Resistência à flexão e microestrutura de vidro-cerâmicas feldspáticas processadas por injeção em moldes à alta temperatura

Enquanto os métodos tradicionais de processamento de restaurações cerâmicas tornaram-se notórios por sua complexidade, as técnicas mais modernas vêm privilegiando a simplicidade de execução e a automação. Dentre estas, destaca-se a injeção em moldes, que recentemente, foi associada a métodos CAD-CAM. Estudos anteriores demonstraram a viabilidade de utilização de um vidro feldspático de baixa expansão térmica, Alpha (Vita Zahnfabrik), para injeção, porém, faltam informações quanto às propriedades mecânicas e a microestrutura deste material quando submetido à injeção. Os objetivos deste estudo são: produzir pastilhas vidrocerâmicas para injeção a quente a partir de Alpha e da mistura deste vidro com partículas de alumina e zircônia; avaliar a resistência à flexão dos materiais processados, e compará-la a um material compatível existente no mercado (PM9 - Vita Zahnfabrik); estudar a estrutura microscópica dos materiais e correlacioná-la com suas propriedades mecânicas; identificar por meio de difração de raios X a formação de fases cristalinas durante as diferentes etapas de processamento. A injeção aumentou a resistência do vidro Alpha devido à redução na quantidade e tamanho dos defeitos internos, principalmente porosidades. Apesar de ter sido observada nucleação de cristais nos dois materiais, durante o processamento, não foi possível determinar de que forma este fenômeno afetou as propriedades mecânicas dos materiais. Não foi detectada alteração no padrão de distribuição das fases cristalinas observadas em microscópio eletrônico de varredura antes e depois da injeção. Não foi verificada diferença estatística significante entre a resistência à flexão de Alpha injetado e PM9. A adição de partículas de alumina e zirconia ao vidro Alpha provocou redução da resistência, devido à formação de aglomerados durante a confecção das pastilhas e a incapacidade da injeção em dispersá-los. Tais aglomerados funcionaram como concentradores de tensões, enfraquecendo o material.

Diseño y programación del control numérico para el mecanizado del escudo del Real Madrid.

[ES]El objetivo de este proyecto es programar el control numérico para la mecanización del escudo del Real Madrid. Para conseguir esto, primero es necesario aprender cómo funcionan los programas que se van a usar. Después de esto se va a crear el archivo CAD, usando el programa Solid Edge. Luego, usando el programa SurfCam Velocity 4.0 se programará el control numérico necesario para la fabricación del escudo.

Análisis del mecanizado de un molde para la fabricación de un logo deportivo.

[ES]Las compañías líderes del mundo textil compiten cada día por ser las número 1 en cuanto a ventas se refiere. Para ello, son necesarias diferentes estrategias de venta. Una de ellas es la adición de diferentes adornos de plástico que hacen que el comprador se fije en sus productos. Por otro lado, las tecnologías de mecanizado están en pleno avance y la fabricación de piezas o moldes es cada vez más eficiente. Por eso en este trabajo se quiere analizar y estudiar la fabricación de un molde de inyección de plástico con el logotipo de una de las marcas más famosas en el mundo, Adidas. Se ha de llevar a cabo un estudio de los posibles materiales a utilizar para el molde, así como, las distintas alternativas de mecanizado que hoy en día se emplean para este tipo de procesos. Además, los avances en los distintos programas CAD/CAM son de especial ayuda para este tipo de trabajos. Estos programas son capaces de trazar las trayectorias más eficientes a la hora de mecanizar distintos tipos de piezas y postprocesar la programación de dichas trayectorias para luego ser introducidas en los centros CNC.

