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.     

EXPERIMENTAL INVESTIGATION ON SURFACE INTEGRITY OF END MILLING NICKEL-BASED ALLOY— INCONEL 718

Inconel 718 is a typical difficult-to-machine material, and its high speed end milling process has wide applications in manufacturing parts from aerospace and power industry. Surface integrity of these parts greatly influences the final characteristics. This paper presents an experimental investigation to evaluate surface integrity behaviors in high speed end milling of Inconel 718 with finishing cutting parameters in terms of surface topography, surface roughness Ra, residual stresses, subsurface microstructure, and microhardness. The results show that abraded marks can be observed on the machined surfaces, and high cutting speed is advisable to get better surface topography and roughness quality. Due to high cutting temperature, residual stress is mainly high tensile stress. After increasing the cutting speed beyond 80m/min, the cutting forces hardly increased and the chips take away more cutting heat, which leads to that the residual stress barely increases. Microstructures in subsurface layers have only slight deformations after high speed milling, and there was also no obvious difference when the cutting speed increased beyond 80m/min against the microhardness in subsurface increases together with the cutting speed.     

Analysis of residual stress and work-hardened profiles on Inconel 718 when face turning with large-nose radius tools

Surface integrity (SI) and, particularly, the residual stress profile, has a great influence on the fatigue life of machined aeronautical critical parts. Among the different cutting parameters that affect the final SI, tool geometry is one of the most important factors. In particular, tool nose radius determines the surface roughness, as well as the thermoplastic deformation of the workpiece. Indeed, the use of large tool nose radius in the industry enables (1) increasing the feed rate while keeping the roughness values below specifications and (2) reducing the influence of the tool wear in the surface roughness. Therefore, in this study, the influence of tool nose radius in the induced residual stress profile and work-hardened layer when face turning Inconel 718 is analysed for a cutting speed range between (30–70 m/min) and a feed rate range of (0.15–0.25 mm/rev). For this purpose, residual stress profiles and work-hardened layer were measured by x-ray diffraction method after machining with a 4 mm nose radius. Then, results have been compared against different tool nose radius studies carried out by other authors for the specified working conditions. Results revealed that residual stress profiles varied when machining with different nose radius for the studied range. In particular, the increase of the nose radius brought to a higher difference between surface tensile stress and subsurface compressive peak stress, which is attributed to an increase of the thermal effect. Moreover, thicker work-hardened layer (around 100 μm) was observed when machining with large-nose radius for the studied working conditions.     

RESIDUAL STRESSES ON INCONEL 718 TURBINE SHAFT SAMPLES AFTER TURNING

Results of X-ray residual stress measurements on Inconel 718 turbine shaft samples are here proposed. The paper presents part of the EU STREP project VERDI activity, where the aim was to supply those who numerically simulate machining process with an experimental database of proved reliability. Measurements were planned on a set of samples machined with different levels of cutting speed and feed rate. Due attention was given to the assessment of the uncertainty of experimental results. A database of surface residual stress values and depth profiles is presented with the estimated uncertainty both on stress and depth values. The stress proved to be always tensile at the surface and compressive below the surface. Higher cutting speed and feed rates produce higher surface tensile stresses but the trends are different for the two measurement directions.     

Optimization of cutting conditions for minimum residual stress,cutting force and surface roughness in end milling of S50C medium carbon steel

Residual stresses are usually imposed on a machined component due to thermal and mechanical loading. Tensile residual stresses are detrimental as it could shorten the fatigue life of the component; meanwhile, compressive residual stresses are beneficial as it could prolong the fatigue life. Thermal and mechanical loading significantly affect the behavior of residual stress. Therefore, this research focused on the effects of lubricant and milling mode during end milling of S50C medium carbon steel. Numerical factors, namely, spindle speed, feed rate and depth of cut and categorical factors, namely, lubrication and milling mode is optimized using D-optimal experimentation. Mathematical model is developed for the prediction of residual stress, cutting force and surface roughness based on response surface methodology (RSM). Results show that minimum residual stress and cutting force can be achieved during up milling, by adopting the MQL-SiO₂ nanolubrication system. Meanwhile, during down milling minimum residual stress and cutting force can be achieved with flood cutting. Moreover, minimum surface roughness can be attained during flood cutting in both up and down milling. The response surface plots indicate that the effect of spindle speed and feed rate is less significant at low depth of cut but this effect significantly increases the residual stress, cutting force and surface roughness as the depth of cut increases.     

