ISSN: 2320-5407 Int. J. Adv. Res. 9(05), 607-616

Journal Homepage: -www.journalijar.com

Article DOI:10.21474/IJAR01/12883 DOI URL: http://dx.doi.org/10.21474/IJAR01/12883

RESEARCH ARTICLE

ABRASIVE JET MACHINING AND OPTIMIZATION OF PROCESS PARAMETERS

Sachin Vinay, Sachin Bhanwal and Sahil Yadav (Under Guidance Of Assistant Professor Mukesh Dadge), Dept. Of Mechanical Engineering, Delhi Technological University, Delhi, India. …………………………………………………………………………………………………….... Manuscript Info Abstract ……………………. ……………………………………………………………… Manuscript History Abrasive Jet Machining also known as micro-abrasive blasting or Received: 20 March 2021 pencil blasting is one of the mechanical energy based economical non- Final Accepted: 24 April 2021 traditional machining process for cutting, deburring, polishing, drilling, Published: May 2021 etching and cleaning of alloys, brittle metals and non-metallic materials

due to its high degree of flexibility and low stress forces with less heat Key words:- Abrasive Jet Machining, FRL, S/N ratio, generation.In AJM process, fine abrasive grits (silicon carbides, Taguchi Method Aluminium oxides, Sodium bicarbonate, Boron Carbides, Crushed glass and Dolomite etc.) of typically ~0.025 mm are accelerated in a high velocity (150-300 m/s) jet of gas stream or air which is generated by converting pressure energy of carrier gas or air to its Kinetic energy and hence high velocity jet and nozzle directs abrasive jet in a controlled manner towards the work surface. Small fractures are created after impacting abrasive particles on the work surface.

Copy Right, IJAR, 2021,. All rights reserved. …………………………………………………………………………………………………….... Introduction:- The abrasive jet machining process is advanced machining that has been employed in many manufacturing and processing industries for drilling and contouring, generating shallow and crevices, and deburring the components, cutting slots, etc. All of these operations can be performed at a faster speed and with a better surface finishing as per the requirement of the industries. This process uses a mixture of abrasive particles like Aluminum Oxide (Al2O3), Silicon Carbide (SiC), Sodium bicarbonate, Dolomite, or Glass beads, and these act as an eroding material and with a carrier like gas or air is used for machining. These mixtures of abrasive particles and air are achieved at very high pressure by a suitable arrangement. This pressurized mixture then flows through a tube and nozzle arrangement. When the pressurized mixture flows through the nozzle then, some pressure energy gets converted into kinetic energy or in a high-velocity jet. When the abrasive mixture at high pressure as well as high velocity strikes the surface of the workpiece the material is removed and takes place by the erosion of workpiece material.

Components Of AJM: Air compressor Usually air is sucked directly from the atmosphere, it is firstdried and made dust free and then compressed to high pressure. Carrier gas pressure is kept between 15 – 20bar,based on the compressor capacity and jet velocityrequirement. Sometimes commercially pure nitrogen orcarbon di-oxide gas is also used to obtain better results forsome specific cases.

FRL High pressure air is passed through a filter regulatorlubricating (FRL) unit to remove any suspended particlessuch as

Corresponding Author:- Sachin Vinay 607 Address:- (Under Guidance of Assistant Professor Mukesh Dadge), Dept. Of Mechanical Engineering, Delhi Technological University, Delhi, India.

ISSN: 2320-5407 Int. J. Adv. Res. 9(05), 607-616 dust or oil. Common compressor is fitted with a FRLunit to make the carrier gas dry and dust free. Presence ofsteam in compressed gas is highly undesirable as it cancoagulate and can cause agglomeration of abrasives during flow through pipelines.

Pressure regulator and flow valve As the names suggest, compressed carrier gas pressure hasto be regulated properly as final jet velocity relies on it. Flowrate is also a crucial parameter that can af ect erosion rate(or MRR) via mixing ratio.

