unit 5 arc welding types and notes.pptx

arc welding

1. Unit 5: Arc welding

2. 4.1 Introduction to welding 4.1.1 Introduction to welding 4.1.2 Classification of welding 4.1.3 Selection of different types of welding processes ER Saurav Kumar Thakur 2

3. 4.1.1 Introduction to welding Welding is the process of joining metal pieces by fusing them together with heat or pressure. Purpose of welding Joining of parts Hard surfacing-valves of an engine Deposit welding-building of worn-out parts ER Saurav Kumar Thakur 3

4. 4.1.2 Classification of welding Forge welding Fusion Welding Arc Welding SMAW(Shield Metal Arc Welding GMAW(Gas Metal Arc Welding) GTAW(Gas Tungsten Arc Welding ) Gas Welding Oxyacetylene MAPP (methylacetylene-propadiene propane) oxy-gasoline Resistance welding Spot Seam Flash Projection precussion ER Saurav Kumar Thakur 4

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6. 4.1.3 Selection of different types of welding processes Welding method can be selected based on following facts: Kind of metal to be weld Cost involved Position to be weld on Nature of products to be fabricated Production techniques ER Saurav Kumar Thakur 6

7. 4.2 Introduction to arc welding 4.2.1 Introduction to arc welding 4.2.2 Arc column theory 4.2.3 Power sources for arc welding 4.2.4 Types of welding: SMAW, GMAW, GTAW 4.2.5 Safety precautions in arc welding ER Saurav Kumar Thakur 7

8. 4.2.1 Introduction to arc welding Principle : The arc burns between melting electrode and work piece. The molten metal is shielded from atmospheric gases by gas and slag produced by electrode. Uses : Aircraft Automotive Bridge building Farm , construction, mining, oil, steel mill ,furnace equipment Machine tools, die Tank and boilers etc ER Saurav Kumar Thakur 8

9. 4.2.2 Arc Column Theory Ion Theory Ion flow : Ions move from the anode to the cathode because metal ions are positively charged and are attracted to the negative cathode.  Ion-gas collisions : As ions move through the air-gap between the electrodes, they collide with gas molecules in the atmosphere.  Thermal ionization : The collisions create a thermal ionization layer, which is a column of ionized gas.  Heat generation : When the ions strike the cathode, heat is generated .   Electron Theory When an electric arc is struck between electrode and work piece, flow of electrons takes place from cathode (electrode) to anode (base metal). However, the mass of the electrons is very small, they travel with very high velocities, and when they strike the surface of the base metal, kinetic energy acquired by these electrons is converted into heat energy. At the same time the positively charged ions traveling from anode to cathode give protecting shield to the flowing electrons as shown in Figure below. ER Saurav Kumar Thakur 9

10. 4.2.3 Power sources for arc welding AC transformer : A power source that uses alternating current  DC rectifier : A power source that produces direct current  AC/DC transformer rectifier : A power source that can use both alternating and direct current  Inverter : A power source that can produce direct current  Engine coupled DC and AC generators : A power source that can be used at sites where there is no domestic line supply  ER Saurav Kumar Thakur 10

11. 4.2.4 Types of welding: SMAW, GMAW, GTAW SMAW SMAW(Shield Metal A rc Welding) also known as MMAW(Manual Metal Arc Welding) or stick welding flux-shielded arc welding . A manual process using a flux-coated consumable electrode . Electric arc (AC or DC) melts the electrode and base metal, forming a weld pool Flux coating breaks down, releasing shielding gas and slag to protect the weld from atmospheric gases preventing oxidation. ER Saurav Kumar Thakur 11

12. Applications and Industries of SMAW Common in maintenance, repairs, and heavy steel construction. Used for welding iron, steel (including stainless), aluminum, nickel, and copper alloys. Construction – Steel buildings, bridges, pipelines, offshore platforms, railway tracks. Manufacturing – Automotive parts, machinery, pressure vessels, storage tanks, pipes, boilers, tools. Maritime – Shipbuilding and repairs. Energy – Power plants, oil & gas, wind turbines, nuclear, hydroelectric. Transportation – Vehicles, aircraft, railcars. Mining & Resources – Equipment, machinery, infrastructure. ER Saurav Kumar Thakur 12

