Intelligent machining methods for Ti6Al4V: a review

Digital manufacturing is a necessity to establishing a roadmap for the future manufacturing systems projected for the fourth industrial revolution. Intelligent features such as behavior prediction, decision- making abilities, and failure detection can be integrated into machining systems with computational methods and intelligent algorithms. This review reports on techniques for Ti6Al4V machining process modeling, among them numerical modeling with finite element method (FEM) and artificial intelligence- based models using artificial neural networks (ANN) and fuzzy logic (FL). These methods are intrinsically intelligent due to their ability to predict machining response variables. In the context of this review, digital image processing (DIP) emerges as a technique to analyze and quantify the machining response (digitization) in the real machining process, often used to validate and (or) introduce data in the modeling techniques enumerated above. The widespread use of these techniques in the future will be crucial for the development of the forthcoming machining systems as they provide data about the machining process, allow its interpretation and quantification in terms of useful information for process modelling and optimization, which will create machining systems less dependent on direct human intervention.publishe

Surface Texture and Micromechanics of Ultra High Molecular Weight Polyethylene (UHMWPE) Orthopaedic Implant Bearings

Tibial bearings of ultra-high molecular weight polyethylene (UHMWPE) were characterized to identify differences in morphology, surface texture (roughness and skewness), and micro-scale mechanical behavior. These orthopaedic implant components were fabricated by direct molding or by machining after isostatic compression molding. Sterilization was by gamma irradiation (3.3 Mrad) in air, followed by shelf aging for 2 years. Comparisons were made between unsterile and sterile bearings to identify differences in structure and properties related to wear debris. Characterization methods included confocal optical microscopy, nanoindentation , small angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and polarized light microscopy. Morphology was compared between bulk and surface (top and bottom) specimens of the bearings. Cryo-microtomy was used to prepare thin specimens transverse to the top surface for polarized microscopy. Nanoindentation was performed on the top bearing surfaces, near areas examined by confocal microscopy. Processing methods affected both small- and large-scale morphology of UHMWPE. Direct molding produced thinner lamellae, thicker long periods, and slightly lower crystallinity than isostatic compression molding. Both bearing types contained a thick interface between the crystalline and amorphous phases. Interfacial free energy varied with interface thickness. Resin particles were consolidated better in direct molded bearings than in machined bearings. Segregated amorphous regions were observed in the machined bearings. Sterilization and shelf aging affected nanometer-scale morphology. Chain scission significantly decreased the interface thickness, causing an increase in lamellar thickness and a small increase in crystallinity. Only a small decrease in the amorphous thickness resulted. Heterogeneous oxidation increased these changes in interface thickness and lamellar thickness at the surfaces. Thin lamellae were created in the direct molded bearing, uniformly through its thickness, following chain scission and crystallization at low temperature. Both surface roughness and morphology affected micromechanical behavior by nanoindentation. Indents must extend deeper than the peak-to-valley height (2 - 11 m) of surface features, near the scale of wear debris. Hardness and elastic modulus correlated with lamellar thickness. Machined bearings were harder and stiffer than direct molded bearings. Sterilization increased lamellar thickness, so properties of the sterile, molded bearing approached those of the unsterile, machined bearing

Characterization and improvement of copper / glass adhesion

The development of glass substrates for use as an alternative to printed circuit boards (PCBs) attracts significant industrial attention, because of the potential for low cost but high performance interconnects and optical connection. Electroless plating is currently used to deposit conductive tracks on glass substrates and the quality of copper / glass adhesion is a key functional issue. Without adequate adhesive strength the copper plating will prematurely fail. Existing studies have covered the relationship between surface roughness and adhesion performance, but few of them have considered the detail of surface topography in any depth. This research is specifically considering the mechanical contribution of the glass surface texture to the copper / glass adhesive bond, and attempting to isolate new ISO 25178 areal surface texture parameters that can describe these surfaces. Excimer laser machining has been developed and used to create a range of micro pattern structured surfaces on CMG glass substrates. Excimer mask dimensions and laser operation parameters have been varied and optimized according to surface topography and adhesion performance of the samples. Non-contact surface measurement equipment (Zygo NewView 5000 coherence scanning interferometry) has been utilized to measure and parameterize (ISO 25178) the surface texture of the glass substrates before electroless copper metallization. Copper adhesion quality has been tested using quantitative scratch testing techniques, providing an identification of the critical load of failure for different plated substrates. This research is establishing the statistical quality of correlation between the critical load values and the associated areal parameters. In this thesis, the optimal laser processing parameter settings for CMG glass substrate machining and the topographic images of structured surfaces for achieving strong copper / glass plating adhesion are identified. The experimental relationships between critical load and areal surface parameters, as well as the discussions of a theoretical approach are presented. It is more significant to consider Sq, Sdq, Sdr, Sxp, Vv, Vmc and Vvc to describe glass substrate surface topography and the recommended data value ranges for each parameter have been identified to predict copper / plating adhesion performance

