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The reliability of the pertinent parameters set of Johnson-Cook constitutive model is highly linked with the friction condition at the tool-chip-workpiece interface. In the present work, a study on the influence of Coulomb’s friction coefficient on the observables such as forces, chip thickness and chip curvature by FE simulation of orthogonal cutting of Ti6Al4V alloy has been carried out. A FE model with an Arbitrary Lagrangian-Eulerian (ALE) approach is employed to simulate the cutting process for different cutting conditions. The simulated results, for a wide range of friction conditions, are analyzed and compared with experimental results. The analysis show that the Coulomb’s friction coefficient has a direct link with the observables. The paper reveals that for accurate prediction of observables an optimized value of the coefficient of friction in correlation with the parameters values of the constitutive model is imperative.

A known problem of additive manufactured parts is their poor surface quality, which influences product performance. There are different surface treatments to improve surface quality: blasting is commonly employed to improve mechanical properties and reduce surface roughness, and electropolishing to clean shot peened surfaces and improve the surface roughness. However, the final surface roughness is conditioned by multiple parameters related to these techniques. This paper presents a prediction model of surface roughness (Ra) using an Artificial Neural Network considering two parameters of the SLM manufacturing process and seven blasting and electropolishing processes. This model is proven to be in agreement with 429 experimental results. Moreover, this model is then used to find the optimal conditions to be applied during the blasting and the electropolishing in order to improve the surface roughness by roughly 60%.

High-precision metal cutting is increasingly relevant in advanced applications. Such precision normally requires a cutting feed in the micron or even sub-micron dimension scale, which raises questions about applicability of concepts developed in industrial scale machining. To address this challenge, we have developed a device to perform linear cutting with force measurement in the vacuum chamber of an electron microscope, which has been utilised to study the cutting process down to 200 nm of the feed and the tool tip radius. The machining experiments carried out in-operando in SEM have shown that the main classical deformation zones of metal cutting: primary, secondary and tertiary shear zones—were preserved even at sub-micron feeds. In-operando observations and subsequent structural analysis in FIB/SEM revealed a number of microstructural peculiarities, such as: a substantial increase of the cutting force related to the development of the primary shear zone; dependence of the ternary shear zone thickness on the underlaying grain crystal orientation. Measurement of the cutting forces at deep submicron feeds and cutting tool apex radii has been exploited to discriminate different sources for the size effect on the cutting energy (dependence of the energy on the feed and tool radius). It was observed that typical industrial values of feed and tool radius imposes a size effect determined primarily by geometrical factors, while in a sub-micrometre feed range the contribution of the strain hardening in the primary share zone becomes relevant.

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.

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.

This paper presents a novel indirect cryogenic cooling system, employing liquid nitrogen (LN2) as a coolant for machining the difficult-to-cut ASTM F-1537 cobalt-chromium (CoCr) alloy. The prototype differs from the already existing indirect cooling systems by using a modified cutting insert that allows a larger volume of cryogenic fluid to flow under the cutting zone. For designing the prototype analytical and finite element, thermal calculations were performed; this enabled to optimize the heat evacuation of the tool from the rake face without altering the stress distribution on the insert when cutting material. Turning experiments on ASTM F-1537 CoCr alloys were performed under different cutting conditions and employing indirect cryogenic cooling and dry machining, to test the performance of the developed system. The results showed that the new system improved surface roughness by 12%, and cutting forces were also reduced by 12% when compared with the existing indirect cryogenic cooling technique.

International audience; To improve surface roughness of components without altering geometrical dimensions, polishing operations are commonly used. These operations may be timeconsuming and expensive. Thus, the prediction of polished surface quality is a key issue to reduce the cost of these operations. Resulting surface quality of polishing operations is the outcome of a large number of local cutting phenomena (grains-material). The control of the multi-scale physical phenomena is a challenge when it comes to simulate these operations. In this paper, an Analytical-Method for Polishing-Surface Prediction (AMPSP) that considers the tool flexibility and each grain-material interaction is proposed. The objective is to predict accurately the polished surface topography and the material removal rate, and to keep the history of all the local cutting phenomena, in order to define a digital twin of polishing operation. Experimental validation demonstrates that this AMPSP predicts the material removal rate (less than 35% of error) and the surface topology (less than a few percent). AMPSP will enable engineers to quickly and accurately predict the polished topology obtained with 5-axis toolpaths.

