12-12-2012, 03:14 PM
WELDING
welding.doc (Size: 311 KB / Downloads: 261)
Welding is a materials joining process which produces coalescence of materials by heating them to suitable temperatures with or without the application of pressure or by the application of pressure alone, and with or without the use of filler material.
Welding is used for making permanent joints. It is used in the manufacture of automobile bodies, aircraft frames, railway wagons, machine frames, structural works, tanks, furniture, boilers, general repair work and ship building.
TYPES
• Plastic Welding or Pressure Welding
The piece of metal to be joined are heated to a plastic state and forced together by external pressure
(Ex) Resistance welding
• Fusion Welding or Non-Pressure Welding
The material at the joint is heated to a molten state and allowed to solidify
(Ex) Gas welding, Arc welding
Classification of welding processes:
(i). Arc welding
1. Carbon arc
2. Metal arc
3. Metal inert gas
4. Tungsten inert gas
5. Plasma arc
6. Submerged arc
7. Electro-slag
(ii). Gas Welding
1. Oxy-acetylene
2. Air-acetylene
3. Oxy-hydrogen
(iii). Resistance Welding
1. Butt
2. Spot
3. Seam
4. Projection
5. Percussion
(iv) Thermit Welding
(v) Solid State Welding
1. Friction
2. Ultrasonic
3. Diffusion
4. Explosive
(vi) Newer Welding
1. Electron-beam
2. Laser
(vii) Related Process
1. Oxy-acetylene cutting
2. Arc cutting
3. Hard facing
4. Brazing
5. Soldering
Arc welding methods
1. Metal arc welding
It is a process of joining two metal pieces by melting the edges by an electric arc. The electric arc is produced between two conductors. The electrode is one conductor and the work piece is another conductor. The electrode and the work piece are brought nearer with small air gap. (3mm app.)
When current is passed an electric arc is produced between the electrode and the work piece. The work piece and the electrode are melted by the arc. Both molten piece of metal become one. Temperature of arc is about 4000°c Electrodes used in arc welding are coated with a flux. This flux produces a gaseous shield around the molten metal. It prevents the reaction of the molten metal with oxygen and nitrogen in the atmosphere. The flux removes the impurities from the molten metal and form a slag. This slag gets deposited over the weld metal. This protects the weld seam from rapid cooling. Fig.1 shows arc welding process.
EquipmentsRefer Fig 2)
• A welding generator (D.C.) or Transformer (A.C.)
• Two cables- one for work and one for electrode
• Electrode holder
• Electrode
• Protective shield
• Gloves
• Wire brush
• Chipping hammer
• Goggles
welding.doc (Size: 311 KB / Downloads: 261)
Welding is a materials joining process which produces coalescence of materials by heating them to suitable temperatures with or without the application of pressure or by the application of pressure alone, and with or without the use of filler material.
Welding is used for making permanent joints. It is used in the manufacture of automobile bodies, aircraft frames, railway wagons, machine frames, structural works, tanks, furniture, boilers, general repair work and ship building.
TYPES
• Plastic Welding or Pressure Welding
The piece of metal to be joined are heated to a plastic state and forced together by external pressure
(Ex) Resistance welding
• Fusion Welding or Non-Pressure Welding
The material at the joint is heated to a molten state and allowed to solidify
(Ex) Gas welding, Arc welding
Classification of welding processes:
(i). Arc welding
1. Carbon arc
2. Metal arc
3. Metal inert gas
4. Tungsten inert gas
5. Plasma arc
6. Submerged arc
7. Electro-slag
(ii). Gas Welding
1. Oxy-acetylene
2. Air-acetylene
3. Oxy-hydrogen
(iii). Resistance Welding
1. Butt
2. Spot
3. Seam
4. Projection
5. Percussion
(iv) Thermit Welding
(v) Solid State Welding
1. Friction
2. Ultrasonic
3. Diffusion
4. Explosive
(vi) Newer Welding
1. Electron-beam
2. Laser
(vii) Related Process
1. Oxy-acetylene cutting
2. Arc cutting
3. Hard facing
4. Brazing
5. Soldering
Arc welding methods
1. Metal arc welding
It is a process of joining two metal pieces by melting the edges by an electric arc. The electric arc is produced between two conductors. The electrode is one conductor and the work piece is another conductor. The electrode and the work piece are brought nearer with small air gap. (3mm app.)
When current is passed an electric arc is produced between the electrode and the work piece. The work piece and the electrode are melted by the arc. Both molten piece of metal become one. Temperature of arc is about 4000°c Electrodes used in arc welding are coated with a flux. This flux produces a gaseous shield around the molten metal. It prevents the reaction of the molten metal with oxygen and nitrogen in the atmosphere. The flux removes the impurities from the molten metal and form a slag. This slag gets deposited over the weld metal. This protects the weld seam from rapid cooling. Fig.1 shows arc welding process.
EquipmentsRefer Fig 2)
• A welding generator (D.C.) or Transformer (A.C.)
• Two cables- one for work and one for electrode
• Electrode holder
• Electrode
• Protective shield
• Gloves
• Wire brush
• Chipping hammer
• Goggles