聚晶金刚石高速研磨实验研究

通过实验对比研究了采用冷却套冷却和不冷却两种情况下,使用树脂结合剂金刚石砂轮高速研磨聚晶金刚石片时,研磨时间、研磨速度和研磨压力等工艺参数对聚晶金刚石片材料去除率及表面质量的影响规律.     

Characterisation of thermal influences after laser processing polycrystalline diamond composites using long to ultrashort pulse durations

The laser processing of cutting tool edges is growing rapidly due to its flexibility, short cycle times and negligible waste. However, the quality of the tool and its cutting edge can vary greatly with different laser parameters and processing strategies. The generation of a graphitic carbon layer and a heat affected zone (HAZ) could occur during laser processing which is expected to reduce the quality and lifetime of the cutting tool. By using focussed ion beam (FIB) techniques to generate a cross section, the graphitic carbon layer and heat affected zone are characterised quantitatively and qualitatively for laser processes and as a reference, lapping and wire electro-discharge machining processes, used in the generation of polycrystalline diamond composite cutting tool edges. A focus is put on laser based techniques which vary in pulse duration from long microsecond pulses down to ultrashort picosecond pulses. A deep insight into the focussed ion beam techniques used and extensive analysis through Raman spectroscopy and energy dispersive X-ray spectroscopy (EDX) into the laser–material interactions are presented.     

Finishing effect of abrasive flow machining on micro slit fabricated by wire-EDM

This experimental research use the method of abrasive flow machining (AFM) to evaluate the characteristics of various levels of roughness and finishing of the complex shaped micro slits fabricated by wire electrical discharge machining (Wire-EDM). An investigative methodology based on the Taguchi experimental method for the micro slits of biomedicine was developed to determine the parameters of AFM, including abrasive particle size, concentration, extrusion pressure and machining time. The parameters that influenced the machining quality of the micro slits were also analyzed. Furthermore, in the shape precision of the micro slit fabricated by wire-EDM and subsequently fine-finished by AFM was also elucidated using a scanning electron microscope (SEM). The significant machining parameters and the optimal combinations of the machining parameters were identified by ANOVA (analysis of variation) and the S/N (-to-noise) ratio response graph. ANOVA was proposed to obtain the surface finishing and the shape precision in this study.     

Basic study on pulse generator for micro-EDM

An RC pulse generator can easily generate a pulse on-time as short as a several dozen nanoseconds in micro-electro-discharge machining (micro-EDM), but its discharge frequency is low due to the time needed to charge the capacitor in micro-EDM, which has a strong negative effect on the pulse generator’s working efficiency. Therefore, a new transistor-type isopulse generator has been developed for micro-EDM in this research. Evaluation of the machining characteristics proved that the transistor-type isopulse generator is suitable for micro-EDM. The experimental results reveal that the transistor-type pulse train generator is unsuitable for micro-EDM due to its low removal rate: 80-ns and 30-ns pulse on-times of discharge current can be obtained by using the transistor-type isopulse generator developed in this research, and the removal rate of this generator is two or three times higher than that of the traditional RC pulse generator.     

An experimental study on the grinding of alumina with a monolayer brazed diamond wheel

A monolayer diamond grinding wheel was fabricated by brazing in vacuum. The wheel was then used to grind alumina at three different grinding speeds. The horizontal and vertical grinding forces, and the grinding temperatures were measured during grinding. SEM observations were made for the ground workpiece surfaces. The influences of the peripheral wheel speed on the grinding forces, specific grinding energy and grinding temperatures were analyzed under different combinations of depth of cut and workpiece velocity. The dependence of the average grinding force per grain and specific grinding energy on the maximum undeformed chip thickness was discussed respectively. It was found that an increase in the peripheral wheel speed reduced grinding force, but increased force ratio, specific grinding energy, and grinding temperature.     

