Little About Welding Process

The development of metal technology provides ease of connection to humanity in the conduct of life. Today, the advancement of science in electronics through That studies look at the characteristics of atoms, have Contributed greatly to the discovery of new materials and also how do the connection. Manufacturing industry can not be separated from the metal connection. The connection is made of metal for Various purposes, Such as to create an item That is not possible with other techniques, facilitate the work, and can Reduced production costs. Switching process is Widely used metal in the manufacturing industry is welding. Metal welding is a fairly precise. Welding does not require a long time, the construction is lightweight, has a pretty good connection strength, and Relatively low cost.

The definition of welding material is a connection Between two or more of the process utilizing the process of diffusion of the material, based on the principles of magnetic bonds Between atoms of the material to be spliced. Welding can be Divided into two types, namely Solid State and Liquid State Welding Welding: Solid State Welding is a welding process in the which objects in the solid state, and usually by using a pressure That Is Often also called Pressure Welding. Solid State Welding process has Several advantages, Such is Able to connect two or more pieces of material That is not the same melting point, the process is rapid, precise, and almost no heat affected areas (heat affected zone / HAZ). However, Solid State Welding also has drawbacks, namely the preparation and the process is complicated connections, so it takes meticulous very high. Included in the Solid State Diffusion Welding Welding of them, Forge Welding, Cold Welding and Friction Welding.

Liquid State Welding is a welding process in a way That would dilute the area until the liquid is spliced ​​together evenly, Provided the material to be jointed should be the same melting point. Grafting material in this way has to be the same material terms, Because to get a perfect connection material temperature should be equal, if not the process of splicing is not going to Happen. Advantages of this welding method is the preparation process and the connection is not complicated, the cost is Relatively inexpensive, easy implementation. The disadvantage is the need of skilled welders, the HAZ the which cause changes in material properties, and there is potential for accident and health impaired welders. Which includes the Liquid State Thermal Welding Welding, Resistance Welding, and Electric Arc Welding.

Very broad application of the welded joints. Welded joints are Widely used in the construction of bridges, buildings, automotive industry, household appliances industry, and even industrial goods with too many plastic materials using the welding process. Variables That Affect the quality of welded joints, Including: materials, welding process, welding methods are used, used welding equipment, skilled welders, welding environment, testing of welding, safety and health.

