高速加工时各切削参数对切削力影响的模拟研究

切削力是切削过程中重要的物理参数之一。本文应用数值模拟,对高速切削加工过程中切削参数(切削速度、进给量、切削深度)对切削力的影响进行了研究,给出了切削力随切削速度、进给量、切削深度的变化规律,对优化高速切削工艺及建立高速切削数据库具有指导意义。     

基于刀具磨损和切屑形成对切削Ti6Al4V的切削力特性研究

为了研究钛合金Ti6Al4V切削过程中的切削力特性,采用硬质合金涂层和无涂层刀具进行了外圆干车削试验,提取切削力信号,通过研究切削力的静动态特性,揭示了切削力与切削速度、刀具材料、刀具磨损以及切屑形成的关系.结果表明:钛合金切削过程中,切削力的静态分量中径向力Fp最大,直接导致刀具后刀面磨损;随着切削速度的变化,切削力的变化是由刀具磨损、材料本身的特性等多方面因素综合作用的结果,切削力动态分量分形维数可用于刀具状态监控;锯齿形切屑的产生与切削力的高频变化有直接的关系,锯齿生成频率可以作为切削力动态分量频率的一个表征,选取适当的切削参数可以降低由于锯齿屑产生引起的切削力振动.     

刀具颤振抑制用机械阻尼器的理论分析及数值模拟

为了抑制高速铣削中的颤振影响,提出在刀具中心插入一个分层梁结构机械阻尼器,依靠刀具与阻尼器间的相对运动产生的摩擦阻尼,以耗散振动能量.通过理论分析和数值模拟的方法分别计算了接触压力和阻尼耗散功率,并对两种结果比较分析,找出了造成结果差异的主要原因.     

On-line cutting state recognition in turning Using a neural network

Tool wear, chatter vibration, chip breaking and built-up edge are the main phenomena to be monitored in modern manufacturing processes. Much work has been carried out in the analysis and detection of these phenomena. However, most work has been mainly concerned with single, isolated detection of such phenomena. The relationships between each fault have so far received very little attention. This paper presents a neural-network-based on-line fault diagnosis scheme which monitors the level of tool wear, chatter vibration and chip breaking in a turning operation. The experimental results show that the neural network has a high prediction success rate.     

Study of fuzzy stochastic limited cutting width on chatter

Fuzzy mathematical theory is applied to drawing the fuzzy stability lobes in which each lobe is characterized by a membership grade of experiential distribution of testing data in the theoretical distribution set of chatter signal. The judgement of limit value of free-chatter cutting width is spread over the fuzzy domain in this paper. The fuzzy combination relationship between the spindle speed and the depth of cut in milling is also addressed. According to the limit width, a safety criterion on which the cutting process is stable is developed. Also, the concept and definition of safety criterion for the cutting process stability operation for fuzzy stochastic meaning are given. Analysis indicates that the fuzzy stability lobes have definite physical significance. First, they can tell us in which status the cutting process is for the drawn lobe. Second, they reflect the probability distribution of the limit value of cut width in the fuzzy domain with respect to the identification of chatter status (fuzzy event). Meanwhile, it indicates that there is a transition between unstable lobes and stable lobes in a stability threshold graph with the influence of both fuzzy stochastic parametric excitation and fuzzy stochastic external excitation. Testing value curves of the fuzzy allowed domain of the limited cutting width are developed via experiment.     

A new process damping model for chatter vibration

This paper presents a new analytical process damping model (PDM) and calculation of Process Damping Ratios (PDR) for chatter vibration for low cutting speeds in turning operations. In this study a two degree of freedom complex dynamic model of turning with orthogonal cutting system is considered. The complex dynamic system consists of dynamic cutting system force model which is based on the shear angle (φ) oscillations and the penetration forces which are caused by the tool flank contact with the wavy surface. Depending on PDR, the dynamic equations of the cutting system are described by a new mathematical model. Variation and quantity of PDR are predicted by reverse running analytical calculation procedure of traditional Stability Lobe Diagrams (SLD). Developed mathematical model is performed theoretically for turning operations in this study and simulation results are verified experimentally by cutting tests.     

Influence of flank texture patterns on the suppression of chatter vibration and flank adhesion in turning operations

In this paper, we propose a practical texture design on the tool flank face for suppressing chatter vibration and flank adhesion. To avoid chatter vibration during cutting, the process damping phenomena can be utilized, where the tool flank face contacts the surface of a finished workpiece to provide a damping effect. As a new technology for an effective process damping, the tool flank texture-assisted technique has been proposed, and its excellent performance in suppressing chatter vibration has been demonstrated. However, issues that can lead to adhesion and tool damage pose challenges from a practical viewpoint. To overcome such issues, this paper proposes new texture geometries that improve the practical performance: parallel line type, vertical line type, and dot type. The results of a series of finite element analyses showed that the effectiveness of process damping depends on the vibration amplitude and wavelength. The proposed flank textures were fabricated on tool flank faces, and turning tests were carried out. The experimental results showed that the proposed tool is stabler than the conventional untextured tool and that it can more effectively improve the critical cutting speed, reduce the vibration amplitude, and decrease the surface roughness after cutting. With the appropriate design of the texture distance, adhesion and tool damage were hardly observed, and a stable and practical cutting could be realized.     

