1. Welding Processes
Prepared by:
MAHESH KUMAR N

2. WELDING PROCESS
It is a process of joining two materials (like or unlike) by the application of heat or heat and pressure using a filler material.
Almost all metals and alloys can be welded.
Heat is the main source of energy which can be obtained by electricity, gas or chemical reaction or friction.
Welding is used for fabrication of components.
Principle of welding:
The material to be joined are held in contact together and the required energy is applied mainly in the form of heat. This heat fuses the material and on cooling the joint solidifies. Pressure can also be applied at the joint.
The joint is called as welded joint.

3. Advantages :
Any metal/alloy can be welded
Any shape of component can be generated
Strength of the joint will be the same as that of the base metal.
Disadvantages:
Harmful radiation and fumes may be generated during the process.
Residual stresses may be setup in the welded joint.
Skilled operator may be required.
Structure of the weld portion will differ from parent metal.
Applications:
Welding finds application in ship building, automobiles, aircraft, power plants, building and bridge constructions, storage tanks, pressure vessels, machine tools, and almost in all sectors, where parts are fabricated as per the needs.
Apart from fabrication work, welding is also used in repair and maintenance work: for Ex. Joining broken parts and rebuilding worn out components.

4. 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

5. Classification of welding processes:
(i). Electric Arc welding
Carbon arc
Metal arc
Metal inert gas
Tungsten inert gas
Plasma arc
Submerged arc
Electro-slag
(ii). Gas Welding
Oxy-acetylene
Air-acetylene
Oxy-hydrogen
(iii). Resistance Welding
Butt
Spot
Seam
Projection
Percussion
(iv)Thermit Welding
(v)Solid State Welding
Friction
Ultrasonic
Diffusion
Explosive
(vi)Radiant energy Welding
Electron-beam
Laser
(vii)Related Process
Oxy-acetylene cutting
Arc cutting
Hard facing
Brazing
Soldering

6. Types of Welding Fusion Welding Pressure Welding Friction Welding
Homogeneous
Heterogeneous
Brazing
Soldering
Gas Welding
Electroslag
MIG
TIG
High Energy Beam
Shielded Metal Arc – “Stick”
Electric Arc

7. Arc welding Equipments:
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
(Note: welding supply may be constant current (C C) or constant voltage (C V).)
Constant Current: varies its out put voltage to maintain steady current
Constant Voltage : will fluctuate its out put current to maintain a set voltage

8. Components of Arc welding

9. Manual Metal Arc Welding (MAW) or Flux Shielded Metal Arc Welding (FSMAW)

10. Principle: the source of heat for arc welding is an ‘electric arc’ generated between two electrically conducting materials.
When the tip of the electrode is brought in contact with the workpiece material, and momentarily separated by small distance of 2-4 mm, an arc can be generated. The electrical energy is thus converted to heat energy. The high heat of the work melts the edges of the workpieces.
The electrode material can be either a non- consumable or a consumable material

11. Arc Welding Equipments

12. Flux Shielded Metal Arc Welding
Manual arc welding process (MAW)
Electric current is used to form an arc between the workpiece and the electrode
Weld is produced using a consumable flux coated electrode (Titania, calcium fluoride, cellulose, iron oxide, etc.)
Various benefits of flux coating includes:
Prevents oxidation of the molten metal
Stabilizes the arc
During welding the flux forms a layer of slag and serves as a shielding gas to protect the weld from atmospheric contamination

13. Process
Electrode brought in contact with workpiece and then pulled away slightly in a sweeping motion to initiate the arc
Electrode begins to melt and the flux disintigrates and forms a shielding gas
As the weld solidifies, slag floats to the surface to protect the weld
Slag is hammered away to reveal the finished weld

14. Advantages Simple and versatile
Unlimited upper bound on material thickness
Skilled welders are able to use SMAW in any position
Significant investment from welding industry
Used to weld ferrous and a few non ferrous metals like aluminium, nickel, copper alloys etc.

