CNC Machine Tools Market Size to Grow by USD 28.18 Bn, Advantages Over

Conventional Machines to Drive Growth - Technavio - cnc lathe insert chart

In conclusion, this study aimed to investigate the impact of surface texturing and the application of CNT-enriched nanofluid lubrication on the cutting performance of cemented carbide cutting inserts during the turning of Al 7075 alloy. The results clearly demonstrated that the use of CNT-enriched nanofluid has significant potential in reducing cutting force and surface roughness and minimizing the size of the built-up edge.

Indexable ceramics are another option. Jack Kohler, applications engineer for Greenleaf Corp., Saegertown, Pa., said the cost of ceramic cutting tools falls somewhere between PCBN and carbide, and offers equivalent or better performance in some applications. “Ceramic does quite well in the 50-HRC to 65-HRC range,” he said. “Cutting speeds would be comparable to PCBN. Figure around 700 sfm on a 55-HRC A-2 tool steel, for example, with only slightly lower tool life.”

Rawat, S. S., Harsha, A., Das, S. & Deepak, A. P. Effect of CuO and ZnO nano-additives on the tribological performance of paraffin oil–based lithium grease. Tribology Transactions 63, 90–100 (2020).

The relationship between the main cutting force, denoted as Fc, in the turning process and the total cutting force FR can be expressed by the Eq. (2)39,40:

When drilling, a force that is directed axially—along the direction of machining. The magnitude of an axial force rises with the drill’s diameter and the chisel edge’s width. Axial force is also known as thrust. When turning and boring, the term “feed force” is commonly used instead of “axial force.” See cutting force.

Gupta, M. K. et al. Measurement and analysis of machining induced tribological characteristics in dual jet minimum quantity lubrication assisted turning of duplex stainless steel. Measurement 187, 110353 (2022).

Kip Hanson is a contributing editor for Cutting Tool Engineering magazine. Contact him by phone at (520) 548-7328 or via e-mail at kip@kahmco.net.

Kohler said he’s seeing increased use of ceramic in high-temperature alloys, such as Inconel 718 and Hastelloy, although he warns shops to steer clear of titanium, as this presents a fire risk because titanium chips can burst into flames at the high cutting speeds common with ceramics. Regardless of the metal being cut, ceramic inserts usually come with a slight hone, land or combination of the two at the cutting edge to prevent chipping and increase strength.

Srivyas, P. & Charoo, M. A Review on Tribological Characterization of Lubricants with Nano Additives for Automotive Applications. Tribology in Industry 40 (2018).

Some of the methods employed to address the challenges associated with cutting fluids include the development of new tool materials, optimization of cutting fluid application through techniques like minimum quantity lubrication machining8, cryogenic machining9, and hybrid machining10, as well as the modification of traditional cutting fluid properties using nanofluids11, and the modification of cutting tool surfaces through approaches like surface texturing12, 13.

Nanofluids refer to a mixture of solid particles with nanometer-scale dimensions suspended in a conventional fluid, forming a solid–liquid composite25. Recently, nanofluids have gained prominence in various engineering applications, such as heat transfer systems and machining processes, owing to their exceptional heat transfer capabilities and tribological properties25. A review of the available literature reveals that the utilization of nanofluids in metal cutting processes enhances heat transfer, resulting in decreased cutting forces, cutting temperature, power consumption, and tool wear26.

The application of surface texturing on cutting tools is acknowledged as a technique to improve the effectiveness of dry machining practices. This approach aims to enhance the tribological conditions between mating surfaces14. By introducing surface textures on cutting tools, the friction coefficient can be reduced through increased lubrication capacity and a decrease in the length of tool-chip contact. Researchers have successfully implemented various types of textures on cutting tool surfaces in drilling15, milling16, turning17, and thread turning18,19,20.

In this equation, As represents the shear plane area, Ac denotes uncut chip cross-section area,  τs signifies the shear strength of the workpiece material, and φ represents the shear angle.

In Eq. (4), Aw represents the contact area between the tool and chip, τc denotes the shear strength of the tool-chip interface, l represents the contact length between the tool and chip, and aw represents the chip width. As illustrated in Fig. 5, the effective contact length of the tool chip can be determined as follows19,39:

Some might wonder about the difference between hard turning the inside of a part (boring) and its outside. Most agree that boring is generally more difficult than OD turning, regardless of material hardness. That’s because boring bars are less rigid than other turning tools, creating problems with chatter and tool deflection. Because quarters are often tight in a bored hole, chip evacuation can be a challenge, leading to coolant starvation and workpiece galling. In addition, achieving sufficient surface speeds becomes increasingly difficult for small part features, such as bores, and PCBN and ceramic inserts require high cutting speeds.

Enlarging a hole that already has been drilled or cored. Generally, it is an operation of truing the previously drilled hole with a single-point, lathe-type tool. Boring is essentially internal turning, in that usually a single-point cutting tool forms the internal shape. Some tools are available with two cutting edges to balance cutting forces.

Workpiece is held in a chuck, mounted on a face plate or secured between centers and rotated while a cutting tool, normally a single-point tool, is fed into it along its periphery or across its end or face. Takes the form of straight turning (cutting along the periphery of the workpiece); taper turning (creating a taper); step turning (turning different-size diameters on the same work); chamfering (beveling an edge or shoulder); facing (cutting on an end); turning threads (usually external but can be internal); roughing (high-volume metal removal); and finishing (final light cuts). Performed on lathes, turning centers, chucking machines, automatic screw machines and similar machines.

Substances having metallic properties and being composed of two or more chemical elements of which at least one is a metal.

“A significant benefit of changing from grinding to hard turning is the reduction in capital investment,” Stewart said. “Grinding, however, does have its place and is, in some instances, a faster process when multiple features are ground simultaneously—a situation that is ideal for high-volume applications. Thus, in a high-volume environment, when there are only one or two features that require finishing, hard turning might be the better process for overall capital investment.

