Electromagnetic chucks can provide variable holding power, which greatly improves their ability to support a wide range of machining applications.
Magnetic chucks are designed for holding ferro-metallic work pieces with a strong, uniform holding force. They consist of an accurately centered permanent magnetic face that works in conjunction with an operator actuated permanent or electromagnet. The work piece closes the magnetic loop to create a secure anchor for the work piece.
Permanent Magnet vs. Electromagnet
Both permanent magnets and electromagnets can be used to produce a magnetic holding force. The choice of a permanent or electromagnetic design is dependent upon both machining applications and externalities. Since permanent magnets do not require electrical power, they are best used when there’s no power available or it is unreliable. On the other hand, the magnetic field of permanent magnetic chucks cannot be adjusted, which can be a drawback for machining applications that require variable holding power. In applications where a variable holding power is required, an electromagnetic chuck is the better solution.
Electromagnetic Chuck Operation
Electromagnetic chucks are constructed with electrical coils wound around a steel core embedded in the chuck. To energize the electromagnetic field, a chuck controller is used to generate a variable DC voltage in the chuck’s coils. The coil’s electromagnetic field causes particles within the ferro-metallic work pieces to be aligned in a common direction. This alignment creates the electromagnetic holding force between the work piece and the chuck. The chuck’s poles are magnetic as long as voltage is applied. The operator can adjust the controller’s DC voltage to vary the strength of the magnetic field, which, in turn, provides the variable holding force.
The Variable Holding Power Advantage
Variable holding power greatly improves the chuck’s ability to support a wide range of machining applications that include cutting, milling, shaping, EDM, high speed cutting operations and thin work for grinding. Electromagnetic chucks can easily be interfaced with machine centers for automation purposes.
Variable holding power is critical for thin work applications. For example, when a part to be machined is thin-0.25 inch or thinner-and the part is presented to a machine operator as one of a stack of similar parts, the piece must be lifted from the stack. Permanent magnets are not designed to lift only one piece from a stack of ferro-metallic parts. However, an electromagnet with variable voltage control allows the operator to decrease the magnetic strength to the point where only one piece at a time can be lifted from a stack of parts.
The variable holding power of electromagnetic chucks give it an advantage over permanent magnetic chucks. But their selection depends both on the machining application and shop safety. Since electromagnets need constant power to operate, a power failure can introduce a worker safety concern. While uninterruptible power supplies, power conditioners and battery backup systems can be integrated into the machining operations to address these concerns, the ultimate decision depends on the design of a particular machining application.