The way of round tube forming is called bending, and the way of square tube forming is called bending. There are two basic bending methods: solid bending and empty bending.
1, solid bent
Solid bending, as the name implies, is compacted bending, and the inner and outer rollers and the inner and outer walls of the tube blank are compacted in both directions during solid bending.
1) The advantages of solid bending are small rebound, accurate forming, and as long as the roller type is accurate, the R of inner Angle forming is more accurate.
2) The disadvantage of solid bending is the stretching/thinning effect. First, the real bending will produce tension at the bending, and the stretching effect will shorten the longitudinal length of the bending line; Second, the metal will be thinned by stretching at the bend.
Empty bending is through the one-way contact between the outer roller and the outer wall of the tube blank to form a bending moment to bend the material. Empty bending will cause compression of the bending line. The compression effect makes the bending line lengthwise and the metal at the bending place appears to accumulate and thicken, which is the compression/thickening effect of empty bending.
1) The advantage of empty bending is that side length bending can be carried out when real bending is not possible, such as the top/side synchronous bending and finishing of square rectangular tube. You can also bend in the air. 0.2t inner Angle without wall rupture.
2) The disadvantage of empty bending is that square rectangular tube in the upper/side synchronous empty bending, due to the pressure of the upper and lower rollers at the same time, the forming force is easy to exceed the critical point, resulting in edge instability concave, and will also affect the stable operation of the unit and forming quality. This is the square tube and circular tube empty bending molding different characteristics.
In practical application, these two basic methods should be configured to a reasonable process position according to the product needs in square rectangular tube forming. Attention should be paid to the effect of tensile/thinning effect of solid bending forming and compression/thickening effect of empty bending forming on product quality, otherwise it will lead to concave side of rectangular pipe forming, longitudinal warping of finished pipe, and difficult to straighten.