Clamping Force’s Control Techniques Of Clamping System Based On Magnetic Powder

The clamping system based on magnetic powder is a new clamping system, using magneticpowder to clamp workpieces. Magnetic powder, filled in the space around the workpiece, aremagnetized and form a unit under magnetic field, generate positive pressure on the workpiece’s wall.According to the principle of the clamping system, magnetic powder and magneto-rheologicalfluid(MRF) can be used as packing mediums. The influence factors and control factors of magneticand non-magnetic workpieces’ clamping force are analyzed under different packing mediums.80mesh reduced iron dust is selected as the magnetic powder by comparing different soft magneticmaterials’ permeability and residual flux density, measuring the friction coefficient between ironpowder of different mesh numbers and the table, observing the dust flying of iron powder of differentmesh numbers. Using finite element method(FEM) to analyze the magnetic field distribution aroundthe cutting tool, which is so small that can be ignored, under different distances between cutting tooland magnetic powder, and different heights of the magnetic powder. The relationship betweenmagnetic induction of the magnetic powder region and exciting current is calculated through magneticcircuit principle. Results show that the reluctance would be larger if the workpiece is non-magneticand the magnetic induction is related to the shape of the workpiece.The impact of types and contents of magnetic particle, base field and additive on MRF’sviscosity and shear yield stress is analyzed based on the flow mechanism of MRF. Using single factormethod to determine the best volume content of magnetic particle and the type of additive andcarbonyl iron dust, silicone oil, sodium sulfonate and silane coupling agents are selected according tothe results. A kind of MRF with good dispersion stability and high shear yield stress is made throughorthogonal design.The system’s working principle and the workpiece’s deflection of clamping system based onmagnetic powder and magnetic chuck are compared. The milling force and clamping force underdifferent mediums are calculated and measured. Results show that the workpiece can be clamped wellin this clamping system.