Aluminium Metal Matrix Composite Machining using ...

Aluminium Metal Matrix Composite Machining using Die Sinking EDM—A Review Vineet Dubey M.Tech Scholar, School of Mechanical Engineering, Shri Mata Vaishno Devi University, Katra, J&K, India E-mail: [email protected] Abstract—Aluminium Metal Matrix Composites are important engineering materials for their property advantage compared to monolithic metals. These materials provide us the opportunity to combine various properties coming from ceramics and metals including higher specific modulus, better wear resistance, increased specific strength, and superior properties at elevated temperatures, into one material. Therefore, AlMMCs have very high potential in a wide range of structural and functional applications, especially in automotive, aerospace, and defence industries. Metal Matrix Composites (MMCs) have proved to be extremely difficult to machine using conventional techniques due to heavy tool wear caused by the presence of the hard reinforcement which has impeded the development of AlMMC. Hence non-traditional machining processes pose a solution for the machining of such matrix composites. Among them, Electrical discharge machining (EDM) is one of the most popular nonconventional machining processes used for machining electrically conductive work material regardless of its hardness. The paper presents a review of EDM process and effect of process parameters on machining of aluminium metal matrix composite. The paper also discusses the chronological research work done in the same area. Keywords: Aluminium Metal Matrix Composite (AlMMC), Electrical Discharge Machining (EDM), Surface Roughness (SR), Metal Removal Rate (MRR), Process Parameters

INTRODUCTION ELECTRICAL DISCHARGE MACHINING Die sinking electrical discharge machining (EDM) is one of the most widely used techniques for the fabrication of die and mould cavities which are finally used for mass production of metals and polymer products by replication such as die casting injection moulding, etc. In die sinking EDM the electrode produces exactly its opposite shape on the work material. The machining performance for the intricate areas such as sharp or pointed corner, flat or pointed areas of electrode, is obviously different because of different concentration of heat and current density. The performance of EDM is usually evaluated by the output parameters namely material removal rate (MRR), electrode wear rate (EWR), wear ratio (WR), machined surface roughness, etc. [1-2]. Electrical discharge machining is a machining method primarily used for hard metals or those that would be very difficult to machine with traditional techniques.

Fig. 1: Schematic Diagram of the EDM Process

In Electrical Discharge Machining the electrode is moved downward toward the work material until the spark gap (the nearest distance between both electrodes) small enough so that the impressed voltage is great enough to ionize the dielectric [4]. Short duration discharges (measured in microseconds) are

Aluminium Metal Matrix Composite Machining using Die Sinking EDM—A Review 29

generated in a liquid dielectric gap, which separates tool and work piece. EDM does not make direct contact between the electrode and the work piece where it can eliminate mechanical stresses chatter and vibration problems during machining [5]. The material in the form of debris is removed with the erosive effect of the electrical discharges from tool and work piece [6].

ALUMINIUM METAL MATRIX COMPOSITE In material composite, when the matrix is a metal or an alloy, we have a “Metal Matrix Composite”. The matrix is essentially a metal, but seldom a pure one. Except sparing cases, it is generally an alloy. Matrix material distinguishes the MMC from the unreinforced matrix in terms of increased strength, higher elastic modulus, high service temperature, improved wear resistance, high electrical and thermal conductivity, low coefficient of thermal expansion and high vacuum environmental resistance. These properties can be attained with the proper choice of matrix and reinforcement. Aluminium metal matrix composite (AMMCs) refer to the class of light weight high performance aluminium centric material systems. The reinforcement in AMMCs could be in the form of continuous/ discontinuous fibres, whisker or particulates, in volume fractions. Properties of AMMCs can be tailored to the demands of different industrial applications by suitable combination of matrix, reinforcement and processing routes. The reinforcements should be stable in the given working temperature and non-reactive too. The most commonly used reinforcements are Silicon Carbide (SiC) and Aluminium Oxide (Al2O3). SiC reinforcement increases the tensile strength, hardness, density and wear resistance of Al and its alloys. The particle distribution plays a very vital role in the properties of the AlMMC and is improved by intensive shearing.

