Thesis (M.S.)--Worcester Polytechnic Institute. / UMI no. 30-31030. Keywords: chip breaking; prediction; turning; grooved inserts. Includes bibliographical references (p. 113-121).

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 108-112). Available also in a digital version from Dissertation Abstracts.

This diploma thesis addresses the issues associated with the theory of chip machining of metals. The theories are supported in many chapters by illustrative images created in the SolidWorks 3D modeler. The introductory part is rather theoretical, describing integrally and systematically the basic terms of splinter machining. The subsequent chapters address the issues of the turning tool edge geometry, different types of tools? materials, chip development, forces, work, temperatures and heat emitted during the work. Furthermore, the diploma thesis also addressed issues related to the machining efficiency. Finally, the conclusion of the thesis consists of a description of the basic types of milling and turn machining

Titanium alloys have outstanding mechanical properties such as high hardness, a good strength-to-weight ratio, excellent fatigue properties and high corrosion resistance. However, several inherent properties including their low thermal conductivity and high chemical affinity to tool materials impairs severely their machinability with conventional machining techniques. Conventional machining of Ti-based alloys is typically characterized by low depths of cuts and relatively low feed rates, thus adversely affecting the material removal rates during the machining process. Recently, a non-conventional machining technique known as ultrasonically assisted turning (UAT) was introduced to machine modern alloys, in which low-energy, high-frequency vibration is superimposed on the movement of a cutting tool during a conventional cutting process. This novel machining technique results in a multi-fold decrease in the level of cutting forces with a concomitant improvement in surface finish of machined modern alloys. Also, since the late 20th century, machining of wear resistant materials that soften when heated has been carried out with hot machining techniques. In this work, a new hybrid machining technique called Hot Ultrasonically Assisted Turning (HUAT) is introduced for processing of a Ti-based alloy Ti-15V3Al3Cr3Sn. In this technique, UAT is combined with a traditional hot machining technique to gain combined advantages of both schemes for machining of intractable alloys. HUAT of the studied alloy was analysed experimentally and numerically to demonstrate its benefits in terms of reduction in cutting forces over a wide range of industrially relevant speed-feed combinations. Thermal evolution in the cutting process was assessed, and the obtained results were compared with FE simulations to gain knowledge of temperatures reached in the cutting zone. The developed novel turning process appeared to improve dry turning of the Ti alloy with significant reduction of average cutting forces without any substantial metallurgical changes in the workpiece material. Nano-indentation, light microscopy and SEM studies were performed to get an insight into the development of hardness in a zone near the machined surface in the workpiece. Backscatter electron microscopy was also used to evaluate the formation of α-Ti during the novel HUAT. No grain changes or α-precipitation were observed in machined workpieces in conventional and hybrid turning processes. 3D elasto-plastic thermomechanically coupled finite-element models for the orthogonal turning process were developed for conventional turning (CT), hot conventional turning (HCT), UAT and HUAT, followed by a more realistic novel 3D finite-element model for the oblique turning process. These 3D models were used to study the effects of cutting parameters (cutting speed, feed rate and depth of cut, ultrasonic vibration, ultrasonic frequency, rake angle and tool nose radius) on cutting forces, temperature in the process zone and stresses. The later model was used to analyse the effect of vibration and heat on the radial and axial components of cutting forces in HUAT, which was not possible with the developed 3D orthogonal-turning model. Comparative studies were performed with the developed CT, HCT, UAT and HUAT finite-element models and were validated by results from experiments conducted on the in-house prototype and in literature. The HUAT for the Ti-15333 was analysed experimentally and numerically to demonstrate the benefits in terms of a significant reduction in the cutting forces and improvement in surface roughness over a wide range of industrially relevant speed-feed combinations.

The diploma thesis deals with the influence of machining technologies (turning, milling, grinding and polishing) on the surface texture of functional surfaces of selected materials from technical plastics. In the first part of the thesis there is a theoretical analysis of the possibilities of machining plastic materials. Furthermore, an analysis of the most commonly used parameters for evaluating the roughness of the machined surface and their effect on functionality is performed. The experimental part of the thesis describes samples preparation, analysis of measured data and subsequent evaluation with benefits for machinery industry.