Cutting tool material consisting of polycrystalline cubic boron nitride with a metallic or ceramic binder. PCBN is available either as a tip brazed to a carbide insert carrier or as a solid insert. Primarily used for cutting hardened ferrous alloys.

Prabhu, S. & Vinayagam, B. Nano surface generation of grinding process using carbon nano tubes. Sadhana 35, 747–760 (2010).

In a study conducted by Xie et al.21, a range of micro-grooves with depths ranging from 7 to 149 μm and aspect ratios between 0.14 and 0.5 were fabricated on the rake face of cutting tools using micro-grinding techniques. The results demonstrated that as the depth of the micro-grooves decreased, the cutting temperature decreased and the shear angle increased. Furthermore, their findings indicated that for improved cutting tool performance, it was necessary for the width of the grooves to be narrower than the chip width. In another study conducted by Fang and Obikawa22, five different types of micro-textures were created on the flank face of carbide inserts. These textures had depths/heights ranging from 10 to 20 μm and widths of 50 μm. The purpose of the micro-textures was to enhance the cooling effectiveness of high-pressure jet coolant during the turning of Inconel 718 alloy. The findings of the study demonstrated that the use of micro-textured tools resulted in reduced flank and crater wear compared to traditional tools. The tool with a micro-pit array with a depth of 10 μm exhibited the best performance, reducing flank wear by 50% compared to the plain tool. Dry turning experiments were performed by Liu et al.23 on green alumina using tools with textured flank faces, and the wear resistance was investigated. The micro-groove dimensions were set at a width of 35 μm, a depth of 20 μm, and a spacing of 200 μm between the grooves. The results revealed a significant reduction in flank face wear when using textured tools compared to conventional tools. Furthermore, it was observed that the micro-grooves on the flank face aligned parallel to the main cutting edge, exhibited superior resistance to flank wear. The researchers concluded that the mechanism responsible for the reduction in flank face wear was the derivative-cutting phenomenon occurring on the flank face. In a separate investigation conducted by Khani et al.18, 20 the effectiveness of textured tools filled with various solid lubricants was evaluated during the threading of Al 7075 alloy. The textured tools featured microholes with a depth, diameter, and pitch distance of 13, 70, and 200 μm, respectively. The study revealed that the use of a microhole textured tool filled with CNT (carbon nanotube) powder enhanced the performance of the thread-cutting process. The results indicated a reduction in cutting forces, built-up edge formation, and tool-chip contact length.

Baskar, N., V. H. & Sankaran, R. Performance of cutting tool with cross-chevron surface texture filled with green synthesized aluminium oxide nanoparticles. Sci. Rep. 9, 1–9 (2019)

Niketh, S. & Samuel, G. L. Surface texturing for tribology enhancement and its application on drill tool for the sustainable machining of titanium alloy. J. Clean. Prod. 167, 253–270. https://doi.org/10.1016/j.jclepro.2017.08.178 (2017).

Tangential velocity on the surface of the tool or workpiece at the cutting interface. The formula for cutting speed (sfm) is tool diameter 5 0.26 5 spindle speed (rpm). The formula for feed per tooth (fpt) is table feed (ipm)/number of flutes/spindle speed (rpm). The formula for spindle speed (rpm) is cutting speed (sfm) 5 3.82/tool diameter. The formula for table feed (ipm) is feed per tooth (ftp) 5 number of tool flutes 5 spindle speed (rpm).

Machining operation in which material is removed from the workpiece by a powered abrasive wheel, stone, belt, paste, sheet, compound, slurry, etc. Takes various forms: surface grinding (creates flat and/or squared surfaces); cylindrical grinding (for external cylindrical and tapered shapes, fillets, undercuts, etc.); centerless grinding; chamfering; thread and form grinding; tool and cutter grinding; offhand grinding; lapping and polishing (grinding with extremely fine grits to create ultrasmooth surfaces); honing; and disc grinding.

Sayuti, M., Sarhan, A. A. & Salem, F. Novel uses of SiO2 nano-lubrication system in hard turning process of hardened steel AISI4140 for less tool wear, surface roughness and oil consumption. J. Clean. Prod. 67, 265–276 (2014).

“A cutting speed of 600 sfm is a good starting point for PCBN,” he said. “We recommend a double-sided round insert where possible, carefully rotating it as the tool wears. Depending on depth of cut, this might provide 10 to 20 uses per side. Some shops are scared off by the relatively high price of these inserts, however. In these cases, we’d likely suggest a PCBN-tipped insert —or even one of our new superhard carbide grades.”

Angle between the side-cutting edge and the projected side of the tool shank or holder, which leads the cutting tool into the workpiece.

Elhami, S., Razfar, M., Farahnakian, M. & Rasti, A. Application of GONNS to predict constrained optimum surface roughness in face milling of high-silicon austenitic stainless steel. Int. J. Adv. Manuf. Technol. 66, 975–986 (2013).

Chetan, Ghosh, S. & Rao, P. V. Application of sustainable techniques in metal cutting for enhanced machinability: A review. J. Clean. Prod. 100, 17–34. https://doi.org/10.1016/j.jclepro.2015.03.039 (2015).

Xie, J., Luo, M. J., Wu, K. K., Yang, L. F. & Li, D. H. Experimental study on cutting temperature and cutting force in dry turning of titanium alloy using a non-coated micro-grooved tool. Int. J. Mach. Tools Manuf. 73, 25–36. https://doi.org/10.1016/j.ijmachtools.2013.05.006 (2013).

Conradi, M., Drnovšek, A. & Gregorčič, P. Wettability and friction control of a stainless steel surface by combining nanosecond laser texturing and adsorption of superhydrophobic nanosilica particles. Sci. Rep. 8, 1–9 (2018).