Topological surface integrity modification of AISI 1038 alloy after vibration-assisted ball burnishing

The objective of this paper is to analyze the effect of the vibration-assisted ball burnishing process on the topology of AISI 1038 flat surfaces, in order to evaluate its feasibility for surface enhancement towards wear prevention and fatigue enhancement in industrial components. With that aim, an experimental campaign based on a Taguchi orthogonal matrix has been deployed. Five factors were studied, namely: preload force, number of passes, feed, initial surface texture and strategy. The topologies of the resulting burnishing patches have been acquired with a non-contact optical device, and the 3D texture parameters have been calculated to quantify the effects of burnishing. In all cases, the bearing capacity of the burnished surfaces was improved, as the proportion of core material is increased due to the deformation of the surface peaks. The initial surface state proved to be the most influential parameter on amplitude, spatial, and volumetric parameters. In all cases, a set of optimal vibration-assisted ball burnishing parameters was found for the sake of reproducibility and systematization of the process. Finally, results have been compared to the conventional ball burnishing process, observing that it presents scratch damage on the surfaces that can be prevented through assistance through vibrations.Postprint (author's final draft

Build orientation, part size geometry, and scan path influence on the microstructure and fatigue life of Ti-6Al-4V fabricated by Electron Beam Melting

Electron beam melting (EBM), a powder bed fusion process, is a rapidly-developing metal additive manufacturing method that allows for fabrication of complex geometries directly from a computer file that would be difficult or impossible to fabricate by traditional methods. EBM holds significant interest in the aerospace industry for the high-strength titanium alloy, Ti-6Al-4V, because of its promising opportunity to reduce buy-to-fly ratios. However, a fundamental understanding of the fatigue-damage tolerance, underlying mechanisms, and impact of processing conditions is required for use of EBM fabrication of critical flight components. To investigate how the EBM process affects components, different parameters were varied and the resulting microstructure and mechanical properties were characterized using 4-point bend fatigue tests, tensile tests, Vickers microhardness indentations, scanning electron microscopy, and optical microscopy.The orientation, scan path, and surface finish were varied and the effects on microstructure, tensile properties, and fatigue behavior are reported and discussed. As expected, the surface roughness left by the EBM fabrication adversely impacts the fatigue behavior and sufficient machining is required to remove all surface roughness effects. It was discovered that the build orientation affects the tensile ductility and fatigue life, but the strength and hardness are largely independent of orientation. The EBM Ti-6Al-4V shows similar fatigue life to conventional material, but is limited by porosity defects. The altered processing parameters affected the fatigue behavior, but promising results indicate that EBM can be a viable manufacturing method for flight critical components

Surface integrity evaluation and the effect of machining-induced surface integrity characteristics on part's performance

Surface integrity (SI) is the integrated surface behavior and condition of a material after being modified by a manufacturing process; it describes the influence of surface properties and characteristics upon material functional performance. As the leading-edge field of manufacturing research, SI finishing/machining and the consequent machining-induced complex combination of surface roughness, residual stress, work-hardening, macro and microstructure transformation, strongly affect the fatigue and stress behavior of machined parts. This kind of influence is particularly sensitive and pronounced in the difficult-to-machine materials, which are typically chosen for the most critical applications in the automobile, aerospace and nuclear industry. Thus, well-designed SI processing requirement and accurate SI evaluation model are essential to control and ensure the surface quality and functional performance for these key parts. In this thesis, an SI descriptive model for quantitative characterization and evaluation of surface integrity is proposed based on five principal SI characteristics. Considering the nature of surface integrity, a conceptual framework of an SI model for machined parts is established, in which the SI model is constructed based on the correlations between SI manufacturing processes, SI characteristics and final functionality. This model offers a theoretical basis and guideline for controlling SI characteristics and improving fatigue properties for machined parts. An empirical model for estimating the SI-characteristics-caused effective stress concentration factor (SCF) is established with fatigue life as the evaluating indicator. For a typical difficult-to-machine material, GH4169 superalloy, usually used in internal combustion engines, its grindability and the influence of processing parameters on the five principal SI characteristics are investigated in detail. The correlations between the processing parameters and the SI characteristics, between the processing parameters and the fatigue properties, and between the SI characteristics and the fatigue properties, are analyzed based on an orthogonally-designed grinding experiment and corresponding rotary bending fatigue testing for GH4169 samples within the selective range of grinding processing parameters. The feasibility and effectiveness of the proposed model for estimating the SI effective SCF are also validated by the experimental results, and this has actually offered an equivalent and convenient means for evaluation of SI and fatigue properties. Finally, the conclusions and contribution of the research are discussed, and potential future work to build on this research is identified