15. Disadvantages
Weld Splatter- caused by oxide which gets very hot when trying to weld
Porosity
Poor Fusion
Shallow Penetration
Applications:
The process finds applications in building and bridge construction, ship building, boiler and pressure vessel fabrication, joining of large pipes and penstock, and in almost all repair and maintenance work

16. Applications of Arc welding
Fabrication Industries
Construction Industries
Automotive industries
Aerospace industries
Marine industries

17. Comparison of A.C. and D.C. arc welding
Alternating Current (from Transformer)
More efficiency
Power consumption less
Cost of equipment is less
Higher voltage – hence not safe
Not suitable for welding non ferrous metals
Not preferred for welding thin sections
Any terminal can be connected to the work or electrode

18. Comparison of A.C. and D.C. arc welding
Direct Current (from Generator)
Less efficiency
Power consumption more
Cost of equipment is more
Low voltage – safer operation
suitable for both ferrous non ferrous metals
preferred for welding thin sections
Positive terminal connected to the work
Negative terminal connected to the electrode

19. What is MIG?
Metal inert gas welding or gas metal arc welding(GMAW) is a group of arc welding process in which the w/ps are joined by the heat obtained from an electric arc struck between a uncoated consumable electrode and the w/p in the presence of an inert gas atmosphere.
The consumable electrode acts as a filler metal to fill the gap between the two workpieces.
Semi-automatic or automatic arc welding process in which a continuous and consumable wire electrode and a shielding gas are fed through a welding gun

21. Specifics
Electrode wire ( mm diameter) can be uncoated, solid or hollow tube with powered alloy (flux) additions in center (metal-cored electrode)
Argon, Helium, O2 or CO2 used as shielding gas, which is the primary protection for the arc and molten metal  no flux needed.
Mixture of argon and carbon dioxide in a 75% to 25% or 80% to 20% mixture is commonly used.
A C is rarely used with MIG instead DC is employed, and the electrode is positively charged. This results in faster melting of the electrode, which increases weld penetration and welding speed.
Weld current: <500 amps used, DC or AC
Max penetration depth: 6-10 mm

22. Advantages Faster than most other welding processes
The electrode and inert gas are automatically fed
Weld deposition rate is high due to the continuous wire feed
No flux is used. Hence no slag formation. This results in clean weld
Thin and thick metals can be welded
Gas metal arc process can be applied to all metals
No slag to be removed, unlike other welding processes
Process can be automated

23. Limitations More costly equipment than SMAW
Rarely used outdoors or in other areas of air volatility
Weld is prone to cracking

24. Applications
Most common industrial welding process, preferred for its versatility, speed and relative ease of adapting the process to robotic automation
Automobile industry uses MIG almost exclusively

25. TIG Welding What is TIG? Tungsten Inert Gas Also referred to as GTAW
Gas Shielded Tungsten Welding
In TIG welding, a tungsten electrode heats the metal you are welding and gas (most typically Argon) protects the weld from airborne contaminants
TIG welding uses a non-consumable tungsten
Filler metal, when required, is added by hand
Shielding gas protects the weld and tungsten
Tungsten inert gas welding or gas tungsten arc welding(GTAW) is a group of arc welding process in which the w/ps are joined by the heat obtained from an electric arc struck between a non consumable tungsten electrode and the w/p, in the presence of an inert gas atmosphere. A filler metal may be added if required, during the welding process.

26. GTAW/TIG Welding Components Gas Tungsten Arc Welding / Tungsten Inert Gas
Constant-current welding power supply
Non-Consumable Tungsten Electrode
Inert Shielding Gas – Usually argon or helium or a mixture
Optional Filler Rod
25% Argon 75% Helium is common mixture.
Autogenous welding does not use filler rod.

27. Tungsten Inert Gas Tungsten electrode acts as a cathode
A plasma is produced between the tungsten cathode and the base metal which heats the base metal to its melting point
Filler metal can be added to the weld pool
TUNGSTEN ELECTRODE
(CATHODE)
POWER SOURCE
TUNGSTEN ELECTRODE
+ +
+ +
- - -
SHIELDING GAS
ARC COLUMN
BASE METAL
PUDDLE
BASE METAL (ANODE)

28. TIG Welding Specifics
Plasma consisting of ionized gases and metal vapors
Various alloys like Zirconium, thorium are alloyed with tungsten to improve arc stability, better current carrying capacity, resistance to contamination etc.
The diameter of the electrode various from 0.5 mm to 6.4 mm
Commonly used to weld thin sections of stainless steel, nickel and copper alloys, as well as light metals such as aluminum, magnesium, titanium.
Either AC or DC can be used to supply the required current . AC is preferred for welding magnesium, aluminium and their alloys, while DC is used for welding stainless steel, nickel, copper and its alloys.
constant-current welding power supply produces energy which is conducted across the arc through a column of highly ionized gas and metal vapors known as a plasma.

