Effects of thickness variation due to presence of roller wake on the thickness measurement using laser ultrasonic technique

Spherical pressure vessels as fuel storage for space uses are usually made by the spinning process and precise control of thickness is a prerequisite. The non-contact thickness measurement method is necessary in such a case. Laser ultrasonic technique (LUT) is highly appreciated in this case of non-contact measurement. As a significant amount of surface roughness, i.e., roller wake produced during radial and axial feeding of the roller to the cylinder, the objective of this study is to investigate the effect of rough surfaces generated by the spinning process on thickness measurement using laser-generated ultrasound through experiment. This paper describes the variations in average thickness and amplitude of thickness measured by contact gauge and LUT at hill and valley portion of the roller wake of spinning processed cylinder. Some underestimation occurs at the hill case. The maximum amount of underestimation was about 0.04 mm. The variation in thickness caused by the spinning process can also be measured with no contact by the proposed LUT method. The maximum relative change in thickness due to the spinning process was about 9.5%. Necessary adjustment based on the finding can be a key to establish an efficient real-time thickness measurement system in the spinning process for economic and reliable production of a spherical pressure vessel.