Tribochemical machining of polycrystalline diamond using ferrous tool materials

Abstract

This article studies the tribochemical machining of polycrystalline diamond (PCD) by utilizing ferrous tool material as the cutter. The influence of cutting parameters and different ferrous materials on the material removal rate of the PCD workpiece has been investigated. The material removal rate increases with the increase of the rpm of ferrous “cutter”, AISI 1020 steel is unable realize the tribochemical machining, and the material removal rate of using AISI 1045 steel was higher than that of using W2-21/2 steel, e.g. when rpm was 3000, the material removal rate of using AISI 1045 was 0.059?mm/min, and using W2-21/2 it was 0.020?mm/min. The surface roughness of the machined PCD workpiece using W2-21/2 (0.40?μm) was slightly improved in comparison to that produced using AISI 1045 (0.47?μm). The influence of hydrogen catalysis on tribochemical machining of PCD has been investigated. Compared with no use of steam, if a large amount of steam is continuously injected the material removal rate will significantly increase, e.g. when the rpm was 3000 (using AISI 1045) the material removal rate of no steam was 0.059?mm/min, while with steam it was 0.082?mm/min.     

Fabrication of polycrystalline diamond microtool using a Q-switched Nd:YAG laser

A Q-switched Nd:YAG laser (1,064 nm, 100 ns) was used to machine 2?×?1.5?×?0.5-mm rhombus-shaped tool inserts from a 60?×?0.5-mm circular disk of polycrystalline diamond. A systematic experimental study was undertaken to examine the effects of pulse repetition rate, feed rate, and number of laser passes on kerf, material removal rate, recast layer, surface morphology, and surface roughness. The optimal laser parameters for generating two-dimensional tool profiles were an average power of 3 W, a pulse repetition rate of 2 kHz, a feed rate of 1 mm/s, and a total of 45 laser passes. The beneficial results were a material removal rate of 0.02 mm³/min, kerf width of 27 μm, cutting edge radius of 6 μm, and surface roughness (Ra) of 0.625 μm. Recast layer formation, undulations, and striations were observed in the laser-cut regions. These features were attributed to the presence of a molten layer of cobalt binder, and amorphous carbon and graphite transitioned from diamond. An intriguing feature is the presence of fine particulate matter ranging in size from nanometers to a few micrometers in the laser-cut regions. It is believed that phase transition of diamond and cobalt during laser machining created thermal expansion mismatch stresses sufficient to fracture the solid into fine fragments.     

Experimental study on fabrication and evaluation of micro pyramid-structured silicon surface using a V-tip of diamond grinding wheel

A mechanical fabrication of micro pyramid-structured silicon surface is proposed using crossed grooving with a 60° V-tip of diamond grinding wheel. It can obtain high form-accuracy, good surface quality and efficient productivity in contrast to laser machining and etching, and also assure a high aspect ratio in contrast to other mechanical processes. In order to describe its micro-structured topography, a white-light interferometer was employed, and its measured point cloud was matched using an Iterative Closest Point (ICP) algorithm. In micro grinding, a novel CNC mutual-wear truing was first developed to sharpen the wheel V-tip; then, the effects of microscopic wheel topography, silicon crystal-orientation and grinding parameter were investigated on ground micro-topography, truing ratio and material removal ratio; finally, its form-accuracy, pyramid top radius, groove tip radius, surface roughness and aspect ratio were evaluated. It is shown that better microscopic grain protrusion topography on wheel V-tip produces much larger material removal ratio and much better micro-structured topography in micro grinding, but it leads to much less truing ratio in finer GC truing. In micro grinding, silicon crystal-orientation has little effect on micro-structured topography due to diamond crystal-orientations that are randomly distributed on wheel V-tip. Although the micro pyramid-structured form error is only about 3.4 μm, its V-groove bottom and pyramidal top have very large form errors (23.1-47.9 μm) due to the sharpness of wheel V-tip and the frangibility of micro pyramid top. On increasing feed speed, its pyramid top radius decreases and its groove tip radius slightly increases, ultimately leading to an increase in aspect ratio, whereas its surface quality descends. It is concluded that the micro-pyramid arrays may be precisely patterned on silicon surface using a SD600 wheel with crossed tool paths, on-machine V-tip truing and the depth of cut in 1 μm.     

Formation of a negative-polarity lightning current pulse using a magnetic explosion generator

Preliminary results on the formation of a current pulse with an amplitude of >50 kA and 2-μs rise time on a standard grounding electrode are presented. The results were obtained using a BMΓ-160 magnetic-explosion generator equipped with a pulse-sharpening device based on electrically explosive copper conductors in an arc-suppressing medium.     

