Fibre coupled diode laser welding of lead alloy

To reach the objective of reducing welding distortions, the Nd: YAG pulsed laser is mainly used in the laboratory. But for low melting point materials such as a lead alloy, a lot of molten pool instabilities can occur during laser/matter interaction. Actually, a porosity previously trapped in a solidified fusion zone can explode when it is partially melted by the next laser pulse. To avoid this phenomenon, a fibre (400 Pm) coupled CW diode laser (500 W) is tested. To reduce equatorial shrinkage, a high welding speed is preferred. 1 mm deep welds are obtained at two different speeds: 50 mm/s (240 W) and 100 mm/s (330 W). All the welds performed on test samples are in accordance with requirements: weld depth, tightness of the welds, distortions lower than 60 Pm. Despite some differences in the casting repeatability, the pressure on joint, the defects in joint and the surface states, a good robustness is expected. However, during welding operations, some interaction instabilities on many welds performed on specific devices are observed. Some possible explanations as oxide layer contamination or different chemical compositions due to casting are considered in order to explain these instabilities.