Welding Shop

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Welding Shop

  1. 1. By: Mr. Sunil Kumar Ojha Assistant Professor Mechanical Engineering Department JRE Group of Institutions Greater Noida
  2. 2.  Joining elements together, which shapes a final product. Assembly process can be made by human workers (uneducated but skilled) or by specialized machines and robots.  Example: Cars, computers, engines, cellophane etc.
  3. 3. Aspect of manufacturing: 1.Impossible to manufacture as a single product e.g chairs, computer, etc. 2.More economical to manufacture as individual components, which are then assembled e.g bicycle 3.For maintenance or replacement purposes e.g. car accessories and engines. 4.Different materials due to different properties requirement e.g. cooking pots and pans. 5.Ease and less costly of transportation e.g. Bicycle
  4. 4.  1. Welding  2. Soldering and Brazing  3. Mechanical Fastening  4. Adhesive Bonding But our presentation will focus on welding
  5. 5.  Mechanical methods ◦ Screwed fasteners, rivets,  Adhesive bonding  Brazing and Soldering ◦ Base metal does not fuse. ◦ Molten filler drawn into close-fit joints by capillary action (surface tension forces). ◦ Brazing filler melts >450 C, solder <450 C  Welding 5 Introduction to welding
  6. 6.  A joint produced by heat or pressure or both So there is continuity of material.  Filler (if used) has a melting temperature close to the base material 6 Introduction to welding welding is the process of joining in which heat is use d to join similar or dis-similar metals with or without t he application of pressure and filler metal.
  7. 7. ◦ Welding is a materials joining process which produces coalescence of materials by heating them to suitable temperatures with or without the application of pressure or by the application of pressure alone, and with or without the use of filler material. ◦ Welding is used for making permanent joints. ◦ It is used in the manufacture of automobile bodies, aircraft frames, railway wagons, machine frames, structural works, tanks, furniture, boilers, general repair work and ship building.
  8. 8.  Buildings and bridges structures;  Automotive, ship and aircraft constructions;  Pipe lines;  Tanks and vessels;  Railroads;  Machinery elements
  9. 9.  Strong and tight joining;  Cost effectiveness;  Simplicity of welded structures design;  Welding processes may be mechanized and automated
  10. 10.  Internal stresses, distortions and changes of micro- structure in the weld region;  Harmful effects: light, ultra violate radiation, fumes, high temperature.
  11. 11.  Solid phase welding ◦ Carried out below the melting point without filler additions ◦ Pressure often used ◦ Union is often by plastic flow  Fusion welding or Liquid Phase Welding ◦ Welding in the liquid state with no pressure ◦ Union is by molten metal bridging 11 Introduction to welding
  12. 12. Welding Fusion Welding Solid State Welding
  13. 13. Fusion WeldingOxyfuel- Gas Welding Pressure- Gas Welding Arc Welding Electron- Beam Welding Laser-Beam Welding Consumable Electrode Non Consumable electrode - Gas tungsten-arc welding -Plasma-arc welding -Atomic Hydrogen Welding - Shielded metal-arc welding -Submerged-arc welding -Gas Metal-arc welding -Flux cored-arc welding -Electrogas welding - Electroslag welding
  14. 14. Solid State WeldingRoll Bonding/ Welding Cold Welding Ultrasonic Welding Resistance Welding Friction Welding Explosion Welding Diffusion Welding -Inertia friction welding - Linear friction welding - Friction stir welding -Resistance spot welding - Resistance seam welding - High-frequency resistance welding - Resistance projection welding - Flash welding - Stud welding - Percussion welding
  15. 15. 1) OXYFUEL-GAS WELDING (OFW) - OFW uses a fuel gas combined with oxygen to produce flame - Function of the flame - act as a source of the heat to melt the metals at the joint. - Common gas welding process uses acetylene (oxyacetylene gas welding - OAW). -Application: structural sheet metal fabrication, automotive bodies, and various repair work.
