A review of developments towards dry and high speed machining of Inconel 718 alloy

International Journal of Machine Tools & Manufacture 44 (2004) 439–456 www.elsevier.com/locate/ijmactool A review of developments towards dry and high speed machining of Inconel 718 alloy ` D. Dudzinski a,∗, A. Devillez a, A. Moufki a, D. Larrouquere b, V. Zerrouki b, J. Vigneau b a Laboratoire de Physique et Mecanique des Materiaux, UMR CNRS 7554, ISGMP, Universite de Metz, Ile du Saulcy, 57045 Metz Cedex 1, ´ ´ ´ France b SNECMA Moteurs, Route Nationale 7, BP 81, 91003 Evry Cedex, France Received 21 March 2003; received in revised form 9 June 2003; accepted 10 June 2003 Abstract The increasing attention to the environmental and health impacts of industry activities by governmental regulation and by the growing awareness in society is forcing manufacturers to reduce the use of lubricants. In the machining of aeronautical materials, classified as difficult-to-machine materials, the consumption of cooling lubricant during the machining operations is very important. The associated costs of coolant acquisition, use, disposal and washing the machined components are significant, up to four times the cost of consumable tooling used in the cutting operations. To reduce the costs of production and to make the processes environmentally safe, the goal of the aeronautical manufacturers is to move toward dry cutting by eliminating or minimising cutting fluids. This goal can be achieved by a clear understanding of the cutting fluid function in machining operations, in particular in high speed cutting, and by the development and the use of new materials for tools and coatings. High speed cutting is another important aspect of advanced manufacturing technology introduced to achieve high productivity and to save machining cost. The combination of high speed cutting and dry cutting for difficult-to-cut aerospace materials is the growing challenge to deal with the economic, environmental and health aspects of machining. In this paper, attention is focussed on Inconel 718 and recent work and advances concerning machining of this material are presented. In addition, some solutions to reduce the use of coolants are explored, and different coating techniques to enable a move towards dry machining are examined.  2003 Elsevier Ltd. All rights reserved. Keywords: Inconel 718; High speed cutting; Dry cutting; Cemented tools; Ceramic tools; Coatings; Minimum lubrication application; Surface integrity 1. Introduction The development of governmental pollution-preventing initiatives and increasing consumer focus on environmentally conscious products has placed increased pressure on industries to minimise their waste streams. In this way, the ISO 14000 international environmental management system standards have been developed to help industries to manage better the impact of their activities on the environment. Particularly concerned is the metal-working sector which includes automotive and aerospace industries. Attention is being directed to the role of cutting fluids in machining, machine tool energy efficiency and the impact of process wastes on the environment. The ADEME, French Agency for Environment and Energy Management, supports a project with the goal of improving the machining processes of difficult-to-cut materials for the aerospace industry, in order to move towards dry cutting operations that are more friendly for environment and health, and in the same way, to reduce energy consumption. The advantages of dry machining are: non-pollution of atmosphere or of water which reduces the danger to health, in particular, skin and respiratory damage, no residue of lubricant on machined components ∗ Corresponding author. E-mail address: [email protected] (D. Dudzinski). 0890-6955/$ - see front matter  2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0890-6955(03)00159-7 13]. are reported and recent innovations of tool coatings for dry machining are discussed. Cutting fluids are employed to remove heat from the workpiece. a rather small part of heat flows to the tool. Machinability of Inconel 718 Nickel-based superalloys are widely employed in the aerospace industry. the latest research carried out on the use of uncoated and coated carbide tools under wet and dry conditions is summarised. Residual stresses have consequences on the mechanical behaviour. Finally. They are known to be among the most difficult-to-cut materials. Residual stresses are also produced by plastic deformation without heat. due to their high-temperature strength and high corrosion resistance. the cutting forces attain high values. the use of cutting fluid leads to an increase of tool life by the reduction of cutting forces (lubrication effect) and temperatures in the tool (cooling effect). when ceramic inserts are employed [1]. The heat generated usually alters the microstructure of the alloy and induces residual stresses. welding and adhesion of nickel alloys onto the cutting tool frequently occur during machining causing severe notching as well as alteration of the tool rake face due to the consequent pull-out of the tool materials. this paper is a general review of the recent developments in the machining of this material and an exploration of the possible ways to dry cutting. They are used for machining nickel-based alloys at higher cutting speeds and some of their results are given. Then. However. Residual stresses are also responsible for the dimensional instability phenomenon of the parts which can lead to important difficulties during assembly [12. That is why high speed machining and dry machining are often associated. High speed machining leads to lower cutting forces. In addition. as well as large microhardness variations [9]. interesting alternatives to conventional flooding coolant supply that are minimum quantity lubrication technologies. the fixtures and the machine tool (cooling effect). in particular in the hot sections of gas turbine engines. it is well known that the lubrication in the cutting zone is not evident and not really effective. Attention is focussed on the Inconel 718 family in the following paragraphs. they are very strain rate sensitive and readily work harden. the tool. / International Journal of Machine Tools & Manufacture 44 (2004) 439–456 which reduces or eliminates cleaning costs and associated energy consumption. causing further tool wear. At high cutting speeds. As a consequence. nickel-based superalloys have high chemical affinity for many tool materials leading to diffusion wear. in particular. these effects are not evident in high speed machining. the highly abrasive carbide particles contained in the microstructure cause abrasive wear. higher removal rates and therefore to lower energy consumption. Heat and deformation generate cracks and microstructural changes. it is necessary to understand well the mechanisms that contribute to tool wear and to workpiece surface integrity when working with Inconel 718. Before introducing dry machining. the highest temperature is obtained at the tool–chip interface which leads to diffusion wear and cutting edge degradation. The heat generation and the plastic deformation induced during machining affect the machined surface. The project is concerned with these two aspects of machining to realise the ecological importance and high performance machining of hard-to-cut aerospace materials. Hence. However. In the first part. the characteristics of Inconel 718 that are responsible for its poor machinability are reviewed and the associated problems are listed. especially on the fatigue life of the workpieces [10. In the first step. no residue of lubricant on evacuated chips which reduces disposal costs and the associated energy consumption. The properties responsible for the poor machinability of the nickel-based superalloys. the dry machining of the Inconel 718 alloy used by Snecma-Moteurs will be studied. Dudzinski et al. in particular for the aerospace components. due to their high strength. Generally. they need to meet functional service requirements. The constant demand to increase productivity and quality has led to the development of ceramic tools.8]. to examine the move towards dry cutting of Inconel 718. The difficulty of machining resolves itself into two basic problems: short tool life and severe surface abuse of machined workpiece [3. The energy consumed in performing a machining operation is mainly converted into heat. it is important to summarise the functions of cutting fluids and to search how the effects of cutting fluids may be substituted. excite the machine tool system and may generate vibrations which compromise the surface quality.11].440 D. The heat generated is mainly dissipated in the chip and in the workpiece. The other important functions of the cutting fluids are to flush away the chips from the cutting zone (flushing effect) and to provide corrosive resistance to the machined component. attention is focussed on the parameters influencing the surface quality during mach- ining Inconel 718. When surfaces are produced. the poor thermal conductivity leads to high cutting temperatures up to 1200 °C at the rake face [7]. especially of Inconel 718. are [2–6]: a major part of their strength is maintained during machining due to their high-temperature properties. Extreme care must be taken therefore to ensure the surface integ- . 