声发射在微铣削过程中监测刀具破损的应用

应用声发射传感器对微铣削过程中的刀具状态进行监测。通过结合传声器传感器,利用小波分析,声发射传感器能更精确有效地监测刀具破损的现象。分别在几种不同的工件材料进行了声发射监测实验。通过该声发射监测刀具破损技术采集得到信号,再利用小波分析对实验数据分析。结果表明,在微铣削中利用声发射信号来监控刀具状态的可行性。     

涡轮叶片蠕变损伤行为及固溶处理对叶片材料性能的影响

涡轮叶片是航空发动机及地面燃气轮机的重要热端部件,研究其损伤行为对涡轮叶片的制造及修复工作均有重要的意义。本文研究了长时与短时服役涡轮叶片的蠕变损伤行为,发现二者在蠕变空洞的形成机理上大致相同,而γ′相与碳化物的退化反应则有所差异,长时服役涡轮叶片的γ′相形貌更加粗大且不规则。对于碳化物,长时服役叶片的碳化物发生了由一次MC型向二次M23C6型的分解,而短时服役叶片的碳化物发生了由MC(1)型向MC(2)型的转化。此外,针对两种不同的叶片材料(K002和GTD-111高温合金),研究了不同的固溶处理制度对γ′相溶解行为的影响,发现提高固溶温度和增加固溶保温时间可以促进两种材料γ′相的溶解行为;而随着固溶时间的增加,两种材料的溶解激活能均逐渐增大,K002合金在不同固溶保温时间中的溶解激活能均大于GTD-111合金。     

热解碳界面层与国产T300 增韧SiC 复合材料拉伸性能关联性初探

在国产T300碳纤维上沉积不同厚度的热解碳形成界面层,通过前驱体浸渍裂解工艺制备“迷你”Cf/SiC复合材料,考察了T300碳纤维在相同工艺过程中其界面层厚度的最优工艺参数,并研究了热解碳界面层与“迷你”复合材料拉伸性能的关联性.采用SEM与Raman手段对Cf/SiC复合材料进行结构表征.结果表明:该复合材料有明显的裂纹偏转,经高温热处理后界面层状结构更加明显,其复合材料的拉伸强度随热解碳厚度的增加其值有先增加后减小的趋势(PyC的厚度在0～150 nm),当界面层厚度约为60 nm时达到最大值(1 385.7 MPa).     

A novel method for solving shortest tool length based on compressing 3D check surfaces relative to tool postures

Solving the shortest tool length quickly under a known tool trajectory in multi-axis machining of complex channel parts is an urgent problem in industrial production. To solve this problem, a novel and efficient method is proposed which is featured by extracting only a few necessary curves from the check surface instead of sampling the entire surface. By rotating and compressing the 3D check surface relative to all tool postures, the boundaries of the area occupied by the 2D compressed surfaces are the essential elements for determining the shortest tool length. A tracking-based numerical algorithm is introduced to efficiently solve the silhouette curves which are formed in compressing. To define the multi-taper shaped tool holding system (THS) which is commonly used in production, a characterization model for THS profile is established. A model for solving the shortest tool length is finally constructed based on the critical interference relationship between the THS profile and all compressed boundary curves. For acceleration, the boundary splines are segmented according to their knot vectors. Then a new concept called the axis-aligned tool length box (AATB) is introduced, which can provide a conservative range of tool length for a spline segment. By scanning the AATBs of all spline segments, the very few effective spline segments that may ultimately determine the shortest tool length are filtered out. This acceleration method makes the solution for the shortest tool length more focused and efficient. The results of experimental examples are also reported to validate the efficiency and accuracy of the proposed algorithm.     

Design and development of a five-axis machine tool with high accuracy,stiffness and efficiency for aero-engine casing manufacturing

In order to satisfy the machining requirements of aero-engine casing in modern aviation industry, this paper investigates three main issues during the design and development process of a five-axis machine tool with high accuracy, stiffness and efficiency, including whole structure design,key components design, and supporting stiffness design. First, an appropriate structure of five-axis machine tool is determined considering the processing characteristics of aero-engine casing. Then, a dual driv...     

新型碳化硅先驱体的制备及其性能研究

采用溶胶凝胶法，以正硅酸乙酯和酚醛树脂为原料，在草酸和六次甲基四胺的催化作用下，制备出了不含硫和氯等有害杂质的均相碳化硅先驱体，并在特定条件下，对所得先驱体进行烧结，使之转化为陶瓷。结果表明，溶胶凝胶法制得的先驱体呈黄色透明的玻璃态，其微观组成为几十纳米的微粒，树脂与SiO2可能通过氢键相互作用，有利于树脂在先驱体中均匀分布而形成均相先驱体，其陶瓷产率为78％；另外硝酸镍的加入对先驱体烧结过程中β-SiC的生成起到明显的促进作用。     

涂层刀具低温铣削SiCp/Al复合材料表面质量研究

在加工过程中,相反的两相特性增加了 SiCp/Al复合材料加工难度,难以获得良好的表面质量.为了提高其切削性能,本文开展20vol％SiCp/Al复合材料铣削加工试验研究,比较常温和低温条件下TiAlN涂层和TiAlSiN涂层两种铣刀的切削性能.结果表明,在低温条件下,两种刀具的切削力增加,铣削后表面铝基体的开裂及剥落...     

Elliptical vibration cutting of large-size thin-walled curved surface parts of pure iron by using diamond tool with active cutting edge shift

Large-size thin-walled curved surface parts of pure iron are crucial in aerospace, national defense, energy and precision physical experiments. However, the high machining accuracy and surface quality are difficult to achieve due to the serious tool wear and deformation when machining the parts with conventional cutting tools. In this paper, an elliptical vibration cutting (EVC) with active cutting edge shift (ACES) based on a long arbor vibration device is proposed for ultra-precision machining the pure iron parts by using diamond tool. Compared with cutting at a fixed cutting edge, the influence of ACES on the EVC was analyzed. Experiments in EVC of pure iron with ACES were conducted. The evolutions of the surface roughness, surface topography, and chip morphology with tool wear in EVC with ACES are revealed. The reasonable parameters of ultra-precision machining the pure iron parts by EVC with ACES were determined. It shows that the ACES has a slight influence on the machined surface roughness and surface topography. The diamond tool life can be significantly prolonged in EVC of pure iron with ACES than that with a fixed cutting edge, so that high profile accuracy and surface quality could be obtained even at higher nominal cutting speed. A typical thin-walled curved surface pure iron part with diameter ∅240 mm, height 122 mm, and wall thickness 2 mm was fabricated by the presented method, and its profile error and surface roughness achieved PV 2.2 μm and Ra less than 50 nm, respectively.