激光参数对陶瓷微孔加工质量的影响

为研究激光加工氧化铝陶瓷高质量微孔的成型工艺,采用皮秒激光自旋切割模式在0.3 mm厚的氧化铝陶瓷上加工直径为0.2 mm的微通孔。研究了激光加工参数(激光功率、离焦量、重复频率、打孔次数及扫描速度)对微孔质量的影响。试验结果表明,随着激光功率的增加,孔的入口、出口直径增大,入口、出口圆度和锥度呈现减小的趋势;随着扫描速度的降低,孔的锥度呈下降趋势;随着负离焦量的增大微孔锥度逐渐减小;重复频率的变化对微孔质量各性能指标影响不大。试验发现激光功率和离焦量是影响微孔质量主要因素。最终在功率为27 W、离焦量为-0.7 mm、扫描速度为400 mm/s、重复频率为100 kHz及打孔次数为10次时获得入口圆度为2.995μm、出口圆度为3.509μm及锥度为5.96°的高质量微孔。     

激光改性后氮化铝基板的可加工性研究

利用激光改性方法研究了被广泛应用在微电子组件封装中的氮化铝（AlN）陶瓷基板在不同气体环境、激光功率、扫描间隔下的可加工性,通过试验测量了AlN试件表面硬度值和元素含量。试验结果表明：在N2、Ar、O2三种气体环境下,试件表面成分主要为AlN、Al和Al2O3,且显微硬度计测得Ar环境下的熔覆层硬度最低,最有利于后续切削加工。在Ar环境下,随着激光功率的增大和扫描间隔的减小,AlN表面改性后的硬度减小,最小值可达到174.83HV,更易进行切削加工。     

国产LTCC材料微波基板特性分析

为了探究国产低温共烧陶瓷（Low Temperature Co-fired Ceramic, LTCC）材料的工程应用前景,促进LTCC材料国产化进程,文中从工程应用的角度出发,使用国产LTCC材料制作了微波基板并进行了相应的测试和研究。研究内容主要包括国产LTCC材料的匹配性能以及基于国产LTCC材料的微波基板的性能和可靠性。研究结果表明,国产LTCC材料的匹配性能满足要求,基于国产LTCC材料研制的微波基板的性能和可靠性与基于进口LTCC材料研制的微波基板相当,满足X波段T/R组件技术要求。     

基于微波热裂法的陶瓷切割技术

针对传统陶瓷切割方法普遍存在的高污染、高噪声、低切割面质量等缺点,提出了一种基于微波热裂法的陶瓷切割方法。阐述了微波热裂法的切割原理, 开发了实验装置,该装置所形成的微波能束为有效加热区域直径约6 mm的圆形热源。通过实验研究了利用该热源切割四种陶瓷（玻璃、碳化硅板、氧化铝板和氧化锆板）的机理。研究结果表明：吸波陶瓷内部的微缺陷处有爆破点产生,这有利于降低陶瓷材料切割所需宏观温度（玻璃：85 ℃,碳化硅：230 ℃）;非吸波陶瓷表面涂覆的石墨层中有微放电痕迹产生,进而可获得偏移较小的切割轨迹;与激光热源相比,微波热源具有更广泛的适用性和更低成本的优点。     

皮秒激光氧化铝陶瓷微孔加工工艺

陶瓷基复合材料因其优异的散热性能、绝缘性、热膨胀系数和物理硬度等,适用于大功率电力电子模块、航空航天和军工电子等领域,但由于在传统加工过程中易出现崩边、层间撕裂等缺陷,且无法实现微孔加工,限制了其应用.针对氧化铝陶瓷高质量微孔加工的需求,采用红外皮秒激光作为光源对氧化铝陶瓷进行了打孔试验研究,分析了激光功率、离焦量和扫...     

