1. V A KUPPUSAMY, M.E., MISTE., Sr. Lecturer / EEE K.S.R. POLYTECHNIC COLLEGE TIRUCHENGODE – 637 215 Prepared by Electric Heating and Welding Unit - V DISTRIBUTION AND UTILIZATION K.S.R. POLYTECHNIC COLLEGE TIRUCHENGODE 637 215

2. Electric Heating Electric heating is preferred over other types of heating method ie., by wool, Coal, Oil and Gas. Practically all heating requirements can be fulfilled by some method of electric heating. Electric heating is based on the principle that when electric current passes through a medium, heat is produced. Introduction

3. Advantages of Electric Heating 1.Economical 2.High efficiency 3.Cleanliness 4.Absence of unwanted gas 5.Ease of control 6.Automatic protection 7.Localized application 8.Uniform heating 9.Low attention and maintenance cost 10.Better working conditions

4. 1.Low temperature heating(up to 400˚C) 2.Medium temperature heating(400 ˚-1150 ˚C) 3.High temperature heating(above 1150 ˚C) The heat from one body to another body can be transferred by any of the following methods. Conduction Convection Radiation

5. The flow of heat from one body to another body dependent on the temperature difference. Two bodies are different temperature to joined together. Conduction refers to the heat transfer that occurs across the medium. Medium can be solid or a fluid. Regions with greater molecular kinetic energy will pass their thermal energy to regions with less molecular energy through direct molecular collisions, a process known as conduction. In metals, a significant portion of the transported thermal energy is also carried by conduction-band electrons.

6. In this process, the heat is transferred by actual motion of the molecules of the substances and it mostly takes place in liquids. This is due to the difference with fluid density at different temperatures. The amount of heat dissipation H = 3.876 x 10 -4 (T 1 -T 2 ) 1.25 watts/cm 2. T1 and T2 are the temperatures in ˚C absolute of the heating surface and air respectively.

7. In this process, the heat is transferred by means of heat waves these waves do not heat the medium in between two bodies and heat the body which intercepts these waves.

9. Classification of Electric Heating :- Electric Heating Power Frequency Heating High Frequency Heating Resistance Heating Arc Heating Dielectric Heating Induction Heating Direct Resistance Heating Indirect Resistance Heating Direct arc Heating Indirect arc Heating Direct core type induction Heating Coreless type induction Heating

10. Power Frequency Electric Heating :- Resistance Heating :- This method is based upon the I 2 R loss. Whenever current is passed through a resistive material heat is produced because of I 2 R loss. There are two methods of resistance heating. Direct resistance heating. Indirect resistance heating.

11. Direct Resistance Heating :- Two electrodes are immersed in the material to be heated. The material called as charge may be in the form of power, pieces or liquid and forms a resistance. In case of D.C or single phase A.C two electrodes are required but there will be three electrodes in case of three phase supply. When metal pieces are to be heated, a powder of high resistivity material is sprinkled over the surface of the charge to avoid direct short circuit. The current is allowed to pass through the charge which heats it up. This method has high efficiency since heat is produced in the charge itself. As the current in this case is not easily variable, automatic temperature control is not possible. However uniform and high temperature can be obtained. Merits:- High efficiency. It gives uniform heat and high temperature.

12. Indirect Resistance Heating :- The current is passed through a high resistance element which is either placed above or below the oven depending upon the nature of the job to be performed. The heat produced in the heating element is directed to the charge either by radiation or by convection. In industrial heating the resistance is placed in a jacket which is surrounded by the charge. This arrangement provides a uniform temperature. Automatic temperature control can be provided in this case. Demerits:- Low efficiency.

13. Radiant Heating or Infra Red Heating :- This used for low and medium temperatures. In this method a special tungsten filament lamp is operated at the temperature of 2300 ˚C. The lamp at this temperature emits a large amount of infra red radiation. Operating the lamp at this temperature also increases the life of the filament. In comparison to other resistance heater, this lamp emits a large amount of heat, which is being reflected to the charge. In this method, heat emission about 7500 watts/m2 can be obtained. The temperature of charge obtained will be 200 to 300 ˚C. This types of heating is employed in drying paint and foundry moulds and plastic heating at low temperatures.

14. Arc Heating :- When a high voltage is applied across two electrodes, separated by an air gap, the air in between gets ionised due to electrostatic forces. The ionised air is a conducting material, therefore the current starts flowing through the air gap in the form of continuous spark, ie., arc with graphite or carbon electrode the temperature obtained from the arc is between 3000 ˚C and 3500 ˚C.

