Suppression of notch wear of a whisker reinforced ceramic tool in air-jet-assisted high-speed machining of Inconel 718

This paper describes the notch and flank wear specific to a SiC whisker reinforced alumina tool in air jet assisted (AJA) turning of nickel-base superalloy Inconel 718 at high cutting speeds. An AJA machining experiment has revealed that the air jet applied to the tool tip in addition to coolant dramatically reduces the depth-of-cut notch wear. As a result, the width of flank wear, but not the size of notch wear, determined the life of a ceramic tool in AJA machining of Inconel 718. This is a reason for the large extension and small variation of the tool life when high speed AJA machining is adopted. The maximum tool life length reached 2160 m at a cutting speed of 660 m/min under the given cutting conditions. Finally, the mechanisms of the notch and flank wear of a SiC whisker reinforced alumina tool in AJA machining are discussed from the viewpoints of tribochemical reactions and tool wear anisotropy.     

Cooling performance of micro-texture at the tool flank face under high pressure jet coolant assistance

Micro-texture at the tool face is a state-of-the-art technique to improve cutting performance. In this paper, five types of micro-texture were fabricated at the flank face to improve the cooling performance under the condition of high pressure jet coolant assistance. By using micro-textures consisted of pin fins, plate fins and pits fabricated 0.3 mm away from the cutting edge, heat transfer from the tool face to coolant was enhanced. The conditions of tool wear, adhesion and chip formation were compared between the micro-textured and non-patterned tools in the longitudinal turning of the nickel-based superalloy Inconel 718. As a result, micro-textured tools always exhibited the reduced flank and crater wear compared with the non-patterned tool, and the rate of tool wear was influenced by the array and height of fin. The energy dispersive spectroscopy analysis of worn flank faces and the electromotive forces obtained from the tool-work thermocouple supported better cooling performances of micro-textured tools. In addition, coolant deposition at flank face evidenced that heat transfer could be promoted by micro-texture near the border of the contact area between the flank wear land and machined surface. Finally, the changes of flow patterns with pit depth are analyzed for pit type tools by computational fluid dynamics. This investigation clearly showed the function of micro-textures for increasing the turbulent kinetic energy and cooling the textured tool face.     

Analysis of tool wear patterns in finishing turning of Inconel 718

This paper focuses on the analysis of tool wear mechanisms in finishing turning of Inconel 718, one of the most used Ni alloys, both in wet and dry cutting. Cemented carbides, ceramics and CBN tools are suitable for machining Ni alloys; coated carbide tools are competitive for machining operations of Ni alloys and widely used in industry. Commercial coated carbide tools (multilayer coating TiAl/TiAlN recommended for machining Ni alloys) were studied in this work. The feasibility of two inserts tested for dry cutting of Inconel 718 has been shown in the work. Experimental test were performed in order to analyze wear patterns evolution. It was found great influence of side cutting edge angle in tool wear mode.     

Evaluation of the Machinability of Nickel-Base,Inconel 718, Alloy with Nano-Ceramic Cutting Tools

The machinability of difficult-to-cut aerospace alloys can be enhanced by the rapid development of cutting tool materials that can withstand machining at high-speed conditions. The performance of nano-grain size ceramic tool materials were evaluated when machining nickel base, Inconel 718, in terms of tool life, tool failure modes and wear mechanisms as well as component forces generated under different roughing conditions. Comparison tests were carried out with commercially available ceramic tool materials of micron-grain composition.

The test results show that the micron grain size commercially available tool materials generally gave the longest tool life. The dominant failure mode is nose wear, while some of the nano-ceramic tools were rejected mainly due to chipping at the cutting edge. This suggests that physical properties and mechanical stability of the cutting edge of the ceramic tools influence their overall performance. It is also evident that chemical compositions of the tool materials played a significant role in their failure. The alumina base ceramics are more susceptible to premature fracture than the silicon nitride base ceramics with higher fracture toughness.     

