COIN SEPARATOR

FABRICATION OF COIN SEPARATOR

SYNOPSIS

In this project we are designed in coin separator. It is separate the different coin in the various trays by using cam method. The operation of coin separator is performed by using by an A.C motor cam mechanism and coin separator tray arrangement. The coin is held at a Hooper which is fixed to the top of the tray. The every tray is having different diameter of holes depends upon the coin diameter. Cam shaft, Ac motor and Coin separator

WORKING PRINCIPLE

In this project we are designed in coin separator. It is separate the different coin in the various trays by using cam method. The operation of coin separator is performed by using by an A.C motor cam mechanism and coin separator tray arrangement. The coin is held at a Hooper which is fixed to the top of the tray. The every tray is having different diameter of holes depends upon the coin diameter. We are put the different coin on the top of tray and to start the motor to rotate the cam by rotating the cam the tray is move towards the forward and reverse direction with the help of shaft witch is connected on the cam. And the coin is separated by the separate arrangement.

ADVANTAGES Simple construction

It is portable

It can be transferred to easily one place to another place

Maintenance cost is low

DISADVANTAGES Additional cost is required to do automation

It is produces small noise

APPLICATIONS

It is very useful in trupathi temple

It is also useful in Transport Corporation and all markets

DRAWING FOR FABRICATION OF COIN SEPARATOR

CAM MECHANISM:

Acamis a rotating or sliding piece in amechanical linkageused especially in transforming rotary motion into linear motion or vice-versa.[1]

HYPERLINK "http://en.wikipedia.org/wiki/Cam" \l "cite_note-2" [2]It is often a part of a rotatingwheel(e.g. an eccentric wheel) or shaft (e.g. a cylinder with an irregular shape) that strikes aleverat one or more points on its circular path. The cam can be a simple tooth, as is used to deliver pulses of power to asteam hammer, for example, or aneccentricdisc or other shape that produces a smooth reciprocating (back and forth) motion in thefollower, which is a lever making contact with the cam. OverviewThe cam can be seen as a device that rotates from circular to reciprocating (or sometimes oscillating) motion.[3]A common example is thecamshaftof anautomobile, which takes the rotary motion of the engine and translates it into the reciprocating motion necessary to operate the intake and exhaustvalvesof thecylinders.

Cams can also be viewed as information-storing and -transmitting devices. Examples are the cam-drums that direct the notes of amusical boxor the movements of ascrew machine's various tools and chucks. The information stored and transmitted by the cam is the answer to the question, "What actions should happen, and when?" (Even an automotive camshaft essentially answers that question, although the music box cam is a still-better example in illustrating this concept.)Displacement diagram

Fig. 2 Basic displacement diagram

Certain cams can be characterized by their displacement diagrams, which reflect the changing position a roller follower (a shaft with a rotating wheel at the end) would make as the cam rotates about an axis. These diagrams relate angular position, usually in degrees, to the radial displacement experienced at that position. Displacement diagrams are traditionally presented as graphs with non-negative values. A simple displacement diagram illustrates the follower motion at a constant velocity rise followed by a similar return with a dwell in between as depicted in figure 2.[4]The rise is the motion of the follower away from the cam center, dwell is the motion where the follower is at rest, and return is the motion of the follower toward the cam center.[5]Plate cam

Fig. 3 Cam Profile

The most commonly used cam is the plate cam which is cut out of a piece of flat metal or plate.[6]Here, the follower moves in a plane perpendicular to the axis of rotation of the camshaft.[7]Several key terms are relevant in such a construction of plate cams:base circle, prime circle (withradiusequal to the sum of the follower radius and the base circle radius), pitch curve which is the radial curve traced out by applying the radial displacements away from the prime circle across all angles, and the lobe separation angle (LSA- the angle between two adjacent intake and exhaust cam lobes).

The base circle is the smallest circle that can be drawn to the cam profile.HistoryAn early cam was built intoHellenisticwater-drivenautomatafrom the 3rd century BC.[8]The use of cams was later employed byAl-Jazariwho employed them in his own automata.[9]The cam and camshaft appeared in European mechanisms from the 14th centuryBasic Motor Theory

Introduction

It has been said that if the Ancient Romans, with their advanced civilization and knowledge of the sciences, had been able to develop a steam motor, the course of history would have been much different. The development of the electric motor in modern times has indicated the truth in this theory. The development of the electric motor has given us the most efficient and effective means to do work known to man. Because of the electric motor we have been able to greatly reduce the painstaking toil of man's survival and have been able to build a civilization which is now reaching to the stars. The electric motor is a simple device in principle. It converts electric energy into mechanical energy. Over the years, electric motors have changed substantially in design, however the basic principles have remained the same. In this section of the Action Guide we will discuss these basic motor principles. We will discuss the phenomena of magnetism, AC current and basic motor operation.

