group 7


Published on

Published in: Education, Business, Technology

group 7

  1. 1.  NAME : MHUMMAD SHAHZEB. ROLL NO : BSME01113093. SECTION : “A”. GROUP : “10”
  3. 3. Welding is a process to join two different or similarpiece of metals with the help of filler rod . It is adifferent process from brazing and soldering.
  4. 4. Filler metals are used to supply additional metal tothe weld zone during welding. They are availableas filler rod or wire and may be bare or coatedwith flux. The purpose of flux is to retardoxidation of the surfaces being welded, bygenerating a gaseous shield around the weldzone. Flux also help to dissolve or remove theoxides and other substances from weld zone. Theflux is enhancing the development of a strongerjoint.
  6. 6. In the late nineteenth century, it was soonrecognized that an arc between two electrodes wasa concentrated heat source that could producetemperature approaching 4000c (7000f).Variousattempts were made to use an arc as the heatsource for fusion welding. A carbon rod wasselected as one electrode and the metal workpiece become the other. If needed , filler metal wasprovided by metallic wire or rod that wasindependently fed into the arc. As processdeveloped, the filler metal replace the carbon rodas the upper electrode. The metal wire not onlycarried the welding current but as it melted in thearc , it also supplied the necessary filler.
  7. 7.  Arc welding is a type of welding that uses awelding power supply to create an electric arcbetween an electrode and the base material to meltthe metals at the welding point. They can useeither direct (DC) or alternating (AC) current, andconsumable or non-consumable electrodes . Thewelding region is usually protected by some typeof shielding gas, vapor, or slag. Arc weldingprocesses may be manual, semi-automatic, or fullyautomated. First developed in the early part of the20th century, arc welding became commerciallyimportant in shipbuilding during the Second WorldWar. Today it remains an important process for thefabrication of steel structures and vehicles.
  8. 8.  A pool of molten metal is formed nearelectrode tip, and as electrode is movedalong joint, molten weld pool solidifies inits wakeARC WELDING:
  9. 9.  Problems with manual welding:◦ Weld joint quality◦ Productivity Arc Time = (time arc is on) divided by(hours worked)◦ Also called “arc-on time”◦ Manual welding arc time = 20%◦ Machine welding arc time ~ 50%
  10. 10.  Consumable – consumed during weldingprocess◦ Source of filler metal in arc welding Nonconsumable – not consumed duringwelding process◦ Filler metal must be added separately ifit is added
  11. 11. Group of fusion welding operations that burnvarious fuels mixed with oxygen OFW employs several types of gases, which isthe primary distinction among the membersof this group Oxyfuel gas is also used in flame cuttingtorches to cut and separate metal plates andother parts Most important OFW process is oxyacetylenewelding
  12. 12. Fusion welding performed by a hightemperature flame from combustion ofacetylene and oxygen Flame is directed by a welding torch Filler metal is sometimes added◦ Composition must be similar to base metal◦ Filler rod often coated with flux to cleansurfaces and prevent oxidation
  13. 13. Oxyacetylene Welding
  14. 14.  Most popular fuel among OFW group becauseit is capable of higher temperatures than anyother◦ Up to 3480C (6300F) Two stage reaction of acetylene and oxygen:◦ First stage reaction (inner cone of flame)C2H2 + O2  2CO + H2 + heat◦ Second stage reaction (outer envelope)2CO + H2 + 1.5O2  2CO2 + H2O + heat
  15. 15.  Maximum temperature reached at tip of inner cone,while outer envelope spreads out and shields worksurface from atmosphere Shown below is neutral flame of oxyacetylene torchindicating temperatures achievedOxyacetylene Torch
  16. 16.  Together, acetylene and oxygen are highlyflammable C2H2 is colorless and odorless◦ It is therefore processed to have characteristicgarlic odor
  17. 17.  C2H2 is physically unstable at pressures muchabove 15 lb/in2 (about 1 atm)◦ Storage cylinders are packed with porous fillermaterial saturated with acetone (CH3COCH3)◦ Acetone dissolves about 25 times its ownvolume of acetylene Different screw threads are standard on C2H2and O2 cylinders and hoses to avoidaccidental connection of wrong gases
  18. 18.  Methylacetylene-Propadiene (MAPP) Hydrogen Propylene Propane Natural Gas
  19. 19. FW processes that cannot be classified as arc,resistance, or oxyfuel welding Use unique technologies to develop heat formelting Applications are typically unique Processes include:◦ Electron beam welding◦ Laser beam welding◦ Electroslag welding◦ Thermit welding
  20. 20. Fusion welding process in which heat forwelding is provided by a highly-focused,high-intensity stream of electrons strikingwork surface Electron beam gun operates at:◦ High voltage (e.g., 10 to 150 kV typical) toaccelerate electrons◦ Beam currents are low (measured in milliamps) Power in EBW not exceptional, but powerdensity is
  21. 21.  When first developed, EBW had to be carriedout in a vacuum chamber to minimizedisruption of electron beam by air molecules◦ Serious inconvenience in production Pumpdown time can take as long as anhour
  22. 22. 1. High-vacuum welding – welding in samevacuum chamber as beam generation toproduce highest quality weld2. Medium-vacuum welding – welding in separatechamber but partial vacuum reduces pump-down time3. Non-vacuum welding – welding done at or nearatmospheric pressure, with work positionedclose to electron beam generator - requiresvacuum divider to separate work from beamgenerator
  23. 23. Advantages: High-quality welds, deep and narrow profiles Limited heat affected zone, low thermaldistortion No flux or shielding gases neededDisadvantages: High equipment cost Precise joint preparation & alignment required Vacuum chamber required Safety concern: EBW generates x-rays
  24. 24. Fusion welding process in which coalescence isachieved by energy of a highly concentrated,coherent light beam focused on joint LBW normally performed with shielding gasesto prevent oxidation Filler metal not usually added High power density in small area◦ So LBW often used for small parts
  25. 25.  No vacuum chamber required for LBW No x-rays emitted in LBW Laser beams can be focused and directed byoptical lenses and mirrors LBW not capable of the deep welds and highdepth-to-width ratios of EBW◦ Maximum LBW depth = ~ 19 mm (3/4 in), whereasEBW depths = 50 mm (2 in)
  26. 26. FW process in which heat for coalescence isproduced by superheated molten metal fromthe chemical reaction of thermite Thermite = mixture of Al and Fe3O4 finepowders that produce an exothermic reactionwhen ignited Also used for incendiary bombs Filler metal obtained from liquid metal Process used for joining, but has more incommon with casting than welding
  27. 27.  (1) Thermit ignited; (2) crucible tapped, superheatedmetal flows into mold; (3) metal solidifies to produceweld jointThermit Welding
  28. 28.  Joining of railroad rails Repair of cracks in large steel castings andforgings Weld surface is often smooth enough that nofinishing is required
  29. 29.  Cracks Cavities Solid inclusions Imperfect shape or unacceptable contour Incomplete fusion Miscellaneous defects