Investigation of surface integrity in dry machining of Inconel 718

Machining of advanced aerospace materials have grown in the recent years although the diffucult-to-machine characteristics of alloys like titanium or nickel-based alloys cause higher cutting forces, rapid tool wear, and more heat generation. Therefore, machining with the use of cooling lubricants is usually carried out. To reduce the production costs and to make the processes environmentally safe, the goal is to move toward dry cutting by eliminating cutting fluids. This objective can be achieved by using coated tool, by increasing cutting speed, and by improving the product performance in term of surface integrity and product quality. The paper addresses the effects of cutting speed and feed on the surface integrity during dry machining of Inconel 718 alloy using coated tools. In particular, the influence of the cutting conditions on surface roughness, affected layer, microhardness, grain size, and microstructural alteration was investigated. Results show that cutting conditions have a significant effect on the parameters related to the surface integrity of the product affecting its overall performance.     

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.     

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。     

刀片钝化半径对高温合金切削质量影响的研究

通过不同钝化半径的刀具对GH4169高温合金进行车削正交试验,结果表明:随着钝化半径的增加,表面残余应力先降低后增加;工件环向残余应力随着钝化半径的增加,工件内部残余压应力最大值增大,影响深度随之增加。由表面粗糙度和表面残余应力的敏感程度可知,进给量是影响表面完整性的最主要因素,其次是切削速度和切削深度。分析了不同钝化半径和切削参数对表面完整性特征的影响规律,建立了表面粗糙度表面残余应力的经验公式,得到了用于精加工GH4169高温合金较好的钝化半径范围0.02~0.03mm,以及较优的切削参数vc=60~70m/min,fn=0.05~0.075mm/r,ap=0.2~0.5mm。     

Development of a pressurized internal cooling milling cutter and its machining performance assessment

In view of the serious problem of milling heat in milling nickel-based superalloys Inconel 718, this paper investigates the heat transfer performance of internal cooling in end milling Inconel 718, and the superiority of internal cooling milling cutter's heat exchange ability during processing is explored. The flow field characteristics of cutting fluid and milling temperature are studied by Computational Fluid Dynamics (CFD) and Finite Element Method (FEM). Compared with external flood cooling, the principle of internal cooling with excellent heat transfer performance is explained and the influence of coolant pressure on lubrication performance is analyzed. Experiments for end milling of Inconel 718 under different cutting speeds and cooling conditions have been carried out. The results indicate that the simulated and measured temperatures showed an acceptable agreement. The internal cooling has better heat transfer performance compared with flood cooling. With the increase of coolant pressure, the heat exchange efficiency is gradually enhanced. When the coolant pressure rises from 2 bar to 10 bar, the milling temperature at the measured point inside the workpiece reduces by 27.55 °C, the surface roughness reduces by 12.0%, the surface residual compressive stress increases by 68.37 MPa and better surface morphology is obtained. Besides, in the experimental range, with the increase of cutting speed, milling temperature increased, the pile-up effect on the sides of scratching was weakened and better machined surface integrity was found.     

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.     

高速铣削 Inconel718已加工表面残余应力的有限元分析

利用有限元法对镍基高温合金Inconel 718的高速正交铣削进行模拟仿真,获得切削力、切削温度和残余应力.结果表明在仿真切削速度100-3000m/min范围内,刀尖峰值温度随切削速度提高而增大,由于高温造成工件软化,从而使切削力随切削速度增大而减小;残余应力层深度在已加工表面O.5mm以下,最大表面残余应力为拉应力...     

Surface roughness modeling in Laser-assisted End Milling of Inconel 718

Inconel 718 is a difficult-to-machine material while products of this material require good surface finish. Therefore, it is essential for the evaluation and prediction of surface roughness of machined Inconel 718 workpiece to be developed. An analytical model for the prediction of surface roughness under laser-assisted end milling of Inconel 718 is proposed based on kinematics of tool movement and elastic response of workpiece. The actual tool trajectory is first predicted with the consideration of overall tool movement, elastic deformation of tool, and the tool tip profile. The tool movements include the translation in feed direction and the rotation along its axis. The elastic deformation is calculated based on the previously established milling force prediction model. The tool tip profile is predicted based on the tool tip radius and angle. The machined surface profile is simulated based on the tool trajectory with elastic recovery, which is considered through the comparison between the minimum thickness and actual cutting thickness. Experiments are conducted in both conventional and laser-assisted milling under seven different sets of cutting parameters. Through the comparison between the analytical predictions and experimental measurements, the proposed model has high accuracy with the maximum error less than 27%, which is more accurate for lower feed rate with error less than 3%. The proposed analytical model is valuable for providing a fast, credible, and physics-based method for the prediction of surface roughness in milling process.     

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.     