Finite element modeling of machining aims for guidance in the choice of the cutting parameters and for the comprehension of the involved phenomena. The modeling of the behavior of the machined material is a key parameter to develop a realistic model. It is nowadays still extremely difficult to acquire experimental data on the material flow stress due to the extreme conditions encountered during machining. Many constitutive models are found in the literature and there is a lack of objective information to choose the best suited for a given application. Four empirical constitutive models are used in this paper to represent the Ti6Al4V titanium alloy during an orthogonal cutting operation. All of them are based on the well-known Johnson-Cook model. The results of this study show that the influence of the constitutive model on the chip morphology and on the cutting force is high and that the strain softening phenomenon should be taken into account to produce a segmented (or saw-toothed) chip as it is experimentally observed. For the cutting conditions adopted, adding damage properties in the chip is moreover required to obtain a morphology close to the experimental reference. All these elements allow to get a reliable numerical model able to reproduce cutting forces and chip morphology (either continuous or segmented) for various cutting conditions.

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.

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.

Chatter vibrations produced during turning of slender parts cause poor workpiece surface finishing and premature tool wear. In this paper, mode coupling in flexible workpiece metal cutting without tailstock is analysed in the state-space domain. The proposed mode coupling model considers mode rotation with the workpiece. Closed form equations are obtained for eigenvalues of the system formed by the cutting process and the mechanical structure, as a function of cutting conditions and workpiece modal parameters. Mode rotation and cutting speed influence on system stability is analysed and chatter-free conditions are determined. Finally, experimental tests are presented to evaluate theoretical formulations in slender workpiece facing operation. By means of a state-space domain analysis of the system formed by the cutting process and the workpiece, it is possible to obtain mathematical formulations that quantitatively relate system natural frequencies to process stability. Therefore, it is possible to detect this type of chatter vibrations before workpiece quality is affected by monitoring vibrations during machining. These formulations facilitate the development of an active vibration control system which will improve process stability.

The constitutive model and its pertinent set of parameters are important input data in finite element modeling to define the behavior of Ti6Al4V during machining process. The present work focusses on comparing different constitutive models and the parameters sets available in literatures and investigating the quality of the predictions when varying uncut chip thickness (40 µm, 60 µm, 100 µm and 280 µm). In addition, temperature-dependent strain hardening factor along with strain softening phenomenon based reconstructed material model is proposed. The results from the numerical simulations are compared with experimental results available in literature. The comparison shows that the force values are highly influenced by constitutive models and the choice of parameters sets, whereas the chip morphologies are mainly influenced by the uncut chip thickness and constitutive models. This work justifies the need for an appropriate set of parameters and constitutive model that replicate the machining behavior of Ti6Al4V alloy for different cutting conditions.

International audience; Finite Element Modelling used to predict machining outcomes needs to be supplied with the appropriate material thermomechanical properties which are obtained by specific testing devices and methodologies. However, these tests are usually not representative of the extreme conditions achieved in machining processes and the obtained material law may not be suitable enough. Inverse identification could address this problem by obtaining material thermomechanical properties directly from machining outcomes such as cutting forces, temperatures, strain or strain rates. Nevertheless, this technique needs to be supplied with accurate machining outcomes. However, some of them such as strain or strain rate are difficult to be properly measured. The aim of this paper is to present a methodology to measure plastic strain and strain rate during orthogonal machining under plane strain conditions. The main idea is to create a physical microgrid in a workpiece and to analyze the distortion suffered by this grid. The novelty of the method consists on its capability of measuring strain and strain rate fields in a very localized area (primary shear zone) using a single image. The methodology was applied in orthogonal cutting of Ti-6Al-4V under cutting conditions that are representative of the broaching process. Experimental results were compared with DIC measurements, analytical results based on unequal division shear zone model, literature results and with numerical fields obtained from an AdvantEdge-2D model.

