Arc Welding

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Arc Welding

  1. 1. LEARNING EXPERIENCE – I Competence: Set Electrical Welding Plant ready for operation by following proper safety Precautions. Enabling objectives: After undergoing the learning experiences in this module you should be able to : Set up arc welding equipment for different operations. Select current and voltage rating for a job. Test the setup Observe safety precautions. Learning Activities: Read information sheet. Complete assignment given in assignment sheet. Complete the practice exercises and check answers.Get the results checked before proceeding to Learning Experience II.
  2. 2. Element: Set up Arc Welding equipment. Information SheetIn various situations you are required to make different shapes with metal components to serve thepurpose. Therefore you need to learn the technique to join metals.Metal Joining Methods: There are three basic types of joining methods. 1) Flexible Joint: This is the simplest process of metal joining in which components can be joined and dis-assembled as and when required without any destruction. Example: Bolting 2) Semi-permanent joint: This is the process of joining in which components can be dis- assembled when required with minor destruction of joining component. Example: Folding, Riveting 3) Permanent Joint: This is the process of joining in which component cannot be disassembled without destruction. Example: Welding, Soldering In this module our focus is only on Welding. Welding is a process of joining metal with the application of heat. Welding is applicable to joining of same metal components.
  3. 3. Applications of Welding: You can see application of welding in various fields like 1) Furniture making 2) Bridge Construction 3) Building construction 4) Doors and window making etc. We shall discuss the process of manual metal arc welding. Welding is a process of joining metal with the application of heat. Welding is applicable to joining of same metal only. Electrical Welding is a fusion welding process. In this process electricity is used to develop heat of fusion. Let’s understand term fusion in following steps: - It is the process of surface heating up to melting point. - Melted joining boundaries become fluid and mix Burning gas together. - Filler rod provides additional material during fusion. - Homogeneous bond is formed when the metal cools from liquid to solid state.Lets learn basics of electricity prior to entering into the subject.
  4. 4. Electric Current : Flow of electricity is called as current. Current is measured in “Ampere”.Types of electric current : There are two types of electric current. 1) Alternating Current (AC) : This is the current which changes its direction and amplitude. Example: Electrical supply in our home. 2) Direct Current (DC) : This is the current which flows in one direction. Example: Car batteryVoltage : This is the pressure which causes current to flow. Voltage is measured in ‘Volts’.Conductor: Substance which allow to electricity to flow through it is known as conductor. Example : Copper, Iron , Aluminium etc.Insulator : Substance which do not allow current pass through it is known as insulator. Example: Wood, Cotton, Rubber etc. Principle of arc welding When electric current flows through a conductor, conductor property restricts this flow. The restriction in flow of electrical energy results in development of heat. Eg. Water heater used at our home. Amount of heat developed depends upon factors 1) Current (I) 2) Resistance of conductor (R) 3) Time of current flow (T) Mathematical relation is as follows: H = I2 RT
  5. 5. Applications 1) Day to day fabrication work 2) Maintenance & repair work 3) Vessel fabrication 4) Piping work 5) Building & bridge construction etc TypesVarious types of arc welding methods have been developed like: Manual Metal Arc Welding Carbon arc welding Atomic hydrogen arc welding Tungsten inert gas arc welding Submerged arc welding Electro-slag arc welding Plasma arc weldingExcept manual metal arc welding rest of the methods are beyond the scope of this training. Advantages 1) This is the simplest of arc welding processes. 2) Equipment are portable and the cost is low. 3) Process has vast application as variety of electrodes are available. 4) A wide range of metal & alloys can be welded by this process 5) Highest weld quality can be achieved in any position. Limitations 1) Mechanizations is difficult 2) Best suitable for short weld length 3) Process is slow 4) Skill is required to produce quality welding joints.
  6. 6. Welding machine: Welding machine is basically a rectifier which converts AC mains supply in to DC supply.Welding accessories: During operation apart from welding machine you need several smallequipments or components as follows. 1) Electrode Holder: This is device, which you use to grip an electrode during welding. Connect electrode holder to the welding machine through an electric cable. You have to always ensure that the holder grip is insulated for safety reasons. 2) Earth clamp: This is a device, which is used for connecting job or worktable to the earth cable.
