一种基于模态耦合的薄壁零件加工可调夹具

针对薄壁零件铣削中制约加工生产效率的再生颤振问题,提出了一种用于薄壁零件加工的,基于串联模态耦合的可调工件夹具。首先,采用串联模态耦合原理设计了可调工件夹具模型,并提出了两种新的最优调谐策略(振幅调谐和负实部调谐),以提高夹具的动态刚度和铣削稳定性;其次,采用旋转弹簧和涡流模块等自适应的机构,以实现夹具模态和零件模态之间的耦合,并引入导电板进行了阻尼调节;最后,通过具有清晰模态的零件铣削试验,对该工件夹具的可行性和有效性进行了试验验证。研究结果表明:该工件夹具具有可行性和有效性,在切削深度为3 mm的情况下,薄壁零件切削表面的粗糙度由Ra 2.4μm降低至Ra 0.9μm;与常规工件夹具相比,该夹具的动态刚度和铣削稳定性得到了显著提高。     

内置被动阻尼器减振铣刀的实验测试

提出一种长径比接近8的内置被动阻尼器减振铣刀结构。开展阻尼器模态测试,确定最优结构设计方案。对内置被动阻尼器减振铣刀进行周向模态测试,研究减振铣刀在不同方位的动力学特性。选取铝合金和钛合金工件材料,开展多组切削参数组合下的切削实验测试。在铝合金切削时,减振铣刀的加工噪声、切削力和表面粗糙度比无阻尼铣刀平均下降了52.1%,49.5%和73.4%;在钛合金全槽铣削时,能够在无阻尼铣刀出现明显颤振的切削条件下实现平稳切削。     

两自由度被动阻尼器设计及数控加工应用

为了对被动阻尼器的设计参数进行优化,抑制切削振动,提高切削效率与质量,通过研究对比各优化准则下单自由度、两自由度、两重及三重阻尼器的抑振性能,表明两自由度阻尼器综合性能更为优越。在此基础上提出一种两自由度阻尼器结构方案,并推导该阻尼器的动力学特性,并结合有限元方法进行验证。设计了弱刚性工装系统并开展切削实验,通过对比阻尼器安装前后工件振动的信号,表明两自由度阻尼器可将切削振动幅值最大降低56.4%。     

薄壁工件铣削加工振动主动控制实验研究

针对薄壁工件在铣削加工过程中的振动问题,采用主动阻尼装置对薄壁工件进行了铣削振动控制实验研究。首先,对主动阻尼装置的原理进行了阐述;然后,建立了薄壁工件的有限元模型,并对其进行了ANSYS模态分析;最后,搭建了铣削振动主动控制试验台,进行了主动控制实验,将惯性作动器分别安装在工件的不同位置和铣床主轴上,对不同工况下主动阻尼装置的振动控制效果进行了对比分析。实验及研究结果表明:主动阻尼装置可以有效抑制薄壁工件的铣削振动,降幅最高可达40.6%;将作动器置于工件的减振效果优于将其置于铣床主轴的效果;且作动器离铣刀切削位置越近,振动控制效果越好。     

基于两自由度被动阻尼器的减振铣刀设计

鉴于航空结构件中大长径比铣刀的刚性较差,严重制约了机床切削效率和加工精度的提高,建立了两自由度被动阻尼器的动力学模型,基于H∞优化准则对阻尼器的阻尼比和频率比进行优化,并分析其对减振性能的影响。提出一种内置两自由度阻尼器长悬伸铣刀结构,在模态和谐响应分析的基础上,设计加工出减振铣刀。模态测试和激振实验结果表明,相比无阻尼空心铣刀,减振铣刀的等效刚度提高了2.5倍,阻尼比提高了46.5%,刀尖频响函数的幅值降低了74%。切削实验表明减振铣刀能显著提高零件加工表面质量。     

螺旋立铣刀切削力建模分析及加工优化研究

铣削加工中铣刀切削刃与工件的相互作用是一个快速、复杂的变化过程,且其受力变化是其它一切物理量变化的根源,因此研究在铣削加工过程中铣削力具有重要意义。这里研究了切削深度对切削力的影响,提出了一个快速反映切削力波动的切削系数。通过时域分析了在不同切削系数状况下的切削力波动与工件加工质量从而验证了方法的有效性。研究结果表明选择合理的切削系数可以降低切削力波动。因此可以通过选择合理的切削深度在保证加工质量的同时提高切削效率。     

采用工程机械配重的ETMD系统阻尼减振研究

为解决工程机械振动剧烈的问题,提出利用其配重设计为扩展调谐质量阻尼器(ETMD)进行了阻尼减振研究.通过建立某型轮式挖掘机有、无ETMD系统的整机阻尼模型,仿真计算得到其不同工况和不同ETMD系统参数下的阻尼性能,并与实验结果进行了对比验证.在B级和C级路面下,有ETMD系统的车身垂向加速度均方根值,相比于无ETMD系统,仿真结果分别降低了6.67％和7.76％,实验结果分别降低了7.19％和8.61％,表明该ETMD系统有效改进了整机阻尼性能.通过分析ETMD系统的阻尼特性,表明存在最优阻尼特性参数使得阻尼性能达到最优.该研究可为工程机械的振动控制提供一种新方法.     

