This set of Phase Transformation Multiple Choice Questions & Answers (MCQs) focuses on “Solidification of Fusion Welds”.
1. Which among the following is a property of fusion welding not of solid state welding?
a) Filler metal is added
b) Heat is applied
c) Used to join metals
d) Nothing can differentiate them
Explanation: In case of a fusion welding coalescence is accomplished by melting the two parts to be joined, in some cases adding filler metal to the joint, but in case of solid state welding filler metal is not added.
2. A fusion-welding operation in which no filler metal is added is referred to as a/an _____
a) Compile weld
b) Autogenous weld
c) Filler Weld
d) Damper weld
Explanation: When the filler metals are not added in a fusion-welding operation then it is referred as an autogenous weld Fusion-welding processes and it uses heat to melt the base metals just like the other fusion welding process. Mainly these fillers are added to facilitate the process and to give a strength or toughness to the joints. .
3. Which among the following is not a fusion welding technique?
a) Arc welding
b) Oxy-fuel welding
c) Resistance welding
d) Diffusion welding
Explanation: Here if we check the first three options they belong to the category of fusion welding technique and they use heat mainly to join the metals but in the diffusion welding two surfaces are held together by using the pressure at a pretty high temperature and the parts coalesce by solid-state diffusion.
4. In which joint type, the parts lie in the same plane and are joined at their edges?
Explanation: This happens in the case of butt joints. Whereas in corner joints the parts in a corner joint form a right angle and are joined at the corner of the angle and in the case of lap joint the joints consist of two overlapping parts.
5. The heat to transform the metal from solid to liquid phase at the melting point, which depends on the metal’s heat of fusion. Calculate the unit energy for melting if the melting temperature is 1000K? (K = 3.33 * 10-6).
Explanation: If we consider a fair approximation the total amount of heat or the quantity of the heat can be calculated using the following equation Um = K(Tm)2, where Um = the unit energy for melting and Tm is the melting point of the metal. Um is the total amount or quantity of heat required to melt a unit volume of metal taking the initial temperature as room temperature.
6. Typical fusion-weld joint in which filler metal has been added consists of several zones.
Explanation: The several zones which include the heat affected zone, fusion zone, the heat unaffected zone that is present away from the fusion zone and weld interface zone.
7. Calculate the net heat available for welding if the heat transfer factor f1, melting factor f2 and the total heat supplied are given as 0.8, 0.9, 1000J respectively?
Explanation: The net heat available for welding is actually the product of the heat transfer factor, melting factor and the total heat supplied. In this case it, H(Tot) = 0.9*0.8*1000J =720J.
8. In the case of arc welding find the arc time, if the time for which the arc is switched on is given as 3hrs and the hours worked with that is given as 1hr?
Explanation: Arc time = Time arc is on/ hours worked. Productivity is also an issue. It is often measured as arc time (also called arc-on time), that is the proportion of hours worked that arc welding is being accomplished.
9. A gas tungsten arc-welding operation is performed at a current of 300 A and voltage of 20V. Calculate the total power in the operation?
Explanation: The total power generated is given as P = IV, so in this case it is 300*20 = 6000W. Power Source in Arc Welding, both direct current (DC) and alternating current (AC) are used in arc welding.
10. If the total power generated is given as 3000W. Calculate the rate of heat generation at the weld if the melting factor is given as 0.6 and the heat transfer factor as 0.8?
Explanation: The rate of heat generation at the weld is given as the product of the total input power, the heat transfer factor and the melting factor. So in this case 0.8*0.6*3000 which gives the required answer 1440J/s.
11. A gas tungsten arc-welding operation is performed at a current of 500 A and voltage of 20 V. The melting factor f2 = 0.5, and the unit melting energy for the metal Um = 10 Jmm-3. Calculate the volume of metal welded? (Heat transfer factor is 0.7)
Explanation: Here the volume of the metal welded can be calculated if we know the total heat generation at the weld. This can be calculated if we know the total power required. So here the total power is given as 500*20 = 10000W, hence the rate is given as 0.7*0.5*10000 = 3500J/sec and the volume is given as 3500/10=350mm/sec.
12. The power source in a particular welding setup generates 4000 W that can be transferred to the work surface with a heat transfer factor = 0.9. The metal to be welded is low carbon steel, whose melting temperature, is 1800 K. The melting factor in the operation is 0.6. A continuous fillet weld is to be made with a cross-sectional area = 20 mm2. Determine the travel speed at which the welding operation can be accomplished? (K = 3.33 *10-6)
Explanation: Let us first find the unit energy required to melt the metal Um, which can be calculated as Um = 3.33*10-6 *18002 = 10.78Jmm-3.To calculate the travel velocity we take the equation f1*f2*R=Um*A*v, hence from this we get the value of v the required velocity, v = (0.9*0.6*4000)/10.3*20 = 10.49mm/sec.
13. The quantity of heat required to melt a given volume of metal does not depend on______
a) The melting point of the metal
b) Composition of elements in the melt
c) The heat to transform the metal from solid to liquid phase at the melting point
d) The heat to raise the temperature of the solid metal to its melting point
Explanation: The quantity of heat required to melt a given volume of metal depends on the melting point of the metal, the heat to transform the metal from solid to liquid phase at the melting point which depends on metals heat of fusion and the heat to raise the temperature of the solid metal to its melting point.
14. A flux is a substance used to prevent the formation of oxides and other unwanted contaminants, or to dissolve them and facilitate removal.
Explanation: A flux is a substance used to prevent the formation of oxides and other unwanted contaminants, 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.
15. Arc shielding is accomplished by covering the electrode tip, arc, and molten weld pool with a blanket of gas or flux, or both, which inhibit exposure of the weld metal to air.
Explanation: At the high temperatures in arc welding, the metals being joined are chemically reactive to oxygen, nitrogen, and hydrogen in the air. The mechanical properties of the weld joint can be seriously degraded by these reactions. Thus, some means to shield the arc from the surrounding air is provided in nearly all AW processes. Arc shielding is accomplished by covering the electrode tip, arc, and molten weld pool with a blanket of gas or flux, or both, which inhibit exposure of the weld metal to air.
Sanfoundry Global Education & Learning Series – Phase Transformation.
To practice all areas of Phase Transformation, here is complete set of 1000+ Multiple Choice Questions and Answers.