Product Code: ICA11_206

Online Measurement and Closed Loop Control of Penetration Depth in Laser Welding Processes
Authors:
Felix Abt, IFSW, Institut fuer Strahlwerkzeuge; Stuttgart Germany
Harald Woelfelschneider, Fraunhofer Institute for Physical Measurement Techniques IPM; Freiburg Im Breisgau Germany
Claudia Baulig, Fraunhofer Institute for Physical Measurement Techniques IPM; Freiburg Im Breisgau Germany
Heinrich Hoefler, Fraunhofer Institute for Physical Measurement Techniques IPM; Freiburg Im Breisgau Germany
Rudolf Weber, IFSW, Institut fuer Strahlwerkzeuge; Stuttgart Germany
Thomas Graf, IFSW, Institut fuer Strahlwerkzeuge; Stuttgart Germany
Presented at ICALEO 2011

The key quality factor for reliable deep penetration laser welding processes is a correct penetration depth. Today, this parameter is only accessible by offline quality control methods. Since the reliability of a butt-joint strongly depends on the penetration depth, it is desirable to have a possibility to measure and control the penetration depth online during the welding process.
In this paper a sensor system for real time measurement and closed loop control of the effective keyhole depth is presented. The sensor is based on a high speed and high resolution laser distance meter. It uses phase shift techniques with optimized modulation frequency and adapted measuring laser power to achieve the required performance. By operating the measurement beam nearly coaxially to the welding laser it is possible to measure to the bottom of the weld capillary. Moving the scanning beam perpendicularly to the welding direction results in measured profiles instead of single points, this allows determining the actual depth of the capillary more precisely.
The experimental results presented in this publication include a comparison of the measured keyhole depth with high speed X-ray videos to quantify the temporal behavior and precision of the sensor system.