基于隐式Adams方法的螺旋曲面铣削系统稳定性预测研究

针对螺杆转子铣削过程中的铣削系统稳定性进行研究。首先通过模态试验获取刀具的模态参数。其次,根据盘铣刀铣削螺杆转子曲面原理建立三自由度铣削力模型和以线性时滞微分方程表示再生型颤振影响的铣削加工动力学模型,并对刀齿铣削周期进行离散。然后,提出基于隐式Adams对螺旋曲面铣削系统稳定性进行预测的方法,在利用隐式Adams方法对动力学方程进行数值求解的基础上,依据Floquet理论判断系统的稳定性,获得螺旋曲面铣削系统的稳定性叶瓣图。最终,根据稳定性叶瓣图选取加工参数进行试验,验证隐式Adams方法在螺旋曲面铣削系统的适用性。试验结果表明：数值求解结果与试验结果吻合程度较高,即采用的隐式Adams方法适用于螺旋曲面铣削系统的稳定性预测。     

基于隐式Adams方法的螺旋曲面铣削系统稳定性预测研究EI北大核心CSCD

针对螺杆转子铣削过程中的铣削系统稳定性进行研究。首先通过模态试验获取刀具的模态参数。其次,根据盘铣刀铣削螺杆转子曲面原理建立三自由度铣削力模型和以线性时滞微分方程表示再生型颤振影响的铣削加工动力学模型,并对刀齿铣削周期进行离散。然后,提出基于隐式Adams对螺旋曲面铣削系统稳定性进行预测的方法,在利用隐式Adams方法对动力学方程进行数值求解的基础上,依据Floquet理论判断系统的稳定性,获得螺旋曲面铣削系统的稳定性叶瓣图。最终,根据稳定性叶瓣图选取加工参数进行试验,验证隐式Adams方法在螺旋曲面铣削系统的适用性。试验结果表明:数值求解结果与试验结果吻合程度较高,即采用的隐式Adams方法适用于螺旋曲面铣削系统的稳定性预测。     

预测铣削稳定性的Hamming线性多步法

针对铣削加工过程中产生的振动现象,提出了一种Hamming线性多步法(HAMM)来预测铣削加工过程中的稳定性。考虑再生颤振的铣削加工动力学方程可以表示为时滞线性微分方程,将刀齿周期划分为自由振动阶段和强迫振动阶段,对强迫振动阶段进行离散,运用HAMM方法构建状态传递矩阵,利用Floquet理论,判定系统的稳定性,获得系统的稳定性叶瓣图。Matlab软件仿真结果表明,HAMM方法是预测铣削稳定性的一种有效方法。随着离散数的增加,HAMM方法的收敛速度要快于一阶半离散法(1st-SDM)和二阶全离散法(2nd-FDM),离散数较少的HAMM方法能达到和离散数较多的1st-SDM方法和2nd-FDM方法的局部离散误差。此外,在单自由度和双自由度动力学模型下,由三种方法的稳定性叶瓣图可以看出,HAMM方法预测铣削稳定性的精度均好于1st-SDM方法和2nd-FDM方法,计算效率远远高于1st-SDM方法和2nd-FDM方法。实验结果表明,HAMM方法是一种有效的预测铣削稳定性的方法。     

基于径向基函数的AL2A12薄壁件铣削稳定性研究

在薄壁件铣削过程中,颤振对工件表面质量有很大影响,在实际加工之前进行铣削稳定性预测,便于获取无颤振的加工条件。基于径向基函数逼近理论,提出一种铣削稳定性预测方法。通过试切法和锤击法获得了AL2A12薄壁件的切削力系数和模态参数,并基于所提出的方法推导了系统的状态转移矩阵,通过Floquet定理来判定系统的稳定性,从而获得了AL2A12薄壁件铣削过程的稳定性图。为了验证所提方法的计算效率,采用相同的系统参数来进行计算。通过与零阶半离散法和全离散法相比,表明在获得的铣削稳定性图一致的前提下,所提方法的计算效率最高。在预测的稳定性图中选择4个参数点,利用参数点所对应主轴转速和轴向切深来加工AL2A12薄壁件,将实际加工结果与稳定性预测结果进行比较,验证了所提预测方法的有效性。通过实际切削表明,在AL2A12薄壁件的加工过程中,当轴向切深相近时,较高的主轴转速可以获得更好的加工表面,同时也可以避免黏刀现象的产生。     

