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.     

Workpiece Surface Integrity and Tool Life Issues When Turning Inconel 718™ Nickel Based Superalloy

Inconel 718 is one of a family of nickel-based superalloys which are used extensively in the aerospace industry in the hot sections of gas turbine engines. The literature detailing the effects of varying operating parameters on tool life when machining nickel based superalloys is comprehensive, however, relatively little of this data refers to their effects on machined workpiece surface integrity. Greater knowledge of the effects of operating parameters on surface integrity is critical to the acceptance of new cutting tool materials, tool geometries, and strategies, especially by the aerospace industry. The article initially reviews prior work on the machinability and surface integrity achieved when turning Inconel 718. Following on from this a series of experiments evaluating the effects of varying cutting tool material, geometry, and operating parameters are detailed.     

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。     

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.     

Performance and wear mechanisms of whisker-reinforced alumina, coated and uncoated PCBN tools when high-speed turning aged Inconel 718

Inconel 718, an efficient superalloy for energy and aerospace applications, is currently machined with cemented carbide tools at low speed (v _c?≈?60 m/min) due to its unfavorable mechanical and thermal properties. The article presents results of a study of superalloy machinability with whisker-reinforced alumina, uncoated and coated polycrystalline cubic boron nitride (PCBN) tools. Turning of age-hardened Inconel 718 (45 HRC) was done under high-speed machining conditions (v _c?=?250…350 m/min). Aspects of tool life, tool wear, and generated surface quality were studied. Application of uncoated PCBN tools resulted in surface quality and force level superior to other tool materials. Considerable sideflow of workpiece material was found to affect surface quality, especially for coated PCBN and ceramic tools. It was found that protective function of the coating, which increases the tool life up to 20 %, is limited only to low cutting speed range. EDX and AFM analyses suggested dominance of chemical and abrasive wear mechanisms. EDX mapping of worn tools pointed absence of diffusional wear for PCBN tools and intensive degradation of whisker reinforcement in ceramic tools due to diffusion of Ni, Fe, and Cr.     

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.     

Chip Formation Mechanism of Inconel 718:A Review of Models and Approaches

Inconel 718,a nickel,chrome and iron alloy,has special advantages,such as high-temperature strength,thermal resistance and corrosion resistance,which facilitate wide usage in the aerospace industry,especially in the hot sec-tions of gas turbine engines.However,machining this alloy is correlated closely with the material's inherent properties such as excellent combination of strength,hardness and toughness,low thermal conductivity and the tendency to adhere to cutting tools.This nickel alloy also contains inclusions of hard abrasive carbide particles that lead to work-hardening of the workpiece material and thus abrasive wear of the cutting tool.That is,the machining of Inconel 718 is always influenced by high mechanical and thermal loads.This article reviews the chip formation mechanism of Inconel 718.One of the main characteristics in machining of Inconel 718 is that it will produce serrated or segmented chips in a wide range of cutting speeds and feeds.Existing studies show that the chip serration or segmentation by shear localization affects the machined surface integrity,and also contributes to the chip's evacuation and the auto-mation of machining operations.Thus,research conclusion indicates that the serrated or segmented chip phenom-enon is desirable in reducing the level of cutting force,and detailed analysis of models and approaches to understand the chip formation mechanism of Inconel 718 is vital for machining this alloy effectively and efficiently.Therefore,this article presents some summaries on the models and approaches on the chip formation in machining of Inconel 718.     

高速车削Inconel 718切削力的试验研究

为了研究高速切削Inconel 718的切削力经验公式和各切削参数对切削力的影响显著程度,应用涂层硬质合金刀具对Inconel 718进行了正交车削试验,得到了硬质合金刀具车削Inconel 718的切削力经验公式。分析结果表明:对切削力影响最大的因素是进给量,切削深度和切削速度对试验结果的影响依次减弱。用涂层硬质合金刀具KC5510精车Inconel 718时,采用小进给量、小切削深度、高切削速度可以得到小的切削力,取得良好的切削效果。     

Finish Machining of Nickel-Base Inconel 718 Alloy with Coated Carbide Tool under Conventional and High-Pressure Coolant Supplies

Single-point turning of Inconel 718 alloy with commercially available Physical Vapour Deposition (PVD)-coated carbide tools under conventional and high-pressure coolant supplies up to 20.3 MPa was carried out. Tool life, surface roughness (Ra), tool wear, and component forces were recorded and analyzed. The test results show that acceptable surface finish and improved tool life can be achieved when machining Inconel 718 with high coolant pressures. The highest improvement in tool life (349%) was achieved when machining with 11 MPa coolant supply pressure at higher speed conditions of 60 m · min^?1. Machining with coolant pressures in excess of 11 MPa at cutting speeds up to 40 m · min^?1 lowered tool life more than when machining under conventional coolant flow at a feed rate of 0.1 mm · rev^?1. This suggests that there is a critical coolant pressure under which the cutting tools performed better under high-pressure coolant supplies.

