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Inconel 718 is a widely used alloy in the aeronautic sector due to its excellent mechanical and corrosion wear resistance under high temperature conditions. However, its good mechanical properties can be a double edge sword in terms of manufacturing, especially in those processes based in mechanical principles, such as machining or forming. Considering that most aeronautic components are exposed to cyclic load and temperature, fatigue resistance becomes critical, and therefore, the finishing processes. The surface integrity of a component plays an important role on its fatigue behaviour, as the most common crack initiation area is usually the surface. The present work compares three different mechanical finishing processes that confer better surface properties to the component: polishing, burnishing, and hammer-peening. Each one achieves different degrees of roughness, and residual stress on the surface. The study is not only focused on the resultant mechanical properties, but also in productivity and process robustness. It is concluded that each technology excels in a different property.

Today’s industrial transformation is taking advantage of the benefits of information and communication technologies (ICT) to evolve into a more decision-making environment in manufacturing. Efficiency, agility, innovation, quality and cost savings are the goals of this transformation in one of the most employed manufacturing processes as is the case of machining. Drilling processes are among the last operations in the different manufacturing stages of machined parts, where an undetected problem can lead to the production of a defective part. Data analysis of sensor signals gathered during drilling processes provides information related to the cutting process that can anticipate non-desired phenomena. This work illustrates the experimental setup for sensorial data acquisition in drilling processes, signal processing techniques and feature extraction methodologies for faster and more robust decision-making paradigms.

A novel methodology to map the friction and normal stress distribution on the rake face using Partially Restricted Contact Length Tools in orthogonal cutting tests is proposed. The influence of cutting speed, feed and coatings on tool-chip friction when machining AISI 1045 is analysed. The results demonstrate that the new methodology can replace the more difficult to use and less robust split-tool method. They confirm two clearly different contact zones: i) the sticking region, governed by the shear flow stress of the workpiece and ii) the sliding region, where the friction coefficient is higher than 1.

Prediction of cutting forces in finishing conditions is becoming essential for the automotive industry, in order to achieve the desired surface integrity and keep controlled phenomena as chatter, especially in workpieces with small thickness walls manufactured by die casting. For predictions, orthogonal to oblique models are widely used, which require a material database as input data. Databases found in the literature have been proven to predict forces accurately in roughing conditions. However, several geometric parameters of the inserts are not taken into account, which could lead to inaccurate predictions in finishing conditions. In this paper, the effects of the cutting edge radius and clearance angle are analysed over the cutting and feed forces during orthogonal turning. A material database for A-356 aluminium alloy is developed following a methodology in accordance with previous research. Finishing face milling tests are carried out for validation, obtaining good agreement with modelled forces.

Employing cutting fluids in machining processes, especially for difficult-to-cut materials, improves machinability through prolonged tool life, improves surface integrity and chip evacuation. However, like oil and water-based cutting fluids are hazardous to the environment and workers’ health, alternative solutions are required. Liquid Nitrogen (LN2) is a cryogenic fluid that can be an option due to its low boiling point (-197oC) and the fact it exists in the atmosphere at room conditions. Nevertheless, the feasibility of cryogenic cooling techniques in machining is not fully understood; this is why the Finite Element Method (FEM) could give an insight into the phenomena happening on the tool-chip/workpiece interface. This research aims to compare fundamental and industrial outputs when turning hardened steel 100Cr6 using Cubic Boron Nitride (CBN) inserts with wiper geometry in dry conditions and with cryogenic cooling. For this purpose, turning experimental tests were performed in both cooling conditions varying the cutting speed (150-550 m/min). Machining forces were measured during the tests, and then tool wear, microstructural damage, and residual stresses of the workpiece were characterised. A nose turning (3D) FEM model was also developed to understand the influence of cooling strategy on the outputs measured experimentally.

Tribofinishing is one of the most popular polishing process in industry. The action of small abrasive media around parts enables to reduce significantly surface roughness and at the same time, to induce compressive residual stresses in the external surface layer. However, few scientific investigations have been made about this process. Whereas most of the previous works were focused on the effect of abrasive grains, the influence of lubrication and especially the filtering of the lubricant on the surface integrity have never been investigated before. This paper aims to study the influence of the presence of debris coming from the part and the media in the polishing process. For that purpose, rough surface parts (Ra~15 µm) have been tribofinished without and with lubrication filtering. Roughness parameters (Ra, RSm and Rsk), the offset between surface profiles and residual stresses have been compared. It is revealed that the lack of filtering leads to the presence of debris coming from the part and the media. This modifies tremendously the action of the media and prevent the surface from being polished properly. The reduction of roughness is saturated and the material is excessively deformed as a consequence of debris incrustations in the surface.

