Estimation of specific cutting energy in an S235 alloy for multi-directional ultrasonic vibration-assisted machining using the Finite Element Method

The objective of this work is to analyze the influence of the vibration-assisted turning process on the machinability of S235 carbon steel. During the experiments using this vibrational machining process, the vibrational amplitude and frequency of the cutting tool were adjusted to drive the tool tip in an elliptical or linear motion in the feed direction. Furthermore, a finite element analysis was deployed to investigate the mechanical response for different vibration-assisted cutting conditions. The results show how the specific cutting energy and the material’s machinability behave when using different operational cutting parameters, such as vibration frequency and tool tip motion in the x-axis, y-axis, and elliptical (x-y plane) motion. Then, the specific cutting energy and material’s machinability are compared with a conventional turning process, which helps to validate the finite element method (FEM) for the vibration-assisted process. As a result of the operating parameters used, the vibration-assisted machining process leads to a machinability improvement of up to 18% in S235 carbon steel. In particular, higher vibration frequencies were shown to increase the material’s machinability due to the specific cutting energy decrease. Therefore, the finite element method can be used to predict the vibration-assisted cutting and the specific cutting energy, based on predefined cutting parameters.Peer ReviewedPostprint (published version

Manufacturing of high precision mechanical components

The main goal of the thesis is to analyze key aspects of Precision Manufacturing, aiming at optimizing critical manufacturing processes: innovative experimental methodologies and advanced modelling techniques will be applied to cases study of industrial interest which have been successfully optimized

Metal cutting modelling SPH approach

The purpose of this work is to evaluate the use of the smoothed particle hydrodynamics (SPH) method within the framework of high speed cutting modelling. First, a 2D SPH based model is carried out using the LS-DYNA® software. The developed SPH model proves its ability to account for continuous and shear localised chip formation and also correctly estimates the cutting forces, as illustrated in some orthogonal cutting examples. Then, the SPH model is used in order to improve the general understanding of machining with worn tools. At last, a hybrid milling model allowing the calculation of the 3D cutting forces is presented. The interest of the suggested approach is to be freed from classically needed machining tests: Those are replaced by 2D numerical tests using the SPH model. The developed approach proved its ability to model the 3D cutting forces in ball end milling

Development of a new additive for improving machinability of PM steels

Tableau d'honneur de la Faculté des études supérieures et postdoctorales, 2017-2018Bien que la métallurgie des poudres (MP) soit connue comme un méthode de fabrication aux cotes presque finales, un volume ignificatif de pièces MP nécessitent que l’on ait recours à une opération d’usinage. Les opérations d'usinage secondaires sont habituellement requises pour la conformité dimensionnelle ou la production de caractéristiques géométriques compliquées qui ne peuvent pas être obtenues par le procédé de pressage. Cependant, en raison de la présence de porosité, l'usinabilité des pièces en aciers MP est difficile en comparasion aux aciers corroyés et peut ajouter 20% ou plus au coût total de fabrication de ces pièces. Parmi les diverses mesures connues pour améliorer l'usinabilité des aciers MP, l'utilisation d'additifs d'usinage, soit pré-mélangés, soit préalliés, est de loint la méthode la plus utilisée. Il existe des dizaines d'éléments et de composés différents qui peuvent améliorer l'usinabilité à différents niveaux. Néanmoins, leurs effets négatifs sur d'autres propriétés des aciers MP tels que les propriétés mécaniques et la résistance à la corrosion rendent leur utilisation peu intéressante. Dans cette étude, des particules de graphite libre sont présentées comme un nouvel additif qui non seulement améliore significativement l'usinabilité des aciers MP, mais le fait sans affecter de façon notable les propriétés mécaniques et la résistance à la corrosion. Il a été démontré qu'il est possible d'obtenir des particules de graphite libres dans un acier MP par enrobage de celles-ci. Cet enrobage permet d’empêcher le graphite de diffuser dans la matrice de fer pendant le frittage. Dans cette étude, des particules de graphite enrobées de nickel ont été recouvertes de cuivre par le procédé de cémentation. Un traitement thermique a ensuite été réalisé sur ce nouveau matériau afin d’obtenir un revêtement plus uniforme. Les résultats des essais de caractérisation mécanique sur des échantillons frittés (FC-0208) contenant des particules prémélangées de graphite enrobées de cuivre / nickel, soit traitées thermiquement ou non, montrent que ce nouvel additif ne détériore pas les propriétés mécaniques statiques et dynamiques des aciers MP. De plus, la résistance à la corrosion des échantillons contenant cet additif se révèle être la même que celle des échantillons sans additif. Les effets de l’additif non traité thermiquement et traité thermiquement sur l'usinabilité des aciers MP ont également été caractérisés en utilisant un opration de perçage. Les résultats obtenus montrent que ce nouvel additif peut améliorer significativement l'usinabilité en réduisant la force de coupe requise.Although powder metallurgy (PM) is known as a near-net-shape fabrication method, noticeable amount of PM parts need some sort of machining. Secondary machining operations are usually required for dimensional conformance or producing complicated geometrical features that cannot be achieved at the compaction stage. However, due the presence of porosity, machinability of PM steels is difficult compared to wrought steels and can add 20% or more to the overall fabrication cost of PM parts. Thus, improving machinability of PM steels can definitely reduce their production costs. Among the various measures known to improve machinability of PM steels, addition of machining aids, either as admixed or pre-alloyed, is the most popular one. There are tens of different elements and compounds that can improve machinability at different levels. Nevertheless, their negative effects on other properties of PM steel components, such as mechanical properties and corrosion resistance, make their utilization somewhat limited. In this study, free graphite particles are introduced as a new additive that not only significantly improve machinability of PM steels, but also does not affect the mechanical and corrosion properties. It was found that it is possible to have free graphite particles in a PM steel, sintered using conventional sintering conditions, by coating the graphite particles. This coating can prevent graphite from diffusing into the iron matrix during sintering. In this research, nickel coated graphite particles were coated with copper through cementation process. A heat treatment was then performed on this newly developed material to have a more uniform single layer coating. The results of mechanical characterization tests on the copper steel sintered samples containing admixed copper/nickel coated graphite particles, either in the form of non-heat-treated or heat-treated, showed that this new additive does not deteriorate static and dynamic mechanical properties of PM steels. Moreover, the corrosion resistance of the samples containing copper/nickel coated graphite was found to be the same as samples without additive. The effects of non-heat-treated and heat-treated copper/nickel coated graphite on machinability of PM steels were also characterized using drilling test. It was seen that this new additive can significantly improve machinability through reducing the required cutting force

