Tube Bending Question

[charger19690]

Looking for some input on Tube Bending.

Project...

1" Square Tubing, Alum, .065" walls.

We are trying to bend a 4" Inside Radius 90 degree

So we made some dies for our CNC Bender, basically copying other dies we have with the appropriate dimensions for our application.

Bending Die is almost a perfect 4" Diameter, within .005"

The jist of the problem is that there is a Bending Die, Clamping Die, and a Pressure Die.

The actual bend is coming out at 4.2" to 4.3" depending on who is telling the story.

Well the consensus with the "Powers that Be" is to just cut the die by .2" to .3" to get the right inside radius on the part.

My argument is that there is a Mandrel in the inside of the part and I suggested maybe back the Mandrel back some, maybe it's too far past the tangent of the bend, forcing the Bend out and skewing the Bend.

My other argument is to slow the Pressure Die feed down a bit so that the material is actually getting pulled around the Bending Die, versus just pushing it around it.

I don't know much about Bending and this has been a new experience.

The quick little story is that the company decided to make our own dies because we are a Machine Shop. Well the tooling guy and myself designed and made the dies, which turned out mint by the way.

So we handed them over to the welder, which runs the CNC Tube Bender and heard nothing about it.

Then all the "Powers that Be" from the office were standing around it saying how good he did. Well for the past week they all were patting themselves on the back for the great job they did.

Now a week later after some test parts, they inspected some and the radius is big, so I was told indirectly. Me, nor the tooling guy have been told or asked anything at all. Now they are talking about having the tooling guy cut this die up because the radius isn't coming out right. We are only hearing this by gossip in the shop, no direct input.

Well the tooling guy and I were talking today about the gossip and came up with the above suggestions, and told the shop foreman about it, which said our dies wouldn't work to begin with and said the material would crack and break. That didn't happen, but now he said that trying other things wouldn't work either, but probably just have to cut the dies up the difference or what the radius is checking.

I firmly believe that there is a bit of a science to tube bending and just hacking things up isn't where to start. Being that me and the tooling guy are the only ones close to knowing anything about bending, I am asking if anyone here might have some input.

Thanks,

Mike in MN

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[LessOneD]

Hello Mike,
From my "overseas side", if I understood all ...
-no reason to change the "advance position of mandrel", because radius become shorter.
-Try, in case of using "balls", the radius they produce.
-the contact of pressure-die, for sure will be increased a little bit, for more power
-don't change (never !) the advance of "following pressure-die" (?).

... and give me some news !