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.     

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.     

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.     

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.     

Effect of valency on material removal rate in electrochemical machining of aluminium

Material removal rate (MRR) of aluminium work piece has been obtained by electrochemical machining using NaCl electrolyte at different current densities and compared with the theoretical values. It has been observed that resistance of the electrolyte solution decrease sharply with increasing current densities. The over-voltage of the system initially increases and then attains a saturation value with increasing current densities. The material removal rate, determined experimentally, almost corresponds to theoretical value with Al³⁺ state. On the other hand, taking into account over-voltage, MRR comes out be 72%. It appears that removal of a fraction of aluminium occurs in Al⁺ which subsequently gets converted into Al³⁺ through a series chemical reactions. A mechanism of such chemical reactions is proposed.     

A wafer-scale material removal rate profile model for copper chemical mechanical planarization

Chemical mechanical polishing (CMP) models based on the Preston equation, which states that the material removal rate (MRR) is proportional to the product of the pressure and relative velocity, have focused on representing the average MRR as a function of the pressure and relative velocity. In this study, we tried to establish a semi-empirical CMP model, which can provide the MRR profile. The model is based on a modified form of the Preston equation and involves the use of a spatial parameter (Ω). The relative velocity distribution, normal contact stress distribution, and chemical reaction rate distribution are considered for obtaining the MRR profile in the copper CMP process. The results of the modeling and experimental analysis performed in this study facilitate process optimization and provide information that can contribute to the development of a wafer-scale CMP simulator.     

固结磨料抛光垫作用下的材料去除速率模型

在对研磨抛光过程作出适当简化的基础上，推导出了固结磨料研具研磨抛光工件的去除速率模型，并进行了数值模拟。结果表明：固结磨料研磨加工时的去除速率不仅与工件的材质有关，还与固结磨料研磨盘的结构与加工参数相关；去除速率与相对速度V成正比，与压力的3／2次方成正比，与磨料直径成反比，并随着凸起间距的增加而下降。     

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 material removal analysis of electrochemical machining using flat-end cathode

Electrochemical machining (ECM) has been increasingly recognized for the potential for machining, while the precision of the machined profile is a concern of its application. A process to erode a hole of hundreds of micrometers on the metal surface is analyzed in the current paper. A theoretical and computational model is presented to illustrate how the machined profile evolves as the time elapses. The analysis is based on the fundamental law of electrolysis and the integral of a finite-width tool. The paper also discusses the influence of experimental variables including time of electrolysis, voltage, molar concentration of electrolyte and electrode gap upon the amount of material removal and diameter of machined hole. The results of experiment show the material removal increases with increasing electrical voltage, molar concentration of electrolyte, time of electrolysis and reduced initial gap. The time of electrolysis is the most influential factor on the produced diameter of hole.     

Modeling of material removal rate in electric discharge grinding process

The mechanism of material removal in electric discharge grinding (EDG) is very complex due to interdependence of mechanical and thermal energies responsible for material removal. Therefore, on the basis of conceived process physics for material removal, an attempt has been made to predict the material removal rate (MRR). The proposed mathematical model is based on the fundamental principles of material removal in electric discharge machining (EDM) and conventional grinding processes. The inter-dependence of the thermal and mechanical phenomena has been realized by scanning electron microscopy (SEM) characterization of the samples machined at different processing conditions. The key input process parameters like pulse on time, pulse current, gap voltage, duty cycle, pulse off time, frequency, depth of cut, wheel speed and table speed are co-related with MRR for three distinct idealized processing conditions. The constant showing the extent of interdependence of two phenomena were evaluated by experimental data. The obtained expressions of MRR have been validated for processing conditions other than those used for obtaining constants. It was found that the discharge energy plays prominent role in material removal. The percentage difference in experimental findings and theoretical predictions was found to be less than 3%.     

基于正交试验的PCD材料磨除率和磨耗比的研究

通过金刚石砂轮刃磨聚晶金刚石(PCD)材料的正交试验,对各刃磨工艺参数包括砂轮的速度v、工作台调定压力Fa、进给量f对刃磨时磨除率Q和磨耗比G的影响,做了系统的研究,并通过回归分析得出了磨除率和磨耗比的回归方程.试验结果表明,进给量是对磨除率和磨耗比影响最大的因素,且随着进给量的增大,磨除率和磨耗比都呈明显增大的趋势,而砂轮的速度和工作台调定压力对磨除率及磨耗比的影响均不显著.     

