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PLUME EMISSION ANALYSIS UNDER TIME-RESOLVED SPECTROSCOPY FOR LASER WELDING CONTROL - PEANUTS

Exploitable results

An on line analyzer has been developed to study and measure atmospheric pollution. Complex spectra within the ultraviolet (UV), visible (VIS), near infrared (NIR) range can be detected with high S/N ratio and dynamic of up to 16 bit (1 to 65000 grey level).
By simultaneous spectroscopy, which means broad band measurements of light, on line monitoring has been achieved of environmental problems in atmosphere, or of processes in metal production, or of laser surface treatments, such as welding, coating, cutting and ablation. Laser induced plasma, emission of laser fluorescence is generated in medicine eg PDT or in industry eg metal analysis. Advantages include on line monitoring and possible process control or quality control.
The aim of the research was to develop a system to provide real time control of the laser welding process of metals using simultaneous multichannel analysis of the plasma plume generated at the interaction point between carbon dioxide laser beam and workpiece. The achievements so far are: measurements with different metals, thickness parameters, laser power variation between 1.2 and 5.8 kW have been performed; special analysis and processing software with a parameter library have been developed; identification of significant parameters during welding for process control have been achieved; prototype system development is almost completed to allow monitoring and alarm operation during welding. Engineering of the developed prototype is needed before the system can be exploited. Applications operated with or without success in the following areas: invisible cutting of composites by YAG lasers can be controlled; waste materials can be sorted using YAG laser influenced fluorescence; remote control of petrochemical waste handling (flame control, etc); highly compley alloys treated by laser machining can be handled and controled remotely using plasma analysis; for simple metal laser welding applications this system is too complex and too expensive.
An on line analyzer for complex optical spectra such as X-ray, vacuum ultraviolet (VUV), ultraviolet (UV), visible (VIS) and near infrared (NIR) has been developed. Images up to 5 MHz rep-rate can be detected with an outstanding sensitivity and S/N ratio.
A monitor has been developed which analyzes on line simultaneous complex optical spectra originated by plasma or fluorescence which are either laser induced or of chemical origin. The monitor is useful in processor such as: laser surface treatments eg welding, cutting, ablation, coating, etc; etch processes of semiconductors; non laser applications eg coating process of thin films. This online monitor allows detection and control in situ. Tungsten inert gas (TIG) welding processes can be monitored on line to achieve documented quality control.
An analyzer has been developed which allows detection of images and spectra of up to 16 bit (1 to 65000 grey level) with a sensitivity of single photons in low light level applications. Fast kinetic images or spectra with femtosecond endurance can be detected.
On line multielement spectra analysis and image analysis has been achieved by means of a very sensitive optical multichannel analyzer, optimized to measure fast kinetic events, such as flow and flames.
A single channel system for spectroscopy analysis has been developed. This low cost system has good potential for steel welding with laser or with traditional welding systems.