Metodología para el análisis del comportamiento y caracterización de los aceros inoxidables austeníticos en el torneado de alto rendimiento

198 p.En esta tesis se han estudiado diversos aspectos relacionados con el torneado de los materiales en condiciones de corte severas, con el objetivo de mejorar el rendimiento del mecanizado de estos materiales. Para ello, se ha trabajado en un rango de velocidades muy superior al recomendado por los fabricantes de herramientas. En este marco de trabajo se han desarrollado tres estudios con las siguientes líneas de investigación. En el primer estudio se ha analizado el rendimiento de herramientas de metal duro recubiertas con tecnología PVD (Physical Vapour Deposition) con recubrimientos nanoestructurados y las técnicas de pre-tratamiento de Micro-Blasting y Drag-Finish, en el torneado de aceros inoxidables austeníticos en régimen de alta productividad. En el segundo estudio se ha analizado el comportamiento del material cuando se mecaniza en seco a altas velocidades de corte. Este estudio ha permitido encontrar la velocidad crítica a la cual el material experimenta un cambio en su comportamiento durante el proceso de cizalladura. Además se ha determinado el rango de velocidades de corte donde el comportamiento del material es favorable y por tanto son condiciones adecuadas para alcanzar un mecanizado de alto rendimiento. En el tercer estudio se ha desarrollado un modelo de predicción de fuerzas para la operación de torneado que incorpora la geometría de la herramienta, por lo que su campo de aplicación se extiende a herramientas con diferentes geometrías de corte. Este modelo se ha ampliado incluyendo el efecto del desgaste en incidencia de la herramienta sobre las fuerzas de corte. Además se ha caracterizado el acero inoxidable AISI 303 y se han obtenido las curvas de desgaste de la herramienta cuando se mecaniza a elevadas velocidades de corte y se ha establecido un criterio de fin de vida de herramienta que permite trabajar en máquinas automáticas en condiciones de corte severas y a la vez segura

Heat treatments for improved quality binder jetted molds for casting aluminum alloys

The objective of this paper was to investigate the most suitable heat treatment for casting molds manufactured by binder jetting. For this purpose, the printed molds were subjected to different heat treatments and the properties of the molds were analyzed. Tests were performed at different temperatures and times to investigate their effect on the water and volatile substances content; the joining among particles; and the porosity, roughness, and compression strength of the printed molds. Moreover, to relate the properties of the mold with the quality of the castings, aluminum alloy specimens were cast and the dimensional accuracy, surface roughness, mechanical strength, and porosity were evaluated. This research leads to the conclusion that the binder jetting process, using calcium sulfate powder, is useful for manufacturing molds for casting aluminum alloy. To improve the mold quality and, consequently, the casting quality, heat-treatment is necessary. The best mold properties were obtained at 250 °C for 1.5 h.S

Application of a force sensor to improve the reliability of measurement with articulated arm coordinate measuring machines

A study of the operator contact force influence on the performance of Articulated Arm Coordinate Measuring Machines (AACMMs) is presented in this paper. After developing a sensor capable of measuring the contact force applied by an operator, a ring gauge has been used to analyse the relationship between the contact force and diameter and form errors measured with the AACMM. As a result, contact force has been proved as one of the main factors influencing the AACMM performance. A probe deflection model based on the Finite Element Method (FEM) has been also proposed in order to obtain the AACMM probe deflection caused by contact force. This allows measurement correction by comparing them with reference values, specifically, a ring gauge. Experimental test results show a significant measurement improvement that minimizes diameter error. Finally, an uncertainty evaluation for the contact force sensor and AACMM measurements with and without probe deflection model has been carried out in order to validate the ability of the sensor and the methodology followe

Automatic classification of pores in aluminum castings using machine learning

[Resumen] La inspección de la porosidad de piezas fabricadas se ha realizado tradicionalmente mediante el uso de microscopía manipulada por parte de un técnico humano. Sin embargo, la persona involucrada necesita experiencia en esta tarea, y la cantidad de piezas que se pueden inspeccionar por unidad de tiempo es limitada. La presencia de porosidad en el material es crítica, ya que puede afectar negativamente a las propiedades mecánicas y la calidad de la pieza. En este trabajo se propone automatizar la clasificación de los defectos de porosidad que aparecen en el interior de las piezas fabricadas por fundición. En primer lugar, adquirimos imágenes a partir de piezas de aluminio fabricadas por dos métodos de fundición: uno tradicional usando molde de arena y otro más moderno con la técnica de fabricación aditiva Binder Jetting (BJ). Luego, recortamos regiones con y sin poros, que posteriormente caracterizamos usando descriptores SIFT codificados en características de BoVW para alimentar y entrenar dos clasificadores SVM: uno para predecir si la imagen contiene poro o no, y el otro para indicar si el poro detectado es debido al efecto de gases o por contracción durante la solificación.[Abstract] Porosity inspection of manufactured parts has traditionally been performed using microscopy manipulated by a human technician. However, the person involved needs experience in this task, and the number of parts that can be inspected per unit of time is limited. The presence of porosity in the material is critical, as it can negatively affect the mechanical properties and the quality of the part. In this paper, we propose to automate the classification of the porosity defects that appear inside the parts manufactured by casting. First, we acquire images from aluminum parts manufactured by two casting methods: a traditional one using sand molding and a more modern one with the Binder Jetting (BJ) additive manufacturing technique. Then, we crop regions with and without pores we later describe using SIFT descriptors encoded into BoVW features to feed and train two SVM classifiers: one for predicting if the image contains a pore or not, and the other for also indicating if the pore detected is due to the effect of gases or by shrinkage during solidification.Ministerio de Ciencia, Innovación y Universidades; DPI2017-89840-

