1. UNIT—II JOINING PROCESS
WELDING:
Process of joining similar metals with the application of heat and with or without the application of pressure.
While welding the edges of metal pieces are either melted or brought into plastic condition.
Used in the manufacturing of Auto mobiles bodies, structural work, tanks, and general machine repair work. In the industries , welding is used in refineries and pipe line fabrication.

2. TYPES OF WELDING PROCESS
Plastic Welding (or) Pressure Welding:
Metal pieces are heated to plastic state and pressed together.
Ex: Electric resistance welding
Fusion Welding (or) Non-pressure welding:
Metal is heated to molten state.
Ex: Gas welding, Arc welding

3. Classification of welding processes:
1: Gas Welding
(a) Air Acetylene
(b) Oxy  Acetylene
(c) Oxy Hydrogen Welding
2: Arc Welding
(a) Carbon Arc welding
(b) Plasma Arc welding
(c) Shield Metal Arc Welding
(d) T.I.G. ( Tungsten Inert Gas Welding)
(e) M.I.G. ( Metal Inert Gas Welding)

4. (c) Projection welding (d) Resistance Butt welding
3: Resistance Welding:
(a) Spot welding
(b) Seam welding
(c) Projection welding
(d) Resistance Butt welding
(e) Flash Butt welding
4: Solid State Welding:
(a) Cold welding
(b) Diffusion welding
(c) Forge welding
(d) Fabrication welding
(e) Hot pressure welding
(f) Roll welding

5. 5: Thermo Chemical Welding
(a): Thermit welding
(b): Atomic welding
6:  Radiant Energy Welding
(a): Electric Beam Welding
(b): Laser Beam Welding

8. GAS WELDING
Joining of metals with the help of high temperature flame and filler rod.
Flame is generated by mixture of Oxygen and Acetylene.
Mixture of combustible gases are also be used.

9. TYPES OF GAS WELDING Oxy-Acetylene welding Air-Acetylene welding
Hydrogen-Acetylene welding

10. Oxy-Acetylene welding

11. The temperature generated during the process is 33000c
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.

12. METHODS OF WELDING Leftward or Forward Welding Blow pipe 60-70 degrees
Filler rod degrees
Rightward or backward welding
Blow pipe degrees
Filler rod degrees

13. FLAT HORIZONTAL OVERHEAD VERTICAL Welding Positions
INCREASING DIFFICULTY
FLAT
HORIZONTAL
OVERHEAD
VERTICAL

14. TYPES OF FLAMES

15. NEUTRAL FLAME CARBURISING FLAME Oxygen and Acetylene ratio is equal.
Temperature about 3250° C.
Used to weld carbon steels, Cast iron, Copper, Al etc.
CARBURISING FLAME
Oxygen and Acetylene ratio is 0.95 to 1
Three Zones
Luminus Zone.
Intermediate cone of white colour.
Outer envelope.
Temperature about 3150° C
Used to weld monel metal, high carbon steel, alloy steel.

16. Equipments OXIDISING FLAME Gas Cylinders Pressure Regulators
Oxygen and Acetylene ratio is 1.2 to 1.5
Temperature about 3480° C
Used to weld Copper, Bronze, Zinc-Bearing alloys..
Equipments
Gas Cylinders
Pressure Regulators
Pressure Gauges
Welding Torch
Hose and Hose fittings
Safety Devices

17. OXYGEN CYLINDER ACETYLENE CYLINDER 12500-14000 kN/m2
Cylinder capacity 6.23m3
Black Or Green
ACETYLENE CYLINDER
kN/m2
Maroon

18. PRESSURE REGULATORS Pressure of gas depends
on the thickness of the metal
to be welded

19. PRESSURE GAUGE WELDING TORCH Two Pressure gauges
One to show the cylinder pressure and another one is to show working pressure
WELDING TORCH

