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。     

Modeling the machining stability of a vertical milling machine under the influence of the preloaded linear guide

The prediction of machining stability is of great importance for the design of a machine tool capable of high-precision and high-speed machining. The machining performance is determined by the frequency characteristics of the machine tool structure and the dynamics of the cutting process, and can be expressed in terms of a stability lobe diagram. The aim of this study is to develop a finite element model to evaluate the dynamic characteristics and machining stability of a vertical milling system. Rolling interfaces with a contact stiffness defined by Hertz theory were used to couple the linear components and the machine structures in the finite element model. Using the model, the vibration mode that had a dominant influence on the dynamic stiffness and the machining stability was determined. The results of the finite element simulations reveal that linear guides with different preloads greatly affect the dynamic behavior and milling stability of the vertical column spindle head system. These results were validated by performing vibration and machining tests. We conclude that the proposed model can be used to accurately evaluate the dynamic performance of machine tool systems designed with various configurations and with different linear rolling components.     

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。     

An active method of monitoring tool wear states by impact diagnostic excitation

This paper presents an active method of monitoring tool wear states by using impact diagnostic excitation in the machining process. Because the dynamic characteristics of tool vibration in machining process will change with the tool wear development, the damping ratio, which is one of the important dynamic characteristics of tool vibration, will be used for monitoring the tool wear states in machining. In order to obtain the damping ratio, impact diagnostic excitation was applied to the tool in the feed direction and the signals of the tool vibration were measured for some flank wears under different cutting conditions. The signals were analyzed through FFT analyzer and computer, and then the damping ratio of the tool vibration in the feed direction was calculated. The experimental results have shown that the damping ratio measured by impact excitation increases linearly with tool wear development and the increment of the damping ratio is different for each cutting condition, but the damping ratio can be uniquely determined through the flank worn area. To explain the reason for increase with tool wear development, the damping mechanism on the flank worn land was also discussed. The results of the discussions and numerous cutting experiments have indicated that the presented active method could be used for effectively monitoring the tool wear states in machining.     

基于动力学的机床加工运动分析

数控定梁龙门机床的加工精度受多种因素影响,包括零部件的制造、装配误差、材料的刚度阻尼、振动、材料切削厚度等。从提高机床加工精度出发,根据拉格朗日动力学原理建立了机床的动力学模型;分析横梁、床身等部件的自由度关系,建立了机床运动学模型;采用ADAMS软件仿真机床的瞬态动力和运动关系,对比研究了不同的瞬态切削力变化对机床切削位移、速度的影响。结果表明:当机床切削厚度增大时,切削力、切削速度和切削加速度会随之增大,同时切削速度和加速度的变化滞后切削厚度和切削力的变化;在切削受力突变处切削速度有波动,移动加速度有突变,波动时间滞后切削力突变时间。仿真结果与实际机床加工情况吻合,为机床加工的运动分析提供参考。     

Statistical investigation of modal parameters of cutting tools in dry turning

It is very important that optimized cutting parameters be selected in controlling the quality required for surface finishes. Unfortunately, surface roughness does not depend solely on the feed rate, the tool nose radius and cutting speed; the surface can also be deteriorated by excessive tool vibrations, the built-up edge, the friction of the cut surface against the tool point, and the embedding of the particles of the materials being machined. Hence, the forces, which can be considered as the sum of steady, harmonic and random forces, act on the cutting tool and contribute to the modification of the dynamic response of the tool, by affecting its stiffness and damping. These stiffness and damping variations are attributable to parameters that cannot be easily predicted in practice (regenerative process, penetration rate, friction, variation in rake angle, cutting speed, etc.). Furthermore, the effects of cutting parameters, which also contribute to the variation in the tool’s modal parameters, are more useful for controlling tool vibration. This study focuses on the collection and analysis of cutting-force, tool-vibration and tool-modal-parameter data generated by lathe dry turning of mild carbon steel samples at different speeds, feeds, depths of cut, tool nose radii, tool lengths and workpiece lengths. A full factorial experimental design (288 experiments) that takes into consideration the two-level interactions between the independent variables has been performed. This analysis investigated the effect of each cutting parameter on tool stiffness and damping, and yielded an empirical model for predicting the behavior of the tool stiffness variation.     

基于工艺系统刚度的加工误差分析

在切削加工过程中,工件和刀具正确的相对位置是保证零件加工精度的必要条件.工艺系统刚度及精度是影响工件、刀具位置的关键因素.因此研究工艺系统刚度,对提高零件的加工精度具有十分重要的意义.文章基于切削加工中工件的准静态受力分析,运用经典Hertz接触理论和有限元的方法,提出计算工艺系统刚度的新方法.该方法避免了有限元计算中接触单元的使用,无需多次非线形迭代计算.给出了基于工艺系统刚度的工件加工误差预报模型.     