PAST RESEARCH WORK IN EDM OF ALMMC Ramulu and Taya found machinability of 15 vol. % and 25vol. % SiC whisker/ 2124 aluminium matrix (SiCw/Al) composites [3]. It was found that material removal rate increases with increase in power of electrode. MRR in 15 vol. %SiCw/2124 Al is >25 vol. % SiCw/2124 Al. MRR obtained by using copper electrode is 5-10% less than thatof obtained when using brass electrode. 25 vol. % SiCw/Al took higher machining time than in 15%SiCw/Al composite. Hung et al. in 1994 investigated the feasibility of applying EDM process for cast aluminium matrix composite reinforced with silicon carbide particles [7]. They developed the statistical model to predict the effect of process parameters on MRR, re-cast layer, and SR. It was revealed that the presence of SiC particles results in reduced MRR. This is because these particles shield the aluminium matrix and protect it from being vaporized. It was reported that MRR and depth of recast layer is mainly controlled by input power and the current alone dominates the surface finish of machined surface. Hocheng et al. have made a preliminary study of MRR of SiC/Al composite [8]. Material removal characteristics of single and continuous discharge were checked. The study starts from single discharge and relationship between crater size and set discharge parameters was found. Two heat conduction models were used to calculate crater size. The material removal rate is greatly improved as expected. For effective machining of SiC/Al, large current and short on-time is recommended. Karthikeyan et al. worked on mathematical modelling for electric discharge machining of aluminium–silicon carbide particulate composites [9]. They investigated the effects of the percentage volume of SiC, current and pulse duration on the MRR, TWR, and SR. The MRR increases with an increase in the current and decreases with an increase in the percentage volume of SiC and the pulse duration. The TWR increases with an increase in the current and the percentage volume of SiC, but decreases with an increase in the pulse duration. The surface roughness increases with an increase in the current, the percentage volume of SiC and the pulse duration.

30 National Conference on Futuristic in Mechanical Engineering

Yan and Wang investigated the machining characteristics of Al2O3/6061Al composite using rotary electro-discharge machining with a tube electrode [10]. They concluded that the machining process of the Al2O3/6061Al composite by EDM-drilling is feasible in comparison to other machining processes. Sinking EDM becomes an optimal choice in the machining of Al2O3/6061Al composite owing to its easy control in operation and precise criterion of high complex-shape demand. The observed value of MRR with rotating hollow tube electrode is found higher than that of with solid electrode. Muller and Monaghan presented details and results of an investigation into the machinability of SiC particle reinforced aluminium matrix composites using different nonconventional machining processes such as electro discharge machining, laser cutting and abrasive water jet [11]. The size of the craters increases with increased discharge energy. Also, relatively small amount of sub-surface damage is found on the cut surfaces after machining (depending on the chosen machining settings). The research work focuses mainly on influence of reinforcement on surface quality of machined material. Ramulu et al. carried out experimental work on the effect of surface roughness generated by machining process on mechanical properties of 15 vol. %SiCp/A336 AlMMC [12]. The goal of the experiment was to study the fatigue behaviour of machined surface. The yield and ultimate strength of material were found to reduce with increase in MRR. The machining results in clearly observable surface damage of material, resulting in inferior surface integrity. Mohan et al. evaluated the machining feasibility of Al-SiC composites [13]. The objective was to investigate influence of process parameters, electrode material, and volume percentage of SiC particle on performance measures. Electrode polarity, discharge current, pulse duration, and electrode rotation were taken as parameters. Al-20% SiC and Al-25% SiC composite samples were taken for study. Copper and brass were selected as electrode material. The MRR was found high with positive polarity and increased with increase in current. It was more with brass electrode in comparison with copper electrode. The increase of either the pulse duration or volume percentage of SiC results in decrease in MRR and it increases with increase in rotational speed. The TWR was less when volume percentage of silicon carbide particle was less and increased with increase in current. The surface roughness value decreased with decrease in pulse current and increased with increase in volume percentage of SiC. P. Narender Singh et al. worked on optimization by gray relational analysis of machining parameters on machining Al-10%SiCp composites [14].The multi-response optimization of the process parameters viz., metal removal rate, tool wear rate, taper, radial overcut, and surface roughness on electric discharge machining of Al-10%SiCp as cast metal matrix composites using orthogonal array with gray relational analysis was reported. The research work is focused on parameter optimization by applying gray theory. Gray analysis provides excellent solution to uncertain, multi-input, and discrete data problems. Since EDM process is of similar nature, therefore, the method is highly useful in parameter optimization of such experimental work. P. Narender Singh et al. in the same year worked on Al- 10% SiCp as-cast metal matrix composites [15]. The objective of the work was to investigate the effect of current, pulse on-time and flushing pressure on metal removal rate, tool wear rate, taper, radial overcut, and surface roughness of machined material. Many conclusions were drawn by experimentation. MRR was found higher for larger current and pulse on-time settings at the expense of taper, radial overcut, and surface finish. Electrode wear was also found to be higher, even larger than the material removal rate for larger current settings. Mohan et al. investigated the machining characteristics of SiC/6025 Al composite using rotary electro-discharge machining with a tube electrode [16]. The objective of research work was to investigate effects of discharge current, pulse duration, SiCp percentage, tube electrode hole diameter, and speed of electrode rotation on performance measures. The effect of drilling with the rotating tube electrode resulted in higher material removal rate than the rotating solid electrode. The MRR and SR improve with the decrease in holediameter but electrode wear increases. The increase in volume percentage of SiC has resulted in decrease in material removal rate, surface roughness, and increase in