  16. 16. - OAW process utilizes the heat generated by the combustion of acetylene gas (C2H2)in a mixture of oxygen. - These primary combustion process, occurs in the inner core of the flame, involves the reaction of: C2H2+ O---->2CO + H2+ Heat (1/3 total heat generated in the flame) - The secondary combustion process involves further burning of hydrogen and carbon monoxide: 2CO + H2+1.5O2------>2CO2+ H2O + Heat (2/3 of the total heat)
  17. 17. a. General view of oxy torch b. Cross-section of a torch used in oxyacetylene welding. The acetelyne valve is opened first; the gas is lit with spark lighter or a pilot light; then the oxygen valve is opened and the flame adjusted. c. Basic equipment used in oxyfuel-gas welding. All acetylene fittings are left handed while oxygen are right handed. Oxygen regulators are usually painted green, acetelyne regulators red.
  18. 18. Flame types 1. Neutral - ratio 1:1 , no excess oxygen 2. Oxidizing - greater oxygen supply (excess oxygen), harmful for steel due to oxidizes. Only suit for nonferrous metal like copper & copper based alloys. 3. Carburizing - insuffientof oxygen (excess acetytelene), low temperature, thus suitfor applications requiring low heat like brazing, soldering, flame hardening. Filler metals 1. To supply additional metal to the weld zone during welding. 2. Filler rods or wire and may be coated by flux 3. The purpose of flux is to retard oxidation of the welded surfaces.
  19. 19. Fusion Welding Process 2) PRESSURE GAS WELDING - Involved with two components starts by heating the interface. - Once when the interface begins to melt, the torch is withdrawn. - A force is applied to press both components together and maintain until the interface solidifies. - The joined end with the occurrence of a flash.
  20. 20. 3) ARC-WELDING PROCESSES - In arc welding, the heat is obtained from electrical energy – by using AC or a DC power supply. - The process involved can be either consumable or non- consumable electrode. - An arc is produced between the tip of electrode and the work piece which need to be welded. - The arc produces temperatures approximately 30,00 degrees Celsius.
  21. 21. Advantages ◦ Most efficient way to join metals ◦ Lowest-cost joining method ◦ Affords lighter weight through better utilization of materials ◦ Joins all commercial metals ◦ Provides design flexibility Limitations  Manually applied, therefore high labor cost.  Need high energy causing danger  Not convenient for disassembly.  Defects are hard to detect at joints.
  22. 22. a.) NON CONSUMABLE ELECTRODE - The electrode is a tungsten electrode type. - Need externally supplied shielding gas because of the high temperature involved in order to prevent oxidation of the weld zone. - DC is used and the polarity is important. - For straight polarity which is also known as direct-current electrode negative (DCEN); the workpiece is positve (anode) , while the electrode is negative (cathode).
  23. 23. - It will produce welds that are narrow and deep. - For reverse polarity which is also known as direct-current electrode positive (DECP); the workpiece is negative and electrode positive. - In this process, weld penetration is less, and the weld zone is shallower and wider.
  24. 24. i) GAS TUNGSTEN-WELDING (GTAW) - Also known as TIG welding - Suitable for thin metals. - This process is expensive because of the cost of inert gas - Provides welds with very high quality and surface finish - Filler metal is supplied from a filler wire - The shielding gas is usually argon or helium
  25. 25. - This filler metals are similar to the metal that need to be welded, and flux is not used. - In this operation, tungsten electrode is not consumed, therefore a constant and stable arc gap is maintained at a constant current level. - Power supply either 200A DC or 500A AC; depending on the metals to be welded. - Generally, AC is suitable for aluminum and magnesium. - Thorium or zirconium may be used in the tungsten electrodes to improve the electron emission characteristics.
  26. 26. - Contamination of the tungsten electrode by molten metal ca cause discontinuities in the weld. - Therefore, contact between the electrode with the molten metal pool should be avoided. Non Consumable Electrode
  27. 27. ii) PLASMA-ARC WELDING (PAW) - In this welding operation, a concentrated plasma arc is produced and directed towards the weld area. - The arc is stable and the temperature can reaches up to 33,000 degrees celsius. - PAW has less thermal distortion, and higher energy concentration – permitting deeper and narrower welds. - Plasma: it is an ionized hot gas composed of nearly equal number of electrons and ions.
