用任意空间曲线控制的复杂组合曲面数控加工算法研究

提出了一种基于参数曲面三角化的复杂曲面刀具轨迹生成方法。即利用给定的任意空间曲线作为控制边界,构造新的参数曲面,在此简单参数曲面上生成刀具轨迹。离散化复杂组合曲面为若干平面三角片,投影已生成的刀具轨迹到平面三角片上,再考虑加工精度、余量、干涉等,便可得到复杂组合曲面的刀具轨迹。根据该方法还可以获得指定加工区域的刀轨。     

Tool wear during high speed turning in situ TiCp/TiBw hybrid reinforced Ti-6Al-4V matrix composite

Chipping, adhesive wear, abrasive wear and crater wear are prevalent for both the polycrystalline diamond(PCD) and the carbide tools during high speed turning of TiC_p/TiB_w hybrid reinforced Ti-6Al-4V(TC4) matrix composite(TMCs). The combined effects of abrasive wear and diffusion wear caused the big crater on PCD and carbide tool rake face. Compared to the PCD, bigger size of crater was found on the carbide tool due to much higher cutting temperature and the violent chemical reaction between the Ti element in the workpiece and the WC in the tool.However, the marks of the abrasive wear looked much slighter or even could not be observed on the carbide tool especially when low levels of cutting parameters were used, which attributes to much lower hardness and smaller size of WC combined with more significant chemical degradation of carbide. When cutting TC4 using PCD tool, notch wear was the most significant wear pattern which was not found when cutting the TMCs. However, chipping, adhesive wear and crater wear were much milder when compared to the cutting of titanium matrix composite. Due to the absence of abrasive wear when cutting TC4, the generated titanium carbide on the PCD protected the tool from fast wear, which caused that the tool life for TC4 was 6–10 times longer than that for TMCs.     

环形气囊抛光非均匀性的研究

针对环形气囊抛光光学元件表面时产生的抛光非均匀性现象,简要介绍了环形气囊抛光技术的运动方式和实验平台的主要组成部分。介绍了环形气囊的抛光机理,基于Preston方程,分析了抛光非均匀现象产生的原因和解决途径,通过调整环形气囊抛光头与工件之间的相对运动方式和调整环形气囊抛光头与工件之间的相对位置等两种方法,消除了工件中心抛光效果差的现象,实现了工件表面的均匀性抛光。     

Luminescent Nanocrystalline Silicon Carbide Thin Film Deposited by Helicon Wave Plasma Enhanced Chemical Vapour Deposition

Hydrogenated nanocrystalline silicon carbide (SiC) thin films were deposited on the single-crystal silicon substrate using the heli-con wave plasma enhanced chemical vapor deposition (HW-PECVD) technique. The influences of magnetic field and hydrogen dilution ratio on the structures of SiC thin film were investigated with the atomic force microscopy (AFM), the Fourier transform infrared ab-sorption (FTIR) and the transmission electron microscopy (TEM). The results indicate that the high plasma activity of the helicon wave mode proves to be a key factor to grow crystalline SiC thin films at a relative low substrate temperature. Also, the decrease in the grain sizes from the level of microcrystalline to that of nanocrystalline can be achieved by increasing the hydrogen dilution ratios. Transmis-sion electron microscopy measurements reveal that the size of most nanocrystals in the film deposited under the higher hydrogen dilution ratios is smaller than the doubled Bohr radius of 3C-SiC (approximately 5.4 nm), and the light emission measurements also show a strong blue photoluminescence at the room temperature, which is considered to be caused by the quantum confinement effect of small-sized SiC nanocrystals.     

