Development of low vacuum laser welding technique using an aerodynamic window

Abstract

In order to realize deep laser welding, conceptual application of a supersonic jet as an aerodynamic window was investigated. Detailed characteristics of the supersonic jet as the aerodynamic window were studied experimentally. Flow field of the supersonic jet was examined based on the schlieren flow visualization technique. As compared to a free-vortex flow design applied to the aerodynamic window nozzle, in the case of supersonic jet, oblique shock waves were captured both at the nozzle exit edge and the shear layer on the aerodynamic window. The velocity field under the condition that the shock - expansion wave was formed in the aerodynamic window was measured by the PIV (Particle Image Velocimetry) system (Koncerto II, Seika Digital Image Corp.) . Both the vorticity magnitude and angular momentum were analyzed. Level of the vorticity magnitude in the core region of the supersonic jet was smaller by one-order than that in the shear layer in the region corresponding to the passage of laser-light (θ = 30 to 40° and r = 23.8 to 27.1 mm). The radial and circumferential velocity product in this region was similar to that observed under the free-vortex condition. In addition to the measurement mentioned above, pressure behavior was investigated using a multi-pressure measuring system (Scanivalve Corp. ZOC33). When the reservoir pressure was set at 800 kPa and diffuser width as 30.0mm, cavity pressure was reduced to 10.0 kPa. Under this reduced pressure environment, penetration depth increased by 2.6 times compared to penetration depth under atmospheric pressure environment. The effectiveness of the supersonic free-vortex aerodynamic window system tested in the high power laser welding manufacturing has been proven by the present study.

Keywords

• supersonic flow
• aerodynamic window
• schlieren
• flow visualization
• piv
• high power laser welding