Study of surface quality in high speed turning of Inconel 718 with uncoated and coated CBN tools

Inconel 718 is known to be among the most difficult-to-machine materials due to its special properties which cause the short tool life and severe surface damages. The properties, which are responsible for poor machinability, include rapid work hardening during machining; tendency to weld with the tool material at high temperature generated during machining; the tendency to form a built-up edge during machining; and the presence of hard carbides, such as titanium carbide and niobium carbide, in their microstructure. Conventional method of machining Inconel 718 with cemented carbide tool restricts the cutting speed to a maximum 30?m/min due to the lower hot hardness of carbide tool, high temperature strength and low thermal conductivity of Inconel 718. The introduction of new coated carbide tools has increased cutting speed to 100?m/min; nevertheless, the time required to machine this alloy is still considerably high. High speed machining using advanced tool material, such as CBN, is one possible alternative for improving the productivity of this material due to its higher hot hardness in comparison with carbide tool. This paper specifically deals with surface quality generated under high speed finishing turning conditions on age-hardened Inconel 718 with focus on surface roughness, metallographic analysis of surface layer and surface damages produced by machining. Both coated and uncoated CBN tools were used in the tests, and a comparison between surfaces generated by both tools was also discussed.     

Wear mechanism of coated tools in the turning of ductile cast iron having wide range of tensile strength

In this study different specimens of ductile cast iron with tensile strength ranking from 400 MPa to 675 MPa were turned with K15 carbide, TiN coated and TiAlN coated tool in order to investigate wear mechanism and performance. Cutting forces and cutting temperature were similar for both coated tools, however flank wear and BUE were the lowest on the TiAlN coated tool, for this reason the TiAlN coated tool is suitable in the machining of ductile cast iron. The proposed tool wear mechanism is based on like-intermittent cutting caused by the pass from hard matrix to the soft graphite occasioning wear by adhesion. The analysis of the flank wear on coated tools is proposed by means of the wear curves in logarithmic scale instead of the usual linear scale. In this way, the change in wear rate is easily observed. This phenomenon was related with the wear out of the coating layer. The partial loss of the coating layer on cutting edge was confirmed by the EDS mapping images and SEM photographs.     

Effect of coating layer loss on the wear rate change of coated carbide tools in turning process

This paper reports an experimental study of flank wear on TiN- and TiAlN-coated carbide tools in the turning of AISI 1045, AISI 4135, ductile cast iron, and Inconel 718, and it was conducted with the purpose of showing the relationship between the change in wear rate and the loss of coating layer on the cutting edge. It was found that the relation between cutting distance and flank wear in log-log scale clearly shows the change in wear rate, thus providing a straightforward way to determine the relation between worn out coating layer and increase in wear rate. This relation was confirmed by analyzing the presence of coating layer before and after the inflection point appears by means of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) photographs. It was observed that the coating layer on the flank face is worn away and finally is worn out. However, even if the layer on the flank face is worn out, tool wear is suppressed as long as the coating layer on the cutting edge exists. On the other hand, when the coating layer on the cutting edge is worn out, the wear resistance of the tool depends on the substrate; thus, the wear rate increases. According to the results, as the cutting speed increases, the change in wear rate appears in a shorter cutting distance, making flank wear to be high. High pressure and high temperature act on the rake face; thus, thermal stability of the coating layer in the cutting edge is important. A low cutting speed decreases cutting efficiency, but a high cutting speed causes flank wear to be high; therefore, in order to optimize machining cost, an acceptable cutting speed, from the standpoint of tool wear, should be selected.     

Wear Behavior of PVD and CVD Coated Carbide Tools when Face Milling Inconel 718

The wear behavior of two types of coated cemented carbide tools has been studied when face milling a nickel-based superalloy Inconel 718. PVD-TiN and CVD-TiCN+Al₂O₃ tools were used. It was found that the coatings were detached after only five seconds of cutting. An attrition type wear mechanism associated with workpiece material adhesion was observed which eventually led to severe chipping, flaking, plastic deformation and cracking. It was noted that the coatings had no significant effect on tool performance under the cutting conditions tested.     

镍基合金Inconel718可切削加工性的试验研究

Inconel718是一种高强度耐热镍基合金,具有优良的高温强度、高温硬度和耐蚀性,在高温条件下能长期工作,已被广泛地应用于宇航工业、航空工业的涡轮发动机和相关零件的制造。分析Inconel718的机械性能、微观组织结构及其对切削加工性能的影响并进行了相关的试验验证,在试验数据的基础上,研究Inconel718中含碳量对切削过程中刀具磨损的影响。试验结果表明,Inconel718中含碳量在刀具后刀面磨损中起着非常重要的作用,Inconel718合金中含碳量越高,合金中所含的细微硬质夹杂物也越多,在切削过程中使刀具产生严重的后刀面磨粒磨损,从而降低材料的切削加工性。     

Experimental Study on Wear Characteristics of PCBN Tool with Variable Chamfered Edge