  7. 7. 3) Welding cable: You require welding cable for current flow from welding machine to electrode welding cables carry heavy current so you must be careful about - Proper size of cable - Tight cable connection - Good insulation 4) Welding screen: This is a device, which protects your eyes and face from spark and radiations. Different shades of colors are used in welding screen. You have to select correct shade with respect to welding current as shown in the table.Practice 1: Assemble electrical welding machine and accessories and test the setup.Current and voltage setting: You may have to join different pieces in the real work situation.Different current or voltage settings are required for the different jobs. To set current adjust knobprovided to the required value. You will learn current requirement in the next element.
  8. 8. Testing of setup: 1. Ensure that you have taken precaution against electrical shock. 2. Switch on the main switch - You will observe that the main line signal on machine starts glowing, at the same time voltmeter also shows the supply voltage. - You can listen to a humming sound from machine. 3. Grip electrode in the holder
  9. 9. 4. Rub or touch electrode on metal piece 5. If arc generates, it shows that machine is ready for welding.Safety Precautions: You must take following precautions while working with electrical weldingequipment. 1) Wear your safety clothing and chipping goggles. 2) Keep other devices ready, like welding screen, holding tools etc. 3) Ensure you are wearing shockproof gloves and shoes. 4) Get main supply connection done through skilled electrician 5) Ensure that electrical joints are proper. 6) Check by yourself that the cable and electrode holder are not damaged. 7) Do not allow unwanted persons in the working area. 8) Check by yourself the operation of main switch, current setting knob and earth clamp.
  10. 10. Common tools: During operation you will also need some other tools for holding, cutting andmarking purpose. Steel Rule: This is a tool that you can use to measure length and marking points. It contains graduations in mm, cm and inch. Precautions: 1. Save edges and corners from wear & tear. 2. Do not use in place of screw driver. Try square: This is a tool used to check rightness (90° angle) of the edges. Set base along one of the edge and check gap along other edge opposite to light source. If you cannot see light, means edges are at right angles. Precautions: Do not use as hammer or screwdriver. Center Punch: This is a tool used for marking points on the sheets. Centre punch is used for marking centers for radius and marking points on a job.
  11. 11. Scriber : This tool consists of sharp points asshown in figure. Scriber is used to mark lines on ajob by scratching.Precautions: 1. Do not use as center punch. 2. Save points from damages.Compass : This tool consists of two pivoted legswith sharp points. Compass is used to markcircles and arcs. To mark arc or circle place oneof the leg on center point marked with centerpunch. Set other leg so that point-to-pointdistance is equal to the radius of the curve withsteel rule. Hold grip handle and rotate about thecenter.Hammer: This is a commonly used tool. Hammeris used to blow impact. Different types ofhammers are available according to purpose ofuse.Chisel: This is tool used for cutting metal piecesand removing welds.
  12. 12. Tong: This a tool used to hold hot pieces.Hacksaw: This a tool used to cut metal alongstraight line. It consists of frame and blade. Bladecan be replaced whenever required. In case ofhacksaw blade, tension is very important,improper tension causes damage to the blade. Tocheck tension tap blade with finger, ringing soundindicates proper tension.File: This is a tool used for finishing and removingburrs. Files are available in different shapes androughness. Bastard file, rough files and fine filesare used for heavy, medium and fine cutsrespectively.Chipping hammer: This is the tool, which helpsyou to remove slag from the weld.Wire brush: This is a device, which you need forcleaning of job before welding operation.
  13. 13. Self TestAnswer the following.Q1. What is the source of heat of fusion in Q5. Write two limitations of electrical welding.electrical welding?Q2. What is the unit of current? Q6. What is the purpose of electrode holder?Q3. Write two applications of electrical welding. Q7. List two safety precautions.Q4. Write two advantages of electrical welding. Q8. What is the function of chipping hammer?Write True (T) or False (F): 1) AC current flows only in one direction. 2) Ampere is the unit of voltage. 3) Insulator does not allow current to flow through it. 4) Welding machine converts AC current to DC current. 5) Chipping hammer is used to remove weld.
