光学自由曲面反射镜模芯的镜面成型磨削

采用精密修锐修整的圆弧形粗金刚石砂轮在CNC精密磨床上进行了数控成型磨削加工,实现了高效镜面磨削。分析金刚石砂轮圆弧形轮廓的成型修整原理,建立了圆弧形修整的数控模式。通过建立曲面数控成型磨削的行走轨迹算法,实现了自由曲面的圆弧包络成型磨削加工。分析了磨削工艺参数和砂轮出刃形貌参数与超光滑表面形成的作用机制,进行了镜面磨削试验并检测表面微观形貌和粗糙度,分析实现镜面磨削的脆/塑性磨削转换机理。理论分析表明,降低砂轮行走速度,提高砂轮转速以及改善出刃形貌可以获得纳米级粗糙度的超光滑磨削表面。试验结果显示,先将砂轮修锐修整再控制砂轮行走速度小至15 mm/min时,表面粗糙度小于10 nm以下,且微观加工表面没有发生脆性破坏,形成镜面。加工高速钢自由曲面时,面形误差(PV值)可以达到10 μm以下,表面粗糙度R_a可以达到约16 nm。实验结果表明:利用数控技术和粗金刚石砂轮可以实现自由曲面模芯的高效镜面磨削加工,保证了高精度的光学自由曲面反射镜注塑模芯。

Mirror form grinding of free-form surface of reflector mould core

In order to assure form accuracy and surface roughness of optic free-form surface of injection mould core, form grinding of free-form surface was conducted in CNC precision grinder by use of precisely dressed and trued arc-shaped coarse diamond grinding wheel to realize effective mirror grinding. The form truing principle of arc-shaped diamond grinding wheel was investigated to establish number control mode of arc-truing, and wheel path algorithm for equal- envelope-height grinding was established to realize CNC grinding of free-form surface. Then, formation of super-smooth ground surface was theoretically analyzed in connection with grinding parameters and wheel topography. The theoretical analysis shows that super-smooth ground surface of nanometer order can been produced by increasing wheel rotating speed, decreasing wheel moving speed and improving wheel topography. Experimental results show that surface roughness of R_a<10 nm may be obtained by use of dressed and trued wheel with wheel moving speed in less than 15 mm/min, and no brittle cracks on microscopic ground surface. The form accuracy of PV < 10 μm and the surface roughness of R_a<20 nm can be obtained when machining the free-form surface of high-speed steel.