PREDICTION OF BURR SIZE IN DRILLING OPERATION OF AL 2014 ALLOY USING TAGUCHI DESIGN METHOD

Transcription

1 International Journal of Lean Thinking Volume PREDICTION OF BURR SIZE IN DRILLING OPERATION OF AL 2014 ALLOY USING TAGUCHI DESIGN METHOD Reddy Sreenivasulu a*, Chalamalasetti SrinivasaRao b a Department of Mechanical Engineering, R.V.R. & J.C.College of Engineering (Autonomous), Chowdavaram, Guntur, Andhra Pradesh, India. a Department of Mechanical Engineering, University College of Engineering, (Autonomous) Andhra University, Visakhapatnam, Andhra Pradesh, India. A B S T R A C T This paper presents the influence of cutting parameters like cutting speed, feed rate, drill diameter, point angle and clearance angle on the burr size of Al 2014 alloy during drilling on CNC vertical machining center. A plan of experiments based on Taguchi method has been used to acquire the data. An orthogonal array, signal to noise (S/N) ratio and analysis of variance (ANOVA) are employed to investigate machining characteristics using HSS twist drill bits with variable tool geometry and maintain constant helix angle of 450. Confirmation tests have been carried out to predict the optimal setting of process parameters to validate the proposed method and obtained the values mm and mm for burr height and thickness respectively. K E Y W O R D S Al 2014 Alloy; Drilling, Taguchi method; S/N ratio; ANOVA. A R T I C L E I N F O Received 18 Aug 2016 Accepted 15 Dec 2016 Available online 5 Jan 2017 * Corresponding author: Reddy Sreenivasulu rslu1431@gmail.com, Tel.:

2 1. Introduction Drilling is a machining process used to create or enlarge holes into or through a workpiece material. The process is performed with the use of a drill, which works by rotating at a fast speed while simultaneously being fed into the workpiece, removing incremental amounts of workpiece material. The drill itself, which performs the cutting action, has multiple cutting edges and flutes running along its length that allow the chips of workpiece material to be carried away. During the drilling process, burrs form on both the entry and exit surfaces as a result of plastic deformation of the workpiece material. Burrs are simply small amounts of attached material that protrude from the original entry and exit surfaces around the drilled hole. An illustration of the drilling process as well as both entry and exit burr formation is shown in Fig1. They are generally unwanted, and commonly need to be removed depending on the specific desired part geometry. If they are not removed, they can cause misalignment with adjacent parts. Because of strain-hardening effects, burrs are typically harder than the original material (J.C. Aurich, 2009), meaning that contact between two adjacent parts with the burr in between can cause cracks to form and can reduce the overall fatigue life of the assembly. The burrs can also get detached from the surface and get trapped between mating surfaces leading to three-body abrasion and eventual failure of the assembly, among numerous other potential problems. Figure 1. Entry and exit burr formation 1.1. Back ground on Literature It is necessary to differentiate investigations which cover burr form and others that cover the topic of minimizing burrs. Gillespie and Blotter (1976) already observe that burrs cannot be prevented by changes in feed, speed, or tool geometry alone. Still, the size of burrs produced can be minimized significantly by choosing appropriate machining parameters. To minimize and prevent burrs it is necessary to examine the entire cutting process. It is not sufficient to change only one process parameter as there are many influences between the parameters. Burr formation is affected by various parameters. Major effects are workpiece material, tool geometry, tool wear, tool path and machining parameters. In most cases a change of workpiece material is not possible. As to an improved tool path, this approach is also limited, as complex geometries would require burr optimized tool paths that prolong cycle time as negative effect. Wang and Zhang (2004) investigate cutting burrs. The main factors of cutting direction burr formation are cutting parameters, the shape of the workpiece end, cutting tool geometry and workpiece material. The burr height in cutting direction is reduced with the increase in the depth of cut, feed, cutting edge angle and back rake angle. An increase of corner radius leads to increasing burr height. Pai-chung Tseng etal (2003) focused on Burrs formation Prediction and Minimization on end milling using Taguchi Method to plan experiments. The S/N ratio and the statistical tools such as the 48

