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Content archived on 2024-04-19



A new technology to weld aluminium alloys with 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 available at the first years 1990.
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 work-piece 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.
Welding of advanced materials offers considerable problems. In various industry sectors, e.g. the car, utility vehicle, rail road and aerospace industry, the limitations of conventional welding techniques restrict the use of advanced materials, such as aluminium alloys or high strength steels, as well as new,advantageous design. An example for the latter are lean manufacturing concepts which require low disortion welding. Another example for optimized design enabled by laser welding are tailored planks. YAG laser welding offers a solution for many of these advanced materials as well as for other difficult to weld materials like e.g. Zn coated stell. The proposed project will develop high power YAG laser welding to a state where industrial work pieces can be welded. This includes CW lasers and pulser-sustainer lasers. CW YAG lasers,which are now available for the first time with the data which allows such industrial applications, are capable to perform high quality welds with a depth of 5 mm in steel, but only of about 1 mm in aluminium. For a higher depth of weld and for difficult welding tasks, the present project proposes the development of pulser-sustainer lasers. Welding tests show that these lasers will extend the high quality weld regime of CW YAG lasers to higher welding depth. The project focuses on the development of the application technology. In addition, the pulser-sustainer laser and other major hardware components will be developed or adapted to the needs of the project.

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Centro Ricerche Fiat SCpA
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Strada Torino 50
10043 Orbassano Torino

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