单晶金刚石微型刀具刃磨试验研究

刀具刃磨质量是影响零件加工质量的重要因素之一。为提高单晶金刚石刀具刃磨质量,采用铜盘、铁盘、铜基碳化钨盘和铝基碳化硅盘四种不同的磨盘进行刃磨对比试验。观测分析刃磨后磨盘的表面形貌、材料去除率和刀具的刃口形貌、圆弧半径。结果发现:铜盘和铁盘刃磨过程中不能保证单晶金刚石的完整性,铜基碳化钨盘和铝基碳化硅盘加工可以获得较好的刀具质量。而铜基碳化钨盘通过促进单晶金刚石的氧化反应,在刃磨后获得的刀具刃口圆弧半径稳定在1 μm以内。      

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.     

Mechanism and prediction of failure of diamond films deposited on various substrates by HFCVD

Diamond films were deposited on the WC-Co cemented carbide and Si3N4 ceramic cutting tool substrates by hot-filament-assisted chemical vapour deposition. The adherence property of diamond films was estimated using the critical load (Pcr) in the indentation test. The adhesive strength of diamond films is related to the intermediate layer between the film and the substrate. Poor adhesion of diamond films to polished cemented carbide substrate is owing to the formation of graphite phase in the interface. The adhesion of diamond films deposited on acid etched cemented carbide substrate is improved, and the peeling-off of the films often happens in the loosen layer of WC particles where the cobalt element is nearly removed. The diamond films' adhesion to cemented carbide substrate whose surface layer is decarbonizated is strengthened dramatically because WC phase forms by reaction between the deposited carbon and tungsten in the surface layer of substrates during the deposition of diamond, which results in chemical combination in the film-substrate interface. The adhesion of diamond films to silicon nitride substrate is the firmest due to the formation of chemical combination of the SiC intermediate layer in the interfaces. In the piston-turning application, the diamond-coated Si3N4 ceramic and the cemented carbide cutting tools usually fail in the form of collapsing of edge and cracking or flaking respectively. They have no built-up edge(BUE) as long as coating is intact.As it wears through, BUE develops and the cutting force on it increases 1 - 3 times than that prior to failure. This can predict the failure of diamond-coated cutting tools.     

An experimental study on a novel diamond whisker wheel

This study proposes a novel diamond whisker wheel for grinding of advanced materials. The wheel is designed to have preferable spatial distributions and orientations of diamond whiskers which are prepared using a laser cutting technique. To obtain desirable cutting edge geometries, the whisker edges are formed on a lapping machine with diamond powders. The whisker wheel is used in a machining test on a silicon carbide particulate reinforced aluminum alloy and compared with a tungsten carbide milling cutter. The whisker wheel grinding provides better surface finish and significantly reduced machining force than for milling at the same material removal rate.     

金刚石膜涂层硬质合金工具研究进展及产业化前景

金刚石具有最高的硬度，极低的摩擦因数，最高的热导率和极佳的化学稳定性，因此是最理想的工具涂层材料。由于金刚石膜涂层硬质合金工具可能具有金刚石的硬度和硬质合金的强韧性的结合．因此20余年来一直受到世界各国的普遍关注。本文综述了金刚石膜涂层硬质合金的研发历史与现状，并针对目前的市场状况和未来的发展进行了评述。     

Effects of the friction coefficient on the minimum cutting thickness in micro cutting

In the ultra precision diamond cutting process, the rake angle of the tool is likely to become negative because the edge radius of tool is considerably large compared to the sub-micrometer depth of cut. The round edge of the tool might sometimes cause plowing results in a poor surface, or burnishing which results in a shiny surface depending on the depth of cut. This study deals with the relationship between the friction of a tool-workpiece and the minimum cutting thickness in micro cutting. Proposed is an ultra precision cutting model in which the tool edge radius and the friction coefficient are the principal factors determining the minimum cutting thickness with a continuous chip. According to the model, a smaller edge radius and a higher friction coefficient make the cutting depth thinner. The experimental results verify the proposed model and provide various supporting evidence.     

