Experimental Investigation Nano Particles Influence in NPMEDM to Machine Inconel 800 with Electrolyte Copper Electrode

The recent technology of machining hard materials is Powder mix dielectric electrical Discharge Machining (PMEDM). This research investigates nano sized (about 5Nm) powders influence in machining Inconel 800 nickel based super alloy. This work is motivated for a practical need for a manufacturing industry, which processes various kinds of jobs of Inconel 800 material. The conventional EDM machining also considered for investigation for the measure of Nano powders performances. The aluminum, silicon and multi walled Carbon Nano tubes powders were considered in this investigation along with pulse on time, pulse of time and input current to analyze and optimize the responses of Material Removal Rate, Tool Wear Rate and surface roughness. The Taguchi general Full Factorial Design was used to design the experiments. The most advance equipments employed in conducting experiments and measuring equipments to improve the accuracy of the result. The MWCNT powder mix was out performs than other powders which reduce 22% to 50% of the tool wear rate, gives the surface roughness reduction from 29.62% to 41.64% and improved MRR 42.91% to 53.51% than conventional EDM.


Introduction
The most modern advanced material removal process which is useful to enhance machining performance and efficiency is Powder Mixed dielectric fluid in Electrical Discharge Machining (PMEDM). It enlarges the machining efficiency and surface finish by faster sparking and increase thermal conductivity within discharge arise results faster erosion from the work piece's surface. Jeswani (1981) investigated the effect of the addition of Graphite powder in Kerosene and used as dielectric in EDM. The authors highlighted that generally the mix of Nano powder in electrical discharge machining for increasing material removal rate (MRR) and Tool wear rate (TWR). And in specific the addition of graphite Nono powders in kerosene for using as the dielectric medium (4g/l) brought improvement of 60% material removal rate and 15% of Tool wear rate in 10μm inter Electrode Gap and 30% reduction of breakdown voltage in the 50µm inter Electrode Gap. Kuldeep  The trend shows that MRR will increase further with further increase in concentration and the TWR increase with a lower range of powder concentration but then decrease. The Shriram et al. (2014) analyzed the effect of PMEDM in machining Tungsten Carbide of different grades W20, W30 and W40 with powders of Al, Gr and SiC in the concentration of 4, 8 and 12g/l respectively powder separately. The authors reported that the maximum MRR gained at 8 g/l of SiC powder with Flushing pressure 1.5 Kg/cm2. Tzeng and Lee [11] investigated the effect of Al, Cr, Cu and SiC powders on PMEDM in machining SKD-11 and reported that the properties of powders like concentration, density, size, thermal conductivity and electrical resistivity are significantly influenced in the machining performance and in particularly at a fixed concentration, the smallest size of the particle led to highest MRR. Hence, in this research, we used Nono sized particles as a very fine powder for and about to 5 mm in size were used, hence the process is Nano Powder Mix Electric Discharge Machining (NPMEDM). That is this paper deals about NPMEDM, in which about 5Nm sized particle powders of multi wall CNT mixed in kerosene dielectric, SiC Nano Powder Mixed in kerosene dielectric fluid, and TiC Nano Powder Mixed in kerosene dielectric fluid along with kerosene and servotherm oil dielectric environments considered with other process parameters with three level of Peak Current, Pulse on Time, and Pulse off time to optimize the responses of MRR, TWR and SR in machining Inconel 800 work material with electrolyte copper electrode. With the best literature available till now, no such work was reported in any literature.

3.1: Need For the Research
Inconel or incony series are Nickel based super alloys which are widely used in high temperature and high pressure applications such as, nuclear reactors, gas turbines, high temperature chemical vessels and electric power generation equipment (Hewidy et al. (2005)). The Incony 800 has high thermal strength, highly abrasive carbide particles high hardness, low thermal diffusivity. But Inconel 800 has high tendency to welding with tool material and forming built-up edge, which extremely difficult-to-machine (Narutaki et al. (1993)). Hence it is challenging to machine Incony 800 in Traditional machining processes. Alternatively the non-traditional machining methods like The Electro Chemical Machining, Abrasive water jet machining, Laser beam Machining, Electrical Discharge Machining (EDM) are attractive alternative offers for such hard materials. So in this study the Incony 800 material machining process is preferred.

3.2: Aluminum Nano particles
The most and widely used powders in PMEDM are Si and Al. The mixing of Aluminum powder in dielectric and machining with copper electrode is suggested for machining W300 Die Steel (Syed and Kuppan (2012)), for AISI D3 die steel (Jamadar and kavade (2014)), for H13 Steel (Gurtej et al. Here the Al powder mixed with kerosene and stirred continuously about 8 to 9 hours in the Magnetic stirrer for reducing the size of Particles as very fine and about to 5 Nm, before they mix in the actual dielectric.

