While welding with oxy-acetylene or arc welding the welder faces main difficulty of oxidation. To avoid oxidation fluxes are used but fluxes are also corrosive in nature that’s why these welding process (oxy-Acetylene and electric arc) can’t be used on A/C equipment. For A/C equipment advanced welding techniques are used. These techniques are TIG, MIG, EBW, etc.
Gas Tungsten Arc Welding (GTAW)
Gas tungsten arc welding uses the heat of an electric arc between a tungsten electrode and the base metal. A Separate welding filler rod is fed into the molten base metal, if needed. A shielding gas flows around the arc to keep away air and other harmful materials. This process is called as TIG (Tungsten Inert Gas) welding.
Gas tungsten arc welding is particularly desirable when welding stainless steel, aluminum, titanium, and many other nonferrous metals.
Figure “Gas Tungsten Arc Welding Plant” illustrates a typical station for gas tungsten arc welding. An AC-DC welding machine may be used with a regulated flow of a shielding gas such as argon or helium. The shielding gas flows from a cylinder through a regulator, flow meter, and a hose to the GTAW torch.
The welder normally manually operates the torch (electrode holder) and the filler metal. This torch has a gripping device to hold the tungsten electrode. A heat- resistant gas flow cup or nozzle surrounds the electrode. Some small capacity torches are air-cooled. Large torches are water cooled.
Heating properties of the arc may be controlled by changing current and arc length. The diameter of the tungsten electrode, thickness and kind of base metal, will determine welding amperage. GTAW welding may be done in any position with excellent results.
Gas tungsten arc welding generates intense heat and light, with no metal spatter. The welder must wear a welding helmet, gloves, and welder’s clothing.
Gas Metal Arc Welding (GMAW)
In gas metal arc welding, figure “Gas Metal Arc Welding Plant“, an electric arc produces heat between a continuously fed metal electrode and the base metal. The arc is shielded by a gas. This process is popular in production and repair shops. It is often called MIG (Metal Inert Gas) welding.
As shown in figure “Gas Metal Arc Welding Plant“, a shielding gas cylinder, regulator, flow meter, and hose provide a flow of shielding gas to the arc. Shielding gases such as carbon dioxide, argon, or helium may be used. An electrode-feeding device supplies metal electrode continuously. A torch and cable carry the electrode wire, current and shielding gas to the arc. The torch usually has a trigger switch for starting and stopping the electrode feed and gas flow.
A constant voltage DC welder is used with this process. The desired voltage is set on the welding machine. Current is changed by adjusting the wire feed speed. Speed controls for the wire are usually mounted in the wire feed mechanism.
Shielded gas volume adjustments are made at a gas flow meter on the regulator. The kind of shielding gas used usually depends on the metals being welded.
The welder must follow these points:-
(a) Select the electrode size.
(b) Set the desired voltage.
(c) Adjust the shielding gas flow.
(d) Adjust the rate of electrode feed.
(e) Control the torch movement and electrode extension. (The electrode extension is the distance from the torch tip to the arc.)
The welder must wear an approved helmet, gloves, and welder’s clothing. The welding area must have good ventilation.
Inertia (or) Friction Welding
Inertia or Friction welding is a pressure process where stored kinetic energy is used to generate the required heat for fusion. The two work pieces to be joined are axially aligned, one is held stationary by means of a chuck or fixture and other is securely clamped in a rotating spindle.
The rotating member brought up to a certain speed so as to develop sufficient energy. Then the drive source is disconnected and the pieces are brought into contact under a recomputed thrust load. At this point the kinetic energy contained in the rotating mass converts to frictional heat. The metals at this point get softened, permitting the work pieces to be forged together.
Advantages – The main advantages of friction welding process are:-
(a) It produces improved welds at higher speed and lower cost.
(b) It requires less electric current
(c) The costly copper fixtures for holding the parts are not required, as required in flash and butt-welding.
(d) There is less shortening of the component, which often results in flash or butt welding.
(e) The heat affected zone adjacent to the weld is confined to a narrow band and therefore does not draw the temper of the surrounding area.
Explosion Welding (EXW)
Explosion welding joins metals together by using a powerful shock wave. This creates enough pressure between two metals to cause surface flow and cohesion. It is often used to weld large sheets together. In one common application, it is used to weld thin stainless steel sheet to mild steel sheet. It is also used for welding aluminum and molybdenum together.
The energy source is the tremendous shock wave caused by igniting an explosive material. The operation requires very careful setup. Bonding takes place in an instant. Such welding is done either in a safety chamber, or less frequently, underwater.
Safety is very important! Both the explosives and fixtures must conform to approve written specifications. The welder must be protected from the sound of the explosion by wearing industrial “ear muffs” and/or ear plugs. Face shields, safety helmets, and approved clothing should be used. Special permits are required from government authorities because of the explosives used.