Study of the final stage of the piercing process with and without a centering recess on two-high screw rolling mills with guide drive disks

As part of the work performed, an analysis of the unsteady final stage of piercing on a two-high screw rolling mill with guide drive disks was carried out based on numerical methods for studying metal forming processes. The implementation of numerical research methods was carried out using piercing process modeling in the Qform software product based on the finite element method. Using a description of the nature of the shape change of the rear end of the workpiece in the deformation center of the piercing mill, the mechanism of defect formation on the rear end of the sleeve when using a non-centered workpiece is described. The cause of defect formation on the rear end of the sleeves (“skirt”, “penny”, “earring”) is the action of the piercing mandrel on the deformed workpiece and the formation of a sink mark on the rear end of the workpiece in the final stage of deformation. When using rear centering, no metal delamination is formed on the end surface of the sleeves. Therefore, the accuracy of the rear ends of the pipes increases, the durability of the rolling mill mandrels increases, which is very important for piperolling units with a continuous rolling mill operating on a retained or partially retained and movable mandrel. But due to the rear centering on the inner surface of the sleeves, there is a high probability of internal defects. The cause of the defect is two types of destruction: metal peeling due to the formation of internal shrinkage (1) and annular destruction of the metal during the immediate approach of the transforming bottom of the recess to the end of the mandrel (2).The work was carried out within the framework of a comprehensive project on the topic “Development and implementation of integrated technologies for production of seamless pipes from new-generation steels with controlled corrosion resistance under complicated operating conditions for the fuel and energy complex of the Russian Federation” within the framework of Agreement No. 075-11-2023-011 dated 10.02.2023 according to the Decree of the Government of the Russian Federation No. 218 dated 09.04.2010.