飞刀铣削中高速气浮电主轴转子动态特性研究

在实际的加工过程之中,加工表面的质量会由于转子振动而降低.多种作用力可导致转子振动,这些作用力包括不平衡磁拉力、加工过程中产生的切削力以及由于质量的不平衡分布导致的离心力.为深入分析这一问题,开展了气体静压轴承电主轴高速飞刀铣削过程中的转子动态特性研究.考虑上述作用力建立了一个五自由度的转子动力学铣削模型,并给出了不平衡磁拉力的计算公式;轴承的平移刚度、平移阻尼、角刚度和角阻尼的计算公式采用线性摄动法推导得出.转子动力学方程采用牛顿-欧拉方程推导得出,并利用特征方程、系统初始条件、阻抗法、状态空间模型等条件进行求解.对转子在空切削、不连续切削下的动态特性进行了数值仿真.研究发现,空切削时,转子形心的运动轨迹随运动状态变化,平稳状态时,在径向方向呈现为规则的圆形;切削过程中,主轴转子的振动特性受到转子质量偏心引起的离心力和周期性的切削力的共同影响.     

非线性磁悬浮转子系统的不平衡响应分析

考虑漏磁及磁饱和等非线性因素对磁悬浮轴承支承特性的影响,建立非线性磁悬浮转子系统动力学模型,分析运行参数和控制参数对系统不平衡响应的影响,结果表明:负载较大时,非线性磁悬浮转子系统不平衡响应更复杂;相同转速范围内非线性磁悬浮转子系统更易失稳;比例系数较大和微分系数较小会使非线性磁悬浮转子系统振幅增大,不平衡响应明显.     

计及不平衡磁拉力的高速空气静压电主轴动力学分析

根据不平衡磁拉力作用机理,在电主轴动力学建模时将其等效为具有"负刚度"的支承元件;基于传递矩阵法建立计及不平衡磁拉力的高速空气静压电主轴的动力学模型,利用MATLAB7.0软件对最高工作转速为25×104r/min空气静压高速电主轴动力学特性进行计算。结果表明:计入磁拉力后电主轴的前3阶临界转速有一定程度的降低,且该电主轴工作转速远远高于1阶临界转速,属于挠性轴范畴。可以看出:1阶振型脆弱点在主轴前端,2阶振型脆弱点在主轴前端和转子轴段。     

主动磁悬浮电主轴最佳切削速度区间研究

为研究主动磁悬浮电主轴在不同速度区间内的振型和振幅对工件加工精度的影响过程和机理,基于转子动力学、电磁学和金属切削理论,采用有限元法对"磁悬浮轴承-主轴"系统在切削过程中的一系列物理现象进行理论分析和定量解释。结果表明:系统振型是影响系统运行品质及加工质量的重要因素;主轴的最佳切削速度由主轴的振型、工件形位精度及系统在负载激励下的动态响应共同决定;工件的实际形位精度由系统在负载激励下的最大单向振动响应幅值决定。     

主轴-切削交互过程建模与高速铣削参数优化

高速切削参数的合理选择是困扰企业的一个难题,过于保守的切削用量限制了高速机床性能的发挥和生产效率的提高.以高速铣削加工为对象,考虑高速旋转主轴的离心力和陀螺力矩效应,基于Timoshenko梁单元和Jones轴承模型建立高速主轴-刀具系统动力学模型.将主轴-刀具动态特性与高速铣削过程耦合,研究高速主轴-刀具系统动力学特性与切削过程之间交互机理,推导闭环动态铣削系统的特征方程.基于上述理论分析,提出基于主轴-切削交互过程模型的高速铣削切削参数优化方法,并应用于某型直升机的铝合金变速箱端盖加工中,通过选用最佳切削深度和主轴转速,使变速箱盖前端面内侧壁的加工效率提高了275％.     

