Many different energy sources can be used for welding, including a gas flame, an electric arc, a laser, an electron beam, friction, and ultrasound. While often an industrial process, welding may be performed in many different environments, including open air, under water and in outer space. Welding is a potentially hazardous undertaking and precautions are required to avoid burns, electric shock, vision damage, inhalation of poisonous gases and fumes, and exposure to intense ultraviolet radiation.
Until the end of the 19th century, the only welding process was forge welding, which blacksmiths had used for centuries to join iron and steel by heating and hammering. Arc welding and oxyfuel welding were among the first processes to develop late in the century, and electric resistance welding followed soon after. Welding technology advanced quickly during the early 20th century as World War I and World War II drove the demand for reliable and inexpensive joining methods. Following the wars, several modern welding techniques were developed, including manual methods like shielded metal arc welding, now one of the most popular welding methods, as well as semi-automatic and automatic processes such as gas metal arc welding, submerged arc welding, flux-cored arc welding and electroslag welding. Developments continued with the invention of laser beam welding, electron beam welding, electromagnetic pulse welding and friction stir welding in the latter half of the century. Today, the science continues to advance. Robot welding is commonplace in industrial settings, and researchers continue to develop new welding methods and gain greater understanding of weld quality.
Types of Welding:
There are several types of welding.They are
*Gas welding
*ARC welding
*Resistance welding
*Solid state welding
*Radiant energy welding
*Thermo chemical welding
Gas welding
1.Air acetylene welding:
Air acetylene welding is one type of gas welding process, where unit body is produced by the heating work piece. The heat is produced from mixture of acetylene and air. Weld joint is made without the application of pressure and with or without use of filler metal.
Bunsen burner working principle is followed in air acetylene welding torch. A certain amount of pressure acetylene gas is flowing through Bunsen jet torch and same time a suitable amount of air included. Such this a weld-able flame is produced.
First acetylene gas is flown through a proper hose and it is regulated by a valve system. Acetylene gas is mixed with automatic included air for combustion. During combustion required amount of oxygen is obtained from air. There a special designed torch is used.
Applications:
*The flame temperature is lower than the other kind of fuel acetylene and oxygen welding. The following application-
*Where soft solder is required for copper plumbing.
*Lead welding purposes (of course small cross section).
*Small thickness copper sheet welding.
*Refrigerant copper tube joining.
2.Oxy acetylene welding:
Oxy-acetylene welding is one of the flame welding or gas weld process, because the flame is produced of mixture of gasses in a combustion chamber for heat provided to the job. Oxy-acetylene mixture of gasses most commonly used for producing high temperature 32600C.It is oldest development fusion welding process. No pressure is required on the job to be welded, the heat is drive to welding the pieces. The acetylene is obtained by the action of oxygen and calcium carbide.
CaC2 + 2H2O = Ca(OH)2 + C2H2
The gas acetylene( C2H2 )is play the most important role in Oxy-acetylene welding because it has the highest calorific value.
Applications:
*In gas welding the heating and cooling rate is slow, so it is advantage in some material welding from welding failure.
*The flame can be controlled easily where need low and high temperature for welding or brazing or soldering.
*Filler metal deposit rate can be controlled easily, because source of heat and filler metals are separate.
*Preheating facility is in welder’s hand. So where required it can be applied.
*In comparison of other welding process, it is low cost and low maintenance.
3.Oxy hydrogen welding:
In producing of flame to welding generally oxy-acetylene is the most convenient. In there acetylene is used as a fuel gas, which is combusted with oxygen to produce a flame. There are various type of fuel gas is used for flame, like butane, propane, hydrogen, natural gas etc. That is depend on type of material, how temperature is required for welding etc.
The chemical composition of oxy-hydrogen welding flame is
2H2 + O2 → 2H2O
It is indicate that the produced flame is strongly oxidizing flame. Where low melting temperature is required for welding there can be oxy-hydrogen flame is used. The metal like lead, aluminium etc. low melting temperature materials can be welded.
In oxy-hydrogen gas welding equipments are more or less same as oxy-acetylene, only differ in pressure control valve regulator. In this welding a special type of regulator is used. In this type of flame no carbon is existed. Steel welding can not
possible with oxy-hydrogen flame. Because it needs higher temperature. Higher temperature can be obtained by increasing of oxygen, but flame can not be obtained perfectly. In oxy-hydrogen flame there are no facilities to combustion the both gases as oxy-acetylene. So, it not possible to obtained neutral flame.
