Effect of Direct and Indirect Cryogen Application Methods on the Turning Forces, Tool Wear and Surface Finish of a Nickel Based Alloy (Nimonic 90)

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1 5 th International & 26 th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12 th 14 th, 2014, IIT Guwahati, Assam, India Effect of Direct and Indirect Cryogen Application Methods on the Turning Forces, Tool Wear and Surface Finish of a Nickel Based Alloy (Nimonic 90) Chetan 1*, Bikash Chandra Behera 2, Sudarsan Ghosh 3, P Venkateswara Rao 4 1* Department of Mechanical Engineering, IIT Delhi, , chetan.harry@gmail.com: 2 Department of Mechanical Engineering, IIT Delhi, , bikash.nitr@gmail.com: 3 Department of Mechanical Engineering, IIT Delhi, , sudarsan.ghosh@gmail.com: 4 Department of Mechanical Engineering, IIT Delhi, , pvrao@mech.iitd.ernet.in: Abstract Due to the stricter environment legislation and also due to an increase in the occupational diseases amongst the workers, it is necessary for the manufacturing sector to shift towards sustainable production techniques. Many researchers have reported that the application of Cryogen in metal cutting could improve the machinability of some materials without any ill effects on environment and health of workers. In machining, Cryogen can be used in two ways: (a) direct method and (b) indirect method. In direct cryogen application method, cryogenic gas from a suitably designed nozzle is directly applied to the tool-chip interface. While in indirect cryogen application cryogenic treatment is done on the cutting tool which may be subjected to a temperature below 0 C for a prolonged duration of time. This paper presents the comparison between the direct and indirect cryogen application methods during machining of Nimonic 90, a widely used nickel based super alloy. The measurement of Tool wear, surface roughness and cutting forces has been carried out for both these methods to determine the more effective method which can be used successfully during machining of the alloy. Keywords: Cryogenic cooling, Cryogenic treatment, Machinability, Nimonic, Sustainability 1 Introduction Machining is one of the most widely used manufacturing operation all over the world. It has been estimated that machining contributes towards 5% GDP in developed world (Jayal et al., 2010). On the other hand, it has also been noticed that machining operation has detrimental effects on surrounding environment and workers health (Marksberry, 2007). In order to make machining operations more ecologically viable and environmental friendly, it is necessary to introduce sustainability in it. Sustainability in metal cutting process can serve many benefits such as: 1) reduction in overall cost, 2) reduction in power consumption, 3) reduction in wastage, and 4) enhanced operational safety. Several sustainable techniques like dry cutting, cryogenic cooling (direct or indirect application), minimum quantity lubrication (MQL) and compressed air cooling have been evolved in recent years to make machining process more cleaner and greener (Sharma et al., 2009). Many difficult to machine materials like Inconel 718 and Ti6Al4V based alloys have been machined successfully using sustainable techniques (Ezugwu et al., 2003). Nimonic is another important nickel based alloy which is being widely used in automobile, aerospace, marine and locomotive industry. Despite of its poor machinability, very few literatures are available about the machining characteristics of Nimonic alloys. 2 Literature review 2.1 Sustainable machining techniques In machining operation it s mandatory to use cutting fluids or metal working fluids (MWFs) for enhancing life of cutting tool and surface integrity of work piece. It is an estimate that 16% of the total manufacturing cost is associated with these MWFs (Abele and Frohlich, 2008). The use of metal working fluids is a biggest problem for manufacturing sector because these are considered to be potential sources of air and water pollution. These cutting fluids are also cause of many respiration and skin related problems amongst the workers. In order to eradicate these problems, sustainable techniques like dry cutting, cryogenic processing and cryogenic cooling are found to be promising options (Lawal et al., 2013). 2.2 Dry cutting In this process machining is performed in the absence of pollution causing cutting fluids. Dixit et al. (2012) suggested many advantages of dry cutting as listed below 108-1

