Experience with shipyard installation of a hybrid pipe welding system
Laser-Gas Metal Arc (GMA) hybrid welding is fast making the transition from laboratory to production, in industries as diverse as shipbuilding to automobile manufacture. For the past 3 years, our team has striven to both develop a hybrid welding process for steel pipe, and to specify, build, and install a hybrid pipe welding system in a General Dynamics NASSCO shipyard. In March 2007, the system was successfully installed into the shipyard. This work presents a summary of our continued experimental explorations into various practical aspects of hybrid welding, discusses the system design, and provides an overview of the installation of the system into the shipyard. Test results are presented, as well as lessons learned throughout the project.
Low heat input welding for thin steel fabrication
As thinner members are used in marine construction, the use of conventional joining techniques results in significant angular and buckling distortion due to the inherent high heat input with these processes. Several low heat input alternatives, including laser beam, gas metal arc, and hybrid laser arc welding, are explored. The paper focuses on process development, real time distortion measurements, and implementation of these processes.
Heat balance and flow conditions for electron beam and laser welding
The conditions of energy and material flow during beam welding are investigated theoretically to determine the factors which govern the shape of the vapor cavity and of the molten zone. Flow conditions in the horizontal plane determine the dimensions of the weld. Material is moved around the advancing vapor cavity mainly by liquid flow, but there is some vapor flow across the cavity, providing the pressure which drives the liquid. The pressure inside the vapor cavity and its variation with depth is governed by surface tension, by the hydrostatic pressure in the liquid, and by the viscous forces acting on the vapor stream. These factors govern the radius of the cavity as a function of depth. The penetration is limited by the beam power or by the absorption of the beam. For the laser beam, absorption is decreased in the hot center, and beam penetration increases with power, but is insensitive to collimation. For electrons, absorption occurs mainly near the walls of the cavity, and the beam penetration depen...