Deep drawing rip outs verses lubricant question

I think the question is, "Why would more lubricity lead to parts
ripping out?"
Maybe someone can tell me the answers or help me ask the right
question.
Here are the details. We deep draw little cans from 0.010" thick pure
niobium. Most of them are cylindrical with a flat bottom. The corner
radius on the bottom varies but 0.020" would be representative. A
typical diameter is about 0.625" with typical height of 0.500".
Our niobium is specified to have an elongation of 24 - 28%, ultimate
strength of about 47 ksi and yield strength of 30 ksi. The modulus of
elasticity is 14900 ksi
The punch and die clearance is about .001" more than the material
thickness. The clearance could increase to 0.003". Generally the
hold down pressure is negligible.
If we have consistent trouble with rip outs, we will go to a double
draw or triple draw. Of course, we would prefer to avoid the extra
expense.
We had a part that was ripping out about 15% of the time. I tried a
supposedly superior oil based lube designed for drawing. We washed
the discs before applying it. After wiping it off as normal, we had
100% rip outs with the new lube. Even after wiping as much off as
possible, we there was still a thin film and we had 100% rip outs.
Before going to a double draw, I observed that the partially drawn
disk was very wrinkled. So I assumed the hold down wasn't doing the
job. I tried a different part with a different set of tooling with
more pressure on the hold down. We tried soaking the discs in our old
water based lube and not wiping them as usual. The result was no
wrinkles but 100% of these parts ripped out, too.
The operators tell me that all the cans will rip out if we have too
much lubricant. Therefore, they wipe them with their hands before
drawing.
It appears that the slipperier the discs are, the more likely they
will rip during drawing. I would think it would be just the opposite.
Can anyone help?
Reply to
B Williams
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#1 Have you ever drawn these cups before???? Is this new fabrication for you??? What was your elongation (I'm assuming in 2")before - have you verified it???
#2 For deep drawing you can never have low enough friction. How do you quantify "slipperier".
#3 IMHO you have poor lubrication - the tearing out of cup clearly shows you have enough force to do the job! HAve you use a coating like lime or a soap on the disk to help lubrication?? E.P. (Extra Pressure) Greases Tried????
Ed Vojcak
Reply to
Edward D. Vojcak
Thanks for the reply.
We have over 100 different niobium cans that we have been doing for several years. I have recently been assigned the task to improve things so I am looking at processes that may have been acceptable in the past but aren't anymore. The elongation hasn't really changed but we haven't had outside verification confirming what the vendor says is actually true.
I can't currently quantify it. The test lube "feels" slipperier and with both lubes, more lube feels slipperier than less lube. I also felt you could never have too little friction. That's why it doesn't make sense that we have higher yields when they wipe off the lube.
The normal lube we use is actually classified as soap. The test lube is rated E.P.
B Williams
Reply to
B Williams

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