LCP 基板制作工艺及其在微波无源电路中的应用

液晶聚合物（LCP）基板是继低温共烧陶瓷（LTCC）后的新一代微波毫米波基板材料,具有损耗小、成本低、使用频率范围大、强度高、重量轻等许多独特的优点。文中详细介绍了LCP制作工艺,对基于LCP基板的微波平面传输线的性能进行了分析,并设计出两层基板的X波段21dB耦合器,为基于LCP多层基板的微波无源电路研制打下基础。     

微波基板表面可焊性镀层的制备及性能评估

文中针对低温共烧陶瓷（Low Temperature Co-fired Ceramic, LTCC）微波多层基板高密度布线和多深腔的结构形态,结合化学镀工艺过程及原理,讨论了采用化学镀在LTCC微波多层基板表面制备可焊性镀层的工艺难点。针对某微波多层基板化学镀生产中出现的漏镀和渗镀缺陷,深入分析了各影响因素及作用机理,借助扫描电子显微镜（Scanning Electron Microscope, SEM）、能谱仪（Energy Dispersive Spectrometer, EDS）等微观分析手段,确定了引起漏镀和渗镀缺陷的主要原因,采取酸漂洗、增强玻璃刻蚀条件等措施,解决了漏镀和渗镀的难题。对可焊性镀层的附着力和键合可靠性进行了测试评价,结果表明,金属浆料及可焊性镀层均附着良好,键合强度较高,键合点可靠,能很好地满足微波组件的应用要求。     

大尺寸LTCC 基板高钎透率焊接工艺研究

低温共烧多层陶瓷（Low Temperature Co-fired Ceramic, LTCC）技术在军工电子领域的应用越来越广泛,但是大尺寸多腔体LTCC 基板的钎透率一直是制约LTCC 基板应用范围进一步扩展的重要因素。文中研究了基板可焊性、平面度以及回流焊接工艺等因素对LTCC 基板钎透率的影响规律,并在此基础上完善了大尺寸多腔体LTCC 基板的回流焊接工艺。基板与壳体焊接一次成形,有效控制了焊料流淌;基板钎透率达到95% 以上,避免了对焊缝和多余焊锡的返工返修工作。这些都推动了大尺寸多腔体LTCC 基板在微波组件中的批量应用。     

雷达功率组件的金刚石微通道热沉激光加工工艺

为研究雷达功率组件金刚石微通道热沉的加工难题,开展了飞秒激光加工多晶金刚石微流道的工艺研究,仿真模拟了飞秒激光作用于金刚石表面的温度场分布,以及诱导去除过程,理论与实验研究了金刚石的烧蚀阈值,系统研究了激光能量、扫描速度、扫描次数、焦点位置等参量及其优化工艺参数对金刚石微槽尺寸的影响规律.结果表明:当飞秒激光功率大于0...     

压路机轴承座加工工艺及专用夹具

振动压路机球铰轴承座由1个底板和1个立板组焊而成,其中底板下侧为基准面（A面）,底板上加工有1个直径为15₀^+0.036mm的通孔和1个直径为10₀^+0.036mm的通孔;立板上加工有1个直径为50₀^+0.036mm的通孔及直径为56mm的油槽。如图1所示。由于直径为56mm的油槽在镗床上加工比较困难,我们决定在普通车床上加工轴承座立板上的直径为50₀^+0.036的通孔及直径为56mm的油槽。为此编制了加工工艺,设计了专用夹具。1.编制加工工艺     

CO2 Laser Processing On Ceramic Substrates Of Light Emitting Diode Assisted By Compressed Gas

The use of ceramic substrates in high power LEDs is becoming increasingly common. However, the brittleness of ceramics makes them difficult to process and susceptible to cracking. This study used a CO₂ laser with auxiliary gas to drill and cut Al₂O₃ and AlN ceramic substrates. The authors investigated the influences of parameters such as auxiliary gas pressure, laser power, repetition rate, and working speed on processing quality, in terms of pattern size, surface roughness, hole taper angle, and fracturing. The experiment results show that Al₂O₃ low-cost processing can be achieved with low laser power and high auxiliary gas pressure. In contrast, AlN has a high melting point and high thermal conductivity, for which lower auxiliary gas pressure is required to ensure high-quality processing.     