Magnetism

Now, before we discuss basic motor operation a short review of magnetism might be helpful to many of us. We all know that a permanent magnet will attract and hold metal objects when the object is near or in contact with the magnet. The permanent magnet is able to do this because of its inherent magnetic force which is referred to as a "magnetic field". In Figure 1 , the magnetic field of two permanent magnets are represented by "lines of flux". These lines of flux help us to visualize the magnetic field of any magnet even though they only represent an invisible phenomena. The number of lines of flux vary from one magnetic field to another. The stronger the magnetic field, the greater the number of lines of flux which are drawn to represent the magnetic field. The lines of flux are drawn with a direction indicated since we should visualize these lines and the magnetic field they represent as having a distinct movement from a N-pole to a S-pole as shown in Figure 1. Another but similar type of magnetic field is produced around an electrical conductor when an electric current is passed through the conductor as shown in Figure 2-a. These lines of flux define the magnetic field and are in the form of concentric circles around the wire. Some of you may remember the old "Left Hand Rule" as shown in Figure 2-b. The rule states that if you point the thumb of your left hand in the direction of the current, your fingers will point in the direction of the magnetic field.

Figure 1 - The lines of flux of a magnetic field travel from the N-pole to the S-pole.Figure 2 - The flow of electrical current in a conductor sets up concentric lines of magnetic flux around the conductor.Figure 3 - The magnetic lines around a current carrying conductor leave from the N-pole and re-enter at the S-pole.

When the wire is shaped into a coil as shown in Figure 3, all the individual flux lines produced by each section of wire join together to form one large magnetic field around the total coil. As with the permanent magnet, these flux lines leave the north of the coil and re-enter the coil at its south pole. The magnetic field of a wire coil is much greater and more localized than the magnetic field around the plain conductor before being formed into a coil. This magnetic field around the coil can be strengthened even more by placing a core of iron or similar metal in the center of the core. The metal core presents less resistance to the lines of flux than the air, thereby causing the field strength to increase. (This is exactly how a stator coil is made; a coil of wire with a steel core.) The advantage of a magnetic field which is produced by a current carrying coil of wire is that when the current is reversed in direction the poles of the magnetic field will switch positions since the lines of flux have changed direction. This phenomenon is illustrated in Figure 4. Without this magnetic phenomenon existing, the AC motor as we know it today would not exist.

Figure 4 - The poles of an electro-magnetic coil change when the direction of current flow changes.Magnetic Propulsion Within A Motor

The basic principle of all motors can easily be shown using two electromagnets and a permanent magnet. Current is passed through coil no. 1 in such a direction that a north pole is established and through coil no. 2 in such a direction that a south pole is established. A permanent magnet with a north and south pole is the moving part of this simple motor. In Figure 5-a the north pole of the permanent magnet is opposite the north pole of the electromagnet. Similarly, the south poles are opposite each other. Like magnetic poles repel each other, causing the movable permanent magnet to begin to turn. After it turns part way around, the force of attraction between the unlike poles becomes strong enough to keep the permanent magnet rotating. The rotating magnet continues to turn until the unlike poles are lined up. At this point the rotor would normally stop because of the attraction between the unlike poles. (Figure 5-b)

Figure 5If, however, the direction of currents in the electromagnetic coils was suddenly reversed, thereby reversing the polarity of the two coils, then the poles would again be opposites and repel each other. (Figure 5-c). The movable permanent magnet would then continue to rotate. If the current direction in the electromagnetic coils was changed every time the magnet turned 180 degrees or halfway around,then the magnet would continue to rotate. This simple device is a motor in its simplest form. An actual motor is more complex than the simple device shown above, but the principle is the same.

AC Current

How is the current reversed in the coil so as to change the coils polarity, you ask. Well, as you probably know, the difference between DC and AC is that with DC the current flows in only one direction while with AC the direction of current flow changes periodically. In the case of common AC that is used throughout most of the United States, the current flow changes direction 120 times every second. This current is referred to as "60 cycle AC" or "60 Hertz AC" in honor of Mr. Hertz who first conceived the AC current concept. Another characteristic of current flow is that it can vary in quantity. We can have a 5 amp, 10 amp or 100 amp flow for instance. With pure DC, this means that the current flow is actually 5,10, or 100 amps on a continuous basis. We can visualize this on a simple time-current graph by a straight line as shown in Figure 6.

Figure 6 - Visualization of DCBut with AC it is different. As you can well imagine, it would be rather difficult for the current to be flowing at say 100 amps in a positive direction one moment and then at the next moment be flowing at an equal intensity in the negative direction. Instead, as the current is getting ready to change directions, it first tapers off until it reaches zero flow and then gradually builds up in the other direction. See Figure 7. Note that the maximum current flow (the peaks of the line) in each direction is more than the specified value (100 amps in this case). Therefore, the specified value is given as an average. It is actually called a "root mean square" value, but don't worry about remembering this because it is of no importance to us at this time. What is important in our study of motors, is to realize that the strength of the magnetic field produced by an AC electro-magnetic coil increases and decreases with the increase and decrease of this alternating current flow.