Figure 10 displays the surface roughness (Ra) of machined workpieces using T-Pe textured tools under various lubrication conditions. As previously mentioned, surface texturing on the rake face had an insignificant impact on surface finish. However, when the T-Pe textured tool was utilized with CNT-enriched nanofluid lubrication, an improvement in surface finish was observed. The chart illustrates that Ra was enhanced by 15% and 19% when employing 1% and 3% concentration nanofluids, respectively, compared to dry machining with the T-Pe textured tool. This improvement can be attributed to the stable cutting conditions achieved during the turning process with the T-Pe tool under nanofluid lubrication. Figure 11 exhibits dynamic force profiles for different tools. It is evident from the figure that the fluctuation of cutting force was reduced when using the T-Pe tool with CNT nanofluid lubrication compared to dry conditions. This reduction in fluctuation resulted in a more stable cutting environment, leading to a superior surface finish.

Specifically, when comparing the non-textured tool to the application of the T-Pe tool under dry cutting conditions, a decrease of up to 14% in the average main cutting force was observed. Among the investigated textures, the T-Pe texture exhibited superior performance in terms of surface roughness. The implementation of surface textures led to a reduction in friction force, resulting in a decreased height of the built-up edge (BUE). In the absence of lubrication, the height of the BUE was reduced by 19%, 36%, 43%, and 50% for the T-C, T-Pa, T-Ch, and T-Pe tools respectively, in comparison to the non-textured tool.

The cutting tools in the experimental tests were cemented carbide CNMA120408 inserts. To engrave microtextures, an Nd: YAG laser from Jinan Xinchu Laser Inc. was employed, operating at a wavelength of 1064 nm, a repetition rate of 20 kHz, and a pulse duration of 10 ns. In order to generate microtextures on the rake face of the tools, the cutting insert was fixed on a computer-controlled translation table, and the laser beam was focused on the rake face perpendicularly and scanned to generate microgrooves. After the laser micro-machining, ultrasonic cleaning was applied to clean the inserts. Following the laser micro-machining, ultrasonic cleaning was performed to ensure the cleanliness of the inserts. In this research, a Fiber laser with a maximum power output of 30 W was utilized for the purpose of texturing the tools. Figure 1 provides a visual representation of the tools in both their plain and textured states, as observed through SEM images. The dimensions of the textures were determined based on a thorough review of relevant literature sources22,23, as well as a series of preliminary experiments. Previous research conducted by other scientists has demonstrated that micro-grooves with depths ranging from 10 to 100 μm, widths between 20 and 50 μm, and spacing of 100–300 μm have yielded favorable outcomes in terms of cutting performance. Hence, the selected dimensions for the microgrooves were as follows: a width of 50 μm, a spacing of 150 μm, and a depth of 10 μm. The tool configurations used in this study included linear textures perpendicular to the chip flow direction, linear textures parallel to the chip flow direction, circular textures, and linear cross-hatch textures, referred to as T-Pe, T-Pa, T-Ch, and T-C, respectively. The non-textured plane tool was denoted as T0. Figure 2 provides a depiction of the cross-section profile of a single microgroove generated on the rake face of the carbide insert. The tool with linear textures perpendicular to the chip flow direction, linear textures parallel to the chip flow direction, circular textures, and linear cross-hatch textures were nominated T-Pe, T-Pa, T-Ch, and T-C, respectively, while, the non-textured plane tool was named T0. Figure 2 shows the cross-section profile of an individual microgroove created on the rake face of the carbide insert.

Sivaiah, P., Ajay Kumar, G. V., Singh, M. M. & Kumar, H. Effect of novel hybrid texture tool on turning process performance in MQL machining of Inconel 718 superalloy. Mater. Manuf. Process. 35, 61–71. https://doi.org/10.1080/10426914.2019.1697444 (2020).

Condition whereby excessive friction between high spots results in localized welding with subsequent spalling and further roughening of the rubbing surface(s) of one or both of two mating parts.

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“Hard turning offers lower machine investment, reduced setup and tool inventory, fewer operations, faster cycle times and greater process flexibility,” he said. “Unfortunately, many shops can use it only for semifinishing of parts prior to grinding, primarily because the majority of CNC lathes are unable to achieve the extreme tolerances and form accuracy produced by cylindrical grinding machines.”

For future studies, it would be beneficial to investigate the online application of ultrasonic probe homogenizer during the turning process to enhance the stability of the nanofluids. This could provide more control and consistency in the lubrication process, leading to further improvements in cutting performance.

Horn added to its Supermini line for boring workpieces as hard as 66 HRC without the use of PCBN. Image courtesy Horn USA Inc., Nico Sauermann.

Pradhan, S., Das, S. R., Jena, P. C. & Dhupal, D. Investigations on surface integrity in hard turning of functionally graded specimen under nano fluid assisted minimum quantity lubrication. Adv. Mater. Process. Technol. 8, 1714–1729. https://doi.org/10.1080/2374068X.2021.1948706 (2022).

Ceramics should be run dry in hardened materials, Kohler said. He recommends Greenleaf’s WG-600 silicon-nitride grade—a CVD-coated version of the company’s whisker-reinforced WG-300—as a good starting point for most hardened steels, as well as its new XSYTIN-1, a phase-toughened ceramic grade designed specifically for high-performance roughing and interrupted cuts.

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As depicted in Fig. 4, the utilization of textured tools led to a slight reduction in the main cutting force. Among the various textured tools, the T-Pe tool with linear micro-grooves perpendicular to the chip flow direction exhibited the lowest cutting force. The results indicate that, on average, the main cutting force of the T-Pe tool was reduced by 7%, 10%, and 14% at cutting speeds of 33 m/min, 47 m/min, and 66 m/min, respectively, compared to the non-textured tool. The performance of the T-Pe tool in reducing cutting forces was observed to be superior to that of the T-Pa, T-CH, and T-C tools. This can be attributed to the fact that in the T-Pa, T-CH, and T-C tools, there was a higher degree of plastic deformation in the chip material compared to the T-Pe tool, which led to greater adhesion of the work material on the rake face, resulting in higher cutting forces.