Increased stability in machining processes is highly desired by all machining industries when vibrations and specially chatter occur. This phenomenon is defined as a self-excited vibration that occurs due to the regeneration of waviness of the workpiece surface. In machining industry, the trend is to rely on the trial and error method or mere experience when deciding the machining spindle speeds, depths of cut and tool stick-outs, all of which are parameters directly related to chatter occurrence. Currently, the shortest possible tool stick-out is chosen by default, but literature has proven that longer stick-outs may bring some advantages when it comes to material removal rates. Aiming to prove this theory, this paper will discuss the influence of the tool stick-out on machining chatter occurrence. To that end, the effect of the tool stick-out on the modal parameters of the system, on the Stability Lobe Diagram (SLD) and on productivity will be analysed. Therefore, a number of Tap-Tests to different tool/tool-holder/stick-out combinations have been performed, in order to gather the data (FRFs and SLDs) where the analysis is based on. Last but not least, some machining tests have been conducted aiming to compare the theoretical chatter occurrence conditions, provided by the SLD, with the experimental ones. For that, two Al5083 workpieces have been slot milled under different cutting conditions, facilitating the unexpected results wherein the conclusions have been based upon.

Composites materials and especially FRP are increasingly employed in many fields of applications (transport, aerospace, …) due to the current trend of improving global energy performances of new designs notably by mass saving. However the use of metallic materials such as aluminum and titanium alloys is still necessary in many cases and a lot of structures are made of a dual technology called stacks (panels composed of different layers of FRP and metal bounded together). Combining the different properties of these materials offers many advantages regarding the mechanical and structural aspects. This is nevertheless for the same reason that machining and especially drilling stacks is a laborious task: the tools and cutting conditions are way too divergent to avoid vibrations, problems of dimensional tolerances and delamination of the composite. The knowledge and characterization of the drilling cutting forces is a first step to solve these issues. The purpose of this article is to provide an accurate macroscopic analytical model fitted for stacks and compare it quantitatively with experimental tests. The given model is divided in two parts (i.e. respectively adapted for the two materials) and is based on the discretization of the cutting edge. The proposed algorithm is able to predict accurately drilling force and torque along time in function of the cutting conditions, the tool and material configurations. A reverse least squared method is used to obtain the empirical input parameters, allowing to minimize the number of experimental drilling tests to obtain the empirical input parameters.

Ferrite–Pearlite (FP) steels are used in many automotive components. However, their machinability in low cutting speed processes appears to be highly dependent on their metallurgical state. An experimental approach combining broaching and tribological tests under machining-like conditions was developed to determine the key FP features driving machining performance. Fundamental tests were performed on fifteen variants so as to cover a wide range of microstructural properties under dry and lubricated conditions using both uncoated and TiN coated High Speed Steel (HSS) tools. The correlation between the microstructure, tribology and outputs such as machining forces and chip thickness ratio is presented.

This study generated novel behavioural data for three engineering steels undergoing a turning process. The materials were hardened 410, PH13-8Mo and 300M, two stainless steels and one high strength steel respectively. A primary aim was obtaining low machined surface roughness. A surface finish investigation compared tool geometries and tool materials. Multi-response cutting parameter screening was undertaken using a novel trade study and iteration method, where the calculated cut quality was used to identify better feed rates and surface speeds. In addition the sub-surface machined microstructure was examined.\ud \ud \ud \ud Tools with a small nose radius produced the roughest surfaces. A surface roughness below 0.4 μm Ra could be consistently achieved on all three materials using rhombic wiper inserts and a feed rate up to 0.1 mm/rev. PH13-8Mo had the lowest machined surface roughness, as low as 0.11 μm in terms of Ra. In the parameter screening stage a generalised recommendation for good cut quality was a surface speed of at least 120 m/min and a feed rate of 0.088 mm/rev. The microstructure examination showed that for all materials under the conditions tested, there was no evidence of white amorphous layer formation and there was grain deformation for the 410 material only.

