【作者】 曾晰；

【导师】 计时鸣；

【作者基本信息】 浙江工业大学 ， 机械电子工程， 2013， 博士

【摘要】 激光强化技术可大幅提高模具表面的硬度、耐磨性和耐腐蚀性,改善模具使用性能和提升使用寿命,但另一方面其高硬度自由曲面面形的复杂性、局域强化带来的硬度差异却制约了后续表面精密加工的开展。鉴于模具表面激光强化处理具有良好的应用前景,解决其光整加工的技术难题对于激光强化技术在模具领域的应用具有重要的现实意义。针对上述问题,本文提出了一种基于软固结磨粒气压砂轮的光整方法。为了提升高压环境下砂轮橡胶基体的抗撕裂特性,提出采用添加短纤维增强砂轮基体的方法,给出了复合材料模量与强度预测模型；对气压砂轮的力学特性进行了分析,并通过仿真进行了验证；采用离散元分析方法对软固结形态下的磨粒动态特性进行了研究；最后对软固结磨粒气压砂轮的材料去除特性进行了分析,并通过试验进行了验证。本文具体内容如下：(1)针对复合材料中纤维的无序分布特性,建立了多维网状分布模型,提出采用取向因子对其纤维分布特性进行整体归一化,对Halpin-Tsai方程进行了修正,并建立了复合材料的模量预测模型和强度预测模型,实现了芳纶浆粕纤维对丁苯橡胶的增强,制备了不同纤维体积分数和不同尺寸的气压砂轮半球形增强橡胶基体。通过拉伸试验对上述理论模型进行了验证,得出通过增加纤维所占体积分数或使用低模量的橡胶基质,纤维在橡胶基体中的性能越接近单一性,预测模型将更加准确。上述问题的讨论将为气压砂轮后续各项性能分析奠定基础。(2)建立了气压砂轮橡胶基体接触力学模型,对接触过程进行了数值模拟,得出结论：气压砂轮表面接触应力随着纤维体积分数的增加而增加,同样也随着原橡胶基体弹性模量的增加而增加,但砂轮接触应变却随之减少：结合层间弹性力学体系理论,分析了气压砂轮动态变化下的载荷作用规律,建立了气压砂轮双层弹性力学模型；分别以复合橡胶层厚度和磨粒粘结层厚度为研究对象进行了仿真,发现低橡胶层厚度有利于提升气压砂轮的自锐性,适合于大曲率表面加工；高橡胶层厚度则有利于提升砂轮接触应力,提高光整效率。以上论述分析了气压砂轮基体的力学特性,并为后续气压砂轮的制备工艺参数提供了依据。(3)采用离散元分析方法,建立了软固结磨粒颗粒间的法向与切向接触模型,分析了磨粒群的蠕变效应,给出了颗粒微观平动与转动位移公式：通过对密集颗粒系统的数值模拟,阐述了蠕变现象的发生过程,并分析了软固结磨粒群和游离磨粒群的接触力网,证实了前者产生的表面接触应力将显著大于后者的接触应力；阐述了软固结磨粒群气压砂轮的低压接触成型制作工艺流程和评价标准,给出了可用于不同加工环境下的磨粒与粘结剂具体配比方案。上述分析描述了软固结磨粒群的微观作用机理,为后续气压砂轮最终材料去除模型的建立提供了依据。(4)建立了气压砂轮表层单颗磨粒的力学模型,得出磨粒群微观作用机理与气压砂轮材料去除特性之间的联系。结合拉宾诺维奇磨损原理,对Preston方程系数进行修正,并对磨粒群在柔性支撑环境下的应力计算进行修正,给出了表层磨粒群在动态变化下的速度计算公式,最终建立了适用于软固结磨粒气压砂轮的材料去除预估模型,并通过试验进行了验证,得出软固结磨粒较游离磨粒有着更高的材料去除能力,而较固着磨粒群则可避免曲面加工时过深的划痕。更多还原

【Abstract】 In mould industry, laser hardening could not only significantly improve surface hardness, wearing resistance and corrosion resistance, but also optimize performance of mould and extend its service life. However, these advantages have also brought tremendous difficulties to the finishing process of laser hardening surface, such as irregular freeform surface, high hardness and local difference of hardness. In the view of its wide future prospects, it becomes very important to figure out this problem.In allusion to the problems above, a new finishing method based on the softness consolidation abrasives (SCA) pneumatic wheel is brought forward in this paper. Firstly, in order to improve the tearing stability of interior rubber of SCA, fiber reinforced method is adopted. Meanwhile, the prediction models of modulus and ruggedness are established. Secondly the mechanics characteristic of hemispheric compound rubber is analysed by the simulation. Thirdly discrete element method is brought in for the research on the dynamic characteristic of SCA. Also moulding process of wheel is introduced. Finally the material removal prediction model of SCA is given, which is verified by the experiments. The main contents in this paper are as followed.(1) The distribution of the fiber in the compound rubber shows a complex poly-dimensional net. Orientation factor is used to normalize the fiber reinforce characteristic. The prediction model of modulus is set up by the modified Halpin-Tsai equation. At the same time, the prediction model of ruggedness is given. The test that Aramid Pulp is added to the Styrene-Butadiene rubber is finished and the hemispheric compound rubbers are created with kinds of size and different fiber volume fraction. The tensile tests’results are in accordance with the prediction model which is proved to be more accurate in the cases of using lower modulus of original rubber and improvement of fiber volume fraction. The points discussed above lay the foundations for the succedent performance analysis of pneumatic wheel.(2) The contact process between pneumatic wheel and workpiece is simulated and the conclusions show the stress increases with the improvement of fiber volume fraction and modulus of original rubber. On the contrary, the strain decreases in that case. Combined with the layers’ elastic theory, the dynamic characteristic of the pneumatic wheel is analysed and the relationship between stress and stain is given. The simulation shows that thin layer of compound rubber is beneficial to enhance the softness of the wheel and fit for the machining to surface with large curvature. However, the thick layer of compound rubber can help to concentrate the cutting stress and improve the efficiency of the machining. The analysis of mechanics characteristic of pneumatic in this section provides a basis for the optimization of the manufacturing parameters.(3) According to the soft-ball model of discrete element method, the normal and tangential contact stress formula has been established for the relationship discussion between two particles. The translational and rotational displacement formulas of SCA are given and the creeping phenomenon is proved out by the simulation. It is also verified that the SCA has much more powerful stress net and can supply more cutting stress working on the workpiece than the free abrasives’. Besides, the craft and evaluation criterion of manufacture of SCA has been introduced and the standard of mixture ratio between abrasives and binder is given for adapting to the different machining situation. The discussions above explain the microscopic mechanism of the SCA, which provides the basis for the material removal model in the next section.(4) The mechanics model of single particle is analysed and the relationship between microscopic mechanism of the SCA and macroscopic machining charateristic of the pneumatic wheel has been given. Combined with the Rabinoweizc’s theory, the coefficient of Preston equation is established. Meantime, cutting stress is modified in the case of particles’ working under the soft support and velocity formula of SCA is figured out. Finally, the material removal model of pneumatic wheel is given, which has been proved out by the experiments. The experimental results show that the SCA has better material removal ability than the free abrasives’and can avoid the scratches to the freeform surface which the fixed abrasives always left in the same situation. This section finally shows the SCA’s machining ability.更多还原