圆柱内壁件下压装配机械手结构实现及弹簧参数优选

根据特定产品生产工艺要求,设计了一种用于圆柱内壁件作业的内撑式抓取与下压装配机械手。该机械手在手指系统与筒状手掌之间采用弹性连接。在高速作业过程中,这类弹性连接形成手指系统的残留振动。在对机械手结构设计思想与结构介绍的基础上,对机械手系统采用Adams运动仿真,分析了弹簧系统参数对手指系统的残留振动的影响,并对影响机械手振动特性的关键参数——连接弹簧的参数进行了优化选择。实际机械手的运行结果表明,该机械手结构与弹性参数的选择可以很好地满足特定对象的作业要求。     

Accuracy evaluation of machine tools by modeling spherical deviation based on double ball-bar measurements

In this study, the accuracy of a machine tool was evaluated by modeling the spherical deviation based on double ball-bar measurements under unloaded conditions. Circular measurement paths on the XY-, YZ-, and ZX-planes were planned, and three linear axis drives were commanded to follow the paths describing a nominal sphere. The spherical deviation, defined as the maximum radial range of deviations around a least-squares sphere, is affected by the accuracies of the three linear axes together. Therefore, the spherical deviation represents the accuracy of machine tools by quantifying the effect of the accuracies of three linear axes, whereas the circular deviation only quantifies the accuracies of two linear axes among the three linear axes. In this experimental study, spherical deviations of vertical/horizontal machine tools were measured and analyzed under various nominal lengths of a double ball-bar for various feed rates. The measurement uncertainty of the measured spherical deviation was investigated to determine the confidence interval.     

Microstructural evolution and mechanical properties of a β-solidifying γ-TiAl alloy densified by spark plasma sintering

This study deals with the densification of a pre-alloyed Ti–44Al–6Nb–1Mo–0.2Y–0.1B (at.%) powder by spark plasma sintering (SPS). The powder was produced by a plasma rotating electrode process (PREP), and then SPS densified at temperatures between 1200 and 1320 °C. At SPS temperatures below 1240 °C, the α₂-dominated dendritic structure in the PREP powder particles disappeared and the fully dense microstructure mainly consisting of γ and B2 grains formed during SPS, but several original powder particle boundaries (OPBs) still remained. While sintered above 1240 °C, OPBs vanished entirely and an uniform duplex microstructure emerged. Furthermore, fully-lamellar (FL) microstructure with mean colony size smaller than 20 μm was produced via β-homogenization annealing. This FL microstructure renders a good tensile elongation of 1.25% and yield strength of 665 MPa at room temperature. However, instability of α₂/γ lamellar structures was induced by final stabilization annealing, resulting in sharp reduction of both room-temperature ductility and high-temperature strength.     

Machining accuracy improvement for a dual-spindle ultra-precision drum roll lathe based on geometric error analysis and calibration

This paper performs a comprehensive analysis and calibration on the geometric error of the ultra-precision drum roll lathe with dual-spindle symmetrical structure and cross slider layout. Firstly, the volumetric error model which contains all geometric errors of the dual-spindle ultra-precision drum roll lathe (DSUPDRL) is developed based on the combination of the homogenous transfer matrix (HTM) and multi-body system (MBS) theory. Secondly, sensitivity analysis for the volumetric error model is conducted to identify the sensitive geometric error components of the DSUPDRL using an improved Sobol method based on the quasi-Monte Carlo algorithm. The result of sensitivity analysis laid the foundation for the subsequent geometric error calibration. Then, some sensitive error components along the X and Z directions are calibrated using a laser interferometer and a pair of inductance displacement probes. Besides the volumetric error model, the concentricity error caused by dual-spindle symmetrical structure is proposed and calibrated by the on-machine measurement using a classic reversal method. Finally, a large-scale roller mold with a diameter of 250 mm and a length of 600 mm is machined using the DSUPDRL after calibration. The experimental result shows that 1.4 μm/600 mm generatrix accuracy is obtained, which validate the effectiveness of the geometric error analysis and calibration.     

Effect of ultrafine gradient cemented carbides substrate on the performance of coating tools for titanium alloy high speed cutting

Gradient cemented carbides usually used as substrate for coating tools, and the substrate has different gradient layer thickness and grain size, which would affect the cutting performance of the coating tools. In this study, different contents of Co and cubic carbonitride were added, the ultrafine gradient cemented carbides with different gradient layer thickness and grain size were prepared by one-step sintering, and then the CAT films (films containing Cr, Al and Ti, basically.) were deposited on alloy surface by Arc Ion Plating (AIP) in Ar gas atmosphere for titanium alloy high-speed cutting. The influence of Co and cubic carbonitride content on the microstructure of alloy and the cutting performance of coated tools was studied. The results show that the gradient layer thickness could be controlled by changing the Co and cubic carbonitride contents, and then affected the cutting performance. The coating tools enhanced cutting performance obviously by reducing the flank wear in the high-speed Ti-alloy cutting. A thinner gradient layer can be formed in alloys that with a lower Co addition, thus leading to tools chipping during high-speed cutting Ti-alloy. The wear resistance and the cutting performance of the tools could be improved by adding cubic carbonitride. The Co10Ti3-CAT coated tool has the best cutting performance. And the wear resistance of Co8Ti4-CAT coated tool can be increased by 50% compared to substrate.     

