A Hybrid Machining Process Combining Micro-EDM and Laser Beam Machining of Nickel–Titanium-Based Shape Memory Alloy

Micro-electrical discharge machining (EDM) is a slow process as compared to laser machining, on the contrary laser machining lacks good surface quality. To overcome the drawbacks of both these processes, this paper suggests a hybrid machining process which combines laser and micro-EDM processes for drilling microholes in advanced engineering materials such as Nickel–Titanium (Ni–Ti)-based shape memory alloy. To achieve the objective of the suggested hybrid process, pilot holes are drilled with laser machine and rimmed out by micro-EDM drilling. The suggested process requires investigation of various combinations of micro-EDM drilling process conditions to obtain optimum machining parameters for the hybrid process. It has been found that the proposed hybrid machining process resulted in 50–65% reduction in machining time without affecting the quality of microholes as compared to the standard micro-EDM process.     

A resonant accelerometer with two-stage microleverage mechanisms fabricated by SOI-MEMS technology

We present the design, fabrication, and testing of a push-pull differential resonant accelerometer with double-ended-tuning-fork (DETF) as the inertial force sensor. The accelerometer is fabricated with the silicon-on-insulator microelectromechanical systems (MEMS) technology that bridges surface micromachining and bulk micromachining by integrating the 50-/spl mu/m-thick high-aspect ratio MEMS structure with the standard circuit foundry process. Two DETF resonators serve as the force sensor measuring the acceleration through a frequency shift caused by the inertial force acting as axial loading. Two-stage microleverage mechanisms with an amplification factor of 80 are designed for force amplification to increase the overall sensitivity to 160 Hz/g, which is confirmed by the experimental value of 158 Hz/g. Trans-resistance amplifiers are designed and integrated on the same chip for output signal amplification and processing. The 50-/spl mu/m thickness of the high-aspect ratio MEMS structure has no effect on the amplification factor of the mechanism but contributes to a greater capacitance force; therefore, the resonator can be actuated by a much lower ac voltage comparing to the 2-/spl mu/m-thick DETF resonators. The testing results agree with the designed sensitivity for static acceleration.     

Impact force measurement of an actuator arm of a hard disk drive

Impact forces of an actuator arm of a hard disk drive (HDD) are measured by means of modifying the levitation mass method (LMM) whose basic concept was proposed by the first author. In the LMM, force is measured as the inertial force of a mass levitated with sufficiently small friction using an aerostatic linear bearing. The Doppler frequency shift of the laser beam reflecting from the mass is accurately calculated from the waveform recorded using a digitizer. The velocity, the position, the acceleration and the inertial force of the mass are calculated from the measured time-varying Doppler frequency shift. In the experiments, the mechanical response of an actuator arm of a HDD against an impact load and the inertial force of the actuator arm in free oscillation are measured. The importance and the problems concerning the present knowledge on the impact force of an actuator arm of a HDD are also discussed.     

非接触磁耦合光纤光栅位移传感器

研发了一种基于光纤Bragg光栅（fiber Bragg grating,FBG）技术的非接触磁耦合位移传感器．两块扁圆柱型硬磁铁通过软铁连接起来,形成一U型传感探头．该U型探头与被测物形成一闭合磁路,实现间隙与磁耦合力的转换,再通过一平面薄板结构将磁耦合力转变为光纤FBG的轴向应变．通过理论和实验详细地分析研究了上述两个关键技术环节．研究表明：该非接触位移传感器为一非线性传感器,非线性主要是由于磁耦合力与间隙的平方成反比这一传感器固有特性以及漏磁,特别是漏磁随间隙增加而变大造成的该非线性传感器的数据处理结果为：随机不确定度为0．23％;回程误差为0．376％;传感器综合误差为±0.606％     

A Study on Plasma Channel Expansion in Micro-EDM

Micro-electrical discharge machining (EDM) is derived from traditional EDM and widely used in the micro-fabrication field. By using narrow-width pulse power generators, micro-EDM can be applied to machining work with smaller gaps and at low energy levels, which demonstrates a different electrodischarge process and material erosion characteristics, compared with traditional EDM. Through in-depth study on micro-EDM and magnetic fluid dynamics (MHD), a comprehensive plasma model has been established consisting of the breakdown and the expansion stages. In addition, theoretical calculation based on the model is performed, followed by results analysis. Finally, micro-EDM experiments are conducted to verify the feasibility of the model and the correctness of the results analysis.     

