2nd International Iron and Steel Symposium (IISS’15), April 1-3, 2015, Karabuk, Turkey
CRYOGENIC COOLING-INDUCED MACHINING PERFORMANCE OF AISI 1045 STEEL
a
Yusuf Kaynaka Department of Mechanical Engineering, Faculty of Technology, Marmara University, Istanbul, Turkey E-mail:
[email protected]
Abstract This paper presents an analysis of experimental results on cutting forces, chip-tool contact length, chip breakability, and machining-induced layer of AISI 1045 steel from cryogenic cooling and comparison with the results from dry machining processes. The experimental study illustrated that cryogenic cooling helps to improve machining performance of AISI 1045 steel by reducing cutting force components, chip-tool contact length, and substantially increasing chip breakability. Findings also demonstrates that compared to dry machining, cryogenic machining has much larger effect on surface and subsurface microstructure of AISI 1045 steel. Keywords: Cryogenic machining performance
machining,
AISI
1045
steel,
1. Introduction The term cryogenics refers to the science of very low temperatures [1]. Liquid nitrogen is the most commonly used element in cryogenics and it is produced industrially by fractional distillation of liquid air and is often referred to by the abbreviation, LN2 [2]. Nitrogen melts at −210.01 °C and boils at −198.79 °C, it is the most abundant gas, composes about four-fifths (78.03%) by volume of the atmosphere. It is a colorless, odorless, tasteless and nontoxic gas [2]. Since it is environmentally-friendly, and nontoxic gas, it also contributes to process sustainability particularly in machining [3]. Cryogenic cooling as an emerging approach gains more interest by machining community. This is mainly due to the fact that it provides some substantial benefits from machining performance and surface integrity point of view in machining of various engineering materials [4].The main contribution of cryogenic cooling in terms of machining performance are reduced tool wears including flank wear, crater wear, notch wear,[5-7] reducing force components [6, 8]. According to the literature, the main reason of reduced tool wear resulting from cryogenic machining is substantially reduced cutting temperature [5]. It was also confirmed that some materials shows different thermomechanical response at cryogenic temperature than that of room temperature or elevated temperature that leads to reduced stress requirement to deform the some engineering materials, and consequently cutting force components in cryogenic machining reduces as compared to other cooling or lubricating conditions in machining processes [5]. Besides, as cryogenic cooling helps to reduce progression of tool wear with respect to time that also directly influences generated cutting force components [9]. On the other hands, by reducing surface © IISS’15, Karabük University, Karabük, Turkey
roughness, increasing compressive residual stress on the surface and subsurface of machined components, and by reducing grain size on the surface and subsurface of machined components cryogenic cooling helps to improve functional performance of machined components [4, 10, 11]. These desired outcomes in terms of surface integrity characteristics resulting from cryogenic machining are also relevant to the cooling aspect of cryogenic machining. Although the contribution of cryogenic cooling in machining of various materials in terms of machining performance have been investigated in detail, some materials’ group that have wide applications in various industries have not been studied adequately as yet. The main focus in open literature to understand the role of cryogenic cooling in machining process is high temperature alloys such as Inconel 718 [9, 12, 13], Ti-6Al-4V [12, 14-18], and other engineering materials. Although steels are one of these materials [19-21], but further investigation is particularly required to not only understand machining performance but also other measureable characteristics. In this study, the effects of cryogenic cooling on machining performance measures such as cutting force components, chip breakability, and surface integrity characteristics such as microstructure and machining-induced layer were presented and obtained results were compared to dry machining process.
2. Experimental Procedure Orthogonal cutting tests were conducted on a MAZAK QT10 Turning Center. Medium-carbon AISI 1045 steel disks were used as work materials. The mechanical properties of work materials used in this study are presented in Table 1. The diameters of the disks before and after machining are 152 mm and 76 mm, respectively and the width is 3 mm. TNMA 432 K21 (ISO TNMA 220408) tools with -6 degree rake angle were used in orthogonal cutting tests. It should be noted that in each experiment, new cutting tool was used. Tool holder was an MTCNN-124 NF6. During the machining tests, uncut chip thickness was kept constant as 0.1 mm, and cutting speeds were also allowed to vary at 160, 240, and 320 m/min. Table 1 Mechanical properties of AISI 1045 steel. UTS(MPa) 585
YS(MPa) 505
Elongation (%) 12
Hardness HBN) 200
In orthogonal cutting processes, two different cutting conditions were considered. One was dry cutting in which no cooling or lubricant was used. Another was cryogenic cooling condition. The cryogenic coolant was liquid nitrogen, applied under 1.5 MPa pressure. Application of
Kaynak, Y.
