EBW -2

Advantages of EBW:
1) High penetration to width can be obtained, which is difficult with other welding processes.
2) High welding speed is obtained.
3) Material of high melting temperature can be welded.
4) Superior weld quality due to welding in vacuum.
5) High precision of the welding is obtained.
6) Distortion is less due to less heat affected zone.
7) Dissimilar materials can be welded.
8) Low operating cost.
10) Reactive materials like beryllium, titanium etc. can be welded.
11) Materials of high melting point like columbium, tungsten etc. can be welded.
12) Inaccessible joints can be made.
13) Very wide range of sheet thickness can be joined (0.025 mm to 100 mm)
Disadvantages of EBW:
1) Very high equipment cost.
2) High vacuum is required.
3) High safety measures are required.
4) Large jobs are difficult to weld.
5) Skilled man power is required.
Applications of EBW
1.Electron beam welding process is mostly used in joining of refractive materials like columbium, tungsten, ceramic etc. which are used in missiles.
2. In space shuttle applications wherein reactive materials like beryllium, zirconium, titanium etc. are used.
3. In high precision welding for electronic components, nuclear fuel elements, special alloy jet engine components and pressure vessels for rocket plants.
4. Dissimilar material can be welded like invar with stainless steel.

Electron Beam Welding

Electron Beam Welding (EBW) is a fusion welding in which coalescence is produced by heating the workpiece due to impingement of the concentrated electron beam of high kinetic energy on the workpiece. As the electron beam impinges the workpiece, kinetic energy of the electron beams converts into thermal energy resulting in melting and even evaporation of the work material.

Principles:
In general, electron beam welding process is carried out in vacuum. In this process, electrons are emitted from the heated filament called electrode. These electrons are accelerated by applying high potential difference (30 kV to 175 kV) between cathode and anode. The higher the potential difference, the higher would be the acceleration of the electrons. The electrons get the speed in the range of 50,000 to 200,000 km/s. The electron beam is focused by means of electromagnetic lenses. When this high kinetic energy electron beam strikes on the workpiece, high heat is generated on the work piece resulting in melting of the work material. Molten metal fills into the gap between parts to be joined and subsequently it gets solidified and forms the weld joint.

EBW Equipment:
An EBW set up consists of the following major equipment:
a) Electron gun,
b) Power supply,
c) Vacuum Chamber, and
d) Work piece handling device.

Electron-Gun: An electron gun generates, accelerates and aligns the electron beam in required direction and spots onto the workpiece.
Emitter/Filament: It generates the electrons on direct or indirect heating.

Anode: It is a positively charged element near cathode, across which the high voltage is applied to accelerate the electrons. The potential difference for high voltage equipment ranges from 70- 150 kV and for low voltage equipment from 15-30 kV. Grid cup: Grid cup is a part of triode type electron gun. A negative voltage with respect to cathode is applied to the grid. The grid controls the beam.

Focusing unit: It has two parts: Electron focusing lens and deflection coil. Electron focusing lens focuses the beam into work area. The focusing of the electrons can be carried out by deflection of beams. The electromagnetic lens contains a coil encased in iron. As the electrons enter into the magnetic field, the electron beam path is rotated and refracted into a convergent beam. The extent of spread of the beam can be controlled by controlling the amount of DC voltage applied across the deflection plates.

Electron gun power supply: It consists of mainly the high voltage DC power supply source, emitter power supply source, electromagnetic lens and deflection coil source. In the high voltage DC power supply source the required load varies within 3-100 kW. It provides power supply for acceleration of the electrons. The potential difference for high voltage equipment ranges from 70-150 kV and for low voltage equipment 15-30 kV. The current level ranges from 50-1000 mA. In emitter power supply, AC or DC current is required to heat the filament for emission of electrons. However DC current is preferred as it affects the direction of the beam. The amount of current depends upon the diameter and type of the filament. The current and voltage varies from 25-70 A and 5-30 V respectively. The power to the electromagnetic lens and deflection coil is supplied through a solid state device.

Vacuum Chamber: In the vacuum chamber pressure is reduced by the vacuum pump. It consists of a roughing mechanical pump and a diffusion pump. The pressure ranges from 100 kPa for open atmosphere to 0.13-13 Pa for partial vacuum and 0.13-133 mPa for hard vacuum.As the extent of vacuum increases, the scattering of the electrons in the beam increases. It causes the increase in penetration.

