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

Abstract

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.

Material Flow in Infeed Rotary Swaging of Tubes

“…The tube workpieces were made from rods, the wall thickness was controlled by the drill. In the experiment, anisotropic property of the workpiece material and the fluctuation (the feed per stroke and stroke height) of the rotary swaging system could also be a reason of deviation [ 28 ]. In the view of the FE model, the simplified 2D–asymmetric model and the rigid feeding strategy could also bring deviation.…”

Finite Element Analysis and Experimental Evaluation of Residual Stress of Zr-4 alloys Processed through Swaging

“…The swaging dies perform high frequency radial movements with short strokes. Rotary swaging (RS) can be performed under hot and cold conditions, depending on the swaged material, required surface quality and final properties [1,2]. Infeed rotary swaging, the work piece is fed axially inside the set of dies but in the recess swaging process, the work piece is not fed axially forward or outward (Figure 1a).…”

“…Therefore, the infeed swaging process is often utilized in the situation where the work piece is necked from one end. The recess swaging process is often used to reduce the diameter at a certain position of the work piece, or to form a concave profile [1][2][3][4][5][6]. [5], the influence of friction and the die angle on residual stresses [6] and temperature distribution during the process [9,10].…”

“…Using Forge NxT commercial software, FEA was conducted for an elastic-viscoplastic material model [12]. [2] and (b) the zones of the swaging process [3], with permission from Elsevier, 2020. [2] and (b) the zones of the swaging process [3], with permission from Elsevier, 2020.…”

“…Forge 2011 3D was used for FEA of copper AISI C11000 tube that suffers triaxial stress during the rotary swaging process [3]. Fluctuations in the stroke height, which are in the range of the tolerance of the components of the swaging head, has led to strong fluctuations in residual stress distribution [2]. The 2D axisymmetric and 3D FE analysis is used in modelling residual stresses and forging load in the cold radial forging process.…”