In machining of Ti-6Al-4V, it is commonly reported the appearance of segmented chip produced by adiabatic shearing (at high cutting speeds) and lack of ductility (at low cutting speeds). Moreover, machining is a manufacturing process that is based on applying external energy to the workpiece to produce a separation of a material layer. Thus, to analyze the physics involved in the new surface generation and in the chip segmentation process, it is necessary to apply ductile failure models. However, the characterization of fracture models in machining conditions (temperature, strain rate, stress triaxiality, Lode angle etc.) is an arduous task. Therefore, to define a ductile failure model applicable to machining it is almost inevitable to apply inverse simulations strategies to obtain reliable results in the not tested conditions. Nevertheless, there is few information about the influence of the input parameters of ductile failure model in fundamental outputs and even less in surface integrity aspects. The aim of this research was to conduct a sensitivity analysis of the influence of the input parameters of a physical based ductile failure model not only in fundamental variables (forces, temperatures and chip morphology) but also on surface integrity (surface drag). To this end, a subroutine was developed for the ductile failure model and it was implemented in the Finite Element Method (FEM) software AdvantEdge. Subsequently, using a statistical software and the Design of Experiments (DOE) technique the influence of the input parameters of the failure model on the outputs was analyzed.

International audience; Surface integrity directly affects the mechanical behavior of the workpiece, which is especially relevant on fatigue behavior. To characterize the quality of the machined surface, aspects such as material damage, roughness or residual stress are considered. Measurement of the material damage of the surface is characterized in some cases as surface drag, depth of the affected machining zone, a phenomenon which takes place due to plastic strain in the surface layer caused by machining stress which could have an influence on residual stress. Surface drag measurement done with optical microscopes has relevant uncertainty. In this paper, a methodology to measure the surface drag with lower uncertainty is proposed. The method consists of measuring the deformation of a grid as a result of the machining process. The grid was created with micromilling. The method was applied to analyze the effect of feed on the surface integrity after orthogonal cutting of Ti-6Al-4V. The depth of the affected layer was measured using a 3D optical measuring device (Alicona Infinite Focus IFG4) and compared with numerical simulations and a good agreement was achieved. In comparison with optical microscope results, it can be concluded that traditional method underestimates surface drag

Broaching is a unique machining process with high accuracy and surface quality, which is employed in mass and batch production for the manufacture of components with highly complex geometries. It involves the use of multiple-edged complex tools in which the cutting edges are arranged with an offset also known as “rise per tooth” that determines the depth of cut per tooth. This paper presents the state-of-the-art of both the experimental and modelling aspects of broaching, and identifies the most important features related to this machining process. This includes a critical assessment of specifically designed broaching setups and their applicability and/or limitations compared to the machines used in industry. Contributions from academia and industry are included to support a comprehensive report of recent advances, as well as a roadmap for future developments.

Machining processes are subjected to machining vibrations and specially to chatter. This self-excited vibration determines the productivity of the processes. Over the years, many studies have been developed analysing the influence of the tool and machine structure on chatter. However, not many studies have been carried out on the workpiece material influence on chatter. The workpiece material is a characteristic settled form the drawings that cannot be changed. Due to this, in which extent the SLD (Stability Lobe Diagram) is affected by the workpiece material parameters is essential to increase the chatter knowledge. To that end, an experimental study of the workpiece influence on chatter was carried out, stablishing specific cutting force and Process Damping Wavelength as the main cause parameters of this influence. In order to obtain the necessary data to demonstrate the influence of both parameters on SLD, some experimental tests were carried out milling 34CrNiMo6 and Al 6082. Thus, these results showed how the SLD is affected.

The ploughing force related with action of edge radius is an important factor which influences flow stress, chip formation or surface integrity. Some fraction of the cutting forces are called parasitic (additional) forces and they do not contribute on chip formation process. These forces are usually assumed to be the cutting force (constant value) for zero feed. However, this effect is related with the edge radius. To improve force modelling prediction, a new mechanistic model to predict cutting force considering edge radius is presented. The model was developed for two cutting speeds and in a wide range of feeds for three edge radii. The model was validated with additional experimental tests, achieving relative errors lower than 3%.

The aim of the present paper is to study by Finite Element Method (FEM) the hard turning of 42CrMoS4 steel. A numerical and experimental study was carried out to analyze the effect that cutting parameters have on cutting and feed forces, temperatures on the cutting zone, contact length and chip morphology. A flow stress model for the FEM model was developed by dynamic compression tests. Experimental tests were done to establish the accuracy of the FEM model, developed in DEFORM. The tendencies of both frameworks agreed in forces and temperatures. Greater differences were found for contact length and chip thickness predictions.

A new flow stress model is proposed to describe the behaviour of ferrite–pearlite steels based on microstructure properties, including the effect of high strains, strain rates and temperatures. The model introduces strain hardening as a function of the pearlite ratio, interlamellar spacing and ferrite grain size. A non-linear thermal softening, and the coupling between strain rate and temperature are also introduced. Tested on a 2D ALE model, predicted cutting forces, tool temperatures, chip thickness and tool wear results obtained good agreement when compared to orthogonal cutting tests of four ferrite–pearlite steels, covering a wide range of microstructure variants.