Recent advances in turning with textured cutting tools: A review Journal of Cleaner Production 137701–715 https://doi.org/10.1016/j.jclepro.2016.07.138 (2016).

Opinions vary on the definition of hard turning. Some industry experts say it’s the single-edge cutting of hardened steels from 58 to 68 HRC, while others suggest hard turning begins at 45 HRC and includes hardened irons and superalloys. All, however, agree it presents difficulties but is quite manageable provided the right cutting tools, machine and process parameters are used.

In Fig. 6, the surface roughness (Ra) of workpieces machined using various textured and non-textured tools is presented. The chart demonstrates that the surface roughness of the machined workpieces improves as the cutting speed increases. This improvement can be attributed to the reduction in built-up edge size and the increased stability of the machining conditions at higher cutting speeds. As a result, the surface finish is enhanced 40.

The frictional force between the chip and the rake face during the turning process can be described by Eqs. (4) and (5)39,40:

The solution, experts agree, is to apply the shortest tool possible relative to tool diameter, preferably no greater than a 4:1 length-to-diameter (L:D) ratio. Boring bars should be on center or, in some cases, a few tenths (0.0003") above center to allow for deflection. And use a boring insert with a 0° lead angle whenever possible, so cutting forces are directed opposite the direction of cut.

Khani, S. Experimental study on the effect of CNT-enriched nanofluid lubrication on the performance of textured cutting tool in the turning of aluminum 7075 alloy. Sci Rep 13, 22584 (2023). https://doi.org/10.1038/s41598-023-48796-w

Hasin, F. et al. Impact of nanoparticles on vegetable oil as a cutting fluid with fractional ramped analysis. Sci. Rep. 13, 7140. https://doi.org/10.1038/s41598-023-34344-z (2023).

In material removal processes, traditional cutting fluids have been employed to lubricate the interfaces between the tool and chip as well as the tool and workpiece, dissipate heat generated within the cutting zone, and facilitate the removal of chips from the machining area. The utilization of cutting fluids has resulted in enhanced productivity in manufacturing. However, the costs associated with cutting fluids and the health risks associated with exposure to cutting fluid mist have prompted researchers to explore approaches aimed at reducing or eliminating the reliance on these fluids. Some of these methods include the utilization of textured tools and the incorporation of nanofluids.

In the Eq. (6), the contact length is represented by l, the effective contact length is denoted as le, wg signifies the width of the microgrooves, pg represents the spacing of the microgrooves, and n indicates the number of grooves in the contact area. According to Eq. (6), the effective contact length decreases with the generation of microgrooves on the rake face. Consequently, the contact area (Aw) and friction force (Ff) decrease. On the other hand, there is a correlation between the main cutting force and the friction force, which can be expressed as follows39,40:

Furthermore, the micro-grooves positioned perpendicular to the chip flow direction serve as chip breakers, facilitating the chip's swift and effortless detachment from the rake face. Consequently, the tool-chip contact area is diminished. According to Eq. (4), a decrease in the contact area results in a reduction of the frictional force, thereby leading to a decrease in the total cutting force. As a result, the micro-grooves oriented perpendicular to the chip flow direction exhibited a smaller tool-chip contact area compared to other tools, resulting in a greater reduction in cutting force.

Tatiana et al.24 conducted a study to assess the performance of straight and zig–zag patterns created on the rake face of carbide tools using ultrashort laser pulses during the turning process of martensitic stainless steel. The research aimed to compare the performance of these patterns in terms of cutting forces, power consumption, and workpiece cylindricity deviation. The findings indicated that the straight pattern demonstrated superior performance compared to the zig–zag pattern across the evaluated parameters.

The decrease in the main cutting force when using micro-textured tools can be elucidated as follows:

Despite these capabilities, some parts are not suitable for hard turning. Bearing seals, for example, often call for ground surfaces, which eliminate the possibility of fluid escaping through what is essentially a microscopic thread-wide channel produced by single-point turning. And the “white zone” created when material softens and subsequently rehardens during turning (and grinding to a lesser extent) may cause premature component failure. Sheehy said both of these situations can be minimized with the right tooling and a few process adjustments.

The remarkable properties of aluminum alloys, such as their impressive strength and stiffness-to-weight ratio, high corrosion resistance, excellent electrical and heat conductivity, and favorable formability, make them widely utilized in industries such as machinery manufacturing, aerospace, marine, and automobile1. While aluminum alloys possess favorable cutting properties attributed to their low strength, they tend to exhibit adhesion between the tool and chip on the rake face during machining operations2. Traditionally, cutting fluids have been employed to mitigate friction and adhesion in the machining process. However, the use of cutting fluids poses risks to machine operators, leads to damage to machine tool rails, and contributes to environmental pollution. In light of these concerns, there is a growing demand to minimize or eliminate the use of cutting fluids and transition towards dry machining methods that align with environmentally friendly manufacturing processes. To address these concerns, optimization studies have been conducted3, 4 and various sustainable approaches have been adopted in manufacturing to promote greener and cleaner production and mitigate the limitations associated with dry machining5,6,7.

Kamel, B. M., El-Kashif, E., Hoziefa, W., Shiba, M. S. & Elshalakany, A. B. The effect of MWCNTs/GNs hybrid addition on the tribological and rheological properties of lubricating engine oil. J. Dispersion Science and Technology 42, 1811–1819 (2021).

Graham said the company’s TH carbide can successfully turn materials up to 65 HRC and, unlike PCBN, is available in a range of geometries and chipbreaker configurations. And carbide is less prone to breakage in some applications—a casehardened shaft, for example, where it’s possible that softer material might be encountered, which would quickly dissolve the cutting edge and spell near-certain doom for the PCBN insert.

Danish, M. et al. Environmental, technological and economical aspects of cryogenic assisted hard machining operation of inconel 718: A step towards green manufacturing. J. Clean. Prod. 337, 130483 (2022).

