陶瓷材料可加工性的二级模糊综合评判

文章以陶瓷材料的物理力学性能参数为依据,应用模糊综合评判原理,建立了工程陶瓷材料可加工性的二级模糊综合评判模型,提出了一种对工程陶瓷材料可加工性进行综合评判的新方法。选择陶瓷材料的5个性能参数构成因素集合,根据提出的评判方法,对四种典型工程陶瓷材料的可加工性进行评价,并根据综合评价指标进行排序。结果表明,该方法的评判结果合理,评价方法易于运用计算机来处理,简单实用。此方法将工程陶瓷材料的可加工性的评价建立在材料性能参数分析的基础上,在机械加工之前即可确定材料的可加工性。评价结果对工程陶瓷材料加工过程中工具和工艺参数的确定具有指导作用。     

基于雷达图法的材料切削加工性评价

提出一种材料切削加工性综合评价方法——雷达图法,制定了基于雷达图法的材料切削加工性综合评价的各项指标,并对各指标进行标准化、归一化处理。通过提取雷达图的特征向量,采用特定综合评价函数,实现雷达图法的数值定量评价。对两种涂层硬质合金刀具切削加工FGH95时的切削加工性进行综合的评价,对试验所得数据进行标准化、归一化处理,绘制出FGH95材料切削加工性的雷达图。     

Surface integrity of milling in-situ TiB2 particle reinforced Al matrix composites

The preparation process and material properties of in-situ TiB₂ particle reinforced Al matrix composites are quite different from conventional ex-situ Al matrix composites (SiC_p/Al composites). Most researches have been carried out mainly focus on the machinability of SiC_p/Al composites, but few studies about the machinability of in-situ TiB₂ particle reinforced Al matrix composites have been published. To address this issue, experimental researches were conducted to investigate the surface integrity (surface roughness, residual stress, microhardness, surface topography, defects) of milling in-situ TiB₂ particle reinforced Al matrix composites in this paper. By examining the machined surface with SEM and EDS for different machining parameters, the influences of cutting speed, feed rate, cutting depth and width on surface integrity were investigated. The results show that feed rate has the dominant influence on surface roughness. As the feed rate increases, the surface roughness increases accordingly. Residual stress decreases and transfers from compressive stress to tensile stress as milling speed gets larger and feed rate decreases. Microhardness variation is not evident below the machined surface. Besides, unlike ex-situ Al matrix composites, pull-out or fractured particles were rarely found on the machined surface of in-situ TiB₂/Al composites.     

Effects of microstructure and strength on wear performance in rough milling of austempered ductile iron

The machinability of various grades of austempered ductile iron (ADI) has been investigated for rough milling operations. ADI 900, ADI 1050 and ADI 1200 grades were commercially produced, commercially heat treated and machined under controlled conditions using coated carbide inserts with coolant in the laboratory. The milling performance of the various grades was compared to that of AISI/SAE 4340 with similar hardness. In this study, machinability characteristics relative to wear rate (ISO 8688-2) and machining forces were measured and related to initial microstructure and properties. These preliminary results have been used to establish initial rough milling machining guidelines for machining ADI with coated carbide milling inserts.     

电阻率对工程陶瓷电火花加工性能的影响研究

常用的工程陶瓷电阻率较高,直接采用电火花加工,性能较差。以ZnO/Al_2O_3陶瓷为例,研究了电阻率和脉冲宽度、脉冲间隔、工具极性等工艺参数对电火花加工工艺性能的影响。结果表明:采取合适的放电加工参数,在ZnO/Al2O3的电阻率达到3410Ω·cm时仍可对其进行有效的电火花加工。     

Characteristic evaluation of Al_2O_3/CNTs hybrid materials for micro-electrical discharge machining

The characteristic evaluation of aluminum oxide (Al2O3)/carbon nanotubes (CNTs) hybrid composites for micro-electrical discharge machining (EDM) was described. Alumina matrix composites reinforced with CNTs were fabricated by a catalytic chemical vapor deposition method. Al2O3 composites with different CNT concentrations were synthesized. The electrical characteristic of Al2O3/CNTs composites was examined. These composites were machined by the EDM process according to the various EDM parameters, and the cha...     

