P.J. Arrazola

Radiation thermometry applied to temperature measurement in the cutting process

Temperature measurement of cutting tools used in machining processes has great technological importance, and it is interesting in a large number of industrial applications because wear is directly related to this variable. The influence of emissivity on the temperature measurement using radiation thermometers and the dependence of the measured temperature on the emissivity as a function of the surface roughness and the oxidation state is studied in this paper. Emissivity is measured using the direct radiometric method for uncoated P10 tungsten carbide inserts. Theoretical temperature shifts produced by changes in emissivity are estimated for several types of radiation thermometers, and these shifts are compared to the experimental temperature measurements carried out in the orthogonal turning process of cylindrical samples of 42CrMo4 steel with different machinability grades.

3D FINITE ELEMENT MODELLING OF CHIP FORMATION PROCESS FOR MACHINING INCONEL 718: COMPARISON OF FE SOFTWARE PREDICTIONS

Many efforts have been focused on the development of Finite Element (FE) machining models due to growing interest in solving practical machining problems in a computational environment in industry. Most of the current models are developed under 2D orthogonal plane strain assumptions, or make use of either arbitrary damage criterion or remeshing techniques for obtaining the chip. A complete understanding of the material removal process together with its effects on the machined parts and wear behaviour of the cutting tools requires accurate 3D computational models to analyze the entire physical phenomenon in materials undergoing large elastic-plastic deformations and large temperature changes as well as high strain rates. This work presents a comparison of 3D machining models developed using commercially available FE softwares ABAQUS/Explicit© and DEFORM™3D Machining. The work material is chosen as Inconel 718, a difficult-to-cut nickel-based alloy material. Computational results of temperature, strain and stress distributions obtained from the FE models for the effect of cutting speed are presented in comparison with results obtained from experimental tests. In addition, modified material model for Inconel 718 with flow softening is compared with the Johnson-Cook model. The predictions of forces and chip formation are improved with the modified material model.

On the machining induced residual stresses in IN718 nickel-based alloy: Experiments and predictions with finite element simulation

Abstract 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.

New Methods for Tool Failure Detection in Micromilling

Abstract A major issue in micromilling is unpredictable tool life and premature tool failure. The specific acoustic footprint and very small removal rates during machining as well as the use of small diameter cutters makes the detection of tool breakage a very difficult task. Thus, it is essential to develop new tool monitoring systems to increase the process productivity, reduce machining costs, and at the same time improve the precision and quality of machined components. This paper analyses three cost-effective and reliable methods for tool breakage detection: an on-line laser system, an on-line tool-workpiece voltage monitoring system, and a programming solution employing an off-line laser system. In order to verify the capability of these three methods, a series of experiments were conducted on an ultra-precision micromilling machine. This involved the machining of test parts in brass, aluminium, steel, and polymethylmethacryate (PMMA) with cutters from 0.5 mm down to 0.1 mm in diameter. The results of these tests are analysed and the technological capabilities of the three studied monitoring approaches are then compared. In addition, the possibility of developing an integrated solution that combines the capabilities of these three monitoring methods is discussed and conclusions made about the feasibility of such an approach.

Influence of Heat Treatment on the Machinability of Titanium Alloys

Orthogonal cutting force measurements and single-point tool life tests were conducted in order to analyze the sensitivity to heat treatment on the machinability of three titanium alloys: Ti6Al4V, Ti-5Al-4V-0.6Mo-0.4Fe (TIMETAL® 54M), and Ti6246. The Ti6246 alloy showed the highest tool wear rates and the higher cutting forces in all the heat treatment conditions which could be related to its higher mechanical properties. TIMETAL® 54M alloy, a newly developed alloy with similar mechanical properties to the more commonly used Ti6Al4V, showed the lowest wear rates. Microstructural changes due to heat treatment have some influence in the machinability of the alloys. The β annealed samples of the Ti6Al4V and TIMETAL® 54M alloys, with a very coarse lamellar microstructure, showed considerably shorter tool life and higher cutting forces. The rest of the heat treatments showed no significant influence in the machining behavior of the analyzed alloys as they do not cause important microstructural changes.