3 main effect analysis and variance analysis are adopted, to obtain the optimal parameters combination. The results show that, the amount of exit burrs can be effectively reduced by adjusting the cutting speed and feed rate with existing manufacturing conditions. V N Gaitonde et al (2005) presented genetic algorithm (GA) applications to RSM models in their paper to reduce burr size reduction in drilling process for mild steel. The effect of cutting speed, feed, drill diameter, point angle and clearance angle on Burr height and thickness has been investigated. The usefulness of GA in multi-objective drilling burr size optimization problems is demonstrated through simulation. V N Gaitonde et al (2006) presented the exit burr formation in drilling us influenced by cutting conditions and drill geometry. They presented the application of Taguchi s analysis for simultaneous minimization of burr height and burr thickness. In that investigation they found optimal values of cutting speed, feed, point angle and lip clearance angle to minimize burr height and burr thickness during drilling of AlSl 316L stainless steel. Lauderbaugh (2009) used simulation tools and analysis of variance to identify the influence of process parameter on the height of exit burrs and concluded that feed rate, chisel-edge to drill diameter ratio, drill diameter, yield strength and point angle are significant for the height of exit burrs. E.Kilickap (2010) considered application of Taguchi and RSM for minimizing the burr height and surface roughness in drilling Al 7075.The optimization results showed that the combination of low cutting speed, low feed rate and point angle is necessary to minimize both burr height and surface roughness. Sanjib Kundu etal (2014) suggested by Taguchi s method to minimize drilling burr of an aluminium alloy using HSS drill within the domain of experiments considered using a back-up support. It is found out that back-up support yields much better result than that of normal drilling process. Moderate cutting velocity, low feed and wet condition with water cooling were observed to minimize burr height using a back-up support. Machining environment is found to be the most significant parameter for reducing burr height. Das, R, Barik, T (2014) conducted an experimental study and analysis on burr formation on the aluminum channel in drilling process with backup support. ANOVA results found that the drill bit diameter and spindle speed are most effecting parameters in burr formation. Based on the experimental results they concluded that the burr formation in channels highly depends on the spindle speed. The thickness of the channels also effect the burr formation i.e. the higher thickness channel needs more force during drilling. There an optimum spindle speed exists for a selected channel thickness, for which the average burr height is lowest Back ground on Aluminium Alloys At present, aluminium is used in the aviation industry everywhere in the world. The casing of the first Soviet satellite was made of aluminium alloys. The body casing of American Avantgarde and Titan rockets used for launching the first American rockets into the orbit, and later on spaceships, was also made of aluminium alloys. They are used for manufacturing various components of spaceship equipment: brackets, fixtures, chassis, covers and casing for many tools and devices. Aluminium alloys have a certain advantage for creating space equipment units. High values of specific strength and the specific rigidity of the material enabled the tanks, inter-tank and casing of the rocket to be manufactured with high longitudinal stability. The advantages of aluminium alloys also include their high performance under cryogen temperatures in contact with liquid oxygen, hydrogen, and helium. The so-called cryogen reinforcement happens in these alloys, i.e. the strength and flexibility increase parallel to the decreasing temperature. Engineers and manufacturers never cease to study the properties of aluminium, developing more and more new alloys for construction of aircraft and spaceships. 2xxx, 5xxx, 6xxx, and 7xxx series alloys are widely used in automotive and aviation industries. 49

4 2. Experimental Procedure 2.1. Material The composition of Alluminium 2014 alloy consists of Chromium: 0.1%, Copper: 3.9% - 5%, Iron: 0.5%,Magnesium: 0.2% - 0.8%,Manganese: %, Silicon: 0.5% Titanium: 0.15%, Titanium : 0.2% Zinc: 0.25% and remaining is alluminium Schematic machining: In this study, the experiments were carried out on a CNC vertical machining center (KENT and ND Co. Ltd, Taiwan make) shown in Figure2 to perform different size of holes on Alluminium 2014 alloy work pieces by alter the point and clearance angles on standard HSS twist drill bits using tool and cutter grinder as shown in Figure3 and maintain constant helix angle of 45 degrees. Furthermore the cutting speed (m/min), the feed rate (mm/rev) and drill diameter are regulated in this experiment. Figure 2. CNC machining center, controller and fixing a work piece in a wise Figure 3. Tool and Cutter grinder for alteration of angles on HSS twist drill bits 50

5 3. Motivation of The Present Work 3.1. Methodology The orthogonal array forms the basis for the experimental analysis in the Taguchi method. The selection of orthogonal array is concerned with the total degree of freedom of process parameters. Total degree of freedom (DOF) associated with five parameters is equal to 10 (5X2).The degree of freedom for the orthogonal array should be greater than or at least equal to that of the process parameters. There by, a L27 orthogonal array having degree of freedom equal to (27-1) 26 has been considered, which is used to optimize the cutting parameters for surface roughness and circularity deviation using the S/N ratio and ANOVA for machining of Alluminium 2014 alloy and predicted results were nearer to the experimental results. Although similar to design of experiment (DOE), the taguchi design only conducts the balanced (orthogonal) experimental combinations, which makes the taguchi design even more effective than a fractional factorial design. By taguchi techniques, industries are able to greatly reduce product development cycle time for design and production, therefore reducing costs and increasing profit. Confirmation test have been carried out to compare the predicted values with the experimental values confirm its effectiveness in the analysis of burr height and thickness Experimentation as per Taguchi Method: A plan of experiments based on Taguchi technique has been used to acquire the data. An orthogonal array, signal to noise (S/N) ratio and analysis of variance (ANOVA) are employed to investigate the drilling characteristics of Alluminium alloys using HSS twist drill bits. The complete procedure in Taguchi design method can be divided into three stages: system design, parameter design, and tolerance design. Of the three design stages, the second stage the parameter design is the most important stage. Taguchi s orthogonal array (OA) provides a set of well-balanced experiments (with less number of experimental runs), and Taguchi s signal-to-noise ratios (S/N), which are logarithmic functions of desired output in the optimization process. Taguchi method uses a statistical measure of performance called signal-to-noise ratio. The S/N ratio takes both the mean and the variability into account. The S/N ratio is the ratio of the mean (Signal) to the standard deviation (Noise). The ratio depends on the quality characteristics of the product/process to be optimized. The machining parameters and their levels are given in Table1. Plan of experiments based on Taguchi orthogonal array and observed responses shown in Table 2. Table 1. Machining parameters and their levels LEVELS FACTORS CUTTING SPEED (rpm) FEED RATE (mm/min) DRILL DIAMETER (mm) POINT ANGLE CLEARANCE ANGLE A B C D E

