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切削性能是评价数控机床好坏的重要指标之一,在结构设计阶段必须加以考虑。以提高实验室自主研发的立卧转换四轴联动数控机床的切削性能为目的,研究基于动力学特性与切削特性耦合的机床结构设计优化方法。首先结合切削加工中的颤振稳定域理论,通过实验获取机床刀尖频响函数和切削力系数,预测切削加工时的三维颤振稳定域图(主轴转速-切宽-切深)及颤振频率图(主轴转速-切宽-频率)。其次采用实验模态技术对整机进行结构动力学测试及分析,在获取可视化振型的基础上,分析引起机床发生颤振,并导致切削性能降低的结构设计上的缺陷。在此基础上,改进主轴头结构并比较刀尖频响函数,结果表明系统动刚度约增加28.2%,机床抵抗切削颤振的能力得到明显加强。 相似文献
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为了对细长轴的加工颤振进行稳定性研究,在对细长轴切削颤振机理的研究基础上,建立了刀具和细长轴耦合振动的两自由度系统的再生型颤振分析模型。利用解析法对时滞的动力学方程进行稳定性分析,得出了关于切削宽度和转速的稳定性切削极限图。从结果中可以得出两自由度系统的极限切削宽度比单自由度系统减小了28.6%。该成果可以为柔性零件的高效稳定加工提供理论切削参数。在车铣复合中心上进行了细长轴的切削颤振实验,通过与稳定性极限图的对比,发现实验结果与理论研究相吻合,并且总结出颤振发生前后刀具和细长轴的振动特性变化规律。这种振动特征的变化过程是对加工颤振进行监测和预警的重要识别指标 相似文献
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针对立铣刀高速车铣加工,基于其切削原理采用解析法建立三维颤振稳定域的理论模型。在立铣刀四轴车铣加工模态试验基础上,仿真分析了颤振稳定域叶瓣图,结果表明立铣刀高速车铣加工产生颤振的条件与铣刀几何形状、工件材料、铣刀转速、切削深度和机床结构的频率响应函数等密切相关。在进行车铣切削颤振稳定域试验时,其切削力频谱分析的结果表明:当刀齿切入频率起主导作用时,切削过程是无颤振和稳定的;当系统模态频率起主导作用时,将产生颤振并测得切削力和表面粗糙度值都大于或高于无颤振情况。因此该理论模型及仿真结果对立铣刀车铣加工零件的加工效率和加工精度可提供相应的理论指导。 相似文献
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切削过程再生颤振的模糊稳定性分析 总被引:6,自引:0,他引:6
在机床切削颤振分析中首次考虑了模糊不确定性因素的影响,利用模糊数学分析方法详细论述了切削过程再生颤振的模糊稳定性分析问题,给出了模糊稳定性极限切削宽度集合的可能性分布及其置信区间表达式,最后依据本文的理论分析,经计算机编程绘制了模糊稳定性图 相似文献
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取自刀架的振动加速度时间历程被分为三大部分:无颤振切削状态,过渡切削状态和颤振状态。这里分别从热力学角度和几何角度描述了切削系统的动力学行为,给出了与无颤振切削状态和颤振状态相对应的振动加速度时间序列的概率密度分布和三维重构吸引子。并计算了各阶段的Lyapunov 指数和 Kolmogrov 熵。同时绘制并讨论了Lyapunov 指数和 Kolmogrov 熵与切削加工参数的关系曲线。研究表明: Lyapunov 指数和 Kolmogrov 熵与切削加工参数的关系曲线变化趋势相同,看起来象稳定阈图,这些曲线对切削加工参数的选择具有指导作用。并且,当切削状态从无颤振状态过渡到颤振状态时,Lyapunov 指数和 Kolmogrov 熵将随振动幅值的增大而增大。 相似文献
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本文研究了切削加工稳定图中相邻两个不稳定叶瓣之间的控制规律。经理论和实验分析给出的规律表明,颤振振幅和切宽的关系在切宽较大时,由右边不稳定叶瓣的左侧控制;而在切宽较小时,由左边不稳定叶瓣的右侧控制。该规律能全面描述机床双频颤振现象和颤振过程主频带移动的原因。 相似文献
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在机床切削加工过程中,由于系统内部激发及反馈的相互作用,工件和刀具之间常常会发生强烈的振动,称为“颤振”。机床颤振会使加工过程变得不稳定,造成加工表面质量和金属切削率的下降,严重时甚至会破坏刀具和机床。因此,颤振成为提高机床加工能力的最主要障碍。对振动加以控制,掌握其规律是当面急需解决的难题。 相似文献
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《International journal for numerical methods in engineering》2018,113(9):1488-1506
In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method. 相似文献
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Standards are the basis for production enterprises to organize production ex-factory inspection trade 《中国标准化(英文版)》2008,25(1):24-25
Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.…… 相似文献
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Steffen Müller-Probandt 《材料科学与工程:中英文B版...》2018,(4):161-177
We associate a variety of innovations with the term "Industry 4.0". The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di... 相似文献
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A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa. 相似文献
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On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.…… 相似文献
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Janet Lang 《Materials and Manufacturing Processes》2017,32(7-8):857-866
ABSTRACTThe production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them. 相似文献
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Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß. 相似文献
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C. Qihong W. Zhan‐Wen J. Yi J. Yehua L. Fei F. Hanguang 《Materialwissenschaft und Werkstofftechnik》2014,45(7):582-590
In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M2(B,C), (W,Mo)2(B,C), M3(B,C), M23(B,C)6 type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm2. The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K1 mill housing of bar mill. 相似文献
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S. K. Malhotra Paramanand Singh A. Thirunavukkarasu 《Materials and Manufacturing Processes》2006,21(7):652-657
Al2O3-ZrO2 nanocomposites were developed starting with the solgel process. Composite alumina-zirconia nanopowders were synthesized from metallorganic precursors (Aluminium secondary butoxide and zirconium Iso propoxide) using the solgel process. The parameters affecting the synthesis—solvent, concentration of precursor, R/H ratio (i.e., dilution of water in solvent)—were varied as also the temperature and pH. BET and TEM were used to measure nanosize. Diffuse reflectance spectroscopy and also qualitative optical absorption led to identical particle size estimate. The variation of process parameters was used to study the effect and interdependence of process parameters. Artificial Neural Networks was used to rigorously analyze the process. Although this led to confirmation of interdependence of parameters, the presence of a single overwhelming solvent variable was also established. Then the optimal process was used to synthesize more nanopowder. To produce bulk nanocomposite the nanopowders were sintered by varying the temperature and time period. The sintered lithoids were probed with a vickers hardness tester to measure elastic modulus, hardness, and fracture toughness. The results showed high elastic modulus, modest hardness, and very high fracture toughness. 相似文献