Effect of build orientation and surface finish on surface resistance in microwave components produced by Selective Laser Melting

A number of metal surfaces, produced by Selective Laser Melting, have been compared from a microwave perspective. Test pieces were produced in Aluminium (Al10SiMg), Titanium (Ti6Al4V) and Cobalt Chrome in two orthogonal build orientations, half of which were grit blasted. Surface resistance measurements at 5.7 GHz were taken using a “lift-off” dielectric resonator method. The losses were compared with roughness measurements from drag profilometry. Microwave losses were found not to monotonically depend on root-mean-square surface roughness, which was attributed to the different size distributions of roughness features. Grit blasting a sample typically reduced its surface resistance but the effect was much more significant in vertically produced surfaces. These results have major implications for parts used in microwave applications.