微小型零件的微细切削加工工艺研究

文章研究了微小型零件的微细切削加工工艺,微细切削加工微小型零件具有较大的工艺和成本优势,适应微小型零件产品批量化、加工柔性化、材料多样化的发展趋势.微小型零件按照加工工艺特征大致可分为微小型轴类、三维结构件、板类和齿轮类零件,总结和分析了上述零件的工艺特征和加工方式,介绍了微小型加工机床和刀具的选用原则,包括如何合理选择微细切削刀具的材料、特征尺寸和结构.微小型零件必须根据机床功能和零件自身结构特点确定装夹方式,并进行准确定位.最后,归纳和总结了微小型零件进行微细切削数控加工工艺设计时应遵循的原则,并进行了详细论述.微细切削加工中,采用合理的数控加工工艺和走刀路线,可以实现微小型零件的精确、高效加工,适应批量化的产品需求.     

微圆弧金刚石刀具修磨技术研究

微圆弧金刚石刀具是超精密加工中的重要应用工具,基于机械研磨法开展微圆弧金刚石刀具修磨技术研究。通过分析微圆弧金刚石刀具制备技术现状和制备难点,设计一种微圆弧金刚石刀具的修磨技术路线。通过修磨实验解决难磨、易磨方向定位,刀尖容易崩刃及精修刀尖圆弧等技术难点,制备刀尖半径R 8.2μm的微圆弧金刚石刀具。利用原子力显微镜和高倍光学显微镜进行观测,结果表明:前刀面粗糙度R_a=1.50nm,刀尖轮廓波纹度优于0.1μm,与进口高精度刀具指标相当。将其应用在微结构的超精密切削中,取得良好效果。      

Electrochemical micromachining using vibratile tungsten wire for high-aspect-ratio microstructures

Electrochemical micromachining can remove electrically conductive materials with the transferring of ions, so that high precision is achievable. A novel method for fabricating high-aspect-ratio microstructures by electrochemical micromachining using vibratile tungsten wire was proposed in this paper. The slight vibration of tungsten wire can improve the machining stability. The relations between the machining accuracy and machining parameters were experimentally studied. Micro groove with the width of 15 μm was machined, and micro sharp-angles structure with aspect ratio of 10 was obtained experimentally.     

The effect of vibration cutting on minimum cutting thickness

In the ultra-precision diamond cutting process, the rake angle of the tool becomes negative because the edge radius of a tool is considerably larger compared to the sub-micrometer depth of the cut. The effects of plowing due to the large negative rake angle result in an unstable cutting process without continuous chip. For this reason, it is important to determine minimum cutting thickness in order to enable greater machining accuracy to be obtained by fine and stable machining. It was previously reported that the critical depth of cut with a continuous chip was determined by the tool sharpness and the friction coefficient between a workpiece and a tool [S.M. Son, et al., Effects of the friction coefficient on the minimum cutting thickness in micro cutting, International Journal of Machine Tools and Manufacture 45 (2005) 529–535]. For the same edge radius of a tool, the higher the friction coefficient of the tool–workpiece, the thinner the minimum cutting thickness becomes. Therefore, it is believed that increasing the friction coefficient by a physical method would be effective to achieve thinner stable cutting. In this study, the possibility of reducing the minimum cutting thickness was investigated through changing the friction coefficient of a tool–workpiece. The vibration cutting method is applied to increase the friction coefficient. Experimental results show that the cutting technology is efficient for increasing the friction coefficient and decreasing the minimum cutting thickness. The minimum cutting thickness was reduced by about 0.02–0.04 μm depending on materials and vibration conditions.     

Proposal of ‘ImpEC (impact excitation cutting)’ for realization of high-flexibility and high-efficiency micro/nano surface texturing

In this paper, a novel micro/nano surface texturing method, namely ‘ImpEC (impact excitation cutting)’, is proposed. To machine micro/nano-textures, vibration cutting and fast tool servo have been utilized. However, the former one is limited to formation of periodical combination of sine waves since the resonance(s) of the cutting tool system is used, and the latter one is limited in terms of efficiency since it has conventionally been utilized within the bandwidth of the servo system, e.g. 3 kHz. Hence, conventional methods cannot realize high flexibility and high efficiency simultaneously. In the proposed ImpEC (impact excitation cutting), the frequencies higher than the resonant frequency are also used, and a series of impacts (pulses) are utilized to diminish the residual vibration. The proposed cutting method can create structures in a short time since the high frequency components are also used, and it can also realize high flexibility since a variety of texturing motions without residual vibrations can be triggered at any timing. The effectiveness of the proposed method is verified both analytically and experimentally.     