Temperature measurement in metal cutting is of central importance as tool wear and surface integrity have been demonstrated to be temperature dependent. In this context, infrared thermography is presented as a reliable technique to determine tool temperatures and thermal fields at near real-time. However, a constraint of this technique is that temperatures are measured on the tool side faces normal to the cutting edge but offset from the tool/chip contact. In the present research, tool/chip contact temperatures were calculated from the tool side based on analytical theories of heating and the principles of heat generation in cutting processes. The required inputs were commonly measurable variables (cutting and feed forces, chip thickness and tool/chip contact length). The proposed approach was combined with a new calibration method in which a calibration curve that directly relates real and radiated temperatures is obtained, instead of measuring the emissivity of the radiating surface. As a case study, the research was conducted on a set of four ferrite-pearlite steels (16MnCr5, 27MnCr, C45 and C60). The results demonstrated the effectiveness of the method to establish the real influence of the cutting conditions (cutting speed and feed) and to distinguish the effect that different work material microstructures have in tool/chip temperature. Furthermore, the results showed a high degree of accuracy and less than 12% deviation from the trends when compared with 2D cutting simulations.

In depth understanding of tool-chip friction behavior is a significant aspect for tool wear performance in steels. In the present work attention has been paid to the strain mode of the chip section in contact with the rake surface of the tool, and its influence on the mechanics of material removal. There is a multitude of evidence for the existence of qualitatively different cutting regimes in orthogonal machining of annealed AISI-1045 steel with uncoated P15 carbide cutting tools in dry conditions at cutting speeds between 5 and 200 m/min. The evaluation of chip morphology and microstructure, and cutting and feed forces, revealed an abrupt step-like transition at a cutting speed in the range of 50–60 m/min, which was attributed to the transition from built-up edge (BUE) mode developed at low cutting speed, to the mode at which the chip slides directly over the tool surface. These qualitatively distinct mechanisms of tool-chip interaction are determined by two different microstructural effects: work hardening by severe plastic deformation and microstructural softening by dynamic recrystallization (DRX). It is argued that the onset of DRX is the reason for further instability of BUE and thus is the main cause of change of the cutting regime.

A new method for measuring temperature in the rake face of a tool during dry orthogonal cutting using thermography is presented. In addition, a new technique is also used to calibrate the infrared camera. Using this technique, real temperature values from camera response are directly obtained without the need for emissivity correction. Emissivity is thus not an uncertainty source. These techniques were applied to machining AISI 4140. Rake face temperatures are reported and correlation with cutting forces outlined. The set-up effectively showed temperature distribution on the rake face.

A material database for JETHETE-M152 was developed applying a novel methodology for improving the precision of cutting forces. This approach defines a variable specific edge force depending on the feed rate and cutting edge geometry. Applying this methodology, accurate predictions could be obtained when using complex shape inserts with different micro-geometries or with feed rates lower than the cutting edge radius. These predictions showed an improvement compared to those of the strategy of keeping constant the specific edge coefficient. Furthermore, an orthogonal to oblique transformation technique was applied to predict the cutting forces in face and side milling. The results showed good agreement with experimental results.

The performance of aeronautic critical components is strongly dependent on its fatigue behavior, which is directly linked to their surface integrity condition. Broaching operation is a machining operation extensively used for the manufacturing of some features due to the good dimensional quality and surface integrity condition obtained. Thus, the characteristics of surface integrity obtained in broaching is a key aspect to be considered for the improvement of the fatigue life. This work proposes a Finite Element Method (FEM) model for the prediction of the surface integrity (material damage and residual stresses) of the workpiece obtained after the broaching process using the commercial finite element software DEFORM 2D. The model includes a self-characterized Johnson-Cook flow stress constitutive law for the titanium alloy Ti64. Experimental tests were carried out in an EKIN RAS 10x160x320 hydraulic broaching machine at different cutting conditions for the validation of the predictive model. Apart from the fundamental output variables, such as, forces and chip morphology, a comprehensive study of the surface integrity of the machined piece was done. The residual stresses generated by the cutting process were measured by the hole-drilling technique. Microstructural alterations (material damage) of the workpiece was analyzed by optical microscopy and Scanning Electron Microscope. Finally, the surface topography was examined by contact and optical profilometers. The results of the predictions showed significant good agreement with the experimental tests.

Life assessment of components working in aero-engines at elevated temperatures is critical. Machining has a serious effect on these nickel-based alloys, for example in turbine discs, affecting their life in service. Machining (turning, broaching…) modifies surface roughness, thickness of the affected substrate layer (including the effect of possible broken carbides) and residual stress distribution near the component surface. On top of that, it is possible to shot-peen or not the component, which again modifies its surface integrity. The aim of this work is to discern among the effect of the different parameter: roughness, damage and residual stresses on fatigue performance and optimum machining conditions.

