Distortion Characteristics of Ordinary Rolling
Rolling is a metal plastic forming process, which is widely used in the production of metal parts. In metal rolling process, the surface of the rolled material gradually deforms, and finally form to a predetermined shape. In the process of hot rolling and cold rolling, however, the deformation and strain of the material also cause the change of its length and width, which significantly affects the dimensional accuracy of the rolled product. These dimensional changes result from the distortion patterns of the rolled material and they are collectively referred to as distortion characteristics of rolling.
In order to ensure the accuracy of the product, it is necessary to analyze and control the distortion characteristics of rolling. Generally speaking, the distortion of rolling process, is the result of combination of two types of deformation, i.e., initial strain, caused by force and global strain, caused by the geometrical restrictions.
The initial strain in the rolling process is caused by the direct force applied to the surface of the rolled material. The force during rolling can be either a compression force or a tensile force. The compression force causes the rolled material to shorten its length, while the tensile force causes it to lengthen its length. Moreover, both the compression force and the tensile force are not evenly distributed in the rolling process, which makes the material not only change its shape, but also still presents some wrinkles, which is further discussed in the following content.
The global strain caused by geometrical restrictions arises from the interaction between the tools and the rolled material. The global strain is always compressive or tensile, however, its magnitude and direction always change in the rolling process due to the tools shape, size, and position. This strain causes strain difference in the rolled material, generating a new strain pattern on the surface of it.
The distortion characteristic of rolling process is generally divided into two categories: primary and secondary distortion. The primary distortion is caused by the compression of the rolled material due to the force and the global strain, which cause the overall wrinkles, curves and other shape changes on the surface. The secondary distortion is caused by the strain difference generated from the primary distortion. It is characterized by some tiny wrinkles or curved shapes on the surface, which is the result of the change of the global strain in the rolling process.
Overall, the distortion characteristics of rolling is related to the deformation of material caused by force, geometrical restrictions, and strain difference. It is important to analyze and control these characteristics if manufacturers need to maintain the accuracy of the product.
