Being milling operations some of the most common in industry, one of the main concerns of this manufacturing technology is the tendency of introducing high magnitude tensile residual stresses in the machined surface [1], very harmful against fatigue. To assure a high surface integrity of the workpiece, with compressive residual stresses near the surface, usually postprocessing operations are used, such as deep burnishing and shot peening among others [2]. In this article a different approach is proposed, in which the milling operation is done under an externally applied bending load, leading to easily controllable compressive stresses in the machined surface, beneficial against fatigue. In order to achieve these results, it is needed to perform the milling operation in a volume of material under externally introduced tensile stresses, which are generated in the convex surface of the bent component. This article presents a simple fixture design to efficiently achieve this objective, and the experimental validation of the introduced residual stresses using this method. To introduce uniform bending loads to the workpiece while being machined, the chosen method consists in bending the workpiece against a cylindrical shape. Although this method could be used for different kinds of operations, the scope of this research was limited to the analysis of pocket milling operations in aluminium alloy. In this article, both theoretical bases and experimental results are presented, showing positive results and the introduction of compressive residual stresses in the milling operation using the proposed fixture. References: [1] M. Soori, B. Arezoo. (2022) A Review in Machining-Induced Residual Stress. Journal of New Technology and Materials, volume 12, issue 1, pages 64-83. https://hal.science/hal-03679993/. [2] A. Klumpp, et al. (2014) Mechanical Surface Treatments. Conference: ICSP-12 Goslar, Germany, pages 12-24.

Inconel 718 is a nickel-based superalloy widely used in the aerospace industry for its excellent mechanical properties and high temperature resistance. It is commonly used in critical components such as turbine discs and gas turbine engine blades. Although much research has been carried out on tool wear and performance in the machining of nickel-based superalloys, the specific effects of broaching on surface integrity remain less well explored. In particular, the influence of cutting-edge radius on residual stress generation, material deformation and subsurface properties during broaching has not been thoroughly investigated. The broaching cutting process is achieved by passing multiple cutting edges through the passage of a multi-strand tool. It is known that if one cutting edge causes damage to the integrity of the surface, subsequent cutting edges can replicate or increase the initial damage to the material, so it is imperative to analyse the performance of the cutting edge. This study examines the impact of cutting-edge microgeometry on surface integrity during single-pass dry broaching of Inconel 718 at a relatively high cutting speed of 20 m/min. Cutting edges were prepared using a brushing technique with ceramic fibre brushes to achieve controlled cutting-edge radii. A combination of experimental tests and numerical simulations were used to evaluate the effects of cutting-edge radius and the Rise per Tooth (RPT) on residual stress formation and material response. Residual stresses were evaluated by X-ray diffraction (XRD) and were complemented by Hole drilling tests to measure subsurface stresses. In addition, Vickers microhardness tests were performed to analyse hardness variations in the surface and subsurface layers and scanning electron microscopy (SEM) images were used to investigate the depth of microstructural deformation achieved. The results indicate a strong correlation between edge radius and residual stress distribution, with a critical transition observed around 15 µm. A larger edge radius led to increased microstructural deformation, hardness variations, and higher surface tensile stresses. However, it also contributed to the formation of a beneficial compressive stress layer beneath the tensile zone, potentially enhancing fatigue resistance. Furthermore, the depth of deformation was significantly affected by edge radius variations, demonstrating a direct relationship with surface residual stresses. These findings provide valuable insights for optimizing broaching tool design, improving surface integrity, and enhancing the mechanical performance of aerospace components.

The surface stress and hardness after cutting affect the fatigue strength and wear resistance of the products. Therefore, it is important to estimate the surface hardness and residual stress after cutting operations. This study proposes a method to estimate the surface hardness and residual stress of carbon steel in turning by using analytical information of the cutting process. The machined surface properties depend on the strain, strain rate, stress and temperature fields in the vicinity of the cutting edge and the workpiece surface during cutting. Therefore, these physical state indices are estimated from the measured cutting force and flank wear width using a three-dimensional cutting model, and the hardness and residual stress are estimated using a linear regression model. The accuracy of the residual stress and hardness estimation was investigated through a series of turning tests where the cutting force,cutting temperature, flank wear width, chip thickness, hardness and residual stress were measured. In addition, the influence of modelling errors in the model-based simulation on the accuracy of hardness and residual stress estimation was analyzed. The experimental results verified that a high coefficient of determination of about 0.8 - 0.9 is achieved in the hardness and residual stress estimation. The high estimation accuracy was approximately achieved by the proposed method regardless of modelling errors in cutting temperature and shear angle. However, non-linearity in the effect of cutting temperature on hardness slightly degraded the accuracy of hardness estimation. This fact indicates the importance of using non-linear modeling for estimation.

Micro-texturing of surfaces through laser ablation is a developing technology that aims to improve the tribological properties of surfaces by reducing the friction coefficient and increasing wear resistance during friction-related processes such as cutting operations. Reducing the friction coefficient during cutting-related processes has been focused on in order to enhance the life of the cutting tool itself and of lubricants involved. Laser-induced micro-textures produced on cutting tools can change the tool chip interface contact and friction process, decreasing the friction coefficient by increasing the load-bearing capacity of the fluid and by acting as secondary lubrication reservoirs under lubricated conditions or by reducing the contact area between the tool and the chip under dry friction conditions. While current research has tested the tribological effects of different micro-textures on cutting tool friction performance, further analysis is needed to improve the friction reduction of micro-textured cutting tools. The purpose of this study will be to find optimal micro-texture shapes, which will decrease the friction between the tool and the chip under lubricated conditions. Computational Fluid Dynamic (CFD) simulations will be used in order to test the performance of micro-texture shapes under lubricated friction, which will then be verified through friction experiments of laser micro-textured cutting tools. The proposed micro texture shape, after conducting the needed analysis, will be effective at decreasing the friction coefficient at the tool-chip interface compared with other conventional shapes. The expected micro-texture can be significant in extending the lifespan of cutting tools and lubricants under different cutting process conditions.