TYPES OF WELDING
Plastic welding:
Here the pieces of metal to be joined are heated to the plastic state and then forced together by external pressure without the addition of filler material. Forge welding, resistance welding and the thermite welding with pressure are the examples of this class.
Fusion welding:
here, the metal at the joint is heated to a molten state and allowed to solidify.In this method material used during welding process. This includes gas welding, arc welding and the thermit welding.
Various types of fusion welding are,
Oxy-fuel gas: It's a versatile process used for welding sheet metal and small pipes.
Shield metal arc: Its used in all fields of engineering for all metal/alloys expect copper and low melting materials.
Submerged arc: Its used for boilers, pressure vessels, ship welding, automobile industry.
Gas tungsten Arc: It is used for welding all engineering metals except zinc.
Gas metal arc: It is used for general engineering in all fields for welding carbon steels, alloy steels, stainless steel, aluminium, nickel alloys.
Resistance welding: Used for welding of sheet metals of all engineering metals (except Cu, Ag) in automobile and air craft industries, pipe and tubing production.
Electro slag Welding: used for thick sections of pressure vessels, press frames, shafts of carbon, low and high alloy steels.
Thermit welding: it is used for welding parts, copper conductors, copper/steel joints.
Plasma arc: It is used mainly for reactive metals and all engineering metals except zinc.
Electron Beam: It is used in nuclear and aerospace industry for all metals, particularly reactive metals, Ni, Ti, Zirconium and stainless steel.
Laser Beam: It is used for deep hole drilling, repairs, in electronic industry and special applications.
Solid phase welding:
As already indicated these welds are made by the creation of metallic bond between the two surfaces being joined. The surface to be joined are brought so much close together that atoms are separated by less than the relaxation distance over which the inter-atomic forces act, thus creating a bond. however it is very difficult to bring a sufficiently large area into intimate contact due to surface asperities on the metals and the oxide films and impurities on the surfaces which act as a barrier between the metals. Sufficient pressure has to be applied to cause plastic flow of the two surface and to make large areas to come into intimate contact. since such intimate contacts under cold conditions are difficult, most solid phase welding processes are performed hot. heating also lowers filed strength and enables lower pressures to be used, metals or evaporates the surface contaminants, permits growth and coalescence of grains across the interface, causes surface and volume diffusion across the interface.
The fig shows how the force between atoms varies with change in distance between them. Under equilibrium condition, distance is dc and force nil. When external tensile force is applied, distance increase dc and on compression it decreases. It is interesting to note that inter-atomic force increase considerably below dc and tends to be zero after a few multiples of dc. Thus if two metallic surfaces are brought so much close together that their grain boundaries contact each other than the surface will adhere to each other with the large force. It is therefore, essential that the contaminated layers of oxides and adsorbed gases present on the surface of metal under normal atmosphere are removed by scratch brushing. The two metal surface are then brought into contact, the real contact taking place through a small area of asperities. The metallic bridging occurs even in the presence of adsorbed surface layers.
Following variables play important role in solid phase welding
⦁ Surface deformation.
⦁ Surface oxide layers and oil films.
⦁ Recrystallisation and grain growth at the interface.
⦁ diffusion
Cold welding:
Cold welding is a pressure welding process in which ductile materials can be welded without the application of heat or electric current. Weld is effected by making the metals to be joined to flow at room temperature by subjecting them to sufficient pressure. Required welding pressure is applied to overlapping surfaces with tool dies designed to cause controlled deformation of considerable extent. Cold welds are characterised by deep indentation on the outer surfaces of the work pieces. This process is best suited to high purity and commercially pure aluminium, but can used for many nonferrous metals. This can also be used to join metals of different hardness like copper to aluminium.
For satisfactory results there should be direct and intimate contact between the surfaces to be welded, and the tool dies must be of proper design to provide the degree of compression required for the weld. The two surface should be free of grease and oxides. Even fine remarks in some cases may render defective joints. Usually surface is cleaned by a motor-driven rotary-brush to cut through the film of oxide and to expose the clean metal under-Neath. Symmetrical tool dies must apply pressure over a comparatively narrow strip and in such a manner that the metal can away form the weld on both sides. Satisfactory welds may be produced with either an impact blow or a slow squeeze. For successful weld, the original thickness must be squeezed or reduced by a certain minimum percentage determined by the materials to be joined. for joining metals of different hardness, the width of the dies must be adjusted according to their respective hardness ratios, in order to share the final thickness at the insert somewhat like plastic moulding.
Some of the cold welding techniques,
⦁ Trap welding.
⦁ wave welds.
⦁ Stagger weld.
⦁ Sandwich welding.
