【作者】 宗文俊；

【导师】 程凯； 李旦；

【作者基本信息】 哈尔滨工业大学 ， 机械制造及其自动化， 2008， 博士

【摘要】 随着超精密切削加工技术的应用与推广,超精密切削的加工精度逐渐向纳米尺度及其极限精度发展。在超精密切削加工中,为了使加工零件获得纳米、亚纳米特征的加工精度,除了需要超精密的车床、高分辨率的检测仪器和超稳定的加工环境外,高精度的金刚石刀具是必须具备的条件,尤其是圆弧刃金刚石刀具。机械刃磨技术以设备低廉、工艺简单等优点,成了目前金刚石刀具制备行业最常用的技术。但现阶段的机械刃磨技术只能加工出切削刃钝圆半径(切削刃钝圆半径亦称锋利度)为70~80nm的金刚石刀具,该指标已远远不能满足当前超精密切削加工技术发展的需求,在某种程度上却成了超精密切削加工技术发展的制约瓶颈。因此,如何突破这一技术瓶颈以获取小于50nm甚至更锋利切削刃钝圆半径的廉价金刚石刀具成了现阶段超精密切削加工技术发展亟需解决的问题。本论文围绕高精度圆弧刃金刚石刀具的机械刃磨工艺,先从加工机理入手,提出了金刚石晶体材料的脆塑转变机械研磨机理,建立了具有各向异性特征的金刚石晶体材料去除方式的动态脆塑转变临界研磨深度的理论计算模型。根据脆塑转变研磨理论,本文对金刚石晶体易磨和难磨方向表层材料的不同研磨去除机理进行了统一解释,并对金刚石晶体研磨效率的各向异性进行了量化比较。根据理论推导的动态脆塑转变临界研磨深度,本文深入分析了各刃磨工艺参数对刀具切削刃钝圆半径刃磨质量的影响,建立了可稳定获取30~55nm切削刃钝圆半径的机械刃磨工艺。此外,本文采用时间序列分析方法,构建了金刚石刀具切削刃钝圆半径随刃磨时间变化的指数与自回归耦合时间序列预测模型,由此可根据切削刃钝圆半径的具体刃磨要求确定刀具刃磨时间,减少了不必要的重磨或过磨及昂贵的刃口检测,提高了生产效率,降低了生产成本。根据脆塑转变机械研磨理论,本文又从理论上推导出了金刚石晶体的动态微观机械强度,包括动态微观抗拉、抗压和剪切强度,通过对比分析金刚石晶体难易磨方向的动态微观机械强度,探索出了金刚石刀具要获取最锋利的刀具刃口需以金刚石晶体易磨方向的动态微观抗拉强度作为前后刀面的设计准则,而金刚石刀具要获取最佳抗磨损性能则需以金刚石晶体难磨方向的动态微观抗拉强度作为前后刀面的设计准则。基于金刚石晶体的动态微观机械强度,本文通过分析刀具刃口的受力情况,从理论上推导出了金刚石刀具的刃口极限锋利度,即(110)晶面作前刀面时可以达到1~6nm,而(100)晶面作前刀面时则可达2~5nm。根据理论推导的假设条件,开发出了新型的热-机耦合刃磨工艺。刃磨实验结果表明,前后刀面分别定向为(110)和(100)晶面的金刚石刀具经过新工艺处理可获取2~9nm的切削刃钝圆半径,实验数据与理论值很好的吻合。另外,本文经过对单晶硅进行大量的超精密切削实验,发现了金刚石刀具发生急剧磨损的主要原因是刀具后刀面的沟槽磨损。进一步的研究又表明,沟槽磨损的产生则是由于碳化硅和类金刚石超硬微颗粒形成后在金刚石刀具后刀面发生刻划和耕犁所导致。最后,本文基于有限元仿真技术和通用旋转组合实验设计方法,建立了高导无氧铜超精密切削的已加工表面残余拉应力和残余压应力对刀具几何参数的二次回归数学模型,由此通过分析刀具几何参数对残余应力的影响,优选出了适于塑性材料超精密切削加工的金刚石刀具几何参数,即在切削刃钝圆半径100~300nm、切削速度2~10m/s、前角-15°~ 15°和后角2°~10°的取值范围内,刀具的优化参数为:前角5°,后角10°,刀具切削刃钝圆半径则越小越好。更多还原