The guarantee of surface integrity has become a primary objective for researchers when analysing the reliability of machined aircraft aluminium alloy structural parts in high-speed machining. This work studies the effect of cutting speed on the surface integrity of face milled 7050-T7451 aluminium workpieces. First, 7050-T7451 aluminium workpieces were face milled under dry conditions using three cutting speeds (200, 800, 1400 m/min) at constant feed (0.20 mm/tooth) and depth of cut (1 mm). An indexable face milling cutter with a diameter of 50 mm with five uncoated inserts was used in the face milling tests. During the machining process, cutting forces were acquired employing a Kistler dynamometer in order to understand the influence of the mechanical load on the final surface quality. The surface roughness produced by the milling process was measured using a portable rugosimeter. The residual stresses generated by the cutting process were measured by the hole-drilling technique. In addition, small specimens were cut out from the workpieces and microstructural alterations of the surface layer were analysed employing optical microscopy techniques. The results demonstrate that the magnitude of residual stresses and the thickness of the affected layer is sensitive to the cutting speed, while surface roughness and microstructural defects do not show significant variations for the tested conditions.

The machining of difficult-to-cut materials involves limitations leading to low productivity in conventional machining processes due to high cutting forces and tool wear rates. The ultrasonic assisted machining techniques have been reported to reduce these drawbacks significantly, enabling the increase of productivity when machining this kind of materials. In the case of the reductions on cutting forces and their control, they can lead to important improvements concerning achievable Material Removal Rates (MRR) on processes where the maximum cutting forces are limited due to part-tool deflections or the appearance of chatter vibrations. The present study analyses the cutting force reductions generated when ultrasonically assisted turning of Ti6Al4V. The obtained results were analyzed for identifying the most relevant parameters generating such force reductions. Finally, an empirical model was developed allowing the calculation of the cutting forces to be generated during ultrasonic assisted turning operations of Ti6Al4V.

Drag finishing is one of the mass finishing processes that enhances surface roughness on complex parts due to the mechanical action of abrasive media. Due to the complexity of the process, industrial practice is based on experience. This paper proposes a model simulating abrasive media flowing around a part during a drag finishing operation at a macroscopic scale. The 2D model is based on an Arbitrary Lagrangian Eulerian (ALE) formulation that provides relevant mechanical parameters such as the distribution of stresses (normal and shear stresses) and sliding velocities between abrasive media and the surface to be polished. Abrasive media are modelled as a continuous material with a Drucker-Prager plastic constitutive equation. This last has been calibrated as a result of triaxial testing, commonly used to characterise soils in civil engineering. Two abrasive media (spherical and pyramidal shape) having the same composition were characterised. Pyramidal media exhibit significantly higher rheological behaviour compared to spherical one. The model is shown to be very sensitive to the media's rheological behaviour but also to the immersion depth. Pyramidal media leads to much higher normal and shear stresses, which are even higher at deeper immersion depths. Drag finishing experimental tests were carried out to evaluate the efficiency of the model. The correlation between experimental drag finishing tests and numerical test results reveals the physical mechanisms at the interface between media and the surface. Spherical media, with a small/orthogonal orientation impact angle, promotes plastic deformation, while the main mechanisms becomes cutting at higher impact angles. However, pyramidal media promotes cutting irrespective of the orientation angle. Moreover, it was concluded that the optimal mechanical loading combination happens between 30 and 60° for both medias, as the shearing energy reaches its maximum value.

With the increase in performance of machining operations, noise levels have become an occupational health and safety problems. Identification of the main sources of noise emission when milling an aluminium component was analyzed. A machining centre, equipped with microphones, was installed in an anechoic chamber. Testing demonstrated that the part's stiffness is the most critical parameter. Cutting speed, feed and axial depth of cut tend to increase sound pressure level by increasing the impact energy, whereas radial depth of cut is not a sensitive parameter. Moreover the diameter of mills, as well as their unbalance, should be limited.

International audience; Surface integrity induced by machining process affects strongly the performance of functional products, for instance, the fatigue life as well as the resistance to stress corrosion cracking. Consequently, it is relevant to evaluate the induced properties on and beneath the machined surfaceto ensure the good performance of the mechanical components while operating under either static or cyclic loads. Furthermore, this is even more important when designing critical components that withstand high loads at high temperatures. In this context, many studies have been carried out in order to characterize the surface integrity (residual stresses, surface roughness, micro-hardness of the affected layer) when machining Inconel 718. However, so far, the cryogenic effect on surface integrity of Inconel 718 is not well established although some preliminary works have already been developed. Therefore, this work aimed to point out the performance of cryogenic machining using the carbon dioxide CO2 as a cryogenic cutting fluid, considering as a reference the conventional lubrication. A comparative study has been carried out during turning operations of Inconel 718 using the same cutting parameters and the same tool geometry. Microhardness measurements showed that the CO2 condition induced higher strain hardening near the surface while conventional condition did not generate notable difference compared to the bulk material microhardness. With respect to residual stresses, results showed that conventional lubrication generated higher tensile residual stress near the surface along the cutting direction when using new tools. As for CO2 cryogenic condition, lower tensile residual stresses have been obtained near the surface. In addition, CO2 condition induced the largest compressive peak when using new and semi−worn tools in comparison with conventional lubrication.

