Correct Answer - Option 1 : Statement I is true, Statement Il is true
Resistance Welding:
Processes in which welding heat is produced by the resistance offered to the passage of electric current through the two metal pieces being welded.
These processes differ from the fusion processes in the sense that no extra metal is added to the joint using a filler wire or electrode.
According to Joule’s law, the heat produced (H) electrically is given by,
H = I2Rt J
Here, R is the contact resistance between the two metals being welded together.
Advantages:
- Heat is localized where required
- Welding action is rapid
- No filler material is needed
- Requires comparatively lesser skill
- Is suitable for large quantity production
- Both similar and dissimilar metals can be welded
- The parent metal is not harmed
- Difficult shapes and sections can be welded.
Note: The only disadvantages are concerning a high initial as well as maintenance cost.
Arc Welding Machines:
Arc welding is never done directly from the supply mains, special welding machines are used which provided currents of various characteristics.
The use of such machines is essential for the following reasons:
- To convert AC supply into DC supply when DC welding is desired.
- To reduce the high supply voltage to a safer and suitable voltage for welding purposes.
- To provide the high current necessary for arc welding without drawing a correspondingly high current from the supply mains.
- To provide suitable voltage/current relationships necessary for arc welding at minimum cost.
There are two general types of arc welding machines:
(a) DC welding machines
(i) motor-generator set
(ii) a.c. transformers with rectifiers
(b) AC welding machines