2. The feed rate and the depth of cut were 0. the PVD–TiN coated . good thermal shock properties. high hot hardness. workpiece surface roughness and cutting force components have been considered as the performance indicators for tool life. Rahman et al. This diffusion of the work elements into the cutting tool may be explained by the very high cutting temperature (about 1000 °C) during the experiments. Two types of inserts were used: K type substrate. Turning. the wear was more irregular. while drilling has received little attention. However. Most of the major parameters including the choice of tool and coating materials. respectively. must be controlled in order to achieve adequate tool lives and surface integrity of the machined surface [9. [15] performed extensive research on the end milling of Inconel 718. 0. Over the years. They studied the effect of the side cutting edge angle (SCEA). Most published work on the machining of nickel-based alloys deal with turning. see for example Fig. Fig.4 mm/rev) and three cutting speeds (30. In addition. the sticking layer also could be found. The tool life was investigated in the full immersion and half immersion (both in up cut and down cut). then with milling. but comparatively. cutting speed and feed rate. tool life increases as the SCEA increases from 5 to 45°. This improves heat removal from the cutting edge. For nickel-based alloys. In the following. they found for the cutting speed V = 35 m / min. the heat generated during the cutting process is distributed over a greater length of the cutting edge lS. with the increasing demand to achieve fast material removal and better surface quality. and multi Al2O3 CVD coated cemented carbide. Machining Inconel 718 with carbide tools Cemented carbide tools are still largely used for machining the nickel-based superalloys. Dry cutting resulted in the best tool performance. the flank wear length was larger and the groove was deeper. From the cutting tests. machining method. Built-upedge (BUE) was formed at a cutting speed of 35 m/min with chipping of the cutting edge. that there were no change of tool elements but Ni and Fe diffused into the cutting tool for the two cemented carbide tools. the depth of cut was fixed to 2 mm. they concluded that full immersion increased tool life in comparison with half immersion and down cut gave better performance than the up cut end milling. cutting speed. 3. it was found that a tool life range of 5–10 min can be obtained at cutting speed of 19. lubrication.0 mm. in dry turning of Inconel 718.32 m/min. Dudzinski et al. the concept of high speed machining refers to speeds over 50 m/min approximately. For these increasing values of the SCEA. Turning experiments were conducted under wet conditions. For the two inserts. adequate chemical stability at elevated temperature. 3. coated cemented carbides have been developed. In order to achieve higher cutting speeds. tool geometry.09 mm/tooth and axial depth of cut of 1. Throughout the experiments. the machining performances with air assistance and micropulverisation were compared with those of dry cutting. CrN and TiN coatings) for milling operations (contouring) at a high cutting speed of 200 m/min. milling and drilling are common operations carried out in the manufacture of jet engine mounts and blades. high strength and toughness. Flank wear of the inserts. The cutting speed was either 35 or 15 m/min. depth of cut. Moreover. Alaudin et al. they observed a sticking layer very close to the cutting edge.5 mm. especially Inconel 718. When P20 carbide was used. TiN PVD coated cemented carbide. / International Journal of Machine Tools & Manufacture 44 (2004) 439–456 441 rity of the component during machining. distributes the cutting forces over a larger portion of the cutting edge. high speed machining was introduced and the use of the cemented carbide tools has become more problematic. reduces tool notching and substantially improves tool life.1.3 and 0. the performance of coated and uncoated carbide tools in machining Inconel 718 is presented. a feed rate of 0. Derrien and Vigneau [16] tested uncoated and coated carbide (K20 grade. 2.D. on the tool life for three feeds (0. Liao and Shiue [14] analysed the wear mechanism of two cemented carbide tools: K20 and P20 grades. In addition. 40 and 50 m/min). the use of carbides for cutting tools has been established. 1.5 mm.04 mm/tooth and a depth of cut of 0. while turning and drilling are the predominant machining operations in the manufacture of disks for gas turbines.11]. feed rate.10 mm/rev and 1. [4] presented a work which discusses the machinability of Inconel 718 subjected to various machining parameters including tool geometry. Cutting tools for machining Inconel 718 The requirements for any cutting tool material used for machining nickel-based alloys should include [3]: good wear resistance. the temperature of the tool–chip interface related to the undeformed chip thickness t1 certainly decreases. feed of 0.2. On the wear surface of the K20 carbide. They showed that TiN coated carbide has the lowest wear. Using the electron probe microanalyser (EPMA) to analyse the concentrations of tool elements and work elements beneath the rake face. They carried out tests under dry conditions with uncoated tungsten carbide inserts (K20 grade). The Al2O3 CVD coated cemented carbide exhibited more severe notch wear at all three angles tested and might not be suitable for cutting Inconel 718. / International Journal of Machine Tools & Manufacture 44 (2004) 439–456 Fig.15 mm/rev and 1. only the average temperature of the contact area can be measured. [17] conducted dry turning experiments to identify the tool wear mechanism clearly when a commonly used coated cemented carbide tool cuts Inconel 718. respectively. carbide insert exhibited excellent resistance to depth of cut notch wear at the approach angles of 15° and 45°. During interrupted cutting. Furthermore. The end of life for all the three coated tools was dictated by maximum flank wear or nose wear. Inconel 718 adhered to the rake face of the major cutting edge and the adhering material became a stable BUE protecting the face.5 mm. Effect of SCEA on tool life for a cutting speed of 30 m/min and different feed rates using the Al2O3 CVD cemented coated tool. TiN/TiC multilayered coating). It has been verified that gradually reducing the undeformed chip thickness at the end of cutting will help to reduce the separation of BUE and. With this method. 100 and 150 m/min. This type of insert performed best at the speed of 30 m/min and the feed rate of 0. and later. The hard particles contained in the Inconel 718 alloy were certainly responsible for abrasive wear of the coating film on the flank face. the feed rate and the depth of cut were maintained constant and equal to 0. 3.4 mm/rev at 45° approach angle.t1 is the undeformed chip thickness. Wear advances as the number of repetitions increases. For this reason. At the lower cutting speed of 46 m/min. Coatings increase wear resistance and may reduce cutting forces and temperatures at the tool edge and thereby indirectly affect the deformation and fracture behaviour of the tool. the work material adhered to the surface of the worn area of the flank and tool material was repeatedly being removed. when the wear reaches the cemented carbide material. In addition. the rate of wear increases. At both speeds. Jindal et al.2 mm/rev and the depth of cut was 0. During continuous cutting at a speed of 30 m/min. material adhering to the rake face (BUE) is removed.442 D. f is the feed. Dudzinski et al. SCEA or approach angle. The maximum flank wear was about 0. lS is the length of the engaged cutting edge. The tool was a square tip made of coated cemented (P20. TiAlN has a significantly higher hardness than TiCN or TiN above 750 °C which will translate into improved resistance to abrasive wear. at this temperature. Fig. The cutting speeds were 30. the flank wear progresses faster at a cutting speed of 100 m/min. From Rahman et al. TiAlN and TiCN coated tools performed significantly better than tools with TiN coatings. Also.2 mm/rev with an approach angle of 45°. the TiAlN tools exhibit lower nose and crater wear than the TiCN and TiN coated tools. The cutting temperature at 30 m/min was 990 °K and at 100 m/min it was 1320 °K.TiCN and TiAlN coatings on cemented carbide substrate (WC—6 wt% Co alloy) in the turning of Inconel 718 with coolant. 