2 Effect of Direct and Indirect Cryogen Application Methods on the Turning Forces, Tool Wear and Surface Finish of a Nickel Based Alloy (Nimonic 90) The problems like water and soil contamination are absent in dry machining. No extra chemical treatment is required for cleaning dry waste like swarfs and chips. The solid waste can directly used for recycling purpose. It also cut down the cost associated with coolant thereby makes machining process more economic. Dry machining also helps in improving tool life in certain intermittent machining operations like milling process. Spur and Lachmund (1995) used CBN and ceramic tools for machining of cast iron. They have concluded that CBN tools are best suited for machining of cast iron due their high thermal conductivity. Devillez et al. (2007) tried machining of Inconel 718 with coated and uncoated tools under dry mode. The magnitudes of cutting and feed force were found to be more in uncoated tools in comparison to coated tools. They concluded that machinability of this alloy can further be improved by doing nano structured coating on cutting inserts. The methods such as: Surface texturing on cutting tool, machining with solid lubricants and minimum quantity lubrication can also be employed to further enhance the sustainability of dry turning process. 2.3 Cryogenic processing Cryogenic processing is the treatment of cutting tools below 0 C to enhance its mechanical properties. This is an indirect cryogenic method in which various gases such as CO 2, nitrogen and helium are used in liquefied form. Soaking temperature, cooling rate and tempering rate are the main parameters considered during cryogenic treatment. These terms have their usual meaning as given below Soaking temperature: Temperature at which specimen has to be placed for prolonged period. Cooling rate: Rate of change of temperature from room temperature to soaking temperature. Tempering rate: rate of change of temperature from soaking temperature to cooling temperature. Many researcher have carried out this subzero treatment on various tool steels by varying these important parameters. Mohan Lal et al. (2001) have cryogenically treated T1, M2 and D3 type tool steels. They have achieved 110% increase in the tool life of T1 tool followed by M2 and D3 tool steels. Meng et al. (1994) have shown an increase of 600 % in the wear resistance of tool steel by cryogenic processing. Recently, Gill et al. (2011) carried out shallow (-110 C) and deep (-196 C) treatment of coated carbide tool. They were successful in achieving 24% and 20% increase in the tool life of shallow and deep treated tools respectively during machining of C-65 steel. 2.4 Cryogenic cooling This is also known as a direct method of cryogenic application in which the jet of liquid nitrogen is applied directly to the cutting zone. Many researchers have achieved increase in tool life with the help of cryogenic cooling. Cooling with cryogen not only removes heat from cutting zone but also reduces the coefficient of friction by making lubricating cushion between chiptool interface. Recently, Kaynak (2014) performed the machining of Inconel 718 under dry, MQL and cryogenic conditions. The temperature reduction of 50% and 25% is achieved with cryogenic cooling as compare to both dry and MQL conditions respectively. Similarly, significant reduction in the amount of flank wear and radial forces is obtained in cryogenic condition in comparison to other conditions. Likewise, Dhananchezian and Kumar (2011) have performed machining of Ti6Al4V under cryogenic and wet conditions. They have achieved a reduction of 35% in surface roughness with cryogenic machining over wet machining. The cryogenic cooling also helped in reducing cutting forces, cutting temperature and tool wear over wet machining. 2.5 Machining of Nimonic alloy Nimonic alloys are widely used in making turbine blades, hot working tools, high temperature springs, exhaust valves, shafts, turbine rings and many other high temperature resisting components. Ezugwu et al. (2004) carried out machining of Nimonic C-263 alloy with coated carbide tools using coolant of various concentrations (3%, 6% and 9%). 3% coolant concentration worked best at lower cutting speeds of 68 and 85 m/min for improving tool life. At higher cutting speed of 136 m/min, 6% coolant concentration gave best results followed by 9% and 3% coolant concentrations. Recently during dry cutting of Nimonic C-263 alloy, it has been observed that both feed rate and depth of cut significantly influence the surface finish, tool wear and cutting forces in comparison to cutting speed (Ezilarasan et al., 2013). Though Nimonic is an important alloy but very few literatures are available regarding its machining. So, this work is an attempt to gather more information regarding machining characteristics of this alloy using sustainable techniques

