Main characteristics of strip deformation during straight LSAW pipe forming

The deformation process of LSAW steel pipe and tube blank in the forming machine is very complicated, which includes three parts: longitudinal deformation, transverse deformation of straight seam steel pipe and section deformation.

(1) Longitudinal deformation. Longitudinal deformation refers to the deformation of the tube blank in the direction of the rolling line during the process of changing from a flat shape to a cylindrical shape. Longitudinal deformation is not uniform. In the preforming section, the extension L' of the edge part of the strip is greater than the extension L of the central part, reaching the finishing frame before closing the hole pattern, and the extension L of the central part is larger than the extension L' of the edge part. This longitudinal non-uniform deformation is the main characteristic of strip deformation in the continuous roll forming process.

(2) Lateral deformation. Lateral deformation refers to the bending deformation of the cross-section of the tube blank in each forming frame, that is, the deformation generated by the forming hole pattern. The problem of the transverse bending deformation of the tube blank in each specific pass frame is the problem of the roll pass design.

(3) Section deformation. Section deformation refers to the change in the wall thickness of the steel pipe after forming (in fact, after sizing and straightening) compared with the thickness of the slab. The change of section wall thickness is less obvious when forming thicker wall steel pipes. When thin-walled pipes are formed, on the one hand, the thickness of the straight seam steel pipe is slightly thicker than that of the slab; The wall thickness of the edge portion is smaller than that of the bottom portion of the tube due to the extension of the edge. Since the deformation of the section is very small and has no great influence on the quality, it can be ignored, and generally no key research is done.

(4) Edge extension and springback. The deformation of the strip in actual forming is much more complicated than the above-mentioned situation. In the general continuous roll forming process, the strip is actually formed in sections, which is called step forming. During the step forming, the edge of the strip will generate a wave shape, which will cause the local stress of the strip to increase.

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