机床刀具可靠性及寿命评估

为了评估金属切削刀具的可靠性,提出了机床切削刀具可靠度和平均寿命的概率评估方法,利用马尔科夫链蒙特卡洛法解决了描述刀具故障率的Weibull比例危险模型参数贝叶斯点估计及区间估计难题,所提评估方法可给出刀具可靠度、故障率、平均寿命及其下限的估计值。通过实例分析表明:刀具可靠度随切削用量和切削时间的变化非单调下降,而平均寿命随切削用量的变化而波动变化。所提方法综合考虑了切削用量和验前经验,给出的刀具可靠度和平均寿命估计更符合实际加工条件。     

刀具混合三参数Weibull比例危险模型及可靠性评估

机床刀具故障往往是在多种失效原因的共同作用下发生,不同加工时段故障数据分布不同。为了准确评估刀具的可靠性,综合考虑切削用量等因素的影响,采用混合Weibull分布并结合比例危险模型对刀具故障数据进行建模。所得模型参数较多,用马尔科夫链蒙特卡洛仿真方法解决了模型参数估计难题。该方法可给出刀具可靠度、平均寿命、刀具寿命标准差、故障率及平均剩余寿命等可靠性指标。通过对一工程实例进行分析,展示了该模型的应用价值。     

单面切削深孔钻的合理参数

钻削直径在φ22mm以下的深孔广泛地使用装有硬质合金刀片和引导部分的单面切削刀具。它适于向刀具内部输送润滑冷却液,但是它的制造和使用水平还不适宜于采用较大的切削用量。典型结构的单面切削刀具由刀杆和镶有硬质合金块的切削刃与两个引导组成。在刀头上开有输送润滑冷却液的通道,硬质合金块以楔形面同刀杆相联接。刀具的刀杆和整块硬质合金工作部分都采用120°扇形横截面的V形结构,但是这种刀具不能满足提高切削用量的要求。列宁格勒机械学院实验室从对难加工钢深孔钻削进行多次强化试验,得出用刀具的最佳参数来加工直径10～22mm的孔以提高抗振性和工艺可靠性。一种     

刀具寿命变异系数的试验研究

刀具寿命变异系数是评价刀具可靠性的重要指标之一．本文通过切削试验，从工件材料、刀具几何角废、刀具磨钝标准及切削用量等方面全面探讨了影响刀具寿命变异系数的各种因。提出了降低刀具寿命变异系数，提高刀具可靠性达到加工经济性的途径．     

刀具磨损寿命分布规律的现场验证

通过对数控机床加工情况的现场调查，验证了关于刀具磨损寿命分布规律的研究成果，分析了刀具可靠性对切削加工过程的影响，建立了应根据刀具的可靠性来决定换刀间隔和切削用量，并提出了提高刀具可靠性的具体措施。     

基于回归正交设计的刀具磨损研究

通过回归正交试验法设计车削模拟方案,在Deform 3D软件中对车削进行了有限元仿真模拟.建立了车削中车削速度、进给量、背吃刀量与刀具磨损之间的回归方程,并进行了方差分析,验证了模型的可靠度.得出了金属切削过程中刀具磨损量随切削用量的变化规律.分析结果为车削工艺参数优化及建立车削数据库奠定了基础.     

基于枪钻的42CrMo合金钢深孔钻削分析

在深孔钻削加工42CrMo合金钢时,易造成切削温度高、刀具磨损快等问题,从而影响加工质量。针对某传动轴的深孔加工,为得到合适的切削参数、保证技术要求,利用DEFORM-3D有限元分析软件设计正交仿真试验,分析不同切削参数对切削温度和刀具磨损的影响,得到最佳的切削用量。加工结果表明,枪钻用此切削用量进行深孔加工可以满足技术要求,为优化枪钻加工42CrMo合金钢时的切削用量、提高产品质量和降低刀具磨损提供了指导。     

恒定加工条件及定期补偿下的刀具渐变可靠性灵敏度分析方法

据统计,由刀具失效导致的停机时间超过机床被迫停机时间的1/3,故开展刀具渐变可靠性及其灵敏度分析的研究对提高机床的运行可靠性具有重要意义。采用连续时间、连续状态、具有非减独立增量的非平稳Gamma过程描述刀具磨损量的变化过程。根据加工偏差不大于机床给定加工精度的原则,构建刀具制造及磨损量检测有无误差两种情形下、恒定加工条件及定期补偿的刀具渐变状态函数,由此推导出相应的渐变可靠度模型。在此基础上给出渐变可靠度模型对各个参数的灵敏度计算方程。通过数值实例分析,阐述了通过提出的渐变可靠性模型及灵敏度分析方法提高刀具运行可靠性的应用过程。这一工作为提高恒定加工条件及定期补偿下刀具的运行可靠性提供切实可行的理论和方法基础。     