On the application of replica molding technology for the indirect measurement of surface and geometry of micromilled components

The evaluation of micromilled parts quality requires detailed assessments of both geometry and surface topography. However, in many cases, the reduced accessibility caused by the complex geometry of the part makes it impossible to perform direct measurements. This problem can be solved by adopting the replica molding technology. The method consists of obtaining a replica of the feature that is inaccessible for standard measurement devices and performing its indirect measurement. This paper examines the performance of a commercial replication media applied to the indirect measurement of micromilled components. Two specifically designed micromilled benchmark samples were used to assess the accuracy in replicating both surface texture and geometry. A 3D confocal microscope and a focus variation instrument were employed and the associated uncertainties were evaluated. The replication method proved to be suitable for characterizing micromilled surface texture even though an average overestimation in the nano-metric level of the Sa parameter was observed. On the other hand, the replicated geometry generally underestimated that of the master, often leading to a different measurement output considering the micrometric uncertainty

Study and characterisation of surface integrity modification after ultrasonic vibration-assisted ball burnishing

Tesi en modalitat de cotutela: Universitat Politècnica de Catalunya i Université Toulouse III Paul Sabatier. Aplicat embargament des de la data de defensa fins a gener de 2020Premi extraordinari doctorat UPC curs 2017-2018. Àmbit d’Enginyeria IndustrialThis dissertation is an experimental research project into the mechanical effects of the ultrasonic vibration-assisted ball burnishing process on the surface integrity of surfaces machined through ball-end milling. Due to the lack of commercial tools able to perform this process, the study includes firstly the design and characterization of a prototype to that effect. An experimental analysis is then undertaken, applying the process to AISI 1038 and Ti-6Al-4V surfaces of high industrial and aeronautical value. The experimental campaign is designed based on a Taguchi orthogonal array that includes five factors, namely: preload, number of passes, feed velocity, strategy and initial surface texture. Results are analyzed in terms of topological characteristics, residual stress and hardness, in order to identify and understand the impact of process parameters on surface integrity, to define the best parameters for performing the process and to assess the positive effects caused by the introduction of vibrations as a means of assistance. Results reveal that the initial texture is the most influential parameter on all outcomes. Texture results show that the vibrations can enhance the roughness and texture results, as long as they have sufficient low initial amplitude. Furthermore, only the preload and number of passes influence the results, with a pair of values being found in all cases that serve a threshold from which further plastic strain is detrimental for the final surface topology. In terms of residual stress, all parameters are influential in the results, especially the burnishing strategy, through which a certain component of the residual stress tensor can be adequately reinforced. Finally, the burnishing operation proves to modify the hardness of deep layers down to 0.5 mm, applying the vibration-assisted process. .e main conclusion is that the optimal parameters for performing the process are different with regards to the optimization objective. Some useful combinations are proposed for performing the process depending on the desired targetEsta tesis es un estudio experimental que versa sobre los efectos del proceso de bruñido con bola asistido por vibraciones ultrasónicas sobre la integridad superficial de superficies mecanizadas mediante fresa hemisférica. Dada la indisponibilidad de herramientas comerciales capaces de efectuar este proceso, el estudio incluye en primer lugar el diseño y caracterización de un prototipo a tal efecto. Posteriormente, se realiza un análisis experimental aplicando el proceso sobre superficies de dos aleaciones de interés industrial y aeronáutico, AISI 1038 y Ti-6Al-4V, siguiendo un diseño de experimentos fraccionario basado en una matriz ortogonal de Taguchi. Para ello, cinco factores son incluidos en el modelo, a saber: la precarga, el número de pasadas, la velocidad de avance, la estrategia de bruñido, y la textura de la superficie de partida. Los resultados se evalúan en términos de textura, tensiones residuales y dureza, para identificar y comprender el impacto de este proceso y de sus parámetros de operación sobre la integridad superficial, para definir los mejores parámetros a aplicar para cada material, y con el fin de evaluar los efectos positivos provocados por la introducción de las vibraciones como medio de asistencia. Los resultados revelan que la textura inicial es el parámetro que define en mayor medida el estado de las superficies finales. Los resultados de textura evidencian que las vibraciones pueden mejorar en mayor medida la topología de las superficies objetivo, siempre que éstas sean suficientemente finas. Además, sólo la precarga y el número de pasadas influyen en el resultado, encontrando en todo caso un par de valores limítrofe a partir del