subject: Electro-Permanent Magnetic Chuck: Minimal Work Piece Distortion [print this page] Electro-Permanent Magnetic Chuck: Minimal Work Piece Distortion
Electro-permanent magnetic chucks only require electrical power to turn the magnetic holding force on and off. This means the chuck runs cold thereby minimizing heat build-up, parts distortion and power consumption.
Heat buildup during machining processes can produce undesirable effects such as an increase in rejected parts and rework due to thermal parts distortion, as well as an increase in scrap. This all adds up to an increase in cycle time and material costs and a decrease in tool life. Electro-permanent magnetic chucks have the ability to counter these undesirable effects in two ways. They run de-energized or cold so they do not add into the total heat pattern of the workpiece. Like all magnetic chucks, they fully hold the workpiece from centerline to outside edge. This feature reduces chatter and vibrations.
The Basics of Magnetic Chucks
There are three basic types of magnetic chucks: permanent magnetic, electro-magnetic and electro-permanent. The permanent magnetic chuck is based on the magnetism created by permanent magnets and do not require electrical power to operate, which makes them failsafe, but they do not have a variable holding power capability. Electromagnetic chucks use a controller to generate a D.C. voltage in a coil wound around the chuck's pole pieces to create the magnetic work holding force. The D.C. chuck controller provides a means to vary the chuck's magnetic holding force. But electro-magnetic chucks require continuous electrical power to operate. Electro-permanent magnetic chucks combine features of both permanent magnetic and electro-magnetic chucks.
Electro-permanent: Hybridizing The Magnetic Circuit
Electro-permanent magnetic chucks are a hybrid of the permanent and electromagnetic chuck types. They are constructed with a coil wound around permanent magnetic material embedded in the chuck plate. When a DC voltage is applied, the magnetic material is charged, which takes about 1 second, and binds the workpiece to the chuck even after power is removed. Another function of the coil is to control the amount of magnetic force of the chuck to give it a variable holding power capability similar to electromagnetic chucks. Power is required is de-energize the magnetic field.
These chucks will remain magnetic even when power is removed. This gives them both a failsafe advantage over electromagnetic chucks and eliminates the accidental release of work piece. Since they maintain their magnetic holding force without the consumption of electrical power, these chucks increase the energy efficiency of the process, which reduces costs to the entire enterprise. They can be used with surface grinders, electric processing machine tools, as well as in casting, drilling, planning and boring machines. They can generate enough holding force for heavy cuts and thrusts during grinding, planning and milling operations.
Minimizing Parts Distortion
By not needing constant electrical power to maintain their work holding force, the chucks run cooler, which minimizes heat build-up and mechanical distortion of the chuck and work piece. Due to their uniform holding power, these chucks produce less chatter and tool wear.
Off-Machine Pallet Loading
Since electro-permanent magnetic chucks can be disconnected from electrical power once they are charged, they are portable. This feature enables them to be good candidates for off-machine pallet loading and tombstone applications.
