Vacuum forming molds for large parts?

[gijim]

Hi all,

I have a car body panel that I would like to make out of ABS plastic. It is approximately 25" x 25" x 3-5" deep. I have the plug ready to go, but now I don't know what I need to do next.

Since it is such a large part, I don't think making a mold out of aluminum or anything will be cost effective. The current plan is, to create a mold out of fiberglass, and use that for vacuum forming the 1/8" ABS onto.

I believe I will try to learn how to vacuum bag the fiberglass to keep it strong, and make it conform to the shape of the panel.

Are there any tips/tricks or suggestions on this proceedure? Will fiberglass work OK for the high temp of the molten ABS? Thanks in advance,

 

[gijim]

Oh, I guess I should mention 2 other things... It is a relatively low volume mold, I don't think there will be much more than 50-100 pieces made.

Somebody also mentioned I could use some regular polyester resin, mix in powdered aluminum, and make my own casting resin for it? Anybody heard of doing this?

 

[patprimmer]

Fibreglass will work.

Wood will work.

You say you have a plug. Do you mean a male form of the mould, if so, you can simply drape the preheated abs over the plug and press it into shape by hand while wearing leather gloves.

Regards

eng-tips, by professional engineers for professional engineers
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[gijim]

Yes, plug as in "prototype of exactly what I want to produce". It's a combination of fiberglass and bondo. Ugly, but in the right shape and smooth

I can't put the ABS on it directly because then it'd be oversized by the thickness of the plastic.

 

[patprimmer]

If you flop a Fiberglas mould off it, you will get some shrinkage as the resin sets then your parts will be undersized. Your resin supplier should be able to offer "minimal shrinkage" grades.

Other option is to cut up your existing plug and glue it back together after closing it up by the width of the saw cuts. Do as many cuts as necessary to get the size correct, then smooth off the joints.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.