High power diode lasers cut thick metal sheets

THE term “high brightness”, which combines high optical power with good beam quality was so far only marginally related to High Power Diode Lasers (HPDL). Therefore, cutting of several mm thick steel sheets with good quality and reasonable cutting speed by means of HPDL was hardly conceivable so far.

Through recent progress on HPDL modules and their optical interconnection using special micro-optics, a 2.5 kW laser with high power and also high brightness was now demonstrated by LIMO Lissotschenko Mikrooptik GmbH.

2.5 kW High Power Diode Laser from LIMO (upright in the centre) coupled with an industrial CNC machining facility (left) for metal cutting at the Laser Centre of the University of Applied Sciences Münster (LFM)

The specialists for laser beam shaping in Dortmund have studied the potential for applications in materials processing together with the Laser Centre at the University of Applied Sciences Münster (LFM). For this purpose, the light of the 2.5 kW laser was fed by an optical fiber (core diameter 400 microns) to a newly designed processing head from LIMO (focal length 120 mm). The metal processing was performed on an industrial CNC machining facility (Fig. 1). The cutting process was optimized using the methodology of “Design of Experiments” including variation of nozzle geometries and diameters.

Metal sheets of 6 mm thickness were cut at high speed by means of a 2.5 kW High Power Diode Laser (LIMO). Left: stainless steel (1.1 m/min.); right: mild steel (2.0 m/min.)

LIMO and the LFM co-operate within the joint project BRILAMET (brilliant high power diode lasers for metal processing) which is funded by the German Federal Ministry of Education and Research (BMBF). This project is supported by the BMBF program "KMU-Innovativ, Optische Technologien" (Optical Technologies in innovative small and medium-sized enterprises, promotional reference: 13N12282). As a result of a successful milestone, laser cutting of steel was demonstrated: 6 mm thick stainless steel (1.4301) was cut at 1.1 m/min and 6 mm thick mild steel (1.0038) at 2 m/min. In both cases, a very good cutting quality was achieved with a roughness Rz < 35 microns and a negligible dross on the kerf (< 30 microns) (Fig. 2). In the further course of the project, these investigations will be continuously extended. LIMO is going to increase the optical output power of the laser up to 4 kW while keeping the brightness on a high level.