4.Pressure gas welding:
The pressure gas welding is define as, the coalescence body is produced by the heating of weld metal and heat source is some gas of mixture. Then apply the pressure on weld metal to completed the pressure gas welding. Any kind of filler metal is not used in this welding process.
This welding technique is commonly used in sheet metal welding, pipe welding, railroad joining etc.
Any kind of edge preparation is not required in this type of welding method.
ARC Welding
In electric arc welding is only a electrical spark, otherwise it is nothing. It is fusion welding process. It is work in a closed electrical circuit in which current flows. If a small gap formed in the circuit then there an electrical spark is occurred, which is called electrical arc. In this spark or arc are contain a huge amount of temperature like 34000C-40000C. Due to this huge temperature, the weld metal can be fuse in arc welding process.
In the arc welding the heat is produced through an electrode or arc welding rods. The electric arc is produced between consumable electrode and the work piece. The current is continuously supplied through the consumable electrode and fillet deposited on work piece. Thus the electric arc welding process is carried out. The electrode which is passing the current is made with flux coated, these types of electrode is called bar electrode. The coating flux are melt at the time of welding and deposited upper level of filler metal as a slag, which is removed by chipping or grinding process after normal cooling. The filler metal is called electrode in arc welding practice.
1.Carbon arc welding:
The carbon-arc welding is the another type of arc welding. Where carbon or graphite are used as a electrode. There are two methods used for produced an arcs, the single-carbon process and another is the twin-carbon process. The main difference is, the twin-carbon arc welding carried electrically independent torch. The carbon-arc welding is invariably carried out with direct current. The heat is produced between carbon electrode and work piece, base metal melts with this heat and additional filler metal can be added where extra metal needed. The essential point of this carbon-arc welding is that the filler rod quite difference from the ordinary filler rod. Because it can not be connected with current source.
*Work piece distortion is less.
*Process is suitable for any kind of joint.
*Weld heat can be controlled very easily through changing of arc length.
*Welders are made skilled in short time.
*It is simple welding process.
*Big range of metals and their alloys can be welded.
2.Tig welding:
TIG welding means Tungsten Inert Gas welding is the special designed welding system. In arc welding we have seen coated electrodes are used, a protective enveloped gases formed around the weld zone from attack the atmosphere oxygen and nitrogen . In the TIG welding there inert gasses are used . The arc is maintained between the tip of tungsten which worked as a electrode and work piece. A special type electrode holder is made for the inert gases spread on the weld bid concentrically. The tungsten non-consumable electrodes are used for tig weld. The filler rod is additionally added to the weld joint.
In this process Alternating current (AC) or Direct Current (DC) may be used, which depends upon the type of metal to be welded. The Direct Current with straight polarity is used for welding copper or its alloys, stainless steel and reverse polarity used for magnesium. The Alternating Current or AC is used for welding steel, cast iron, aluminium and magnesium. This Tungsten Inert Gas or TIG weld is best suited for the thin cross-section metals. It may be operated in
TIG Welding Principle
manual or automatic controlling system. This welding process can be used for continuous, spot or intermittent weld joints. This method is suitable of most metals and alloys except lead and zinc, because due to their lower melting point temperature, they are vaporized early and make dull the electrode. It has specific welding metals to be welded like– copper alloys, aluminium alloys, magnesium alloys, nickel alloys, zirconium alloys, beryllium alloys, titanium alloys, carbon steels, alloy steels, stainless steels and refractory metals.
The inert gas for TIG welding:
The atomic weight of Argon is 39.94 and melting point is –1880C. The density is 10 times more than Helium. It is comparatively easily obtained from air and liquefied it then distilled. It has better electrical properties than Helium. It produced stable arc when using alternating current due to lower ionization voltage.
Advantages:
1. This welding process is better controlled by welder, because of clear visibility of produced arc and melting base metal.
