PRESS FORMING OF PRISMATIC AND SCREW-SHAPED SECTIONS OF M4 COPPER

The paper considers pressing methods for prismatic and screw-shaped metal sections. An example of cold pressing of a M4 copper billet to produce a solid square section making is provided. The paper compares traditional pressing (extrusion) and extrusion with subsequent pressing and torsion (extrusion and screw pressing) with regard to mechanical characteristics, energy intensity and fracture pattern of copper samples. At the same time, extrusion and screw pressing of a billet was carried out in one device within one process operation. Bulk copper billets ∅11,7×60 mm were subjected to prismatic and screw-shaped section pressing in one pass at the room temperature. A hydraulic press was used for billet pressing with a punch. Solid copper prismatic and screw-shaped sections with a square section of 8×8 mm were obtained following the deformation processing. The paper presents findings on mechanical properties, deformation regularities, and the fracture mechanism during monoaxial stretching of M4 commercial copper samples in the as-delivered and as-hardened states. Mechanical tests for monoaxial stretching of samples with working dimensions of ∅3×15 mm was made using the UTS-20k testing machine at a constant loading rate of 3,33·10^–5 m·s^–1. A certain strength improvement of copper extruded in one pass at a room temperature was found. Screw pressing after extrusion ensures a higher ductility as compared to the original state and extrusion. The paper describes a fractographic investigation of fractures in samples using the Hitachi TM 3030 scanning electron microscope in the secondary electron mode. The paper demonstrates that the fracture mechanism of copper samples in the as-delivered state, as well as following the extrusion and extrusion and screw pressing, is qualitatively the same. Fracturing of M4 copper samples both in the original state and following deformation processing under the indicated regimes occurred by a mechanism of ductile fracture. It was found that copper subjected to extrusion and screw pressing featured greater energy intensity due to higher ductility. The fracture in the fibrous area of the sample subjected to extrusion and screw pressing is notable for the tiered arrangement of pit blocks. Large pits and micropits in all copper states are present both in the fibrous area and in the peripheral area of the cut.

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