Elias Rigoberto Ledesma Orozco

OPTIMIZACIÓN PARAMÉTRICA DEL PROCESO DE ENGATILLADO LINEAL POR ROLDANA PARA CHAPAS METÁLICAS

The present work, focus on the parametric optimization of geometric parameters for Roll Hemming process. Here, the parameters of interest are the Roller radius, the angle for pre-hemming stage and the fillet radius. The main objective is to improve the quality parameters of the process: Roll-In, Roll-Out and wrinkling. Furthermore, a comparison between results generated, in numerical and experimental studies, with optimum and non-optimal parameters, is presented. Finite Element Analysis (FEA) Software, ANSYS Workbench 15® was implemented for numerical simulation of the process. For the experiments, a 6 degree of freedom (DOF) NACHI SRA210 industrial manipulator was used. From numerical results, 2 Rollers were developed with optimum (10.18 mm of radius) and non-optimal (25 mm of radius) parameters. Multiple tests of roll hemming in straight paths were performed on several 0.9 mm thick Aluminum sheets 6011 (120 x 100 mm2). Similar to simulation, the analysis of the obtained results shows that the Roller with optimum parameters generates the best quality in hemmed samples.

ACEROS AVANZADOS: COMPARACIÓN DEL COMPORTAMIENTO MECÁNICO EN EL ESTAMPADO DE UN TRAVESAÑO DE AUTOMOVIL

One of the fundamental objectives of the automotive industry today is the fuel economy; therefore, reducing vehicle weight has been pushed to the limit especially in the new body designs, without neglecting the passengers passive safety that these structures should provide. Thus, the achievement of these goals is only possible through the implementation of advanced high strength materials along with new design techniques and their associated manufacturing processes. In this investigation, a study of the implementation of three steels, categorized by the AISI, as advanced high strength steels (AHSS) in the manufacture of a cross bar is done. The results obtained are compared each other and with similarly obtained results considering a conventional high-strength steel (CHSS) possessing superior forming properties, but lower resistance properties regarding AHSS considered in this study . To this goald the foundation of the simulation process all necessary operations are presented to perform the sheet forming of a cross car for commercial vehicle floor and a comparative performance takes place between the four selected steels. A safety factor regarding the FLD curve is proposed. The use of appropriate material models of deformation processes involved in forming sheet and the correct definition of the mechanical properties associated with them are essential.

RESPUESTA ESTRUCTURAL DE CARTILAGO VISCOELASTICO DE RODILLA EN UN CICLO DE CAMINATA

El modelo de comportamiento estructural de cartilago es un tema de interes para realizar simulaciones biomecanicas de rodilla. Recientemente, los modelos elasticos isotropicos han sido aplicados para modelar el comportamiento de este tejido a pesar de su naturaleza viscoelastica. Por lo anterior, en este reporte se presenta la aplicacion de un modelo viscoelastico en un modelo de elemento finito de rodilla tridimensional para analisis a traves del tiempo de la respuesta estructural del cartilago durante un ciclo de caminata. Este trabajo considero ademas comportamientos estructurales hiperelasticos no lineales para los diversos tejidos blandos de la rodilla. Los resultados mostraron que considerar el efecto viscoelastico afecta los resultados y comportamiento estructural del tejido encontrando diferencias significativas (hasta 253% en esfuerzos) con simulaciones realizadas por otros autores que consideraron modelos isotropicos lineales. Finalmente, los resultados permitieron identificar zonas criticas de esfuerzo del cartilago articular cuando es sometido a un ciclo completo de caminata. El modelo de elemento finito de rodilla reportado en este trabajo permitira adicionalmente analizar diversos factores como variaciones de peso, angulo de alineacion y desgaste de cartilago que generan enfermedades que afectan el comportamiento estructural de la rodilla.

