Optimal Selection of Machinable Volumes

A brief review of the process planning literature is provided. One of the basic issues in process planning is the feature recognition. In the paper rather than representing a part with features, the representation using machinable volumes is emphasized. A model for the selection of machinable volumes with minimum corresponding machining costs, fixture and tool utilization costs is formulated. The model is illustrated with a numerical example. Computational results for five existing parts are presented.     

A comparative evaluation method of machinability for mica-based glass-ceramics

The machinability of mica glass-ceramics is evaluated using a tool dynamometer. Several samples with different chemical compositions and microstructures were tested in turning operations using TiCN cermet tools. The cutting rate dependence of specific cutting energy has been studied to find a simple method for the evaluation of machinability. The mechanical strength, the surface roughness of the machined surface and the fracture toughness were measured to support the machining behaviour. For the determination of machinability, the specific cutting energy at low cutting rate conditions, neglecting an elastic impact effect, and the slope of the log-log plot of the specific cutting energy versus cutting rate were considered as the reasonable parameters. These results are correlated with the microstructure and the hardness of the workpiece. In particular, the microhardness of the sample is shown to control the cutting characteristic.     

低熔可切削生物活性微晶玻璃的研究

选择一种出SiO₂-MgO-Al₂O₃-K₂O-CaO-P₂O₅-F基础玻璃体系,并添加不同量的ZnO,制备出性能良好的可切削生物微晶玻璃.结果表明,由于ZnO的添加,可使母玻璃的熔化温度由1450℃降至1300℃,可切削生物活性微晶玻璃的母玻璃能够在较低的温度熔化制备.母玻璃晶化后析出相主要为云母相和氟磷灰石相;各种晶相的组合形貌为花瓣形态,其断口呈现穿晶断裂的特征,并有晶体拔出,使材料具备了较高的强度;由于析出了较多的云母相,该微晶玻璃兼具良好的可切削性能.     

以Ba云母为主晶相的可切削玻璃陶瓷

基于Ｂａ０．５Ｍｇ３（Ｓｉ３ＡｌＯ１０）Ｆ２－Ｍｇ２Ａ１４Ｓｉ５Ｏ１８－Ｃａ３（ＰＯ４）２系统，制备出了以含Ｂａ碱士云母为主晶相的可切削玻璃陶瓷，弯曲强度σｂ＝２２９ＭＰａ，断裂韧性Ｋｌｃ＝２．４８ＭＰ·ｍ１／２；钻孔速度大于７ｍｍ／ｍｉｎ．优良性能的获得借助于Ｂａ云母玻璃陶瓷可控的显微组织，即相互交错的云母体和“卷心菜”的组织特征．观察到了两类类型的断口形貌：云母晶体层内断的层状花样和沿（００１）晶面层间断的小刻面花样．     

Machinable volume extraction for automatic process planning

This paper describes an algorithm to extract machinable volumes that need to be removed from a stock, given a boundary model of the part. 'Machinable' implies that these volumes are extracted and arranged in a hierarchy such that each volume in the list is accessible for machining after its preceding volume has been machined, These volumes can be used to automate process planning and NC too! path generation. The algorithm identifies the cavity volumes in the part with respect to outermost faces in the part and fills them with the appropriate primitive volume to obtain the stock from which the part can be realized. Unlike the decomposition-based approaches reported, this algorithm directly identifies primitive volumes that when combined form the cavity volumes corresponding to the machining features. Primitive volumes enable handling parts with interacting Features and renders redundant the additional processing of machining features required to generate a NC tool path. The primitive machinable volumes arc cuboids, wedges and collars. The algorithm handles both prismatic and cylindrical (turned) components. Results of implementation for prismatic and turned components are provided and the extension of the algorithm to handle preformed stock is discussed.     

