基于NC物理仿真的钛合金薄壁件颤振预测研究

针对钛合金薄壁零件在铣削加工过程中存在的切削颤振问题,以多框类零件为对象,建立了基于NC物理仿真的钛合金薄壁零件颤振预测模型,解决了钛合金零件在工艺准备初期即实现颤振的预报。首先通过试验与仿真相结合的方式,获取工艺系统的颤振稳定域,并进行稳定域内参数优化;其次通过建立有限元模型,进行零件模态分析,获取零件加工过程中的动态特性,确定最优刀具路径;最后利用NC物理仿真软件对零件进行切削过程仿真,预测切削过程中颤振是否发生。结果表明,通过此类技术,可直观有效地跟踪加工过程,提高薄壁件加工稳定性。     

微细铣削加工再生颤振的研究(英文)

微细铣削是利用微铣刀在高转速下加工复杂三维结构的制造技术。再生型颤振能引起刀具的严重磨损,降低零件的加工质量,是微细铣削加工面临的主要挑战之一。铣削加工过程中切削系数和系统动态特性的多变影响颤振稳定性。针对该问题,建立了考虑再生效应的微铣削动态铣削力模型和颤振稳定域解析模型,通过模态试验获得机床 - 刀具系统的频响函数,综合使用铣削稳定性判据进行数值分析,获得了颤振稳定域解析解。最后进行了颤振稳定性加工实验,验证了建立的颤振系统动力学模型和颤振解析模型的正确性。     

MDH80加工中心铣削稳定性研究

为了提高发动机缸体与缸盖结合面的表面加工质量,研究了铣削加工过程中的颤振稳定性问题。进行了刀具—主轴锤击模态试验和铣削力仿真实验,获得了所用刀具的低阶模态参数及铣削力系数。构建了铣削颤振的稳定性叶瓣图,用于指导切削参数的选择和优化。通过该方法可以选取合适的主轴转速和切削深度,避免加工过程中颤振的发生,提高工件表面的加工精度,并对加工刀具及机床本身有保护作用,可提高其使用寿命。     

铣削加工颤振稳定域影响参数研究及优化

建立圆柱形铣刀铣削加工动态切削数学模型,采用一种解析法计算并绘制稳定域图,获取加工稳定性随工艺参数变化的规律。分析系统参数对铣削加工颤振稳定特性的影响,提高固有频率、增大系统刚度和阻尼有助于提高系统加工稳定性。基于动态变化的稳定域图及共振功率半频带频率,提出一种铣削稳定性约束下铣削参数优化模型,获取最大加工效率下的主轴转速、径向进给量及轴向进给量参数的最优值。开发铣削稳定性分析仿真软件,实现铣削颤振稳定域分析、共振区域分析、铣削参数优化等功能。将复杂设计分析过程工程实用化,具有工程应用价值。该方法同样可推广到磨削、车削的颤振分析。     

基于斜角切削模型的铣削加工稳定性研究

针对零件加工过程中发生的颤振现象,结合大型A/B摆五轴龙门铣床,在斜角切削模型的基础上进行了铣削稳定性的研究。基于斜角切削的工作正交平面和法平面参考坐标系,引入切削力系数的修正形式;将切削刃微元在局部坐标系下进行切向、径向分解,经过坐标变换得到在整体坐标系下的切削分量,通过积分求和得到整个铣刀上的切削力。在此基础上采用完全离散解析法对颤振稳定域叶瓣图进行仿真,仿真结果表明,铣削过程中参数选取与颤振临界切削深度存在非线性关系;随着斜角切削刃倾角的增大,临界切削深度加深,稳定区域变大,铣削加工颤振的稳定性得到改善。     

