By | April 11, 2015
  1. Arc welding
    1. Carbon arc welding
    2. Metal inert gas welding
    3. Tungsten inert gas welding
    4. Atomic hydrogen welding
    5. Plasma arc welding
    6. Submerged arc welding
    7. Electro slag welding
  2. Gas welding
    1. Oxy-acetylene welding
    2. Air-acetylene welding
    3. Oxy hydrogen welding
  3. Resistance welding
    1. Butt welding
    2. Spot welding
    3. Seam welding
    4. Projection welding
    5. Percussion welding
  4. Thermite welding
  5. Solid state welding
    1. Friction welding
    2. Explosive welding
    3. Ultrasonic welding
    4. Diffusion welding
  6. Newer welding
    1. Electron beam welding
    2. Laser welding
  7. Welding related processes
    1. Oxy-acetylene cutting
    2. Arc cutting
    3. Hard facing
    4. Brazing
    5. Soldering

Arc welding

In arc welding, the edges of two metal parts are melted by an electric arc and the joint is made. An electrode made of a suitable metal is utilized for this purpose. The electrode is taken closer to the parts to be joined and electric current is supplied to both the parts and the electrode. An electric arc is made between the electrode and the metal parts. This arc generates high temperature and melts the metal parts. The parts are joined at this molten state. The filler metal in the form of electrode is deposited along the joint. The metal parts are joined without the application of any pressure. Electrical energy is converted into heat energy in arc welding.

The distance between the metal parts and the electrode should be around 3mm. The heat generated during arc welding ranges from 5000°C to 6000°C. A generator or a transformer supplies the required current to both the electrode and the metal parts. The electrodes are flux coated to prevent the molten metal from reacting with the atmosphere.

Arc welding

Gas welding

Gas welding is the process of melting and joining metal parts by means of a gas flame. Generally pressure is not applied during the process of gas welding. Oxygen and acetylene gases are made to pass through the welding torch. These gases are mixed at the required ratio at the torch and the tip of the welding torch is ignited to produce the flame. Because of the heat generated by the flame, the edges of the metal parts are melted. Filler rod provides the additional metal required for making the joint. The flux coated on the electrodes prevents oxidation and removes impurities. This method is suitable in welding metal parts of thickness varying from 2mm to 50 mm. The temperature of the flame is around 3200°C.

Resistance Welding

Resistance welding

The process of resistance welding involves

  • developing electrical resistance in the parts of the joint to bring them into a plastic state and
  • applying pressure on the parts to make the joint

Two copper electrodes are connected to an electric circuit of low resistance. The parts to be welded are placed between the electrodes. When current is allowed to pass through the electrodes, high electrical resistance is developed at the joint. Because of the resistance, heat is generated at the joint. The metal parts reach plastic state at this high temperature.

At this point, pressure is applied by means of either mechanical or hydraulic or pneumatic power source to make the joint. Current is provided by a suitable A.C. transformer. Resistance welding is useful in welding sheet metal, bars and pipes.

Resistance welding

Thermite welding

A method of welding in which thermite, a mixture of powdered aluminum or magnesium and iron scale, is used to heat the metal.

If aluminum-based thermite is used, the parts being joined are placed in a refractory mold and heated, and a thermite melt, which is ignited by an electric arc or a primer, is pouredover the area to be welded. As the molten iron becomes alloyed with the base metal, it forms a durable joint. Welding with aluminum-based thermite is used to join steel and cast ironparts—for example, for welding rails or pipes, filling weld cracks, or fusing surfaces during repair work. Magnesium-based thermite is used primarily to join telephone and telegraphlines and the strands of cables. A cylindrical thermite charge is prepared, with an axial channel for the wire and a recess in the end plate for the primer. The ends of the wire to bewelded are inserted in the charge, after which the charge is ignited and the wire is clinched. Magnesium-based thermite can also be used to weld small-diameter pipes.

Solid state welding

Solid state welding is a group of welding processes which produces coalescence at temperatures essentially below the melting point of the base materials being joined, without the addition of brazing filler metal. Pressure may or may not be used. These processes are sometimes erroneously called solid state bonding processes: this group of welding processes includes cold welding, diffusion welding, explosion welding, forge welding, friction welding, hot pressure welding, roll welding, and ultrasonic welding.

Types Welded Joints

In all of these processes time, temperature, and pressure individually or in combination produce coalescence of the base metal without significant melting of the base metals.

Solid state welding includes some of the very oldest of the welding processes and some of the very newest. Some of the processes offer certain advantages since the base metal does not melt and form a nugget. The metals being joined retain their original properties without the heat-affected zone problems involved when there is base metal melting. When dissimilar metals are joined their thermal expansion and conductivity is of much less importance with solid state welding than with the arc welding processes.

Time, temperature, and pressure are involved; however, in some processes the time element is extremely short, in the microsecond range or up to a few seconds. In other cases, the time is extended to several hours. As temperature increases time is usually reduced. Since each of these processes is different each will be described.

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