Experimental investigation on electrochemical grinding (ECG) of alumina-aluminum interpenetrating phase composite

The present paper focuses on the evaluation of material removal rate (MRR), surface finish, and cutting forces during electrochemical grinding of Al₂O₃/Al interpenetrating phase composite. The effect of electrolyte concentration, supply voltage, depth of cut, and electrolyte flow rate on machining performances has been studied. The characteristic features of the electrochemical grinding (ECG) process are explored through Taguchi-design-based experimental studies with various process parametric combinations and finally the process has been optimized. The mechanism of material removal and surface characteristics under different grinding conditions have been studied through SEM micrograph. Besides, another set of experimental investigation has been carried out in order to identify the influence of different type of electrolytes and degree of reduction in grinding force in ECG. Finally, a comparative study of conventional and electrochemical grinding of this special class of material has been carried out.     

磁场电化学磁粒复合光整加工实验研究

开发出一种新的光整加工工艺－磁场电化学磁粒复合光整加工。研究了磁场环境下离子运动轨迹方程,分析了复合光整加工的原理并进行了相应的实验,由于洛仑兹力和电场力的综合作用,改变了离子运动轨迹,使被加工表面峰点电流密度更集中,磁场的搅拌作用,加快了电化学过程,使极间电流密度增大,蚀除速度加快,磁场电化学磁粒复合光整加工,与磁粒光整加工,电化学磁粒光整加工相比,提高了加工效率,改善了表面粗糙度。     

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.     

Synchronous finishing processes using a combination of grinding and electrochemical smoothing on end-turning surfaces

A new finishing mode has been utilized as an effective finishing tool design with an electrode and a nonconductive grindstone to execute grinding and electrochemical smoothing synchronously. This mode can be used for various end-turning operations. Through simple equipment attachment, grinding and electrochemical smoothing can follow the cutting process on the same machine. Among the factors affecting electrochemical smoothing, grinding performance combined with electrochemical smoothing, is primarily discussed. In the experiment, different types of electrodes are used with continuous and pulsed direct current. The control factors include die material, chemical composition, and concentration of the electrolyte. The experimental parameters are finish tool and workpiece rotational speed, flow rate of electrolytes, gap width between electrode and workpiece, electrical current density and pulsed period, and finishing tool geometry. High workpiece and electrode rotational speed produces a better finish. A thin electrode is associated with higher current density and provides larger discharge space for a better finish. Pulsed direct current can promote the effect of electrochemical finishing. Decreasing the height of the finish tool to a partial-form tool is associated with less restricted electrolyte flow and more discharge space, which creates better finishes than the full-form tools. The grindstone, with an adequately convex shape, also appeared to have an adequate initial gap width between the electrode and workpiece, which matches enough current density and obtains a better finish. The most effective geometric design for the finishing tool and the advantage of the low-cost equipment in electrochemical smoothing, following end-turning, is investigated in this study.     

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.     

Factors affecting surface finish when grinding titanium and a titanium alloy (Ti-6Al-4V)

Under conventional grinding conditions redeposition which degrades surface finish occurs when grinding titanium and a titanium alloy (Ti-6Al-4V). To prevent redeposition and hence to obtain optimum surface finish the following grinding conditions are required: a soft grade (H) silicon carbide wheel running at 10 m s^?1, a sulphur-chlorinated cutting oil grinding fluid and a relatively high table speed (0.2 m s^?1), and the wheel should be re-dressed prior to taking the finishing passes (about ten) at a wheel downfeed of 2.5 μm.     

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.     

Grinding-aided electrochemical discharge machining of particulate reinforced metal matrix composites