  28. 28. - This plasma initiated between the tungsten electrode and the small orifice by a low current pilot arc. - Operating current: usually below 100A. - Filler metal is fed into the arc during welding process. - There are two methods of plasma-arc welding: a) Transferred-arc method - Work piece being welded is part of the electrical circuit. The arc transfers from the electrode to the work piece. b) Nontransferred method - The arc occurs between the electrode and the nozzle. The heat is carried to the workpiece by the plasma gas.
  29. 29. - Welding speeds from 120 to 1000 mm/min. - Can be welded with part thickness less than 6mm.
  30. 30. i) SHIELDING METAL-ARC WELDING - Old method , simplest, held manually. - Most of all industries and maintenance welding currently performed with this process. - The electric arc is generated by touching the tip of a coated electrode against the workpiece. - Need to have a sufficient distance and movement to maintain the arc. Consumable Electrode
  31. 31. - The heat generated, melts a portion of the electrode tip, its coating, and the base metal in the intermediate arc area. - The molten metal consists of a mixture of the base metal (work piece), the electrode metal, and substance from the coating on the electrode; thus this mixture forms the weld when it solidifies. - The electrode coating deoxidizes the weld area and provides a shielding gas to protect it from oxygen in the environment. Consumable Electrode
  32. 32. - The equipment consists of a power supply, cables and electrode holder. - Power supply: can be either DCor AC, ranges between 50 to 300A. - For sheet metal welding, DC is preferred because of the steady arc produces. Consumable Electrode
  33. 33. ii) SUBMERGED-ARC WELDING (SAW) - The weld arc is shielded by a granular flux consisting of lime, silica, manganese oxide,calcium flouride. - The flux is fed into the weld zone from a hopper by gravity flow through a nozzle. - The thick layer of flux completely cover s the molten metal and it prevents from spatterand sparks. - The flux also acts as a thermal insulator by promoting deep penetration of heat into theworkpiece. Consumable Electrode
  34. 34. - The consumable electrode is a coil of bare round wire 1.5 to 10 mm in diameter; andfed automatically through a tube which is called welding gun. - Electric current: range between 300 to 2000 A. - Power supply: single or three phase power point; rating up to 440V. - Due to flux is a gravity fed type; therefore this welding process is limited largely towelds into flat or horizontal position. Consumable Electrode
  35. 35. - Circular weld can be made on pipes or cylinders ²provided that they are rotated during welding process. -Suitable for carbon and alloy steel and stainless steel sheet or plates. - Welding speeds: as high as 5 m/min. Consumable Electrode
  36. 36. iii) GAS METAL-ARC WELDING - Also known as metal inert-gas (MIG). - The weld area is shielded by an effectively inert atmosphere of argon, helium, carbondioxide, or other various gas mixtures. - The temperatures generated are relatively low. - Suitable only for thin sheets which is less than 6mm. Consumable Electrode
  37. 37. -The consumable bare wire is fed automatically through a nozzle into the weld arccontrolled by wire-feed drive motor. -There are 3 types of GMAW process: a)Spray transfer. b)Globular transfer. c)Short circuiting. Consumable Electrode
  38. 38. a) SPRAY TRANSFER - Small size of molten metal droplets from the electrode are transferred to the weld area at a rate of several hundred droplets per second. - The transfer is spatter free and very stable. - Using high DC current and voltages with large diameter of electrodes.  - The electrodes are used with argon or an argon rich gas mixture act as a shielding gas. Types of Gas-Metal Arc Process
  39. 39. b) GLOBULAR TRANSFER - Utilizes with carbon-dioxide-rich gases, and globules are propelled by the forces of the electric-arc transfer of a metal, resulting in considerable spatter. - High welding current are used - greater weld penetration and higher welding speed c) SHORT CIRCUITING - The metal is transferred in individual droplets, as the electrode tip touches the molten weldmetal and short circuits. - Low currents and voltages are utilized. - Electrodes are made from small-diameter wire. - Power required: § 2 kW. Types of Gas-Metal Arc Process
  40. 40. iv) ELECTRON BEAM WELDING - Can be welded almost any metal; butt or lap welded and the thicknesses up to 150mm. - The thickness of the workpiececan range from foil to plate. - Generally, there is no involvement of shielding gas, flux, or filler metal. - Distortion and shrinkage in the weld area is minimal. - Heat is generated by high velocity narrow-beam electrons. - Capacity of electron guns range up to 100 kW. Consumable Electrode
