Hello Everyone,
I am trying to bend "C" shaped channels that are 8ft long and are made from 40 thou. thick 2024-T3. The flanges are 3/4" and the channel has a 2" I.D. Here is a CAD drawing:
So, I start with a straight strip of material that is 3.6" wide and 8ft long. I put the piece into the press brake and bend the 1st flange to 90deg. Here is a section view of the press brake "air gap" bending process that I am using:
When I take the (now) L shaped part out of the press brake - it has a very uniform, gentle bow the entire length of the piece. Here's an exagerated (for clarity), simulated CAD drawing:
If I place a long straight edge along (and tangent to) the side opposite the flange and then measure the distance from the straight edge to the far corners it is just a hair less than 1/8" on both sides. This is over 8 ft, so it is not a lot of bow, but it is defintely there.
My 1st thought was that my press brake was causing this. Then, after a lot of "thinking chair" time - I decided that this a function/property of the metal (material) and not the press brake. I have three main reasons why I think it is the metal causing this bow and not the brake, and they are:
1. I got similar results when trying to use a sheet metal (leaf type) brake. Only it was worse with that brake because I could not get a consistent angle of bend along the entire flange. The press brake will give me a consistent angle of bend if I use a "crowning" technigue to essentially overbend the middle more than the ends.
2. The bow in the material comes out OPPOSITE what you'd think, by using the crowning technique that I mentioned above. I flex the beam that holds the upper dia down into the lower die farther in the middle than on the ends (by about 0.015" - give or take). If anything, this should cause the bow to be opposite of what I am actually getting.
3. It is a property of all metals to thin down when stretched (also known as "necking" - I think). Since the material is being stretched somewhat along the entire radius of the flange, it must be shrinking a little bit every unit length (couple thous per inch for example).
So, I think that what is happening is that the side with the 1st flange on it now has "shrunk" buy a small amount and has caused this nice gentle bow in the piece. Also, the bow is so even and uniform, I don't think the press brake could cause this bowing phenomenon. Seems to me that if it was the press brake, the bow would come out more accentuated in some areas and less in another - like, it would be more crooked than bowed.
What say the experts out there? Have I analyzed this correclty or am I totally out to lunch and doing this all wrong?
Thanks for the help and insight.
R/Todd
I am trying to bend "C" shaped channels that are 8ft long and are made from 40 thou. thick 2024-T3. The flanges are 3/4" and the channel has a 2" I.D. Here is a CAD drawing:
So, I start with a straight strip of material that is 3.6" wide and 8ft long. I put the piece into the press brake and bend the 1st flange to 90deg. Here is a section view of the press brake "air gap" bending process that I am using:
When I take the (now) L shaped part out of the press brake - it has a very uniform, gentle bow the entire length of the piece. Here's an exagerated (for clarity), simulated CAD drawing:
If I place a long straight edge along (and tangent to) the side opposite the flange and then measure the distance from the straight edge to the far corners it is just a hair less than 1/8" on both sides. This is over 8 ft, so it is not a lot of bow, but it is defintely there.
My 1st thought was that my press brake was causing this. Then, after a lot of "thinking chair" time - I decided that this a function/property of the metal (material) and not the press brake. I have three main reasons why I think it is the metal causing this bow and not the brake, and they are:
1. I got similar results when trying to use a sheet metal (leaf type) brake. Only it was worse with that brake because I could not get a consistent angle of bend along the entire flange. The press brake will give me a consistent angle of bend if I use a "crowning" technigue to essentially overbend the middle more than the ends.
2. The bow in the material comes out OPPOSITE what you'd think, by using the crowning technique that I mentioned above. I flex the beam that holds the upper dia down into the lower die farther in the middle than on the ends (by about 0.015" - give or take). If anything, this should cause the bow to be opposite of what I am actually getting.
3. It is a property of all metals to thin down when stretched (also known as "necking" - I think). Since the material is being stretched somewhat along the entire radius of the flange, it must be shrinking a little bit every unit length (couple thous per inch for example).
So, I think that what is happening is that the side with the 1st flange on it now has "shrunk" buy a small amount and has caused this nice gentle bow in the piece. Also, the bow is so even and uniform, I don't think the press brake could cause this bowing phenomenon. Seems to me that if it was the press brake, the bow would come out more accentuated in some areas and less in another - like, it would be more crooked than bowed.
What say the experts out there? Have I analyzed this correclty or am I totally out to lunch and doing this all wrong?
Thanks for the help and insight.
R/Todd