20. HOSE AND HOSE FITTINGS

21. Filler and flux materials
d = Welding rod diameter
t = Thickness of base plate in mm
S.No
Material to be welded
Welding rod chemical composition 1
L-C Steels
0.08%C, 0.36%Mn, 0.13%Cr, 0.013%Ni, 0.20%P 2
Mn-Steels
0.14%C, 0.12%Si, 0.81%Mn, 0.25%Ni 3
Cr-Steels
0.24%C, 0.21%Si, 0.42%Mn, 0.96%Cr, 0.17%Ni, 0.35%S

22. FLUX Except Lead, Zinc all metals require fluxing.
Also needed for Cast iron and Stainless steel.
Fluxes composes of Borates and Boric Acid, Soda ash and Small amount of other compounds such as Sodium Chloride, Ammonium Sulphate, Iron Oxide.
Equal amount Boric Acid and Soda Ash, 2% Aluminium Sulphate and 15% powdered iron makes Flux.

23. ARC WELDING
Metal pieces are joined melting their edges by an electric arc.
Electric Arc produced between Two Conductors
Elctrode is one conductor and Workpiece is another conductor.
Small Air-gap 3mm.

24. ARC WELDING EQUIPMENTS

28. Arc Welding Equipments

29. Arc welding electrodes
Non-consumable electrodes
Made of Carbon, Graphite, Tungsten
Carbon and Graphite – D.C Welding
Tungsten – Both
Filler material added separately.
Consumable electrodes
Bare Electrodes
Flux or lightly coated electrodes
Coated or extruded electrodes

30. Flux or lightly coated electrodes 1-5% of electrode weight
Bare Electrodes
Used to weld wrought iron and mild steel.
Hand arc welding – Sticks or rods
Automatic welding – Coil
Flux or lightly coated electrodes
1-5% of electrode weight
Light coating is given to increase stability and ionizing coatings.
Chalk parts and Water glass parts
Used to weld non critical structures.

31. Coated electrodes Electrode size 1-2 mm layer
15-30% of the weight of the electrode rod.
Electrode size
3.2, 4, 5, 6, 8, 9, 12 mm diameter and length 350 or 450 mm.

32. FUNCTIONS OF COATINGS Improves arc stability.
Provides gaseous atmosphere to prevent Oxygen, Hydrogen and Nitrogen.
Provides a protective slag over hot metal.
Provides flux to remove oxides and other impurities.
Reduces spatter of weld metal.
Slows down the cooling rate of weld.

33. ELECTRODE COATINGS
Slag formation ingredients: Asbestos, Mica, Silica, Titanium oxide, iron oxide, calcium carbonate and aluminium oxide.
Arc stabilizing ingredients: Potassium silicate, Mica, Calcium oxide, Sodium oxide, magnesium oxide.
Deoxidizing ingredients: Cellulose, Dolomite, Starch, Dextrin, Wood flour, graphite
Binding Materials: Sodium silicate, Potassium silicate, asbestos.
Alloying constituents to increase the strength of the weld.

34. RESISTANCE WELDING
Uniting two pieces of metal by the passage of a heavy electric current while the surfaces are pressed together.
Factors:
Welding current
Welding pressure
Time of application
Contact area of electrodes

35. Electrodes Advantages Disadvantages Steel with copper Copper cadmium
Copper chromium
Advantages
No filler material needed.
Requires little skill.
Can weld dissimilar metals.
Disadvantages
High cost of equipment.
Limited to process.

36. Resistance spot welding
3000 – A, depending on the material and thickness.
Steel, Copper, Brass and light alloys can be joined.
Application: Fabrication of sheet metal products.

37. Resistance seam welding
Welding currents range from 2000 – 5000 A.
Welding speed 1.5 m/min.
Application: Pressure tanks, Evaporators, Condensers.

38. Resistance butt welding
Upset Welding

39. Percussion Welding
0.5 to 0.38mm

40. Resistance projection welding
Stud Welding

41. TIG Welding Also called as Gas Tungsten Arc Welding (GTAW).
Inert Gas – Gas which does not combine chemically with the metal being welded.
Argon & Helium
Strond welds
Alloys of Al, SS, Ni, Cu, CS.
Dissimilar metals can be welded.