Owing to heavy dynamic and thermal loads, PCBN tools are seriously worn during hard cutting, which largely constrains the improvement of their machining performance. Therein, the chamfered structure of a cutting edge has a notable influence on the tool wear. Thus, a comparative study was carried out on the wear morphology and wear mechanism of PCBN tools with either a variable chamfered edge or an invariable chamfered edge. The results indicate that, for a PCBN tool with a variable chamfered edge, the rake wear area is far from the cutting edge and slowly extends toward it. A shallow large-area crater wear occurs on the rake face, and the flank wear area has a long triangular shape with a smaller wear area and width, and the cutting edge remains in a good state during the cutting process. In contrast, for a PCBN tool with an invariable chamfered edge, a deep small-area crater appears on the rake face,and the wear area is close to the cutting edge and quickly extends toward it. Thus, it is easy for chips to accumulate in the crater, resulting in large-area and high-speed wear on the flank face. In addition, the tool shows a weak wear resistance. In the initial wear stage, the rake wear mechanism of the two cutting tools is a mixture of abrasive, oxidation, and other types of wear, whereas their flank wear mechanism is dominated by abrasive wear. With an aggravation of the tool wear, the oxidation and di usion wear mechanism are both increasingly strengthened. The rake wear of the cutter with a variable chamfered edge showed an obvious increase in the oxidation and di usion wear, as did the flank wear of the cutter with an invariable chamfered edge. This study revealed the wear mechanism of the PCBN tool with a variable chamfered edge and provided theoretical and technological support for its popularization and application in the machining of high-hardness materials.     

Evaluation of machining performance in cryogenic machining of Inconel 718 and comparison with dry and MQL machining

There has been significant work on establishing relationships between machining performance and the cutting parameters for various work materials. Recent trends in machining research show that major efforts are being made to understand the impact of various cooling/lubrication methods on machining performance and surface integrity characteristics, all aimed at improving process and product performance. This study presents the experimental results of cryogenic machining of Inconel 718, a high-temperature aerospace alloy, and comparison of its performance in dry and minimum quantity lubrication machining. Experimental data on force components, progressive tool wear parameters such as flank wear, notch wear, crater wear, cutting temperature, chip morphology, and surface roughness/topography of machined samples are presented. New findings show that cryogenic machining is a promising research direction for machining of high-temperature aerospace alloy, Inconel 718, as it offers improved machining performance in terms of reduced tool wear, temperature, and improved surface quality. It was also found that the number of nozzles in cryogenic machining plays a vital role in controlling cutting forces and power consumption in cryogenic machining of Inconel 718.     

Effect of tool edge wear on the cutting forces and vibrations in high-speed finish machining of Inconel 718: an experimental study and wavelet transform analysis

High-speed machining has been receiving growing attention and wide applications in modern manufacture. Extensive research has been conducted in the past on tool flank wear and crater wear in high-speed machining (such as milling, turning, and drilling). However, little study was performed on the tool edge wear??the wear of a tool cutting edge before it is fully worn away??that can result in early tool failure and deteriorated machined surface quality. The present study aims to fill this important research gap by investigating the effect of tool edge wear on the cutting forces and vibrations in 3D high-speed finish turning of nickel-based superalloy Inconel 718. A carefully designed set of turning experiments were performed with tool inserts that have different tool edge radii ranging from 2 to 62???m. The experimental results reveal that the tool edge profile dynamically changes across each point on the tool cutting edge in 3D high-speed turning. Tool edge wear increases as the tool edge radius increases. As tool edge wear dynamically develops during the cutting process, all the three components of the cutting forces (i.e., the cutting force, the feed force, and the passive force) increase. The cutting vibrations that accompany with dynamic tool edge wear were analyzed using both the traditional fast Fourier transform (FFT) technique and the modern discrete wavelet transform technique. The results show that, compared to the FFT, the discrete wavelet transform is more effective and advantageous in revealing the variation of the cutting vibrations across a wide range of frequency bands. The discrete wavelet transform also reveals that the vibration amplitude increases as the tool edge wear increases. The average energy of wavelet coefficients calculated from the cutting vibration signals can be employed to evaluate tool edge wear in turning with tool inserts that have different tool edge radii.     