基于主轴系统动力学的铣削稳定性建模与分析

高速切削技术具有加工精度高和表面质量好的特点,但在切削难加工材料时易发生颤振。基于主轴系统动力学进行铣削稳定性的建模与分析,采用有限元法建立主轴系统动力学模型,重点考虑主轴旋转时产生的离心力对结合面刚度的影响,分析主轴转速对结合面刚度和主轴系统频响函数的影响规律。结合主轴系统动力学特性和动态铣削过程建立铣削动力学模型,利用全离散法进行铣削稳定性预测,分析主轴转速、刀具直径和刀具悬伸量对铣削稳定域的影响规律。     

永磁同步型磨削电主轴偏心振动分析及实验*

电主轴是将旋转主轴与电机转子集成为一体的主轴单元,结构复杂,由于加工或装配误差等原因,电主轴转子会存在着一定的偏心量,为探求由于电主轴偏心所导致的转子振动特性,建立了电主轴转子偏心模型,采用Maxwell应力张量法计算了偏心造成的不平衡磁拉力(UMP),将UMP解析式代入Jeffcott转子模型,得到了转子偏心振动方程。以某磨床的永磁同步电主轴为研究对象,利用有限元方法分析了UMP,发现作用于转子的UMP始终指向气隙最小的方向,研究了不同转速下转子在质量偏心离心力和UMP作用下的振动响应。研究结果表明,电主轴在低速运行时,UMP为转子振动的主要来源;随着转速的增加,质量偏心离心力对转子振动的影响更加明显,而UMP大小保持不变,其频率随转速增加而增大,对转子振动的作用随之减弱。对某机床厂所研发永磁同步型磨削电主轴在试运行时产生的振动问题进行了实验,对主轴振动频谱分析后判断实验电主轴存在静态偏心,测得主轴轴心轨迹对前述分析进行了验证。     

《机械工程学报》英文版2008年第21卷第1期目次、摘要预告

微铣削切屑成形的解析模型李成峰1来新民1李红涛1彭林法1倪军2(1.上海交通大学机械与动力工程学院上海200240;2.密西根大学吴贤铭制造研究中心美国密西根州48109)为精确描述微铣削切屑成形过程,提出一个新的切削成形解析模型。常规尺度铣削切屑成形模型将刀具齿尖轨迹简化为圆,并忽略主轴跳动度的影响;微观尺度铣削则需综合考虑刀具齿尖的摆线轨迹和刀具     

覆盖件模具曲面曲率特征对球头刀铣削力的影响

针对自由曲面模具的铣削加工,提出一种综合考虑曲面曲率、刀具前倾角和侧偏角的瞬时铣削力预报方法。基于曲面几何特征,研究了进给方向、行距方向曲率半径对刀具切削角度的影响,以及刀具前倾角和轴向切触角对未变形切屑厚度的影响;基于微分思想,将自由曲面加工中任意刀齿切削周期内的切触区进行离散,结合三维次摆线切削轨迹建立未变形切屑模型,得到适合于自由曲面三轴球头铣削的瞬态铣削力,该模型能够综合考虑曲面曲率特征变化、刀具工件切触角度变化;基于二次曲面模具模型进行铣削加工试验,试验测试结果表明,预报的铣削力和试验测量结果在幅值上和变化趋势上具有一致性,在平稳切削时最大铣削力预测误差值在12%以内,验证了该方法能有效地预报自由曲面模具的球头铣削的瞬态铣削力。     

转子—滚动轴承—机匣耦合系统的不平衡/松动耦合故障非线性动力学

建立含转子不平衡/松动耦合故障的转子-滚动轴承-机匣耦合系统动力学模型.在模型中,考虑转子不平衡和轴承座松动故障的耦合、滚动轴承间隙、滚动轴承滚珠与滚道的非线性赫兹接触力以及由滚动轴承支撑刚度变化而产生的变柔性振动.运用数值积分方法获取系统响应,并利用振幅-转速曲线、分叉图、相平面图、频谱图、Poincaré断面图和轴心轨迹图研究系统的分叉与混沌运动,分析旋转速度、轴承座质量、转子偏心量、轴承座与机匣间的连接刚度以及机匣与基础间的连接刚度对系统响应的影响,得到了在不平衡/松动故障耦合下的转子-滚动轴承-机匣系统动力响应规律.     