A grinding-aided electrochemical discharge machining (G-ECDM) process has been developed to improve the performance of the conventional ECDM process in machining particulate reinforced metal matrix composites (MMCs). The G-ECDM process functions under a combined action of electrochemical dissolution, spark erosion, and direct mechanical grinding. The tool electrode has a coating containing a hard reinforcement phase of diamond particles. The MMC employed in this study was Al₂O₃ particulate reinforced aluminum 6061 alloy. The material removal mechanism of this hybrid process has been analyzed. The results showed that the grinding action can effectively remove re-cast material deposited on the machining surface. The surface roughness (R _a) measured for the G-ECDM specimen was ten times smaller than that of the specimen machined without grinding aid (i.e., ECDM alone). Moreover, the material removal rate (MRR) of G-ECDM was about three times higher than that of ECDM under the experimental conditions of this study. The voltage waveform and crater distribution were also analyzed, and the experimental results showed that the G-ECDM process operates in a stable condition. The relative importance of the various processing parameters on MRR was established using orthogonal analysis. The results showed that MRR is influenced by the machining parameters in the order of duty cycle?>?current?>?electrolyte concentration. This study showed that the G-ECDM process is superior to the ECDM process for machining particulate reinforced MMCs, where a higher machining efficiency and a better surface quality can be obtained.     

Some factors affecting the efficiency of individual grits in simulated grinding experiments

This study of the mechanics of grinding used a single grit approach and involved the development of a high frequency dynamometer to measure grinding forces at speeds of up to 37 m s^?1. Experiments have been carried out using idealised cutters to simulate abrasive grits; the grinding forces, the grinding coefficient and the specific energy were measured for a wide range of cutting speeds and workpiece hardness. For a grit of a given geometry the main factors affecting efficiency were found to be the hardness of the workpiece and the cutting speed.A theoretical model of the grinding process has been developed which enables normal grinding forces to be predicted from the flow pressure of the workpiece and the geometry and cutting efficiency of the grit.The implications of the work are discussed with particular reference to surface finish.     

EXPERIMENTAL INVESTIGATIONS INTO THE INFLUENCE OF MAJOR OPERATING PARAMETERS DURING MICRO-ELECTRO DISCHARGE DRILLING OF CEMENTED CARBIDE

Present study investigates the influence of major operating parameters on the performance of micro-EDM drilling of cemented carbide (WC-10wt%Co) and identifies the ideal values for improved performance. The operating parameters studied were electrode polarity, gap voltage, resistance, peak current, pulse duration, pulse interval, duty ratio, electrode rotational speed and EDM speed. The performance of micro-EDM drilling process was evaluated by machining time, material removal rate (MRR), relative electrode wear ratio (RWR), spark gap, surface finish and dimensional accuracy of micro-holes. It has been found that there are two major conflicting issues in the micro-EDM of carbide. If the primary objective is to obtain better surface finish, it can be obtained by the sacrifice of high machining time, low MRR and high RWR. However, for faster micro-EDM, the surface roughness is higher and electrode wear is again much higher. It is concluded that negative electrode polarity, gap voltage of 120 V, resistance of 33 Ω, peak current of 8 A, pulse duration of 21 μs, pulse interval of 30 μs, duty cycle of 0.47, electrode rotational speed of 700 rpm and EDM speed of 10 μm/s can be considered as ideal parameters to provide improved performances during the micro-EDM of WC-Co.     

Optimization of the chemical mechanical polishing process for optical silicon substrates

Chemical mechanical polishing (CMP) experiments are performed to study the effects of four key process factors on the flatness and surface finish of the polished optical silicon substrates and on the material removal rate (MRR). The experimental results and analyses reveal that the pad rotational speed and polish pressure have significant effects on the MRR, the interaction of the polish head rotational speed and slurry supply velocity and the interaction of the polish pressure and polish head rotational speed have significant effects on the flatness, and the pad rotational speed has a significant effect on the surface roughness R _t of the optical silicon substrates polished. The optimal combination of the four factors investigated is a polish pressure of 9,800 Pa, a pad rotational speed of 20 rpm, a polish head rotational speed of 20 rpm, and a slurry supply velocity of 100 ml/min. A confirmation CMP experiment has been carried out using the optimal process parameter setting obtained from the design of experiments analyses. The goal to attain optical silicon substrates with nanometric surface roughness and micrometric flatness by an optimized CMP process with a high MRR simultaneously so as to reduce the polishing time to only 15 min from over 8 h has been achieved.     