基于微放电加工元件轮廓测量的探针制造

为了推动微加工和微机械技术的进步，微型零件轮廓和尺度测量方法的发展非常重要．可行方法之一就是使用带微探头的小型三维轮廓测量仪．这种仪器的探头必须针对某个零件的测量，按照最佳外形制造．微放电加工有着极小加工力，可用于各种探头的制造，本研究中用它进行探头加工．用这种方法制造了多种探头，将其装在基于扫瞄隧道显微技术(STM)的小型三维轮廓测量仪上．所制造的探头已被成功地用于各种微元件测量，结果表明此方法可行．     

Application of multi-criteria decision making methods for selection of micro-EDM process parameters

Ti-6Al-4V super alloy is an important engineering material with good strength to weight ratio and a wide range of applications in a number of engineering fields because of its excellent physical and mechanical properties.This work determines optimum process parameters such as pulse on time,peak current,gap voltage and flushing pressure,which influence the micro-electro discharge machining(EDM) process during machining of Ti-6A1-4V using combined methods of response surface methodology(RSM) and fuzzy-technique for order preference by similarity to ideal solution(TOPSIS).Central composite design(CCD) is used in the experimental investigation.A decision making model is developed to identify the optimum process parameters in the microEDM process,which influences several machining criterions such as material removal rate(MRR),tool wear rate(TWR),overcut(OC) and taper.Triangular fuzzy numbers are used to determine the weighting factor for each process criterion.Further a fuzzy-TOPSIS method is used to select the most desirable factor level combinations.The proposed technique can be used to select optimal process parameters from various sets of combinations of process parameters in a micro-EDM process.     

Inertial sensor technology trends

This paper presents an overview of how inertial sensor technology is applied in current applications and how it is expected to be applied in nearand far-term applications. The ongoing trends in inertial sensor technology development are discussed, namely interferometric fiber-optic gyros, micro-mechanical gyros and accelerometers, and micro-optical sensors. Micromechanical sensors and improved fiber-optic gyros are expected to replace many of the current systems using ring laser gyroscopes or mechanical sensors. The successful introduction of the new technologies is primarily driven by cost and cost projections for systems using these new technologies are presented. Externally aiding the inertial navigation system (INS) with the global positioning system (GPS) has opened up the ability to navigate a wide variety of new large-volume applications, such as guided artillery shells. These new applications are driving the need for extremely low-cost, batch-producible sensors     

精梳机钳板机构低阶谐振现象及其成因分析

精梳机钳板机构是一平面二自由度七杆机构,运用机构弹性动力学理论分析该机构的低阶谐振现象,并探索其成因。结合钳板机构的实际工况建立动力学方程,利用振型叠加法求解,分析其低阶谐振现象。构建四种方案,从刚体惯性力、加压弹簧恢复力、冲击力三个方面探索钳板机构低阶谐振的成因。结果表明:钳板机构产生低阶谐振的主要原因是加压弹簧恢复力唤起的前三阶振型的简谐共振,刚体惯性力对谐振点响应没有作用但会影响机构的响应值,冲击力对机构响应值以及谐振点响应的影响都不大。     

New CMOS-compatible mechanical shear stress sensor

A new approach to the measurement of mechanical stresses is presented. The new sensor design utilizes the fact that shear stresses in the silicon lattice generate an electric field perpendicular to an electric current. The sensor effect is characterized by a new piezo-bridge-coefficient, which relates the sensitivity of the sensor structure to its crystallographic orientation. The sensor is based on a CMOS-compatible structure. It offers the possibility to realize highly sensitive single-element stress sensors for use in MEMS or in smart force measurement strips, as well. An example of a signal conditioning circuit is shown. Special designs with improved sensitivity and low noise are presented. The response to parasitic magnetic fields is measured and strongly reduced. Furthermore, the temperature behavior was analyzed and finally optimized     

Fabrication and functional characterization of engineered features on pyrolytic carbon

Engineered features on pyrolytic carbon (PyC) have been reported to improve the functional performance of the bio-implants. This paper is focused on the functional characterization of micro-features created on the surface of PyC. Two different types of micro-features (wide channels and arrayed holes) have been created by micro-electrical discharge machining (micro-EDM). Two other micro-features (fine channels and micro-pillars) have been created by micromilling process. Coliform bacterial strain was isolated from a sample of water and grown on all four textured. Cell growth was carried out on an unmachined surface to see the behavior of the isolated bacterial strain on the textured/non-textured surfaces. The samples were examined under SEM before and after wash to see cell growth and cell adhesion capability of the textures. The wide channels by micro-EDM show the maximum cell growth but poor cell adhesion. 184% higher cell growth has been observed on the wide channels in comparison with unmachined surface. The fine channels by micro-milling show comparatively lower growth but the cell adhesion on this surface was found excellent. 71% cells remain unwashed after washing of the surface having fine channel textures. It means that the channels structure shows the maximum cell growth and adhesion independent of machining process.     

