Slotted-electrical discharge diamond cut-off grinding of Al/SiC/B4C hybrid metal matrix composite

Advanced manufacturing industries need materials with high strength and low weight in the fields of advanced engineering, such as automobiles and aeronautics. Metal matrix composites (MMCs) are one of the advanced engineering materials that meet the above requirements. To enhance the properties of MMCs, researchers added an additional phase of reinforcements into single reinforced MMCs; such developed MMCs are known as hybrid MMCs. The additional phase of reinforcements enhances the properties of MMCs, but simultaneously leads to rapid tool wear and poor machinability. This study developed an innovative hybrid machining process (HMP) consisting of electrical discharge grinding and diamond grinding in such a way that both the processes occur alternately with equal intervals due to the rotation of a slotted abrasive grinding wheel. The performance of the hybrid process was tested on an Al/SiC_p/B₄C_p work-piece in cut-off grinding mode. The experiments were conducted on an electrical discharge machining machine, which consists of a separate attachment on a vertical column to rotate the wheel. Pulse current, pulse on-time, pulse off-time, wheel RPM, and abrasive grit number were taken as input parameters while material removal rate (MRR) and average surface roughness were taken as output parameters. Result were shown that the HMP gives higher MRR with better surface finish as compared to the constituent processes. Pulse current ranging from 3 A to 21 A, pulse on-time ranging from 30 μs to 200 μs, and pulse off-time ranging from 15 μs to 90 μs were also found to be more suitable for higher MRR, and a wheel RPM at 1300 RPM was more suitable for higher MRR with better surface finish.     

Application of non-dominated sorting genetic algorithm for multi-objective optimization of electrical discharge diamond face grinding process

Hybrid machining processes (HMPs), having potential for machining of difficult to machine materials but the complexity and high manufacturing cost, always need to optimize the process parameters. Our objective was to optimize the process parameters of electrical discharge diamond face grinding (EDDFG), considering the simultaneous effect of wheel speed, pulse current, pulse on-time and duty factor on material removal rate (MRR) and average surface roughness (Ra). The experiments were performed on a high speed steel (HSS) workpiece at a self developed face grinding setup on an EDM machine. All the experimental results were used to develop the mathematical model using response surface methodology (RSM). The developed model was used to generate the initial population for a genetic algorithm (GA) during optimization, non-dominated sorting genetic algorithm (NSGA-II) was used to optimize the process parameters of EDDFG process. Finally, optimal solutions obtained from pareto front are presented and compared with experimental data.     

Diamond face grinding of WC-Co composite with spark assistance: Experimental study and parameter optimization

Electro-discharge machining (EDM) characteristics of tungsten carbide-cobalt composite are accompanied by a number of problems such as the presence of resolidified layer, large tool wear rate and thermal cracks. Use of combination of conventional grinding and EDM (a new hybrid feature) has potential to overcome these problems. This article presents the face grinding of tungsten carbide-cobalt composite (WC-Co) with electrical spark discharge incorporated within face of wheel and flat surface of cylindrical workpiece. A face grinding setup for electro- discharge diamond grinding (EDDG) process is developed. The effect of input parameters such as wheel speed, current, pulse on-time and duty factor on output parameters such as material removal rate (MRR), wheel wear rate (WWR) and average surface roughness (ASR), are investigated. The present study shows that MRR increases with increase in current and wheel speed while it decreases with increase in pulse on-time for higher pulse on-time (above 100 μs). The most significant factor has been found as wheel speed affecting the robustness of electro- discharge diamond face grinding (EDDFG) process.     

Mathematical modeling and machining parameter optimization for the surface roughness of face gear grinding

Face gear is an important part in the power transmission of helicopter, but its grinding is a difficult problem. In order to enhance the finishing machining surface quality of face gear, the mathematical formula of the residual height of motion trajectory of abrasive grains was obtained, and the model of grinding surface roughness of face gear was corrected. In addition, machining parameter optimization for grinding surface roughness on a five-axis blade grinding machine was investigated by orthogonal experiment method. The experiment results indicated that disk wheel spindle speed and feed velocity of the disk wheel are more significant effect factors among the three factors. The calculation results of model showed that the maximum error comparing with the experiment results is not more than 13.5 %, which suggests that the mathematical model is reasonable.     