13. 4.2.4 Types of welding: SMAW, GMAW, GTAW ER Saurav Kumar Thakur 13 Main components Electrode Holder : A clamping tool designed to firmly grip the electrode in place. Power Supply : The core component of the stick welder, responsible for delivering the required electrical current Cables : The conduits that transport electrical current throughout the system. Ground Clamp : completes the electrical circuit by attaching to the workpiece .

14. 4.2.4 Types of welding: SMAW, GMAW, GTAW ER Saurav Kumar Thakur 14

15. Q. Roles/Function of Stick Welding Electrodes The SMAW electrode serves several key purposes: Transmits Current : Carries electrical current from the welding machine to the work piece. Acts as Filler : Melts during welding to create the weld joint. Provides Protection : The flux coating shields the weld from atmospheric contamination, oxidation. Matches Base Metal : The core metal rod is designed to be compatible with the base material . ER Saurav Kumar Thakur 15

16. SMAW Advantages Versatile – Works in all positions and various metals. Portable – Compact equipment, welds anywhere with power. No gas needed – Flux coating provides shielding. Easy to learn – Simple, low-cost setup. Minimal prep – Handles slightly dirty surfaces. Outdoor-friendly – Works in windy conditions. Deep penetration – Ideal for thick metals. SMAW Disadvantages Slow – Lower speed than MIG or flux core. Messy – Produces slag and spatter. Skill-dependent – Requires welder experience. Fumes – Needs ventilation. Frequent stops – Electrode changes reduce efficiency. Limited for thin metals – Can be tricky on thinner materials. Not for reactive metals – Less effective on some alloys. ER Saurav Kumar Thakur 16

17. 4.2.4 Types of welding: SMAW, GMAW, GTAW GMAW(Gas Metal Arc Welding) Also known as MIG (Metal Inert Gas) Welding because inert gas like Helium, Argon is used for shielding. Also can be called as MAG( Metal Active Gas) Welding if reactive gases like CO 2 , O 2 are used. High deposition rate welding process Copper Coated Mildsteel wire fed from spool Semiautomatic welding process ER Saurav Kumar Thakur 17

18. Tools and equipment used in MIG Power Source : MIG uses a DC constant voltage transformer Wire feeder : Wire Feeder is required to feed electrode wire continuously and smoothly to the welding gun. Conduit and Hoses : Conduit facilitates feeding of wire to torch and hoses supply shielding gas. Welding Gun : It transfers welding current to wire and provides gas for shielding arc and weldpool . Gas cylinder contains shielding gas to protect weld area form gases like O 2 ,Nitrogen which can cause porosity, oxidation ,fusion defects. Argon and CO 2 is mixed as according to depth of penetration required. ER Saurav Kumar Thakur 18

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20. MIG Parameters/Variables Welding Current: Depend son metal thickness and metal transfer mode For thickness < 6mm current should be 100-200 amp For thickness > 8mm current should be 450-700 amp b. Gas Flow Rate(L/min): 10 l/min for spray 15 l/min for globular 20-25 l/min for dip mode c. Length of electrode d. Arc Voltage ER Saurav Kumar Thakur 20

21. e) Polarity It indicates the direction of current in that circuit. Since Current moves in one direction only in D.C welding Machine, so polarity is important. Straight Polarity (DCSP)/ Direct Current Electrode Positive(DCEN) Electrode connected to negative terminal of generator and work piece connected to positive terminal In straight polarity 2/3 of heat will be at the workpiece and 1/3 will be at the electrode. Deeper penetration Reversed Polarity(DCRP)/Direct Current Electrode Positive(DCEP) Electrode cable connected to positive terminal of generator and workpiece to Shallower Penetration ER Saurav Kumar Thakur 21

