With this, the optical and mechanical properties are defined.
After the production, there is a second step (e.g. using the LDS process) in order to activate the additives. This is important to allow metallisation of the part in a third step.
The metallisation is used to create the circuit lines in order to prepare the base for mounting SMD elements for completing the electrical function of an MID part.
Besides this, the MID technology is widely used in creating antenna for mobile communication.
MID-sample model with LED display and sensor pads.
Related topics:
IoT
Miniaturization
This glossary of plastic industry is provided by PLEXPERT Canada Inc.
Jul 17, 2019
In injection molding, part inserts are commonly used to produce parts.
First, the part inserts are added into the cavity, after that the melt over molds it on one side.
This is why the process is called “Overmolding”.
The advantage of this process is that the materials are connected due to the hot melt by a strong bond.
Gluing of the different parts is unnecessary in this case.
This process is often used with films as part inserts.
It is important to control the process temperatures since a melting of the insert is not or only partially wanted.
Injection Molding Process: The bicycle helmet is manufactured by
overmolding of the PC-Shell with the EPS core.
Related topics:
Gluing
This glossary of plastic industry is provided by PLEXPERT Canada Inc.
Oct 13, 2020
In injection molding the plastic melt shrinks during cooling down.
Therefore after a volumetric filling of the cavity additional material is pushed into the cavity to compensate the shrinkage.
The phase where the screw still apply pressure to the melt is called packing phase.
Packing pressure (and packing time) is hereby essential.
Too much packing pressure leads to overmolding and flash formation.
Not enough packing pressure results in sink marks, voids and higher shrinkage.
Often a profile is used to apply pressure during the packing phase.
Forward movement of the screw during the
packing phase
Related topics:
This glossary of plastic industry is provided by PLEXPERT Canada Inc.
Nov 29, 2018
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.
