TWI Industrial Member Report Summary 843/2006
By G Shi, G Verhaeghe and P Hilton
Laser beam welding, as a substitute for conventional welding, provides advantages in terms of lower heat input and because of this, less distortion in the components being joined. However, some industry sectors are still hesitant to introduce lasers onto the shop floor, primarily because of the large capital investment and the precise joint fit-up required for laser welding. The accuracy in part fit-up required for autogenous laser welding is not always possible to achieve in today's production processes, which require flexibility and automation, while maintaining a high standard of weld quality. More tolerant welding procedures and/or process control must be integrated into automated welding systems to maintain weld quality. It is known that the combination of an electric arc with the laser beam can significantly improve the gap bridging capability of the laser process, but whatever process is used, a first stage in any adaptive process control, is to be able to effectively monitor the welding process in order to provide the necessary feedback parameters. It is therefore necessary to examine the performance of commercially available and newly developed laser weld quality monitors, to determine the range of imperfections which they can detect and their sensitivity to such imperfections. Only when this information is fully understood can the output from these types of detectors be used to provide useful feedback signals for real-time process control.
A collaborative project was initiated in 2002 between a number of European industrial companies and RTOs to address the topic of process monitoring and control, named IPCIM (Integrated Control of Laser Welding For Improved Weld Quality). The main objective of IPCIM was 'to develop new and innovative welding techniques for new materials (or products) and to develop welding control techniques for welding sheet and plate steel in manufacturing industry'. The project work was carried out jointly by the IPCIM project partners which included, as well as TWI:
- Fraunhofer ILT, Germany (Co-ordinator).
- Trumpf Lasertechnik GmbH, Germany.
- Thyssen Laser-Technik GmbH, Germany.
- Precitec Optoelektronik GmbH & Co. KG, Germany.
- Groupement d'Etude et de Recherche pour les Applications Industrielles des Lasers de Puissance, France.
- Lappeenranta University of Technology, Finland.
- Instituto Superior Técnico, Portugal.
- Wedeco KFT, Hungary.
- Volvo Construction Equipment, Sweden.
- Bay Zoltán Institute for Materials Science and Technology, Hungary.
The work reported here was carried out at TWI as part of the IPCIM project. The main work was to assess the effectiveness of a range of commercially available photodiode based sensors to detect, in real-time, engineered factors causing weld imperfections, when welding the T-joint configuration in medium to thick section (6-12mm) steels.
- To develop procedures for laser and hybrid laser-MAG welding of fully penetrating T-joints in 6mm to 8mm and 8mm to 12mm C-Mn steel, with acceptable weld quality.
- To develop techniques for simulating weld imperfections during laser and hybrid laser-MAG welding of medium to thick section stiffened steel structures.
- To assess the effectiveness of different commercially available sensors to detect, in real-time, engineered factors causing weld imperfections typically observed when welding the steel T-joint configuration.