The cutting forces generated in machining are responsible for the tool deflection, part distortion, and features as chatter; therefore, their accurate estimation is fundamental to defining stable and safe working conditions to increase workpiece accuracy and productivity. Turn-milling is a conventional milling operation while the workpiece is simultaneously rotating. These operations enable manufacturing pieces with bosses or eccentricities; particularly, in large-sized industries such as aeronautics, naval power, and nuclear energy. Despite its wide use, relatively few studies are available regarding cutting forces and their implication in the process. Then, the effects of some cutting parameters over the process are not well detailed, for example, the tool profile and eccentricity. The numerical model presented in this research covers the cases of tool eccentricity and tool profile, such as torus and spherical end mills in orthogonal turn-milling operations. The model accurately determines the uncut chip geometry, validated theoretically against a CAD representation of the chip with errors below 3%. Furthermore, a set of milling trials was proposed to compare the chip mass and the cutting forces estimated by the model with those measured from the trials in torus and spherical profiles. The experimental validation results correlate in both tests presenting in the case of the mass errors below 3.5% and the cutting-forces errors around 12%. The validated model allows exploring a wider scenario of simulations where the eccentricity and the tool profile are the studied variables. The main findings drawn from the experiments and simulations are that the tool profile and the eccentricity affect the material removal rate. Its wrong selection reduces the chip volume and leaves material where it is supposed to be removed; then, the geometrical errors force to reprocess the workpiece, negatively impacting manufacturing productivity.

The finite element approach is often adopted to study the machining process. The Lagrangian and Eulerian formulations or even Arbitrary Eulerian-Lagrangian (ALE), one of their combinations, are the most employed in the current literature; each having their pros and cons. One of the most challenging issue in finite element modelling is the large strains during the cutting process that induce high deformation levels in the elements of the mesh. Remeshing contributes to decreasing mesh deformation but the criterion adopted to control it influences the results. The Coupled Eulerian-Lagrangian (CEL) method proposes to combine the Lagrangian and Eulerian formalisms without any element deformation problem. This paper studies its implementation in Ti6Al4 V orthogonal cutting. The results are then compared to an experimental reference, as well as more standard models: an ALE model developed with Abaqus, an implicit Lagrangian model developed with Deform and an explicit Lagrangian model developed with AdvantEdge. The comparison is mainly based on the cutting forces and the chip morphology. It shows that the CEL formulation is a competitive alternative to the more standard models.

An adaptive control is proposed for dry surface grinding to extend the use of the wheel without needing to be dressed, preserving at the same time the surface integrity of the workpiece. The implementation of this adaptive control needs to use predictive models of thermal damage, as in the case of Malkin's model, which calculates the allowable grinding power before the workpiece gets burnt for any working condition. In this latter case, the adaptive control of the cutting depth condition requires solving a quartic equation. Since the analytical procedures for solving quartics given in the literature are quite cumbersome to implement in the numeric control of the grinding machine, we propose a closed analytic formula in order to compute directly the unique positive solution. Moreover, we can enhance Malkin's model in order to consider an arbitrary heat flux profile entering into the workpiece and the kinematical correction to the geometrical contact length, in such a way that we can still using the latter solution to the quartic equation.

In manufacturing aeronautical critical components, such as turbine discs commonly made of Inconel 718, surface integrity is crucial to ensure their fatigue life. Among the machining processes used, the drilling operation is one of the most critical as overheating can occur causing thermal damage to the hole. The amount of heat dissipated could determine the nature of deformation in the machining of Inconel 718. Nevertheless no detailed studies have determined experimentally the differences between the fractions of heat transferred to the workpiece ( β ) for dry and lubricated drilling. In this context, the thermal and mechanical loads (measured by IR technique and a piezoelectric dynamometer) affecting the drilling of Inconel 718 have been studied. Four different cutting conditions both in dry and lubricated conditions were tested. In order to obtain β , the study presents a model based on a new experimental method. The maximum β values were achieved in the unlubricated tests (around 0.20). By contrast, in the lubricated tests β range from 0.065 to 0.078. Therefore the fraction of heat conducted to the workpiece show maximum differences of 72% and minimum of 57% depending on the application or not application of coolant. Additionally, the obtained trends of β relative to Peclet number (that is dependent on the cutting speed, feed and drill diameter) are shown.

