2.3 JOINING MATERIALS WELDING The joining of materials is an important technology in many manufacturing industries: a large number of processes are used to assemble individual parts into a larger, more complex component or assembly. The selection of the appropriate joint type is determined by the type of materials to join. Joining processes include: , , , mechanical and adhesive Mechanical fastening can be used to provide either temporary or permanent joints, while adhesive bonding, welding, brazing, and soldering processes are mainly used to provide permanent joints. welding brazing soldering fastening, bonding. 1 DO Can you define the difference between “permanent” and “semi-permanent” joining? 1 Welding is defined as the union of metals by heat action, with or without another metal’s contribution. It is a permanent joining process which exists in many different forms to weld a wide variety of materials in infinite ways; the following are some of the most important ones. Welding Fusion welding The process involves localised melting and solidification. The two main types of fusion welding are: fusion melting : When similar material combinations or materials belonging to the same family (e.g., two types of stainless steel) are joined. The weld is made by melting the of the two workpieces and allowing them to fuse together on cooling, or by using a filler material of identical composition of the welded metals; Autogenous edges : When materials with different alloys (e.g., carbon steel and stainless steel) are joined. The weld is obtained by adding extra material during the process through the melting of a or . Dissimilar filler rod filler wire All welding processes which use gas as the heating source – MIG, TIG , oxy-fuel welding, oxyacetylene welding – are examples of fusion welding. 1 MORE MIG (Metal Inert Gas) and TIG (Tungsten Inert Gas) welding use a gas jet around a filler wire. The main difference is the electrode they use to create the arc. MIG uses a consumable solid wire that is machine fed whereas TIG welding uses a non-consumable electrode. 1 Electric arc welding processes use electricity to produce the intense heat necessary for welding. Some electric arc processes use a consumable that melts and becomes part of the weld metal. Electric arc welding welding electrode Laser beam welding is a fusion welding process in which two metal pieces are joined together by the use of a laser. The laser beam arcs focused to the cavity between the two metal pieces to be joined and produce heat that melts the material and fills the cavity. After cooling, a strong weld is formed between the two pieces. It is a very efficient welding process, mostly used in the automotive industry, which can be automated with robotics machinery easily. Laser beam welding Plasma welding is a method that produces a plasma arc between the electrode and the material. The resulting high heat concentration enables precise high-speed welding: it is in fact one of the best methods for automotive welding. Plasma welding Plasma welding