0Cr18Ni9耐热钢车削试验研究

以0Cr18Ni9耐热钢为研究对象进行车削试验,得出切削用量对刀具耐用度的影响规律,确定每种刀具的最佳切削速度,分析了刀具磨损破损机理。     

PCD刀具高速车削高强铝合金切削力仿真

通过回归正交设计和单因素试验设计方案,利用DEFORM-3D有限元仿真软件进行PCD刀具高速车削高强铝合金的切削力仿真;建立了切削力与切削用量之间的预测模型,并通过方差分析验证了模型的可靠性。利用切削用量单因素试验仿真的方法研究了切削用量对切削力的影响规律及其机理;利用刀具参数单因素试验仿真的方法研究了刀具参数对切削力的影响规律及其机理。研究结果为PCD刀具高速车削高强铝合金工艺参数的优选提供了理论依据。     

Dynamic reliability sensitivity of cemented carbide cutting tool

Influence of geometric and cutting parameters of cemented carbide cutting tool on reliability of cutting tool has become more and more mature, yet influence of its physical and material parameters on reliability is still blank. In view of this, cutting test and fatigue crack growth test of YT05 cemented carbide cutting tool are conducted to measure such data as the original crack size, growth size, times of impact loading, number and time of cutting tool in failure, and stress distribution of cutting tool is also obtained by simulating cutting process of tools. Mathematical models on dynamic reliability and dynamic reliability sensitivity of cutting tool are derived respectively by taking machining time and times of impact loading into account, thus change rules of dynamic reliability sensitivity to physical and material parameters can be obtained. Theoretical and experimental results show that sensitive degree on each parameter of tools increases gradually with the increase of machining time and times of impact loading, especially for parameters such as fracture toughness, shape parameter, and cutting stress. This proposed model solves such problems as how to determine the most sensitive parameter and influence degree of physical parameters and material parameters to reliability, which is sensitivity, and can provide theoretical foundation for improving reliability of cutting tool system.     

Statistical model to determine surface roughness when milling hastelloy C-22HS

The aim of this study is to develop the surface roughness prediction models, with the aid of statistical methods, for hastelloy C-22HS when machined by PVD and CVD coated carbide cutting tools under various cutting conditions. These prediction models were then compared with the results obtained experimentally. By using response surface method (RSM), first order models were developed with 95 % confidence level. The surface roughness models were developed in terms of cutting speed, feed rate and axial depth using RSM as a tool of design of experiment. In general, the results obtained from the mathematical models were in good agreement with those obtained from the machining experiments. It was found that the feed rate, cutting speed and axial depth played a major role in determining the surface roughness. On the other hand, the surface roughness increases with a reduction in cutting speed. PVD coated cutting tool performs better than CVD when machining hastelloy C-22HS. It was observed that most of the chips from the PVD cutting tool were in the form of discontinuous chip while CVD cutting tool produced continuous chips.     

基于数控刀具耐用可靠度分析

通过数控加工工艺特点分析,提出数控刀具的技术要求。并分析数控刀具损坏形式,提出了数控刀具的可靠度概念、性质及刀具耐用可靠度,介绍改善数控刀具耐用可靠度的优化要点。     

An accuracy design approach for a multi-axis NC machine tool based on reliability theory

Accuracy design constitutes an important role in machine tool designing. It is used to determine the permissible level of each error parameter of a machine tool, so that any criterion can be optimized. Geometric, thermal-induced, and cutting force-induced errors are responsible for a large number of comprehensive errors of a machine tool. These errors not only influence the machining accuracy but are also of great importance for accuracy design to be performed. The aim of this paper is the proposal of a general approach that simultaneously considered geometric, thermal-induced, and cutting force-induced errors, in order for machine tool errors to be allocated. By homogeneous transformation matrix (HTM) application, a comprehensive error model was developed for the machining accuracy of a machine tool to be acquired. In addition, a generalized radial basis function (RBF) neural network modeling method was used in order for a thermal and cutting force-induced error model to be established. Based on the comprehensive error model, the importance sampling method was applied for the reliability and sensitivity analysis of the machine tool to be conducted, and two mathematical models were presented. The first model predicted the reliability of the machine tool, whereas the second was used to identify and optimize the error parameters with larger effect on the reliability. The permissible level of each geometric error parameter can therefore be determined, whereas the reliability met the design requirement and the cost of this machining was optimized. An experiment was conducted on a five-axis machine tool, and the results confirmed the proposed approach being able to display the accuracy design of the machine tool.     

