再生型机床切削颤振系统稳定性极限预测

机床切削加工一般都是在有振纹的表面上进行的,由振纹再生效应引发的再生型切削颤振是机床切削颤振的主要形态.本文推导了再生型切削颤振系统极限切削宽度随机床主轴转速变化的理论计算公式,提出了机床切削系统稳定性极限预测方法,并就试验系统的切削稳定性极限进行了预测,实测结果表明,试验结果与预测结果基本相符.     

利用电流变材料在线改变镗杆固有频率抑制切削颤…

金属切削加工中,再生型颤振是一种不易于通过机械结构改良克服的影响切削加工质量,刀具切削不稳定现象。本文通过连续小范围的改变切削系统固有频率,实现了再生型切削颤振的在线抑制。这种方法非常适用于受加工需要而无法提高切削稳定性的镗削及钻削加工。     

车削加工颤振稳定性可靠度蒙特卡罗法仿真

在工程实际中,车削系统刚度、阻尼及切削力等参数的随机性严重影响车削加工的稳定性。针对此问题,提出了一种车削加工再生型颤振稳定性可靠度计算方法。考虑随机因素的影响,采用蒙特卡罗数值模拟方法,研究车削加工再生型颤振稳定性的统计分布规律。建立车削加工再生型颤振动力学模型,采用拉氏变换获取机床车削的极限切削宽度及所对应的主轴转速。根据数控车床切削系统动力学参数的分布信息抽取样本,代入再生型颤振模型进行计算,获取极限切削宽度的样本,并统计其概率特性,以实际切宽是否小于极限切宽为判别条件提出一种基于蒙特卡罗模拟的车削加工再生型颤振稳定性可靠度预测方法。     

再生型切削颤振诊断技术的研究

本文着重讨论了再生型切削颤振的诊断原理和诊断方法。理论分析和试验结果都证明,再生型切削颤振系统的稳定性与被切工件前后两转向振纹的相位差ψ存在某种对应关系;因此,可通过实际测量切削过程中相位差ψ的大小来诊断现场加工中发生的颤振是否属于再于型颤振。相位差ψ与颤振频率、工件转速有关,为使诊断结果准确可靠,本文试验工作采用了频率细化技术。     

再生型切削颤振系统极限切削宽度探究

建立了数控再生型切削颤振系统的模型,推导再生型切削颤振的系统极限切削宽度计算公式.通过具体的试验和数学公式,基于Simulink对极限宽度进行仿真,能够很好地归纳出再生型颤振系统极限切削宽度,对实际加工有很好的指导作用.     

振动切削中刀尖圆弧半径对难切削材料加工的影响

通过对振动切削和传统切削的再生颤振发生机理的仿真计算,提出了在振动切削中采用较大刀尖圆弧半径刀具的加工方法解决难切削材料加工中的再生颤振及刀具强度问题。实验证明了这一新加工方法的有效性,并取得了精度高、稳定性好的加工效果。     

变螺旋铣刀的切削颤振预测新方法

针对变螺旋铣刀切削过程颤振预测建模问题,提出了一种变螺旋铣刀铣削过程稳定性分析新方法.建立了变螺旋铣刀切削过程动态切削力模型,并构建了包含分布再生时滞的铣削系统周期微分方程.在切削深度方向上进行时滞近似,将系统方程转化为多时滞微分方程.基于全离散法获得方程的离散映射形式,进而确定系统的稳定性域,提出了适用于本文预测模型...     

基于变速切削方法抑制再生颤振的研究与应用

在分析各种抑制切削颤振方法的基础上,通过利用变速切削方法抑制再生颤振的实验,给出一定切削条件下的实验结果,该实验结果显示了变速切削在抑制再生颤振方面的突出效果,并进一步分析了变速切削方法在抑制再生颤振上的应用前景。     

整体叶轮非均匀加工余量颤振稳定域仿真与试验研究

针对整体叶轮加工过程中半精/精加工工艺,提出一种基于再生型颤振控制的整体叶轮非均匀余量加工工艺优化策略。借助有限元分析软件获取工艺系统的近似铣削力系数和固有频率,基于再生型颤振分析理论建立了均匀余量叶片和非均匀余量铣削加工稳定性极限叶瓣对比图。最后通过对均匀余量和非均匀余量两种叶片进行切削试验验证,证明了该非均匀余量工艺优化设计策略对抑制颤振有明显的效果,对整体叶轮实际加工和生产有一定的指导意义。     