低熔化温度可切削玻璃陶瓷的成分研究

低熔点氧化物Li2O和ZnO使SiO2-Al2O3-MgO—K2O-B2O3-Li2O-ZnO-F系的熔化温度和析晶温度大大降低。ZnO还有扩大玻璃形成区的作用，使较高Li2O含量的玻璃可以获得透明。通过优选SiO2，Al2O3和MgO的成分，得到的玻璃陶瓷中除有足够数量的互相搭接良好的云母晶体外，还可以获得堇青石的晶体，它们分布在的云母晶体之间，使玻璃相减少。从而减小了晶体间的平均自由程，提高了可切削玻璃陶瓷的强度。     

Si3N4／BN层状复合陶瓷的防弹结构设计

提出混杂结构设计的构思，并成功地制备了具有混杂结构的Si3N4／BN层状复合陶瓷，同时研究了材料的抗穿甲燃烧弹冲击的能力。研究发现，具有混杂结构的Si3N4／BN层状复合陶瓷的防护系数为10．50，略低于Si3N4块体陶瓷，但明显高于多层Si3N4／BN层状复合陶瓷，而且具有较高的抵抗整体破坏的能力。研究表明通过适当的防弹结构设计，可以获得抗穿甲燃烧弹冲击能力较高的Si3N4／BN层状复合陶瓷。     

氟金云母陶瓷车削加工中切削温度实验研究

通过硬质合金刀具车削氟金云母陶瓷实验,研究可加工陶瓷切削温度。以特征温度表征切削温度研究氟金云母可加工陶瓷车削加工中的切削温度。结果表明,特征温度随转速的变化幅度小;随着进给速度增大,特征温度整体上是下降的,并且进给速度在0.1~0.12 mm/r间,特征温度下降幅度较大;在特征温度随着切削深度增加而增加的过程中,存在一个下降阶段,而且下降阶段结束后,特征温度增长幅度变大。同一工艺参数下随切削次数的增加,测得的特征温度升高,其原因是:每次切削中,摩擦热主导温度变化,随切削次数的增加,刀具磨损量增大,特征温度升高。由于陶瓷低导热性和脆性,切削温度振颤不明显。     

Chemical composition of new copper alloys for machining and its effect on their susceptibility to corrosion cracking

Zinc‐containing copper alloys, the so‐called α + β brasses, are commonly used in contact with potable water. These materials are alloyed with lead to improve machinability. In wrought special brass alloys, reducing the content of this alloying element or replacing it with alternative alloying additions may give rise to a new type of machinable copper alloys which differ from the original alloys by their contents of other modifier elements such as Si (or possibly, Mg, Bi, and P). These alloys have a very low content of lead required for the break‐up of chips during machining. Even though these types of brass exhibit a very good machinability, the effects of their chemical composition on the resistance of the alloy to corrosion cracking have not yet been given sufficient attention. This paper aims to present an assessment of three new types of machinable copper alloys regarding their susceptibility to stress corrosion cracking, in comparison to that of the lead‐alloyed variety, in 0.05 M NaCl, NaNO₂, and Na₂SO₄ solutions. The slow strain rate test has been used for this purpose, and its results were correlated with metallographic evaluation of the number and depth of the cracks observed on the test specimen surfaces on completion of the test.     

Characterization and machining of alumina ceramic reinforced with lanthanum phosphate

Increasing demand for materials for severe working environment necessitates the use of ceramics. Fiber/whisker reinforcement in the structure can lead to certain defects such as debonding/delamination. Hence one can resort to particulate reinforcements. Of late attempts have been made to introduce dispersion strengthened/particulate reinforced ceramic composites. Addition of lanthanum phosphate (LaPO₄) and cerium phosphate (CePO₄) to alumina (Al₂O₃) matrix has been attempted. In this study Al₂O₃/LaPO₄ composites containing different LaPO₄ content have been assessed for the significance of LaPO₄ content on structure-property and consequent machinability. Ultrasonic drilling trials have been carried out. The response of the material to the machining environment has been assessed by monitoring the acoustic emission (AE) from the composites and defects induced during machining.     