Constrained grinding optimization for time,cost, and surface roughness using NSGA-II

Selection of parameters in machining process significantly affects quality, productivity, and cost of a component. This paper presents an optimization procedure to determine the optimal values of wheel speed, workpiece speed, and depth of cut in a grinding process considering certain grinding conditions. Experimental studies have been carried out to obtain optimum conditions. Mathematical models have also been developed for estimating the surface roughness based on experimental investigations. A non-dominated sorting genetic algorithm (NSGA II) is then used to solve this multi-objective optimization problem. The objectives under investigation in this study are surface finish, total grinding time, and production cost subjected to the constraints of production rate and wheel wear parameters. The Pareto-optimal fronts provide a wide range of trade-off operating conditions which an appropriate operating point can be selected by a decision maker. The results show the proposed algorithm demonstrates applicability of machining optimization considering conflicting objectives.     

Optimization of machining parameters in the abrasive waterjet turning of alumina ceramic based on the response surface methodology

A study on the radial-mode abrasive waterjet turning (AWJT) of 96 % alumina ceramic is presented and discussed. An experimental investigation is carried out to explore the influence of process parameters (including water pressure, jet feed speed, abrasive mass flow rate, surface speed, and nozzle tilted angle) on the material removal rate (MRR) when turning 96 % alumina ceramic. The experiments are conducted on the basis of response surface methodology (RSM) and sequential approach using face-centered central composite design. The quadratic model of RSM associated with the sequential approximation optimization (SAO) method is used to find optimum values of process parameters in terms of surface roughness and MRR. The results show that the MRR is influenced principally by the water pressure P and the next is abrasive mass flow rate m _a . The optimization results show that the MRR can be improved without increasing the surface roughness when machining 96 % alumina ceramic in the radial-mode abrasive waterjet turning process.     

Effect of high speed turning operation on surface roughness of hybrid metal matrix (Al-SiCp-fly ash) composite

This paper explains the effect of turning parameters such as cutting speed, feed rate, depth of cut and cutting tool nose radius on surface roughness of hybrid metal matrix (Al-SiC_p-Fly ash) composite. Experiments have been conducted based on the orthogonal array L16(4)⁵ and surface roughness was tested on the composites turned by an high speed CNC centre lathe. Analysis of variance (ANOVA) was performed to predict the significant parameters and their contribution towards surface finish of the composite. A mathematical model was developed using non-linear regression analysis. Taguchi method and Genetic algorithm have been employed to optimize the turning parameters for optimum surface roughness of the composite. The optimum turning parametric conditions have been checked with the confirmation experiments. It has been noted that the optimum condition of genetic algorithm exhibited better results than the experimental results based on the orthogonal array and the optimum condition of Taguchi method.     

Genetic Algorithm (GA) for Multivariable Surface Grinding Process Optimisation Using a Multi-objective Function Model

A genetic algorithm (GA) based optimisation procedure has been developed to optimise the surface grinding process using a multi-objective function model. The following ten process variables are considered in this work: wheel speed, workpiece speed, depth of dressing, lead of dressing, cross-feedrate, wheel diameter, wheel width, grinding ratio, wheel bond percentage, and grain size. The procedure evaluates the production cost and production rate for the optimum grinding conditions, subject to constraints such as thermal damage, wheel-wear parameters, machine-tool stiffness and surface finish. A worked example is used to illustrate how this procedure can be used to produce optimum production rate, low production cost, and fine surface quality for the surface grinding process.     

Investigating material removal rate and surface roughness using multi-objective optimization for focused ion beam (FIB) micro-milling of cemented carbide

Cemented carbide has been investigated as a useful material for the fabrication of micro devices. Focused ion beam (FIB) micro-milling has been found to be one of the most appropriate methods for the fabrication of micro devices. The experimental FIB micro-milling on cemented carbide have been conducted according to the L₁₆ orthogonal array of Taguchi technique. Beam current, extraction voltage, angle of beam incidence, dwell time and percentage overlap between beam diameters have been considered as process variables of FIB micro-milling in experimental design. Material removal rate (MRR) and surface roughness have been determined experimentally for FIB micro-milling of cemented carbide and beam current has been identified as the most significant parameter. The minimum surface roughness of 5.6 nm has been reported on cemented carbide, which is not a usual practice to achieve on such polycrystalline material, and hence it may be considered as a significant research contribution. Maximum MRR of 0.4836 μm³/s has been reported. Moreover, genetic algorithm toolbox of MATLAB has been utilized for multi-objective optimization between MRR and surface roughness. The corresponding optimum values of MRR and surface roughness for multi-objective optimization have been represented by pareto optimum solution generated by genetic algorithm. The research work presented in this paper determines the setting of process parameters of FIB micro-milling for achieving a specific combination of MRR and surface roughness on cemented carbide.     