基于稳定性理论的机床动态优化方法的研究

基于建立的刀具-工件铣削再生颤振多自由度动力学模型,研究了考虑机床结构参数和加工参数的切削稳定性评价方法。提出了基于稳定性理论以扩大稳定性区域和最大材料切除率为优化目标的机床全生命周期稳定性动态优化方法。在设计阶段,通过对影响稳定性的工艺参数动力修改扩大稳定区域;在生产阶段,进行刀具装夹结构和切削参数的优化,进一步扩大稳定区并确保稳定切削下的最大材料切除率。     

Automatic selection of spindle speed for suppression of regenerative chatter in turning

The paper presents a new spindle speed regulation method to avoid regenerative chatter in turning operations. It is not necessary to analyse complex cutting dynamics to search for stable spindle speeds to eliminate regenerative chatter. The metal removal rate is also greatly improved by using this method. The stability lobe diagram for the stability limit of chip width and chatter frequency versus spindle speed is derived by using the Nyquist stability criterion. It is shown that stable spindle speeds can be automatically obtained when the chatter frequency is found. Computational simulations and experimental cutting tests are performed to illustrate the proposed method.     

Method for early detection of the regenerative instability in turning

Nowadays, approaches in chatter detection and control are based on chatter prediction, by using a machining system dynamic model, or on chatter detection by different techniques, but after chatter onset. They are not efficient because the models are complicated and specific (in the first case) respectively because of chatter unwanted consequences occurrence (in the second case). This paper presents a method for early detection of the process regenerative instability state (as a specific process current dynamical state), based on cutting force monitoring. Using the cutting force records, the process current dynamical state is assessed. Appropriate cutting force signal features are defined, based on signal statistic processing, signal chaotic modeling or signal harmonic analysis, and used on this purpose. The process dynamical state evolution is modeled aiming the features values prediction. Two types of models were used in this purpose: linear and neural. The instability regenerative mechanism is identified by using either dedicated features or input variable selection. The method was conceived and experimentally implemented in the case of turning process. The results show the method reliability and the possibility of using it in developing an intelligent system for stability control.     

Unique regenerative chatter in wiper-turning operation with burnishing process Part 1: Prediction and analytical investigation of generation mechanism,critical stability,and characteristics

The purpose of this paper is to understand the generation mechanism and to propose an analytical model of a unique regenerative chatter with the burnishing process in wiper-turning operations. The authors have found a unique chatter when using wiper inserts, which cannot be explained by the existing chatter theory found in the literature. The authors believe that this occurs because of the burnishing process of the wiper insert, which is the only difference from ordinary turning. At first, the burnishing process, which accompanies wiper inserts, is explained, and the turning operation with this process and the well-known regenerative effect in the cutting process is discussed. Then, the stability of the turning process with the regenerative effects in the cutting and burnishing processes are investigated, and an analytical model is proposed to evaluate the critical stability. Finally, the stability analysis of this unique chatter is conducted, and its generation mechanism and characteristics are examined clearly.     

Proposal of novel spindle speed variation profile with constant acceleration rate for improvement of chatter stability

Spindle speed variation (SSV) is one of the effective methods which suppresses regenerative chatter. However, regenerative chatter can grow even if SSV is applied. In the previous work, the chatter growth characteristics in SSV were clarified. The chatter frequency changes proportionally to the varying spindle speed, and it causes the change of the magnitude of the dynamic compliance. Hence, chatter can be suppressed through SSV since the dynamic compliance usually reduces as the chatter frequency changes. A greater compliance reduction can be obtained by a higher rate of spindle speeds in two consecutive revolutions at the same angular position, i.e., acceleration rate. From the investigations in the previous work, limitation of the conventionally utilized SSV profiles is found as follows: the acceleration rate always fluctuates with speed variation and the chatter vibration grows where the acceleration rate is insufficient for suppression, and hence suppressing chatter in all sections of SSV is difficult. In this paper, a new SSV profile with a constant acceleration rate, namely CAR-SSV, is proposed to overcome the limitation of chatter stability improvement by utilizing conventional SSV profiles. The magnitude of the acceleration rate is kept constant to realize the chatter suppression effect throughout the cutting process. Through time-domain simulation and cutting experiments, the chatter stability of CAR-SSV is investigated based on the previously introduced chatter stability evaluation indices. Influence of the parameters of CAR-SSV on the stability is investigated, and an appropriate strategy for setting SSV parameters to achieve higher stability is discussed. In addition, in order to verify the effectiveness of the proposed profile, the stabilities of conventional SSV profiles and CAR-SSV are compared through time-domain simulations and cutting experiments.     

