Entwicklung und Qualifizierung eines einfachen Online-Qualitätsüberwachungssystems für das industrielle Laserstrahlhartlöten: Abschlussbericht zum Forschungsvorhaben "EQOS". Berichtszeitraum: 01.05.2008 bis 31.07.2011. Förderkennzeichen BMWi IN 7023 - 16IN0632-0633

Abstract

Laser brazing makes it possible to join even thin-walled components at high speeds while producing seams with surface qualities. excellent For this reason, laser brazing is particularly suitable for joining car body parts which will be in direct view of the customer. Typical examples for this are automotive roof seams and two-piece tailgates. For these types of applications, the demands in regard to productivity, cost-effectiveness and quality are exceptionally high. Despite the use of sophisticated processing systems, sporadic seam irregularities like pores may still occur. In consequence, a wide range of post-process quality control systems is being used industrially to perform quality checks on laser brazed seams. However, this post-process approach to quality control rarely measures up to existing technological challenges. To offer a new solution for this challenge, the goal of the research project EQOS was to develop a new type of quality control system, which can detect several process and quality parameters online during the actual joining process. In a first step towards achieving this goal, the process mechanisms leading to the formation of seam defects were analyzed in detail. These analyses made it possible to reproduce different types of seam defects in a controlled environment for the purpose of testing, developing and qualifying the process control system. The analysis results also form a suitable foundation for developing new methods of detecting seam defects and new strategies of preventing seam defects. The next step in developing an online control system was the design of the optical system for performing the process control. For this purpose, two cameras operating in the visible (VIS) and near infrared (NIR) spectral range were coaxially integrated into the beam path of the laser processing head. This approach made it possible to monitor the process zone in both spectral ranges during the actual joining process. The third major work package of this project was the development of a software capable of automatically evaluating the camera images. For this purpose, different software modules with the capability of detecting individual defect types or process parameters were initially developed. These individual modules were subsequently successfully joined in a combined module for evaluating the seam quality. The combined result of these different tasks is a prototype system with online operating capabilities. It is based on an industrial brazing head with tactile seam guidance. The prototype was able to meet all technical requirements which were defined at the beginning of the project. Thus, the feasibility of performing a reliable online control of laser brazing processes could be successfully demonstrated. In conclusion, there is a wide range of potential applications for this type of system in the automotive sector. Additionally, the results of this project offer various opportunities for subsequent scientific research and industrial product development