electrode wear. The increase in rotational speed of the tube electrode has produced higher material removal rate, electrode wear, and better surface quality. Seo et al. investigated on machining of functionally graded 15–35 vol. %SiCp/ Al composites [17]. The material was drilled to assess the machinability and workpiece quality as a function of SiCp percentage, resulting dimensional quality of hole, surface topography, and metallurgical integrity of subsurface. MRR showed an increasing trend with increase in product of peak current and pulse on time up to the optimum value and then decreases. Material removal rate also increases with increase SiCp percentage. Larger tool wear is reported with a combination of high peak current and low pulse on-time. Sushant Dhar et al. worked on mathematical modelling of cast Al–4Cu–6Si alloy–10 wt. %SiCp composites [18]. The objective of the work was to evaluate effect of current, pulse on-time and air gap voltage on material removal rate, tool wear rate, and radial overcut. The mathematical model developed can be used to predict the optimal conditions suitable for machining of the work samples. Linear programming was used to find the optimum conditions for maximum MRR with reduced TWR and radial overcut. All the three performance measures increased significantly in a nonlinear fashion with increase in current. The material removal rate and radial over cut were found to increase with increase in pulse duration. Akshay Dvivedi et al. investigated the machinability of Al6063 SiCp metal matrix composite and obtained optimal setting of process parameters [19]. The material was developed using melt stir-squeezequench casting route and characterized for density, porosity and electrical conductivity. Increase in electrical parameters beyond optimum setting resulted not only in a decrease in MRR but also increased TWR with dimensional inaccuracy. Also, it was found that high value of pulse current, pulse-on time, and pulse offsetting results in maximum MRR within selected range of process parameters. A. Riaz Ahamed et al. worked on the application of EDM investigate the effect of EDM parameters namely current, pulse on time, pulse off time, and flushing pressure on the material removal rate (MRR) and surface roughness (SR) while machining hybrid composites Al–5%SiC–5% B4C (sample I) and Al– 5%SiC–5%Glass [20]. MRR and SR was taken as response parameter, sand tubular copper electrode was used as a tool. fairly long duration spark is necessary to remove material which has embedded in it hard particles such as B4C and SiC with a fairly sufficient time after sparking for the dielectric with a fairly larger value of flushing pressure to flush away the removed material in the case of sample I. & a condition of a slightly higher on time and a slightly reduced flushing pressure, dependent on the wettability of the matrix with the reinforcements, is observed in sample II. M. Kathiresan et al. studied EDM on the aluminium alloy-silicon carbide composite workpiece using a copper electrode. [21].Studies showed that the MRR and the surface roughness are greatly influenced by the current and percentage weight silicon carbide. The MRR increases with an increase in the current and decrease in the percentage weight of silicon carbide. The surface finish improves with decrease in the current and increase in the percentage weight of silicon carbide. A. Mouangue Nanimina et al. studied machining performance characteristic on AMMC reinforced with 30 % Al2O3 in comparison with Aluminium 6061 [22]. Key process parameters such as current, pulse on and pulse off were varied to determine their influences on MRR and TWR of the reinforced MMC. It was seen that a high value of peak current and on time increases rapidly MRR of Al6061 rather than AMMC while it decreases with increasing of off time. Tool wear was more at low peak current and on-time than off-time. C. Velmurugan et al. investigates the effect of parameters like current, pulse on time, voltage and flushing pressure on MRR, tool wear rate as well as SR on the machining of hybrid Al6061 metal matrix composites reinforced with 10% SiC and 4%graphite particles [23]. Metal removal rate of the composite increases with increase in current, pulse on time and flushing pressure of the dielectric fluid while it decreases with increase in voltage. Tool wear rate of the developed composite increases with increase in current and voltage and it decreases with increase in pulse on time and flushing pressure of the dielectric fluid. Surface roughness of the composite during electric discharge machining increases with increase in current, pulse on time, voltage and flushing pressure.


