Generation of residual stresses in rotary swaging process

Infeed rotary swaging is an established incremental cold forming production technique for axisymmetric workpieces. Among others, work hardening as well as near net shape forming are advantages of this production technique. Due to the incremental open die forging process, the rotary swaging induces a complex material flow history which is dependent on the process control. This material flow history influences the material modifications such as work hardening as well as residual stresses. In this study, the properties of steel tubes were investigated after rotary swaging using varying parameters by experimental and simulation analysis. In particular, the influence of lubrication with different feeding velocities was analysed. The workpiece quality, the hardness and the residual stresses were characterized in detail. After rotary swaging, an influence of the process parameters on the geometrical and surface quality could be observed. The workpieces showed significant work hardening which was higher at the surface and process dependent, while below 100 μm, this increased hardness was observed over the complete wall thickness independently of the process parameters. The residual stress state was highly fluctuating at the surface and was in tensile for all conditions. The results showed that the process parameters influenced the properties near the surface, while a few hundred micrometers below the surface, the workpiece properties seemed to be driven only by the total deformation

Generation of residual stresses in rotary swaging process

Infeed rotary swaging is an established incremental cold forming production technique for axisymmetric workpieces. Among others, work hardening as well as near net shape forming are advantages of this production technique. Due to the incremental open die forging process, the rotary swaging induces a complex material flow history which is dependent on the process control. This material flow history influences the material modifications such as work hardening as well as residual stresses. In this study, the properties of steel tubes were investigated after rotary swaging using varying parameters by experimental and simulation analysis. In particular, the influence of lubrication with different feeding velocities was analysed. The workpiece quality, the hardness and the residual stresses were characterized in detail. After rotary swaging, an influence of the process parameters on the geometrical and surface quality could be observed. The workpieces showed significant work hardening which was higher at the surface and process dependent, while below 100 μm, this increased hardness was observed over the complete wall thickness independently of the process parameters. The residual stress state was highly fluctuating at the surface and was in tensile for all conditions. The results showed that the process parameters influenced the properties near the surface, while a few hundred micrometers below the surface, the workpiece properties seemed to be driven only by the total deformation

Influence of Process Fluctuations on Residual Stress Evolution in Rotary Swaging of Steel Tubes

Infeed rotary swaging is a cold forming production technique to reduce the diameter of axisymmetric components. The forming is achieved discontinuously by a series of radial strokes that are spread over the shell of the part. Due to tolerances within the rotary swaging machine, these strokes perform individually and the resulting stroke pattern is not homogeneous with regards to circumferential and longitudinal distribution. Nevertheless, in combination with the high number of performed strokes and the large contact area between the dies and the part, the external part properties, such as diameter, roundness and surface roughness, show even values along the finished part. In contrast, strength-defining internal part properties, like microstructure and residual stress components, are more sensitive to the actual pattern and temporal sequence of the individual strokes, which is investigated in this study. The impact of process fluctuations during the conventional process, which are induced by the tolerances of machine tool components, was verified by numerical simulations, physical tests and measurements of residual stress distributions at the surface and at depth. Furthermore, a method is introduced to maintain the stroke following angle ∆φ at zero by flat dies, and thus the actual pattern and temporal sequence of the strokes was homogenized. The results show that the residual stress fluctuations at the surface could be controlled and reduced. Furthermore, it is demonstrated that the depth profile of the residual stresses at a distance of 300 µm from the surface developed independently from the process fluctuations