Calculating Sheet Metal K-Factor

Calculating Sheet Metal K-Factor




First of all if you are not familiar with what a K-Factor is, let’s refresh. The K-Factor is the ratio between the neutral line of the metal to the thickness of the metal. The neutral line is an imaginary line that runs by the center of the metal before it is bent whose length does not change during the bending. The K-Factor is a geometric relationship, meaning it’s not something you can measure directly. The K-Factor is useful in inputing into software to automate the calculation of of flat patterns.

If you have a Bend Allowance (BA) or Bend Deduction (BD) you can calculate it directly. Below are the equations necessary to calculate the K-Factor if you have the bend allowance or bend deduction obtainable. If you don’t have these we will give a tutorial how calculate them below.

K-Factor = t / Material Thickness

K-Factor = (180 × Bend Allowance) / (π × Bend Angle × Material Thickness) – Radius / Material Thickness

K-Factor = (( 2 × tan((Bend Angle / 2) × (Material Thickness + Radius)) – Bend Deduction) × 360 / Bend Angle / (2 × π ) – Radius) / Material Thickness

So what to do if you don’t have either of those? Maybe you’re starting to work with a new machine, starting at a new company, trying to enhance accuracy, or maybe you’re just disinctive.

obtain some strips of metal of consistent size and thickness. I would recommend a piece approximately 3″ by 12″. To short and it will be difficult to keep up in the brake, to thin and it won’t be a consistent bend. Carefully measure and record the pieces. For the sake of the tutorial let’s say our pieces are 3″ by 12″ and 16 gauge (.060″). Take the parts to the brake and put a 90° bend in the center of each. Measure and record the flange lengths left by the bend. (Lets assume they measure 1.42″ on average). Deduct the two flange lengths from the original flat pattern to acquire the Bend Allowance. (3-1.42*2=.16) Measure the inside radius of the bend. Use a radius gauge to measure the inside radius. (For our tutorial lets use a radius of.079″)

Now we have all of the information we need to calculate a K-Factor: K = (180 × BA) / (π × B< × Mt.) - Rp. / Mt. (For our tutorial K=(180*90)/(3.1415*90*.06)-.079/.06=.38)

A K-Factor will typically range between .3 and .5 though smaller and larger K-Factors are possible.




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