29. TIG Welding Advantages
Offers greater operator control than competing procedures
Stronger, higher quality welds
Attractive “stitched” finish
No “smoke and spatter”
Some welds require no filler material (edge, butt and corner joints)
Highly resistant to cracking (ductile) and corrosion over long time periods
Welds more metals and metal alloys than any other process
High quality and precision
Pin point control
Aesthetic weld beads
No flux or slag
No smoke or fumes
Safer in dangerous environments
Autogenous welds.

30. TIG Welding Disadvantages
Many consider this the most difficult of all the popular welding processes
Torches often require a cooling system (such as water cooled torches, Amps)
Requires venting of shielding gas and particulate matter
Speed of process
Lower filler metal deposition rates
Good hand-eye coordination a required skill
Brighter UV rays than other processes
Slower travel speeds than other processes
Equipment costs tend to be higher than other processes
Touching the weld pool can contaminate the weld.
Weld Craters and associated cracks can occur near the end of a weld.
Water cooled torches not mobile.

31. TIG Welding Safety
Intense ultraviolet radiation requires special eye protection (welding helmet) and complete skin coverage to avoid sunburn
Requires ventilation of gases to avoid inhalation of dangerous fumes
Be aware of fire hazard
Curtains to protect personnel.
Heavy metal fumes, cleaners and degreasers broken down to phosgene from chlorinated products.

32. TIG Welding Major Players
Miller
Lincoln Electric

33. Metal arc welding

34. Arc Welding Uses an electric arc to coalesce metals
Arc welding is the most common method of welding metals
Electricity travels from electrode to base metal to ground

35. Submerged Arc Welding (SAW)
Submerged arc welding (SAW) is a group of arc welding process in which the w/ps are joined by the heat obtained from an electric arc struck between a bare consumable electrode and the w/p.
The arc is struck beneath a covering layer of granulated flux. Thus, the arc zone and the molten weld pool are protected from atmospheric contamination by being ‘submerged’ under a blanket of granular flux (oxides of calcium, silicon, magnesium, aluminium or manganese along with alloying elements depending on the requirements).
A layer of granulated mineral material covers the tip of the electrode, the arc and the workpiece in order to protect the work from contaminations in the air. This gives the name ‘submerged arc welding’.
Pressure is not used

36. Submerged arc welding:
Fig : Schematic illustration of the submerged-arc welding process and equipment. The unfused flux is recovered and reused .

37. A sustained arc, shielded by molten slag, is maintained in consumable-electrode welding by the (a) shielded metal-arc, (b) submerged arc, and (c) electrogas methods.

38. Advantages of SAW
High productivity process, due to high heat concentration
Weld deposition rate is high due to continuous wire feed
Deep weld penetration
Less smoke, as the flux hides the arc. Hence, improved working conditions
Can be automated
Disadvantages of SAW
The invisible arc and the weld zone make the operator difficult to judge the progress of welding
Use of powdered flux restricts the process to be carried only in flat positions
Slow cooling rates may lead to hot cracking defects
Need for extensive flux handling
Applications : used especially for large products, and in the fabrication of pressure vessels, penstocks, boilers etc.

39. GAS WELDING
Gas welding is a fusion welding process in which the w/ps are joined by the heat of a strong flame generated by the combustion of a fuel gas and oxygen. The fuel gas may be acetylene, hydrogen, propane or butane.
Sound weld is obtained by selecting proper size of flame, filler material and method of moving torch
The temperature generated during the process is 33000c (oxy-
acetylene – upto c and oxy-hydrogen – upto 25000c)
When the metal is fused, oxygen from the atmosphere and the torch combines with molten metal and forms oxides, results defective weld
Fluxes are added to the welded metal to remove oxides
Common fluxes used are made of sodium, potassium. Lithium and borax.
Flux can be applied as paste, powder, liquid. solid coating or gas.

40. Arc welding Most efficient way to join metals
Advantages
Most efficient way to join metals
Lowest-cost joining method
Affords lighter weight through better utilization of materials
Joins all commercial metals
Provides design flexibility
Limitations
Manually applied, therefore high labor cost.
Need high energy causing danger
Not convenient for disassembly.
Defects are hard to detect at joints.