Figure 7 - Visualization of AC.Basic AC Motor Operation

An AC motor has two basic electrical parts: a "stator" and a "rotor" as shown in Figure 8. The stator is in the stationary electrical component. It consists of a group of individual electro-magnets arranged in such a way that they form a hollow cylinder, with one pole of each magnet facing toward the center of the group. The term, "stator" is derived from the word stationary. The stator then is the stationary part of the motor. The rotor is the rotating electrical component. It also consists of a group of electro-magnets arranged around a cylinder, with the poles facing toward the stator poles. The rotor, obviously, is located inside the stator and is mounted on the motor's shaft. The term "rotor" is derived from the word rotating. The rotor then is the rotating part of the motor. The objective of these motor components is to make the rotor rotate which in turn will rotate the motor shaft. This rotation will occur because of the previously discussed magnetic phenomenon that unlike magnetic poles attract each other and like poles repel. If we progressively change the polarity of the stator poles in such a way that their combined magnetic field rotates, then the rotor will follow and rotate with the magnetic field of the stator.

Figure 8 - Basic electrical components of an AC motor.This "rotating magnetic fields of the stator can be better understood by examining Figure 9. As shown, the stator has six magnetic poles and the rotor has two poles. At time 1, stator poles A-1 and C-2 are north poles and the opposite poles, A-2 and C-1, are south poles. The S-pole of the rotor is attracted by the two N-poles of the stator and the N-pole of the rotor is attracted by the two south poles of the stator. At time 2, the polarity of the stator poles is changed so that now C-2 and B-1 and N-poles and C-1 and B-2 are S-poles. The rotor then is forced to rotate 60 degrees to line up with the stator poles as shown. At time 3, B-1 and A-2 are N. At time 4, A-2 and C-1 are N. As each change is made, the poles of the rotor are attracted by the opposite poles on the stator. Thus, as the magnetic field of the stator rotates, the rotor is forced to rotate with it.

Figure 9 - The rotating magnetic field of an AC motor.One way to produce a rotating magnetic field in the stator of an AC motor is to use a three-phase power supply for the stator coils. What, you may ask, is three-phase power? The answer to that question can be better understood if we first examine single-phase power. Figure 7 is the visualization of single-phase power. The associated AC generator is producing just one flow of electrical current whose direction and intensity varies as indicated by the single solid line on the graph. From time 0 to time 3, current is flowing in the conductor in the positive direction. From time 3 to time 6, current is flowing in the negative. At any one time, the current is only flowing in one direction. But some generators produce three separate current flows (phases) all superimposed on the same circuit. This is referred to as three-phase power. At any one instant, however, the direction and intensity of each separate current flow are not the same as the other phases. This is illustrated in Figure 10. The three separate phases (current flows) are labeled A, B and C. At time 1, phase A is at zero amps, phase B is near its maximum amperage and flowing in the positive direction, and phase C is near to its maximum amperage but flowing in the negative direction. At time 2, the amperage of phase A is increasing and flow is positive, the amperage of phase B is decreasing and its flow is still negative, and phase C has dropped to zero amps. A complete cycle (from zero to maximum in one direction, to zero and to maximum in the other direction, and back to zero) takes one complete revolution of the generator. Therefore, a complete cycle, is said to have 360 electrical degrees. In examining Figure 10, we see that each phase is displaced 120 degrees from the other two phases. Therefore, we say they are 120 degrees out of phase.

Figure 10 - The pattern of the separate phases of three-phase power.To produce a rotating magnetic field in the stator of a three-phase AC motor, all that needs to be done is wind the stator coils properly and connect the power supply leads correctly. The connection for a 6 pole stator is shown in Figure 11. Each phase of the three-phase power supply is connected to opposite poles and the associated coils are wound in the same direction. As you will recall from Figure 4, the polarity of the poles of an electro-magnet are determined by the direction of the current flow through the coil. Therefore, if two opposite stator electro-magnets are wound in the same direction, the polarity of the facing poles must be opposite. Therefore, when pole A1 is N, pole A2 is S. When pole B1 is N, B2 is S and so forth.

Figure 11 - Method of connecting three-phase power to a six-pole stator.Figure 12 shows how the rotating magnetic field is produced. At time1, the current flow in the phase "A" poles is positive and pole A-1 is N. The current flow in the phase "C" poles is negative, making C-2 a N-pole and C-1 is S. There is no current flow in phase "B", so these poles are not magnetized. At time 2, the phases have shifted 60 degrees, making poles C-2 and B-1 both N and C-1 and B-2 both S. Thus, as the phases shift their current flow, the resultant N and S poles move clockwise around the stator, producing a rotating magnetic field. The rotor acts like a bar magnet, being pulled along by the rotating magnetic field.