1. [18] studied the relative merits of PVD– TiN. The inserts performed satisfactorily even at the highest speed of 50 m/min and at the highest feed rate of 0. w is the width of cut. This is due to the high-temperature causing diffusion and surface oxidation at high speeds. Fig. Itakura et al. The temperature was measured using the tool–workpiece thermocouple method. The tested cutting speeds were 46 and 76 m/min. The coating film on the rake face wears off. Continuous and interrupted experiments were conducted. causing the coating film to flake. [4]. the feed rate was 0. In the same way. Since the substrate material was the same for all the coated tools. there was almost no rake wear but only flank wear.25 mm. an excellent performance of the TiAlN coated tools was noted. as a result. the observed differences in tool lives and wear behaviour were attributed to the coatings. will reduce the separation of coating film from the rake face. stable adhesion of the BUE is no longer possible and wear advances on both rake and flank faces.15 mm after a cutting time of 5 min. it exhibits good hightemperature chemical stability. This high-temperature . 2. leading to higher oxidation resistance. . 4. depth of cut = 1. Depth-of-cut notching was also observed.52 mm. 3. from Jindal et al.15 mm / rev. Finally.125 mm/ rev. Finally. Coated flaking was observed early in the cut at the depth of cut region for all the coated tools tested. Dudzinski et al. They performed Inconel 718 turning tests with a coolant and different PVD coated carbide cutting tools at 61 and 76 m/min. depth of cut = 1. TiCN and TiAlN coated inserts in turning Inconel 718 (feed = 0. The extensive BUE and coating peeling seen with CrN coated tools at a cutting of 90 m/min suggests Fig. the TiAlN coating imparts excellent crater resistance. Fig. 6. [18]. Fig. the longest one occurred with TiAlN coated tools at 90 m/min with a workpiece angle of 45°. TiAlN has the lowest thermal conductivity among the three coatings tested. A three factor. [19]. Prengel et al. Performance of TiAlN–monolayer and TiAlN–multilayer coated carbide tools in turning Inconel 718. oxygen and nitrogen during the machining operation. [2]. feed = 0. full factorial cutting experiment design at two levels was outlined with the workpiece inclined at 45° and 60° from the horizontal. [2] detailed experimental work using TiAlN and CrN coated tungsten carbide (K10 grade carbide) end mills for dry machining up to 150 m/min rectangular blocks of Inconel 718.15 mm / rev. Sharman et al.1 mm/tooth. TiAlN coated tools performed better than CrN coated tools due to their higher hardness and oxidation resistance. 5. The notching was heavily influenced by burr formation on the uncut diameter. Fig. Configuration of ball end milling tests performed by Sharman et al. The main failure mode in Inconel 718 machining was abrasive nose wear accompanied by plastic deformation. All the tests resulted in low tool lives. Axial and radial depths of cut: 0. depth of cut = 1.27 mm. feed = 0. 4. / International Journal of Machine Tools & Manufacture 44 (2004) 439–456 443 Fig. however. As a result. aluminium. from Prengel et al. The two tested cutting conditions were: cutting speed = 61 m / min. (b) maximum flank wear as a function of time (cutting speed = 46 m /min). stability is a result of the tendency of TiAlN coating to form a protective outermost layer of Al2O3 and an intermediate layer comprising titanium. feed rate: 0. cutting speed = 76. cutting speed = 46 and 76 m / min).D. 5. One large notch located towards the high speed position together with a smaller notch at the leading edge position was generally evident. [19] confirmed the conclusion of the previous work but with a multilayer coated tool.2 m / min. This should result in lower tool tip temperatures as much of the heat generated during machining would be carried away by the chip.5 and 1 mm. Fig. (a) Tool lives of PVD–TiN. The TiAlN-multilayer showed some advantages over the TiAlN-monolayer and TiN/TiCN/TiAlN-multilayer coating particularly at a higher speed of 76 m/min.5 mm. 0. The cutting speeds were 25. this was probably due to better chip sliding and a reduced cutting temperature with this coating.14 mm per tooth. Dudzinski et al. [2]. this failure mode is mainly due to the hardening of the material during machining. The BUE is not always stable and is sometimes repeatedly removed with tool material leading to important notching at the depth of cut and at the tool nose and coating Fig. .and multilayer coated and uncoated inserts. This phenomenon appeared for uncoated or CrN/TiN coated tool and was attenuated with TiN/AlTiN nanolayer coated insert. The work of Jawaid et al. 0. TiN/AlTiN nanolayer coating presents a better resistance to welding. Abrasive wear is mainly due to carbide particles in Inconel 718. 9. cutting speed. [20] studied TiN/AlTiN and CrN/TiN nanolayer coatings deposited on a K20 cemented carbide and its machining performance was tested by turning Inconel 718 alloy. Lubricated tests were carried out.1%. The performance of the nanolayer coated tools was compared with that of classical mono. depending on the cutting conditions. According to the authors. 9. 0. results of the machining tests.4% VC) tool performed better than the PVD–TiN layer coated tools at the lowest cutting speed of 25 m/min and for both feed rates in terms of tool life and of volume of metal removed. The high hardness of the TiN/AlTiN nanolayer coating (Hardness HV0. 7. 7. Work material adheres to the cutting edge to form a BUE. 6. Flank wear developed either on the main cutting edge or on the nose. As summary. that CrN has a higher chemical affinity to Inconel 718 than TiAlN. Premature removal of the coating layers from the tool–chip contact zone hindered the overall performance of the PVD–TiN layer coated tools at a cutting speed of 25 m/min. respectively. [5] is concentrated on the wear behaviour of two different grades of single layer PVD–TiN coated and uncoated tungsten carbide insert when face milling Inconel 718 for various cutting conditions. An emulsion with 6% concentration was used as a coolant. 50. In addition. The notching is influenced by burr formation on the uncut diameter.14 mm per tooth. / International Journal of Machine Tools & Manufacture 44 (2004) 439–456 Fig. From Jawaid et al. [5]. Average flank wear when face milling Inconel 718. C was an uncoated tungsten carbide insert (WC 90. controlled the tool life at all cutting conditions for all the three types of inserts. The uncoated carbide (WC 90. (b) at feed rate 0. Dry ball end milling of Inconel 718 with coated carbide tools. High-temperature resistance of AlTiN included in this coating allows better resistance to the BUE phenomenon than CrN/TiN nanolayer coating.5 mm.5% Co.05 = 3900) provides better abrasion resistance than classical multilayer and monolayer structures. it appears from previous studies that adhesion and abrasion are dominant when machining Inconel 718. The depth of cut was 1 mm and the feed rates were 0. A and B were two different grades of single layer PVD–TiN layer coated tools.4% VC).1%. The depth-of-cut notch is considered as a determinant for tool life when machining Inconel 718. feed and depth of cut were 40 m/min.444 D. Table 1. 75 and 100 m/min for the coated tools and 25 and 50 m/min for the uncoated tool.08 mm per tooth. (a) at feed rate 0.2 mm/rev and 1. from Sharman et al.5% Co. Abrasive nose wear and chipping at the cutting edge were the main failure modes observed. Fig. Ducros et al.08 and 0. the TiC added alumina ceramic tool showed very small flank and notch wear at the cutting speed of 500 m/min. has a significant influence on the tool life [4] and for interrupted cutting such as end milling. its relative low cobalt content increases its abrasion resistance.5 mm. However. The K20 grade (WC 93%. a TiN/AlTiN nanolayer coating gave good results when machining Inconel 718 with low BUE phenomenon and reduced abrasion wear [20]. and TiC added alumina ceramic Al2O3–TiC under high speed turning tests of Inconel 718 up to 500 m/min. This is due to its high hot hardness and high compressive strength. hot hardness and low chemical affinity resulting in longer tool life in comparison with carbide tools. The Al2O3– TiC ceramic showed very small flank wear VB under the same testing cutting conditions but a maximal value for VN around a cutting speed of 100 m/min.Al)N coating is most suitable in dry machining of difficult-to-cut materials such as Inconel 718.D. it has been shown that the PVD (Ti. the major disadvantages of ceramic tools are their low resistance to mechanical shock or low fracture toughness and their low thermal conductivity. feed rate f = 0. Tool life was determined by an average flank wear of 0. In addition. 