Through yesterday's article, we learned about the importance of magneto rheological polishing fluid in magneto rheological polishing. Today, we will learn about its working mechanism.

Magnetorheological polishing fluid is a complex multiphase magnetic colloid formed by the uniform dispersion of micron sized magnetic sensitive particles (such as carbonyl iron powder) and nano sized polishing powder particles in the base liquid. Usually, additives are added to the base solution to improve the performance of the suspension, including surfactants that enhance the magnetorheological effect and dispersants that prevent particle aggregation.

The research shows that the magnetorheological effect of micron scale magnetorheological fluid (MR) is more obvious than that of nanometer scale (~10nm) Ferrofluid. The reason is that the particles in the nano Ferrofluid are single domain magnetic particles, and the viscosity changes little in the high magnetic field environment, resulting in low shear stress; Micron sized particles in magnetorheological fluids are multi domain magnetic particles with high saturation magnetization. Under the action of a magnetic field, there is strong interaction between particles, which is conducive to chain formation.

In the process of magneto rheological polishing, the magneto rheological polishing fluid is transported to the polishing area by a circulating pump. When entering the polishing area, a high gradient magnetic field causes the magneto rheological effect of the magneto rheological polishing fluid, which changes from a liquid to a quasi solid in the polishing area (Figure b). This kind of quasi solid ribbon is a flexible polishing mold that achieves material surface removal through the complex mechanical and chemical coupling of polishing powder particles.

The sufficient dispersion of particles, especially polishing powder particles, in magnetorheological polishing fluids is directly related to their effective use, but excessive additives can affect the chain formation of magnetic particles under the action of a magnetic field. The dispersion of micro and nano particles must meet both the thermodynamic and kinetic conditions required for their full dispersion. The thermodynamic condition for sufficient dispersion is to increase the height of the energy barrier and reduce the potential well, generally achieved by controlling particle size and surface potential; The kinetic condition is to provide fully dispersed energy through physical or chemical means. To achieve good dispersion effect, physical means are usually used for pre dispersion, followed by chemical means for stabilization.

At present, the dispersion and characterization of biphasic particles, rheological behavior and particle forces, and the mechanism of interaction between magnetorheological polishing fluids and material surfaces are the research focuses of magnetorheological polishing fluids.