Materials Science and Manufacturing Engineering Miscellaneous


Materials Science and Manufacturing Engineering Miscellaneous

Materials Science and Manufacturing Engineering

Direction: Resistance spot welding of two steel sheets is carried out in lap joint configuration by using a welding current of 3 kA and a weld time of 0.2 s. A molten weld nugget of volume 20 mm3 is obtained. The effective contact resistance is 200 micro-ohms. The material properties of steel are given as (i) latent heat of melting 1400 kJ/kg, (ii) density 8000 kg/m3, (iii) melting temp 1520°C (iv) specific heat 0.5 kJ/kg°C. The ambient temp is 20°C.

  1. Heat (in Joules) used for production weld nugget will be (assuming 100% heat transfer efficiency)









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    I = 3000 A
    t = 0.2 sec
    R = 200 μΩ
    V = 200 mm3
    LH = 1400 kJ/kg
    ρ = 8000 kg/m3
    C = 0.5 kJ/kg °C
    Heat Generation = I2 RT
    = 3000 × 200 ×10-6 × 0.2 = 360 Joules.
    Heat utilised for production of weld Nugget
    = m [LH + C∆T]
    800 × 20 × 10-9[1400 + (1500 × 0.5)] × 1000
    = 344 Joules

    Correct Option: C

    I = 3000 A
    t = 0.2 sec
    R = 200 μΩ
    V = 200 mm3
    LH = 1400 kJ/kg
    ρ = 8000 kg/m3
    C = 0.5 kJ/kg °C
    Heat Generation = I2 RT
    = 3000 × 200 ×10-6 × 0.2 = 360 Joules.
    Heat utilised for production of weld Nugget
    = m [LH + C∆T]
    800 × 20 × 10-9[1400 + (1500 × 0.5)] × 1000
    = 344 Joules


  1. Aluminium strips of 2 mm thickness are joined together by resistance spot welding process by applying an electric current 6000 A and 0.15 second. The heat required for melting aluminium is 2.9 J/mm3. The diameter and thickness of the weld nugget are found to be 5 mm and 2.5 mm respectively. Assuming the electrical resistance to be 75 micro ohms, the percentage of total energy utilized in forming the weld nugget is









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    hn = 2.5 mm, I = 6000 A
    R = 75 µΩ, t = 0.15sec
    dn = 5 mm Energy/Volume = 2.6 J/mm3
    Energy generated = I2 R t
    = 60002 × 75 × 10-6 × 0.15 = 405 J
    Energy Required = 2.9 × volume of Nugget

    = 2.9 ×
    π
    d2nhn
    4

    = 2.9 ×
    π
    522.5 = 142.35 joules
    4

    Efficiency =
    142.35
    × 100 ≃ 35%
    405

    Correct Option: B

    hn = 2.5 mm, I = 6000 A
    R = 75 µΩ, t = 0.15sec
    dn = 5 mm Energy/Volume = 2.6 J/mm3
    Energy generated = I2 R t
    = 60002 × 75 × 10-6 × 0.15 = 405 J
    Energy Required = 2.9 × volume of Nugget

    = 2.9 ×
    π
    d2nhn
    4

    = 2.9 ×
    π
    522.5 = 142.35 joules
    4

    Efficiency =
    142.35
    × 100 ≃ 35%
    405



  1. Consider the following statements: The magnitude of residual stresses in welding depends upon
    1. Metal melted/deposited
    2. Design of weldment
    3. Support and clamping of components
    4. Welding process used
    Which of the statements given above are correct?









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    Residual stress depends on welding parameters such as current, voltage, speed, current.

    Correct Option: B

    Residual stress depends on welding parameters such as current, voltage, speed, current.


  1. Two 8 mm thick steel plates are placed 5 mm apart and welded by a butt joint. Welding is carried out at 20 V and speed of 5 mm/s. Heat transfer efficiency is 0.80. If the heat required to melt steel is 10 J/mm3 and melting efficiency is 0.625. The weld current (in amperes) will be









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    t = 8 mm, Gap = 5mm
    V = 20 volts, v = 5 mm/s
    ηHt = 0.8, H = 10J/mm, ηm = 0.625
    I =?
    Volume of weld pool = 8 × 5 × x
    = 40 x mm3
    Heat Required = 10 × 40 x = 400 x J
    Heat Generated

    = ηHtηm
    VIx
    v

    = 400=
    0.625 × 20 × I × x × 0.8
    5

    I = 200 A

    Correct Option: B

    t = 8 mm, Gap = 5mm
    V = 20 volts, v = 5 mm/s
    ηHt = 0.8, H = 10J/mm, ηm = 0.625
    I =?
    Volume of weld pool = 8 × 5 × x
    = 40 x mm3
    Heat Required = 10 × 40 x = 400 x J
    Heat Generated

    = ηHtηm
    VIx
    v

    = 400=
    0.625 × 20 × I × x × 0.8
    5

    I = 200 A



  1. In a fabrication shop, a T-joint is to be made between two plates using a chin intermittent, double fillet weld of 6 mm leg length. The intermittent welds are 40 mm long and spaced 80 mm apart, edge to edge. The welding symbol of the joint is









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    Correct Option: D