利用电火花加工方法对模具进行表面涂层的研究

介绍了一种可在普通电火花加工机床上实现的金属模具表面涂层新方法,在大量试验的基础上对模具钢涂层的工艺及特性进行了详细分析。结果表明,用电火花加工的方法对模具钢表面进行涂层可以明显改善其性能,将该方法在冲模上进行了试验,试验表明,有涂层的模具寿命较未涂层的模具寿命有显著提高。     

Anomalous influence of polarity in sink EDM of titanium alloys

An anodic tool polarity is generally adopted in sink electrical discharge machining (EDM) to maximize material removal relative to tool wear. Sink EDM of Ti and Ti6Al4V is however atypical in that these materials necessitate a cathodic tool polarity. Adding to the intrigue is γ-TiAl, which machines better under the conventional anodic polarity. This research focused on clarifying the phenomena behind this interesting behavior by investigating removal mechanisms over a range of relevant process conditions. The anomaly is demonstrated to arise from the polarity-dependent nature and extent of TiC formation on the work surface, which significantly affects material removal.     

Finishing effects of spiral polishing method on micro lapping surface

This study presents a spiral polishing method and a device for micro-finishing purposes. This novel finishing process has wider application than traditional processes. This offers both automation and flexibility in final machining operations for deburring, polishing, and removing recast layers, thereby producing compressive residual stresses even in difficult to reach areas. Applying of this method can obtain a fine polished surface by removing tiny fragments via a micro lapping generated by transmission of an abrasive medium through a screw rod. The effect of the removal of the tiny fragments can be achieved due to the function of micro lapping. The method is not dependent on the size of the work-piece's application area in order to carry out the ultra precise process. The application of this research can be extended to various products of precision ball-bearing lead screw. The proposed method produces products with greater precision and more efficiently than traditional processes, in terms of processing precisions and the surface quality of products. These parameters used in achieving maximum material removal rate (MRR) and the lowest surface roughness (SR) are abrasive particle size, abrasive concentration, gap, revolution speed and machining time.     

Studies on the material removal rate of two-phase eutectic alloys by EDM process

Two types of permanent mould materials, spheroidal graphite (SG) cast iron and Al-Si alloy with various compositions, were selected to study the effect of heterogeneous second phase on material removal rate (MRR) by the electro-discharge machining (EDM) process. Fe-Si alloy and Al-1wt%Si alloy with a mainly single-phase structure were also prepared for comparison.

Experimental results indicated that the amount and morphology of second phase particles significantly influence the material removal rate (MMR). This is closely related to ridge density and discharge density during the EDM process.

The EDMed surface of the specimens had a continuously ridged appearance and the ridge density increases with higher amount of second phase. Worthy of notice is that the graphite particles are embedded in the troughs on the EDMed surface of SG cast iron, while the eutectic silicon particles are located on the ridge region in the case of Al-Si alloys.     

Machining characteristics of magnetic force-assisted EDM

The gap conditions of electrical discharge machining (EDM) would significantly affect the stability of machining progress. Thus, the machining performance would be improved by expelling debris from the machining gap fast and easily. In this investigation, magnetic force was added to a conventional EDM machine to form a novel process of magnetic force-assisted EDM. The beneficial effects of this process were evaluated. The main machining parameters such as peak current and pulse duration were chosen to determine the effects on the machining characteristics in terms of material removal rate (MRR), electrode wear rate (EWR), and surface roughness. The surface integrity was also explored by a scanning electron microscope (SEM) to evaluate the effects of the magnetic force-assisted EDM. As the experimental results suggested that the magnetic force-assisted EDM facilitated the process stability. Moreover, a pertinent EDM process with high efficiency and high quality of machined surface could be accomplished to satisfy modern industrial applications.     

Investigation on the influence of the dielectrics on the material removal characteristics of EDM

A systematical and comprehensive investigation of the material removal characteristics of the electrical discharge machining (EDM) process using various dielectrics as the working fluids was conducted in this work. Five dielectrics, including gaseous dielectrics, air and oxygen, and liquid dielectrics, de-ionized water, kerosene and water-in-oil (W/O) emulsion were used as the working fluids. The whole geometry parameters of the craters, including the recast material in the craters, were precisely determined by metallographic method. The volume of melted and removed material and removal efficiency in different dielectrics were comparatively investigated. By relating the material removal characteristics to the evolution of the discharge generated bubbles in different dielectrics which was done by computer simulation, it seems that the pressure above the discharge point is an important factor that can affect material removal characteristics. The results of this work were supposed to be helpful for further clarifying the complicated material removal mechanism of EDM.     

