Method and apparatus for short-circuit welding

A welding system for welding workpieces of dissimilar first and second metals with workpiece edges located proximate one another, said system comprising:

• a supply of welding electrode with an alloying material to join said first and second metals at said edges, said alloying material being tailored according to properties of both said first and second metals;
• a wire feeder adapted to direct said electrode toward said workpiece edges;
• a switching power source coupled with said electrode and providing current to said electrode in the form of a plurality of small width current pulses constituting a series of welding cycles to deposit molten metal from said electrode to said workpieces, each of said welding cycles including:
• an arc condition during which said electrode is spaced from said workpieces, an arc is formed between said electrode and said workpieces, and molten metal is formed on an end of said electrode, a short-circuit condition during which said molten metal on said end of said electrode contacts said workpiece and then transfers from said electrode to said workpiece, and a metal breaking fuse condition during which said molten metal separates from said end of said electrode;
• and a waveform generator coupled with said power source and controlling said current supplied to said electrode in each said welding cycle according to a detected start of said short-circuit condition and according to a detected or anticipated start of said metal breaking fuse condition;
• wherein said waveform generator causes said switching power source to provide a controlled boost pulse to said electrode during said arc condition to establish an arc length and to form said molten metal on said end of said electrode, and to provide a controlled background current to said electrode following said boost pulse to control heating of said arc until a short-circuit condition of a subsequent welding cycle.

In a pipe welding system for welding longitudinal ends of pipe sections together, a method of joining ends of two pipes formed of dissimilar first and second metals, said method comprising:

• (a) providing first and second pipes formed of different first and second metals, respectively;
• (b) locating first and second pipes in axial alignment with ends of said first and second pipes in spaced relationship to provide a gap therebetween;
• (c) providing a welding electrode having alloying material tailored according to properties of both said first and second metals;
• (d) directing said electrode toward said pipe ends;
• and
• (e) energizing said electrode to create a sequence of welding cycles, said welding cycles individually comprising:
• an arc condition during which an arc is formed between said electrode and said pipes and molten metal is formed on an end of said electrode, a short-circuit condition during which said molten metal on said end of said electrode contacts said pipes and then transfers from said electrode to said pipes, and a metal breaking fuse condition during which said molten metal separates from said end of said electrode, wherein energy provided to said electrode is controlled according to a detected start of said short-circuit condition and according to a detected or anticipated start of said metal breaking fuse condition.