the cryogenic cooling during the orthogonal cutting operation is shown in Figure 1. Liquid nitrogen (LN2) was delivered to the cutting region through two nozzles each with a 4.78 mm diameter. One of them was placed to the rake face of cutting tool; while another was placed to the back of the tool holder to deliver liquid nitrogen towards to cutting tool tip as shown in Figure 1. Cutting tool
Applying LN2 from flank face and rake face
AISI 1045 steel
disc Figure 1. Experimental setup. Cutting force components were measured using a KISTLER 9121 three-component piezoelectric dynamometer. The edge radius of each cutting tool used in these series of experiments were measured through interferometry optical profiler ZYGO 3D - New View 7300, as shown in Figure 2. The edge radius of the tools varied between 42 to 44 µm.
3. Results and Discussions 4.1. Cutting Force Components Determining the role of cooling/lubrication on cutting force components in machining processes of any work materials can be helpful to understand the relationship between utilized cooling/lubrication and cutting force components. It is generally desired to reduce cutting force components in machining process of any materials particularly difficult-tocut materials. Although the focused work material in this study, AISI 1045, is not categorized as a difficult-to-cut material, it is necessary to observe the role of cryogenic cooling on force variation during cutting of this material. The measured cutting forces as a function of various cutting speeds under dry and cryogenic cooling conditions are shown in Figure 3. It can be seen from the figure that increased cutting speed leads to reduced force components but the percentage of reduction varies with cutting condition. Greatest reduction is observed in dry cutting considering both cutting force and radial forces. Variation of forces with cutting speed is much smaller in cryogenic machining. Besides, it should be noted that in all three cutting speed values, force requirement to cut this material in cryogenic machining is much smaller than dry cutting as shown in Figure 3. While the difference between dry and cryogenic is relatively small in terms of cutting forces over the various cutting speed, considering radial forces, the difference is much larger in between cryogenic machining and dry machining, as shown in Figure 3.
Figure 3. The effect of various cutting speeds on force components at dry and cryogenic cooling condition. Considering Merchant’s approach, it is possible to calculate coefficient of friction under dry and cryogenic machining conditions by using the following equation [22], (1) Figure 2. Measurement of cutting tool edge radius using ZYGO 3D-New View 7300 optical profiler. Where F is the friction force on the rake face, and N is the Nikon EPIPHOT 300 inverted Metallurgical Microscope with objective lenses ranging from 2.5X to 50X was used to measure tool-chip contact length. To examine the machined surface and subsurface damage after the dry and cryogenic machining processes, specimens were hotmounted in cross-section, ground and polished using conventional techniques, and etched using a 3% Nital solution. The microstructure of these specimens was examined by digital optical microscopy.
normal force, respectively. is the cutting force, and is the thrust force. µ is the coefficient of friction between cutting tool and chip. α is the rake angle of cutting. The calculated coefficient of friction for dry and cryogenic machining conditions at various cutting speeds are presented in Figure 4. Tool-chip friction in cryogenic machining is much smaller than (more than 20 percents) dry machining throughout the various cutting speeds. This can be attributed to the effects of cryogenic temperature
Kaynak, Y.
on deformation response of AISI 1045 steel. It should be also considered that liquid nitrogen might show lubrication effect during cutting and thus contact friction and thus force components gets smaller in cryogenic machining.
Coefficient of Friction, µ
Dry Machining Condition
Cryogenic Machining Condition
0.7 0.6 0.5 0.4 0.3 0.2 0.1
Producing such small chips in cryogenic machining is attributed to low cutting temperature. It was reported in the literature that this material’s failure strain is significantly affected from temperature, namely below approximately 180 °C, much smaller strain is required for this material to be failure [23]. Considering the delivering approach to liquid nitrogen implemented in this study much effectively cooling the work material and chip down was achieved. Delivering liquid nitrogen through flank face cools the work material and during cutting process, liquid nitrogen delivered from rake face cools the just newly produced chip, and consequently material becomes much brittle. İmmediate changed temperature of chip during deforming should be also taken into account as an important factor for producing such a small chips in cryogenic machining.
