What is K - Factor in Sheet Metals?

In sheet metal, the K-factor is the ratio of the neutral axis to the material thickness. The inside portion of the bend contracts as a piece of metal is created, while the outer portion expands (see Figure ). The neutral axis is the region where the material does not change, except that it travels from its original location at 50% of the material thickness toward the inside surface of the bend. It represents the transition between compression and expansion. Bending results in elongation because the neutral axis relocates rather than changing its length.

The physical characteristics of the material, its thickness, the interior bend radius, and the manner of forming all affect how far the neutral axis shifts. Refer the metal sheet in the figure above. When a material is bent, the inner and outer portions both experience compression and tension. This changes the length of both inner and outer surfaces. There is a Neutral Plane between both these planes where the change in length is Zero. This is where the transition from Compression to Tension takes place.

You can predict where the neutral axis will go by multiplying the material thickness by the standard default K-factor value of 0.446. In essence, what we're doing is pushing the measured length from a bigger radius—specifically, the neutral axis' length at 50% of the material thickness—onto a smaller radius. We have surplus material, or elongation when the same total measured length is dispersed throughout the smaller radius.

Consider 0.060-inch-thick material. You can predict where the neutral axis will be by multiplying the material thickness by the standard default K-factor value of 0.446. In essence, what we're doing is pushing the measured length from a bigger radius—specifically, the neutral axis' length at 50% of the material thickness—onto a smaller radius. We have surplus material, or elongation when the same total measured length is dispersed throughout the smaller radius.

Mathematics behind K- Factor 

As said, K-factor is a ratio of t/Mt the K-factor is defined mathematically as t/Mt, where t is the neutral axis location and Mt is the material thickness. Because of the specific properties of any given metal, there is no easy way to calculate that value perfectly. Generally, some reference charts are used to find the values. 

The K-factor is usually somewhere between 0.3 and 0.5. Should you wish to calculate the K-factor rather than use a chart, you will need some test pieces—a sample set of four or five pieces should do nicely for this purpose. You need to perform some lab tests to decide the values for the specimen.

As said, The value of the K-factor depends on :

1. a) Material Thickness
2. b) Material Properties 
3. c) Bend Radius

Introduction to Y-factor 

It is nothing but the derived factor out of K-factor in cases of an extra stretch to the materials. 

The formula for it is : 

Y factor = `(K Factar)* pi/2`

It is just the part constant used to calculate the developed length of sheet metals in extra stretch/load scenarios. 

The default value for Y-factor is 0.5