船用螺旋桨分区域加工共振控制研究

为了解决螺旋桨叶片等薄壁件在加工中因振动而难以达到加工精度要求的问题,给出了一种通过调节主轴转速来实现薄壁件分区域加工共振控制的方法。通过模态锤击实验获取不同切削区域工件与刀具的固有频率,结合工件与刀具的固有频率及其与刀具齿数的关系,确定薄壁类零件不同区域加工的主轴转速,进而减弱和避免加工过程中的振动。通过薄板切削实验,验证了分区域加工共振控制方法对避免铣削加工振动和提高加工质量的有效性。将所提方法应用于螺旋桨叶片加工过程中,有效地解决了螺旋桨叶片等薄壁类零件的弱刚性及其不同区域动态特性分布的差异性而导致精加工过程中极易发生振动的问题。     

薄壁筒车削颤振稳定性预测

切削颤振是制约薄壁筒工件加工质量和效率的主要因素之一。采用半离散法对含有时滞项的动力学方程进行稳定性预测分析,结合薄壁筒工件切削振动试验,研究刀具、工件动力学参数匹配关系变化对切削加工稳定性的影响。通过仿真分析得出:随着刀具刚度或固有频率的提升,切削系统稳定性呈上升趋势,但过度提升刀具刚度并不会有效提升切削稳定性;在刀具与工件固有频率接近处,切削系统的稳定性较差;适当调整刀具动态特性参数有利于提高柔性工件切削加工的稳定性;切削过程中,时变的切削位置和工件尺寸会引起切削系统动态特性的变化。根据时变稳定性预测图,从稳定性分析角度解释了一次走刀切削试验中薄壁筒工件表面出现不同加工形貌的原因。     

基于稳定性分析的起落架型腔加工参数优化

颤振是影响加工效率的重要因素,文章针对型腔加工中刀具端的动态特性,研究了稳定性加工边界预测,进而得到稳定加工的优化参数,实现加工效率的提高。针对型腔加工中刀具端的多阶模态动态特性,建立了模态坐标下的考虑多阶模态的稳定性预测模型。考虑型腔环切加工过程中的不同刀具轨迹方向,利用稳定性预测模型对不同方向上的轨迹进行了稳定加工边界预测,计算得到了相应的稳定性lobe图。根据稳定性lobe图,分析了经验加工参数的合理性,并给出了利用稳定性加工边界优化的加工参数,提高了型腔的加工效率。     

高速铣削加工表面位置误差的频域分析（英文）

在高速铣削加工过程中,提高轴向切削深度和主轴转速可以获得较高的材料去除率,然而限制轴向切削深度提高的一个因素是加工颤振。高速铣削系统动态失稳可能导致加工零件的表面几何精度偏差。分析高速铣削的表面位置误差对表征切削过程、刀具寿命估算和加工优化都起着重要作用。因此,在不考虑再生颤振影响的前提下,提出了一种数值分析和加工实验相结合的方法来研究表面位置误差。首先,构建了高速铣削加工过程模型,然后建立了动态铣削力模型,并推导了表面位置误差的分析方法。通过数值分析和铣削实验相结合,得到了高速铣削加工的稳定性叶瓣图。接下来,研究了逆铣削加工过程的表面位置误差,并详细分析了主轴转速和轴向切削位置对表面位置误差的影响规律。最后,把稳定性叶瓣和表面位置误差数据组合在同一个图里得到了高速铣削加工的综合分析图。借助综合分析图,能预测表面位置误差和优化高速铣削的工艺条件。     

高速铣削加工表面位置误差的频域分析

在高速铣削加工过程中,提高轴向切削深度和主轴转速可以获得较高的材料去除率,然而限制轴向切削深度提高的一个因素是加工颤振.高速铣削系统动态失稳可能导致加工零件的表面几何精度偏差.分析高速铣削的表面位置误差对表征切削过程、刀具寿命估算和加工优化都起着重要作用.因此,在不考虑再生颤振影响的前提下,提出了一种数值分析和加工实验相结合的方法来研究表面位置误差.首先,构建了高速铣削加工过程模型,然后建立了动态铣削力模型,并推导了表面位置误差的分析方法.通过数值分析和铣削实验相结合,得到了高速铣削加工的稳定性叶瓣图.接下来,研究了逆铣削加工过程的表面位置误差,并详细分析了主轴转速和轴向切削位置对表面位置误差的影响规律.最后,把稳定性叶瓣和表面位置误差数据组合在同一个图里得到了高速铣削加工的综合分析图.借助综合分析图,能预测表面位置误差和优化高速铣削的工艺条件.     