En usinage, la zone de coupe présente des conditions de température, des cinétiques thermiques, des déformations et des pressions extrêmes. Dans ce contexte, être capable de relier les variations des conditions de coupe (vitesse de coupe, avance, lubrification, usure, outil,…) à l’intégrité de la surface usinée constitue un objectif scientifique majeur. Cette thèse s’intéresse au cas du tournage finition du 15-5PH (acier inoxydable martensitique utilisé, entre autre, pour la fabrication des pièces de rotor d’hélicoptère ainsi que les pompes et les vannes de circuit primaire de centrale nucléaire) et s’inscrit dans le cadre du projet MIFSU (Modélisation de l’Intégrité et de la Fatigue des Surfaces Usinées).Dans un premier temps, le comportement du matériau a été étudié afin d’alimenter les simulations d’usinage. Des essais de dilatométrie libre ont été conduit afin de calibrer les cinétiques d’austénitisation du 15-5PH pour des vitesses de chauffe élevées (jusqu’à 11000 °C/s). Les paramètres du modèle de changement de phase de Leblond ont alors été identifiés. De plus, des essais de compression dynamique (dε/dt allant de 0.01 à 80 /s et ε > 1) ont été réalisés pour calibrer une loi de comportement élasto-plastique aux grandes déformations avec une sensibilité à la vitesse de déformation. Ces essais ont aussi permis de mettre en évidence des phénomènes de recristallisation dynamique et leurs influences sur la contrainte d’écoulement du matériau. Un modèle de recristallisation dynamique a donc également été mis en œuvre.En parallèle, un modèle numérique de prédiction de l’intégrité des surfaces tournées a été construit. Ce modèle repose sur une méthodologie dite « hybride » (développée au cours de la thèse Frédéric Valiorgue pour l’acier AISI 304L) qui consiste à supprimer la modélisation de l’outil de coupe et de la formation du copeau, et à remplacer l’impact thermomécanique de ces derniers sur la surface usinée par des chargements équivalents. Une étape de calibration de ces chargements a donc été réalisée à travers des essais de coupe orthogonale et de frottement (étude de sensibilité des efforts d’usinage, du coefficient de frottement et du coefficient de partage thermique) aux variations des paramètres de coupe.Enfin, les résultats des simulations numériques de tournage portant sur la prédiction des changements de microstructure (austénitisation et recristallisation dynamique) ainsi que des contraintes résiduelles ont été comparés aux résultats issus d’une campagne d’essais de chariotage. / During machining, extreme conditions of pressure, temperature and strain appear in the cutting zone. In this thermo-mechanical context, the link between the cutting conditions (cutting speed, lubrication, feed rate, wear, tool coating…) and the machining surface integrity represents a major scientific target. This PhD study is a part of a global project called MIFSU (Modeling of the Integrity and Fatigue resistance of Machining Surfaces) and it focuses on the finish turning of the 15-5PH (a martensitic stainless steel used for parts of helicopter rotor). Firstly, material behavior has been studied in order to provide data for machining simulations. Stress-free dilatometry tests were conducted to obtain the austenitization kinetics of 15-5PH steel for high heating rates (up to 11,000 ° C/s). Then, parameters of Leblond metallurgical model have been calibrated. In addition, dynamic compression tests (dε/dt ranging from 0.01 to 80/s and ε > 1) have been performed to calibrate a strain-rate dependent elastoplasticity model (for high strains). These tests also helped to highlight the dynamic recrystallization phenomena and their influence on the flow stress of the material. Thus, recrystallization model has also been implemented.In parallel, a numerical model for the prediction of machined surface integrity has been constructed. This model is based on a methodology called "hybrid" (developed during the PhD thesis of Frédéric Valiorgue for the AISI 304L steel). The method consists in replacing tool and chip modeling by equivalent loadings (obtained experimentally). A calibration step of these loadings has been carried out using orthogonal cutting and friction tests (with sensitivity studies of machining forces, friction and heat partition coefficients to cutting parameters variations).Finally, numerical simulations predictions of microstructural changes (austenitization and dynamic recrystallization) and residual stresses have been successfully compared with the results of an experimental campaign of turning.