Design resources for overmolding
Design resources for overmolding
(OP)
I'm the only engineer for a start-up company and have been assigned to redesign several parts. I'm having trouble with redesigning a thumb lever (1" tall, 1.25" ID, 2mm wall ring with a .5"x.25" lever protruding from one side). The owner of the company wants a rubber feel (TPE or Silicone) but neither of these will be strong enough for the force applied. This leads me to an over molded Nylon or ABS part, but I'm having trouble finding information on how to design, shut offs, flash prevention, peel prevention, etc.
Can the community point me to a book or other resources to help me learn how to make a manufacturerable overmolded part? Also does anyone have a company they would recommend to manufacture the part?
thanks in advance
ps. this is my first foray into plastic part design
Can the community point me to a book or other resources to help me learn how to make a manufacturerable overmolded part? Also does anyone have a company they would recommend to manufacture the part?
thanks in advance
ps. this is my first foray into plastic part design





RE: Design resources for overmolding
Another good option to get some ideas is to go and purchase some plastic cooking implements with soft touch handles. Have a good look at how they do it, cut them up to look into section sizes etc.
Once you have a handle (pun intended) on some of the parameters, go and see an injection moulder. There is a bit of an art to over-molding.
Craig Pretty
Tru-Design Plastics
RE: Design resources for overmolding
Best advice for any molding job. Talk to the people who do it every day, and have seen the mistakes made in design and mold tooling engineering.
RE: Design resources for overmolding
RE: Design resources for overmolding
racookpe, thanks for the suggestion, but I over simplified the part in my original post and won't be able to find something "over the counter".
RE: Design resources for overmolding
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RE: Design resources for overmolding
In this round of production an over molded part is going to be cost prohibitive for our start up. Does Eng-Tips have any tips on a rubbery or soft touch spray on coating? Does anyone have an idea on the longevity of adhesion for the Alsa soft touch paints?
thanks in advance.
RE: Design resources for overmolding
RE: Design resources for overmolding
RE: Design resources for overmolding
Another possibility is to use a room-temp vulcanizing rubber, like silicone or urethane, and make your own mold tool for compression or squirt-fill molding. Tough to do these without getting a somewhat bubbly coating, but it can be done.
Hm, just reread your op, and it looks like you want something tougher than silicone. The urethanes can get pretty hard, but you may want to think about an epoxy too.
RE: Design resources for overmolding
In my previous post about the soft coating, I was thinking of an abs/nylon substrate that is coated to feel soft.
RE: Design resources for overmolding
htt
http://www.apainfo.com/product_literature/main.asp
http:/
In the realm of the dip coating posted above here is one of many companies that makes several varieties of Plastisols or Organosols.
There are as many types as the chances of winning the lottery.
ht
RE: Design resources for overmolding
If you choose a commercial supplier of this process they should be able to remove bubbles by placing under vacuum etc. Throughput can be quite good through some of these manufacturers. I would recommend our local supplier, but being in NZ it would not be of much use.
Here is a supplier of predominantly wheels that I came across when trying to find an alternative supplier for our work. It would appear from their capabilities that they can handle custom work ins hort or long runs. htt
Craig Pretty
Tru-Design Plastics
RE: Design resources for overmolding
http://www.chemionics.com/plastisol.htm
RE: Design resources for overmolding
Here are a couple of different options for soft-touch coatings:
waterborne, soft-touch coatings from Bayer
htt
Makrofol® Softtouch and Bayfol® Softtouch films
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Alsa Soft Feel Paint coating
http:/
RE: Design resources for overmolding
Looking at tvp's post for the alsa coatings, it looks like that is a two-part sprayable urethane. Sounds like you can make that work, and it's just a matter of figuring out how to make it adhere (talk to the supplier), and what coating durometer/finish gives your boss a warm fuzzy. Urethanes are inherently sticky, so you really shouldn't have any trouble, unless you are trying to make it stick to teflon...