基于三角网格曲面模型的刀位轨迹计算方法

离散三角网格模型在CAD/CAM中应用很广,但针对该模型的刀位轨迹自动生成算法并不多见。在正确重建网格模型的拓扑关系基础上,给出了新的曲面几何特性分析方法,并提出了具有特色的精确的刀位轨迹计算方法,克服了直接由网格模型求交计算刀位方式存在的精度问题。测试结果显示,该方法简捷、可靠,能够达到实用化要求,并显著提高了刀位计算精度和加工效果。

面向快速成形的复杂曲面重建技术研究

针对快速成形工艺特点，提出了一种基于实物的复杂曲面几何重 建的方法。由此直接生成的快速成形机优化STL接口文件，实现了反求容差与模型网格数的 最佳匹配，避免了由通用软件转换存在的错误和繁复，提高了成形设备的前处理效率，并为 反求工程与快速成形技术的有机集成提供了可靠途径。

切割排料问题的研究及算法实现

随着目前国内及国际市场竞争的日益激烈，各行各业更加意识到节省成本、提高经济效益的迫切，对于制造业，其经济效益直接体现在产品上，原材料的利用率在其中起着至关重要的作用。在制造业中，原材料的质地及加工工艺都不尽相同，所以如何分配原材料以满足生产需求一直是制造业中关注的问题之一，切割排料问题正是从这一实际需求中产生的。J本课题以生产实际中经常遇到的一维二维切割排料问题为研究对象，深入地分析了它们的特点及各方面的限制条件，在此基础上提出了各自的数学模型，并且结合计算机技术开发了应用系统，实现了理论和实际的结合。本课题的研究内容主要包括:1.对切割排料问题的产生及分类作了详细地阐述，使切割排料问题从空间角度成为一个有机的体系，对于理解和解决实际问题提供了理论依据。2. 针对维切割排料问题，从实际问题分析着手，以delayed column generation 算法为主要方法，并对其作了相应的改进，同时开发了一维切割排料系统。3. 详细地讨论了各种二维规则矩形切割排料问题，针对它们的不同特点及工艺要求，提出了各自的数学模型，以近似算法、背包算法等不同方法为基础，得到了不同的解决方案，同时形成了面向实际的应用系统框架。4. 对于二维不规则零件切割排料问题，以转化为主要指导思想，通过不同方法得到转化后的二维规则矩形切割排料问题，应用前面得到的方法使问题解决大为简化。结合AUTOCAD 系统开发了实际应用系统。5. 结合沈飞公司实际需求，提出了饭金加工CAD/CAM 系统集成方案，使前面开发的应用系统与生产实际有了结合的途径，为其在实践中得到广泛的应用打下了良好的基础。

