Calculating K-Factors 1

[Updraft]

I got tired of teaching my sheet metal vendors how to calculate K-Factors so I put something together for them. (Most of them just used trial and error methods to develop their flat patterns or blindly used a single value without understanding why and when it was valid!)

There are probably some here who can make good use of it as well so I thought I'd post it.

Enjoy!

- - -Updraft

 

[MadMango]

Updraft,

Thanks, this looks really good. One of my first SolidWorks jigs was at a company that was predominately a sheet metal fabricator. We soon learned that math alone was not enough to get accurate K-factors, as even the type of tooling, tooling clearances, and wear could cause variations. We created test strips for the various metals and tooling and machines, and finally had a matrix of K-factors to use for a given situation. After this, it was easy for our shop to hold +/-.010 on 10-16 gauge parts.

Of course this really only worked so well since we manufactured our own parts. Many times you can arm a vendor with data, but still can't get them to pull the trigger.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of these Forums?

 

[TheTick]

If I have to tell a vendor something so basic, I do not use them.

 

[drawoh]

Updraft,

I agree with TheTick. My vendors ask for my SolidWorks files so they can flatten the part and plug in their K factors.

I expect my fabricators to know more about fabricating than I do. All I do is accept the SolidWorks default K factor.

JHG

 

[Updraft]

This comes from the last place I worked where we did or own sheet metal and I had to teach the other engineers about K-factors. It made a huge difference.

MadMango, you are correct that the particular tooling makes a big difference. That actually made this type of spreadsheet all the more valuable since it made it easy for the shop to make a few simple measurements and give us accurate K-factors. I've had shops use this to calculate different K-factors between brake forming and forming in a hard die; different values even though the IBR and thickness were the same. We even identified differences when bending with the grain vs. cross-grain. As a result we were able to routinely achieve +/-.004 for most cases (with Cpk=1.33).

I prefer the top-notch vendors as you guys have indicated, but I don't mind helping out the guys I'm forced to deal with. After all, it is in my best interest to help them.

- - -Updraft