剪切增稠抛光方法的基础研究

发布时间：2018-02-22 21:32

本文关键词： 抛光剪切增稠抛光剪切增稠超精密加工高效加工剪切增稠抛光液材料去除率表面粗糙度　出处：《湖南大学》2015年博士论文　论文类型：学位论文

【摘要】：如何实现目标工件的高效、高质量、低成本加工是目前精密与超精密加工领域的研究热点。为此,本文提出一种基于非牛顿幂律流体剪切增稠效应的新型加工方法——剪切增稠抛光(Shear-thickening Polishing,STP):利用非牛顿幂律流体抛光液的剪切增稠流变特性达到增强把持磨粒的约束力而形成类似“柔性固着磨具”、增大接触区域面积而具有良好的面形适应性,从而可实现工件表面的高效精密抛光。针对剪切增稠抛光方法的材料去除机理和工艺技术进行研究,围绕高性能抛光液的制备及其流变性能、加工过程中的材料去除率、表面质量等关键技术问题展开探索,建立了拥有自主知识产权的高效精密剪切增稠抛光理论基础及工艺技术。主要研究内容包括:(1)对STP加工方法的可行性进行研究。分析加工过程的主要影响因素,并通过FLUENT软件对具有剪切增稠效应的抛光液(一种非牛顿幂律流体)流场CFD仿真,对加工原理的有效性进行对比仿真验证。在此基础上,采用剪切增稠抛光液对GCr15轴承钢工件进行抛光的材料去除率(Material Removal Rate,MRR)约为对照组(相同初始黏度的非剪切增稠流体抛光液)的10倍,且表面粗糙度由Ra 101.33 nm降至Ra7.80 nm,远低于对照组(仅下降至Ra 96.81 nm),证明剪切增稠抛光加工方法的可行性,为后续深入研究提供理论基础。(2)对剪切增稠抛光液(Shear-thickening Polishing Slurry,STPS)的制备方法及性能进行研究。在实现STP加工原理的前提下,确定原料易获取、环境友好、合适的剪切增稠抛光基液(Shear-thickening Based Fluid,STBF),构建了STPS的制备工艺流程。采用上述工艺制备出Al_2O_3基STPS,其具有剪切稀化和可逆的剪切增稠效应,随着剪切应力变化而实现Al_2O_3“粒子簇”形成与消失,从而能够达到STP技术所需抛光液的流变特性。(3)对STPS的流变行为进行深入研究,确定剪切增稠条件和各粘性参数的数值计算。研究发现,随着剪切速率的增大,STPS存在着3个明显的黏度区域:剪切稀化区域I、剪切增稠区域II、剪切稀化区域III。STPS发生剪切增稠的阈值为变化范围10~1000 s-1,尤其在剪切速率变化范围200~1000 s-1可达到剪切增稠效应而实现工件的高效抛光。随后,计算得到STPS本构方程中的粘性参数(包括稠度系数K和粘性指数n)的精确解,为STP的材料去除率模型的建立等后续研究提供了理论基础。(4)针对STP加工的材料去除机理进行理论研究。依据Preston方程和流体动力学理论,构建了STP加工的MRR模型。经试验研究,由MRR模型得出的理论值与试验的测量值的相对误差仅为6.12%,证明MRR模型具有一定的有效性。对MRR和表面粗糙度Ra的试验研究显示:随着抛光速度(U)、磨粒浓度(w%)的增大,MRR随之增大,但其随磨粒粒径(d)的减小而增大;随着U、w%的增大,表面粗糙度Ra减小,表面质量提升,但在本试验条件下,d的变化对工件表面粗糙度Ra的影响较小。(5)对STP加工工件的表面粗糙度模型及表面演化进行研究。依据工件布氏硬度(BHN)的计算、剪切增稠机制和塑性压痕的磨料磨损理论,建立了STP的表面粗糙度预测模型。通过试验验证了表面粗糙度预测模型的有效性,工件表面粗糙度的理论值与试验值的最大误差仅为8.29%。该模型的建立,有利于对塑性工件加工的表面质量控制,并开展了STP加工Cr12Mo1V1的表面演化研究。延伸研究了STP加工单晶硅片,为脆性材料的表面粗糙度预测模型的建立提供基础。(6)对STP加工工艺进行研究。通过田口法的正交实验,获得了本加工条件下的优化工艺参数:抛光速度300rpm、磨料粒度4000#、磨料浓度23 wt%为最佳参数组合。利用优化的STP加工工艺对Cr12Mo1V1进行试验加工,其MRR达到13.69μm/h;加工0.5 h,表面粗糙度由Ra 105.95 nm快速下降至Ra 5.1 nm。采用STP、双平面方式研磨抛光(结合化学机械抛光)圆柱工件进行对比研究,STP工艺的MRR是双平面方式研磨工艺的2倍以上,为化学机械抛光的4倍;工件经STP后的表面粗糙度从Ra 125 nm下降到Ra 5.1 nm,而双平面方式研磨抛光的工件表面粗糙度由Ra 76 nm下降至Ra 16.6 nm;同等条件下,前者所获工件圆度误差为RONt 0.376mm,后者所获圆度误差为RONt 0.390mm,说明STP具有良好的抛光效率和加工质量。利用STP对Si_3N_4陶瓷进行加工,150 min后表面粗糙度由Ra 110.90 nm降至Ra 7.20 nm,且MRR为2.04μm/h;在STP-1型试验样机上应用小抛光工具头对抛物面反射面(HPM38模具钢)进行STP加工的探索研究,120 min后获得表面粗糙度Ra 4.73 nm,面形误差PV值达到0.86μm。试验表明,STP不仅能高效抛光硬脆性材料,并具有复杂曲面超精密抛光的应用潜力。上述结果表明,剪切增稠抛光(STP)是一种基于非牛顿幂律流体剪切增稠效应的新型高效、高质量、低成本加工方法。
[Abstract]:How to achieve the goal of workpiece efficient, high quality, low cost of processing is currently hot research fields of precision and ultra precision machining. Therefore, this paper proposes a new polishing - shear thickening processing method of thickening effect of non Newtonian power-law fluid shear based on (Shear-thickening Polishing, STP): the use of shear non Newtonian fluid slurry thickening rheological properties to enhance the control of particle binding and the formation of similar "flexible fixed abrasive, contact area increases and the surface has good adaptability, which can achieve high efficiency and precision polishing of the workpiece surface. According to the removal mechanism and technology of shear thickening polishing method was studied, and its preparation rheological properties on high performance liquid polishing system, in the process of material removal rate, surface quality and other key technical problems to start exploring the established with independent intellectual property Thickening polishing theory and technology of high precision shearing power. The main research contents include: (1) to study the feasibility of STP processing method. The main factors affecting the analysis process, and through the FLUENT software with the shear thickening effect of the polishing liquid (a non Newton power-law fluid flow field CFD simulation) comparison of the results of simulation, the validity of the processing principle. On this basis, the shear thickening liquid polishing polishing of GCr15 bearing steel workpiece material removal rate (Material Removal, Rate, MRR) about the control group (the same initial viscosity of non shear thickening fluid polishing liquid) 10 times, and the surface roughness from Ra 101.33 nm to Ra7.80 nm, much lower than the control group (only 96.81 down to Ra nm), to demonstrate the feasibility of shear thickening polishing method, provide a theoretical basis for further research. (2) the shear thickening liquid polishing (Shear-t HICKENING Polishing Slurry, STPS) preparation and performance research. In the premise of realizing the principle of STP processing, easy to obtain raw materials to determine, environmentally friendly, the appropriate shear thickening liquid (Shear-thickening Based polishing Fluid, STBF), the construction