41. GAS WELDING EQUIPMENT... 4. Hoses 5. Welding torch 6. Check valve
1. Gas Cylinders
Pressure
Oxygen – 125 kg/cm2
Acetylene – 16 kg/cm2
2. Regulators
Working pressure of oxygen 1 kg/cm2
Working pressure of acetylene 0.15 kg/cm2
Working pressure varies depends upon the thickness of the work
pieces welded.
3. Pressure Gauges
4. Hoses
5. Welding torch
6. Check valve
7. Non return valve

42. Typical Oxyacetylene Welding (OAW) Station

43. Oxy-Acetylene welding

44. Typical startup procedures
Verify that equipment visually appears safe IE: Hose condition, visibility of gauges
Clean torch orifices with a “tip cleaners” (a small wire gauge file set used to clean slag and dirt form the torch tip)
Crack (or open) cylinder valves slightly allowing pressure to enter the regulators slowly
Opening the cylinder valve quickly will “Slam” the regulator and will cause failure.

45. Typical startup procedures
Never stand directly in the path of a regulator when opening the cylinder
Check for leaks using by listening for “Hissing” or by using a soapy “Bubble” solution
Adjust the regulators to the correct operating pressure
Slightly open and close the Oxygen and Acetylene valves at the torch head to purge any atmosphere from the system.

46. Typical startup procedures
Always use a flint and steel spark lighter to light the oxygen acetylene flame.
Never use a butane lighter to light the flame

47. TYPES OF FLAMES…
Oxygen is turned on, flame immediately changes into a long white inner area (Feather) surrounded by a transparent blue envelope is called Carburizing or reducing flame (30000c)
Used for welding monel (Ni-Cu alloys), and a few non-ferrous metals.
Carburizing flame should not be employed for welding steel, as unconsumed carbon may be introduced into the weld to produce a hard and brittle deposit.
Addition of little more oxygen give a bright whitish cone surrounded by the transparent blue envelope is called Neutral flame (It has a balance of fuel gas and oxygen) (32000c)
Used for welding steels, aluminium, copper and cast iron
If more oxygen is added, the cone becomes darker and more pointed, while the envelope becomes shorter and more fierce is called Oxidizing flame
Has the highest temperature about 34000c
Used for welding brass and brazing operation.
It should not be used for welding steel, as it oxidizes the steel

48. Oxyfuel Gas Welding
Fig : Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame. The gas mixture in (a) is basically equal volumes of oxygen and acetylene.

49. Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame.

50. Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations:
(a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame.

51. Types of flames Neutral flame Oxidising flame Carburising flame
Filler Metals :
Additional material to weld the weld zone
Available as rod or wire
They can be used bare or coated with flux
Flux, if required, may be used during the process, it can be directly applied to the surface of the workpiece, or the heated end of the filler metal may be dipped in a flux material and used

52. Flame Settings
There are three distinct types of oxy- acetylene flames, usually termed:
Neutral
Carburizing (or “excess acetylene”)
Oxidizing (or “excess oxygen” )
The type of flame produced depends upon the ratio of oxygen to acetylene in the gas mixture which leaves the torch tip.

53. Pure Acetylene and Carburizing Flame profiles

54. Neutral and Oxidizing Flame Profiles

55. Flame definition
The neutral flame (Fig. 4-1) is produced when the ratio of oxygen to acetylene, in the mixture leaving the torch, is almost exactly one-to-one. It’s termed ”neutral” because it will usually have no chemical effect on the metal being welded. It will not oxidize the weld metal; it will not cause an increase in the carbon content of the weld metal.
The excess acetylene flame (Fig. 4-2), as its name implies, is created when the proportion of acetylene in the mixture is higher than that required to produce the neutral flame. Used on steel, it will cause an increase in the carbon content of the weld metal.
The oxidizing flame (Fig. 4-3) results from burning a mixture which contains more oxygen than required for a neutral flame. It will oxidize or ”burn” some of the metal being welded.