Improvements of machinability of aerospace-grade Inconel alloys with ultrasonically assisted hybrid machining

Aerospace-grade Ni-based alloys such as Inconel 718 and 625 are widely used in the airspace industry thanks to their excellent mechanical properties at high temperatures. However, these materials are classified as ‘difficult-to-machine’ because of their high shear strength, low thermal conductivity, tendency to work-harden and presence of carbide particles in their microstructure, which lead to rapid tool wear. Machining-induced residual stresses in a machined part is an important parameter which is assessed since it can be used to evaluate overall structural resilience of the component and its propensity to fatigue failure in-service. Ultrasonically assisted turning (UAT) is a hybrid machining technique, in which tool-workpiece contact conditions are altered by imposing ultrasonic vibration (typical frequency ~ 20 kHz) on a tool’s movement in a cutting process. Several studies demonstrated successfully the resulting improvements in cutting forces and surface topography. However, a thorough study of UAT-induced residual stresses is missing. In this study, experimental results are presented for machining Inconel 718 and 625 using both conventional turning (CT) and UAT with different machining parameters to investigate the effect on cutting forces, surface roughness and residual stresses in the machined parts. The study indicates that UAT leads to significant cutting force reductions and improved surface roughness in comparison to CT for cutting speeds below a critical level. The residual stresses in machined workpiece show that UAT generates more compressive stresses when compared to those in CT. Thus, UAT demonstrates an overall improvement in machinability of Inconel alloys

Effects of cutting angle, edge preparation, and nano-structured coating on milling performance of a gamma titanium aluminide

Gamma titanium aluminides are intermetallic alloys. Recently, they have been evaluated as important contenders for structural applications in the automotive and aerospace sectors. This is due to their excellent high-temperature performances and their significantly lower density compared to Nickel-based superalloys. In this paper, an analysis of machinability of a gamma TiAl obtained via an electron beam melting (EBM) process is presented. The effects of tool geometry modifications, in terms of cutting tool angles and cutting edge preparation, were investigated. The reduction of radial rake angle and the drag finishing process for cutting edge preparation resulted in an increase of the tool life of the carbide end mills. Nanogradient tool coatings were also observed to affect tool wear during milling tests, and the results highlight that AlSiTiN coating performs better compared to CrAlSiN coating. A post-coating polishing treatment was also taken into account, and it allowed a further reduction of tool wear. The overall results indicate that the machinability of this difficult-to-cut material can be significantly improved by an adjustment of the cutting edge geometry, and by using an AlSiTiN coating syste

Emergent Structure Detection for Multi-Axis Machining

This paper examines the phenomenon of emergent structures that occur in the transient stock material during multi-axis rough machining from a plurality of fixed orientations. Taking the form of thin webs and strings, emergent structures are stock material conditions that can lead to catastrophic failure during machining, even when tool path verification is successful. We begin by discussing the motivation for use of fixed orientations in multi-axis machining using multiple automated setups via rotary axes, which enables fast processing and ‘first part correct’ machining. Next, we demonstrate how unintended emergent structures occur in this paradigm of machining and can lead to catastrophic failure of the tool or work piece. Our original work focuses on the problem of geometric detection of these structures during process planning and prior to tool path planning, to the end of altogether avoiding emergent structure formation. To quickly simulate the machining process, we present an object-space method for determining the transient state of stock material based on the inverse tool offset. To identify emergent structures within this transient stock state, we propose a metric based on the medial axis transformation. Finally, we present our implementation of these methods and demonstrate realtime computation appropriate for an optimization scheme to eliminate emergent structures. Our methods provide consistent and logical results, as demonstrated with several freeform component examples. This work enables the development of robust algorithms for autonomous tool path planning and machining in multi-axis environments

