EXPERIMENTAL INVESTIGATION OF DRY DRILLING OF AUSTENITIC STAINLESS STEEL

Transcription

1 EXPERIMENTAL INVESTIGATION OF DRY DRILLING OF AUSTENITIC STAINLESS STEEL M. Arun 1, N. Arunkumar 2 and R.Vijayaraj 3 1 Department of Mechanical Engineering Anna University, Chennai, Tamilnadu, India 2 Department of Mechanical Engineering, St. Joseph s College of Engineering, Chennai, Tamilnadu, India 3 Dhanalakshmi Srinivasan college of Engineering, Department of Mechanical Engineering, Chennai, Tamilnadu, India ABSTRACT Austenitic stainless steel is difficult to drill using conventional High Speed Steel tools. Hence Cemented carbide, coating of in High Speed Steel and on Cemented carbide drills are investigated in drilling of AISI 316 Stainless steel. Three cutting s and three feed rates are used to conduct different experiments. To reduce the number of experiments, Taguchi s L9 Orthogonal array is used. Different parameters like cutting force, surface roughness, Roundness error and Burr height were ascertained for all the experiments. The experiments shows that HSS required less cutting force for machining, while had less surface roughness. In case of Roundness error HSS gave less roundness error and for Burr height had highest burr height. Keywords: austenitic stainless steel, cutting force, surface roughness, roundness error, burr height. INTRODUCTION Austenitic stainless steel is one of the most important grades of stainless steel as it has a variety of engineering applications particularly when resistance to corrosion is a primary requirement. However, low thermal conductivity and work hardening characteristics have made it difficult to machine with conventional cutting tools under normal operating condition. Amongst traditional machining processes, drilling is one of the most important metal cutting operations, comprising approximately 33% of all metal cutting operations [1]. Hence drilling consist of several parameters such as drill tool geometry, property of work material working conditions that influence the quality of the hole produced. These parameters influence the output of machining in terms of cutting force, roundness error, formation burr height. During dry machining the tool is subjected to high temperature. So it is necessary for a tool to have enough hot hardness. A comparison between monolayer and multilayer TiN coated drills were done by WenChou Chen et al [2] and found that multilayer drill has best performace. Sílvia do Nascimento Rosa et al [10] drilled AISI 1548 steel using and TiAlCrSiN pvd coated cemented carbide drill and found that the performance of TiAlCrSiN coated drill had good performance in terms of surface roughness and tool wear. Ula sçayda et al[3] used HSS, k20, TiN coated drills for dry drilling of AISI 304 stainless steel and measured surface roughness, roundness error and exit burr height. It was concluded that TiN coated drill has the best performance in terms of surface finish and burr height. V.N.Gaitone et al [4] used Taguchi L9 Methodology to design the number of experiments for drilling of AISI 316L by varying the input parameters cutting, point angle, lip angle and found that point able has major influence on burr height. TsannRong Lin et al [5] studied the behavior of a TiNcoated carbide drill with curved cutting edges during the high machining of stainless steel AISI304 and measured surface roughness and burr height. The objective of this work is to determine the effect of machining parameters on three types of drills (HSS,, ). The output parameters such as cutting force, surface Roughness, roundness error and exit burr height were to be measured and to use Taguchi method of design of experiment for obtaining the least number of experiment without losing any reliable information. EXPERIMENT The experiments were conducted in CNC Vertical Milling machine with VIKING MILL control system working on 5Hp spindle motor Figure1. force was measured by using Kistler Piezo electric dynamometer. The work material AISI 316 SS of dimension 150 x 100 x 22 mm were machined. The composition of AISI 316 was measured by using optical emission spectroscopy. The hole depths for all trials were kept constant of about 15mm. Three coated drills HSS,, drills were used. Roundness error and exit burr height were measured by using Sapphire 564 Coordinate Measuring Machine Fig.no.2. A minimum of 8 points were measured for calculating the roundness error and three points were measured for burr height and its average was obtained. 1232

2 Figure1. Viking mill VMC. Figure2. Coordinate measuring machine. Table1. Composition of AISI 316. Elements C S Mg K S Mo N Amount (%) Diameter Flute length Overall length Table2. Tool specification. 10mm 90mm 115mm Point angle Tool Type HSS, DESIGN OF EXPERIMENT The Taguchi method is an experimental design to find the optimal values by using minimal number of experiments [6]. The selection of which OA to use predominantly depends on the following items, in order of priority [7]: The number of factors and interactions of interest. The number of levels for the factors of interest. The desired experimental resolution, or cost limitations. The first two points makes the orthogonal array smaller number of experiments while the third one gives a high resolution. Table3. Taguchi orthogonal array L9 with 3 factors and 3 levels. Factors (m/min) (mm/rev) HSS

