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.     

Influence of microstructure on ultraprecision grinding of cemented carbides

The influence of microstructure on the ultraprecision grinding response of a series of cemented carbides for spherical mirrors was characterized by means of optical and laser interferometry, atomic force microscopy, scanning electron microscopy and X-ray diffraction. Surface roughness, form accuracy, grinding-induced residual stress and material removal behaviors were studied as a function of tungsten carbide (WC) grain size. In connection with the removal mechanisms in ultraprecision grinding, microindentations performed on each material showed similar deformation patterns, all in the plastic regime. The microstructure of WC-Co materials was found to have little influence on the nanometre surface roughness and submicron form accuracy. However, the X-ray stress measurements indicated that the microstructure of carbide materials had a significant influence on the grinding-induced residual stresses; i.e. an increase in grinding-induced residual compressive stress with an decrease in WC grain size. No grinding-induced cracks were observed in the ground cemented carbide surfaces. The material removal in ultraprecision grinding was considered to occur within the ductile regime. The formation of microgrooves and plastic flow regions via slip bands of WC grains along the cobalt binder without visible resultant microfracturing of WC grains were the dominant removal mechanisms.     

Boring and face grooving using micro turning tools

Micro turning tools with outside diameters of 25–50 μm were fabricated using cemented tungsten carbide by electrical discharge machining and used for micro boring and micro face grooving. The new process used could improve the hole circularity down to 0.25 μm and provide smooth-finished surfaces. From a set of experiments, the limit depth of cut and feed rate that can prevent tool breakage were determined. Compared with previous studies, the current study paved the way for applying removing processes with micro tools to boring and face grooving.     

Investigation on the surface formation mechanism in micro milling of cemented carbide

Cemented carbide is widely applied in optical glass molding process due to its excellent properties. The surface quality of cemented carbide mold is directly related with the glass element quality, mold life and production cost. In this paper, micro milling experiments were conducted on cemented carbide to investigate the surface formation mechanism. The surface morphology characteristics of different material removal modes were compared. Both the surface formation mechanism and damage behavior during micro milling process were analyzed in detail. The machining parameters selection strategy was suggested to obtain the high material removal rate and smooth surface quality. The surface quality was found to be less affected by the machining parameters when cemented carbide is removed with ductile mode than brittle mode.     

Influence of the cemented carbide specification on the process force and the process temperature in grinding

Cemented carbides are hard and brittle materials. Their material properties are adjusted by their chemical composition, in particular their average hard phase grain size and their binder fraction. The research paper focusses on grinding of cemented carbides with cobalt (Co) as binder and tungsten carbide (WC) as hard phase material. Within the research paper, it is discussed if and to what extent the cemented carbide composition affects the occurring thermo-mechanical load collective in the grinding process. In particular, the influence of the average WC grain size and the cobalt fraction on the thermo-mechanical load collective is investigated and explained by the cemented carbide material properties. The results of the publication contribute to a knowledge-based design of cemented carbide grinding processes.     

基于电火花线切割加工的微细阵列电极加工

介绍了微细阵列电板的应用情况及其电火花线切割加工的特点.以硬质合金为材料,采用电火花线切割加工方法进行了微细阵列电极的加工实验,总结出了不同加工因素对加工结果的影响规律.     

激光功率与扫描速度对微织构形貌影响试验研究

激光加工技术以其清洁高效、自动化程度高、加工过程方便易控制等突出的优势,目前已成为加工微织构的首选方式.在加工过程中,激光参数是影响微织构尺寸参数和形貌的重要因素.采用激光技术在硬质合金刀具表面加工微织构,分析并揭示了激光功率和扫描速度对微织构的尺寸和形貌的影响机制,进而确定了加工微织构的最优激光参数.     

Modelling and analysis of micro scale milling considering size effect, micro cutter edge radius and minimum chip thickness

This paper presents mechanisms studies of micro scale milling operation focusing on its characteristics, size effect, micro cutter edge radius and minimum chip thickness. Firstly, a modified Johnson–Cook constitutive equation is formulated to model the material strengthening behaviours at micron level using strain gradient plasticity. A finite element model for micro scale orthogonal machining process is developed considering the material strengthening behaviours, micro cutter edge radius and fracture behaviour of the work material. Then, an analytical micro scale milling force model is developed based on the FE simulations using the cutting principles and the slip-line theory. Extensive experiments of OFHC copper micro scale milling using 0.1 mm diameter micro tool were performed with miniaturized machine tool, and good agreements were achieved between the predicted and the experimental results. Finally, chip formation and size effect of micro scale milling are investigated using the proposed model, and the effects of material strengthening behaviours and minimum chip thickness are discussed as well. Some research findings can be drawn: (1) from the chip formation studies, minimum chip thickness is proposed to be 0.25 times of cutter edge radius for OFHC copper when rake angle is 10° and the cutting edge radius is 2 μm; (2) material strengthening behaviours are found to be the main cause of the size effect of micro scale machining, and the proposed constitutive equation can be used to explain it accurately. (3) That the specific shear energy increases greatly when the uncut chip thickness is smaller than minimum chip thickness is due to the ploughing phenomenon and the accumulation of the actual chip thickness.     