Parametric optimization of CNC turning process for hybrid metal matrix composite

Machining of hybrid metal matrix composite is difficult as the particulates are abrasive in nature and they behave like a cutting edge during machining resulting in quick tool wear and induces vibration. An attempt was made in this experimental study to evaluate the machining characteristics of hybrid metal matrix composite, and a mathematical model was developed to predict the responses, namely surface finish, intensity of vibration and work-tool interface temperature for known cutting condition while machining was performed in computer numerical control lathe. Design of experiments approach was used to conduct the trials; response surface methodology was employed to formulate a mathematical model. The experimental study inferred that the vibration in V _x, V _y, and V _z were 41.59, 45.17, and 26.45 m/s², respectively, and surface finish R _a, R _q, and R _z were 1.76, 3.01, and 11.94 μm, respectively, with work-tool interface temperature ‘T’ of 51.74 °C for optimal machining parameters, say, cutting speed at 175 m/min, depth of cut at 0.25 mm and feed rate at 0.1 mm/rev during machining. Experimental results were in close conformity with response surface method overlay plot for responses.     

Grinding of aluminium silicon carbide metal matrix composite materials by electrolytic in-process dressing grinding

The grinding cost of metal matrix composite materials is more due to low removal rates and high rates of wear of super abrasive wheels. This electrolytic in-process dressing (ELID) technique uses a metal-bonded grinding wheel that is electrolytically dressed during the grinding process for abrasives that protrude continuously from super abrasive wheels. This research carries out ELID grinding using various current duty ratios and conventional grinding of 10% SiC_p reinforced 2,124 aluminium composite materials. Normal forces and tangential forces are monitored. Surface roughness of the ground surface, Vickers hardness numbers and metal removal rate (MRR) are measured. The results show that the cutting forces in the ELID grinding are unstable throughout the grinding process due to the breakage of an insulating layer formed on the surface of grinding wheel and are less than conventional grinding forces. A smoother surface can be obtained at high current duty ratio in ELID grinding. The micro-hardness is reduced at high current duty ratio. In ELID, the MRR increases at high current duty ratio. The results of this investigation are presented in this paper.     

Experimental study and parameter design of electro-discharge diamond grinding

Electrical discharge diamond grinding (EDDG), which integrates diamond grinding and electro-discharge machining (EDM), is a new hybrid machining process for shaping electrically conductive very hard materials. The process employs synergetic interactive effect of electro-discharge action and abrasion action to increase machining performance. This paper presents an investigation on the experimental study and machining parameter design of electro-discharge diamond grinding (EDDG). The EDDG setup was designed and fabricated, and experiments were conducted on high speed steel (HSS) workpiece under varying current, pulse-ontime, duty factor and wheel speed. The settings of machining parameters were determined by using the Taguchi experimental design method. The level of the machining parameters on the MRR is determined by using analysis of variance (ANOVA). The optimum machining parameter combination was obtained by using the evaluated S/N ratio.     

Electrical discharge abrasive drilling of hard materials using a metal matrix composite electrode

The main object of the present work was to develop an electrical discharge abrasive drilling (EDAD) methodology to remove the re-solidified layer through the grinding induced by a metal matrix composite electrode prior to the re-solidification of molten material. A metal matrix composite (Cu/SiC_p) electrode, with an electroless pretreatment of Cu coating on SiC_p to enhance bonding status between Cu and SiC_p, was made with a rotating device and this was employed to study the EDAD technology. The machinability of the mold steel HPM50 and tungsten carbide P20 was investigated by the combined technologies of EDAD. The machined surfaces of these materials were examined by scanning electron microscopy (SEM) and their surface roughness measured by a profilemeter. From the experimental results, it was found that the EDAD machining efficiency was three to seven times than that of normal EDM operation for mold steel. However, the efficiency improvement is hardly detectable for tungsten carbide. In addition, the surface roughness of both materials could be improved in comparison with that achieved after EDM.     