  14. 14. Solution to Self testA1. Electricity is the source of heat of fusion in A5. The two limitations areelectrical welding. 1) Mechanizations is difficult. 2) Best suitable for short weld length.A2. The Unit of current of current is Ampere. A6. This is device, which you use to grip an electrode during welding.A3. The two applications are A7. Two safety precautions are as follows1) Furniture making2) Bridge Construction. 1) Wear safety clothing and chipping goggles. 2) Ensure you are wearing shockproof gloves and shoes.A4. The two advantages are A8. This is the tool, which helps you to remove1) This is the simplest of arc welding slag from the weld.processes.2) Equipment is portable and the cost is low.True and False:1) False2) False3) True4) True5) True
  15. 15. LEARNING EXPERIENCE – IICompetence :Fabricate articles using electrical welding techniques.Enabling objectives :After undergoing learning experiences you should be able to : Perform pre-welding operations. Select equipment and accessories Select appropriate voltage and current setting for a job. Fabricate articles using arc-welding equipment. Perform post weld operations.Learning Activities : Read information sheet. Complete assignment given in assignment sheet. Complete the practice exercises and check answers.Get the results checked before completion of the module. Element: Fabricate different articles using Electrical welding equipment
  16. 16. Information sheetIn the last element you learnt about the setup and general information. To use electrical weldingmachine to fabricate an article you should know : - How welding takes place. - What is the procedure? - How to select correct electrode. - How to prepare an edge. - What are the common defects? As you already know in the arc welding heat of fusion is produce by electrical energy. When you perform arc welding you will have to make arrangements as shown in the figure First you have to generate the arc by bringing electrode near the job. When there is small air gap between electrode and the job, arc is generated. The arc causes heating of job boundaries to molten state at the same time melt the electrode. When this molten filler material deposits on job it causes a homogenous bond.How to produce an arc:Before starting welding operation you should
  17. 17. Clean the work piece mechanically or chemically to remove rust, oil and grease etc. This ensures proper bonding of metal during welding.Set the work piece on worktable in flat position.Wear your safety clothes and devices.Check machine for proper connections and damaged cablesSelect suitable welding electrode as per the table and fix to the electrode holder.Switch on the welding machineSet current and voltage ratio.Strike an arc. You can strike arc in two ways: By Scratch: Keep welding screen in front of your eyes. Bring electrode near the job, so that electrode is at an angle of 750-800 with the job surface and tip is about 2-3 cm above the surface. Twist your wrist quickly. While doing so, electrode scratches the job. This action generates an arc. You should see this arc through the welding screen and maintain a gap equal to the dia of rod.
  18. 18. By tap: - Touch electrode to the job. - Lift the electrode slowly; this action will generate an arc. - Maintain the arc. - If electrode sticks to the job you should remove it quickly from the job to prevent overheating just twist you wrist to withdraw it.How to produce a welding bead: - Generate arc. - Maintain electrode angle 900 with 0 surface and 70 with line of weld. - Move electrode vertically down smoothly so that arc is maintained. - Withdraw electrode quickly at the end of welding.To perform correct welding selection of correct electrode is essential, so lets learn about theelectrodes.While performing arc welding you need an electrode. It basically serves two purposes. 1) It completes welding circuit. 2) It provides additional material during fusion. An electrode is made of metallic wire of standard dia and length. This wire is coated with amaterial known as flux but sometimes not. Various types of electrodes are available in the market, therefore electrodes are classified in different categories.
  19. 19. Classification is based upon 1) Method of coating 2) Coating factor 3) Type of flux coating 4) Core wire materialCoating factor: This is the ratio of coating dia to the core wire dia. Coating dia Coating factor = --------------------------- Core wire dia 1) If ratio is 1.25 to 1.3 electrode is light coated. 2) If ratio is 1.4 to 1.5 electrodes is medium coated. 3) If ratio is 1.6 to 2.2 electrodes is heavy coated.Function of flux: During welding flux performs following functions 1) It stabilizes the arc. 2) It protects molten metal from oxidation. It compensates loss of elements burnt.Types of flux 1) Cellulose Flux: This flux contains cellulose. These types of flux give deep penetration and form very less slag during welding. 2) Rutile flux : This flux contains silicate and some part of cellulose. These fluxes are used for wider gap filling. 3) Iron oxide flux: This flux contains iron oxide and silicates. 4) Basic flux : This flux contains fluoride and calcium carbonate. Basic flux form large pool of molten metal and slag.Codification of Arc Welding ElectrodesNecessity of coding: As you know various types of electrodes are available for different purposes.
