TWI Industrial Member Report Summary 924/2009
By J E Blackburn and C M Allen
This report addresses the use of a directed gas jet for achieving consistently low internal porosity content laser welds in titanium alloys. In particular, despite earlier examples of laser welding titanium using a directed gas jet to control porosity successfully, questions remain:
- To what tolerances must the parameters be set, eg jet position, angle and gas flow rate, and still achieve acceptable welds?
- By what mechanism is the jet creating welding conditions that produce welds with low internal porosity content welds?
To answer these questions, this project has focused on Nd:YAG laser welding titanium alloys 3.2mm in thickness. The effects on internal porosity content of gas jet set-up parameters are addressed, and the robustness of this method to variations in parameters determined.
In terms of the specificity of the work, it should be noted that a directed gas jet has also been used for producing low internal porosity content laser welds in 3, 5 and 9.3mm thickness Ti-6Al-4V (Hilton et al, 2007). In this earlier work, a range of welding speeds and laser powers were used, depending on the material thickness. Welding speeds from 0.9 (9.3mm thickness material) to 5.2m/min (3mm thickness material) were used. Similarly, laser powers from 2.9 (Nd:YAG laser welding of 3mm thickness material) to 6.7kW (Yb fibre laser welding of 9.3mm thickness material) have been used. This last point illustrates that a directed gas jet can also be used in conjunction with a Yb fibre laser to produce low internal porosity content welds.
- Determine the processing factors significant in controlling weld metal porosity when laser welding titanium alloys using fibre-delivered lasers with a directed Ar gas jet.
- Establish the tolerance windows of these factors.
- Give practical recommendations to achieve robust laser welding of titanium alloys with low internal porosity content.