Electric Welding Interview Questions and Answers:
1. What is welding ?
Ans. Welding is a materials-joining process that produces coalescence of materials by heating them to the welding temperature, with or without application of pressure or by the application of pressure alone, and with or without the use of filler metal.
2. “All metals can be joined by one welding process or another”. Comment on this statement.
Ans. The above statement needs slight modification and may be stated as follows.
All metals commercially employed for structural or strength parts are weldable. In general, metal that have a low melting point or low strength would not be welded.
3. What are the different types of electric welding ?
Ans. Electric welding may be resistance welding or arc welding. Resistance welding includes butt welding, spot welding, projection welding seam welding and percussion welding. Arc welding is subdivided into five groups namely carbon arc welding, metal arc welding, atomic hydrogen arc welding, inert gas metal arc welding and submerged arc welding.
4. What is the difference between plastic welding and fusion welding ?
Ans. In the plastic welding, also called the pressure welding, the pieces of metal to be joined are heated to a plastic state and then forced together by external pressure whereas in fusion welding, also called the non-pressure welding, the material at the joint is heated to a molten state and allowed to solidify. Former one includes forge welding, resistance welding, thermit welding and gas welding while the latter includes gas welding, arc welding and thermit welding without pressure.
5. What is resistance welding ?
Ans. Resistance welding is a group of welding processes that produce coalescence of the faying surfaces with the heat obtained from resistance of the work to the flow of welding current in a circuit of which the work is a part and by the application of pressure.
6. What is the fundamental difference between electric arc welding and resistance welding ?
Ans. The resistance welding processes differ from arc welding in that pressure is used but filler metal or fluxes are not.
7. Why alternating current is found most suitable for resistance welding ?
Ans. Alternating current is found most suitable for resistance welding as it can provide any desired combination of current and voltage by means of a transformer.
8. Explain the theory of arc production.
Ans. An electric arc is produced when two conductors (electrode and metal piece) are connected to a suitable source of electric current momentarily in contact and then separated by a small distance. Both dc and ac can be used for producing an electric arc, however, dc provides more steady arc.
Basically an arc is nothing but an electric discharge through a path of ionised particles of air. The electrical energy is converted into heat at a temperature of about 5,000°C.
9. What is meant by negative resistance characteristic of an electric arc and what precautions are taken for ill effects due to this ?
Ans. Negative resistance characteristic of an arc means decrease in arc resistance with the increase in temperature or current. The reduced resistance causes further increase in current and, therefore, steady arc cannot be obtained. For obtaining steady arc, supply source should have a drooping characteristic (i.e., voltage decreasing with the increase in current).
Steady arc for dc welding can be obtained by using differential compound wound generator. The control may be obtained by tapping the series field or by providing a suitable shunt across the series field winding. The open-circuit voltage is adjusted from shunt field.
In an ac welding sets, welding transformer is used and drooping characteristic is obtained by using external reactor.
10. What are the fluxes used in arc welding ?
Ans. In arc welding, flux coated electrodes are used. The fluxes used are silicon oxiders, graphite, sodium silicate, calcium oxide and aluminium in right proportions. Sometimes, the electrodes are washed (lightly coated) of several tenths of millimetres thickness, lime mixed with soluble glass.
The heavy coated electrodes have coating composed of ionising (chalk) deoxidising (aluminium, ferro-manganese etc.), gas generating (starch), sag forming (kaoline), alloying and binding materials.
11. What are the qualities of good weld ?
Ans. The weld is said to be good weld if it is free from external defects such as irregular width and heights of beads, deviation of the weld from the prescribed dimensions, unfilled craters on the surface of welds, undercuts, slag on the surface of welds, porosity in the outer layer of the welds, visible cracks in and around the weld and internal defects such as poor fusion, hidden porosity in the deposited metal, hidden cracks in the weld and parent metal, poor fusion between layers in multiple layer welding, and entrapment of slag and oxides.
12. What is main drawback of electron beam process ?
Ans. The main drawback of electron beam process is its high capital cost. The price of the equipment required is very high, and it is expensive to operate, due to the requirement of vacuum pumps. In addition, fitup must be precise and locating the parts w.r.t. the beam must be perfect.
13. The location of the focal point of the beam w.r.t. the surface of the work piece is very important in laser beam welding. Why ?
Ans. Maximum penetration occurs when the beam is focused slightly below the surface. Penetration is less when the beam is focused on the surface or deep within the surface.
14. What is meant by welding electrode ?
Ans. An electrode is a piece of wire or rod (of a metal or alloy), with or without flux covering, which carries current for welding.
15. What type of dc generator is used in electric arc welding ?
Ans. Differential compound wound de generator.