Micro cutting in the micro lathe turning system

As an application of cutting for the manufacture of micro mechanical parts and as a trial of the development of a miniature machining system matching the micro size of the work piece, a micro lathe turning system has been developed. A work material 0.3 mm in diameter is clamped and cut to a minimum of 10 μm in diameter with a rotation speed up to 15,000 rpm. The whole size of the equipment is about 200 mm which can be set under an optical microscope. A micro diamond single point tool has been applied to the cutting of various shapes, and the usefulness of such a micro cutting tool for the various forms has been confirmed. Cutting force has been investigated using a three directional force sensor and the possibility of the reduction of resistant force to improve working accuracy and to apply to micro parts has been examined.     

深冷处理对硬质合金的影响

综述了国内外硬质合金深冷处理的工艺过程及其深冷处理对硬质合金微观组织、相结构、残余应力状况、机械性能与切削性能的影响。深冷处理工艺包括降温和保温两个基本阶段,部分研究增加回火处理;深冷处理后硬质合金中η相含量增多且尺寸减小,Co对WC的粘结更紧密,但也有认为微观组织形貌变化不大的观点;Co相由面心立方向密排六方转变,而WC相变化不大;深冷处理可提高硬质合金耐磨性和延长使用寿命已得到共识,但对表面残余应力状况及硬度等影响尚存在不同观点。探索深冷处理对硬质合金的作用机理,并进行工艺参数的优化是目前研究工作的方向。     

Characterization of the transition from ploughing to cutting in micro machining and evaluation of the minimum thickness of cut

When the machining process is miniaturized two process mechanisms, ploughing and chip formation, are essential and a critical cutting thickness needs to be exceeded so that not only ploughing will occur but chips will also be formed. The ploughing effect thereby influences the chip formation process, workpiece surface roughness, burr formation and residual stress state after processing and is therefore of great interest. In order to optimize the machining process a better understanding of the minimum thickness of cut is crucial.The changes in surface topography along the cutting track occurring during machining with a constant feed rate of the cutting tool were analyzed. The influence of the built-up edge phenomena on the micro machining process was investigated for normalized AISI 1045 using confocal white light microscopy and scanning electron microscopy. Furthermore the sin²ψ-method was applied in order to study the residual stress state in the workpiece surface induced by the machining process. Both surface layer properties investigated, surface roughness and residual stresses, show a characteristic transition indicating a change in the dominating process mechanisms. Based on these results a model is developed to determine the minimum thickness of cut. The minimum thickness of cut is found to significantly decrease with higher cutting velocities and to moderately increase with higher cutting edge radii. In addition a propagation of error for the values obtained with the model was performed, proving the quality of the model developed.     

超细WC粉末微观缺陷的研究

超细WC粉末是制备超细硬质合金的主要原材料,本文采用XRD﹑SEM﹑TEM等分析手段,研究了三种不同粒度的超细WC粉末中微观缺陷的种类及其在晶粒中的分布,探讨了超细WC粉末微观缺陷的形成原因。分析结果表明:超细WC粉末主要为多晶颗粒,其位错密度较大,高于常态下一般的金属或合金。其微观缺陷的存在形式主要有位错﹑层错﹑孪晶等。在钨转化为碳化钨的相变过程中,钨原子密度由6.309 446个/nm3降低为3.211 922个/nm3,体积膨胀31%,为了释放其中的应力,必须存在有数量较多的缺陷。     

高效加工硬质合金沉孔用新型金刚石工具与工艺研究

介绍了一种加工硬质合金沉孔用新型金刚石工具与加工工艺。采用电镀和烧结金刚石磨头在数控铣床上,以螺旋进刀的加工方式,在不同进刀量和进给速度条件下,研究加工效率和磨头寿命的关系;研究不同尺寸、槽型的电镀和烧结金刚石磨头对不同材质的硬质合金沉孔的加工效率和沉孔精度等的影响;并采用扫描电镜（SEM）和光学显微镜分析金刚石磨头的显微组织。结果表明:与电镀金刚石磨头相比,烧结金刚石磨头具有更好的使用寿命和加工效率,将传统硬质合金沉孔（φ13 mm×5 mm）每孔的加工时间由2 h缩短为10~15 min,且每只磨头的打孔寿命约为33~42个。该研究有望进一步增大硬质合金等硬脆带孔材料的应用范围。      

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.     

Effect of machining parameters and coating on wear mechanisms in dry drilling of aluminium alloys

The temperature generated by friction and plastic deformation in the secondary shear zone strongly controls tool wear. At lower cutting speeds tool wear is not severe insofar as the temperature is not significant. When the cutting speed is increased, there is a transition in wear mechanisms from abrasion and/or adhesion to diffusion. In the present paper, the change in wear mechanisms as a function of cutting speed and coating material is discussed. The cutting tests were performed on a rigid instrumented drilling bench without the use of cutting fluids. AA2024 aluminium alloy was used to investigate the wear mechanisms of cemented tungsten carbide and HSS tools. Three cutting speeds (25, 65 and 165 m/min) and a constant feed rate of 0.04 mm/rev were selected for the experiments. The best results in terms of maximum and minimum hole diameter deviations and surface roughness are obtained for the uncoated and coated tungsten carbide drills. The results also show that HSS tool is not suitable for dry machining of AA2024 aluminium alloy.     

