Abstract
Axial cracking and circumferential wrinkling are found at the end of seamless steel tubes during multi-pass large deformations pushing diameter-reducing (PDR), which seriously affects product quality. However, the cracking and wrinkling mechanism of PDR has not been elucidated yet. In this paper, the Equation of circumferential residual stress at the end was deduced from the warping deformation and shear stress. It is revealed that the circumferential residual stress in the end warping area from the inner to outer surface is tensile, and the generation mechanism of circumferential wrinkling on the inner wall at the end was revealed through the deformation analysis of PDR. The geometric model of the tube with periodic alternating variation of wall thickness was established to reveal the generation and development of circumferential wrinkling. In addition, the four-pass PDR experiments and simulations were developed to reveal the influence of reducing pass and wall thickness deviation on the end warpage, unevenness and circumferential residual tensile stress. The pushing-pulling diameter-reducing (PPDR) method was proposed to control the wrinkling and cracking. The simulation and experimental results showed that the end warpage, unevenness and circumferential residual tensile stress are all greatly decreased, and the risk of axial cracking and circumferential wrinkling is eliminated.
Highlights
pushing diameter-reducing (PDR) refers to the cold forming method that consists of reducing the tube diameter by a conical die [1,2]
X-rayand method and simulation, the resultsthat showed wall thickness deviationdeviation by the X-ray method simulation, the results showed the circumferential residual stress is tensile from the inner to outer the end, it is that the circumferential residual stress is tensile from the innersurface to outeratsurface atand the end, compressive and tensile attensile the inner andinner outer surface sizingof area, respectively
It can be found that the end warpage is greatly decreased by the pushing-pulling diameter-reducing (PPDR), PPDR, while the sizing area diameter is increased, which indicates that the deformation while the sizing area diameter is increased, which indicates that the deformation difference difference in the bending stage is decreased
Summary
PDR refers to the cold forming method that consists of reducing the tube diameter by a conical die [1,2]. It has the advantages of high production efficiency, low manufacturing cost and simple die structure and has been widely used in the manufacturing of reducing tubes in automobiles, engineering machinery and aerospace [3,4,5]. Sadok et al [10] analyzed the strain state of the reducing tube by finite element simulation and carried out the hardness measurement; the results showed that the reducing deformation is uneven, and the maximum effective strain is on the tube’s inner surface
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