Study On Dynamic Shear Thickening Abrasive Flow Machining Technology And Compound Micro Grinding Experiment

It is difficult to manufacture the micro end of the polishing tool in the traditional finishing process of the micro structure metal molding core.Moreover,the uneven contact between the polishing tool and the micro structure surface makes it difficult to control the pressure of the machined surface.Therefore,based on the hydrodynamic and shear thickening effects,a new method of hydrodynamic shear thickening abrasive machining and composite micro grinding is proposed in this paper.Its technical features are:the combination of micro forming grinding and surface finishing,the integration of micro grinding,and surface polishing of die steel can be realized on the same machine tool and the same station.Firstly,based on the basic principle of dynamic pressure shear thickening abrasive flow processing,the material removal model of single abrasive and the whole processing area is constructed by using the simulation analysis of the abrasive fluid pressure field and velocity field in the processing area.The results show that the stronger hydrodynamic pressure will be produced at high speed,small clearance,and high viscosity.Compared with ordinary abrasive fluid,shear thickening abrasive fluid has better pressurization ability on the surface of workpiece,stronger holding ability on abrasive particles and higher material removal efficiency.In order to investigate the influence of particle size and particle concentration on the holding forces of abrasive flow,a basic experimental study on the rheological properties of abrasive particles was carried out.The results show that the rheological properties of the abrasive particle size are different between micron and submicron scales.When the particle size is 1～2μm,the viscosity of the abrasive flow is independent of the shear rate.The micron-scale solid particles of the thickener can be consolidated around the abrasive particles to maintain the effect.When the shear rate is greater than the critical value of 10 s^-1,the abrasive flow will gradually produce a strong shear thickening effect.Moreover,the greater the concentration of abrasive particles,the greater the viscosity of abrasive fluid,the stronger holding ability on abrasive particles.Then,the experiment of abrasive flow machining die steel with a particle size of 3μm and8μm was carried out.The shear rate of the abrasive flow was increased by increasing the grinding wheel speed and reducing the machining gap.The results showed that:when the speed is too small and the machining gap is too large,The generated hydrodynamic pressure is too small to effectively remove the material;the greater the viscosity of the abrasive fluid,the greater the holding force,the more effective abrasive particles,and the higher the surface quality.Shear thickening abrasive flow processing can reduce the surface roughness by about 63%to50 nm compared to non-shear thickening.Finally,the micro-grinding of a 106μm consolidated abrasive wheel with dynamic pressure shear thickening abrasive flow was carried out.The results show that the machining quality of the micro structure surface can be improved,and the burr on the microstructure edge can be removed.The edge burr of ordinary micro grinding can be reduced from 5μm to 0.3μm by using 8μm abrasive particles,but the coarser abrasive particles will increase the surface roughness.Finally,the surface roughness can be reduced from 78 nm to 16 nm by using the shear thickening abrasive flow with particle size of 50 nm combined with the micro grinding of the consolidated abrasive wheel with particle size of 44μm.