Bending Davit Arms

[zakk]

We wish to construct a press that will allow us to cold bend A36 solid round bar 90 degrees for use in davit arms. In sizing the press, we need to know how large of a hydraulic ram to use. There are a lot of tube and sheet bending formulas out there,but little on solid rounds. Any suggestions where to find formulas for force required and springback?

 

[boo1]

I would consider the use on pipe to be more effecient than solid bar. Use the section modulus and the material yield strength to determine the design moment required. The geometry and moment gives the required force. System pressure and Actuator area are matched to the required force.

 

[deanc]

Based on my past experience,I would form it hot. There is lots of variation in A36 bar.

 

[zakk]

boo1:
The problem is the difference between pipe O.D. and solid bar O.D. We current 'farm out' the bending of 5/8" to 2.00" solid round bar and we wish to build a press to do it ourselves. Nomimal pipe O.D. won't work.

Deanc:
We currently have the bar cold bent and it works well for our application. Heating would make life easier in some respects, but it's another step and cost we wish to avoid, and cold bending seems to work with the product we are receiving.

I guess I could get more specific: how much hydraulic force is required to cold bend a 2.00" diameter solid round bar 90 degrees with a 4.00" inside radius? It is doable and our supplier doesn't want to give up any information, naturally.

 

[dimjim]

How long are the legs on each side after
bending? I would think a coil spring
manufacturer could give you some formulas
from their experience. How many pieces
are you making?

 

[JStephen]

Figure you'll essentially need to yield the entire area of the bar, plus go over that somewhat, and you should be able to calculate the moment required from that. The force required would depend on the geometry of the bending set-up. Look at your mill certs to get an idea of actual yield stresses on the material you're using.

 

[GregLocock]

The moment of plasticity of a section is the yield stress*the first moment of area


Where the first moment of area is the integral of dA*z

where dA is a small area and z is its distance from the bend axis.

Sorry I haven't got time to work it out, but it would be roughly 3/4*d/4*d*d/2*2 or a bit less

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[deanc]

If you want to cold form this I would build a set of 3 point open air dies. The farther apart the bottom contact points are the less tonnage it will take. I would use a good round nose 2"r for the top.

500 ton press should be adequate if you have a 12" spread on the bottom. Once you get your stroke set your off and running. Be prepared to scrap a few for set up.

Make sure you build it strong and anchor it well so it does not take off on you.

If you have a good press brake operator who has done AR plate....they should be able to set this up.

Another option would be a "wrap around" such as an Erhle Former. Moving table which wraps the part around a fixed die. Not many of these around,job shops have most of them.

Note: If I did not have the equipment or the right people I would still form it hot.