56. Welding practice & equipment
STEPS :
Prepare the edges to be joined and maintain the proper position  
Open the acetylene valve and ignite the gas at tip of the torch
Hold the torch at about 45deg to the work piece plane
Inner flame near the work piece and filler rod at about 30 – 40 deg
Touch filler rod at the joint and control the movement according to the flow of the material

57. Torch used in Gas Welding
Gas torch or welding torch is that part, the welder holds and manipulates to make weld. The oxygen and acetylene gas from the respective cylinder enters the gas torch where they are mixed in suitable proportions and issued from the torch to burn in the atmosphere.
Construction and working:
The gas torch consists of three parts:
Torch Body
Mixing chamber
Torch tip

58. Torch used in Oxyacetylene Welding
Fig : (a) General view of and (b) cross-section of a torch used in oxyacetylene welding. The acetylene valve is opened first; the gas is lit with a park lighter or a pilot light; then the oxygen valve is opened and the flame adjusted. (c) Basic equipment used in oxyfuel-gas welding. To ensure correct connections, all threads on acetylene fittings are left- handed, whereas those for oxygen are right- handed. Oxygen regulators are usually painted green, acetylene regulators red.

60. Typical torch styles
A small welding torch, with throttle valves located at the front end of the handle. Ideally suited to sheet metal welding. Can be fitted with cutting
attachment in place of the welding head shown. Welding torches of this general design are by far the most widely used. They will handle any oxyacetylene welding job, can be fitted with multiflame (Rosebud) heads for heating applications, and accommodate cutting attachments that will cut steel 6 in. thick.
A full-size oxygen cutting torch which has all valves located in its rear body. Another style of cutting torch, with oxygen valves located at the front end of its handle.

61. Welding Techniques
There are two techniques in gas welding process depending on the way in which the welding rod or the welding torch may be used. They are:
Forehand or Leftward technique: it is used for welding thin metals having thickness less than 5 mm.
In forehand technique, the welder holds the welding torch in his right hand while the filler rod in his left hand, and proceeds from the right end of the w/p towards the left end
2. Backward/Backhand or Rightward technique: it is used for welding metals having thickness over and above 5 mm.
In backhand technique, the welder holds the welding torch in his right hand while the filler rod in his left hand, and proceeds from the left end of the w/p towards the right end

64. Advantages:
Process is simple and inexpensive
Eliminates skilled operator
Controlling temperature is easy
Quantity of O2 and C2H2 gases can be independently controlled for good welding
Temperature of the flame can be controlled depending on the thickness and type of the material being welded
Disadvantages:
Acetylene gas is slightly costlier
Not suitable for thick and high melting point metals
Refractory metal like tungsten, molybdenum etc., and reactive metals like zirconium, titanium etc., cannot be gas welded
Acetylene gas is highly explosive. Hence, precautions should be taken during its storage and welding

65. Special Type of Welding Processes

66. Resistance Welding Developed in the early 1900’s
A process in which the heat required for welding is produced by means of electrical resistance across the two components. A certain pressure is applied to the w/ps to complete the weld
Principle: when electric current flows through a material, it offers resistance to the flow of current resulting in heating of the material. The heat generated is used to make a weld between two or more w/ps.
The heat generated in the material is given by joules law:
H α I2RT or H = k I2RT
Where, H= Heat generated in the material in Joules
I = Flow of current through the material in Amperes
R= Electrical Resistance of the material in Ohms
T = Time in Seconds
K = a constant, usually 0.24

67. RW does not requiring the following: Consumable electrodes
Shield gases
Flux
Advantages of Resistance Welding:
Fast rate of welding possible
No filler rod required
Semi skilled workers can be employed
Both similar and dissimilar metals can be welded
Very high reliability and reproducibility obtained in the welds
Semi automatic equipments can be used
Disadvantages of Resistance Welding:
Initial cost of equipment is high
Needs good control and maintenance of equipments
Higher thickness of metal cannot be welded

68. Applications of Resistance Welding:
Used for joining sheets, bars, rods and tubes
Used for welding aircraft and automobile parts
Used for general engineering fabrication purposes like grills, containers, tanks etc.
Types of Resistance Welding:
Butt welding
Spot welding
Seam welding
Projection welding
Percussion welding (N A for VTU )

69. Resistance Spot Welding
Spot welding is a resistance welding process in which the two overlapping workpieces held under pressure are joined together in one spot (location), Hence the name spot welding.
RSW uses the tips of two opposing solid cylindrical electrodes
Pressure is applied to the lap joint until the current is turned off in order to obtain a strong weld
Fig: (a) Sequence in the resistance spot welding