钛合金TC4切削过程流动应力模型研究

运用有限元技术对切削过程进行仿真可以预测切削力、切削温度、应力分布,优化刀具参数和切削条件。建立适合于切削条件中大应变、高应变率条件下材料的流动应力模型,是切削过程有限元仿真的关键技术。文章通过正交切削实验和有限元迭代的方法,修正了难加工材料TC4在大应变、高应变率条件下的J-C流动应力模型,使修正模型能够适应切削仿真中的大应变、高应变率要求。计算结果表明,采用新的J-C流动应力模型进行计算,所得主切削力值与实验测量值的平均误差从36.28%降为12.06%,进给力的平均误差由原来的61.03%降为现在的25.57%。该修正的流动应力模型比用霍普金森实验所得到的流动应力模型更适合于切削过程的有限元仿真,可以提高切削仿真的计算精度。     

数控机床主轴系统动力学特性分析方法研究

数控机床主轴系统的动力学特性直接影响着机床的加工精度、加工效率。文章在总结前人研究成果的基础上,对数控机床主轴系统动力学分析方法进行了综述研究。介绍了表征主轴系统动力学特性的参数,主要有静刚度、动刚度、极限切削宽度、固有频率及振型、阻尼特性和动响应。对现有的关于主轴系统动力学特性分析方法进行了归纳与总结,主要包括有限元法、传递矩阵法、阻抗耦合法、实验法等。指出了主轴系统结合部的动力学建模与参数辨识是研究主轴系统动力学特性的关键问题。最后,简要论述了主轴系统动力学研究的发展趋势,即未来应从主轴系统的精准建模、动力学综合优化和动态测试及分析等方面进行深入研究。     

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。     

Flank face texture design to suppress chatter vibration in cutting

Process damping is useful in improving chatter stability in a low cutting speed range. This paper presents a texture design on tool flank faces that can effectively generate process damping. A convex structure on the flank face dampens chatter vibration even at general cutting speeds. An orthogonal cutting simulation utilizing a finite element analysis was conducted to estimate process damping force coefficients that are the functions of cutting and vibration conditions and tool geometry. Sufficient damping effect was predicted using the proposed texture via a chatter stability analysis in frequency domain. Face turning experiments verified the significant chatter suppression effect.     

Chatter suppression in micro end milling with process damping

Micro milling utilizes miniature micro end mills to fabricate complexly sculpted shapes at high rotational speeds. One of the challenges in micro machining is regenerative chatter, which is an unstable vibration that can cause severe tool wear and breakage, especially in the micro scale. In order to predict chatter stability, the tool tip dynamics and cutting coefficients are required. However, in micro milling, the elasto-plastic nature of micro machining operations results in large process damping in the machining process, which affects the chatter. We have used the equivalent volume interface between the tool and the workpiece to determine the process damping parameter. Furthermore, the accurate measurement of the tool tip dynamics is not possible through direct impact hammer testing. The dynamics at the tool tip is indirectly obtained by employing the receptance coupling method, and the mechanistic cutting coefficients are obtained from experimental cutting tests. Chatter stability experiments have been performed to examine the proposed chatter stability model in micro milling.     

三轴卧式加工中心主轴静刚度仿真与试验研究

对卧式加工中心主轴系统静刚度进行了仿真和试验研究.研究发现:经有限元方法计算获得的结果与试验有较好的对应性;主轴静刚度在卸载时要大于加载时,卸载时主轴系统弹性恢复迟滞,并且加载曲线与卸载曲线不封闭,卸载时主轴变形恢复不到起点,进而影响加工精度.因此,提高系统刚度十分必要,可通过合理设计机床主轴结构、减小主轴悬伸量、提高传动部件单位质量刚度等方法提高切削系统刚度.     

Tool wear monitoring for micro-end grinding of ceramic materials

As grinding process usually is a final step of a machining procedure, excessive grinding tool wear could deteriorate both workpiece surface quality and its dimensional accuracy. This becomes more severe in the case of microgrinding than in conventional grinding because microgrinding wheels are more sensitive to tool wear. An effective tool wear monitoring technique is, therefore, crucial for maintaining consistent machining quality and high efficiency in microgrinding. In this paper, the influence of tool wear and tool stiffness on microgrinding process signals such as grinding force, grinding system vibration, acoustic emission signal and spindle load, are analyzed during end grinding of ceramic materials. To indicate the actual wear status of a microgrinding wheel, this study proposed a new monitoring parameter by fusing grinding force and system vibration signals, based on the concept of varying cutting stiffness. This new monitoring parameter is then experimentally tested in microgrinding a series of ceramic miniature features with consistent and inconsistent geometry.     

