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The surfaces of machined workpieces contain the signature of the manufacturing process. Indeed, the surface inaccuracies can be related to process parameters and machine vibrations. This paper aims at using process monitoring to identify... more
The surfaces of machined workpieces contain the signature of the manufacturing process. Indeed, the surface inaccuracies can be related to process parameters and machine vibrations. This paper aims at using process monitoring to identify the origin of surface topography defects. Thus, vibration and other process parameter measurements are correlated with profile measurements to establish the relationship between vibrations and surface topography for various process conditions. As each machine and process anomaly is reflected differently in the time and frequency domain, different analyses are applied both to temporal signals such as vibrations and to geometric signals obtained from the micro-geometry of the workpiece. Experimental results validate the diagnostic method and verify that the procedure is effective for the identification of topography defects originated not only from chatter vibrations but also from forced vibration coming from the kinematical chain (unbalance, beating....
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La aparicion de vibraciones autoexcitadas en el proceso de fresado es uno de los mayores inconvenientes a la hora de incrementar el ratio de arranque de viruta. La estabilidad del proceso, para cada conjunto... more
La aparicion de vibraciones autoexcitadas en el proceso de fresado es uno de los mayores inconvenientes a la hora de incrementar el ratio de arranque de viruta. La estabilidad del proceso, para cada conjunto maquina/herramienta/material-pieza, y para cada tipo de operacion, viene determinada por los denominados diagramas de lobulos, que discriminan las condiciones de corte estable e inestable. Para hacer frente al fenomeno del chatter, algunos autores han propuesto el empleo de estrategias encaminadas a distorsionar la excitacion provocada por el golpeo periodico de los dientes de la fresa sobre la pieza. Entre estas tecnicas cabe senalar las de variacion de velocidad de cabezal (SSV), que se tratan en este articulo. Tras una breve revision del estado del arte en este campo, tanto en el modelado como en la aplicacion de estas tecnicas, se presenta un modelo numerico de corte, contrastado y validado mediante ensayos experimentales. Posteriormente, y a partir de un estudio en simulacion, se presentan y comparan distintas estrategias de mecanizado basadas en la variacion de la velocidad del cabezal. Asi, se examina la influencia de estas estrategias en los diagramas de lobulos para distintas condiciones de operacion. Los resultados, analizados al final del articulo, son un paso previo a su validacion experimental e implementacion industrial.
Research Interests: Philosophy and Humanities
La aparicion de chatter o retemblado en el proceso de mecanizado es uno de los mayores inconvenientes a la hora de incrementar el ratio de arranque de viruta, debido a que puede conllevar un mal acabado superficial y la rotura de... more
La aparicion de chatter o retemblado en el proceso de mecanizado es uno de los mayores inconvenientes a la hora de incrementar el ratio de arranque de viruta, debido a que puede conllevar un mal acabado superficial y la rotura de elementos mecanicos. Este problema esta cada dia mas vigente debido a que los requerimientos de precision de las piezas hace a los disenadores huir de la friccion en los guiados, a que las piezas son cada vez mas ligeras y a que los requerimientos de productividad van aumentando. Los amortiguadores activos comandados por una estrategia de control permiten aumentar el amortiguamiento estructural sin modificar la maquina, aumentando de esta manera la zona libre de vibraciones. En este trabajo se muestra el actuador electromagnetico disenado integramente en IK4-IDEKO para la eliminacion de chatter en operaciones de mecanizado. Ademas del diseno del mismo, se pueden observar los diferentes ensayos de validacion (temperatura, linealidad...) que se han llevado a cabo en dicho actuador y los resultados de mejora que se han obtenido al introducirla en un centro de mecanizado.
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In external cylindrical grinding machines, measuring systems are occasionally mounted on a gantry type frame. The modes of this structure are potentially harmful within the operation range of the grinding wheel in a standard machine... more
In external cylindrical grinding machines, measuring systems are occasionally mounted on a gantry type frame. The modes of this structure are potentially harmful within the operation range of the grinding wheel in a standard machine configuration, since the rotation of the wheel can enter into resonance, thus avoiding a correct determination of the on-line measurement. The resonance problem can be successfully dealt with the use of a variable stiffness vibration absorber which autonomously adapts its stiffness to tune according to the mode to be damped, increasing the dynamic stiffness along the whole operation range of the wheel. In this work, a variable stiffness self-tunable vibration absorber prototype has been built and a new tuning function has been derived in order to minimize the response at the frequency coincident with the rotating speed of the wheel. Finally, validation tests have been performed in a scale supporting structure and the vibration reduction improvement compa...
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During thin-walled part milling, a dominant flexible direction perpendicular to the feed motion is most likely to exist, which allows to formulate the stability problem in the frequency domain in a very simple form. By these means, the... more
During thin-walled part milling, a dominant flexible direction perpendicular to the feed motion is most likely to exist, which allows to formulate the stability problem in the frequency domain in a very simple form. By these means, the existence of optimal engagements under up-milling strategy for achieving a theoretical infinite Hopf stability have already been demonstrated. However, period-doubling chatter can also pose a limit to the productivity in thin wall milling, but the knowledge on optimal engagements that can cancel this kind of chatter is inexistent. This paper discusses the effect of the radial engagement and number of flutes on flip stability in a dimensionless way and independent on the system dynamics. Up- and down- milling strategies are compared: a larger period-doubling prevalence is identified in the former, although in terms of absolute critical depth of cut, up-milling outperforms down-milling for most of the practical cases. It is also demonstrated that even t...