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Mig Welding

METAL INERT GAS WELDING With a 'flat' volts/amps characteristic an attempted alteration in arc length (volts) will have little effect, hence arc length (volts) remains constant but a significant change in current will result. This is often referred to as the 'self-adjusting arc'. Metal Inert Gas (MIG) welding is a 'flat' arc process (constant) voltage. Also known as Metal Active Gas (MAG); CO2; Metal-arc Gas Shielded, flux core and GMAW (US). MIG can be used on all materials, in all positions, with high productivity and low heat input. There is no CO2 MIG welding with stainless steel. Normally DC positive though some flux core uses DC negative. Type of Operation.             Manual, mechanised, semi-automatic and automated (robotics). Mode of Operation. An arc is maintained between the end of the bare wire electrode and the work piece. The wire is fed at a constant speed, selected to give the required current, and the arc length is controlled by the power source. The operator is not therefore concerned with controlling the arc length and can concentrate on depositing the weld metal in the correct manner. Hence the name 'semi-automatic' for manual operation, in which wire, gas and power are fed to a hand held gun via a flexible conduit. The process can be operated at high currents (250 - 500 A) when metal transfer is in the form of a 'spray', but, except for aluminium, this technique is confined to welding in the flat and horizontal positions. For vertical and overhead welding special low current techniques must be used, i.e. 'dip' transfer or pulsed arc. The arc and weld pool are shielded by a stream of gas. The electrode can be solid or flux cored. (In mechanised MIG and submerged arc welding the process may also be operated using constant current or drooping arc characteristics). MIG/MAG Process Characteristics. The heat source used to melt the parent metal is obtained from an electric arc that is formed between the end of a consumable electrode wire and the work piece. The arc melts the end of the electrode wire, which is transferred to the molten weld pool. The electrode wire is fed from a spool that is attached to the wire driving system and passes through a set of rolls, which are driven by a variable speed electric motor. By varying the speed of the motor, the level of the welding current can be adjusted - high wire feed speed gives high welding current. Altering the voltage can also vary the arc length - high voltages give longer arc lengths and vice versa. In order to prevent the air reacting chemically with the molten metal, a shielding gas of either CO2 or argon/CO2 mixture is passed over the weld zone from a nozzle attached to the welding gun or torch. This protects the molten droplets passing across the arc and the molten weld pool. Electrical power for the process is a direct current that is obtained from a transformer-rectifier. The welding gun or torch is connected to the positive pole of the power supply unit and electrical contact to the wire is obtained as close to the arc as possible by means of a copper contact tip or tube. The metal at the end of the electrode is melted and transferred to the molten weld pool. The two main types of transfer are: Spray or globular transfer. Short-circuiting or dip transfer. Spray Transfer/Globular Transfer.             This type of metal transfer generally occurs at high current and high arc voltage ranges, e.g., 250 - 600 Amps at 28 - 40 volts. As the current is increased the rate at which the droplets are transferred across the arc increases and they become smaller in volume. The droplets can be seen in a high-speed cine film but cannot be seen with the naked eye. It appears as if there is a spray of metal. The type of shielding gas greatly affects the current rate at which the spray transfer occurs. The use of CO2 as a shielding gas requires a much greater current density than argon to produce the same droplet rate. With the use of high currents giving strong magnetic fields very directional arcs are produced. In argon shielding gases the action of these forces on the droplets is well balanced and transfer from wire to work is smooth with little or no spatter. However, with a CO2 shield the forces tend to be out of balance giving rise to an arcing condition that is less smooth and spatter levels are heavier. Metal transfer under these conditions is normally called globular or free flight. The welding conditions that give spray or globular transfer are normally associated with high deposition rates on medium and thick sections giving high productivity. It has a higher heat input and can only be used in the flat and HV positions except when welding aluminium when it can be used in all positions. Short Circuiting Arc/Dip Transfer. When using lower arc voltages and currents, generally in the 16 - 26 volt and 60 - 180 ampere ranges, metal transfer takes place during short circuits between the electrode and the weld pool, giving a lower heat input. These follow a consistent sequence of alternate arcing and short circuiting causing the end of the electrode wire to dip into the weld. As the wire touches the weld pool there is a rise of current, the resistance of the wire causes heating and the end of the electrode melts. The wire necks due to a magnetic pinch effect and the molten metal flows into the pool. During this short circuit period the current delivered by the power source is much higher than during arcing - typically 1000 - 1500 amps. This creates high forces that have an explosive effect on the weld pool and spatter is considerable. To reduce this effect an inductance is connected in series with the power supply and the arc to reduce the rate of rise of current during the short circuit period. The short circuit is cleared more slowly and gently, and the spatter is reduced to an acceptable level. Ideally the droplets are transferred in an almost irregular dip/arc cycle taking place about 50 - 200 times a second. Too little inductance gives rise to unstable arcing conditions, excessive spatter and lack of fusion defects. The dip transfer mode is used for the welding of thin sheet and medium plate, and for all thicknesses when welding in the vertical or overhead positions. (With thicker plate there can be lack of fusion problems.) Mixed Arc Transfer. This is a globular transfer using medium volts and medium amperes. It is generally unusable having an unstable arc and high spatter levels. Use is mainly with flux cored wires in filling passes. Pulsed Arc Transfer. This is a synergic transfer of 50 - 250 kilohertz that combines short circuit and spray transfers. It uses high and low voltages and amperages, and can be used in all welding positions on plate thicknesses greater than 6 millimetres. Welding Variables And Parameters.             1.   Electrode extension - affects the amperage. Stick out length should be 10 - 15 mm. 2.   Inductance - ' smoothes' the arc characteristic. Also called the choke. Set low gives                                                             excess penetration and high, no penetration.             3.   Wire feed speed - amperage. Controls fusion and penetration.             4.   Travel speed - controls depth of penetration.             5.   Gas flow rate - protects weld from atmosphere.             6.   Voltage - set on the welding machine and controls the arc length.             7.   Tilt angle - back or fore hand should be not greater than 15° from the perpendicular.             The welding position and type of weld are further variables to be considered. Welding Sets. Sets are manufactured in a range of sizes, identified by current, similar to metal arc welding. Currents below 200 A can only give dip transfer operation, suitable for welding steel only. Larger sets may have the wire reel and motor as a separate unit, so it can be placed near the job. Controls on the set adjust output voltage and may allow a choice of inductance. The wire speed control will be on the wire feed unit. Electrical input is from single phase 240 V mains for small sets, or three phase 415 V for medium size and upwards. Output is always DC with a flat output characteristic for semi automatic and drooping output for mechanised. Sets which supply current in pulses (at 40 - 200 per second) give improved results on some jobs. Because the 'pulse-MIG' increases the number of controls, an electronic 'synergic' control system varies all the parameters in step to simplify adjustments. Sets often have a built-in holder for a gas cylinder. A set will usually be supplied with a suitable welding gun. Heavy duty guns may be water cooled and the set may have a water tank and cooling radiator built in. When welding aluminium the wire is soft and tends to kink when pushed through a hose. A gun carrying a small reel of wire - 'reel-on-gun', obviates this. MIG Welding Gun.Accessories. Welding cables      Similar to manual metal arc - one set usually included. Connectors to set.  Clamps or clips. Gun and connecting hose assembly to suit current, usually supplied with set. Gas regulators and hose, connections to suit. Vaporiser for carbon dioxide gas on industrial sets. Cylinder stand. Spares. The following parts come into contact with the wire - spares are needed to replace worn parts, or if wire size or type is changed. Inlet and outlet guides      On drive assembly. Drive rolls.                      Contact tip in gun - needs fairly frequent replacement. Gas shielding nozzle for gun - various sizes to suit different jobs. Wire conduit liner - spring steel coil (like curtain wire) for steel electrode wire, or plastic tube for aluminium. Typical Defects and Causes. Lack of fusion. Excessive penetration. Silica inclusions (with steel only). Solidification (centreline) cracking.             a.         Spray transfer current too high.             b.         Deep narrow prep. Porosity.             a.         Gas flow too high or too low.             b.         Blocked nozzle.             c.         Leaking gas line.             d.         Draughty conditions.             e.         Nozzle to work distance too long.             f.          Painted, primed, wet or oily work surface.             g.         Damp or rusty wire. Lack of penetration.             a.         Current too low.             b.         Prep to narrow.             c.         Root face too thick.             d.         Root gap too small.             e.         Worn tip causing irregular arcing.             f.          Irregular wire feed.             g.         Poor technique.             h.         Mismatched joint. Undercut.             a.         Speed too high.             b.         Current too high.             c.         Irregular surface.             d.         Wrong torch angle. Spatter.             a.         Inadequate choke.             b.         Voltage too low.             c.         Rusty or primed plate. Crater cracking.             a.         Poor finishing technique. Applications.             Structural steel.             Aluminium sections.             Stainless steel and nickel alloys.             Some offshore applications (flux core only).