Rao, S. N., Satyanarayana, B. & Venkatasubbaiah, K. Experimental estimation of tool wear and cutting temperatures in MQL using cutting fluids with CNT inclusion. Int. J. Eng. Sci. Technol. 3, 2928–2932 (2011).

Sharmin, I., Gafur, M. A. & Dhar, N. R. Preparation and evaluation of a stable CNT-water based nano cutting fluid for machining hard-to-cut material. SN Appl. Sci. 2, 1–18 (2020).

Wang, X. et al. Nanofluids application in machining: a comprehensive review. Int. J. Adv. Manuf. Technol., 1–52 (2023).

Haddadzade, M., Razfar, M. & Farahnakian, M. Integrating process planning and scheduling for prismatic parts regard to due date. Int. J. Industrial and Manuf. Engineering 3, 248–251 (2009).

Turning machine capable of sawing, milling, grinding, gear-cutting, drilling, reaming, boring, threading, facing, chamfering, grooving, knurling, spinning, parting, necking, taper-cutting, and cam- and eccentric-cutting, as well as step- and straight-turning. Comes in a variety of forms, ranging from manual to semiautomatic to fully automatic, with major types being engine lathes, turning and contouring lathes, turret lathes and numerical-control lathes. The engine lathe consists of a headstock and spindle, tailstock, bed, carriage (complete with apron) and cross slides. Features include gear- (speed) and feed-selector levers, toolpost, compound rest, lead screw and reversing lead screw, threading dial and rapid-traverse lever. Special lathe types include through-the-spindle, camshaft and crankshaft, brake drum and rotor, spinning and gun-barrel machines. Toolroom and bench lathes are used for precision work; the former for tool-and-die work and similar tasks, the latter for small workpieces (instruments, watches), normally without a power feed. Models are typically designated according to their “swing,” or the largest-diameter workpiece that can be rotated; bed length, or the distance between centers; and horsepower generated. See turning machine.

Khani, S., Shahabi Haghighi, S., Razfar, M. R. & Farahnakian, M. Improvement of thread turning process using micro-hole textured solid-lubricant embedded tools. Proc. IMechE Part B J. Eng. Manuf. 235, 1727–1738. https://doi.org/10.1177/09544054211019929 (2021).

“Hardinge Super-Precision lathes offer 0.1μm programmable resolution,” he said. “Axial errors are mapped and compensated for electronically. All mating surfaces within the machine are hand-scraped, the linear guide ways and ballscrews are oversized, and the base of the machine is filled with composite polymer for vibration damping. Not only does this produce the accuracy and rigidity needed to replace many grinding operations, it also increases tool life during hard turning by up to 30 percent.”

Distance between the bottom of the cut and the uncut surface of the workpiece, measured in a direction at right angles to the machined surface of the workpiece.

“An often-overlooked component of ID work is accounting for the axial, radial and tangential cutting forces produced when turning,” said Mike Csizmar, regional sales manager at Horn USA Inc., Franklin, Tenn. “This is also true on external operations, but due to the increased L:D ratios associated with boring, these forces become more pronounced, affecting dimensional qualities. If you have a choice, axial (Z-axis) cutting force is preferred. A rule of thumb is that DOC should be equal to or greater than the tool nose radius, thus generating greater axial force. This provides the ability to control chatter, diameter and taper in a more efficient manner, and allows you to get the most out of your cutting tool.”

Some machine builders, Hardinge included, offer turning and grinding machines, making them trusted advisers on which process is most suitable for a given part. Another is EMAG LLC USA, Farmington Hills, Mich., which also offers machines that grind and hard-turn. The company’s director of sales, Kirk Stewart, agreed that hard turning offers many opportunities for improvement in productivity and part quality, and proper machine design is critical to success.

Liu, Y. et al. Wear resistance of carbide tools with textured flank-face in dry cutting of green alumina ceramics. Wear 372–373, 91–103. https://doi.org/10.1016/j.wear.2016.12.001 (2017).

Xing, Y., Deng, J., Wang, X., Ehmann, K. & Cao, J. Experimental assessment of laser textured cutting tools in dry cutting of aluminum alloys. J. Manuf. Sci. Eng. 138, 071006. https://doi.org/10.1115/1.4032263 (2016).

Fang, Z. & Obikawa, T. Cooling performance of micro-texture at the tool flank face under high pressure jet coolant assistance. Precis. Eng. 49, 41–51. https://doi.org/10.1016/j.precisioneng.2017.01.008 (2017).

Let’s start with cutting tools. Don Graham, manager of education and technical services for Seco Tools LLC, Troy, Mich., said that if the setup is fairly rigid and the correct cutting parameters can be achieved, indexable PCBN inserts are generally the best bet for hard turning.

According to Eq. (3), a decrease in shear strength (τs) and an increase in shear angle (φ) result in a reduction in the main cutting force.

This paper investigates the impact of surface texturing and the use of CNT-enriched nanofluid lubrication on the cutting performance of cemented carbide cutting tools during the turning process of aluminum 7075 alloy. Aluminum 7075 is widely utilized in various industries due to its exceptional properties, including high corrosion resistance, a favorable strength-to-weight ratio, and good formability. However, this alloy tends to excessively adhere to the cutting tool at the tool-chip interface, which negatively affects the machining process. Previous research has proposed different solutions, but the current study focuses on implementing the two most effective approaches to minimize adhesion phenomena. The first approach involves modifying the contact area by creating a pattern on the tool's rake face, while the second approach utilizes CNT-enriched nanofluid lubrication to reduce friction in the tool-chip interface. Various types of surface textures were fabricated on the rake face, and experimental tests were conducted to identify the most effective texture. The findings showed that using textured tools with micro-grooves perpendicular to the chip flow direction, with CNT-enriched nanofluid lubrication, resulted in significant reductions in main cutting force, built-up edge, and surface finish. The decreases were up to 32%, 37%, and 19%, respectively, compared to dry turning conditions.

