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# GATE 2020: Manufacturing Quiz 8

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Question 1

Which one of the following is a solid state joining process?

Question 2

In an arc welding process, the voltage and current are 25 V and 300 A respectively. The arc heat transfer efficiency is 0.85 and welding speed is 8 mm/sec. the net heat input (in J/mm) is:

Question 3

During a steady-state gas metal arc welding with direct current electrode positive, the welding current, voltage and welding speed are 150A, 30V, 6 m/min. A metallic wire electrode of diameter 1.2 mm is being feed at a constant rate of 12 m/min. The density, specific heat, and melting temperature of the wire electrode are 7000 kg/m3, 500 J/kg, 1530 °C. Assuming ambient to be 30 °C and neglect latent heat of melting, further consider that (2/3)rd of the total electrical power is available for melting. The melting efficiency of the wire electrode (%) is

Question 4

In arc welding of a butt joint, the welding speed is to be selected such that highest cooling rate is achieved. Melting efficiency and heat transfer efficiency are 0.5 and 0.7, respectively. The area of the weld cross section is 5 mm2 and the unit energy required to melt the metal is 10 J/mm3. If the welding power is 2 kW, the welding speed in mm/s is closest to

Question 5

For spot welding of two steel sheets (base metal) each of 3 mm thickness, welding current of 10000 A is applied for 0.2 s. The heat dissipated to the base metal is 1000 J. Assuming that the heat required for melting 1 mm3 volume of steel is 20 J and interfacial contact resistance between sheets is 0.0002Ω, the volume (in mm3) of weld nugget is _________.

Question 6

Two 1 mm thick steel sheets are to be spot welded at a current of 5000 A. Assuming effective resistance to be 200 micro-ohms and current flow time of 0.2 second, heat generated during the process will be _________.
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