3 5 th International & 26 th All India Manufacturing Guwahati, Assam, India Technology, Design and Research Conference (AIMTDR 2014) December 12 th 14 th, 2014, IIT 3 Experimental details 3.1 Workpiece Material Nimonic 90 (UNS N07090) is nickel-chromium- super alloy. cobalt based high temperature resistance This alloy is quite popular in aerospacee industry because of its high strength to weight ratio and high creep resistance up to 920 C. In the present study Nimonic 90 bar of 60 mm diameter and 300 mm m length has been used. The average micro hardness of this alloy was found to be 445 HV, measured according to ASTM standard. Composition of this alloy has been confirmed with the help of EDAX analysis and the result of which is given in table 1. Figure 1: Cryogenic treatment set-up Table 1: Chemical composition of Nimonic 90 alloy Element Ni Cr Co % Ti Al Cutting tool Uncoated carbide inserts with specifications CNMG12408-THM-F have been used for carrying out turning experiments. EDAX analysis of cutting tool was also performed to know about its main constituent. The tool inserts consist of mainly tungsten, carbon and cobalt (binder) listed in table 2. Table 2: Composition of cutting insert Element W C Co % Cryogenic treatment of cutting tool (Indirect cryogenic application) Cryogenic treatment enhances the wear resistance and hot hardness of cutting tool. To achieve this, deep cryogenic treatment of carbide tools has been carried out under controlled environment as shown in Figure 1. The cutting tools were kept at -196 C soaking temperature for duration of eight hours. These inserts were cooled from room temperature to soaking temperature at a cooling rate of 2 C/ C/min. In order to avoid thermal cracking the inserts weree brought back to room temperature at a heating rate of 1 C/min as shown in Figure 2. Figure 2: Cryogenic treatment cycle Many authors claimed that cryo-treatment of cutting inserts leads to the precipitation of hard eta phase particles. To confirm this claim, specimen of treated and untreated carbide inserts has been prepared for microstructure identification. ASTM B standard procedures for the cemented carbides has been followed to check any modification in the microstructure due to sub zero treatment. Figure 3 revealed the difference between the microstructure of untreated and treated inserts. Dense distribution of black eta phase particles has been found in treated insert as compared to untreated insert

4 Effect of Direct and Indirect Cryogen Application Methods on the Turning Forces, Tool Wear and Surface Finish of a Nickel Based Alloy (Nimonic 90) 3.5 Experimental plan All experiments have been carried out on Leadwell T-6 turning centre. Kistler piezoelectric multicomponent dynamometer has been used to measure the cutting forces under different conditions. The surface roughness has been measured with the help of Taylor Hobson Surface roughness instrument. Lastly, the tool wear is measure with the help of Ziess Stereo Discovery V.20 microscope. Further details of experiments are provided in table 3. Table 3: Machining conditions Cutting Environment Dry, Dry (Cryo treated tools), Cryogenic Cutting Speed (m/min) 40,60,80 Depth of cut (mm) 1 Feed rate (mm/rev) 0.1 Nimonic bar dimensions (mm) Diameter= 60, Length= Results and Discussions Figure 3: microstructure of treated and untreated insert. (a) Dense eta phase distribution in treated inserts (b) Sparse eta phase distribution in untreated insert. 3.4 Cryogenic cooling (Direct cryogenic application) In direct cryogen application method, cryogen has been directly applied to the cutting zone as shown in Figure 4. Unlike indirect cryogenic approach, untreated tools have been used during direct cryogenic cooling method. All experiments have been conducted under dry, cryo treated and cryogenic conditions. Cutting forces, tool wear and surface roughness have been measured for all these conditions at different speeds after 60 seconds of machining. Comparison of all these output parameters has been presented in this paper. Figure 5 shows the comparison of main cutting force (Fz) for all 3 conditions. At all 3 cutting speed values, dry condition yielded the highest values of cutting force as compared to