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K- factor / sheet-metal flat pattern calculations - SMLease Design

K-Factor is a very useful term in sheet metal part design and manufacturing. K Factor is used by manufacturer for the calculation of flat pattern of sheet metal parts. Designers use k-factor to determine manufacturability of their designed parts.

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Bending is a manufacturing process by which metal can be deformed plastically to change its shape. Material is stressed beyond its yield strength but below ultimate tensile strength to achieve desired shape. This results in the change of surface area.

After bending there is some increase in the total length e.g. (Length + Height) is not equal to Flat Length.

Flat Length = Length + Height - Bend Deduction

 

 


Bend Deduction/Allowance

When sheet metal is bent, the inside surface of the bend is compressed and the outer surface is stretched. Somewhere in between the thickness of material lies neutral axis: Line with-in thickness that is neither compressed nor stretched.

Location of neutral line varies depending on the material, Temperature, direction of material grain, tooling conditions.

What is K-Factor

When sheet metal is bent, the inside surface of the bend is compressed and the outer surface is stretched. Somewhere in between the thickness of material lies neutral axis: Line with-in thickness that is neither compressed nor stretched.

The K-Factor in sheet metal Bending is the ratio of the position of neutral axis to the material thickness. Term k-factor is used in cad programmes to calculate sheet-metal blank size. 

 

What is Neutral Axis?

When metal is bent the top section is going to undergo compression and the bottom section will be stretched.  The line where the transition from compression to stretching occurs is called the neutral axis.

Location of neutral line varies depending on the material, Temperature, direction of material grain, tooling conditions.

K-FACTOR = Position Of Neutral Axis / Material Thickness

 

Calculation for Bend Deduction / Allowance

Best way is calculate bend deduction / allowance is by reverse engineering.

 

Step: 1 Take a blank of a particular thickness size and material (e.g.150X150X1mm)

Step: 2 Measure the Length A and B

Step: 3 Bend Deduction = Flat Length – A – B

Step: 4 do this iteration 2 to 3 times to get exact value of Bend Deduction

This bend iteration can be done for different thickness and materials.

 

 

Relationship in between Bend allowance and Bend Deduction –

 

 

Bend Deduction = 2 X OSSB - Bend Allowance

 

 

 

 

 

 


 

 


Relationship between K- Factor and Bend Deduction

 


Facts about K-Factor:

  • When a part is bent with sharp inside radius, as compared to the thickness, It will stretch more on the outside, which means neutral axis will lie closer to the inside of the bend. Whereas when part is gradually bent will have less outside stretch that means neutral axis will lie closer to the centre of the part.
  • Since the inside compression cannot exceed the outside tension, the k-factor can never exceed .50 in practical use. This means that the neutral axis cannot go beyond the middle of the sheet thickness.
  • With the increase in thickness value of k factor reduces.
  • With the increase in hardness value of k-factor reduces.

 


What Is Y Factor

Some of Design Software use Y-Factor instead of K-factor to calculate flat pattern in sheet-metal design. There is a direct relationship between K and Y factor.

 

The K-Factor is used to calculate flat patterns because it is directly related to how much material is stretched during the bend.  It’s used to determine Bend Allowance and Bend Deductions.

Download K-Factor Calculator

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