石墨电极在彩电模具电火花加工中的应用

通过彩电前壳模具喇叭网孔镶件电火花加工,对紫铜电极和石墨电极加工结果进行分析比较,指出石墨材料在制作大电极,特别是在对电极损耗有严格要求的电火花加工时,石墨电极比紫铜电极有许多优点。指出专用石墨作电火花加工电极的优势正逐渐被大家认识,将成为企业首选的电火花加工电极材料。     

混粉电火花放电蚀坑及温度场仿真研究

混粉电火花加工是一种新型加工工艺,通过在工作液中添加微细粉末,显著改善加工表面粗糙度。电火花加工表面粗糙度的形成与放电蚀坑大小有直接关系,而放电蚀坑大小与单次脉冲放电温度场有密切联系。为了进一步提高混粉加工表面质量,利用ANSYS软件对放电点温度场进行了模拟与分析,得到了工件表层温度场的分布规律,揭示了材料去除机制,阐明了加工表面粗糙度与温度场的关系,对预测和改善混粉加工表面质量及日后生产实际应用提供了一定的理论依据。     

Investigation of the spark cycle on material removal rate in wire electrical discharge machining of advanced materials

The development of new, advanced engineering materials and the need for precise and flexible prototypes and low-volume production have made the wire electrical discharge machining (EDM) an important manufacturing process to meet such demands. This research investigates the effect of spark on-time duration and spark on-time ratio, two important EDM process parameters, on the material removal rate (MRR) and surface integrity of four types of advanced material: porous metal foams, metal bond diamond grinding wheels, sintered Nd-Fe-B magnets, and carbon–carbon bipolar plates. An experimental procedure was developed. During the wire EDM, five types of constraints on the MRR due to short circuit, wire breakage, machine slide speed limit, and spark on-time upper and lower limits are identified. An envelope of feasible EDM process parameters is generated for each work-material. Applications of such a process envelope to select process parameters for maximum MRR and for machining of micro features are discussed. Results of Scanning Electron Microscopy (SEM) analysis of surface integrity are presented.     

A study on the optimal fabrication method for micro-scale gyroscopes using a hybrid process consisting of electric discharge machining,chemical etching or micro-mechanical milling

For productive manufacturing of an accurate small-scale wine-glass gyroscope, a hybrid fabrication process consisting of either electric discharge machining, chemical etching, or micro-mechanical milling have been proposed. A comparison of silicon cavity fabrication processes has been conducted in terms of productivity, quality and geometrical accuracy, aiming at the use of the cavity as a mold for creating a thin wall diamond hemisphere, which is the main component of a wine-glass gyroscope. The results have shown that the EDM process, combined with chemical etching, can yield the highest productivity but with limited shape accuracy. The use of mechanical micro-milling, while less productive than EDM and etching, produces a superior quality and geometric accuracy.     

Influences of pulsed power condition on the machining properties in micro EDM

Micro EDM is one of the most powerful technologies which are capable of fabricating micro-structure. However, there are many operating parameters that affect the micro EDM process. Since the EDM is basically a thermal process, the supplying electrical condition can be an important factor. The conditions generally consist of several parameters such as electrical current, voltage, pulse duration, spark gap, and others. Those are decisive in removal rate, wear rate, and machining accuracy, which are characteristics of EDM. In this study, the influences of EDM pulse condition on the micro EDM properties were investigated. Voltage, current, and on/off time of the pulse were selected as experimental parameters based on a simple equation for the material removal rate. The pulse condition is particularly focused on the pulse duration and the ratio of off-time to on-time, and the machining properties are reported on tool wear, material removal rate, and machining accuracy. The experimental results show that the voltage and current of the pulse exert strongly to the machining properties and the shorter EDM pulse is more efficient to make a precision part with a higher material removal rate.     

Reliability of electrode wear compensation based on material removal per discharge in micro EDM milling

This paper investigates the reliability of workpiece material removal per discharge (MRD) estimation for application in electrode wear compensation based on workpiece material removal. An experimental investigation involving discharge counting and automatic on the machine measurement of removed material volume was carried out in a range of process parameters settings from fine finishing to roughing. MRD showed a decreasing trend with the progress of the machining operation, reaching stabilization after a number of machined layers. Using the information on MRD and discharge counting, a material removal simulation tool was developed and validated.     

