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Joining Processes WELDING

Joining Processes WELDING. WELDING. Definition: Material joining process. Two parts connected at their contacting surfaces by suitable heat and pressure. Many welding processes are accomplished by heat alone, some others by heat and pressure, and some with pressure only.

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Joining Processes WELDING

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  1. Joining ProcessesWELDING

  2. WELDING Definition:Material joining process. Two parts connected at their contacting surfaces by suitable heat and pressure. Many welding processes are accomplished by heat alone, some others by heat and pressure, and some with pressure only. In some welding operations a filler material is used. Welding operation usually applied to metals but also used for plastics. 2

  3. Joining Processes Parts produced by any of the manufacturing processes can be made into larger, more complex bodies via Joining processes • Creating a metallurgical bond by adhesion and diffusion • Joining by fusion with the use of various heat sources • Brazing or soldering with a lower-melting metal • Mechanical fastening

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  5. Fusion Welding Processes

  6. Chemical reactions Burning gases GAS WELDING Heat from electricity Arc ARC WELDING SYSTEMS Resistance welding Sources of Energy for Fusion Welding • Light • LASER

  7. Three Specific Types of Welding Modules • In this Welding, Cutting, and Brazing module, three specific types of welding are covered. These are listed below: • Oxygen-fuel gas welding and cutting • Arc welding and cutting • Resistance welding

  8. Resistance Welding • Definition: • This is a group of fusion welding processes that use heat and pressure to make the coalescence. • The heat comes from electrical resistance to current flow at the site of the weld. • The processes include: • Spot Welding • Projection Welding • Seam Welding Note: FP&M only does spot welding.

  9. Resistance Welding • Spot Welding • A process typically used in high-volume, rapid welding applications. • The pieces to be joined are clamped between two electrodes under force, and an electrical current is sent through them.

  10. Welding/Cutting Hazards • Potential Hazards • Fires may start by hot materials igniting nearby combustibles. • Burns to the operator may occur if unprotected skin comes into contact with the extremely hot work. • Magnetic fields could easily destroy/disrupt electronic components, stored data if not careful.

  11. Welding/Cutting Hazards • Potential Hazards Cont.: • Metal fumes from vaporizing of the work with the extremely hot arcs may be inhaled into the worker’s lungs. • Certain metals and metal oxide fumes, including zinc, cadmium and beryllium, produce serious illnesses when inhaled. • Fluxes used with welding to create inert atmospheres at the point of the weld also present inhalation hazards. • All welding and cutting must have adequate ventilation to protect the person doing the welding and those working around the welding area.

  12. Weld Joint StructureCharacteristics of a typical fusion-weld zone in oxyfuel-gas and arc welding. Microhardness (HV) profile across a weld bead. A fusion joint is far from homogenous. Degree of inhomogeity increases from pure metals to multiphase alloys.

  13. Typical weld zone in arc and gas welds • The base material adjacent to the melt boundary is exposed to high temperatures, and the properties and structure are changed within the heat-affected zone. • Cold worked base material will show recrystallization in HAZ, with coarse grain sizes. • In either case, a coarse-grained structure of lower strength exits at the melt boundary. Melt

  14. Weldability and Weld Quality- Welding Defects-

  15. Welding Defects • Fusion welding defects due wrong heat input, insufficient rate of weld metal deposition, and cooling. • Lack of bonding or gas porosity due to surface contaminants, including oxides, oils, etc. • Undesirable reactions with surface contaminants • Solidification cracks in the weld. • 5. Solidification shrinkage coupled with solid shrinkage imposes internal tensile stresses on the structure, may lead to distortion. • 6. Gases released or formed during welding (eg CO) can lead to porosity which weakens the joint and acts as a stress raiser.

  16. Weld joint There are 5 basic joint types in welding Butt joint: Two materials are in the same plane, joined from the edges. Corner joint:The corners of two materials form a right angle and joined. Lap joint: Two parts overlaps. Tee joint: One part is perpendicular to the other, making a T shape. Edge joint: Edges of the two materials joined. 16

  17. Weld Joints 17

  18. Types of weld Fillet weld: Used in T joints,corner joints, lap joints. Groove weld:Used in butt joints. Plug weld: Used in lap joints. Slot weld: Used in lap joints. Spot weld: Used in lap joints. Seam weld: Used in lap joints. Flange weld:Used in edge joints. Surfacing weld:Not a joining process, it is used to increase the thickness of the plate, or provide a protective coating on the surface. 18

  19. Fillet Weld Slot and Plug Weld Groove weld 19

  20. Metal Treatment • Preheating the weld zone – reduces energy input, cooling rates in the weld and HAZ, reduces differential shrinkage, residual stresses, and distortion. • Postwelding heat treatment of the entire welded structure • Stress-relief anneal reduces residual stresses to acceptable level. • Normalizing a steel wipes out most undesirable effects of welding. • Full heat treatment (quenching and tempering of steels) • Peening (hammering or rolling) of weld bead improves the strength of welds.

