How to get circle to shrink the way I want? Fixtures?

By djbeatsent
Published: January 11th, 2012

We are injection molding a part that has a very thin walled diamter of about 1.5 inches. It is shrinking out of round. Would making a fixture that had an out-of-round post on it work? This way it would force it to be in round? Any ideas?

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This has been helpful. With

Submitted by ronnan on May 1, 2012 - 3:50pm.

This has been helpful. With this kind of information I can now make my own sleek new fixture, that would be an interesting experience.

Happy New Year Sam! You would

Submitted by Anonymous on January 13, 2012 - 3:55pm.

Happy New Year Sam!
You would make an excellent writer for PT, but I think it is hard to make a living as a writer anywhere these days. So:

"KEEP ON MOLDING"!
brent

Brent has just made a

Submitted by Anonymous on January 12, 2012 - 4:05pm.

Brent has just made a generous offer and those folks certainly know their business! Ultem is a difficult animal to tame if you don't approach it with the proper equipment and technique. Let his tooling folks have alook if possible to see your options.

Happy New Year Brent and all my fellow Molders !

Sam

PS: I will be actively seeking employment as soon as I finish my next prototype
It would be nice to write for Plastics Today !

We run both filled and

Submitted by Anonymous on January 11, 2012 - 4:40pm.

We run both filled and unfilled ULTEM resins and maintain TIRs of, in some cases tenths of a thousandth of an inch.
Mold design,construction,gating,packing and steel temps all play an important part of consistency.
CF PEI is hard to purge out and also feed in some screw designs.
If you want to send further info you can contact me/us at: www.matrixtooling.com

We like to help fellow molders!

Keep on Molding!

brent

Moving the gate may not be an

Submitted by djbeatsent on January 11, 2012 - 9:39am.

Moving the gate may not be an option, and the material is a carbon filled Ultem. Pretty tough stuff.

I expect tooling mods and

Submitted by rickbatey on January 11, 2012 - 9:29am.

I expect tooling mods and process mods will be required to correct the out of round condition you speak of. Short of that, you will have to use the mold as a very expensive part fixture.
How much TIR do you have? What is the resin? Melt and mold temp.?
Rick.