Rubber pad forming?

[classictrial]

Wonder if anyone can provide any info on what could be achieved in regard to rubber pad forming, using a 30 ton shop press?

Looking to form small motorcycle parts out of 2mm aluminuim sheet, and wonder if this sort of thing would be viable using a smallish shop press, or is a 4 post press intended for rubber pad forming needed for this type of thing?

TIA

Chris

 

[CESSNA1]

CLASSICTRIAL: Elastomeric (rubber) parts are usually molded under heat from various eleastomeric compounds and additives that are mixed. You can cut elastomeric parts out of sheets and blocks and other molded shapes of the stuff, but that is about it.

Regards
Dave

 

[GregLocock]

Um, no, the OP wants to know about the use of conformable tooling when pressing aluminium sheet parts.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Fabrico]

OP, look up "rubber pad forming" on the internet, lots of info.

 

[berkshire]

classictrial (Automotive)
You realise that you have a double post going on this subject.
I would suggest confining this to the Aircraft Engineering forum. You have a good chance that the same people are going to reply to you anyway.
B.E.

 

[notnats]

We used to use a rubber pad to cut a polygonal blank about 200mm x 100mm from 1.6mm aluminium in a 40 ton press brake. We never formed anything bigger than 100 x 25mm. Not because we couldn't, but because we didn't need to

Jeff

 

[classictrial]

Anyone have any idea on the max draw depth and size of forming box, that could be used with a 30 ton shop press? (using 2mm aluminuim sheet)

TIA

Chris

 

[berkshire]

classictrial (Automotive)
Figure that you are going to need 4000 to 6000 psi to get a decent form on 2mm aluminium and interpolate from there.
B.E.

 

[classictrial]

Thanks Berkshire........sorry for my ignorance, but how would I calculate forming pressure, taking into account the variable of the rubber?

Chris

 

[berkshire]

classictrial (Automotive)
The rubber is incompressible, it deforms and flows around your forming die taking your work piece with it. calculate the area of your work piece and divide it into your available tonnage, this will give you the tonnage per square inch or sq mm.
Having looked at your other post today and seeing what you are up to,it appears that you are using matched tooling with a rubber face rather than a true rubber die You may get your basic form this way but you will not have much detail, you may have better results if you can reduce your thickness a little to say 1.5 or 1.7mm.
You may also need to make several forming dies of different heights to do this in stages or you may end up with wrinkles in the parts if you try to do a deep form without using a draw ring. The book "Forming Alcoa Aluminum" I mentioned before has a description of how to use a draw ring in a true rubber die.
Let me know how you get on with this.
B.E.

 

[berkshire]

classictrial (Automotive)
I mis-read your post on the other forum. The description you gave there was for a tradditional trapped rubber forming box. I am not sure you have enough tonnage to make your tank in two halves. However you may have enough if you make it in quarters.
Good luck.
B.E.

 

[classictrial]

Thanks for your responses. The tanks we are looking to form are not very big, about 15inches long, and 8 wide. They are intended for a BSA 441 MX chassis kit, that is being manufactured by a friend of mine.

I think we are going to be looking at a forming box perhaps 6 inches deep, with enough area to cover the cast aluminuim forming tool we have had made, with maybe 2 inches extra area along the sides of the box.

Was thinking of using polyurethane sheets one on top of the other, to take up the depth of the forming box. If the press we already have, is not up to the job, then we are going to have to look for something more powerful, possibly a four post design.

If any of the above sounds like a non-starter, would be great if someone could point out my mistakes, as I really only have very basic knowledge of this process.

Thanks

Chris

 

[berkshire]

classictrial (Automotive)
I think you are on the right track, look for a urethane of about 60 to 70 durometer hardness.
you may have to cut holes in some of the bottom sheets, that is the ones furthest away from your form die to allow the part to expand into the box without overloading your press.
Good luck.
B.E.

 

[classictrial]

Thanks Berkshire.......will get hold of some urethane sheet, and give it a try.

Chris

 

[Compositepro]

Check-out this link

http://www.tinmantech.com/html/articles_by_the_tinman.php

Ther are some very practical articles on forming aluminum sheet.

 

[classictrial]

Thanks Compositepro...........one final question on this subject, before we actually start making forming box, and giving it a try: What thickness urethane sheets would be best to use, bearing in mind forming box is going to be about 6 inches deep?

Chris

 

[berkshire]

Classictrial
check out this thread on an earlier forum thread2-97825
This contained a discussion on rubber pad forming with larger machines. It had one or two links in the UK to people with specific knowlege of rubber and urethane pads.
B.E.