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排序方式: 共有140条查询结果,搜索用时 218 毫秒
71.
电火花-电解复合穿孔(ECDD)加工方法有望实现难加工材料涡轮叶片气膜冷却孔无重铸层高效加工,为了进一步提升小孔孔壁的加工质量,提出了在工件底部填充冰层的电火花-电解复合穿孔加工新方法。分析了冰层辅助对复合加工过程中两极之间电流电压的波形、复合穿孔的加工效率、小孔的出入口孔径、孔壁重铸层去除等的影响,进行了冰层辅助与无冰层辅助电火花-电解复合穿孔对比试验。试验表明:冰层辅助加工可以在小孔穿透之后形成充分的反向冲液,有效地解决小孔穿透之后的漏液问题。在增加底部停顿时间的基础上,即小孔穿透后管电极到达预设深度继续停留一段时间,延长管电极对孔壁的电解作用时间,可以显著提高重铸层的去除效果,有望实现小孔整个孔壁重铸层的完全去除。 相似文献
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根据电火花细微孔加工的工艺特点,研制了以大功率场效应管为开关器件的独立式适应控制微能脉冲电源。在进给控制系统上增加了自适应控制环,实现开路快速进给,短路和拉弧快速回退电极并切断脉冲电源的功能。应用不同的电规准及工艺条件进行微孔加工实验,获得了一些工艺规律的初步结果。 相似文献
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为提高某典型蒙皮框桁结构产品端框钻导孔的工作效率,提出去除用样板划桁条轴线、改用在端框钻孔机上钻桁条定位孔的方法,考虑程序可读性和运行时不易出错,选用分开钻铆钉底孔和桁条定位孔的方案。根据实际装配情况对桁条定位孔进行轴向偏差补偿,并设计钻划一体式刀,在钻桁条定位孔时进行划窝,整体效率提升1.3倍。 相似文献
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通过灌河大桥22号试桩的静载试验,研究了湿作业成孔钻孔灌注桩的时间效应。该工程运用了桩端后压浆技术,为研究压浆前后桩的承载性能的变化,试验采用了自平衡方法,在桩身设置了双荷载箱,并分别在压浆前后进行了试验。该桩的上段桩不受桩端后压浆的影响,对比该桩的上段桩在不同时间的试验结果,其极限承载力和刚度随时间增长,证实了湿作业成孔的钻孔灌注桩存在时间效应。湿作业成孔钻孔灌注桩的时间效应的机理复杂,分析表明,其受桩周应力场变化、桩周土体性质、泥皮变化和桩底沉渣性质等多种因素的影响。 相似文献
79.
Drilling load modeling and validation based on the filling rate of auger flute in planetary sampling 总被引:1,自引:0,他引:1
Some type of penetration into a subsurface is required in planetary sampling. Drilling and coring, due to its efficient penetrating and cuttings removal characteristics, has been widely applied in previous sampling missions. Given the complicated mechanical properties of a planetary regolith, suitable drilling parameters should be matched with different drilling formations properly. Otherwise, drilling faults caused by overloads could easily happen. Hence, it is necessary to estab-lish a drilling load model, which is able to reveal the relationships among drilling loads, an auger's structural parameters, soil's mechanical properties, and relevant drilling parameters. A concept for the filling rate of auger flute (FRAF) is proposed to describe drilling conditions. If the FRAF index under one group of drilling parameters is less than 1, this means that the auger flute currently removes cuttings smoothly. Otherwise, the auger will be choked with compressed cuttings. In dril-ling operations, the drilling loads on the auger mainly come from the conveyance action, while the drilling loads on the drill bit primarily come from the cutting action. Experiments in one typical lunar regolith simulant indicate that the estimated drilling loads based on the FRAF coincide with the test results quite well. Based on this drilling load model, drilling parameters have been opti-mized. 相似文献
80.
R. Duffard K. Kumar S. Pirrotta M. Salatti M. Kubínyi U. Derz R.M.G. Armytage S. Arloth L. Donati A. Duricic J. Flahaut S. Hempel A. Pollinger S. Poulsen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
We propose a dual-rendezvous mission, targeting near-Earth asteroids, including sample-return. The mission, Asteroid Sampling Mission (ASM), consists of two parts: (i) flyby and remote sensing of a Q-type asteroid, and (ii) sampling of a V-type asteroid. The targeted undifferentiated Q-type are found mainly in the near-Earth space, and to this date have not been the target of a space mission. We have chosen, for our sampling target, an asteroid from the basaltic class (V-type), as asteroids in this class exhibit spectral signatures that resemble those of the well-studied Howardite–Eucrite–Diogenite (HED) meteorite suite. With this mission, we expect to answer specific questions about the links between differentiated meteorites and asteroids, as well as gain further insight into the broader issues of early Solar System (SS) evolution and the formation of terrestrial planets. To achieve the mission, we designed a spacecraft with a dry mass of less than 3 tonnes that uses electric propulsion with a solar-electric power supply of 15 kW at 1 Astronomical Unit (AU). The mission includes a series of remote sensing instruments, envisages landing of the whole spacecraft on the sampling target, and employs an innovative sampling mechanism. Launch is foreseen to occur in 2018, as the designed timetable, and the mission would last about 10 years, bringing back a 150 g subsurface sample within a small re-entry capsule. This paper is a work presented at the 2008 Summer School Alpbach,“Sample return from the Moon, asteroids and comets” organized by the Aeronautics and Space Agency of the Austrian Research Promotion Agency. It is co-sponsored by ESA and the national space authorities of its Member and Co-operating States, with the support of the International Space Science Institute and Austrospace. 相似文献