激光金属沉积成形过程热行为的研究

激光金属直接快速成形技术是在80年代末期出现的快速原型技术（Rapid Phototyping, RP）基础上结合同步同轴送料激光熔敷（On-axis Laser Cladding）技术发展起来的一项先进制造技术。它涉及机械、激光、计算机辅助设计（CAD）、计算机辅助制造（CAM）、计算机数字控制（CNC）、材料科学等领域的关键技术。它突破了传统快速成形工艺方法和成形材料的局限，是目前快速成形诸多方法中研究最多、最有发展前途的新型制造技术。它基于材料累加思想，能够在无需任何刀具和模具的情况下由CAD模型直接驱动沉积成形金属零件，从而大大缩短了新产品的研发周期并节省了大量的资源。中国科学院沈阳自动化研究所开展了该技术的研究，并研制开发了激光金属沉积成形系统（Laser Metal Deposition Shaping, LMDS）。本文介绍了金属零件激光直接快速成形技术的原理和特点，分析了当前金属零件激光快速成形过程数值模拟研究的热点和发展趋势。结合激光金属沉积成形系统的研究需要和遇到的实际问题，阐述了激光、金属粉末和基板三者之间的相互作用，利用有限元的方法数值模拟了各种影响成形精度和效率的因素对激光金属沉积成形系统过程热行为的影响，包括不同扫描方式、不同基板预热温度等，并利用激光金属沉积成形系统系统进行了验证。具体的研究内容如下： 1. 阐述了激光与金属粉末之间的相互作用。激光快速成形过程中，高功率激光束与基板金属交互作用产生熔池，同步送入的金属粉末在熔池内被迅速熔化然后迅速凝固。熔池内的冶金动力学过程包括传热、传质、对流及气-液界面冶金反应和固-液界面扩散等与工艺质量的好坏密切相关，直接影响成形零件内气体和夹渣物的吸收、聚集和逸出，进而影响成形零件的微观组织、成分变化及其它物理冶金性能。基于熔池内传质、传热及流动对成形层的组织和性能的决定性作用，建立了激光金属沉积成形过程的数学模型和有限元模型。 2. 利用有限元分析中的“单元生死”技术，通过APDL语言编程建立了激光金属沉积成形系统过程三维多道多层的数值模拟模型，得到了激光金属沉积成形系统过程中试样和基板内的温度、温度梯度以及热应力分布规律。 3. 研究了沿长边平行往复扫描、沿短边平行往复扫描以及层间正交变向平行往复扫描等不同扫描方式对激光金属沉积成形系统过程热行为的影响，得到了不同扫描方式下试样和基板的温度、温度梯度和热应力变化规律，并结合快速凝固理论对这一过程中出现的现象进行解释。 4. 为了实现基板的预热，根据热传导理论自主设计开发了用于激光金属沉积成形系统过程的基板预热系统。该系统由基板预热器、智能PID控制器以及计算机串口温度检测和反馈控制等部分组成，具有结构简单、功能完善、可靠性高等特点。它既可以通过智能PID控制器实现对基板预热温度的控制，也可以通过计算机串口实现对基板预热温度的实时检测、记录以及反馈控制，从而使基板预热温度在室温～600℃之间连续调节。此外，它的计算机串口温度检测模块还可以用来实现对激光金属沉积成形系统成形过程基板温度的实时监测，为数值计算提供较为准确的边界条件以及用来检验和校正数值模型的正确性与可靠性。 5. 利用数值模拟的方法研究了基板预热温度分别在室温、200℃、300℃、400 ℃、500 ℃、600 ℃时对激光金属沉积成形系统过程温度、温度梯度以及热应力的影响。在相同的条件下，利用激光金属沉积成形系统系统和基板预热系统进行了实际成形实验。对成形实验得到的试样进行了深入的研究，包括：成形试样的成形高度和表面质量与基板预热温度的关系；成形试样的利用扫描电镜分析成形试件沉积层的显微组织特征；利用能谱仪分析沉积层合金元素的化学成分偏析情况。 6. 建立了集数值模拟和成形加工于一体的软件平台。它既可以实现简单零件变模型尺寸、变热物性参数和变工艺参数的数值模拟，也可以直接驱动激光金属沉积成形系统完成简单零件的快速成形。这为研究各工艺参数如激光功率、扫描速度、送粉速率、光斑尺寸以及基板预热温度等对激光金属沉积成形系统过程的影响提供了一个平台。