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Oxy acetylene welding process

Welding with gas created by burning fuel gas mixed with atomic number 8 (O2), giving rise to a extreme temperature flame (3000o) were ready to soften the parent metal and filler metal. style of fuel used alkyne gas, fuel or gas, therefore the approach this fastening oxy-acetylene fastening is termed or legendary by the name of the inorganic compound weld. alkyne flame is obtained from burning a combination of atomic number 8 and alkyne gas accustomed heat the metal till it Reaches the temperature of the parent metal. Welding can be performed with or without filler metal. Oxygen is obtained from electrolysis of water or liquefaction process. Oxygen is commercially Generally come from the air liquefaction process in the which oxygen is separated from the nitrogen. Oxygen is stored in steel cylinders at a pressure of 14 MPa. Acetylene gas (C2H2) is produced from the reaction of calcium carbide with water. Rising gas bubbles and sediment That Occurs is calcium oxide. Reactions occur in acetylene cylinder That is:

CaC2 + 2H2O ® Ca (OH) 2 + C2H2

calcium carbide acetylene gas Cretaceous shallow water

When the count was approximately 1 kg CaC2 Produce 300 liters of acetylene. The nature of acetylene (C2H2) the which is a fuel gas is colorless, non-toxic, odorless, lighter than water, growing niche to separate Themselves when there is an increase of pressure and in temperature (above 1.5 bar and 350 ° C), soluble in a porous mass (acetone).

