Study On A New Micro Machining Technology Based On The Magnrtorhological Effect Of Abrasive Slurry

As a type of smart material, magnetorheological (MR) fluids are suspensions of micron-sized magnetizable particles dispersed in a carrier medium with small concentrations of stabilizers, and exhibit the peculiar rheological properties that are induced by the externally controllable magnetic field. The MR properties can be manipulated and controlled in real time by varying the strength of the field. In the absence of magnetic field, MR fluids exhibit Newtonian behavior, and they are abruptly transformed within milliseconds into a plastic like solid under an applied magnetic field. Based on the MR effect of abrasive slurry, an innovative superfine polishing technique is presented to resolve problems related to the polishing of micro-apparatuses using the micro-tool. In this technique, the particle-dispersed MR fluid is used as a special instantaneous bond to cohere abrasive particles in the MR fluid so as to form a dynamical tiny grinding wheel to machine the brittle materials.This work analyzed firstly the component, characteristics and rheological mechanism of MR Fluid, and developed a MR fluid for polishing. Then the experimental set-up was designed based on the principle of the dynamical tiny grinding wheel to machine the workpiece by a fixed-point machining mode. Furthermore, experiments were carried out to investigate the effects of different parameters of MR fluid (such as grain sizes, species and concentration of abrasive particles) and process parameters (such as machining gap between the workpiece and the rotation tool, machining time and rotation speed of the tool) on the machining effect. The characteristics of the machined workpiece surfaces are analyzed by means of optical microscope, SEM, Talysurf roughness tester and ferrograph.Experimental results indicate the following conclusions: the tiny grinding wheel based on the MR effect of abrasive slurry can effectively polish hard brittle materials; a better polishing surface can be obtained by the silicon oil-based MR fluid; using harder abrasives (such as diamond) can achieve greater material removal rate and rougher surface, whereas smoother surface can be obtained by using softer abrasives (such as Al₂O₃); the largest material removal rate will obtain when the grain size of diamond abrasives is close to that of carbon iron particles; and perfect polishing surface can be obtained in the case of the content of 3 wt.% diamond particles. In addition, the material removal performance of dynamical tiny grinding wheel will enhance by adding some fibres to MR fluid. Greater material removal rate can be obtained when machining gap is 60μm & 90μm, machining time is 20min and rotational speed is 2000rpm & 2700rpm. The material removal of dynamical tiny grinding wheel based on MR effect can be explained by Preston's empirical equation, and the material removal modes of polishing glass are the plastic removal mode and the brittle fracture mode by analyzing micro-structure of the polishing surface and cutting chips.