Inconel 718 is commonly used in structural critical components of aircraft engines due to its properties at high temperatures. In order manufacture the final part, these components have to be machined, so the final surface integrity obtained after machining becomes a key issue. Residual stresses, which are included in surface integrity, are an important issue. Although much of the research carried out on machining induced residual stresses has been empirical, finite element modelling appears to be a complementary solution to gain understanding of it. However, some of the major drawbacks still need to be solved before it can become a reliable tool for industry, such us the identification of input parameters and computational cost. This paper deals with the study of machining induced residual stresses. An orthogonal cutting 2D finite element model was used and a sensitivity analysis was conducted to determine the influence of model input data on the predicted residual stresses. The results obtained from the sensitivity analysis showed that material constitutive law was the most relevant input data when predicting residual stress fields. Importantly the material behaviour at a high heating rate in adition to high strain rate must be considered.

Machining operations affect the properties of the final surface layer, and these can impact on its functional performance, particularly on fatigue behaviour. Among the properties of the machined surface, surface topography is one major parameter affecting fatigue behaviour. The literature review has demonstrated that stress concentration factors Kt of the surface provide a more reliable estimation of the impact on the fatigue behaviour of machined components. Finite Element (FE) simulations can accurately calculate the stress concentration factor of machined surfaces, but they incur a high computational cost. Recent advances have shown that analytical models can reliably determine stress concentration factors of 2D roughness profiles. However, analytical models that predict stress concentration factors of 3D surface topographies are still lacking. This paper is aimed at developing an analytical method to calculate the stress concentration factor Kt of 3D surfaces generated by machining operations. To validate the model, a specimen of 7475-T7351 aluminium alloy was face milled and its surface topography was characterised using an Alicona IFG4 profilometer. Stress concentration factors were calculated in the selected surface regions using the proposed analytical model, and later compared to results obtained by FE simulations. The mean difference in the stress concentration factor Kt calculated by the proposed analytical and FE models is of 1.53%. Importantly, the developed analytical model reduces the computing time by 3000 times compared to FE models, and enables the analysis of larger surfaces.

International audience; The most important challenges when machining difficult-to-cut alloys used in critical applications consist mainly in increasing tool life as well as improving the component surface integrity. In particular, the nickel based alloys exhibit very low thermal conductivity inducing higher cutting temperature and thereby rapid tool wear. In this context, cryogenic machining is a promising approach that enhances cooling efficiency either when using the liquid nitrogen LN2 or the carbon dioxide LCO2. According to previous works, cryogenic machining has been carried out on several work materials such as titanium alloys and nickel based alloys. Their findings figured out that longer tool life and better surface integrity were obtained when machining titanium alloys, unlike nickel based alloys. In this work, a comparative study has been carried out in order to investigate the cryogenic machining performance during turning operation of Inconel 718 with respect to tool wear behavior and surface integrity of the machined part. In fact, two cryogenic fluids were employed namely LN2 and LCO2 considering as a reference the conventional lubrication. This study illustrates that conventional lubrication and LCO2 cryogenic cooling allowed to obtain similar machining time, tool wear and surface finish. Nevertheless, LN2 cryogenic machining resulted in the lowest tool life as well as the poorest surface finish. Moreover, residual stresses have been measured beneath the machined surfaces when machining using new tools and tools with different levels of tool flank wear. It was observed that compared to conventional lubrication, both cryogenic conditions showed better results with respect to residual stress profiles along the machined surfaces

This paper analyzes the effect of tool wear on residual stresses when turning. Inconel 718 discs were machined for prolonged periods at several cutting speeds, feed-rates and depth of cut. Tests were interrupted to measure and relate tool wear with the subsequent residual stress measurements. The discussion of experimental results is supported by orthogonal cutting simulations. It was found a critical tool wear where tensile surface residual stresses were maximum, decreasing for lower and higher values of tool wear. Nevertheless, it was observed that the compressive residual stress layer increased with increasing tool wear.

Cryogenic machining together with minimum quantity lubrication (MQL), is claimed to be a promising alternative to flood cooling in industrial applications since it avoids the use of large amounts of cutting fluids and it improves the functional performance of machined components through its superior surface integrity characteristics. In this paper, the suitability of replacing conventional cutting fluids by liquid nitrogen cooling + MQL for finishing operations in industry will be discussed. Turning operations have been carried out on Inconel 718, in finishing conditions similar to those utilized in industry for the machining of nickel-based superalloys. With both cooling/lubricating approaches, the coolant has been applied to the rake face of the tool. Tool wear and surface integrity in terms of surface roughness, microstructural damage and microhardness profile have been analysed. The results show that conventional cooling is the best option from both the machinability and the surface integrity point of view.

Infrared radiation thermometer is used to measure the temperature of tool during dry orthogonal cutting of titanium alloys. The accuracy of measured temperature depends on several parameters such as the experimental set-up, physical acquisition data system and physical characteristic of the tool. These parameters are identified, their uncertainty estimated and the way they influence the final temperature discussed.

Tool life is usually measured by end tool life tests, however, such experiments are costly and time consuming. Establishing correlation between these tests and shorter and cheaper tests is consequently of great interest. Experimental results from dry orthogonal cutting tests are reported and a good correlation between temperature reached at the tool and tool life test is shown.

