K-FACTOR/BEND ALLOWANCE

[Riaan14]

Hi guys,

Wonder if you could help me?

I am using Inventor for sheet metal work with the default K-factor values. When I give my flat pattern to the bending company to bend, the finished product is always smaller as it must be. So all the other parts that is supposed to fit inside is way to big.

I do not have so much knowledge of sheet metal and all the values, so I figured the default Inventor K-factor value is suppose to be correct? 0.44.

The bending company uses Trumph machines, so can it be that the machines needs different K-factors?

Or could it be human error with the bending?

If someone could give me some advice.

Thank you

[Frederick_Law]

K-Factor depend on material, bend radius, bend angle.

Ask the forming company for K or allowance.

Or give them final product and let them work out allowances.

K-Factor in all CAD software are not "correct".

[mcgyvr]

😋

First mistake = you gave a flat pattern to an outside company..

Second mistake = you assumed Inventors data was correct.

K factors MUST be determined for each machine/process/bend radius you intend to use. There is no "one size fits all" value. 

A sheet metal company should be given the drawing showing the part in the "as formed" state and its their job to calculate the flat pattern given their known bend allowances,etc... There are very few if any cases where you should provide a flat pattern to an outside company. If they aren't capable of determining the flat pattern size then find another sheet metal vendor as they are not qualified to be one. 

If you are making the parts in house then you must determine accurate kfactors to use. We do that by actually bending a sample and then calculating the correct k factor given the flat length and then entering the lengths of the as formed legs. (There is software to calculate that for you)..

I have a table of every material we bend and the die radius and v dies being used. But when I provide a drawing to our sheet metal vendor is the "as formed" drawing/views only.. 

[jeff]

Hello!

That is 100% correct. K-Factors need to be calculated for every material type, thickness, bend radius, and die opening and the only way to do that is bending up real-world samples and taking precise dimensions of all the results. We use a program called BendWorks for the K-Factor calculations (which doesn't seem to be available anymore) and we've built up a library of sheet metal styles over the years which give us incredibly accurate results on the shop floor. We have, in the past, provided our sheet metal template file to customers that use Inventor (and us for fabricating their parts) so that when DXF files or models come in; they are accurate for our equipment.

Here's the thing; those sheet metal styles will really only be accurate for OUR SHOP because of the tooling we own. If a customer took their flat files to the guy up the street, the chances of them being correct are very slim. So, yes, you should NEVER provide flat files to an outside source unless they've given you the correct K-Factor values to use on their equipment.

[jeff]

Spoke too soon!

BendWorks is available for download here: https://bendworks.software.informer.com/ 

It is probably not being developed any further.

[riaan.bekker]

Hi All.

Thanks for all your advice.

It appears that the 0.44 K-factor is to small, so I made 3 samples with 3 bigger K-factors and asked the bending company to bend it, then I will see if we can get to a good result via trial and error.

Also here in my country, the companies do not except responsibility for there work, thus you are responsible to supply the flat patterns, so that when something is wrong it is your fault.

Can someone please point me to a website where I can find information regarding the K-factors for aluminium and the bending radius's?

I have some difficulty finding there correct information.

[Frederick_Law]

K-factor works only if all the bends are same angle and radius.

A bend table will work better.

You will not find specific K-factor for any material.

You need to bend a piece and calculate.

https://www.machinemfg.com/fabrication-calculator/

K go from 0-1.

0 means to use inside bend arc length.

1 means to use outside bend arc length.

http://sheetmetal.me/formulas-and-functions/k-factor/

[jeff]

Wow,...they won't accept responsibility for incorrect blanks? Do they have a "we dare you to do business with us" line in their mission statement? This is the problem with supplying flat files to an outside contractor,... you are left twisting in the wind when it comes to producing quality parts. I would be shopping hard for a different company to work with.

What version of Inventor are you using? I'd be willing to share my Sheet Metal template but, of course, as I stated in the previous post, there is no guarantee that it will be correct for the company you do business with because every shop will be using different tools.

[Riaan14]

Hi Jeff,

I am using 2019 currently. I understand that it will probably not work 100%, but at least I can look at it to set up my own one.

Thanks

[jeff]

Here's our Sheet Metal template file.

In case you don't know,...open the IPT file and then save it as a template file.

Again, no guarantee that these numbers will work for you but they are 100% accurate for our shop with our tooling.

[jeff]

I should mention that we don't run sheets heavier than 0.250" here so the list of materials ranges from 20ga up to 1/4".