Fundamental of Welding Science and Technology NPTEL ANSWERS : WEEK 4

Week 4: Assignment 4

ANSWERS WEEK 5

An increase in radial pressure gradient dominates which of the following factors:

 Fusion depth decreases

 Fusion depth increases

 Constricts the arc

 Diverges the arc column

C

1 point

If the arcing time is 3 min, then duty cycle of welding machine as per the European standard is

 10%

 30%

 60%

 80%

C

1 point

Increased arc blow results in:

 Steady arc

 Low spatter

 Poor weld bead appearance

 All of these

D

1 point

Which of the following (s) is (are) an arc initiation process:

 Scratching method

 Taping method

 Both (a) and (b)

 None of these

C

1 point

Arc blow can be minimized by:

 Increase in traverse speed

 Using long arc

 Superimposing counter-acting longitudinal magnetic field

 Larger diameter electrode

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1 point

In welding, stable arc signifies as:

 Uniform and steady arc

 Uniform and unsteady arc

 Non-uniform and steady arc

 Non-uniform and unsteady arc

A

1 point

Consider the following statements:

        1. In arc welding 65 % to 75 % heat is generated at anode.

        2. Duty cycle in case of arc welding is the cycle of complete welding of workpiece from the beginning.

        3. Arc blow is more common with DC welding.

Which of the statements are correct?

 1, 2 and 3

 1 and 2

 2 and 3

 1 and 3

D

1 point

For a particular condition if the welding speed decreases, then:

 Arc blow increases

 Deflection of arc decreases

 Deflection of arc increases

 Arc blow decreases

D

1 point

Which force is responsible for rotating arc?

 Asymmetric radial force

 High velocity gas jet force

 Surface tension force

 Lorentz force

A

1 point

In welding, DCEP signifies:

 Direct current electric positive

 Direct current electrode positive

 Direct current electric pulse

 Direct current electrode pulse

B

1 point

Welding voltage across the arc coloumn can be expressed as V = A + B*L; where A denotes:

 A: Voltage drop taking place across anode and cathode drop region

 A: Voltage drop taking place across cathode drop region

 A: Voltage drop taking place across anode drop region

 A: Voltage drop along arc gap

A

Fundamental of Welding Science and Technology : WEEK 4

 

Fundamental of Welding Science and Technology NPTEL ANSWERS : WEEK 4

Arc blow can be minimized by:

 Increase in traverse speed

 Using long arc

 Superimposing counter-acting longitudinal magnetic field

 Larger diameter electrode

C

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Fundamental of Welding Science and Technology NPTEL ANSWERS : WEEK 5 (1)

Fundamental of Welding Science and Technology NPTEL ANSWERS : WEEK 5

PART 1

ASSIGNMENT 6 CLICK HERE

1. To study the metal transfer in SMAW or SAW

 High speed camera is used

 IR camera is used

 X-rays is used

 none of these

C                    LECTURE 1

1 point

2. Lorentz force in welding metal transfer is a type of

 Electromagnetic force

 Retard force

 Gravity force

 All of these

A                   LECTURE 1

1 point

3.  The necking force in metal transfer in welding is

 Directly proportional to square of welding current

 Inversely proportional to square of welding current

 Directly proportional to welding current

 Inversely proportional to welding current

A                     LECTURE 1

1 point

4. Streaming spray metal transfer occurs:

 At a current which is higher than rotating spray metal transfer current

 At a current which is less than projected spray metal transfer current

 At a very low current which is just higher than short-circuiting metal transfer current

 At a current which is less than rotating spray metal transfer current

D                     LECTURE 2

1 point

5. In welding the globular metal transfer occurs

 Above the transition current

 Below the transition current

 Both (a) and (b)

 None of these

B                          LECTURE 2

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Fundamental of Welding Science and Technology NPTEL, WEEK-3

 Fundamental of Welding Science and Technology

Week 3: Assignment 

1 point

Which one of the following gas atmosphere is readily used to promote thermionic emission more readily due to its least ionization potential?