0 160
240
320
4.3. Chip-Tool Contact Length
Cutting Speed, (m/min)
Collected chips from dry and cryogenic machining conditions under various cutting speeds are presented in Figure 5. The large difference between dry and cryogenic machining in terms of chip breakability can be seen in Figure 5. Cryogenic cooling makes substantial contribution on chip breakability by generating small chips in machining process of AISI 1045 steel. However, obtained chips in dry machining are long and snarled chips, as illustrated in Figure 5. This form of chips is not desired as it deteriorates the machined surface and controlling cutting process becomes difficult. Dry
V= 240 m/min V= 360 m/min
Lc
V= 360 m/min
V= 160 m/min
Cryogenic
V= 160 m/min
4.1. Chip Breakability
Chip-tool contact length (Lc) with various cutting speeds in dry and cryogenic machining is presented in Figure 6. It is an obvious that increased cutting speed results in reduced chip-tool contact length in both machining conditions. Besides, cryogenic machining results in smaller contact length in comparison with the contact length measured resulting from dry machining. Dry Cryogenic
V= 240 m/min
Figure 4. Coefficient of friction under dry and cryogenic cooling conditions at various cutting speeds.
Figure 6. Optical microscopy photographs showing the effect of cutting speeds on tool-chip contact in dry and cryogenic machining.
10 cm
Figure 5. Produced chips in dry and cryogenic machining.
The quantitative comparison of tool-chip contact length measured from dry and cryogenic machining is presented in Figure 7. Cryogenic cooling reduces chip-tool contact length more than 10 percents. Reduced contact length with cryogenic machining can be attributed to its cooling effects. Cooled down just newly produced chips become much brittle and thus contact length gets smaller. The current study shows good agreement with previous studies [24] where reduced contact length due to cooling effects was observed. Reduced contact length as cutting speed
Kaynak, Y.
increases is mainly due to the changed frictional conditions between chip and cutting tool’s rake face. Chip-tool contact length, Lc , (mm)
Cryogenic Machining Condition
Dry Machining Condition
0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 160
240
320
Cutting Speed, (m/min)
Figure 7. Chip-tool contact length as a function of various cutting speeds in dry and cryogenic cutting process.
It should be noted that no grain refinement is observed under optical microscopy as seen in Figure 8. However, grain inclinations are observed in the sample machined under cryogenic cooling condition. This should be attributed to the cold deformation associated with cryogenic machining and resulting much larger mechanical loading on the surface and subsurface. However, in dry cutting process, temperature is much greater than cryogenic machining and thus grain inclination is not observed. It should be also noted that further investigation utilizing Scanning Electron Microscopy (SEM) and even Atomic Force Microscopy (AFM) analysis are needed to be identify and characterize microstructural changes on the machining-induced layer. But under optical microscopy, it is obvious that compared to dry machining, cryogenic machining has much greater impact on the surface and subsurface of machined AISI 1045 steel.
4. Conclusions
4.4. Cutting-induced Layer In addition to understanding the role of cryogenic cooling on machining performance of AISI 1045 steel, it is also required to examine the effects of cryogenic coolingassisted cutting on microstructural properties of this material. Figure 8 shows the microstructural images of machined AISI 1045 steel under dry and cryogenic cooling conditions. Machined surface
In this study, the effects of cryogenic cooling on machining performance measures such as cutting force components, chip breakability, chip-tool contact length, and machininginduced layer in orthogonal cutting process of AISI 1045 steel were presented. The obtained results from cryogenic cutting were compared with the results obtained from dry machining. Cryogenic machining helps to reduce cutting force components, coefficient of friction between tool and chip, and chip-tool contact length as compared to dry machining in machining of this particular material. Besides, cryogenic machining has much substantial effect on subsurface of machined AISI 1045 steel as compared to dry machining by leading to grain inclination in subsurface of machined parts. Based on the obtained results, cryogenic machining seems to be promising approach in machining process of steels to improve the machining performance.
Acknowledgments
Dry (V= 360 m/min) Inclined grains
Machined surface
Cryogenic (V= 360 m/min) Figure 8. Optical microscopy images of microstructure of AISI 1045 steel parts’ machined surface and subsurface.
Author thanks Prof. I.S. Jawahir and Institute for Sustainable Manufacturing (ISM) for providing all required equipment to conduct this study.
References [1] Shokrani, A., et al., State-of-the-art cryogenic machining and processing. International Journal of Computer Integrated Manufacturing. 1-33, 2013. [2] Yildiz, Y. and M. Nalbant, A review of cryogenic cooling in machining processes. International Journal of Machine Tools & Manufacture. Vol. 48, 9, 947-964, 2008. [3] Jayal, A., Badurdeen, F., Dillon, O.W., Jawahir, I.S., Sustainable manufacturing: Modeling and optimization challenges at the product, process and system levels. CIRP Journal of manufacturing science and technology. Vol. 2, 3, 144-152, 2010. [4] Kaynak, Y., T. Lu, and I.S. Jawahir, Cryogenic machining-induced surface integrity: A review and comparison with Dry,MQL, and Flood-cooled machining. Machining Science and Technology: An International Journal. Vol. 18, 2, 149-198, 2014.
