Jean Lu Lebrun

Residual stress analysis in orthogonal machining of standard and resulfurized AISI 316L steels

Abstract Residual stresses induced by orthogonal cutting in AISI 316L standard and resulfurized steels have been investigated, with attention given to the role played by the cutting parameters, such as cutting speed, feed rate, tool geometry and tool coating. Depth profiles of residual stress have been determined using the X-ray diffraction technique. The effect of cutting conditions and tool nature on residual stresses are analyzed in association with thermal and mechanical events, recorded during the cutting tests. The tool temperature distribution has been determined by a specific CCD infrared camera technique and the cutting forces by a Kistler table set up on the lathe.

X-ray macrostress determination on textured material; use of the ODF for calculating the X-ray compliances

A highly textured material with a mechanical anisotropic behavior of the single crystal cannot anymore be considered as composed of quasi-randomly orientated grains. In that case the commonly used sinΨ method for residual stresses determination by X-ray diffraction does not satisfy the hypothesis assumed. The macroscopic elastic behavior cannot anymore be described by only two Radio-crystallographic Elastic Constants (REC) and the 2θvs sin2Ψ is no more linear. In order to take into account this grain distribution anisotropy in the material, a method of calculating the REC is proposed. The coefficients of the orientation distribution function, now easily available, allows a complete description of the texture and a “weighting” of the single-crystal elastic constants. The relationship between the macroscopic scale and the microscopic one is done assuming Reuss’ hypothesis. The validity of these calculations is tested by the comparison with experimental results obtained on highly textured low-carbon steel sheets for various diffracting planes, applied strengths, and texture symmetries. Complete stress tensors are determined and commented upon. Some conclusions are drawn up on the influence of the diffracting planes used (multiplicity, Г factor) and of the texture intensities.

MACHINING RESIDUAL STRESSES IN AISI 316L STEEL AND THEIR CORRELATION WITH THE CUTTING PARAMETERS

It is well known that machining results in residual stresses in the workpiece. These stresses correlate very closely with the cutting tool geometrical parameters as well as with the machining regime. This paper studies the residual stress induced in turning of AISI 316L steel. Particular attention is paid to the influence of the cutting parameters, such as the cutting speed, feed and depth of cut. In the experiments, the residual stresses have been measured using the X-ray diffraction technique (at the surface of the workpiece and in depth). The effects of cutting conditions on residual stresses are analyzed in association with the experimentally determined cutting forces. The orthogonal components of the cutting force were measured using a piezoelectric dynamometer.

Experimental Assessment of Temperature Distribution in Three-Dimensional Cutting Process

Abstract In metal cutting a large amount of the external energy supplied to the cutting system is converted into heat. Therefore, the study of the thermal phenomenon developed in the metal cutting process is of prime concern. This phenomenon has a great influence on many metal cutting variables as tool wear, residual stress, and part distortion. This article presents the experimental analysis of the temperature distribution in the three-dimensional cutting process. Specially designed thermal imaging equipment, included both hardware and software, was developed in order to determine the temperature distribution in the deformation zone. A detailed description of this equipment, its calibration procedure and a full analysis of the emissivity of the cutting system components (chip, tool, and workpiece) are discussed. The designed thermal imaging equipment was proven to be very powerful to analyze the influence of the cutting parameters (cutting speed, cutting feed, depth of cut, work material, tool geometry, and tool material) on this temperature distribution. This equipment can also be useful for the construction and validation of numerical and analytical models of the three-dimensional cutting process.

Effect of Laser Assistance Machining on Residual Stress and Fatigue Strength for a Bearing Steel (100Cr6) and a Titanium Alloy (Ti 6Al 4V)

The use of Laser Assisted Machining (LAM) can improve different aspects of the machinability of high strength materials. A study was undertaken to determine the optimum cutting parameters and to quantify their influence on fatigue strength according to the type of microstructure created. Two different materials were studied: a bearing steel (100Cr6 / AISI 52100) and an aeronautical titanium alloy (Ti6Al4V). In the bearing steel a significant increase of the fatigue resistance was observed due to the transformation of the surface layer into martensite. For the titanium alloy, a slight reduction in the fatigue strength was found as in this case the microstructure and residual stress state of the surface layer was less beneficial. The surface roughness has also been measured and no significant variation has been observed for different laser powers in each material.