Industrial processes are being developed under a new scenario based on the digitalisation of manufacturing processes. Through this, it is intended to improve the management of resources, decision-making, production costs and production times. Tool control monitoring systems (TCMS) play an important role in the achievement of these objectives. Therefore, it is necessary to develop light and scalable TCMS that can provide information about the tool status using the signals provided by the machine. Due to the lack of this type of systems in industrial environments, this work has two main objectives. First, the predictive capacity of statistical features in the time domain of internal and external signals for the prediction of tool wear in drilling processes was analysed. To this end, a methodology based on automatic learning algorithms was developed. Secondly, once the most sensitive signals to tool wear were identified, algorithms with signals of a certain tool geometry were trained and a model was obtained. Then, the model was tested using signals from two different tool geometries. The experiments were carried out on a vertical milling machine on a steel with composition 35CrMo4LowS under pre-established cutting conditions. The results show that the most sensitive signals to monitor the tool wear in the time domain are the feed force (external) and the z-axis motor torque (internal). The models created for the fulfilment of the second objective show a great capacity of prediction even when dealing with tools with different geometrical characteristics.

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.

Broaching is a widely used finishing operation for the manufacturing of transmission gears which are commonly made of steel AISI 1045. Therefore, there is a high interest for industry to understand the metal cutting process and modeling could shed light on it. In the present work, an innovative methodology to establish a hybrid model based on the combination of empirical, numerical, and analytical approaches is presented. The hybrid model improves the cutting force, feed force, and chip thickness predictions when compared to the results obtained with the empirical, numerical, or analytical ones separately. The empirical model was developed by carrying out experimental tests under orthogonal condition close to broaching. The analytical method uses the Oxley law extended to the proposed flow stress model. DEFORM-2D software was used for the finite element model development with a specific subroutine for the constitutive model. The influence of each approach in the hybrid model was calculated based on a statistical analysis between experimental and model results. Moreover, to achieve better predictions in the numerical and analytical models, the material was characterized by static and dynamic compression tests to take into account strain softening and coupling between strain rate and temperature phenomena, not considered in the commonly used Johnson-Cook law. Furthermore, the hybrid model was validated with additional experimental tests, to demonstrate its validity in a wide range of cutting conditions. The relative error obtained with the hybrid model in force and chip thickness predictions were 6% and 12%, respectively, reducing more than three times the maximum error in comparison to any other approach.

Large aluminium monolithic parts used in the aeronautic industry frequently show significant geometric distortions after the machining process. These distortions are the consequence of the initial residual stresses of the raw material as well as machining-induced residual stresses. Therefore, to minimise distortions, it is fundamental to understand the effect of the different parameters of the manufacturing process and define the optimum manufacturing strategy. This work studies the effect of initial residual stresses of aluminium plates and the residual stresses generated by the machining process on the final geometric distortions of the part. First, 7175-T7351 aluminium bars (40 mm wide × 38 mm thick × 400 mm long) were face milled at two different cutting conditions reducing the thickness to 6 mm. The distortions were measured in a coordinate measuring machine. The results revealed that the machining strategy significantly influenced the distortions, as a difference of 65% on distortions was found between the two cutting conditions. In addition, an FEM model to predict distortions was developed. This model considers initial residual stresses (measured by the contour method) and residual stresses induced by the machining process (measured by the hole drilling technique). Once the FEM model was validated, the study was extended to more complex geometries. These new studies revealed that final distortions are sensitive to machining-induced residual stresses. Furthermore, this finding indicates that it is possible to define machining conditions which generate desirable residual stress profiles to minimise part distortion.

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.