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Turning with ceramic inserts is usually done dry. Here the toolholder is mounted face up, driving cutting forces down into the machine’s load-bearing surfaces. Image courtesy Greenleaf.

Figure 7 illustrates the size of the built-up edge (BUE) for different tools. It is evident that the textured tools exhibit a lower BUE compared to the non-textured tools. The height of the BUE for the non-textured tool (T0) was measured as 567 μm, whereas it was reduced to 460 μm, 363 μm, 326 μm, and 284 μm for the T-C, T-Pa, T-Ch, and T-Pe tools, respectively. This reduction corresponds to a decrease of 19%, 36%, 43%, and 50%, respectively. Therefore, the use of micro-textured tools results in a reduction in the adhesion of work material on the rake face. As discussed earlier, surface texturing of the rake face reduces the friction force between the tool and chip, leading to decreased heat generation and subsequently minimizing the adhesion of work material on the rake face.

Khanali, M., Farahnakian, M., Elhami, S. & Khani, S. Tribological properties of vibro-mechanical texturing during face turning processes. Int. J. Lightweight Mater. Manuf. 5, 91–101 (2022).

Cutting tool materials based on aluminum oxide and silicon nitride. Ceramic tools can withstand higher cutting speeds than cemented carbide tools when machining hardened steels, cast irons and high-temperature alloys.

where β is the friction angle, and α is the rake angle. By substituting Eq. (1) into Eq. (2), we obtain the main cutting force relation expressed in Eq. (3)39,40:

Hardness is a measure of the resistance of a material to surface indentation or abrasion. There is no absolute scale for hardness. In order to express hardness quantitatively, each type of test has its own scale, which defines hardness. Indentation hardness obtained through static methods is measured by Brinell, Rockwell, Vickers and Knoop tests. Hardness without indentation is measured by a dynamic method, known as the Scleroscope test.

Condition of vibration involving the machine, workpiece and cutting tool. Once this condition arises, it is often self-sustaining until the problem is corrected. Chatter can be identified when lines or grooves appear at regular intervals in the workpiece. These lines or grooves are caused by the teeth of the cutter as they vibrate in and out of the workpiece and their spacing depends on the frequency of vibration.

The main limitation of the study is the current delivery method of the nanofluid to the cutting zone, which is in the splash mode. We acknowledge that better results could be achieved by designing a more effective nozzle that ensures the efficient delivery of the fluid directly to the cutting area.

Therefore, it can be inferred that the main cutting force, Fc, decreases when the friction force, Ff, is reduced.

Ramón-Raygoza, E. et al. Development of nanolubricant based on impregnated multilayer graphene for automotive applications: Analysis of tribological properties. Powder Technology 302, 363–371 (2016).

Groove or other tool geometry that breaks chips into small fragments as they come off the workpiece. Designed to prevent chips from becoming so long that they are difficult to control, catch in turning parts and cause safety problems.

“Alternatively, when the machine architecture allows, a combined configuration of turning and grinding can become very attractive for mid-volume requirements, an architecture that EMAG machines inherently provide.”

The results indicate that the fabrication of microtextures on the rake face of cemented carbide tools does not have a substantial impact on the surface roughness.

Grinding operation in which the workpiece is rotated around a fixed axis while the grinding wheel is fed into the outside surface in controlled relation to the axis of rotation. The workpiece is usually cylindrical, but it may be tapered or curvilinear in profile. See centerless grinding; grinding.

Tom Sheehy, applications engineering manager for Hardinge Inc., Elmira N.Y., said hard turning can be performed on virtually any lathe and provides many benefits.

Research has been conducted on cutting fluids based on carbon nanotubes (CNTs) to examine their impact on machining performance. For instance, Prabhu27 investigated the grinding of AISI D2 tool steel using dry conditions, conventional cutting fluid, and a nanofluid containing CNTs as a lubricant. The experimental results demonstrated that the utilization of a CNT-enriched nanofluid led to a significant improvement in surface finish, achieving a nano-level quality as opposed to a micro-level finish. In a separate investigation by the same author28, the addition of carbon nanotube particles to SAE20W40 oil was found to enhance the heat-absorbing capacity of the lubricant. The research findings demonstrated that the utilization of a cutting fluid based on carbon nanotubes resulted in improved surface finish and reduced occurrence of micro-cracks during the grinding process of D3 tool steel. Experimental research was conducted by Rao et al.29 to assess the cutting temperature and tool wear in the turning process. The results of the research indicated that the inclusion of CNT particles resulted in a reduction in nodal temperatures, leading to improved surface finish and increased tool life. The experimental results also indicated that the addition of CNT nanoparticles to conventional cutting fluid increased its thermal conductivity. Furthermore, it was observed that the thermal conductivity of the nanofluid increased with rising temperatures. These properties collectively highlighted the superior performance of CNT-based nanofluids in comparison to conventional coolants30. The application of multi-walled carbon nanotubes with minimum quantity lubrication (MQL) in hard turning of AISI H13 steel showcases the effectiveness and productivity of using nanofluid-MQL in conjunction with carbide tools for machining hot work tool steel in industrial applications31, 32.

Figure 8 illustrates the impact of using CNT-enriched nanofluid lubrication on the main cutting force. The experimental results revealed that compared to dry cutting with the T-Pe textured tool, the main cutting force decreased by up to 21% and 32% when utilizing 1% and 3% CNT nanofluid, respectively. Consequently, an increase in the concentration of nanoparticles improved the lubrication capability of the nanofluid. Figure 9 schematically demonstrates that carbon nanotubes dispersed in the nanofluid penetrate between the tool and chip, functioning as nano-bearings, as discussed in several articles 41,42,43,44. This alteration in the relative motion between the tool and chip, from sliding to rolling, accounts for the reduction in friction and cutting force. In essence, the decrease in friction and cutting force can be attributed to the nano-bearing effect, which is based on the rolling motion of carbon nanotubes.