Analysis of a free machining α+β titanium alloy using conventional and ultrasonically assisted turning

Rapid advancements in power generation and aviation industries have witnessed a widespread use of titanium and its alloys in many applications. This is primarily due to their excellent mechanical properties including, amongst other, high strength-to-density ratio, outstanding fatigue properties and corrosion resistance with the ability to withstand moderately high temperatures. However, this combination of properties results in poor machinability of the material, increasing the cost of components machined with conventional cutting techniques. Recently, Ti 6Al 2Sn 4Zr 6Mo, a modern titanium alloy with improved mechanical properties, has been introduced as a possible replacement of Ti 6Al 4V in aerospace industry. However, its poor machinability and formation of long chips in conventional turning are main limitations for its wide-spread application. Therefore, a new alloy based on Ti 6Al 2Sn 4Zr 6Mo, namely Ti 6Al 7Zr 6Mo 0.9La, was developed; it shows enhanced machinability generating short chips during metal cutting, which prevents entanglement with cutting tools improving productivity. To further enhance the machinability of this material, a novel hybrid machining technique called ultrasonically assisted turning (UAT) was used. Experimental investigations were carried out to study the machinability, chip shapes, cutting forces, temperature in the process zone and surface roughness for conventional and ultrasonically assisted turning of both alloys. UAT shows improved machinability with reduced nominal cutting forces, improved surface roughness of the machined workpiece and generation of shorter chips when compared to conventional machining conditions.     

工程陶瓷引弧微爆炸加工技术参数分析及性能特点

从系统组成、工作原理、工艺参数、技术特点等方面,介绍了一种新开发的适用于工程陶瓷材料粗加工的引弧微爆炸加工技术,分析了影响加工过程的典型工艺参数,总结了该技术的性能特点。引弧微爆炸加工系统的主要部件为专用脉冲电源及微爆炸发生器,系统工作时生成的微爆炸等离子体射流具有高温高压特性,作用于陶瓷材料表面生成一个圆形蚀坑。加工过程中的工艺参数主要包括喷嘴孔径、工作电流、工作气压、工作脉宽及工作距离。该技术具有低成本、工艺灵活、热损伤小、加工范围广及加工后表面粗糙等特点。     

Machining characteristics and fracture morphologies in a copper-beryllium (Cu-2Be) alloy

The technology of materials removal is improved greatly by the introduction of advanced cutting tools like cubic boron nitride, ceramics, polycrystalline diamond and the more recent whisker-reinforced materials. In this paper, the influence of cutting temperature on machinability, mechanical properties, microstructure, and fracture morphology of Cu-2Be alloy using a polycrystalline diamond cutter is investigated. The information on machining, microstructure, and fracture morphology of Cu-2Be alloy are very useful to understand their fabrication characteristics and the basic mechanisms of its deformation and fracture. The machinability (in terms of surface finish) of Cu-2Be alloy is evaluated as a function of cutting temperature, resulting from wet and dry cutting. Machining is carried out on a Hardinge Cobra 42 CNC machine (Hardinge Inc., Elmira, NY), and the machining parameters used—cutting speed, depth of cut, and feed rate—are kept constant during both wet and dry cutting. The machined surface finish on Cu-2Be alloy is measured using a surface finish analyzer (Surftest 401, series 178) technique. The machined specimens are examined for their strength and hardness properties using a standard Universal Testing Machine and Rockwell hardness tester, respectively. Wet cutting (using coolants) produced a smooth surface finish when compared with dry cutting of the Cu-2Be alloy. The machined specimens are examined for their microstructural features using a Nikon optical microscope. The specimens are etched using a suitable etchant solution for revealing such microstructure constituents as grain size, phase proportions, and the possible overheated areas (especially in dry cutting). The fractured surfaces from the tensile and impact toughness tests are investigated for their fracture morphologies (dry and wet cutting) using a microprocessor-controlled scanning electron microscope (Jeol Model JSM 5910 LV). A detailed analysis is also made to understand and interpret the basic fracture mechanisms responsible for crack initiation and crack propagation. The Cu-2Be alloy showed relatively higher mechanical properties in wet cutting in comparison to dry cutting operations. Fracture studies demonstrated intergranular and ductile fractures as dominant modes of fracture mechanisms in Cu-2Be alloy.     

High Speed Turning of H-13 Tool Steel Using Ceramics and PCBN

H-13 is the toughest tool steel used in machined die casting and forging dies. Due to its extreme hardness and poor thermal conductivity high speed cutting results in high temperature and stresses. This gives rise to surface damage of the workpiece and accelerated tool wear. This study evaluates the performance of different tools including ceramics and PCBN using practical finite element simulations and high speed orthogonal cutting tests. The machinability of H-13 was evaluated by tool wear, surface roughness, and cutting force measurements. From the 2D finite element model for orthogonal cutting, stresses and temperature distributions were predicted and compared for the different tool materials.     