S. Gopalakannan et al. developed a mathematical model and analysed the effect of EDM parameters on the performance characteristic of MMC using RSM approach [24]. They used Al7075 reinforced with 10 wt% B4C. The experiment revealed that pulse on time and pulse current are significant factor affecting MRR, with an increase in pulse on time the MRR increases and then decreases with further increase of pulse time. The higher pulse off time resulted in lower EWR value. The SR value increases with an increase in pulse current and pulse on time. U.K. Vishwakarma et al. developedan axisymmetric thermal model to predict the material removal rate in Al6063/SiC composite during EDM [25]. FEA based model has been developed to analyse the temperature distribution and its effect on material removal rate. To validate the model, the predicted theoretical MRR is compared with the experimentally determined MRR values. The model developed in present study can be further used to obtain residual stress distributions, thermal stress distribution mechanism of reinforcement particle bursting phenomenon. S. Murugesan et al. attempted to find the optimal machining condition under which a blind hole can be drilled using a multihole electrode [26]. Workpiece used was Al6061/ 15 wt% SiC and the electrode used was copper rod with an array of 2 mm hole drilled in it. In this study the machining parameters namely electrode polarity, discharge current, pulse on time, pulse off time and dielectric pressure was optimized with performance characteristics including machining time, EWR and SR. Discharge current was found to be the most significant controlling parameter. Singh applied the designs of experiments and grey relational analysis (GRA) approach to optimise parameters for electrical discharge machining process of 6061Al/Al2O3p/20P aluminium metal matrix composites [27]. The process parameters included one noise factor, aspect ratio having two levels and five control factors, viz. pulse current, pulse on time, duty cycle, gap voltage and tool electrode lift time with three levels each. The MRR. TWR and SR were selected as the evaluation criteria. It was found that the pulse current has the strongest effect among the other process parameters used to study the multiperformance characteristics. Nanimina et al. investigated effect on surface finish of alumina reinforced AMMC and aluminium alloy by EDM process using electrolytic copper electrode [28]. It was found that the surface finish properties of AMMC are more sensitive to the variation of the EDM input process parameters as compared to aluminium alloy. Craters and micro-cracks observed were deeper and larger at higher peak current, longer on-time and shorter off-time. Surface roughness of AMMC is coarser as compared to aluminium. Debaprasanna et al. work demonstrates the preparation of AlSiC metal matrix composite through powder metallurgy route and the effect of six process parameters on electric discharge machining of MMC. A hybrid optimization technique (fuzzy-PCA) along with Taguchi’s design is proposed to find out the optimal setting of process parameters to simultaneously improve four responses [29]. It is observed that the process parameter such as discharge current, pulse-on-time, duty factor, and flushing pressure have the significant effect on the multi performance characteristic. The effect of weight percentage and mesh size of silicon carbide in MMC has relatively less contribution in improving multi performance characteristic. S. Kasman et al. studied the effect of EDM parameters on the surface roughness was investigated for Al/B4Cp MMCs[30]. Samples were manufactured through a conventional powder metallurgy (P/M) process. The electrode material used in the experiments was graphite. Results showed that the Ra value was increased with increasing the current, pulse-on-time, pulse-on-time and amount of particle reinforcement. S. Gopalakannan et al. conducted studies on EDM process and the mathematical models of the MRR, EWR, and SR to correlate the dominant machining parameters, including the voltage, pulse current, pulse on time, and pulse off time in the EDM of aluminium MMNC [31]. It was found that main significant factors that affect the MRR are pulse current, pulse on time, and pulse off time whereas


