Deep penetration laser welding in low gravity

Abstract

A comparison of laser penetration welding interactions under a range of gravity conditions has been performed in an attempt to separate the roles gravity and surface tension play in the interaction. Laser processing was performed under low (10-2 g) and high (1.8 g) gravity conditions using NASA’s KC-135 microgravity aircraft, and for several orientations under 1 g conditions. CO2 laser penetration welding of polypropylene plastic was performed to directly observe and record changes in weld keyhole morphology with gravity. Bead on plate welds were performed to observe keyhole shape and measure weld penetration. Penetration depths were measured using digital frame grabbing techniques. A model considering thermal conduction and hydrodynamic surface effects was developed to predict keyhole penetration as a function of applied laser power and gravity magnitude and direction. This study provided the first direct observations of keyhole behaviour under low gravity conditions and proved the viability of keyhole welding in low gravity. Keyhole shape changes significantly with gravity while changes in penetration are relatively small. The model closely predicts the observed penetration behaviour.A comparison of laser penetration welding interactions under a range of gravity conditions has been performed in an attempt to separate the roles gravity and surface tension play in the interaction. Laser processing was performed under low (10-2 g) and high (1.8 g) gravity conditions using NASA’s KC-135 microgravity aircraft, and for several orientations under 1 g conditions. CO2 laser penetration welding of polypropylene plastic was performed to directly observe and record changes in weld keyhole morphology with gravity. Bead on plate welds were performed to observe keyhole shape and measure weld penetration. Penetration depths were measured using digital frame grabbing techniques. A model considering thermal conduction and hydrodynamic surface effects was developed to predict keyhole penetration as a function of applied laser power and gravity magnitude and direction. This study provided the first direct observations of keyhole behaviour under low gravity conditions and proved the viability of keyhole w...