Kaynak, Y.
[5] Kaynak, Y., Karaca, H.E., Noebe, R.D., Jawahir, I.S., Tool-wear analysis in cryogenic machining of NiTi shape memory alloys: A comparison of tool-wear performance with dry and MQL machining. Wear. Vol. 306, 51-63, 2013. [6] Bermingham, M., et al., New observations on tool life, cutting forces and chip morphology in cryogenic machining Ti-6Al-4V. International Journal of Machine Tools and Manufacture. Vol. 51, 6, 500-511, 2011. [7] Wang, Z. and K. Rajurkar, Cryogenic machining of hard-to-cut materials. Wear. Vol. 239, 2, 168-175, 2000. [8] Kaynak, Y., Karaca, H.E., Noebe, R.D., Jawahir, I.S., Analysis of Tool-wear and Cutting Force Components in Dry, Preheated, and Cryogenic Machining of NiTi Shape Memory Alloys. Procedia CIRP. Vol. 8, 498503, 2013. [9] Kaynak, Y., Evaluation of machining performance in cryogenic machining of Inconel 718 and comparison with dry and MQL machining. International Journal of Advance Manufacturing Technology. Vol. 72, 5-8, 919-933, 2014. [10] Jawahir, I.S., et al., Surface integrity in material removal processes: Recent advances. CIRP AnnalsManufacturing Technology. Vol. 60, 2, 603-626, 2011. [11] Jawahir, I.S., Y. Kaynak, and T. Lu, The Impact of Novel Material Processing Methods on Component Quality, Life and Performance. Procedia CIRP. Vol. 22, 33-44, 2014. [12] Wang, Z.Y. and K.P. Rajurkar, Cryogenic machining of hard-to-cut materials. Wear. Vol. 239, 2, 168-175, 2000. [13] Courbon, C., et al., Tribological behaviour of Ti6Al4V and Inconel 718 under dry and cryogenic conditions– application to the context of machining with carbide tools. Tribology International. 2013. [14] Hong, S.Y., Y.H. Ding, and W. Jeong, Friction and cutting forces in cryogenic machining of Ti-6Al-4V. International Journal of Machine Tools & Manufacture. Vol. 41, 15, 2271-2285, 2001. [15] Hong, S.Y., I. Markus, and W. Jeong, New cooling approach and tool life improvement in cryogenic machining of titanium alloy Ti-6Al-4V. International Journal of Machine Tools & Manufacture. Vol, 41, 15, 2245-2260, 2001. [16] Bermingham, M.J., et al., New observations on tool life, cutting forces and chip morphology in cryogenic machining Ti-6Al-4V. International Journal of Machine Tools & Manufacture. Vol. 51, 6, 500-511, 2011. [17] Yasa, E., S. Pilatin, and O. Çolak, Overview of cryogenic cooling in machining of TI alloys and a case study. Journal of Production Engineering. Vol. 15, 2, 1-9, 2012. [18] Strano, M., et al., Comparison of Ti6Al4V machining forces and tool life for cryogenic versus conventional cooling. Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture. 2013. [19] Dhar, N.R., S. Paul, and A.B. Chattopadhyay, The influence of cryogenic cooling on tool wear, dimensional accuracy and surface finish in turning AISI 1040 and E4340C steels. Wear. Vol. 249, 10-11, 932-942, 2001. [20] Paul, S., N.R. Dhar, and A.B. Chattopadhyay, Beneficial effects of cryogenic cooling over dry and wet machining on tool wear and surface finish in
[21]
[22]
[23]
[24]
turning AISI 1060 steel. Journal of Materials Processing Technology. Vol. 116, 1, 44-48, 2001. Paul, S. and A. Chattopadhyay, The effect of cryogenic cooling on grinding forces. International Journal of Machine Tools and Manufacture. Vol. 36, 1, 63-72, 1996. Merchant, M.E., Mechanics of the metal cutting process. II. Plasticity conditions in orthogonal cutting. Journal of applied physics. Vol. 16, 6, 318-324, 1945. Autenrieth, H., Schulze, V., Herzig, N., Meyer, L.W., Ductile failure model for the description of AISI 1045 behavior under different loading conditions, Mech. Time-Depend Mater. Vol. 13, 215-231, 2009. Tasdelen, B., H. Thordenberg, and D. Olofsson, An experimental investigation on contact length during minimum quantity lubrication (MQL) machining. Journal of materials processing technology. Vol. 203, 1, 221-231, 2008.