Counterbalance of cutting force for advanced milling operations

The goal of this work is to concurrently counterbalance the dynamic cutting force and regulate the spindle position deviation under various milling conditions by integrating active magnetic bearing (AMB) technique, fuzzy logic algorithm and an adaptive self-tuning feedback loop. Since the dynamics of milling system is highly determined by a few operation conditions, such as speed of spindle, cut depth and feedrate, therefore the dynamic model for cutting process is more appropriate to be constructed by experiments, instead of using theoretical approach. The experimental data, either for idle or cutting, are utilized to establish the database of milling dynamics so that the system parameters can be on-line estimated by employing the proposed fuzzy logic algorithm as the cutting mission is engaged. Based on the estimated milling system model and preset operation conditions, i.e., spindle speed, cut depth and feedrate, the current cutting force can be numerically estimated. Once the current cutting force can be real-time estimated, the corresponding compensation force can be exerted by the equipped AMB to counterbalance the cutting force, in addition to the spindle position regulation by feedback of spindle position. On the other hand, for the magnetic force is nonlinear with respect to the applied electric current and air gap, the characteristics of the employed AMB is investigated also by experiments and a nonlinear mathematic model, in terms of air gap between spindle and electromagnetic pole and coil current, is developed. At the end, the experimental simulations on realistic milling are presented to verify the efficacy of the fuzzy controller for spindle position regulation and the capability of the dynamic cutting force counterbalance.     

Spindle vibration suppression for advanced milling process by using self-tuning feedback control

The goal of this work is to concurrently counterbalance the dynamic cutting force and regulate the spindle position deviation under various milling conditions by integrating active magnetic bearing (AMB) technique, fuzzy logic algorithm, and an adaptive self-tuning feedback loop. The experimental data, either for idle or cutting, are utilized to establish the database of milling dynamics so that the system parameters can be on-line estimated by employing the proposed fuzzy logic algorithm as the cutting mission is engaged. Based on the estimated milling system model and preset operation conditions, i.e., spindle speed, cut depth, and feed rate, the current cutting force can be numerically estimated. Once the current cutting force can be real time estimated, the corresponding compensation force can be exerted by the equipped AMB to counterbalance the cutting force, in addition to the spindle position regulation by feedback of spindle position. At the end, the experimental simulations on realistic milling are presented to verify the efficacy of the fuzzy controller for spindle position regulation and the capability of the dynamic cutting force counterbalance.     

考虑结合面和轴向力的主轴系统动力学特性

汽车覆盖件淬硬钢模具由于硬度高,在铣削过程中动态铣削力大,易发生颤振,而主轴系统动力学特性直接影响铣削稳定性。为了准确建立主轴系统动力学模型,考虑主轴系统铣削状态下产生的轴向铣削力和离心力对主轴结合面接触刚度的影响。通过分析得到,轴向铣削力对主轴结合面接触刚度有强化作用,使主轴系统固有频率有微小的增加;而离心力对结合面接触刚度有软化作用,随着主轴转速升高,系统的固有频率减小,尤其高转速时主轴系统的动力学特性偏差较大,对比而言离心力的软化作用多于轴向铣削力的强化作用,故主轴系统在铣削过程中动力学特性相比静止无载状态下仍是软化现象;分析结合面预紧力、刀具参数等因素对主轴系统动力学特性的影响规律,为准确分析主轴系统动力学特性和预测铣削稳定性提供理论参考。     