可加工陶瓷研究的新进展

从微观结构设计出发,进行可加车性能的研究已成为陶瓷材料研究领域的热点之一。从改善陶瓷材料可加工性的方法着手,简要介绍可加工陶瓷研究的新进展,并对各种方法的优点与不足之处进行评述。     

可切削加工陶瓷材料研究进展

从玻璃陶瓷、氧化物陶瓷和非氧化物陶瓷三个方面比较全面地回顾了可加工陶瓷的研究进展,介绍了其制备工艺、可加工机制及强韧化机制,评述了国内外研究现状．并对可加工陶瓷研究的发展趋势提出了作者的观点．     

一种可切削玻璃陶瓷的压痕断裂特性

将断裂韧性测试的压痕方法与压痕弯曲方法相结合，独立地分离出了压痕残余应力因子ｘ，使其成为可测参量，并建立了压痕一压痕弯曲的断裂韧性测试方法．将这种方法应用于一种可切削玻璃陶瓷的测试，获得的Ｋ１ｃ值为Ｋ１ｃ＝２．０３ＭＰａ·ｍ１／２，与单边切口法（ＳＥＮＢ）获得的Ｋ１ｃ值有较好的一致性．测得的残余应力因子Ｘ＝０．０９３，符合Ａｎｓｔｉｓ经验公式的预测．     

含Zn生物玻璃、玻璃陶瓷与聚酯复合骨组织工程支架的制备及性能

采用溶胶凝胶法在58S生物玻璃的基础上用氧化锌取代3? mol％的氧化钙制备了含锌的生物玻璃粉体 (58S3Z),对合成的粉体采用有机泡沫浸渍法在700℃及1200℃制备出58S3Z-700℃、58S3Z-1200℃玻璃及玻璃陶瓷多孔支架。在所得支架表面涂覆PLGA及PBS薄膜制备出58S3Z-1200℃-PLGA及58S3Z-1200℃-PBS复合支架。对其形貌、 孔隙率、 力学性能、 体外降解性及细胞相容性进行了系统研究。复合后多孔支架仍然保持三维连通的多孔结构,孔隙率与复合前(86.9%±0.8% (58S3Z-700℃),80.1%±0.6% (58S3Z-1200℃)）相比稍有下降,分别为75.9%±0.6% (58S3Z-1200℃-PLGA)和77.9%±0.9% (58S3Z-1200℃-PBS)。但复合多孔支架显示出较高的抗压强度,分别达到1509.4 kPa±162.8 kPa (PLGA) 和901.6 kPa±94.5 kPa (PBS),与玻璃和玻璃陶瓷支架 (258.4 kPa±23.6 kPa) 相比具有较大的提高。体外降解实验表明58S3Z-1200℃-PLGA、58S3Z-1200℃-PBS复合多孔支架可降解, 经过28天的浸泡其失重率分别达到13.3％和2.1％。体外研究结果表明:58S3Z玻璃陶瓷支架复合PBS或PLGA后支持成骨细胞黏附、铺展和生长。这种新型的复合支架具有三维的网状多孔结构,良好的力学性能、降解性和细胞相容性,有望成为一种较理想的骨组织工程支架。      

纳米AlN/BN复相陶瓷的显微结构与性能

采用尿素与硼酸的反应, 在850℃氮气氛下, 合成了纳米BN?包裹的AlN粉料, 通过TEM观察, BN粒径为20～30nm. 通过热压烧结制备出纳米h-BN包裹的AlN/BN 复相陶瓷, SEM/TEM观察, h-BN呈细针状, 针长100～400nm, 针宽为30～50nm. 当h-BN含量≥20wt%时, 其硬度显著降低, 提高了材料的可加工性能.     

