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Bend Deduction


New member
I am new to Pro/Sheetmetal. Although I have been using Pro for 4yrs. I am designing a lot of sheetmetal parts with bends, my bend shop asked that if I could supply the bend deduction values it would help him out. My questions is: Will Pro give this info? if so how?

Thank You
There are several controls (inputs) that affect the resultant flat pattern for a given material thickness.

Working at MEP in Laval Canada for a while, their manufacturing engineer(s) helped me to interpolate/extrapolate specific values (inputs) thought to give us the closest measurable output of the finished parts. We focused on internal bend radii and initial bend Y factor and k factor for the few selected stock thicknesses of sheetmetal that were being formed on break presses after being cut with Laser metal cutters, or Finn Power, Amada Punches, or Strippit Tooling.

It was odd but MEP (metal fab shop) and BTU Intl.(client) often used extremely small inside radii for 90-degree bends, in the order of R.005. I thought it odd to be defining bends where the inside radius so significantly smaller than the material's thickness. But that was what they found to work. That gave raise to problems with accuracy on larger part having such a small radius. Sheet metal materials will usually have an INITIAL BEND Y FACTOR set at 0.5 (there is no immediate consideration of malleability or even ductility). In conjunction with the K FACTOR entered for the sheetmetal model, you can expect different outputs for standard 90-degree bends; let alone other acute, or obtuse bends, when the flat pattern is developed. Once the radius and initial_bend_y_factor were controlled, tweaking to get the desired output was done through the k factor. That was their logic and it worked well for them. I believe it came after significant trial and error.

The INITIAL_BEND_Y_FACTOR was sometimes up around .62, or down nearer .54, but not the default of .50, nor did I see it set smaller than .50. Their third party software worked splendidly. It was the effort to orient the part with grain direction sensitivity, and analyzing the post flat-pattern to make sure the Pro/ENGINEER SHEETMETAL model was close to representing the formed final product. It was an education. They took our arm waving design intent, made the part, then we often worked backward to get Pro/E to agree with the intended finish product.

So the bend deduction values are the compensating stretch based on the materials' natural properties, material thickness, your chosen bend radii, the sheetmetal value of k factor and the material's initial bend y factor. With all those variables, it's like putting 5 dice in the cup and hoping to roll Yahtzee or Kismet on the FIRST roll!

Thanks for reading

Jon Bixby
Pro/Sheetmetal is great!

check out Pro/HELP for details of how the K & Y factors are worked out.

There are three things you can look at straight away:

1. set up> Sheet Metal>Bend Allow>Bend Table

Pro/E has 3 default tables that hold information for sheet parts, I use TABLE 2 for mild steel parts (int Rad = T) works fine for me.

2. to get the info quickly use the top menu


this will show the details of bends you have on the model.

3. modify the part will show the 'De.L.' developed length of the part.

Also see the topic about flat patterns.

BUT keep in mind the properties of each sheet of metal varys within limits and can affect bending. (it's a good excuse!)


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