Arc Welding Concept and Process

Arc weld Concept and ProcessArc dyers rocket is a cognitive process of the alliance join processes which contains-1 Arc conjoin processes (non consumable electrodes)Gas tungsten electric automobile cut dyers rocketPlasma crook weldAtomic hydrogen conjoin2 Arc conjoin processes (consumable electrodes) screened on the wholeoy emission weldSubmerged curtain c all(prenominal) conjoinGas metallic element kink joinFlux cored sparkle conjoinElectro gunslinger joinElectro slag join3 Electron lance weld4 Laser beam weldThe main idea of fusion join is the partial going and fusion of the join amid cardinal members and a filler metals may be drop.In the slew welding process, the lighting up enquired is obtained from electrical energy. An arc is produced between the catch on of the electrode and excogitate firearm to be welded, by victimisation an AC or a DC force play supply.Shield metal arc welding (SMAW) is 1 of the oldest, simplest, and most versatile joining processes. About 50% of on the whole industrial and maintenance welding menstruationly is performed by this process.The electric arc is generated by touching the tip of a cover electrode against the hold physical composition and withdrawing it fastnessily to a distance sufficient to maintain the arc. The take fire generated melts a portion of the electrode tip, its coating and the brutish metal in the immediate arc argona and this mixture forms the weld when it solidifies.Classification Of Arc WeldingThe arc welding classified into many instances employ in the industrial range each one have receiptss and defects different from the separate caseful, So that the substance ab personar select the required graphic symbol according to the requirements and the economy aspects. In the under figure we show for the classification of arc welding which appear in the industrial (3.1)Chart keySMAW shield metal arc weldingSAW submerged arc weldingTIG tungst en inert gas arc weldingMIG metal inert gas welding glove plasma arc weldingESW electro slag weldingThe above graph list for the figures of the arc welding which employ in the industrial fields.Advantages of arc welding in that respect are nigh characteristic for the arc welding rather than the another methods to joining metals which it array the advantages of the arc welding listed as be impoverishedStrong and tight joiningCost effectiveness ( arc welding have low capital and running costs)Simplicity of welded twist designFigure 3.2 arc welding usage in the industry(http//64.78.42.182/sweethaven/BldgConst/Welding/lessonmain.asp?lesNum=4modNum=1)Principals And DefinitionShield metal arc welding (SMAW) submit as process in which coalescence of metal produced by the incite which generated from the electric arc that it maintained between the tip of the consumable electrode and the base metal in the welding region. The contiguous figures show the circuit designd in the shield metal arc weldingPower planningThe shield arc welding index source provides perpetual actual (cc) it may be alternative on-line(prenominal) (Ac) or direct menstruation (DC) depending on the electrode being use, but the best welding usually used the direct real (DC) as agent supply for the circuit.The marrow of power required to welding process calculated from the relation(P= IV) Where I form the current V represent the voltagesIn the selection process for the power supply we notice that the voltage equal to constant value so that the current is the main parameters in the selection process which discussed in the next sectionCurrent SettingThe amount of current needed to melt the work piece and the electrode tip depends on several factors as s igniteh and position of the jointWork piece type and its thicknessElectrode type and its diameterIn facts most of welder select the current depending on the diameter of the used electrode which it measured from the inner section witho ut the coated diameter as showing in the below figureA basic pass of arc welding electrodes by Bruce Bauerleinhttp//www.metalweb new-sprung(prenominal)s.com/howto/weldrod.htmlhttp//www.weldershop.info/282/types-of-welding-electrodes/ElectrodeThe electrode used in (SMAW) process exist from metal rod coated in metal mixture called menstruate which gives off gases as it decomposes to prevent weld contamination , introduces deoxidizer to purify the weld , causes weld- protection slag and provides alloying elements to improve the weld feeling. there are ternion types from the electrode used in (SMAW) process which discussed below.Fast fill electrode this type from electrode designed to melt quickly so that the welding speed be maximized. This type used when we weld in the normal case in good welding so we can weld with broad(prenominal) speed so we use this electrode type.Fast freeze electrode this type from electrode designed to solidify quickly making welding in a mannequin of positions possible by preventing the weld pool from shifting.Intermediates electrodes the commonly used type and it intermediate in cardinal case melting and in freezing but if we weld with high speed with using this type we get poor quality so that this type is not suitable in case of high speed.The American welding society established system that used to point electrodes by using four or five digital number. cover electrodes made of mild vane or low alloy steel carry the symbol of (E) followed by their number. the first