Plastic welding:
Here the pieces of metal to be joined are heated to the plastic state and then forced together by external pressure without the addition of filler material. Forge welding, resistance welding and the thermite welding with pressure are the examples of this class.
Fusion welding:
here, the metal at the joint is heated to a molten state and allowed to solidify.In this method material used during welding process. This includes gas welding, arc welding and the thermit welding.
Various types of fusion welding are,
Oxy-fuel gas: It's a versatile process used for welding sheet metal and small pipes.
Shield metal arc: Its used in all fields of engineering for all metal/alloys expect copper and low melting materials.
Submerged arc: Its used for boilers, pressure vessels, ship welding, automobile industry.
Gas tungsten Arc: It is used for welding all engineering metals except zinc.
Gas metal arc: It is used for general engineering in all fields for welding carbon steels, alloy steels, stainless steel, aluminium, nickel alloys.
Resistance welding: Used for welding of sheet metals of all engineering metals (except Cu, Ag) in automobile and air craft industries, pipe and tubing production.
Electro slag Welding: used for thick sections of pressure vessels, press frames, shafts of carbon, low and high alloy steels.
Thermit welding: it is used for welding parts, copper conductors, copper/steel joints.
Plasma arc: It is used mainly for reactive metals and all engineering metals except zinc.
Electron Beam: It is used in nuclear and aerospace industry for all metals, particularly reactive metals, Ni, Ti, Zirconium and stainless steel.
Laser Beam: It is used for deep hole drilling, repairs, in electronic industry and special applications.
Solid phase welding:
As already indicated these welds are made by the creation of metallic bond between the two surfaces being joined. The surface to be joined are brought so much close together that atoms are separated by less than the relaxation distance over which the inter-atomic forces act, thus creating a bond. however it is very difficult to bring a sufficiently large area into intimate contact due to surface asperities on the metals and the oxide films and impurities on the surfaces which act as a barrier between the metals. Sufficient pressure has to be applied to cause plastic flow of the two surface and to make large areas to come into intimate contact. since such intimate contacts under cold conditions are difficult, most solid phase welding processes are performed hot. heating also lowers filed strength and enables lower pressures to be used, metals or evaporates the surface contaminants, permits growth and coalescence of grains across the interface, causes surface and volume diffusion across the interface.
The fig shows how the force between atoms varies with change in distance between them. Under equilibrium condition, distance is dc and force nil. When external tensile force is applied, distance increase dc and on compression it decreases. It is interesting to note that inter-atomic force increase considerably below dc and tends to be zero after a few multiples of dc. Thus if two metallic surfaces are brought so much close together that their grain boundaries contact each other than the surface will adhere to each other with the large force. It is therefore, essential that the contaminated layers of oxides and adsorbed gases present on the surface of metal under normal atmosphere are removed by scratch brushing. The two metal surface are then brought into contact, the real contact taking place through a small area of asperities. The metallic bridging occurs even in the presence of adsorbed surface layers.
Following variables play important role in solid phase welding
⦁ Surface deformation.
⦁ Surface oxide layers and oil films.
⦁ Recrystallisation and grain growth at the interface.
⦁ diffusion
Cold welding:
Cold welding is a pressure welding process in which ductile materials can be welded without the application of heat or electric current. Weld is effected by making the metals to be joined to flow at room temperature by subjecting them to sufficient pressure. Required welding pressure is applied to overlapping surfaces with tool dies designed to cause controlled deformation of considerable extent. Cold welds are characterised by deep indentation on the outer surfaces of the work pieces. This process is best suited to high purity and commercially pure aluminium, but can used for many nonferrous metals. This can also be used to join metals of different hardness like copper to aluminium.
For satisfactory results there should be direct and intimate contact between the surfaces to be welded, and the tool dies must be of proper design to provide the degree of compression required for the weld. The two surface should be free of grease and oxides. Even fine remarks in some cases may render defective joints. Usually surface is cleaned by a motor-driven rotary-brush to cut through the film of oxide and to expose the clean metal under-Neath. Symmetrical tool dies must apply pressure over a comparatively narrow strip and in such a manner that the metal can away form the weld on both sides. Satisfactory welds may be produced with either an impact blow or a slow squeeze. For successful weld, the original thickness must be squeezed or reduced by a certain minimum percentage determined by the materials to be joined. for joining metals of different hardness, the width of the dies must be adjusted according to their respective hardness ratios, in order to share the final thickness at the insert somewhat like plastic moulding.
Some of the cold welding techniques,
⦁ Trap welding.
⦁ wave welds.
⦁ Stagger weld.
⦁ Sandwich welding.
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