15. Induction Heating :- Induction heating is based on the principle of transformers. There is a primary winding through which as a.c current is passed. The coil is magnetically coupled with the metal to be heated, which acts as the secondary. When an a.c current is passed through the primary winding, an electric current will be induced in the metal. This induced current produce heat in the metal. High Frequency Electric Heating :-

16. Induction Stove:- Its modern electric cooker which works on the principle of electromagnetic induction to heat vessels. Copper wire is placed underneath the cooking vessel. A.C flows through the coil which produces an alternating magnetic field. This field induces an electric current known as eddy current in the vessel. As a result, the body of the cooking vessel will be heated quickly, which will in turn cook the food inside. This heat is proportional to I 2 R loss. The heart of such system is the electronic control system. It is a combination of power stage coupled with a digital control system and thermal management system.

17. High frequency eddy Current Heating :- High frequency eddy current heating is nothing but a form of induction heating. Usually it is used for hardening, annealing and tempering of machine parts. The machine part to be heated is surrounded by a coil through which an alternating current at high frequency is passed. The electromagnetic field developed in the coil produces heating effect in the desired area of the machine parts or metal. The heating effect is due to eddy current set up in the machine parts. Due to skin effect the induced heating current concentrate near the surface of the conductor through which flux is set up.

18. Dielectric Heating :- This is also sometime called as high frequency capacitance heating. If non metallic material ie., insulators such as wood, plastics, china clay, glass, ceramics etc are subjected to high voltage A.C current, their temperature will increase after some time. This increase in temperature is due to the conversion of dielectric loss into heat. The dielectric loss is dependent upon the frequency and high voltage. Therefore for obtaining high heating effect high voltage at high frequency is usually employed. The metal to be heated is placed between two sheet type electrodes which forms a capacitor.

19. Electric Furnaces:- The material of the heating element should have following important properties. High Resistivity. Low temperature co-efficient of resistance. High melting point. Free from oxidation. Withstand vibrations. Anti-corrosive. Mechanical Strength. Resistance Furnaces:- Requirements of Heating Element materials:-

20. Commonly used Heating Element Materials:- The material which are mostly useful for heating elements may be of the following types. Nickel chromium alloy – containing 80% nickel and 20% chromium. Nickel Chromium iron alloy – containing about 65% nickel, 15% chromium and 20% iron. Property Resistance in ohm-m Melting point Limiting temperature Temperature co- efficient (upto 500 ˚C) per ˚C Specific heat J/kg - ˚C Density in gm per c.c Nickel - Chromium 1.03 x 10-6 1375 ˚C 1000 ˚C 0.000098 441 8.35 Nickel – Chromium - iron 1.06 x 10-6 1400 ˚C 850 ˚C 0.000202 467 8.27

21. Resistance Furnaces for Special Purposes:- The most important applications of resistance oven are known as Air Circulation OvenBright Annealing Furnace Air Circulation Oven:- The heat is transferred to the charge by convection method. These are usually employed for drawing and hardening steel wire and providing heat treatment to soft metals like aluminium etc., Gas or air is passed over the heating elements which are screened so as not to provide any radiation heat to the charge. The hot gas or air is passed through the furnace containing charge. The hot gases circulating in the furnace, heat up the charge uniformly blowers and fans are used to circulation the gases or air. The direction of flow of air circulation is reversed periodically in order to make the distribution of heat more uniform.

22. Bright Annealing Furnace:- Which the charge is heated and is followed by slow cooling for elimination of brittleness. If the cooling is done in air, due to oxygen and water vapours the charge surface is covered with scale formation, resulting into a dull finish. In this type of furnaces, the charge is heated in a sealed furnace and the air is discharged during heating through a non return valve. Thus the cooling is carried out in an air free atmosphere and it keeps the surface of the charge bright.

23. Temperature control of Resistance Furnaces:- The temperature in resistance ovens can be controlled by varying the current. There are various methods by which the variation in current can be obtained. Varying the Number of Elements. Varying the Number of Elements. Resistance ovens number of heating elements are used. Elements in the circuit is decreased or increased. Drawback of such an arrangement does not provide uniform heating. Change in Connections. Change in Connections. Method by changing the connections of the elements either in series or parallel or series parallel grouping. In certain cases these elements can either by arranged in delta or star.