Improving machinability of Inconel 718 with a new hybrid machining technique

In this paper, by joining three non-traditional machining methods — plasma-enhanced machining, cryogenic machining, and ultrasonic vibration assisted machining — a new hybrid machining technique for machining of Inconel 718 is presented. Cryogenic machining reduces the temperature in the cutting zone, and therefore decrease tool wear and increases tool life, while plasma-enhanced machining helps to increase the temperature in the workpiece to make it softer. Also, applying ultrasonic vibrations to the tool helps to improve cutting quality and to prolong tool life by lowering, mainly, the cutting force and improving the dynamic cutting stability. This study experimentally investigates the effect of cutting parameters on cutting performance in the machining of Inconel 718 and compares the results of hybrid machining and conventional machining (CM). It is found that the hybrid method results in better surface finish and improves tool life in hard cutting at low cutting speeds as compared to the CM method.     

Nonlinear adaptive backstepping control for variable-speed wind energy conversion system-based permanent magnet synchronous generator

Tool wear degradation and working status of slotting cutter have a great effect on the surface quality of rotor slot; therefore, tool condition monitoring and its degradation estimation are needed for guaranteeing slot machining quality. This paper proposes a two-phase method based on acoustic emission (AE) signal classification and logistic regression model for slotting cutter condition monitoring and its degradation estimation. In the first phase, the failure reliability estimation models corresponding to different machining processes are established considering the variability of process system like tool regrinding times and material randomness of workpiece. In the second phase, the most appropriate estimation model corresponding to the optimum cluster is selected and used for failure reliability estimation and status determination of slotting cutter. This approach has been validated on a CNC rotor slot machine in a factory. Experimental results show that the proposed method can be effectively used for cutting tool degradation estimation and status determination of slotting cutter with high accuracy.     

自由曲面5轴数控加工刀位轨迹的生成算法

应用计算几何技术来决定优化的刀具定位和刀具姿态以实现环形刀的5轴自由曲面数控加工。环形刀起切削作用的环形部分曲率半径的变化范围更大,而且刀具姿态随曲率而变化。这些特性使得该方法比平底刀且固定刀具姿态的加工方法更优越。分三部分来实现：①优化刀具定位和刀具姿态。②刀具轨迹规划。③干涉检测。     

Experimental investigation of machining characteristics and chatter stability for Hastelloy-X with ultrasonic and hot turning

Ultrasonic-assisted machining is a machining operation based on the intermittent cutting of material which is obtained through vibrations generated by an ultrasonic system. This method utilizes low-amplitude vibrations with high frequency to prevent continuous contact between a cutting tool and a workpiece. Hot machining is another method for machining materials which are difficult to cut. The basic principle of this method is that the surface of the workpiece is heated to a specific temperature below the recrystallization temperature of the material. This heating operation can be applied before or during the machining process. Both of these operations improve machining operations in terms of workpiece-cutting tool characteristics. In this study, a novel hybrid machining method called hot ultrasonic-assisted turning (HUAT) is proposed for the machinability of Hastelloy-X material. This new technique combines ultrasonic-assisted turning (UAT) and hot turning methods to take advantage of both machining methods in terms of machining characteristics, such as surface roughness, stable cutting depths, and cutting tool temperature. In order to observe the effect of the HUAT method, Hastelloy-X alloy was selected as the workpiece. Experiments on conventional turning (CT), UAT, and HUAT operations were carried out for Hastelloy-X alloy, changing the cutting speed and cutting tool overhang lengths. Chip morphology was also observed. In addition, modal and sound tests were performed to investigate the modal and stability characteristics of the machining. The analysis of variance (ANOVA) method was performed to find the effect of the cutting speed, tool overhang length, and machining techniques (CT, UAT, HUAT) on surface roughness, stable cutting depths, and cutting tool temperature. The results show both ultrasonic vibration and heat improve the machining of Hastelloy-X. A decrease in surface roughness and an increase in stable cutting depths were observed, and higher cutting tool temperatures were obtained in UAT and HUAT compared to CT. According to the ANOVA results, tool overhang length, cutting speed, and machining techniques were effective parameters for surface roughness and stable cutting depths at a 1% significance level (p ≤ 0.01). In addition, cutting speed and machining techniques have an influence on cutting tool temperature at a 1% significance level (p ≤ 0.01). During chip analysis, serrated chips were observed in UAT and HUAT.