Evaluation of HVOF-sprayed WC-Co coatings for wood machining

A great concern to save the amount of tungsten carbide used in various mechanical components has become important because of an increase of global demand and the resultant sharp rise in the price in recent years. Sintered tungsten carbide (WC) tools are usually used in woodworking industry because of their excellent combination of hardness and toughness. However, the actual area necessary for cutting is very small compared to the overall cutting tool body. In this work, three high-velocity oxy-fuel (HVOF) sprayed WC-Co coatings with different carbide size (0.2, 2, and 6 µm) on high speed tool steel substrates were fabricated and then grinded to produce cutting tools. Characterization of the deposited coating was done by scanning electron microscope, X-ray diffraction, hardness and indentation fracture toughness tests. The wood machining tests were performed on natural wood (Apitong) and medium density fiberboard (MDF) to study their performance as a cutting tool. The results showed that the hardness values of the coatings were approximately the same as that of sintered material, while the fracture toughness values were significantly lower. The wood machining tests on Apitong revealed that the coating tools were worn by the same level of edge recession as the sintered material. However, they showed numerous edge chippings over the worn surfaces and the level of edge chipping tended to increase with reducing the carbide size. The wood machining tests on MDF revealed that the coating tools were worn by the same level of edge recession in the low density wear zone as the sintered material but by a significantly higher level in the high density wear zone.     

Characteristics of high speed micro-cutting of tungsten carbide

In this study, experiments are carried out to evaluate the characteristics of high speed cutting of tungsten carbide material using a Makino V55 high speed machine tool with cubic boron nitride (CBN) tool inserts. The cutting forces were measured using a three-component dynamometer, the surface roughness of the machined workpiece was measured using a Mitutoyo SURFTEST 301, and the machined workpiece surfaces and the chip formation were examined using a scanning electron microscope (SEM). Experimental results indicate that the radial force F_x is much larger than the tangential force F_z and the axial force F_y. Two types of surfaces of the machined workpiece are achieved: ductile cutting surface and fracture surface. Continuous chips and discontinuous chips are formed under different cutting conditions. Depth of cut and feed rate almost have no significant effect on the surface roughness of the machined workpiece. The SEM observations on the machined workpiece surfaces and chip formation indicate that the ductile mode cutting is mainly determined by the undeformed chip thickness when the tool cutting edge radius is fixed. Ductile cutting can be achieved when the undeformed chip thickness is less than a critical value.     

Profile error compensation approaches for parallel nanogrinding of aspherical mould inserts

This paper reports a parallel nanogrinding protocol for fabricating aspherical mould inserts. In the protocol, a preliminary grinding cycle was first employed, which significantly reduced the effect of the initial wheel geometry error on the ground profile accuracy. A new compensation approach was developed. The compensation used the ground profile measured from a Talysurf profilometer to modify the NC tool path for the next grinding cycle. The tool path was modified by offsetting the residual profile error along the normal direction of a grinding point, rather than in the horizontal direction commonly used in the conventional method. The performance of the developed method was evaluated by fabricating aspherical mould inserts on cemented tungsten carbide. The result indicated that the residual profile error after two grinding cycles was reduced to approximately 0.4 μm in PV, with average surface roughness of below 10 nm, which is more efficient than the conventional compensation process.     

研磨刀架结构对金刚石刀具刃口质量的影响

金刚石刀具刃口锋利度和刀面表面粗糙度对所加工零件的质量有着重要影响。较好的研磨刀架结构将有助于降低因刀架而产生的振动扰动,获得高质量的刀具刃口。通过改进刀架结构,使刀具刃口锋利度从300 nm提高到了50 nm,表面粗糙度从15 nm提高到了0.5 nm,刀具刃口质量得到了明显改善。     

用金刚石磨头数控加工轴对称非球面光学玻璃透镜

为了提高轴对称非球面透镜的形状精度,降低其精加工成本,用金刚石小磨头在不同的加工参数和数控走刀轨迹条件下对K9光学玻璃透镜进行铣磨实验加工。透镜的轮廓精度用三坐标测量机测量,通过测量的数据点计算非球面透镜的法向轮廓度误差,并用数控加工时磨头的有效切削半径进行补偿。实验结果表明:当数控走刀轨迹为平行精加工和等高精加工时,加工后非球面透镜的面型精度最大轮廓度偏差PV和误差平均值RMS分别为54.48 μm和22.88 μm、98.46 μm和28.88 μm;通过优化金刚石磨头的有效切削半径可以提高非球面透镜加工的面型精度,平行精加工后优化的非球面透镜面型精度PV和RMS值分别为44.52 μm和7.37 μm。      

Precision Cutting of Aspherical Ceramic Molds with Micro PCD Milling Tool

In order to machine micro aspheric molds and dies made of ceramics, micro milling tools made of polycrystal diamond (PCD) are developed. Twenty cutting edges are ground and polished with diamond wheels and loose abrasives on the edge of a small cylindrical PCD tool shank. Some micro aspheric molding dies made of binder-less tungsten carbide were cut with the PCD milling tool developed. The molds and dies were cut in the ductile mode. The form accuracies of the micro aspherical mold and the micro lens array mold obtained were less than 100 nmP-V and the surface roughness 15 nmRz.     

