变截面涡旋盘齿面粗糙度的双预测模型

目的精确预测三段基圆变截面涡旋盘齿面粗糙度,确定合理的铣削参数,提高变截面涡旋盘齿面的加工质量。方法首先在正交试验的铣削参数条件下,用XK714数控铣床对毛坯件进行铣削加工,获得三段基圆变截面涡旋盘,用SJ-210表面粗糙度测量仪测量已加工涡旋齿侧面的粗糙度值。然后利用铣削参数和测量的粗糙度值,建立齿面粗糙度的多元回归预测模型和改进的BP神经网络预测模型及双预测模型,并验证该三种模型的精确度。最后对单一因素条件下的粗糙度进行预测、分析。结果经过计算可得,齿面粗糙度的多元回归预测模型的平均误差为1.43%,最大误差为3.09%。改进的BP神经网络预测模型的平均误差为1.33%,最大误差为3.22%。两种模型的预测平均值作为双预测模型时,预测平均误差为0.627%,最大误差为1.51%。结论齿面粗糙度的双预测模型的平均误差明显降低,同时可以避免单一预测模型产生主观预测误差。各铣削因素对粗糙度的影响程度不同,进给量fz吃刀深度ap刀具转速n侧吃刀量ae。随着进给量、吃刀深度、侧吃刀量的增加,齿面粗糙度值增加;随着刀具转速升高,齿面粗糙度值降低。     

纵扭复合超声端面铣削表面微结构建模与试验研究

目的 对纵扭复合超声端面铣削加工表面微结构进行预测,以优化加工参数。方法 对纵扭复合超声端面铣削进行运动学分析,并在其基础上建立三维运动轨迹方程。对刀尖轨迹仿真,且研究该运动方式下的加工特性。通过对切削刃和工件离散化建立纵扭复合超声端面铣削表面微结构理论模型,并利用MATLAB进行三维表面仿真。对TC4钛合金进行超声振动切削试验。结果 理论仿真和切削试验结果均表明超声纵扭端面铣削时,随振幅的增加,由振动引起的表面微观结构特征愈加明显。扭纵幅值比增大时,加工表面微观结构凹坑效应弱化,At/Al=0.55时,加工表面呈条形片状微观结构。振动频率和主轴转速会影响表面微观结构单元的疏密程度。结论 加工表面微结构的生成与振动频率、振幅、扭纵复制比、切削速度等加工参数相关,铣削实验得到的加工表面变化趋势与表面理论模型吻合,该表面模型能够优化超声加工参数。     

Production of Ag−ZnO powders by hot mechanochemical processing

Ag–CdO composites are still one of the most commonly used electrical contact materials in low-voltage applications owing to their excellent electrical and mechanical properties. Nevertheless, considering the restriction on using Cd due to its toxicity, it is necessary to find alternative materials that can replace these composites. In this study, the synthesis of Ag?ZnO alloys from Ag?Zn solid solutions was investigated by hot mechanochemical processing. The hot mechanochemical processing was conducted in a modified attritor mill at 138 °C under flowing O₂ at 1200 cm³/min for 3.0 h. The microstructure and phase evolution were investigated using X-ray diffractometry, field emission gun scanning electron microscopy and transmission electron microscopy. The results suggest that it is possible to complete the oxidation of Ag?Zn solid solution by hot mechanochemical processing at a low temperature and short time. This novel synthesis route can produce Ag?ZnO composites with a homogeneous distribution of nanoscale ZnO precipitates, which is impossible to achieve using the conventional material processing methods. Considering the fact that the fundamental approach to improving electric contact material performance resides in obtaining uniform dispersion of the second-phase in the Ag matrix, this new processing route could open the possibility for Ag?ZnO composites to replace non-environmentally friendly Ag?CdO.     

Fe掺杂及球磨处理对Sm_2Co_(17)合金结构和磁性的影响

用电弧熔炼法制备Sm2(FexCo1-x)17(x=0,0.3和0.7)母合金锭,均匀化退火后采用球磨方法制备纳米晶合金粉末。研究了Fe掺杂及球磨处理对Sm2(FexCo1-x)17合金结构、居里温度及永磁性能的影响。实验结果表明,随着Fe含量增多,合金中1∶5相逐渐减少,当x=0.7时,形成单相2∶17型化合物,同时居里温度从938℃(x=0)下降到590℃(x=0.7)。球磨处理过程有利于形成单相2∶17纳米合金粉,饱和磁化强度随着球磨时间的增加逐渐增大,同时内禀矫顽力和磁能积与球磨时间的关系呈两头下降的趋势。球磨时间在0.5~1 h时,纳米合金粉末的永磁磁性能达到最佳,Sm2Co17的最佳磁性能为4πMs=0.65 T,iHc=246.8 k A/m,(BH)max=25.5 k J/m3。     