The main objective of this study is to implement a reliable FE model of the orthogonal machining of a Nickel based superalloy for the prediction of microstructural changes occurring during the process. A FE numerical model was properly calibrated using an iterative procedure based on the comparison between simulated and experimental results. A user subroutine was implemented in the FE code to simulate the dynamic recrystallization and consequently the grain refinement and hardness variation when orthogonal cutting of Nickel based superalloy is performed. Thus, Zener-Hollomon and Hall-Petch equations were implemented to predict the grain size and micro hardness, respectively. In addition, the depth of the affected layer was predicted using the critical strain equation. The obtained results proved the adequacy of the proposed model showing a good agreement between the simulated and the experimental results.

Inducing thermo-mechanical loads during the machining of hard materials lead to the severe grain refinement and hardness variation into the machined surface. This variation significantly affects the performance and the service quality of the products. Inconel 718 superalloy is one of the difficult-to-machine materials employed widely in aerospace industries and its surface characteristics after final machining process is really important. The main objective of this study is to implement a reliable finite element (FE) model for orthogonal machining of Inconel 718 alloy and prediction of the microstructure changes during the process. At first, experimental results of cutting forces, chip geometry and maximum temperature were taken into account to identify the most suitable material model out of the seven models found in the literature. Then, the FE numerical model was properly calibrated using an iterative procedure based on the comparison between simulated and experimental results. Moreover, a user subroutine was implemented in FE code to simulate the dynamic recrystallization and, consequently, to predict grain refinement and hardness variation during the orthogonal cutting of Inconel 718 alloy. Zener–Hollomon and Hall–Petch equations were employed to respectively predict the grain size and microhardness. In addition, the depth of the affected layer was controlled using the critical strain equation. As overall, a very good agreement has been found between the experimental and simulated results in term of grain size, microhardness and depth of the affected layer.

Turn-milling operations are machining processes that couple the rotational movement of the workpiece while conventional milling is carried out. This technology is an interesting alternative for machining large work diameters or massive eccentric parts as in the large format or aeronautic industries. Adding a rotational movement to the workpiece presents several advantages, but it is difficult to set the cutting parameters in the optimum operation window. The literature describes some approaches to predict the cutting forces based on the uncut chip geometry however, the effect of the cutting parameters is not well understood. This research presents a new approach to predict the instantaneous uncut chip geometry in orthogonal centric turn-milling operations based on the boundary lines of the uncut geometry. The accurate prediction of this geometry is fundamental to understanding the process mechanics, the cutting force and the machining temperature predictions. The presented models are able to predict the uncut chip geometry in large and small depth of cut regimens and were used to predict the cutting forces in several scenarios. The force predictions were validated with experimental data, demonstrating a good correlation with experimental data and overall error of around 15%. The findings presented in this research therefore could provide theoretical foundation for efficient machining strategies in the orthogonal centric turn-milling operations.

Residual stresses after machining processes on nickel-based super alloys is of great interest to industry in controlling surface integrity of the manufactured critical structural components. Therefore, this work is concerned with machining induced residual stresses and predictions with 3-D Finite Element (FE) based simulations for nickel-based alloy IN718. The main methods of measuring residual stresses including diffraction techniques have been reviewed. The prediction of machining induced stresses using 3-D FE simulations and comparison of experimentally measured residual stresses for machining of IN718 have been investigated. The influence of material flow stress and friction parameters employed in FE simulations on the machining induced stress predictions have been also explored. The results indicate that the stress predictions have significant variations with respect to the FE simulation model and these variations can be captured and the resultant surface integrity can be better represented in an interval. Therefore, predicted residual stresses at each depth location are given in an interval with an average and standard deviation.

Tensile residual stresses are very often generated on the surface when machining nickel alloys. In order to determine their influence on the final mechanical behaviour of the component residual stress stability should be considered. In the present work the evolution of residual stresses induced by machining in Inconel 718 under static loading at room temperature has been studied. An Inconel 718 disc has been face turned and specimens for tensile tests have been extracted from the disc. Then surface residual stresses have been measured by X-ray diffraction for initial state and different loading levels. Finally, a finite element model has been fitted to experimental results and the study has been extended for more loading conditions. For the studied case, it has been observed that tensile residual stresses remain stable when applying elastic loads but they increase at higher loads close to the yield stress of the material.