钢结硬质合金GT35切削去除机理研究

为研究金刚石磨粒刀具切削钢结硬质合金GT35的微观刻划过程与材料去除机理,以单颗粒金刚石刻划实验为研究手段,分析其微观切削力的影响因素及材料的微观去除过程。通过单颗粒金刚石变切深实验发现,切削力与切痕截面积之间呈线性关系,获得的线性比例系数k的估计值可通过单颗粒金刚石等切深实验修正。随后,通过扫描电镜对GT35材料表面切痕形貌进行观测,并用激光共聚焦显微镜对其形貌进行三维建模,研究不同刻划深度下的材料去除模式。结果表明:修正后k(F_x)为0.026 29 N/μm2（R₁=0.990 46）,k(F_z)为0.046 42 N/μm2（R₂=0.994 08）; 调质GT35材料在多种切深下均以塑性去除为主,其中切痕底面呈现明显塑性剪切去除状态,切痕边缘位置呈现一定的脆性断裂状态。刀具在切削过程中会在刀尖处形成材料堆叠死区,引起刀具崩刃及磨损,且切痕表面形貌的形成与刀具磨损密切相关。      

Tool flank wear prediction in CNC turning of 7075 AL alloy SiC composite

Flank wear occurs on the relief face of the tool and the life of a tool used in a machining process depends upon the amount of flank wear; so predicting of flank wear is an important requirement for higher productivity and product quality. In the present work, the effects of feed, depth of cut and cutting speed on flank wear of tungsten carbide and polycrystalline diamond (PCD) inserts in CNC turning of 7075 AL alloy with 10 wt% SiC composite are studied; also artificial neural network (ANN) and co-active neuro fuzzy inference system (CANFIS) are used to predict the flank wear of tungsten carbide and PCD inserts. The feed, depth of cut and cutting speed are selected as the input variables and artificial neural network and co-active neuro fuzzy inference system model are designed with two output variables. The comparison between the results of the presented models shows that the artificial neural network with the average relative prediction error of 1.03% for flank wear values of tungsten carbide inserts and 1.7% for flank wear values of PCD inserts is more accurate and can be utilized effectively for the prediction of flank wear in CNC turning of 7075 AL alloy SiC composite. It is also found that the tungsten carbide insert flank wear can be predicted with less error than PCD flank wear insert using ANN. With Regard to the effect of the cutting parameters on the flank wear, it is found that the increase of the feed, depth of cut and cutting speed increases the flank wear. Also the feed and depth of cut are the most effective parameters on the flank wear and the cutting speed has lesser effect.     

Analysis of tool wear and residual stress of CVD diamond coated cemented carbide tools in the machining of aluminium silicon alloys

Aluminium alloys have found increasing applications in the automotive and aeronautical industries in recent years. Due to their extraordinary properties however, the machining of these alloys still poses difficulties, and requires the optimized combination of cutting tool material and geometry. The potential of CVD diamond coated carbide tools has been demonstrated in recent years, however tool wear and short tool life remain as issues to be resolved. Key to increasing the tool life of CVD diamond coated tools is the further development of the coating process to optimize the coating adhesion. An understanding of the substrate and coating residual stress profiles must be gained in order to achieve this. Compressive residual stresses in cutting tools can lead to a higher crack resistance, but also to early coating delamination and tool failure. To analyze the influence of residual stresses on the coating quality and tool life, the residual stress profiles of tungsten carbide substrates and CVD diamond coatings were measured using X-ray and synchrotron radiation. The influence of the tungsten carbide substrate type and the CVD diamond coating process on the residual stress profiles was thus determined. In order to analyze the performance of the coated tools and the influence of the residual stresses on the tool lifetime, machining tests were performed with two aluminium silicon alloys. The tool wear, tool lifetime and workpiece quality were examined. Finally, many of the commonly used wear tests used to analyze the wear resistance of tool coatings cannot be implemented for CVD diamond coatings due to their high hardness. An impact test was therefore constructed to allow the determination of the wear resistance of CVD diamond tools.     

Conservation law of surface roughness in single point diamond turning

In this work, a comprehensive model is established to predict the surface roughness achieved by single point diamond turning. In addition to the calculation of the roughness components in relation to the kinematics and minimum undeformed chip thickness, the newly developed model also takes the effects of plastic side flow and elastic recovery of materials as machined into account. Moreover, the ‘size effect’ has also been successfully integrated into the model, i.e. an inflection point appears in the trend line of predicted surface roughness as the ratio of maximal undeformed chip thickness to cutting edge radius (h_Dmax/r_n) is equal to one unit. Face turning experiments validate that the maximal prediction error is only 13.35%. As the ratio of h_Dmax/r_n is higher than one unit, both the prediction and experiments reveal that a conservation law exists in diamond turned surface roughness, owing to the competitive effects of kinematics, minimum undeformed chip thickness, plastic side flow and elastic recovery of materials on surface formation. Under the conservation law, the freedom control for an invariable surface roughness can be fulfilled in response to a quantitative ratio of h_Dmax/r_n, either through an accurate configuration of feed rate and depth of cut with fixed tool nose radius and cutting edge radius, or by a reasonable selection of tool nose radius and controlled cutting edge radius with designed feed rate and depth of cut.     

