The magnetic upper plate’s function is to hold the upper punches, its advantages are fast installation/uninstallation, Mainly its types are:
Electro-magnetic upper plate
A relatively cheap magnet that requires electricity to operate, can get heated due to electricity running through it, care should be taken as it loses its magnetism during power outage.
Permanent Magnetic plate
More expensive than the electro-magnet, but safer as it doesn’t lose its magnetism during power outages, also it consumes less electricity