Figure 12 - How three-phase power produces a rotating magnetic field.Up to this point not much has been said about the rotor. In the previous examples, it has been assumed the rotor poles were wound with coils, just as the stator poles, and supplied with DC to create fixed polarity poles. This, by the way, is exactly how a synchronous AC motor works. However, most AC motors being used today are not synchronous motors. Instead, so-called "induction" motors are the workhorses of industry. So how is an induction motor different? The big difference is the manner in which current is supplied to the rotor. This is no external power supply. As you might imagine from the motor's name, an induction technique is used instead. Induction is another characteristic of magnetism. It is a natural phenomena which occurs when a conductor (aluminum bars in the case of a rotor, see Figure 13) is moved through an existing magnetic field or when a magnetic field is moved past a conductor. In either case, the relative motion of the two causes an electric current to flow in the conductor. This is referred to as "induced" current flow. In other words, in an induction motor the current flow in the rotor is not caused by any direct connection of the conductors to a voltage source, but rather by the influence of the rotor conductors cutting across the lines of flux produced by the stator magnetic fields. The induced current which is produced in the rotor results in a magnetic field around the rotor conductors as shown in Figure 14. This magnetic field around each rotor conductor will cause each rotor conductor to act like the permanent magnet in the Figure 9 example. As the magnetic field of the stator rotates, due to the effect of the three-phase AC power supply, the induced magnetic field of the rotor will be attracted and will follow the rotation. The rotor is connected to the motor shaft, so the shaft will rotate and drive the connection load. That's how a motor works! Simple, was it not?

Figure 13 - Construction of an AC induction motor's rotor.

Figure 14 - How voltage is induced in the rotor, resulting in current flow in the rotor conductors.MILED STEEL:

Mild steelis a type ofsteelthat only contains a small amount ofcarbonand other elements. It is softer and more easily shaped than higher carbon steels. It also bends a long way instead of breaking because it is ductile. It is used innailsand some types ofwire, it can be used to make bottle openers, chairs, staplers, staples, railings and most common metal products. Its name comes from the fact it only has less carbon than steel.

Some mild steel properties and uses:

Mild steel has a maximum limit of 0.2% carbon. The proportions of manganese (1.65%), copper (0.6%) and silicon (0.6%) are approximately fixed, while the proportions of cobalt, chromium, niobium, molybdenum, titanium, nickel, tungsten, vanadium and zirconium are not.

A higher amount of carbon makes steels different from low carbon mild-type steels. A greater amount of carbon makes steel stronger, harder and very slightly stiffer than a low carbon steel. However, the strength and hardness comes at the price of a decrease in the ductility of this alloy. Carbon atoms get trapped in the interstitial sites of the iron lattice and make it stronger.

What is known as mildest grade of carbon steel or 'mild steel' is typically low carbon steel with a comparatively low amount of carbon (0.16% to 0.2%). It hasferromagneticproperties, which make it ideal for manufacture of many products.

The calculated average industry grade mild steel density is 7.85 gm/cm3. Its Young's modulus, which is a measure of its stiffness is around 210,000 MPa.

Mild steel is the cheapest and most versatile form of steel and serves every application which requires a bulk amount of steel.

The low amount of alloying elements also makes mild steel vulnerable to rust. Naturally, people prefer stainless steel over mild steel, when they want a rust free material. Mild steel is also used in construction as structural steel. It is also widely used in the car manufacturing industry.

Mild steel is used in almost all forms of industrial applications and industrial manufacturing. It is a cheaper alternative to steel, but still better than iron.

WELDING:

Weldingis afabricationorsculpturalprocessthat joins materials, usuallymetalsorthermoplastics, by causingcoalescence. This is often done bymeltingthe workpieces and adding a filler material to form a pool of molten material (theweld pool) that cools to become a strong joint, withpressuresometimes used in conjunction withheat, or by itself, to produce the weld. This is in contrast withsolderingandbrazing, which involve melting a lower-melting-point material between the workpieces to form a bond between them, without melting the workpieces.

Many differentenergy sourcescan be used for welding, including a gasflame, anelectric arc, alaser, anelectron beam,friction, andultrasound. While often an industrial process, welding may be performed in many different environments, including open air,under waterand inouter space. Welding is a potentially hazardous undertaking and precautions are required to avoidburns,electric shock, vision damage, inhalation of poisonous gases and fumes, and exposure tointense ultraviolet radiation.

Until the end of the 19th century, the only welding process wasforge welding, whichblacksmithshad used for centuries to join iron and steel by heating and hammering.Arc weldingandoxyfuel weldingwere among the first processes to develop late in the century, andelectric resistance weldingfollowed 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 likeshielded metal arc welding, now one of the most popular welding methods, as well as semi-automatic and automatic processes such asgas metal arc welding,submerged arc welding,flux-cored arc weldingandelectroslag welding. Developments continued with the invention oflaser beam welding, electron beam welding,electromagnetic pulse weldingandfriction stir weldingin the latter half of the century. Today, the science continues to advance.Robot weldingis commonplace in industrial settings, and researchers continue to develop new welding methods and gain greater understanding of weld quality.

