四辊冷带轧机再生颤振稳定性的统一理论

研究了四辊冷带轧机三倍频和五倍频颤振的产生机理，分析了由于负阻尼效应所导致的轧机再生颤振现象，提出了再生颤振稳定性分析的统一模型，并对其进行了理论探讨。在此基础上，通过轧机颤振的现场测试数据论证了再生颤振理论模型的正确性及其工业价值，并用数值仿真方法给出了再生颤振统一模型的稳定性图。     

滚珠丝杠磨削再生颤振极限预测方法研究

介绍了滚珠丝杠磨削过程中的再生颤振对提高工件质量和生产效率的影响;在滚珠丝杠磨削振动系统动力学模型的基础上,提出了确定磨削再生颤振模型参数的方法,获得了符合在实际磨削中的再生颤振稳定性极限图。结果表明,通过对磨削滚珠丝杠的磨削试验,验证了对磨削滚珠丝杠再生颤振系统研究的有效性和实用性。     

轧机颤振建模及理论研究进展

轧机颤振是由系统结构动力学与轧制过程动力学相互耦合导致的一种自激振动,对轧机颤振的研究除了需要合理有效的结构模型,还有赖于对轧制过程的精确表征。现有的轧机结构模型除了考虑三倍频、五倍频及扭振三种基本振动形式和多方向多模态的耦合问题,还有通过张力模型和时滞传递模型耦联而建立的多机架连轧模型。此外,多种非线性因素和非对称特征对轧机颤振的影响也越来越受到重视。Slab分析方法是轧制过程建模最重要和广泛的方法,包括不同变形条件下屈服准则的建立、摩擦模型的确定以及应力分布的计算。基于Slab分析法建立的轧制过程模型包括稳态轧制模型、考虑辊缝波动量的准静态模型以及同时考虑辊缝波动及其波动速度的动态轧制模型。将动态轧制力作为反馈激励源,作用于相应的轧机结构模型,从而可以构建轧制过程与系统结构相耦合的颤振动力学模型,研究系统的稳定性及失稳准则。     

微铣削再生颤振动力学建模及稳定性分析

再生颤振是制约微铣削加工效率和加工质量的主要因素.以微铣削加工为研究对象,建立了考虑再生效应的微铣削颤振系统动力学模型和颤振稳定域解析模型,通过模态实验获得机床-刀具系统的频响函数,在此基础上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,实验结果与仿真结果吻合良好,验证了建立的微铣削颤振系统动力学模型和颤振稳定域解析模型的正确性.     

切入式无心外圆磨再生型磨削颤振的动态特性分析

对引起无心磨砂轮表面再生磨削颤振的原因进行了分析,基于再生颤振机理,建立了无心磨砂轮表面再生磨削颤振的动力学模型,并通过拉氏变换和经典控制理论建立了砂轮表面再生磨削颤振系统框图.然后通过系统传递函数的特征方程,得到砂轮表面再生磨削颤振系统的稳定性条件.此外,提出了通过比较砂轮的磨损深度与极限磨削深度的方法来判断砂轮表面是否会发生再生磨削颤振,从而为优化无心磨工艺参数,提高加工精度提供了理论基础.     

高速铣削再生颤振稳定性预测与验证

再生型颤振是制约高速铣削加工效率和零件加工质量的主要因素。以高速铣削加工为研究对象,建立了考虑再生效应的高速铣削动态铣削力模型和颤振稳定域解析模型,通过模态实验获得机床-刀具系统的频响函数,在此基础上综合使用铣削稳定性判据进行数值分析,获得了高速铣削颤振稳定域的解析解。最后,进行了零件颤振稳定性铣削加工实验,实验得到的结果与仿真结果吻合良好,由此验证了建立的颤振系统动力学模型和颤振稳定性解析模型的正确性。     

冷连轧机颤振的一种振因研究

颤振是冷连轧生产中常见的现象,对这种现象的研究一直是工程界所关心的课题。研究了某钢厂冷连轧机的颤振问题,它的颤振特点是生产中该机组中的第五号机座出现低速颤振现象,即工作速度仅为设计速度的百分之四十分左右,严重制约了生产率。从扭振分析入手,对其传动系统上扭振三角波信号进行了充分的讨论,提出该轧机机座上的颤振原因是由上下支撑辊的相对辊径差所引起的速差所致。还给出了以速差为主变量的颤振自激因子计算公式,并以该轧机的轧制工艺为例进行了计算,证明了该轧机的颤振起因,这个结果为轧机的避振方法提供了理论指导。     