Abrasive feeder and mixing chamber Fine grain abrasive powders initially maintained atatmospheric pressure at primary chamber are allowed to flow to secondary chamber and then to the mixing chamberunder the assistance of low amplitude vibration. Compressedcarrier gas is also passed through this mixing chamber andthus momentum transfer takes place between gas andabrasives. So abrasives gain momentum in terms of velocityand start flowing with carrier gas through the pipeline.During mixing, the predefined mixing ratio is maintained bythe amplitude and frequency of the vibration and pressure ofcompressed gas has no influence on it. Flow and pressureregulating valves are also employed here to control flowrate and pressure of gas-abrasive mixture.

Nozzle Gas-abrasive mixture is directed towards the nozzle, whichconverts the hydraulic energy (pressure) into kinetic energyand thus a high velocity abrasive jet is obtained. The nozzleis kept at a particular distance over the work surface. Thus gap is termed as stand-of distance (SOD) and it is a paramount factor that governs machining accuracy.Inclination angle, the angle between work surface and jetaxis, is also controlled by orienting the nozzle. Moreover, thenozzle is mounted on a slider to impart necessary motions as per the required profile of cut.

Working chamber A closed working chamber is indispensably necessary toavoid pollution. Workpiece, mounted by fixtures, is placedwithin this chamber. A vacuum cleaner is connected to theworking chamber for removing tiny suspended abrasives from air before discharging it to the atmosphere.

Process Parameters In Abrasive Jet Machining: In any machining process or simply in a process, there exist some input variables called parameters or more precisely known as process parameters, which influence the output of the processes. In the abrasive jet machining, our main focus is to get higher material removal rate, better surface finishing, high accuracy, at a faster rate, etc. the principle of the AJM is based on the principle of erosion by high velocity jet abrasive jet. The variables that influences the erosion are: ● Material and density ● Average flow stress ● Ductility and brittleness the impinging particles ● Elasticity of the material ● Shape and geometry of impinging particles ● Impinging particle diameter or grit diameter ● Speed and angle of impact ● Distance between the nozzle mouth and work piece ● Mixing ratio ● Gas pressure

During the machining process for a particular material some variable like material property no longer remains a variable. The variables that truly can be considered as parameters are abrasive velocity and angle of impact, distance between the nozzle mouth and the workpiece, mixing ratio, jet pressure and, shape and grit diameter, etc. Lets, take a look at some of them.

Grid Diameter And The Shape Of Abrasive: The shape of the abrasive particle can be considered as spherical in shape with smaller spherical grits on the surface. However, the material removal rate (MMR) is higher in a case of irregular shaped abrasive particles than the spherical shaped abrasives.

Smaller the grit size gives better surface finishing, generally used for the purpose of cleaning, polishing and grooving, but it gives a comparably lower material removal rate. Larger size of grit diameter gives rough surface finishing and generally used for cutting and peening, but it gives comparably higher material removal rate.

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Nozzle Tip Distance Or Stand Off Distance: Nozzle Tip Distance (NTD) is the distance between the nozzle tip and the workpiece.Metal Removal Rate (MRR) increases with an increase in nozzle tip distance up to a certain limit then MRR remains constant to some extent and then MRR decreases with an increase in nozzle tip distance. Nozzle tip distance also influences the shape and diameter of the cut and for optimum performance, a nozzle tip distance of 0.25 to 0.75 mm is provided.

Fig 1:- Nozzle tip distance.

Abrasive Flow Rate: Abrasive Mass Flow Rate: The mass flow rate of the abrasive particles is a significant procedure parameter that impacts the metal removal rate in abrasive jet machining. In AJM, the mass flow rate of the gas (or air) in an abrasive jet is contrarily corresponding to the mass flow rate of the abrasive particles. Because of this reality, when persistently expanding the abrasive mass flow rate, Metal Removal Rate (MRR) first increments to an ideal worth (as a result of the increment in the number of rough particles hitting the workpiece) and afterward diminishes. However, if the blending ratio is steady then Metal Removal Rate (MRR) consistently increases with an increase in rough mass flow rate.