ProcessesArcMain article:Arc weldingThese processes use awelding power supplyto create and maintain an electric arc between an electrode and the base material to melt metals at the welding point. They can use eitherdirect(DC) or alternating (AC) current, and consumable or non-consumableelectrodes. The welding region is sometimes protected by some type of inert or semi-inert gas, known as a shielding gas, and filler material is sometimes used as well.

Power suppliesTo supply the electrical energy necessary for arc welding processes, a number of different power supplies can be used. The most common welding power supplies are constantcurrentpower supplies and constantvoltagepower supplies. In arc welding, the length of the arc is directly related to the voltage, and the amount of heat input is related to the current. Constant current power supplies are most often used for manual welding processes such as gas tungsten arc welding and shielded metal arc welding, because they maintain a relatively constant current even as the voltage varies. This is important because in manual welding, it can be difficult to hold the electrode perfectly steady, and as a result, the arc length and thus voltage tend to fluctuate. Constant voltage power supplies hold the voltage constant and vary the current, and as a result, are most often used for automated welding processes such as gas metal arc welding, flux cored arc welding, and submerged arc welding. In these processes, arc length is kept constant, since any fluctuation in the distance between the wire and the base material is quickly rectified by a large change in current. For example, if the wire and the base material get too close, the current will rapidly increase, which in turn causes the heat to increase and the tip of the wire to melt, returning it to its original separation distance.[1]The type of current used also plays an important role in arc welding. Consumable electrode processes such as shielded metal arc welding and gas metal arc welding generally use direct current, but the electrode can be charged either positively or negatively. In welding, the positively chargedanodewill have a greater heat concentration, and as a result, changing the polarity of the electrode has an impact on weld properties. If the electrode is positively charged, the base metal will be hotter, increasing weld penetration and welding speed. Alternatively, a negatively charged electrode results in more shallow welds.[2]Nonconsumable electrode processes, such as gas tungsten arc welding, can use either type of direct current, as well as alternating current. However, with direct current, because the electrode only creates the arc and does not provide filler material, a positively charged electrode causes shallow welds, while a negatively charged electrode makes deeper welds.[3]Alternating current rapidly moves between these two, resulting in medium-penetration welds. One disadvantage of AC, the fact that the arc must be re-ignited after every zero crossing, has been addressed with the invention of special power units that produce asquare wavepattern instead of the normalsine wave, making rapid zero crossings possible and minimizing the effects of the problem.[4]ProcessesOne of the most common types of arc welding isshielded metal arc welding(SMAW);[5]it is also known as manual metal arc welding (MMA) or stick welding. Electric current is used to strike an arc between the base material and consumable electrode rod, which is made of filler material (typically steel) and is covered with a flux that protects the weld area fromoxidationand contamination by producingcarbon dioxide(CO2) gas during the welding process. The electrode core itself acts as filler material, making a separate filler unnecessary.[5]

Shielded metal arc welding

The process is versatile and can be performed with relatively inexpensive equipment, making it well suited to shop jobs and field work.[5]

HYPERLINK "http://en.wikipedia.org/wiki/Welding" \l "cite_note-Cary103-6" [6]An operator can become reasonably proficient with a modest amount of training and can achieve mastery with experience. Weld times are rather slow, since the consumable electrodes must be frequently replaced and because slag, the residue from the flux, must be chipped away after welding.[5]Furthermore, the process is generally limited to welding ferrous materials, though special electrodes have made possible the welding ofcast iron,nickel, aluminum,copper, and other metals.[6]Gas metal arc welding(GMAW), also known as metal inert gas or MIG welding, is a semi-automatic or automatic process that uses a continuous wire feed as an electrode and an inert or semi-inert gas mixture to protect the weld from contamination. Since the electrode is continuous, welding speeds are greater for GMAW than for SMAW.[7]A related process,flux-cored arc welding(FCAW), uses similar equipment but uses wire consisting of a steel electrode surrounding a powder fill material. This cored wire is more expensive than the standard solid wire and can generate fumes and/or slag, but it permits even higher welding speed and greater metal penetration.[8]Gas tungsten arc welding(GTAW), or tungsten inert gas (TIG) welding, is a manual welding process that uses a nonconsumabletungstenelectrode, an inert or semi-inert gas mixture, and a separate filler material.[9]Especially useful for welding thin materials, this method is characterized by a stable arc and high quality welds, but it requires significant operator skill and can only be accomplished at relatively low speeds.[9]GTAW can be used on nearly all weldable metals, though it is most often applied tostainless steeland light metals. It is often used when quality welds are extremely important, such as inbicycle, aircraft and naval applications.[9]A related process, plasma arc welding, also uses a tungsten electrode but uses plasma gas to make the arc. The arc is more concentrated than the GTAW arc, making transverse control more critical and thus generally restricting the technique to a mechanized process. Because of its stable current, the method can be used on a wider range of material thicknesses than can the GTAW process and it is much faster. It can be applied to all of the same materials as GTAW except magnesium, and automated welding of stainless steel is one important application of the process. A variation of the process isplasma cutting, an efficient steel cutting process.[10]Submerged arc welding(SAW) is a high-productivity welding method in which the arc is struck beneath a covering layer of flux. This increases arc quality, since contaminants in the atmosphere are blocked by the flux. The slag that forms on the weld generally comes off by itself, and combined with the use of a continuous wire feed, the weld deposition rate is high. Working conditions are much improved over other arc welding processes, since the flux hides the arc and almost no smoke is produced. The process is commonly used in industry, especially for large products and in the manufacture of welded pressure vessels.[11]Other arc welding processes includeatomic hydrogen welding,electroslag welding,electrogas welding, andstud arc welding.[12]Gas weldingMain article:Oxy-fuel welding and cuttingThe most common gas welding process is oxyfuel welding,[13]also known as oxyacetylene welding. It is one of the oldest and most versatile welding processes, but in recent years it has become less popular in industrial applications. It is still widely used for welding pipes and tubes, as well as repair work.[13]The equipment is relatively inexpensive and simple, generally employing the combustion of acetylene inoxygento produce a welding flame temperature of about 3100 C.[13]The flame, since it is less concentrated than an electric arc, causes slower weld cooling, which can lead to greater residual stresses and weld distortion, though it eases the welding of high alloy steels. A similar process, generally called oxyfuel cutting, is used to cut metals.[13]ResistanceMain article:Resistance weldingResistance welding involves the generation of heat by passing current through the resistance caused by the contact between two or more metal surfaces. Small pools of molten metal are formed at the weld area as high current (1000100,000A) is passed through the metal.[14]In general, resistance welding methods are efficient and cause little pollution, but their applications are somewhat limited and the equipment cost can be high.[14]

