Workshop Technology
The welding set up is said to have straight polarity, when

Work is connected to the positive terminal and the electrode holder is earthed
Work is connected to the negative terminal and the electrode holder is earthed
Work is connected to the negative terminal and the electrode holder to the positive terminal
Work is connected to the positive terminal and the electrode holder to the negative terminal

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Workshop Technology
Piercing is an operation of cutting

A flat sheet to the desired shape
A number of holes evenly spaced in a regular pattern on a sheet of metal
A cylindrical hole in a sheet of metal by the punch and the die
A hole (other than cylindrical) in a sheet of metal by the punch and the die

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