加工工艺对7075 铝合金紧固孔表面质量的影响

为确定最佳制孔工艺、获得理想表面特性,从表面完整性和疲劳寿命角度对7075铝合金飞机紧固孔表面质量进行了实验性和数值仿真研究.通过比较常规多步制孔和钻扩铰一步复合工艺(Winslow),发现钻扩铰多步慢进给工艺(DBM)和Winslow所产生的表面具有较小的Ra值,较少的加工缺陷、较大的残余压应力及较高的疲劳强度,而后者的Ra值低于前者60％,疲劳寿命高于前者23％;基于实验数据,建立了切削参数对表面粗糙度和残余应力影响的经验公式;应用数值仿真分析了加工过程中应变和切削温度的变化规律;探讨了Winslow工艺的强化机理;指出适当减少进给量、增加切削速度能够提高紧固孔的表面质量.     

Developing a novel radial ultrasonic vibration-assisted grinding device and evaluating its performance in machining PTMCs

Particle-reinforcing titanium matrix composites(PTMCs) exhibit the sharp raising applications in modern industries owing to its extraordinary physical and mechanical properties. However, the poor grindability and unstable grinding processes due to the existence of TiC particles and TiB short fibres inside PTMCs, leading to the sudden grinding burn and low material removal rate.In this work, a novel radial ultrasonic vibration-assisted grinding(RUVAG) device with a special cross structure was dev...     

Characteristics of surface and subsurface of formed thread parts by axial-infeed thread rolling process

The thread rolling process has been widely applied to manufacture high-performance thread parts. In this process, the evolutions of surface and subsurface are frequently introduced, which affect the working performance of manufactured parts. In this study, an axial-infeed thread rolling process (ATRP) is employed, and the macro-meso surface characteristics under different lubrications and operating conditions are investigated. Moreover, the distributions of microstructure and hardness on the subsurface of formed tooth are analyzed in detail, along with the study of stress state and yield strength change. It is found that the MoS₂ grease is more effective in reducing the surface roughness and defects than the lubrication oil and water-base graphite during the ATRP process. Increasing rolling speed improves the quality of surface morphology and can reduce the surface roughness. On the subsurface of bottom and flank, intensive shear stress occurs in a narrow region, resulting in the elongation and refinement of the grains and increasing the low angle grain boundary fraction. Based on the grain size and plastic strain, the yield strength is predicted. The maximum yield strength and hardness on the bottom of formed tooth are improved by 41.2% and 39.4%, respectively.     

S-A模型在分离流动模拟中的改进

基于湍流不平衡性的分析,通过修正雷诺应力以及模型系数的计算,提高了S-A模型在二维边界层以及三维叶栅的分离流动上的预估能力。修正后的S-A模型给出了与实验吻合较好的结果,在对于分离流动的预估能力上优于原始模型。     

Performance evaluation of creep feed grinding of γ-TiAl intermetallics with electroplated diamond wheels

This paper evaluates the performance of creep feed grinding γ-TiAl intermetallic (Ti-45Al-2Mn-2Nb) using electroplated diamond wheels. Firstly, a comparative analysis with the grinding results by using electroplated CBN wheels was conducted, mainly involving abrasive wheel wear behavior and maximum material removal rate below surface burn limit. It was found that the diamond wheel would produce much better grinding results including lower wheel wear rate and higher maximum material removal rate. Then the surface integrity obtained at different level of material removal rate was characterized with the utilization of the diamond wheel. The poor ductility of this γ-TiAl intermetallic material was found to have a marginal effect on the surface integrity, as no severe surface defects such as material pullout were generated during the stable wheel wear stage. For the involved operating parameters, a deformation layer was produced with ∼10 μm or more in thickness depending on the material removal rate used. Meanwhile, a work-hardened layer extending to more than 100 μm was produced with a maximum microhardness of above 520 HV_0.05 (bulk value 360 HV_0.05). The residual stress remained compressive, with a value of above −100 MPa and even up to −500 MPa for an elevated material removal rate. Shearing chip was the main chip type, indicating good wheel sharpness in the grinding process.     

空空导弹的攻击区与截获区

空空导弹的综合性能一贯以“攻击区”表示。现代火控技术采用了离轴瞄准、发射,提出了三种追踪方式(前置、后置及纯追踪),并用“截获区”表示。研讨了“攻击区”“截获区”的确定方法,建立了数学模型,作了算例,讨论了计算结果。     

线接触零件部分热弹流润滑油膜厚度公式

采用弹性流体动力润滑理论和部分弹性流体动力润滑理论的分析方法,对弹流及部分弹流润滑线接触问题进行数值求解。通过联立求解结果,分析了接触表面间油膜厚度随载荷、滚动速度、滑滚比和进油温度等因素的变化规律,获得不同工况条件下的油膜厚度值,并依此提出一种新的油膜厚度公式。新公式考虑了热效应及表面粗糙效应影响,可用于高温、高速、重载工况。计算结果比Dowson-Higginson油膜厚度公式更符合于实验数据。     

升力面方法在冲压空气涡轮性能计算中的应用

应用现代螺旋桨升力面元方法计算冲压空气涡轮的气动性能,叶片采用单层涡模型,尾涡采用与Goldstein假设一致的刚性尾涡,将螺旋马蹄尾涡视为开口涡环以便于编程。对一个模型冲压空气涡轮作数值计算,在小负荷和较大负荷工况下风能利用系数均与实验值符合的较好,涡元控制点的诱导速度和环量分布合理。      

阻尼器-滑动轴承-转子系统的非谐调运动及突跳特性分析

挤压油膜阻尼器—滑动轴承—柔性转子系统是一类强的非线性动力系统,其中包含一些复杂的非线性现象,文中主要对系统的非谐调运动、突跳行为进行了理论分析。研究表明：系统存在二次Ｈｏｐｆ分岔,并导致准周期运动;存在重复的倍周期分岔,导致次谐运动;突跳是鞍—结分岔产生的结果。     

Vibration suppression of thin-walled workpiece machining considering external damping properties based on magnetorheological fluids flexible fixture

Milling of the thin-walled workpiece in the aerospace industry is a critical process due to the high flexibility of the workpiece. In this paper, a flexible fixture based on the magnetorheological(MR) fluids is designed to investigate the regenerative chatter suppression during the machining.Based on the analysis of typical structural components in the aerospace industry, a general complex thin-walled workpiece with fixture and damping constraint can be equivalent as a rectangular cantilever beam. On the basis of the equivalent models, natural frequency and mode shape function of the thin-walled workpiece is obtained according to the Euler–Bernoulli beam assumptions. Then,the displacement response function of the bending vibration of the beam is represented by the product of all the mode shape function and the generalized coordinate. Furthermore, a dynamic equation of the workpiece-fixture system considering the external damping factor is proposed using the Lagrangian method in terms of all the mode shape function and the generalized coordinate, and the response of system under the dynamic cutting force is calculated to evaluate the stability of the milling process under damping control. Finally, the feasibility and effectiveness of the proposed approach are validated by the impact hammer experiments and several machining tests.