Pulsed laser ultrasonic excitation and heterodyne detection for in situ process control in laser 3D manufacturing

Abstract

An all optical, in situ, process control diagnostic is presented with applicability to additive manufacturing. The diagnostic combines laser ultrasonics with laser heterodyne spectroscopy to measure the local temperature in the heat affected zone. The technique is time resolved (ns resolution) and can be adapted to measuring the cooling rate at the process location. With this knowledge, it permits the development of a corrective action step if the heating/cooling properties are found to be outside acceptable bounds. Feasibility of the diagnostic is presented using solid metal coupons of aluminum, stainless steel, and copper.