熔融沉积快速成型技术中成型材料温度对工件的影响

成型产品的质量精度一直是制约熔融沉积快速成型技术发展的核心问题。本文主要从成型材料温度方面对成型试件进行深入研究,通过不同材料温度探究对试件成型后的实际翘曲变形。运用具体实验和有限元分析模拟两种分析方法,描述出不同成型材料温度对熔融沉积快速成型试件的翘曲变形影响。实验和软件模拟结果表明:成型材料温度在合理范围内变化会对试件造成一定的翘曲影响,而扫描速度、扫描方式等其他因素也会交叉影响成型试件的成型精度。     

石英玻璃飞秒激光微连接及其接头性能

飞秒激光的低热输入、极小热影响区的特点使其在微米尺度材料连接领域有明显的应用潜力。为研究飞秒激光进行玻璃连接的可行性及其接头性能,测定了其接头的拉剪强度并分析了接头断裂前后的形貌特征。证明了飞秒激光连接玻璃的可行性,并发现玻璃试样之间的间隙对飞溅有明显影响。拉剪试验测得的接头强度在6.4~40.4MPa之间。结果表明,在激光平均功率较大,焊缝间距较小的条件下,连接试样容易在母材中断裂,使得接头的强度相比于断裂在界面上的试样强度降低一半以上。     

三辊卷板机卷制任意锥筒的调整计算及卷制过程

针对三辊卷板机卷制任意锥筒难度较大的情况,经过长期对卷板机的设计和研究,通过分析卷板的工艺原理和三辊卷板机的工作原理,利用卷板机上轴辊的调整规律,推导出较为实用的数学公式。避免在卷制锥筒时反复进行多次操作,降低了劳动强度,从而提高了生产率。     

Fabrication and characterization of Si3N4 whisker-reinforced SiO2 ceramic for radome materials

Fused silica ceramic has become one of the most widely used radome materials in the world since the 1970s. But its poor mechanical properties restricted its application to some extent. To improve the mechanical properties of the fused silica ceramic and keep its characteristic for radome materials, silicon nitride (Si₃N₄) whisker-reinforced fused silica ceramics were prepared by a slip-casting method in the work. The influence of Si₃N₄ whisker contents on the properties of the slurry was studied, indicating that the preferable pH values of the slurry were 4–6 and whisker contents were 10 wt.%. The flexural strength of as-prepared Si₃N_4w/SiO₂ ceramic was about 74.35 MPa, exhibiting an increase of 7.75% over that of the pure silica sample. Its dielectric constant in the range from 8 to 12 GHz and tanδ under 10 GHz were, respectively, 3.37 and .0011. It is of great interest to find that Si₃N_4w/SiO₂ has excellent oxidization resistance and its mass maintains even at 1270°C.     

N‐Heterocyclic Carbene‐Catalyzed Umpolung Formal [3+3] Cycloaddition of Enals with Isatogens: Access to Fused Indolin‐3‐ones with a Tetrasubstituted Carbon Stereocenter

A novel synthetic method to access fused indolin‐3‐ones with a tetrasubstituted carbon stereocenter has been developed via NHC‐catalyzed umpolung formal [3+3] cycloaddtion of enals with isatogens. This methodology could be also applied for the quick construction of the 6‐5‐5 tricyclic pyrrolo[1,2‐a]indole skeleton which is frequently found as a core structure of many indole alkaloids.

     

Synthesis of Heterocycle‐fused Pyridine N‐Oxides from Oximes and Diazo Compounds via RhIII‐Catalyzed C?H Activation and Annulation

A Rh^III‐catalyzed tandem C H activation and C N bond formation reaction between oximes and diazo compounds for the synthesis of heterocycle‐fused pyridine N‐oxides has been developed. The reaction exhibits good functional group tolerance and regioselectivity. After simple transformation, the 1‐substituted, 1,3‐disubstituted, 1,4‐disubstituted and 1,3,4‐trisubstituted heterocycle‐fused pyridines were all obtained in high efficiency. Moreover, this strategy has also been expanded to the synthesis of a key intermediate for the construction of one potential anti‐HIV agent.

     

基于支持向量回归的熔丝制造3D打印能效优化模型

基于响应面法和支持向量回归模型对熔丝制造3D打印能效进行预测与优化。首先,利用田口方法设计六因素三水平正交试验,通过响应面法分析得出对加工能效影响较为显著的3个因素即层高、打印速度和热床温度;然后,通过支持向量回归方法建立加工能效预测模型,并与BP神经网络方法进行对比,结果表明支持向量回归方法建模预测性能更优;最后,建立以加工时间和能效为目标的优化模型,利用NSGA-Ⅱ、MOEA/D、SPEA2和MOPSO 4种算法分别对模型进行求解,分析比较4种算法的Pareto前沿,结果表明NSGA-Ⅱ算法在求解此问题时综合表现最佳,对比NGSA-Ⅱ算法求得的优化结果与试验结果可知,NSGA-Ⅱ算法具有有效性和合理性。     

不同熔渣对钢包铝镁铬材料渣蚀行为的影响

选取冶炼取向硅钢和铝镇静钢的精炼终渣及钢包用铝镁铬砖,采用静态坩埚法于1600 ℃×3 h下进行熔渣侵蚀试验,对渣蚀后试样作显微结构分析,并测定熔渣的化学成分和熔化温度.结果显示,随着熔渣中Al2O3含量的升高和碱度的增加,熔渣的熔点升高,粘度增加.粘度较大的熔渣与耐火材料接触后扩散较慢,对耐火材料的侵蚀和渗透减弱.并且当熔渣与耐火材料的反应产物为高熔点的CA2、CA6和MA尖晶石相且连续交错分布时,能堵塞液相扩散通道,抑制熔渣向耐火材料内部的进一步渗透.     

激光靶光电探测系统优化设计

介绍了一种新颖的激光光幕靶弹丸速度测量系统.系统由半导体激光光源准直、扩束形成原向反射屏反射后形成一定直径的反射光斑,光斑经用以扩大接收面积的光纤光锥会聚后由光电探测器接收.给出了苏格兰片反射率测试的方法和测试结果以及3 mm飞行物体的过靶波形.试验结果表明,采用原向反射屏和光纤光锥构成的光电探测系统具有较高的信噪比和灵敏度.     

Effects of laser polishing on surface quality and mechanical properties of PLA parts built by fused deposition modeling

Fused deposition modeling (FDM) produces parts through layer by layer on the top of each other, making it almost impossible to obtain smooth printed parts. Hence, there is a huge demand for the postprocessing of the FDM-printed parts. Laser polishing is a novel technique that can be used to polish products to obtain a smoother surface. The aim of this work was to explore the feasibility of surface-finishing FDM-printed polylactic acid (PLA) parts by laser polishing. The surface roughness, surface morphology, dynamic mechanical analysis (DMA), and tensile properties were investigated. The results indicated that the lower laser power and the bigger laser beam diameter within a certain range could facilitate the formation of smoother surface. With optimized parameters, the surface roughness was reduced by 90.4%. DMA showed that the storage modulus (E’) and glass transition temperature of PLA specimens were significantly improved due to the decrease of molecular mobility of denser structures. Moreover, the tensile strength and Young's modulus of the PLA specimen were also significantly increased after laser polishing. The fracture morphologies were observed, and the possible strengthening mechanism was also discussed. These results indicated that laser polishing could be an efficient method for surface polishing of FDM parts. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48288.