【Abstract】 With the ever-increasing application and popularization of diamond turning technology, the resultant accuracy achieved with diamond turning is approaching towards the nanometric level or even more less, namely the extreme scale. For diamond turning as well known, to realize the nanometer or even sub-nanometer machining accuracy requires the ultra-precision machine tool, the associated high-resolution metrology equipments and the super-stable environment, whilst the high-accuracy diamond cutting tool is also quite crucial, especially for the rounded diamond cutting tool. Advantaged in the cost-effective setups and the simplified processes, the mechanical lapping is a conventional but the most popular method to fabricate diamond cutting tool. Resorting to the state-of-the-art of mechanical lapping, however, the cutting edge radius, namely tool sharpness, can only be sharpened down to about 70~80nm, which is far from the meeting to the development of diamond turning technology. Obviously, the 70~80nm’s bottleneck has restricted the development of diamond turning technology to great extent. And as a result, how to break through such bottleneck so as to achieve a cheaper tool with a cutting edge radius of less than 50nm or even less as finished has been an urgent and challenging problem in current diamond turning field.Therefore in present work, with a view to obtain the high-accuracy rounded diamond cutting tool by means of mechanical lapping, a brittle-ductile transition theory is proposed primarily to account for the lapping mechanism of crystal diamond. As expected, a theoretical model is constructed to calculate the anisotropically critical depths of cut, which act as the switches of the dynamic brittle-ductile transition of lapped crystal diamond in different orientations and on different planes. According to the lapping theory proposed above, the material removal mechanism of lapped crystal diamond is explained systematically in both‘soft’and‘hard’directions. And additionally, the anisotropism of the material removal rate of crystal diamond induced by mechanical lapping is compared quantitatively with respect to the anisotropism of dynamic critical depth of cut. In terms of the dynamic critical depths of cut deduced from brittle-ductile transition theory, the lapping parameters affecting the finished cutting edge radius are analyzed in detail secondly. As a result the mechanical lapping procedure enabling of achieving a tool with a cutting edge radius of 30~55nm is established. Furthermore, the time series analysis method is introduced into this work to model the cutting edge radii’s changing rules dependent on lapping time. Finally, a time series prediction model that couples with the exponential function and autoregressive equation is developed to describe the changing laws. Using this model as expected, the lapping time can be determined accurately with respect to the consumer-required cutting edge radius, which visibly avoids the unwanted over-lapping or under-lapping and reduces the expensive inspections on cutting edge. Then the production efficiency is improved and the cost is cut down in return.According to the brittle-ductile transition lapping theory thirdly, the dynamic micro mechanical strengths of crystal diamond are deduced in different directions and on different planes, including the tensile, shearing and compressive strengths. Comparing the dynamic micro mechanical strengths indicates the dynamic micro tensile strength in the‘soft’direction should be employed as the designing criterion for the crystal orientation on rake and flank faces of diamond cutting tool regarding the most sharpened cutting edge to be finished, and the tensile one in the‘hard’direction, however, should be selected as the designing criterion for the rake and flank faces orientation regarding the strongest resistance to wear.Moreover, being dependent on the dynamic micro mechanical strengths, the impact stresses around the cutting edge during dynamic mechanical lapping are analyzed, and therefore the ultimate sharpness of diamond cutting tool is deduced in theory, i.e. that while the (110) plane or (100) plane is oriented as the rake face, the cutting edge radius can be sharpened down to 1~6nm and 2~5nm, respectively. In terms of the boundary conditions that assumed in the theoretical deduction, an elegant lapping method, namely thermo-mechanical coupled lapping process, is developed. By this means, the validation experiments are performed finally with a tool that orients the (110) plane as rake face and the (100) plane as flank face. And the results imply the cutting edge radius has been sharpened down to 2~9nm, which is well consistent with the ultimate value deduced theoretically. Through a large number of diamond turning tests on silicon wafers fifthly, a novelty finding is demonstrated that the groove wearing mark on tool flank face contributes to the heavy wearing process. The followed in-depth investigations indicate the generation of groove wear is due to the formation of micro super hard particles, i.e. the silicon carbide and diamond-like carbon, which in return have the enough hardness to scratch and plough on flank face so as to form the groove wearing marks.In the last section, in order to optimize the geometry of diamond cutting tool, finite element simulation and general rotatory combination design methods are employed to model the quadratic regression equations of tensile and compressive residual stresses, which generate within the near surface layer of OFHC copper during machining and are considered as a function of tool geometry. And then the related analyses are carried out for tool geometries that influence the residual stresses. The results indicate that when cutting edge radius ranges from 100nm to 300nm, cutting velocity ranges from 2m/s to 10m/s, rake angle ranges from -15°to 15°and flank angle ranges from 2°to 10°, a rake angle of 5°, a clearance angle of 10°and a sharpened as possible cutting edge radius are the optimum geometry for a diamond cutting tool to cut the ductile materials.更多还原