COMPUTATIONAL WELDING MECHANICS

Weld Procedure

Associated with each weld pass in each weld joint is a weld pool. The weld pool may have any shape and size but its geometry must be specified as input data. If someone has a particularly complex weld pool, they could provide an STL file written by a CAD program. For many arc welds, an adequate approximation of the geometry of the weld pool can be provided by a half sphere, actually a half ellipsoid, with the length of each semi-axis specified independently. For a half sphere there are five semi-axes. For a Tee - joint, one might choose to describe the geometry of the weld pool by a 3/4 sphere or ellipsoid. Then it has six semi-axes and two of the eight octants of the sphere are missing. The weld pool moves along the weld joint from a specified starting point to a specified end point. The weld pool is always oriented by its position on the weld joint “ribbon” and the welding direction on the ribbon.

For each weld pass, filler metal is usually added. Associated with each weld joint, a mesh will be made automatically that includes joint preparation, weld pool and weld reinforcement. The joint preparation can be specified as an ordered set of 2D points, in effect line segments, for each ‘side of the weld joint’. We prefer the points be ordered CCW when looking in the welding ribbon direction, i. e., if one swims along the curve, the base metal is on the left side. The cross-section of each weld pass can be specified by an ordered set of points. Again we prefer the points be ordered CCW, i. e., if one swims along the curve, the weld pool metal is on the left side. Usually the weld mesh will overlap the mesh for the structure as a whole. The automatic meshing code will deal with this issue.

For welds, the values of the welding speed, power and arc efficiency are useful. If the weld is pulsed or if weaving is used, that information should be specified. If an estimate of the power density, thermal flux or mass flux distribution from the arc to the weld pool surface is known, that would be useful information.

A weld pass could have more than one weld pool.