3.3: Silicon Nono Particles
Banker (2014) state that the abrasive powders like Sic and alumina in mixed with dielectric improves the MRR. Mohri et al. investigated the effects of Si powder addition and reduced surface roughness about 2µm. Pecas and Henriques (2003) investigated and reported that the positive influence of 2 g/l concentrations of the silicon powder towards the reduction of the operating time required to achieve a specific surface quality in machining AISIH13 mould steel. Sukhvir and Jujhar (2014) used silicon powder in the dielectric fluid of the EDM ranging from 0.4g/l to 2 g/l and reported that the optimal MRR and TWR obtained with Powder Concentration =1.  CNT based nano fluids is of special interests to researchers because of its novel properties like efficient thermal conductors (Thermal conductivity 3,000 W/mK in axial direction and small values in a radial direction), high strength to weight ratio, amazing strength (Young's modulus of 1TPa), exclusive current carrying capacity (Conductivity of CNTs is 109 A/cm2) electrical properties, excellent field emitter and has a high aspect ratio. The CNTs are fullerene-related to structures that consist of either a grapheme cylinder or a number of concentric cylinders (Darji et al. 2014). The authors investigated MWCNTs NPMEDM for EN-31 Steel, with 0.5 g/l mixed with kerosene and reported that the MRR was improved averagely 19% and TWR was decreased averagely 8.51% with respect to the input parameter. Hence multi wall CNT stirred continuously with kerosene about 8 to 9 hours to reducing the maximum size of about 5 Nm before they added in to dielectric of the EDM.

3.5: Nano powder Concentration
Yan and Chen (1994) reported that the powder particles contribution in the reduction of surface cracks and improve surface finish (lowest surface roughness), for obtaining homogeneity of white layer formation and maintain a correct balance of the discharge energy density and the discharge rate were observed for a powder concentration within the range of 2 to 5 g/l. So here 2g/l is preferred for both Aluminum and silicon powder mix with kerosene. The amount of kerosene added in size reduction process were included total mixing ratio. In case of MWCNT, Mai and Hocheng (2011) warned that high concentrations of CNT powder in the gap often made the EDM process unstable. So this study considered the same 0.5g/l with kerosene as dielectric and 2g/l for aluminum and silicon Nono powder with kerosene to machine inconel 800 nickel based super alloy.

Experimental Design
This research is motivated for an industrial requirement. The manufacturer deals various kinds of jobs of inconel 800. The practical issues like, statistical approximation and formula based parameter computations often difficult to fix the parameter for machining. Sometimes the calculated parameters couldn't produce the required finish due to statistical approximation or labor mistake of calculating parameters. And the manufacture demanded that a parameter choice table (like paint shade card for selecting the suitable/desired colour) to fix factored for desired responses and for their regular use. Hence the research is designed completely experimental. Taguchi general full factorial design was preferred for the experimental design.
The Taguchi General full factorial is used to design the experiments and the same was used for analyzing the influencing of factors considered for producing optimal responses. The factors were taken in the rage they used for processing the order. The factors with their levels and responses considered were furnished in the Table 1. The factors of Input Current, Pulse on Time, pulse off time and the nano-powders and their concentrations for mix with kerosene to use as dielectric fluid were preferred based on the literature review to analyze the response like tool wear rate, Material removal rate and surface roughness. The objective is investigating the influence of nano-particle (nono-powder) suspension on dielectric fluid in machining hard nickel based super alloy inconel 800 work piece. The experimental design is tabulated in Table-2a to Table -2l. Total 108 experiments were obtained from the MINITAB release 16 software, for three levels of parameters in pulse on time, pulse off time, Current and 4 levels of dielectric medium (3x3x3x4 =108).

Experimental Method
The EDM set-up employed in this experimental study is Electronica Machine Tools make Xpert 1model die sinking type CNC EDM machine. Kerosene is a dielectric fluid in this machine because of its property of very low viscosity and it gets flushed away easily. The fixed time of 5 minutes per experimental was permitted. The dielectric mediums are considered separately in the conduct of experiments. The Taylor Hobson makes, Surtronic3+ branded contact type profile-meter was employed in surface roughness measurement with 0.8mm cut length and sampling number is three. The laboratory balance of semi micro with an accuracy of 0.00001g, was employed in measuring weight loss tool and work material in before and after every run to compute MRR and TWR. The observations of Experiments servotherm oil mixed with Kerosene dielectric fluid environment. It is conventional practices to machine Inconel 800 jobs by the manufacturers in other words, no powder mixed in dielectric fluid or conventional EDM and not PMEDM environment. In the case of Nano Powder mixed EDM, the environments of Aluminum nano-powder mixed with Kerosene dielectric fluid, silicon nano-powder mixed with the Kerosene dielectric fluid environment and MWCNTs Nonopowder mixed with the Kerosene dielectric fluid environment was separately considered for experimentation due to practical constraints of random experiments those environments as in order of expernet run. The observations were recorded as per Taguchi general Full Factorial Design of Experiments in Table 2a to Table 2l.