螺旋锥齿轮数控铣齿加工过程几何仿真研究

利用面相对象技术和CAD系统的三维建模功能及其ObjectARX技术，根据螺旋锥齿轮的加工原理，提出了CNC铣齿机、齿坯和刀具三维模型的构建方法以及基于全局光照明的加工环境光照计算的具体方法。利用齿坯实体模型和刀具实体模型做布尔减运算，来实现模拟工件材料的去除过程；同时，采用全局光照明模型建立了具有真实感的数控加工虚拟现实环境。实际应用表明，该系统不但实现了螺旋锥齿轮的计算机辅助铣齿，提高了加工效率，降低了加工成本；而且还提供了非常真实的仿真效果。所获仿真结果可为齿面接触分析、有限元应力分析、齿轮的数控加工等提供精确的三维几何模型。     

Analysis of the machining accuracy when dry turning via experiments and finite element simulations

Workpiece and tool are subjected to severe mechanical and thermal loads when turning. These loads cause thermal expansions and mechanically induced deflections of the tool and the workpiece. Such deformations induce deviations from the nominal workpiece geometry. In order to decrease these deviations, the cutting condition needs to be optimized prior to actual machining. In this paper, the accuracy of machining when dry turning aluminum is analyzed via experiments and finite element simulations. For this purpose, seven characteristic values were used: the forces, the deflection of the workpiece, the quantity of heat in the workpiece, the temperature distribution in the workpiece, the temperature of the tool, the temperature of the tool holder, and the actual dimension of the workpiece after turning. These experimentally determined results serve in addition as boundary conditions for a 3D finite element model of the workpiece, which calculates the deformations of the workpiece. The continuous removal of material affecting the temperature distribution in the workpiece is considered. The actual dimensions of the workpiece after turning revealed a remarkable influence of the cutting condition used on the accuracy of machining. Differences of up to 116 μm regarding the deviation from the nominal workpiece diameter of 30 mm were observed. The analysis of the machining accuracy reveals that particularly the use of both high cutting speeds and feeds enhances the accuracy of machining when dry turning aluminum.     

涡轮叶片切削参数研究与仿真

为解决涡轮叶片可选加工参数较多、加工质量与效率难以保证的难题,提出一种涡轮叶片的五轴加工工艺。利用解析分析的方法建立切削力理论模型,对比验证切削力经验公式的模型精度。结合工件受力变形有限元模型,选取优化后的切削参数,并利用可视化软件实现对叶片无偏摆点铣与侧铣程序的编制与仿真。可视化仿真结果表明：该加工工艺及参数下,可获得加工精度较高的叶片表面;点铣法加工精度较高,通用性强,与侧铣法相比效率较低。铣削试验结果表明：仿真表面结果与试验表面在变化规律上吻合良好,证明了所提工艺与参数的有效性,提升了涡轮叶片的制造精度与效率。     

高精度复杂型线刀具制造工艺与装备研究

以高精度复杂型线刀具制造工艺与装备为研究对象，以菌形叶片叶根型线加工专用刀具为切入点，通过分析叶根型线的特点及加工工艺的优劣，确认以单边两次成型加工作为刀具加工工艺方案；并在此基础上确定刀具的轮廓度精度、前后刀面表面粗糙度等各项参数及精度要求。通过分析专用刀具的加工要求，确定专用磨床的整体布局及结构方案，并对机床的关键部件磨削装置的结构做了具体设计与阐述。分析磨削点在B轴回转轴线延伸线上的结构优点可知，B轴回转的角度误差未使磨削点位置发生偏差，可有效提升刀具的加工精度。为验证设计的合理性，通过制造与装配机床，利用雷尼绍XK10激光校准仪检测可知，几何精度均达到设计要求。最后，采用设计的刀具加工工艺方案及专用磨床对某菌形型线刀具进行加工，Zoller检测仪检测结果表明：刀具轮廓公差为工作面±0.005 mm,其余面±0.015 mm。     

基于CAE和神经网络的切削参数优化

提出了一种以变形加工误差为约束的基于有限元分析和神经网络的切削参数优化方法.针对复杂工件夹具系统在切削过程中的变形问题进行有限元刚度计算,然后通过神经网络的方法拟合切削参数和工件夹具系统变形误差之间的关系.并以加工生产效率最大化为目标,在保证加工精度的前提下优化切削参数.从而实现以工艺成本最小化来提高零件的加工精度.     

人造金刚石新型槽刀的研制

本文针对硬质合金刀具切削中硅铝合金活塞槽存在的问题,研制出一种新型人造金刚石切槽刀。使用该刀,加工效率可提高二倍,加工成本降低62％,并且还提高了加工精度。从本文研究结果可以看出,人造金刚石刀具加工硅铝合金与硬质合金刀具相比,具有许多优点,是值得进一步开发和推广的刀具。本文不仅探讨了人造金刚石切槽刀的制造,还探讨了对刀具备参数的检测。