Effect of Electrode Size on the Performances of Micro-EDM

Understanding the effect of processing parameters on the tool electrode wear during micro-electrical discharge machining (micro-EDM) is helpful to predict and compensate the electrode wear, so as to improve the machining precision. In this paper, experiments are carried out and the influences of tool electrode diameter on the micro-EDM process are discussed based on the skin effect and area effect. It is demonstrated that the machining speed, tool wear, and taper rate are different with the increase of tool electrode diameter. Due to the skin effect and area effect, larger electrode diameter results in higher material removal rate along with higher tool wear rate. The electrode material removal increment is more than the workpiece material removal increment with the increase of tool electrode diameter, which leads to the increase of relative tool wear ratio. Discharge energy is concentrated on the tool surface which enhances the possibility of discharge on the side face and the corner of the tool electrode during the micro-EDM, especially when drilling with a larger tool electrode. As a result, a tool electrode with larger diameter results in a higher taper rate.     

Research on ultrasonic-assisted drilling in micro-hole machining of the DD6 superalloy

The DD6 nickel-based superalloy exhibits remarkably high temperature properties; therefore, it is employed as a crucial structural material in the aviation industry. Nevertheless, this material is difficult to process. Ultrasonic-assisted drilling (UAD) combines the characteristics of vibration processing technology and conventional drilling technology, significantly improving the machinability of difficult-to-machine materials. Thus, UAD experiments were performed on micro-hole machining of DD6 superalloy in this study. The effects of amplitude, frequency, spindle speed, and feed rate on thrust force, machining quality, and drill bit wear were studied; thereafter, a comparison was drawn between these effects and those of conventional drilling (CD). The experimental results reveal that the thrust force decreases with an increase in spindle speed or a decrease in feed rate for both UAD and CD. UAD can significantly reduce the thrust force. With the same processing parameters, the greater the amplitude, the greater the reduction of the thrust force. The surface roughness of the hole wall produced by UAD is lower than that of CD. Compared with CD, UAD reduces the burr height, improves machining accuracy, and reduces drill bit wear.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00301-6     

在微细电火花铣削中介质对电极损耗的影响

在微细电火花加工（EDM）中电极损耗是不可避免的,而针对电极损耗的研究大都是在油工作液中,很少针对气中放电时的电极损耗进行研究．气中电火花加工普遍采用管状电极,所以为了获得尺寸更小的工件,通过反拷块可磨削出微米级的实心电极,并采用外部充气的方式,可实现微米级三维结构的气中电火花加工．实验考虑了影响气中放电电极损耗的各种因素．通过观察微细电火花三维铣削放电现象与结果,可得到气中放电的规律．由于电火花加工中电极损耗是不可避免的,所以在三维铣削加工中对电极进行在线检测并补偿,工件成形精度大大提高．对刀具路径进行合理规划,可以缩短加工时间．与油中电火花铣削相比,气中电火花加工时电极损耗更低,加工表面质量更好．     

Studies on the surface of high-performance alloys machined by micro-EDM

Micro-electrical discharge machining (EDM) is used in the fabrication of Ti-6Al-4V, SUS304, and SKH59 alloys, which are important aviation materials. EDM influences the surface morphologies of these materials and directly affects their reliability during use. However, current research focusing on the morphology of surfaces machined by micro-EDM is rare. Traditional surface evaluation parameter such as R_a cannot describe the surface morphology machined by micro-EDM precisely. Therefore, systematic research on surface morphology of the aforementioned alloys is presented in the study. Based on a novel evaluation method combining fractal theory with wavelet filters, first, comparative experiments on surface morphology evaluations of different materials were conducted and discussed. Second, two different pulse power supplies were studied to explore the effect of pulse power on the high-performance alloy surface. Third, three different micro-EDM processing methods were compared to study their effects on the surfaces of high-performance alloys. Finally, different machining parameters such as discharging energies, rotation speeds of the tool electrode, and gap voltages were set to investigate their effects on the surface morphology. The results showed that different materials, pulse power supplies, processing methods, and machining parameters greatly influence the surface morphology quality, and appropriate machining advice is proposed.     