一种高效率汽车调整臂壳体夹具的设计与分析

为提高汽车调整臂壳体工件的加工精度与效率,针对铣削前后两平行端面工序,提出一种快速装夹铣削夹具。该夹具能够利用卧式铣床一次走刀完成两个工件的该工序加工,大幅度提高生产效率。通过剖析夹具的整体结构和夹紧力计算,运用有限元分析法确定夹具的易损位置,指导夹具后期维护。对调整臂壳体工件进行模态分析与变形分析,避免加工共振并确保夹具满足加工精度要求。该夹具大幅缩短加工时间,提高加工精度与稳定性,取得了良好的实际应用效果。     

一种考虑工件材料表面硬度的铣床功率模型

为了降低车间加工能耗、提高制造过程能量效率,建立了铣床待机状态、辅助状态、空载状态、切削状态下的功率模型。针对铣床切削功率,提出一种考虑材料硬度和主轴转速对材料去除功率影响的切削功率改进模型,对同一机床铣削多种工件材料情况的能耗进行评估,从而在一定程度上扩展现有铣削功率模型的适用范围。针对被测试机床润滑冷却系统工作特性导致待机功率存在间歇变化,提出一种分段函数式待机功率表达模型,相比现有常数式待机功率模型,该模型能够更好地反映机床待机功率情况;经实验研究和实例验证,所提改进功率建模方法及其模型具有良好的平面铣削加工能耗预测准确性。     

铣削加工粗糙度的智能预测方法

提出了一种基于最小二乘支持向量机的铣削加工表面粗糙度智能预测方法.首先进行了铣削工艺参数对工件表面粗糙度影响的正交实验,再通过对主轴转速、进给速率和切削深度三因素,以及各因素之间交互三水平实验的数据分析,找出了铣削工艺参数对工件表面粗糙度影响的一些规律.利用最小二乘支持向量机算法建立了铣削预测模型,通过该模型能在有限实验基础上利用工艺参数方便地得到粗糙度预测值.实际预测表明,在相同情况下,该模型构造速度比反向传播神经网络建模预测方法高2个～3个数量级,预测精度高10倍左右.     

Optimization of the Tuned Mass Damper for Chatter Suppression in Turning

The tuned mass damper(TMD) has been successfully applied to the vibration control in machining,while the most widely adopted tuning is equal peaks,which splits the magnitude of the frequency response function(FRF) into equal peaks.However,chatter is a special self-excited problem and a chatter-free machining is determined by FRF at the cutting zone.A TMD tuning aiming at achieving the maximum chatter stability is studied,and it is formulated as an optimization problem of maximizing the minimum negative real part of FRF.By employing the steepest descend method,the optimum frequency and damping ratio of TMD are obtained,and they are compared against the equal peaks tuning.The advantage of the proposed tuning is demonstrated numerically by comparing the minimum point of the negative real part,and is further verified by damping a flexible mode from the fixture of a turning machine.A TMD is designed and placed on the fixture along the vibration of the target mode after performing modal analysis and mode shape visualization.Both of the above two tunings are applied to modify the tool point FRF by tuning TMD respectively.Chatter stability chart of the turning shows that the proposed tuning can increase the critical depth of cut 37% more than the equal peaks.Cutting tests with an increasing depth of cut are conducted on the turning machine in order to distinguish the stability limit.The tool vibrations during the machining are compared to validate the simulation results.The proposed damping design and optimization routine are able to further increase the chatter suppression effect.     

半主动电流控制阻尼器的调谐减振性能研究

随着建筑高度不断增加,低频振动严重影响其安全运行。被动式阻尼器仅在调谐点处具有良好的减振效果,存在减振带宽较窄的问题,磁性液体为解决这个问题提供了新的途径。以磁性液体为工作液体,提出一种半主动调谐式电流控制阻尼器。首先,建立了阻尼器固有频率的理论模型,表明通过调节电流可改变固有频率。其次,搭建测试平台,进行了不同激励下阻尼器的调谐减振能力测试。结果表明半主动电流控制阻尼器的减振率为22%左右,调谐液体滚球阻尼器的减振率仅为12.3%左右,且调谐液体滚球阻尼器与主结构的频率比>1.11时,减振率将低于10%,半主动电流控制阻尼器则具有良好的鲁棒性,可以有效降低位移响应,弥补了被动式阻尼器减振带宽较窄的不足。     

颗粒阻尼铣刀主要填充参数对切削性能影响的正交试验分析

采用正交试验方法,选取颗粒阻尼铣刀主要填充参数(颗粒填充率、颗粒密度、颗粒直径)作为试验因素,以加工后工件表面粗糙度作为铣刀切削性能影响因素的评价指标,设计L9(34)正交试验表得到9组方案。运用极差分析方法确定影响铣刀切削性能的主要因素和次要因素,找到试验因素对铣刀切削性能的影响规律,最终得出最优方案组合,并用方差分析方法对其进行验证。     

