Bending device Calculate required forces

[wirdwild]

Hello everyone, I have a question about calculating forces when bending.
I want to bend a flat sheet completely round using a cylindrical mandrel and two bending forms.

Bending sequence:
1. as you can see in the picture, the force is transmitted from above via the two bending mandrel heels (the force is distributed evenly, 2x Fmin/2, so to speak).
2) In the first step, the sheet is pressed completely into the radius of the lower mold by the bending mandrel.
3 The bending mandrel remains in the mold.
4. then the second mold comes from above and the sheet metal is bent completely round to form a tube.
The sheet metal is not clamped, but placed loosely against a stop.
This means that the sheet metal can move during the bending process and does not start to flow as in deep drawing, for example, where the sheet metal is clamped. This is also intended.


Data on the bending mandrel:
Effective area for bending: 250 mm
Diameter: 24.8 mm
Material: Heat-treated steel (used for punching tools)

Data on the sheet metal:
Sheet metal: DC04
Yield strength Re: 210N/mm^2
Tensile strength Rm: 270N/mm^2
Sheet width: 250mm
Sheet thickness: 0.5 mm

Data on the molds:
Length: 250 mm
Inner radius: 12.5 mm

In the attached pictures you can see the rough structure of how the bending should be done and how the sheet metal is bent step by step.
The sheet metal is only bent as an example.

I had various aspects in mind here, such as the fact that the sheet metal is compressed and there is a solidification during pressing into the mold.
Is the required force minimally increased or is a constant force assumed?
Do you calculate with a projected area?
What other aspects play a role? - I could very probably neglect friction forces, as they are too irrelevant.

I am looking for the minimum Force F required to achieve plastic and complete deformation into the two shapes.


If you have any solutions for this or even the solution, that would be very cool.

Greetings wirdwild

 

[Lumber Jim]

It looks like you should do some research on press break tonnage calculations since that is basically what you are attempting to determine if a theoretical answer is necessary but just at a much smaller scale compare to what I'm used to seeing.
Here are a few calculators to give you an idea for where to start and what to consider to determine the answer you are looking for.

https://www.e-ci.com/press-brake-tonnage-load-calculator
https://www.pacific-press.com/hydraulic-press-and-press-brake-calculators/bending-force-calculator/

note that these are for "air bending" and what you ultimately want to determine is the "coining" requirements to fully set the material in the bottom of the die.

I couldn't find any references off hand for coining tonnage... but they are out there.

You should think more about the steps you have outlined... it's going to take more than 3. Going from 2 to 3 isn't possible with your current dies if you want a round part in the end...

Your top die would need to be split and both new dies would need to approach the lower die at an angle from opposite sides of the round mandrel in order to force the edge of the sheet around toward a close up seam.

You'll need to understand K factor for the material, the amount of coining that will take place to set the material, and the raw material will need to be positioned fairly precisely over the lower die.

This is to arrive at the appropriate starting sheet width to achieve a close up seam that has an appropriate gap once the forming is complete. When you release the part from the die your close up seam will open if not welded in the die and if you weld it you will have trouble getting the part off the round mandrel.

If the sheet is too wide you will see buckling and rippling of the material once the dies are closed and then opened to reveal the part. You may end up with some trouble getting the part free from the lower die depending on how you set everything up.

You might be better off looking at the process for how welded pipe and tube is made... depending on how many of theses parts are needed.

or find a way to make 1" thin walled tube work for your application....




Best of luck!