Nickel-based alloys are widely employed in the manufacturing of aero-engines. These alloys are difficult to machine, and tensile residual stresses are generated during machining. These tensile residual stresses can negatively affect the performance of aero-engine components. Nevertheless, residual stresses can vary due to thermal or mechanical loading. These variations must be considered to evaluate the real influence of residual stresses on component behavior. This paper studies the effect of thermal loads on machining-induced residual stresses in the alloy Inconel 718. A ring-shaped Inconel 718 part was face-turned, and specimens were extracted from it. Specimens were exposed at 550 and 650 °C for 10 min, 1 and 10 h. Residual stresses were measured, and microstructure was observed before and after thermal exposure. Residual stress variations found after thermal exposure were the consequence of two factors: relaxation of strain bands during the early stage of exposure and diffusion-controlled creep. In addition, a modified Zener-Wert-Avrami model is proposed to predict residual stress relaxation caused by the diffusion-controlled creep. Once having fitted the modified Zener-Wert-Avrami model, the study was extended for a wider range of temperatures (400-650 °C). This analysis showed that surface residual stresses do not relax significantly at temperatures below 500 °C.

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.

Drag finishing is a widely used superfinishing technique in the industry to polish parts under the action of abrasive media combined with an active surrounding liquid. However, the understanding of this process is not complete. It is known that pyramidal abrasive media are more prone to rapidly improving the surface roughness compared to spherical ones. Thus, this paper aims to model how the shape of abrasive media (spherical vs. pyramidal) influences the material removal mechanisms at the interface. An Arbitrary Lagrangian–Eulerian model of drag finishing is proposed with the purpose of estimating the mechanical loadings (normal stress, shear stress) induced by both abrasive media at the interface. The rheological behavior of both abrasive slurries (media and liquid) has been characterized by means of a Casagrande direct shear test. In parallel, experimental drag finishing tests were carried out with both media to quantify the drag forces. The correlation between the numerical and experimental drag forces highlights that the abrasive media with a pyramidal shape exhibits a higher shear resistance, and this is responsible for inducing higher mechanical loadings on the surfaces and, through this, for a faster decrease of the surface roughness.

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.

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.

Titanium alloys are widely employed in many aerospace components due to their high strength-to-weight ratio, good corrosion resistance and fatigue properties, maintained at relatively high temperatures. Nevertheless, machining these materials efficiently has become a challenge in a sector that demands high productivity rates and minimal manufacturing times. This work analyses the machinability of the α + β Ti-6Al-4V alloy in rough turning. Since oxygen is one of the elements that most affects the mechanical properties of titanium alloys, the aim is to understand its influence on the machinability of these materials. To do so, two different oxygen contents of 1200 and 2000 ppm are tested. A comprehensive material characterisation of both materials is carried out in order to clearly establish their differences: chemical composition, microstructure and mechanical properties (yield strength and hardness of the phases by nanoindentation). Machining trials consist of (i) tool life tests, which include a tool wear analysis, and (ii) cutting fundamental turning tests, in which the cutting forces and the chip form are studied. The work concludes that Ti-6Al-4V alloy with the highest oxygen content has the worst machinability (~15 % lower compared to lowO), due to its higher volume fraction of β + αs phase, slightly harder αp and greater yield strength, which generates higher mechanical and thermal tool wear. Thus, oxygen is a key composition element that should be controlled in machining titanium alloys, if robust results in tool life are expected to be obtained.

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.

Corrigendum to “Mechanical characterization and modelling of Inconel 718 material behavior for machining process assessment” [Mater. Sci. Eng. A 682 (2017) 441–453]

Aluminium alloys are of the most used alloys in the aeronautic industry. Increasing knowledge in machining and prediction of chip formation in these materials is crucially important to design better components with enhanced functional performance. To achieve this, a new finite element modelling strategy is developed to incorporate material damage and softening in the Coupled Eulerian-Lagrangian (CEL) formulation for the machining of AA2024 alloy. The CEL modelling technique is adopted to simulate chip formation at high cutting speeds. An orthogonal cutting setup is used to compare the modelling predictions with experimentally measured cutting forces and chips sections. The proposed model shows a good ability to reproduce the experimental results and to predict the trends induced by variations in the cutting conditions.

