The use of a combination of 2 or 3 Nd:YAG lasers having each an output power of 3 or 4 kW is presented in the case of heavy section welding. We discuss the main difficulties that are occurring for these conditions. The strategy leading to the welding of sample thickness up to 60 mm is presented.
State of the art of welding with carbon-dioxide laser radiation is to weld steel material up to a wall thickness of 20 mm in one pass utilizing beam powers up to 20 kW. Welding material exceeding 20 mm wall thickness requires the application of multiple pass techniques. Since the process behavior deviates from the conventional deep penetration effect measures due to beam handling and shaping have to be taken into account. Within the paper the effects of beam oscillation and focused beam shaping on the process will be discussed. Experimental results concerning the influence of beam characteristics, beam handling, and wire feed on the seam quality will be presented. The experiments were carried out by means of a modern beam source with a nominal output power of 20 kW which offer the opportunity of raw beam shaping by a telescope. The material applied was a fine grain structural steel. The application of multiple pass welding with laser radiation offers great opportunities in industries dealing with materials of high wall thickness.
Surface treatments with remelting have often irregular quality. This article presents on-line control of laser melting which induces an improved quality of the treatment and more regular results. In order to build up a regulator, different sensor have been experimented. Responses are analyzed versus static and dynamic process commands. The molten depth is estimated on-line from molten pool dimensions measured by the CCD camera and image on-line processing. A state model is developed. The system is controlled by three variables: sample velocity, laser power and intensity distribution. The outputs of the system are the depth and width of the melted zone, and the temperature field. The commands and the outputs are chosen in accordance with the application under consideration. Therefore the process has been regulated.
The possibilities of pulsed laser welding of aluminium alloys monitoring are investigated. Simple finite element modeling of conduction and keyhole welding has been carried out. A complete instrumentation has been set up, including beam and plasma monitoring and impact shape and size measurements. This set up enables a real time monitoring of the seam and the detection of critical defects.
In order to control CO2 laser treatments, a precise knowledge of the CO2 radiation- surface coupling is required. For this purpose, numerical identifications of the absorption coefficient, either with temporal resolution in non stationary 1D configuration or with spatial resolution in a stationary 2D configuration, were achieved from thermal cycles measurements and simulations. Evolutions of the coupling during laser treatment were studied both in the case of coated steel hardening (graphite and manganese phosphate coatings) and in the case of solid state nitridation of titanium alloys. Moreover, the determination of the CO2-surface coupling for those thermodiffusional solid state laser processes had been used to correlate experimental treated depths to those obtained by a simple thermodiffusional model taking into account carbon or nitrogen diffusion under a calculated thermal cycle.
In order to control CO2 laser surface treatments, a precise knowledge of the CO2 radiation-surface coupling is required. For this purpose, numerical identification of the absorption coefficient, either with temporal resolution in non stationary 1D configuration or with spatial resolution in a stationary 2D configuration, were achieved from thermal cycles measurements and simulations. Evolutions of the coupling during laser treatment were studied both in the case of coated steel hardening (graphite and manganese phosphate coatings) and in the case of solid state nitridation of titanium alloys. Results were interpreted in terms of chemical evolutions of the surface; moreover, the influence of a reflective shielding gaz device covering the substrate was also pointed out.
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