Welding

Welding is a process in which two or more parts are joined permanently at their touching surfaces by the force of heat and/or pressure. Often a filler material is added that helps in the merging. The parts that are joined together by welding are called a weldment. Factors affecting Weld-ability 1. Melting Point 2. Thermal conductivity 3. Thermal Expansion 4. Surface condition 5. Change in Micro structure. Welding is mainly used in metal parts and their alloys. Welding is of two types : Fusion welding and Solid state welding.1 Fusion welding : In this the base metal is melted by means of heat. Ina fusion welding operation, a filler metal is added to the molten pool to facilitate the process and provide bulk and strength to the joint. The most commonly used fusion welding processes are: arc welding, resistance welding, oxyfuel welding, electron beam welding and laser beam welding. 2. Solid-state welding: In this method joining of parts takes place by the application of pressure or a combination of heat and pressure. No filler metal is used in this . The most commonly used solid-state welding processes are: diffusion welding, friction welding, ultrasonic welding. Arc welding is a method of permanently joining two or more metal parts. It consists of combination of different welding processes wherein merging is done by heating with an electric arc, (mostly without the application of pressure) and with or without the use of filler metals that again depends upon the base plate thickness. A joint is achieved by melting and fusing the adjacent portions of the separate parts. The finally welded joint has a strength approximately equal to that of the base material. 

The arc temperature is maintained approximately at 4400°C. To prevent oxidation, a flux material is used which decomposes under the heat of welding and releases a gas that shields the arc and the hot metal. Precautions in Arc welding courses in kerala 1. Due to the intensity of heat and light rays from the electric arc, the operator’s hand face and eyes are to be protected while arc is in use 2. Heavy gloves are worn 3. Hand shield or a helmet with window of coloured glass must be used to protect the face 4. The space for the electric arc welding should be screened off from the rest of the building to safeguard other workmen from the glare of the arc.The second basic method employs an inert gas to form a protective envelope around the arc and the weld. The commonly used gases are Helium, argon, and carbon dioxide . Other processes that are used in the industry are as follows: 1. Diffusion bonding (DB): in this method parts are pressed together at an elevated temperature below the melting point for a period of time. 2. Explosion welding (EXW): In this method the parts to be welded are driven together at an angle with the help of an explosive charge and fuse together from the friction of the impact. 3. Ultrasonic welding (USW) for metals: This process makes use of transverse oscillation of one part against the other to develop sufficient frictional heat for fusion to occur. 4. Electro slag (ESW) and Electro gas (EGW) processes: In these a molten pool of weld metal contained by copper “shoes” is used to make vertical butt welds in heavy plate.