COMPUTATIONAL WELDING MECHANICS

Weld Procedure

A weld procedure is a specification for a weld joint defined on a cross-section of the weld joint. It specifies the number of weld passes, the position and shape of the nugget for each pass and the details of the weld process for each pass. The details include the type of weld process, type and size of consumables, welding current, voltage, welding speed, preheat, interpass temperature, the qualifications of the welder, etc.

A weld procedure that has been tested and proved to meet the standards of a testing organization is called a qualified weld procedure. Companies can have libraries with tens or hundreds of qualified weld procedures.

The weld procedure is usually not designed for a particular weld joint in a particular structure. A weld procedure is usually designed to be used for a fairly wide class of weld joints. In terms of object oriented software engineering, weld procedures should be implemented as an abstract class and each instance of a weld procedure should be instance of that class. Each weld joint must specify one weld procedure but no weld procedure should specify a weld joint. Table 7-1 shows an example of a weld procedure.

Preheat may be necessary depending on plate meterial.

If a capability of predicting the weld pool geometry is available, it could be used to predict the weld pool geometry for each weld pass.

A linear correlation between the depth and the length of the weld pool is found in laser beam welding experiments with varied laser beam power. Approximately 50-90% of the weld pool length (increasing with welding speed) results from conductive heat transport (with the fusion zone convexity contributing approximately 20-30%). The remaining 50-10% of the weld pool length (decreasing with welding speed) results from convective heat transport, [26].

The prescribed temperature distribution function proposed by Goldak, (see chapter III) has been developed to model weld pools with more complex geometry.

Fusion welding processes, in which the metal parts are heated until they melt together, can be performed with or without the addition of filler material. Arc welding, electron beam welding and laser welding belong to this category of welding processes. Radaj [31] gives more insight into the different processes and phenomena of which one should be aware.

Welded Structures & Applications of Welding in Indust. Fields 251