Sheet metal unfold/flat pattern isnt the same irl... Settings?

[waterjetZXA5D]

Hello

Im a rookie in Fusion. The sheet metal is the most relevant thing for me at the moment. But its not working in real Life for me. If I insert exactly the same dimensions to a simple 90 degree bend in Fusion and then in our pressbrake the flat pattern dimension has a differens in between 0,5mm-1,5mm depending on the thicknes of the material. I have made some tests in different thicknesses in mild steel and calculated the K-factor and radius that I have insert to Fusion. I thought that was the problem but it wasnt… I still have the same issue. We manufactor some details that has to be in better tolerence than in 0,5-1,5mm. Is there anyone out there having the same problem and maybe a sollution at it?

Thanks

/Mattias

[TheCADWhisperer]

Can you File>Export and then Attach a *.f3d file that illustrates the issue and include information on observed discrepancy?

[waterjetZXA5D]

Hello

Thanks for you replay and sorry for the delay. Busy as hell... I think I have find a solution. I change the radius in the sheet metal rule. As an example our pressbrake displays that we will get a radius at 2,6mm when bending 90 degree in 1,5mm stainless steel. But with this value in the rule I got 1mm difference in the flat pattern between our pressbrakeprogram and Fusion 360. I changed the radius to 2,895mm in the rule and now I got the right dimension at the flat pattern.

[TheCADWhisperer]

From your text description it sounds like you are not doing this correctly.

Attach file here.

[waterjetZXA5D]

Okey here is the dimensions of the flat pattern fron both Fusion & Pressbrakeprogram. In this case I just go with defoult settings in the rule. Radius = Thickness. Difference is about 4,5mm.

Fusion 360Pressbrake

[TheCADWhisperer]

File>Export and Attach *.f3d file here.

[waterjetZXA5D]

Okey... 🙂

[TheCADWhisperer]

Sheet metal stretches on the outside of a bend and compresses in the inside of a bend.

The neutral plane - location between outside of bend and inside of bend - is dependent on material properties, thickness, bend radius and bend angle. 

This is set with k-factor.

The Bend Radius is determined by the tooling used - should not make changes to this except to match the tooling.

I have two questions from your table image.

Q1.   Is this your Thickness.  1.5mm

Q2. is this your Bend Radius (all bends R2.6mm)?  (Bend Radius is given as the inside radius.)

Q3. In the part file that you attached what is the purpose of the Unfold/Refold (rather than Flat Pattern)?

I have to get some other work done - I will be back in a couple of hours to continue the discussion of sheet metal rules.

[waterjetZXA5D]

Yes I know this about bending metal. I have made some tests in different thicknesses and have calculate the K-factor. I tried to insert that results from my tests to the rule but that didnt change the dimensions that much. 

Q1. Yes that is the thickness.

Q2. Yes this is the radius our pressbrakeprogram with choosen tools says its gonna be. But Im not sure if that is the reality at the final product. When I change the value in the rule to: Thicknes * 1,93, the radius in Fusion will be 2,895mm and with that I get the right unfolded/flat pattern dimensions compared to the pressbrakeprogram.

Q3. I have used it just to measure the unfolded body to compare with pressbrakeprogram.

Thanks for your time! 

[TheCADWhisperer]

You must find the correct k-factor (bend allowance) for each process, material and bend radius.

Many companies generate a bend table based on test strips and keep it updated.

See the Flat Pattern of the Attached file.

https://en.wikipedia.org/wiki/Bending_(metalworking)#K-factor

[waterjetZXA5D]

Thanks! I read at the web that I have to find the right K-factor and I did a bunch of tests 3 weeks ago in the pressbrake and calculated the results in a program called Bend Works. But those K-factor numbers I get from that didnt make my day... Im at home at the moment so I dont have those results with me but I remember that I got numbers that was much higher than the ordinary/default around 0,44. But I think I understand it better now after your explanation and I know what I have to do.