9. silicon nitride Si3N4 ceramic. In the cutting speed range of 400–500 m/min.5 mm. peeling. depth of cut d = 1.19 mm/rev and a depth of cut of 0. 0 not significant. In the paper by Narutaki et al. Machining Inconel 718 with ceramic tools The advantages of ceramic tools are [8]: high-temperature resistance enables them to be used at high cutting speeds. In comparison with the TiN and TiCN coatings. a depthof-cut notch width of 1 mm or a nose wear of 0. in addition.2.2 mm/rev in turning. [21]. the flank temperature attained 1250–1300 °C. high-temperature chemical stability. especially the SCEA. 7% Co) cemented carbide seems to be the best for cutting Inconel 718. / International Journal of Machine Tools & Manufacture 44 (2004) 439–456 445 Table 1 Cutting tool failures of different coatings used for turning Inconel 718. In addition. Superior oxidation resistance. high hot hardness and low thermal conductivity are the principal reasons of its performance [18]. up to 200 m/min with carbide tools. under dry conditions. It has been shown also that the cutting geometry. Dudzinski et al. Cutting conditions were: cutting speed V = 40 m / min. [20]. The low toughness is the biggest problem when cutting nickel-based alloys.5 mm Cutting tool and coating Tool life Depth-of-cut notching after Flank wear VB (µm) after BUE after 4 min 4 min machining (2 passes) 4 min machining (2 passes) machining (2 passes) +++ + ++ ++ + 0 500 300 400 250 300 100 +++ + ++ + + 0 Uncoated Commercial multilayer TIN/TiAlN (26 layers) Multilayer CrN/TiN Nanolayer CrN/TiN Multilayer TiN/AlTiN Nanolayer TiN/AlTiN 4 min 6 min 5 6 6 7 min min 30 s min min 30 s The wear was: +++ very important. The cutting speeds usually employed.8 mm.1– 0. wear characteristics of three ceramics tools were examined: SiC whisker-reinforced alumina Al2O3 ceramic. The hard particles contained in Inconel 718 produce severe flank wear. + beginning. the authors estimated the rake and the flank temperatures during the tests. Due to the high cutting temperatures. Another interesting point of this work was the discussion on tool geometry. From Ducros et al. the down cut gives better results [15]. the notch wear VN and the flank wear VB with the SiC whisker and the Si3N4 ceramics became very large at higher speeds or higher feed rates. ++ important.16] tested with success higher cutting speeds. The high thermal conductivity and low thermal expansion coefficient of the K20 grade also improves performance by reducing the thermal shock [8]. The wear of the SiC whisker and of the Si3N4 ceramics increases drastically over the cutting temperature of 1300 °C (the melting point of Inconel 718 is 1550 °C). The SiC whisker ceramic showed the best performance in respect of notch wear VN at the side cutting edge in the speed range of 100–300 m/min with a feed rate of 0. diffusion tests between the three chosen ceramics and . However. Fig. Fig. in the presence of 10% water-based coolant and the use of these ceramics tools was discussed. Some authors [2. abrasion and corrosion resistance. are in the range of 20–30 m/min and up to 50 m/min for coated tools. Flank wear and notching are the main failure modes which limit the tool life. the feed rates are about 0. Recently. 3.2 mm / rev. oxidation and diffusion also occur [17]. 8. Using a thermocouple method. Plastic flow took place . Cutting temperature when machining Inconel 718 with Si3N4 ceramic tool. from Narutaki et al. Kitagawa et al. With the SiC whisker ceramic. 8. They postulated that temperature has an important role in tool wear. They measured it in the rake face and in the flank of the tool. Si3N4 and Al2O3– TiC. The same conclusion was also obtained by Kitagawa et al. The flank wear is generally considered as a kind of mechanical wear. Therefore. this mechanism was temperature dependent. [7]. such as an abrasive wear. for the SiC whisker and the Si3N4 ceramic tools flank abrasive wear was accompanied by diffusion. in the presence of 10% water-based coolant. From Narutaki et al. / International Journal of Machine Tools & Manufacture 44 (2004) 439–456 Fig. taking into account the decreasing of notch wear at higher cutting speed. 10. However. Fig. Inconel 718 were carried out. [7] investigated tool wear and cutting tool temperature by means of turning experiments up to 300 m/m. Performances of two types of ceramic. Dudzinski et al. They observed also the chip morphology: with increasing cutting speed. [21]. 9. the Ni diffused into the tool. up to about 1200 °C. Fig. have been investigated. with increasing cutting speed. These tests showed that the Al2O3–TiC ceramic tool was the most stable to Inconel 718. With the Si3N4 ceramic. However. [21]. They confirmed that notch wear VN (at the side cutting edge) and VN (at the end cutting edge) were the major types of wear observed when cutting Inconel 718. Si diffused into Inconel 718 and Cr in the alloy. All the temperatures rose monotonically. Influence of cutting speed and of feed on notch wear VN and flank wear VB. they estimated that the wear characteristics observed cannot be explained by temperature alone and that the wear is rather developed by an abrasive process than a thermally activated adhesion mechanism. In addition.446 D. large plastic flow towards the side of the chip could be depicted at a speed of 150 m/min. as it has more thermal wear resistance than the other tools in high speed machining. Flank wear VB remained lower in the whole tested speed range. the Al2O3– TiC ceramic tool was the best cutting tool. when turning Inconel 718 with ceramic tools. The maximum notch wear observed for the Al2O3– TiC ceramic tool around the cutting speed of 100 m/min was a kind of transfer type wear generated by an adhesion of work material to the tool. which is a thermally activated process. serrations in the chip became obvious and the chip thickness decreased. the tool cutting edge temperature is reduced. from Kitagawa et al. El-Wardany et al. Increasing the SCEA reduces the wear. the temperature at the tool tip depends on the nature of the tool and workpiece materials and on their thermal diffusivity. different tool geometry. According to the authors. on the work surface and a burr was generated by the side cutting with a maximum height at the same cutting speed. 12. Turning Inconel 718 with an Al2O3–TiC ceramic cutting tool. from Narutaki et al.19 mm / rev). but with a further increase in the cutting speed up to 720 m/min. they estimated the cutting edge temperature during tests at cutting speeds up to 500 m/min by measuring the rake face temperature with a thermocouple located very close to the tool tip. A tool with a large cutting edge radius (button type with nick) corresponding to a high value of the SCEA showed better performance in terms of tool wear. 11.5 times higher than at 1000 °C. Fig. The effect of tool geometry on cutting temperature was also discussed by El-Wardany et al. / International Journal of Machine Tools & Manufacture 44 (2004) 439–456 447 Fig. the cutting edge temperature decreases. Fig. consequently. and rake angles) were tested. leading to a lower heat generation during cutting and. Different geometrical tool configurations (different nose radii. Dependence of flank wear VC = VB and notch wear VN and VN on cutting speed at cut distance of 50 m with an Al2O3–TiC ceramic tool (depth of cut = 0. 11. angles of approach. . the tool tip area available for heat conduction decreases making the local temperature to rise. from El-Wardany et al. In addition.D. [22] when turning hardened steel with an Al2O3–TiC ceramic cutting tools. In the same paper. the authors showed that there exists an optimal negative rake angle for which the temperature is minimum during cutting. 