Calcium carbide is a hard, like stone, gray and formed as a result of Reaction Between Calcium and coal in electric kitchen. The reaction is then crushed, selected and stored in a sealed steel drums. Acetylene gas can be obtained from the acetylene generator acetylene gas produced by mixing carbide with water or can now be purchased in the gas tubes ready for use. To be safe acetylene gas pressure in the tube should not exceed 100 kPa, and kept mixed with acetone. Acetylene tube filled with a porous filler material is saturated with acetone, then filled with acetylene gas. Tubes of this type can accommodate acetylene gas pressurized to 1.7 MPa.

Principle of welding is not too complicated. Simply by adjusting the amount of acetylene gas and oxygen, then ends with a flame near the flame Brought Will Arise. But the amount of acetylene gas and oxygen should be arranged so as to turn the pressure bit by bit. Acetylene gas when it is turned on the flame of the flame used to remove soot. If the acetylene gas too little is played, then the weld will not light.

Speed ​​of recall of gas per hour from an acetylene cylinder must not be Greater than 20% (one fifth) of its contents, so That gas can be flowed acetone (acetylene cylinders must always be perpendicular).

Flame combustion in oxy-acetylene welding may change depending on the ratio Between oxygen gas and the gas asetilennya. There are three Kinds of fire in the oxy-acetylene welding as shown in the figure below:

More acetylene flame (flame carburizing)
That if too many comparisons used the acetylene gas in the inner cone and outer cone will Arise a new cone of blue flame. Among the light cone and the outer sheath of the cone will have whitish, Whose length is determined by the amount of excess acetylene. This will cause the liquid metal carburizing. Flash is Widely used in metal welding monel, nickel, Various types of steel and a variety of non-ferrous material surface hardening.

Neutral flame
This Occurs when the flame of oxygen and acetylene ratio of about one. Flame consists of a cone in a shining white and blue cone outer nodes. Required oxygen flame comes from the water. The maximum temperatures as high as 3300 to 3500 ° C is reached at the end of the flame cone.

More oxygen flame (flame oxidation)
When oxygen gas is more than is needed to Produce the neutral flame flame Becomes shorter and the color changed to purple cone. This flame will cause oxidation or decarburization process on the liquid metal. This oxidation is the flame That must be used in fusion welding of brass and bronze, but not recommended for other welding.

Because it is Able to change the composition of the molten metal excess acetylene flame and the flame of oxygen excess can not be used to weld steel. At the end of the temperature of the cone in approximately 3000 ° C and in the middle of the cone is approximately 2500 ° C.

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Resistance Welding Machines Control

Welding is employed in several forms. Today, natural philosophy, and alternative small-size devices ar growing within the fastening trade, a sector sensitive to the resistance fastening method. this is often the body, through the temperature of contact and coalesced weld tannagagi twofold once the new components, that may be a thermal method. This methodology is analogous to alternative heat waterproofing, however with some variations. the primary of those variations, of course, the scale of the parts and solder. Microelectrodes micro-resistance fastening machines ar unbroken, artisan fastening method itself, the box containing the management natural philosophy and controls, and also the fastening head consists of the workpieces in tiny and place them connected. Points or contact points instead of themselves as micro-electrodes, 0.010 sq. centimetre in size, very small. one among the foremost precise management of electrical welders and weld heads, terribly precise management of the energy of the electrodes wouldn't disrupt the weak.

There are three types of micro-resistance welding electrode welding, dig welding, projection welding straight through. A weld line, welded to each other as objects to be constructed in contrast to the two electrodes, such as electricity, Cut, a heating of the weld. Along the length of a welding electrodes or workpieces, except for the two overlapping sites to be moved to form a continuous series, in fact, a single weld line. A humpback welding projections extending in fact its name from the two surfaces. If this method is a thin piece of a larger piece of welding, thermal balance, the improvement will reduce the amount of energy to dig a welded reasons, a number of uses, so that a plurality of pulse welding with spot welding.


Parallel to the weld gap to the following two types of micro-resistance welding mentioned in the preface. Both the type of welding electrodes, making approached in the same direction. With an insulating layer on the opposite side of the pieces of this technique is especially useful when welded. Currently, there are two things in a series configuration of the electrode assembly and the other electrode, an electrode and allows the flow. Welding step, the contact electrode material and the flow passes through the interface that all objects.