  41. 41. - The kinetic energy of the electrons is converted into heat as they strike the workpiece. - Required special equipment to focus the beam on the workpiece, typically in vacuum. - The higher the vacuum, the more the beam penetrates, and the greater is the depth-to width ratio, range between 10 and 30. - Sizes of the welds are much smaller compared to conventional process. - Parameters can be controlled accurately at welding speeds as high as 12 m/min; thiscan be done by using automation and servo motor. Consumable Electrode
  42. 42. v) LASER-BEAM WELDING - Utilizes a high power laser beam as the source of heat. - The beam can focused onto a very small area, and due to this it has high energy density and deep penetrating capability. - This process is suitable for welding deep and narrow joints with depth-to-width ratios ranging from 4 to 10. - The laser beam may be pulsed for a application such as the spot welding of thinmaterials with power level up to 100 kW. Consumable Electrode
  43. 43. - Minimum shrinkage and distortion, good strength and generally are ductile and free ofporosity. - Can be automated to be used on a variety of materials with thicknesses up to 25mm. - Typical metals and alloys welded: aluminum, titanium, ferrous metals, copper. - Welding speeds: range from 2.5 m/min to as high as 80 m/min for thin metals. Consumable Electrode
  44. 44. Advantages of LBW over EBW: Laser beams can be shaped, manipulated, and focused optically by using fiber optics, therefore the process can be automated easily.The beams do not generate x-rays. The quality of the weld is better than in EBW with less tendency for incomplete fusion, spatter, porosity, and less distortion. Example of laser Welding: laser welding of razor blades Consumable Electrode
  45. 45. 52 Introduction to welding Thermit welding
  46. 46. THERMIT WELDING (TW) Thermit Powder Molten Crucible R A I L S Mould Igniter Molten metal flows down developed in 1893 Flame heating gate Thermit powder: Fe2O3 + 2Al = 2Fe + Al2O3
  47. 47. THERMIT WELDING (TW)
  48. 48. Solid-State Welding Processes
  49. 49. • Forge Welding • Cold Welding • Roll Welding • Resistance Welding • Hot pressure Welding • Diffusion Welding • Explosion Welding • Friction Welding • Ultrasonic Welding
  50. 50.  Pressure is applied to the workpieces through dies or rolls  Preferably both work pieces should be ductile  The work pieces should cleaned thoroughly  Can not join dissimilar metals Fig: The roll bonding or cladding process
  51. 51.  Surfaces of the two components are subjected to a static forces and oscillating shearing force  Produces a strong, solid-state bond  Versatile and reliable for joining metals Fig: a) Components of an ultrasonic welding machine for lap welds.The lateral vibration of the tool tip c ause plastic deformation and bonding at the inte rface of the work piece b)Ultrasonic some weldi ng using a roller c)An ultrasonically welded part
  52. 52.  Developed in the 1940’s  Parts are circular in shape  Can be used to join a wide variety of materials Fig: Sequence of operation in the friction welding process 1)Left-hand component is rotated at high speed. 2) Ri ght-hand component is brought into contact under an axial force 3)Axial force is increased;the flash begins to for m 4) Left-hand component stops rotating;weld is completed.The flash can subsequently be removed by machini ng or grinding
  53. 53.  Process can be fully automated  Can weld solid steel bars up to 250mm in outside diameter Fig:Shape of friction zone in friction welding,as a function of the force applied and the rotational speed
  54. 54.  Developed in the early 1900’s  A process in which the heat required for welding is produced by means of electrical resistance across the two components  RW does not requiring the following: ◦ Consumable electrodes ◦ Shield gases ◦ Flux
  55. 55.  RSW uses the tips of two opposing solid cylindrical electrodes  Pressure is applied to the lap joint until the current is turned off in order to obtain a strong weld Fig: (a) Sequence in the resistance spot welding
  56. 56.  Surfaces should be clean  Accurate control of and timing of electric current and of pressure are essential in resistance welding Fig: b)Cross-section of a spot weld,showing the weld nugget and the indentation of the electrode on the sheet surfaces.This is one of the most commonly used process in sheet- metal fabrication and in automotive-body assembly
