Effect of Gases on the Performance of Cryogenically Treated Tungsten Carbide Inserts in Turning

Transcription

1 Effect of Gases on the Performance of Cryogenically Treated Tungsten Carbide Inserts in Turning 89 Effect of Gases on the Performance of Cryogenically Treated Tungsten Carbide Inserts in Turning Ashwani Kumar*¹, Dilbag Singh², Nirmal S Kalsi² ¹Department of Mechanical Engineering, A.B.I.E.T Kotli, Pathankot Punjab India ²Department of Mechanical Engineering, Beant College of Engineering and Technology, Gurdaspur, Punjab, India Abstract: In this paper, an attempt has been made to study the effect of gases as a cutting fluid on the performance of cryogenically treated tungsten carbide insert in turning process. The experiments were performed in turning AISI 1040 steel under dry, nitrogen and carbon dioxide gas environments. The input variables were cutting speed, feed and depth of cut and the response parameters were cutting force and tool wear. ANOVA was performed to study the effect of input parameters on response parameters. Turning with nitrogen and carbon dioxide as the cooling media shown reduction in cutting force and tool wear as compared to dry turning. The lowest cutting force and tool wear was observed in turning using carbon dioxide gas as compared to nitrogen gas and dry turning. Keywords: Deep cryogenic treatment, tungsten carbide, analysis of variance 1. INTRODUCTION Machining is the most widespread metal shaping process in manufacturing industry. The conventional machining processes include turning, milling, boring, drilling, shaping etc. From these processes, turning is a widely used machining process in which a single point cutting tool removes material from the surface of a rotating cylindrical work piece. The material removed in the form of chips slides on the rake face of the tool, subjecting it to high normal and shear stresses. Most of the mechanical energy used to form the chip is converted into heat, which produces high temperatures in the cutting region [1]. High cutting temperature adversely affects tool life, dimensional and form accuracy and surface integrity of the product. Traditionally, high temperature in the cutting zone has been controlled by using cutting fluids. But, cutting fluids cause environmental and health problems. The cutting fluids are the major source of pollution from the machining industry and its disposal cost is also increasing due to strict environmental regulations. These regulations have been forcing manufacturers to reduce or eliminate the use of cutting fluids. Therefore, researchers are continuously evaluating possible environment friendly alternatives in machining processes to reduce the heat generation in the cutting zone and to extend the tool life. Some of these alternatives approaches are minimum quantity lubrication, solid lubrication, cryogenic cooling and use of compressed air and gases. The compressed gases as a cutting fluid have * Corresponding Author: ashwani.gsp@gmail.com been used since 1930s [2]. These are cheap, pollution-free, eco-friendly and are good coolant and lubricant. Although, some studies have been carried out to improve the machining performance with the application of gases, but there is still need to increase the life of a cutting tool. In these days, cryogenic treatment of the cutting tools is done to enhance their performance. 2. LITERATURE REVIEW Researchers have done work to study and improve the tool wear and other machining output parameters of various materials by cryogenic treatment. The cutting tool industry has recognized the benefits of the cryogenic process. A few researchers have studied the impact of cryogenic treatment on tungsten carbide inserts. Some studies related to the cryogenic treatment of cutting tool materials and use of gases as a cutting fluid in turning process have been reported in the literature. Ay et al., [3] performed an experimental study to monitor temperature variations of the tool and work piece in orthogonal cutting. They used uncoated carbide inserts as cutting tool and cast iron, AISI 1045 steel, copper and 6061 aluminum as work piece material. According to their study the maximum temperature was found on the rake face of the tool. Seah et al. [4] studied the effect of watersoluble lubricants on tool wear in turning of AISI 1045 and AISI 4340 steel with an uncoated tungsten carbide insert. The results of their study showed no significant difference between machining with water-soluble lubricants and dry machining. Klocke et al., [5] have studied