1. this can be explained by the fact that for smaller nose radius. widths of tool chamfer. Fig. Dudzinski et al. The thermal conductivity of the Inconel 718 increases linearly with temperature and its value at 1300 °C is 1. see Fig. In addition. was tested by Narutaki et al. 12. The thermal diffusivity is a measure of transient heat flow and is defined as the thermal conductivity divided by the product of specific heat times density. Increasing the angle of approach reduced the undeformed chip thickness t1 and increases the width of cut w. Although the rake temperature was found to increase with the increase of the cutting speed [21]. [21] corresponding to increasing value of the SCEA. [7]. effect of cutting speed on tool edge temperature. An interesting result emerged. Increasing the angle of approach (SCEA) reduced the cutting edge temperature. To reduce the notch wear of the Al2O3–TiC at low cutting speed.5 mm. the measured temperatures increase to the range of 650–850 °C. 10. They confirmed the superiority of the Al2O3–TiC ceramic on the Si3N4 one over a cutting speed of 250 m/min. [21]. [22] present experimental results concerning turning Inconel 718 with an Al2O3–TiC ceramic cutting tool. initially with an increase of cutting speed from 110 to 510 m/min. feed rate = 0. [22]. The cutting edge temperature decreased with the increasing tool nose radius. The variations with temperature of density and Fig. Li et al. Modes of Failure at 1. amount of plastic deformation on the tool rake face. The optimum performance was obtained at cutting speed of 700 m/min or higher. increasing the immersion ratio improved the tool life. depth of cut notch wear and trailing edge wear. (a) End milling Inconel 718 with a SiC whisker-reinforced ceramic tool. Elbestawi et al. For higher cutting speeds (400–700 m/min). The cutting process was more stable during dry cutting tests at high speeds. Modes of Failure at 1.00). at cutting speeds of 1000 and 2000 m/min. 0. the feed rates were 0. Tool life of ceramic tools is severely limited by excessive notching in the depth of cut region. at 720 m/min. and feeds of 0. They provided a stronger cutting edge aiding notch wear resistance. This high value of the workpiece’s thermal diffusivity is accompanied by lower values of the tool’s thermal diffusivity. A transition is observed at 240 m/min. El-Wardany and Elbestawi [24] extended their end milling experiments of Inconel 718 up to 2000 m/min using flood coolant. 13a.22 mm/rev and the depth of cut was 1.5 µm. The depth of cut notch wear was the dominant failure mode for tool at full immersion. As in the previous work.08. 14. therefore. Maximum productivity was obtained with the TiAlN coated ceramic.5 mm). a feed of 0.15 mm/tooth. Round inserts improved the cutting performance in comparison with square ones. They observed three main types of tool wear: flank wear. Hence. and feeds from 0. from Elbestawi et al. and cutting speeds from 200 to 400 m/min. the increase of thermal diffusivity with temperature is due to thermal conductivity variations. The coatings protected the ceramic tool as a thermal barrier and they increased the ceramic tool life. Therefore. at cutting speeds ranging from 200 to 700 m/min. Some tests were performed under dry conditions. Fig. The cutting speeds were 300.25 to 1. At the cutting speed of 720 m/min. only crater wear was developed on the tool accompanied by a small Fig.18 mm/tooth. hence.2 mm/tooth and full immersion (the depth of cut was 0.25 mm depth of cut and 0.448 D.7 µm was produced. lower immersion ratios and higher feeds. For these conditions. they used round inserts of SiC whisker-reinforced ceramic. The best combination of cutting conditions was a speed of 1000 m/min. caused by welding and pull-out. ceramics are poor heat conductors which make them vul- . the cutting edge was covered with workpiece material caused by pressure welding between the work and the tool.12 and 0. with minimum damage to the tool nose at lower speeds (120 m/min). Dudzinski et al. the thermal diffusivity of the tool is affected by the welded layer. Fig.5 mm for all the tests. [23] investigated the failure characteristics and the cutting performance of silicon carbide (SiC) whisker-reinforced ceramic tools during milling of Inconel 718.25 immersion. the mode of tool failure was flaking of the rake face caused by the sticking of the workpiece on it. and the surface finish was about 0.75 and 1. axial depths of cut in the range from 1 to 2 mm.2 mm/tooth. the tool tip temperature attains a higher value. about 800 °C. They performed machining tests on a vertical boring mill under dry conditions. 13b.5 and 0. Gatto and Iuliano [25] coated 20% SiC whiskerreinforced Al2O3 tools with CrN and TiAlN using PVD in order to minimise the temperature effect and to obtain an increase in tool life. Further increasing the speed to 300 m/min leads to a reduction in notching and an increase in nose and flank wear. which may be due to the relatively low mechanical toughness of ceramic tools. This pressure welding appears when the rake temperature approaches the melting temperature of Inconel 718. trailing edge wear and/or flank wear were the dominant modes.25 mm depth of cut and full immersion. Various immersion ratios were considered (from 0. The tool life in terms of volume of material removal was three times that removed by cutting speeds higher or lower that this optimal speed and a surface finish of 0. the dissipation of heat at high cutting speed is higher through the workpiece than through the tool and assures low values of tool tip temperature. 400 and 530 m/min. / International Journal of Machine Tools & Manufacture 44 (2004) 439–456 specific heats for Inconel 718 are not thought to be major. 13. Flank wear VB and notch wear VN were measured and statistical models were proposed. [23]. (b) End milling Inconel 718 with a SiC whisker-reinforced ceramic tool. They performed cutting tests using round and square inserts. and feed of 0. In addition.10 to 0. Sialon ceramic tools are prone to notch wear. Fig. [6] used Sialon (Si3N4–Al2O3) ceramic tools for turning tests of Inconel 718.05 to 0. 27] were used to assist the machining of such materials. localised heating may soften the material and reduce the shear strength and strain hardening associated with chip formation. At high temperatures above 750 °C. Resultant cutting force vs. where V is the cutting speed. 16. f the feed and d the depth of cut. [30]. An alternative solution to enhancing the machining performance of hard-to-cut materials is to reduce the cutting temperatures by the application of a high pressure waterjet coolant [28]. [27]. From Hong et al. [27]. Dudzinski et al. Assisted machining of Inconel 718. . but the chip temperature is a little higher than in conventional machining. They can withstand higher cutting speeds (above 200 m/min) than uncoated and coated carbide tools.D. 17. the notching is eliminated and the tool life is increased. 16. Q = Vfd. [27] showed that the cutting forces decrease with increasing the surface temperature. surface oxidation was observed. Leshock et al. The flow rate of the cryogenic fluid is proportional to the heat generated in the cutting process. Fig. this problem should be resolved by a more accurate control of the plasma arc. 15. Fig. Fig. surface temperature for various cutting speeds (feed = 0. However. ceramic tools have large usage possibilities. therefore. However. Dry machining Inconel 718 with coated ceramic tools. Coatings may be used to improve the cutting performance of ceramic tools. The cooling effect obtained with this Fig. Yield stress of Inconel 718 vs. cryogenic fluid is applied directly to the cutting edge where the material is cut and heat is generated. nerable to thermal cracks. With PEM. from Gatto and Iuliano. During plasma enhanced machining (PEM). temperature from Leshock et al. beyond 530 °C. 14. and the surface roughness is also improved. preventing the workpiece from becoming distorted due to extreme heating or cooling. To minimise waste. during PEM of Inconel 718 with ceramic inserts (aluminium oxide reinforced with silicon carbide whiskers) from Leshock et al. tool life and surface finish) in hard-to-cut materials is hot machining. Dry conditions are generally recommended during machining with ceramic tools. Maximum productivity values Q. 17. Fig.3. the values refer to a machined volume of 40 cm3. Fig. leading to higher flank wear rates [27]. Another possibility is to use liquid nitrogen as coolant [29. 15. 