Study On Micro Machining With Instantaneous Tiny-Grinding Wheel Based On The Electro-Magneto-Rheological Effect Of Abrasive Slurry

Similar to the electrorheological fluid (ERF) and magnetorheological fluid (MRF), the electro-magneto-rheological fluid (EMRF) is one kind of controllable suspension with micron-sized particles dispersed in a carrier medium. In the absence of external electric or magnetic field, EMRF presents a Newtonian behavior and abruptly transforms into high viscosity plastic-like solid from low viscosity fluid within milliseconds under an applied electric or magnetic field. Moreover, the rheological property of EMRF exhibits synergistic effect under the combination of electric and magnetic field, which is stronger than that under external electric or magnetic field.Based on the electro-magneto-rheological (EMR) effect of abrasive slurry, the particle-dispersed EMR fluid is used as a special instantaneous bond to cohere abrasive particles and micron-sized dispersed particles so as to form a dynamical, flexible tiny-grinding wheel to polish optical glass, ceramic and other brittle materials with a high efficiency.Based on the principle of the dynamical tiny grinding wheel, the experimental set-up was designed to machine the workpiece in a fixed-point machining mode. By analyzing the components, characteristics and rheological mechanisms of EMR Fluid, we developed an EMR fluid for polishing. Furthermore, experiments were carried out to investigate the influence of the EMR fluid's parameters (such as abrasive sizes, species and concentration), process parameters (such as machining gap between workpiece and tool, machining time and rotation speed of the tool), and parameters of the synergistic effect (such as the direction of external electric and magnetic fields, and their intensities) on the polishing effect. The characteristics of the machined workpiece surfaces were analyzed by the means of optical-microscope, SEM and Talysurf roughness tester.Experimental results indicate the following conclusions: the tiny grinding wheel based on the EMR effect of abrasive slurry can effectively polish the hard-brittle materials; the electro-magneto-rheological fluids with Fe₃O₄ powder as dispersed particles can achieve the fine polishing effect; harder abrasives (such as diamond) can achieve greater material removal rate and rougher surface, whereas better surface can be obtained by using softer abrasive (such as Al₂O₃); the maximum material removal rate will be obtained when the size of the diamond particles is about 7μm and the concentration is 3～6%; different shapes of tools will influence the distribution of electric or magnetic field, which will result in the different micro-topographies and shapes of the workpiece surfaces; material removal rate will increase with the increase of external field, and the maximum material removal rate can be obtained when the machining gap is 5μm, the machining time is 10min and the rotation speed is 3300rpm; the combination of external fields and magnet field has a great influence on the synergistic effect, which plays a great role in the polishing effect; greater material removal will be obtained with the same direction of external electric and magnetic fields; the combination of stronger electric field and weaker magnetic field can result in the better synergistic effect; according to the analysis of surface micro-topography, the material removal of dynamical tiny grinding wheel based on the EMR effect can be explained by Preston's empirical equation, and the mode of material removal exists two kinds of removal mode: the plastic removal mode and the brittle removal mode.