Welding is a materials joining process used in making welds. A weld is a localized coalescence of metals or nonmetals produced either by heating the materials to a suitable temperate with or without the application of pressure, or by the application of pressure alone, with or without the use of filler metal. Coalescence is a growing together or a growing into one body, and is used in all of the welding process definitions. A weldment is an assembly of component parts joined by welding, which can be made of many or few metal parts. A weldment may contain metals of different compositions, and the pieces may be in the form of rolled shapes, sheet, plate, pipe, forgings, or castings. To produce a usable structure or weldment, there must be weld joints between the various pieces that make the weldment. The joint is the junction of members or the edges of members which are to be joined or have been joined. Filler metal is the material to be added in making a welded, brazed, or soldered joint. Base metal is the material to be welded, soldered, or cut.

The properties of a welded joint depend partly on the correct preparation of the edges being welded. All mill scale, rust, oxides, and other impurities must be removed from the joint edges or surfaces to prevent their inclusion in the weld metal. The edges should be prepared to permit fusion without excessive melting. Care must be taken to keep heat loss due to radiation into the base metal from the weld to a minimum. A properly prepared joint will keep both expansion on heating and contraction on cooling to a minimum.

Preparation of the metal for welding depends upon the form, thickness, and kind of metal, the load the weld will be required to support, and the available means for preparing the edges to be joined.

There are five basic types of joints for bringing two members together for welding. These joint types or designs are also used by other skilled trades. The five basic types of joints are described below and shown in figure 6-16.

Types of welds and welded joints

(1) B, Butt joint – parts in approximately the same plane. (2) C, Corner joint – parts at approximately right angles and at the edge of both parts. (3) E, Edge joint – an edge of two or more parallel parts. (4)

L, Lap joint – between overlapping parts.

(5) T, T joint – parts at approximately right angles, not at the edge of one part.