6 Table 2. Plan of experiments based on Taguchi orthogonal array and observed responses R U N CUTTING SPEED (RPM) FEED RATE (mm/min) TAGUCHI RESPONSE DESIGN TABLE DRILL DIAMETER (MM) POINT ANGLE (Degrees) CLEARANCE ANGLE (Degrees) BURR HEIGHT (mm) BURR THICKNESS (mm) S A B C D E H T

7 3.3. Analysis of the S/N Ratio In the Taguchi method, the term signal represents the desirable value (mean) for the output characteristic and the term noise represents the undesirable value (Standard Deviation) for the output characteristic. S/N ratio used to measure the quality characteristic deviating from the desired value. The S/N ratio = -10 log (M.S.D), Where M.S.D is the mean square deviation for the output characteristic. The S/N ratio table for observed responses is shown in Table 3. Table 3. Signal to Noise Ratios for Smaller is better Level cutting speed(rpm) A feed rate (mm/min) B drill diameter(mm) C point angle(deg) D clearance angle(deg) E Delta Rank Results and Discussions From main effects plot of S/N ratio for, the optimum parameters combination for burr height and burr thickness are A2B1C2D1E1 corresponding to the largest values of S/N ratio for all control parameters. From Table 3, it is observed that feed rate, point angle, drill diameter, cutting speed and clearance angle has the order of influence on burr height and burr thickness during drilling of Al 2014 alloy. Figure 4. Main effect plots of S/N ratio 53

8 Figure5. Interaction plot for burr height Figure6. Interaction plot for burr thickness 5. Results Of ANOVA The purpose of the analysis of variance (ANOVA) is to investigate which design parameters significantly affect the quality characteristic. Table 3 shows the results of ANOVA for burr height, cutting speed, feed rate, drill diameter, point angle and clearance angle are the significant cutting parameters for affecting the burr height. Table 4 shows the results of ANOVA for burr thickness, cutting speed, feed rate, drill diameter, point angle and clearance angle are the significant cutting parameters for affecting the burr thickness. Table 3: Results of ANOVA for burr height Table 3: Results of ANOVA for burr height Symbol Cutting Parameters DOF SS MS F A Cutting speed significant B Feed rate significant C Drill diameter significant 54

9 D Point angle significant E Clearance significant angle Error Total F table at 95%confidence level is F0.05, 2, 16 = 3.63, F exp F table Table 4. Results of ANOVA for burr thickness Symbol Cutting DOF SS MS F Parameters A Cutting speed significant B Feed rate significant C Drill diameter significant D Point angle significant E Clearance significant angle Error Total F table at 95%confidence level is F0.05, 2, 16 = 3.63, F exp F table Table 5. Optimal values of individual machining characteristics machining characteristics Optimal combination of parameters Significant parameters(at 95% confidence level) Predicted optimum value Burr height (H) A2B1C2D1E1 A,B,C,D,E Burr thickness (T) A2B1C2D1E1 A,B,C,D,E Experimental value Confirmatory experiments were conducted for burr size corresponding their optimal setting of process parameters to validate the used approach and obtained the values of 0.232mm, 0.173mm for burr height, burr thickness respectively. Predicted and experimental values of responses are depicted in table5. 6. Conclusions The machining characteristics of Al 2014 alloy have been studied. The primary machining characteristics such as burr height and burr thickness were studied for drilling. The results obtained from the experiments as follows. From S/N Ratio response graph, the combination of parameters having the values of 800 rpm, 0.3 mm/min,10mm.118 degrees and 4 degrees obtained for cutting speed, feed rate drill diameter, point angle and clearance angle respectively for optimizing burr size. From the results of ANOVA for cutting speed, feed rate, drill diameter, point angle and clearance angle, all parameters are significant for all responses, for this cutting speed, drill geometry are more significant. References J.C. Aurich. Burrs: Analysis, control and removal CIRP Annals - Manufacturing Technology, 58 (2009) Gillespie LK, Blotter PT The Formation and Properties of Machining Burrs. Transactions of ASME Journal of Engineers for Industry 98(1976):

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