cryo-treated and cryogenic conditions. At both 40 m/min and 80 m/min cutting speeds, the reduction of approximately 4.5% was observed in cutting force magnitude with cryo treated condition as compared to dry condition. Whereas for the same speed levels the cutting force magnitude was found to be reduced by 10% with cryogenic cooling condition as compared to dry environment. The reduction in cutting force under cryo-treated condition was mainly due to the formation of hard eta phase particles during cryogenic treatment of the tool which has resulted in an improvement in the wear resistance capability of the tool. While the formation of lubrication film during cryogenic cooling condition could be considered as the possible reason for cutting force reduction under cryogenic machining. The reduction in the amount of temperature sensitive tool wear such as: adhesion wear and diffusion wear during cryogenic cooling could also be a reason for reduction in cutting force values during direct cryogenic cooling. Figure 4: schematic of direct cryogenic cooling 108-4

5 5 th International & 26 th All India Manufacturing Guwahati, Assam, India Technology, Design and Research Conference (AIMTDR 2014) December 12 th 14 th, 2014, IIT Fz(N) Cutting speed(m/min) Figure 5: Comparison of cutting force v/s cutting speed under different cutting conditions The surface roughness was also measured for all 3 cases as shown in Figure 6. Surface roughness in case of cryo-treated tools was found to be almost equal the 3 different cutting speed conditions. Cryogenic cooling resulted into inferior surface roughness than dry and cryo-treated conditions. At 40 m/min, cryo-treated tool outperformed both dry and direct cryogenic condition in terms of surface finish value. At this condition surface roughness of 0.66 μm was obtained with indirect cryogenic method. Whilst surface roughness of 0.86 μm and 0.99 μm was produced by dry and direct cryogenic condition respectively. It has also been observed that with higher cutting speeds of 60 m/min and 80 m/min, dry condition provided better surface roughness as compared to both cryogenic application methods. Absence of built up edge formation and material softening due to higher temperature at higher cutting speed could be considered as the reason for improvement in surface finish. At all cutting speeds, cryo treatment method outperformed direct cryogen method in terms of surface finish. As compared to cryogenic cooling, the surface roughness was improved by 33%, 37% and 25% with cryo-treated tools at 40 m/min, 60 m/min and 80 m/min respectively. It could be concluded that workpiece became brittle and hardened with the direct application of liquid nitrogen in direct cryogenic cooling method which resulted into poor surface roughness as compared to dry and cryo-treated conditions. surface roughness(μm) Dry Cutting speed(m/min) Cryo-treated Cryogenic Dry Cryo-treated Cryogenic Figure 6: Comparison of surface roughness v/s cutting speed under different cutting conditions Flank wear of cutting insert was measured with the help of Carl Ziess microscope for each condition after 60 sec of machining. Figure 7 shows the flank wear images for all the 3 conditions at 40 m/min. It has been found that tool wear in dry condition was more than direct and indirect cryogenic conditions as shown in Figure 8. At 40 m/min, the flank wear values of µm, µm and µm was observed with dry, cryo-treated and cryogenic conditions respectively. Both cryo treatment and cryogenic cooling application method increased the tool life by 30% and 36% respectively over dry cutting at lower speed level. At higher cutting speed of 60 m/min and 80 m/min, cryogenically treated tools performed slightly better than untreated tools used in dry cutting. An improvement of approximately 8% has been observed with cryo-treated tools over dry condition at higher cutting speeds. The improvement observed in the tool life of cryo-treated inserts was mainly due to the changed microstructure. Rise in cutting zone temperature could be the possible reason of early tool failure under dry cutting condition. As compared to dry and treated tools, the better tool life has been observed with direct cryogenically cooled tools. At a cutting speed of 80 m/min, direct cooling has shown a tool life improvement of 90% and 77% as compared to dry and indirect cryogen methods respectively. Possibly a drastic reduction in cutting tool temperature because of the cryogen has resulted in such improved behaviour. (a) (c) (b) Figure 7: Flank wear at 40 m/ /min under all 3 conditions (a) Dry cutting condition (b) Indirect cryogenic condition (cryo-treated tool) (c) Direct cryogenic condition 108-5

