提出一种基于非牛顿幂律流体剪切增稠效应的新型抛光方法——剪切增稠抛光(Shear thickening polishing,STP),通过对剪切弹性层理论的研究,推导出剪切增稠抛光中非牛顿幂律流体与工件之间的剪切弹性层最小厚度方程。在此基础上,根据Preston方程,建立加工过程中的材料去除数学模型。当流速U一定时,非牛顿剪切增稠幂律流体相对于牛顿流体或剪切稀化流体能够使得加工获得更高的材料去除率(Material removal rate,MRR),随着黏性指数n的不断增加,MRR会进一步增大。当黏性指数n和稠度系数K分别为2和0.32时,随着U的增大,MRR呈现幂函数增长趋势,说明增大流速,有利于提高加工效率。在STP加工系统上进行ϕ20 mm的GCr15轴承钢圆柱工件的加工试验,经过90 min的STP后,表面粗糙度由Ra 105.95 nm降至Ra 5.99 nm,MRR达到2.1 μm/h。MRR理论值与试验值之间的相对误差仅为6.12%,试验结果证明所建MRR模型具有一定的有效性。
Based on the non-Newtonian power-law fluid with shear thickening mechanism, shear thickening polishing (STP) as a novel ultra-precision machining method is proposed. The minimum thickness between non-Newtonian fluid of shear thickening polishing and workpiece is deduced through the study on the theory of shear elastic layer. According to Preston equation, the material removal mathematics model is deduced and founded. At constant velocity of flow (U), non-Newton shear thickening power-law fluid compared to the Newton fluid or shear thinning fluid can achieve higher material removal rate (MRR). MRR will further increase with the increasing of viscosity index n. When n is equal to 2 and consistency index K is equal to 0.32, MRR is exponential growth trend with the increase of U, which shows that increasing velocity improves the machining efficiency. Then a machining experiment of GCr15 bearing steel curved surface material is carried out on a shear thickening polishing machining system, the surface roughness of workpiece is decreased from Ra 105.95 nm to Ra 5.99 nm after 90 min processing, and mirror effect can be achieved. MRR of GCr15 (bearing steel) is up to 2.1 μm/h. The average error between the material removal theoretical value and processing experiment result is only 6.12%. The validation of established material removal mathematics model is verified.
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