two . The first two or tierce digits of the number specify the tensile skill of the weld metal, in thousand pounds per square inch . The penultimate digit primarily identifies the welding positions permissible with the electrode, typically using the values 1 (normally fast-freeze electrodes, implying all position welding) and 2 (normally fast-fill electrodes, implying horizontal welding only). The welding current and type of electrode covering are specified by the last two digits together. compositors case for electrode serial numberE7018E indicates electrode70 indicates 70,000 psi tensile strength1 indicates use for welding in all positions8 indicates low hydrogen2. Cables there are two cables work cable which committed the base metal and the electrode cable which connected to the electrode one of them represent validating and the other represent the negative side this according to the mansion of the welding processWelding Trouble ShootingThis section discuss to the move shooting may faced it during the welding speed as1-Porosity sensitive cavities or holes resulting from gas pockets in weld metal.www.miller.com.pdfThe porosity in welding it may be caused by the smirchy on work piece and the corrective action to face it by Remove all grease, oil, moisture, rust, paint, coatings, slag, and dirt from work surface sooner welding.Excessive Spatter scattering of melt metal particles that cool to solid form near weld beadwork as sho wn in the below figure.www.miller.com.pdfThe main causes to excessive spatter is the current too high for electrode and it avoid by decrease current or select larger electrode.3- Distortion contraction of weld metal during welding that forces base metal to move.www.miller.com.pdfDistortion in the welding appear as result to excessive heat input. And there is many ways to reckon this problem asUse restraint (clamp) to hold base metal in positionMake tack welds along joint before starting welding unconscious process.Select lower amperage for electrode. emergence travel speedLack of Penetration shallow fusion between weld metal and base metal.www.miller.com.pdfThe lack of penetration appears as result for many causes as showing belowPossible causesCorrective actionImproper joint preparationMaterial too thick. Joint preparation and design must provide access to bottom of groove.Improper weld technique.1-Keep arc on leading edge of weld puddle.2-Reduce travel speed.Insufficient heat i nput.Increase amperage. Select larger electrode and increase amperageAdvantages Of Shield Metal Arc WeldingThe shield arc welding have main further that represent the advantages as belowStrong and tight joining rather than the other methodsCost effectiveness (have low capital and running cost)The arc welding Simplicity of welded structures designMay be mechanized and automated or manual in some dutyDisadvantages Of Arc WeldingThe using of the shield metal arc welding lead to some defects asInternal stresses, distortion and change for the microstructure in the weld region contract harmful effects as radiation and fumesApplication Of The Shield Arc WeldingThe arc welding it can be used in many applications asBuildings and bridges structuresAutomotive, ship and aircraft constructionsPipe linesTanks and vessels (2.2) signTo introduce what the signaling means and the different type of the polarity, first of all the project will show what is the difference between AC and DC?AC And DC Cur rentWhat Is The AC Current?It means alter current. In this current the electric charge flow periodically policy changes watchfulness. The electric charge in this case will move for instance retrospective then it will reverse the direction again to move forward, then backward then forward over and over again.The waveform for alter current is a sine wave. But sometimes in certain(prenominal) applications the waveform differs like square wave or triangular wave.Dc CurrentWhat Is The DC Current?It means direct current because the electric charge in direct current moves in a constant direction, and that is the difference between DC and AC. The DC could be produced by such sources like thermocouples, batteries and solar cells.We can use a rectifier which is a current-switching brass to obtain direct current from an alternating current. The concept of rectifier is containing electromechanical elements or electronic elements which allow current to flow only in one direction.AC And DC Welding MachinesThe welder or welding machine is the power source that we used in arc welding. There are three basic types of weldingmachines used now which are rectifiers, motor- generators and transformersMotor generator welding machines (direct current welding machines)The motor generator could be powered by diesel motor, electrical or gasoline motor. We can use the gasoline and diesel motors in places where the electricity is not available or hard to penetrate it like deserts. With these machines we could generate either direct or alternating current. There are new and old machine types of these machines, the older type require reversing the cable connections in order to change the polarity. But in the new machines you can change the polarity from welding in the direct current mode to alternating current mode by turning a switch.Theadvantages of a (dc) welding generatorThe main advantage of a direct-current (dc) welding generator is that you can weld with either reverse or immediately polarity.Almost