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Welding of advanced materials with high power continuous wave and Pulser-sustainer yltrium aluminium garnet laser

A new technology to weld aluminium alloys with (neodymium-yltrium aluminium garnet (Nd-YAG) laser has been developed. The objective was to remove the limitation of weld depth and of weld quality of 2 kW continuous or pulsed Nd-YAG lasers. The analysis of the weld quality with different laser mode has been done. The modes considered were: continuous, pulsed, pulsed-sustainer with a continuos mode superimposed to a pulsed mode, and the Q switched mode. The best quality was achieved with continuous mode using a high beam quality laser source. In fact, the beam spot on the material had to be so little to reach the threshold intensity of about 1.5E6 W cm{-2} even with power levels of 2 kW. In this condition better key-hole stability produced better weld quality. Successive pulses produced the opening and closing of the key-hole. With pulse-sustainer mode and Q switching mode the additional energy of the pulse created unstable conditions for the key-hole and the melt pool. Two ranges of process parameters have been developed experimentally. Two millimetre thick aluminium alloy sheets have been welded with 3 kW of continuous power at speeds up to 10 m/min. In order to weld thickness up to 5 mm, 5 kW of continuous power has been delivered to the workpiece using a new optical head with twin fibre system to sum two laser beams. Weld speeds up to 2.5 m/min have been reached. The other technological issues addressed by the project were the mathematical models of the welds, the monitoring on line the weld quality, and the movement of the optical head connected to the laser sources with fibres along a three dimension path using an anthropomorphic robot. Positive answers to these issues have also been given.

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Paolo GAY
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