There are three types of magnetic chucks: permanent, electro magnetic and permanent electro magnetic. Permanent magnets switch on and off through the alignment of permanent magnets within the chuck to the mild steel surface on top of the chuck.

Permanent magnets are restricted in their clamping force by one’s ability to overcome the magnetic resistance in turning the chuck on and off. Historically, permanent magnets were only used for grinding and EDM because of the limited clamping forces as a result of the magnetic resistance.

Electro magnetic chucks use a constant supply of electric current through a coil around a soft iron core to create the magnetic field perpendicular to the coil. Electro magnets can generate large magnetic fields, but if power is lost, so too is the magnetic clamping – making them impractical for pallet changers and machining centers. In addition, it is important to note that electricity through an electro magnet generates significant amounts of heat within the chuck and on the surface.

Permanent electro magnetic workholding has made significant strides in the past 10 years, especially with the advancements in neodymium magnets. Neodymium iron boron (NdFeB) magnets are smaller and more powerful than other types of permanent magnets. Therefore, magnetic fixturing is more powerful and more compact.

In addition to neodymium, permanent electro magnets also use alnico magnets as the magnetic switch. The magnet can be turned on or off by changing the polarity through a pulse of electric current. This cycle takes less than one second. Permanent electro magnets only require electricity to turn the magnet on and off – no electricity is required to maintain the magnetic field .