6 Effect of Direct and Indirect Cryogen Application Methods on the Turning Forces, Tool Wear and Surface Finish of a Nickel Based Alloy (Nimonic 90) Flank wear(μm) Figure 7: Comparison of Flank wear v/s cutting speed under different cutting conditions 5 Conclusions Cutting force, surface roughness and tool wear have been measured under dry, indirect and direct cryogenic environment for machining of Nimonic 90 bars. The major conclusions that can be drawn from the experimental results are as follows: 1. Cryo-treated cutting tool inserts outperformed untreated inserts under dry cutting condition in terms of cutting force, surface finish and tool life at the selected cutting speed levels. 2. Direct cryogenic application has also emerged as a better cutting environment for the sustainable machining of Nimonic 90 alloy. 3. From surface finish point of view the cryo-treated method yielded better results as compared to dry and direct cryogenic condition. 4. Overall both direct and indirect cryogenic methods are found to be better than dry cutting approach. These methods are not only eco friendly but also save the cost of machining by increasing tool life. Therefore, using cryogenic approaches one can bring sustainability to the metal cutting process. Acknowledgement The Authors want to greatly appreciate the help rendered by Dr. Jagtar Singh (Associate Professor in Mechanical Engineering Department) of SLIET Longowal, for providing cryogenic treatment facility. References Cutting speed(m/min) Dry Cryo-treated Cryogenic Abele, E. and Frohlich, B. (2008), High speed milling of titanium alloy, APEM Journal, Vol. 3, pp Devillez, A., Schneider, F., Dominiak, S., Dudzinski, D. and Larrouquere, D. (2007), Cutting forces and wear in dry machining of Inconel 718 with coated carbide tools, Wear, Vol. 262, pp Dhananchezian, M. and Kumar, P. M. (2011), Cryogenic turning of the Ti 6Al 4V alloy with modified cutting tool inserts, Cryogenics, Vol. 51, pp Dixit, U. S., Sarma, D. K. and Davim, J. P. (2012), Dry Machining, Environmentally Friendly Machining, Vol. pp Ezilarasan, C., Senthil kumar, V. S. and Velayudham, A. (2013), An experimental analysis and measurement of process performances in machining of nimonic C-263 super alloy, Measurement, Vol. 46, pp Ezugwu, E. O., Bonney, J. and Olajire, K. A. (2004), The Effect of Coolant Concentration on the Machinability of Nickel-Base, Nimonic C-263, Alloy, Tribology Letters, Vol. 16, pp Ezugwu, E. O., Bonney, J. and Yamane, Y. (2003), An overview of the machinability of aeroengine alloys, Journal of Materials Processing Technology, Vol. 134, pp Gill, S. S., Singh, J., Singh, H. and Singh, R. (2011), Investigation on wear behaviour of cryogenically treated TiAlN coated tungsten carbide inserts in turning, International Journal of Machine Tools and Manufacture, Vol. 51, pp Jayal, A. D., Badurdeen, F., Dillon Jr, O. W. and Jawahir, I. S. (2010), Sustainable manufacturing: Modeling and optimization challenges at the product, process and system levels, CIRP Journal of Manufacturing Science and Technology, Vol. 2, pp Kaynak, Y. (2014), Evaluation of machining performance in cryogenic machining of Inconel 718 and comparison with dry and MQL machining, The International Journal of Advanced Manufacturing Technology, Vol. pp Lawal, S. A., Choudhury, I. A. and Nukman, Y. (2013), A critical assessment of lubrication techniques in machining processes: a case for minimum quantity lubrication using vegetable oil-based lubricant, Journal of Cleaner Production, Vol. 41, pp Marksberry, P. W. (2007), Micro-flood (MF) technology for sustainable manufacturing operations that are coolant less and occupationally friendly, Journal of Cleaner Production, Vol. 15, pp Meng, F., Tagashira, K., Azuma, R. and Sohma, H. (1994), Role of eta carbide precipitations in the wear resistance improvements of Fe 12Cr Mo V 1.4C tool steel by cryogenic treatment, ISIJ Int, Vol. 34, Mohan Lal, D., Renganarayanan, S. and Kalanidhi, A. (2001), Cryogenic treatment to augment wear resistance of tool and die steels, Cryogenics, Vol. 41, pp Sharma, V. S., Dogra, M. and Suri, N. M. (2009), Cooling techniques for improved productivity in turning, International Journal of Machine Tools and Manufacture, Vol. 49, pp Spur, G. and Lachmund, U. (1995), Trockenbearbeitung von graugub mit hohen schnittgeschwindingkeiten, ZWF, Vol. 90, pp