This set of Manufacturing Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Manufacturing Engineering Questions & Answers – Fusion Welding Processes-1”.
1. Consider a situation in which a welding operation is being performed with V = 20 volts, I = 200 A, and the cross-sectional area of the weld bead is 30 mm2. Estimate the welding speed if the workpiece and electrode are made of (a) aluminum, (b) carbon steel, and (c) titanium. Use an efficiency of 75%.
a) 35 mm/s
b) 34.5 mm/s
c) 36 mm/s
d) 46 mm/s
Explanation: For aluminum, the specific energy required is u = 2.9 J/mm3
v = e(VI/uA)
= (0.75) [(20/200)/(2.9/30)] = 34.5 mm/s.
2. Upon which of the following parameters does the current intensity in arc welding depend?
a) Stability of arc
b) Electrode diameter
c) Gap between the electrode and parent metals
d) Thickness of parent metals
Explanation: Electrodes for consumable arc-welding processes are classified according to the following properties:
i) Strength of the deposited weld metal
ii) Current (Ac or Dc)
iii) Type of coating.
3. In which of the following welding processes we use two non-consumable electrodes?
c) Atomic hydrogen
d) Submerged arc
Explanation: Non consumable electrodes are the ones that are not consumed during the process of welding. GTAW (Gas Tungsten Arc Welding)/TIG (Tungsten Inert Gas Welding), AHW (Atomic Hydrogen Welding), CAW (Carbon Arc Welding) processes use non-consumable electrodes.
4. Which of the following brazing process is good for mass scale joining?
Explanation: Furnace brazing is a semi-automatic used widely in industries and are best suited to large scale production operations.
5. For grey cast iron, which of the following welding methods is preferable?
b) Submerged arc
c) Gas flame
d) Electric arc
Explanation: As the percentage of carbon in grey cast iron is less, therefore MIG welding is preferable.
6. Due to which of the following reasons, flux is not used in atomic hydrogen welding?
a) The burning hydrogen shields the molten metal
b) Two electrodes are coated which gradually release the flux
c) The filler rod is coated with flux
d) One of the two electrodes is coated which releases the flux
Explanation: Separate flux/ shielding gas is not required in atomic hydrogen welding. The hydrogen envelop itself prevents oxidation of the metal and the tungsten electrode.
7. In resistance welding, between the electrodes, the nature of current and voltage parameters being used?
a) high current, high voltage
b) low current, high voltage
c) low current, low voltage
d) high current, low voltage
Explanation: High current produces more heat. When we use a low voltage power source, it allows a welder to have some reasonable over the small lighting bolts we use to fuse metal together.
8. Which of the following welding process in which heat is produced for welding by a chemical reaction?
a) Resisting welding
b) Thermit welding
c) Forge welding
d) Gas welding
Explanation: The thermite process is a chemical reaction in which a metal oxide (preferably molten) is displaced by another molten metal which is more reactive than the metal in the metal oxide, releasing a lot of heat. Example:
2Al + Fe2O3 → Al2O3 + 2Fe
2Fe + Cr2O3 → Al2O3 + 2Cr
Here aluminium is more reactive than Iron and Chromium and displaces it from their oxides. This reaction is used commercially to weld broken metallic parts. Railway lines are joined in the same manner.
9. The maximum diameter of electrodes being used in submerged arc welding?
a) 30 mm
b) 20 mm
c) 15 mm
d) 10 mm
Explanation: A consumable electrode can be used by the submerged arc welding which is a loop of bare round wire with 1.5 mm to 10 mm diameter. It can be fed routinely throughout the welding gun, and the submerged arc welding electrode composition depends on the welded material.
10. In arc welding, arc is created between the electrode and work by?
a) Contact resistance
b) Flow of voltage
c) Flow of current
d) Electrical energy
Explanation: All arc welding utilizes the transfer of electrical energy to heat energy. An arc is a sustained electric discharge through this ionised gas column called plasma between the two electrodes. In order to produce the arc, the potential difference between the two electrodes (voltage) should be enough to allow them to move across the air gap. The larger air gap requires higher potential differences. If the air gap becomes too large for the voltage, the arc may be extinguished.
11. The coating material used for the electrode is termed as?
c) Protective layer
Explanation: Flux is a substance used to prevent the formation of oxides and the other unwanted contaminations, or to dissolve them and facilitate removal. During welding the flux melts and becomes a liquid slag, covering the operation and protecting the molten weld metal the slag hardens upon cooling and must be removed later by chipping or brushing.
12. Which of the following welding process in which two pieces to be joined are overlapped and placed between two pointed electrodes?
a) Seam welding
b) Resistance welding
c) Projection welding
d) Spot welding
Explanation: Spot welding is the simplest and most used resistance welding process. Welding may be performed by means of single (most common) or multiple pairs of electrodes (as many as a hundred or more), and the required pressure is supplied through mechanical or pneumatic means.
13. Which of the following gases are used in Tungsten inert gas welding?
a) Helium and neon
b) Hydrogen and oxygen
c) Argon and helium
d) Carbon dioxide and hydrogen
Explanation: In the TIG welding process the arc is formed between a pointed tungsten electrode and the workpiece in an inert atmosphere of argon or helium.
14. Which of the following materials necessitates preheating in welding?
c) Cast iron
d) Stainless steel
Explanation: As the weldability of cast iron usually decreases as the amount of free carbon in cast iron increases, so it is preheated to a dull red and then welded.
15. The temperature, in arc welding, is of the order of?
Explanation: One of the main functions of the arc is to produce heat. The heat of the arc melts the surface of the base metal and the end of the electrode. The electric arc has a temperature that ranges from 3000 to 20,000°C.
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