2 90 Ashwani Kumar, Dilbag Singh and Nirmal S. Kalsi the effect of cutting fluid on tool wear for wet and dry cutting environments. According to their study, there are many risks and costs are associated with the use of flood cutting fluids. Cakir et al.,[6] investigated the effects of cutting fluid, some gases applications and dry cutting on cutting forces, thrust forces, surface roughness, friction coefficient and shear angle in turning of AISI1040 steel material with P20 grade cutting insert. Nitrogen, oxygen and carbon dioxide gases instead of cutting fluid have been used and the results were compared to wet and dry machining processes. The carbon dioxide gas produces lower friction coefficient and higher cooling effect. These effects caused the lowest cutting force in carbon dioxide gas application as compared to other gases. Junyan Liu [7] Investigated the effects of carbon dioxide gas, oxygen gas, water vapor and mixture of vapor and gas on main cutting force, cutting temperature, chip deformation coefficient, rake face wear, and tool flank wear in turning ANSI 1045 steel material with cemented carbide tool. It was found that as compared with dry cutting and wet cutting, cutting force have been reduced by 20 40% and 10 15%, respectively, with application of water vapor, gas and mixture of vapor and gas as lubricant. Stanford et al., [8] experimentally investigated the performance of uncoated turning tools during turning of plain carbon steel EN32b under flood coolant, compressed air, ambient temperature nitrogen gas environment, cold nitrogen gas, liquid nitrogen gas environment, and dry conditions. It is revealed that uncoated tools used in nitrogen-cutting environment can provide a 55% reduction in crater wear and 30% reduction in flank wear as compared to that under other environment. Han Manlin et al., [9] performed high speed cutting experiments on titanium alloy Ti6Al4V with uncoated WC- Co cemented carbide inserts. Comparisons were made to study the influence of different cutting media such as air jet, nitrogen gas jet and dry cutting conditions on machining titanium alloy with uncoated cemented carbide inserts. The result showed that nitrogen gas jet had more suitably decreased the cutting temperature, and improved the contact conditions at chip-tool interfaces than air jet and dry conditions. Nitrogen gas jet is an excellent cutting medium for green high speed machining of titanium alloy. Singh Dilbag et al., [10] experimentally investigated solid lubricant as an alternative to the cutting fluids to reduce friction and to improve the surface finish while hard turning of bearing steel. The results of their study indicated that there is a considerable improvement in the performance of hard turning of bearing steels using molybdenum disulphide as a solid lubricant when compared with dry hard turning in terms of surface roughness. Ying-lin ke et al., [11] suggested that nitrogen gas can be used to prevent chips burning in the high-speed cutting of Ti-6Al-4V. The high speed flowing of nitrogen gas speeds up the chips leaving, and prevents the chips from burning. The cutting force was reduced. Seah et al. [12] studied the effect of cryogenic treatment (CT) on cobalt bonded tungsten carbide (WC- Co) tools and found that CT increases its wear resistance. This is due to an increase in the number of n-phase particles after CT, a theory which he supported with photographs taken using a scanning electron microscope (SEM). In addition, the cryogenically treated tools also performed better than the untreated tools at higher cutting speeds. Reddy et al., [13] investigated the effect of deep cryogenic treatment on coated tungsten carbide ISO P-30 turning tool inserts. Machining studies were conducted on C45 work piece using both untreated and deep cryogenically treated tungsten carbide cutting tool inserts. It was found that lower flank wear and cutting forces and better surface finish were obtained with deep cryogenically treated tungsten carbide cutting tools as compared to untreated carbide tools. Yong et al., [14] performed experiments to study the performance of cryogenically treated tungsten carbide cutting inserts during orthogonal turning of medium carbon steel. The results of their study shows that cryogenically treated tools perform best when the tool temperature is kept low, their