电火花机械复合磨削反应烧结SiC陶瓷的表面特征

研究了基于电火花机械复合磨削技术加工的反应烧结碳化硅(RB-SiC)陶瓷的表面特征。用电火花机械复合磨削(EDDG)、电火花磨削(EDG)以及普通磨削(CG)三种方法加工RB-SiC陶瓷,并采用激光共聚焦显微镜和扫描电子显微镜对加工后的SiC陶瓷的表面粗糙度、表面形貌及微观裂纹进行测量和对比试验,获得了RB-SiC陶瓷的EDDG加工特性。实验显示:EDDG加工的RB-SiC陶瓷的表面粗糙度优于EDG加工的表面粗糙度,为0.214 9μm,但比CG加工的表面粗糙度0.195 6μm略差。对加工后的SiC陶瓷表面形貌观察显示,传统磨削加工后的表面存在明显划痕,EDG加工表面主要由放电凹坑组成,而EDDG加工表面同时存在放电凹坑和磨削划痕;另外,传统磨削表面也存在磨削裂纹和晶界裂纹,但EDG加工后的表面只存在热裂纹,而EDDG加工后的表面存在磨削裂纹和热裂纹,不过热裂纹可以用金刚石磨粒磨削去除。对比实验显示RB-SiC陶瓷的EDDG加工与EDG和CG加工获得了不同的表面特征。     

气中电火花加工颗粒增强金属基复合材料的有限元分析

根据傅里叶热传导理论,建立了气中电火花放电加工颗粒增强金属基复合材料的二维有限元仿真模型。利用有限元软件ANSYS分别采用高斯热源模型和均匀热源模型对单脉冲放电加工金属基复合材料的温度场进行数值模拟。根据温度场的分布情况,对比分析了在两种不同热源模型下放电凹坑的形貌、直径和深度,并与实验结果进行比较,结果表明,与高斯热源模型相比,均匀热源模型能较好地预测单脉冲放电加工金属基复合材料的放电凹坑特征。根据电火花加工金属基复合材料的特点,对均匀热源模型中所采用的放电通道半径进行了修正,结果表明,修正后的模型能够比较准确地模拟单脉冲放电加工金属基复合材料放电凹坑的几何特征。     

Molecular dynamics modeling of a single diamond abrasive grain in grinding

In this paper the nano-metric simulation of grinding of copper with diamond abrasive grains, using the molecular dynamics (MD) method, is considered. An MD model of nano-scale grinding, where a single diamond abrasive grain performs cutting of a copper workpiece, is presented. The Morse potential function is used to simulate the interactions between the atoms involved in the procedure. In the proposed model, the abrasive grain follows a curved path with decreasing depth of cut within the workpiece to simulate the actual material removal process. Three different initial depths of cut, namely 4 ?, 8 ? and 12 ?, are tested, and the influence of the depth of cut on chip formation, cutting forces and workpiece temperatures are thoroughly investigated. The simulation results indicate that with the increase of the initial depth of cut, average cutting forces also increase and therefore the temperatures on the machined surface and within the workpiece increase as well. Furthermore, the effects of the different values of the simulation variables on the chip formation mechanism are studied and discussed. With the appropriate modifications, the proposed model can be used for the simulation of various nano-machining processes and operations, in which continuum mechanics cannot be applied or experimental techniques are subjected to limitations.     

Single discharge thermo-electrical modeling of micromachining mechanism in electric discharge machining

In this study, single discharge thermo-electrical model of workpiece material removal in electrical discharge machining (EDM) was developed. Developed model includes generation of energy in liquid media, variation of plasma channel radius and transfer of heat from the channel by the electrical discharge. Effect of generated energy in plasma channel on workpiece removal was theoretically investigated by using different experimental parameters used in literature. The developed model finds the temperature distribution in the workpiece material using finite element solver ANSYS Workbench (v.11) software. It’s assumed that the workpiece material reaches the melting point of workpiece material was removed from the surface. Electrical discharge process was simulated by using transient thermal analysis. The developed model has also been validated by comparing the theoretically obtained material removal values with the experimental ones.     

