Multi Objective Optimization Using Taguchi Grey Relational Analysis (GRA) for CNC Turning of Poly-ether-ether-ketone (PEEK) Polymer

Transcription

1 Multi Objective Optimization Using Taguchi Grey Relational Analysis (GRA) for CNC Turning of Poly-ether-ether-ketone (PEEK) Polymer Multi Objective Optimization Using Taguchi Grey Relational Analysis (GRA) for CNC Turning of Poly-ether-ether-ketone (PEEK) Polymer Bhagwan F Jogi 1 *, Monish Tarekar 2, Rinul M Dhajekar 3 and Raju Pawade 4 1,4 Associate Professor, Mechanical Engineering, Dr. Babasaheb Ambedkar Technological University, Lonere, Raigad, Maharashtra, India ,3 M.Tech. Student, Department of Mechanical Engineering, Dr. Babasaheb Ambedkar Technological University. India SUMMARY The paper attempts to implement the multi objective optimization methodology for poly-ether-ether-ketone (PEEK) polymer by using CNC turning machine. For the same, Taguchi based L 18 experiments were carried out on CNC turning lathe using TiC and TiN coated carbide inserts. Further, the process performance is measured in terms of cutting forces and surface roughness. The optimized machining parameters were determined using Grey Relational Analysis (GRA). The analysis of results shows that cutting speed: 377 m/min, feed rate: 0.05 mm/rev, depth of cut: 2 mm and TiC insert exhibits better results. Keywords: Grey relational analysis, Poly-ether-ether-ketone, TiN insert, TiC insert 1. INTRODUCTION Poly-ether-ether-ketone (PEEK) is a high performance thermoplastic having semi-crystalline in nature. It has various industrial applications like automotive industry (gears, bearing, etc.), bioapplications (biomedical implants), chemical Industries (chemical storage) and aerospace industry (brackets, impeller, etc.). It is one of the alternatives for aluminum due to its high strength, low density, toughness, better environmental resistance with high service temperature 1. Its glass transition temperature (T g ) and crystalline melt transition temperature (T m ) are approximately 143 C and 343 C respectively 2. The good surface finish is desirable for the application point of view. However, there are various machining parameters viz. feed rate, depth of cut, cutting speed, cutting fluid and tool material affect the machined surface condition 3. Related to PEEK, Rahman et al. 4 studied the machinability aspects of *Corresponding author s bfjogi@dbatu.ac.in Smithers Information Ltd., 2016 carbon/peek composites polymer. They found that the surface finish of the work-piece is attributed to softening action of the polymer. Davim et al. 7 and Davim and Reis 8 were resulted that while machining of PEEK and reinforced PEEK, the better performance parameters (cutting force, specific cutting pressure and surface roughness) can be achieved at higher service temperatures. Furthermore, the investigations is carried out by Davim and Mata 6,9 on fiber reinforced plastics (FRP) and carbon/peek materials using different cutting tools such as cemented carbide and polycrystalline diamond (PCD). They revealed that the performance of PCD cutting tool is better than the carbide tool. Petropoulos et al. 5 observed that the surface roughness is more dominated by the feed rate. Hence, it is planned to study the effect of machining parameters on PEEK rod using CNC turning by TiC and TiN inserts. Machining parameters viz. cutting force, feed, and depth of cut, are optimized by using Taguchi array followed by grey relation analysis (GRA) method to optimize cutting force and surface finish. 2. EXPERIMENTAL DETAILS 2.1 Materials PEEK polymer material is supplied by Evonic, Germany having brownish grey in color, under the trade name as KETRON PEEK-1000 Natural 400R. The work material is in the form of cylindrical rod having diameter 22 mm and length 1600 mm. 2.2 Cutting Tool Inserts and Tool Holder In this study, the cutting tool inserts are selected having TiAlN coating by physical vapour deposition (PVD) method. Its specifications are CNMG MS KC 5525 having 0 clearance angle and 80 rhombus shape with corner radius of 0.8 mm. The tool holder used for clamping the insert is PCLNR 2525 M, WIDIA make with specifications 95 approach angle and -6 back rake angle. Furthermore, the ceramic insert AW20 is also used having specifications 0 clearance Polymers & Polymer Composites, Vol. 24, No. 7,

