Need Help With A Forming/bending Die

markknx

markknx

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So here is what I am working with, A HF hydraulic shop press, a home made brake attachment, and a squared top die 1-1/2" x 6" long. Also a adjustable bottom die I made.
20150728_150918.jpg
Here is what I am trying to do form a piece of 11g. into a u shape 1-1/2" inside.( Actually I did get it but not without some hand bending.)
20150728_150953.jpg
The issue is when I press the part though It bends but it springs back enough to cause the part to be flared. I set the clearance between the top and bottom dies with a scrap of 11g on each side to a slide fit. I have seen dies set up to fold a box shape before with the sides coming out at 90deg. do I need to mill a relief in the sides of the top die? or what am I missing?

As you guys can tell I am no die maker. Hoping someone with some die make experience can set me straight. I managed to make this one work but I would like to be able to make these kinds of bends whenever the need arises. The first photo shows my crude set up the second shows the part I was making. Any help would be appreciated.
Mark
 
Yes you have to beable to bend it past 90 to get a 90. Or use alot of heat.
 
Spring back is a part of bending things. I am sure there are even tables for calculating the amount of spring back for just about any material. Wouldn't surprise me if it was even in the Machinery's Handbook.
Relieving the sides will not do much. As stated above, you need to bend past 90 degrees.

Looking at your set up, I think you can get there.
Bend as you do now.
rotate the work 90 degrees so that half the channel is above the top, and half below.
Insert a piece of piano wire in the corner between the clamp and the work, and close the clamp tightly
Lower the ram to bend the rest of the way.

If you are doing a lot of this, you need to just bite the bullet and fabricate a bending jig. A simple plate with a hefty rotating point for a second plate and 2 meters of cheater bar will make short work of that bend.

PS, Make sure you use lube in your jig. It looks like you are bending dry, you will get less spring back with lube. You need something that can withstand high pressure. Google up "swaging lube" for a home brew recipe. At the very least, use a hypoid gear oil.
 
This is known a Air Bending or Forming, the part will always spring after forming, Closed Die forming or Coining works much better but is often well out of the financial reach of hobbyists as it requires 20-30 times the force therefore dies that can handle such forces.

If the tools shown are all that you have to work with then your only choice is to square up the channel flanges in a second press operation. Worst case press them hot.

A very simplistic explanation here. https://en.wikipedia.org/wiki/Bending_(metalworking)
 
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What is the inside radius of your bend. Rule of thumb is inside radius is three times the metal thickness. The photos didn't fully open so I couldn't see. As someone pointed out you need to relieve or taper the punch so the top is smaller than the bottom. There is a formula for bend allowance so spring back is at a minimum.

Good luck
 
Thanks Guys,
No this was a one off part but I was trying to solve the problem now for future bending.

Joshua not sure where you are saying to put the piano wire. Thinking of this as a C channel are you saying between the face of the channel and the clamp? so it will act like a roller or under the toe? I did use bearing grease probably not the best thing but what I had. I will look up swaging lube later on.

More or less the second press operation is what I did I pinched it in the bench vise while lightly heating the corners. I was worried if I did not the face would bow from the bending. this part is to bridge a crack in a friends wooden kitchen stool. so inside is very critical and the face being flat is a must. I made the punch the way I did as I wanted to try forming this way. Also it was less work then making an off set punch to allow for the leg of the first bend. Well this is how we grow and learn. Thanks again guys for you help. I will study the things you have provide me with.
Mark
 
Inside is about 3/16. That radius had to be pretty tight to match the leg on the chair. as it sits it is about twice the thickness of the material.
Mark
 
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