光学微结构超精密多轴铣削加工技术

采用单点金刚石飞刀加工可以直接加工出具有纳米级的表面粗糙度和亚微米级形状精度的光学微结构元件而不需要后续处理。通过超精密飞刀加工微V沟槽的实验,分析了主轴转速、进给速度、切削深度和切削行间距对微V沟槽加工精度的影响,并对切削参数进行优化。最后,利用优化后的切削参数加工出微V沟槽结构。实验结果显示,超精密飞刀加工微V沟槽可达到满足光学微结构加工精度的要求。     

Identification and control for micro-drilling productivity enhancement

Micro-hole drilling (holes less than 0.5 mm in diameter with aspect ratios larger than 10) is gaining increased attention in a wide spectrum of precision production industries. Alternative methods such as EDM, laser drilling, etc. can sometimes replace mechanical micro-hole drilling, but are not acceptable in PCB manufacture because they yield inferior hole quality and accuracy. The major difficulties in micro-hole drilling are related to the wandering motions during the inlet stage, high aspect ratios, high temperature, etc. However, of all the difficulties, the most undesirable ones are the increases in drilling force and torque as the drill penetrates deeper into the hole. This is mainly caused by chip-related effects. Peck-drilling is thus widely used for deep hole drilling despite the fact that it leads to low productivity. Therefore, in this paper, a method for cutting force regulation is proposed to achieve continuous drilling. A proportional plus derivative (PD) and a sliding mode control algorithm will be implemented and compared for controlling the spindle rotational frequency. Experimental results will show that sliding mode control reduces the nominal torque and cutting force and their variations better than PD control, resulting in a number of advantages, such as an increase in drill life, fast stabilization of the wandering motion, and precise positioning of the holes.     

Dynamic rotating-tool turning of micro lens arrays

Diamond micro milling of high-quality micro lens arrays suffers from low machining efficiency, due to the inevitable milling marks along tangential feed direction and the slow spiral tool path interpolated by multiple linear axes. In this article, an advanced cutting process is proposed, namely dynamic rotating-tool (DRT) turning, in which a U-axis attachment on a rotary stage is developed to enable synchronous cutter rotation and radial feed motions of a diamond turning tool. This method is experimentally verified and compared with milling, with significantly enhanced surface quality and machining efficiency, thus bringing a new perspective into ultra-precision machining.     

Theoretical and experimental analysis of nano-surface generation in ultra-precision raster milling

The fabrication of high-quality freeform surfaces is based on ultra-precision raster milling, which allows direct machining of the freeform surfaces with sub-micrometric form accuracy and nanometric surface finish. Ultra-precision raster milling is an emerging manufacturing technology for the fabrication of high-precision and high-quality components with a surface roughness of less than 10 nm and a form error of less than 0.2 μm without the need for any additional post-processing. Moreover, the quality of a raster milled surface is based on a proper selection of cutting conditions and cutting strategies.Due to different cutting mechanics, the process factors affecting the surface quality are more complicated, as compared with ultra-precision diamond turning and conventional milling, such as swing distance and step distance. This paper presents a theoretical and experimental analysis of nano-surface generation in ultra-precision raster milling. Theoretical models for the prediction of surface roughness are built. An optimization system is established based on the theoretical models for the optimization of cutting conditions and cutting strategy in ultra-precision raster milling. A series of experiments have conducted and the results show that the theoretical models predict well the trend of the variation of surface roughness under different cutting conditions and cutting strategies.     

微磨料空气射流加工技术的发展

微磨料空气射流加工(MAJM)技术是对硬脆材料进行微细加工的一种非常有潜力的技术，特别是对复杂的三维微细结构的加工。微磨料空气射流加工技术是基于传统的喷砂技术发展起来的，通过由空气喷射磨料微粒形成高速气流冲击工件表面而去除工件材料。与其它的加工技术相比，微磨料空气射流加工具有环境友好、易于控制、无热影响区、切口质量好等优点。本文介绍了此技术的基本加工原理、特点以及加工过程中的影响因素，论述了微磨料空气射流加工的材料冲蚀机理和切口特征。重点分析了一些主要的加工参数，例如空气压力、磨料材料、尺寸、供给率、喷嘴的形状和尺寸、喷射距离以及工件材料，对切削性能和切口特征的影响。并提出了微磨料空气射流加工技术中有待进一步深入开展的研究工作。     

