MEASUREMENT AND PREDICTION OF ENERGY-TRANSFER EFFICIENCY IN LASER-BEAM WELDING

The absorption of laser energy by the workpiece during laserbeam weldi ng (LBW) has been studied through direct measurements of heat input ob tained with a Seebeck envelope calorimeter. The experiment compared wo rkpiece materials with contrasting thermal properties (304 stainless s teel, 1018 steel, tin), and varied the laser power, travel speed, and focus spot size in order to determine their effects on two figures of merit: the energy transfer efficiency and the melting efficiency. An u ncertainty analysis of the experimental measurements and calculated pa rameters has been included. The energy transfer efficiency during lase r beam welding was found to increase with beam intensity from 0.20 to 0.90 and to stabilize at a high value at intensities greater than 30 k W/cm. No correlation with energy transfer efficiency was found for eit her the fusion zone depth-to-width ratio or the travel speed. Measured melting efficiencies for laser welding were found to be no higher tha n the theoretical maximum value of 0.48 which can be obtained with con ventional are welding processes. However, improved melting efficiency over conventional processes was obtained due to the shapes of laser we lds that create two-dimensional heat flow in nominally three-dimension al heat flow applications. A mathematical model for laser welding has been developed using dimensionless parameters that relate the size of a laser weld to the net heal absorbed by the workpiece. Through applic ation of this model, the energy transfer efficiency for continuous wav e laser welding processes can be calculated after measurements of weld cross-sectional area have been made. Use of this model is expected to assist in optimization of laser welding for any type of material when it is used to select processing regimes that maximize melting efficie ncy and energy transfer efficiency.