  21. Oxyacetylene Gas Welding Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing, flame. The gas mixture in (a) is basically equal volumes of oxygen and acetylene. (d) The principle of the oxyfuel-gas welding operation.

  22. Oxyacetylene Torch The acetylene valve is opened first; the gas is lit with a spark lighter or a pilot light; then the oxygen valve is opened and the flame adjusted. Basic equipment used in oxyfuel-gas welding. To ensure correct connections, all threads on acetylene fittings are left-handed, whereas those for oxygen are right-handed. Oxygen regulators are usually painted green, and acetylene regulators red.

  23. Oxyfuel gas welding 23

  24. Oxygen-fuel gas welding & Cutting • The elements of Oxygen-fuel gas welding and cutting: • General Requirements • Cylinders • Service Pipe Systems • Pipe System Protection

  25. Oxygen-fuel gas welding and cutting • General Requirements • Focuses on using Acetylene Safely • Flammable • Unstable • Cannot be adjusted above 15 psi • Safe Work Practices • Blow out cylinder valve • Turn on cylinder valve first and then adjust the regulator pressure screw. • Never stand in front or behind a regulator when opening the cylinder valve • Open cylinder valve slowly • The pressure adjusting screw: • Turning clockwise allows the gas allows to flow. • Turning counterclockwise reduces or stop the gas flow.

  26. Oxygen-fuel gas welding and cutting • General Requirements Cont.: • Safe Work Practices • Purge oxygen and acetylene passages • Light the acetylene • Never use oil or grease • Do not use oxygen as a substitute for air • Keep your work area clean

  27. Oxygen-fuel gas welding and cutting • Cylinders • Cylinder approval and marking • marked for the purpose of identifying the gas content, with either the chemical or trade name of the gas • Storage of cylinders • Storage area must be well ventilated • Cylinders must be at least 20 feet from combustibles • Valves must be closed • Valve protection must be in place • Inside storage must be limited to 2,000 cubic feet. • Cylinders must be stored in upright position • Oxygen must be at least 20 feet from fuel gas or 5 feet with a 1/2 hour fire barrier • Separate oxygen from fuel gas

  28. Oxygen-fuel gas welding and cutting • Cylinders Cont.: • Operating Procedures • Operation must emphasize the absence of oily or greasy substances. Follow these rules of operation: • Cylinders, cylinder valves, couplings, regulators, hose, and apparatus shall be kept free from oily or greasy substances. • Oxygen cylinders or apparatus shall not be handled with oily hands or gloves. • A jet of oxygen must never be permitted to strike an oily surface, greasy clothes, or enter a fuel oil or other storage tank.

  29. Oxygen-fuel gas welding and cutting • Service Pipe Systems • There are special requirements for service pipe systems when using oxygen or acetylene. • Oxygen • Acetylene or Acetylene Compounds

  30. Oxygen-fuel gas welding and cutting • Pipe System Protection • The entire service pipe system must be protected against build-up of excessive pressure and leaks. This protection is accomplished with: • Protective equipment • Regulators • Proper hose and hose connections.

  31. Oxygen-fuel gas welding and cutting • Pipe System Protection Cont.: • Protective equipment is divided into the two categories listed here: • Pressure Relief Devices • The pressure relief device should discharge upwards to a safe location. • Pressure relief valves are required in fuel-gas piping systems to prevent excessive pressure build up within the system.

  32. Oxygen-fuel gas welding and cutting • Pipe System Protection Cont.: • Approved protective equipment shall be installed in fuel-gas piping to prevent: • Backflow of oxygen into the fuel-gas supply system • Passage of a flash back into the fuel-gas supply system • Excessive back pressure of oxygen in the fuel-gas supply system.

  33. Arc Welding 34

  34. t Arc Welding and Cutting • Definition: • A fusion process wherein the coalescence of the metals is achieved from the heat of an electric arc formed between an electrode and the work. • Application • Installation • Operation & Maintenance

  35. Arc Welding & Cutting • Application • Applies to a large and varied group of processes that use an electric arc as the source of heat to melt and join metals. • Installation • Arc welding requires proper installation of equipment. • A critical part of installation is ensuring that proper grounding is completed.

