On-Line Laser-Ultrasonic Measurement System (Sensors & Controls)
Develop and demonstrate a laser-ultrasonic system to measure wall thickness and eccentricity of steel seamless mechanical tubing in a piercing mill.
The wall thickness of the rotating and translating tube will be measured with ultrasound generated and detected by lasers. The thickness of the wall at the measurement location will be determined from the measurement of the time of flight between two consecutive echoes (or the initial surface pulse and the first echo, if the second echo is unavailable) and knowledge of the acoustic velocity. Velocity calibration as a function of temperature will be obtained by heating a piece of steel of the same grade and monitoring temperature on line by a pyrometer.
More precisely, since the calibration takes into account thermal expansion, the on-line measurement will yield the wall thickness when the tube is at ambient temperature.
The coordinates of the measurement points on the tube surface will be obtained by two Laser Doppler Velocimetry (LDV) systems. Two simultaneous velocity measurements will be made and numerically integrated to determine displacement from a known starting point. One LDV system will measure the displacement along the tube axis, whereas the other will measure the circumferential displacement. A thickness map of the tube will be plotted, and from this information eccentricity will be determined at various locations along the tube axis.
This laser-ultrasonic system integrated with velocimetry and pyrometry measurement techniques will operate from a standoff distance (several feet), perform 100 ultrasonic measurements of wall thickness per second and determine the coordinates of the measurement locations on the tube at the same rate, and provide a complete thickness map of the tube to determine eccentricity. The specifications of the integrated laser-ultrasonic system will include:
- an accuracy and precision of wall thickness measurement of 0.0005" and ±0.5% at room temperature, respectively,
a ±0.2" maximum position error along tube length, and
a ±0.1 rotation maximum position error along the circumference.