6.1: Material Removal Rate
The material removal rate performance by nano particle suspended EDM machining on Inconel 800 nickel based super alloy material is graphically illustrated in the Figure 1 to  Figure  6 and Figure 9 are the MRR when the Peack current 15A. It is observed that when the input current increases the MRR increases, when the pulse on time increases the MRR increases. At high pulse on time the NPMEDM performance is more significant than lower pulse on time. When the pulse off time increases, the MRR increases. Hence all these parameters influence the MRR performance of NPMEDM. The NPMEDM performance with MWCNT is most significant and MRR is high at high plus off time, high pulse on time and High input current. The low MRR observed at no nano powder mixed in dielectric environment machining.

6.2: Tool Wear Rate
The influence of the factors in reduction of tool wear was depicted in the figure 10 to Figure 18. From These graphs in the Firure 10 to Figure 12 TWR performance given by Nano Powders in NPMEDM at Current 5A, 10A and 15A respectively, when the Pulse off time is 3 µs, the the Firure 13 to Figure 15 is for Pulse off time 4 µs and the the Firure 16 to Figure 18 for the Pulse off time is 5µs. The Figure 10, Figure 13 and Figure 16 are the TWR when peak Current 5A, the Figure 11, Figure 14 and Figure 17 are the TWR when peak Current 10A, and the The Figure 12, Figure 15 and Figure 18 are the TWR when peak Current Current 15A. The tool wear rate is high at no nano powder mixed in dielectric environment machining. The addition of nano powder decreases the tool wear. The high tool wear reduction by nano fluids was observed at higher pulse on time as well as high pulse off time. The input current influence on tool wear rate. At higher the current the tool wear also higher.  TWR performance of Nano Powders in NPMEDM at Current 15A and Pulse off time 5 µs

6.3: Surface Roughness
The surface roughness is one of the measures of performance of surface quality. As above way the surface roughness performances were depicted from Figure 19 to Figure 27. And it is evident form those graphs that surface roughness reduction in NPMEDM is highly significant. The lower surface roughness was observed at 6 µs pulse on time. The higher the surface roughness was observed at higher pulse on time. Like above all the factors influence in roughness of machined work piece. The roughness reduction is steep when adding nano sized abrasive powders (Al and Si) in dielectric fluid but best MWCNT as nano-powder in NPMEDM.     Figure 27. Surface Roughness performance of Nano Powders in NPMEDM at Current 15A and Pulse off time 5 µs

Conclusion
The NPMDEM machining on inconel 800 material experimentally investigated and analyzed well. The NPMEDM performances were compared with conventional EDM with equal priority. The result shows that the NPMEDM outperforms in terms of higher material removal rate, minimum tool wear and minimal surface roughness in machined work piece. In particularly MWCNTs powder mixed NPMEDM environment. All the factors which considered for investigation were contributing for the response of MRR, TWR and SR. The observation table can be used for parameter setting to obtain desired result by the manufacturer like shade card for pain selection. It is easy and convenient to indentify suitable parameters for desired outcome of jobs. Here some in specific conclusions The Input current significantly influence in MRR. The pulse on time and pulse off time influence in responses were clearly depicted in figure 1 to figure 3.
The minimum material removal rate (0.04721g/min) was observed in silicon powder mixed NPMEDM environment at pulse off time 3 µs, pulse on time 7µs and the input current of 10A and the highest material removal rate 1.435926 g/min observed in at pulse off time 5 µs, pulse on time 8µs 10A current at MWCNT mixed NPMEDM in machining inconel 800 work piece.
In the case of roughness of machinated surface, the minimum roughness of 0.88 µm was observed in MWCNTs mixed NPMEDM at current 5A, pulse on time 6µs and pulse off time 3µs. the highest roughness of 2.54 µm conventional EDM of kerosene mixed with EDM oil in dielectric fluid environment in the parameters of 15A current, pulse on time 8µs and pulse off time 5µs. in case of NPMEDM 2.35 µm roughness in aluminum nano powder mix case at 15A current, pulse on time 8µs and pulse off time 5µs.
The maximum tool wear 0.00859 g/min was observed in conventional EDM at 15A current, pulse on time 8µs and pulse off time 5µs. In case of NPMEDM, the MWCNTs mixed NPMEDM environment produces 0.00753 g/min of tool wear at 15A current, pulse on time 6µs and pulse off time 3µs. but the same NPMEDM environment produced minimum tool wear of .00025 g/min at 5A current, pulse on time 6µs and pulse off time 3µs