2 Bhagwan F. Jogi, Monish Tarekar, Rinul M. Dhajekar and Raju Pawade angle and 80 rhombus shape with corner radius of 0.4 mm i.e. Aluminazirconia (with 90% Al2O3 + 10% ZrO2). For AW20 insert, top clamping type tool holder, CCLNR2525 M12- MN7 Kennametal make is used. 2.3 Machine and Equipment High-speed precision CNC Lathe (Jobber XL Make, Model NH-22) having 7.5 HP electric motor and 5000 rpm is used for experimental work. The surface roughness was measured using Mitotuyo surface roughness tester SJ 301 (Figure 1). Cutting force component during turning operation measured by Kistler make cutting forces dynamometer (Figure 2) built in charge amplifier (model-2825a) with control unit type 5233 A. Resolution Figure 1. Surface roughness tester of the dynamometer 1 mn and online forces were measured using dynoware software. Data acquisition of 500 Hz sampling rate was used. To understand the surface topography, scanning electron microscopy (SEM) analysis is also carried out to on few selected samples. As PEEK is a polymeric material and nonconductive in nature, gold sputtering is carried out before performing the SEM study to avoid the charging. 2.4 Experimental Plan and Procedure It was observed from the past research that the machining parameters influence the turning process considerably. The factors and their levels were selected based on past research 1,4,8-10. The depth of cut in certain range, possess less effect on output parameters. Hence the depth of cut was kept constant 1,4,8,9. Three machining parameters, such as insert type, cutting speed, and feed rate are selected for the study based on the past experiences and literature survey. Further, CNC turning is carried out on PEEK rod with TiN and TiC coated cutting tool inserts on CNC lathe by designing Taguchi L18 orthogonal array. These 18 experiments will give approximately 99% accurate results. Table 1 shows the variation of the process parameters. After that surface roughness and cutting force were measured. Furthermore, grey relational analysis (GRA) is carried out on the obtained results. It avails single response optimization situation from multiple response process optimization problems RESULTS AND DISCUSSION Figure 2. Dynamometer Table 1. Input factor and their levels Factors Machining Symbol Unit Level 1 Level 2 Level 3 Parameters Low Medium High Variable Cutting Speed V m/min Feed Rate F mm/rev Depth of Cut D mm In Taguchi L18 array number of experiments will be reduced to 18 instead of 27 with almost same accuracy. The results obtained from Taguchi orthogonal L18 array were used for performing grey relational analysis (GRA) to optimized input parameters, for low surface roughness and cutting force. The stepwise procedure of Taguchi-GRA optimization is shown in Figure 3. According to the GRA experimental design, grey relational coefficients (GRCs) of surface roughness (arithmetic mean roughness Ra, peak to valley height Rt), feed force (Fx), thrust force (Fy), and cutting force (Fz) were calculated. Further, average of all GRCs provides grey relational grade (GRG) for each experiment as shown in the Table 2. It was clearly observed that PEEK polymer turning process parameters setting of experiment number 12 has the highest grey relational grade value. Therefore, experiment 12 was the optimal process parameters setting for minimum surface roughness and 524 Polymers & Polymer Composites, Vol. 24, No. 7, 2016

3 Multi Objective Optimization Using Taguchi Grey Relational Analysis (GRA) for CNC Turning of Poly-ether-ether-ketone (PEEK) Polymer cutting force (i.e. the best multiperformance characteristics) among the eighteen experiments. In other words, the optimum conditions for PEEK turning performance of surface roughness and cutting force was found as cutting speed: 377 m/min, feed rate: 0.05 mm/rev and depth of cut: 2 mm. Tool inserts also plays important role in the PEEK machining performance. It is observed that TiC inserts exhibits lower surface roughness and cutting force compared to TiN insert during PEEK turning. Further, it is also found that level of influence on process parameters for surface roughness and cutting force are shown in the response Table 3. The level of significance is calculated as follows: i) group the grey relational grades by factor level for each column in the orthogonal array ii) take the average of coefficients and grade values for each experiment of the central composite design. The response table provides significance effects of process parameters on surface roughness. Table 3 depicts the level of significance of the input factors over the multi-performance characteristics. It is found that, the most effective controllable factor has maximum difference between average grey relational grade levels. Figure 3. Flow chart of Taguchi grey relational analysis 11 It is observed that feed rate exhibits highest value as It indicates that feed rate is more dominant than the cutting speed on PEEK turning Table 3. The response table for grey relational grade (GRG) Process Average grey relational grade by factor level (Max Min) Parameters Level 1 Level 2 Level 3 Cutting Speed Feed Rate R (µm) GRC of R F (N) GRC of F F (N) GRC of F F (N) GRC of F GRG Table 2. The calculated grey relational coefficient and grey relational grade for 18 experimental run Expt. R a (µm) GRC of No. R a t t x x y y z z Polymers & Polymer Composites, Vol. 24, No. 7,

