Metal inert gas welding:
- For welding of high thickness materials, that are made up of Al, Mg, Cu and its alloys are used for maintenance in aero scope, automobile and spacecraft industries.
- Arc is generated between a consumable electrode which is in the form of wire and the work piece
- By continuously feeding the electrode material gap between the work pieces, which is going to be filled where the joints are produced
- Liquid metal in the weld pool can be protected by creating inert gas atmosphere.
- Direct current reverse polarity can be used in this technique. Due to the heat generation on the electrode, direct current reverse polarity is maximized. With this weld the deposition rate is increased and welding speed can be increased.
- By supplying very high amount of current heat generation is increased on electrode and the work piece.
- Consumable electrodes are stress-free to supply
- Filler rod is not required
- Process of welding must be simple
- Inert gas shield will help to protect the weld automatically
- Improper welding leads to form solid impurities over the liquid weld
- This welding process exposes the welders to dangerous gases
- Before starting the process the electrode and work piece should be kept clean
Submerged arc welding:Advertisement:
- This technique will be used for welding of high thickness materials i.e. is greater than 75mm thickness in a single pass.
- Arc is generated in between the consumable electrode and the work piece
- By supplying very high rate of current, filler material is melted at a faster rate and at as well as at the base material, liquid metal will be formed.
- This will react with the flux material and it will form slag
- By moving the electrode down arc will be sub merged inside the slag such that it is not visible
- Due to this the heat transfer that is done happens of the arc will be minimized
- Slag inclusions can be reduced and also weld spatter can be minimized
- Direct current reverse polarity can be used to maximize the melting rate of electrode 20 kg/hr.
- Welding speed is very high that is nearly 5m/min
- In this process solid granulate flux is used
- Due to high temperatures the liquid metal in the weld pool and the solid granulate flux is easily melted. which forms a slag
- To supply the flux material continuously through the hollow tubular cross section, solid flux material will be fed to the weld pool at a constant rate.
- This technique can be automatic or semi-automatic, due to this constant voltage or constant current type of welding machines that are used.
- To minimize the leakage of liquid metal in different directions, where the copper plates are provided with internal cooling channel in the front, back and bottom of the work piece.
- To minimize the heat transfer rate of the liquid metal cooling water is circulated through the cooper plates
- This process is preferred for the ship building, pressure vessel fabrication
- Welding of high thickness materials can be done
- Metal deposition rate must be high
- The process is suitable for low alloys , carbons and alloy steels
- Smallest of welding fume and arc discernibility
- Minimum operating skills are required
- Welding process can be done in the flat or horizontal position only
- Due to more amount of liquid metal in the weld pool residual stresses are observed in the welded joint at very high rate.
- To avoid that heat treatment is required
- Heat affected zone is maximum
- Maintenance is essential to preserve accurate electrode alignment
- Tip and weld pool are beneath solid flux cover
- For welding of the sheets at the faster rate this technique can be used.
- Two sheets which are to be welded are held between two copper electrodes which are in the form of rollers
- High frequency power supply is allowed through the copper electrodes
- Due to contact resistance between the two work pieces surfaces heat generation takes place.
- By applying the pressure with rotating rollers lumps are formed, and due to rotation of the rollers continuous spots are formed which overlap.
- Due to this, leak proof joints can be produced
- Fabrication of fuel tanks
- Mufflers in exhaust pipes in automobiles
- There is no requirement of the filler materials
- No Associated gases and flumes
- Clean weld is possible
- Difficult to weld the material which have a thickness of 3mm
- Complex control is required to regulate the speed of the electrode and also current needs to be provided for overlapping the weld.
- To produce the joints in the sheets without any indentation marks, this technique can be used
- On one of the sheet which is to be joined provide projections by using embossing technique
- The two sheets are held between large size copper electrodes, through which high frequency power supply is passed
- At the contact of the projections sheet material heat is generated, by applying the pressure the nuggets are produced
- Due to more number of nuggets in a given cycle and the large area of the copper electrodes, the indentation on the sheet is neglected
- Production rate is high in this technique, which is used for mass production only.
- This technique can be preferred for welding of the sheets in the automobile industry without any indentation.
- During the welding process more than one hole is performed. The operation process is fast.
- Current and pressure required for the welding process is less
- Closer spacing must be possible
- For mass welding parts electrode can be shaped and it must act as an assembly fixture
- Suitable for the automation process
- There is no usage of filler materials
- Uniform weld is obtained during the process
- On the thin work pieces projections cannot be made
- Thin wok pieces cannot bear the electrode pressure
- Equipment used for the process is high
- After completion of the process additional operations are to be done
Flash butt welding:
- This technique is used for joining of the two pieces end to end, which is known as butt joint
- The two pipes which are to be joined in which one is a stationary and other is having axial movement
- By holding the two pieces in the electrode holders, high frequency power supply is given.
- The axial movement of one of the pipe at the contact is due to the contact resistance heat that is generated
- After obtaining sufficient heat by switching off the power supply, increase the axial pressure to produce the joint.
- At the contact of the two pipe from both the sides, the material is melted and nugget is formed throughout the circumference of the pipe
- In pipes and long tubes this process is used for producing the joints
- There is no requirement of the filler materials
- Due to application of elevated pressure we can see the oxides, impurities and scales on the weld joints
- This process is suitable for the Parts which have the similar cross sectional area.
High-frequency resistance welding:
- This technique is used to produce long length metallic pipes from the sheets
- In between the two welding rollers, with the help of the mandrel the sheet must be made to bend to get desired shape.
- By providing the copper electrodes at the pipe high frequency power supply is produced
- Due to high frequency the electrode will move from one end to other end in the presence of air gap. With this heat is generated at the two ends by applying the pressure by using the rollers joint can be produced.
