Which method is primarily used for changing the shape of sheet metal?

The method primarily used for changing the shape of sheet metal is crimping. This process involves deforming the sheet metal through mechanical force, creating a change in shape by bending or compressing the material at specific points. Crimping is commonly used to create joints, seams, or fittings by joining two pieces of metal together or by altering the contour of a single piece for various applications.

Welding, while it does involve fusing metal pieces together and can change their overall shape, primarily focuses on joining materials rather than reshaping them. Punching is a process where holes are made in the metal, which does not alter its shape significantly. Embossing, on the other hand, adds a raised or recessed design to the sheet metal but does not generally change its fundamental shape for structural purposes. Therefore, crimping is the most appropriate method among the choices provided for the specific purpose of changing the shape of sheet metal.