Balling phenomena during direct laser sintering of multi-component Cu-based metal powder

The balling processes during direct laser sintering of a multi-component Cu-based metal powder, which consisted of a mixture of Cu, Cu–10Sn and Cu–8.4P, were investigated. Three kinds of balling mechanisms under different laser processing conditions were proposed. It shows that scanning the initial tracks onto a cold powder bed gives rise to the first line scan balling, due to the high thermal gradients imposed on the melt. Using a higher scan speed leads to the ‘shrinkage-induced balling’, because of a significant capillary instability effect. The ‘self-balling’ prevails at a high laser power combined with a low scan speed, which is ascribed to an excessive liquid formation and a too long liquid lifetime.