Fixed abrasive diamond wire machining—part II: experiment design and results

Experimental results from fixed abrasive diamond wire machining of wood and foam ceramics are presented. Three types of wood—pine, oak, and fir, and three types of foam ceramic—silicon carbide, zirconia, and zirconia toughened alumina, are tested. The research investigates the life of diamond wire and effects of process parameters on the cutting forces, force ratio, and surface roughness. A scanning electron microscope is used to study the worn diamond wire, machined surfaces, and debris. The diamond wire saw is demonstrated to be very effective in machining foam ceramics. The wire life for cutting wood at slow feed rates is low. The short tool life for dry cutting of wood indicates that more research in new fixed abrasive diamond wire and wire saw machining technologies is necessary.     

Optimization of electrical discharge machining process parameters for Al6061/cenosphere composite using grey-based hybrid approach

Fly ash has congregated considerable attention as a potential reinforcement for aluminum matrix composites (AMCs) to enhance selective properties and reduce the cost of fabrication. However, poor machinability of such AMCs limits their application. The present study focuses on the preparation of cenosphere fly ash reinforced Al6061 alloys by compo casting method. X-ray diffraction analysis of the prepared AMCs exposes the presence of cenosphere particles without any formation of other intermetallic compounds. In this study, electrical discharge machining (EDM) was engaged to examine the machinability of the prepared metal matrix composite (MMCs). The measured performance characteristics for the various combinations of input process parameters were considered to be MRR, EWR and SR. Face centered central composite design (CCD) of response surface method (RSM) was employed to design the number of experimental trials required and a hybrid approach of grey-based response surface methodology (GRSM) was imposed for predicting the optimal combination of processing parameter in EDM process. Generous improvement was observed in the performance characteristics obtained by employing both the optimal setting of machining parameters. The optical 3D surface profile graphs of the ED machined surface also revealed the improvement in surface quality and texture employing the optimal processing conditions proposed by hybrid GRSM approach.     

纤维增强聚硅氧烷衍生SiOC陶瓷复合材料研究进展

由于性价比优势明显，聚硅氧烷衍生硅氧碳（SiOC）陶瓷成为有机聚合物衍生陶瓷技术领域的重要研究内容。对纤维增强SiOC复合材料的研究则是推动聚硅氧烷衍生SiOC陶瓷技术发展的里程碑事件，多年来取得了显著进展，应用前景广阔。本文从不同种类的增强纤维入手，总结了纤维增强聚硅氧烷衍生SiOC陶瓷复合材料的研究现状；面向高温结构应用和功能特性拓展，提出了后续发展建议，指出了需要解决的关键问题。     

An experimental investigation into the orthogonal cutting of unidirectional fibre reinforced plastics

This paper aims to understand the machinability of epoxy composites reinforced by unidirectional carbon fibres when subjected to orthogonal cutting. It was found that the subsurface damage and its mechanisms of a machined component are greatly influenced by fibre orientation. The material’s bouncing back is a characteristic phenomenon associated with the cutting of a fibre-reinforced composite. Three distinct deformation zones appear, i.e., chipping, pressing and bouncing when the fibre orientation is <90°. Otherwise, fibre-bending during cutting will become more significant and subsurface damage caused by fibre-matrix debonding will be severer. As a result, surface roughness, subsurface damage and cutting forces all change dramatically with the fibre orientation. It was also found that the curing conditions of making the composites do not have an obvious effect on the machinability, though the mechanical properties of the materials vary.     

灰度模糊算法优化Al-SiC-Gr混合金属基复合材料的加工参数

石墨颗粒增强金属基复合材料能够提供更好的切削加工性能和摩擦性能。用灰度模糊算法优化Al-SiC-Gr混合金属基复合材料的加工参数,以获得到具有优秀综合性能的材料。当混合金属基复合材料中SiC-Gr的质量分数分别为5%、7.5%和10%时,对应的拉伸强度分别为170、210和204 MPa。另外,与另外2种材料相比,Al-10%（SiC-Gr）复合材料具有更好的切削加工性能。与其他的灰度技术相比,灰度模糊逻辑算法在输出方面提高了推理的合理性,降低了不确定性。实验结果表明,在设置的相同加工参数下,与其他的灰度技术相比,灰度模糊逻辑算法的推理合理性从0.619提高到0.891,且同时保证材料具有更好的综合性能。