Improving the shape and dimensional accuracy of hollow semi-finished products during hot reverse extrusion from square workpieces

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Stamping of round hollow semi-finished products by hot reverse extrusion from round and square workpieces is the first stamping step in the manufacture of hollow products for special purposes. These products require certain mechanical properties along the wall height and in the bottom part, which can be achieved by working out the metal structure by plastic deformation. The bottom part is worked out by reverse extrusion. The wall properties are obtained in the following stages of drawing the semi-finished product with thinning after extrusion. The use of square workpieces results in more intensive working out of the bottom of the semi-finished products during the reverse extrusion. However, as a result of extrusion, four protrusions appear at the end of the semi-finished product wall in places that match the corner areas of the workpiece. The presence of protrusions leads to the need for an additional operation of cutting the end of the semi-finished product before extrusion, as well as to an increase in metal usage. Therefore, an urgent task is to study the method of eliminating protrusions in the semi-finished product and the additional cutting operation.To improve the accuracy of the shape and size of hollow semi-finished products during hot reverse extrusion from square workpieces.Elimination of protrusions is achieved by forming chamfers in the corner zones of the square workpiece by preliminary deposition before extrusion.The finite element method (FEM) was used to model the processes of hot deposition of corner zones on a square workpiece and subsequent reverse extrusion with the dispensing of round hollow semi-finished products. The dimensions of the chamfers on the high-carbon steel workpiece were determined, which ensured the elimination of protrusions at the end of the wall of the round semi-finished product after extrusion. The dependence of the deposition and extrusion forces on the punch movement was determined. The specific forces on the deforming tool were determined. The distributions of stresses, strains, and temperature in the deformed metal at the end of deposition and extrusion are presented. The working out of the metal structure by hot plastic deformation is evaluated. The design of a stamp for deposition and extrusion is developed.The geometry of a square workpiece with chamfers in the corner zones was determined, which ensures the elimination of protrusions at the wall end during hot reverse extrusion with the dispensing of round hollow semi-finished products