1. True bend

Solid bend, as the name implies, is a compression bend, where both the inner and outer rolls compress the inner and outer walls of the billet in both directions during the bending process.

1) The advantages of actual bending are minimal springback, accurate shaping, and as long as the roller profile is accurate, the R value for inner angle shaping is also precise.

2) The drawback of solid bending is the stretching/thinning effect. Solid bending causes stretching at the bend, leading to a reduction in the longitudinal length of the bend line. The metal at the solid bend area becomes thinner due to stretching.

2. Empty Bend

Air bending forms a bending moment by the single-directional contact between the outer roller and the outer surface of the billet, causing the material to bend. Air bending results in compression along the bend line, which leads to longitudinal elongation of the bend line. Metal堆积 at the bend area thickens, demonstrating the compressive/thickness-increasing effect of air bending.

1) The advantages of open bending include the ability to bend lengths when actual bending is not possible, such as simultaneous bending and finishing of the top/side edges of square tubes. Open bending can also bend internal angles with a radius of R<0.2t without causing the tube wall to crack.

2) The drawback of the empty bend is that when the square or rectangular tube is being bent simultaneously on the top or side, due to the simultaneous application of pressure by the upper and lower rolls, the forming force may exceed the critical point, causing instability and inward bowing at the edges. This also affects the stable operation of the equipment and the quality of the forming process. This is a different characteristic when square or rectangular tubes and round tubes are bent empty.

In practical applications, these two fundamental methods should be configured to reasonable process positions based on product requirements in the square tube forming process. Attention should be paid to the stretching/thinning effect of actual bending forming and the compressing/thickening effect of hollow bending forming, as they can affect product quality. Otherwise, the side edges of the square tube may indent, the finished tube may warp longitudinally, and it will be difficult to straighten.