Fusion-Welding Processes And Unconventional Welding Methods ( Manufacturing Engineering – I ) MCQs – Mechanical Engineering MCQs
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Mechanical Engineering MCQs – Fusion-Welding Processes And Unconventional Welding Methods ( Manufacturing Engineering – I ) MCQs
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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
Answer: b
Explanation: For aluminum, the specific energy required is u = 2.9 J/mm3
Therefore,
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
Answer: b
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?
a) MIG
b) TIG
c) Atomic hydrogen
d) Submerged arc
Answer: c
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?
a) Furnace
b) Induction
c) Dip
d) Torch
Answer: a
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?
a) MIG
b) Submerged arc
c) Gas flame
d) Electric arc
Answer: a
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
Answer: a
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
Answer: d
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
Answer: b
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
Answer: d
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
Answer: d
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?
a) Flux
b) Slag
c) Protective layer
d) Deoxidiser
Answer: a
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
Answer: d
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
Answer: c
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?
a) Copper
b) Aluminium
c) Cast iron
d) Stainless steel
Answer: c
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?
a) 30000°C
b) 55000°C
c) 20000°C
d) 70000°C
Answer: c
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.
Fusion Welding Processes – 2
1. Which of the following is used to generate Acetylene gas?
a) Calcium
b) Carbon
c) Calcium carbonate
d) Calcium carbide
Answer: d
Explanation: Acetylene is a hydrocarbon consisting of two carbon atoms and two hydrogen atoms. The simplest process reacts calcium carbide with water to produce acetylene gas and a calcium carbonate slurry, called hydrated lime. The chemical reaction may be written as CaC2 + 2H2O → C2H2 + Ca (OH)2.
2. Striking voltage as compared to a voltage during arc welding is?
a) less
b) same
c) more
d) can’t say
Answer: c
Explanation: The minimum voltage enough to arc across a given gap is called as the striking voltage. It is more than the arc voltage in arc welding.
3. How many zones are there in a carburising flame?
a) one
b) two
c) three
d) four
Answer: c
Explanation: If the oxygen is insufficient for full combustion, the flame is known as a reducing, or carburizing, flame. The temperature of a reducing flame is lower; hence, such a flame is suitable for applications requiring low heat, such as brazing, soldering, and flame-hardening operations.
4. Due to which of the following reasons distortion in welding occurs?
a) Oxidation of weld pool
b) Use of high voltage
c) Improper clamping
d) Use of high current
Answer: c
Explanation: As if the clamping is improper the weld will not be at the right place.
5. In reverse polarity welding _____________
a) work piece is connected as negative, and holder is earthed
b) electrode holder is connected to negative and work piece to positive
c) electrode holder is connected to positive and work piece to negative
d) both electrode holder and work piece are connected to negative
Answer: c
Explanation: In direct current reverse polarity (DCRP) or direct current electrode positive (DCEP), when base metals relate to the negative terminal of the power source and electrode relates to the positive terminal.
6. Where does maximum flame temperature occur?
a) Next to inner cone
b) At the inner cone
c) At the tip of the flame
d) At the outer cone
Answer: b
Explanation: Maximum flame temperature occur at inner cone. As flame moves from inner to outer temperature drop takes places.
7. In which of the following welding processes, electrode gets consumed?
a) TIG welding
b) Resistance welding
c) Thermit welding
d) Arc welding
Answer: d
Explanation: As in arc welding, welding is totally dependent on electrode, so it will be consumed.
8. Which of the following statements about welding is incorrect?
a) Increased corrosion resistance
b) Even materials like stainless steel and aluminium can be welded
c) No flux required
d) High welding speed
Answer: c
Explanation: Flux is mainly used for the following purposes: (a) It prevents the oxidation o the surface of the weld which can contaminate the welded potion, (b) It helps in forming alloy at the welded portion which improves the strength, (c) In arc welding the flux coating helps in directing the spark that’s why the electrode is kept concave in shape so that spark can be precisely directed towards the cavity where welding has to be performed.
9. Where is half corner weld used?
a) where efficiency of the joint should be 50 percent
b) where longitudinal shear is present
c) where severe loading is encountered, and the upper surfaces of both pieces must be in the same plane
d) For welding materials heavier than 12 gauge
Answer: d
Explanation: The half-open corner joint is used for welding materials heavier than 12 gauge.
10. Which of the following percentage of carbon in steel is most weldable?
a) 0.15
b) 0.25
c) 0.35
d) 0.8
Answer: a
Explanation: Low carbon steel is typically the most readily welded steel in a room temperature environment.
11. In which of the following metals does the phenomenon of ‘weld decay’ occurs?
a) stainless steel
b) cast iron
c) carbon steel
d) bronze
Answer: a
Explanation: Weld decay is a form of intergranular corrosion, usually of stainless steels or certain nickel-base alloys, that occurs as the result of sensitization in the heat-affected zone during the welding operation.
12. On which of the following principles does the ‘positive pressure type torch’ work?
a) equal volume
b) positive pressure
c) equal pressure
d) equal flow
Answer: c
Explanation: There are two types of welding and cutting torches commonly used. They are the positive-pressure type (also known as an equal pressure type or medium type pressure type torch), and the injector type.
13. Why is post cleaning necessary at brazed joint?
a) to avoid corrosion
b) to avoid slagging
c) to avoid oxidation
d) to avoid scaling
Answer: a
Explanation: Depending on the brazing process, we may need to perform post-braze joint cleaning to remove residual flux. This step is crucial for several reasons; including the corrosive nature of most fluxes and the possibility that excess flux could contribute to joint failure. The most common cleaning methods involve water-specifically soaking/wetting and quenching.
