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Validation Guidance - Plastic Injection Molding Process


Albert Barr

Please find a link here to a useful adjunct for optimizing or troubleshooting the molding process.

[Link Removed due to posting restrictions]

The link from the above post is broken, but I was able to locate the document being referenced (attached.) Because of my lurker status, I cannot post the direct links in this message, but it came from Westlake Chemical's website- you can look for it there, or feel free to PM me for the direct link.

This was an immensely helpful document for me, so I wanted to make sure the data remained available for all.

:thanx: Many thanks to Sturmkind for bringing this up in the first place- I'd have never found it without your tip.


Form a team of production, maintenance and quality primarily.
Study the moulding properties of the raw material that is to be used.
Set up the injection moulding machine with all service connections in good order.
Ensure all meters on the machine have valid calibration.
set the zone temperatures of the barrel (material TDS will give you the guidelines)
determine the shot weight and set same
set the injection pressure
ensure that the mold is in order by the tool maintenance and good for use
load mold on machine and set the mold clamping pressure
if the mold needs an MTC (mold temp controller) install same
fix the holding time after injection
try shots and fine tune parameters till you get the parts per requirement
fix the parameters and run several batches to ensure it works well over time
train people who handle the machine about the parameters and maintenance of tool and machine, about its calibration and record same.
(i am not an expert in plastics, but i have tried answering from my experience with suppliers).
I have a 5 MB .pdf <operator handbook for plastic injection moulding> and it cannot be attached here due to limitations of size. Tell me how I can send it to you as a guidance document in the validation.
Hello i see that this forum is from a while ago. But i would like the operator handbook for plastic injection moulding if you could help with that. Thank you


Captain Nice
Staff member
I am more than willing to send to anyone interested in the document said by me earlier. Just PM me your e-mail id to do it. As I have said in that post, it is due to the size of the .pdf file that I am unable to post it as attachment.
@somashekar - Old thread, but if you still have the file you can email it to elsmarmarc@gmail and I will see that a link to it is put in this thread.

Bev D

Heretical Statistician
Staff member
Super Moderator
Is it an unreasonable request that my OQ Cpk be =/> 1.33 for High, Low, and nominal settings?
Yes, but probably not in the way you mean. If your Customer has a requirement for a process to meet Cpk > 1.33 then it must meet that at all levels of allowed material, equipment and process settings (OQ). Since you will allow these settings during normal production adn normal production must be capable of > 1.33 then yes, your OQ must meet > 1.33. It is only common sense...If you feel this is oppressive then perhaps your min/max settings are too wide? Or you needed to better negotiate the price or challenge the Customer’s specifications.

But the unreasonable part may be that you have one of those common injection molding situations where tool wear dictates that you start at one side of the specification that allows for the wear to move the parts to the other end of the specification to maximize the life of the tool. In this case Cpk should be calculated only for the starting side of the specification. In this case Cpk > 1.33 is more difficult to meet. And it may be unreasonable, given the absurdity of the assumption of a Normal distribution and that ‘long’ tail that doesn’t exist...but that is a different kind of discussion with your Customer.

Ronen E

Problem Solver
Staff member
Super Moderator
IM tools that are properly designed, built and maintained don't really wear out in that manner. Cheap and nasty tools (or trying to cut maintenance corners) will make maintaining a stable process very difficult on an ongoing basis, regardless of any methodological maneuvers for initial qualification.
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