TWI Industrial Member Report Summary 978/2010
By Chris Allen
The requirements for precise workpiece fit-up and accurate alignment of the laser beam with the joint line, pre-requisites for high quality laser welds, continue to act as a brake to the wider take-up of laser welding, and now, with higher brightness fibre and disk laser sources, potentially never more so.
Requirements could be relaxed and weld quality maintained if a sensor and control system were implemented, capable of automatically measuring the joint characteristics and providing feedback to compensate for joint fit-up variations. One laser-based welding process to which simple controls have already been applied is hybrid laser-arc welding (Shi and Hilton, 2005). In general, hybrid welding can be carried out with productivity at least equal to that of laser welding, whilst at the same time already having some ability to accommodate larger fit-up gaps due to the wire feed addition from the arc. Hybrid welding is already used in the shipbuilding and automotive industries, and is being investigated for oil and gas pipe welding applications, and for use in the assembly of pressure vessels, storage tanks, and off-road vehicles.
The current work has continued the development of hybrid welding with adaptive control, using a high brightness laser in combination with some of the latest sensing and control technology available. As a test case, hybrid butt welding procedures have been developed for 6mm thickness laser cut EN 1.4301/AISI 304 stainless steel plates, as would interest fabricators working in the nuclear, chemical and food industries.
This work has resulted in the first instance, which TWI is aware of, of adaptive control of more than one welding parameter simultaneously during the hybrid welding of stainless steels, more than doubling fit-up tolerances. Furthermore, the concepts demonstrated in this project can be applied equally to other fusion weldable materials, in other thicknesses, with other welding processes and with other joint configurations, following appropriate selection of equipment and development of welding procedures.
- Develop and demonstrate adaptive control algorithms for laser hybrid applications with variable joint fit-up conditions in stainless steels.
- Establish the tolerance limits when adaptive welding on butt joints with different joint fit-up conditions.
- Examine the capability of automatic weld bead inspection after hybrid laser-arc welding of stainless steel with adaptive control.