A method for measuring tool temperature in the tool/chip contact zone of the rake face of a tool during dry orthogonal cutting using thermography is presented. This method used a new calibration method that combined with a standard camera calibration allows to estimate surface emissivity. The effect of material deposition and tool oxidation on the emissivity is analyzed. These techniques effectively showed thermal field on the rake face when machining AISI 4140.

Machining is a quite relevant process on industry. However, despite its industrial importance, many parameters of the process are still chosen through empirical testing which is traduced in high time-consuming and costs. Based on that, an alternative approach to empirical methods is needed. Any other approach (numerical, analytical) needs a previous material characterization, which clearly influences on the accuracy of the predictions. This paper studies the effect that material characterization has on fundamental variables predictions, such as cutting forces, temperature and strain rate. A comprehensive analytical study has been carried out, based on Oxley theory and Johnson-Cook material law. Also the contact was considered, qualitatively, based on Coulomb friction law. The final aim of the paper is to present a comprehensive sensitivity study of the flow stress parameters for a widely used aeronautical alloy (Ti-6Al-4V).

One of the current trends in machining is the reduction or elimination of the use of cutting fluids to reduce economic and ecological costs. As a consequence, heating of the workpieces is increased, leading to greater thermal distortion. This distortion can be predicted using the finite-element method (FEM), provided heat input to the workpiece for the machining operation is known. The aim of this research is to determine the quantity and ratio of heat generated in drilling operations and to quantify the heat transferred to the workpiece based on cutting speed and feed rate. Thus, a detailed study of workpiece heating during the drilling process with minimum quantity of lubricant was conducted, and a combination of experimental and numerical data was used to obtain these parameters. The experiments were carried out on aluminium (Al2017) samples. Drilling torque and temperature of the workpiece were measured. The cutting procedure involved drilling a O10 × 15 mm blind hole using uncoated cemented carbide tools. Temperature was measured by infrared methods, and cutting torque was obtained using a piezoelectric dynamometer. The FEM model was developed using the general-purpose software ABAQUS/Standard© v6.5 and the inverse simulation technique was used to calculate heat input to the workpiece for each machining condition. As a general conclusion, an increase in cutting speed and feed rate leads to a decrease in heat input and temperature in the workpiece and thus, thermal distortion of the part.

The microstructure of materials has a significant influence on tool life, however most of the research in modelling to date considers the material as homogeneous. This research aims to develop a microstructure-based Finite Element Model in order to qualitatively analyze the influence of the scale of the microstructure on the generated tool wear. In particular, this paper is focused on the orthogonal cutting process of a ferrite-pearlite dual-phase steel using uncoated carbide tools. Based on individual mechanical properties of these phases, a 3D coupled Eulerian Lagrangian heterogeneous model was developed. An empirical tool wear rate prediction model was implemented by a user subroutine in both models (heterogeneous and homogeneous) to predict wear and wear rate values. A comparison between the microstructure-base model (heterogeneous) and the homogeneous model considering wear and wear rate values was made. The results demonstrate the validity of microstructure-based Finite Element Model for an improved prediction of the wear phenomena.

The final aim of finite elements modelling is to help in the choice of the cutting parameters and in the comprehension of the involved phenomena. Representing correctly the behaviour of the machined material is hard due to the extreme conditions encountered, although this is a key parameter to develop a realistic model. Four laws are used in this paper to represent the Ti6Al4V. They are all based on the Johnson-Cook law. This study shows that the influence of the behaviour law is high on the chip morphology and on the forces and that the strain softening phenomenon should be taken into account. For the cutting conditions adopted, it is however necessary to add damage properties in the chip to obtain a morphology and a cutting force evolution close to the experimental reference.