考虑刀杆结构非线性的铣削过程颤振稳定性与主共振

研究考虑铣刀杆结构非线性和阻尼的颤振稳定性以及主共振。将刀杆简化为平面弯曲悬臂梁结构模型。为了在模型中考虑结构阻尼的影响,假定刀杆由黏弹性材料构成。结合包含再生时滞效应和周期激励的切削力模型,根据Hamilton原理建立非线性运动方程。采用Galerkin法将非线性偏微分运动方程进行化简,导出主坐标表示的非线性常微分运动方程。通过时域数值积分得到铣削系统的稳定性lobes图。采用多尺度法对非线性常微分运动方程进行摄动求解,导出非线性切削系统在周期激励下的主共振响应的近似封闭解。研究刀杆的几何尺寸、结构阻尼、切削力系数、切削深度、齿数和切削力幅值等参数,对铣削过程非线性lobes图以及主共振响应曲线的影响。结果表明,增加刀杆的长度或者降低铣削过程的临界切削深度;切削力系数越大,临界切削深度越小;增加结构阻尼能够明显提高铣削过程的颤振稳定性;主共振响应峰值向右偏斜,由于切削系统存在三次刚度非线性,主共振响应曲线表现出典型的硬弹簧Duffing振子的特性,出现跳跃性和多值区域。     

基于瞬时铣削力系数法的拼接模具铣削稳定性研究

在拼接模具铣削过程中,由于拼接过缝处硬度差的影响致使铣削力发生突变并加剧振动,进而降低工件表面质量和刀具的使用寿命。针对上述问题本文首先建立了拼接过缝区域的切屑厚度模型,分析了切屑厚度与铣削力系数的关系;然后运用基于Runge-Kutta法的全离散法求解铣削动力学方程,由于瞬时铣削力系数随切削参数的变化而变化,故基于该方法可获得上限和下限的多条稳定性预测曲线,并利用最小包络法形成上、下限的带状区域作为最终的稳定边界;最后综合运用时域、频域分析来验证铣削稳定性预测曲线的准确性。提出的稳定性预测模型可以为大型汽车覆盖件铣削加工过程提供理论参数依据,并解决铣削拼接处冲击载荷引起的振动问题。     

多输入多输出有界变时滞非线性系统的绝对稳定性判据

以时滞反馈控制系统为背景，通过建立Liapunov-Razumilhin函数来分析多输入多输出变时滞系统零解的绝对稳定性，通过对时滞界估计来达到系统零解的绝对稳定性判定。并且通过计算机仿真来说明所得两判据及变时滞界的一些特殊现象。     

地震作用下主动减震结构的时滞离散最优控制

对地震作用下线性时滞结构的离散最优控制方法进行研究,按时滞量为采样周期的整数倍和非整数倍两种情况,将时滞连续控制系统离散为形式上不包含时滞的标准离散形式,采用连续时间形式的性能指标函数,按照离散最优控制方法进行控制设计.所得出的控制律表达式中,除了含有当前的状态反馈外,还包含有前若干步控制项的组合.最后结合一个三自由度建筑结构模型进行仿真计算,结果表明,算法中采用连续时间形式的性能指标函数优于离散形式的性能指标函数,此方法易于保证控制系统的性能和稳定性,而且可以看到,控制系统的时滞量并非越短越好.     

捕食者和食饵都具有阶段结构的时滞捕食系统的稳定性和Hopf分支（英文）

自然界中,种群增长往往有一个增长和发育的过程M.在不同的年龄阶段,捕食者和食饵会表现出不同的生长特性.此外,时滞对微分方程解的拓扑结构也有很大的影响.许多情况下时滞会破坏正平衡点的稳定性,产生Hopf分支.本文以幼年捕食者到成年捕食者的生长时间为时滞,建立捕食者和食饵都具有阶段结构的时滞捕食系统,利用无限维系统的持久性理论和Hurwitz准则,给出了系统的永久持续性生存和系统共存平衡的局部稳定性条件.以时滞为参数,得出了系统Hopf分支存在性,利用规范型理论和中心流形定理确定了Hopf分支的方向以及Hopf分支周期解的稳定性.最后,通过选取满足定理条件的参数,得到了引起Hopf分支的临界值,并用数值例子验证了定理结论.     

一类具比例时滞细胞神经网络反周期解的指数稳定性

本文针对一类具比例时滞细胞神经网络反周期解的全局指数稳定性进行研究.首先利用非线性变换将一类具比例时滞的细胞神经网络等价变换成一类具常时滞变系数的细胞神经网络.然后通过构造合适的时滞微分不等式和利用不等式技巧,得到了保证该系统反周期解的存在性和全局指数稳定性时滞依赖的充分条件.最后数值算例结果验证所得结论的正确性和与以往文献相比较低的保守性.     