effectiveness can be extended if coolants or suitable methods of cooling are used to keep the tool temperatures low. CT improves the resistance to chipping of tools and also improves flank wear resistance. It was also shown that cryogenically treated tools perform better while performing intermittent cutting operations. Vadivel [15] carried out machining operation on nodular cast iron is using cryogenically treated and untreated coated carbide inserts. The cryogenically treated coated carbide inserts exhibit better performance based on surface roughness of the work piece, power consumption and flank wear than untreated coated carbide inserts. The SEM analysis concludes that the wear resistance of cryogenically treated coated carbide inserts is higher than that of the untreated ones. Kalsi N.S. et. al., [16] reviewed the CT of tool materials and concludes that deep cryogenic treatment has favorable influences on the performance of steels. B.R. Ramji [17] studied the effect of CT on the performance of coated carbide inserts in turning grey cast iron work piece. The cryogenically treated carbide inserts showed lesser flank wear and reduced surface roughness as compared to non treated inserts. Jiang et al [18] investigated the effect of CT on the mechanical and magnetic properties of WC- 8wt. % Co cemented carbides and showed that cryogenic treatment enhances hardness, compression strength, wear resistance and fatigue resistance, while the bending strength and toughness are not changed. The change of the mechanical properties highly depends on the soaking time. The review of literature clearly indicated that the CT improves the properties of the tool material. Cryogenically treated tools perform better when the tool temperature is

3 Effect of Gases on the Performance of Cryogenically Treated Tungsten Carbide Inserts in Turning 91 kept low. Their effectiveness can be extended if coolants or suitable methods of cooling are used to keep the tool temperatures low. But, conventional coolants cause environmental and health problems. Therefore the application of gases on the cryogenically treated tools is an alternative approach. Gases are cheap, pollution-free, eco-friendly and are good coolant and lubricant. So, the present work is based on some experimental investigation on the effect of nitrogen and carbon dioxide gases on the performance of cryogenically treated tungsten carbide inserts in turning. The results were compared to dry machining. The experiments were performed at different input parameters i.e. cutting speed, feed and depth of cut. The effect of these parameters on cutting forces and tool wear were evaluated as per L27 Taguchi design. 3. EXPERIMENTATION To fulfill the objectives of present work, experiments were performed on AISI 1040 steel by cryogenically treated tungsten carbide inserts under both dry and gaseous cooling environments. For this experimentation a high power rigid lathe of HMT (LB-17 model) was used. The cutting tools were purchased from Mitsubishi, India. The tungsten carbide cutting tools were of rhombic type having designation CCMT09T304. These cutting tools were deep cryogenically treated. For cooling and lubrication, nitrogen and carbon dioxide gases were used. These gases were impinged from a mild steel nozzle having diameter 1.40 mm. The nozzle was mounted on the saddle so that both the saddle and nozzle moved together and there is no static force of the gas systems on the dynamometer. The gases were impinged along cutting edge of the insert, so that the gas reaches as close to the chip-tool and the work-tool interfaces as possible. The nitrogen and carbon dioxide gas jet was used mainly to target the rake surface and flank surfaces along the cutting edge and to protect the flank to enable better dimensional accuracy. The pressure of nitrogen and carbon dioxide gases has been kept at 3bar. The material selected for the experiment was AISI 1040 steel having diameter 63mm and length 540 mm. This material is being used for manufacturing machine tools, shafts, axels, bolts etc. The chemical composition of work piece material is shown in Table1. Table1 Chemical Composition of AISI 1040 Steel (wt %) C Si Mn P S Fe The response parameters analyzed were cutting force and tool wear. The cutting force was measured by using a dynamometer for each machining condition. The tool was attached on dynamometer and static calibration of total system was completed before