This document discusses mechanical joints and welding. It provides information on different types of mechanical joints like screws and rivets. It then discusses various welding processes like oxy-fuel gas welding, shield metal arc welding, and gas tungsten arc welding. Different welding joints are also illustrated like butt joints, lap joints, and tee joints. The document concludes with discussing welding terminology, classification of welding joints based on stress, and design considerations for welding joints.

1. Mechanical Joints

2. Methods of joining materials
 Welding
 Mechanical joints
– Screw fasteners
– Rivets
 Adhesives

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. 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. • 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. • Pressure welding or resistance
welding
Spot welding
Seam welding

7. Welding joints:
Butt joint Lap joint
Double butt joint
Edge joint
Tee joint
Corner joint

8. Welding terminology

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. Class 1-
Longitudinal shear
Area of shear = 2 a L
Where, a = 0.707 h L
L
h
a

11. Class2
-transverse shear+ tension
Area of shear = 2 h L
Area of tension = 2 h L
L h h

12. Class3
– pure tension
Area of tension = h L
h

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. 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. 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. 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

22. Thank You