摘要
微细铣削加工在制造业中有着较强的竞争力,并且随着科学技术水平的提高和社会的不断进步,民用和军工等领域对复杂微小尺寸光机电元器件需求日益增大,微细铣削加工在这些领域扮演着十分重要的角色。但在微细铣削过程中常常有切削颤振现象发生,其极大地影响机床加工性能、刀具的使用寿命和元件的加工质量,甚至会导致噪声等环境污染。本文针对铣削加工中主要的颤振形式—再生型切削颤振进行了分析,结合铣削加工参数(N,r,aε,kt,kr)和系统动力学参数(kx,ky,(?)x,(?)y,ωnx,ωny)建立了两自由度铣削系统动力学模型,利用Matlab软件得到切削过程的稳定性曲线,根据稳定性曲线预测加工过程的极限切削条件,从而选择合理的切削加工参数。论文着重分析了系统动力学参数变化对稳定性极限切深的影响规律,并得知各参数的变化不仅使稳定性曲线在纵坐标方向上有偏移,在横坐标上也有变化,此外又分析了各因素对最小极限切深的影响,从中得到刀具齿数的变化对最小极限切深的影响最为敏感的结论。同时论文在所建立的两自由度动力学模型基础上,利用稳定性曲线中的切削系统参数,计算出了X、Y方向上的平均铣削力。
另外根据上述稳定性曲线,选择一组低于临界颤振条件的切削参数,以此切削参数为基础,对铣削过程进行有限元仿真和切削实验,然后根据二者的切削过程是否发生颤振及二者所得铣削力数据的比对结果,验证动力学模型的合理性和仿真模型的可靠性。对于仿真,用Deform-3D软件分析刀具在接触工件、切入工件刀具直径1/4处、切入工件刀具直径3/4处、完全切入工件以及刀具进入稳态切削等状态的应力和应变,据此分析了工件内部的弹性流动和塑性流动以及当工件发生大幅度塑性变形时,材料从工件表面发生去除的情况。根据Deform-3D软件分析结果,论文还研究了铣削过程工件所受到的作用力,得知在上述的五个状态中铣削力逐渐增加,其中在第三个状态切削力显著增大,达到五个切削状态的最大值,而后又降低,说明在切削过程存在弹性积累,使得刀具的切削负载增大,作用力急剧上升。
对于实验考证,论文利用立扬MVL1300型立式加工中心对铣削加工过程中X、Y、Z三个方向的切削力进行了测试,将实验得到的切削力数据和软件仿真分析结果进行了对比分析,比对结果表明：仿真预测的铣削力数据与实验结果存在一定误差,但总体趋势上相符,基本验证了仿真模型的可靠性,同时根据实验和仿真中切削过程是否发生颤振验证了动力学模型的合理性；在文章最后将实验结果与理论计算的平均铣削力进行了比对,所得数据虽然存在误差,但都在一个数量级上,也验证了理论模型的合理性。
论文工作得到科技部国际合作与交流专项项目(2010DFA72000)和教育部高等学校博士学科点专项基金(200801831024)的资助。
Micro-milling has Strong competitiveness in the manufacturing. With the improvement of science and technology and the progress of society, the demand for complex Optoelectronic components with micro-size is growing no matter in civil use or in national defense industry. Thus micro-milling is playing a very important role in the milling process. However, the chatter which accompanies the milling process often affects the processing properties of machine tools, life of tool and machining quality of workpiece, even produce the noise pollution. Based on the above mentioned, this paper analyzed the main chatter form-regenerative chatter in milling process. Meanwhile the paper established the cutting process dynamic model for the two degrees of freedom based on the cutting parameters of the milling process (N, r, ae, kt, kr) and the dynamics parameters of the chatter system(kx, ky, (?)x, (?)y,ωnx,ωny),then the stable curve of the cutting process was obtained using MATLAB software. Thus the appropriate cutting parameters were selected according to the limit cutting conditions predicted by stable curve. This paper mainly analyzed the laws that how the changes of the system dynamics parameters effected the stability limit depth of cut. And then got to know the factors not only made the stable curve changes in the vertical coordinate direction; there were also changes in the horizontal axis. And the paper also analyzed the factors'effect on the minimum limit depth of cut, and the result showed that the change of the number of teeth for tools is most sensitive to the minimum limit depth of cut. At the same time, using the two degrees of freedom dynamic model and the cutting system parameters, it calculated the average milling force in X, Y directions.
In addition, chose a group of cutting parameters which is below the critical cutting conditions according to the stability curve. Based on the cutting parameters, Did the finite element simulation and cutting experiments in cutting process and contrast analysis results.then tested the rationality of the dynamics model and the reliability of the simulation model. Using Deform-3D,got the diagram of the stress and strain in five states, when the cutter was getting ready to cut into the workpiece, cut into the workpiece at 1/4 diameter of the cutter, cut into the workpiece at 3/4 diameter of the cutter, exactly completely cut into the workpiece and the cutter got into stable cutting. Then analyzed the elastic flow、the plastic flow in the workpiece and the macroscopic situation that the material removed from the surface of the workpiece, according to the diagram and the situation that when there is a large number of plastic deformation in the workpiece. And it also analyzed the force on the workpiece during the milling process using the Deform-3D software. In the five above states, the cutting force showed a gradual increase. But in the third state, the cutting force has a sharp increase which was the largest one in the five states. And then the force decreased, indicating that there is a flexible accumulation process during the cutting process. This process made the load of the cutter became larger and the force increased dramatically.
As to the experiments, this paper tested the cutting force on the X, Y, Z three directions in the machining centre using LiYang MVL1300. The data from the Deform software was compared with experimental cutting force data. Although there was deviation among the comparison, they basically correspond with each other in the trend. This proved that the simulation model was reliable. The curve is also reliable according to the experiment and the simulation (flutter didn't occur when it below the critical cutting conditions). When we compared the experimental data with the theoretic average milling force, we got to know that there was deviation, but they were in the same magnitude. This also proved the rationality of the theory.
This paper had gotten help from the special project of ministry of science and technology for international cooperation and exchanges(2010DFA72000) and special funded projects of the doctoral program of higher education for ministry of education (200801831024)
引文
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