Effect of microwave heat treating processing on frictional behaviour of aluminium alloy 2900 composites

The sliding wear behaviour of microwave processed, SiC_p and Al₂O_3p reinforced aluminium alloy 2900 and 2024 metal matrix composites prepared by powder metallurgy method was investigated in a pin on disc system. The objective is to determine the effects of novel alloying elements of AA 2900, ceramic addition and microwave aging process on the strength to tribological properties. This composite is evaluated to be an effective replacement for conventionally available AA 2024 composites in brake applications. Compared to conventional heat treating processes, microwave processing used for heat treating the samples is observed to be novel method in improving the strength–microstructural–tribological properties. AA 2900 with 6 wt-% Al₂O₃ exhibited good strength to microstructure relationship with excellent wear characteristics compared to AA 2024 composites which are governed by alloying elements in AA 2900. 2 H aged AA 2900 with 6 wt-% Al₂O₃ sample exhibited good frictional coefficient values with good density and strength characteristics. Hence, it is observed that alloying elements in AA 2900 and microwave processing have enhanced the strength to tribological behaviour where the property enhancement is achieved only through ceramic reinforcements.     

Experimental research on electrical discharge machining characteristics of engineering ceramics with different electrical resistivities

Electrical discharge machining (EDM) is the extensively used nonconventional material removal process for machining engineering ceramics provided they are electrically conductive. However, the electrical resistivity of the popular engineering ceramics is higher, and there has been no research on the relationship between the EDM parameters and the electrical resistivity of the engineering ceramics that can be machined effectively by EDM. This paper investigates the effects of the electrical resistivity and the EDM parameters on the EDM performance of ZnO/Al₂O₃ ceramic in terms of the machining efficiency and the quality. The experimental results showed that the electrical resistivity and the EDM parameters such as pulse on-time, pulse off-time, and peak current had the great influence on the machining efficiency and the quality during electrical discharge machining of ZnO/Al₂O₃ ceramic. Moreover, the electrical resistivity of the ZnO/Al₂O₃ ceramic, which could be effectively machined by EDM, increased with increasing the pulse on-time and peak current and with decreasing the pulse off-time, respectively. Furthermore, the ZnO/Al₂O₃ ceramic with the electrical resistivity up to 3,410 Ω cm could be effectively machined by EDM with the appropriate machining condition.     

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.     

Predictive model and process parameters optimization of Nd:YAG laser micro-turning of ceramics

The present work highlights laser micro-turning operation of 10-mm diameter cylindrical-shaped alumina (Al₂O₃) ceramic using pulsed Nd:YAG laser. The paper also addresses development of mathematical models for correlating the various micro-machining parameters such as laser beam average power, pulse frequency, workpiece rotational speed, assist air pressure, and Y feed rate with the response criteria such as surface roughness and deviation in turned depth for achieving desired surface quality as well as dimensional accuracy during micro-turning operation using Nd:YAG laser system. Response surface methodology-based design of experiments has been adopted for the experimentation. This investigation also highlights the various test results that confirm the validity and correctiveness of the developed mathematical models through analysis of variance test. The test results were analyzed through various response surface plots to study the effect of the process parameters on the aforementioned responses. The results of validation experimentation show a good agreement for the developed empirical models. Sensitivity analyses of the developed models have been done to find out the variation in the output with respect to variations in the significant input process parameters. Moreover, multi-performance optimization has been done to find out the optimal parametric setting for achieving the desired process performances. Analysis also has been made based on scanning electron microscopy micrographs of the laser micro-turned surface achieved during machining at multi-criteria optimization setting.     

Tribological behaviour of steel‐alumina sliding pairs under boundary lubrication conditions

The tribological behaviour of oil‐lubricated steel‐alumina sliding pairs was investigated using a ball‐on‐disc tribometer at room temperature. Commercial bearing balls of 10 mm diameter were mated to 99.7% Al₂O₃ discs, and additive‐free mineral oil was fed into the contact area. The sliding speed and the applied normal load were varied, and the initial surface roughness of the Al₂O₃ disc was altered using different polishing and grinding procedures. The results showed that the surface roughness of the ceramic discs dominated the tribological behaviour under the given experimental conditions. The sliding speed as well as the normal load showed less effect on the friction behaviour, but the amount of wear depended strongly on the normal load. From the results it was concluded that improvement of the surface roughness and optimised surface machining of the ceramic material can be essential for improving the tribological performance for boundary‐lubricated steel‐ceramic sliding pairs.     