CNC grinders are routinely called upon to produce part roundness of 1μm (0.00004"), maintain diametral tolerances of ±2.5μm (0.0001") and impart surface finishes as fine as 8 rms or finer. Sheehy said the only way a CNC lathe can compete in this arena is if it is designed from the ground up for hard turning.

Khani, S., Haghighi, S. S., Razfar, M. R. & Farahnakian, M. Optimization of dimensional accuracy in threading process using solid-lubricant embedded textured tools. Mater. Manuf. Process. https://doi.org/10.1080/10426914.2021.1926492 (2021).

The performance of the cutting process was enhanced by using the T-Pe tool with linear microgrooves arranged perpendicular to the direction of chip flow, as indicated by the outcomes of dry turning tests comparing various textured tools and a conventional tool. To assess the impact of nanofluid lubrication on cutting performance, experimental turning tests were conducted using the chosen tool while employing nanofluid lubrication. The subsequent results are provided below.

Khani, S., Razfar, M. R., Haghighi, S. S. & Farahnakian, M. Optimization of microtextured tools parameters in thread turning process of aluminum 7075 aerospace alloy. Mater. Manuf. Process. https://doi.org/10.1080/10426914.2020.1772485 (2020).

Hard turning is used to finish a variety of parts, such as bearing journals and races, brake drums and rotors, cylinder bore liners, gears, pinions and splines—or to semifinish those same components prior to grinding. Properly applied, it achieves an accuracy best measured in microns and, in many cases, is faster and more cost-effective than cylindrical grinding.

Derakhshan, M. M. & Akhavan-Behabadi, M. Mixed convection of MWCNT–heat transfer oil nanofluid inside inclined plain and microfin tubes under laminar assisted flow. Int. J. Therm. Sci. 99, 1–8 (2016).

Figure 12 presents the impact of surface texturing and nanofluid lubrication on the size of the built-up edge (BUE). The results demonstrate a significant reduction in BUE size when CNT-enriched nanofluid coolant is used during the turning process with the T-Pe textured cutting tool. As previously mentioned, the addition of CNT nanoparticles to the base coolant enhances the tribological performance of mating surfaces. Consequently, the friction coefficient between the chip and tool decreases, leading to a reduction in friction force at the rake face. This decrease in friction force results in reduced heat generation, which helps mitigate the adhesion of work material to the rake face.

Mbambo, M. C. et al. Thermal conductivity enhancement in gold decorated graphene nanosheets in ethylene glycol based nanofluid. Sci. Rep. 10, 14730. https://doi.org/10.1038/s41598-020-71740-1 (2020).

Dimension that defines the exterior diameter of a cylindrical or round part. See ID, inner diameter.

Engagement of a tool’s cutting edge with a workpiece generates a cutting force. Such a cutting force combines tangential, feed and radial forces, which can be measured by a dynamometer. Of the three cutting force components, tangential force is the greatest. Tangential force generates torque and accounts for more than 95 percent of the machining power. See dynamometer.

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Khajehzadeh, M., Moradpour, J. & Razfar, M. R. Influence of nanolubricant particles’ size on flank wear in hard turning. Mater. Manuf. Process. 34, 494–501 (2019).

In summary, the findings of this study demonstrate that the creation of appropriate micro textures on the rake face of the turning tool can significantly enhance the machining performance of Al 7075 alloy. Moreover, the use of CNT nanofluid further enhances the performance of the turning process by reducing cutting force, minimizing the size of the built-up edge, and improving surface roughness. These results highlight the potential of surface texturing and the application of CNT-enriched nanofluid lubrication as effective strategies for optimizing cutting processes and achieving improved machining outcomes.

Prabhu, S. & Vinayagam, B. K. AFM investigation in grinding process with nanofluids using Taguchi analysis. Int. J. Adv. Manuf. Technol. 60, 149–160 (2012).

The turning experiments were carried out using a TB50NR Lathe equipped with cemented carbide CNMA120408 inserts. Workpieces made of cold-rolled Al 7075 alloy bars with a diameter of 30 mm and a length of 450 mm were employed. The cutting tests were conducted at three cutting speeds (Vc), 33 m/min, 47 m/min, and 66 m/min, with a fixed depth of cut (ap) of 0.75 mm and a feed rate (af) of 0.14 mm/rev. To measure cutting forces, a KISTLER Company turning dynamometer 9272-type with three components was employed. A piezoelectric dynamometer was mounted on the tool post and a tool holder was attached to it. As the cutting operation took place, mechanical forces exerted on the cutting tool were converted into electrical signals by the piezoelectric sensor and then transferred to the charge amplifier. After amplification, the signals were transmitted to the data acquisition system and subsequently transferred to a PC for analysis using the Dyno-Ware software. In every experiment, the PCE-RT Roughness Tester was utilized to measure the surface roughness (Ra). To accomplish this, three specific areas on the machined surface were selected for measurement. The measurements were taken in these regions, and the average of the three measurements was recorded as the Ra value. The tracing velocity and the sampling length were consistently maintained at 0.5 mm/s and 0.8 mm, respectively. The height of the built-up edge was measured using an optical Dino-Lite AM-413ZT microscope with DinoCapture 2.0 software. Tool images were captured, and measurements were taken using calibration tools for precise evaluation of the built-up edge size. SEM analysis was employed to examine the texture patterns on the rake face. The experimental setup for the cutting tests is depicted in Fig. 3.

Santana, T. D., de Rossi, W., Barbosa, P. A. & Bertolete, M. Performance of cutting-tool patterns textured via ultrashort laser pulses in the turning of martensitic stainless steel under dry and lubricated conditions. Proc. IMechE Part B J. Eng. Manuf. https://doi.org/10.1177/09544054231166461 (2023).

