Make a mold. Either make a plaster mold of an existing sculpture or use the lost-wax process. Pour in the molten metal and wait until it has completely cooled before cleaning. Sculpt the metal using a grinder, chisel and a metal file. When casting metal, welding is saved for attaching pieces together to make a larger piece. Heavy bronze pieces are usually welded to a base.
Sculpt metal using power tools, hand tools, or your welding torch. You can cut holes, geometric shapes, or precise shapes. The tools needed for cutting thick pieces of metal are band saws, lathes, or metal presses. You can also use hand tools on certain types of metal. Hacksaws work well; a simple hammer can create effects. Wire sculptures are popular; the process is similar to drawing with a line. Wire can be cut, tied and welded to itself. Use low heat and solder for best results.
Shape metal using a welding torch. Thin sheets can be heated enough to make it malleable. Use gravity by softening heavy elements, or burn holes into sheet metal. Bend, twist and shape your metal suing homemade bending jigs. Clamps can be used to bend metal around a frame. Simple shapes can be accomplished with your hands. If you want to do more, use tools and heat the metal to become softer. Think about how a blacksmith makes wrought iron. A good blacksmith can make anything from nails to axles to horseshoes.
Look at other sculptures. Identify which techniques were used. Art history is filled with examples of welded sculptures. The American artist Alexander Calder created the large orange sculpture called "Stegosaurus." The minimal art works by Carl Andre invoke the human form by contrasting it with the pure industrial. The most famous shaped and welded sculpture may be the Statue of Liberty. "The Thinker" is a great work by French artist Auguste Rodin. Abstract metal artist Richard Serra made works from slag thrown against a wall.