Application of nano electrolyte in the electrochemical discharge machining process

As a nontraditional machining process, electrochemical discharge machining (ECDM) can apply to hard and brittle materials such as glass and ceramic. Improvement of process efficiency is an important topic that has been addressed in many investigations using various techniques such as magnetic field and ultrasonic vibrations.Nano particles are new and advanced materials that can be dispersed in a fluid to obtain a nano fluid with desirable specifications. This method can be implemented in the ECDM process by the application of the nano electrolyte. Nano electrolyte can present enhanced properties, in particular enhanced electrical and thermal conductivities which lead to more powerful discharges and greater material removal.In order to study the variation of discharge physics, consequent captures from discharges were taken. Besides using current signal diagrams, larger numbers of discharges were found using nano electrolytes. Results of hole depth showed that both Cu and Al₂O₃ nano electrolytes improved the hole depth as 21.1% and 18.7%, respectively. An undesirable effect of nano electrolyte was observed on the entrance overcut, which raised 8.3% and 10.7% using Cu and Al₂O₃ nano electrolytes, respectively, in comparison to the simple electrolyte. This drawback is negligible compared to the significant improvement of hole depth. SEM images of tool wear showed larger molten materials on the tool main edges by the application of nano electrolyte.     

Surface Abuse Associated with Finish Turning of Gray Cast Iron with Ceramic Tools

Machining trials were carried out on a G-17 cast iron using round and square-shaped pure oxide (≥99 vol. % Al₂O₃ + ≤ 1 vol. % ZrO₂), mixed oxide (70 vol. % Al₂O₃ + 30 vol. % TiC) and silicon coarbide whisker-reinforced (75 vol. % Al₂O₃ + 25 vol. % SiC) ceramic tools in order to study the extent of damage on the machined surfaces. G-17 is a BS 1452 (1977) designation and equivalent to ANSI/ASTM A48-83 grade 40 designation. The test results show that the round-shaped ceramic tools produced better surface finish and less damage than square inserts under the cutting conditions investigated due to their increased nose radius, which increased the tool-workpiece contact area during machining. The surface finish deteriorates with prolonged machining and an increase in the depth of cut. The hardness values of the surface layer were generally above the average hardness value of the base material due to the hardening of the surface layer as a result of the high pressure, compressive stress and temperatures generated at the cutting edge during machining. A higher rate of hardening was observed when machining with the mixed oxide and SiC whisker-reinforced ceramic tools due, perhaps, to the relatively high temperatures generated at the higher cutting speed (500 m/min.) used.     

An electron microprobe and cathodoluminescence study of chemical reactions between tool and workpiece when turning steel with alumina-based ceramics

Crater wear of alumina-based ceramic cutting tools when machining steel is predominantly dependent upon superficial plastic deformation. Such tool surface deformation may be greatly affected by chemical reactions with workpiece material. Crater surfaces of worn alumina-based ceramic tools in Coromant grade CC 620 (a pure ceramic, containing Al₂O₃ and ZrO₂) have been analysed by electron microprobe and cathodoluminescence after turning steel SS 2541 (similar to AISI 4337). It was found that the deformed surface layer had increased concentrations of iron and magnesium. Both these elements were probably present as spinel phases FeO. Al₂O₃ and MgO. nAl₂O₃ in solid solution. The spinel phases have higher yield strengths and probably also higher ductility than alumina itself, which may explain why wear rates are reduced when such compounds are found at the alumina tool-chip interface.     

Wear behavior of some cutting tool materials in hard turning of HSS

This study presents an assessment of the performance of four cutting tool in the machining of medium hardened HSS: polycrystalline c-BN (c-BN+TiN), TiN coated polycrystalline c-BN (c-BN+TiN), ceramic mixed alumina (Al₂O₃+TiC), and coated tungsten carbide (TiN coated over a multilayer coating (TiC/TiCN/Al₂O₃)). The Al₂O₃+TiC and the coated carbide tools can outperform both types of c-BN at high cutting speeds. Raman and SEM mapping revealed an alumina tribo-layer that protects the surface of the Al₂O₃+TiC cutting tool. The high chemical and thermal stability of Al₂O₃ tribo-films protects the tool substrate because it prevents the heat generated at the tool/chip interface from entering the tool core.