【作者】 翟元盛；

【导师】 梁迎春；

【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】 随着航空航天、高精密仪器仪表和精密机械等技术的发展,对各种高精度复杂零件的使用性能要求越来越高。在精密超薄切削过程中,由于切削厚度较小,切削刃钝圆半径对切削过程的影响已不容忽视,亚表层损伤给零件性能带来极大影响,导致零件合格率极低。因此,通过精密切削提高加工表面质量,减小变质层和残余应力一直是国内外精密切削领域重要的研究课题。本文通过精密超薄切削高强度弹性合金3J33实验,研究切削参数、刀具几何参数和切削力等对表面粗糙度及变质层的影响规律。首先,建立精密超薄正交切削力模型,把切削力分解为第一变形区的分力和钝圆半径变形区的耕犁力。在改进的Oxley切削模型的基础上研究了第一变形区和第二变形区的切削能,并运用能量最小原理计算剪切角,获得第一变形区的切削分力;基于滑移线场理论建立刀具钝圆半径变形区的耕犁力模型。考虑尖刃刀和圆弧刃刀具超薄切削时的流屑角,将精密正交切削力模型应用于尖刃刀和圆弧刃刀具精密超薄切削力的计算,为后续的研究工作提供了理论基础。第二,根据弹塑性变形理论和有限元方法,在修正的库仑定律刀/屑摩擦方程和局部网格重划分准则的基础上,利用有限元分析软件Msc.Marc对精密超薄切削过程进行了正交切削和圆弧刃切削过程模拟。研究正交切削过程刀具前角和钝圆半径对切削力、切削温度和应力分布的影响。圆弧刃切削过程分析了刀尖圆弧半径和钝圆半径对切削力、切削温度和应力分布的影响。模拟结果表明切削变形区为一个局部不均匀的高应力区,为实验分析提供了参考数据。第三,采用正交实验法,研究切削参数对尖刃刀超薄切削力的影响,建立精密超薄切削力的预测模型。采用旋转正交实验法研究切削参数(进给量和背吃刀量)和刀尖圆弧半径对圆弧刃刀具精密超薄切削力的影响,建立切削力的二次方程,并通过实验验证切削力的理论值和有限元模拟结果。第四,在考虑进给量和刀尖圆弧半径对表面粗糙度影响的基础上,着重考虑精密超薄切削力对加工表面粗糙度的影响,提出了用可靠的修正系数,并基于遗传算法对表面粗糙度理论模型加以修正。基于遗传算法,采用旋转正交实验法建立圆弧刃精密超薄切削表面粗糙度预测模型,分析切削参数(进给量和背吃刀量)和刀尖圆弧半径对表面粗糙度的影响。最后,用扫描电子显微镜检测加工变质层的显微组织,确定加工变质层厚度,同时采用显微硬度法研究亚表层的加工硬化程度。研究结果表明:变质层的晶粒在切削过程受到拉伸和扭曲,其晶粒流动方向和母材的晶粒流动方向不同,因此精密加工的变质层主要受机械应力引起塑性变形层,没有明显的热影响区和相变特征;精密加工的塑性变形层深度较小;切削用量越大,塑性变形层越深,表面硬化程度也越大。更多还原

【Abstract】 With the development of the aerospace industry, high accuracy instrument, and precision mechanery, the demands for the service performance of components with complex small features are increasing more and more. The tool edge radius plays an important role in chip formation because undeformed chip thickness is very small in super-thin precision cutting. However, the performance of components will be failure due to damaged layer. Many researchers have put their attentions on reducing damaged layer, residual stress and improving machined surface quality with precision cutting technolagy. In this study, the effects of cutting paraments, tool geometries and cutting forces on surface roughness and damaged layer are studied in super-thin precision cutting 3J33.Firstly, the cutting force model of orthogonal super-thin precision cutting is studied with the cutting force divided into the chip formation force due to the primacy deformation zone and the ploughing force due to tool edge radius. By applying the minimum energy principle to cutting energy composed of the cutting and friction energy in the primary and secondary deformation zones on the basis of modified Oxley’s machining model, the shear angle in the primary deformation zone is estimated and the chip formation force is calculated. With the aid of a slip line field model, ploughing forces due to the tool edge radius are studied. The orthogonal super-thin precision cutting forces model is extended to 3D cutting forces model of sharp-nosed tool and nose radius tool considering chip flow angle to lay a theoretical foundation for the subsequent research works.Secondly, the friction between the tool and the chip is assumed to follow a modified Coulomb friction law and the adaptive remeshing technique is used for the formation of chip. A two-dimensional and a three-dimensional finite elements model for super-thin precision cutting using the commercial software Msc.Marc on the base of thermo-elastic-plastic deformation theory and FEM. The effect of edge radius and rake angle on cutting forces, temperature distribution, and stress distribution are investigated in the two dimensional finite element analysis. The effect of edge radius and nose radius on cutting forces, temperature distribution, and stress distribution are investigated in the three dimensional finite element analysis. The simulation results demonstrate the behaviors of the non-uniform intense stress fields in deformation zones of precision cutting to give useful data for experimental analysis.Thirdly, a mathematical model for cutting force in super-thin precision cutting with sharp-nosed tool is developed in terms of cutting parameters by orthogonal experimental test. A second order mathematical model for cutting forces in super-thin precision cutting with nose radius tool is developed in terms of cutting parameters (feed rate and depth of cut) and nose radius by the quadratic rotary combination design. The experimental cutting forces are used to testify the theoretical model for turning with nose radius tool and simulation results obtained from finite element analysis.Moreover, the theoretical model for surface roughness, which is taken as a function of variables feed and tool corner radius, is modified by cutting forces using a Genetic Algorithmic (GA) approach. A second order predictive model for surface roughness in super-thin precision cutting with nose radius tool is developed in terms of cutting parameters (feed rate and depth of cut) and nose radius by the quadratic rotary combination design using GA approach. Lastly, the mechanical and thermal effects on microstructure and hardness of super-thin precision turned sub-surfaces are studied both with a scanning electron microscope (SEM) analysis and microhardness test using microindentation. A thin disturbed or plastically deformed layer is distinguished by the presence of grains that are elongated and rotated in the direction of cutting.No significant heat affected layer and phase transformation is found below the machined surface in all the tests. It also implies that mechanical deformation plays a larger role during super-thin precision turning. It was also found that the hardness of the plastically deformed layer differed from the bulk hardness of the workpiece. Larger cutting parameters (depth of cut and feed rate) usually give rise to deeper mechanical affected layers.更多还原