TWI Industrial Member Report Summary 86/1979
By S A Westgate and R M Rivett
A number of projection designs, both embossed and solid, have been studied for welding 1.0 and 1.6mm 5182, 2117, 2036 and 2002 aluminium alloys.
Standard IIW and Humpage embossed projections are not satisfactory for 1mm aluminium alloys because of their low strength. Consistent welds can be made in lmm 5182 material using a stronger, annular embossed projection, with an electrode life of 1000 welds. Solidification cracking and porosity can be severe however when using embossed projections, particularly with the more crack susceptible alloys such as 2117 when this problem limits electrode life to about 100 welds.
Solid projection designs allow a more efficient forging of the weld nugget and higher quality welds can be made with fewer solidification defects. The types of solid projection studied were arc deposited, coined and resistance formed. Electrode lives were limited to about 400 welds using arc deposited projections in 1mm 5182 by concave electrode wear leading to wandering of the weld from the projection site. Less than 5% sheet separation and minimal sheet surface marking can be achieved particularly when using scratch brushed material.
Limited consistency trials using the more practical coined projections in 1mm 5182 and 2117 alloys produced satisfactory welds and an average electrode life of 780 welds was achieved with mill finished 5182. Projections could not be consistently raised by the resistance forming technique and such projections were not used for welding trials.
When welding 1.6mm 2117 material inconsistent results occurred due to severe solidification cracking when using either domed embossed or coined projections.