TWI Industrial Member Report Summary 546/1996
I A Jones
Welds made using lasers can be prone to porosity, especially in deep or partial penetration joints. This report suggests potential shielding gases for control of porosity to levels specified in a recently published CEN quality standard.
A laser welding procedure offers an alternative to other techniques which gives rapid, low distortion joining for a wide range of application areas. The deep and narrow weld can, however, be prone to porosity, particularly at the weld root of partial penetration welds. The occurrence of porosity can give problems in NDE by masking more important imperfections, and in severe cases can lead to a reduction in mechanical properties. The most important factors involved are the welding parameters (power, speed, position, etc), the process gas type, the material composition and the condition of the joint prior to welding (oxide scale, cleanliness). These factors have been shown to affect the size and number of pores present. A CEN standard for quality levels in power beam welds is soon to be published which specifies porosity requirements. There is therefore a need to quantify the importance of these process parameters in relation to the quality standard.
- To determine the effect of plasma control gas compositions and base metal compositions on porosity levels in full and partial penetration autogenous laser welds in 6mm thick mild steel.
- To examine the effect of wires containing various deoxidising and surface active elements on porosity in wire fed laser welds in 6mm thick mild steel.