The pipe bender bends the pipe in the same way as the sheet material bends. In the case of pure bending, when the pipe with outer diameter D and wall thickness t is bent by the action of external moment M, the outer wall of the neutral layer is subjected to tensile stress σ1, and the wall becomes thinner. The inner wall of the neutral layer is subjected to tensile stress σ1, and the wall becomes thicker. Moreover, the shape of the cross section changes from circular to approximately elliptical due to the effect of the resultant force F1 and F2. When the deformation is too large, cracks will occur on the outside wall and wrinkles will appear on the inside wall.

The degree of deformation of the pipe depends on the size of the relative bending radius R/D and the relative thickness t/D, and the smaller the value of R/D and t/D, the greater the degree of deformation. In order to ensure the forming quality of pipe fittings, the deformation degree must be controlled within the permissible range. The bending limit of pipe fittings depends not only on the mechanical properties and bending methods of materials, but also on the use requirements of pipe fittings. The forming limit of pipe fittings should contain the following contents:

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

2) In the compression deformation zone inside the neutral layer, the thin-walled structure under tangential compressive stress will not exceed the instability and wrinkle;

3) If the pipe has ellipticity requirements, control the distortion of its section;

4) If the pipe has the strength requirement to withstand the internal pressure, the forming limit of the wall thickness reduction is controlled. Article source address: http://www.cn-wgj.com