An improved cutting force model for micro milling considering machining dynamics

Micro milling, as a versatile micro machining process, is kinematically similar to conventional milling; however, it is significantly different from conventional milling with respect to chip formation mechanisms and uncut chip thickness modelling, due to the comparable size of the edge radius to the chip thickness, and the small per-tooth feeding. Considering tool runout and dynamic displacement between the tool and the workpiece, the contour of the workpiece left by previous tool paths is typically in a wavy form, and the wavy surface provides a feedback mechanism to cutting force generation because the instantaneous uncut chip thickness changes with both the vibration during the current tool path and the surface left by the previous tool paths. In this study, a more accurate uncut chip thickness model was established including the precise trochoidal trajectory of the cutting edge, tool runout and dynamic modulation caused by the machine tool system vibration. The dynamic regenerative effect is taken into account by considering the influence of all the previous cutting trajectories using numerical iteration; thus, the multiple time delays (MTD) are considered in this model. It is found that transient separation of the tool-workpiece occurring at a low feed per tooth, caused by MTD and the existing cutting force models, is no longer applicable when transient tool-workpiece separation occurs. Based on the proposed uncut chip thickness model, an improved cutting force model of micro milling is developed by full consideration of the ploughing effect and elastic recovery of the workpiece material. The proposed cutting force model is verified by micro end milling experiments, and the results show that the proposed model is capable of producing more accurate cutting force prediction than other existing models, particularly at small feed per tooth.     

A novel chatter stability criterion for the modelling and simulation of the dynamic milling process in the time domain

The modelling of the dynamic processes in milling and the determination of chatter-free cutting conditions are becoming increasingly important in order to facilitate the effective planning of machining operations. In this study, a new chatter stability criterion is proposed, which can be used for a time domain milling process simulation and a model-based milling process control. A predictive time domain model is presented for the simulation and analysis of the dynamic cutting process and chatter in milling. 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. The cutting force is determined by using a predictive machining theory. A numerical method is employed to solve the differential equations governing the dynamics of the milling system. The work proposes that the ratio of the predicted maximum dynamic cutting force to the predicted maximum static cutting force can be used as a criterion for the chatter stability. Comparisons between the simulation and experimental results are given to verify the new model.     

高速电主轴动态及热特性研究

以高速加工中心用电主轴为研究对象,对其动态特性进行了仿真分析,得到其低阶频率和振型,为电主轴的稳定性研究提供了理论依据。同时,分析了转速、切削力和润滑方式等因素对电主轴温度的影响。     

A combined repetitive control for precision rotation of magnetic bearing

In this paper, we focus on improving the rotational accuracy of the magnetic bearing under the consideration of the unbalance force of the spindle and the unbalanced magnetic pull of the motor. First, the vibrations of the spindle are analyzed. Next, in order to suppress the vibrations of the spindle, a combined repetitive control method is proposed, which includes a space domain repetitive compensator and a time domain repetitive compensator. Furthermore, the experimental results show that the proposed method is effective for suppressing the vibrations of the spindle and the rotational accuracy is improved from 301.2 to 21.9 nm at 2880 min⁻¹.     

Comprehensive measurement and evaluation system of high-speed motorized spindle

Reducing the manufacturing time is the trend of high-precision manufacturing, and the precision of a work-piece is very important for manufacturing industry. The high-speed motorized spindle is the most critical part and becoming more widely used in the machine tool at present, and its precision may affect the overall performance of high-speed cutting. Most of the studies on high-speed cutting are focused on the cutting force, the vibration of the spindle and effects of the spindle’s thermal deformations; hence, how to roundly measure and objectively evaluate high-speed spindle is an imminence question of it because the comprehensive dynamic properties and evaluation system of spindles directly affect the cutting ability of the whole machine tool before they are manufactured. This paper presents a comprehensive measurement and evaluation system of high-speed motorized spindle, which reflects the overall performance of motorized spindle and bases on international standard.     

径向跳动对球面铣刀切削力的影响研究

研究了径向跳动对刀齿的实际切削半径、切屑形状以及切屑厚度的影响机理。研究了各刀齿沿刀刃螺旋线的切削微元实际切削半径的数学表示和变化规律,实际切削半径的变化改变了刀齿的切削路径,使各刀齿上切屑形状分布不均匀。建立了三维切削下切屑厚度的数学表示,提出了递延累加切屑厚度计算算法。实验验证表明,计算的切削力与测量结果能很好地吻合,瞬时切削力、切削力峰值、平均切削力的预测精度达到85%以上。