The first step is to perform micro-resistance welding, the copper electrode on the other two parts over the place. Next, the welding head, welding, narrow, two pieces brought to a point near the bottom of the upper electrode. Transfer the pieces to the point of intersection of the two current electrodes are pressed together. There is a connection between the two electrodes to heat the material quickly, but both were to dissolve. Power when weld between the two parties to form, cooling the molten zone and solidifies.

Micro resistance welding systems for automotive, aerospace, medical and electronics manufacturing, including the majority of areas, including in many applications. Micro resistance welding of thin wires soldered to the rest of widespread PCB pads are used for the electronic industry. Some of the naming of this type of welding, sensors, lights, batteries, used in the manufacture of solar panels and smoke detectors. Automobile sector, micro-resistance welding of light, air bag systems, electronic sensors and controls used.

In short, the most popular form of micro-resistance welding connection hardware. It would be cheaper for a clean, safe and fast. The usefulness of micro-resistance welding to the development of the industry.

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Electric Arc Welding Technology

Electric Arc Welding

For centuries wrought las used as the primary process to connect the metal without much experience growth. In the early 19th century, found a new way, namely electric arc welding flame (Electric Arc Welding) with a carbon rod electrode without the wrapper by using the battery as a power source. The main weakness of electric welding process is the oxidation of carbon is high relative to the weld (weld easily rust) so that the welding is widely used.

At the same time, in 1877, found weld resistance (Resistance Welding). A British physicist, James Joule, recognized as the inventor. In 1856 he heat up two pieces of wire with electric current. During the heating process, the wires are pressed to each other. It turns out the two wires are tied to each other after heated.

In further development, resistance welding produces several types of welding processes, eg welding flash (Flash Welding) in the electrical resistance 1920. Welding achieve glory of being created different types of robots. Developed to meet the needs of the various forms of electrical resistance welding includes welding point, interval, seam (line) and projection. Welding Process implement this in the heat and press. Electrode serves as a channel for the flow and pressure plate-shaped workpiece.

In the next decade, introduced last hermit (Thermit Welding) by adding a chemical process is repertoire welding technology. Welding termit by pouring molten metal between two metal end which would be connected so it would melt. After freezing the fused metal and liquid metal is poured to function as an added ingredient.

In the late 19th century found oxy acetylene welding, weld it managed to shift the use of welding wrought and dominate the welding process for several decades to develop electric welding ..
In 1925, oxy acetylene welding repair is shifted by the electric arc welding in which welding arc is wrapped electrode wear. After the fire, wrapping electrode produces gas and slag. Gas protects the weld crater of oxidation during the welding process is underway. Protect the weld slag during the freezing process to cool (until the slag is cleaned). Limitations of arc welding electrode rod is limited so long electrode any given period should stop changing the welding electrode. More material efficiency is far from 100% because I had no butt.

Starting from this weakness was then in the late 1930s created an arc welding electrode coils. In principle, the welding is not necessary to stop before reaching the end of the weld line. And welding can be done by automatic or semi automatic. Used as a protective flux. Flux outlined shortly in advance so that the electrode electric arc flame hidden by the flux. Advantage, the operator is not dazzled by the flame of an electric arc, weakness, limited to the welding position just under the hands of the other positions scattered flux will fall before the function.

In 1941 in the United States found Tungsten electrode. Tungsten is not melted by the heat of the flame of an electric arc that does not feed in the weld. Core is used as a protective gas (Inert) which can persist for some time on his condition. Core gas ejected stricken welds so the welds protected from oxidation. Because it uses the core as a protective welding welding is often called TIG welding (Tungsten Inert Gas).

The successful use of gas tungsten core pad pad pad pad electrode also tried the roll in the early 1950s. This process is hereinafter referred to as Gas Metal Arc Welding (GMAW) or MIG welding (Metal Inert Gas). Because metered gas is very expensive then used a mixture of argon and oxygen gas or CO gas is quite active. Welding is commonly called the Metal Active Gas (MAG). Can also be used protective argon mixture with CO for not more than 20% the result is quite good because it does not leave the slag. Please note that the protective gas is more expensive gas, then the way is only used for special purposes.