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23. f) Modes of metal Transfer Globular Dip Spray pulse ER Saurav Kumar Thakur 23

24. GTAW GTAW refers to Gas tungsten arc welding also called as TIG(Tungsten Inert Gas ) Non consumable electrode tungsten is used (although gets depleted in very long term in practical) Filler rod is added by the operator Flux is not used M.P of tungsten is 3350 o C Principle of Operation: An electric arc is formed between a non-consumable tungsten electrode and the workpiece , generating the heat required for welding.​ An inert gas, typically argon or helium, shields the weld area to prevent oxidation and contamination ER Saurav Kumar Thakur 24

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26. Equipment Components: Power Source: Provides a constant current suitable for maintaining a stable arc.​ Tungsten Electrode: Non-consumable and can withstand high temperatures( 3350 o C ) without melting. ​ Inert Gas Supply: Protects the weld pool from atmospheric contamination . Filler Material (optional): Added separately when needed to reinforce the weld .( note: If thickness of workpiece less than 5 mm filler material not used ) ER Saurav Kumar Thakur 26

27. ER Saurav Kumar Thakur 27 Advantages of GTAW/TIG Welding: Produces high-quality, precise welds with excellent finish.​ Suitable for welding thin materials and a wide range of metals, including stainless steel, aluminum, and magnesium.​ Provides greater control over the welding process compared to other methods.​ Less heat affected zone(HAZ) All position possible and neat and clean. Applications: Commonly used in industries requiring high-quality welds, such as aerospace, automotive, and piping systems.​ Ideal for tasks where precision and aesthetics are crucial Aluminium and its alloy ,magnesium and its alloy, stainless steel (SS), copper and nickel alloys.

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29. 4.2.5 Safety precautions Ventilation : Ensure there is adequate ventilation to remove fumes, gases, and dust.  Protective clothing : Wear fire-retardant clothing, gloves, shoes, and a face mask.  Eye protection : Wear eye protection at all times to protect against eye flash and slag while chipping too. Electrical safety : Ensure the welder is properly installed and grounded. Avoid touching any electrode or circuit while the power is on.  Fire safety : Weld only in a fire safe area and keep flammable materials away.  Fumes and gases : Avoid breathing fumes and gases by wearing a respirator if necessary.  First aid : Keep a well-stocked first aid kit handy.  Training : Ensure that welders are trained when new equipment and techniques are adopted.  Warning labels : Ensure that welders have access to labels on containers of materials and safety data sheets.  After use switch off the machine ,remove the weld rod. ER Saurav Kumar Thakur 29

30. Safety Precautions ER Saurav Kumar Thakur 30

31. Power sources ER Saurav Kumar Thakur 31

32. 4.3 Arc Welding equipment and accessories 4.3.1 Arc welding machines: types, uses and care 4.3.2 Problems in welding machines: troubles, causes and remedies 4.3.3 Arc welding machine and operators’ accessories. ER Saurav Kumar Thakur 32

33. Welding machines Sizes of welding machine are rated based on their approximate amperage capacity at 60 % duty cycle for example 150-200 ampere machine for light to medium duty welding. 250-300 ampere for average welding requirements ,used in plants for production, maintenance ,repair, all general shop welding. 400-600 ampere for heavy duty welding,used for heavy structural work ,fabrication of heavy machine parts ,tank welding etc ER Saurav Kumar Thakur 33

34. Classificatoin based on type of current Direct current rectifier arc welding machine used for MMAW, inert gas welding ,SAW(submerged arc welding) 3 major components transformer ,rectifier for converting A.C to D.C, and vent fan for cooling Alternating current arc welding machine A.C and D.C Rectifier Welding Machines Engine powered dc welding machines ER Saurav Kumar Thakur 34

35. Welding machines Types 1)MIG Welding Machine Metal inert gas welding machines are generally used for large and thick materials. In this, the welder needs to use a consumable wire as both an electrode and a filler material. This process is faster than TIG welding, resulting in a shorter time and lower production costs. The machine works in  single-phase, three-phase , and all in one. ER Saurav Kumar Thakur 35

36. Welding machines ER Saurav Kumar Thakur 36 2) TIG Welding machine Tungsten inert gas welding machines are better for thin metals and smaller projects because they produce precise and clean welds it is used in many industries, such as aviation, aerospace, and sheet metal operations.