3.124 mm / rev). [25]. Inconel 718 exhibits significantly reduced yield stress. / International Journal of Machine Tools & Manufacture 44 (2004) 439–456 449 Fig.30]. Application of liquid nitrogen to the cutting zone. Assisted machining for Inconel 718 One approach to enhance the machining performance (in terms of material removal rate. Localised heat sources such as laser and plasma [26. cavities. Jacobson et al. the compressed air failed to infiltrate into the tool–chip interface or tool–workpiece and the advantage of the proposed cooling system was reduced. one also increases the strain rate in the process which gives more mechanical work leading to compressive stress. surface irregularities. High tensile stresses generated by the machining of work hardening alloys can be highly deleterious to fatigue performance. Tearing on the machined surface of a component reduces its fatigue strength. however. [32].125 mm/min and a constant depth of cut of 2. at a speed of 210 m/min. surface integrity is important for the components submitted to high thermal and mechanical loads during their use. Structures in aerospace applications are subjected to severe conditions of stress. Residual stresses are an effect from both heat generated and mechanical work going into the surface and subsurface. Section size is continually reduced in order to minimise weight so that surface condition has an ever-increasing influence on its performances. nitrogen is expensive and does not recycle. [36] and Kishawy and Elbestawi [37] studied the phenomenon of material side flow which represents an important aspect of machined surfaces. while mechanical influences contribute to compressive residual stresses. we present some results about surface finish during machining Inconel 718 and the main parameters which affect the surface integrity are identified. metallurgical alterations including microstructural distortion. temperature and hostile environments. the introduction of a compressive mean stress will increase the allowed alternating stress for a given fatigue life.5 mm with coated TiAlN carbide tool. macro. The compressed chilly air is jetted through the nozzle enabling adiabatic expansion and leading to a temperature in the jet of about 12 °C. Axinte and Dewes. The effect is most significant in the high cycle fatigue regime where the applied stress magnitude is not sufficient to significantly relax the residual stresses produced during manufacturing. Coolant was not used because of the low thermal shock properties of ceramics. phase transformations. This cooling technique was tested in ball end milling at cutting speeds of 90 and 210 m/min. Ezugwu and Tang [9] carried out turning tests on Inconel 718 alloy using round. Service histories and failure analyses of dynamic components show that fatigue failures almost always nucleate on or near the surface of a component. microdefects such as laps and inclusions. Dudzinski et al.and microstructure and hardness of the surface. [32]. Kim et al. long continuous chips were produced due to the ductility of the work material. Bresseler et al. feed rate of 0. The round inserts produced better surface finish than the rhomboid inserts. a feed rate of 0. A tensile mean stress reduces the allowed alternating stress in service. Plastic deformation was evident by the observation of the elongation of grains and orientation under the machined surface. BUEs or deposits of debris. The work material was not the . their measurement and causes in machining processes. In the same way. Under the chosen conditions.450 D. increasing the strain rate in the cutting zone introduces more generated heat.and rhomboid-shaped pure oxide (Al2O3 + ZrO2) and mixed oxide (Al2O3 + TiC) ceramic tools. Surface integrity when machining Inconel 718 For safety critical industries such as aerospace. Residual stress strongly affects the fatigue life of a component. Thermal effects tend to give tensile stresses. structural changes in the machined surface layer. microhardness variations. The drier air exchanges heat in an aircooler system and its temperature decreases down to about 2 °C. Hence. macro. By considering stress corrosion resistance. All the rhomboid-shaped ceramic tools failed after machining for 1 min due to severe notching at the depth of cut. They added residual stresses and a minimal fatigue testing to give a ‘standard’ data set. heat affected layers. Inconel 718 alloy was machined at a speed of 152 m/min.0 mm. Such changes occur due to thermal and mechanical loads during machining. which involves surface finish (roughness and waviness).and microcracks. feed and tool wear on surface material side flow quality during dry hard boring and hard turning. Conversely. The tool life was significantly improved at 90 m/min. Brinksmeier et al. [34] have noted that when increasing cutting speed during hard turning of bainitic steels. tensile residual stresses are the main problems identified. However. / International Journal of Machine Tools & Manufacture 44 (2004) 439–456 method is stronger than with waterjet cooling and the temperature dependent wear reduced significantly in the tests of machining titanium and Inconel 718 alloys. much attention should be paid to surface characteristics of components [33]. They have shown that the geometry of cutting tools plays an important role in determining the nature of machined surfaces. The hardness of the workpiece surface layer increased with prolonged machining due to plastic deformation and to the high rate of work hardening of Inconel 718. which has a tendency to produce tensile stress at the machined surface. [31] proposed a cooling system which uses compressed air. nose radius.1 mm/tooth. [35] give a good overview of the subject of residual stresses. Tearing of the surface layer of the Inconel 718 was observed in all machining trials. In the following. 4. They conducted experiments in order to study the effect of cutting edge preparation. Field and Khales [33] proposed a minimum surface integrity data set. depth of cut of 0. it is again recognised that the surface of a component is a primary factor in determining susceptibility to attack and subsequent failure. Overheating/burning. Similar stress profiles were found by Derrien and Vigneau [16] and Guerville and Vigneau [11]. 20. affecting a layer of 400 µm with an extreme value of 1500 MPa. Comparable residual stress profiles were also obtained after ball end milling by Ng et al. / International Journal of Machine Tools & Manufacture 44 (2004) 439–456 451 Inconel 718 alloy but a hardened steel. a maximum compressive stress value of 500 MPa and a 100 µm affected layer. dry conditions) and conventional machining (18 m/min. At higher cutting speeds of 410 and 810 m/min. low residual stresses were found.06 and 0. from Derrien and Vigneau [16]. [39]. On the other hand. 0. Point milling Inconel 718 with carbide K20: comparison of residual stresses profiles after high speed machining (200 m/min. Guerville and Vigneau [11]. the tensile stress dropped to 0. [38]. [38]. Near surface residual stress distributions in Inconel 718 arising from a turning operation were studied by Schlauer et al. Cutting speeds were 10. It was followed by a layer with compressive stresses that is several times thicker than the tensile layer. hence to a deterioration in surface quality. 18. . For contouring operations at V = 200 m / min (f = 0. for the point milling tests. When the cutting speed was increased. 810 m/min). Fig. In addition. 18. dry conditions) and conventional machining (16 m/min. emulsion 5%).5 mm). of 16 m/min and wet conditions. their work is important to identify the generally parameters influencing surface quality. 20. especially during finishing operations. They carried out high speed and dry milling tests (contouring and point milling) with uncoated cemented carbide K20 mills.04 mm / tooth and depth of cut = 0. 410. Dudzinski et al. 410 and 810 m/min and for the feed were 0. However.06 mm/rev and the three tested cutting speeds (10. 19. Within 10 µm from the machined surface. High tensile stress Fig. The cutting conditions were very similar to orthogonal cutting. Contouring Inconel 718 with a carbide K20 tool: comparison of residual stresses profiles after high speed machining (200 m/min. They verified that cutting edge preparation has a significant effect upon the material side flow.01. the workpiece surface was inclined with an angle of 45° from the horizontal. From Schlauer et al.11 mm/rev. The cutting tool used was a SiC whisker-reinforced alumina Al2O3 ceramic.5 mm in down milling. The tests were performed at a cutting speed of 90 m/min. an increase in the tool nose radius leads to the ploughing of a large part of the chip and in consequence to severe material side flow on the machined surface. with a maximum tensile stress at the surface. 