External Reference Samples for Residual Stress Analysis by X-Ray Diffraction

The GFAC (French Association for residual stress analysis) decided in 2007 to work on external reference samples for residual stress analysis by X-ray diffraction as defined in the XPA 09-285 and EN 15305-2009 standards. Seven materials are studied: ferritic steel, martensitic steel, aluminium alloy, titanium alloy, 2 types of Nickel-Chromium alloy and tungsten thin layers deposited on silicon wafers. The purpose of this external round robin campaign is threefold: (i) to give possibilities for each laboratory involved in the campaign test to obtain external reference samples for each material tested, (ii) to validate a common procedure for qualification of external samples and (iii) to commercialise validated external reference samples through the GFAC association. A common approach of X-Ray diffraction parameters, samples geometry and standard procedure has been chosen and adopted by each laboratory involved in these tests. No indication in terms of residual stress calculation method is given; the choice of the method (centroid, middle point, maximum of peak, fitting…) is the choice of the laboratory according to their X-ray diffraction set-ups, softwares and experience. Once all samples are analysed, values given by each laboratory are compared and analysed.

Residual Stress in High-Pressure Water Jet Assisted Turning of Austenitic Stainless Steel

In this paper, the effect of a high pressure water jet, directed into the tool chip interface, on surface residual stresses and chip shape, in face turning of AISI 316L stainless steel has been investigated. Tests have been carried out with a standard cutting tool. This tool is not specifically meant for the machining of this type of material. The cutting speeds used were 80 m/min and 150 m/min, with a constant feed rate of 0.1 mm/rev and a constant cutting depth of 0.1 mm. Three jet pressures were used: 20, 50 and 80 MPa. Residual stress profiles have been analysed using the X-ray diffraction method in both longitudinal and transversal directions. The results show that by using a high pressure jet directed into the tool-chip interface, it is possible to create a well fragmented chip in contrast to the continuous chip formed using dry turning. It is also possible to control the chip shape and increase tool life. When the jet pressure is increased the residual stress at the surface decreases however it is increased by an increase in cutting speed. It can be concluded that surface residual stresses can be reduced by the introduction of a high pressure water jet. A reduction in the residual stress value by about 20 to 40 % can be observed when using high pressure water jet assisted turning compared to dry turning. Also, it has been observed that the jet pressure does not have a great influence on the depth affected by residual stress and by hardening.

X-Ray Diffraction Analysis of Residual Stresses in Alumina-Chromium Composites and Comparison with Numerical Simulations

Residual stresses in alumina chromium composites have been determined using X ray synchrotron diffraction at LURE. Results show that non-negligible residual stresses exist in the composites. Mean residual stresses calculated by finite element show discrepancies with experimental values that are discussed in relation with experimental difficulties and calculation assumptions.

Residual Stresses Induced by Machining of a Plain Carbon Steel Using Coated and Uncoated Commercial Tungsten Carbide Tools

It is well known that machining results in residual stresses in the workpiece. These stresses correlate very closely with the cutting parameters (cutting tool geometry and material, work material, and machining regime). This paper concentrates on the residual stress induced by turning of AISI 1045 steel. Particular attention is paid to the influence of the cutting speed and tool material. In experiments, the residual stresses have been measured using the X-ray diffraction technique (at the surface of the workpiece and in depth). Special attention was paid to the influence of the coating applied to the carbide inserts on the residual stresses due to machining. These residual stresses were analyzed accounting for the thermal and mechanical phenomena during machining. The temperature distribution on the tool and chip has been determined experimentally using specially designed infrared equipment installed on the lathe. Three orthogonal components (Fc, Ff and Fp) of the cutting force were measured using a piezoelectric dynamometer. For the range of cutting parameters used in the machining tests, the results show that the coated tool produce the tensile residual stresses, which are critical in the performance of the machined components.

Study of Residual Stresses and Cold Working Generated by Machining of AISI H13 Steel

Attempts were made to study the influence of actual machining factors (polishing, grinding, milling, EDM) on residual stresses repartition, metallurgical structures and cold working of HI3 steel used for injection moulds. This study was mainly performed by X-ray diffraction method.