A review on the conventional and micro-electrodischarge machining of tungsten carbide

The capability of machining intricate features with high dimensional accuracy in hard and difficult-to-cut material has made electrodischarge machining (EDM) process as an inevitable and one of the most popular non-conventional machining processes. In recent years, both EDM and micro-EDM processes are being used extensively in the field of mould making, production of dies, cavities and complex 3D structures using difficult-to-cut tungsten carbide and its composites. The objective of this paper is to provide a state of the art in the field of EDM and micro-EDM of tungsten carbide and its composites. The review begins with a brief introduction on the EDM and micro-EDM processes. The research and developments in electrodischarge machining of tungsten carbide are grouped broadly into conventional EDM of tungsten carbide, micro-EDM of tungsten carbide and current research trends in EDM and micro-EDM of tungsten carbide. The problems and challenges in the area of conventional and micro-EDM of tungsten carbide and the importance of compound and hybrid machining processes are discussed. A summary of the future research directions based on the review is presented at the final section.     

Damage-free machining of monocrystalline silicon carbide

Cutting tests of monocrystalline SiC, on the surface of which an amorphous layer was preformed by ion implantation, were performed. Ductile-mode machining was observed at a depth of cut smaller than 60 nm. At a depth of cut larger than 60 nm, cracks were observed on the work surface. However, transmission electron micrographs show that crack propagation was obstructed at the interface between the amorphous and crystalline layers even under brittle-mode machining, and no subsurface damage extended into the crystalline layer. The results suggest that the damage-free machining of monocrystalline SiC is possible by surface modification to an amorphous structure.     

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.     

Efficient machining of complex-shaped seal slots for turbomachinery

Complex sealing arrangement in turbomachinery can increase turbine efficiency by reducing leakage of high-pressure cooling flows into the hot gas path. While die-sinking EDM is widely used to machine straight seal slots, electrode preparation and wear make it less efficient for complex shapes. This paper presents research on optimisation of a variant of EDM milling using process control and fluid dynamics simulation to exploit optimal machining conditions. The analysis demonstrates a stable process to machine complex shaped slots by focusing on the key requirements for large-scale turbomachinery component manufacture, namely productivity, surface integrity and process monitoring.     

工程陶瓷超声加工的基础试验研究

介绍了工程陶瓷超声加工的基本原理以及加工过程中材料去除机理。对超声加工陶瓷的基本规律进行了实验研究，并对实验中发现的问题进行了探讨。     

A study on the effect of tool nose radius in ultrasonic elliptical vibration cutting of tungsten carbide

Nowadays, ultrasonic elliptical vibration cutting (UEVC) technique is being successfully applied for ultraprecision machining of difficult-to-cut materials. Previous study reported that the tool geometry especially tool nose radius notably influences the performance of 1D ultrasonic vibration cutting (UVC). However, the effect of tool nose radius in the UEVC technique is yet to be studied. This study aims to investigate the effects of tool nose radius on the UEVC performance in terms of cutting force, tool wear and surface finish when machining a hard-to-cut material, sintered tungsten carbide (WC), using PCD tools. The experimental results show that the UEVC technique performs remarkably better in all aspects at a 0.6 mm nose radius compared to a lower (e.g. 0.2 or 0.4 mm) and a higher nose radius (e.g. 0.8 mm). When machining about 412 mm² surface area, an average surface roughness, R_a of 0.010 μm is achieved with a 0.6 mm nose radius. Analyses are conducted to justify the findings in this study.     

Influence of silicon powder-mixed dielectric on conventional electrical discharge machining

Electrical discharge machining (EDM) is a technological process with a large industrial implementation. Its use is particularly intense when very complex shapes on hard materials with a high geometrical and dimensional accuracy are required. However, the technological capability of the process has limited its application when the specification of the part surface quality imposes polished and mirror-like characteristics. The addition of powder particles in suspension in the dielectric modifies some process variables and creates the conditions to achieve a high surface quality in large areas. This paper presents a new research work aiming to study the performance improvement of conventional EDM when used with a powder-mixed dielectric. A silicon powder was used and the improvement is assessed through quality surface indicators and process time measurements, over a set of different processing areas. The results show the positive influence of the silicon powder in the reduction of the operating time, required to achieve a specific surface quality, and in the decrease of the surface roughness, allowing the generation of mirror-like surfaces.     