 He

 Ar

 N2

 CO2

C

1 point

Which one of the factors plays a key role in exhibiting thermionic emission rapidly?

 Concentration of electron decrease, absolute temperature decrease

 Current density increase, absolute temperature increase

 Current density and absolute temperature remain same

 None of these

B

1 point

Variable speed feed drive system compensate variation in arc length by:

 Increase or decrease of electrode feed rate

 Self-regulation of arc length characteristics

 Sensing the fluctuation with the help of diode

 None of these

A

1 point

For maintaining arc length constant speed feed drive system is used with _____ power supply

 CV

 CC

 Dynamic characteritics

 None of these

A

1 point

Pulsed mode of power supply provides:

 AC along with pulsed mode

 DC along with pulsed mode

 AC

 DC

NOT AVAILABLE :B

1 point

Which statement is true for dynamic characteristics of power sources?

 Inductor is used to increase the current which provides better melting rate

 Transistor is used to increase the current which provides better melting rate

 Inductor is used to decrease the current which provides stability of arc

 Thyristor is used to decrease the current which provides stability of arc

C

1 point

Which one of the welding process uses combined characteristics of power source?

 GMAW-P

 ESW

 PAW

 EGW

D

1 point

Which pair of the welding process uses constant voltage power source characteristics?

 GTAW and SMAW

 SMAW and PAW

 MIG and FCAW

 None of these

C

1 point

In which of the welding processes constant current power supply is used?

 Plasma arc welding

 Metal Inert gas welding

 Shielded metal arc welding

 Laser welding

C

1 point

Arc length-voltage characteristics for a welding operation is given by V = 20 + 4 L. If the arc length varies between 4 mm to 6 mm and welding current varies between 450 A to 550 A. Assuring linear power source, calculate (a) Open circuit voltage (b) Short circuit current

 50 V and 700 A

 60 V and 800 A

 70 V and 900 A

 80 V and 1000 A

D (Not Sure)

Fundamental of Welding Science and Technology NPTEL ANSWERS : WEEK 2

Fundamental of Welding Science and Technology NPTEL ANSWERS : WEEK 2

Week 2: Assignment 2

     This weld symbol is used when the welding machine is:

 Fixed

 Portable

 Automatic

 None of these

D

1 point

The flare-bevel groove can be represented as:

 

 

 

 

A

1 point

The symbol for seam welding:

 

 

 

 

D

1 point

If the total welding cycle time is 10 min, dwell time is 4 min and arcing time is 5 min, then duty cycle of welding machine as per the American standard is:

 65%

 50%

 75%

 80%

B

1 point

Duty cycle is the ratio of

 welding cycle time to melting time

 Welding cycle time to arcing time

 Arcing time to welding cycle time

 Melting time to welding cycle time

C

1 point

If the current at 100% duty cycle is 250 A, then what should be the required current for 50% duty cycle?

 335.55 A

 353.55 A

 300.65 A

 325.55 A

B

1 point

In Motor-generator set for arc welding which of the generator is readily used:

 Shunt type

 Differentially compound type

 Level compound type

 Series type

B

1 point

Arc discharge accounts for:

 Low current and medium voltage

 Low voltage and high current

 High voltage and very low current

 Low current and low voltage

B

1 point

The range of open circuit voltage (OCV) in case of rectifiers is in the range of:

 50-80 V

 70-90 V

 100-120 V

 30-50 V

A

1 point

In case of welding Aluminum using unequal dwell which of the following is kept generally:

 Electrode positive is more than electrode negative

 Electrode positive is less than electrode negative

 Electrode positive is equal to electrode negative

 None of these

B

1 point

If the open circuit voltage is 60 volt and the short circuit current is 20 amperes. Then determine the voltage required for welding if the current required during welding is 10 amperes:

 60 V

 30 V

 40 V

 20 V

B

1 point

In a linear arc welding process, the heat input per unit length is inversely proportional to

 Welding voltage

 Welding current

 Welding speed

 Duty cycle of the power source

C