激光再制造关键技术及其工艺试验研究

激光再制造技术是在20世纪80年代末期出现的激光熔覆技术基础上结合再制造技术所发展起来的一项先进制造技术，它利用高能激光束局部熔化零件表面形成熔池，同时将金属合金粉末同步送入熔池而形成与基体金属冶金结合的熔覆层，赋予零部件耐高温、耐腐蚀、耐磨损、抗疲劳等性能。该技术融合了激光技术、材料科学、数控加工、CAD/CAM技术、光电检测技术、机构设计技术、优化设计和系统仿真等相关领域的关键技术，是一门全新的光、机、电、计算机、自动化、材料综合交叉的制造技术。它的出现给机电设备的再制造带来了全新的理念，解决了很多传统再制造技术无法解决的难题，极大的带动和促进了再制造产业的发展，具有广阔的应用前景，产生了巨大的经济、社会和环境效益。 目前，国内外激光再制造技术的研究尚处于萌芽阶段，研究还没有形成系统化，仍然有很多关键技术需要进行深入细致的研究。本文在国家863计划、中科院知识创新基金和地方科技攻关等项目的支持下，系统地研究了激光再制造的关键技术，在建立各项关键技术知识点分析和理论研究的基础上，给出了关键技术的实施路线和解决方案，为激光再制造技术的工艺试验和工业化应用提供了理论依据和技术支持。具体的研究内容如下： （1） 进行了激光再制造系统本体研究，在系统地研究了各功能模块的基础上，提出了各功能模块选择的原则，有效的避免了搭建再制造系统时各功能模块任意选择的误区。针对国产激光器不稳定和使用寿命短等缺点，借鉴固态激光器的结构原理，设计开发了新一代模块化CO2激光器；针对国产送粉系统不稳定、送粉不均匀等缺点，设计开发了一种新型内外双水冷的同轴送粉喷嘴，经过试验测试，此喷嘴可长时间连续稳定运行，满足工业化生产的需要。基于模糊数学理论的优化设计方法，自主开发了一套三维多功能激光再制造系统，该系统结构完整、功能完善、性能可靠，可以对大型设备零部件进行激光修复和激光淬火。 （2） 进行了激光再制造熔池温度场检测系统的研究，建立了一套在线、小视场、大量程、高精度红外测温系统；通过红外滤光片的选择和设计，有效解决了传统3CCD相机比色测量的准确度差和精度低的问题；提出了一种红外热像系统位置标定的方法，为其它领域红外系统的摄像机标定提供了研究基础；进行了各加工工艺参数对熔池温度场稳定性影响的研究，从而更加了解了激光熔覆凝固成型的原理。同时，进行了熔覆层厚度检测系统的研究，建立了一套单CCD应用线结构光测量熔覆层厚度的系统，并对系统的构成、系统的标定和测量原理进行了分析和研究，从而实现了熔覆层厚度由定性测量向定量测量的跨越。 （3） 进行了工业生产中常见装备及其零部件的失效分析研究，提出了一套按照增加熔覆层性能的失效原因分类原则；进行了激光熔覆粉末种类及其特点的研究，提出了一套激光熔覆粉末的选择原则，给出了各类熔覆层应该采用的熔覆粉末的具体配比方案，从而为激光再制造技术的工业应用奠定了基础。 （4） 进行了激光再制造工艺设计研究，详细分解了激光熔覆过程中涉及到的各工艺步骤，如光束选择、送粉方式、不同基材的熔覆工艺、预处理工艺、预热处理、加工路径规划和后处理等，结合大量的工艺试验，提出了各工艺的选择原则；提出了激光比能量、送粉速度、搭接率、预热温度、预置粉末厚度和保护气流量是影响激光再制造熔覆层质量的最重要工艺参数，并结合工艺实验验证了这些工艺参数对熔覆层质量的实际影响；进行了熔覆层质量的宏观判据和微观判据研究，给出了宏观判据现象产生的原因和微观判据测量的方法，从而为激光再制造技术的工业应用铺平了道路。 （5） 在解决了上述激光再制造关键技术的基础上，进行了板坯结晶器激光再制造工艺试验研究，分析了板坯结晶器的失效原因，并根据失效分析设计和选择熔覆粉末，然后对每种熔覆粉末进行了熔覆工艺设计，采用正交试验法获得了各加工工艺的最佳工艺参数，并制备了相应的样件；然后对样件熔覆层的各种宏观现象和微观性能测试的进行了分析，包括孔隙率、浸润性、微观形貌、显微硬度、成分偏析、金相研究、抗腐蚀性和抗热疲劳性能等，从而得出了大面积板坯结晶器激光熔覆的最佳熔覆粉末、最佳工艺和工艺参数等，并进行了窄板结晶器的激光再制造。

Automating Mechanical FMEA Using Functional Models

Hughes, N., Chou E., Price, C. J. Lee M. H.(1999). Automating Mechanical FMEA Using Functional Models, Proceedings 12th Int. Florida AI Research Soc. Conf. (FLAIRS-99), AAAI Press, May 1999, pp. 394-398.

Avaliação dos tipos de reabilitações fixas dento-suportadas em dentes anteriores

Projeto de Pós-Graduação/Dissertação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Mestre em Medicina Dentária

Qual a eficácia clínica do sistema CEREC com os seus diferentes materiais para reabilitação em prótese fixa e sobre implantes?

Projeto de Pós-Graduação/Dissertação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Mestre em Medicina Dentária

Application of Internet techniques into online collaborative design and manufacture

A research project in Web-enabled collaborative design and manufacture has been conducted. The major tasks of the project include the development of a Web-enabled environment for collaboration, online collaborative CAD/CAM, remote execution of large size programs (RELSP), and distributed product design. The tasks and Web/Internet techniques involved are presented first, followed by detail description of two approaches developed for implementation of the research: (1) a client-server approach for RELSP, where the following Internet techniques are utilized: CORBA, Microsoft’s Internet information server, Tomcat server, JDBC and ODBC; (2) Web-Services supported collaborative CAD which enables geographically dispersed designers jointly conduct a design task in the way of speaking and seeing each other and instantaneously modifying the CAD drawing online.