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。     

Image processing for chatter identification in machining processes

Identifying chatter or intensive self-excited relative tool–workpiece vibration is one of the main challenges in the realization of automatic machining processes. Chatter is undesirable because it causes poor surface finish and machining accuracy, as well as reducing tool life. The identification of chatter is performed by evaluating the surface roughness of a turned workpiece undergoing chatter and chatter-free processes. In this paper, an image-processing approach for the identification of chatter vibration in a turning process was investigated. Chatter is identified by first establishing the correlation between the surface roughness and the level of vibration or chatter in the turning process. Images from chatter-free and chatter-rich turning processes are analyzed. Several quantification parameters are utilized to differentiate between chatter and chatter-free processes. The arithmetic average of gray level G _a is computed. Intensity histograms are constructed and then the variance, mean, and optical roughness parameter of the intensity distributions are calculated. The surface texture analysis is carried out on the images using a second-order histogram or co-occurrence matrix of the images. Analysis is performed to investigate the ability of each technique to differentiate between a chatter-rich and a chatter-free process. Finally, a machine vision system is proposed to identify the presence of chatter vibration in a turning process.     

Development of a novel boring tool with anisotropic dynamic stiffness to avoid chatter vibration in cutting: Part 1: Design of anisotropic structure to attain infinite dynamic stiffness

This paper presents a novel design method of the anisotropic structure to attain infinite dynamic stiffness to avoid chatter vibration in boring operations. Because a long and slender tool is used for boring operations, the stiffness of the tool holder is likely to decrease, resulting in low chatter stability. Although it is difficult to improve the stiffness of the boring holder itself, the nominal dynamic stiffness for the cutting process can be improved by designing an appropriate anisotropy in the dynamic stiffness of the boring tool. In this study, we formulate a theoretical relationship between the mechanical structural dynamics and chatter stability in boring operation and present the basic concept of tool design with anisotropic structure. In the actual tool design, ideal anisotropy may not be realized because of the influence of design error. Therefore, an analytical study was conducted to clarify the influence of the design error on the vibration suppression effect. Analytical investigations verified that the similarity of the frequency response functions in the modal coordinate system and the design of the compliance ratio according to the machining conditions are important. Furthermore, we designed a boring tool with an anisotropic structure which can achieve the proposed anisotropic dynamics. The frequency response function was evaluated utilizing FEM analysis. The estimated anisotropic dynamics of the proposed structure could significantly improve the nominal dynamics for boring operations.     

Wash-out滤波器的切削颤振控制研究

研究应用Wash-out滤波器对正交切削过程中颤振的控制.首先,根据需要引入的Hopf分岔点来选择控制点,并在该点将原系统Jordan化.然后,对引入的Wash-out滤波器按Hopf分岔条件确定其线性增益和非线性增益,将系统的亚临界Hopf分岔控制为超临界Hopf分岔,削弱受控切削系统的颤振振幅.理论分析和数值模拟结果验证了该控制方法在切削颤振控制中的有效性.     

Time domain coupled simulation of machine tool dynamics and cutting forces considering the influences of nonlinear friction characteristics and process damping

A higher machining ability is always required for NC machine tools to achieve higher productivity. The self-oscillated vibration called “chatter” is a well-known and significant problem that increases the metal removal rate. The generation process of the chatter vibration can be described as a relationship between cutting force and machine tool dynamics. The characteristics of machine tool feed drives are influenced by the nonlinear friction characteristics of the linear guides. Hence, the nonlinear friction characteristics are expected to affect the machining ability of machines. The influence of the contact between the cutting edge and the workpiece (i.e., process damping) on to the machining ability has also been investigated. This study tries to clarify the influence of the nonlinear friction characteristics of linear guides and ball screws and process damping onto milling operations. A vertical-type machining center is modeled by a multi-body dynamics model with nonlinear friction models. The influence of process damping onto the machine tool dynamics is modeled as stiffness and damping between the tool and the workpiece based on the evaluated frequency response during the milling operation. A time domain-coupled simulation approach between the machine tool behavior and the cutting forces is performed by using the machine tool dynamics model. The simulation results confirm that the nonlinear frictions influence the cutting forces with an effect to suppress the chatter vibration. Furthermore, the influence of process damping can be evaluated by the proposed measurement method and estimated by a time domain simulation.