The characteristics of the bending process of the bending machine

The bending of pipes by a pipe bending machine is the same as the bending of sheet metal. In the case of pure bending, when a pipe with an outer diameter of D and a wall thickness of t is bent under the action of an external force moment M, the outer wall of the neutral layer is subjected to tensile stress σ Under the action of 1, the pipe wall becomes thinner; Tensile stress on the inner wall of the neutral layer σ Under the action of 1, the pipe wall becomes thicker. Moreover, the shape of the cross-section changes from circular to approximately elliptical due to the combined forces F1 and F2. When the deformation is too large, cracks will appear on the outer pipe wall and wrinkles will appear on the inner pipe wall.

The degree of deformation of pipes depends on the relative bending radius R/D and the relative thickness t/D values. The smaller the R/D and t/D values, the greater the degree of deformation. To ensure the forming quality of pipe fittings, it is necessary to control the degree of deformation within the allowable range. The bending forming limit of pipe fittings not only depends on the mechanical properties and bending methods of the material, but also considers the usage requirements of the pipe fittings. The forming limit of pipe fittings should include the following contents:

1) The maximum elongation deformation in the tensile deformation zone outside the neutral layer does not exceed the allowable plastic value of the material, resulting in fracture;

2) Within the compression deformation zone on the inner side of the neutral layer, the thin-walled structure subjected to tangential compressive stress shall not exceed instability and wrinkle;

3) If there is a requirement for ellipticity in the pipe fitting, control its cross-section to produce distortion;

4) If the pipe fittings have strength requirements to withstand internal pressure, control the forming limit of wall thickness reduction.