Wear of CBN Tools in Ultra-Precision Machining of STAVAX

CBN cutting tools are widely used in ultra-precision machining of STAVAX (specialized stainless steel) mould inserts for injection moulding of optical lenses. This paper will report on experiments carried out to investigate the wear of CBN tools with different grain sizes and various CBN/TiN ratios in ultra-precision machining of STAVAX. The tool-wear characteristics were observed to be greatly dependent on the tool type, hardness of the STAVAX and cutting parameters used. In the machining of STAVAX with a hardness of 55 HRC, fine-scale cavities were formed on the rake face and as such the surface damage acted like a chip breaker resulting in formation of cracks. While the flank faces of all tool types showed a similar wear resistance, it was observed that a combination of a higher percentage of TiN binder and smaller grain size led to greater wear resistance on the rake face. It was found that the formation of cracks on the rake faces could be prevented by means of either increasing the cutting speed or reducing the hardness of the machined workpiece.     

Effect of cutting speed on cutting forces and wear mechanisms in high-speed face milling of Inconel 718 with Sialon ceramic tools

In this paper, a series of milling tests were carried out in order to identify the effects of cutting speed on cutting forces and tool wear when high-speed face milling Inconel 718 with Sialon ceramic tools. Both down-milling and up-milling operations were conducted. The cutting forces, tool wear morphologies, and the tool failure mechanisms in a wide range of cutting speeds (600–3,000 m/min) were discussed. Results showed that the resultant cutting forces firstly decrease and then increase with the increase of cutting speed. Under relatively lower cutting speeds (600 and 1,000 m/min), the dominant wear patterns is notching. Further increasing the speed to more than 1,400 m/min, the notching decreases a lot and flank wear becomes the dominant wear pattern. In general, at the same cutting speed, flaking on the rake face and notching on the flank face are more serious in down-milling operation than that in up-milling operation with the same metal removal volume. However, the surface roughness values for down-milling are lower than that for up-milling.     

Evaluation of machining performance of STAVAX with PCBN tools

A study was undertaken to investigate the wear characteristics of polycrystalline cubic boron nitride (PCBN) cutting tools and surface integrity during machining of STAVAX (specialised stainless steel) with and without coolant. Plastic deformation and formation of overtempered martensite and white layer (untempered martensite) were the dominant subsurface and surface defects. It was found that decreasing the hardness of the STAVAX from 55 HRC to 40 HRC could result in fracture on the flank face, leading to a deterioration of the surface finish. It was observed that low CBN content tools (60%CBN/40%TiN) exhibited greater fracture resistance than high CBN content tools (85%CBN/15%TiN, 90%CBN/10%Co). Although coolant could not bring about a reduction in the flank wear, it was effective in reducing the subsurface and surface defects, and in preventing chipping of the tool edge, leading to an improved surface finish. A superior surface finish (Ra<0.3 m) was obtained with cutting fluid using a tool with a radius of 0.8 mm, depth of cut of 0.05 mm and feed rate of 0.05 mm/rev.     

Wear mechanisms of WC coated and uncoated tools in finish turning of Inconel 718

This paper presents the results of an experimental investigation on the wear mechanisms of uncoated tungsten carbide (WC) and coated tools (single-layer (TiAlN) PVD, and triple-layer (TiCN/Al₂O₃/TiN) CVD) in oblique finish turning of Inconel 718. Tool wear rate and wear mechanisms were evaluated for cutting speeds, 50<V<100 m/min, and feed rates, 0.075<f<0.125 mm/rev, at a constant depth of cut of 0.25 mm. It was concluded that abrasive and adhesive wear were the most dominant wear mechanisms, controlling the deterioration and final failure of the WC tools. While the triple layer CVD coated tools exhibited the highest wear resistance at high cutting speeds and low feeds, uncoated tools outperformed the single and multi-layer coated tools in the low range of cutting speeds and intermediate feeds. The cutting tool with single-layer PVD coating outperformed the other tools at the medium cutting speed.     

Failure mechanisms of a PCD tool in high-speed face milling of Ti–6Al–4V alloy

High-speed milling tests were carried out on Ti–6Al–4V titanium alloy with a polycrystalline diamond (PCD) tool. Tool wear morphologies were observed and examined with a digital microscope. The main tool failure mechanisms were discussed and analyzed utilizing scanning electron microscope, and the element distribution of the failed tool surface was detected using energy dispersive spectroscopy. Results showed that tool flank wear rate increased with the increase in cutting speed. The PCD tool is suitable for machining of Ti–6Al–4V titanium alloy with a cutting speed around 250 m/min. The PCD tool exhibited relatively serious chipping and spalling at cutting speed higher than 375 m/min, within further increasing of the cutting speed the flank wear and breakage increased greatly as a result of the enhanced thermal–mechanical impacts. In addition, the PCD tool could hardly work at cutting speed of 1,000 m/min due to the catastrophic fracture of the cutting edge and intense flank wear. There was evidence of workpiece material adhesion on the tool rake face and flank face in very close proximity to the cutting edge rather than on the chipped or flaked surface, which thereby leads to the accelerating flank wear. The failure mechanisms of PCD tool in high-speed wet milling of Ti–6Al–4V titanium alloy were mainly premature breakage and synergistic interaction among adhesive wear and abrasive wear.     