we can weld all ferrous and non-ferrous metals.We can use DC in practically all welding operations so we can consider that DC is most universal in application.The sidetrack of generators like rectifier and transformer a sets is not affected by normal variations in power line voltage.Diesel driven generators form self-contained units.Disadvantages of a (dc) welding generatorThe initial cost is highThe machine operation is noisyThe maintenance cost is highAC transformers welding machinesThe static-transformer type is the arc welding machines that we used in alternating current. As shown in the figure 2.18The advantages of these types ofmachines are lightest, smallest and least expensive welders made. We can use 200, 300, and cd ampere ratings for manual operation in industrialapplications. But in light industrial, job/shop and garage welding we could use machines with a 150-ampere rating. These types of transforms fit with arc- stabilizing capacitors.Th e advantage of a (AC) transformer welding machineThe main advantage of (AC) transformer welding machine is the freedom from arc blow. The arc blow causes the arc to wander while you are using large coated electrodes or welding in corners on heavy metal. The arc blow a lot occurs when welding with direct current machines.PolarityWhat is the polarity?Polarity is the direction of the current flow in a circuit. There are two types of polarity reverse polarity and straight polarity. In the straight polarity the work piece is positive and the electrode is negative. The electrons move from the electrode to the work piece. In the reverse polarity the work- piece negative and the electrode is positive. The electrons move from the work piece to the electrode ac and dc current was briefly covered.The effect of polarityThe polarity affects the amount of heat which is going to the base metal. You can direct the amount of heat to where it is needed as per the application you working in by chang ing the polarity. If you postulate to direct the majority of heat toward the work piece, you must use straight polarity. That type of polarity being used in some welding situations when it is desirable to have more heat on the work piece because of its size to melt the base metal than the electrode. We can use straight polarity for all mild-steel, bare, or lightly coated electrodes. If you want to concentrate the heat on the electrode, you can use reverse polarity because in this type less heat is concentrated at the work piece which allow filler metal to cool faster, giving it great holding power because of this reverse polarity is being used when you are making vertical and overhead welds. Reverse polarity could be used in the welding of nonferrous metals such as bronze, aluminum and nickel.Heat alter ZoneHeat affected regularize definition.The heat affected zone (HAZ) represented by the area of base material subjected to the high heat in order to achieve the welding process. The area which subjected to change in its microstructure and mechanical properties. SMAW process give a highly heat engrossment in specified region called (fusion zone), produced in the region of heat affected zone. To calculated the amount of heat in the HAZ the following formula used.Q =60 VI / 1000SWhere Q = heat input (kj/mm), V = voltage (V), I = current (A), and S= welding speed (mm/ min). (2.10)The molten occur in the fusion region not in the heat affected zone. So that the HAZ modify to a high enough temperature for sufficient period that grain produce occurred. Heat affected zone is that location of the base metal which in it the mechanical properties and the microstructure have been affected by the heat of welding process.The heat affected zone is subjected to a complex thermal cycle (sudden alter followed by rapid cooling) in which all temperatures from the melting range of the metal down to much lower temperatures are involved and HAZ therefore consists of a series o f graded structures ringing the weld bead. HAZ usually contains a variety of microstructures different from the remaining part from the base metal.The width of HAZ varies according to the welding process and technique in arc welds it extends only a a couple of(prenominal) mm from the fusion boundary,The HAZ in most metal welding process of normal structure welded in one run with coated electrodes that to carve up it to four basic region.Classification And DesignationThe classification of electrodes is done by one of the three following categories1 Strength of the deposited weld metal2 Current (ac or dc)3 Types of coatingThe identification of electrodes is by numbers and letters as shown in the next table. Typical coated electrode dimensions are in the range of 150 to 460 mm (6 to 18 in.) in length, and 1.5 to 8 mm (1/16 to 5/16) in diameter.Specifications for electrodes and filler metals (including dimensional tolerances, quality control procedures, and processes) are publishe d by the American welding society (AWS) and the American national standards institute (ANSI). Some specifications appear in the aerospace materials specifications (AMS) by the society of automotive engineers (SAE). Electrodes are sold by cant over and are available in a wide variety of sizes and specifications.Electrodes Types And ChoicesWhen the select of a suitable electrode is needed, many considerations are taken such asQuality of weldPenetrationUsed current whether AC or DCCrack resistant