24. Adding a variable external resistance in series with the element. Adding a variable external resistance in series with the element. Resistance in series with the element is changed. It changes the voltage acting across the element. Thus the temperature is varied. This method is not economical because there is a waste of electrical energy in the series resistance. Changing transformer tapping's. Changing transformer tapping's. In order to change the voltage, across the element the tapping's of the transformer placed in the circuit is changed. Thereby the current in the circuit is varied. Due to the change of current there is a variation in the temperature.

25. Arc Furnace:- High voltage is applied across two electrodes, separated by an air gap, the air in between gets ionised due to electrostatic forces. The ionised air is a conducting material, therefore the current starts flowing through the air gap in the form of continuous spark. With graphite or carbon electrode the temperature obtained from the arc is between 3000 ˚C and 3500 ˚C. The heating chamber of the furnace is constructed with refractory lining supported on a frame work. There are two types of arc furnace. They are Direct are furnace. Indirect are furnace.

26. Direct Arc Furnace:- In this type the charge acts as another electrode. There are two carbon or graphite electrodes and the arc is developed at two places. The arc is directly in contact with the charge and the arc is due to the current in the charge, therefore the charge is heated to very high temperature. Direct arc furnace are used for steel production. The power factor of such furnace are about 0.8. the usual size is 5 to 10 tonnes capacity.

27. Indirect Arc Furnace:- The arc is produced between two electrodes and the heat is transmitted to the charge by radiation. The construction of such type of furnace limits the use of two electrodes, thereby only single phase supply is used. The current does not flow through the charge, hence there is no automatic stirring. So the furnace is required to be rocked mechanically. Indirect arc furnaces are used for melting non ferrous metals.

28. Power Supply for Arc Furnace:- The arc used for melting and refining of steel requires power of about 500 KW per tonne for small furnace of ½ tonne capacity. But the requirement of power is reduced to 200 KW per tonne for very large furnaces of 50 to 100 tonne capacity. For the purpose of refining only the power requirement is 100 to 120 KW per tonne. Thus it will be seen that the power consumption of the arc furnace is very high. The arc voltage is usually in the range of 50 to 150 V. Hence for obtaining above mentioned power, high magnitude of current is required. Therefore low voltage and high current secondary winding furnace transformer is used. For voltage regulation tapping's are provided in the primary.

29. Control of Arc Furnace:- The power input for obtaining best operating conditions and temperature can be controlled by Varying the resistance of the arc by increasing or decreasing the distance between the gaps. By changing the tapping’s of transformer on the primary side which results in variation of voltage across the furnace. For complete control of furnace temperature and to achieve best operating conditions both voltage and electrode controls are employed.

30. Reasons for employing low voltage and high current supply:- Power supply for electric arc furnace is of low voltage high current type. This is due to the following reasons. Heating effect is proportional to the square of the current, therefore heavy currents are needed. By using low voltage and high current the electrodes are kept very near to the charge as the arc is of small length. Thus arc remains away from the roof and therefore life of the roof refractory is increased. The low voltage at the secondary reduces the insulation and safety considerations.

31. Direct Core Type Induction Furnace:- It consists of an iron core, crucible and primary winding connected to an A.C supply. The charge is kept in the crucible, which forms a single turn short circuited secondary circuit. The current in the charge is very high in the order of several thousand amperes. The charge is magnetically coupled to the primary winding. The charge is melted because of high current induced in it. When there is no molten metal, no current will flow in the secondary. The start the furnace molten metal is poured in the annular hearth or a sufficient quantity is left in the oven from the previous charge.

32. This type of furnace has following draw backs:- The magnetic coupling between the primary and secondary is very weak, therefore the leakage reactance is very high. This causes low power factor. Low frequency supply is necessary because normal frequency causes turbulence of the charge. If current density exceeds about 5 amps/mm 2 the electromagnetic force produced by this current. Hence the heating of the metal is interrupted. It is called pinch effect. The crucible for the charge is of odd shape and inconvenient from the metallurgical point of view. The furnace cannot function if the secondary circuit is open. It must be closed. For starting the furnace either molten metal is poured into the crucible or sufficient molten metal is allowed to remain in the crucible from the previous operation. Such furnace is not suitable for intermittent services.

33. Ajax Wyatt Vertical core type furnace:- It has a vertical channel for the charge, thus the crucible used is also vertical. The principle of operation is that of a transformer in which the secondary turns are replaced by a closed loop of molten metal. The placed on the central limb of the core. Hence leakage reactance is comparatively low and power factor is high. Inside of the furnace is lined with refractory depending upon the charge. The top of the furnace is covered with an insulated cover which can be removed for charging.