Cutting forces increased with increasing cutting speed due probably to reactive forces introduced by the high-pressure coolant jet. Tool wear/wear rate increased gradually with prolonged machining with high coolant pressures due to improved coolant access to the cutting interface, hence lowering cutting temperature. Nose wear was the dominant tool failure mode when machining with coated carbide tools due probably to a reduction in the chip-tool and tool-workpiece contact length/area.     

Wear behavior of adaptive nano-multilayered AlTiN/MexN PVD coatings during machining of aerospace alloys

Machining of aerospace materials is one of the major challenges of modern manufacturing. Application of nano-multilayered AlTiN/Me_xN PVD coatings (where Me_x is a transition metal of V-VI groups of periodic table) to cemented carbide tooling results in a significant tool life improvement under conditions of cutting hard to machine alloys such as Ni-based Inconel 718 superalloy and Ti-based TiAl6V4 alloy. Microhardness and coefficient of friction of the coatings were measured during this experiment. Investigations of the coated tool life, wear behavior, chip formation (chip type and undersurface morphology) for cutting tools with nano-multilayered PVD coating were also performed. Morphology of worn tools has been studied using SEM and EDX. This study will show that metallurgical design of the nano-multilayered coating should be tailored to its application. To achieve better tool life when machining Inconel 781, adaptive nano-multilayered AlTiN/MoN coating is recommended, whereas a AlTiN/VN coating is better suited to machining TiAl6V4 alloy. A driving force behind selecting these coatings was a noticeably lower coefficient of friction at elevated temperatures.     

Investigation and optimization of lubrication parameters in high speed turning of superalloy Inconel 718

Dry machining is sometimes less effective when higher machining efficiency, better surface finish quality, and severe cutting conditions are required. For these situations, semi-dry operations utilizing very small amount of cutting fluids called minimum quantity lubrication is expected to become a powerful tool and played a significant role in a number of practical applications. It has been observed from the literature survey that a systematic research work has to be carried out to determine the optimum quantity of lubricant with appropriate cutting conditions for achieving better machinability characteristics of a material. Hence, an attempt has been made in this paper to enhance the machinability characteristics in high speed turning of superalloy Inconel 718 using quantity of lubricant, delivery pressure at the nozzle, frequency of pulses, direction of application of cutting fluid, cutting speed, and feed rate as the process parameters. Results indicated that the use of optimized minimum quantity lubrication parameters under pulsed jet mode leads to lower cutting force, cutting temperature, and flank wear.     

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.     

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.     

Study of surface quality in machining nickel-based alloy Inconel 718

In machining operation, the surface quality is one of the most important requirements for many workpieces. Because of the special physical and chemical properties, good-machined surface quality becomes a key issue to solve in machining Inconel 718. In this paper, PVD-TiAlN-coated carbide tools were used to turn Inconel 718. Based on observing the tool wear and machined surface morphology, the main factors affecting surface quality at different cutting speeds were analyzed. The optimal cutting temperature was calculated, according to the above analysis and Archard adhesion wear model, and further cutting parameters optimization was conducted, on the basis of the proposed optimal cutting temperature. The optimized cutting parameters based on optimal cutting temperature can be considered to improve surface quality.     

用于加工Inconel718的切削刀具发展现状

镍基高温合金Inconel718具有熔点高、热传导率低、加工硬化现象严重的特点,被认为是最难加工的金属材料之一。近年来,随着航空航天、能源动力技术的飞速发展,Inconel718高温合金的应用越来越多,其高速、高效切削的加工需求也日益扩张,其切削工艺的制定、尤其是切削刀具的选择越来越重要。本文综述了常用于加工In-conel718的刀具(高速钢、硬质合金、陶瓷、立方氮化硼)及其涂层刀具的加工性能,分析了不同涂层对于刀具寿命和工件表面质量的影响,对硬质合金刀具和陶瓷刀具作了详尽的对比分析。最后,对高速钢、陶瓷、硬质合金和立方氮化硼刀具切削Inconel718的应用情况进行了总结,给出了Inconel718高温合金切削加工刀具选择的有益参考。     

Improving surface integrity in finish machining of Inconel 718 alloy using intelligent systems