Mixing Ratio: It determines the concentration of the abrasive particles in the abrasive jet and it can be defined as the ratio of the mass flow of the abrasive to the mass flow of the carrier gas. The concentration of the abrasives can be increased by simply increasing the percentage of the abrasives in the mixture. The increased percentages cause the increased in the number of strikes impact (micro cutting action) on the workpiece per unit time, hence there is an increase in the material removal rate. However, it is important to note that, continuous increase in the concentration of abrasive particles in the jet causes reduction in the MRR after a certain limit because further increase in abrasive lowers the jet velocity (as gas pressure is constant) and unavoidable collision (invites to loss of kinetic energy).

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Fig 2:- mixing ratio vs MRR.

Gas pressure: Air or gas pressure has a direct impact on the metal removal rate. The metal removal rate is directly proportional to air or gas pressure in abrasive jet machining.

The velocity of abrasive particles: Whenever the velocity of abrasive particles is increased, the speed with which the abrasive particles hit the workpiece also increases. This is the reason that in abrasive jet machining, the metal removal rate increases with an increase in the velocity of abrasive particles.

Effect of impingement angle on AJM performance: The angle between the work surface and abrasive jet axis is known as the Impingement angle also called spray angle or impact angle is denoted by (θ). Practically its value lies between 60º – 90º. Deeper penetration can be achieved by a large angle, smaller the angle causes an increase in the machining area. The impingement angle (θ) of values lies between 70º – 80º provides better results in terms of material removal rate in an abrasive jet machining process.

Material removal rate and its estimation The knowledge of material removal rate (MRR) is beneficial for selecting process parameters and choosing the feed rate of the nozzle. It also enables an accurate estimation of productivity, delivery time along production cost. The analytical formula for MRR can be found by equating kinetic energy that is available with the work done required for during an indentation of a certain cord length on a specific work material where kinetic energy of abrasive grits that is utilized for erosion is used in analytic formula.

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Fig. 3:- ef ect of process parameter on MRR.

Experimentation and analysis Experiment The aim of present work is to find out the ef ect of grit size on output parameters during making holes on ceramic tiles. Experiments were conducted to study the various process parameters which af ect the MRR and Taper produced during the drilling operation on ceramic tiles .The input parameters for the experiment are Pressure, SOD, Nozzle diameter and the responses are MRR and Taper. In this method all of the observed values of MRR and Taper were calculated based on “Higher is better” and “Lower is better” respectively. L9 orthogonal array has been used i.e. a total 9 sets of experiments were conducted. Experiments were carried out setting the process parameters at three levels as given in Table 1.

Table 1:- List of process parameters and levels. S. No. Parameter Level 1 Level 2 Level 3 1 Nozzle Dia (mm) 2 2.5 3 2 Stand-off-distance 5 7 9 3 Pressure (kgf/cm^2) 9.5 10.5 11.5

The feasible combinations of the input parameters along with the output parameters (MRR and Taper) have been shown in Table 3 and Table 4 respectively. MRR of each sample (ceramic plate) was calculated after completion of experiment:

MRR= (W1- W2) / (T)(1) Where: W1 is the initial weight of ceramic tile (gm) and W2 is the final weight of ceramic tile (gm) T = Machining time in seconds. For calculating Taper; Taper = Upper diameter- lower diameter/2

From Table 3, it has been found out that larger MRR of 0.0121 gm/sec is obtained at parametric combinations such as ND of 3 mm, SOD of 9 mm and pressure of 10.5 kgf/cm2 and minimum Taper of 0.02 mm is obtained at parametric combinations such as ND of 2.5 mm, SOD of 5 mm and pressure of 10.5 kgf/ cm2 .

