Workshop Technology
Piercing is an operation of cutting

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

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Workshop Technology
The purpose of a riser is to

Act as a reservoir for the molten metal
Deliver molten metal into the mould cavity
Deliver the molten metal from pouring basin to gate
Feed the molten metal to the casting in order to compensate for the shrinkage

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