2. High quality of welding is obtained on thin metal from TIG welding process.
3. No flux inclusion is occurred in welding joint, because there no need any kind of flux for welding.
4. All welding position can be performed by this process.
5. Minimum cleaning is required after welding.
3.Mig welding:
Metal Inert Gas or MIG weld process have in common the electrode used as the filler wire which is continuously fed and heating the job with an arc is established on the work, total or partial inert gas used for shielding the produced arc. There is no flux used for weld, helium, argon, carbon-dioxide or some gas mixture is used to shield for the arc and molten metal from atmosphere.
There are two types of MIG welds are used, one fully automated and other is semi-automated. The semi-automated version is used in very largely.
Principle operation:
This welding process is said for semi-automated MIG welding. Check the electrical supply, water supply and gas flow in before going to ignition started. Then set the feed of electrode and proper current also. The electrode should be projected about 12-16 mm from the torch tip before going to start arc. The arc length should be maintaining about 2-4mm and the torch tip should be 10-12mm from the work piece. To produce the arc the shielding gas and proper current supply is to be on and scratch the electrode against the job, then moved forward to carry out MIG welding. Always take in mind that the electrical supply, gas flow and water supply should be on. The torch is moved along the joint for carrying out the welding process and the torch angle is about 700with the horizontal.
Application:
MIG welding has large used in automobile industry, aircraft parts welding, pressure vessel manufacturing and many other places.For welding tool steels, carbon, silicon and low allow steels, stainless steel, aluminium and its alloy, magnesium, nickel and its alloy, copper and its alloy, titanium and so many metals.
It is used for refrigerator parts manufacturing .
Advantages:
There are many advantages of MIG welding mention bellow:
*Joints can produce with deep penetration.
*The metals thickness can not be vary with this MIG welding process. Thick and thin metals are welded very effectively.
*This welding process is very suitable for large scale production unit because, it can be performed much faster than other types of welding process like TIG etc.
*Large amount of metal can be deposited on the work piece.
MIG welding process can reduces the welding cost, because it produces neat and clean metal deposit on the work piece. Spatter free and smooth welding surface is produced, so it is no need to extra cleaning.
4.Submerged arc welding:
Submerged welding is an arc welding process, where welding joint is made by producing an electrical arc or arcs set up between the bare metal electrode and weld metal. This welding process held totally hide condition under a blanket or granular material (flux). There are no pressure is required and continuously fed the bare electrode act as a filler metals on the joints for melt.
Submerged welding principle:
In submerged arc welding process a bare electrode is used and flux is used as a granular material. An electric arc is produced between bare electrode and job. The molten filler metal is covered with flux. This flux is shielded the molten metal contamination from atmospheric gas. This process can be automatic or semi automatic control.
Submerged welding advantages:
*High rate of filler metal deposition and deep penetration is occurred.
*Submerged welding operation can be performed considerably higher speed.
*Weld distortion is less on weld metal.
*Molten filler metal deposited uniformly and possess good ductility and good corrosion resistance properties.
*Due to high filler metal deposition the thick material can be welded easily and smoothly.
*patter less smooth weld shape is obtained.
For welding with submerged welding no edge preparation is required under half inch plate thickness.
5.Shielded metal arc welding:
Shielded metal arc welding means, it is one type of arc welding process. Where weld joint is produced by heating the work piece with an electrical arc which is produced between shielded or coated electrode and work piece. In this welding process necessary filler metal is obtained from electrode. Coating or flux of electrode is used for shielding the melting metal from atmospheric harmful gas, maintaining arc stability, cleaning weld surface etc.
Shielded metal arc welding principle:
Heat is obtained in shielded metal arc welding from electric arc strike between coated arc electrode and weld metal. If more or less metal deposit and more or less fusion rate is required on weld metal, thus heat variation controlled by higher or lower current. The produced electric arc melts the coated electrode’s end and work piece also. Thus the fusion process is started and the filler material droplets are transferred from coated electrode to weld metals. This molten metal bonded the both work piece which to be weld. The coated of electrode is melt on the molten metal and produced a gaseous shielding and slag for atmospheric gaseous contamination of molten filler metal.
Shielded metal arc welding advantages:
The equipment of this arc welding is comparatively low and portable. It is the simplest welding process. Various type metal can be weld. Highest quality of welding can be obtain and welding operation can be performed in any position.