Experimental set up details AJM set up of size 200.66 cm × 91.44cm × 60.96 cm has been fabricated as shown in Fig.2. which consists of mixing chamber (hopper), nozzle, compressor, machining chamber, FRL unit and pressure gauge and nozzles of brass material of dif erent sizes i.e. 2 mm, 2.5 mm, and 3 mm.The list of components along with specification is shown in the Table 2. To withstand many operations, brass is the preferable material to manufacture nozzles. To view the progress of abrasive machining, transparent glass is used to cover up the working chamber. Thus it makes the machine environment friendly. In this investigation ceramic tiles having thickness of 5 mm were used as a workpiece material. Initial and final weights (after machining) of ceramic tiles specimens were measured with the help of digital balance for the calculation of the MRR. First the abrasive particles sizes of 60 µm were fed in the hopper carefully and then compressor connections were checked. After clamping the specimen properly on the test

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ISSN: 2320-5407 Int. J. Adv. Res. 9(05), 607-616 rig, the compressor was switched on. Abrasive grains were mixed with air jet coming from the compressor and focused on the specimen with help of nozzle and same experiments were conducted with abrasive particles size of 120 µm. By using the levels of Taguchi analysis dif erent readings of output responses have been found out. By using the Taguchi method all obtained results were analyzed and compared with ANOVA.

Table 2:- List of components with specification. S. No. Component Specification 1 Reciprocating Air 2 H.P Compressor 2 Nozzle Brass 3 Pressure gauge 0-14.06 kgf/(range) 4 FRL unit 0-10.55 kgf/(range) 5 House pipe PVC 6 Angle rod of table M.s (762) 7 M.S Plate 45.72 cm/60.96 cm (size) 8 Base of table 60.96 cm/91.44 cm (size) 9 Mixing Chanmber Mild steel of length 195 mm 10 Glass (for safety) 45.72 cm/45.72 cm (size)

Table 3:- experimental design matrix : mean value and S/N ratio for MRR( 60µm).

Table 4:- experimental design matrix of 120 µm

Results And Discussion:- The ef ect of process parameters on output such as material removal rate and Taper was determined using the taguchi method of optimization. In AJM process the most significant parameter was performed using ANOVA

Optimization of process parameters The experimental results have been transformed into means and Signal-to-Noise (S/N) ratio and it is shown in Table 3. for an abrasive size of 60 µm. The mean and S/N ratios for MRR have been calculated by statistical software “MINITAB 18.

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Table 3:- Mean value and S/N ratio for MRR for 60 µm.

Table 4:- Response table for Signal to Noise Ratio for MRR.

From the response table of S/N ratio (Table 4), the rank order of process parameters has been achieved as StandOf Distance, Nozzle Diameter and gas Pressure by taking abrasive size of 60 µm

Fig4:- Main effect plot for SN ratios MRR.

Fig.4. depicts the variation of S/N ratio for MRR with respect to input process parameters. The experimental results have been transformed into means and signal-to-noise (S/N) ratio and it is shown in Table 7 for abrasive size of 120 µm.

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Table 7:- Mean value and S/N ratio for MRR for 120 µm.

Table 8:- Response table for Signal to Noise Ratio for MRR.

From the response table of S/N ratio (Table 8), the rank order of process parameters has been achieved as StandOf Distance, Nozzle Diameter and gas Pressure by taking an abrasive size of 120 µm.

Fig.5:- main effect plot for SN ratio for 120µm.

Fig.5. depicts the variation of S/N ratio for MRR with respect to input process parameters. From the plot it has been observed that the MRR is increasing and decreasing as the Nozzle Diameter increases whereas for SOD and Pressure MRR is increasing.

Analysis of Variance (ANOVA) For abrasive size of 60 µm ANOVA test was performed to identify the most significant process parameters and determine the % contribution of

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ISSN: 2320-5407 Int. J. Adv. Res. 9(05), 607-616 process parameters on MRR. ANOVA test was performed at a significance level of 95% contribution level.

Table 9:- Results of Analysis of Variance of S/N ratio for MRR (*Significant Factor) 60 µm.