Spot welder

Spot weldingis a popular resistance welding method used to join overlapping metal sheets of up to 3mm thick.[14]Two electrodes are simultaneously used to clamp the metal sheets together and to pass current through the sheets. The advantages of the method includeefficient energy use, limited workpiece deformation, high production rates, easy automation, and no required filler materials. Weld strength is significantly lower than with other welding methods, making the process suitable for only certain applications. It is used extensively in the automotive industryordinary cars can have several thousand spot welds made byindustrial robots. A specialized process, calledshot welding, can be used to spot weld stainless steel.[14]Like spot welding,seam weldingrelies on two electrodes to apply pressure and current to join metal sheets. However, instead of pointed electrodes, wheel-shaped electrodes roll along and often feed the workpiece, making it possible to make long continuous welds. In the past, this process was used in the manufacture of beverage cans, but now its uses are more limited.[14]Other resistance welding methods includebutt welding,[15]flash welding,projection welding, andupset welding.[14]Energy beamEnergy beam welding methods, namelylaser beam weldingandelectron beam welding, are relatively new processes that have become quite popular in high production applications. The two processes are quite similar, differing most notably in their source of power. Laser beam welding employs a highly focused laser beam, while electron beam welding is done in a vacuum and uses an electron beam. Both have a very high energy density, making deep weld penetration possible and minimizing the size of the weld area. Both processes are extremely fast, and are easily automated, making them highly productive. The primary disadvantages are their very high equipment costs (though these are decreasing) and a susceptibility to thermal cracking. Developments in this area includelaser-hybrid welding, which uses principles from both laser beam welding and arc welding for even better weld properties,laser claddingandX-ray welding.[16]Solid-state

Solid-state welding processes classification chart[17]Like the first welding process, forge welding, some modern welding methods do not involve the melting of the materials being joined. One of the most popular,ultrasonic welding, is used to connect thin sheets or wires made of metal or thermoplastic by vibrating them at high frequency and under high pressure.[18]The equipment and methods involved are similar to that of resistance welding, but instead of electric current, vibration provides energy input. Welding metals with this process does not involve melting the materials; instead, the weld is formed by introducing mechanical vibrations horizontally under pressure. When welding plastics, the materials should have similar melting temperatures, and the vibrations are introduced vertically. Ultrasonic welding is commonly used for making electrical connections out of aluminum or copper, and it is also a very common polymer welding process.[18]Another common process,explosion welding, involves the joining of materials by pushing them together under extremely high pressure. The energy from the impact plasticizes the materials, forming a weld, even though only a limited amount of heat is generated. The process is commonly used for welding dissimilar materials, such as the welding of aluminum with steel in ship hulls or compound plates.[18]Other solid-state welding processes includefriction welding(includingfriction stir welding),[19]electromagnetic pulse welding,[20]co-extrusion welding,cold welding, diffusion welding,exothermic welding,high frequency welding,hot pressure welding,induction welding, androll welding.[18][GeometryMain article:Welding joints

Common welding joint types (1) Square butt joint, (2) V butt joint, (3) Lap joint, (4) T-joint