Surface integrity and material removal mechanisms associated with the EDM of Al2O3 ceramic composite

Electric discharge machining (EDM) has been proven as an alternate process for machining complex and intricate shapes from the conductive ceramic composites. The performance and reliability of electrical discharge machined ceramic composite components are influenced by strength degradation due to EDM-induced damage. The success of electric discharge machined components in real applications relies on the understanding of material removal mechanisms and the relationship between the EDM parameters and formation of surface and subsurface damages. This paper presents a detailed investigation of machining characteristics, surface integrity and material removal mechanisms of advanced ceramic composite Al₂O₃–SiC_w–TiC with EDM. The surface and subsurface damages have also been assessed and characterized using scanning electron microscopy (SEM). The results provide valuable insight into the dependence of damage and the mechanisms of material removal on EDM conditions.     

High speed versus conventional grinding in high removal rate machining of alumina and alumina–titania

High removal rate (up to 16.6 mm³/s per mm) grinding of alumina and alumina–titania was investigated with respect to material removal and basic grinding parameters using a resin-bond 160 μm grit diamond wheel at the speeds of 40 and 160 m/s, respectively. The results show that the material removal for the single-phase polycrystalline alumina and the two-phase alumina–titania composite revealed identical mechanisms of microfracture and grain dislodgement under the grinding conditioned selected. There were no distinct differences in surface roughness and morphology for both materials ground at either conventional or high speed. An increase in material removal rate did not necessarily worsen the surface roughness for the two materials at both speeds. Also the grinding forces for the two ceramics demonstrated similar characteristics at any grinding speeds and specific removal rates. Both normal and tangential grinding forces and their force ratios at the high speed were lower than those at the conventional speed, regardless of removal rates. An increase in specific removal rate caused more rapid increases in normal and tangential forces obtained at the conventional grinding speed than those at the high speed. Furthermore, it is found that the high speed grinding at all the removal rates exerted a great amount of coolant-induced normal forces in grinding zone, which were 4–6 times higher than the pure normal grinding forces.     

基于非接触给电的高主轴转速微细电火花加工特性研究

在实现非接触给电的微细电火花加工的基础上,分别研究了圆柱电极和削边电极的主轴转速对材料去除率及电极损耗的影响。结果表明:无论是圆柱电极还是削边电极,随着主轴转速的提高,材料去除率增加,电极损耗率降低;且在削边电极的情况下,主轴转速的提高对于材料去除率和电极损耗率的改善更明显。     

Finite element prediction of material removal rate due to electro-chemical spark machining

Electro-chemical spark machining (ECSM) is an innovative hybrid machining process, which combines the features of the electro-chemical machining (ECM) and electrodischarge machining (EDM). Unlike ECM and EDM, ECSM is capable of machining electrically non-conducting materials. This paper attempts to develop a thermal model for the calculation of material removal rate (MRR) during ECSM. First, temperature distribution within zone of influence of single spark is obtained with the application of finite element method (FEM). The nodal temperatures are further post processed for estimating MRR. The developed FEM based thermal model is found to be in the range of accuracy with the experimental results. Further the parametric studies are carried out for different parameters like electrolyte concentration, duty factor and energy partition. The increase in MRR is found to increase with increase in electrolyte concentration due to ECSM of soda lime glass workpiece material. Also, the change in the value of MRR for soda lime glass with concentration is found to be more than that of alumina. MRR is found to increase with increase in duty factor and energy partition for both soda lime glass and alumina workpiece material.     

Modeling of material removal rate and surface roughness in finishing of bevel gears by electrochemical honing process

This paper describes mathematical modeling of material removal rate (MRR) and surface roughness of the bevel gears finished by the electro-chemical honing (ECH) process. Since, ECH hybridizes electrochemical dissolution (ECD) and mechanical honing therefore, contribution of ECD in MRR and surface roughness has been modeled using Faraday's law of electrolysis while contribution of mechanical honing has been modeled considering material removal as a phenomenon of uniform wear and using Archard's wear model. Formulations are also proposed for computing the surface area, required by these two models, along the inter-electrode gap (IEG) based on the geometry of the straight bevel gear tooth surfaces. The developed models were experimentally validated using an indigenously developed experimental setup for finishing of bevel gears by ECH based on an envisaged novel concept of twin complementary cathode gears. An aqueous solution containing 25% NaCl + 75% NaNO₃ was used as the electrolyte. The predicted values of MRR and surface roughness have shown close agreement with the experimental values. The experimental results, SEM images and bearing area curve have shown appreciable improvement in the surface roughness and surface integrity ensuring better operating performance of the gears finished by ECH within an optimized finishing time of 2 min.     

