Pipe bending is one of the most common operations formoizmenyayuschih cold forming, which is widely used for a variety of sheet metal, rolled sections, tubes and wire for this operation is used tube bending machine. In the process of bending the metal is subjected to simultaneous action of tensile and compressive forces. On the outer side of the material in place of the bend metal fibers are stretched and their length increases, the inside of the fibers are compressed, and their length is shortened. Only the core layer or the neutral line, at the time of the fold does not undergo contraction and expansion. Length neutral axis after bending workpiece does not change. In cases where the bending stresses do not exceed the limit of elasticity, deformation will be elastic piece, and after removal, the stress will take its billet original appearance.
There is another type of bending, which provides accurate angles and radii. This so-called flexible with stretching, bending when logging in is subjected to additional tensile force with bending tool. In this case all the fibers have tensile and observed only a slight reduction in cross-sectional area, while the angle and bending radius remain unchanged. The greatest distribution in the tool bench and work practices were bending. Upon receipt of parts with very small radii of bending a risk of breaking the outer layer of the workpiece in place as a result of bending excessive for the material elongation of this layer. Increases the risk of bursting due to the presence of surface defects piece (cracks, tearing). The value of the minimum allowable bend radius depends on mechanical properties of the workpiece material, the applied bending technology and the quality of the workpiece. Parts with very small radii of curvature should be made of plastic materials or pre- expose the raw material to heat treatment – annealing.