Plastic Molding Defects And How To Troubleshoot A Mold
The process of troubleshooting a mold because of plastic molding defects
does not have to be some kind of black art that only a molder with 30 years experience can be good at. In
fact, it can be a very methodical and logical process.
The main things to keep in mind when working to eliminate plastic molding defects are
common sense and an objective view of the process. Very often the obvious is overlooked in search for a more
A very interesting study done over a 30 year period by Texas Plastic Industries revealed that there are four main
causes of defects.
The molding machine 60%
This somewhat flies in the face of the usual outlook by molding techs and processors.
Most of the blame usually falls on the material and then the operator. This, however, shows a much different
If the problem stems from the injection molding machine 6 times out of ten, it surely makes sense to begin by
looking there first. I have personally worked on mold grooming programs that seemed to go on forever, when the
actual cause was a machine platen out of square.
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Start by looking for the simple solution, look for common sense answers before moving
into complex solutions. Is the cooling working properly, are the heating bands functioning correctly? What about
hot tips nozzles and plastic temperatures?
Did someone inadvertently change the material cushion? Try to visualize the entire
process and make sure each of the necessary functions is as it should be. Sometimes it is something totally
ridiculous and easily overlooked.
Allow troubleshooting to takes it's time
It takes time for the machine and mold to adapt to any change in process. Until the
process has had time to stabilize it makes no sense to make a determination or try another modification.
For example: if you increase the barrel temperature, the flow rate will be altered
after just several minutes. Yet in just a few more minutes, the injection speed will be affected because the
material is now flowing easier. And this, in turn, can cause flash to develop after a few more minutes.
One troubleshooting try at a time please
If the change in parameters did not solve the problem, reverse the change back to
it's original state before attempting another change. This obviously requires time and make the entire process more
costly, or so it seems.
Yet, if this is not done, and changes are made one right after the other, the entire
process becomes a muddled mess with total confusion. So, it is important for the troubleshooter to act with a
strategic plan, take his time, do one thing at a time and remain objective.
Do not force the process on a new mold to reach dimensions
The main problem with using this approach is that it minimizes the process window
that is needed when later changes must be made. A new operator, different machine, or new material can all require
the full range of the process window to obtain a satisfactory part.
As you can see, troubleshooting plastic molding defects is a complex process, but one
that can be made much easier by following the above mentioned tips.