X-ray Residual Stress Measuring in Actual Production Process

Author:  Kan Aoki, Yuji Kobayashi
Source:  ICSP-13
Doc ID:  2017119
Year of Publication:  2017
Introduction: Shot peening is applied to improve fatigue strength of metal parts such as gears and springs. The effect of improving fatigue strength is mainly produced by residual stress that is induced by shot peening. The residual stress changes with the intensity of the shot peening processing. Therefore, a method to represent the degree of processing was necessary. Dr. Almen of the United States acquired a patent for an evaluation method using Almen strips in 1994 (OS patent 23450440). According to this description, the arc height is the residual stress imparted by shot peening. But it is described that if the material is different for the same shot peening conditions, the residual stress is different. On the other hand, the application range of shot peening is expanding. Therefore, it is not suitable for current materials and applications. Recently, the Japanese automobile industry uses one piece flow manufacturing, which not only maintains high quality but also reduces the total cost, including quality management. In actual production, some parameters that are required in drawing should be measured for quality checking. In my opinion, residual stress after shot peening should be measured too. Normally, X-ray diffraction analysis is used to measure the residual stress on metal parts. But the measuring time is very long, such as 10 to 15 minutes. Thus, this measuring is difficult to integrate into one piece flow manufacturing. We developed an X-ray residual stress measuring device that can measure stress in a short time. Because the residual stress measurement is fast, it can be applied to one piece flow manufacturing. In this study, with inspection management by Almen strips, the effectiveness of this X-ray residual stress measuring device in the actual production process was confirmed.

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