有限元法中间构形初始解预示的Laplace-Beltrami方程法

一步有限元法具有高效的计算能力,在板料成形模拟方面得到了广泛的应用,但它存在应力计算精度不足的问题。为弥补这一不足,通过增加中间构形的方式,人们提出多步有限元法。而中间构形需根据初始解迭代计算获得,因此,初始解预示算法是多步有限元法的一个关键问题。该文把中间构形解耦分解为弯曲变形和拉伸变形两个独立的变形过程,且将弯曲变形作为中间构形的初始解预示,改善了多步有限元法的稳定性;并根据大位移小应变理论,建立了节点的位移约束条件;进一步,首次通过Laplace-Beltrami方程的建立和求解,实现了中间构形初始解的快速预示,该方法易于编程实现,稳定性好。通过典型零件数值算例的高效准确计算,验证了该算法的可行性和有效性。     

Prediction of cutting force based on machining parameters on AL7075-T6 aluminum alloy by response surface methodology in end milling

Cutting forces modeling is the basic to understand the cutting process, which should be kept in minimum to reduce tool deflection, vibration, tool wear and optimize the process parameters in order to obtain a high quality product within minimum machining time. In this paper a statistical model has been developed to predict cutting force in terms of geometrical parameters such as rake angle, nose radius of cutting tool and machining parameters such as cutting speed, cutting feed and axial depth of cut. Response surface methodology experimental design was employed for conducting experiments. The work piece material is Aluminum (Al 7075-T6) and the tool used is high speed steel end mill cutter with different tool geometry. The cutting forces are measured using three axis milling tool dynamometer. The second order mathematical model in terms of machining parameters is developed for predicting cutting forces. The adequacy of the model is checked by employing ANOVA. The direct effect of the process parameter with cutting forces are analyzed, which helps to select process parameter in order to keep cutting forces minimum, which ensures the stability of end milling process. The study observed that feed rate has the highest statistical and physical influence on cutting force.     

一种整体叶盘加工预变形控制方法

为解决钛合金整体叶盘薄壁弯扭跨音速叶片叶型制造过程中存在的加工变形大、铣削稳定性差等问题,本文提出了一种整体叶盘加工预变形控制方法。采用叶型三维检测技术获取叶型位置度和扭转角,利用叶型铣削变形误差反向补偿方法控制叶片弯曲及扭转变形。在整体叶盘上进行了实验验证,结果表明该方法可有效提高叶型加工精度和成品合格率,具有技术借鉴价值。     

Reliability analysis of chatter stability for milling process system with uncertainties based on neural network and fourth moment method

A reliability analysis of the milling system with uncertainties is developed in this paper to predict reliable chatter-free machining parameters. The chatter reliability refers to the probability of no chatter for the dynamic milling system. Then a reliability model is established to predict the chatter vibration, in which the dominant modal parameters of the dynamic milling system are defined as random variables. To solve the reliable model with the second-order fourth-moment (SOFM) method, the limiting axial cutting depth is substituted by an explicit expression obtained using a neural network. Therefore, after distributions of the random parameters are experimentally determined, the reliability of the given machining parameters can be computed with the SOFM method. Furthermore, a reliable stability lobe diagram (RSLD) can be plotted to obtain more reliable and accurate stable region instead of the conventional SLD. A case study is performed to validate the feasibility of the proposed method. The reliability of the milling system was calculated with the SOFM method, the first-order second-moment (FOSM) method and the Monte Carlo simulation (MCS) method. The results from the SOFM method and MCS method were found to be more consistent. Moreover, a RSLD with the reliability level 0.99 was compared with a conventional SLD plotted using the mean values of the random parameters. Chatter tests shown that the RSLD with the higher reliability level was more accurate for predicting the chatter-free machining parameters.     

An efficient algorithm for automatic machining sequence planning in milling operations

Machining sequence planning can be considered as one of the most important functions of manufacturing process planning. However, less attention has been paid to automation of this function in contemporary computer-aided process planning systems. This paper describes an efficient algorithm for automatic machining sequence planning in 2.5D milling operations. It is programmed in LISP and forms the machining sequence planning module of a CIM system. This module is integrated with a feature-based design system that determines required machining operations and parameters for each machining operation. This information is then sent to the machining sequence planning module for determining proper machining sequence plans for producing the part. The algorithm generates feasible machining sequences based on the bilateral precedence between machining operations. The algorithm results in minimized tool changes.     