Welds can be geometrically prepared in many different ways. The five basic types of weld joints are the butt joint, lap joint, corner joint, edge joint, and T-joint (a variant of this last is thecruciform joint). Other variations exist as wellfor example, double-V preparation joints are characterized by the two pieces of material each tapering to a single center point at one-half their height. Single-U and double-U preparation joints are also fairly commoninstead of having straight edges like the single-V and double-V preparation joints, they are curved, forming the shape of a U. Lap joints are also commonly more than two pieces thickdepending on the process used and the thickness of the material, many pieces can be welded together in a lap joint geometry.[21]Many welding processes require the use of a particular joint design; for example, resistance spot welding, laser beam welding, and electron beam welding are most frequently performed on lap joints. Other welding methods, like shielded metal arc welding, are extremely versatile and can weld virtually any type of joint. Some processes can also be used to make multipass welds, in which one weld is allowed to cool, and then another weld is performed on top of it. This allows for the welding of thick sections arranged in a single-V preparation joint, for example.[22]

The cross-section of a welded butt joint, with the darkest gray representing the weld or fusion zone, the medium gray the heat-affected zone, and the lightest gray the base material.

After welding, a number of distinct regions can be identified in the weld area. The weld itself is called the fusion zonemore specifically, it is where the filler metal was laid during the welding process. The properties of the fusion zone depend primarily on the filler metal used, and its compatibility with the base materials. It is surrounded by theheat-affected zone, the area that had its microstructure and properties altered by the weld. These properties depend on the base material's behavior when subjected to heat. The metal in this area is often weaker than both the base material and the fusion zone, and is also where residual stresses are found.[23]QualityMain article:Weld quality assurance

The blue area results from oxidation at a corresponding temperature of600 F(316C). This is an accurate way to identify temperature, but does not represent the HAZ width. The HAZ is the narrow area that immediately surrounds the welded base metal.

Many distinct factors influence the strength of welds and the material around them, including the welding method, the amount and concentration of energy input, theweldabilityof the base material, filler material, and flux material, the design of the joint, and the interactions between all these factors.[24]To test the quality of a weld, eitherdestructiveornondestructive testingmethods are commonly used to verify that welds are free of defects, have acceptable levels of residual stresses and distortion, and have acceptable heat-affected zone (HAZ) properties. Types ofwelding defectsinclude cracks, distortion, gas inclusions (porosity), non-metallic inclusions, lack of fusion, incomplete penetration, lamellar tearing, and undercutting. Welding codes and specifications exist to guide welders in proper welding technique and in how to judge the quality of welds.[24]Methods such asvisual inspection,radiography,ultrasonic testing,dye penetrant inspection,Magnetic-particle inspectionorindustrial CT scanningcan help with detection and analysis of certain defects.

Heat-affected zoneThe effects of welding on the material surrounding the weld can be detrimentaldepending on the materials used and the heat input of the welding process used, the HAZ can be of varying size and strength. Thethermal diffusivityof the base material plays a large roleif the diffusivity is high, the material cooling rate is high and the HAZ is relatively small. Conversely, a low diffusivity leads to slower cooling and a larger HAZ. The amount of heat injected by the welding process plays an important role as well, as processes like oxyacetylene welding have an unconcentrated heat input and increase the size of the HAZ. Processes like laser beam welding give a highly concentrated, limited amount of heat, resulting in a small HAZ. Arc welding falls between these two extremes, with the individual processes varying somewhat in heat input.[25]

HYPERLINK "http://en.wikipedia.org/wiki/Welding" \l "cite_note-26" [26]To calculate the heat input for arc welding procedures, the following formula can be used:

whereQ= heat input (kJ/mm),V= voltage (V),I= current (A), andS= welding speed (mm/min). The efficiency is dependent on the welding process used, with shielded metal arc welding having a value of 0.75, gas metal arc welding and submerged arc welding, 0.9, and gas tungsten arc welding, 0.8.[27]Lifetime extension with aftertreatment methods

Example: High Frequency Impact Treatment for lifetime extension

The durability and life of dynamically loaded, welded steel structures is determined in many cases by the welds, particular the weld transitions. Through selective treatment of the transitions bygrinding (abrasive cutting),shot peening,High Frequency Impact Treatmentetc. the durability of many designs increase significantly.