37. Welding machines 3) SMAW Welding machine Generally, shielded metal  arc welding  machines work on the principle of heat produced by an electric arc. These are also known as stick welding, which uses an electric current flowing through the gap between the metal and welding stick (filler rod). SMAW machines are operated by both AC and DC currents. ER Saurav Kumar Thakur 37

38. Welding machines 4) Transformer Welding Machine It is a  step-down transformer  that converts high voltage, low-amperage AC input current into low voltage, high-amperage AC welding current. The transformer welding machine can run on single-phase power. ER Saurav Kumar Thakur 38

39. Welding machines problems, causes and remedies Breakdown of common welding machine problems: Electrical Issues: Power fluctuations:  Too high or too low voltage can cause unstable welding.  Overheating:  Excessive welding can lead to overheating of internal components.  Overload protection tripping:  Pushing the machine beyond its capacity can trigger safety mechanisms.  Wire Feeding Issues (MIG/MAG): Wire feed inconsistencies:  Erratic wire feed can lead to poor weld quality.  Wire jams:  Clogged wire feeder mechanism can disrupt the welding process.  ER Saurav Kumar Thakur 39

40. Welding machines problems, causes and remedies Shielding Gas Problems (MIG/TIG): Incorrect gas flow:  Too little or too much shielding gas can cause porosity and spatter.  wrong gas composition:  Using the wrong shielding gas for the material can lead to poor weld quality.  ER Saurav Kumar Thakur 40

41. Welding machines problems, causes and remedies Proper Maintenance: Regular cleaning and lubrication of the welding machine are crucial to prevent malfunctions.  Correct Settings: Selecting the appropriate welding parameters based on the material and desired weld quality is essential.  Operator Skill: Skilled welding technique is key to minimizing defects and ensuring consistent weld quality. ER Saurav Kumar Thakur 41

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43. 4.4 Arc welding electrode: classification, application and care ER Saurav Kumar Thakur 43

44. Arc welding electrode Classification of Arc Welding Electrodes : Mainly two types Consumable I) Coated Electrode II) Bare Electrode Non consumable Further Classification Low Hydrogen Electrodes: Considered the most versatile, with a coating containing minimal hydrogen, ideal for high-strength welds on carbon and low-alloy steels, requiring careful drying before use due to moisture sensitivity.  Cellulosic Electrodes: Primarily used for deep penetration in root passes, especially in pipe welding, with a coating rich in cellulose that generates a thick slag cover.  Iron Powder Electrodes: High deposition rate, suitable for fast filling of large gaps, often used with a DC reverse polarity.  Basic Electrodes: Contain a high proportion of calcium carbonate or calcium fluoride, providing good arc stability and slag removal, often used for welding in all positions.  ER Saurav Kumar Thakur 44

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46. Arc welding electrode Application of Arc Welding Electrodes: Mild Steel Welding: Low hydrogen electrodes are widely used for general-purpose welding on mild steel.  High-Strength Steel Welding: Specific low hydrogen electrodes are chosen for welding high-strength steels where superior mechanical properties are required.  Stainless Steel Welding: Dedicated stainless steel electrodes are needed to achieve proper corrosion resistance.  Pipe Welding: Cellulosic electrodes are often used for root passes due to their deep penetration capabilities.  ER Saurav Kumar Thakur 46

47. Arc welding electrode Care of Arc Welding Electrodes: Storage: Keep electrodes in a dry, airtight container to prevent moisture absorption, especially for low hydrogen electrodes.  Drying: Before use, low hydrogen electrodes should be properly dried according to manufacturer's instructions to remove moisture.  Handling: Avoid touching the electrode coating with bare hands to maintain its integrity.  Electrode Selection: Choose the correct electrode type based on the base metal, welding position, desired mechanical properties, and current type.  ER Saurav Kumar Thakur 47

