Long-pulse quasi-CW laser cutting of metals

Long-pulse quasi-CW laser cutting of metals is well suited to small-scale manufacturing settings where process flexibility is of high value and investment capacity is limited. This process refers to cutting operations performed with millisecond laser pulses obtained through modulation of the pump source to achieve continuous-wave (CW) operation over limited time intervals. The ability to minimize heat conduction losses, comprising the vast majority of absorbed laser power at low velocity, allows processing of relatively thick sections compared to what would be possible at the same average power with a CW laser source. The present study quantifies the reduction in heat conduction losses with pulsed exposure by employing a simple power-balance representation of the heat flow problem. Laser-cutting experiments are performed with inert and active assist gases on 1- and 4-mm thick steel samples, varying peak power (0.3–3 kW), pulse energy (0.3–12 J), repetition rate (25–1000 Hz), and velocity (1–40 mm/s). The lowest minimum laser cutting power and highest cutting efficiency are achieved with maximum peak power and lowest permissible pulse overlap for a continuous cut. Under these conditions, heat conduction losses are reduced by more than 60% with nitrogen assist gas compared to CW exposure and more than 50% with oxygen. The calculated average cutting front temperatures are 450–630 ∘C and 620–900 ∘C, respectively, well below the melting temperature of steel. Lowest dross adhesion and cut edge surface roughness are obtained with oxygen assist gas, leading to both the lowest minimum average cutting power and highest cut quality. These results demonstrate an efficient process that improves the feasibility of low velocity laser cutting and therefore the range of industrial applications in which laser technology can employed.