34. Ajax Wyatt Vertical core type furnace:- The molten metal in the ‘V’ portion acts as a short circuited secondary. When primary is connected to the A.C. supply, high current will be induced in the short circuited secondary. This current melts the charge. As the furnace is having a narrow V-shape at the bottom, the molten metal will be accumulated at the bottom and even a small amount of charge will keep the secondary completed. Hence chances of discontinuity of the circuit are less. Cont.…

35. Indirect core type Induction Furnace:- In this furnace, a suitable element is heated by induction which, in turn, transfers the heat to the charge by radiation. So far as the charge is concerned, the conditions are similar to those in a resistance oven. the secondary consists of a metal container which forms the walls of the furnace proper. The primary winding is magnetically coupled to this secondary by an iron core. When primary winding is connected to a.c. supply, secondary current is induced in the metal container by transformer action which heats up the container.

36. The metal container transfers this heat to the charge. A special advantage of this furnace is that its temperature can be automatically controlled without the use of an external equipment. The part AB of the magnetic circuit situated inside the oven chamber consists of a special alloy which loses its magnetic properties at a particular temperature but regains them when cooled back to the same temperature. As soon as the chamber attains the critical temperature, reluctance of the magnetic circuit increases manifold thereby cutting off the heat supply. The bar AB is detachable and can be replaced by other bars having different critical temperatures. Indirect core type Induction Furnace:- Cont.…

37. In this furnace there is no core and thus the flux density will be low. Hence for compensating the low flux density, the current supplied to the primary should have sufficiently high frequency. The flux set up by the primary winding produces eddy currents in the charge. The heating effect of the eddy currents melts the charge. Stirring of the metals takes place by the action of the electromagnetic forces. Coreless furnace may have conducting or non conducting containers. Which container is made up of conducting material. The container act as secondary winding and the charge can have either conducting or non conducting properties. Coreless Induction Furnace:-

38. Thus the container forms a short circuited single turn secondary. Hence heavy current induced in it and produce heat. This heat produced is transferred to the charge by convection. To prevent the primary winding from high temperature, refractory linings are provided between primary and secondary windings. Which the container is made of ceramic material and the charge must necessarily have conducting properties. The flux produced by the primary winding produces eddy currents in the charge. The heating effects of the eddy currents melts the charge. Stirring action in the metals takes place by the action of the electromagnetic forces. Coreless Induction Furnace:- Cont.…

39. Welding:- Welding is a process of joining two similar metal by heating. The metal parts are heating to melting point. In some case the pieces of metal to be joined are heated to plastic stage and are fused together. Introduction:- In electric welding process, electric current is used to produce large heat, required for joining two metal pieces. There are two methods by which electric welding can be carried out. These are (i) Resistance Welding (ii) Arc Welding Electric welding:-

40. 1.Resistance Welding 1. Butt Welding 2. Spot Welding 3.Seam Welding 4. Projection Welding 5.Flash Welding 2.Arc Welding 1.Carbon Arc Welding 2.Metal Arc welding 3.Automatic hydrogen arc welding 4.Inert gas metal arc welding 5.Submerged arc welding Types of electric welding: -

41. Requirements of Good Welding:- A good weld should have the following characteristics. Uniformly rippled surface of the weld. Even contour of the weld. Even width of the weld. Absence of surface defects like overlap, under cut, crack, and surface porosity. Absence of internal defects like blow holes hidden porosity in the deposited metal, hidden cracks in the weld and work piece.

42. Preparation of work for Welding:- It is desirable that provision may be made for expansion and contraction wherever possible. The cleaning of the surface is another factor. The cleaning can be done be wire brushes, machining or sand papering. If impurities present tend to make the joint weaker as the welded portion is filled with gas and slag and metal becomes brittle. Good preparation of joint design is to keep the cross section of the added material as small as possible. Joint should not oxidise at high temperatures. Because oxidation at high temperature makes the defective weld. In arc welding the flux is coated on the electrodes. The flux forms a protective coating of slag over the weld metal and creates a non-oxidising atmosphere.