基于Deform的大长径比PCD微铣刀结构设计及参数优化

微细铣削技术是最适合加工高深宽比微结构的微细加工技术之一,而微铣刀制约着微细铣削技术的发展。针对高深宽比微结构的微细铣削加工,设计一种大长径比PCD直刃微铣刀,通过Deform有限元仿真研究不同微铣刀结构参数对铣削力和毛刺高度的影响规律。进一步地,采用多目标曲面响应分析方法对侧刃后角、底刃后角和底刃倾角3个因素进行试验设计,得到优化后的微铣刀结构参数为侧刃后角30°,底刃后角15°和底刃倾角7°。      

Development of monitoring system on the diamond tool wear

Recently, ultra-precision machining using a single crystal diamond tool has been developing very rapidly, especially in the fields of production processes for optical or magnetic parts such as magnetic discs, laser mirrors, polygon mirrors and copier drums. As a result, it has been successfully extended to machine various soft materials, generating mirror-like surfaces to sub-micron geometric accuracy with the ultra-precision CNC machine and the single crystal diamond tool. With the real cutting operation, the geometric accuracy and the surface finish attainable in machined surfaces are mainly determined by both of the sharpness of a cutting tool and stability of the machine vibration. In this study, for monitoring the progress of machining state for assuring the machining accuracy and the surface quality, a new monitoring method of machining states in face-cutting with diamond tool is proposed, using the frequency response of multi-sensors signal, which includes wear state of tool in terms of the energy within the specific frequency band. A magnetic disc is machined on the ultra-precision lathe.     

Fundamental investigation of ultra-precision ductile machining of tungsten carbide by applying elliptical vibration cutting with single crystal diamond

This paper presents essential investigations on the feasibility of ductile mode machining of sintered tungsten carbide assisted by ultrasonic elliptical vibration cutting technology. It lays out the foundations toward efficient application of elliptical vibration cutting technology on tungsten carbide. Tungsten carbide is a crucial material for glass molding in the optics manufacturing industry. Its grain size and binder material have significant influence not only on the mechanical and chemical properties but also on the machining performance of tungsten carbide. In order to investigate the influence of material composition on tungsten carbide machining, a series of grooving and planing experiments were conducted utilizing single crystal diamond tools. The experimental results indicated that as compared to ordinary cutting where finished surface deteriorates seriously, ductile mode machining can be attained successfully by applying the elliptical vibration cutting technique. It was also clarified that the binder material, the grain size, cutting/vibration conditions as well as crystal orientation of the diamond tool have significant influence on the tool life and the machined surface quality. Based on these fundamental results, feasibility of micro/nano-scale fabrication on tungsten carbide is investigated. By applying amplitude control sculpturing method, where depth of cut is arbitrary changed by controlling the vibration amplitude while machining, ultra-precision textured grooves and a dimple pattern were successfully sculptured on tungsten carbide in ductile mode.     

Elliptical Vibration Cutting of Tungsten Alloy Molds for Optical Glass Parts

Elliptical vibration cutting is applied to ultra-precision machining of tungsten alloy molds for optical glass parts in the present research. The tungsten alloy is expected as a new mold material instead of conventional ones such as sintered tungsten carbide and CVD-silicon carbide. However, it cannot be finished precisely by ordinary cutting because of rapid tool wear, brittle fracture and adhesion to the tool. Therefore, the ultrasonic elliptical vibration cutting is applied to the ultra-precision machining of tungsten alloy. Practical ultra-precision molds are obtained by the elliptical vibration cutting, and they are applied to glass molding successfully.     

Ultra-precision machining of Fresnel microstructure on die steel using single crystal diamond tool

With the increasing demand for the replication of structured optical elements such as Fresnel lenses and prism arrays, more attention is being paid to the development of ultra-precision diamond machining technology for the fabrication of die steel molds. However, the machining process would be a catastrophic failure because of rapid and excessive tool wear if a diamond tool is used to machine die steel. In the present paper, a micromachining method for fabricating microstructures on die steel using single crystal diamond tool is presented. The presented technology is based on a thermochemical technique that uses plasma nitriding treatment to suppress the rapid and excessive tool wear in the diamond machining of steel. Experimental findings revealed that severe chemical tool wear, which is the main wear mechanism in the diamond machining of steel, was reduced significantly after plasma nitriding treatment, and a mirror-quality surface with an average surface roughness of 20 nm root-mean-square (RMS) was achieved over a cutting distance of approximately 5.4 km. Furthermore, a Fresnel microstructure with surface roughness RMS better than 40 nm was precisely fabricated on AISI 4140 die steel using single crystal diamond tool.     