Resistance welding
Spot welding joint is one type of electric resistance welding. Generally joining the sheet to sheet, sheet to rolled sections, wire to wire etc. by this spot weld process. The spot welding is very effectively, which can replace the rivet joints and is very speedy process, this spot welding machine does not need skilled operator, it can be operated by semi-skilled labour.
The principle of spot welding is shown in the bellow diagram. In this machine basically having a transformer core (T) which is having a primary winding (PW). This primary winding tapped at a number of points. The secondary winding (SW)
has the two ends of a circuit (C) which is connected two arms made of copper or bronze. Each side has a copper electrode, this electrode of spot welding produce the sufficient heat to fuse the joining metal. The lower arm is generally stationary and upper arm is movable (upward and downward). The technical terms are rocker arms or electrode arms. The electrodes of spot welding is cooled by water, the water is passing through the inter looped water line.
The essential factor of spot welding-
*The welding current.
*The time of current application.
*The pressure of electrodes.
*The shape or area of electrodes.
*The surface condition of welded material.
Advantages of spot welding-
*In this welding process is free from fumes and spatter.
*Generally it has nothing maintenance or no skilled persons are required for maintenance.
*No skilled persons are need to operate the spot welding.
*Welding cost is minimum.
2.Seam welding:Seam welding is the one type of resistance welding and also another modification of spot welding. The basic chief difference of spot weld and seam weld is that the formation of electrode. They are usually power driven and rotate whilst gripping the work. The current is supplied through the rotatable wheel and melt the metal. The edges of the two sheets must be overlap, so that the welding heat can be developed in joining interface of the sheet metal. The large manufacturing of cylindrical container, drum, pipe, etc. is best suited by these types of welding.
When the body is being performed into a
tube, the overlapping edge made in united piece which is called longitudinal welding and the end position fitted of assembly work welding is called circumferential welding.
The use of seam welding is mainly designated for the thin sheet metal, the sheet metal often welded which should not exceed 1/8 inch. The welding speed may vary with the sheet gauge. The special machines are employed for the faster welding speed. In the bellow diagram shown the basic principle of seam welding.
Generally two types of seam welding machines found 1) Circumferential Seam Welding Machine 2) Longitudinal Seam Welding Machine. They are called because of the types of welding joint performance. Although the Universal Seam Welding Machine can perform both operation. By the changing of electrode assembly the circumferential welding can be converted into longitudinal welding.
In the seam welding operation, the sheets to be welded are properly overlapped and positioned between the both rollers. The clamp may be provided for the holding properly and applying the pressure. A current is provided through rollers to the material contact with them. The sufficient heat is produced and material reached in plastic stage. The welding operation done by pressure applied with both rollers and applied current.
The another important factor with roller cooling efficient. The huge amount of heat is developed through the rollers, so its required sufficient cooling system, which is increase the life of roller electrodes. The removal of heat from region of the work the special type roller is used. Which is cooling system is provided. After a short period of use the edges of the electrodes require trimming, the trimming operating can not be obtained by filling operation. The trimming or re-shaping operation of copper alloy electrode properly done with lath machining. The another process to reshaping the electrode fit into the roller machine, which have plus point is no material loss happened. The self trimming device is widely used which is which keeps the edge of electrode constantly good condition.
3.Percussion welding:
Principle of percussion welding:
The following steps are involved in percussion welding process—
*The wok-pieces should be cleaned from dirt, grease, paint etc. foreign particles.
*The wok-pieces are clamped rigidly in the machine table.
*Which face to be weld, that brought together face to face and light forces applied.
*The work-piece brought to touch in slightly and established a flow of current. Then electrical arc is produced in the interface of the work-piece.
*At this time light force is applied each other as shown in the picture with arrow sign. After a certain time the switch of the current and hold the job till cool down.
*Applied force is released from both end.
*Work-pieces are unclamped.
*Now work-piece made united.
Application of percussion:
This process contributes itself to a variety of commercial applications, such as butt welding steel or other metals with out flash. Joining the aluminium rods, bars or tubes to copper, steels or non ferrous alloys to corrosion resistance alloys, silver contact finger to copper studs, threaded steel studs to aluminium and satellite tips to steel or non-ferrous shanks.
Percussion welding used in telephone industry for connecting leaded components to the terminals.
4.Projection welding:
Projection welding principle:
The working principle of projection welding is more or less similar of spot welding.