基于改进模糊熵和灰关系的滚动轴承性能退化评估

针对模糊熵在提取滚动轴承性能退化特征时敏感度较低的问题,提出了一种基于类Sigmoid函数的改进模糊熵,并将其用于滚动轴承退化特征提取.针对传统的滚动轴承性能退化评估方法局部化的问题,提出了一种基于灰关系的滚动轴承性能退化评估方法,该方法使用灰关系理论评估提取的滚动轴承退化特征与可靠性之间的关系,从而达到从滚动轴承可靠...     

玻璃沉积物对La2Ce2O7/YSZ涂层高温下热冲击性能的影响

目的 为了探究玻璃沉积物CMAS(CaO-MgO-Al2O3-SiO2)对新型结构热障涂层在1250 ℃下的热冲击寿命的影响,揭示热障涂层的失效行为。方法 通过火焰喷涂技术将制备的CMAS粉体均匀地沉积到铈酸镧/氧化钇部分稳定二氧化锆双陶瓷层热障涂层(LC/YSZ DCL-TBCs)和梯度热障涂层(LC/YSZ FGM-TBCs)的表面,于1250 ℃热冲击实验中进行涂层样品的抗热冲击性能及失效机理研究。利用扫描电镜(SEM)和能谱仪(EDS)追踪CMAS的位置,观察CMAS与涂层反应层的厚度与形貌。采用X射线衍射仪(XRD)测试反应层产物,并总结其失效方式。结果 高温热冲击结果显示梯度涂层的热冲击寿命(435次)远高于双陶瓷层热障涂层的寿命(229次),约为铈酸镧/氧化锆双陶瓷层热障涂层寿命的1.9倍。铈酸镧层与梯度层都能在一定程度上阻碍CMAS渗入涂层内部,提高其CMAS腐蚀条件下的热冲击寿命。双陶瓷层热障涂层与梯度热障涂层的失效均是以层状剥落为主,剥落层主要是CMAS与LC的反应层以及反应层下的烧结层,反应层是由Ca2(LaxCe1-x)8(SiO4)6O6-4x、萤石相和MgAl2O4等难熔氧化物组成,这层致密氧化物类似于密封层,能阻止CMAS继续渗入。结论 功能梯度结构具有比双陶瓷层结构更优异的抗CMAS热冲击性能和更好的应力耐受性。     

基于GA–BP神经网络的汽车内饰板虚拟制造研究

目的 以某汽车内饰板为研究对象进行虚拟制造,以提前得到相对准确的工艺参数并减少成形缺陷的产生。方法 研究了工艺参数对产品拉延成形质量的影响,并确定了拉丁超立方抽样区间,在抽样区间内抽取60组样本数据,以最大减薄率为目标值,以前50组样本数据为测试集、后10组样本数据为预测集,使用基于GA–BP神经网络的遗传算法得到最优工艺参数,并将其代入有限元分析软件DYNAFORM中进行虚拟制造。结果 训练后GA–BP模型的预测值与期望值最大误差为0.299 7%,最大预测误差率为1.747 38%;遗传算法预测的最大减薄率为16.548%,虚拟制造得到的减薄率为16.167%,虚拟制造值与预测值的大小仅相差0.318%,仿真误差的误差率为2.36%。结论 虚拟制造结合先进算法的优化方法可以指导后续生产。     

基于数字孪生的产品设计过程和工作量预测方法

为解决由于实际产品设计过程和理想的仿真过程状态不一致而导致的产品设计复杂性预测不准确的问题,研究了基于数字孪生的产品设计过程及其工作量预测方法.构建了产品设计数字孪生系统五维结构模型.详细定义了虚拟空间的产品设计数字孪生模型,包括功能数字孪生模型、设计师数字孪生模型和设计活动数字孪生模型.从知识的角度出发,提出了产品设...     

Optimization of concrete hollow brick using hybrid genetic algorithm combining with artificial neural networks

A structure optimization of concrete hollow brick with four rectangle enclosures is carried out to minimize the equivalent thermal conductivity (ETC) in the constraint of variable shape and position parameters. During the optimization hybrid genetic algorithm (HGA) is developed combining with artificial neural networks (ANN). The modified Latin hypercube sampling (i.e. the maximum minimum distance criterion) is employed to make a robust decision. The ETC of the samples is computed using the finite volume method (FVM) on the basis of 3D multi-mode heat transfer simulation. It indicates that the well-trained ANN can accurately predict the ETC of the concrete hollow brick which matches very well with data obtained from the FVM simulation. The optimization obtains 21.69% improvement on the ETC for the given range of design parameters. The optimized concrete hollow brick owns the largest void volume fraction, the minimum rid and wall thickness, same width of the enclosure, and the optimum staggered arrangement with two same large enclosures and two same small enclosures, which is resulted by the multi-mode heat transfer characteristic of the concrete hollow brick. A novel method of the optimum concrete hollow is proposed to construct new concrete hollow brick with many rows of enclosures. Relative Staggered Ratio (RSR) is used to discuss the effect of the staggered form. By combining two or more rows of the optimized enclosures to one brick with the same size the efficiency to block heat transfer is evidently improved. It is concluded by the present work that the combination of ANN and HGA and the popularizing method are powerful to the optimization of the concrete hollow brick.