树脂结合剂金刚石砂轮磨削铁氧体陶瓷磨削力的实验研究

通过一系列的实验，研究了树脂结合剂金刚石砂轮磨削铁氧体陶瓷材料时磨削力的变化规律及其特点。通过磨削对比实验方法分析磨削铁氧体陶瓷时，磨削用量对磨削力大小的影响。通过砂轮速度，磨削深度，横向进给速度和纵向进给速度等因素影响磨削力大小变化的数据及磨削力信号特征处理的分析和比较，分析了对铁氧体材料磨削时产生的磨削力影响的一些规律，表明铁氧体陶瓷磨削时磨削力变化的特有规律．     

Simulation of effects of metal phase in a diamond grain and bonding type on temperature in diamond grinding

Manufacturing diamond wheels on various bonds is a relatively high-cost process, requiring high labour and high consumption of expensive diamond grains but yielding relatively low productivity. With better knowledge of the various factors involved in the sintering process, the most efficient combinations can be found, leading to higher productivity. Currently, there are no scientifically based recommendations for the choice of the rational combinations of strength, brand of grain, graininess and concentration with the physical–mechanical properties of bonds. The aim of this research is the development of a technique for the theoretical definition of an optimal combination of strength properties of diamond grains and bond to provide maximum retention of diamond grain integrity during the process of diamond wheel manufacture. This is investigated using 3D simulations of the deflected mode of the sintering area of the wheel's diamond-bearing layer.     

Empirical modeling and optimization of wire electrical discharge machining

Wire electrical discharge machining is a widely used process in manufacturing industries to machine complex profiles. The performance of any machining process is based on choosing the right combination of input parameters. Metal removal rate and surface roughness are the most important output parameters, which decide the performance of a machining process. The selection of optimal parameters in wire electrical discharge machining is difficult as it is a complex process and involves a large number of variables. The present work models the metal removal rate and the surface roughness in terms of the input variables using the response surface methodology and, consequently, the developed mathematical models are utilized for optimization. Since the influences of machining parameters on the metal removal rate and the surface roughness are opposite, the problem is formulated as a multiobjective optimization problem. Non-dominated sorting genetic algorithm is then applied to obtain the Pareto-optimal set of solutions.     

Experimental investigations into rotary mode electrochemical discharge drilling (RM-ECDD) of metal matrix composites

Abstract

In the present work, rotary mode electrochemical discharge drilling (RM-ECDD) was employed to machine the Al-6063 SiC_p metal matrix composites (MMC’s). The effect of various process parameters such as applied voltage, pulse on time, tool rotation rate, electrolyte concentration and current on quality characteristics (hole over cut and depth of penetration) of the drilled holes was investigated. The underlying material removal mechanism during the machining of MMC’s with RM-ECDD is also proposed by considering the scanning electron micrographs (SEM) and simulation results as an evidences. A comparative analysis between RM-ECDD and ECDD was performed during the machining of MMC’s. The experimental results reveal that the integration of tool rotations in ECDD successfully evacuates the sludge/debris from the machining zone, and it also replenishes the electrolyte effectively. Therefore the use of RM-ECDD improves the aspect ratio (L/D), and it exhibits 23.07 times higher L/D ratio than the ECDD process. In ECDM, the discharge characteristics are very important outcome that explores the significant details of the involved mechanisms and phenomena of the process. In the present research, a DSO recorded voltage signals were used to understand the discharge behavior and their characteristics at different parameter combinations. This paper also presents a second-order mathematical models to determine the relation between input process parameters and quality characteristics. Desirability based multi objective optimization approach was employed to optimize the process parameters.     

电镀金刚石砂轮端面磨削Al2024/SiCp试验研究

使用电镀金刚石砂轮对SiC颗粒增强Al2024复合材料进行端面磨削加工试验研究.研究结果表明,端面磨削加工能获得高质量的加工表面,在所采用的试验参数范围内,表面粗糙度在Ra为0.185μm和Ra为0.5121μm之间,已加工表面残余应力表现为压应力;磨削加工参数对切向力和法向力的影响不大,并且在不同的加工条件下均保持较小数值.轴向磨削力大于其他两个方向的磨削力,并且随着磨削深度的增大而明显增大.