What is K-factor and how do I use it?

This may help. Its a good introductory piece to working with sheet metal parts in solidworks.

The basic answer is where in the bend the center line falls, and how much the outside of the bend "stretches" and how much the inside of the bend "compresses" when being bent.
I do a lot of very small aluminum sheet metal parts that are .050 or .063 thick and we use as a standard a K-Factor of .4 for all the bends.
It's not alot, but I hope it helps.
Good Luck!

Thumb Rule of K-Factor
for everyone find and calculation of bending lenth with easy method
was taught a rule of thumb:
Radius < Thickness, K=.25
Radius < 2 * Thickness, K=.33
Radius > 2 * Thickness, K=.5

i hope its help to learn

From personal experience: Consult the sheet metal fabricator about the BA (Bending allowance), radius and K Factor - some figures may be used based on a rule of thumb or based on other people's experience, however, it's best if the fabricator gives you the table with sheet material type, thickness and BA and K factor. For the same sheet thickness, but different type (Chrome SS or Plain Carbon S) all these three parameters might be different with the same length and angle of the bend you need to design on a sheet metal. A wrong setting usually ends up with inadequate clearances or the holes don't match on overlapping sheet surfaces , etc... I designed several cases for electronics and just as an example, if the "knife" (tool) radius is 0.8, that doesn't mean that every sheet material will bend at that radius, thus, it will result with misaligned edges, holes and become useless. Fortunately, laser cutting is an advanced technology, no need to invest into expensive pressing tools to get a different version of the unfolded piece, just fix the drawing and there you go :)

Tanel another option that is not so close to the theory of this pdf but you will help a lot the guys on the bending machine is the following.
Unfold your sheet metal part and by adjusting the K-Factor try to bring your bending line in a desirable distance.
For instance you have SM thickness 1mm and you look for a flange of 10mm that means efectively that your bend-line should be in a distance from the edge between 8.8 to 9.5 depends on the Factor you choose.
Of course you know that ideally the K factor should be 0.5 and for this value you should get something around 9.178mm from the edge.
So try to find through your factor where you gonna get a clear 9 as the 9.178 will not make any difference, normally these decimals are included in the tollerances of the operator and the bending machine.