- For welding of the objects that are in solid state this technique is used.
- By keeping the two objects one over the other the external pressure is applied on the work piece
- At the contact of the two work pieces oxide layers are broken and below this new surface is in contact with each surface of the object
- By applying very high pressure due to plastic or permanent deformation atomic interactions will take place at the contact of two work pieces in the solid state.
- Cladding of the materials to increase the corrosive resistance.
- Joining of the material in solid state for small objects like transistors
- Welding of the objects in explosive areas
- Joining of wires if they will break during wire drawing operations
- This technique is preferred for the materials which are having low strength like Aluminum, copper and their alloys
- For welding of the solid objects end to end this technique is preferred
- One of the objects which are to be welded will be under rotation at a given speed and other will be having axial movement.
- Moving the object axially makes contact with rotating objects
- Due to rubbing action initially oxide layers which are formed on the surface will be cleaned.
- Due to rubbing action friction will be developed and heat is produced at the contact of the two surfaces.
- After receiving sufficient amount of heat, this increases the axial pressure and the joint is produced due to forging action
- This technique will be used for welding of solid objects similar or dissimilar, same or different cross sections are seen in automobile and aerospace industries.
- Welding of drill bit to shank
- Joining of axel and hub
- Joining of valves to the pipes
- For joining of high thickness materials which are to be welded in solid states that are made up of similar or dissimilar materials this technique can be used.
- The two plates which are to be welded, one is fixed on the ground it is known as flyer plate
- By using the detonator explosive material will start burning and releases more amount of energy
- This will be transferred to the flyer plate, which later hits on the surface of the target plate with maximum impact forces.
- Due to severe plastic deformation at the contact of the two surfaces, joints can be produced
- The flyer plate maintains some distance from the target plate to gain the momentum for the flyer plate. This distance will depend on the thickness of the flyer plate.
- Flyer plate makes some inclination with horizontal surface this is due to giving of weld direction to the work piece
- Helps in joining of similar and dissimilar materials like titanium to steel , aluminum to steel, Aluminum to copper
- Joining of tubes to tube sheet of heat exchanger
- Cladding of high thickness materials
- Joining of valves to pipes
- Accuracy of the joint may be less
- Controlling of explosive material energy is difficult
- For joining of less thickness materials that is 1mm or less than 1mm can be possible
- High-frequency power supply will be given to the transducer
- It will convert the high frequency power supply to high frequency ultrasonic liberations
- These vibration will be transferred to the work piece through clamp and sonotrode
- Due to this vibrations dynamic cut off stress can be developed on the work surface, and the oxide layer will be removed
- If the temperature reaches 0.5 times of the melting temperature the material will becomes soft, then the static load needs to be applied onto the work piece
- Due to this joint will be formed between the two surface of the sheet
- Accuracy of the joint is more and initial investment of the setup is more.
- It will be used in-fabrication of diodes, transducers etc.. in electronic industries
- Armature windings
- Internal defects can be noticed and sized
- Contact must be done to one side of the material
- We never find any dangerous radiations
- Irrespective of the orientation planar defects can be detected
- High skilled labor is required.
- Misreading of the signal results the repairs
- Large grain size in the welds causes the mask defects.
- This is similar to the black smity operation
- The objects which are to be welded are heated upto recrystallization temperature
- At this temperature the work piece material becomes soft
- The two objects are kept on the anvil, and the force is applied manually by using the hammer.
- Due to this at the contact of the two surfaces due to plastic deformation joint can be produced
- The accuracy of the joint which is produced will depends on skill level of the operator
- This technique will be used for welding of the material in agriculture sector with less accuracy
- Due to heating of the material there is a possibility of oxide formation on the surface of the object
- To overcome these flux materials like borax will be used.
- It is used for joining of brittle material to the ductile materials like wrought iron to the low carbon steels
- In this technique joint is produced by means of pure diffusion process
- In diffusion atomic movement will take place in solid state due to emery difference
- The two objects which are to be welded will be in animate contact
- The energy difference is created between the surfaces by applying the pressure, heat or pressure alone
- Diffusion is a rate process; diffusion time will depends on rate of energy difference.
- By heating the material and applying the pressure continuously diffusion time can be reduced
- Due to heating of the material there is a possibility of oxide formation
- Due to this strength of the joint may be reduced
- To overcome this inert gas atmosphere will be created
- Accuracy of the joint will be very high
- Welding of metal to non-metals
- Joining of cutting tools
- Making of laminates
- Due to cold working process the base metal is not changed
- This process is suitable for joining of dissimilar metals
- Continuous weld joint must be made
- With the process clean joint is produced
Electro slag welding:
- For joining of high thickness materials. This technique can be preferred
- By separating the two work pieces with a given root gap, number of electrodes will be provided along the width of the work piece and these will be connected to number of power sources
- By applying very high rate of current with direct current straight polarity heat generation can takes place on the work piece as well as on the electrode
- Due to this molten liquid metal will be formed at the bottom of the work surface
- By applying the flux material, to the liquid metal slag is produced
- If we continue the process due to arc generation the amount of heat accumulated is very high due to flow of the liquid metal in vertical upward direction
- This is to overcome, after getting sufficient amount of heat and slag by moving the electrode in downward direction
- It will be contact with slag and arc will be extinguished due to short circuit and heat generation will be continued further due to resistance heating of the slag material
- By allowing the cooling water through the copper plates heat will be transferred at a maximum rate, where the liquid metal will get solidify
- Fabrication of press frame design
- Design of rolling mill frames and ship hulls
- Design of locomotive frames
- Time taken to solidification is very high
- Coarse grain structure will be developed in the weld bead
- It is very ductile and soft
- Heat affected zone is maximum
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