A fine tool servo system for global position error compensation for a miniature ultra-precision lathe

There is an increasing demand for single-point diamond turning to manufacture micro components as well as micro features on a large workpiece surface. In order to obtain high accuracy and a fine surface finish of the large area workpiece, position control of machine tool has become the main concern to achieve the high precision position control. A coarse-fine servo system is able to provide a cost-effective solution. This system can provide information on the entire guidance errors profile data and simultaneously compensate the error in real-time by using the fine position control technique. In this study, a piezoelectric actuator based fine tool servo (FTS) system has been developed and it has been incorporated with a miniature ultra-precision lathe. A cost-effective position sensitivity detector (PSD) is integrated in the FTS design, which is able to measure the global straightness error of the translational slide accurately. The detected error signals are compensated by the FTS during the turning process. For better tracking performance, a proportional-integral (PI) feedback controller has been implemented and tested in this study. Experimental results show that the developed FTS can effectively and successfully compensate the micro waviness error which is caused by the x-axis translational slide of the miniature ultra-precision lathe.     

Analytical modeling and experimental validation of micro end-milling cutting forces considering edge radius and material strengthening effects

This paper presents a novel micro end-milling cutting forces prediction methodology including the edge radius, material strengthening, varying sliding friction coefficient and run-out together. A new iterative algorithm is proposed to evaluate the effective rake angle, shear angle and friction angle, which takes into account the effects of edge radius as well as varying sliding friction coefficient. A modified Johnson–Cook constitutive model is introduced to estimate the shear flow stress. This model considers not only the strain-hardening, strain-rate and temperature but also the material strengthening. Furthermore, a generalized algorithm is presented to calculate uncut chip thickness considering run-out. The cutting forces model is calibrated and validated by NAK80 steel, and the relevant micro slot end-milling experiments are carried out on a 3-axis ultra-precision micro-milling machine. The comparison of the predicted and measured cutting forces shows that the proposed model can provide very accurate predicted results. Finally, the effects of material strengthening, edge radius and cutting speed on the cutting forces are investigated by the proposed model and some conclusions are given as follows: (1) the material strengthening behavior has significant effect on micro end-milling process at the micron level. (2) Cutting forces predicted increase with the increase of edge radius. (3) Considering varying sliding friction coefficient can enhance the sensitivity of the predicted cutting forces to cutting speed.     

工艺参数对单晶硅超精密加工切削力的影响

为了了解单晶硅超精密车削过程中不同切削参数及刀具前角对切削力的影响,利用单晶金刚石车刀对单晶硅进行单因素变量超精密车削试验。试验结果表明:进给量f和切削深度a_p对X、Y、Z方向的切削力F均有增大的趋势;而在切削速度v_c增加时,各方向的F逐渐减小;切削前角减小时,切削力反而增大。通过各因素对切削力F的变化幅值可以得到,对F影响较大的参数为a_p及f。选取最佳组合参数对单晶硅进行超精密切削试验,得到极为光滑的表面。     

单晶Cu材料纳米切削特性的分子动力学模拟

建立了单晶Cu纳米切削的三维分子动力学模型,研究了不同切削厚度下纳米切削过程中工件缺陷结构和应力分布的规律.纳米切削过程中,在刀具的前方和下方形成变形区并伴随缺陷的产生,缺陷以堆垛层错和部分位错为主.在纳米尺度下,工件存在很大的表面应力,随着切削的进行,工件变形区主要受压应力作用,已加工表面主要受拉应力作用.随着位错在晶体中产生、繁殖及相互作用,工件先后经过弹性变形——塑性变形——加工硬化——完全屈服4个变形阶段,随后进入新的循环变形.结果表明:工件应力-位移曲线呈周期性变化;切削厚度较小时,工件内部没有明显的层错产生,随着切削厚度的增大,工件表面和亚表层缺陷增加;切削厚度越大,对应应力分量值越小.     

基于微电铸工艺的高深宽比引信开关制作

为满足军事武器系统对引信开关的不断需求,采用光刻和精密微电铸工艺在金属基底上制作了一款具有高深宽比结构的引信开关。研究了超声波辅助显影和曝光剂量对胶膜制作的影响,解决了高深宽比胶膜制作难的问题。采用优化电铸液参数及电铸前胶膜预处理的方法,解决了电铸层与基底界面结合失效的问题。引入尺寸误差补偿的方法,降低了因溶胀和去胶释放等工艺带来的制作误差。最终制作出结构尺寸为4000μm×3900μm×360μm、最小尺寸为20μm、最大深宽比为14∶1的开关结构,为制作高深宽比金属微结构提供了一种可行的工艺参考方案。