Effects of pressure and shear stress on material removal rate in ultra-fine polishing of optical glass with magnetic compound fluid slurry

Optical glasses used in a range of industrially important optoelectronic devices must be polished to nano-level roughness for proper device operation. Polishing process with magnetic compound fluid slurry (MCF polishing) under a rotary magnetic field is an influential candidate for the method to precisely polish optical glass. MCF slurry has been successfully utilized to polish a variety of materials, ranging from soft optical polymers to hard optical glasses. MCF was developed by mixing a magnetic fluid and a magnetorheological fluid with the same base solvent, and hence includes not only μm-sized iron particles but also nm-sized magnetite particles. To elucidate the behaviour of material removal in MCF polishing, this study measured the normal and shear forces generated in the polishing zone during polishing. From these measurements, the distributions of pressure P and shear stress τ were obtained. The distribution of material removal rate (MRR) was investigated through spot polishing of borosilicate glass. The effects of three process parameters, namely magnet revolution speed, MCF carrier rotational speed and working gap, on pressure P, shear stress τ and the MRR were also investigated. The results revealed that P is higher near the centre of the interacting area (i.e. the polishing spot centre) and the point of maximum shear stress τ appears at about 5 mm from the polishing spot centre. All of P, τ and MRR are sensitive to MCF carrier rotational speed and working gap but insensitive to magnet revolution speed. Shear stress is more sensitive to these process parameters than the pressure. Cross-sectional profiles of the polishing spots exhibit a characteristic symmetric W-shape; material removals are minimal at the spot centre and maximal at approximately 8.2–10.2 mm from the spot centre depending on the process parameters. MRR is proportional to the MCF carrier rotational speed and is negatively correlated with working gap. An MRR model involving both the pressure and shear stress in MCF polishing is proposed. In the model, MRR is more dominated by shear stress than by pressure.     

砂带磨削Q235钢工艺参数对去除率的影响

采用盘圆砂钢机对Q235钢进行了砂带磨削试验研究,对磨削后工件的材料去除率进行了分析,讨论了其最佳工艺参数组合。结果表明:在盘圆砂钢机砂带磨削Q235钢过程中,线材速度对材料去除率的影响最为显著,其次为工作台转速、砂带粒度,砂带张紧力的影响最小。仅考虑对材料去除率的影响时,最佳工艺参数组合为:砂带张紧力200 N,工作台转速500r/min,砂带粒度120#,线材速度为50m/min。此时得到的材料去除率为6.860 2g/s。     

Experimental evaluation of strains in the tension–compression using a new tool geometry, X-Die

Sheet-metal forming involves a complex distribution of strains throughout the part. The strains occur due to tension, compression and a mix of both. A geometry has been developed, the X-Die, in order to gain insight into the strain behavior of different materials. The X-Die enables strain paths far into the tension–compression region, thus creating the possibility to extend the experimental base both for definition and for further extrapolation of the forming limit curve (FLC) in the tension–compression region, as well as to evaluate FE-simulation results for the same region.

The experimental results show that the strain signature is impacted by material quality. In qualities such as extra high strength steel (EHSS) and aluminum the strains do not reach as far into the tension–compression region as the strains do in e.g. mild steel. This is due to failure in plane strain tension. Strain paths in materials such as mild steel and high strength steel (HSS) reach far into the tension–compression region before failure. Use of the X-Die provides possibilities to reach farther into the tension–compression region compared with traditional test methods for creating a forming limit diagram (FLD).

Use of the X-Die yields well-defined strain signatures. These clearly defined strain signatures are favorable for comparison with numerical simulations, especially for strain signatures in the tension–compression region.

Furthermore, the experiments using the X-Die indicate that a possible additional forming limit curve, which intersects the original forming limit curve (shear failure), exists so far into the tension–compression region that it is not applicable.

Even though the experiments indicate compression strains >100% (material DX56D), the experiments show potential for an experimentally determined extrapolation of the FLC up to 75% compression strain. The results of the experiments indicate that the X-Die geometry is suitable as a supplementary tool in identifying the strain behavior of different materials far into the tension–compression region and is also a good tool for verification of numerical results in the tension–compression region.     

Si3N4陶瓷引弧微爆炸加工材料去除率建模与分析

利用引弧微爆炸加工装置,以氮化硅工程陶瓷为加工对象,对引弧微爆炸加工过程的喷嘴烧损及材料去除率进行了研究。通过喷嘴烧损实验,研究了喷嘴烧损规律及喷嘴直径对材料去除率的影响;利用正交实验方法,建立了材料去除率经验模型并分析了材料去除率随加工参数的变化规律。结果显示:喷嘴直径随着脉冲次数的增加而扩展,当直径在2.4～2.8 mm之间时,可以产生最好的加工质量和最大的材料去除率;四个主要加工参数对材料去除率的影响显著,材料去除率随着工作电流、工作气压、工作脉宽的增大而增大,随着工作距离的增大而减小;建立的指数型经验模型简单可靠,与实验结果吻合良好,可以用于材料去除率的预测及控制。