4 Bhagwan F. Jogi, Monish Tarekar, Rinul M. Dhajekar and Raju Pawade Figure 4. Main effect plots of grey relational grade for turning process Figure 5. SEM images of machined PEEK (V = 377 m/min, f = 0.05 mm/rev, D = 2 mm) relationship to cutting force and surface roughness At high cutting speed no feed marks are observed Taguchi-grey relational analysis method is efficient, systematic and simple approach for the multiobjective optimization. desired output, low surface roughness and cutting force. Figure 4 depicts the main effect plots of grey relational grade for turning process. It is found that the same results about major contributing parameters in PEEK turning operation which shows cutting speed slightly more important than the insert type. Significance level of process parameter as: feed rate, cutting speed, type of tool inserts and depth of cut while PEEK polymer turning operation. To understand the surface irregularities caused by turning of PEEK, scanning electron microscopy (SEM) is performed on the sample of experiment no 12 as it exhibits better results. The images are captured in magnification of 100X and 3000X as shown in Figure 5. It is found that no feed marks are observed on SEM images. It gives lower surface roughness with lower cutting force. The better surface finish is achieved at high speed. 4. CONCLUSIONs The input factors: feed rate, cutting speed, and type of insert are statistically significant effect on the surface roughness (R a ) while turning of PEEK polymer. Taguchi grey relational analysis (GRA) reveals that the most influencing factor affecting the turning process performance is feed rate. The order of importance of the input factor to the multiperformance characteristics is feed rate, cutting speed, insert, and insert cutting speed. The optimum parameters found from GRA are cutting speed: 377 m/min, feed rate: 0.05 mm/rev, and depth of cut: 2 mm with TiC insert For lower surface roughness and cutting force: TiC coating insert preferable as compared to TiN insert Among all parameters, feed rate shows strongest dependent References 1. Mata F., Gaitonde V.N., Karnik S.R., Davim J.P. Journal of Materials Processing Technology, 209, (2009), Alauddin M., Choudhury I.A., E1 Baradie M.A., Hashmi M.S.J. Journal of Material Processing Technology, 54, (1995), Boothroyd G. and Knight W.A., Fundamental of machining and machine tools, Taylor and Francis, NW, USA, (2006), Rahman M., Ramakrishna S., Thoo H.C. Machine Science and Technology, 3, (1999), Petropoulos G., Mata F., Davim J. Materials and Design, 29, (2008), Davim J.P. and Mata F. Materials and Design, 29, (2008), Davim J.P., Reis. P., Lapa V., Conceicao C. Composite Structure, 62, (2003), Davim J.P. and Reis P. International Journal of Advance Manufacturing Technology, 23, (2004), Davim J.P. and Mata F. Material Design, 27, (2006), Davim J.P., Mata F., Gaitonde V.N., Karnik R.S. Journal of 526 Polymers & Polymer Composites, Vol. 24, No. 7, 2016

5 Multi Objective Optimization Using Taguchi Grey Relational Analysis (GRA) for CNC Turning of Poly-ether-ether-ketone (PEEK) Polymer thermoplastic composite materials, 23, (2010), Mathew M. and Rajendrakumar P.K. Materials and Design, 32, (2011), Datta S., Bandyopadhyay A., Rai P.K. International Journal of Manufacturing Technology, 39, (2008), Polymers & Polymer Composites, Vol. 24, No. 7,

6 Bhagwan F. Jogi, Monish Tarekar, Rinul M. Dhajekar and Raju Pawade 528 Polymers & Polymer Composites, Vol. 24, No. 7, 2016