An experimental study on microcutting of silicon using a micromilling machine

Micro-end-milling can potentially create desired 3D free-form surface features on silicon using ductile machining technology. A number of technological barriers must be overcome for micro-end-milling to be applied in the cutting of single crystal silicon. To produce smooth surfaces on brittle materials, such as silicon, it is important that the material be machined in the ductile mode. A major limitation of machining brittle materials is that the process of removing the material can generate subsurface damage. We have carried out an experimental study to find the optimum cutting conditions for obtaining ductile regime machining using a micromilling machine. The ductile and brittle regimes in the machining of silicon using diamond-coated end mills were demonstrated by machining grooves. The force ratio, F_t/F_c, was used to determine the milling performance on silicon. The experimental data show that the dominant ductile cutting mode was achieved when F_t/F_c?>?1.0.     

An experimental study on damage detection of structures using a timber beam

Using vibration methods for the damage detection and structural health monitoring in bridge structures is rapidly developing. However, very little work has so far been reported on timber bridges. This paper intends to address such shortcomings by experimental investigation on a timber beam using a vibration based method to detect damage. A promising damage detection algorithm based on modal strain energy was adopted and modified to locate/evaluate damage. A laboratory investigation was conducted on a timber beam inflicted with various damage scenarios using modal tests. The modal parameters obtained from the undamaged and damaged state of the test beam were used in the computation of damage index, were then applied using a damage detection algorithm utilising modal strain energy and a statistical approach to detect location of damage. A mode shape reconstruction technique was used to enhance the capability of the damage detection algorithm with limited number of sensors. The test results and analysis show that location of damage can be accurately identified with limited sensors. The modified method is less dependent on the number of modes selected and can detect damage with a higher degree of confidence.     

An experimental investigation on micro machining of fine-grained graphite

Industrial applications of the micro milling process require sufficient experimental data from various micro tools. Research has been carried out on micro milling of various engineering materials in the past two decades. However, there is no report in the literature on micro milling of graphite. This paper presents an experimental investigation on micro machinability of micro milling of moulded fine-grained graphite. Full immersion slot milling was conducted using diamond-coated, TiAlN-coated and uncoated tungsten carbide micro end mills with a uniform tool diameter of 0.5 mm. The experiments were carried out on a standard industrial precision machining centre with a high-speed micro machining spindle. Design of experiments (DoE) techniques were applied to design and analysis of the machining process. Surface roughness, surface topography and burrs formation under varying machining conditions were characterized using white light interferometry, SEM and a precision surface profiler. Influence of variation of cutting parameters including cutting speeds, feedrate and axial depth of cut on surface roughness and surface damage was analysed using ANOVA method. The experimental results show that feedrate has the most significant influence on surface roughness for all types of tools, and diamond tools are not sensitive to cutting speed and depth of cut. Surface damage and burrs analysis show that the primary material removal mode is still brittle fracture or partial ductile in the experimental cutting conditions. 3D intricate micro EDM electrodes were fabricated with good dimensional accuracy and surface finishes using optimized machining conditions to demonstrate that micro milling is an ideal process for graphite machining.     

The design and optimization of micro polycrystalline diamond ball end mill for repairing micro-defects on the surface of KDP crystal

Micro-milling is a promising approach to repair the micro-defects on the surface of KH₂PO₄ (KDP) crystal. The geometrical parameters of micro ball end mill will greatly influence the repairing process as a result of the soft brittle properties of KDP crystal. Two types of double-edged micro ball end mills were designed and a three-dimensional finite element (FE) model was established to simulate the micro milling process of KDP crystal, which was validated by the milling experiments. The rake angle of −45°, the relief angle of 45° and the cutting edge radius of 1.5–2 μm were suggested to be the optimal geometrical parameters, whereas the rake angle of −25° and the relief angle of 9° were optimal just for micro ball end mill of Type I, the configuration with the rake angles ranging from 0° to 35°, by fully considering the cutting force, and the stress–strain distribution over the entire tool and the cutting zone in the simulation. Moreover, the micro polycrystalline diamond (PCD) ball end mills adopting the obtained optimal parameters were fabricated by wire electro-discharge machining (WEDM) and grinding techniques, with the average surface roughness Ra of tool rake face and tool flank face ∼0.10 μm, and the cutting edge radius of the tool ∼1.6 μm. The influence of tool's geometrical parameters on the finished surface quality was verified by the cutting experiments, and the tool with symmetric structure was found to have a better cutting performance. The repairing outlines with Ra of 31.3 nm were processed by the self-fabricated tool, which could successfully hold the growth of unstable damage sites on KDP crystal.     

