Welding is the economical method of joining process metal parts as permanent. Any metals can be welded, but some are easier to weld than others. Welding is most used for joining pipes in the mechanical work. To join it, the metals must be prepared about the geometry of welding joint type a fillet or groove joints. Then, the metals are heated until to the melting point with a pressure or filler metal or neither. Furthermore, the melted metals will be cooling off and become unity metals. Many types of welding process can be used to joints metals parts. The welding processes that often used in mechanical works are Shielded Metal Arc Welding (SMAW), Gas Tungsten Arc Welding (GTAW) and Submerged Arc Welding (SAW). Choosing the welding process depends on several aspects such as type and thickness of materials used, field conditions of the welding job and economical aspect.
The first welding process is SMAW. It is a welding process by using the coating electrode that can make shielding gas when it burns. The electrical arc is caused from power source which the base metal as a positive pole and another side electrode as a negative pole. It produces a heat that causes the electrode and base metals are melting together. The shielding gas that produced from coating electrode use to protect the molten weld metals so that not interact with the atmosphere especially oxygen. A small diameter electrode uses at low electrical current in any welding position for a tiny material of carbon steel. The other way, a large diameter electrode uses at high electrical current in a horizontal position for a thick material of carbon steel. For example, an electrode in SMAW according to AWS (American Welding Society) is E 7018. SMAW welding process has several advantages are can be used on almost of the carbon steels type, simple process and tools in use and low cost.
The second welding process is GTAW, which also called TIG (Tungsten Inert Gas). It is a welding process by using non-consumable electrode and a shielding gas blown during the process. The electrode is made from tungsten rod or wolfram, whereas the shielding gasses are Helium, Argon or Carbon dioxide. The Electrical arc is caused between electrode and base metal, whereas the shielding gas is used to protect electrode and molten weld. In general, the electrode as a negative pole in welding for Carbon Steels, Stainless steels and Titanium, and the electrode as positive pole in welding for Aluminum and Magnesium. One of the electrodes types GTAW according to AWS is ER70SG. The applications of GTAW process are use in carbon steels pipe which have thickness about 5 mm and diameter about 4 Inch, or all diameter for Stainless steels. GTAW also can use for Stainless steels tiny plate or Aluminum pipes. If the pipe thickness is more than 6 mm, so the welding process will be a combination between GTAW and SMAW.
The third welding process is SAW. It is a welding process that the electrical arc and molten weld are protected by liquids flux and particles flux which granular shape. The electrode tip goes into the flux a while electrical arc does not function. SAW are operated in two ways that are a mechanic system for flat welding position and semi-automatic for acquiring a consistent quality weld. SAW usually use on a thick plate of Carbon steels or all grade of alloy steels.
Base on the paragraphs above, there are many types to execute joining metals by a welding process. The welding process can be chosen base on the material type and process characteristic. Three of famous methods used in mechanical work are SMAW, GTAW, and SAW.