Experimental Analysis of Aluminium Metal Matrix Composites using Electrochemical Micromachining

Experimental Analysis of Aluminium Metal Matrix Composites using Electrochemical Micromachining

M. Siva,

PG scholar, Department of Aeronautical Engineering, Excel Engineering College, India

A. Karthikeyan,

Professor & Head, Department of Aeronautical Engineering, Excel Engineering College, India

P. Muthukumar,

Assistant Professor, Department of Aeronautical Engineering, Kathir College of Engineering, India

Abstract: Extravagant application of AMMC (Aluminium Metal Matrix Composites) in various fields of engineering has a unique property. Though there are vast combinations of metal composites, aluminium is a significant and readily combinable metal. In this research paper reinforcement of aluminium with Fly ash and magnesium oxide is proposed and fabricated AMMC by stir casting method and tested in EMM (Electrochemical Micromachining) using Taguchis quality technique.

Keywords: Stir casting method, Electrochemical Micromachining, Taguchi, L9, Metal Matrix Composite, Material removal rate, Overcut.

1. INTRODUCTION

   Nowadays, Aluminium composites are the demanding one in various fields like Aerospace, Mechanical etc. Everyday new combinations of composites have been developed by many researchers. In this paper a typical combination of AMMC (Aluminium Metal Matrix Composite) is fabricated & its properties are founded. To find a material application it is essential to identify its process parameters and the same is founded by experimenting in EMM (Electrochemical Micromachining).

2. LITERATURE REVIEW

   Aluminium Metal Matrix Composites is a widely applicable one. Many investigations have been carried out to bring out the uses of it since 19th century. K.L. S.Kumar reported that Inclusion of silicon carbide particle has a significant influence on MRR [1]. Basavarajappa gave a report on drilling of Sicp, Sicp-graphitic reinforced composites and concluded that feed rate is the main factor which influences the thrust force in composites. The surface finish increases with increase in cutting speed but decreases with increase in feed rate [2].

   B. Babu,

   PG Scholar, Department of Mechanical Engineering, Karpagam University, Coimbatore, Tamilnadu, India

   1. Ragoth Singh,

      Assistant Professor, Department of Mechanical Engineering, Karpagam College of Engineering, India

   2. Surendar,

   Assistant Professor, Department of Mechanical Engineering, Kathir College of Engineering, India

   Based on the Al-Sic (15p) study done by Ramanujam, the desirability function analysis of the experimental results of surface roughness and power consumption can convert optimization of the multiple performance characteristics into optimization of the single performance characteristic called composite desirability value [3].Experimenting AL/Sic b , Noorul concluded that Grey relational analysis in the Taguchi method for the optimization of the multi response problems is a very useful tool for predicting the surface roughness , cutting force and torque. From this analysis, it is revealed that point angle cutting speed and feed rate are prominent factors which affect drilling. In addition to that they gave an information that the best performance characteristics was obtained with Tin coated Hss drill with the lower cutting point angle of 900, higher feed of 0.2 mm/rev and higher cutting speed of 87.96m/min [4].Thanigaivelan in his research derived a conclusion that electrolyte concentration influences the overcut and MRR

   .Abrasive and adhesive wear are found to be predominant during machining the composite Al/Sic/B4c [5]. Joardar reported that linear, quadratic and interaction terms are all significant for the estimation of surface roughness . Electrochemical machining over the EDM is high material removal rate and the big machining surface .Metal removal rate increases with voltage, feed rate and electrolyte concentration in electrochemical machining . The optimum fabrication parameters for maximum values of tensile strength and impact strength and minimum value of abrasion loss were determined using response surface methodology. Composites with higher concentrations of reinforcements are failed prior to 50% deformation .Squeeze pressure plays a dominant role in improving surface finish [6].Thus on reviewing the above reports Aluminium is ready to combine with many varieties of metal combinations. In this paper Aluminium is combined with unique combinations of metals and parameters like overcut, MRR, electrolyte concentration, frequency are studied using EMM (Electrochemical Micromachining).

3. Experimental Details

1. Preparation of AL/Flyash/Mgo Composite.

   Objective of the New composite material

   Selection of combination of metals

   Optimization of material composition

   Optimization of Casting method

   Experimental Work- Stir Casting Process

   Desired thickness – Rolling Process

   Fig .1. Flowchart showing the steps in forming metal matrix composites

   This is a new combination of low cost composite is mainly aimed to achieve high hardness and high temperature withstanding capability. This MMC (Metal Matrix Composite) is aimed to use in high temperature conditions like engine (internal parts combustion chamber) or anywhere according to its strength and process parameters.

   Material Composition

   Aluminium (90%)

   Fly Ash (5%)

   Magnesium Oxide(5%)

   Fig.2. Chart showing the material composition

   In this new composite combination of Aluminium alloy (LH6), Magnesium oxide and Flyash is proposed. Mgo gives high temperature withstanding capability to heat. Fly ash is used as a good hardener and gives strength to the composite. If this combination is combined desired objective of the new composite can be achieved. This is a trial and Error method. To select the material composition in a composite combination the base metal- here aluminium is to be used in large quantity. The adders like Mgo and flyash is used 5% each.