Design and Coupled Thermo-Mechanical Analysis of Silicon Carbide Primary Mirror Assembly

Based on the principle that the thermal expansion coefficient of the support structure should match that of the mirror, three schemes of primary mirror assembly were designed. Of them, the first is fused silica mirror plus 4J32 flexible support plus ZTC4 support back plate, the second K9 mirror plus 4J45 flexible support plus ZTC4 support back plate, and the third SiC mirror plus SiC rigid support back plate. A coupled thermo-mechanical analysis of the three primary mirror assemblies was made with finite element method. The results show that the SiC assembly is the best of all schemes in terms of their combination properties due to its elimination of the thermal expansion mismatch between the materials. The analytical results on the cryogenic property of the SiC primary mirror assembly show a higher surface finish of the SiC mirror even under the cryogenic condition.     

虚轴磨床加工球面铣刀的工艺模型

前刀面与后刀面的刃磨加工是球面铣刀加工工艺中最复杂的加工模型,尤其是球面端刃的前后刀面的加工模型,是研究的热点问题.虚轴机床的结构与传统机床不同,机床的运动控制特性也不同,需要特别加以考虑.详细研究了阿基米德螺旋线和圆弧轨迹2种球面端刃前刀面曲线的生成模型,计算了加工这2种前刀面曲线时相应机床运动的位置控制参数,由此提出了适合于虚轴机床的球面铣刀前后刀面刃磨的工艺模型及相应的加工工艺方法,解决了采用6USP虚轴机床加工球面铣刀的工艺问题.使加工模型简化而且合理,提高了虚轴机床的加工效率和精度.      

碳化硅基直流固态断路器短路保护方法

碳化硅器件比硅器件具有更低的导通电阻,用其制作直流固态断路器可以大大降低其通态损耗,减轻散热压力。然而相比于硅器件,由于碳化硅器件管芯面积小,电流密度大,其短路能力相对较弱,短路保护要求更高。为确保碳化硅器件安全可靠工作,提高碳化硅基直流固态断路器的可靠性,对比分析了硅基与碳化硅基MOSFET的短路能力,揭示了其器件恶化机理,研究了栅源极电压箝位方法,并结合去饱和检测,提出了一种基于源极寄生电感的"软关断"短路保护方法,制作了直流固态断路器样机进行实验验证。实验结果表明,所提方法可以降低功率器件的关断电压应力、抑制短路电流,适合碳化硅基直流固态断路器短路保护。     

松软土壤环境下月球车动力学与控制的仿真工具

  开发一种月球车三维可视化动力学与控制的仿真工具。该工具融合多刚体系统动力学、车轮-土壤交互动力学以及运动控制系统模型,可以模拟松软土壤与复杂地形等环境,评估月球车在这些环境下的运动状况,并研究如爬越松软土壤的大角度坡面等关键工况下的运动控制方法及其优化。最后给出月球车在该仿真工具上运动控制的应用实例。     

一锅法合成SiC-ZrC复相陶瓷前驱体及其性能

以甲基三氯硅烷、二氯二甲基硅烷、二氯二茂锆以及金属钠为原料,通过一锅反应合成出一种全新的SiC-ZrC复相陶瓷前驱体(HBZS)。利用TG、FTIR、XRD及SEM等对HBZS的热解行为、分子结构以及热解产物的微观形貌与结构进行了全面分析。结果表明:HBZS在900℃时可以完全裂解转化成SiC-ZrC复相陶瓷,陶瓷收率可达60%以上;裂解产物中ZrC相晶粒尺寸极小(10～45 nm)且均匀分散于连续的SiC相中。该前驱体可用于制备SiC-ZrC陶瓷纤维及陶瓷基复合材料。     

航空复杂壳体高精度孔系精密加工技术

针对航空复杂壳体典型高精度孔系加工时间长、刀具数量多、加工效率低成本高等问题,根据其结构特点及精度要求,设计螺旋槽内冷式台阶钻头、直线刃内冷式台阶铰刀,改进专用复合成型刀具的结构设计,逐步优化调整切削参数.通过多次切削工艺试验摸索匹配专用复合成形刀具的最优工艺参数,形成了适用于航空复杂壳体高精度孔系精密加工的工艺解决方案,并验证可行.