Sheetmetal Folding and k-Factor

Quite often I hear Inventor users saying: “the folded part didn’t come out like it was in the model, I even gave them a flat pattern!” The flat pattern feature in Inventor is not all that accurate if you don’t have the sheetmetal style set correctly to suit material, tooling and processes used to form the part. k-Factor is a useful number that when used along with a correct bend radius can give sheetmetal flat patterns that will fold up very accurately. “So how do I work out this magic k-Factor?” you ask. The easiest and most accurate way to do this is:

  1. Cut out a rectangle of material that you want to fold, say 100mm x 50mm. Measure accurately, and record, length and thickness.
  2. Mark a bendline across the centre of the rectangle and form a 90 degree fold with a press-brake or whatever you are using to do your folding.
  3. Measure, with a vernier caliper, the length of each side and record these (I’ve called them “Leg 1 Length” and “Leg 2 Length”
  4. Measure and record, using a radius gauge, the Inside bend radius.
  5. Plug these numbers into the calculator I’ve created here, and voil√†, you have your k-Factor to put into your sheetmetal style in inventor.

To check your result, create a sheetmetal style in inventor that has the measured bend radius, k-Factor (from the calculator), and measured thickness, and create a sheetmetal part using this style. Sketch a rectangle, create a face from it, put another sketch line across it in the center, create a 90 degree bend and using the measure command, compare it with your real sample. They should be pretty close. If not, maybe your bend radius is not quite right as it’s a very difficult thing to measure accurately. You can fine tune the k-Factor if necessary.
Note that you will need to repeat this process any time you change material, thickness, tooling etc.

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