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  1. 1. Introduction to Welding Dr. H. K. Khaira Professor in MSME MANIT, Bhopal
  2. 2. Welding • Welding is the process of joining together pieces of metal or metallic parts by bringing them into intimate proximity and heating the place of content to a state of fusion or plasticity
  3. 3. Welding • A concentrated heat source melts the material in the weld area; the molten area then solidifies to join the pieces together • Sometimes a filler material is added to the molten pool to strengthen the weld
  4. 4. following are the key features of welding: • The welding structures are normally lighter than riveted or bolted structures. • The welding joints provide maximum efficiency, which is not possible in other type of joints. • The addition and alterations can be easily made in the existing structure. • A welded joint has a great strength. • The welding provides very rigid joints. • The process of welding takes less time than other type of joints.
  5. 5. largely used in the following fields of engineering: • Manufacturing of machine tools, auto parts, cycle parts, etc. • Fabrication of farm machinery & equipment. • Fabrication of buildings, bridges & ships. • Construction of boilers, furnaces, railways, cars, aeroplanes, rock ets and missiles. • Manufacturing of television sets, refrigerators, kitchen cabinets, etc.
  6. 6. Types of Welding • Fusion Welding • Pressure Welding
  7. 7. Fusion Welding
  8. 8. Fusion Welding It is defined as melting together and joining metals by means of heat. It uses heat to melt the base metals and may add a filler metal. The thermal energy required for these operations is usually supplied by chemical or electrical means. Filler metals may or may not be used.
  9. 9. Welding Metallurgy The base metal(s) and filler metal mix together during melting, forming an alloy when they solidify The solidification of the metals can be considered as casting a small amount of metal in a metal mold
  10. 10. Fusion Welding • All fusion welding process have three requirements. – Heat – Shielding – Filler metal • The method used to meet these three requirements is the primary difference between welding processes.
  11. 11. Types of Fusion Welding (i). Arc welding • Carbon arc • Metal arc • Metal inert gas • Tungsten inert gas • Plasma arc • Submerged arc • Electro-slag (ii). Gas Welding • • • Oxy-acetylene Air-acetylene Oxy-hydrogen (iv). Thermit Welding (vi)Newer Welding – Electron-beam – Laser
  12. 12. Types of Fusion Welding (i). Gas Welding 1. Oxy-acetylene 2. Air-acetylene 3. Oxy-hydrogen (ii). Arc welding 1. Carbon arc 2. Metal arc 3. Metal inert gas 4. Tungsten inert gas 5. Plasma arc 6. Submerged arc 7. Electro-slag (iv). Thermit Welding (v)Newer Welding 1. Electron-beam 2. Laser
  13. 13. Pressure Welding When pressure is used to join two metal parts with or without heat, it is known as pressure welding.
  14. 14. Types of Pressure Welding Processes (i). Resistance Welding 1. Butt 2. Spot 3. Seam 4. Projection 5. Percussion (ii). Solid State Welding 1. Friction 2. Ultrasonic 3. Diffusion 4. Explosive
  15. 15. Factors Affecting Welding • • • • Heat source Weld Metal Protection Heat affected zone Weldability
  16. 16. Heat Sources
  17. 17. Heat Sources in Welding • • • • • • 1. Combustion of fuel gas 2. Electric arc 3. Electrical resistance 4. Friction 5. Chemical reaction 6. Other sources
  18. 18. Power density of heat sources • As the power density of the heat source increases, the heat input to the workpiece that is required for welding decreases. • Power density we get – Deeper weld penetration – Higher welding speeds – Better weld quality – Less damage to the workpiece
  19. 19. Variation of heat input to the workpiece with power density of the heat source.
  20. 20. Variation of weld strength with unit thickness of workpiece heat input per unit length of weld. Heat input Weld strength
  21. 21. Power density of heat sources • Heat input Weld strength
  22. 22. Weld Metal Protection
  23. 23. Weld Metal Protection • During fusion welding, the molten metal in the weld “puddle” is susceptible to oxidation • Must protect weld puddle from the atmosphere
  24. 24. Weld Metal Protection • Methods – Weld Fluxes – Inert Gases – Vacuum
  25. 25. Weld Fluxes • Typical fluxes – SiO2, TiO2, FeO, MgO, Al2O3 – Produces a gaseous shield to prevent contamination – Act as scavengers to reduce oxides – Add alloying elements to the weld – Influence shape of weld bead during solidification
  26. 26. Inert Gases • Argon, helium, nitrogen, and carbon dioxide form a protective envelope around the weld area • Used in – MIG – TIG – Shielded Metal Arc
  27. 27. Vacuum • Produce high-quality welds • Used in electron beam welding • Nuclear/special metal applications – Zr, Hf, Ti • Reduces impurities by a factor of 20 versus other methods • Expensive and time-consuming
  28. 28. Heat affected zone
  29. 29. Heat affected zone The surrounding area of base metal that did not melt, but was heated enough to affect its grain structure is known as heat affected zone
  30. 30. Heat affected zone
  31. 31. Heat affected zone
  32. 32. Heat affected zone
  33. 33. Weldability
  34. 34. Weldability • Weldability is the ease of a material or a combination of materials to be welded under fabrication conditions into a specific, suitably designed structure, and to perform satisfactorily in the intended service
  35. 35. Weldability • 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 of service (e.g., extreme temperatures, corrosive environments, fatigue, high pressures, etc.)
  36. 36. Summary Fusion welding melts the material then allows it to solidify and join it together Solid-state welding uses pressure, and sometimes heat, to allow the metal to bond together without melting Welding allows the production of parts that would be difficult or impossible to form as one piece