  36. Arc Welding & Cutting • Operation & Maintenance • All connections to the machine shall be checked to make certain that they are properly made. • The work lead shall be firmly attached to the work. • Magnetic work clamps shall be free from adherent metal particles of spatter on contact surfaces. • Coiled welding cable shall be spread out before use to avoid serious overheating and damage to insulation.

  37. Arc Welding & Cutting • Operation and Maintenance Cont.: • During welding operations, cables with splices within 10 feet (3m) of the holder shall not be used. • Welders should not coil or loop welding electrode cable around parts of their body. • Cables with damaged insulation or exposed bare conductors shall be replaced. • Joining lengths of work and electrode cables shall be done by the use of connecting means specifically intended for that purpose. • The connecting means shall have insulation adequate for the service conditions.

  38. Methods of Arc Welding • Three Types of Welding Methods: • Tungsten Inert Gas Welding (TIG) • Gas Metal Arc Welding (MIG) • Shielded Metal Arc Welding (SMAW)/ Stick Welding

  39. Electric Arc Welding Direct Current Electrode Negative (DCEN): Deeper weld. Direct Current Electrode Positive (DCEP): Shallower and Wider • Heat is produced from electric arc between workpiece and electrode material for melting the workpiece material. • AC and DC are used • An Inert gas shields both electrodes • Most heat energy is due to electron flow to metal Heat input H- heat input, E, Voltage, I, Current, and v the velocity of the arc travels along the weld line

  40. Electric Arc Welding- Classification - • The Electrode • Consumable: melts and serves as a filling material • Non-consumable: does not melt, parent metal is used, or a separate filler rod • Coated or Uncoated • Coating • Provides a gaseous shield to prevent oxidation • Lowers the voltage needed to establish the arc • May provide slag-blanket to protect the joint • Add alloying elements to enhance the properties of the joint.

  41. Non-Consumable Electrode Arc Welding • Gas Tungsten Arc Welding ( TIG) • Plasma arc welding • Atomic hydrogen welding

  42. Non-Consumable-Electrode Welding: Gas Tungsten-Arc Welding (GTAW) • Nonconsumable gas tungsten Inert gas welding (TIG) • Weld zone is protected by inert gas • DC with straight polarity is used with steel, cast iron, and stainless • AC with Al, Mg alloys where ac helps in stripping the oxide • Both hand and automatic operations are possible • The process demands considerable skill but produces very high-quality welds on almost any material • No weld spatter or slag formation

  43. Consumable Electrode Arc Welding Processes • Shielded metal arc welding • Submerged arc welding • Gas metal arc welding

  44. Consumable Electrode Arc Welding Shielded-Metal Arc Welding Schematic illustration of the shielded metal-arc welding process. About 50% of all large-scale industrial welding operations use this process.

  45. Consumable-Electrode Welding: Gas Metal-Arc Welding (GMAW) - MIG • Consumable gas metal-arc welding (MIG) • Consumable electrode is metal which melts to become part of the weld seam. • Weld zone is protected by a gas or a flux • No slag is formed • Several layers could be build with little or no intermediate cleaning • It is suitable for most metals • Wire electrode can be supplied in long, coiled lengths which allow uninterrupted welds in any welding position.

  46. Consumable Electrode Arc Welding Gas - Gas Metal-arc Welding Process- (a) Schematic illustration of the gas metal-arc welding process, formerly known as MIG (for metal inert gas) welding. (b) Basic equipment used in gas metal-arc welding operations.

  47. Other Welding Processes High Energy Beam Welding • Electron Beam welding (EBW) • Heat is produced by high velocity electron gun in a narrow beam • No filler material • High rate of heating results in greater depth and heat-affected zone is very small • Suitable for welding refractory materials like: molybdenum and zirconium • Requires a vacuum (limitation) • x-ray will be generated around the welding gun which may be cancerous

  48. High Energy Beam Welding • LASER Beam welding (LBW) • Uses a focused high power monochromatic light beam as a source of heat to the metal • Beam can be directed to the welding spot with a lens • Depth of welding similar to electron beam welding • Vacuum is not necessary (advantage) • Workpiece usually needs protection by a gas • Process is suitable for automation • Welding speeds can be upto 7 m/min

  49. Laser beam welding 50

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