Materials Science and Manufacturing Engineering Miscellaneous
- 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 = Varc20 + 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 = 5mmCorrect 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 = Varc20 + 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
- 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.
- 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.
- 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 speedHt = 20 × 250 × 0.70 5
Ht = 0.7kJ/ mmCorrect Option: C
Net heat input per unit length,
Ht = V.I × η v
V = voltage, I = current, A
v = welding speedHt = 20 × 250 × 0.70 5
Ht = 0.7kJ/ mm
- 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/sSpecific Energy = 2100 A × V
Transferred Power = 0.7 × 3000 = 2100 J/SV = 2100 14 × 20
V = 7.5mm/sCorrect 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/sSpecific Energy = 2100 A × V
Transferred Power = 0.7 × 3000 = 2100 J/SV = 2100 14 × 20
V = 7.5mm/s