Forming Thin Copper Sheets into a Mold 1

[lutomr]

I'm trying to get a thin copper sheet approx. .004 thickness to stay in a mold so that I can pour silicone into the copper and form it into the shape I want. Problem is that the copper wants to spring up out of the mold. Has anyone used a process that would help me out in this situation? The copper sheet is approx. 6" wide but the width of the mold is 2.4" or so. In the attached picture is the cross section of the mold, roughly. Both of the radii are a controlled dimension that the copper would have to form to tightly. All thoughts and questions are appreciated.

thanks!

 

[ornerynorsk]

drill some vacuum holes in the mold and apply vacuum to hold your foil in place.

 

[lutomr]

We tried that and it was near impossible to get the seal of the foil to the mold perfect enough for the vacuum to hold it in place. Thanks for the idea though.

 

[hendersdc]

You could try a couple strips of double-sided adhesive in the radii and just peel it off after the silicone sets.

 

[mfgenggear]

it's been a while since I have worked with sheet metal.

I remember using tooling holes in the work, (2)holes across length wise, nest the the parts with tooling pins in the
die, this will prevent the stock from moving.

the pins should clear the mating die.

good luck

 

[MikeHalloran]

That's a very deep draw, even in annealed copper. Without a draw radius, you really don't have a chance.


Two alternatives come to mind:

1. Tig weld two blanks together and inflate them between two molds. Hydraulic fluid is safer than air, and you may need more pressure than you can easily get in air. The liquid also gives you better control over the strain rate.


2. Repousse.




Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

3. IF it's a surface of revolution:
Start with a shallow draw of thicker copper, then spin it in a lathe and iron it down over a wooden plug. You can reduce the wall thickness as you iron it down. Just like metal spinning, more plastic deformation.

Skill intensive, but not so much as repousse.



Mike Halloran
Pembroke Pines, FL, USA

 

[mcgyvr]

What's the point of the copper? Mold release aid?

The have adhesive backed copper tape in various sizes.
What about contact cement/spray adhesive?

 

[lutomr]

The purpose of the copper is to shield the cables. This whole molding operation is to encapsulate a wire cable assembly in silicone. I'm trying to do this all in one shot and not in multiple steps. The copper encapsulates the silicone and then there is even another molding operation to encapsulate that whole thing in more silicone. Trick is to get the inner silicone molded piece to bond to the copper. Attached is a new picture of what the cross section actually looks like from my solidworks design.

I saw some posts that about drawing the copper. I am not going to be drawing it in, it comes in pre-cut sheets, what I need is to find a way to form it to the walls of the mold so that I don't have to mold the silicone then wrap the copper around it manually, I'm trying to do it all in one process. The tape ideas might work, however this copper comes with a phenolic primer on it, and I'd have to see how the adhesive works with that material.

 

[Compositepro]

It sounds like you are using work hardened copper, which is very springy and not ductile. Use annealed copper if you want it to form in your mold. If you need to use hard copper you must preform it to shape in another tool first. There will be lots of spring-back so the forming tool will be a different shape than the finished shape of the part.

 

[MikeHalloran]

Sorry, when you talked about copper stock in small sheets, I thought you were making a pot, not a pipe.

How long is this pipe?



Mike Halloran
Pembroke Pines, FL, USA

 

[lutomr]

To Compositepro the stock copper is 110 Annealed - Copper (Cu), Annealed-Wrought (ANN-Type W) – 99.9% pure copper.

To MikeHallroan, for the actual production size this will be about 10' (ft) long. Right now I'm trying to do samples about 1'-2' long.

 

[mfgenggear]

need more information about the forming process you are using.

I use form these type of parts with no issues.

the other way is to pinch the outer edges with an outer die , then the inner die punches the center.

need to clamp this thing so it doesn't move.
the tooling holes is the other way.