<p>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 roughness is produced during the spinning process which imparts a substantial amount of thickness variations and this variation is needed to find out. Thereby, the processing parameter can be adjusted to control the roughness as well as thickness. Efficient measurement technique can help to establish the improved real-time thickness measurement system to reduce cost, inspection, and production time and finally, more reliable spherical pressure vessel by using spinning process. 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 spinning process on thickness measurement using laser generated ultrasound through experiment. 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. The thickness measurement of spinning processed alumnium alloy 6061-O cylinder of initially about 3 mm thickness with multiple roller passes by laser ultrasonic using time of flight method is presented. The contact gauge measured the thickness at open ends. The generating laser is a Nd:YAG laser operating at a wavelength of 1064nm and having a pulse width of 10 ns with a maximum energy of 400mJ was used to generate longitudinal wave and a receiving laser of 1550nm pulse width, continuous wave, 2W power with two-wave mixing in a photorefractive crystal was used to measure thickness at open ends as well as deformed parts of the spun cylinders. This paper describes the variations in average thickness and amplitude of thickness when measured by contact gauge and LUT at hill and valley portion of the roller wake of spinning processed cylinder. Comparison of the thickness changes due to rough surfaces (spiral wake produced by the spinning process) measured using LUT shows good agreement with the one measured by contact gauge. Some underestimation occurs at hill case and overestimation occurs at valley case. The maximum amount of underestimation in average thickness occurs about -0.36%. Underestimation in the amplitude of thickness of about 1% is found. Accuracy of about ±5µm between average thickness value of laser and contact gauge is obtained in case of the non-processed cylinder. The variation in thickness caused by the deformation can also be determined by the proposed laser UT method. The change in thickness from the measurement portion of the 1st roller pass to the measurement portion of the end of the conical part is about 9.5%.</p>

Effects of Thickness Variation Due to Presence of Roller Wake on the Thickness Measurement Using Laser Ultrasonic Technique

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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