影响铣削颤振稳定性的因素与规律分析

应用Altintas切削颤振理论实现了铣削颤振的预测,并对影响铣削稳定性的机床系统因素进行了分析。研究发现,稳定性叶瓣图会受到机床的主轴-刀具系统模态参数影响,尤其是模态刚度、阻尼比和固有频率。另外,通过系统动刚度相同的条件下不同的阻尼比和模态刚度组合对铣削稳定性的影响分析发现,模态刚度对系统稳定性的影响要大于阻尼比的影响程度。分别对影响铣削加工稳定性的刀具参数、工件材料特性以及切削参数等因素及其对铣削稳定性的影响规律进行了分析。结果显示:减小刀具齿数、刀具螺旋角和刀具悬伸量,并增大刀具直径对于改善切削颤振有益;具有较小切向切削力系数和径向切削力系数的材料更容易实现稳定切削;减小铣削宽度,并采用顺铣方式,系统的临界切深更大。     

RCPM—A new method for robust chatter prediction in milling

The reliability of conventional chatter prediction algorithms is limited by the inaccuracy of machining system dynamic models. In this paper, a new probabilistic algorithm for a robust analysis of stability in milling, which performs the stability analysis on an uncertain dynamic milling model, is presented. In this approach, model parameters are considered as random variables, and robust analysis of stability is carried out in order to estimate system's probability of instability for a given combination of cutting parameters. By doing so, probabilistic instead of deterministic stability lobes are obtained, and a new criterion for system stability based on level curves and gradient of the probabilistic lobes can be applied to identify optimal robust stable cutting conditions. Experimental validation consisted of different phases: firstly, machining system dynamics were estimated by means of pulse tests. Secondly, cutting force coefficients were determined by performing cutting tests. Eventually, chatter tests were performed and the experimental stability lobes were compared with the predicted robust stable regions.     

Extension of Tlusty׳s law for the identification of chatter stability lobes in multi-dimensional cutting processes

Chatter vibrations in cutting processes are studied in the present paper. A unified approach for the calculation of the stability lobes for turning, boring, drilling and milling processes in the frequency domain is presented. The method can be used for a fast and reliable identification of the stability lobes and can take into account nonlinear shearing forces, as well as process damping forces. The applicability of Tlusty׳s law, which is a simple scalar relationship between the real part of the oriented transfer function of the structure and the limiting chip width, is extended to milling and any other multi-dimensional chatter problem without neglecting the coupled dynamics. The given analysis is suitable for getting a deep understanding of the chatter stability dependent on the parameters of the cutting process and the structure. Basic examples based on experimental data of real machine tools include the dependence of the stability behavior on the rotational direction in turning, the effect of axial–torsional structural coupling in drilling, and the dynamics of slot milling.     

Maximizing Chatter Free Material Removal Rate in Milling through Optimal Selection of Axial and Radial Depth of Cut Pairs

Chatter vibrations in milling, which develop due to dynamic interactions between the cutting tool and the workpiece, result in reduced productivity and part quality. Several stability models have been considered in previous publications, where mostly the stability limit in terms of axial depth of cut is emphasized for chatter free machining. In this paper, it is shown that, for the maximization of chatter free material removal rate, radial depth of cut is of equal importance. A method is proposed to determine the optimal combination of depths of cut, so that chatter free material removal rate is maximized. The application of the method is demonstrated on a pocketing example where significant reduction in the machining time is obtained using the optimal depths. The procedure can easily be integrated to a CAD/CAM system or a virtual machining environment in order to identify the optimal milling conditions.     