Electrical discharge machining using simple and powder-mixed dielectric: The effect of the electrode area in the surface roughness and topography

Electrical discharge machining (EDM) is one of the most widely disseminated manufacturing technologies, in particular as regards the generation of accurate and complex geometrical shapes on hard metallic components. Nevertheless current EDM technologies have major limitations when dealing with fine surface finish over large process area. Indeed this is one reason that explains the need of final manual polishing of mould cavities performed by EDM. Recently EDM with powder-mixed dielectric (PMD-EDM) has been a focus of an intense research work in order to overcome these technological performance barriers. This paper presents a research work within the objective to acquire deep knowledge on EDM technology with powder mixed dielectric and to compare its performance to the conventional EDM when dealing with the generation of high-quality surfaces. In particular the analysis of the effect of the electrode area in the surface quality measured by the surface roughness and craters morphology was carried out for both technologies. The results achieved evidenced a linear relationship between the electrode area and the surface quality measures as well as a significant performance improvement when the powder mixed dielectric is used.     

电火花技术在弹簧高精度端面加工中的应用研究

某航空飞行器的尾斜轴有一种弹簧,其两端面形位公差要求高。通过研究弹簧的特性及加工性能、电火花加工技术原理,结合电火花加工机床结构和功能特点,运用数控技术,探索采用电火花加工技术加工弹簧高精度端面,提出实施方案、采取的措施、解决问题的途径。应用结果表明:电火花加工方法可有效解决弹簧端面加工过程中的变形问题,能稳定可靠地保证弹簧端面高精度技术要求。目前此方法已成功运用在多种高精度端面弹簧的加工工艺上,完全满足用户需求,效果理想,具有重要的推广应用价值。     

Experimental characterization of dry EDM performed in a pulsating magnetic field

This paper presents an investigation of the hybrid dry EDM process performed in a pulsating magnetic field for improving process performance. In this study, the pulsating magnetic field is applied tangential to the electric field, for increasing the movement of electrons and degree of ionization in the plasma. Experiments with parametric variations showed that this hybrid approach leads to productivity-improvement by 130% and zero tool wear as compared to the dry EDM process without the magnetic field. The improvement in surface quality is illustrated by scanning electron microscopy (SEM).     

Evaluation of surface roughness in laser-assisted machining of aluminum oxide ceramics with Taguchi method

This paper evaluates laser-assisted machining (LAM) as an economically viable process for manufacturing precision aluminum oxide ceramic parts. Because it is locally heated by an intense laser source prior to material removal, LAM leads to higher material removal rates, as well as improved control of workpiece properties and geometry. To assess the feasibility of the LAM process and better understand its governing physical phenomena, experiments were conducted to obtain different measures of surface roughness for Al₂O₃ workpieces machined by laser-assisted turning using a Nd:YAG laser.The experimental results were analyzed using the Taguchi method, which facilitated identification of optimum machining conditions. The findings indicate that rotational speed, with a contribution percentage as high as 42.68%, had the most dominant effect on LAM system performance, followed by feed, depth of cut, and pulsed frequency. LAM's most important advantage is its ability to produce much better workpiece surface quality than does conventional machining, together with larger material removal rates (MRR) and moderate tool wear.     

Improvement effects of vibration on cutting force in rotary ultrasonic machining of BK7 glass

Rotary ultrasonic machining (RUM) exhibits a high potential for a significant reduction in the cutting force, which directly associates with tool wear, machining accuracy, machining temperature, and surface integrity. However, the improvement mechanisms of the ultrasonic vibration on the cutting force are still not fully recognized, restricting the currently optimization methods for further reducing the cutting force occurred during the RUM process. In this research, by incorporating the kinematics principles of the abrasive, the evolution features of the material strain rate in the loading phase were first discussed with respect to the indentation mechanics theory. Taking these features into account, the RUM scratching tests were carried out on the polished specimen surfaces under various process parameters to capture the integrated damage patterns evoked in the high strain rate stage. Following, the comparative indentation tests were respectively conducted on the RUM scratches and the gentle polished surfaces. The indentation-induced damage structures and the load–displacement curves were characterized and assessed to investigate the improvement mechanisms of the superimposed ultrasonic on the cutting force in formal RUM process. It was found that superimposing an ultrasonic vibration led to the incipient cracks nucleated in the abrasive loading phase, and their propagations would increase the material removal rate (MMR) obtained in formal RUM process. Furthermore, the incipient cracks provided a shielding effect to the indentation force, which was a dominant factor in diminishing the cutting force of the diamond tool. The nucleation of the incipient cracks resulted in more energy dissipation after the abrasives penetrating into the hard substrate of the material, which would lead to a higher residual stress on final RUM surface. In addition, a failure pattern (plastic deformation or brittle fracture) evolution model involved in abrasive loading phase was developed with respect to the strain rate effects of the material.     