  20. 20. It is necessary for you to identify suitable electrode for your purpose. You can chose appropriateelectrode only if you can understand special number i. e. code of an electrode.Electrode coding mainly consists of: 1) Prefix E to indicate coated electrode for manual metal arc welding. 2) Type of flux A – Acid, B – Basic ,C – Cellulose, R – Rutile , S – Others 3) Mechanical properties: These are the Code Ultimate Yield properties of weld in terms of strength. Refer Tensile Strength Strength (min) N/mm2 N/mm2 table, You can find that code no 4 corresponds 4 410-510 330 to Ultimate tensile strength in the limit of 410- 5 510-610 360 510 N/mm2 while Min yield strength to 330 N/mm2 Code Welding position 4) Welding position: Refer corresponding 1 All table code 2 indicates that welding rod is 2 All except vertical 3 Flat butt, flat fillet unsuitable for vertical position otherwise can be 4 Flat butt, flat fillet used for all other welding positions. 5 Vertical down 6 Any other 5) Welding voltage : Refer the table , code 3 Code Polarity in Open circuit indicates that 70 volts Ac is necessary to use DC welding Voltage in AC Welding this electrode. 0 - Ve - 1 +Ve/-V e 50 2 -Ve 50 3 +Ve 50 4 +Ve/-Ve 70 5 -Ve 70 6 +Ve 70 7 +Ve/-Ve 90 8 -Ve 90Thus a code ER 4211 representsManual metal arc electrode covered with rutile coating, having ultimate 410-510 N/m2, yield strength330 N/mm2 elongation 22%, can be used for all welding position, voltage required 50V.Arc Length: When you produce an arc, the distance between electrode and the job is called as arc
  21. 21. length Short Arc: If you maintain distance between electrode and job less than the dia of electrode, the arc produced is short arc. Characteristics 1) You can hear popping sound. 2) You can observe rapid filler rod consumption 3) You can observe convex weld bead formation. 4) You can observe more fusion and penetration. 5) You can see less spatters You can see irregular ripples Long Arc: If you maintain the distance between electrode and job more than the dia of filler rod while welding, the arc produced is long arc. Characteristics 1) You can hear humming sound 2) You can observe un-stability of arc 3) You can see more spatters 4) You can observe poor fusion & penetration 5) You can see wide and coarse ripple. Normal Arc: If you maintain the gap between job and electrode equal to the dia of electrode, the arc produced is normal arc. Characteristics 1) You hear cracking sound 2) You can see less spatters 3) You can observe correct fusion & penetration
  22. 22. 4) You can see proper shaped weld bead.Welding Joints & Positions Type of welding joint refers to the shape formed by placement of joining edges. There are 5 basic types of joints. 1) Butt joint 2) Corner joint 3) Edge joint 4) Lap joint 5) Tee joint Flat Position: In this position nozzle points towards the ground. Nozzle is moved in any direction. Horizontal Position: In this position nozzle points towards vertical plane opposite to your body but moves only left to right or right to left.
  23. 23. Vertical Position: In this position nozzle pointstowards vertical plane opposite to your body but moves only up and down. Overhead Position: In this position nozzle points towards the plane above your head. Nozzle can be moved in any direction.
  24. 24. Types of weldWeld type refers to the ways of depositing metal on joining pieces. There are 4 basic types of weldsas follows Bead weld: This type of weld is formed when one or more weave beads are deposited on unbroken surface. The purpose of this weld is to obtain desired property or dimension. Application: This type of weld is used for strengthening the metal sheet, repair of worn out shafts etc. Butt weld: Butt weld is formed when the metal to be deposited penetrates the cavity formed by pieces to be joined which are in same plane. Application: This type of weld is used to join pieces, which are in same plane e.g. Pipe joints. Fillet weld: Fillet weld is formed when metal is deposited at the line of interface for joining Application: This weld is used for joining pieces, which are not in the same place. Butt weld: Butt weld is formed when the metal to be deposited penetrates the cavity form by pieces to be joined which are in same plane. Application: This type of weld is used to join pieces, which are in same plane e.g. Pipe joints.
  25. 25. Fillet weld: Fillet weld is formed when metal is deposited at the line of interface for joining. Application: This weld is used for joining pieces, which are not in the same place.Other terms related to weld Leg Length: The distance between points where two ends of weld deposit touches the plate being joined on either side of a tee joint and point of joint. Reinforcement : Excess metal deposited over the surface of parent metal.
  26. 26. Root: The distance between parts to bejoined. This distance is filled by weldment.Root face: Face below the chamferedsurface.Root run: The first run of weld deposited overthe joint.Sealing run: Small weld deposited at one sidefor sealing purpose.