基于ATmega16实现手摇脉冲发生器输出脉冲控制

针对数控系统手摇脉冲发生器模块的脉冲漏计、电动机脉冲输出滞后或因脉冲输出不连续导致电动机振动等现象,基于ATmega16单片机设计了手摇脉冲发生器控制模块,采用"预测脉冲发生周期"和"随动检测"、"补偿输出控制"的软件实现方法,实现了数控系统在手轮高倍率选择状态下的稳定输出控制。     

An experimental analysis of a flaring process for tube ends using a novel spinning tool

The flaring of tube ends are typically performed using electromagnetic forming, or punch-and-die method, both of which cost time and effort. In this work, a new method of tube flaring using a metal spinning process is proposed. An experimental study was carried out to flare the end of aluminium tubes. A multifunction tool was designed based on the flaring ratio to widen the tube end. Several flared specimens were conducted at different working conditions. The effects of working conditions such as flaring ratio, axial feed rate (mm/rev), and rotating speed (rpm) on the flaring loads were investigated. An experimental analysis was carried out to illustrate the effect of the working conditions on the characteristics of the formed part. The analysis showed that these working conditions have a clear influence on wall thickness, surface hardness, and flaring loads.     

A CFD-aided experimental study on bending of micro glass pipettes

This paper presents a study on the temperature profile in the bending process of glass pipettes. To prevent undesirable deformation of the pipette at its bending section, such as kink and constriction, several factors influencing the bending quality are investigated, including the width and temperature of the heating element, heating and bending time. Taguchi method is used to study the key factors and to identify an optimal parameter combination. ANSYS is also employed to study the heat transfer and temperature distribution in the heating zone. It is concluded that the temperature distribution in the bending area is critical to the bending quality, and the width of the heating element decisively determines the temperature distribution.     

A high-voltage nanosecond pulse generator based on a barrier discharge

One of the specific features of the barrier electric discharge is the short duration of microdischarge processes that last about tens of nanoseconds. A high-voltage nanosecond pulse generator based on a barrier electric discharge is presented. A voltage of tens of kilovolts is usually applied to electrodes of the discharge cell. The peak values of the current pulse may be very high (from a few amperes to several tens of amperes). The presented high-voltage nanosecond pulse generator, having a sufficiently simple design, ensures quite good pulse repetition stability, and, when necessary, allows one to easily tune characteristics of pulses and their repetition rates by changing the geometrical, electrical, and physical-chemical parameters of the setup.     

脉冲编码器、测速发电机性能自动测试分析系统

脉冲编码器、测速发电机是传动系统中常用的速度传感器,其性能分坏直接影响控制系统的品质指标。本文设计实现了一种基于微机脉冲编码器,测速发电机性能自动测试系统,对该系统的硬件构成和软件分析功能进行了详细讨论。     

新型三维微动台的设计与试验分析

研究设计一种新型的、以压电陶瓷为驱动器的三维微动台结构。该微动台以柔性铰链为弹性导轨实现了微定位。 分析所采用的直圆柔性铰链的参数变化对其造成的性能影响;提出一种新型柔性铰链结构,利用有限元分析软件AN SYS对这种新型结构进行理论分析和试验测试。试验表明:采用这种柔性铰链结构的微动台刚度比较小、运动耦合误差 小,定位精度优于±0.01μm。     

基于 CPLD的双通道高压脉冲信号源

针对声波测井压电陶瓷换能器容性大的负载特性,采用单片机和CPLD相结合的方式设计了一种输出幅度高、驱动电流大、脉冲宽度可调的双通道高压脉冲信号源。系统利用C8051F350单片机及PWM控制芯片MM33060A,并结合自耦变压器反激式升压电路将12 V直流供电电压抬升至300 V。采用CPLD产生精确的频率可控的300 V脉冲电压,利用脉冲变压器进一步提升电压,得到了上千伏的高压激励脉冲。实验结果标明,设计的信号源在激励压电陶瓷换能器时,负载上得到了比较理想的波形,波形上升沿陡峭,无拖尾及振荡现象,满足实际应用需求。