Algorithms and machining experiments to reduce depth errors in servo scanning 3D micro EDM

In servo-scanning 3D micro electro discharge machining (SS-3D MEDM), the depth errors of 3D micro cavities are accumulated layer by layer due to the contour scanning process with keeping discharge gap for compensating axial electrode wear in real time. In this research, the errors’ causes were analyzed, and then a layer depth constrained algorithm (LDCA) and an S-curve accelerating algorithm (SCAA) were proposed to reduce the depth errors. By LDCA, over-cutting errors can be avoided by controlling a tool-electrode feed maximum at every scanning spot. As a supplementary algorithm for LDCA, SCAA can compensate insufficient-machining errors at start and end of scanning paths. Implementation process and control strategy of the algorithms were also described. The purpose of this research is to efficiently machine complex 3D micro-cavities with high accuracies of shape and surface. By use of computer-aided manufacturing software of Pro/Engineer to plan complex 3D scanning paths, machining experiments were carried out to verify the proposed algorithms. The experimental results show: Typical 3D micro cavities <800 μm can be automatically machined, and the machining accuracies of micro surfaces and edges are obviously improved, and the depth errors can be controlled within 2 μm, and the material removal rate reaches 2.0 × 10⁴ μm³/s with tool electrode of ∅80 μm and its rotational speed of 1000 r/min. In addition, the 3D micro cavities designed on unknown edge or hollow workpieces can be successfully formed.     

A study on the evaluation of the micro grooving using the AE technology

This study describes evaluation and monitoring methods of machining characteristics for developed micro grooving machines. Experiments were conducted under various process conditions such as spindle revolution speed, feed rates, and depth of groove. V and U shape of blades and STD11 were used in this experiment. The status of grooving was evaluated through analysis of the acoustic emission (AE) signal resulted in each process condition. Based on the analysis, this paper examines the possibility of monitoring adapting fuzzy logic. In conclusion, this paper presents the possibility of monitoring in process adapting AE technology and appropriate micro grooving conditions.     

精密车削Cr12模具钢的切削力研究

利用SB—CNC超精密车床精密车削Cr12钢的切削试验。研究了切削速度、进给量和切削深度对切削力的影响变化规律，并分析了产生这些变化的原因。结果表明提高切削速度能减小切削力，而进给量越大。切削力也越大；但刀尖圆弧对径向切削分力和轴向切削分力的影响很大。在小切深时。径向切削分力大于轴向切削分力。随着切深的增加，径向分力越来越小。轴向分力越来越大，当切深大于圆弧半径时。径向切削力保持不变。     

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.     

微铣削刀具磨损研究现状

在微制造领域,微铣削因具有加工材料的多样性和能实现三维曲面加工的独特优势而受到越来越多学者的关注,但是微铣刀的快速磨损严重影响了微铣削技术的应用.研究表明微铣刀的磨损主要发生在刀尖部位,刀具磨损呈现显著的尺度效应.分析了微铣刀的磨损机理、刀具磨损的影响因素和改善措施以及刀具磨损状态的监控,并指出了今后研究值得注意的发展方向.     

Surface generation modeling of micro milling process with stochastic tool wear

Micro milling is widely used to manufacture miniature parts and features at high quality with low set-up cost. To achieve a higher quality of existing micro products and improve the milling performance, a reliable analytical model of surface generation is the prerequisite as it offers the foundation for surface topography and surface roughness optimization. In the micro milling process, the stochastic tool wear is inevitable, but the deep influence of tool wear hasn't been considered in the micro milling process operation and modeling. Therefore, an improved analytical surface generation model with stochastic tool wear is presented for the micro milling process. A probabilistic approach based on the particle filter algorithm is used to predict the stochastic tool wear progression, linking online measurement data of cutting forces and tool vibrations with the state of tool wear. Meanwhile, the influence of tool run-out is also considered since the uncut chip thickness can be comparable to feed per tooth compared with that in conventional milling. Based on the process kinematics, tool run-out and stochastic tool wear, the cutting edge trajectory for micro milling can be determined by a theoretical and empirical coupled method. At last, the analytical surface generation model is employed to predict the surface topography and surface roughness, along with the concept of the minimum chip thickness and elastic recovery. The micro milling experiment results validate the effectiveness of the presented analytical surface generation model under different machining conditions. The model can be a significant supplement for predicting machined surface prior to the costly micro milling operations, and provide a basis for machining parameters optimization.     