硬态切削高强度钢表面完整性的研究

高强度钢45CrNiMoVA以其良好的力学性能,被广泛作为车辆悬挂系统弹性零件扭杆的材料。45CrNiMoVA是典型的高强度钢,属于难加工材料,扭杆在实际应用中通常经常承受大应力、应变、冲击影响,疲劳寿命成为影响其断裂失效的重要参数。表面质量能够影响材料的疲劳强度、磨损率、耐腐蚀性等特征。硬态切削可以有助于在简化加工工艺的同时,达到预期的表面质量。对于已知的各种参数,如切削速度、进给率和切削深度对表面完整性都有很大的影响。在本试验中,表面完整性主要通过表面粗糙度、残余应力、微观硬度等方面进行分析。     

深冷处理对PCBN刀具切削性能的影响研究

针对PCBN刀具在硬切削加工中磨损严重、切削寿命短的问题,开展了PCBN刀具深冷处理试验和经深冷处理的PCBN刀具高速硬车削AISI 4340钢的试验,研究深冷处理对PCBN刀具表面完整性(包括微观形貌、粗糙度、显微硬度和残余应力)及切削性能的影响规律,探究提高PCBN刀具耐磨性和刀具寿命的方法。研究结果表明,经过深冷处理之后,刀具表面缩松缩孔等缺陷明显减少甚至消失,表面形貌得到改善,但刀具表面粗糙度增大;刀具表面显微硬度、残余应力均得到提高;表面形貌和表面残余应力对刀具寿命影响较大,其次是表面显微硬度,表面粗糙度对刀具寿命影响较小。深冷处理后,刀具黏结、氧化磨损减少,刀具寿命较未处理刀具提高24.78%,可见,深冷处理可有效改善PCBN刀具表面完整性,从而提高刀具寿命。     

Intelligent optimization and selection of machining parameters in finish turning and facing of Inconel 718

The heat-resistant super alloy material like Inconel 718 machining is an inevitable and challenging task even in modern manufacturing processes. This paper describes the genetic algorithm coupled with artificial neural network (ANN) as an intelligent optimization technique for machining parameters optimization of Inconel 718. The machining experiments were conducted based on the design of experiments full-factorial type by varying the cutting speed, feed, and depth of cut as machining parameters against the responses of flank wear and surface roughness. The combined effects of cutting speed, feed, and depth of cut on the performance measures of surface roughness and flank wear were investigated by the analysis of variance. Using these experimental data, the mathematical model and ANN model were developed for constraints and fitness function evaluation in the intelligent optimization process. The optimization results were plotted as Pareto optimal front. Optimal machining parameters were obtained from the Pareto front graph. The confirmation experiments were conducted for the optimal machining parameters, and the betterment has been proved.     

Research on surface integrity of grinding Inconel718

Inconel718 is widely used in the aerospace industry; the finished surface quality has significant effect on service performance of component. The surface integrity in grinding Inconel718 respectively by using a vitrified bond single alumina (SA) wheel and a resin cubic boron nitride (CBN) wheel were investigated. First, effects of different grinding parameters on grinding temperature and grinding force and grinding chips feature by using a SA and a CBN wheel respectively were investigated. Then, the surface roughness and topography by using a SA and a CBN wheel through single factor experiment were compared, and in the grinding parameters range of the present study, the better surface can be obtained by a SA wheel. Finally, surface integrity by using a SA wheel and the different grinding depth was studied and analyzed by the grinding temperature and the grinding force. It was possible to conclude that better surface can be achieved by using a SA, and taking a _p?=?0.005 mm, v _w?=?16 m/min, v _s?=?25 m/s for grinding Inconel718. In this grinding case, the surface roughness was Ra0.112 μm, the surface residual stress was +700Mpa, and the surface hardness was 440 HV; the depth of residual stress layer was 40～60 μm, the depth of softened layer was 30～40 μm and the depth of plastic deformation layer was 10～15 μm.     

Incone1718镍基高温合金的切削性能仿真

在考察Inconel718镍基高温合金的化学成分和有关性能的基础上,通过Deform-3D软件对其进行车削仿真,分析影响Inconel718镍基高温合金切削性能的主要因素,给出其最佳的切削速度、进给量和背吃刀量的组合.研究了不同换热系数和刀-屑摩擦因数对Inconel718镍基高温合金切削性能的影响,找到了恰当的冷却润滑方式.     

Optimum surface roughness in end milling Inconel 718 by coupling neural network model and genetic algorithm

In this study, optimum cutting parameters of Inconel 718 are determined to enable minimum surface roughness under the constraints of roughness and material removal rate. In doing this, advantages of statistical experimental design technique, experimental measurements, artificial neural network and genetic optimization method are exploited in an integrated manner. Cutting experiments are designed based on statistical three-level full factorial experimental design technique. A predictive model for surface roughness is created using a feed forward artificial neural network exploiting experimental data. Neural network model and analytical definition of material removal rate are employed in the construction of optimization problem. The optimization problem was solved by an effective genetic algorithm for variety of constraint limits. Additional experiments have been conducted to compare optimum values and their corresponding roughness and material removal rate values predicted from the genetic algorithm. Generally a good correlation is observed between the predicted optimum and the experimental measurements. The neural network model coupled with genetic algorithm can be effectively utilized to find the best or optimum cutting parameter values for a specific cutting condition in end milling Inconel 718.