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Nickel-based super alloys are widely employed in critical applications, mainly in aerospace, marine, and chemical industries, concerning the production of high-performance artifacts. These alloys are considered as hard-to-cut materials, because of their modest machinability, so it is very difficult to implement in an industrial context high-speed machining processes that can lead to higher quality products, with improved mechanical characteristics and higher dimensional accuracy, and increase productivity. Among these alloys stands out Waspaloy, thanks to its very high mechanical properties, such as stiffness and strength to weight ratio. In order to implement effective machining processes, it is important to analyze the behavior of the material during machining in terms of variables of industrial interest (forces, tool wear, etc.). The aim of this paper is to disclose the results of an experimental investigation aimed to determine the effects of different cutting parameters on cutting forces, chip morphology, tool wear, and temperature at tool-chip interface, during orthogonal machining of Waspaloy (45 HRC). Experiments were performed in different lubri-cooling conditions (dry, wet, and cryogenic) and at varying cutting conditions (cutting speed and feed rate).

The phenomenological models for material flow stress and fracture, typically used in the Finite Element simulations of machining Nickel-based alloys, are often deemed to represent only certain metallurgical material states. In contrast, these models are not suitable to describe the constitutive behavior of the workpiece for different metallurgical states (i.e., annealed, aged, etc.) and, consequently, different hardness values. Since the description of the material behavior requires correct formulation of the constitutive law, new flow stress models which include also the hardness effect should be developed and used, for computer simulation of machining Nickel-based alloys. This paper describes the development of a hardness-based flow stress and fracture models for machining Inconel 718 alloy which can be applied for a wide range of work material hardness. These models have been implemented in a non-isothermal viscoplastic numerical model to simulate the influence of work material hardness on the chip formation process. The predicted results are being validated with experimental results properly carried out for this research. They are found to satisfactory predict the cutting forces, the temperature and the chip morphology from continuous to segmented chip as the hardness values change. Copyright © 2013 Elsevier B.V.

The accuracy of the results obtained from FEM simulation of machining operations depends on the accuracy of input data. Among these, the flow stress data of the workpiece are extremely important together with the friction along the tool-chip interface. In this study, an identification procedure for the determination of material parameters that are used for the FEM simulation of machining processes is proposed. The procedure is based on the coupling of a numerical identification procedure and Arbitrarian Lagrangian Eulerian (ALE) Finite Element simulations of turning operations. An experimental campaign was developed in order to calibrate the model and to validate the procedure. The basic idea is to utilize only machining tests to properly define the material behaviour of the workpiece material, taking also into account the thermal phenomena involved in the process. The preliminary results of this analysis are discussed in the paper.

In this paper the prediction of tool wear on carbide uncoated tools was taken into account. In particular, two different tool wear models based on the diffusion mechanism and on the abrasion mechanism were considered. The calibration of the utilized models was done using the results obtained by experimental analysis performed on an orthogonally machined AISI 1020 tube. Once the calibration was executed, numerical simulations, for both the utilized tool wear models, were simultaneously performed with the aim to test the capability of the proposed numerical procedure. The comparison between the two tool wear mechanisms for predicting the flank tool wear is discussed in the paper.

Finite Element simulation of orthogonal cutting is nowadays assuming a large relevance; in fact a very large number of papers may be found out in technical literature on this topic. In recent years, numerical simulation was performed to investigate various phenomena such as chip segmentation, force prediction and tool wear. On the other hand, some drawbacks have to be highlighted; due to the geometrical and computational complexity of the updated-Lagrangian formulation mostly used in FE codes, a cutting time of only a few milliseconds can be effectively simulated. Therefore, steady-state thermal conditions are not reached and the simulation of the thermal phenomenon may be ineffective. In order to overcome such problem two different approaches are proposed in this paper. The former is based on a pure thermal simulation once the thermal flow on the tool is properly calculated. The latter, on the contrary, is based on an artificial modification of the heat transfer coefficient at the interface between the chip and the tool in the thermo-mechanical simulation. Both of the proposed methodologies are discussed in the paper, highlighting the advantages and the drawbacks of each of them.

