14 June 1995 High-efficiency interferometer for noncontact detection of ultrasounds
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Abstract
Semi-solid metalworking (SSM) incorporates elements of both casting and forging for the manufacture of near-net shape discrete parts. The SSM process capitalizes on thixotropy, a physical state wherein a partially molten material behaves like a fluid when a shear stress is applied. Effective process control depends on the accurate measurement of the ratio between solid and liquid in the feedstock. Due to the high temperature of the material, only noncontact measurements are practical. Surface temperature measurements are not reliable and do not give accurate readings of the bulk material temperature. Since the speed of sound changes during the transition from the solid to the liquid state, ultrasonics offers the potential to determine when a material becomes semi-solid. This paper summarizes attempts to use this change as the means of measuring the solid fraction of semi-solid feedstock. A real time solid fraction sensor system using noncontact laser ultrasonics was developed to measure the SSM material's solid fraction during heating. The system includes a high power Nd:Yag laser for ultrasound generation and a Fabry-Perot interferometer for receiving. The interferometer was optimized for maximum light efficiency and for immunity to the electro-magnetic noise generated by the induction furnaces used in heating the SSM billets. Tests have demonstrated excellent signal to noise ratio at room temperature and at temperatures up to 579 degrees C. A summary of the test results is presented.
© (1995) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Robert Czarnek, Chin-Jye Yu, F. Robert Dax, "High-efficiency interferometer for noncontact detection of ultrasounds", Proc. SPIE 2544, Interferometry VII: Techniques and Analysis, (14 June 1995); doi: 10.1117/12.211881; https://doi.org/10.1117/12.211881
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