Low‐cost dye‐sensitized solar cells with ball‐milled tellurium‐doped graphene as counter electrodes and a natural sensitizer dye

This paper presents a facile and economic development of dye‐sensitized solar cells using a nonprecious counter electrode made from ball‐milled tellurium‐doped graphene (Te‐Gr) and a natural sensitizer extracted from Calotropis gigantea leaves. The prepared materials were characterized using various techniques, such as Raman spectroscopy, X‐ray diffraction (XRD), atomic force microscopy (AFM), impedance spectroscopy, and scanning electron microscopy with built‐in energy‐dispersive X‐ray spectroscopy (SEM with EDS). The electrochemical activity of the produced counter electrodes and the impedance of the fabricated cells were examined and discussed to devise plans for future enhancement of cell performance. A clear pattern of improvement was found when using cost‐effective Te‐Gr relative to the costly platinum counter electrodes, especially when compared with cells employing another natural sensitizer. The results show approximately 51% enhancement over chlorophyll‐based cells made from spinach, where the added advantage in our approach is the utilization of an abundant plant extract with little nutritional appeal.     

Effect of milling on the anisotropic grain growth in a sintered Ba5Nb4O15 specimen and its effect on microwave dielectric properties

In this study, relationships between the processing, microstructure, and properties of barium niobate (Ba₅Nb₄O₁₅) are investigated. The milling of a Ba₅Nb₄O₁₅ powder in water is effective with respect to size reduction. However, after milling in water, BaCO₃ is formed within the slurry. With the increase in the amount of BaCO₃ formed, the aspect ratio of the elongated Ba₅Nb₄O₁₅ grains increases. The formation of the elongated Ba₅Nb₄O₁₅ grains prohibits the densification. Hence, the microwave dielectric properties, including permittivity and quality factor, are poor because of the low density. In addition, milling in ethanol is carried out for comparison: A lower amount of BaCO₃ is formed after milling in ethanol; the extent of anisotropic grain growth is thus reduced.     

Exothermic reaction characteristics of continuously ball-milled Al/Ni powder compacts

Self-propagating reactions in compacted pellets of continuously low-energy ball-milled aluminium (Al) and nickel (Ni) powders at a composition corresponding to AlNi₃ were investigated. The formation of a bi-modal structure with nanoscale lamellae of Al and Ni surrounding thicker Ni layers was observed. The milled powder sizes decreased for milling durations longer than 4 h, but the pellet green densities remained mostly constant for longer than 2 h of milling. The ignited pellets observed using high-speed optical and infrared imaging revealed that the thermal wave velocity, maximum reaction temperature, ignition initiation duration and ignition temperature decreased with increasing milling times due to solid-state diffusion. X-Ray Diffraction (XRD) analysis after ignition tests showed that the AlNi₃ amount increased with milling time. Thermal analysis using interrupted Differential Scanning Calorimetry (DSC) in combination with XRD revealed that the ball-milled pellets have similarities to nanoscale magnetron sputtered multilayer foils in terms of phase formation sequence and exothermic peak shifts.     

Optimal control for chatter mitigation in milling—Part 2: Experimental validation

The productivity of milling operations in chatter-free conditions can be improved using active structural methods. This paper presents the use of a mechatronic system integrated into the spindle unit combined with two different optimal control strategies. The first one aims to minimize the influence of cutting forces on tool tip deviations. The second one explicitly considers the process interaction and attempts to stabilize the overall closed-loop system for specific machining conditions. The first part of this two-part paper describes the modeling and formulation used for both strategies. In this second part, the experimental validation of the proposed concept is presented.     

薄壁零件高速铣削加工变形模型及变形规律研究

针对集中载荷作用下薄壁零件(两邻边固定、两邻边自由的矩形)的变形问题建立静态铣削力模型。利用ANSYS 14.0有限元软件进行仿真加工,研究了铝合金薄壁件在数控铣削过程中切削力不变时,零件在长度和高度方向的变形情况以及不同铣削力对变形的影响。得出薄壁零件在顺铣过程中的变形规律并提出了预防措施。