SERRATED CHIP PREDICTION IN FINITE ELEMENT MODELING OF THE CHIP FORMATION PROCESS

A 2D Finite Element Model set up using the Arbitrary Lagrangian Eulerian (A.L.E) formulation proposed in Abaqus/Explicit (v6.4) is employed to predict serrated chip formation during cutting process. No artificial criterion is employed to create the chip or to initiate serrated chip formation. The sensitivity of serrated chip prediction to numerical and process parameters is analyzed in this paper. Experimental tests in orthogonal cutting conditions on machining of AISI-4140 with coated and uncoated cemented-carbide inserts were carried out to validate numerical results. They showed significant influence of cutting speed and rake angle on the serrated chip phenomena. The comparison between numerical and experimental results showed a good qualitative agreement and underlined the outstanding influence of the element dimensions employed in Finite Element Modeling (F.E.M.) tests.

Numerical modelling of 3D hard turning using arbitrary Lagrangian Eulerian finite element method

In this paper, 3D Finite Element Method (FEM)-based numerical modelling of precision hard turning has been studied to investigate the effects of chamfered edge geometry on tool forces, temperatures and stresses in machining of AISI 52100 steel using low-grade Polycrystalline Cubic Boron Nitrite (PCBN) inserts. An Arbitrary Lagrangian Eulerian (ALE)-based numerical modelling is employed for 3D precision hard turning. The Johnson-Cook plasticity model is used to describe the work material behaviour. A detailed friction modelling at the tool-chip and tool-work interfaces is also carried. Work material flow around the chamfer geometry of the cutting edge is carefully modelled with adaptive meshing simulation capability. In process simulations, feed rate and cutting speed were kept constant and analysis was focused on forces, temperatures and tool stresses. Results revealed good agreements between FEM results and those reported in literature about experimental ones.

FINITE ELEMENT MODELING OF OBLIQUE MACHINING USING AN ARBITRARY LAGRANGIAN–EULERIAN FORMULATION

A 3D finite element model (FEM) of the oblique chip formation process was proposed in Abaqus/Explicit™ (v6.5) using an Arbitrary Lagrangian Eulerian (ALE) formulation. The sensitivity of the obtained results to variations of tool geometry angles, tool-chip friction, and cutting conditions was analyzed. Experimental tests were carried out on AISI-4140 steel using uncoated cemented carbide tools under oblique cutting conditions for validation of the FEM results, and a good qualitative agreement between them was obtained. The analysis highlighted the need for a proper identification of the friction on the tool-chip interface for the accurate reproduction of the chip formation process by means of finite element modeling.

Precision, Stability and Productivity Increase in Throughfeed Centerless Grinding

Centerless grinding is a high precision manufacturing process commonly applied to the mass production of many industrial components. However, workpiece roundness is critically affected by geometric lobing and no practical tool has been developed to solve the problem in throughfeed working mode. Based on simulation methods previously applied to plunge grinding, a new software tool has been developed in this work. The software determines the optimal working configuration and can be used to reduce set-up time and improve three important features: 1) Precision, as the roundness error is rapidly corrected at the optimal configuration. 2) Productivity, since the workpiece stock can be significantly reduced. 3) Stability, because the process is less sensitive to the original roundness error of the workpiece.

Characterization of Friction and Heat Partition Coefficients during Machining of a TiAl6V4 Titanium Alloy and a Cemented Carbide

This article aims at characterizing the frictional behavior of a TiAl6V4 alloy and a carbide tool under extreme conditions corresponding to those occurring at the cutting tool–work material interface. A specially designed open tribometer was used to characterize the macroscopic friction coefficient, heat partition coefficient, and adhesion in the contact versus sliding velocity and contact pressure. It has been shown that titanium leads to intense adhesion, which seems to be even more intensive with high contact pressure and high sliding velocity, which limits the local sliding movement at the interface (stuck layer). However, the tribometer provides the evolution of an apparent friction coefficient and a macroscopic heat partition coefficient related to the shearing of titanium between the adhesive layer and the bulk material. An increase in sliding velocity or contact pressure induces a small decrease in the apparent friction coefficient as well as the heat partition coefficient. It has been shown that adhesion is thermally activated by a combination of contact pressure and sliding velocity, which leads to a threshold effect. Furthermore, the application of an emulsion showed a small decrease in the apparent friction coefficient associated to a decrease in adhesion. Finally, this work provides quantitative data on the apparent friction and heat partition coefficients versus sliding velocity and contact pressure that can support the development of macroscopic cutting models for titanium alloys.