Analysis of microstructure and defects in 17-4 PH stainless steel sample manufactured by Selective Laser Melting

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Design of a TCM System Based on Vibration Signal for Metal Turning Processe

Este artículo presenta un estudio sobre la identificación del estado de desgaste de la herramienta de corte mediante el análisis de señales de vibración en operaciones de torneado en seco de acero. Al analizar la evolución del valor RMS y los espectros de frecuencia FFT de la señal, se ha desarrollado un sistema de monitoreo de condición de herramienta en línea. El propósito principal es determinar el instante desde el cual la condición de la herramienta se considera inaceptable, lo que afecta la calidad del proceso de mecanizado. Después del análisis que se llevó a cabo el, la conclusión principal es que tanto el RMS como los rangos de amplitud de frecuencia de ciertas bandas de espectro, están relacionados con el desgaste de la herramienta

Towards Functional Parts by Binder Jetting Calcium-Sulphate with Thermal Treatment Post-Processing

[EN] The objective of our research is to improve the properties of calcium-sulphate hemihydrate parts printed by binder jetting. In this paper, we show the thermal treatment results when using temperature time ramps on binder-jetted ceramic parts without infiltrating. The results show that the mechanical properties of printed parts are improved substantially. Two different thermal cycles were investigated for their effect on the dehydration process of CaSO4·½H2O using infrared analysis. The thermal-treated samples were compared with respect to porosity, surface roughness, compression strength and dimensional and weight variation. The proposed thermal treatment significantly improves the compression strength in a short time, guaranteeing dimensional stability while providing a good surface. This improvement in mechanical properties offers a great chance for using binder-jetted parts as functional components, for example, in the casting field or the medical sector (scaffolds).SIAgencia Estatal de Investigació

Structural Phase Transitions of Hybrid Perovskites CH₃NH₃PbX₃ (X = Br, Cl) from Synchrotron and Neutron Diffraction Data

Methylammonium (MA) lead trihalide perovskites, that is, CH3NH3PbX3 (X = I, Br, Cl), have emerged as a new class of light-absorbing materials for photovoltaic applications. Indeed, since their implementation in solar-cell heterojunctions, they reached efficiencies above 23%. From a crystallographic point of view, there are many open questions that should be addressed, including the role of the internal motion of methylammonium groups within PbX6 lattice under extreme conditions, such as low/high temperature or high pressure. For instance, in MAPbBr3 perovskites, the octahedral tilting can be induced upon cooling, lowering the space group from the aristotype Pm3¯m to I4/mcm and Pnma. The band gap engineering brought about by the chemical management of MAPb(Br,Cl)3 perovskites has been controllably tuned: the gap progressively increases with the concentration of Cl ions from 2.1 to 2.9 eV. In this chapter, we review recent structural studies by state-of-the-art techniques, relevant to the crystallographic characterization of these materials, in close relationship with their light-absorption properties

Influence of Post-Processing on the Properties of Multi-Material Parts Obtained by Material Projection AM

[EN] The great geometric complexity that additive manufacturing allows in parts, together with the possibility of combining several materials in the same part, establishes a new design and manufacturing paradigm. Despite the interest of many leading sectors, the lack of standardization still makes it necessary to carry out characterization work to enjoy these advantages in functional parts. In many of these techniques, the process does not end with the end of the machine cycle, but different post-processing must be carried out to consider the part finished. It has been found that the type of post process applied can have a similar effect on part quality as other further studied process parameters. In this work, the material projection technique was used to manufacture multi-material parts combining resins with different mechanical properties. The influence of different post-processing on the tensile behavior of these parts was analyzed. The results show the detrimental effect of ultrasonic treatment with isopropyl alcohol in the case of the more flexible resin mixtures, being advisable to use ultrasonic with mineral oil or furnace treatment. For more rigid mixtures, the furnace is the best option, although the other post-processing techniques do not significantly deteriorate their performance.S