48. Arc welding electrode ER Saurav Kumar Thakur 48

49. Arc welding electrode ER Saurav Kumar Thakur 49

50. Heat Affected Zone and Fusion Zone Fusion Zone - The fusion zone is the region of the base metal that is actually melted. The depth of fusion is the distance that fusion extends into the base metal or previous welding pass. Heat Affected Zone (HAZ) - When the weld pool is cooling and solidifying, the majority of the heat flows through the parent metal alongside the joint. The structure of the steel in the area surrounding the weld, which has not melted will be altered by the intense heat of the weld. This is referred to as the heat-affected zone (HAZ) on the base metal ER Saurav Kumar Thakur 50

51. Heat Affected Zone and Fusion Zone ER Saurav Kumar Thakur 51

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53. Heat Affected Zone and Fusion Zone ER Saurav Kumar Thakur 53

54. Distortion in Weldments When a piece of metal is heated, the metal expands and upon cooling the metal contracts and tries to resume its original shape. But in welding process, expansion and contraction forces may not be uniform throughout all parts of the metal. This is due to the difference in the temperature of the weld metal and the base metal regions near the weld that leads to internal stresses causing bending, buckling and rotation. The displacement arising out of these forces are called distortion ER Saurav Kumar Thakur 54

55. Distortion in Weldments ER Saurav Kumar Thakur 55

56. 4.5 Arc Welding fundamentals and techniques: 4.5.1 Condition of welding table and welding machine 4.5.2 Influencing factors in arc welding: position, face protection, arc length, Angles of electrode, Travel speed of electrode, amperage 4.5.3 Method, application and advantages of striking an arc (tap, Scratch) 4.5.4 Weld movement: types, application and advantages 4.5.5 Welding joints: types and application 4.5.6 Defects on welding process, cause and their possible remedies ER Saurav Kumar Thakur 56

57. Welding Table A welding table should be stable and heat resistant, while a welding machine should be able to melt metal to create new shapes or combine metals.  Welding table condition Stability A welding table should be stable enough to hold heavy loads without warping or tipping over. This is important for precise welds, especially on large or intricate projects.  Heat resistance A welding table should be able to withstand the high temperatures generated by welding without warping or degrading.  Protection A welding table should contain sparks, slag, and hot metal to prevent damage to the work environment.  ER Saurav Kumar Thakur 57

58. Welding Table Surface A welding table's surface should be durable, heat resistant, and have high tensile strength. Steel is the standard material for welding tables because of its durability.  Welding machine condition Heat production A welding machine produces heat to melt metal, allowing it to be shaped or combined with other metals.  Type There are different types of welding machines, including spot welders, brazing/MIG welders, and stud welders.  ER Saurav Kumar Thakur 58

59. Striking the arc ER Saurav Kumar Thakur 59

60. Scratching method ER Saurav Kumar Thakur 60

61. Tapping method ER Saurav Kumar Thakur 61

62. W elding Joints ER Saurav Kumar Thakur 62

63. Welding Joints ER Saurav Kumar Thakur 63

64. Welding Defects a) Cracks - Cracks can occur in both the base metal and the weld metal as a result of welding. The cracks are mainly caused by three principle reasons: • High carbon and alloy content of the base metal, Hydrogen and nitrogen absorption • Rapid cooling rate.(Uneven heating and cooling leads to residual stress build up, so preheating shall be done to remove residual stress ) Aspects of base metal and weld metal composition are very important as is also the need for low hydrogen electrodes to be dry . The presence of iron sulphide in the weld metal is most likely to produce solidification cracks on contraction. Remedy Preheating can be done to remove localized stress,correct the welding procedure ER Saurav Kumar Thakur 64

