what material for molding clear plastic?

[mc-motorsports]

I have a used mold base and I need to make inserts for a part that will be optically clear plastic. What material do I use? I know it's going to be tool steel, or mold steel, aluminum is out, has to make 600 parts without being repolished if possible (don't think that's asking much, is it?).

What grade steel should I use for this application?

Would A2 or O1 work? Needs to be .750" thick and 1.5" wide.

TIA,
MC

[plastibob]

420 SS polished to an SPI#A1

[plastibob]

One other note: gate and gate location are important as well as venting for lenses.

[mc-motorsports]

Originally Posted by plastibob 420 SS polished to an SPI#A1

And if told you I was making this on a bridgeport? I'm limited to 2600 RPM. TIaLN coated carbide tooling?

[plastibob]

If you don't want to mess with stainless I've made lens molds with P-20 ultra which is tougher than regular p-20 but still machines easy and has excellent polishabliltiy.

[mc-motorsports]

do you have a good online source for online tool steels such as P20 ultra? I went to mcmaster and P20 is only available in rod and bar? and there is no listing for P20 ultra.

And is P20 prehardened 4140?

[mc-motorsports]

Just a question, what about 52100? I have coniderable experience with making tooling out of 52100 which is my prefered tool steel. Just wondering.

Thanks for the help!

[plastibob]

P20 is essentially a modified 4140. You can get the super from Dunn Specialty steels www.sunnsteel.com. The P20 is easier to machine than the 52100. I wouldn't recommend using the 52100 for a mold application. If your only talking 600 pieces you can make it easy on yourself and use 7075 aluminum.

[mc-motorsports]

??? 600 pieces is an estimated 1 day run which will keep the customer busy for a while. I would guess a 600 piece run, then the mold will sit for a while, 3 months to a year? I can only guestimate.

If I used 7075, would that be ok for an optically clear plastic molded cover? Right now the parts are made from lexan, milled and cold formed, basically some tabs bent 90*. The customer is pickey, no scratches, he's also my father, trust me, he's anal about that stuff!

If money and machine time didn't matter, and you were limited to 2600 RPM, up to 100 imp feedrates though, what material would you use?

Thanks for the link, I'll check that out.

MC

[plastibob]

Since your not using a filled material and considering your machine I would use the 7075. I buy my 7075 material through yarde metals dropzone. Most of my molds are aluminum and you can run thousands of parts off them. Right now your machining polycarbonate I would look at acrylic which is more optically clear and easier to process than the polycarbonate.

[plastibob]

I missed you calling it a cover I thought it was a lens, the same applies but another molding material you may look at is SAN as it's pretty tough, scratch resistant, inexpensive and molds easy it also has better chemical resistance than polycarbonate. I'm not sure what environment this cover is in.

[mc-motorsports]

It's NDA kinda stuff, but it's a cover to keep your arm and hands off of nicely engraved or plated parts. Will be exposed to sunlight, normal UV rays. Right now the parts are just cut out of lexan sheet, I don't even take the plastic off, just drill some holes to mount them to a fixture, bolt them down and cut them out 6 sheets thick. After that, my job is done, I charge $1 each, but then they have to be lightly deburred and the tabs bent 90* so there is a lot of man hours in handling time plus material costs...$$$.

The molded part should cost $.45 each according to the mold shop, they donated an obsolete mold base, should only have to clip sprues and lightly deburr any edge flashing.

For the aluminum mold, 7075-T7351 or 7075-T651 or does it not matter?