A Novel Ferrofluidic Inclinometer

Inertial transducers based on the use of ferrofluids as inertial mass can be of great interest due to their peculiarities and due to the advantages that they show when compared to traditional devices. Ferrofluids are special solutions of magnetic particles in a carrier liquid whose density and other physical features can be controlled by an external magnetic field. In this paper, the development of a ferrofluidic inclinometer, which exhibits a tunable operating range and a valuable metrological feature and an intrinsic robustness against inertial shocks, is presented. The device consists of one excitation coil and two sensing coils wound around a glass pipe where a drop of ferrofluid is contained in a water environment. The magnetic force, which is induced by the excitation coil, attracts the ferrofluidic mass in a position that depends on the device inclination. The voltage at the output of the two sensing coils is related to the ferrofluidic mass displacement and thus reflects the tilt to be measured. Analytical models, simulations, and experimental results are presented to demonstrate the suitability of the proposed approach.     

《基于动力学响应失效模式的悬臂转子可靠性分析》

基于悬臂转子的动力学响应失效模式,通过对影响悬臂转子安全性的外载荷、几何特征、材料特性等敏感参数的分析,分别建立了悬臂转子静态响应和动态响应的极限状态方程。对每个极限状态方程,使用泰勒级数对非线性极限状态方程在设计点处进行线性化,运用一次二阶矩理论,得到相应的可靠度指标。对比考虑和忽略惯性力影响下的可靠度指标和可靠度结果,分析惯性力对可靠性分析结果的影响,建立针对该类悬臂转子的有效的可靠性分析方法。     

Effect of Thermal and Material Anisotropy of Pyrolytic Carbon in Vibration-Assisted Micro-EDM Process

Pyrolytic carbon (PyC) is extremely biocompatible with high directional strength and unique directional thermal conductivity. PyC is used in biomedical devices like cardiovascular implants and finger prosthesis. Microfeatures on PyC have been proven as performance-driving agents in many cases. This work is focused on micro-electric discharge machining (micro-EDM) characterization of PyC to understand the effect of material/thermal anisotropy on the process response. An L9 Taguchi design of experiments has been performed to analyze the effect of gap voltage, capacitance, and frequency on the MRR, surface quality, and dimensional accuracy. MRR increases by 16% with vibration in AB plane machining. In C plane, the effect of vibration on MRR is not favorable. MRR reduces by 56% if the machining plane changes from AB to C due to the lower thermal conductivity along C. Surface roughness decreases by an order of magnitude if machining plane changes from AB to C; surface roughness of 65 nm has been achieved in C plane under certain conditions. The error in dimensional accuracy in C plane is 46% lower than AB plane. EDS shows noncontaminated machined surface. Finally, micro-EDM process has been used to create microfeatures in PyC, which could potentially improve/alter the desired surface quality.     

基于均力结构60MN叠加式力值传递系统

针对60MN力标准机开展国际力值比对的需求,提出了一种带均力结构的叠加式力值传递系统。采用理论和数值模拟的方法分析了力值传递系统中的侧向力分布及均力结构对侧向力的影响,并通过实验进行了验证。结果表明,均力结构不但能减小传递到每个子传感器上的侧向力,而且能将侧向力较均匀地分配到各子传感器上,减小旋转效应对系统的影响。采用均力结构的力值传递系统能满足国际大力值比对与量值溯源的计量性能要求。     

铝合金车轮机加立车压爪紧固螺栓断裂问题的分析及优化

目的 研究分析立车压爪螺栓工作过程中的受力情况,寻求螺栓断裂的原因,并通过优化改进夹具结构,实现提高螺栓使用寿命的目的。方法 采用压力传感器系统,实测压爪压力,并建立力学模型,结合螺栓的力学性能参数,推断螺栓断裂的原因。结果 通过优化改进夹具结构,将螺栓承受的部分弯矩转移到压爪和压爪轴上,能够延长螺栓的使用寿命。结论 螺栓断裂主要是由于螺栓反复加载过程中出现了疲劳损伤,导致螺栓断裂。