Material removal mechanisms in precision machining of new materials

Modern-day products are characterised by high-precision components. A wide range of materials, including metals and their alloys, ceramics, glasses and semiconductors, are finished to a given geometry, finish, accuracy and surface integrity to meet the service requirements. For advanced technology systems, demands for higher fabrication precision are complicated by the use of brittle materials. For efficient and economical machining of these materials, an understanding of the material removal mechanism is essential. This paper focuses on the different material removal mechanisms involved in machining of brittle materials.     

振动辅助切削加工技术研究现状

随着精密与超精密加工技术的不断发展和成熟,将振动辅助切削技术应用到精密与超精密加工中去已成为发展的一个必然趋势。结合国内外研究人员的研究成果,介绍了超声振动辅助切削技术的基本原理,综述了超声振动辅助切削技术的优势以及研究现状。     

不同材料去除模式下激光加热辅助切削氮化硅陶瓷表面粗糙度研究

激光加热辅助切削因其工艺空间大、经济性高、可得到高质量表面成为工程陶瓷等脆硬材料的高效加工方式。通过改变激光功率和切削深度两组单因素试验,研究了激光加热辅助切削氮化硅陶瓷（Si3N4）不同加工状态下表面粗糙度值的变化规律。结果表明:材料被塑性去除时,Ra和Rq值均小于被脆性去除和产生热损伤时得到的值。未产生热损伤时,Ra和Rq值随工件软化程度增大而减小。在塑性去除模式下,轮廓高度幅值曲线更加趋于对称和正态分布,表面轮廓更加精细。     

Effects of cryogenic treatment and refrigerated air on tool wear when machining medium density fiberboard

Cooling of cutting tools with liquid coolants and lubricants is impractical when machining dry wood or wood composites. This study examines the combined effect of cryogenic tool treatment and using refrigerated air for cooling tools on reducing tool wear. A total of four, double-flute, solid, tungsten carbide router bits were used to machine medium density fiberboard with a CNC router. Three of the four tools were cryogenically treated to below −149 °C. During cutting, refrigerated air was applied to two tools, while the other two cut at ambient temperature. All tools were examined under the stereo light microscope to capture images in order to measure tool wear. Elemental analysis was performed using scanning electron microscopy to determine the percentage of specific elements present on clearance faces of tools after cutting was completed. Results show that less tool wear occurs when using refrigerated air and cryogenic treatment, thereby increasing tool life when cutting medium density fiberboard.     

Precision ultrasonic machining process: a case study of stress analysis of ceramic (Al2O3)

Recent study and development activity in the field of precision ultrasonic machining (USM) process has focused on the ceramic (Al₂O₃). This paper first analyzes the USM process, mechanism, dynamics, and trends. It then discusses, in detail, the USM process applications on the ceramic (Al₂O₃).     

45°分型面橡胶模具的数控车削加工工艺分析

针对45°分型面橡胶模具在加工关键部位时存在的特殊位置要求问题进行了详细分析,从零件的结构分析、工件的装夹、工艺路线的确定、加工参数和刀具的选择等方面进行了系统的探讨。采用数控车削加工方法,从而提高了产品加工质量和可靠性。     

Diamond machining of silicon: A review of advances in molecular dynamics simulation

Molecular dynamics (MD) simulation has enhanced our understanding about ductile-regime machining of brittle materials such as silicon and germanium. In particular, MD simulation has helped understand the occurrence of brittle–ductile transition due to the high-pressure phase transformation (HPPT), which induces Herzfeld–Mott transition. In this paper, relevant MD simulation studies in conjunction with experimental studies are reviewed with a focus on (i) the importance of machining variables: undeformed chip thickness, feed rate, depth of cut, geometry of the cutting tool in influencing the state of the deviatoric stresses to cause HPPT in silicon, (ii) the influence of material properties: role of fracture toughness and hardness, crystal structure and anisotropy of the material, and (iii) phenomenological understanding of the wear of diamond cutting tools, which are all non-trivial for cost-effective manufacturing of silicon. The ongoing developmental work on potential energy functions is reviewed to identify opportunities for overcoming the current limitations of MD simulations. Potential research areas relating to how MD simulation might help improve existing manufacturing technologies are identified which may be of particular interest to early stage researchers.     