42. Mig welding Tungsten electrode is replaced with consumable electrode.
Electrode is driven through same type collet that holds a tungsten electrode by a set of drive wheels.

43. Difference between TIG and MIG welding

44. Submerged Arc welding Flux powder is fed into the hopper.
Arc submerged in the flux material.
No Spatter or gases.
No reaction with atmosphere.
High strength and ductility.

45. Flux Core Welding

46. Flux Core Welding
Flux cored arc welding is similar to a gas metal arc welding.
Electrode is tubular in shape and is filled with flux.
Cored electrodes produce more stable arc improve weld contour and produce better mechanical properties.
Flux is more flexible than others.

47. Electro slag welding (ESW)

48. Similar to Electro gas welding.
Difference is Arc is started between electrode tip and bottom part of the part to be welded.
Flux added first and then melted by the heat on the arc.
Molten slag reaches the tip of the electrode and the arc is extinguished.
Heat is then continuously produced by electrical resistance of the molten slag.
Single or multiple solid as well as flux-cored electrodes may be used.
Applications: Welding of heavy steel forgings, Large steel castings, Thick steel plates.

49. Electro gas welding (EGW)
EGW is welding the edges of sections vertically in one pass with the pieces placed edge to edge.
Weld metal is deposited into weld cavity between the two pieces to be joined.
Mechanical drives moves shoes upwards.
Single and multiple electrodes are fed through a conduit and a continuous arc is maintained using flux-cored electrodes at up to 750 A.
Process capabilities :
Weld thickness ranges from 12mm to 75mm
Metals welded are steels, titanium, aluminum alloys
Applications are construction of bridges, pressure vessels, thick walled and large diameter pipes, storage tanks and ships.

50. Special Welding Processes
Laser beam welding
Electron beam welding
Friction welding
Diffusion welding
Plasma arc welding
Thermit welding
Flame cutting

51. Laser Beam Welding

52. Solidification of the weld pool surrounded by the cold metal is as fast as melting.
Since the time when the molten metal is in contact with the atmosphere is short, no contamination occurs and therefore no shields (neutral gas, flux) are required.
Laser Welding is used in electronics, communication and aerospace industry, for manufacture of medical and scientific instruments, for joining miniature components.

53. Electron beam welding

54. The electrons are emitted by a cathode (electron gun).
Due to a high voltage (about 150 kV) applied between the cathode and the anode the electrons are accelerated up to 30% - 60% of the speed of light.
Operation done in vacuum to prevent the reduction of electron velocity.
Kinetic energy of the electrons converted into heat energy and the metal is fused.
Welding of Automobile, Aerospace and Airplane.

55. FRICTION WELDING

56. Friction Welding
Friction Welding is a Solid State Welding process, in which two cylindrical parts are brought in contact by a friction pressure when one of them rotates.
Friction between the parts results in heating their ends.
Forge pressure is then applied to the pieces providing formation of the joint.
Carbon steels, Alloy steels, Tool and die steels, Stainless steels, Aluminum alloys, Copper alloys, Magnesium alloys, Nickel alloys, Titanium alloys may be joined by Friction Welding.

57. Diffusion Welding
Diffusion Welding is a Solid State Welding process, in which pressure applied to two work pieces with carefully cleaned surfaces and at an elevated temperature below the melting point of the metals. Bonding of the materials is a result of mutual diffusion of their interface atoms.
In order to keep the bonded surfaces clean from oxides and other air contaminations, the process is often conducted in vacuum.
No appreciable deformation of the work pieces occurs in Diffusion Welding.
Diffusion Welding is able to bond dissimilar metals, which are difficult to weld by other welding processes: Steel to tungsten, Steel to niobium, Stainless steel to titanium, Gold to copper alloys.
Diffusion Welding is used in aerospace and rocketry industries, electronics, nuclear applications, manufacturing composite materials.