Modelling and simulation of chatter in milling using a predictive force model

A predictive time domain chatter model is presented for the simulation and analysis of chatter in milling processes. The model is developed using a predictive milling force model, which represents the action of milling cutter by the simultaneous operations of a number of single-point cutting tools and predicts the milling forces from the fundamental workpiece material properties, tool geometry and cutting conditions. The instantaneous undeformed chip thickness is modelled to include the dynamic modulations caused by the tool vibrations so that the dynamic regeneration effect is taken into account. Runge–Kutta method is employed to solve the differential equations governing the dynamics of the milling system for accurate solutions. A Windows-based simulation system for chatter in milling is developed using the predictive model, which predicts chatter vibrations represented by the tool-work displacements and cutting force variations against cutter revolution in both numerical and graphic formats, from input of tool and workpiece material properties, cutter parameters, machine tool characteristics and cutting conditions. The system is verified with experimental results and good agreement is shown.     

Theoretical-experimental modeling of milling machines for the prediction of chatter vibration

Productivity of high speed milling operations can be seriously limited by chatter occurrence. Chatter vibrations can imprint a poor surface finish on the workpiece and can damage the cutting tool and the machine. Chatter occurrence is strongly affected by the dynamic response of the whole system, i.e. the milling machine, the tool holder, the tool, the workpiece and the workpiece clamping fixture. Tool changes must be taken into account in order to properly predict chatter occurrence. In this study, a model of the milling machine-tool is proposed: the machine frame and the spindle were modeled by an experimentally evaluated modal model, while the tool was modeled by a discrete modal approach, based on the continuous beam shape analytical eigenfunctions. A chatter identification technique, based on this analytical-experimental model, was implemented. Tool changes can be easily taken into account without requiring any experimental tests. A 4 axis numerically controlled (NC) milling machine was instrumented in order to identify and validate the proposed model. The milling machine model was excited by regenerative, time-varying cutting forces, leading to a set of Delay Differential Equations (DDEs) with periodic coefficients. The stability lobe charts were evaluated using the semi-discretization method that was extended to n>2 degrees of freedom (dof) models. The stability predictions obtained by the analytical model are compared to the results of several cutting tests accomplished on the instrumented NC milling machine.     

Generalized dynamic model of metal cutting operations

This paper presents a unified mathematical model which allows the prediction of chatter stability for multiple machining operations with defined cutting edges. The normal and friction forces on the rake face are transformed to edge coordinates of the tool. The dynamic forces that contain vibrations between the tool and workpiece are transformed to machine tool coordinates with parameters that are set differently for each cutting operation and tool geometry. It is shown that the chatter stability can be predicted simultaneously for multiple cutting operations. The application of the model to single-point turning and multi-point milling is demonstrated with experimental results.     

An expert troubleshooting system for the milling process

Common problems experienced in milling processes include forced and chatter vibrations, tolerance violations, chipping and premature wear of the tools. This paper presents an expert system which attempts to troubleshoot the source of milling problems by utilising dynamics data coupled with the opinion of the operator and acoustic Fourier spectrum data taken from the cutting process. The expert system utilises a fuzzy logic based process to interpret the signals and information, and recommends possible alterations to the process to achieve high-performance milling operations.Specific inference engines were developed to assess the chatter stability, variation in cutting force coefficient, tool run-out and forced vibration characteristics of the system. Lastly, a stability lobe plot interpretation engine to automate the lobe selection process and recommend new, chatter free cutting conditions, was also developed. The chatter stability inference engine was tested with real cutting data, through acoustic measurements taken from various cutting conditions on an aluminium milling process. The chatter inference engine successfully determined the stability of the system for each sampled cutting condition. The robustness of the troubleshooting system depends on the accuracy of acoustic and frequency response measurements.