Forming method of circular tube is called bending, and the forming method of the rectangular tube
is called buckling. There are two basic ways to bend forming: solid bending and empty bending.
1, Real bend
Real bend, as the name suggests is the compaction of the bend, the actual time when the inner and outer roller and tube billet two-way compaction.
1) The advantage of solid bending is small rebound, forming accurate, and as long as the roller type is accurate, the angle of the inner corner of the R is more accurate.
2) The disadvantage of real bending is the stretching / ironing effect. First, the actual bend will make the bend at the tensile, stretch effect so that the longitudinal length of the bend line shortened; Second, the real bend bending metal thinning due to stretching.
2, Empty bend
Blank bending through the outer roller and the outer wall of the tube to form a one-way contact bending moment to strip material bending, empty bend will make the bending line compression, the compression effect of the longitudinal elongation of the bending line, bend the accumulation of metal thickening, this is the empty bend compression / thickening effect.
1) The advantage of empty bending is that it is possible to bend the side length when it is impossible to bend it, such as bending and finishing the top / side edges of the square tube
. Blank bending can also bend the internal angle of R <0.2t without rupture of the tube wall.
2) The disadvantage of empty bending is that when the square tube is in the synchronous bending at the upper side / side, the forming force will easily exceed the critical point due to the pressure generated by the upper roll and the lower roll at the same time, which will cause instability of the edge and will also affect unit stable operation and forming quality. This is also the rectangular tube and tube hollow bending different characteristics.
In practical application, these two basic methods should be configured to a reasonable process position according to the product needs in the rectangular tube forming. Attention should be paid to the effect of stretch-thinning effect and void-forming compression / thickening effect on the quality of the product, otherwise, the side will be concave when the rectangular tube is formed, warp longitudinally of the finished tube, and difficult to correct straight.