Fracture strength of machined ceramic crowns as a function of tooth preparation design and the elastic modulus of the cement

Objectives: To determine, by means of static fracture testing the effect of the tooth preparation design and the elastic modulus of the cement on the structural integrity of the cemented machined ceramic crown-tooth complex. 
Methods: Human maxillary extracted premolar teeth were prepared for all-ceramic crowns using two preparation designs; a standard preparation in accordance with established protocols and a novel design with a flat occlusal design. All-ceramic feldspathic (Vita MK II) crowns were milled for all the preparations using a CAD/CAM system (CEREC-3). The machined all-ceramic crowns were resin bonded to the tooth structure using one of three cements with different elastic moduli: Super-Bond C&B, Rely X Unicem and Panavia F 2.0. The specimens were subjected to compressive force through a 4 mm diameter steel ball at a crosshead speed of 1 mm/min using a universal test machine (Loyds Instrument Model LRX.). The load at the fracture point was recorded for each specimen in Newtons (N). These values were compared to a control group of unprepared/unrestored teeth. 
Results: There was a significant difference between the control group, with higher fracture strength, and the cemented samples regardless of the occlusal design and the type of resin cement. There was no significant difference in mean fracture load between the two designs of occlusal preparation using Super-Bond C&B. For the Rely X Unicem and Panavia F 2.0 cements, the proposed preparation design with a flat occlusal morphology provides a system with increased fracture strength. 
Significance: The proposed novel flat design showed less dependency on the resin cement selection in relation to the fracture strength of the restored tooth. The choice of the cement resin, with respect to its modulus of elasticity, is more important in the anatomic design than in the flat design. © 2013 Academy of Dental Materials.

A systematic review and meta-analysis of the survival of non-feldspathic porcelain veneers over 5 and 10 years

PURPOSE: This systematic review aimed to report and explore the survival of dental veneers constructed from non-feldspathic porcelain over 5 and 10 years.

MATERIALS AND METHODS: A total of 4,294 articles were identified through a systematic search involving all databases in the Cochrane Library, MEDLINE (OVID), EMBASE, Web of Knowledge, specific journals (hand-search), conference proceedings, clinical trials registers, and collegiate contacts. Articles, abstracts, and gray literature were sought by two independent researchers. There were no language limitations. One hundred sixteen studies were identified for full-text assessment, with 10 included in the analysis (5 qualitative, 5 quantitative). Study characteristics and survival (Kaplan-Meier estimated cumulative survival and 95% confidence interval [CI]) were extracted or recalculated. A failed veneer was one which required an intervention that disrupted the original marginal integrity, had been partially or completely lost, or had lost retention more than twice. A meta-analysis and sensitivity analysis of Empress veneers was completed, with an assessment of statistical heterogeneity and publication bias. Clinical heterogeneity was explored for results of all veneering materials from included studies.

RESULTS: Within the 10 studies, veneers were fabricated with IPS Empress, IPS Empress 2, Cerinate, and Cerec computer-aided design/computer-assisted manufacture (CAD/CAM) materials VITA Mark I, VITA Mark II, Ivoclar ProCad. The meta-analysis showed the pooled estimate for Empress veneers to be 92.4% (95% CI: 89.8% to 95.0%) for 5-year survival and 66% to 94% (95% CI: 55% to 99%) for 10 years. Data regarding other non-feldspathic porcelain materials were lacking, with only a single study each reporting outcomes for Empress 2, Cerinate, and various Cerec porcelains over 5 years. The sensitivity analysis showed data from one study had an influencing and stabilizing effect on the 5-year pooled estimate.

CONCLUSION: The long-term outcome (> 5 years) of non-feldspathic porcelain veneers is sparsely reported in the literature. This systematic review indicates that the 5-year cumulative estimated survival for etchable non-feldspathic porcelain veneers is over 90%. Outcomes may prove clinically acceptable with time, but evidence remains lacking and the use of these materials for veneers remains experimental.