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Estimating bending length

Main principle of plate metal bend

Bending shapes plate metals. The area of the sheet plate close to the inward side is pressed, and the outside area is extended. The most perfect area is the mid side, which is not stretched or compressed. This is referred to as a neutral level, which is the mark to calculate bending. In general, the length from neutral level to the inner side of bending can be referred to as K-factor.

Plate metal bending estimation methods

1. Bending compensate method

See in the figure below.

LT = D1 + D2 + BA  LT、D1、D2、BA as shown in fig1,2

2. Bending subtraction method

LT = L1 + L2- BD   

LT、L1、L2 shown in fig1,2. BD is the subtraction valuation, which is the withdrawal quantity.

3. Bending compensation BA and bending subtraction BD ratio.

TAN(A/2) = (L1-D1)/(R+T) 

The same reason TAN(A/2) = (L2-D2)/(R+T) 

The ratio between the compensation quantity BA and the subtration quantity BD is:

BA= 2(R+T)TAN(A/2)-BD   In case of 90degrees bend, BA = 2(R+T)-BD, therefore tBA + BD= 2(R+T)

Inserting K ratio

In general, the coefficient of the length (t) from neutral level to the inner side of bend and density (T) is referred to as K-factor. K=t/T 

BA=Pi(R+K*T)A/180 Mostly K-factor source is provided by manufacturers of metal plates, testing records, manual guides and so on and it is dependent on sheet types, density, processing specifications like bending semi diameter, bottom die slot breadth, device speed and so on.


Introducing bending neutral level as well as K-factor makes it easy to estimate the improved length and learning K-factor influences. There are two ways to estimate bending expansion:

Bending compensate mode:

LT = D1 + D2 + BA = D1 + D2 + Pi(R+K*T)A/180

Bending subtraction mode:

LT = L1 + L2 – BD = L1 + L2-2(R+T)- Pi(R+K*T)A/180

Subtraction valuation mainly depends on sheet material, density, bending semi diameter, V groove breadth. Bend line is half of the subtraction value.

Let`s take X subtraction value, expansion ratio will be  

b=B-0.5X   c=C-0.5X   a=A-X




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