59. Plasma Arc Welding is the welding process utilizing heat generated by a constricted arc struck between a tungsten non-consumable electrode and either the work piece (transferred arc process) or water cooled constricting nozzle (non-transferred arc process). Plasma is a gaseous mixture of positive ions, electrons and neutral gas molecules. Transferred arc process produces plasma jet of high energy density and may be used for high speed welding and cutting of Ceramics, steels, Aluminum alloys, Copper alloys, Titanium alloys, Nickel alloys. Non-transferred arc process produces plasma of relatively low energy density. It is used for welding of various metals and for plasma spraying (coating). Since the work piece in non-transferred plasma arc welding is not a part of electric circuit, the plasma arc torch may move from one work piece to other without extinguishing the arc.

60. Flame Cutting
Oxy-fuel welding (commonly called oxyacetylene welding, oxy welding, or gas welding in the U.S.) and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals, respectively.
 Pure oxygen, instead of air, is used to increase the flame temperature to allow localized melting of the workpiece material (e.g. steel) in a room environment.
A common propane/air flame burns at about 2,000 °C (3,630 °F), a propane/oxygen flame burns at about 2,500 °C(4,530 °F), and an acetylene/oxygen flame burns at about 3,500 °C (6,330 °F).

61. Welding Defects

63. Soldering
Soldering and brazing are adhesive bonds, whereas welding is a cohesive bond.
Soldering is an operation of two or more parts together by molten metal.
Soldering should not be used where much strength is required, where the joint will be subjected to vibration or heat.

64. Classification of Soldering Methods
Soldering iron methods
Torch method
Dip and wave methods
Induction method
Resistance method
Furnace and hot plate method
Spray method
Ultrasonic method
Condensation method

65. Types of Solder Soft Solder, which is usually a lead-tin mixture.
Hard solders
Brass solders (Copper-zinc alloy)
Silver solders (Copper-silver alloy)
Copper solders
Nickel-silver solders

66. Flux or Soldering fluid
During soft soldering flux is necessary to cover the surface of the components and solder with a film so that the formation of an oxide is prevented.
Fluxes are of two kinds:
Those which not only protect the surface, but play an active chemical part in cleaning it.
Ex: Zinc chloride(killed sprits), Ammonium chloride.
Those which protect previously cleaned surface.
Ex: Tallow, resin, vaseline, olive oil. (Fluxite)

67. Advantages Low cost. Simplicity and cheapness in equipment.
Properties of base metal not affected.
APPLICATIONS
Connection in wireless set(radio), T.V sets.
Wiring joints in electrical connections, battery and other terminals.

68. Brazing
Brazing is a soldering operation using brass as the joining medium
It is simply a form of hard soldering using a copper-zinc alloy.
Brass used for making the joint in brazing is called as “Spelter”
Three brazing alloys are:
Copper-70%, Zinc-30%; Melting point-960˚C
Copper-60%, Zinc-40%; Melting point-910˚C
Copper-50%, Zinc-50%; Melting point-870˚C
The filler penetrates the gap by capillary attraction.

69. Fluxes
When hard soldering, the chief flux is borax(Powder, granulated or stick form).
Action of the flux:
To prevent an oxide forming.
A cleansing medium to remove dirt.
It aids the capillarity of the molten metal.

70. Brazing Methods Torch brazing Furnace brazing Resistance brazing
Induction brazing
Dip brazing
Laser brazing and Electron beam brazing

71. Brazing Procedure The surfaces to be joined are thoroughly cleaned.
Then a paste of flux and spelter is kept in the joint.
Flame is directed over the joint.
The flux and spelter will soon melt and fill the recess between the joint.
When the joint is hot common salt is put to soften the glossy hard flux.

72. Adhesive bonding

73. Bonding Procedure Preparing the surface Application of adhesive
Metals surfaces cleaned by chemical etching and mechanical abrasion.
Application of adhesive
Spraying, roller or knife coating,
Assembly
Curing the joint
Apply adequate pressure during curing.
Curing period 30 mins at 145˚C
Large components- 1.4 Mpa pressure & 175˚C