The two surfaces of weld metal are held together in under pressure by the electrodes. When an electrical current flown through the weld electrode, it causes the projecting metals are melts and fuse the both material which is contacted. Thus the weld joint is made.
In single operation a number of joint is made. The joint strength is depend on nature of projection. There are three types of projections are used in projection welding process.
The cone type
The button type
The spherical type
The button type projection is used for joining of thin flat sheet metals (24-13 gauge). The cone type projection is used on 12 to 5 gauge metal sheets. The spherical type projection is used on higher thickness of metal.
Advantages of Projection welding:
*A many number of weld joint can be performed at a time.
*Rust, coating, oil etc. are not affected in this welding process.
*Electrode life is longer than spot welding electrode, because it has lesser wire resistance property.
*It has better heat control for different material composition and thickness.
Projection welding applications:
*In sheet metal welding.
*In ship building works.
*In automobile workshop.
*In refrigeration works.
Solid state welding
1.Friction welding:
The friction welding is one of the solid state welding process, where weld joint is made by heating is created from mechanically induced sliding motion between rubbing surface in under pressure.
The heat is generated by co-efficient of friction of the material. To get a quick heat from surface area, when the rotational speed is high.
Friction welding principle:
In this welding process the fusion is produced by rotating one of the weld parts to be joined against the fixed surface of the other part. Until fusion temperature is obtained in weld parts the rotation of rotating parts will be in high speed and under low pressure. Large amount of pressure will be applied in until both weld parts are welded.
Different types of material can be welding by this process. The materials are-
Carbon steel, alloy steel, copper to carbon steel, copper to aluminium, aluminium and its alloy, brass to bronze, tool steel, stainless steel, stainless steel to aluminium, tungsten, etc.
Friction welding advantages:
*It requires less time operation.
*Operational hazardous is less.
*The characteristic changing of granular structure is less.
*The weld joint may have not heat treated again.
*It has no need of flux, filler. So it is free of smoke, spatter and slag.
*Simplicity of operation.
*Power requirement is less.
Friction welding applications:
*Drill, tap, reamer etc. joining with shank.
*To joining of steering shaft and worm gear, engine valves, power transmission shaft etc.
*To production of bimetallic shaft joining.
*To produce a bimetallic fastener which is used in nuclear plant.
2.Cold welding:
The cold welding process is performed in solid state, where metal joint is produced in the room temperature and also under of mechanical pressure. The joint is made without of filler rod.
The main characteristic of this welding process is total absence of heat and flux.
A specially designed die is used for restricting or controlling the deformation of weld parts. The pressure is applied by manually or with power driven. The amount of pressure is applied on three factor-
1. Nature of surface area of die.
2. Thickness of the metal.
3. Characteristic of material.
Cold welding materials:
Cold welding process is most suitable for welding of non-ferrous metals.
Aluminium and its alloys.
Aluminium to copper.
Copper to its alloys.
Silver to copper or its alloys.
Copper to nickel.
Nickel to iron.
Cold welding applications:
*During the drawing operation of wires, the broken wires are joined by this welding process.
*This welding process is used in electronics industries for joining of small transistors.
*It has specific use in welding metals in explosive areas.
3.Ultrasonic welding:
Ultrasonic is a rate of high frequency method, which is too much high that the note produced lies beyond the range of human hearing. The vibration is the source of energy or frequency.
Ultrasonic welding is a solid state of welding process where joint is produced by the local application of high frequency to the work pieces which are held together under pressure. The average frequency is used in ultrasonic welding is about 20 kHz and lower cases 10 kHz, but in some special circumstances is used high frequency as 170 kHz.
It is a molecular movement process by which the combination of pressure and high vibration. The metallic bonding is carried out in solid state, without applying of heat, filler rod or high pressure.
First only degreasing should require from weld surfaces because, it can not be removed by this welding process. Otherwise the insulation coating, moisture, oxides are split up and removed very easily by ultrasonic high frequency.
Which work pieces to be weld that should be well clamped between the sonotrode tip and anvil. The contacting face of weld tip and anvil is made of HSS or High Speed Steel because of here wear can occur during welding (HSS is the wear resistant metal). The sonotrode and anvil in which surfaces to be contacted with work piece, that should be well surface finish. It is usual to have a slightly radius surface on the sonotrode tip face, the ratio is about 50 to 100 times the thickness of the weld material.