This paper describes the results of an experimental investigation aimed to st udy the machinability of AA7075 T6 (160 HV) for aerospace industry at high cutting speeds. The paper investigates the effects of different lubri-cooling strategies (cryogenic, M QL and dry) during high speed turning process on cutting forces, tool wear, chip morphology and cutting temperatures. The cutting speeds selected were 1000m/min, 1250m/min and 1500 m/min, while the feed rate values used were 0.1mm/rev and 0.3 mm/rev. The results of cryogenic and M QL application is compared with dry application. It was found that the cryogenic and M QL lubri-cooling techniques could represent a functional alternative to the common dry cutting application in order to implement a more effect ive high speed turning process. Higher cuttingparameters would be able to increase the productivity and reduce the production costs. The effects of the cutting parameters and on the variables object of study were investigated and the role of the different lubri-cooling conditions was assessed.

Thermography (thermal imaging) is a well-established experimental method for studying cutting tool temperature distributions. In one form, cutting edge temperatures within the chip / tool contact area are deduced from thermal images of tool faces normal to the cutting edge but offset from the contact region. In general practice, the offset is made as small as possible (<< 1 mm) and it is assumed that the observed temperature is the same as that within the contact. In this short communication an approximate analytical model is developed for the influence of the offset on the observed temperature. The predictions from the model are compared with previously unpublished existing results on the machining of Ti alloys (Ti6Al4V and Ti5Al4V) and on steel (AISI 4140). It is shown that ignoring the offset may introduce underestimates of cutting edge temperature of ≈ 30% or more. This is large compared to the usually considered uncertainties of ± 5% from camera and tool emissivity calibration. There is a need for a ...

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.

During surgical interventions where bone machining operations are involved (drilling, sawing, etc.), bone tissue may be damaged by the mechanical and thermal loads, and thus, working conditions should be selected in order to reduce or avoid this problem. In this study, with the purpose of reducing the damage induced when drilling, an analysis and improvement of the geometry of a surgical drill bit had been done. As baseline, a commercially available stainless steel surgical drill indicated for implant site preparation had been considered. The influence of the rake angle, margin width, and body thinning over the workpiece temperatures, cutting forces, and surface roughness has been determined by a sensitivity study. First, eight drill bits had been fabricated on hard metal and drilling tests on bovine femoral cortical bone were done. These tests showed that the rake angle is the most influential factor among the analyzed, both for temperatures and cutting efforts. The two drill designs which achieved the lowest workpiece temperatures, cutting forces, and surface roughness had been fabricated also in surgical stainless steel and tested at wider cutting condition range of cutting speed and feed rates. These two drill bits reduced workpiece temperatures about 50 %, feed force about 60 %, and cutting torque up to 50 %, while the surface roughness was improved significantly when compared with the commercial surgical drill bit at the same cutting conditions. Comparing stainless steel and hard metal drills, no appreciable effects of the tool material have been detected over the measured output variables. This study shows how remarkable improvements on the design of surgical drills could be achieved by defining the influence of the rake angle, margin width, and body thinning when drilling bone.

Inconel 718 superalloy is one of the difficult-to-machine materials which is employed widely in aerospace industries because of its superior properties such as heat-resistance, high melting temperature, and maintenance of strength and hardness at high temperatures. Material behavior of the Inconel 718 is an important challenge during finite element simulation of the machining process because of the mentioned properties. In this regard, various constants for Johnson–Cook’s constitutive equation have been reported in the literature. Owing to the fact that simulation of machining process is very sensitive to the material model, in this study the effect of different flow stresses were investigated on outputs of the orthogonal cutting process of Inconel 718 alloy. For each model, the predicted results of cutting forces, chip geometry and temperature were compared with experimental results of the previous work at the different feed rates. After comparing the results of the different models, the most suitable Johnson–Cook’s material model was indentified. Obtained results showed that the selected material model can be used reliably for machining simulation of Inconel 718 superalloy.

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.