组装间隙对铜和陶瓷套封结构钎焊的影响

为掌握铜与陶瓷内套封结构的钎焊工艺,以套封长度20 mm的铜柱和陶瓷套的内套封结构为研究对象,选用Ag72Cu丝状钎料,采用Mo-Mn金属化法和真空钎焊工艺,开展了钎焊试验。针对套封结构的组装间隙开展了试验研究,通过破坏性试验和金相观察,分析了内套封结构的外观成型,钎料填缝性能和接头界面组织。结果表明,制定的组装方案定位容易,装配难度小。在拟定工艺下施焊,钎料填满整条焊缝,钎缝结合良好。0.3~0.4 mm的组装间隙能较好的保证钎焊质量。间隙较大时,界面迁移扩散明显。     

Micromilling characteristics and electrochemically assisted reconditioning of polycrystalline diamond tool surfaces for ultra-precision machining of high-purity SiC

The production of extremely thick silicon carbide (SiC) has recently become possible with the advent of a specific chemical vapor deposition process. Ultra-precision machining of high-purity SiC has been performed by using a polycrystalline diamond (PCD) micromilling tool to investigate the machining characteristics. Results indicate that a high-quality surface (R_a = 1.7 nm) can be obtained when the removed chips are thin enough to achieve ductile mode machining. Micron-sized wells and groove structures with nanometer-scale surface roughness were successfully machined by using the PCD tool. In addition, a new electrochemically assisted surface reconditioning process has been proposed to remove the contaminant material adhered onto the PCD tool surfaces after prolonged machining.     

A study of three-dimensional shape machining with an ECμM system

This paper presents an electrochemical micromachining (ECμM) system developed with a machining gap control system. As a preliminary, electrochemical machining (ECM) experiments are carried out. The optimum machining condition of ECM is determined in terms of machining voltage, machining pulse length, amplitude of the electrode for flushing out contamination, and electrolyte concentration. After the preliminary ECM experiments, three-dimensional shape micromachining is carried out under the optimum condition. First, a prismatic electrode with a 200-μm square as the base shape is machined by ECM. Next, three-dimensional shape micromachining is carried out by scanning the prismatic electrode. A three-dimensional shape with sub-millimeter range is successfully machined.     

放电加工用金属结合剂碳化硅工具的研究

本文利用热压烧结工艺制备了含有20vol％～50vol％SiC的放电加工用金属结合剂工具电极。采用非均相沉淀包裹法制得Cu包SiC复合粉体。并对试样的气孔率、电阻率、抗弯强度进行了研究,结果表明,随着SiC含量的增加,试样气孔率和电阻率提高,而抗弯强度下降;在20vol％-50vol％SiC含量范围内,采用直接混合法和包裹法制备的试样具有大致相同的气孔率、电阻率,但包裹法的强度却大大提高。用X—ray衍射、扫描电镜（SEM）、能谱分析（EDAX）等测试手段对试样进行了成分和微观形貌分析。研究结果表明,包裹法制得的Cu结合SiC试样,SiC分散更均匀,并通过形成Cu2O—SiO2共熔物（玻璃相）来提高SiC和Cu的界面结合强度。     

加工过程物理仿真技术研究

加工过程仿真是虚拟制造的底层关键技术，同时也是数字化制造系统的重要组成部分，而物理仿真是其中的研究重点和难点。建模难，通用性和实用性差是目前物理仿真中存在的主要问题。文章总结了物理仿真的研究内容和方法，分析了研究中存在的问题及加工过程建模的常用方法。