2.3 JOINING MATERIALS 48 Can you define the difference between permanent and semipermanent joining? 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. Plasma welding ONLINE RESOURCES TIG welding notes Underwater welding autogenous: autogeno bond: attaccare, unire brazing: brasatura edge: bordo, margine fastening: fissaggio filler rod: bacchetta d apporto filler wire: filo d apporto molten pool: bagno di fusione soldering: saldatura eterogena welding: saldatura welding electrode: elettrodo per saldatura 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: welding, brazing, soldering, mechanical fastening, and adhesive bonding. 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 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. Fusion welding The fusion melting process involves localised melting and solidification. The two main types of fusion welding are: Autogenous: 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 edges 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; Dissimilar: 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 filler rod or filler wire. TIG welding All welding processes which use gas as the heating source MIG, TIG , oxy-fuel welding, oxyacetylene welding are examples of fusion welding. Electric arc welding Electric arc welding processes use electricity to produce the intense heat necessary for welding. Some electric arc processes use a consumable welding electrode that melts and becomes part of the weld metal. Laser beam welding Laser beam welding is a fusion welding process in which two metal pieces are joined together by the use of a laser. The laser beams are 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. Plasma 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 automatic welding. 100 Shaping and joining materialS MechPower.indb 100 30/01/24 17:08