   Fig.3. Furnace set up

   Based on the cost, processing method and permanent moulding, stir casting method is chosed. Stir

   Casting is a liquid state method of composite materials fabrication, in which a dispersed phase (ceramic particles, short fibers) is mixed with a molten matrix metal by means of mechanical stirring. The aluminium alloy was melted in an electric resistance furnace shown in fig.3.having a clay graphite crucible. The melt was mechanically stirred by an impeller after addition of pre-heated Magnesium oxide particles (pre heat temperature=9000C average particle size

   =37m). The processing of the composite was carried out at a temperature of 7500C with a stirring speed of 500 rpm. The melt was poured at a temperature of 7450C into die. The material of desired thickness can be achieved by using rolling process. This is done to decrease the material thickness to 0.2mm (if needed).This will be helpful to find the performance parameters of the material to test in EMM (electro chemical micromachining).

   TABLE .1. Chemical composition of Al LM6

   Component	Wt %
   Cu	0.1
   Mg	0.1
   Si	10-13
   Sn	0.05
   Mn	0.5
   Fe	0.6
   Ni	0.1
   Pb	0.1
   Zn	0.1
   Ti	0.2
   Al	85

   Fig.4.Casted Work piece

2. EMM setup and working

   The Electrochemical Micromachining shown in fig.5 consists of the following subsystems-Mechanical Machining Unit, Tool Electrode Feeding System, Electrolyte Supply System and Pulsed Power Supply System. The electrolyte supply and cleaning system consist of a pump and a filter. A pulsed power supply stainless steel electrode, sodium nitrate of varying concentrations used as electrolytes of 20 V and 30 A with the capability for varying voltage, current.

   Fig.5.EMM Set up

3. EMM Test Procedure

   The AMMC (of reduced thickness) is cut to 50x50mm.The initial weight of AMMC sheet is noted. According to Taguchi technique (Optimization technique to find the material process parameters) L9, L27.Before starting drilling the following factors are fixed,

   • Current <1 amp (for Accuracy-when current increased speed increases results in improper drilling)

   • Electrolyte Concentration -0 to 50 (Sodium nitrate

     + water for corrosion resistance).

   • Voltage -0 to 30

   • Frequency 0 to 90

TABLE.2.Machining Parameters

The initial weight & final weight of the Work piece after drilling is noted. The radius of the drill is founded by viewing the drilled work piece in computer through microscope. The Overcut can be founded by using the formula,

Overcut = Tool radius Actual drill radius

The Material removal rate (MRR) can be founded by using the formula,

MRR= (F.W. I.W.) / (Machining time).

This step is repeated for 27 experimental times of 3×3 fixed levels of factors, to get better results. The fig.6. below show the Al-Flyash-Mgo composite after L27orthogonal array of experimental runs.

Fig.6.Drilled Work piece

The Microholes drilled using electrochemical micromachining is viewed largely using a computer- microscope set up which is shown in fig.7&8. This is used to find the radius of the each microhole, which would help in calculating the overcut.

Fig.7. Microscope & Computer view

Fig.8. Drilled Microholes

The following table 3 shows the results of the L27 orthogonal array,

TABLE. 3. Experimental Results of L27

Fig.10. S/N curves for Material Removal Rate

1. Verification Test

   The following table 4. shows the predicted value and the repeated experimental value to verify, it.

   For Material Removal Rate(MRR)
   Level	A1B1C1 (Initial level)	A2B2C3 (Prediction & Experiment)	Improvement
   S/N ratio	-11.903	-7.731	35.5.%
   For Overcut
   Level	A1B1C1 (Initial level)	A3B1C3 (Prediction & Experiment)	Improvement
   S/N ratio	-46.079	-37.605	18.04%

   TABLE.4.Verification Table

   1. Graphical Analysis

      1. S/N Curves for Overcut

         In terms of process parameters like Overcut smaller is better. Hence the minimum values are chosen. The optimal values for minimum overcut were machining voltage of 9 V

         ,electrolyte concentration of 18 g/l, and frequency of 50 Hz.The following S/N ratio curve in fig.4.1. shows the machining parameters for the minimum overcut,

         Fig.9. S/N curves for Overcut

      2. S/N Curves for MRR

      In terms of process parameters like Metal Removal Rate Larger is better. Hence the maximum values are chosen. The optimal values for maximum MRR were machining voltage of 7 V, electrolyte concentration of 24 g/l, and frequency of 50 Hz. The following S/N ratio curve shows the machining parameters for the maximum MRR,

      1. Conclusion

         From the S/N graph and the verification table it is shown that,

         1. The optimal values for maximum MRR were machining voltage of 7 V, electrolyte concentration of 24 g/l, and frequency of 50 Hz.

         2. The optimal values for minimum overcut were machining voltage of 9 V, electrolyte concentration of 18 g/l, and frequency of 50 Hz.

         3. Based on the Verification test, the improvements of the MRR from the initial machining parameters to the optimal machining parameters are about 35.5 % and the Overcut is improved by 18.04 %

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