43. Resistance Welding The A.C supply is given to the primary winding of the transformer through a controlled contactor. The welding transformer is a step down transformer. The secondary voltage is in the order of 1 to 10 volts. But the current may range from 50 to 1000 amperes. The various types of resistance welding are i) Butt welding ii) Spot weldingiii) Seam welding iv) Projection Welding v) Flash welding

44. The process heat is generated by contact resistance between two components. The metal parts are joined end to end. Sufficient pressure is applied along the axial direction Suitable for welding pipes, wires and rods. Butt Welding: -

45. Joining or fabricating sheet metal structure. Only provides mechanical strength and is not air or water tight. The plates are overlapping each other b/w two electrodes. Spot Welding: -

46. Series of continuous spot welding. Making continuous joint between two overlapping pieces of sheet metal. Two wheels or roller type electrodes are used Normally rotating wheels are used. Seam Welding: -

47. Projection welding is a development of resistance spot welding. In spot welding, the size and position of the welds are determined by the size of the electrode tip and the contact point on the workpieces. whereas in projection welding the size and position of the weld or welds are determined by the design of the component to be welded. The force and current are concentrated in a small contact area which occurs naturally Projection Welding: -

48. Advantages of Projection Welding: 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. Hence, clean weld joints are obtained. Disadvantages of Projection Welding: Projections cannot be made in thin work pieces. Thin work pieces cannot withstand the electrode pressure. Equipment is costlier. Applications of Projection Welding: Used for welding parts of refrigerator, condensers, refrigerator racks, grills etc.

49. Flash Welding is a Resistance Welding (RW) process, in which ends of rods (tubes, sheets) are heated and fused by an arc struck between them and then forged (brought into a contact under a pressure) producing a weld. The welded parts are held in electrode clamps, one of which is stationary and the second is movable.Resistance Welding (RW)arcforged Flash Welding method permits fast (about 1 min.) joining of large and complex parts. Steels, Aluminum alloys, Copper alloys, Magnesium alloys, Copper alloys and Nickel alloys may be welded by Flash Welding. SteelsAluminum alloysCopper alloysMagnesium alloysCopper alloysNickel alloys Thick pipes, ends of band saws, frames, aircraft landing gears are produced by Flash Welding. Flash Welding: -

50. Benefits Flash welding is ideally suited to producing butt welds in large or complex sections. Weld time is relatively short, from a few seconds for the thinnest sections to a few minutes for the largest. Risks The main hazards are: (i) the risk of crushing fingers or hands; (ii) burns or eye damage from splash metal. Flash Welding: -

51. Arc welding uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct (DC) or alternating (AC) current, and consumable or non-consumable electrodes. The welding region is sometimes protected by some type of inert or semi-inert gas, known as a shielding gas, and/or an evaporating filler material. The process of arc welding is widely used because of its low capital and running costs. Electric Arc Welding: -

52. Arc Welding types i.Carbon Arc Welding ii.Metal Arc welding iii.Automatic hydrogen arc welding iv.Inert gas metal arc welding v.Submerged arc welding

53. Carbon Arc Welding (CAW) is a welding process, in which heat is generated by an electric arc struck between an carbon electrode and the work piece.weldingelectric arccarbon The arc heats and melts the work pieces edges, forming a joint. Carbon arc welding is the oldest welding process. If required, filler rod may be used in Carbon Arc Welding. End of the rod is held in the arc zone. The molten rod material is supplied to the weld pool. Shields (neutral gas, flux) may be used for weld pool protection depending on type of welded metal. Shields Carbon Arc Welding: -

54. Advantages of Carbon Arc Welding: Low cost of equipment and welding operation; High level of operator skill is not required; The process is easily automated; Low distortion of work piece. Disadvantages of Carbon Arc Welding: Unstable quality of the weld (porosity); Carbon of electrode contaminates weld material with carbides. Carbon Arc Welding has been replaced by Tungsten Inert Gas Arc Welding (TIG, GTAW) in many applications.Tungsten Inert Gas Arc Welding (TIG, GTAW) Modification of Carbone Arc Welding is Twin Carbon Electrode Arc Welding, utilizing arc struck between two carbon electrodes.