In machining of hard materials, surface integrity is one of the major customer requirements which comprise the study of the changes induced to the workpiece. Surface roughness and residual stress are often considered as the most significant indications of surface integrity. Inducing tensile residual stress during the machining processes is a critical problem which should be avoided or minimized to obtain better service quality and component life. This problem becomes more evident in the presence of rough machined surface because fatigue life of manufactured components might be decreased significantly. Inconel 718 superalloy is one of the hard materials used extensively in the aerospace industries. It is prone to tensile residual stress in machined surface. Thus, controlling and optimizing residual stress and surface roughness in machining of Inconel 718 are so needed. Intelligent techniques based on the predictive and optimization models can be used efficiently for this purpose. In this study, the optimal machining parameters including cutting speed, depth of cut, and feed rate were accessed by intelligent systems to evaluate the state of residual stress and surface roughness in finish turning of Inconel 718. The results of experiments and analyses indicated that implemented techniques in this work provided a robust framework for improving surface integrity in machining of Inconel 718 alloy. It was shown that cutting speed has more effect on surface integrity than other investigated parameters. Also, depth of cut and feed rate were found in the moderate range to obtain satisfactory state of tensile residual stress and surface roughness.     

Improving machinability of Inconel 718 with a new hybrid machining technique

In this paper, by joining three non-traditional machining methods — plasma-enhanced machining, cryogenic machining, and ultrasonic vibration assisted machining — a new hybrid machining technique for machining of Inconel 718 is presented. Cryogenic machining reduces the temperature in the cutting zone, and therefore decrease tool wear and increases tool life, while plasma-enhanced machining helps to increase the temperature in the workpiece to make it softer. Also, applying ultrasonic vibrations to the tool helps to improve cutting quality and to prolong tool life by lowering, mainly, the cutting force and improving the dynamic cutting stability. This study experimentally investigates the effect of cutting parameters on cutting performance in the machining of Inconel 718 and compares the results of hybrid machining and conventional machining (CM). It is found that the hybrid method results in better surface finish and improves tool life in hard cutting at low cutting speeds as compared to the CM method.     

The performance Of DLC-coated and uncoated ultra-fine carbide tools in micromilling of Inconel 718

Coating is an important factor that affects cutting-tool performance. In particular, it directly affects surface quality and burr formation in the micro milling process. After the micromechanical machining process, surface quality is very hard to increase by a second process (grinding, etc.). In addition, in micromechanical machining, the cutting tool needs to have a good resistance to wear, owing to the fact that the cutting process is carried out at high speed. In this study, the machinability of Inconel 718 superalloy was investigated, using a Diamond Like Carbon (DLC) coated tool. The experimental tests were carried out in dry cutting conditions for different feed rates and depth of cuts. It was found that the dominant wear mechanism for all cutting parameters was identified to be abrasive and diffusive wear. Besides, a significantly Built Up Edge (BUE) formation was observed in uncoated tool. The results clearly show that DLC coating significantly decreased BUE. In addition, a smaller cutting force and better surface roughness were obtained with a DLC-coated tool. In conclusion, DLC coating can be used in micro milling of Inconel 718. It reduces the BUE and burr formation, improves surface roughness.     

Development of a novel cubic boron nitride cutting tool with a textured flank face for high-speed machining of Inconel 718

Nickel-based superalloys such as Inconel 718 offer several advantages, including high-temperature strength and high corrosion resistance; this has led to a rapid increase in the demand for such materials, particularly in the aircraft industry. In contrast, these alloys are known to be among the most difficult-to-cut materials because of their mechanical and chemical properties, and tools used for this purpose have extremely short lifetimes. Recently, cubic boron nitride (CBN), which is the second hardest of all known materials, has received significant attention as a material for cutting tools and has already established itself in many fields of application. However, the performance of CBN tools is still insufficient for practical use, especially in the high-speed machining of Inconel 718. To overcome this problem, we first conducted orthogonal cutting experiments on Inconel 718 and performed cross-sectional observations of the CBN cutting tool in order to identify its wear mechanisms in continuous cutting operations under high-speed machining conditions (300 m/min). As a result, it was found that fatal tool failure occurs through crater and flank wear because of diffusion led by high cutting temperatures and subsequent chip adhesion to the tool flank face, accompanied by cutting edge chipping. Based on these results, a CBN cutting tool with a textured flank face was newly developed to improve the cutting tool life. Experimental: results showed that micro grooves generated on the flank face significantly suppressed the cutting edge chipping and remarkably extended the lifetime of the CBN tool during high-speed machining of Inconel 718.