experiment. The flank wear was measured using metallurgical microscope (YUCON Japan). The experiments were performed at different input parameters i.e. cutting speed, feed and depth of cut. The experimental set up is shown in Fig. 1. The effect of these parameters on cutting force and tool wear was evaluated as per Taguchi design, using L27 orthogonal array as shown in Table 2. This orthogonal array consists of 27 rows corresponding to the number of experiments and 13 columns to study 13 three level factors. Figure 1: Photographic View of the Experimental Set Up Table 2 Experimental Layout using L27 Orthogonal Array S.No. Cutting speed Feed (f) Depth of cut Environment (V) m/min. mm/rev (d) mm Dry N CO N CO Dry CO Dry N N CO Dry CO Dry N Dry N CO CO Dry N Dry N CO N CO Dry

4 92 Ashwani Kumar, Dilbag Singh and Nirmal S. Kalsi 4. RESULT AND DISCUSSION Taguchi method was used to analyze the results of cutting force and tool wear, on basis of smaller is better criteria. The results were analyzed using ANOVA for identifying the significant factors affecting these parameters. Analysis of Variance is a statistical method used to compare two or more means. The main effect plots for the means for cutting force and tool wear were obtained using Minitab 14.1 statistical software. 4.1 Analysis of Variance for Cutting Forces Main effect plots for mean cutting forces are shown in the Fig. 2, which shows the variation of cutting forces with the input parameters. It is observed that cutting forces increases frequently with increase in depth of cut and feed. With the increase in feed and depth of cut, material removal rate increased resulting in increase in the cutting force. The cutting force decreased with the increase in speed. As speed increased, the co-efficient of friction at the chiptool interface on the rake face was decreased. In case of gases, the lowest cutting force was achieved by using carbon dioxide gas as compared to nitrogen gas and dry turning. This was due to cooling and lubrication by the use of gases which reduced the coefficient of friction at the interface of the tool and chip over the rake face. The cutting force has changed depending on the type of gas applied in machining. Carbon dioxide gas application produced the lowest cutting force as compared to nitrogen gas. The ANOVA results for the mean cutting forces are given in Table 3. ANOVA results show that cutting speed, feed, depth of cut and cooling environment affect the cutting forces. The case smaller is better was considered for cutting forces. The rank assigned to various input parameters are shown in Table 4. It is clear that depth of cut is the most significant factor affecting the cutting forces. Cutting speed and gases has also a significant amount of impact on cutting forces. Feed has a little impact on cutting forces. Figure 2: Main Effects Plot for Means for Cutting Forces (Smaller is Better) Table 3 Analysis of Variance for Means for Cutting Forces Source DF Seq SS Adj SS Adj MS F P % P Cutting speed (V) Feed (f) Depth of cut (d) Environment V*f V*d f*d Residual error Total

5 Effect of Gases on the Performance of Cryogenically Treated Tungsten Carbide Inserts in Turning 93 Table 4 Response Table for Means for Cutting Forces Level Cutting speed (v) Feed (f) Depth of cut (d) Environment Delta Rank Analysis of Variance for Tool Wear Flank wear is the most important tool wear occurring in machining operation. The flank wear is primarily attributed to rubbing of the tool along the mechanical surfaces, causing abrasive, diffusive and adhesive wear mechanisms and also high temperature, which affect the tool material properties as well as the work piece surface. Main effect plots for mean tool wear are shown in the Fig. 3, which shows the variation of tool wear with the input parameters. The tool wear increased frequently with increase in depth of cut. This is due to increase in the cutting forces which weaken the tool. The strength of the tool is reduced because high cutting temperature is produced due to increase in the rate of plastic deformation. The tool wear increased with the increase in cutting speed. Increase in cutting speed causes higher cutting temperature. As a result the strength of the tool reduced and flank wear increases rapidly. Figure 3: Main Effects Plot for Means for Tool Wear (Smaller is Better) Table 5 Analysis of Variance for Means for Tool Wear Source DF Seq SS Adj SS Adj MS F P % P Cutting speed (V) Feed (f) Depth of cut (d) Environment V*f V*d f*d Residual error Total

