Friedhelm Dorsch

Detection of faults in laser beam welds by near-infrared camera observation

We monitor thin disk laser beam welding processes coaxially through the welding optics with a camera that is sensitive in the near-infrared (NIR) spectrum (1200…1700u2005nm). With this sensor we detect the thermal radiation from the process zone and we can analyze it in real-time during the welding process. From the observed features we monitor the laser weld in respect to various welding faults.In particular, we analyze the thermal trace of the weld seam and its vicinity. For lap joints the analysis of the thermal trace enables us to detect missing fusion immediately and in real-time. This in-situ online heat flow thermography is a unique method to detect “false friends” during the welding process itself.We monitor thin disk laser beam welding processes coaxially through the welding optics with a camera that is sensitive in the near-infrared (NIR) spectrum (1200…1700u2005nm). With this sensor we detect the thermal radiation from the process zone and we can analyze it in real-time during the welding process. From the observed features we monitor the laser weld in respect to various welding faults.In particular, we analyze the thermal trace of the weld seam and its vicinity. For lap joints the analysis of the thermal trace enables us to detect missing fusion immediately and in real-time. This in-situ online heat flow thermography is a unique method to detect “false friends” during the welding process itself.

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 1u2005µm, 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.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 1u2005µm, 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 obser...

Sensor assisted (remote) welding processes

Remote welding is widely used in automotive applications like car seats or doors. This technology is able to increase productivity and quality while reducing cost and weight of the parts.Using pathfinding and detection of the position of the welding sample in a remote welding system flange size can be reduced even more. With this technology a fillet weld which requires much higher positioning accuracy than overlap weld is possible. The pathfinding and position detection systems are directly connected to the scanner control unit and therefore the correction of the geometry can be done online in real time. Moreover the gap size can be measured and with this information the user can actively adjust to the new welding situation and prevent a fault. In addition new welding applications with this novel sensor system are shown, e.g. door welding with reduced flange and fillet weldRemote welding is widely used in automotive applications like car seats or doors. This technology is able to increase productivity and quality while reducing cost and weight of the parts.Using pathfinding and detection of the position of the welding sample in a remote welding system flange size can be reduced even more. With this technology a fillet weld which requires much higher positioning accuracy than overlap weld is possible. The pathfinding and position detection systems are directly connected to the scanner control unit and therefore the correction of the geometry can be done online in real time. Moreover the gap size can be measured and with this information the user can actively adjust to the new welding situation and prevent a fault. In addition new welding applications with this novel sensor system are shown, e.g. door welding with reduced flange and fillet weld