Snap Fit Designs for Plastic Injection Molding
Snap Fit Designs for Plastic Injection Molding
(OP)
Hi,
I'm designing a product that needs to have snap fit features in two mating components (think clam shell), but the mold needs to be a straight pull (i.e. no cams, sliders, side actions, etc). What kinds of features might I explore to achieve this?
Can anyone recommend a book that illustrates many different kinds of snap features? This is the only one I can find: http://www.amazon.com/First-Snap-fit-Handbook-Creating-Attachments/dp/1569903883 Has anyone read this one? Would it provide the information I'm seeking?
I'm designing a product that needs to have snap fit features in two mating components (think clam shell), but the mold needs to be a straight pull (i.e. no cams, sliders, side actions, etc). What kinds of features might I explore to achieve this?
Can anyone recommend a book that illustrates many different kinds of snap features? This is the only one I can find: http://www.amazon.com/First-Snap-fit-Handbook-Creating-Attachments/dp/1569903883 Has anyone read this one? Would it provide the information I'm seeking?
Thanks,
John





RE: Snap Fit Designs for Plastic Injection Molding
That's an excellent book and will answer all of your questions. Other places to look for information are the various plastic design guides put out by the resin manufacturers (the old GE one was pretty good if you can find it).
Snaps with no action will probably require bypass shut-offs (holes) in the clamshells to form the undersides of the snaps. If that's a problem then you might consider crush pins for assembly. I've used them many times for small parts.
-b
RE: Snap Fit Designs for Plastic Injection Molding
I haven't used crush pins before. Does the book discuss crush pins? Or is this not even an injection molding process?
Thanks,
John
RE: Snap Fit Designs for Plastic Injection Molding
The parts we used this on were small, perhaps 2-4" in length. The pin diameters were about .060"-.080" with 4 pointed ribs (imagine a square section superimposed on the round pin) with .005" or so of interference. We generally tweaked rib height by a couple of thou once or twice to improve the fit.
-b
RE: Snap Fit Designs for Plastic Injection Molding
RE: Snap Fit Designs for Plastic Injection Molding
RE: Snap Fit Designs for Plastic Injection Molding
http://www.ets-corp.com/tools/development.htm
H
www.tynevalleyplastics.co.uk
RE: Snap Fit Designs for Plastic Injection Molding
Both axial faces of the collet's teeth were beveled, as were the ends of the groove in the cylinder, so without the limiting sleeve, the collet could be pulled off the cylinder as easily as it was pushed on.
Which was also the trick to molding the collet's internal teeth without a collapsible core. When the part was pulled hot from the mold, the collet teeth were splayed out plastically. The molding press operator wrapped a rubber band around the teeth to pull them back into alignment while the part cooled.
It worked great in glass filled nylon. Glass filled polyester became too rigid too quickly, and the teeth cracked during extraction.
Where I'm going with that story: It may be possible to mold your snap fit features in such a way that ejection deforms them, and the press operator immediately restores them to the proper position while the part is still hot. ... but success depends a lot on what material you're using and what sort of relationship you have with your molder, and what your application requirements actually are.
Mike Halloran
Pembroke Pines, FL, USA
RE: Snap Fit Designs for Plastic Injection Molding
Q: Why does the tooling need to be "straight pull"? If it's a cost thing, then (imho) you have the wrong toolmaker! Unless the volumes are not at least in double figures, the cost benefit should be better.
Mike: I hope this is not another "trade secret" like the location ring size optimization!
Cheers
H
www.tynevalleyplastics.co.uk
RE: Snap Fit Designs for Plastic Injection Molding
"... another "trade secret" like the location ring size optimization!"
Huh?
Have you confused me with someone else?
Have I forgotten an instance in which I was more of a PITA than usual?
Mike Halloran
Pembroke Pines, FL, USA
RE: Snap Fit Designs for Plastic Injection Molding
Mike, Insulating tape:
H
www.tynevalleyplastics.co.uk
RE: Snap Fit Designs for Plastic Injection Molding
RE: Snap Fit Designs for Plastic Injection Molding
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RE: Snap Fit Designs for Plastic Injection Molding
Thanks,
John
RE: Snap Fit Designs for Plastic Injection Molding
http://hom