Found the next arc welding electrode welds with a protective roll floured. In order to be used in all positions, such as perforated pipe electrodes are made to put the flux. The process is relatively cheaper than gas arc welding, it can be to any position and can be developed technical welding semi-automatic or fully automatic welding is called the flux cored arc welding electrodes (Flux Core Arc Welding) electrodes Then there are the components to be mounted on the other. This is called weld stud welding. Stud mounted on the main body through three stages, namely the setting position, the search ends and the main body studs and stud pressure on the main body shortly after the arc flame is turned off.

After that developed electric welding high frequency is 10 000 to 500 000 Hz. High-frequency electric welding is often called induction welding. Judging from the unification process of the workpiece, solid welding including welding aided by heat to break down a layer of oxidation or dirt on the surface of the workpiece. Produced heat the workpiece surface is very thin so it is suitable for welding thin plate.

In the 1950s, transforms electrical energy into a beam of electrons fired from the workpiece. Greater the heat generated and the dimensions of the former electron is much smaller than electric arc flame, welding very quickly so it is suitable for mass production. Hot region becomes more narrow so it is suitable for materials sensitive to thermal changes. Excellent weld quality and accuracy, it's just very expensive equipment. This method is called las electron (Electron Beam Welding).

Scratch Welding
In 1950, AL Chudikov, a mechanic from the Soviet Union, put forward its observations on the theory of mechanical power can be converted into heat energy. Friction that occurs in the engine parts that move caused many losses as partly generated mechanical power turns into heat. Chudikov argue, so the bias should be used in the welding process. After going through a trial and he succeeded in welding research by utilizing the heat caused by friction. To increase the heat that occurs, the workpiece is not rotated but only pressed one against another. Pressure also serves to accelerate fusion. This is called friction welding (Welding Friktion)

Plasma Welding
Electric arc plasma flame welding (Plasma Arc Welding). Plasma process is an improved welding tungsten actually, it's just an electric arc burning between the electrodes do not appear to work but the object appears between the tip electrode with the gas flowing around the core. Welding plasma was better than tungsten because of arc welding flame that appears more stable power with a smaller diameter so that the heat is more concentrated. Faster welding process bias, in addition to tungsten never touch the workpiece.

Sound Welding
Earlier in the year 1960 was marked by the discovery of welding that uses high frequency sound (Ultrasonic Welding). It also uses an electric welding process works, there is no power at the workpiece, the heat generated merely the result of processes and it is only helpful in the process of unification of the workpiece.

Voice used ranged from 10 000 to 175 000 Hz, the sound vibrations transmitted through electrode mounted on the workpiece. Then pressure is applied to the workpiece during the process. Advantages of this process is suitable for thin objects and not affected the type of material to which you connect. Not wearing thermal energy as the primary energy is its own advantages in certain materials and thin, it's just less work for the workpiece thickness above 2.5 mm x 2.

Various forms of ultrasonic welding:
Wedge reed spot.
Leteral drive spot.
Overthung copuler spot.
Line.
Ring.
Continuous seam.

Explosive Welding (Explosive Welding or EXW)

Explosive Welding (Explosive Welding or EXW) was developed from the observation of one's days of World War I, there are fragments of a powerful bomb attached to the other metals fell. Carl's research conclude that shrapnel is attached because the effects of jet in the event of collision. The effects of jet capable of cleaning dirt on the surface of the object so that it contacts between atoms both objects and generate a strong enough.

Laser Welding.
In 1955, the physicists found laser beam, simply speaking rays produced at a particular wavelength and parallel, then enlarged, light is then focused. The heat generated at the focus point is very high. By the year 1970, the laser began to apply the base pad, as the laser beam can be accurately adjusted so that the laser welding very suitable for special equipment.

Laser welding can be used to weld objects with a thickness of 0.13 mm to 29mm at the sliding speeds ranging from 21 mm / sec to 1.2 mm / s. Issues arising pedestal pad as well as laser welding electron, the workpiece is very small rift between 0.03 to 0.15. Up at this time a lot of classification methods used in the welding field, is due to the agreement in terms of these things. In the conventional ways of classifying these at this time can be divided into two groups, namely the classification based on the work and the classification based on energy use.

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