Study of ductile mode cutting in grooving of tungsten carbide with and without ultrasonic vibration assistance

In this study, ductile mode chip formation in conventional cutting and ultrasonic vibration assisted cutting of tungsten carbide workpiece material has been investigated through experimental grooving tests using CBN tools on a CNC lathe. The experimental results show that as the depth of cut was increased there was a transition from ductile mode to brittle mode chip formation in grooving both with and without ultrasonic vibration assistance. However, the critical value of the depth of cut for ductile mode cutting with ultrasonic vibration assistance was much larger than that without ultrasonic vibration assistance. The ratio of the volume of removed material to the volume of the machined groove, f _ab , was used to identify the ductile mode and brittle mode of chip formation in the grooving tests, in which f _ab <1 indicates ductile mode chip formation and f _ab >1 indicates brittle mode chip formation. For the same radius of tool cutting edge, the value of f _ab at the ductile-brittle transition region either with or without ultrasonic vibration was less than 1. However, the f _ab value with ultrasonic vibration assistance was close to 1. The experimental results demonstrate that ultrasonic vibration assisted cutting can be used to improve the ductile mode cutting performance of tungsten carbide work material.Nomenclature A amplitude - A ₁ , A ₂ cross-section areas of the ridge - A _V cross-section area of the groove - A _W the value of A _V subtracted by A ₁+A ₂ - f vibration frequency - f _ab ratio of work material removal - t time - v nominal cutting speed - v _u vibration velocity - v _t true cutting speed in ultrasonic cutting - angular frequency     

天然金刚石刀具的研磨及其刃口半径检测技术

指出了天然金刚石刀具的刃口锋利度对现代超精密切削加工的重要影响,介绍了国内外天然金刚石刀具研磨技术的发展现状,以及我国金刚石刀具刃磨技术中普遍存在的问题。详细叙述了对刃磨后刀具刃口半径检测的几种可行方法,展望了刃口半径检测技术的前景。     

16Mn钢焊接件疲劳裂纹扩展的微观特征研究

研究了在循环载荷作用下,16Mn钢焊接件疲劳裂纹的扩展情况.通过光学显微镜观察了裂纹扩展的微观特征,发现了裂纹在焊接结构不同部位的扩展路径方式并分析了显微组织对裂纹扩展的影响.裂纹在母材处为穿晶扩展,在热影响区和焊缝金属中的扩展为穿晶和沿晶混合型.     

Effects of the cutting feed, depth of cut, and workpiece (bore) diameter on the tool wear rate

Most published studies on metal cutting regard the cutting speed as having the greatest influence on tool wear and, thus, tool life, while other parameters and characteristics of the cutting process have not attracted as much attention in this respect. This is because of the existence of a number of contradicting results on the influence of the cutting feed, depth of cut, and workpiece (bore) diameter. The present paper discusses the origin of the aforementioned contradicting results. It argues that, when the optimal cutting temperature is considered, the influence of the aforementioned parameters on tool wear becomes clear and straightforward. The obtained results reveal the true influence of the cutting feed, diameter of the workpiece, and diameter of the hole being bored on the tool wear rate. It was also found that the depth of cut does not have a significant influence on the tool wear rate. The obtained results provide methodological help in the experimental assessment and proper reporting of the tool wear rates studied under different cutting conditions.     

Precision machining of micro tool electrodes in micro EDM for drilling array micro holes