  57. 57.  RSEM is modification of spot welding wherein the electrodes are replaced by rotating wheels or rollers  The electrically conducting rollers produce a spot weld  RSEM can produce a continuous seam & joint that is liquid and gas tight Fig : (a) Seam-Welding Process in which rotating rolls act as electrode (b) Overlapping spots in a seam weld. (c) Roll spot weld (d) Resistance-welded gasoline tank
  58. 58.  RPW is developed by introducing high electrical resistance at a joint by embossing one or more projections on the surface to be welded  Weld nuggets are similar to spot welding Fig: a) Resistance projection Welding b)A welded bracket c) & d) Projection welding of nuts r threaded hosses and stack
  59. 59.  The electrodes exert pressure to compress the projections  Nuts and bolts can be welded to sheet and plate by this process  Metal baskets, oven grills, and shopping carts can be made by RPW
  60. 60.  Heat is generated from the arc as the ends as the two members contacts  An axial force is applied at a controlled rate  Weld is formed in plastic deformation Fig : (a)Flash-welding process for end-to –end welding of solid rods or tubular parts (b) & (c) Typical parts made by flash welding (d)Design Guidelines for flash welding
  61. 61.  Small part or a threaded rod or hanger serves as a electrode  Also called as Stud arc welding  Prevent oxidation to concentrate the heat generation  Portable stud-welding is also available Fig:The sequence of operation in stud welding,which is used for welding bars threaded rods and various fasteners onto metal plates
  62. 62.  Percussion welding (PEW) is a type of resistance welding that blends dissimilar metals together. Percussion welding creates a high temperature arc that is formed from a short quick electrical discharge. Immediately following the electrical discharge, pressure is applied which forges the materials together. This type of joining brings the materials together in a percussive manner.  Percussion welding is similar to flash welding and upset welding but is generally considered to be more complex. It is considered to be more complex because it uses an electric discharge at the joint, followed by pressure being applied to join the materials together. Percussion welding is used to join dissimilar metals together, or used when flash is not required at the joint. This type of welding is limited to the materials having the same cross sectional areas and geometries. Percussion welding is used on materials that have small cross sectional areas.  Advantages of using percussion welding types include a shallow heat affected zone, and the time cycle involved is very short. Typical times can be found to be less than 16 milliseconds.
  63. 63. Forge Welding - Welding process in which components to be joined are heated to hot working tempe rature range and then forged together by hammering or similar means - Historic significance in development of manufacturing Technology - Process dates from about 1000 B.C., When blacksmiths learned to weld two pieces of metal - Of minor commercial importance today except for its variants
  64. 64. Roll Welding (ROW) - SSW process in which pressure sufficient to cause coalescence is applied by means of rolls, either with or without external heat - Variation of either forge welding or cold welding, depending o n whether heating of work parts is done prior to process - If no external heat, called cold roll welding - If heat is supplied, hot roll welding
  65. 65. Roll Welding
  66. 66. Roll Welding Application - Cladding stainless steel to mild or low alloy steel for corrosion resistance -Bimetallic strips for measuring temperature - “Sandwich" coins for U.S mint
  67. 67. Diffusion Welding (DFW) - SSW process uses heat and pressure, usually in a controlled atmosphere, with sufficient time for diffusion and coalescence to occur - Plastic deformation at surfaces is minimal - Primary coalescence mechanism is solid state diffusion - Limitation: time required for diffusion can range from seconds t o hours
  68. 68. DFW Applications - Joining of high-strength and refractory metals in aerospace and nuclear industries - Can be used to join either similar and dissimilar metals -For joining dissimilar metals, a filler layer of different me tal is often sandwiched between base metals to promote diffusion
  69. 69. Explosion Welding (EXW) - SSW process in which rapid coalescence of two metallic surfaces is caused by the energy of a detonated explosive -No filler metal used -No external heat applied - No diffusion occurs -time is too short -Bonding is metallurgical, combined with mechanical interlocking that results from a rippled or wavy interface between the metals
  70. 70. Explosive Welding -Commonly used to bond two dissimilar metals, in particular to clad one metal on top of abase metal over large areas