MetallurgyMost solids used are engineering materials consisting of crystalline solids in which the atoms or ions are arranged in a repetitive geometric pattern which is known as alattice structure. The only exception is material that is made from glass which is a combination of a supercooled liquid and polymers which are aggregates of large organic molecules.[28]Crystalline solids cohesion is obtained by a metallic or chemical bond which is formed between the constituent atoms. Chemical bonds can be grouped into two types consisting ofionicandcovalent. To form an ionic bond, either avalenceorbondingelectron separates from one atom and becomes attached to another atom to form oppositely chargedions. The bonding in the static position is when the ions occupy an equilibrium position where the resulting force between them is zero. When the ions are exerted intensionforce, the inter-ionic spacing increases creating an electrostatic attractive force, while a repulsing force undercompressiveforce between the atomic nuclei is dominant.[28]Covalent bonding is when the constituent atoms lose an electron(s) to form a cluster of ions, resulting in an electron cloud that is shared by the molecule as a whole. In both ionic and covalent boding the location of the ions and electrons are constrained relative to each other, thereby resulting in the bond being characteristicallybrittle.[28]Metallic bondingcan be classified as a type of covalent bonding for which the constituent atoms of the same type and do not combine with one another to form a chemical bond. Atoms will lose an electron(s) forming an array of positive ions. These electrons are shared by the lattice which makes the electron cluster mobile, as the electrons are free to move as well as the ions. For this, it gives metals their relatively high thermal and electrical conductivity as well as being characteristicallyductile.[28]Three of the most commonly used crystal lattice structures in metals are thebody-centred cubic,face-centred cubicandclose-packed hexagonal. Ferriticsteelhas a body-centred cubic structure andaustenitic steel,non-ferrous metalslikealuminium,copperandnickelhave the face-centred cubic structure.[28]Ductility is an important factor in ensuring the integrity of structures by enabling them to sustain local stress concentrations without fracture. In addition, structures are required to be of an acceptable strength, which is related to a material'syield strength. In general, as the yield strength of a material increases, there is a corresponding reduction infracture toughness.[28]A reduction in fracture toughness may also be attributed to the embitterment effect of impurities, or for body-centred cubic metals, from a reduction in temperature. Metals and in particular steels have a transitional temperature range where above this range the metal has acceptable notch-ductility while below this range the material becomes brittle. Within the range, the materials behavior is unpredictable. The reduction in fracture toughness is accompanied by a change in the fracture appearance. When above the transition, the fracture is primarily due to micro-void coalescence, which results in the fracture appearingfibrous. When the temperatures falls the fracture will show signs of cleavage facets. These two appearances are visible by the naked eye. Brittle fracture in steel plates may appear as chevron markings under themicroscope. These arrow-like ridges on the crack surface point towards the origin of the fracture.[28]Fracture toughness is measured using a notched and pre-cracked rectangular specimen, of which the dimensions are specified in standards, for example ASTM E23. There are other means of estimating or measuring fracture toughness by the following: The Charpy impact test per ASTM A370; The crack-tip opening displacement (CTOD) test per BS 7448-1; The J integral test per ASTM E1820; The Pellini drop-weight test per ASTM E208.[28]Unusual conditions

Underwater welding

While many welding applications are done in controlled environments such as factories and repair shops, some welding processes are commonly used in a wide variety of conditions, such as open air, underwater, andvacuums(such as space). In open-air applications, such as construction and outdoors repair, shielded metal arc welding is the most common process. Processes that employ inert gases to protect the weld cannot be readily used in such situations, because unpredictable atmospheric movements can result in a faulty weld. Shielded metal arc welding is also often used in underwater welding in the construction and repair of ships, offshore platforms, and pipelines, but others, such as flux cored arc welding and gas tungsten arc welding, are also common. Welding in space is also possibleit was first attempted in 1969 byRussiancosmonauts, when they performed experiments to test shielded metal arc welding, plasma arc welding, and electron beam welding in a depressurized environment. Further testing of these methods was done in the following decades, and today researchers continue to develop methods for using other welding processes in space, such as laser beam welding, resistance welding, and friction welding. Advances in these areas may be useful for future endeavours similar to the construction of theInternational Space Station, which could rely on welding for joining in space the parts that were manufactured on Earth.[29]Safety issues

Arc welding with a welding helmet, gloves, and other protective clothing

Welding can be dangerous and unhealthy if the proper precautions are not taken. However, with the use of new technology and proper protection, risks of injury and death associated with welding can be greatly reduced.[30]Since many common welding procedures involve an open electric arc or flame, the risk of burns and fire is significant; this is why it is classified as ahot workprocess. To prevent injury,welderswearpersonal protective equipmentin the form of heavyleatherglovesand protective long sleeve jackets to avoid exposure to extreme heat and flames. Additionally, the brightness of the weld area leads to a condition calledarc eyeor flash burns in which ultraviolet light causes inflammation of thecorneaand can burn theretinasof the eyes.Gogglesandwelding helmetswith dark UV-filtering face plates are worn to prevent this exposure. Since the 2000s, some helmets have included a face plate which instantly darkens upon exposure to the intense UV light. To protect bystanders, the welding area is often surrounded with translucent welding curtains. These curtains, made of apolyvinyl chlorideplastic film, shield people outside the welding area from the UV light of the electric arc, but can not replace thefilterglass used in helmets.[31]Welders are often exposed to dangerous gases andparticulatematter. Processes like flux-cored arc welding and shielded metal arc welding producesmokecontaining particles of various types ofoxides. The size of the particles in question tends to influence thetoxicityof the fumes, with smaller particles presenting a greater danger. This is due to the fact that smaller particles have the ability to cross theblood brain barrier. Fumes and gases, such as carbon dioxide,ozone, and fumes containingheavy metals, can be dangerous to welders lacking proper ventilation and training.[32]Exposure tomanganesewelding fumes, for example, even at low levels (