Wear prediction in machining has been recently studied by FEM although the use of numerical methods for such applications is still a very challenging research issue. In fact, wear phenomenon involves many aspects related to process mechanics which require a very accurate modelling. In other words, only a very punctual code set-up can help the researchers in order to obtain consistent results in FE analysis. The high relative velocity between chip and tool requires effective material models as well as friction modelling at the interface. Moreover the prediction of temperature distribution is another critical task; in the paper some different procedures are discussed. Subsequently a wear model is presented and calibrated in order to obtain a suitable tool to be implemented in a FE code with the aim to describe the wear evolution during the simulation process. A proper designed experimental campaign supplied some reference data for model set-up and verify in the practical application. All these aspects are carefully discussed in the paper.

Among the innovative sheet metal forming processes, Single Point Incremental Forming (SPIF) represents the simplest and the cheapest one. Despite its relevant advantages, up to now no specific CAE tools for SPIF were developed and the tool trajectory is generally defined utilizing CAD/CAM software developed for machining applications. In the paper an innovative monitoring and control approach, aimed to define and in-process update the most relevant process parameters during an industrial SPIF operation, is proposed. The strategy utilizes as monitoring variable the punch force trend: a set of preliminary tests demonstrated, in fact, its suitability as “spy variable” of the process mechanics and, in particular, of excessive sheet thinning and material failure approaching.

The use of numerical simulations for investigating machining processes is remarkably increasing because of the simulation cost is lower than the experiments and the possibility to analyze local variables such as pressures, strains, and temperatures is allowable. Process simulation is very hard from a computational point of view, since it frequently requires remeshing phases and very small time steps. As a consequence, the simulated cutting time is usually of the order of few milliseconds and no steady cutting conditions are generally achieved, at least as far as thermal conditions are concerned. Therefore, nowadays numerical prediction of cutting temperatures cannot be considered fully reliable. In the paper this issue was taken into account: a mixed Lagrangian-Eulerian numerical approach was utilized and the global heat transfer (film) coefficient at the tool-chip interface was derived through an inverse approach. Finally, the dependence of the film coefficient on pressure and temperature on the rake face was investigated.

Despite the development of high performance finite element-based codes, the simulation of machining still represents a very hard task due to the geometric complexity of the real chip-tool systems and the high cutting speed that requires very long simulation times. For these reasons, many aspects related to machining are not very clear and so easy to simulate. In this paper a rigorous investigation on the role played by the implemented friction model within a 2D simulation of orthogonal cutting was carried out, taking into account different models proposed by the researchers in the last years. The main simulation results were compared with experimental measurements in order to verify if it is possible to identify the best model. Once the comparison with mechanical variables was completed, a subsequent study on temperature predictions utilizing the above friction models was executed as well. The results of this integrated numerical and experimental work are carefully reported in the paper.

In this paper an experimental investigation was conducted to determine the effects of the tool cutting-edge geometry, workpiece hardness, cutting speed, and microstructural changes (white and dark layers) on the residual stresses in dry orthogonal hard machining of AISI 52100 steel. X-ray diffraction technique was used to obtain in-depth residual stresses profiles in both axial and circumferential directions. The results show that tool geometry, workpiece hardness and cutting parameters significantly affect the surface residual stress, maximum compressive residual stress below the machined surface and its location. Moreover, microstructural analysis shows that thermally-induced phase transformations have a significant impact on the magnitude and location of this maximum compressive residual stress peak.

The applications of numerical simulation to machining processes have been more and more growing in the last years: today a quite effective predictive capability has been reached, at least as far as global cutting variables (for instance cutting forces) are concerned. On the other hand, the capability to predict local cutting variables (i.e. pressure on the tool, temperature distribution, residual stresses in the machined surface) has to be heavily improved and verified. At the same time, effective experimental procedures for validating numerical results have to be developed. In this work two different approaches were implemented for temperature measuring: a thermocouple based approach and a thermographic analysis were developed. As well the effectiveness of a couple of typologies of numerical simulation was investigated; the former was a 2D fully thermo-mechanical analysis, the latter a 3D pure thermal one. The results of the study permit to assess that a thermo-mechanical simulation does not permit a satisfactory temperature prediction, while an integrated approach including analytical models and pure thermal FE simulations promises relevant advantages.