Where, DF=Degrees of freedom, Seq SS=Sequential sum of squares, Adj SS=Adjusted sum of square, Adj MS=Adjusted mean square and F=Fisher ratio.

For abrasive size of 120 µm ANOVA test was performed to identify the most significant process parameters and determine the % contribution of process parameters on MRR. ANOVA test was performed at a significance level of 95% contribution level.

Table 10:- Results of Analysis of Variance of S/N ratio for MRR (*Significant Factor) 120 µm.

The conclusion made from above Table.9 and Table.10 is that, stand-of distance, gas pressure and nozzle diameter are significant factors as corresponding P values are less than 0.8 and the developed model is significant.

From the results obtained by ANOVA it has been established that the most significant parameter is stand of distance (SOD) for controlling MRR in AJM based on the present analysis as it has highest percentage of contribution of 22.12% by using abrasive size of 60 µm and 43.28% by using 120 µm respectively compared to that of gas pressure and nozzle diameter

Future Scope It is very clear that AJM is a Non-conventional machining process which is used as a multipurpose system. It is also the most ef ective among various af ordable systems. This system is eco-friendly. Even some of the companies in India like ABB, L & T and ESSAR are already using this system with CNC programming. This system is also used as Water Jet Machining (WJM) in which abrasives such as garnet, diamond or powders can be mixed into the water to make slurry with better cutting properties than straight water. Further development in WJM is called Hydrodynamic Jet Machining (HJM) which combines the principle of Water Jet Machining and Abrasive Jet Machining process.

Conclusion:- Maximum value of MRR is 0.0284 gm/sec at pressure of 9.5 kgf/cm^2, SOD of 9mm and Nozzle Diameter of 2.5mm for abrasive size of 120µm.

Minimum taper value of 0.02 and optimum parametric conditions such as pressure 9.5 ,SOD 5 ND 2 for abrasive size of 120µm.So if the size of abrasive particles increases MRR increases and Taper decreases.

Statistical results (at a 95% confidence level) show that the nozzle diameter, Stand-of distance and pressure have percentage contribution of11.11%, 43.28% and 3.16% on MRR by using abrasive of size120 µm and 22.12%,6.58% and 18.28% by using abrasive of size 60 µm.

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From the results obtained by ANOVA it has been found out that the Stand-of distance is the most Significant parameter during abrasive jet machining of ceramic tiles.

Reference:- 1. D.V. Srikanth, M. Sreenivasa Rao, “Application of Taguchi & Response surface methodology in Optimization for machining of ceramics with abrasive jet machining”, 4th International Conference on Materials Processing and Characterization, Vol.2, No.4-5, 2015, pp. 3308-3317. 2. D.V. Srikanth, Dr. M. Srinivasa Rao, “Metal Removal and Kerf Analysis in Abrasive jet drilling of Glass Sheets”, 3rd International Conference on Materials Processing and Characterization, Vol.6, 2014, pp.1303- 1311. 3. K. Siva Prasad, G. Chaitanya, “The Research Review on Abrasive Machining”, International Journal on Recent Technologies in Mechanical and Electrical Engineering, vol.3, No.6,2016, pp.19-27. 4. Nageshwar K. Rao V, D. V. Srikanth, Vijayasree K., “Optimization of Process Parameter of Abrasive Jet Machining on Epoxy Glass Fiber Composite”, Internal Journal of Scientific Research and Education, Vol. 3, No.9, 2015, pp.4577-4587. 5. R. Balasubramaniam, J. Krishnan, N. Ramakrishnan „Investigation of AJM for deburring‟ a Central Workshops, Bhabha Atomic Research Centre, Mumbai, India, Journal of Material Processes and Technology, vol. 79,1998, pp.-52-58. 6. El-Domiaty, H.M. Abd El-Hafez, M. A. Shaker, „Drilling of Glass Sheets by Abrasive Jet Machining‟, World Academy of Science, Engineering and Technology, vol. 3, No.8, 2009, pp. 61-67.

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