轧机整体耦合建模问题研究

轧机振动一直是制约轧制发展的重要问题。建立有效的轧机系统动力学模型是研究轧机振动问题的基础,而已有的研究在轧机系统耦合建模方面仍存在着许多不足。通过分析轧机不同类型振动产生的机理及其相互关系,建立能够表征板带轧机垂直-水平-扭转以及轧件水平颤振的耦合振动结构模型;基于Bland-Ford-Hill轧制力模型,并进一步考虑振动状态下辊缝动态变化的影响,建立动态轧制过程模型;在此基础上,将动态轧制力及动态轧制力矩作为反馈激励源,作用于轧机振动结构模型,构建全新的动态轧制过程与轧机系统结构相耦合的轧机颤振整体耦合动力学模型。通过将所建模型的仿真结果与2030冷连轧机组振动测试数据的对比,验证此模型的正确性和有效性。结果表明,轧机颤振整体耦合动力学模型能够合理表征振动过程中轧机系统结构和轧制过程的耦合关系,为深入研究轧机综合振动特性提供理论基础。     

工业数据驱动下薄板冷轧颤振的LSTM智能预报

冷轧机颤振问题由来已久,随着更薄规格、更高强度和更快速度的要求,该问题更加突出,诱发机理复杂多变且隐蔽,过度依赖经验判断难以及时有效地抑制颤振的发生,基于历史振动大数据实现冷轧颤振的智能预报是面向智能轧制的重要应用场景。考虑冷轧颤振工业数据的多源、多态与强耦合特征,通过多源数据的采集交互、时刻匹配、频率协同、数据降维等数据预处理建立颤振预报模型的样本空间;基于长短时记忆(Long short–term memory,LSTM)循环神经网络建立轧机颤振能量值的智能预报模型,利用轧件规格、轧辊状况、轧制工艺以及轧机振动状态的历史信息数据,对最为典型和振动频繁的第五机架振动能量值加以预测;分析了不同时间步长对预测效果的影响以获得最优的预测步长,模型预测结果的变化趋势与实际数据的变化趋势基本一致,训练数据集与测试数据集的均方误差较小;然后,将模型应用于未参与训练与测试的实际轧制过程数据,结果表明LSTM模型能够很好地实现颤振预测,且根据设定的报警阈值能够实现提前预报。研究结果表明基于多源历史振动数据的深度学习与挖掘能够实现对连轧颤振失稳的智能预报,不仅能够在实际生产中发挥作用,而且对实现冷轧过程的智能化具有积极的推动意义。     

车削加工颤振稳定性可靠度蒙特卡罗法仿真

在工程实际中,车削系统刚度、阻尼及切削力等参数的随机性严重影响车削加工的稳定性。针对此问题,提出了一种车削加工再生型颤振稳定性可靠度计算方法。考虑随机因素的影响,采用蒙特卡罗数值模拟方法,研究车削加工再生型颤振稳定性的统计分布规律。建立车削加工再生型颤振动力学模型,采用拉氏变换获取机床车削的极限切削宽度及所对应的主轴转速。根据数控车床切削系统动力学参数的分布信息抽取样本,代入再生型颤振模型进行计算,获取极限切削宽度的样本,并统计其概率特性,以实际切宽是否小于极限切宽为判别条件提出一种基于蒙特卡罗模拟的车削加工再生型颤振稳定性可靠度预测方法。     

A novel deep groove machining method utilizing variable-pitch end mill with feed-directional thin support

A novel method for deep groove machining is developed which utilizes a long-shank variable-pitch end mill with a feed-directional thin support in this research. Recently, thin and tall ribs are required for many parts to reduce their weight and material consumption without sacrificing their stiffness and strength. It leads to necessity of deep and narrow grooves in dies and molds for their mass production. However, such deep groove machining is difficult, since long flexible end mills cause severe chatter vibrations induced by regeneration and mode-coupling. There have been many studies on the regenerative chatter vibration, while there have been few studies on the mode-coupling chatter vibration. Both chatter vibrations need to be suppressed in the deep groove machining. In this study, the regenerative chatter vibration is suppressed by employing one of the conventional methods, i.e. a variable-pitch end mill. On the other hand, there is not a good method to suppress the mode-coupling chatter vibration in the deep groove machining. Therefore, a new suppression method is proposed in which the long-shank variable-pitch end mill is supported with a thin plate in the feed direction. The support device and the long-shank variable-pitch end mill are developed and applied to machining of hardened die steel. Validity of the proposed method is verified both analytically and experimentally in this study.     

再生型切削颤振稳定性极限的图解法

分析了再生型切削颤振的稳定性极限,并提出一种简单的确定稳定性曲线的图解法,这种图解法对于分析系统的稳定性更具有直观性,并为抑制再生型切削颤提供了理论依据。     

Unique regenerative chatter in wiper-turning operation with burnishing process Part 1: Prediction and analytical investigation of generation mechanism,critical stability,and characteristics

The purpose of this paper is to understand the generation mechanism and to propose an analytical model of a unique regenerative chatter with the burnishing process in wiper-turning operations. The authors have found a unique chatter when using wiper inserts, which cannot be explained by the existing chatter theory found in the literature. The authors believe that this occurs because of the burnishing process of the wiper insert, which is the only difference from ordinary turning. At first, the burnishing process, which accompanies wiper inserts, is explained, and the turning operation with this process and the well-known regenerative effect in the cutting process is discussed. Then, the stability of the turning process with the regenerative effects in the cutting and burnishing processes are investigated, and an analytical model is proposed to evaluate the critical stability. Finally, the stability analysis of this unique chatter is conducted, and its generation mechanism and characteristics are examined clearly.     