55. Metal arc welding a metal rod of same material as being welded is used as electrode. The electrode also serves the purpose of filler. A metal arc welding AC or DC used. Electric supply is connected between electrode and work piece. The work piece is then suddenly touched by the electrode and then separated from it a little. This results in an arc between the job and the electrode. A little portion of the work and the tip of the electrode melts due to the heat generated by the arc. When the electrode is removed the metal cools and solidifies giving a strong welding joint. Metal Arc Welding: -

56. "A process in which the welding heat is generated by passing a stream of hydrogen through an electric arc between two inclined electrodes. which are usually of tungsten. The high temperature of the arc dissociates molecules of the gas into atoms, a large quantity of heat being absorbed by the hydrogen during dissociation. The average temperature of the flame is approximately 4000 deg. C., As for stainless steels and other special alloys. The hydrogen envelope prevents oxidation both of the metal and the tungsten electrodes, Atomic Hydrogen Arc Welding: -

57.  In gas shielded arc welding, both the arc and the molten puddle are covered by a shield of inert gas.  The shield of inert gas prevents atmospheric contamination, thereby producing a better weld.  The primary gases used for this process are helium, argon, or carbon dioxide.  An arc is struck between tungsten electrode and the work piece.  The helium or argon provide inert atmosphere so that oxidation of the welded joint does not takes place.  This process is particularly employed for welding light alloys, stainless steel and non ferrous metals such as copper, aluminum and their alloys. Inert Gas Metal Arc Welding: - (Helium or Argon Arc Welding)

58.  A process for welding metal sections in which at least two metal work pieces are welded together.  Across a contact area using corpuscular radiation beams to heat the metal in the respective work pieces adjacent said contact area and form a welded joint. Types of radiation welding Electron beam Welding Laser Beam Welding Ultrasonic Welding Radiation Welding: -

59. Electron beam welding is a radiant energy welding process in which the work pieces are joined by the heat obtained from a concentrated beam composed primarily of high- velocity electrons impinging on the surface to be joined. When a tungsten filament is electrically heated in vacuum to approximately 20000C it emits electrons. The electrons are then accelerated towards the hollow anode by establishing a high difference of voltage potential between the tungsten filament and a metal anode. The highly accelerated electrons hit the base metal and penetrate slightly below the base surface. The kinetic energy of the electrons is converted into heat energy. The succession of electrons striking at the same place causes the work piece metal to melt and fuse together.

60. Advantages of Electron Beam Welding: Any metals, including zirconium, beryllium or tungsten can be easily welded. High quality welds, as the operation is carried in a vacuum. Concentrated beam minimizes distortion. Cooling rate is much higher. Heat affected zone is less. Shielding gas, flux or filler metal is not required.

61. Disadvantages of Electron Beam Welding: High capital cost. Extensive joint preparation is required. Vacuum requirements tend to limit the production rate. Size of the vacuum chamber restricts the size of the work piece being welded. Not suitable for high carbon steels. Cracks occur due to high cooling rates. Applications of Electron Beam Welding: Electron beam welding is mainly used in electronic industries, automotive and aircraft industries where the quality of weld required forms the decisive factor.

62. For a welding application, the laser is finely focused as a high-collimated eam of photons that is referred to as a coherrent beam. This monochromatic beam is capable of delivering up to 30,000 W/in2. The most common laser in welding is the CO2 type, which can weld 1/32 in0thich stainless steel. New gas dynamic lasers can weld up to 3/4 in. thick stainless. Cooling system, either gas or liquid is provided to protect the ruby crystal from the enormous amount of heat generated. When the flash tube is connected to a pulsed high voltage source, xenon transforms the electrical energy into while light flashes (light energy).

63. Advantages of Laser Welding: 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. Certain locations in the material that are difficult to reach can be welded easily by this process. Heating and cooling rates are much higher in this process. Also, head affected zone is very small. Hence, the process is ideal for a location which is surrounded by heat sensitive components. Clean weld joints can be obtained by this process.

64. Disadvantages of Laser Welding: Slow welding speeds (25-250 mm/min). Rapid cooling rate cause problems such as cracking in high carbon steels. High equipment costs. Applications of Laser Welding: Used in electronics industry for applications such as connecting wire leads to small electronic components, to weld medical equipments, transmission components in automobiles and in cladding process.

65. In Ultrasonic Beam welding ultrasonic waves are used as the energy source for welding. Ultrasonic waves are sound waves in the frequency range with 20KHz and more. These sound waves are above the human audible range. Ultrasonic welding is a solid state welding process.

66. Advantages of Ultrasonic Welding: Very thin materials can be welded. Material characteristics are not altered since low temperature is involved. Disadvantages of Ultrasonic Welding: Not suitable for ductile materials since they yield under the stresses. Process is limited to only joining thin sections. Quite expensive. Applications of Ultrasonic Welding: For fabrication of nuclear fuels. Used for welding electronic and electrical equipments. Used for refrigeration, air conditioning equipments, containers of explosives.