  27. 27. Common welding defects Undercut: Groove formed in the parent metal. Cause Remedy Current too high Adjust Welding speed fast Adjust Faulty electrode Correct manipulation Wrong electrode angle Correct Overheating of job Correct arc length . Overlap : Molten metal flows over parent metal. Cause Remedy Low current Adjust Slow welding speed Adjust Long arc Adjust Large dia electrode Use correct dia Porosity : Holes or lack of material in weld. Cause: 1.Presence of contamination like moisture. 2. Fast cooling of weld metal 3. Improper cleaning of edges. Remedy: 1. Remove oil , grease , and moisture during pre welding operations. 2. Use good quality of flux. 3. Avoid long arc.
  28. 28. Spatter : Small droplet deposition aroundwelding line. Cause Remedy High welding current Adjust Long arc Correct Poor electrode quality ReplaceMelting of edges: Parent metal melts atedges. Cause Remedy Oversize electrode. Replace High welding current Adjust Wrong electrode Correct manipulationCrack: Hairline separation of metal in theweldment. Cause Remedy Fast cooling Correct Pre-stressed metal Relieve stresses More passes run Reduces passes runIncomplete penetration: Failure of moltenmetal to reach up to root. Cause Remedy Lesser bevel angle Correct Low current Adjust Large dia electrode Replace
  29. 29. Slag Inclusion: Entrapped foreign material. Cause Remedy Incorrect edge Correct preparation Wrong electrode Replace High current Adjust Long arc AdjustAssignment I Join given pieces using square butt joint in flat position.You are provided with: 3. Tack weld on both ends as well as center with 3.15 mm electrode and 1. Safety devices. 130 Amp. 2. Electrical welding equipment 4. Deposit one side single run with 3. Welding accessories. 3.15 mm welding rod and 110 Amp. 4. Piece of M S plate. Maintain electrode 90o with surfaceProcedure: and 80o with line of weld. 1) Clean surfaces and prepare square 5. Move electrode forward steadily. edges. 2) Take safety precautions. 6. Remove slag from weld and inspect. 3) Set pieces as butt joint with root gap 1.5 mm.
  30. 30. Material Name:Size Instructor’s Signature:ScaleAssignment 2 Join given pieces using fillet and lap joint.You are provided with: 5. Deposit root run with 3.15 mm 1. Safety devices. electrode and 130 Amp current.. 2. Electrical welding equipment 3. Welding accessories. 6. Maintain electrode angle 45o with 4. Pieces of MS plate. surfaces and 80o with line of weld.Procedure: 7. Remove slag and clean.. 8. Deposit covering run with weaving 1. Take safety precautions. motion, with 4 mm electrode and 2. Clean surfaces and square the edges. 170 Amp current. 3. Set the pieces in the form of lap joint as 9. Prevent edges from melting. shown. 4. Set job in flat position and tack the pieces 10. Remove slag, clean and inspect for at the ends and center. defects.
  31. 31. Material NameSize Instructor’s SignatureScaleAssignment 3 Join given pieces using fillet weld and corner joint in flat positionYou are provided with: 8. Set current 125 Amp and deposit root 1. Safety devices. run to obtain complete penetration. 2. Electrical welding equipment 9. Remove slag and inspect for defects. 3. Welding accessories. 10. Select 4 mm electrode and set current 4. Pieces of MS plate. to 170 Amp. Deposit intermediate runProcedure: 1. Clean edges and surfaces. with slight weaving. 2. Take safety precautions. 11. Remove slag and inspect for defects 3. Set joining pieces at right angle for 12. Deposit final run using weaving motion. corner joint using fixture. 13. Clean welded joint and inspect for 4. Select welding rod 3.15 mm dia and defects. set current 130 Amp. Starting Date : 5. Tack weld at both the ends. Finishing Date: 6. Clean tack weld and check for alignment. Instructor’s Observations: 7. Keep tacked pieces in flat position.
  32. 32. Material Name:Size Instructor’s Signature:ScaleAssignment 4 Join given pieces using tee fillet jointYou are provided with: 5. Set tee in flat position. 1. Safety devices. 6. Deposit root run with 3.15 mm 2. Electrical welding equipment electrode and 130 Amp current. 3. Welding accessories. 4. Pieces of MS plate. 7. Ensure electrode angle 45o withProcedure: surfaces and 80o with line of weld. 1. Take safety precautions. 8. Remove slag and clean. 2. Clean surfaces and square the edges. 9. Deposit covering run with 4 mm 3. Set pieces in inverted tee (⊥) shape set electrode and 170 Amp current. right angle with square and hold pieces 10. Remove slag, clean and inspect for with the help support. defects. 4. Tack welds the pieces at ends and center.
  33. 33. Material Name:Size Instructor’s Signature:Scale

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