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.
Rotary swaging is an incremental cold forming process to produce axisymmetric workpieces from rods and tubes. The process also induces changes of the microstructure of the material depending on the process parameters. This in turn influences the mechanical properties like hardness as well as the electrochemical properties. As a result of changed electrochemical properties, the passivity of the material and thus the corrosion behavior changes. In order to investigate the influence of rotary swaging on the corrosion behavior of the stainless steel AISI304, deformed micro parts are electrochemically analyzed. The measurements reveal a dependency of corrosion rate and impedance on both feed velocity and final diameter of the rotary swaging process. A higher feed velocity decreases the corrosion rate and increases the impedance indicating a better resistance against corrosion as a side effect of rotary swaging.
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