cual las superficies se ven dañadas. Los resultados de tensiones residuales muestran que todos los parámetros son influyentes en el resultado final, especialmente la estrategia de bruñido, con la que puede modificarse la dirección preferencial del tensor de tensiones superficial. Finalmente, el bruñido demuestra modificar la dureza positivamente hasta capas de aproximadamente 0,5 mm, aplicando el proceso asistido con vibraciones. Se concluye que los parámetros óptimos de proceso son diferentes en función del objetivo de optimización, y deben definirse en base a dos variables de partida: el material objetivo y la textura que éste presenta antes del proceso.Cette thèse étudie les effets du processus de brunissage à bille assisté par vibrations ultrasoniques sur l’intégrité surface des surfaces usinées par fraisage hémisphérique. Compte tenu de l’inexistence d’outils commerciaux capables de réaliser ce processus, l’étude débute par la conception et la caractérisation d’un prototype capable de l’exécuter. Par la suite, une analyse expérimentale est menée, en utilisant le procédé sur les surfaces de deux alliages d’intérêt industriel et aéronautique, AISI 1038 et Ti- 6Al-4V. Pour cela, un plan d’expériences est elaboré à base d’une matrice orthogonale Taguchi. Cinq facteurs sont inclus dans le modèle : la précharge, le nombre de passes, la vitesse d’avance, la stratégie de brunissage et la texture initiale de la surface préalablement usinée. Les résultats sont évalués en termes de texture finale, de contrainte résiduelle et de dureté, pour identifier et comprendre l’impact de ce procédé et des paramètres opératoires sur l’intégrité de surface, pour définir les meilleurs paramètres à appliquer pour chaque matériau, et pour évaluer les effets positifs provoqués par l’introduction de vibrations comme moyen d’assistance. Pour cela, la notion d’intégrité de surface est rappelée, voire redéfinie dans le cas de la texture de surface. En effet, les critères classiquement utilisés se révèlent inaptes à caractériser les surfaces obtenues, et une nouvelle méthodologie d’analyse des topologies de surface est proposée. Les résultats obtenus suite à la réalisation du plan d’expériences révèlent que la texture initiale est le paramètre prépondérant. Les résultats de la topologie de surface montrent que les vibrations peuvent améliorer la rugosité et la texture des surfaces dans la mesure où l’état de surface initial est sufisamment fin. Ensuite, seule la précharge et le nombre de passes influencent le résultat, avec, dans tous les cas, un couple de valeurs limites à partir desquelles les surfaces sont endommagées. Les résultats des contraintes résiduelles montrent que tous les paramètres influent sur le résultat final, en particulier la stratégie de brunissage, avec laquelle la direction préférentielle du tenseur de la contrainte superficielle peut être modifiée. Enfin, le brunissage montre une modification positive de la dureté à des couches d’environ 0,5 mm en appliquant le processus assisté avec vibrations. Nous concluons que les paramètres de processus optimaux sont diférents en fonction de l’objectif d’optimisation, et que certaines combinaisons peuvent être utiles en fonction de ces objectifs.Aquesta tesi és un estudi experimental que tracta sobre els efectes del procés de brunyit amb bola assistit per vibracions ultrasòniques sobre la integritat superficial de superfícies mecanitzades amb fresa hemisfèrica. Degut a la indisponiblitat d’eines comercials capaces d’aplicar aquest procés, l’estudi inclou en primer lloc el disseny i la caracterització d’un prototip capa d’executar-lo. Posteriorment, es realitza una anàlisi experimental aplicant el procés sobre superfícies de dues aliatges d’internes industrial i aeronàutic, AISI 1038 i Ti-6Al-4V, seguint un disseny d’experiments basat en una matriu ortogonal Taguchi. Per això, cinc factors són inclous en el model: la precàrrega, el nombre de passades, la velocitat d’avenç, l’estratègia de brunyit i la textura de la superfície inicial. Els resultats s’avaluen en termes de textura final, tensions residuals i duresa, per identificar i comprendre l’impacte d’aquest procés i dels seus paràmetres d’operació sobre la integritat superficial, definir els millors paràmetres a aplicar per a cada material, i amb l’objectiu d’avaluar els efectes positius provocats per la introducció de les vibracions com a mitjà d’assistència. Els resultats evidencien que la textura inicial és el paràmetre que defineix en major mesura l’estat de les superfícies finals. Els resultats de textura indiquen que les vibracions poden millorar en major mesura la rugositat i textura de les superfícies, sempre que aquestes siguin suficientment fines. A més, només la precàrrega i el nombre de passades influeixen sobre el resultat, trobant en tot cas un parell de valors límits a partir del qual les superfícies són empitjorades. Els resultats de tensions residuals mostren que tots els paràmetres són influents sobre el resultat final, especialment l’estratègia, amb la què es pot millorar la direcció preferencial del tensor de tensions superficial. Finalment, el brunyit demostra modificar la duresa positivament fins a capes d’aproximadament 0.5 mm de profunditat, aplicant el procés assistit amb vibracions. Es conclou que els paràmetres òptims de procés són diferents en funció de l’objectiu d’optimització, i es proposen algunes combinacions que poden ser útils en funció del mateix.Award-winningPostprint (published version