Micro electro discharge machining (micro EDM) is suitable for machining micro holes on metal alloy materials, and the micro holes can be machined even to several microns by use of wire electro discharge grinding (WEDG) of micro electrodes. However, considering practicability of micro holes <Φ100 μm in batch processing, the controllable accuracy of holes’ diameter, the consistency accuracy of repeated machining and the processing efficiency are required to be systematically improved. On the basis of conventional WEDG method, a tangential feed WEDG (TF-WEDG) method combined with on-line measurement using a charge coupled device (CCD) was proposed for improving on-line machining accuracy of micro electrodes. In TF-WEDG, removal resolution of micro-electrode diameter (the minimum thickness to be removed from micro electrode) is greatly improved by feeding the electrode along the tangential direction of wire-guide arc, and the resolution is further improved by employing negative polarity machining. Taking advantage of the high removal resolution, the precise diameter of micro-electrode can be achieved by the tangential feed of electrode to a certain position after diameter feedback of on-line measurement. Furthermore, a hybrid process was presented by combining the TF-WEDG method and a self-drilled holes method to improve the machining efficiency of micro electrodes. A cyclic alternating process of micro-electrode repeated machining and micro holes’ drilling was implemented for array micro holes with high consistency accuracy. Micro-EDM experiments were carried out for verifying the proposed methods and processes, and the experimental results show that the repeated machining accuracy of micro electrodes was less than 2 μm and the consistency accuracy of array micro holes was ±1.1 μm.     

A novel and exact analytical model for determination of critical depth in trapezoidal open channels

Critical depth is a significant parameter in the designing and management of open channels and related hydraulic structures, understanding the flow characteristics and calculations of varied flows (gradually, spatially, etc.). The trapezoidal cross sections are the most commonly used geometric sections in the network of water transmission and distribution channels, thus discussing its geometrical and hydraulic parameters is inevitable. The used nonlinear and mathematical relationships governing the critical depth problem in the trapezoidal channels are implicit and complex, hence the methods of trial and error, graphical and numerical are used to calculate it. In the present study, new explicit equations are presented based on mathematical analysis of the critical depth problem in the trapezoidal channel. Mathematical analysis has led to completely mathematical and analytical solutions having a definite physical (hydraulic) concept. Having the explicit equations provided by the ease of calculation process with no limitation of the application range and high accuracy are the advantages of this analysis. The accuracy of the presented equations is desired and determined according to the required accuracy. The data used for verification of the results are based on the critical flow condition (Froude number equal to 1), which has been generated in a wide and practical range of the geometric and hydraulic characteristics of the channel. Also, the calculated values are compared with the real values of the considered parameter.     

大尺寸缸体密封槽深度检测工具

针对大孔径油缸类零件密封槽直径及其公差难以测量的问题,介绍一种简单实用、方便可靠的检测工具.     

微细立铣削切削振动试验研究

基于45钢微细立铣削试验,分析了微细立铣削切削振动的基本特征,研究了直槽立铣加工时铣削参数对振动加速度和振动位移量影响的基本规律.研究结果表明:在同样的切削工况下,微细立铣削的切削振动远大于大直径立铣刀铣削的情况;铣削参数是振动加速度的主要影响因素,振动加速度随铣削参数的增加都呈上升趋势,但轴向切深H和转速n对振动加速度的影响比进给量f更显著;在一定的参数范围内,减小主轴转速n和增大轴向切深H能够减小振动位移量的大小.     

Delta-perturbation expansion for critical flow depth problem in trapezoidal channels

For man-made and natural channels, the knowledge of the critical depth is an important parameter in the analysis of free surface flow regimes and backwater curves. For trapezoidal channels, a trial and error approach and large sequence computation (iterations or infinitely nested radicals) are needed due to the implicit character of the governing equation. In the present paper, an original analytical solution based on the Delta-perturbation expansion is proposed for the problem of critical depth computation in trapezoidal shaped channels. The obtained explicit analytical expression forms a very precise solution for practical purposes. A series of real canals are treated as examples to illustrate the application of the proposed approach.     

A geometrical model of the cut in five-axis milling accounting for the influence of tool orientation

This paper presents a model of the cut geometry in five-axis milling. This allows the establishment of a better model of cutting force to account for the influence of the tool orientation. The formulation of the width and the thickness of the cut were derived and implemented in a computer simulation. The results of simulations were verified experimentally and a good agreement was obtained. The result shows the importance of including the influence of the tool orientation in the cut cross-section calculation.     