70. Resistance Spot Welding
Surfaces should be clean
Accurate control of electric current and of pressure are essential in resistance welding
Fig: b)Cross-section of a spot weld,showing the weld nugget and the indentation of the electrode on the sheet surfaces.This is one of the most commonly used process in sheet-metal fabrication and in automotive- body assembly

72. Advantages:
Efficient energy use
Limited workpiece deformation
High production rate
Suitable for automation
Filler metals are not required
Disadvantages:
Weld strength is significantly lower when compared to other process.
Silver and copper are difficult to weld because of their high thermal conductivity
Applications:
Extensively used for welding steels, and especially in the automotive industry for cars that requires several hundred spot welds made by industrial robots.

73. Resistance Seam Welding
Seam welding is a resistance welding process in which the overlapping w/ps held under pressure are joined together by a series of spot welds made progressively along the joint utilizing the heat generated by the electrical resistance of the workpieces.
RSEM is modification of spot welding wherein the electrodes are replaced by rotating wheels or rollers
The electrically conducting rollers produce a spot weld
RSEM can produce a continuous seam & joint that is liquid and gas tight
Fig : (a) Seam-Welding Process in which rotating rolls act as electrode (b)
Overlapping spots in a seam weld. (c) Roll spot weld (d) Resistance-welded gasoline tank

75. Advantages:
A continuous overlapping weld produced by the process makes it suitable for joining liquid or gas tight containers and vessels
Efficient energy use
Filler metals are not required.
Disadvantages:
Requires complex control system to regulate the travel speed of electrodes as well as the sequence of current to provide satisfactory overlapping welds
Difficult to weld metals having thickness greater than
3 mm
Applications:
Used to fabricate liquid or gas tight sheet metal vessels such as gasoline tanks, automobile mufflers, and heat exchangers

76. Resistance Projection Welding
Projection welding is a resistance welding process in which the w/ps are joined by the heat generated due to flow of electrical current through them
The resulting welds are localized at predetermined points by projections or intersections.
RPW is developed by introducing high electrical resistance at a joint by embossing one or more projections on the surface to be welded.
Weld nuggets are similar to spot welding
Fig: a) Resistance projection Welding b)A welded bracket c) & d) Projection welding of nuts r threaded hosses and stack

78. Advantages:
More than one spot weld can be made in a single operation.
Welding current and pressure required is less
Suitable for automation
Filler metals are not used
Disadvantages:
Projections cannot be made in thin workpieces
Thin workpices cannot withstand the electrode pressure
Equipment is costlier
Applications:
A very common use of projection welding is the use of special nuts that have projections on the portion of the part to be welded to the assembly.

79. Resistance Butt Welding
Resistance butt welding or Upset welding is a resistance welding process in which the w/ps are joined are heated to elevated temperatures and forged (by applying the desired pressure) at that temperature.

80. Advantages: Joint obtained is clean, since filler metal is not used
Produces defect free joint.
Disadvantages:
The process is suitable for parts with similar c/s area
Joint preparation is must
Applications: used for producing joints in long tubes and pipes

81. Friction Welding

82. Friction Welding Developed in the 1940’s
Friction welding is a solid state welding process in which the w/ps are joined by the heat generated due to the friction at the interface of the two w/ps.
Parts are circular in shape
Can be used to join a wide variety of materials
Fig: Sequence of operation in the friction welding process 1)Left-hand component is rotated at high speed. 2) Right-hand component is brought into contact under an axial force 3)Axial force is increased;the flash begins to form 4) Left-hand component stops rotating;weld is completed.The flash can subsequently be removed by machining or grinding

83. Friction Welding Process can be fully automated
Can weld solid steel bars up to 250mm in outside diameter
Fig:Shape of friction zone in friction welding,as a function of the force applied and the rotational speed

84. Advantages:
Process is simple
Low power requirements
Edge preparation is not required
No filler metal
Dissimilar metals can be easily welded
Disadvantages:
The process is restricted to tubular parts and butt welds