Effects of Coating Materials on the Machinability of a Nickel Base,C-263, Alloy

PVD coated (TiN/TiCN/TiN, TiAIN and TiZrN) and uncoated carbide tools were used to machine a nickel base, C-263, alloy at high-speed conditions. The test results show that the multiple TiN/TiCN/TiN coated inserts gave the best overall performance in terms of tool life when machining at cutting speeds up to 68 m min and at depths of cut of 0.635 mm, 1.25 mm and 2.54 mm. All the tool grades tested gave fairly uniform surface roughness (Ra) values, below the rejection criterion, at lower speed conditions. The TiZrN coated inserts gave the lowest component forces when machining at lower cutting speed conditions while the TiA/N coated inserts gave the lowest component forces when machining at a higher speed of 68 m min^?1 and depth of cut of 1.25 mm. This tool performance can generally be attributed to the difference in their ability to provide effective lubrication at the cutting zone, thermal conductivity of the coating materials as well as the cutting conditions employed. The uncoated carbide tools generally encountered more severe crater wear, chipping/fracture of the cutting edges as well as pronounced notching during machining. This is due to their inability to provide effective lubrication at the cutting zone, thus impeding the gliding motion of the chips along the rake and flank faces respectively, thus accelerating flank wear. Analysis of the worn tool edges revealed adhesion of a compact “fin-shaped” structure of hardened burrs with saw-tooth like edges. This generally alters the initial geometry of the cutting edge, consequently resulting to poor surface finish with prolonged machining.     

A method of using Hoelder exponents to monitor tool-edge wear in high-speed finish machining

Tool condition monitoring is increasingly important as a widespread application of automated, computer numerically controlled machining in a variety of modern industries. Although a significant amount of research on tool condition monitoring in machining has been conducted during the past few decades, the research is primarily focused on tool flank wear. Less attention is paid to tool-edge wear, which is a critical issue in high-speed finish machining where the feed rate is in the same magnitude as tool edge dimensions, and thus, the tool cutting edge is subjected to extensive mechanical and thermal deformation. The present study fills this important research gap in tool condition monitoring. This paper presents a method of monitoring tool-edge wear in the high-speed finish machining of an aerospace superalloy Inconel 718 by extracting Hoelder exponents from wavelet transform analysis of cutting vibrations. A total of 60 cutting experiments were conducted, covering a range of cutting speed and feed rate conditions. The experimental results show that cutting vibrations increase as tool-edge wear develops. Wavelet transform analysis can be employed to identify single local maxima of the cutting vibration signals. As tool-edge wear develops, the values of Hoelder exponents vary from 0.55 to 0.90. It is suggested that under the cutting conditions tested in the present study, 0.8 can be used as the threshold value of Hoelder exponents to differentiate severe and normal tool-edge wear.     

Detection of chipping in ceramic cutting inserts from workpiece profile during turning using fast Fourier transform (FFT) and continuous wavelet transform (CWT)

Ceramic cutting tool inserts are prone to premature failure by chipping instead of gradual wear due to their low impact toughness. Thus, in-process detection of failure of ceramic tools is important to prevent workpiece surface deterioration. The objective of this study is to develop a method of detection of the onset of chipping in ceramic cutting tool inserts during dry finish turning from the workpiece profile signature. The profile of the workpiece surface opposite the cutting side was captured using an 18-MP DSLR camera at a shutter speed of 0.25 ms during the turning of AISI01 oil-hardening tool steel. The edge profile was extracted to sub-pixel accuracy from the 2-D image of the workpiece surface using the invariant moment method. The effect of chipping in the ceramic insert on the surface profile signature of the workpiece was investigated using the fast Fourier transform (FFT) and continuous wavelet transform (CWT). The results show that the stochastic behavior of the cutting process after tool chipping manifest as sharp increase in the amplitude of spatial frequencies below the fundamental feed frequency. The proposed sub-window FFT method is effective in resolving the time resolution by detecting tool chipping at cutting time duration of around 17.13 s. Compared to the sub-window FFT method the CWT method is able to detect the exact onset of chipping in the cutting tool insert.