电解加工在微细制造技术中的应用研究

电解加工是利用阳极金属电化学溶解原理来去除材料的制造技术,这种微去除方式使得电解具有微细加工的可能,这里着重探讨了高频窄脉冲微细电解加工技术、电液束微细电解加工技术和利用电解制备微细电极的工作原理,技术特点,应用领域和加工精度,并详细的讨论了目前微细电解加工脉冲电源和加工设备的研制和发展。     

Fabrication of 3D submicron to micro textured surfaces using backside patterned texturing (BPT)

This work presents a novel fabrication method for submicron to micro size textures on flat surfaces using the backside patterned texturing (BPT). The proposed method utilizes the pre-fabricated macro-features on the backside of work material, and thereafter the front side is face turned with a single point diamond tool to generate textured surfaces. Different from existing texturing methods, BPT produces textured surfaces from submicron to micro scale without any external gadgets such as vibration assisted machining or synchronized tool-spindle motion. The miniature feature arises on the diamond turned surface due to the induced residual stresses when the specimen is unleashed from the machine. To demonstrate the efficacy of the method, a series of machining experiments were conducted to fabricate various types of freeform surface textures like water-drop freeform, cylindrical freeform surfaces, etc. The fabrication methodology of different sizes of bumps with precisely controlled surface quality is illustrated. The texture profiles comprising the deformation height from hundreds of nanometer to few micrometers with mirror surface quality were successfully fabricated on the diamond machined surface. The experimental results suggest that the pre-fabricated pattern, workpiece thickness and machining condition play a critical role to determine the final shape and geometry of generated textures.     

Built-up edge effects on process outputs of titanium alloy micro milling

Built-up edge (BUE) is generally known to cause surface finish problems in the micro milling process. The loose particles from the BUE may be deposited on the machined surface, causing surface roughness to increase. On the other hand, a stable BUE formation may protect the tool from rapid tool wear, which hinders the productivity of the micro milling process. Despite its common presence in practice, the influence of BUE on the process outputs of micro milling has not been studied in detail. This paper investigates the relationship between BUE formation and process outputs in micro milling of titanium alloy Ti6Al4V using an experimental approach. Micro end mills used in this study are fabricated to have a single straight edge using wire electrical discharge machining. An initial experimental effort was conducted to study the relationship between micro cutting tool geometry, surface roughness, and micro milling process forces and hence conditions to form stable BUE on the tool tip have been identified. The influence of micro milling process conditions on BUE size, and their combined effect on forces, surface roughness, and burr formation is investigated. Long-term micro milling experiment was performed to observe the protective effect of BUE on tool life. The results show that tailored micro cutting tools having stable BUE can be designed to machine titanium alloys with long tool life with acceptable surface quality.     

Fundamental study of ductile-regime diamond turning of single crystal gallium arsenide

Gallium arsenide (GaAs) components, ranging from the planar substrate to those possessing complicated shapes and microstructures, have attracted extensive interest regarding their applications in photovoltaic devices, photodetectors and emerging quantum devices. Single point diamond turning (SPDT) is regarded as an excellent candidate for an industrially viable mechanical machining process, as it can generate nano-smooth surfaces, even on some hard-to-machine brittle materials such as silicon and silicon carbide, with a single pass. However, the extremely low fracture toughness and strong anisotropic machinability of GaAs makes it difficult to obtain nano-smooth, crack-free machined surfaces. To bridge the current knowledge gaps in understanding the anisotropic machinability of GaAs, this paper studied the mechanical material properties of (001)-oriented GaAs through indentation tests, assuming the diagonals of the indenter acted in the similar way of the cutting edge of a diamond tool with a negative rake angle. The results showed that the (001) plane of the GaAs material displayed harder and more brittle when indented along direction I (one diagonal of indenter parallel to the <110> orientation) compared to direction II (one diagonal of indenter parallel to the <100> orientation), which coincides with anisotropic machined surface quality by SPDT. This finding reveals, for the first time, that the crystallographic orientation dependence of both hardness and fracture toughness represents the underlying mechanism for the anisotropic machinability of GaAs. The paper presents a novel approach to evaluate the critical depth of cut under a high cutting speed comparable to SPDT and to determine the maximum feed rate for ductile-regime diamond turning. The 26.57 nm critical depth of cut was obtained for the hardest cutting direction using a large negative rake angle diamond tool. Finally, a nano-smooth surface was successfully generated along all the orientations in ductile-regime diamond turning, in which the material removal mechanism is considered as plastic deformation caused by high-density dislocations. The subsurface layer remains to its single crystal structure and no cracks are found under a transmission electron microscope (TEM). The results proves the proposed evaluation approach for the critical depth of cut and the maximum allowed feed rate is highly effective for guiding the ductile-regime machining of brittle materials.