process of the preparation of STPS prepared Al_2O_3 based STPS used. The above process, with shear thinning and shear thickening effect reversible, with the shear stress change and the realization of Al_2O_3 clusters forming and disappearing, the rheological properties of STP technology so as to achieve the required polishing. (3) studied the rheological behavior of STPS, numerical determination of shear thickening conditions and the viscosity parameter calculation. The study found that with the increase of shear rate, STPS has 3 distinct regions: the viscosity shear thinning region I, shear thickening region II, shear thinning region of III.STPS. The threshold for shear thickening The change range of 10~1000 s-1, especially in the high polishing shear rate range of 200~1000 S-1 can achieve the shear thickening effect and workpiece. Then the calculated viscous constitutive parameters in the equations of STPS (including K viscosity coefficient and viscosity index n) exact solutions, provides a theoretical basis for the STP model of material removal rate the establishment of a follow-up study. (4) for the processing of the material removal mechanism of STP theory research. Based on the Preston equation and the theory of fluid dynamics, constructs a MRR model of STP machining. Through experimental research, obtained by the MRR model. The relative error measurement and test the value of only 6.12%, we proved that the MRR model has the effectiveness of MRR. And the experimental research on surface roughness of Ra showed: with the polishing speed (U), particle concentration (w%) increased, MRR increased, but with the particle size (d) decreases with increasing U, the increase of w%, The surface roughness of Ra decreases, the surface quality improvement, but under the conditions of this experiment, the change of D has little effect on the surface roughness of Ra. (5) of STP on the surface roughness of the workpiece surface model and evolution are studied. On the basis of the Brinell hardness (BHN) calculation, the abrasive wear theory of shear thickening the mechanism and plastic indentation, establishes the prediction of STP rough surface model. The test results validate the prediction model of surface roughness, the surface roughness of the workpiece to establish the theoretical value of the maximum error and the experimental value is only 8.29%. of the model, is conducive to the control of the surface quality of the plastic workpiece, and Research on evolution of STP surface processing of Cr12Mo1V1. On the STP wafer processing extension, surface roughness prediction of brittle materials provide a basis model. (6) to study the STP processing technology. Through the orthogonal Taguchi Nori The optimized parameters are obtained under the condition of the processing speed: polishing abrasive particle size 300rpm, 4000#, abrasive concentration 23 wt% was the best combination of parameters. Experiments were carried out on Cr12Mo1V1 processing using STP process optimization, the MRR reached 13.69 m/h; 0.5 h processing, the surface roughness by Ra 105.95 nm rapid decline to Ra 5.1 nm. by STP, double plane polishing (combined with chemical mechanical polishing) cylindrical workpiece were studied and compared with STP process MRR is a dual plane lapping process for more than 2 times, 4 times for chemical mechanical polishing; workpiece by surface roughness after STP Ra from 125 nm down to 5.1 nm and Ra. Double plane polishing workpiece surface roughness by Ra 76 nm down to 16.6 nm Ra; under the same conditions, the former received a degree error of workpiece circle is RONt 0.376mm, the latter the roundness error is RONt 0.390mm, indicating that STP has a good polishing Efficiency and processing quality. The processing of the Si_3N_4 ceramics with STP rough surface after 150 min degree from Ra 110.90 nm to Ra 7.20 nm and MRR 2.04 m/h; application of small polishing tool head of the parabolic reflector in STP-1 experimental prototype (HPM38 steel) STP processing research, 120 min obtained after the surface roughness Ra of 4.73 nm, the surface shape error of the PV value reached 0.86 mu m. test shows that STP can not only hard brittle materials, polishing, and has the potential application of complex surface in ultra precision polishing. The results show that the shear thickening polishing (STP) is a kind of high quality efficient thickening effect. Non Newtonian power-law fluid shear based on low cost processing method.

【学位授予单位】：湖南大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG580.692

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