Bending describes the forming of a workpiece in one to three directions with defined radii. It therefore differs from stretching, which only deforms a workpiece linearly. As a rule, metal bending refers to the one-dimensional forming of profiles or sheet metal.
Forming ranges of materials
Every deformable material has the following three stress ranges:
- elastic range
- deformable range
- separating range
The state until the yield point is reached is called the "elastic range". If a workpiece made of this material is loaded within this range, it springs back to its original state after the load is removed. Workpieces are statically loadable within this range. After exceeding the yield point, the workpiece remains in its formed state. This defines the forming area. After exceeding the forming range, the applied stress reaches the bending strength or elongation at break. The workpiece breaks or tears off. This is also called the "separating area".
These characteristic values of a material are determined by means of tests on a universal tensile machine using specimens formed in accordance with standards.
Metal bending process
Metals are processed into semi-finished products such as blocks, sheets or profiles. Metal bending refers to sheets and profiles. Blocks are machined and further processed into the desired products. Typical metal bending processes are as follows:
- Roll and roller bending
In roller bending, a profile is guided between three rollers. The distance between the lower pair of rollers, the roller cross-section and the immersion depth of the upper roller determine the bending radius. In roller bending, the contour of the roller must exactly match the outer edge of the profile, otherwise there is a risk of pressure marks at the points of contact.
Roll bending is the corresponding process for forming sheet metal. The roller and roll bending machines are used to produce particularly gentle bends and large bending radii. The rollers rotate slightly during metal bending so that pressure points are prevented.
Bending is used in metal bending to produce tight bending radii on sheet metal. The machine required for this is called a bending bench or swivel bending machine. With tool-free swivel bending machines, the sheet metal is bent around a bending point using a lever mechanism. Bending benches work with v-shaped and two-part tools. The sheet is inserted into the open tool. This moves together and bends the sheet in the desired direction. The angle of the tool corresponds to the maximum bending angle on the sheet metal piece.