topic Re: Sheet metal: length on drawing different than model in Manufacturing (CAM)

Sheet metal: length on drawing different than model

bwilliams-4 — Thu, 03 May 2018 02:51:25 GMT

Hello all,I have a question, to which I cannot seem to find an answer. I am hoping y'all will be able to help me.In my work, we use plate steel and bend it. Pretty simple. I use the Sheet Metal application (Creo 3.0, M090), so that I can flat pattern the parts and be able to

Re: Sheet metal: length on drawing different than model

dschenken — Thu, 08 Jun 2017 23:18:29 GMT

The K or Y factor affect this.

In bending it is not possible to compress the metal on the inside of the bend so it has to squeeze sideways which is hard to do. On the outside of the bend it stretches and becomes thinner. Were the metal ideally elastic (which cannot be the case for plastic deformation to work) there would be equal amounts of compression and extension, but it is not, so the effect is unbalanced.

Rather than being the length of the mid plane, the neutral/unaffected length is pushed closer to the inside of the bend in various amounts, depending on the method of fabrication and the extent of the bend. In stretch forming is is even possible to shift the neutral length within the inside radius.

A start value for Y factor is .50 but it really depends on the tooling and the material. See SheetMetal.Me – K-Factor Same thing with springback, which is also not included in these calculations.

Here's a good article SheetMetal.Me – Y-Factor

Re: Sheet metal: length on drawing different than model

StephenW — Fri, 09 Jun 2017 12:10:09 GMT

In addition, you may want to refer to machinery's handbook, they have a section on bending. If you know how the part is manufactured (air bending, bottoming die, etc) and you know the material, you can get some really accurate results based on formulas. If you are sending parts to arbitrary vendors to be manufactured, it may not be a good idea to send flat patterns since you may not know the process they are going to use. If you must send flat patterns, make sure there is a disclaimer about the accuracy of the flat and it is the vendors responsibility to verify all lengths are correct based on their processes.

I have used the centerline method way back. It can be close on thin sheet. It get's wildly inaccurate on thicker plate.

Re: Sheet metal: length on drawing different than model

BenLoosli — Fri, 09 Jun 2017 14:32:34 GMT

Never send a vendor the flat pattern!!! You are not buying that intermediate shape, you are buying the finished bent part. IF you have a good working relationship with a vendor AND you understand their process, then send it as a reference file only. I have been caught with rejected parts in the past where the vendor used our flat pattern and then the final shape was off.

Search online for a paper called BendWorks, The fine art of SheetMetal Bending by Olaf Diegel. It has a good explaination of K and Y factors.

Creo can develop the flat pattern for you without constructing the mid-plane sketches.