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MET 304 Mechanical joint-welding

By Dr.S.G.A

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MET 304 Mechanical joint-welding

  1. 1. Mechanical Joints
  2. 2. Methods of joining materials  Welding  Mechanical joints – Screw fasteners – Rivets  Adhesives
  3. 3. Uses of welding: Ship building, industrial and commercial buildings. Oil pipe -line construction. Automobile, railways and bridges. Machine tools. Farm equipment, home appliances, and air-conditioning units. Computer components. Mining equipment. Boilers, furnaces and vessels. Maintenance and repair of equipment
  4. 4. Welding and cutting processes: Oxy-fuel gas welding (OFW) oxygen and acetylene Shield metal arc welding (SMAW) it is the most popular method because:  High quality weld  Excellent uniformity  High rate  It can be used for variety of materials and thickness.
  5. 5. • Gas tungsten arc welding (GTAW): Clean High quality weld No post weld finishing is required Performed on variety of material • Gas metal arc welding (GMAW): Fast Economical Welding on thin as well as thick plates Reduced post-weld cleanup
  6. 6. • Pressure welding or resistancewelding Spot welding Seam welding
  7. 7. Welding joints: Butt joint Lap joint Double butt joint Edge joint Tee joint Corner joint
  8. 8. Welding terminology
  9. 9. Welding strength:• Welding joints are classified according to the stress exerted on the joint: Class 1- Longitudinal shear Class2- transverse shear+ tension Class3 - pure tension
  10. 10. Class 1-Longitudinal shearArea of shear = 2 a LWhere, a = 0.707 h L L h a
  11. 11. Class2-transverse shear+ tensionArea of shear = 2 h LArea of tension = 2 h L L h h
  12. 12. Class3– pure tensionArea of tension = h L h
  13. 13. Design of welding joint: Welding rods coated with flux table (7.1), (7.3) Uncoated welding rods 80% of table (7.1) ½ inch should be added to the length of weld compensate for the defects which may occur at the beginning and end of welding Stress concentration factors should be taken from table (7.2) For reinforced weld increase the weld area by 20%
  14. 14. Eccentric loads: F L  Thewelds will be subjected to a combination of shear: – Shear caused by direct load – Shear caused by torque. (F L)
  15. 15. Approximate value of the significant stress dA l Oc S r1 r T O Torsional shear stress is proportional to its distance from centroid Assume, on element dA  s = nr where:  n: constant of proportionality  r: distance from the element to O
  16. 16. The external torque  dT = (s dA ) r  Integrated over all the welds in the joint. Thus, T sdAr 2 T n r dA nJ • J is the second polar moment of area of the weld Tr • Substituting for n we get, s J
  17. 17. Thank You