  71. 71. Friction Welding (FRW) - SSW process in which coalescence is achieved by frictional he at combined with pressure - When properly carried out, no melting occurs at faying su rfaces - No filler metal, flux, or shielding gases normally used - Process yields a narrow HAZ - Can be used to join dissimilar metals - Widely used commercial process, amenable to automation a nd mass production
  72. 72. Friction Welding
  73. 73. Application and Limitation of FRW Applications: - Shafts and tubular parts - Industries: automotive, aircraft, farm equipment, pet roleum and natural gas Limitations: - At least one of the parts must be rotational - Flash must usually be removed Upsetting reduces the part lengths (which must be taken int o consideration in product design)
  74. 74. Weldability - Capacity of a metal or combination of metals to be welded into a suitably designed structure, and for the resulting weld joint(s) to possess the required metallurgical properties to perform satisfactorily in intended service Good weldability characterized by:  Ease with which welding process is accomplished Absence of weld defects  Acceptable strength, ductility, and toughness in welded joint
  75. 75.  Metallurgical Capacity ◦ Parent metal will join with the weld metal without formation of deleterious constituents or alloys  Mechanical Soundness ◦ Joint will be free from discontinuities, gas porosity, shrinkage, slag, or cracks  Serviceability ◦ Weld is able to perform under varying conditions or service (e.g., extreme temperatures, corrosive environments, fatigue, high pressures, etc.)
  76. 76. Figure Characteristics of a typical fusion weld zone in oxyfuel gas and arc welding .
  77. 77. Soldering Soldering is a process of joining two metals by using another low temperature metal alloy ( Below 427 degree centigrade) .
  78. 78. Process : The surface to be joined are cleaned are cleaned and a re placed on each other. A flux is employed to prevent oxidation. Zinc chloride is commonly used for this pur pose. The soldering iron is heated either electrically or by some external heat . Then the hot end is dipped int o the flux and solder is pressed against the surface to be joined. A joint is formed by melting the solder.
  79. 79.  The joining of two metal pieces by means of heat and a special filler (Spelter) having a melting point above 427 degree Centigrade but lower than the melting point of the parts to be joined. In brazing the ends of parent metal are not melted but an alloy, having low melting point is used. Temperature is raised to the fusion point of this alloy which when melted runs between the edges due to capillary action and produces thinning effect resulting in brazed joint. Through brazing dissimilar materials can be easily joined. The filler rod is used for joining are of Bronze material ( 60-40% brass main constituent with suitable amount of deoxidizer like silicon and tin etc used).  Application: joining of tubes, radiators, pipes and pipes fitting tool tips electrical items etc.  Advantages: useful for joining of dissimilar material, thin sections easily joined, good surface finish obtained, High production, Less skill, less cost.  Disadvantage: low strength, not applicable for hardened steel and aluminum alloys.
  80. 80.  Inclusion: Entrapment of Slag, Scale, dirt, rust in weld zone etc  Cracks: Discontinuity of weld Metal  Distortion: Change in the indented shape and size of component or structure due to uneven contraction (shrinkage).  Poor Penetration: failure of weld molten metal to reach the bottom of joint.  Porosity: presence of small pores, voids, gases in the weld metal.  Spatter: Deposition of electrode metal particle adjutant to base metal  Undercut: Groove formed in the parent metal at the toe of a weld pass.  Overlapping: molten metal flows over the surface of the base metal.  Inadequate Fusion: sometime the deposited weld metal by electrode does not fuse fully with the base metal due to presence of oxides, dirt, slag or other foreign material.
  81. 81. Defects Reasons  1. Low Penetration  2. Cracks  3. Inclusions  4. Poor Fusion  5. Blow Holes (Porosity)  6. Wrapping  7. Scattering of weld  1.Incorrect current, fast speed of welding  2. selection of wrong electrode, metal contain too much carbon  3. dirty base metal, higher sulfur content, improper removal of slag  4. wrong current setting, wrong clearance between work piece and electrode, fast speed of welding.  5. Wrong arc length, impurities in in base metal, old electrode.  6. uneven heating, overheating, thin cross-section of metals  7. high current, long arc, faulty electrodes.

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