19. This maximum value was three times the one obtained using a conventional speed Fig. Fig. the tensile and the compressive stresses increased and the depth of the layer affected by machining increased too. For the cutting speed of 10 m/min. Although cutting with a small feed improves surface finish.2 mm/tooth and an axial depth of cut of 0. dry conditions). The tool geometry was kept constant. Fig. Residual stress depth profiles for the feed 0. it leads to more material side flow on the machined surface. from Derrien and Vigneau [16]. Fig. a thin layer exhibiting tensile residual stresses was formed near the machined surface. the level of the residual stresses was lower with a maximum tensile stress value of about 750 MPa near the machined surface.D. feed of 0. residual stresses are tensile. Turning Inconel 718 with a SiC whisker-reinforced alumina ceramic tool. Guerville and Vigneau [11]. but it promoted a mist in the environment with problems of odours. bacteria and fungi growth of the overhead flooding system. Nevertheless.13]. [42–47]. They also studied the influence of cutting conditions on the plastic deformation mechanism and then on residual stresses. Then. The test equipment permitted the independent variation of the injection pressure. In particular. Today. It can be noted that this phenomenon is not observed in other nickel-based alloys.1. Only a small amount of lubricant is needed if it is efficiently applied to the cutting zone. The mixture was directed onto the rake face of a carbide tool against the chip flow direction. In contrast. For example. This lubricant is completely used and results in almost dry chips. A high speed electrical mixing chamber facilitated thorough emulsification. all the effects provided by the usual cutting fluid flood-type lubricant are not possible with minimal quantity application or dry cutting alone. In the following. These chips are very similar to those obtained with the Ti–6Al–4V alloy. Reducing costs in the cutting process together with reduced environmental pollution by the use of dry machining is the main key for the industry to remain competitive and profitable in the future [42]. the 5. Dimensional instability of components induces problems during assembly. Machado and Wallbank [44] conducted experiments on turning medium carbon steel (AISI1040) using a Venturi to mix compressed air (the air pressure was of 2. They finally proposed a process parameter optimisation technique to control the dimensional changes within acceptable limits. wet cutting is still largely used in manufacturing industry. followed by highly compressive stress at a shallow depth and the compressive layer was maintained to 150 µm. For this reason. However. 5.452 D. the system needed yet some development to achieve the required effects in terms of cutting forces. / International Journal of Machine Tools & Manufacture 44 (2004) 439–456 values were measured parallel to the feed direction near the machined surface. This is mainly due to the elimination of coolant supply. It combines the functionality of cooling lubrication with an extremely low consumption of lubricant and therefore it has the potential to close the gap between overflow lubrication and dry cutting [43]. cleaning. The way to dry machining The use of coolants. They are thin walled and call for very close dimensional tolerances and good surface integrity. dimensional changes being lowest for the latter material. [12. temperatures. Subhas et al. the results obtained with minimum quantities of cutting fluid application in drilling are excellent compared to the usual flood-type application. the concept of minimum fluid application is developed and then the results of some dry cutting experiments using hard coatings are presented. maintenance and disposal costs [41. The application of a mixture of air + soluble oil was able to reduce the consumption of cutting fluid.42]. The Inconel 718 used for jet engine component is not only known to be difficult to cut but also to reveal dimensional instability after machining [12. Depending on the machined workpiece. Minimal quantity of cutting fluid application The characteristic of the ‘minimal quantity’ application is to substitute all the effects of the coolant lubricant by using jet application to produce effects of equal values. additional use of minimum cooling system of the workpiece and a specially adapted blow-out technology for chip removal are required.13]. in addition to being undesirable to the environment and for the human health. According to Subhas et al. the dimensional instability of Inconel 718 may be attributed to the presence of g phase. Microscopic observations showed that shear localised chips were formed with the Inconel 718 alloy at various cutting speeds. Gas turbine components are complex in their shape. Inconel 718 is more prone to dimensional instability than either titanium alloy or mild steel. even if the obtained results were encouraging. entails high costs in production and disposal. The specimens were machined at identical cutting conditions and the dimensional changes were measured with respect to time up to 220 h after machining. the mixture of air + water was preferred. minimum quantity cutting fluid application have been developed. [12. The two probable causes of this phenomenon are the residual stresses and microstructure changes introduced by the machining process. However.3 bar) with small quantities of a liquid lubricant. Dudzinski et al. water or soluble oil (the mean flow rate was between 3 and 5 ml/min).13] compared the dimensional instability of Inconel 718 with that of Ti–6Al–4V and mild steel. Varadarajan et al. cost savings up to 17% of the total workpiece cost can be made by introducing dry machining. see also the study of Komanduri and Shroeder [40]. [45]. but research and development is being undertaken to minimise the use of coolant lubricants and new concepts of . the flushing effect is not supplied and the cooling effect is partially or not at all (with dry cutting) obtained. Dimensional instability is a change of dimension with respect to time without any further work being done on the component. they observed that negative rake angles increase the residual stresses. The test equipment consisted of a fuel pump generally used for diesel fuel injection in truck engines coupled to a variable electric drive. tool life and surface finish. The ‘minimal quantity’ lubrication is a suitable alternative for economically and environmentally compatible production. [46] developed an alternative test equipment for injecting the fluid and used it with success in hard turning for which a large supply of cutting fluid is the normal practice. The tool coatings can at least partially substitute the eliminated functions of the cutting fluids. [48]. The TiAlNOx consists of two layers: the first layer on top of the substrate surface is a thick TiAlN-coating necessary to achieve good adhesion. The work material was austenitic 22Mn6 steel. multilayer TiN + TiAlN. The removal of chips from the cutting zone is another important aspect. (Ti. Coatings separate tools from the workpiece material in cutting and offer a possibility of replacing coolants. with dry cutting and wet cutting.Al)N has a high oxidation resistance up to 800 °C. in order of 10–50 ml/h. Metallographical studies indicated that the solid lubricant MoS2 is worn after a few machined parts. The used minimal lubricant system worked with a special oil which had food-grade quality. Tools with high hot hardness. the remnant was carried out by work and chips and was too low in volume to cause contamination of the environment. During hard turning of an AISI 4340 hardened steel of 46HRC (460 HV). Compared to . this pollution is a problem for the aerospace components. At this oil volume flow. Lahres et al. Demands placed on coatings for dry machining include reduction of friction to decrease dissipated thermal energy in tool–workpiece contact and protection of heat and diffusion to guarantee high wear resistance at high temperatures. 5. ¨ ¨ Tonshoff and Mohfeld [49] and Tonshoff et al. in particular for dry machining. The air volume flow was about 50 l/min and the air volume oil was about 20 ml/h.Al)N possesses the lowest coefficient of thermal conduction and a considerably increased oxidation stability compared with other hard coatings. Dry cutting Elimination of coolants also involves the absence of their positive effects on the metal cutting processes. single layer (Ti.Al)N film. However. for the same cutting conditions.2. temperatures. Due to the complex thermal and mechanical loads in drilling. [42] presented dry machining of synchronising cones for automotive application. only thermally stable coating layers are applied. while long snarled chips were prevalent during dry turning.05% of that used during wet turning. high refractivity and low coefficients of friction are required and the use of tools with low-adhesion coatings can help greatly. The process must preserve the surface integrity of workpiece and produce stable tool wear suitable for automatic manufacturing systems. the produced chips were dry after leaving the contact zone of the cutting process. hence. a small amount of solid lubricant exists further in the valleys of the tool surface profile and initiates a low friction at the tool–chip interface. In addition. were mixed with compressed air for an external feeding via a nozzle or for internal feeding via spindle and tool. sufficient heat removal and the avoidance of heat build-up above a critical temperature must be guaranteed. In comparison. / International Journal of Machine Tools & Manufacture 44 (2004) 439–456 453 frequency of injection and the rate of injection. the optimum levels for the fluid delivery parameters were: a rate of 2 ml/min. Whereas TiN oxidises at temperatures higher than 600 °C. cutting materials for dry drilling require high hot