The total cutting force, denoted as FR, is determined during the turning process using Eq. (1) 39,40:

Microprocessor-based controller dedicated to a machine tool that permits the creation or modification of parts. Programmed numerical control activates the machine’s servos and spindle drives and controls the various machining operations. See DNC, direct numerical control; NC, numerical control.

To create the nanofluid, the process involved introducing CNT particles into an emulsion-type cutting fluid (AMIX: combined ratio with water of 5%). The concentration of CNT particles in the base fluid was set to 1% and 3% based on previous studies on nanofluid applications in machining processes26, 29, 33,34,35,36. Nanofluids were prepared by dispersing a specific amount of CNTs in the base fluid by using an ultrasonic processor for 6 h generating pulses of 400 W at 24 kHz. This method guarantees the stability of the nanofluid for 24 h37. Table 1 provides an overview of the properties of the nanoparticles.

Tough, difficult-to-machine alloys; includes Hastelloy, Inconel and Monel. Many are nickel-base metals.

Mahapatra, S., Das, A., Jena, P. C. & Das, S. R. Turning of hardened AISI H13 steel with recently developed S3P-AlTiSiN coated carbide tool using MWCNT mixed nanofluid under minimum quantity lubrication. Proc. Inst. Mech. Eng. Part C J. Mech. Eng. Sci. 237, 843–864. https://doi.org/10.1177/09544062221126357 (2022).

Secures a cutting tool during a machining operation. Basic types include block, cartridge, chuck, collet, fixed, modular, quick-change and rotating.

Several research studies have focused on investigating the impact of surface texturing on the cutting performance of cemented carbide cutting tools. Also, there are several research works that investigated CNT-nanofluid application in machining processes26, however, there is a limited number of studies that have explored the combined effect of nanofluid lubrication and surface texturing. Consequently, there exists a research gap in this particular domain. In order to enhance the cutting performance of cemented carbide turning tools, this study proposes the implementation of micro-textured tools, along with CNT-enriched nanofluid lubrication, for the turning process of Aluminum 7075 alloy. Laser micromachining was employed to engrave four different types of textures, including linear and circular arrays, on the rake face of the carbide cutting inserts. Turning tests were subsequently conducted on Aluminum 7075 bars, utilizing both non-textured and textured tools, to determine the optimal texture. Subsequently, a comparative analysis was conducted by employing the selected textured tool under dry conditions and varying concentrations of CNT-enriched nanofluid lubrication.

Figure 4 illustrates the main cutting force observed at various cutting speeds for both non-textured and textured tools. Each bar in the chart represents the average cutting force measured during the turning of Al 7075 alloy. The chart clearly demonstrates that cutting speed exerts a significant influence on the main cutting force. It was observed that as the cutting speed increased, the main cutting force decreased. This phenomenon can be attributed to the thermal softening of the material at higher cutting speeds, resulting in a reduction in shear strength within the shear zone 38. Additionally, the shear angle tends to increase with cutting speed. Consequently, the main cutting force can be effectively reduced by increasing the cutting speed during the cutting process, as further discussed below:

In the case of the cross-hatch pattern, significant chip deformation occurs as the chip traverses the rake face of the tool. This leads to the bending of the chip towards the micro-grooves. Consequently, the actual contact area between the rake face and chip back increases, diminishing the effectiveness of micro-texturing in reducing forces.

Khani, S., Farahnakian, M. & Razfar, M. R. Experimental study on hybrid cryogenic and plasma-enhanced turning of 17–4PH stainless steel. Mater. Manuf. Process. 30, 868–874. https://doi.org/10.1080/10426914.2014.984200 (2015).

Furthermore, the experimental findings using the T-Pe textured tool revealed that increasing the concentration of CNT nanoparticles in the base cutting fluid within the range of 1–3% resulted in significant reductions in the main cutting force (Fc) by approximately 21% and 32%, reductions in built-up edge (BUE) sizes of approximately 22% and 37%, and surface roughness reductions of approximately 15% and 19% respectively.

The experimental findings indicate that increasing the nanoparticle concentration from 1 to 3% leads to a greater decrease in BUE size compared to dry cutting with the T-Pe textured tool. Specifically, the decrease in BUE size increased from 22 to 37%. This can be attributed to the influence of nanoparticle concentration on the thermal characteristics of nanofluids. The thermal conductivity (k) and convection coefficient (h) of nanofluids increases with higher nanoparticle concentrations 33,34. Hence, additional heat can be effectively transferred away from the cutting zone, thereby reducing adhesive wear.

Sharma, A. K., Tiwari, A. K. & Dixit, A. R. Progress of nanofluid application in machining: A review. Mater. Manuf. Process. 30, 813–828 (2015).

Initially, carbide is also less expensive, although Graham pointed out that cost per edge favors PCBN. “PCBN might cost 10 to 25 times more than carbide, but you’re also going to get 50 to 100 times the tool life. Certainly, for high production, PCBN is the way to go.”

Khajehzadeh, M., Moradpour, J. & Razfar, M. R. Influence of nanofluids application on contact length during hard turning. Mater. Manuf. Process. 34, 30–38 (2019).

Fluid that reduces temperature buildup at the tool/workpiece interface during machining. Normally takes the form of a liquid such as soluble or chemical mixtures (semisynthetic, synthetic) but can be pressurized air or other gas. Because of water’s ability to absorb great quantities of heat, it is widely used as a coolant and vehicle for various cutting compounds, with the water-to-compound ratio varying with the machining task. See cutting fluid; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.

Kharanzhevskiy, E. V., Ipatov, A. G., Makarov, A. V. & Gil’mutdinov, F. Z. Towards eliminating friction and wear in plain bearings operating without lubrication. Sci. Rep. 13, 17362 (2023).

Arumugaprabu, V. et al. Performance of surface-textured end-mill insert on AISI 1045 steel. Mater. Manuf. Process. 34, 18–29. https://doi.org/10.1080/10426914.2018.1512119 (2018).