三维激光切割工艺在化铣焊接机匣加工中的应用研究

通过对钛合金焊接机匣化铣结构的分析,设计了化铣工艺流程。针对化铣图形制版质量在化铣工艺流程中的关键作用,确定了化铣图形制版的激光刻型方案。选择通用三维激光切割机做为刻型加工设备,分析了激光刻型过程中要解决的技术问题,并采用分组编程刻型方案解决了通用三维激光器柔性切割轨迹误差技术难题,最后通过多组参数激光刻型试验选择了最佳切割参数,完成了该件化铣前激光刻型。通用三维激光切割机实现化铣图形柔性精确刻型方法,对其它复杂结构件化铣图形制备方案选择具有一定参考价值。     

磁流变智能阻尼器在抑制深孔切削振动上的研究

基于磁流变液的工作原理,设计了一套剪切阀式磁流变阻尼器,用于抑制深孔切削中的振动。分析了磁流变液工作原理,通过对深孔切削系统建立的动力学模型,得出系统的频率响应函数。最后通过MATLAB仿真分析表明:控制磁流变阻尼器的磁场强度可方便调节系统的阻尼率,进而能有效地抑制深孔切削振动的发生。     

Partial Surface Damper to Suppress Vibration for Thin Walled Plate Milling

The material removal rate and required workpiece surface quality of thin-walled structure milling are greatly limited due to its severe vibration, which is directly associated with the dynamic characteristics of the system. Therefore, the suppression of vibration is an unavoidable problem during milling. A novel partial surface damping method is proposed to modify the mode of the thin walled cantilever plate and to suppress vibration during milling. Based on classical plate theory, the design criterion is analyzed and configuration of the partial surface damper is introduced, in which viscoelastic plate and constraining plate are attached to the surface of the plate to increase the system’s natural frequency and loss factor. In order to obtain the energy expression of the cutting system, the Ritz method is used to describe the unknown displacements. Then, with Lagrange’s equation, the natural frequency and loss factor are calculated. In addition, the plate is divided into a finite number of square elements, and the regulation of treated position is studied based on theoretic and experimental analysis. The milling tests are conducted to verify its damping performance and the experimental results show that with treatment of partial surface damper, the deformation of the bare plate is reduced from 0.27 mm to 0.1 mm, while the vibration amplitude of the bare plate is reduced from 0.08 mm to 0.01 mm. The proposed research provides the instruction to design partial surface damper.     

STUDY ON ELECTRORHEOLOGICAL FLUID DAMPER FOR APPLICATION IN MACHINING CHATTER CONTROL

The electrorheological fluid(ERF)is a kind of intelligent material with bright prospects for industry applications, which has viscoelastic characteristic: under the applied electric field. The dynamic model of a milling system with an ERF damper is established, and the chatter suppression mechanism of the ER effect is discussed theoretically. Both the theoretical study and the experimental investigation show that the additional damping and additioaal stiffness produced by the ERF increase with the rise in the strength of electric field E, but their influence on the cutting stability is different. Only when both additional damping and additional stiffress cooperate, the milling chatter can be suppressed quickly and effectively. In additional, an ERF dumper used on the arbor of horizontal spindle milling machine is developed, and a series of milling shatter control experiments are performed. The experimental results show that the milling chatter can be suppressed effectively by using the ER damper.     

A road-adaptive control law for semi-active suspensions

This paper presents a road-adaptive control law for semi-active vehicle suspensions. In semi-active suspensions, damping coefficients are controlled so as to make the actual damper force as close to the desired damper force as possible at any time instance. The proposed control law consists of a road-adaptive sky-hook damping algorithm and a Road Detection Algorithm (RDA). This approach leads to the sprung mass and unsprung mass velocity feedback control law with time varying gains. The gains are tuned by the RDA. To evaluate the performance enhancement brought about by the proposed control law, the performance of a semi-active suspension with the proposed control law is compared to those of the sky-hook controlled semi-active suspension and a passive suspension. The controller has been implemented experimentally on a quarter car test rig and a semi-active damper with a 19 damping rates has been used to generate the desired semi-active force. The proposed control law provides adequate damping for the wheel hop frequency and improved performance compared to that of the sky-hook control law.     

车辆单筒充气磁流变减振器的阻尼力数学模型及试验仿真

介绍一种车辆单筒充气磁流变减振器的结构和工作原理,其内部的磁流变液材料是一种新型的智能材料,其流变特性可随所加载磁场强度的变化而变化,并且这一过程是可逆的,用磁流变液制成的减振器具有体积小、阻尼力大、动态范围广和频响高等优点。研究利用磁流变液的非牛顿宾汉流体模型和流体运动微分方程,建立反映单筒充气磁流变减振器阻尼力特性的数学模型;对单筒充气磁流变减振器进行台架试验,得到不同电流的减振器示功特性图;通过试验测得磁流变减振器的仿真参数,然后在Matlab软件环境下完成阻尼力数学模型的仿真;试验的示功特性与数学模型仿真进行分析比较,结果表明仿真数据与试验数据较吻合,验证了建立的单筒充气阻尼力数学模型的正确性。