Work Piece Handling Device: Quality and precision of the weld profile depends upon the accuracy of the movement of work piece. There is also provision for the movement of the work piece to control the welding speed. The movements of the work piece are easily adaptable to computer numerical control.

Friction Welding -2

Applications of Friction Welding

1.span over wide products for aerospace, agricultural, automotive, defense, marine and oil industries.
2.Automotive parts that are friction welded include gears, engine valves, axle tubes, driveline components, strut rods and shock absorbers
3. Hydraulic piston rods, track rollers, gears, bushings, axles and similar parts are commonly friction welded by the mmanufacturers of agricultural equipment
4. Friction welded aluminum/copper joints are in wide usage in the electrical industry.
5.Stainless steels are friction welded to carbon steels in various sizes for use in marine systems and water pumps for home and industrial use
6.Friction welded assemblies are often used to replace expensive casting and forgings
FRICTION STIR WELDING

Friction Stir Welding (FSW) is another variant process of friction welding
The basic problems with fusion welding of aluminum and its alloys are that they possess:
 Cast brittle dendritic structure,
 Micro porosity,
 Inferior mechanical and fatigue properties,
 Loss of strength in heat affected zone,
 Solidification and liquation cracking,
 Loss of alloying elements from the weld pool.

Inertia welding or (Friction Stir Welding) is a modified form of friction welding, where the moving piece is attached to a rotating flywheel. The flywheel is brought to a specified rotational speed and is then separated from the driving motor. The rotating assembly is then pressed against the stationary member and the kinetic energy of the flywheel is converted into frictional heat. The weld is formed when the flywheel stops its motion and the pieces remain pressed together. Since the conditions of the inertia welding are easily duplicated, welds of consistent quality can be produced and the process can be easily automated.

FSW Application
The industrial application of friction stir welding includes following :
 Aerospace: Wings, fuselage, cryogenic fuel tanks, aviation fuel tanks, aircraft structure, and external aircraft throw away tanks.
 Marine: Deck panes, bulkheads, floors, hull and superstructures, refrigeration plants, internal frameworks, marine and transport structures.
 Railway: High speed trains, container bodies, railway tankers, good wagon and underground rolling stocks.
 Automotive: Engine and chassis cradles, wheel rims, tailored blanks, armour plate vehicles,motorcycle and bicycle frames, buses and airfield vehicles, fuel tankers, suspension parts, crash boxes.
 Construction: Bridges, reactors for power and chemical industries, pipelines, heat exchangers, air conditioners, offshore drilling rigs etc.
 Other applications include: Electric motor housing, connectors, busbars, encapsulation of electronics and joining of aluminum to copper, food tins etc.

Friction Welding

Friction Welding (FRW) is a solid state welding process which produces welds due to the compressive force contact of workpieces which are either rotating or moving relative to one another. Heat is produced due to the friction which displaces material plastically from the faying surfaces.

In friction welding the heat required to produce the joint is generated by friction heating at the interface. The components to be joined are first prepared to have smooth, square cut surfaces. One piece is held stationary while the other is mounted in a motor driven chuck or collet and rotated against it at high speed. A low contact pressure may be applied initially to permit cleaning of the surfaces by a burnishing action. This pressure is then increased and contacting friction quickly generates enough heat to raise the abutting surfaces to the welding temperature. As soon as this temperature is reached, rotation is stopped and the pressure is maintained or increased to complete the weld. The softened material is squeezed out to form a flash. A forged structure is formed in the joint. If desired, the flash can be removed by subsequent machining action. Friction welding has been used to join steel bars upto 100 mms in diameter and tubes with outer diameter upto 100 mm.

Advantages of Friction Welding

1. No filler material, flux or shielding gases are needed.
2. It is an environment-friendly process without generation of smoke, fumes or gases.
3. No material is melted so the process is in solid state with narrow heat affected zone (HAZ).
4. Oxides can be removed after the welding process.
5. In most cases, the weld strength is stronger than the weaker of the two materials being joined. 6. The process can be easily automated for mass production.
7. The process is very efficient and comparatively very rapid welds are made.
8. Plant requirements are minimal and wide variety of metals and combinations can be welded.

Limitations of Friction Welding
1. Process is restricted to Object that can be rotated about its axis
2.one of the component must be ductile when hot, to permit deformations.
3. Preparation and alignment of the workpieces may be critical for developing uniform rubbing and heating
4. Tooling costs are high and free-machining alloys are difficult to weld