GRADE OF STABILITY IN FUZZY CHATTER STABILITY LOBE MODEL IN MILLING

The machining productivity and part quality are typically limited by the regenerative chatter induced by the dynamic interactions of spindle-holder-tool combination system. The conventional chatter stability model predicts the permissible stable axial depth of cut versus spindle speed by plotting the stability lobe diagram which represents two independent regions as absolutely stable zone and instable zone divided by the critical lobe curve. In fact, it is more reasonable to be a transition stage between the stable and instable zone. This paper introduced the grade of stability (GOS) to improve the conventional chatter stability model and study the transition zone in the stability lobe diagram. The variation of transition zone width with the stability sensibilities for different order lobe curve in milling system was analyzed. Sigmoid function was used as the membership function to develop the fuzzy stability lobe model. Then, the fuzzy stability lobe diagram with an adjustable slope coefficient was implemented to improve the mould steel milling process. The improved fuzzy stability model enhances the reliability of stability lobe diagram and guarantees the chatter-free milling process.     

Robust regenerative chatter stability in machine tools

The expeditious nature of manufacturing markets inspires advancements in the effectiveness, efficiency and precision of machining processes. Often, an unstable machining phenomenon, called regenerative chatter, limits the productivity and accuracies in machining operations. Since the 1950s, a substantial amount of research has been conducted on the prevention of chatter vibration in machining operations. In order to prevent regenerative chatter vibrations, the dynamics between the machine tool and workpiece are critical. Conventional regenerative chatter theories have been established based on the assumption that the system parameters in machining are constant. However, the dynamics and system parameters change due to high spindle speeds, tool geometries, orientation of the tool with respect to the rest of the machine, tool wear and non-uniform workpiece material properties. This paper provides a novel method, based on the robust stability theorem, to predict chatter-free regions for machining processes, by taking in account the unknown uncertainties and changing dynamics for machining. The effects of time-variant parameters on the stability are analyzed using the robust stability theorem. The experimental tests are performed to verify the stability of SDOF and MDOF milling systems. The uncertainties and changing dynamics are taken into account in order to accommodate the optimal selection of machining parameters, and the stability region is determined to achieve high productivity and accuracy through applications of the robust stability theorem.     

Low-frequency chatter genesis during inclined surface copy-milling with ball-end mill: Experimental study

In this study low-frequency chatter during machining of inclined surfaces with ball-end mills is experimentally investigated. An explanation of genesis of low-frequency vibrations have been proposed for various conditions: cutting direction, lead angle values, spindle speed, depth of cut. As a result, it has been proven that low-frequency chatter has more significant effect on machined surface than usual chatter. Low-frequency chatter occurs during downward milling, rather than upward milling, especially when lead angle increases. Furthermore, low-frequency chatter takes place in the beginning of cutting process, thereafter develops into steady state of usual chatter, which has no such significant effect on machined surface, as it has been shown. The results are in line with the supposition that low frequency vibrations are caused by sudden and irregular nature of shearing process, when magnitude is small.     

CSP轧机振动的振源研究

针对某厂CSP热连轧机F2和F3机架出现严重的振动问题,为掌握轧机的振动规律并确定振源,首先对振动严重的F2和F3机架进行了现场测试,发现轧机具有4种振动形式。在分析了轧机固有特性以及轧机机械传动系统中潜在致振频率的基础上,确定了这4种振动形式的振动规律和振源,它们分别是轧制界面自激振动引起的固有频率振动、驱动端引起的强迫振动、齿轮座啮合引起的强迫振动、辊面振纹引起的振纹振动。研究发现,F2和F3振动时所表现出的频率虽有不同,但两架轧机的振动内在规律和振源却是相同的,而且在振动形式上表现出较为复杂的耦合振动。     

Proposal of novel chatter stability indices of spindle speed variation based on its chatter growth characteristics

Chatter is one of the most critical problems that causes poor surface quality and restriction of machining efficiency. Spindle speed variation (SSV) is a well-known technique for suppression of regenerative chatter. However, in the authors’ understanding, the chatter suppression effect diminishes when the spindle speed difference between the present and previous cutting moments is small. Furthermore, the stability changes largely according to the spindle speed variation profile which changes with the set condition of SSV parameters, e.g., nominal spindle speed, variation period and variation amplitude. Therefore, SSV parameters should be adequately set to avoid this limitation and to exert its effect throughout the entire duration of cutting. However, there is no clear methodology to determine the optimal condition. This paper presents the characteristics of chatter growth during SSV focusing on the change of chatter frequency, which lead to novel indices to evaluate the chatter stability when cutting with SSV. To verify the validity of the indices, time-domain simulations and the cutting experiments with triangular spindle speed variation (TSSV) are carried out. The influence of SSV parameters on the chatter stability is investigated from the simulation and experimental results. The limitations of widely utilized SSV profiles are discussed.