Publication: Análisis experimental y numérico del proceso de taladrado de materiales compuestos de fibra de carbono
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2016-07
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2016-07-11
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Abstract
El taladrado es un proceso fundamental previo al ensamblaje de componentes estructurales de material compuesto en diversas industrias como la aeroespacial. Los defectos inducidos durante el proceso de arranque de material pueden llevar al rechazo del componente con el consiguiente coste económico. Debido a la falta de homogeneidad y anisotropía de los laminados FRP (Fiber Reinforced Polymers), el proceso de perforación suele llevar asociados fenómenos de daño en el material (como la delaminación, el astillamiento del borde, la formación de grietas o el daño térmico) y el desgaste excesivo de la herramienta debido a la abrasividad de las fibras. Entre los daños mencionados, la delaminación ha sido identificada como el fenómeno más perjudicial, ya que conlleva una pérdida significativa de la resistencia y de la rigidez del laminado y, por consiguiente, afecta a su capacidad de carga. La identificación y prevención de este fenómeno es, por lo tanto, particularmente importante para los componentes de material compuesto sometidos a cargas de compresión, cizalladura, cargas cíclicas o condiciones ambientales adversas durante períodos prolongados de tiempo. El daño en el material también depende de la geometría de la herramienta, del estado de desgaste de la broca y de los parámetros de corte. Por otro lado, es difícil encontrar en la bibliografía modelos numéricos 3D de taladrado que simulen el arranque de viruta incluyendo los movimientos de corte y avance de la broca. Sin embargo, el desarrollo de estos modelos puede ser un método efectivo para realizar estudios de optimización de la geometría de la herramienta y de los parámetros de corte, con el objetivo de mejorar la calidad de los agujeros y reducir el desgaste de la broca. Al mismo tiempo se consigue una reducción de recursos y tiempo en ensayos experimentales. Con el objetivo general de generar nuevo conocimiento sobre el campo del taladrado en materiales compuestos de fibra de carbono, se presenta esta tesis, con dos partes bien definidas. La primera parte, centrada en la experimentación, analiza la influencia de la geometría de la broca y del nivel de desgaste, considerando también la influencia de las variables de entrada (velocidad de avance, velocidad de corte y ángulo de punta) en las fuerzas de corte y el daño por delaminación. Estos ensayos también se utilizaron para la validación de los modelos numéricos desarrollados en la segunda parte, que consiste en la implementación de modelos numéricos 3D de taladrado, basados en el método de los elementos finitos. Estos modelos validados son capaces de predecir el daño y la fuerza de avance para unos determinados parámetros de corte (velocidad de avance y velocidad de corte). Como complemento a ambos estudios, se han utilizado herramientas estadísticas para desarrollar modelos mecanísticos y ecuaciones predictivas útiles para evaluar las tendencias en el daño y apoyar a los modelos numéricos. Los conocimientos derivados de la presente tesis pueden servir de ayuda en la definición del fin de vida de la herramienta y constituyen una herramienta aplicable al diseño de nuevas geometrías de broca para este tipo de operaciones.
Drilling of composite materials, is an essential pre-assembly process, for structural components in the aircraft industry. Induced damage, during the material removal processes, can result in the rejection of components and an increase in production cost. Due to the inherent inhomogeneity and anisotropy of Fiber Reinforced Polymers (FRP) laminates, and to the abrasive properties of the fibers, the drilling process is currently rife with damage phenomenon such as: spalling, delamination, chipping, fiber pull-out, crack formation, or thermal damage. Delamination has been identified as the most detrimental damage phenomenon for structural components as it results in a significant loss of strength and stiffness of the laminate, and consequently its load carrying capacity. Therefore, identification and prevention of this phenomenon becomes particularly important for composite components subject to adverse environmental conditions and compressive, shear, and cyclic loads over extended periods of time. Drilling induced damage depends also on several factors such as, drill bit geometry, cutting parameters, and tool wear. Furthermore, it is difficult to find literature on 3D models of drilling which are suitable for simulating chip removal, including both feed and rotation movements of the drill bit. Developing and using these tools leads to optimization studies about tool geometry and cutting parameters, which ultimately, reduces the number of tests and experimental time required. This thesis has been carried out with the main goal of generating new knowledge in the field of carbon fiber composite drilling and has two main parts. The first part, experimental, analyzes the influence of the drill bit geometry and the wear level considering also the input variables (feed rate, cutting speed, and point angle of the drill bit) in the cutting forces and in delamination damage. The second part, numerical, develops the 3D numerical models of drilling using finite element methodology. Using these models, predictions can be made in regards to the amount of damage caused by different feed forces and different cutting parameters (feed rate and cutting speed). Statistical tools have been used to support this study and to develop predictive and mechanistic models to estimate the damage incurred during the drilling process, evaluate trends, and support the numerical models. The knowledge derived from this thesis can be used to define the cutting life of a tool and will also be very useful in the design of new tool geometries to increase the efficiencies of composite material drilling.
Drilling of composite materials, is an essential pre-assembly process, for structural components in the aircraft industry. Induced damage, during the material removal processes, can result in the rejection of components and an increase in production cost. Due to the inherent inhomogeneity and anisotropy of Fiber Reinforced Polymers (FRP) laminates, and to the abrasive properties of the fibers, the drilling process is currently rife with damage phenomenon such as: spalling, delamination, chipping, fiber pull-out, crack formation, or thermal damage. Delamination has been identified as the most detrimental damage phenomenon for structural components as it results in a significant loss of strength and stiffness of the laminate, and consequently its load carrying capacity. Therefore, identification and prevention of this phenomenon becomes particularly important for composite components subject to adverse environmental conditions and compressive, shear, and cyclic loads over extended periods of time. Drilling induced damage depends also on several factors such as, drill bit geometry, cutting parameters, and tool wear. Furthermore, it is difficult to find literature on 3D models of drilling which are suitable for simulating chip removal, including both feed and rotation movements of the drill bit. Developing and using these tools leads to optimization studies about tool geometry and cutting parameters, which ultimately, reduces the number of tests and experimental time required. This thesis has been carried out with the main goal of generating new knowledge in the field of carbon fiber composite drilling and has two main parts. The first part, experimental, analyzes the influence of the drill bit geometry and the wear level considering also the input variables (feed rate, cutting speed, and point angle of the drill bit) in the cutting forces and in delamination damage. The second part, numerical, develops the 3D numerical models of drilling using finite element methodology. Using these models, predictions can be made in regards to the amount of damage caused by different feed forces and different cutting parameters (feed rate and cutting speed). Statistical tools have been used to support this study and to develop predictive and mechanistic models to estimate the damage incurred during the drilling process, evaluate trends, and support the numerical models. The knowledge derived from this thesis can be used to define the cutting life of a tool and will also be very useful in the design of new tool geometries to increase the efficiencies of composite material drilling.
Description
Mención Internacional en el título de doctor
Keywords
Ensayo de materiales, Taladrado, Materiales compuestos, Fibra de carbono, Modelos numéricos 3D, Método de los elementos finitos