磁力搅拌电火花加工工艺对镍钛合金表面特征及疏水性的影响

采用磁力搅拌电火花加工工艺在镍钛合金表面制备疏水性表面来提高其生物相容性,研究工艺参数对表面特征及疏水性的影响。采用扫描电子显微镜（SEM）对工件表面形貌进行分析,使用光学接触角测量仪和TR200粗糙度仪分别测量接触角和表面粗糙度值。结果表明：磁力搅拌电火花加工参数对表面形貌特征及疏水性影响显著。当电流为1.5 A时,表面熔凝凸起随脉宽的增大而增大,在脉宽为60 μs时其表面含有尺寸合适的熔凝凸起,接触角达到峰值为138.2°;当电流为4.5 A时,表面富含气孔特征,表面气孔的深度在脉宽为60 μs时达到最大值,其表面接触角为133.6°。表面粗糙度对疏水性能无直接影响。采用磁力搅拌电火花加工工艺,可以大幅提升镍钛合金表面的疏水性。     

Study on the inner surface finishing of tubing by magnetic abrasive finishing

With the development of industry manufacturing technology, fine surface finish is in high demand in a wide spectrum of industrial applications. Presently, it is required that the parts used in manufacturing semiconductors, atomic energy parts, medical instruments and aerospace components have a very precise surface roughness. Amongst them, vacuum tubes, wave guides and sanitary tubes are difficult to polish by conventional finishing methods such as lapping, because of their shapes. The surface roughness of these tubes affects the performance of the entire system, but the finishing technology for these tubes is very scant in manufacturing fields. This project was proposed by a Shanghai Far East pharmaceutial and mechanical factory. They stated that the roughness of the inner surface must be less than 0.3 μm Ra after finishing. An internal magnetic abrasive finishing (MAF) process is proposed for producing highly finished inner surfaces of tubes used in this study. The process principle and the finishing characteristics of unbounded magnetic abrasive within internal tubing finishing are described first. MAF setup was designed for finishing three kinds of materials tubing, such as Ly12 aluminum alloy, 316L stainless steel and H62 brass. Experimental results indicated that finishing parameters such as polishing speed, magnetic abrasive supply, abrasive material, magnetic abrasive manufacturing process and grain size have critical effects on the material removal rate (MRR). How the inner surface micro shape changes course during finishing of an aluminous tube is demonstrated.     

A finite element model of EDM based on the Joule effect

A thermal–electrical model was developed for sparks generated by electrical discharge in a liquid media. A cylindrical shape has been used for the discharge channel created between the electrodes. The discharge channel being an electrical conductor will dissipate heat, which can be explained by the Joule heating effect. The amount of heat dissipated varies with the thermal–physical properties of the conductor; as a result, the maximum temperature reached is different. In the present model, the radii value of the conductor is a function of the current intensity and pulse duration. The thermal–physical values used in the model are the average of both the ambient and melting value. Copper and iron are the materials used for anode and cathode, respectively. The Finite Element Analysis (FEA) results were compared with the experimental values of the table of AGIE SIT used by other researchers [D.D. DiBitonto, P.T. Eubank, M.R. Patel, M.A. Barrufet, Theoretical models of the electrical discharge machining process—I: a simple cathode erosion model, Journal of Applied Physics, 66(9) (1989) 4095–4103; M.R. Patel, M.A. Barrufet, P.T. Eubank, D.D. DiBitonto, Theoretical models of the electrical discharge machining process—II: the anode erosion model, Journal of Applied Physics, 66(9) (1989) 4104–4111; P.T. Eubank, M.R. Patel, M.A. Barrufet, B. Bozkurt, Theoretical models of the electrical discharge machining process—III: the variable mass, cylindrical plasma model, Journal of Applied Physics, 73(11) (1993) 7900–7909]. In order to show the universality of the model it was obtained results for all current intensity values of the table. The Tool Wear Ratio (TWR) and Material Removal Rate (MRR) as well as surface roughness results agree reasonably well with the researcher's values found for that table and itself.