A Relationship between Laser Power, Penetration Depth and Welding Speed in the Laser Welding of Steels

Experimental data have been generated for the bead-on-plate keyhole welding of mild steel using the TEM00 beam from a 1.5 kW CO2 laser and a range of material thickness from 0.64 to 2.6 mm. For each thickness, the maximum welding speed was measured for laser powers from 600 to 1500 W, using the criterion of full penetration along a 5 cm length. Analysis of the data has yielded a simple correlation between laser power (P,kW), penetration depth (d,cm) and welding speed (v,cm/s). When the specific welding energy per unit thickness (Pd−1v−1) is plotted against welding speed (v), the data are observed to lie on a single curve. An analytical expression of this relationship has been derived for speeds above 1 cm/s: P=3.83d + 0.69dv (1≤v<10) and P = 1.072dv(10≤v<16). Stainless steel samples yield similar results. This correlation is interpreted in terms of the minimum energy envelope or range for laser welding as proposed by other workers and also in terms of the Swift-Hook and Gick theory of laser welding. The latter predicts that the width of the melted zone has the same welding speed dependence as the parameter Pd−1V−1 for speeds above 1 cm/s. This was confirmed by measurements of the melt width for the mild steel samples.