聚晶金刚石微细球头铣刀刃磨工艺参数优化

针对直径为0.5 mm的聚晶金刚石(PCD)微细球头铣刀刃磨质量控制问题，基于六轴数控刀具磨床几何运动原理，建立PCD微细球头铣刀的砂轮刃磨运动数学模型，开展PCD刀具精密刃磨正交试验，研究刃磨工艺参数对主轴负载率、刀具前刀面表面粗糙度、刀具刃口钝圆半径的影响规律。结果表明:磨削速度对主轴负载率以及刀具前刀面表面粗糙度的影响最为显著，提高磨削速度有利于获得较好的刀面质量；磨削深度对刃口钝圆半径的影响最为显著，减小磨削深度有利于获得锋利的刃口形状。通过合理选择刃磨工艺，PCD微细铣刀直径误差小于4.0 μm，刀具钝圆半径为4.5 μm，刀具角度误差小于1°，无明显刃磨损伤缺陷。      

On-machine dry electric discharge truing of diamond wheels for micro-structured surfaces grinding

Precision grinding with diamond wheels gives a promising alternative to achieve high quality micro-structured surfaces on optical molds. However, it is difficult to true these diamond wheels efficiently, because of the remarkable resistance property and the geometrical limitation of small wheel profile. In this paper, an on-machine dry-EDT method to precision shape and prepare diamond wheels with various profiles was proposed for micro-structured surface grinding. Firstly, the fundamental truing errors were analyzed based on the dry-EDT kinematics. And then the capabilities of dry-EDT truing for high abrasive concentration metal bonded diamond wheels were presented. Next, the effects of kinematic parameters variables on trued wheel profile accuracy were investigated. Finally, the micro-structured surfaces on SiC ceramic and tungsten carbide WC were ground by these trued diamond wheels. The experiments results showed that the arc-shaped diamond wheel (diameter of 200 mm) with 4 μm profile error (PV) and 1.0023 mm profile radius, and the V-shaped diamond wheel with 22.5 μm V-tip radius and 120.03° profile angle could be obtained by on-machine dry EDT. The kinematic parameters of dry-EDT have an important influence on truing profile accuracy of diamond wheels, especially for the tip of V-shaped wheel. The subsequent grinding show that the edge radius of V groove array on SiC is less than 2 μm, while the radius of included corner is around 55 μm. The PV error of ground arc groove array on WC is less than 5 μm. The surface roughness of ground micro-structured surface R_a is 142 nm and 97 nm for SiC and WC, respectively.     

Analysis on ductile mode processing of binderless, nano crystalline tungsten carbide through ultra precision diamond turning

Ultra precision diamond turning is usually applied for processing non ferrous metals, plastics and a few single crystal materials. The machining of hard and brittle material, such as nano crystalline, binderless tungsten carbide has only been investigated within a few publications on a theoretical basis and applying nano indenting. Therefore the goal of this paper is to qualify the ultra precision diamond turning technique for processing nano crystalline, binderless tungsten carbide applying the real process conditions identifying optimal parameters. A potential application of this process would be the mold manufacturing for precision glass molding. Within a systematical procedure the ductile to brittle transition is analyzed as well as the tool wear, varying both, tool geometry and processing parameters. Based on material analysis the critical depth of cut for the material was calculated at 165 nm. This value could be validated in the experiments at the optimal cutting speed of 50 m/min with a feed of 1 μm. Least tool wear was observed at a tool radius of 0.4 mm and a rake angle of −20°. The experiments demonstrate the strong influence of the processing conditions on the achieved results.     

Profile error compensation in ultra-precision grinding of aspheric surfaces with on-machine measurement

A compensation approach based on the on-machine measurement was developed for the grinding of tungsten carbide aspheric moulds. In this approach, the on-machine measurement was employed to eliminate the profile error caused by the re-installation of the workpiece. A new method was proposed to reconstruct the actual ground profile based on the measured profile data. The overall profile error after grinding was obtained by subtracting the target profile from the actual ground profile along normal direction and was then used to generate a new tool path for compensation grinding. The experimental results showed that after three compensation grinding cycles the aspheric surface had a profile accuracy of 177 nm (in PV) with a roughness of 1.7 nm (in R_a). The on-machine measurement was in excellent agreement with the off-machine measurement by commercially available profilometers.