EFECTOS DE MODELOS VISCOELÁSTICOS NO LINEALES EN ANÁLISIS DE ELEMENTO FINITO DE ARTICULACIÓN DE RODILLA

RESUMEN: Los analisis de elemento finito (MEF) de la biomecanica de la articulacion de rodilla, requiere modelos de materiales no lineales para cartilago en casos de rodillas con osteoartritis unicompartimental (OAU). En este trabajo se presenta el analisis de elemento finito de dos modelos de material no lineal para describir el comportamiento mecanico de cartilago en casos de rodillas con OAU. Los modelos de material no lineal seleccionados consideran deformaciones finitas y un comportamiento viscoelastico no lineal a traves del tiempo. Este trabajo considera el modelo viscoelastico generalizado de Maxwell, asi como tambien, las ecuaciones constitutivas hipoelasticas y un modelo hiperelastico de energia potencial de deformacion. El comportamiento de relajacion se simula utilizando las funciones Kernel para relajacion cortante y volumetrica, las cuales estan representadas en terminos de series de Prony. Los modelos de material propuestos son validados con datos experimentales de pruebas de indentacion en cartilago de rodillas de casos con OAU, los cuales han sido previamente reportados. Para la fuerza de reaccion, los modelos de material ajustan bien para carga, relajacion y descarga de los modelos viscohipoelasticos (R2 = 0.974) y viscohiperelasticos (R2 = 0.975). El modelo viscohipoelastico versus modelos elastico lineales se comparan en un modelo tridimensional de articulacion de rodilla; los resultados de esta comparacion mostraron una diferencia maxima de 2.5 entre areas de contacto, 1.5 entre desplazamientos axiales y 1.6 veces entre esfuerzos de von Mises. Los resultados de este trabajo sugieren que el comportamiento viscoelastico del cartilago en OAU puede ser simulado adecuadamente con un modelo viscohipoelastico o viscohiperelastico. Este comportamiento viscoelastico no lineal modifica no solo la respuesta estructural del cartilago, sino tambien puede ser util en el proceso de diseno de protesis unicompartimentales y para entender la degeneracion y desgaste del cartilago que permanece en el otro compartimento en casos de osteoartritis unicompartimental. Palabras clave: Biomecanica, cartilago, viscoelasticidad, elemento finito, rodilla.

ANALISIS TEÓRICO-NUMÉRICO-EXPERIMENTAL DE UN PROCESO DE HIDROCONFORMADO USANDO DIÁMETRO EQUIVALENTE

The main goal of this work is to propose the application of the concept of equivalent diameter in the calculation of the hydraulic pressure required to conduct an hydroforming process in non-circulars pieces. Although this approach was carried out initially for the conventional stamping process, this paper demonstrates that it can also be applied in hydroforming. In a first phase experimental tests were carried out to form a part using this methodology, measuring the reduction in resulting thickness. It was found that difference between the calculated pressure and the experimental required pressure was 2.6%. To perform a numerical-experimental comparison, the simulation of the process was carried out using several material models by explicit finite element method in a commercial software. It was observed that using the material model HILL’90 deviation between experimental and numerical results for the thickness reduction was lower than 5.5%.

MODELADO TRIDIMENSIONAL DE RUGOSIDAD SUPERFICIAL PARA EL PROCESO DE BRUÑIDO

Ball burnishing is a plastic deformation process that improves the surface quality of mechanical parts decreasing roughness. The surface roughness is an important parameter of study; it is known that affects friction, lubrication and wear. In this work, a general methodology for finite element and a programming routine based on Parametric Design Language was developed and validated. This methodology is useful to generate parametric models of three-dimensional rough surfaces in a commercial software of finite element. The routine produces a random surface roughness using the mean (x ?) and standard deviation (s) of a normal distribution of real surface roughness. The routine was used to generate roughness models of rectangular and cylindrical specimens. The nodal density for generating roughness and repeatability for a given surface finish were evaluated to optimize the modeled surface roughness. The numerical results show a good correlation to the experimental results. In a future, the routine can be used to generate models through the finite element method to simulate any machining process with random roughness and this enable to study the processes, allowing reducing the high costs of experimental tests.