Bonding thermosprayed silicon to glass-ceramic

Many materials, among them silicon, fail to form adherent coatings when thermosprayed onto smooth oxide glasses and glass-ceramics. Mechanical bonding is usually possible if the substrate surface is abraded before spraying, but this process also weakens the crack-sensitive substrate. This paper gives the results of examining alternate surface preparations which create a roughened substrate without the usual weakening of the finished article. The methods rely on the ability of mechanically damaged glass articles to heal, i.e. to decrease the flaw population during crystallization. The surface roughness essential to the mechanical bond is produced when the article is in the green or glassy state, and in a subsequent processing step the glass is converted to glass-ceramic by a crystallization heat treatment. The simplest application is the fabrication of roughened durable ceramic substrates for spraying after the crystallization step. Profilometry and measurements of silicon metal coating adhesion to a lithium aluminosilicate glass-ceramic indicate that for hard glasses the crystallization step does not reduce the surface roughness. When high temperature materials are to be used as coatings, the spraying step can be performed while the substrate in the glassy state, and then the entire article is subjected to the crystallization heat treatment. For a silicon-coated glass-ceramic, this method produces significantly improved adhesion over simple mechanical bonding.     

Some aspects of glass-ceramic superconductors

In this review article we have discussed, in brief, the general procedure for making glass-ceramic superconductors and some of their physical properties. All these glasses which become superconductors after properly annealing at higher temperatures are, in general, transition metal oxides (TMO) with copper ions. So the usual theoretical models of polaronic hopping conduction mechanisms are valid for explaining the semiconducting behaviour of these oxide glasses. Some of the transport properties of the glass-ceramic (GC) phases, viscosity of the glassy state, wire making feasibility etc have also been discussed in short.     

Dielectric properties of filled glass-ceramic

Experimental methods are reported and a method is suggested for calculating the dielectric properties of glass-ceramics for electronics.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 59, No. 6, pp. 962–968, December, 1990.     

可加工复相陶瓷材料的研究现状与发展

介绍可加工复相陶瓷的研究发展现状。着重介绍可加工BN系复相陶瓷的研究现状与发展。主要论述可加工BN系复相陶瓷的制备工艺过程及力学性能和可加工性能等。对可加工复相陶瓷材料的研究发展方向作分析和预测。     

Mechanical properties of a transformation-toughened glass-ceramic

The fracture toughness of a transformation-toughened glass-ceramic containing 12 vol% t-ZrO₂ was measured. Heat-treatment conditions were selected to produce from the same glass composition a glass-ceramic which contained 12 vol% m-ZrO₂ in a nearly identical matrix. The transformation-toughened material was found to have a fracture toughness 65% greater than the m-ZrO₂-containing material at room temperature. However, at 77 K both materials were found to have approximately the same fracture toughness. Additionally, the susceptibility of the two glass-ceramics to fatigue was determined. No improvement in fatigue behaviour of the transformation-toughened glass-ceramic over the other glass-ceramic was observed.     

Dynamic fatigue of a hot glass-ceramic

The structures of crystalline silicates are characteristically of low symmetry and large lattice parameters, neither of which feature is conducive to easy plastic deformation by dislocation mechanisms. Non-crystalline silicates, on the other hand, are usually Newtonian fluids at high temperatures and it is flow of the non-crystalline material which is believed to be responsible for the plasticity of hot glass-ceramics. The high temperature dynamic fatigue properties of a Li₂O-ZnO-SiO₂ glass-ceramic have been investigated in order to test ideas suggested by tests previously carried out on the same material at constant stresses and at constant strain-rates.     

Formation of a new bioactive glass-ceramic

A new bioactive glass-ceramic with a nominal composition of CaO (54.5), MgO (6.0), SiO₂ (32.8), P₂O₅ (6.1) and CaF₂ (0.6), by weight ratio, has been developed. The crystalline phases termed hydroxyfluoroxyapatite, akermanite, and wollastonite were found to be present simultaneously at a temperature of 930°C. Furthermore, no cracks appear after the bulk glass is crystallized. This newly developed glass-ceramic has an average flexural strength of 233 MPa and a fracture toughness of 2.95 MPa m^1/2, which are higher values than for dense hydroxyapatite and known glass-ceramic. An apatite layer containing Ca, P and Si is formed on the surface after the glass-ceramic is soaked in a simulated body fluid for a short period of time, which is indicative of a high bioactivity.