Fuzzy controlled backpropagation neural network for tool condition monitoring in face milling

The performance of a fuzzy controlled backpropagation neural network has been studied to predict the tool wear in a face milling process based on simple process parameters and sensor signal features. The results show the potentiality of the method in comparison to the standard backpropagation neural network and one of its variants. The speed of convergence, accuracy of prediction and total time of system development make fuzzy controlled backpropagation an attractive technique amenable for online tool condition monitoring.     

Influence of inner-spraying rotating tool during electrochemical milling of Nimonic-263 alloy

Electrochemical milling (EC milling) has great possibility in consequence of its flexibility and applications in the various manufacturing industries, especially in defense and biomedical industry. In future, it is likely to be one of the most capable, successful, and commercially used unconventional machining processes in the up-to-date manufacturing industries. In this research work, an attempt has been made to develop a versatile in-house EC milling setup to study the impact of inner-spraying rotating tool on the different responses of EC milling. Experiments have been performed on a special type of nickel-based (nickel–cobalt–chromium–molybdenum) superalloy commonly known as Nimonic-263 alloy specially developed for high-temperature and high-strength applications to identify the impact of major process parameters, e.g., feed rate and milling layer depth with and without tool rotation, on the responses like machining depth, side angle, surface roughness, and quality of machined profile. During EC milling of Nimonic-263 alloy, excellent surface finish ranging from 0.06 to 0.08 μm has been attained by employing mixed electrolyte, i.e., NaCl (1 M) and NaNO₃(1 M). With the incorporation of inner-spraying rotating tool, flushing can be improved to a large extent which improves the accuracy of machining.     

多齿铣刀侧铣加工多层CFRP铣削力的建模与仿真

由于碳纤维增强树脂基复合材料(CFRP)的层间结合强度较低,进行切削加工时在切削力的作用下容易出现分层和毛刺等质量缺陷。因此,通过对切削力的预测与控制可以有效提高加工质量。采用瞬时刚性力模型对多齿铣刀侧铣多层CFRP材料的加工过程进行铣削力建模与仿真,分析了多齿铣刀特有的几何结构对切削力的影响。试验中保持切削速度恒定,以不同进给速度分别对45°、0°、-45°和90°这4种典型纤维方向的单向CFRP进行侧铣加工,通过测得的切削力数据计算各自的铣削力系数。根据力学矢量叠加原理得到了多向CFRP铣削力系数的简化计算表达式,最后将计算结果代入铣削力模型得到了各时刻的铣削力仿真值。在同样的试验条件下对该多向CFRP进行侧铣加工验证试验,试验结果表明: 该模型能较好地预测铣削力,最大相对误差小于9%,平均相对误差小于5%,可为铣削参数优化和刀具结构优化提供理论基础。     

On-line condition monitoring of tool wear in end milling using acoustic emission

The monitoring of tool wear is important in maintaining the quality of workpieces produced. This paper presents a methodology to monitor on-line tool wear in end milling using acoustic emission. It is well known that the root-mean-square (RMS) value of the acoustic emission is directly proportional to the power expended in turning. A mathematical model has been developed to predict the RMS value of the acoustic-emission signal in milling. This mathematical model incorporates the machining parameters as variables. The accuracy of the model has been verified by a series of experiments. The experiments were carried out on a Bridgeport milling machine and data was collected and analysed by using an on-line computer data acquisition system. A comparison of the experimental and theoretical RMS values indicates a very good agreement between them. A control strategy similar to the moving average/moving range charts has been developed for monitoring on-line tool wear. The limits for the control charts were obtained from the theoretical equation of statistical quality control. An observation of the control charts clearly indicates the region of tool failure and the time at which the tool failed. The philosophy behind the use of control charts is based on the ease of implementation and widespread use in industry.     

毛坯开槽方式中零件加工变形的演变机理与控制方法

广泛用作飞机薄壁整体结构件毛坯的铝合金厚板,在制造过程中出现的塑性变形不均匀性将导致残余应力的产生。高速铣削过程中残余应力的释放将引起飞机薄壁整体结构件的加工变形,这严重影响加工质量。因此,建立了毛坯释放变形后零件铣削的有限元仿真方法,挠度解析法的计算结果和实验测量的数据均验证了有限元仿真值无论是在趋势上还是变形量上均高度吻合。利用有限元方法揭示了开槽方式对毛坯释放变形的影响规律,分析了零件加工变形与毛坯释放变形之间的关系。结果表明:毛坯释放多大变形量,零件就能减小多大的变形量。在建立毛坯释放变形预测模型的基础上,提出了开槽方式的遗传算法优化方法,随机测试集表明神经网络的预测精度高达95%左右,而三框件在最佳开槽方式下能减小34.5%的变形。