14. While welding, which of the following material welding, neutral flame is not used?
a) cast iron
b) steel
c) copper
d) zinc
Answer: d
Explanation: The neutral flame has a one-to-one ratio of acetylene and oxygen. A neutral flame is named neutral since in most cases will have no chemical effect on the metal being welded. Neutral welding flames are commonly used to weld: mild steel, stainless steel, cast iron, copper, aluminium, etc.
15. Which of the following statements about “projection welding” is correct?
a) It is multi spot welding process
b) It is an arc welding process
c) It is a continuous spot-welding process
d) It is a process used for joining round bars
Answer: a
Explanation: Projection welding is a modification of spot welding in which the weld is localized by means of raised sections, or projections, on one or both workpieces to be joined. This is high-production process, and multiple projection welds can be arranged by suitable designing and jigging.
Unconventional Welding Methods
1. In which welding process the electric energy required for welding is stored in the capacitor?
a) Percussion welding
b) Explosion welding
c) Diffusion welding
d) Thermit welding
Answer: a
Explanation: In percussion welding, two pieces are welded by a high intensity short duration arc followed by very rapid or percussive impacting of the workpieces. There are three different methods of arc initiation in percussion welding viz., low voltage with drawn arc, high voltage breakdown, and ionising by a fusing tip. With each method, the energy source is a bank of capacitors which is charged by a variable voltage transformer cum rectifier unit.
2. In which welding process pressure is applied by detonating a layer of explosive?
a) Percussion welding
b) Explosion welding
c) Diffusion welding
d) Thermit welding
Answer: b
Explanation: In explosion welding, a compression force created by detonation of explosives is used to join overlapping metal sheets. The joining parts are arranged toward each other at an angle of 1-15°, depending on the material and method, and are prepared with a layer of explosive on the top.
3. In which welding the surfaces of two components are subjected to static normal force and oscillating shear stress?
a) Diffusion welding
b) Thermit welding
c) Laser beam welding
d) Ultrasonic welding
Answer: d
Explanation: In ultrasonic welding (USW), the faying surfaces of the two members are subjected to a static normal force and oscillating shearing (tangential) stresses. The shearing stresses are applied by the tip of a transducer similar to that used for ultrasonic machining.
4. In which welding the strength of the weld results due to diffusion and plastic deformation of the flying surface?
a) Diffusion welding
b) Thermit welding
c) Laser beam welding
d) Ultrasonic welding
Answer: a
Explanation: In diffusion welding, the bond strength is achieved by pressure, temperature, time of contact, and cleanness of the surfaces. The strength of the bond is primarily due to diffusion rather than any plastic deformation.
5. In Thermit welding the heat generated is due to the mixing of?
a) Aluminum and copper
b) Aluminum and iron
c) Aluminum oxide and iron
d) Aluminum and iron oxide
Answer: d
Explanation: Thermite welding is a welding process in which the workpiece is joined with the help of molten metal by means of an exothermic reaction. Thermite mixture consists of a metal oxide (usually iron oxide) and aluminum powder. The major application of thermite welding is to weld railway tracks. It is also used to weld heavy machinery.
6. Which of the following welding is also known as arc and gas welding?
a) Electro slag welding
b) Atomic hydrogen welding
c) Laser beam welding
d) Ultrasonic welding
Answer: b
Explanation: Atomic hydrogen welding, also known as AHW, is an arc welding technique that uses an arc which is located between two tungsten electrodes and a hydrogen shielding gas.
7. Which of the following welding is used for welding vertical section in one pass?
a) Electro slag welding
b) Atomic hydrogen welding
c) Laser beam welding
d) Electro gas welding
Answer: d
Explanation: Electro gas welding (EGW) is an vertical positioned arc welding process, is used for welding the edges of sections vertically and in one pass with the pieces placed edge to edge (butt joint).
8. Electron beam welding is carried in?
a) Inert atmosphere
b) Partially filled chamber
c) Vacuum
d) Partially vacuum
Answer: c
Explanation: In electron beam welding process, electrons are emitted from the heated filament called electrode. This is done under vacuum conditions to prevent dissipation of the electron beam.
9. Which of the following welding process the weld joint is obtained by means of filler material and not by melting?
a) Diffusion welding
b) Thermit welding
c) Electroslag welding
d) Brazing
Answer: d
Explanation: A brazed joint is made in a completely different manner from welded joint. The big difference is in temperature-brazing does not melt the base metals. This means that brazing temperatures are invariably lower than the melting points of the base metals. It joins base metals by creating a metallurgical bond between the filler metal and the surfaces of the two metals being joined. The principle by which the filler metal is drawn through the joint to create this bond is capillary action.
10. Which of the following statements is not true?
a) Brazing occurs at a temperature above 450°C
b) Soldering occurs at a temperature below 450°C
c) Epoxy resins are used to join metals, ceramics etc
d) Epoxy resins are not used to join metals, ceramics etc
Answer: d
Explanation: The excellent adhesive properties of epoxy resins are due to the attractive forces between the epoxy resin and the surface of the substrate. Typical epoxy resins have pendant hydroxyl (-OH) groups along their chain which can form bonds or strong polar attractions to oxide or hydroxyl surfaces. Most inorganic surface, i.e., metals, minerals, glasses, ceramics, etc. have polarity so they have high surface energy. Organic polymer surfaces are generally less polar (more covalent) thus lower surface energy.