3 Table4. Experiments. Run T C F CF SN SR SN RE SN EBH SN 1 HSS HSS HSS T Tool Type C (m/min) F (mm/rev) CF Force (N) RE Roundness Error (µm) EBH Exit burr height (µm) SR Surface Roughness (µm) SN Signal to Noise Ratio values RESULT AND DISCUSSIONS Effect of Machining Parameters The graphs were plotted using minitab 17 software Figure3 shows the effect of input paramter on cutting force. The S/N ratio for force decreases with increase in feed also coated drill had less S/N ratio. S/N ratio decreases as the cutting increases. Figure4 show the effect of S/N ratios for Surface Roughness. Here HSS and drill has less S/N Ratios while the S/N Ratio decreases as the feed increases. Figure5 shows the effect of S/N Ratio for Roundness error in which had the least S/N Ratio. S/N Ratio decreases and increases as the cutting increases. The S/N Ratio decreases linearly as the feed increases. Figure6 shows the S/N Ratio for Burr height. has the least S/N Ratio ratio when compared to other tools. The S/N Ratio increases as the cutting increases. But the S/N Ratio decreases as the feed increases HSS Figure3. Main effects plots for SN ratios cutting force HSS Figure4. Main effects plots for SN ratios surface roughness. 1234

4 HSS HSS Figure5. Main effects plots for SN ratios roundness error. Figure6. Main effects plots for SN ratios burr height. Table5. ANOVA and S/N ratio table for cutting force Error Delta Total Rank Table6. ANOVA and S/N ratio table for surface roughness Error Delta Total Rank Table7. ANOVA and S/N ratio table for roundness error Error Delta Total Rank

5 Table8. ANOVA and S/N ratio table for burr height. cutting Error Delta Total Rank ANOVA table is used to find the significance of input parameters and also its contribution of each factor. Hence from Table5 it was found that Tool Type has the highest contribution ratio of about 54.07% for cutting force and for surface Roughness feed has highest contribution of about 30.69% (Table6). In case of Roundness error has major contribution of 62.38% (Table7). Similarly Tool Type has high contribution of about 83.29% (Table8). S/N ratio is used to find the optimum parameters. From table no.5 it is found that the optimum parameter level for cutting force is (2, 1, 2). From Table6 the optimum parameter level is (2, 2, 3). Table7 shows the optimum parameter level for Roundness Error which is (2, 2, 3). The optimum parameter for burr height is shown in table no.8 which is (2, 1, 1). CONCLUSIONS In this study a detailed analyze was done in the effect of cutting, feed and tool type on the cutting force, burr height and Roundness error in dry drilling of AISI 316 was done and the following conclusions were made: The cutting force required to drill the Austenitic stainless steel ( AISI 316 ) using coated HSS and were minimum when compared to coated carbide tools. The roundness error and the burr height were found to be minimum in the drilled hole when drilled using coated HSS tool followed by and coated tool. The surface roughness for the hole is minimum while drilling with coated and slightly greater than drilling with coated HSS and tools. The output parameters were found to be directly proportional to cutting velocity and the feed rate which means that the cutting force, roundness error, burr heights and the surface roughness increases when the cutting and the feed rate increases. Hence we conclude that the coated HSS tool shall be used to drill the 316 grade Stainless Steel with cutting velocity v=14m/min and feed rate f=0.08 mm/rev to get the best results. The carbide tool can also be used but the cost is high compared to the coated HSS tool. REFERENCES [1] Ula sçayda s, AhmetHasçalık, ÖmerBuytoz, and AhmetMeyveci, Performance Evaluation of Different Twist Drills in Dry Drilling of AISI 304 Austenitic Stainless Steel, Materials and Manufacturing Processes. 26: , [2] WenChou Chen, XiaoDong Liu, Study on the various coated twist drills forstainless steels drilling Journal of Materials Processing Technology. [3] Ula s Çayda s, Ahmet Hasçalık, Ömer Buytoz, and Ahmet Meyveci, Performance Evaluation of Different Twist Drills in Dry Drilling of AISI 304 Austenitic Stainless Steel [4] V.N. Gaitone, S.R. Karnik, B.T. Achyuth B. Siddeswarappa Taguchi optimization in drilling of AISI 316L stainless steel to minimize burr size using multiperformance objective based on membership function 2008 Journal of materials processing technology. [5] TsannRongLin, behavior of a TiNcoated carbide drill with curved cutting edges during the high machining of stainless steel 2002 Journal of Materials Processing Technology. [6] I. Asilturk, S. Nes_eli, Multi response optimisation of CNC turning parameters via Taguchi methodbased response surface analysis, Measurement 45 (2012) [7] P.J. Ross, Taguchi Techniques for Quality Engineering, second ed., McGrawHill, New York