7th lec welding


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7th lec welding

  1. 1.  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.
  2. 2.  Plastic Welding or Pressure Welding The piece of metal to be joined are heated to a plastic state and forced together by external pressure (Ex) Resistance welding Fusion Welding or Non-Pressure Welding The material at the joint is heated to a molten state and allowed to solidify (Ex) Gas welding, Arc welding
  3. 3. (i). Arc welding Carbon arc (iv)Thermit Welding Metal arc (v)Solid State Welding Metal inert gas Friction Tungsten inert gas Ultrasonic Plasma arc Diffusion Submerged arc Explosive Electro-slag (vi)Newer Welding(ii). Gas Welding Electron-beam Oxy-acetylene Laser Air-acetylene (vii)Related Process Oxy-hydrogen Oxy-acetylene cutting(iii). Resistance Welding Arc cutting Butt Hard facing Brazing Spot Soldering Seam Projection Percussion
  4. 4. What is fusion welding..? A process in which parts are melted and fused or joint together is called fusion welding. or Fusion welding is a group of processes that bond metal together by heating a portion of each piece above the melting point and causing them to join together.
  5. 5. Types of fusion welding include: Arc welding. Oxy-fuel welding. Metal Inert Gas (MIG). Tungsten Inert Gas (TIG).
  6. 6.  Heat is supplied by various means o Oxyacetylene gas o Electric Arc o Plasma Arc o Laser Filler metal may be added
  7. 7. What is Arc Welding…?Arc welding is a type of welding that uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct (DC) or alternating (AC) current, and consumable or non-consumable electrodes.
  8. 8. Equipments: A welding generator (D.C.) or Transformer (A.C.) Two cables- one for work and one for electrode Electrode holder Electrode Protective shield Gloves Wire brush Chipping hammer Goggles
  9. 9. Transformer:A welding transformer is anelectrical transformer used inwelding power supply.It pulls relatively low currentdrawn from the mains powertypically limited to 15 A andconverts it to the typical 50 Ato 500 A used in arc weldingand higher currents used inspot welding.
  10. 10. Electrode holder:The insulated handle that clampsonto the electrode. The welderholds this during welding tocontrol the arcElectrode:Filler metal coated with flux in theform of a rod or heavy wireElectric cables:Cables are used in welding toconnect work piece withelectric supply.
  11. 11. Welding shield (hood):This is the mask which is worn to protect theperson welding from the bright flash of thearc.Welding gloves:These are special, insulated leather glovesthat reach about 6 inches above the wrists,and protect the hands and lower arms of thewelder (the person welding).Welding leathers:This is an apron like leather jacket thatcovers the shoulders and chest of the welder,used for overhead work where sparks mightignite the welders clothing, or cause burns.
  12. 12.  Gather the tools and materials you will need to beginwelding. Set up a safe work area, preferably with a table constructedof steel or other non-flammable material. Prepare the metal to be welded. Attach clamps to hold your metal pieces together. Attach the ground clamp to the larger piece of stock that isbeing welded. Select the correct rod and ampare range for the work youare attempting.
  13. 13.  Turn on your welding machine. Hold the stinger in your dominant hand by the insulatedhandle. Select the point where you wish to begin your weld. Strike the electrode against the surface of the metal, pullingit back slightly when you see an electric arc occur. Practice traveling across the path of your weld with theelectrode until you can keep a consistent arc, moving at aconsistent speed. Complete Your weld. Clean your finished weld. Paint your weld with a suitable rust-preventative primer toprotect it from corrosion.
  14. 14. Advantages Limitations  Most efficient way to join  Manually applied, therefore metals high labor cost.  Lowest-cost joining  Need high energy causing method danger  Affords lighter weight  Not convenient for through better utilization disassembly. of materials  Defects are hard to detect at  Joins all commercial joints. metals  Provides design flexibility
  15. 15. Types Of Flames:1. Neutral Flame.(5600 to 5900 F)In neutral flame both gases are in equal proportions.2. Oxidizing Flame (Excess of oxygen)(6000 to 6300F)An oxidizing flame is caused by increasing the oxygen from aneutral flame.3. Reducing Flame (Excess of acetylene)(5400 to 5500F)If the oxygen is reduced, a carbonizing flame is created from aneutral flame.
  16. 16. Three basic types of oxyacetylene flames used in oxyfuel-gas welding andcutting operations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame.