Grindability of high-temperature alloy with ceramic alumina wheels

The grindability of high-temperature alloy by using ceramic alumina wheels is studied on the basis of extensive analysis of the grinding force, grinding temperature, surface roughness and topography of ground surfaces, residual stress, hardness distribution of surface layer, and morphology of the surface layer from a metallographic point of view. The grinding burn mechanism of high-temperature alloy is unveiled and the feasible grinding parameters to avoid burning are analyzed. Some conclusions are obtained as follows. Increasing the grinding depth or the wheel velocity makes grinding temperature and residual tensile stress of the surface rise, which deteriorates the surface topography. Appropriate liner velocity of the wheel is 18–22 m/s and the depth of grinding should not exceed 0.02 mm in grinding GH2132 alloy with ceramic alumina wheels to assure the surface quality. When a_p increases enough to cause grinding burn, the strengthening effect of particles ?′ in ? base decrease and the micro-hardness of the surface is obviously lower than that of the base material, which deteriorates the mechanical properties and heat resistance of GH2132 alloy. Results provide a theoretical and experimental basis for technical optimization in the grinding of high-temperature alloy with high efficiency and high quality.     

Photoresist for photochemical machining of alumina ceramic

The applicability of a cyclized polybutadiene rubber as a resist material for photoetching of alumina ceramic in phosphoric acid was studied. Stencil breakdown, change in the stencil thickness during etching, and etch factor were measured. It was found that this material post-baked at temperatures as high as 300°C for 30 min provided good resistance to severe attack by the acid at temperatures of up to 300°C. The effects of post-bake temperature, of etching temperature, of etching time, and of original slot width on etch factor are discussed.     

用灰关联分析法确定性能参数对陶瓷材料磨削加工性的影响

选择反映磨削加工性系统行为的加工过程／输出参数，作为系统特征变量，选择陶瓷材料的性能参数为相关因素变量，应用灰关联分析法，分别生成各变量的处理数据序列，建立系统特征变量和相关因素变量的绝对灰关联度矩阵，利用优势分析原则确定陶瓷材料各种性能参数对其磨削加工性的影响程度。以SiC、Al2O3、Si3N4和ZrO2 4种陶瓷材料为例，应用灰关联分析法确定出4种性能参数对陶瓷材料磨削加工性影响程度的排序。研究实例表明，灰关联分析法是确定陶瓷材料性能参数对磨削加工性的影响程度的一种合理、有效的方法。     

Evolution of residual stresses in micro-arc oxidation ceramic coatings on 6061 Al alloy

Most researches on micro-arc oxidation mainly focus on the application rather than discovering the evolution of residual stresses. However, residual stresses in the surface coatings of structural components have adverse effects on their properties, such as fatigue life, dimensional stability and corrosion resistance, etc. The micro-arc oxidation ceramic coatings are produced on the surfaces of 6061 aluminum alloy by a homemade asymmetric AC type of micro-arc oxidation equipment of 20 kW. A constant current density of 4.4___0.1 A/dm2 and a self-regulated composite electrolyte are used. The micro-arc oxidation treatment period ranges from 10 min to 40 min, and the thickness of the ceramic coatings is more than 20 Bin. Residual stresses attributed to 7-A1203 constituent in the coatings at different micro-arc oxidation periods are analyzed by an X-ray diffractometer using the sin2~u method. The analysis results show that the residual stress in the ceramic coatings is compressive in nature, and it increases first and then decreases with micro-arc oxidation time increase. The maximum stress value is 1 667_＋20 MPa for period of 20 min. Through analyzing the coating thickness, surface morphology and phase composition, it is found that the residual stress in the ceramic coatings is linked closely with the coating growth, the phase composition and the micro cracks formed. It is also found that both the heat treatment and the ultrasonic action release remarkably the residual compressive stress. The heat treatment makes the residual compressive stress value decrease 1 378 MPa. The ultrasonic action even alters the nature of the residual stress, making the residual compressive stress change into a residual tensile stress.     

SG砂轮磨削航空合金温度研究

钛合金和高温合金的导热性差,磨削过程中产生的高温不仅加速砂轮的磨损,而且降低工件表面质量,磨削温度是影响磨削过程的重要参数。本文重点阐述了夹丝半人工热电偶法测温原理及标定方法,并对不同磨削条件下磨削航空合金的温度进行了实验研究。实验选用新型陶瓷氧化铝SG砂轮和普通GC砂轮,分析磨削温度信号的物理意义,系统地研究了磨削用量、磨削方式、砂轮类型以及工件材料对航空合金磨削时温度的影响,为航空合金的高效高精度磨削加工工艺优化提供实验依据。     

陶瓷刀具车削TC4钛合金磨损特性的研究

为研究陶瓷刀具切削钛合金的磨损机理,采用CC6060陶瓷刀片对TC4钛合金进行了干式车削试验。结果表明:陶瓷刀具干式切削TC4钛合金时,磨损形貌以前刀面月牙洼磨损、后刀面沟槽磨损和刀尖破损为主,磨损机理主要是粘结磨损和氧化磨损。随着切削速度的增加,刀具磨损加剧,刀具寿命降低。CC6060陶瓷刀片干式切削钛合金时的使用寿命很低,不适于干式切削钛合金。     

激光辅助加热切削氧化铝工程陶瓷的刀具磨损试验研究

氧化铝工程陶瓷具有较高的强度、硬度和较好的耐磨性,是典型的难加工材料,激光辅助加热切削是加工这种高硬度材料的有效方法之一。通过对氧化铝工程陶瓷在激光辅助加热切削时立方氮化硼(CBN)刀具的磨损试验,研究了激光功率、主轴转速和进给速率等不同工艺参数对刀具磨损所产生的影响。结果发现,CBN刀具的磨损形态主要表现为前刀面和后刀面磨损,造成刀具磨损的主要原因是磨料磨损和粘结磨损;同时还发现,与普通切削相比,采用辅助加热切削可以明显减小刀具的磨损。     

自由轮在自动变速器中的作用

阐述了自由轮在常用自动变速器换档过程中的作用及工作情况，利用杠杆法探讨了自由轮在自动变速器中如何布置，同时分析了自动变速器在换档过程中采用自由轮的利弊。     

陶瓷结合剂CBN砂轮磨削GH4169高温合金的磨削加工性与磨削表面完整性

本文对ＣＢＮ砂轮磨削ＧＨ４１６９高温合金的磨削加工性和磨削表面完整性进行了系统研究。研究了ＣＢＮＳ轮磨削ＧＨ４１６９高温合金时磨削参数对磨削力、磨削温度和磨削比的影响规律；在正交试验和显著性分析的基础上．建立了磨削力和磨削温度的经验公式。在ＣＢＮ砂轮磨削ＧＨ４１６９高温合金磨削表面完整性的试验研究中，对磨削表面粗糙度、磨削表面硬化及磨削表面残余应力进行了研究．建立了表面完整性指标与磨削参数之间的关系。并根据正交试验建立了磨削表面粗糙度的经验公式。     

有机磨削液在氮化硅陶瓷磨削过程中的清洗机理研究

通过一系列试验考察了不同有机物的乳液作为冷却液时金刚石砂轮磨削氮化硅陶瓷的堵塞效果.试验结果表明:短链有机物及烷烃作为磨削液时,金刚石砂轮磨削氮化硅陶瓷会发生堵塞,而包含较强极性基团的长链有机物可以很大程度地降低砂轮堵塞.其原因是烷烃在氮化硅陶瓷表面形成的非极性油膜对非极性的氮化硅磨屑产生较强的吸引而聚集在磨削区,进而导致砂轮堵塞.油膜表面具有一定的极性可以很大程度地缓解磨屑的积聚并降低堵塞现象的发生.通过对几种极性有机物的清洗效果进行分析,探讨了有机物的分子结构特征与其清洗性能的关系.     

Modeling and microstructural modification of alumina ceramic for improved tribological properties

Very simplified models were deduced for identifying important factors influencing friction and wear of ceramics in unlubricated sliding contact. Based on the theoretical predictions, laser surface alloying was used for modifying alumina ceramic by adding hafnia. Tribological tests were run on the modified ceramic, monolithic alumina and two different cutting ceramics on the base of alumina under conditions of unlubricated reciprocating sliding motion against Al₂O₃ balls. The friction coefficient and linear wear of the sliding pairs were substantially reduced and the transition from mild to severe wear shifted to higher applied surface pressure for the microstructurally modified ceramic compared with the monolithic alumina or the cutting ceramics, respectively.     

细长齿斜齿轮的测绘与计算

通过测量细长齿斜齿轮的螺旋角及公法线长度等计算出准确的变位系数,再根据测量所得齿顶无直径及齿根园直径计算出齿顶高系数ha^*和径向间隙系数C^*,这种测量计算方式它使所取参数与被测齿轮的实际参数能完全吻合。     

高温合金GH4169深孔加工研究现状及展望

高温合金是一种高性能的材料,已广泛应用于航空、航天、原子能等行业,目前开始在石油、化工等民用工业中应用。重点通过对国内外切削、钻削现状的阐述和分析,表明了该项技术在国内行业发展中的紧迫性,并指出该研究的重点是如何进行高效的深孔加工技术。     

激光冲击强化对TiAl合金组织和性能的影响

为研究激光冲击强化对TiAl合金组织和性能的影响,利用波长为1 064nm、脉宽为20ns、单脉冲能量为0～22J的Nd:YAG激光器对TiAl合金试件进行了实验研究。采用显微硬度计、表面粗糙度仪和扫描电镜分别测量了激光冲击强化前后的表面显微硬度、粗糙度和表面微观形貌,利用X射线应力分析仪测量了激光冲击强化表面残余应力和晶面极性,并分析了其高温稳定性。实验结果表明:当单脉冲能量增加到9J时,表面显微硬度增加了33.4%,粗糙度由0.042μm增大到了0.285μm,表面残余压应力由20MPa增加到了297MPa,表面微观形貌出现了凸凹不平,局部纹理和层状微结构。将9J激光冲击强化后的试件在650℃下保温4h后,残余压应力值从297MPa降到230MPa,显微硬度值从377HV0.2降到345HV0.2,(002)晶面取向有向中心移回的趋势。得到的数据显示,激光冲击强化能够极大地改善TiAl合金的组织和性能,且具有一定的高温稳定性。     

Long-term lubrication of momentum wheels used in spacecrafts—An overview

Momentum wheels are spacecraft actuators of large angular momentum used for the attitude control and stabilization of spacecrafts. The on-orbit performance of spacecrafts depends largely on the performance of the momentum wheels which in turn depends on its bearings and its lubrication. Currently, the life cycle of spacecrafts are aimed to be around 20–30 years. However, the increases in size, complexity and life expectancy of spacecrafts demand advanced technologies especially in tribology and in turn the development of more innovative lubrication systems for long-term operation. This article reviews the tribological requirements of momentum wheels and the various lubrication systems used in the past and raises a necessity to develop a new system to cope with the new requirements.     

陶瓷刀具在发动机中介机匣加工中的应用

采用陶瓷刀片进行了发动机中介机匣的粗铣切削试验,研究了陶瓷刀片加工镍基高温合金的切削性能,优化了切削参数和走刀路线,分析了高速干式加工的切屑形态,指出应用陶瓷刀具加工镍基高温合金是提高效率、降低成本的有效途径。     

Experimental investigation and numerical analysis for machinability of alumina ceramic by laser-assisted grinding

Alumina (Al₂O₃) ceramic has been widely used in various fields, but it has certain difficulties in machining as a hard and brittle material. While laser-assisted grinding (LAG), an alternative and novel method for fabrication of alumina ceramic, can utilize laser beam to locally heat the workpiece before the ceramic is removed, thereby reducing fracture toughness and keeping the surface integrity. In this paper, a thermal model is established to study and understand the processing mechanism of the LAG process. Meanwhile, an orthogonal experiment is designed and implemented to optimize the grinding process. Then, by analyzing the surface topography, the advantages of LAG are strongly proved. It is found that the temperature modelling results matches experimental results well. The processing parameter that has greatest impact on surface roughness is laser power, followed by grinding depth and wheel speed, and feeding speed at last. The optimal surface roughness value can be obtained by certain processing parameters. Also, compared to conventional grinding (CG), the removal method of alumina ceramics alters from brittle fracture to plastic fracture. Overall, this study clearly elucidates that LAG of alumina ceramic is a very promising machining method, and can be potentially utilized for various industrial, aerospace and automobile applications.     

树脂结合剂金刚石砂轮磨削铁氧体陶瓷磨削力的实验研究

通过一系列的实验，研究了树脂结合剂金刚石砂轮磨削铁氧体陶瓷材料时磨削力的变化规律及其特点。通过磨削对比实验方法分析磨削铁氧体陶瓷时，磨削用量对磨削力大小的影响。通过砂轮速度，磨削深度，横向进给速度和纵向进给速度等因素影响磨削力大小变化的数据及磨削力信号特征处理的分析和比较，分析了对铁氧体材料磨削时产生的磨削力影响的一些规律，表明铁氧体陶瓷磨削时磨削力变化的特有规律．     

Tribological characteristics in high-speed grinding of alumina with brazed diamond wheels

In this work, two brazed diamond wheels fabricated by brazing in vacuum were used to grind alumina at different grinding speeds. During the process, the horizontal and vertical grinding forces were measured by a force measurement device. The grinding forces, specific grinding energy, and friction in grinding of alumina at low and at high speeds were investigated. The results show that the friction coefficient decreases with the increase of the grinding speed and also relates to the grinding mode. A nearly proportional relationship between grinding power per unit width (P _m ) and the rate of plowed surface area generated per unit time per unit width (S _w ) reveals the effects of friction in grinding and most of the grinding energy is expended by friction. The surface energy per unit area generated by plowing friction (J _s ) for high-speed grinding is found to be lower than for low-speed grinding.     

GH4169高温合金铣削力试验研究

针对高温合金材料GH4169的切削加工性差的特点,设计了铣削力测量试验,以研究切削用量、冷却措施等因素对高温合金数控铣削过程产生的铣削力的影响。通过铣削试验分析,得到了切削参数与铣削力的变化曲线,提供了合理的切削参数;利用线性回归方法建立了铣削力经验公式,并通过了试验验证;进行了干切削与乳化液冷却的铣削力对比试验。试验表明选择合理的切削参数和冷却措施能有效抑制铣削力的产生。