High-speed Fabrication of Micro-channels using Line-based Laser Induced Plasma Micromachining (L-LIPMM)

Micro-texturing of surfaces has various applications that often involve texturing over large (macro-scale) areas with high precision and resolution. This demands scalability and speed of texturing while retaining feature sizes on the order of a few ?m. Moreover, micro-channels are a versatile micro-feature that are often used in microfluidic devices and can be arrayed or joined to form patterns and free-form geometries. We present a technique to fabricate micro-channels on surfaces with high-speed and by using a multi-materials process, namely Laser Induced Plasma Micromachining (LIPMM). The process has the potential to machine metals, ceramics, polymers and other transparent, brittle and hard-to-machine materials. The presented technique uses an optical system to modify the laser spot into the shape of a line, to fabricate micro-channels directly without scanning as in the case of a regular circular spot. The process schematics are shown, and micro-machining experiments on polished Aluminum are discussed. Moreover, it is shown that the depth and width of the channels may be varied by changing the process parameters like the pulse energy, pulse frequency and number of exposures

Optimization the machinability and mechanical properties of PM steel components by development a new machining additive

L'usinabilité des composants en acier PM est nettement inférieure à celle des aciers corroyés en raison de la présence de porosité résiduelle et de l'hétérogénéité de leur microstructure. Les problèmes liés à l'usinabilité constituent une part importante des coûts de production globaux des pièces en acier PM. La stratégie la plus populaire pour améliorer leur usinabilité consiste à mélanger un composé chimique, tel que MnS, MoS2 ou BN-h, à la poudre de base. Ces améliorateurs d'usinabilité améliorent le comportement d'usinage des aciers PM en diminuant les forces de coupe impliquées dans la formation de copeaux et en lubrifiant la surface de l'outil de coupe, ce qui en retour réduit à la fois l'usure en flanc et l'usure en cratère. Cette étude met en évidence une nouvelle approche pour développer des activateurs d'usinabilité conçus pour maximiser l'usinabilité des composants d'acier PM sans affecter les propriétés mécaniques ni la résistance à la corrosion. Ainsi, il a été décidé de revêtir les particules de MnS d'une couche de nickel pouvant agir comme une barrière pour neutraliser leur nature hygroscopique et augmenter la résistance à la corrosion des pièces en acier PM. De plus, il a été prévu que les propriétés mécaniques peuvent être améliorées en raison de la formation de liaisons métallurgiques entre le revêtement de nickel des particules de MnS et la matrice d'acier, tandis que le MnS améliore simultanément l'usinabilité de la pièce en acier PM. Une comparaison avec des additifs d'usinage commerciaux a été effectuée en termes d'usinabilité et de propriétés mécaniques. Il a été constaté que la résistance à la corrosion des échantillons contenant du MnS recouvert de nickel était excellent et identique à celle des échantillons sans additifs. De plus, les propriétés mécaniques ne sont pas affectées par la présence de l'additif nouvellement développé par rapport à ce qui a été mesuré lorsque le MnS a été utilisé. Enfin, la caractérisation de l'usinabilité a montré que l'ajout du MnS revêtu de nickel comme additif d'usinage pouvait améliorer l'usinabilité aussi bien que le MnS.Machinability of PM steel components is significantly lower than that of wrought steels due to the presence of residual porosity and the heterogeneity of their microstructure. Machinability-related issues constitute a significant portion of the overall production costs of PM steel parts. The most popular strategy for improving their machinability involves admixing a chemical compound, such as MnS, MoS₂ or BN-h, to the base powder. These machinability enhancers improve the machining behavior of PM steels by decreasing the cutting forces involved with chip formation and by lubricating the surface of the cutting tool, which in return, reduces both flank wear and crater wear. This study highlights a novel approach for developing machinability enhancers engineered to maximize the machinability of PM components without affecting their mechanical properties nor corrosion resistance. Thus, it was decided to coat MnS particles with a nickel layer that can act as a barrier to neutralize their hygroscopic nature and increase the corrosion resistance of PM steel parts. Moreover, it was anticipated that mechanical properties could be improved due to the formation of metallurgical bonds between the nickel coating of the MnS particles and the steel matrix, while the MnS core of the additive would improve machinability of the PM steel component simultaneously. A comparison with commercial machining additives was performed in terms of both machinability and mechanical properties. It was found that the corrosion resistance of the samples containing nickel-coated MnS was excellent and identical to that of samples without additives. Moreover, mechanical properties are not affected by the presence of the newly developed additive compared to what was measured when MnS was used. Finally, machinability characterization showed that the addition of the nickel-coated MnS as a machining additive could improve machinability as well as MnS does