抛光垫特性对硬质合金刀片CMP加工效果的影响

目的研究不同种类的抛光垫对硬质合金刀片表面化学机械抛光(Chemical Mechanical Polishing/Planarization,CMP)加工过程的影响,为实现硬质合金刀片高效精密CMP加工提供有效参考。方法利用Nanopoli-100智能抛光机,通过自制的Al2O3抛光液,分别采用9种不同种类的抛光垫对牌号为YG8的硬质合金刀片进行CMP实验,将0~40、40~80、80~120 min三个加工阶段获得的材料去除率和表面粗糙度进行对比,同时观察最佳的表面形貌,分析抛光垫特性对CMP加工效果的影响。结果在抛光转速60 r/min,抛光压力177.8 k Pa的实验条件下,9种不同类型的抛光垫中仅有5种适合用于YG8硬质合金CMP加工。而且抛光垫的表面粗糙度在YG8刀片CMP加工过程中的影响最为显著,抛光垫表面粗糙度越高,CMP加工的材料去除率越高。此外,抛光垫的使用时间对CMP过程也有影响,抛光垫使用时间越长,CMP的材料去除率越小。结论 YG8硬质合金刀片经5种不同类型抛光垫CMP加工后,其表面的烧伤、裂纹等缺陷均得到了极大改善。当使用细帆布加工40 min时,材料去除率最高,为47.105 nm/min;当使用细帆布加工80min时,表面粗糙度最低,为0.039μm。     

Drilling of X2CrNi 19 11 stainless steel with hiped NiTi coating

This study investigated suitability of TiN and TiCN-coated cemented carbide tools in the machining of conventionally produced stainless steel with HIPed (Hot Isostatic Pressed) NiTi coating. Near-equiatomic nickel–titanium alloy (NiTi) has many attractive material properties, such as pseudo-elasticity and shape memory effects, which result into beneficial engineering properties, e.g. as cavitation resistant coatings in addition to its well-known shape memory properties. Stainless steels are often considered to be poorly machinable materials; materials with high elasticity are also difficult to machine. In drilling stainless steel with a pseudo-elastic coating material, machinability difficulties are caused by the high strength and work hardening rate of steel and the pseudo-elastic properties of the coating material. The machinability was studied by analyzing cemented carbide drills and chips. The interface between stainless steel and NiTi coating was examined with SEM (scanning electron microscopy) and EDS (energy dispersive spectroscopy) analysis. The effect of feed rate on chip formation and tool wear was analyzed. The cutting tests indicated that cutting speeds of 50 m/min, a feed rate of 0.1–0.2 mm/rev, and solid carbide drills can be applied, from a machinability standpoint. A HIPed pseudo-elastic coating decreases machinability. When effective cutting speeds and feed rates were utilized, optimal tool life was achieved without a decrease in coating properties.     

干混合对硬质合金组织结构的影响

采用扫描电镜,通过对WC原料粉末、脱蜡压坯断口与表面、合金抗弯强度样品断口与合金烧结体表面微观形貌以及合金金相组织的观察,研究了干混合对硬质合金组织结构的影响。结果表明,干混合只对压坯成形过程中粉末颗粒的压制行为与烧结过程中合金的致密化行为产生影响,不会对烧结过程中的合金化行为产生影响。压坯中的大孔洞与未压好等压制缺陷以及显著的元素分布不均匀现象难以通过液相烧结得到有效消除,会继续保留至合金中。采用干混合工艺制备合金,合金晶粒均匀、粗大,接近原料粉末的电镜观测粒度。     

Modeling and fabrication of micro tools by pulsed electrochemical machining

Accurate and precise micro tools are essential for the micromachining of complex micro features in a wide range of engineering materials including metals and ceramics. Existing micro tool fabrication processes suffer from drawbacks such as surface cracks, residual stress and deformations. Electrochemical machining of micro tools is proposed in this work to overcome these limitations. In this research, a mathematical model has been developed to predict the diameter of the micro tool fabricated. Experimental verification of the model using an in-house built micro electrochemical machining system reveals good correlation with theoretical predictions. Using the procedure described in this paper, very high aspect ratio (280–450) tungsten micro tools have been produced.     

钢基NiMoCrFeCo-WC涂层螺杆承载应力-扭矩的有限元分析

为研究高强度塑料注射成型过程中碳化钨陶瓷涂层螺杆的承载规律,采用ANSYS有限元模拟计算不同螺棱结构的碳化钨涂层螺杆承载特征,分析钢基材对三段式碳化钨涂层螺杆承载的影响规律,模拟碳化钨涂层螺杆在扭矩载荷作用下的应力/应变变化规律,讨论碳化钨涂层螺杆的承载扭矩与最大应力和最大应变的对应关系,建立碳化钨涂层螺杆临界扭矩的判...