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66. Welding Defects b) Undercut Undercut is the term given to a sharp narrow groove along the toe of the weld due to the scouring action of the arc removing the metal and not replacing it with weld metal. Main cause This type of defect is formed due to the use of excessive current, incorrect electrode angles, too fast travel speed or an excessively long arc. R emedy The defect is detected easily by visual inspection and repaired easily by depositing additional weld material. Decrease amperage ER Saurav Kumar Thakur 66

67. Welding Defects ER Saurav Kumar Thakur 67

68. c) Slag Inclusions Slag is formed in the welding process due to the chemical reaction of the melted electrode coating. It normally consists of metal oxides and other compounds. Since it has less density than the molten weld metal the slag usually floats on the surface. On cooling, this is removed by the welder. But, if the cooling is rapid, the slag may get trapped before it can rise to the surface. When several passes of weld are made to achieve the desired weld size, the slag that forms between each process must be removed completely. Main cause The main reason for slag inclusion is due to the failure to remove the slag fully between runs, excessive weaving and the use of too large an electrode in a narrow groove or too low amperage Remedy Clean surface before welding ,remove impurities. ER Saurav Kumar Thakur 68

69. Welding Defects d ) Lack of Fusion The filler metal melted on top of base metal before base metal is ready to receive it. Main cause • the mating surfaces are not properly cleaned of all coatings such as, slag, oxides etc. • not enough heat (low amperage), too fast welding Remedy Increase amperage ,decrease speed ER Saurav Kumar Thakur 69

70. Welding Defects Inadequate Penetration When the weld penetration is less than that specified it is termed as inadequate penetration. Main cause This type of defect, primarily occurring in groove welds, is due to insufficient groove angles, very large electrodes, inadequate weld current, larger welding rates, or insufficient gaps at the root of welds. Remedy Decrease speed Change angle of electrode Increase amperage Correct electrode size Edge preparation to be checked Back plates to be used ER Saurav Kumar Thakur 70

71. Welding Defects Porosity Porosity is formed when a number of gas pockets or voids are trapped during the cooling process. Main cause Porous welds may arise as a result of coating breakdown due to excessively high current, longer arc length, excessive moisture pickup by the electrode ( particularly low hydrogen types), and impurities absorbed from the base metal. Using wet electrodes is bad practice ER Saurav Kumar Thakur 71

72. Influencing factors in arc welding ER Saurav Kumar Thakur 72 1)Welding Positions F is  fillet , and G is  groove

73. Influencing factors in arc welding 2)Arc length arc length" refers to  the distance between the tip of the welding electrode (whether it's a stick electrode or a tungsten electrode in TIG welding) and the surface of the work piece being welded Impact on weld quality: Too long arc:  Can lead to unstable arc, low heat input, poor penetration, spatter, and undercut.  Too short arc:  Can cause excessive heat, burn-through, distortion, and poor control over the weld pool.  Normal arc length  The correct arc length or normal arc length is approximately equal to the diameter of the core wire of the electrode. ER Saurav Kumar Thakur 73

74. Influencing factors in arc welding ER Saurav Kumar Thakur 74 3)Angles of electrode Butt joint = 90° Lap joint = 45 ° T joint = 45 ° Corner = 90 °

75. Influencing factors in arc welding 4) Travel speed of electrode Travel speed is the speed at which a welding torch or electrode moves across a work piece.  It's usually measured in inches per minute (IPM) or centimeters per minute ( CPM) Factors affecting travel speed  Material thickness : Thicker materials may require slower travel speeds to fill each pass Material sensitivity : Heat-sensitive materials like aluminum may require slower travel speeds to avoid burn through Weld application : The exact travel speed required depends on the type of weld being performed ER Saurav Kumar Thakur 75

76. Influencing factors in arc welding 5) Amperage Amperage is the strength of the electrical current used in welding. It's a measure of how much electricity is flowing through the circuit.  It depends on electrode diameter ,electrode type etc. ER Saurav Kumar Thakur 76

77. Weld motion ER Saurav Kumar Thakur 77

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