6 94 Ashwani Kumar, Dilbag Singh and Nirmal S. Kalsi Table 6 Response Table for Means for Tool Wear Level Cutting speed (v) Feed (f) Depth of cut (d) Environment Delta Rank In case of gases as a cutting fluid, the lowest tool wear was achieved by using carbon dioxide as compared to dry and nitrogen gas. This was due to more cooling and lubrication action of the carbon dioxide gas. The highest tool wear was observed in dry condition. The ANOVA results for the mean tool wear are shown in Table 5. ANOVA results show that machining conditions and environment are affecting the turning process. The rank of importance for various factors in terms of their relative significance is shown in the Table 6. The "smaller is better" criteria is applied for tool wear. From the rank assigned to various input parameters, it is clear that depth of cut is the most significant factor affecting the tool wear. Cutting speed and gases has also a significant amount of impact on tool wear. Feed has a little impact on tool wear. 5. CONCLUSION In the present research work, an attempt has been made to study the effect of nitrogen and carbon dioxide gases on the performance of cryogenically treated tungsten carbide insert in turning AISI 1040 steel. The results were compared with dry turning. The following conclusions are drawn. 1. It was observed that the application of gases results in reduced tool wear and cutting forces as compared with dry machining. 2. Depth of cut has the maximum impact during machining under all conditions. 3. Cryogenically treated tungsten carbide inserts, perform better by using carbon dioxide gas as compared with nitrogen gas and dry turning environments. ACKNOWLEDGEMENT The authors gratefully acknowledge the grant provided by All India Council for Technical Education, New Delhi, India under Research Promotion Scheme, file no. 8023/ BOR/RID/RPS-143/ and 8023/BOR/RID/RPS-73/ to carry out this research. References [1] Xavior M.A., Adithan M., 2009, Determining the Influence of Cutting Fluids on Tool Wear and Surface Roughness During Turning of AISI 304 Austenitic Stainless Steel, Journal of Materials Processing Technology, 209, pp [2] Shaw M.C., 1991, Metal Cutting Principles, Clarendon Press, Oxford, UK. [3] Ay H., Yang W.J., Heat Transfer and Life of Metal Cutting Tools in Turning, International Journal of Heat Mass Transfer, 41(3), pp [4] Seah K.H.W., Li X., Lee K.S., 1995, The Effect of Applying Coolant on Tool Wear in Metal Machining, Journal of Materials Processing Technology, 48(1-4), pp [5] Klocke F., Eisenblatter G., Dry Cutting, Ann. CIRP, 46(2), pp [6] Cak ı r O., Kı yak, M., Altan, E., 2004, Comparison of Gases Applications to Wet and Dry Cuttings in Turning, Journal of Materials Processing Technology, , pp [7] Liu J., Han R., Zhang L., Guo H., Study on Lubricating Characteristic and Tool Wear with Water Vapor as Coolant and Lubricant in Green Cutting, Wear, 262, pp [8] Stanford M., Lister P.M., Morgan C., Kibble K.A., Investigation Into the Use of Gaseous and Liquid Nitrogen as a Cutting Fluid when Turning BS A15 (En32b) Plain Carbon Steel using WC-Co Uncoated Tooling, Journal of Materials Processing Technology, doi: / j.jmatprotec [9] Han M., Li Y., Zhao W., Experimental Study on Cutting Temperature in High Speed Cutting of Ti6Al4V Alloy, Tool Engineering. [10] Singh D., Rao P.V., 2008, Improvement in Surface Quality with Solid Lubrication in Hard Turning, Proceedings of the World Congress on Engineering, 3, WCE, July 2-4, London, U.K. [11] Ke Y., Dong H., Liu G., Zhang M., Use of Nitrogen Gas in High-speed Milling of Ti-6Al-4V, Project Supported by the National High-tech Research and Development Program of China, International Journal of Machine Tools and Manufacture, 49, pp [12] Seah K.H.W., Rahman M., Yong K.H., Performance Evaluation of Cryogenically Treated Tungsten Carbide Cutting Tool Inserts, Proceedings of the Institution of Mechanical Engineers Part B, Journal of Engineering Manufacture, 217(1), pp [13] Reddy T.V.S., Sornakumar T., Reddy M.V., Venkataram R., Senthilkumar A., 2009b. Mach Inability of C45 Steel with Deep Cryogenic Treated Tungsten Carbide Cutting Tool Inserts, International Journal of Refractory Metals & Hard Materials, 27, pp [14] Yong A.Y.L., Seah, K.H.W., Rahman M., Performance Evaluation of Cryogenically Treated Tungsten

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