hardness and high toughness.D.coating. Because of the poor conditions for heat conduction from the drill.Al)N. the rate of fluid was only 0. The investigations performed by the authors revealed that a coolant-rich (60%) lubricant fluid with minimal additives was the ideal formulation. the minimum quantity of cutting fluid method has led to lower cutting forces. a small amount of solid lubricant exists perhaps also on the machined surface. Schulz et al. a single chip can carry a maximum of 1 nl. Therefore. It must be noted that during minimal application. In the first step of their study. For dry cutting operations. it was observed that tightly coiled chips were formed during wet turning and during minimal application. Internal feed systems with their ability to deliver the mixture very close to the drill–workpiece contact point may achieve very good results in terms of surface finish and tool life. better surface finish. The best performance was obtained with the double layer TiAlN + MoS2 coating. [50] presented an interesting paper on (Ti1 x. The major part of the fluid used during minimal quantity application was evaporated. TiAlN + MoS2. longer tool life. Small quantities of lubricant. a pressure of 20 MPa and a high pulsing rate of 600 pulses/min. Dudzinski et al. In the second step. the second is a thin Al2O3-coating used to reduce oxidation and wear. The performance of this coating was almost as good as the one of TiAlN + MoS2 . they investigated new tool coatings with a potential for dry machining: TiAlNOx. dry machining was compared to machining with coolant and with minimal lubricant system. A new series of experiments were performed under minimal lubrication. (Ti. the chips could be declared as being almost dry and passed for metallic recycling without further treatment. Alx)N coatings for wear protection in dry drilling operations of tempered steel. The paper of Klocke and Eisenblatter [47] deals with ¨ drilling tests using minimum cooling lubrication systems which are based on atomising the lubricant directly to the cutting zone. Nevertheless. particularly with TiN coating. The results exhibited an advantage for the minimal lubricant technique and for the dry machining. The formation of a dense Al2O3 top layer increases diffusion and oxidation resistance of the (Ti. Tool coatings play a major part in tool development. [53–56]. Beside the commercially obtainable MoS2 coatings. these coatings retain a high coefficient of friction and require a lubricant. However.Al)N.02–0. Bouzakis et al. Due to the high hardness. TiZrN– ZrO2 and compared with the uncoated and the simple TiAlN coated tool performances. A new highly improved AlTiN film has been developed and proposed by Arndt and Kacsich [57] for dry or minimum quantity lubrication and high speed machining of stainless steel as well as hardened steel up to 63 HRC. and contains hard particles making it a very difficult-to-cut material. Conclusions Inconel 718 is a high strength thermal resistant material alloy. in consequence. Then. The nanolayer structures with higher hardness appear to give encouraging results. under dry conditions may be achieved with coated carbide tools. The depth of affected layer and the tensile and compressive stresses increase when the cutting speed increases. the tool life was remarkably improved. Machining induces plastic deformation and heat generation. compared to uncoated carbide and TiN coated tools. [52]. it has a superior wear behaviour.Al)N coating to form TiAlON [51]. 6.Al)N system has remarkable advantages. the oxide-coated tools show notable advantages for dry drilling in high strength materials. However. It is a highly strain rate sensitive material which work hardens readily. [48] showed the performance of oxide Al2O3 and ZrO2 PVD-coatings in dry cutting operations of high strength graphic cast iron. high hot hardness and low thermal conduction. This type of hard/lubricant coating was proposed for dry machining. A significant reduction of the cutting edge temperature by using the oxide coating was also observed. the consequences are metallurgical transformations and residual stresses in the machined surface layer.Al)N has a high hardness even at elevated temperatures. other low-friction coatings such as tungsten carbide/carbon (WC/C) coatings are available. Different oxide PVD-coatings were tested: TiAlN–Al2O3. Commercial titaniumbased hard coatings like TiN. to the new coating. In addition. For dry drilling operations. It displays high oxidation resistance. Abrasion resistant TiAlN was combined with VN to achieve a wear resistant low friction coefficient coated tool tested with success during dry machining of steels.1) which allows them to be used at high speeds. With the different oxide coatings. . The cutting performances of the new coating were compared with success to other commercial (Ti. Cemented carbide tools are largely used for machining nickel-based alloys at very low cutting speeds of 20–30 m/min. Alumina provides oxidation resistance and is thermally stable. The changed contact conditions will decrease the heat generation. They have also a very low friction (0. the hard coating TiAlCrYN was overcoated with lubricious and non-sticking coating C/Cr and tested on end mills for the machining of extremely abrasive high Co containing Ni-based alloys. The PVD (Ti. Schulz et al. In the same way. A further improvement in dry machining was achieved by adding oxygen to a (Ti. increased resistance and a low friction coefficient even at elevated temperatures. Oxide PVD-coatings specially developed for dry machining additionally combine a reduction of friction at elevated temperatures with high wear resistance. high-temperature chemical stability. TiCN and TiAlN with high hardness even at high temperatures provide a high wear resistance. (Ti. Hard coatings such as TiAlN may increase tool performance and tool life by arresting or slowing down certain types of wear. The advantage is a much better toughness and a reduced risk of cutting edge chipping. improves surface finish. Though the microhardness of TiAlON was lower than (Ti. The improvement of the deposition operation has led.Al)N coating seems to be most suitable. TiAlN–ZrO2. a graded multilayer structure of TiAlON with Al2O3 was developed by providing a stable oxide layer on layer on top of the nitride coating. a solid lubricant such as MoS2/titanium composite coatings may be used to reduce the friction coefficient and then to decrease the cutting forces and temperatures which reduces the local welding and. The BUE is repeatedly removed leading to severe notching.454 D. The MoS2/titanium composite coatings have a much lower wear rate than the traditional hard coatings. The residual stress distribution exhibits a maximum tensile stress near the machined surface and then a compressive stress. TiAlON offered a higher abrasion resistance during dry drilling due to the formation of Al2O3. no published results from these tests have yet been found. to possess better characteristic properties such as high hardness associated to an ultra-fine crystallinity. certainly up to 100 m/min. the tendency for the work material to adhere on the rake face is reduced and the chip flow is improved. Higher cutting speeds. The main wear mechanism is abrasion observed for all the tested tools. The difficulty of machining Inconel 718 resolves into short tool life and poor surface integrity. Welding and adhesion on the cutting tool frequently occur to form a BUE. the K20 grade appears to be the best for cutting Inconel 718. The best wear behaviour in dry drilling of tempered steel was obtained for an Al/Ti ratio equal to 1. They are dedicated to high-temperature performance and for tribological applications. the ternary (Ti. Recent hard coatings are the superlattice structured PVD hard coatings presented by Hovsepian and Munz ¨ [58]. Dudzinski et al. The TiAlN–ZrO2 coating had the best performance.Al)N films. For dry cutting applications. / International Journal of Machine Tools & Manufacture 44 (2004) 439–456 TiN. The substrate of the drilling tool was a fine grain tungsten carbide with 10% of cobalt (K20–40). French Agency for Environment and Energy Management. El-Wardany. International Journal of Refractory Metals and Hard Materials 17 (1999) 163–170. Liao. A. Solid lubricants such as MoS2/titanium composite coatings or WC/C coatings should give useful results when machining Inconel 718 under dry conditions.O. Z. Subhas. Journal of Materials Processing Technology 16 (2001) 244–251. Prengel. El Baradie. Ducros. Bhat Ramaraja. [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] Acknowledgements [17] The research work published in this paper was carried out with the financial aid of ADEME. Li. 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