85. Thermit Welding

86. The high tempr. Obtained from the reaction of finely divided metalic oxide and aliminium is employed to raise the tempr. Of the parts to be welded to above their fusion point.
Thermit welding is based on casting and foundry practice.
Thermit welding or alumino-thermit welding is a fusion welding process in which the w/ps are joined by the heat obtained from a chemical reaction of the thermit mixture. Pressure may or may not be applied during the process.
Chemical Reaction
3Fe3O4 +8Al Fe + 4 Al2O Kcal of Heat
3 Cuo + 2 Al Cu + Al2O Kcal of Heat
The thermit mixture is combination of iron oxide and aluminium powder, and when this mixture is brought to its ignition tempr. Of about 12000C, reaction starts, producing molten iron and slag releasing enormous heat.
the chemical affinity of aluminium for oxygen is the basis for the thermit process

87. Advantages:
Heat required for welding is obtained from the chemical reaction of the thermit mixture. Hence, power supply is not required.
The process is best suitable, particularly in remote locations where sophisticated welding equipments and power supply cannot be arranged.
Disadvantages:
Process consumes more time
Applications: used for repair and welding of large forgings and castings, pipes, mill housings etc.

88. Atomic Hydrogen Welding
It is neither purely an arc welding process nor fully a gas welding process. It is actually combination of both.
The arc produced during the process is not directly used for heating the w/ps, it is used to break up the hydrogen molecules into atoms
H H +H – 422 k J (Endothermic reaction)
When hydrogen is forced through the arc, due to high intensity of heat, its molecules break up into atoms hence the process is called as atomic hydrogen.
When the atomic hydrogen goes out of the arc, the recombination takes place as the atomic hydrogen touches the cold w/ps liberating a large amount of heat.
H + H H K J (Exothermic reaction)
During this (atoms getting transformed back to molecules) the heat energy is liberating and this energy is utilized for welding purposes.

89. The welding torch is constructed such that, it works as electrode holder and also carries gas nozzle.
It supplies gas as well as required current to the arc
For adjustment of distance between the tips of electrodes, a trigger is provided on the torch
The welding torch is moved along the surface to be welded with the arc tip touching the surface. The heat of the arc melts and fuses the workpiece and the filler metal to form a joint.
The fan shaped arc formed obtains its heat not from the combustion, but from the recombination of hydrogen atoms into hydrogen molecule (H2)

91. Advantages:
Intense flame is obtained, which can be concentrated at the joint. Hence, less distortion.
Welding is faster
w/p do not form a part of the electric circuit. Hence, problems like striking the arc and maintaining the arc column are eliminated
Separate flux/shielding gas is not required. The hydrogen- envelope itself prevents oxidation of the metal and the tungsten electrode. It also reduces the risk of nitrogen pick- up
Disadvantages:
Cost of welding by this process is slightly higher than with the other processes
Welding is limited to flat positions only
Applications: AHW is used in those applications where rapid welding is necessary, as for stainless steels and other special alloys

92. Laser welding

93. Laser welding or laser beam welding is a radiant energy welding process in which the w/ps are joined by the heat obtained from the application of a concentrated coherent light beam impinging upon the surface to be joined.
Advantages:
Similar and dissimilar metals can be welded easily
Laser beam can be controlled to a great precision, and hence the welding spots could also be located precisely
Heating and cooling rates are much higher in this process.
Clean weld joints can be obtained by this process.
Disadvantages:
Slow welding speed ( mm/min)
Rapid cooling causes cracking in high carbon steels
High equipment cost
Applications:
Used in electronic industry for applications such as connecting wire leads to small electronic components.

94. Electron Beam Welding

95. Electron beam welding is a radiant energy welding process in which the w/ps are joined by the heat obtained from a concentrated beam, composed primarily of high – velocity electrons impinging on the surfaces to be obtained.
Advantages:
Any metals, including zirconium, beryllium, or tungsten can be easily welded.
High quality welds, as the operation is carried in vacuum
Concentrated beam minimizes distortion
Cooling rate is much higher
Heat affected zone is less
Disadvantages:
High capital cost
Extensive joint preparation is required
Vacuum requirements tend to limit the production rate
Not suitable for high carbon steels
Applications: used in electronic industry, automotive and aircraft industry

96. Welded Zones 3-Distinct zones ZONE –01: Fusion Zone
ZONE – 02: Heat Affected Zone (HAZ)
ZONE – 03: Base Metal Zone

97. Fusion Weld Zone
Fig : Characteristics of a typical fusion weld zone in oxyfuel gas and arc welding.

99. Thank you