ANALYSIS OF FIBER OPTIC SENSOR TO MEASURE VELOCITY DURING ELECTROMAGNETIC FORMING AND WELDING

Previous methods of measuring high velocity deformation in electromagnetic forming and magnetic pulse welding include Photon Doppler Velocimetry (PDV), laser micrometers, and high speed photography. In this paper an alternative method is presented, implementing a fiber optic, reflectance dependent displacement sensor. The sensor is shown to be an attractive low cost solution to measurement of high velocities in high voltage, magnetic environments. Data is shown with respect to sensor characterization including various surface reflectivity values, curvatures, and misalignments; implementation in two forming and welding processes; and verification with high velocity measurement in parallel with PDV. The sensor system is one twentieth the cost of a PDV system, and yet measures velocities accurately to at least 140 m/s. Sensor performance is also enhanced by the use of retroreflective tape, which is shown to increase the displacement range by 9x, decrease sensitivity to misalignment, and increase repeatability and ease of implementation.