切削颤振的动力学模型研究

振动是金属切削加工过程巾经常遇到的一种现象,也是影响零件加工质量和限制生产率提高的主要因素之一。本文在切削颤振机理研究的基础上,对切削颤振的二维稳定性进行了研究,推导出了在稳定性极限条件下,轴向切深和主轴转速的关系,并用Matlab进行了计算仿真。     

Prediction of regenerative chatter in the high-speed vertical milling of thin-walled workpiece made of titanium alloy

With the wide application of high-speed cutting technology, high-speed machining approach of titanium alloy has become one of the most effective ways to improve processing efficiency and to reduce the processing cost, but the cutting chatter which often occurs in the cutting process not only affects the machining surface quality but also reduces the production efficiency. Regenerative chatter is a typical phenomenon during actual cutting, and it has the greatest impact on the cutting process. With the purpose of avoiding regenerative chatter and selecting appropriate cutting parameters to achieve a steady cutting process and a high surface quality, it is necessary to determine the critical boundary conditions where chatter occurs. Built on the work of previous theoretical researches of regenerative chatter, this paper utilized Visual C++ software to calculate the chatter stability domain during the finish machining of titanium alloy. It was shown that the border between a stable cut and an unstable cut can be visualized in terms of the axial depth of cut as a function of the spindle speed. Using the result, it can find the specific combination of machining parameters, which lead to the maximum chatter-free material removal rate. In order to verify the result, the high-speed milling experiment of an I-shaped thin-walled workpiece made of titanium alloy was conducted. It revealed that the actual machining result was consistent with the calculation prediction. This study will offer a useful guide for effective parameter selection in future CNC machining applications.     

Analysis of regenerative chatter suppression with adding the ultrasonic elliptical vibration on the cutting tool

A method is proposed to suppress regenerative chatter in turning operation, in which the ultrasonic elliptical vibration is added on the cutting tool. It results in the fact that the cutting tool is separated periodically from the chip and the workpiece, and the direction of the frictional force between the rake face of the cutting tool and the chip is reversed in each cycle of the ultrasonic elliptical vibration. The experimental investigations show that the regenerative chatter occurring in ordinary turning operation can be suppressed effectively by applying the ultrasonic elliptical vibration on the cutting tool. In order to clearify the reason of the regenerative chatter suppression, theoretical analysis and computer simulation are performed on turning with ultrasonic vibration. There is a good agreement among the experimental investigations, theoretical analysis and the computer simulation.     

微小型无偏正交车铣加工系统稳定性研究

以微小型车铣复合加工系统为对象,通过对微小型车铣加工工艺系统进行分析将其简化为进行端铣研究。针对加工系统中刚度最低的工件系统利用再生型颤振理论进行分析,得到加工稳定性叶瓣图,并且通过实验验证了该叶瓣图的准确性。得到的微小型车铣稳定性叶瓣图可以指导微小型车铣的加工参数选择,提高微小型车铣加工效率。     

Chatter stability of micro end milling by considering process nonlinearities and process damping

The micro end milling uses the miniature tools to fabricate complexity microstructures at high rotational speeds. The regenerative chatter, which causes tool wear and poor machining quality, is one of the challenges needed to be solved in the micro end milling process. In order to predict the chatter stability of micro end milling, this paper proposes a cutting forces model taking into account the process nonlinearities caused by tool run-out, trajectory of tool tip and intermittency of chip formation, and the process damping effect in the ploughing-dominant and shearing-dominant regimes. Since the elasto-plastic deformation of micro end milling leads to large process damping which will affect the process stability, the process damping is also included in the cutting forces model. The micro end milling process is modeled as a two degrees of freedom system with the dynamic parameters of tool-machine system obtained by the receptance coupling method. According to the calculated cutting forces, the time-domain simulation method is extended to predict the chatter stability lobes diagrams. Finally, the micro end milling experiments of cutting forces and machined surface quality have been investigated to validate the accuracy of the proposed model.     

Proposal of novel chatter stability indices of spindle speed variation based on its chatter growth characteristics

Chatter is one of the most critical problems that causes poor surface quality and restriction of machining efficiency. Spindle speed variation (SSV) is a well-known technique for suppression of regenerative chatter. However, in the authors’ understanding, the chatter suppression effect diminishes when the spindle speed difference between the present and previous cutting moments is small. Furthermore, the stability changes largely according to the spindle speed variation profile which changes with the set condition of SSV parameters, e.g., nominal spindle speed, variation period and variation amplitude. Therefore, SSV parameters should be adequately set to avoid this limitation and to exert its effect throughout the entire duration of cutting. However, there is no clear methodology to determine the optimal condition. This paper presents the characteristics of chatter growth during SSV focusing on the change of chatter frequency, which lead to novel indices to evaluate the chatter stability when cutting with SSV. To verify the validity of the indices, time-domain simulations and the cutting experiments with triangular spindle speed variation (TSSV) are carried out. The influence of SSV parameters on the chatter stability is investigated from the simulation and experimental results. The limitations of widely utilized SSV profiles are discussed.