CREO SHEET METAL - K FACTOR & Y FACTOR - NEEDS TO BE CHANGED BASED ON MATERAL THICKNESS

[PM_10839291]

In Creo sheet metal, K factor / Y factor are fixed during the material selection. During modeling, when I change the sheet metal thickness, this K factor / Y factor are not changed automatically. This leads to wrong development length calculation. As per the below mentioned PTC article itself it is mentioned as K factor should change according to the thickness. (K factor = δ/T). This fixed value is blocking me the automating the DL drawing preparation 

https://support.ptc.com/help/creo/creo_pma/r11.0/usascii/index.html#page/sheetmetal/sheetmetaldesign/About_Y_factor_and_K_factor.html

[kdirth]

Creo does not automatically update the K factor when you change material thickness.  K factor is a ratio between the neutral line and the thickness, so the neutral line will move based on the K factor when the thickness changes.

The true K factor you use will depend on material used and process used.  It will also vary some based on thickness, when a large change is made.  You will need to provide the value needed.  That actual value, you will need to determine based on experimentation with your material and process.  Tooling, temperature, lubrication, and actual material will all affect the results.

[PM_10839291]

I agree to your point. I have the K factor value, for all the thickness that I'm using and same was validated with the machines also. Even I have a table also for that.

But the main concern here is during the change management.

While starting the design , I usually select the correct template , so that my K factor value with respect to material thickness is correct.

But during various stages of design & production, I/some other user may increase / decrease the material thickness . I/they can simply go to first feature (extrude 1) and change the thickness. Once it got changed, all other parameters like bending radius are getting updated in all features link flat 1, flat 2...etc. but K factor remains same and being at the different location, it is getting missed by the end users. And it leads to wrong development length.
There should be a feature in creo, the K factor value entry should be near to material thickness edit option or user can feed any standard table for that data.

[BenLoosli]

Where I used to work, we had the K-factor set to .44 since almost all of our material was A36 steel. The thickness of the material had very little impact on the desired flat pattern length when we would unfold the parts. We did not use bend tables, just the raw K-factor setting in config.pro. This was also in Wildfire, before PTC put all of those SMT_* parameters into the files.

If I understand you correctly, you want the K-factor to change if you use a bend table that has different values depending on the material thickness. I can see the need, if there is a significant difference in the developed flat pattern and how the bent parts fit together in an assembly. PTC needs to modify the code so when the material thickness is changed, and a bend table has been specified, the code needs to reread the bend table and get the new K-factor for the new thickness. The same logic would also apply if the material type changed, as that also plays into the correct K-factor being applied.

[vnamboodheri]

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[BenLoosli]

I have always found this pamphlet to be beneficial in understanding bending types and the deduction/allowance factors.

Art of Sheet Metal Bending 

[PM_10839291]

Hi..

Thanks for the reply. 

Theoretically the given statement and creo features are fine. But it is not suitable for the change management process. Creo allows the wrong K factor value to pass it on, There is no alarm / interlock while changing the material thickness to correct the K factor value also. 

[bbrejcha]

The y and k factor also may change with temperature in the shop etc but also grain direction can effect it.  In an early job as a quality control engineer at Siemens,  I've noticed half of the parts come in in at a desiered tolerance and the other half don't.  We figured out because half the parts were rotated for the water jet in the sheet. If you have the flattened state on a drawing usually sheet two the operator that the y & k factor are suggestions for starting and several scraps need to be made to narrow down precisely the flattened state to obtain the desired tolerances in the finished part.  This is why we have quality inspectors on the line. 

This is also why many Sr engineers will recommend not including the flattened state on a detailed drawing. As a training consultant I try to solve problems through education and training as  I suggest otherwise. In Sheet metal training classes I suggest a note be added to flatted state read something like this.  "Y & K factors are mealy suggestions for the operator and should be considered a good starting point for the flattened state of this part.  These variables are not absolute depend on a range of variables in order to obtain desired tolerances."     to avoid confusion we usually let the vendor resolve the flat.   A Partner would be included in your training class. Simply put a Y & K factor would never be ECN'd and everyone should understand.  Training is important.  

Bart Brejcha designengine.com