A frequency converter is employed, which is converted the line frequency 50Hz into high frequency electrical power. A transducer attachment converts the electrical frequency into ultrasonic high frequency energy. The high frequency energy transmitted to the weld joint through the welding tip. A coupler is made the bridge between welding tip and transducer. The tip oscillates on the weld joint with the help of some mechanism.
Dynamic shear stresses are generated in-between the metal interface due to the combine application of static load and high frequency. Because of dynamic stress a plastic deformation is occurred at the interface. The surface coating and other surface thin film does not matter for metallic bond.
Advantages of ultrasonic welding-
*It is no need of heat, filler rod or flux, so, it can be avoided the failure with related these problem.
*No surface finish is required.
*It produced minimum deformation of surface finish.
*Very thin material can be weld.
*Different melting temperature metals can be weld without hazard.
*Different cross sectional metal can be joint together.
Applications of ultrasonic welding-
*It is best suited for thin cross sectional metals.
*Welding the electrical and electronics components.
*Welding the sheet and wire of aluminium.
*Nuclear fuel component welding
4.Forge welding:
Forge welding method is oldest welding process. It has an application of the blacksmith’s method of metals joining.
The metals which to be joint are heated in furnace or some other source of heat to the plastic stage or just bellow the molten stage of metals (looks like very bright). Then heated metals are bring on anvil from heat source and superimposed the both metals where to be joint. Apply the hammering or pressed together until a joint has been created.
The applying of heat must be uniformed. Otherwise the joint is made weak or spongy rough appearance. So heat should not be too high or too little.
To avoidance of oxidation a little amount of flux may be used in weld joint.
Low carbon steel and wrought iron components gives satisfactory weld joints.
There are mainly three types of forge welding method is used -
1.Hammer welding.
2. Roll welding.
3. Die welding.
Advantages of forge welding:
If weld joint is made correctly, then it posses very good quality of joint. The strength of the joint is same as base metals.
Radiant energy welding
1.Laser beam welding:
In general cases heat is required to fuse the metals for any types of welding, in laser beam welding process the heat is obtained from the application of a concentrated coherent light beam which striking upon the weld metal and melt the metal, such this weld joint is obtained, this welding process is called laser welding.
In laser beam, the lights are coherent, i.e. light rays are identical and parallel.
The laser device is generates the concentrating light wave into narrowly and gets the highly intense beam which can imparts tremendous amount of heat energy on a small area, this heat energy can fuse the metals, which we are using for welding purpose.
Principle of laser beam welding
A laser beam is produced inside of the Ruby Crystal. The Ruby Crystal is made of aluminium oxide with chromium dispersed throughout it. Which is forming about 1/2000 of crystal, this less than natural ruby. Silver coated mirrors are fitted internally in the both side of crystal. The one side of mirror has a tiny hole, a beam is come out through this hole.
A flash tube is placed around the Ruby Crystal, which is filled with xenon inert gas. The flash is specially designed such as which is made flash rate about thousands flashes per seconds. The electrical energy is converted into light energy, this is worked by flash tube.
The capacitor is provided for storage the electrical energy and supply the high voltage to flash tube for performed appropriately.
The electrical energy discharged from capacitor and xenon transform the high energy into white flash light rate of 1/1000 per second.
The chromium atoms of Ruby Crystal are excited and pumped into high energy. Due to heat generating the some of this energy is lost. But some light energy reflected mirror to mirror and again chromium atoms are excited until loss their extra energy simultaneously to form a narrow beam of coherent light. Which is come out through the one end tiny hole of crystal’s mirror.
This narrow beam is focused by a optical focusing lens to produce a small intense of laser on the job.
Advantage of laser beam welding
*A different type of material can be welded, which material can not be weld by ordinary welding process that also be welded by laser welding process.
*High melting point and hard material can be weld.
*By laser welding process different thickness and different diameter materials are welded.
*Due to its high beam energy both operation welding and cutting can be made very effortlessly.
*This can be used for micro welding purposes.
