Materials Science and Manufacturing Engineering Miscellaneous


Materials Science and Manufacturing Engineering Miscellaneous

Materials Science and Manufacturing Engineering

  1. The voltage arc length characteristics of a DC arc is given by V = 20 + 40L, where L = arc length in cm. The power source characteristics can be approximated by a straight line. Open circuit is 80 V and short circuit current 1000 Amps. The optimum arc length in mm









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    Constant voltage Characteristics
    V = 20 + 40 L     ...(i)
    Vocv = 80 V,     Iscc = 1000 Amp.

    V = vocv
    vocv
    .I
    1scc

    V = 80 −
    80
    I      ....(ii)
    1000

    Vtransfermer = Varc
    20 + 40L = 80 −
    80
    L
    1000

    I =
    1000
    (60 − 40L)
    80

    Power = V.I.
    For optimum Arc length
    dP
    = 0
    dL

    (20 + 40L)(60 − 40L)
    1000
    .
    80

    Hence L = 0.5 cm = 5mm

    Correct Option: C

    Constant voltage Characteristics
    V = 20 + 40 L     ...(i)
    Vocv = 80 V,     Iscc = 1000 Amp.

    V = vocv
    vocv
    .I
    1scc

    V = 80 −
    80
    I      ....(ii)
    1000

    Vtransfermer = Varc
    20 + 40L = 80 −
    80
    L
    1000

    I =
    1000
    (60 − 40L)
    80

    Power = V.I.
    For optimum Arc length
    dP
    = 0
    dL

    (20 + 40L)(60 − 40L)
    1000
    .
    80

    Hence L = 0.5 cm = 5mm


  1. High alloy steel components are preheated before welding for reducing









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    Due to preheating, thermal conductivity will decrease so less thermal stressese and hence less distortion will take place.

    Correct Option: D

    Due to preheating, thermal conductivity will decrease so less thermal stressese and hence less distortion will take place.



  1. In TIG welding a.... A.... and.... B.... electrode is used









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    Non consumable base electrode is used.

    Correct Option: A

    Non consumable base electrode is used.


  1. A gas t ungst en ar c wel di ng oper at i on i s performed using a current of 250 A and an arc voltage of 20 V at a welding speed of 5 mm/s. Assuming that the arc efficiency is 70%, the net heat input per unit length of the weld will be ____ kJ/mm (round off to one decimal place).









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    Net heat input per unit length,

    Ht =
    V.I
    × η
    v

    V = voltage, I = current, A
    v = welding speed
    Ht =
    20 × 250
    × 0.70
    5

    Ht = 0.7kJ/ mm

    Correct Option: C

    Net heat input per unit length,

    Ht =
    V.I
    × η
    v

    V = voltage, I = current, A
    v = welding speed
    Ht =
    20 × 250
    × 0.70
    5

    Ht = 0.7kJ/ mm



  1. A welding operation is being performed with voltage = 30 V and current = 100 A. The crosssectional area of the weld bead is 20 mm2. The work-piece and filler are of titanium for which of the specific energy of melting is 14 J/mm³.
    Assuming a thermal efficiency of the welding process 70%, the welding speed (in mm/s) is (correct to two decimal places).









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    Voltage = 30 V,
    I = 100 A Area = 30 mm2
    Specific Energy = 14 J/mm3
    ηth = 70%
    welding speed V =?
    Power = V × I = 30 × 100 = 300 J/s

    Specific Energy =
    2100
    A × V

    Transferred Power = 0.7 × 3000 = 2100 J/S
    V =
    2100
    14 × 20

    V = 7.5mm/s

    Correct Option: D

    Voltage = 30 V,
    I = 100 A Area = 30 mm2
    Specific Energy = 14 J/mm3
    ηth = 70%
    welding speed V =?
    Power = V × I = 30 × 100 = 300 J/s

    Specific Energy =
    2100
    A × V

    Transferred Power = 0.7 × 3000 = 2100 J/S
    V =
    2100
    14 × 20

    V = 7.5mm/s