A particle swarm approach for grinding process optimization analysis

Optimization is necessary for the control of any process to achieve better product quality, high productivity with low cost. The grinding of silicon carbide is not an easy task due to its low fracture toughness, therefore making the material sensitive to cracking. The efficient grinding involves the optimal selection of operating parameters to maximize the material removal rate (MRR) while maintaining the required surface finish and limiting surface damage. In this work, optimization based on the available model has been carried out to obtain optimum parameters for silicon carbide grinding via particle swarm optimization (PSO) based on the objective of maximizing MRR with reference to surface finish and damage. Based on statistical analysis for various constraint values of surface roughness and number of flaws, simulation results obtained for this machining process for PSO are comparatively better to genetic algorithm (GA) approach. In addition, the post-optimal robustness of PSO has also been studied. From simulation results together with the proposed robustness measurement method, it has been shown that PSO is a convergent stable algorithm.     

Optimal parameter settings for rough and finish machining of die steels in powder-mixed EDM

The present study was undertaken to identify the appropriate parameter settings for rough and finish machined surface for EN31, H11, and high carbon high chromium (HCHCr) die steel materials in a powder-mixed electric discharge machining process. The effect of seven different process variables along with some of their interactions was evaluated using a dummy-treated experimental design and analysis of variance. Material removal rate (MRR), tool wear rate, and surface finish were measured after each trial and analyzed. The parameter settings for rough and finished machining operations were obtained. EN31 exhibited maximum MRR as compared to the other two materials at similar process settings. Copper (Cu) electrode with aluminum suspended in the dielectric maximized the MRR. Suspending powder in the dielectric resulted in surface modification. Graphite powder showed a lower MRR but improved the surface finish. HCHCr require higher current and pulse on settings for initiating a machining cut and works best in combination with tungsten–Cu electrode and graphite powder for improved finish. The MRR for H11 is lower than EN31 but significantly higher than HCHCr under same process conditions.     

Optimizing machining parameters of silicon carbide ceramics with ED milling and mechanical grinding combined process

A novel combined process of machining silicon carbide (SiC) ceramics with electrical discharge milling and mechanical grinding is presented. The process is able to effectively machine a large surface area on SiC ceramics with a good surface quality. The effect of tool polarity on the process performance has been investigated. The effects of peak current, peak voltage, pulse on-time and pulse off-time on the material removal rate (MRR), electrode wear ratio (EWR), and surface roughness (SR) have been investigated with Taguchi experimental design. The mathematical models for the MRR, EWR, and SR have been established with the stepwise regression method. The experiment results show that the MRR, EWR, and SR can reach 46.2543 mm³/min, 20.7176%, and 0.0340 µm, respectively, with each optimal combination level of machining parameters.     

Modelling and analysis of hybrid electrochemical turning-magnetic abrasive finishing of 6061 Al/Al2O3 composite

This paper integrates the electrochemical turning (ECT) process and magnetic abrasive finishing (MAF) to produce a combined process that improves the material removal rate (MRR) and reduces surface roughness (SR). The present study emphasizes the features of the development of comprehensive mathematical models based on response surface methodology (RSM) for correlating the interactive and higher-order influences of major machining parameters, i.e. magnetic flux density, applied voltage, tool feed rate and workpiece rotational speed on MRR and SR of 6061 Al/Al₂O₃ (10% wt) composite. The paper also highlights the various test results that also confirm the validity and correctness of the established mathematical models for in-depth analysis of the effects of hybrid ECT- MAF process parameters on metal removal rate and surface roughness. Further, optimal combination of these parameters has been evaluated and it can be used in order to maximize MRR and minimize SR. The results demonstrate that assisting ECT with MAF leads to an increase machining efficiency and resultant surface quality significantly, as compared to that achieved with the traditional ECT of some 147.6% and 33%, respectively.