Formation mechanism of process instabilities and strategies to improve welding quality

The deep penetration welding process with CO2 lasers has been employed successfully for many years in industry. It generates little spatter on the work piece surface and therefore produces excellent seam quality at high process speed with good process reliability over a wide range of parameters. With a wavelength around 1 µm, solid-state lasers are being increasingly used in industrial production thanks to simple beam guidance by means of laser light cable and their high electrical efficiency. Disk and fiber lasers have advanced into the domain of CO2 lasers by way of power and beam parameter product. However the seam quality is highly dependent on the focusing conditions used, whereby the mechanisms that cause process instabilities are still not properly understood. Also, at high intensities with high feed rates, considerable spatter is generated on the work piece surface, reducing productivity in applications where the demands on surface quality are high. In this publication, based on online X-ray observation and high-speed imaging, the suitability for welding and the formation mechanism of process instabilities like spattering and humping were compared at different feed rates. Based on a better process understanding strategies which can improve welding quality are presented.