2.Electron beam welding:
Electron beam welding principle:
In electron beam welding the electron or negative charged particle plays the master role. Which is propelled from a negative pole or cathode to positive pole or anode. This system totally performed in high vacuum. To create a vacuum for minimize the loss of electron flow and increases the electron velocity. To obtain high velocity of electron, it should required increase of voltage. The voltage is directly proportional to electron velocity. High velocity electron means the negative charged particle or electron rapidly passing from cathode point to anode point. In other way heat is directly proportional to electron velocity. So more electron velocity means more heat is obtained.
The work piece worked as a anode and filament is cathode. An electromagnetic coil is used in beam gun for focusing the beam on work piece. The produced heat is sufficient to fuse the metal and such this weld joint made.
Electron beam welding advantages:
*A high quality of weld joint is produced in high speed by this welding process.
*Different thickness of material can be welded easily.
*A precision welding joint is possible.
*Much deeper weld joint is obtained in single run.
*Seam and butt welds can be performed metals as thin as 25µm.
Electron beam welding application:
*It can give same performance as TIG and plasma welding.
*This process is used in joining of reactor components.
*It has large use in spaceship building.
*It is used in automobile engine component welding.
Thermo chemical welding
Thermit welding is a chemically reaction welding process. The weld joint is produced by pouring of superheated molten metal around the joint to be welded, applying with or without of pressure. Thermit welding basically called a mixture of finely divided metal oxide and a metal reducing agent as aluminium.
Thermit welding principle:
The necessary heat for joining metal of thermit welding is obtained from chemical reaction of metal oxide and metal reducing agent. Usually iron oxide is used as a metal oxide and aliminium or magnesium is used as metal reducing agent. The strong chemical attraction of aluminium for oxygen is the basis for thermit process. First the thermit mixture is ignited by a burning magnesium ribbon. The ignited temperature of thermit is about 12000C. When ignited in one spot of mixture, the heat reaction spreads through the mass. The aluminium merging with the oxygen of metal oxide and setting free the iron, which is deposited on joint portion into the mold as a highly superheated liquid metal. If theoretical temperature is about 30000C of thermit, due to chilling effect of crucible the temperature is reduced about 25000C. So it is sufficient for welding temperature.
The thermit reaction is required about thirty second to ignite and it is non-explosive process.
Some chemical reaction:
3Fe3O4 + 8Al → 9Fe + 4Al2O3 (719.3 Kcal)
Fe2O3 + 2Al → 2Fe + Al2O3 (181.5 Kcal)
3MnO + 2Al → 3Mn + Al2O3 (403 Kcal)
3CuO + 2Al → 3Cu + Al2O3 (275.3 Kcal)
Thermit welding application :
*It has large application in railway track repairing on the spot.
*It is used in large frame like locomotive frame welding.
*Thermit welding is used in crank shaft welding.
2.Atomic hydrogen welding:
The atomic hydrogen welding is one kind of arc welding process where welding joint is made by heating the work piece with an arc is maintained between two electrodes and same time a hydrogen steam atmosphere is made in welding zone. This stem of hydrogen gas act as a shielding gas also. A filler rod may or may not be used additionally.
Atomic hydrogen welding principle:
In Atomic hydrogen welding the work piece consist may not part of electrical connection for completing electrical circuit. The arc is produced only between two tungsten electrodes. The molecular hydrogen when passing through the electrical arc and then it is broken into atomic hydrogen form. That time it is absorbed heat energy which is supplied from arc. The arc supplies the energy for chemical reaction.
These hydrogen atoms recombine again to form of molecular stage. This recombination take place in the comparatively lower temperature zone as outer zone of arc. This time it releases extra amount of heat energy. This extra heat is added with main arc temperature and it produces much amount of heat, which is utilized for welding purposes. This combine heat is concentrated at high temperature in the small volume of arc.
Atomic hydrogen welding advantages:
*No flux or any kind of shielding gas is required for this welding process.
*Due to high concentration of heat, it can carried out high rate of fusion.
*A uniform and strong weld joint can be produced.
some more information:
Weld symbols:
The weld symbol is providing in drawing for the information concerning the types of welding, size, position etc. of welds in welded joint.
It is specifying the each type of weld.
The weld symbol is providing in drawing for the information concerning the types of welding, size, position etc. of welds in welded joint.
It is specifying the each type of weld.
Published by Ravindra,Mechanical
Question for readers:
How do we welding in underground water?
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