voltage remains insignificant. The pulse current and pulse on time have statistical significance on both EWR and SR. The higher pulse off time offers lower the EWR value. The value SR increases with increase in pulse current and pulse on time, whereas in voltage is concerned SR increases up to 50 V and then decreases with a further increase in voltage. Mwangi J.W. et al. used Taguchi method to optimize the electrical discharge machining method while machining aluminium silicon carbide metal matrix composite [32]. Discharge energy largely influences all the response parameters namely material removal rate, tool wear rate and the quality of the surface generated. An increase in discharge energy results in an increase in both material removal rate and tool wear rate. It also results in an inferior surface quality. The longer the pulse duration, poorer the surface finish. Increase in gap voltage results in an increase in material removal rate up to a maximum after which a further increase results in a decrease in material removal rate. Sarabjeet et al. experimental work reports the results of MMC machined with electric discharge machining [33]. The results were optimized using lexicographic goal programming to predict the ideal parametric combinations for machining of MMCs. From the results, it can be concluded that all the responses have a direct relationship with current, but an inverse relationship with pulse-on time. With straight polarity, it can be concluded that high current and low pulse on-time should be used for maximizing MRR, and for high surface finish, the current and pulse-on time should be set at low level. Balbir Singh et al. experimental work discusses the effect of process variables on MRR of AA6061/10% SiC composite. Machined surface was analysed in comparison with results obtained from basic EDM process [34]. All the selected process parameters play significant role for MRR in both the PMEDM and basic EDM. Higher MRR can be achieved at higher setting of current, pulse on time, and optimum setting of pulse off time and gap voltage. The resolidified layer deposited on surface contain small amount of tungsten reveals transitions from powder-mixed dielectric fluid and consequently enhances surface property. Suresh Kumar et al. investigated to find the influence of process parameters such as pulse current, pulse on time, pulse duty factor, and voltage on the machining of Al6351/ 5 wt%SiC) & 5 wt% B4C hybrid composite through electrical discharge machining. The individual parameters were analysed with an objective to minimize electrode wear ratio (EWR), (SR) and power consumption [35]. As the pulse current increases, the discharge of electric spark energy from the tool increases, which leads to an increase in the EWR. However, pulse on time and the pulse duty factor have a negative influence on EWR.SR was increased with pulse current and pulse duration.

CONCLUSION A review of the research work on aluminium metal matrix composite with specially focussing on sinking EDM is presented in this paper. The research work of the last 20 years has been summarised. It was observed that for each and every method incorporated in EDM process, the objective of the experimentation are the same, to enhance the capability of machining performance, to get better output response, and to have better working conditions. This review can help the researchers working specially on sinking EDM of AlMMC, to get a reliable knowledge of the research work already done in this area.

DISCUSSION AND FUTURE TRENDS After an elaborative study of the published work, it is evident that most of the research work belongs to SiC reinforced metal matrix composites. Limited work can be seen on Al2O3 reinforced and other types. It was revealed that very less work has been reported on MMCs with powder mixed EDM. Also, only aluminium powder and SiC powder have been tried in MMCs. Many other powders like boron carbide, powders of important alloying elements such as manganese, chromium, molybdenum, and vanadium are yet to be tried in the dielectric medium. From the observation of past researches it can be seen that most of the research work has been carried out on optimization of process parameters for improvement


of performance measures. From most of research work, we can see that in the EDM process mainly electrical process parameters and flushing pressure as nonelectric parameter have been taken into account. There is a scope of research work on the effect of non-electrical parameters like workpiece rotation and electrode rotation as very less research work has been reported in these areas.

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