The Y-Factor is simply a variable based of the more commonly used K-Factor. It is derived by taking half of the K-Factor multiplied by pi.

Y={\dfrac{K \cdot \pi}{2}}

The Y-Factor is used, as far as I know, solely by PTC’s Pro-Engineer, now known as Creo Elements/Pro. From and is defaulted at .5, leading to a K-Factor of approximately .318, which is not a terrible starting place for sheet metal design. The Y and K-Factors affect how the part stretches when transitioning from a flat pattern to a finished piece so it is important to understand their values. However to achieve truly accurate parts and designs you are almost always going to have to edit the Y-Factor. To do so there are a few basic methods.

The first method I would recommended is to edit the ‘Material’ file. You can do this by simply using the PTC_INITIAL_BEND_Y_FACTOR parameter when in the Material Definition screen. This will allow you to set specific Y-Factors to your materials. To my best understanding you cannot set specific values to individual gauges, but this is a common limitation with design software. Being able to set a specific factor for each material should get you very close to perfect when designing parts. If, after setting the material, you un-assign your material from the part the K-Factor will remain whatever it was set to last. This should be taken into account when switching materials.

The second method for editing the Y-Factor is to use the ‘Set Up’ command. This will allow you to initialize the Y-Factor creating a new default. New parts created after the set up will have your new Y-Factor as their default. This may not be the best method as different materials will exhibit the need for different Y-Factors. Again you can reference our posting on the K-Factor, complete with charts and explanations.

The third option is to edit your configuration file and permanently set the Y-Factor for all new parts. This is practically speaking the same as using the ‘Set Up’ command and is thusly not recommended if you’re working with a variety of materials, or trying to get very accurate parts.

To add an extra level of accuracy to your parts the Y-Factor can be edited for individual features. This can be beneficial towards the extreme ends of the Bend Angles or radii where the neutral axis becomes less and less aligned to the proper Bend Allowances.

If you wish to avoid using the Y-Factor Pro-Sheet Metal, as well as most design programs, will allow you to substitute a bend table in place of its own calculations. These tables are typically based off of the Machinist’s Handbook, a must have for all manufacturing engineers. These tables were in turn based off of experimentation. As far as I know there is no absolute or all encompassing formula for deducting a flat pattern.

Y-Factor Chart

Below I’ve included a chart based off of our K-Factor chart. This will give you a good starting point when experimenting with Y-Factors in your designs. I know new engineers hate to hear it but experimentation is really the best way to get to a perfect part, however using these charts in addition to what can be learned about tooling geometry and the different types of bending you will certainly be able to get close enough for %99 of applications.


RadiusSoft / AluminumMedium / SteelHard / Stainless Steel
Air Bending
0 - Mt..52.60.63
Mt. - 3*Mt..63.68.71
3*Mt. - >3*Mt..79.79.79
Bottom Bending
0 - Mt..66.69.72
Mt. - 3*Mt..72.74.75
3*Mt. - >3*Mt..79.79.79
0 - Mt..60.64.69
Mt. - 3*Mt..69.72.74
3*Mt. - >3*Mt..79.79.79