TWI Industrial Member Report Summary 1053/2015
By Chris Allen
Background
Heavy industry requires welding processes for thick section joining (t?25mm), meeting quality, property, productivity distortion and economic requirements. Laser beam welding could meet these requirements, but has been limited historically to thinner materials. Nevertheless, multi-pass laser beam melting of a wire feed in to a narrow gap joint configuration could increase the maximum joint thickness achievable.
Key Findings
The multi-pass process has been confirmed as showing promise for thick section narrow gap butt welding. The main conclusions of the trials carried out to develop this process to date are:
- Suitable welding parameters for this process (speed, wire feed rate, beam focus position etc) have been identified.
- Gas flow arrangements for protecting the weld pool against oxidation and dispersing plume have also been developed.
- Stringent inter-run de-slagging is critical to guaranteeing weld quality.
- Butt joints between materials up to at least 50mm in thickness can be completed.
- Cross-weld tensile properties in excess of those of the parent material have been demonstrated.
- Some hardness and toughness values measured from multi-pass welds suggests that further process development and materials selection may be necessary for some applications, e.g. for multi-pass laser welds in carbon steels for sub-ambient temperature or sour service.