Peripheral glass milling for trimmings of several devices and touch panels is studied with measuring cutting forces and observing surface damages. Peripheral millings were performed to cut the end faces of 1 mm thick glass plates. In order to discuss the typical cutting force in glass milling, the cutting forces were compared with those of 0.45% carbon steel (AISI 1045) at high feed rates in a large radial depth of cut. The differences of the cutting force in glass milling from that of metal milling are: (1) the change in the cutting force does not correspond to the uncut chip thickness; and (2) the maximum cutting force does not change with the feed rate. A model is proposed to predict the cutting forces in glass millings, which are performed in ductile, ductile/brittle complex and brittle modes. The cutting force depends on the uncut chip thickness in a ductile mode. In a brittle mode, the mean value of the cutting force does not change though the vibration component becomes large. Because the uncut chip thickness changes with the dynamic displacement of the cutting edge, the cutting process is performed in a ductile/brittle complex mode when the cutting mode changes in ductile–brittle transition. The critical uncut chip thickness at the transition from a ductile to a ductile/brittle complex mode and that of the transition from a ductile/brittle complex to brittle mode are determined in the rate of the cutting force change. The force model is verified by the cutting forces in up- and down-cutting milling operations. Then, the surface finishing and crack propagation in up- and down-cutting millings were analyzed to define the cutter path in glass trimming. Cracks propagate to the surface to be finally finished in down-cutting; while cracks propagate to the chip to be removed in up-cutting. The cutter path in up-cutting milling should be selected to finish the fine surfaces.

International audience; Nickel based alloys are extensively used in the aerospace industry due to the excellent corrosion resistance and high mechanical properties that are maintained up to elevated temperatures (600–800 °C). However, these superalloys are classified as difficult-to-cut and therefore modelling and simulation of the machining processes has become a key in the machinability assessment of nickel based alloys. The reliability of Finite Element Models (FEM) largely depends on the quality of input parameters, one of the most relevant being the constitutive material model representing work material behavior under high strain, strain rate and temperatures. In order to develop a reliable material model, the present work deals with a complete characterization of Inconel 718. Uniaxial compression tests at testing temperatures close to those found in machining (21–1050 °C) and high strain rates (10°−10 2 s −1 ) were performed on the Gleeble 3500 testing machine. Moreover, the microstructural analysis and microhardness measurements of the testing samples were performed, in order to correlate the microstructural state with the mechanical properties of the Inconel 718. Based on this experimental work, a new coupled empirical model is proposed to describe the particular behaviour of nickel based alloys at elevated temperatures and high strain rates. This material behaviour model introduces softening phenomena as well as the coupling between the temperature and the strain rate known to occur experimentally, for machining FEM simulations with Inconel 718 superalloy.

Inconel 718 is commonly used in structural critical components of aircraft engines due to its mechanical thermal properties at high temperatures, which makes it to be considered as a difficult to machine material. In these critical parts, such as disk turbines, surface integrity should be assured in order to ensure the expected fatigue life. In order to determine the influence of feed and depth of cut in residual stresses a finite element facing model has been developed. This model takes into account the complex thermo mechanical phenomena that take place during chip formation process as well as the effect of cyclic loading phenomena due to the successive revolutions. Firstly, full stress, strain and temperature fields are obtained with a Deform 3D v10.2 nose turning model. Those fields are introduced in a multi revolution Abaqus/Standard v6.12 machining model. Finally the residual stresses of the model are extracted as an approach of Hole Drilling measurement technique. The results are in good agreement with empirical measurements.

The development of cutting simulation still requires an improvement in the understanding of the frictional phenomena at the tool-work material interface. This paper introduces a method for a fast identification of friction and heat partition models, based on a special tribometer able to simulate wide ranges of contact pressures and sliding velocities, similar to those occurring along the tool-work material interface in cutting. The method is applied for a wide spectrum of work materials and lubrication conditions. Combined with an analytical post-treatment, this set-up provides a modelling of the frictional behaviour that may improve significantly thermal aspects in cutting simulations.

During the last few decades, there has been significant progress in developing industry-driven predictive models for machining operations. This paper presents the state-of-the-art in predictive performance models for machining, and identifies the strengths and weaknesses of current models. This includes a critical assessment of the relevant modelling techniques and their applicability and/or limitations for the prediction of the complex machining operations performed in industry. This paper includes contributions from academia and industry, and is expected to serve as a comprehensive report of recent progress, as well as a roadmap for future directions. Process models often target the prediction of fundamental variables such as stresses, strains, strain-rates, temperatures etc. However, to be useful to industry, these variables must be correlated to performance measures: product quality (accuracy, dimensional tolerances, finish, etc.), surface and subsurface integrity, tool-wear, chip-form/breakability, burr formation, machine stability, etc. The adoption of machining models by industry critically depends on the capability of a model to make this link and predict machining performance. Therefore, this paper would identify and discuss several key research topics closely associated with predictive model development for machining operations, primarily targeting industry applications.

Orthogonal tests on cylindrical workpieces were carried out to analyze the effect of heat treatment on the machinability of newly developed Ti54 M titanium alloy in comparison with Ti64. This paper focuses on the comparison of forces and temperature of the tool during dry orthogonal cuttings of Ti64 and three different heat treated Ti54 M alloys. Forces and temperature are mainly affected by variation in cutting speed and feed, therefore, the depth of cut is maintained constant while cutting speed and feed are varied. Forces and temperature have been measured and chips are analyzed to establish a direct relationship between machinability and the different heat treatment conditions.