TWI Industrial Member Report Summary 674/1999
I A Jones
The use of laser welding within structural steel construction has been investigated now for many years. In particular there has been much development in the area of ship construction. High power CO2 lasers have been considered for both butt joints and T-joints for flat, stiffened panel fabrication. The main advantages for laser welding leading to reduced manufacturing costs in comparison to arc welding are considered to be:
- Reduced structural distortion leading to reduced re-work.
- Faster joint completion rates.
- More accurate structures permitting easier subsequent assembly of modules.
- Advanced welding process mechanisation and automation.
These benefits can only be realised if laser welds having the quality and properties required by the marine classification societies can be produced in appropriate grade steels in a shipyard environment. The main outstanding weld quality question from previous work was concerned with the avoidance of solidification cracking. It has been proposed that the welding procedures could be altered to reduced cracking tendency, and that it may be possible to alter the steel composition in a way which does not impose a high cost penalty (ie without such stringent controls on sulphur and phosphorus levels, two elements that can increase the propensity for solidification cracking in steels). This report covers an investigation of methods to control cracking by changing the laser welding procedures.
- To increase the economic benefits of laser welding by reducing the restrictions on material specification and welding procedures, which are currently necessary for production of defect free welds in 12mm thick steel.
- To define more accurately the restrictions on welding speed and steel thickness for the avoidance of cracking.
- To investigate the effect of use of different lasers, focusing optics and plasma control systems on weld metal cracking.
- To develop the process, and investigate the effects of tandem beam laser welding with and without filler wire addition.
- To define the level of any link between weld cracking and weld shape, which could subsequently be used to aid weld quality control.