To ensure the desired size of parts after the final bending process using a press brake, the design of sheet metal parts uses various algorithms to calculate the actual length of the sheet metal under the bending condition. One of the most used methods is the simple “pincer rule”, which is based on personal experience in calculation.
However, with the advent and widespread use of computer technology, more people are turning to computer-aided design methods. In general, there are two popular algorithms for sheet metal bending that are widely adopted today. The first one is based on the flexure compensation algorithm and the second one is based on the flexure deduction algorithm.
Bending Compensation Method
The bend compensation algorithm calculates the expansion length (LT) of a part by adding the length of each section of the part after flattening and the length of the flattened bend area, which is known as the “bend compensation” value (BA ). The formula for the length of the entire piece is as follows: LT = D1 + D2 + BA.
It is assumed that the bending area deforms during the bending process. To determine the geometry of the unfolded parts, the following steps must be performed:
- Cut the folded area from the folded part.
- Lay the remaining two sections flat on a flat surface.
- Calculate the length of the bending area after flattening.
- Join the flattened fold area between the two flat sections to get the expanded pieces.
Curvature deduction method
Bend deduction refers to the amount of reverse bending and is a simple algorithm used to describe the sheet metal bending process.
According to this method, the flattening length (LT) of the part is equal to the sum of the length of the two theoretical flat sections extending to the “sharp point” (the imaginary intersection of the two flat sections) minus the bend deduction ( BD value).
Expand the Calculation Principle:
- During the bending process, the outer layer experiences tensile stress, while the inner layers experience compressive stress. There is a layer that is neither tensile nor compressive, called the neutral layer, and undergoes a transition from tension to compression. The length of the neutral layer remains unchanged during the bending process and is equal to its length before bending, becoming the basis for calculating the expansion length of the bent part.
- The location of the neutral layer depends on the degree of deformation.
When the radius of curvature is large and the angle of curvature is small, the degree of deformation is minimal and the neutral layer is close to the center of the sheet thickness.
On the other hand, when the radius of curvature decreases and the angle of curvature increases, the degree of deformation increases and the position of the neutral layer gradually moves toward the inner part of the center of curvature.
The distance from the neutral layer to the interior of the sheet is represented by λ.
Basic Formula for Expansion Calculation:
Expansion length = inner layer + inner layer + compensation value
