Hydraulic Die Forming Discussion Group

Dar Shelton
sheltech@yahoo.com

>I presume the answer, if any, lies in the shape (profile) of the die.

>Thanks for your help.

>Jon Olson
>

I can't exactly picture the desired results from the description ,
but the problem you talk about is a tricky one . If you only want to dome it around the edges , alignment  does have to be perfect; it sounds like this is what you're after . I assume you know about the 2-step   matrix forming , and blanking die cutting (or hand sawing which you likely don't want to do) approach ? Exactness and consistency.

With a pre-cut blank , there isn't any good/easy way to keep the blank aligned as it moves down into the  conforming cavity . (but things happen fast, so do read on (^8  !) .  A thin sheet of urethane might pin the part down well enough as it engages , but it also would be very easy to dislodge the part as you set the urethane onto it, before pressing.  Your best hope may be to have a part that exactly fits inside the rim of the form cavity , and have a shallow cavity, but there's still no guarantee of perfection or consistency that I can think of . In industry things are done where the shape is formed in an oversize blank and then trimmed , I don't know... almost all the time I imagine . Your other best bet would be to adjust your design so that a bit of inexact alignment during forming is not bad . If the part has a more uniform dome that continues closer towards the center, it might be ok for the edges to be slightly off .

I just thought of a thing I tried eons ago  that may work :

I cut a plastic form the same size and shape of the part I wanted and rounded off the edges (1/4" thick  acrylic , 4" across, with
a 1/16" radius rounded adge all around). In the press I set the form with the part on top of it, then on top of that went a urethane pad.
Back to the problem of pad dislodging part ... (thinking)...
You could make a fence that the form and part and urethane fit down into accurately, and also have the male punch fit inside the fence .
That way the pad won't dislodge the part before it engages.

I think that will work . I know it will if you make it right.
Thanks and you're welcome  

Dar
www.sheltech.net