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The productivity of boring operations is limited by chatter vibrations, as an effect of the low dynamic stiffness and damping of these cantilevered structures. The origin of the beforementioned self-excited vibration is mainly related to... more
The productivity of boring operations is limited by chatter vibrations, as an effect of the low dynamic stiffness and damping of these cantilevered structures. The origin of the beforementioned self-excited vibration is mainly related to the dynamic stiffness of the boring bar’s bending mode, which is influenced by the stiffness and damping of the machine tool interface. In this paper a dynamic model is presented, which uses Timoshenko beam theory for the boring bar itself, while the effect of the clamping is experimentally determined applying Receptance Coupling Substructure Analysis (RCSA). The important effect of the boring head at the tool tip is considered on the coupling as well. This way, once the machine interface is characterized, the Frequency Response Functions (FRF) of different boring bars can be predicted.
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Abstract The quality of many metal removal processes is partially defined by the chip formation process. The creation of long chips is one of the main problems in continuous processes like turning. The long chips can scratch the final... more
Abstract The quality of many metal removal processes is partially defined by the chip formation process. The creation of long chips is one of the main problems in continuous processes like turning. The long chips can scratch the final part surface and generate production stops for manual chip removal. In this article, a technique called modulation-assisted machining is used to vary the chip thickness and force the chip breakage. For the heavy duty applications considered here, the oscillation is generated by the ordinary drives of the machine. The limits of the drives are taken into account and the system automatically selects the most appropriate oscillation parameters according to the machine oscillation capability and process parameters. Experimental validations show the effect of this system on the chip length and surface finish.
Research Interests: Computer Science and Chip
Abstract Regenerative chatter is one of the main productivity limiting factors for thin-walled part milling due to their inherently low stiffness and damping properties. This paper presents a new concept called tuneable clamping table... more
Abstract Regenerative chatter is one of the main productivity limiting factors for thin-walled part milling due to their inherently low stiffness and damping properties. This paper presents a new concept called tuneable clamping table (TCT) for thin-walled part machining, which permits controlling the table mode through a rotary spring and eddy current modules. This allows introducing damping to one critical mode of the thin-walled part without any direct contact in the machining area. Two novel frequency tuning strategies to increase the dynamic stiffness and milling stability for the TCT are presented. The concept of TCT is experimentally validated through milling tests, demonstrating a notorious stability increase compared to a regular clamping.
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Cyber-physical production systems (CPPS) are mechatronic systems monitored and controlled by software brains and digital information. Despite its fast development along with the advancement of Industry 4.0 paradigms, an adaptive... more
Cyber-physical production systems (CPPS) are mechatronic systems monitored and controlled by software brains and digital information. Despite its fast development along with the advancement of Industry 4.0 paradigms, an adaptive monitoring system remains challenging when considering integration with traditional manufacturing factories. In this paper, a failure predictive tool is developed and implemented. The predictive mechanism, underpinned by a hybrid model of the dynamic principal component analysis and the gradient boosting decision trees, is capable of anticipating the production stop before one occurs. The proposed methodology is implemented and experimented on a repetitive milling process hosted in a real-world CPPS hub. The online testing results have shown the accuracy of the predicted production failures using the proposed predictive tool is as high as 73% measured by the AUC score.
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Cutting capacity can be seriously limited in heavy duty face milling processes due to self-excited structural vibrations. Special geometry tools and, specifically, variable pitch milling tools have been extensively used in aeronautic... more
Cutting capacity can be seriously limited in heavy duty face milling processes due to self-excited structural vibrations. Special geometry tools and, specifically, variable pitch milling tools have been extensively used in aeronautic applications with the purpose of removing these detrimental chatter vibrations, where high frequency chatter related to slender tools or thin walls limits productivity. However, the application of this technique in heavy duty face milling operations has not been thoroughly explored. In this paper, a method for the definition of the optimum angles between inserts is presented, based on the optimum pitch angle and the stabilizability diagrams. These diagrams are obtained through the brute force (BF) iterative method, which basically consists of an iterative maximization of the stability by using the semidiscretization method. From the observed results, hints for the selection of the optimum pitch pattern and the optimum values of the angles between insert...
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The self-excited vibration, called chatter, is one of the main limitations in metal removal processes. Chatter may spoil the surface of the part and can also cause large reduction in the life of the different components of the machine... more
The self-excited vibration, called chatter, is one of the main limitations in metal removal processes. Chatter may spoil the surface of the part and can also cause large reduction in the life of the different components of the machine tool including the cutting tool itself. During the last 60 years, several techniques have been proposed to suppress chatter. This keynote paper presents a critical review of the different chatter suppression techniques. Process solutions with design and control approaches are compiled to provide a complete view of the available methods to stabilize the cutting process. The evolution of each technique is described remarking the most important milestones in research and the corresponding industrial application. The selection of the most appropriate technique for each specific chatter problem is also discussed considering various aspects of machining processes.
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La presencia de vibraciones autoexcitadas, popularmente denominadas como chatter, supone en la actualidad una de los problemas que limitan la capacidad de corte en mecanizado de alta velocidad. La via mas utilizada a la hora de planificar... more
La presencia de vibraciones autoexcitadas, popularmente denominadas como chatter, supone en la actualidad una de los problemas que limitan la capacidad de corte en mecanizado de alta velocidad. La via mas utilizada a la hora de planificar procesos libres de chatter consiste en la obtencion de los lobulos de estabilidad y la eleccion de condiciones de corte estables que optimicen la tasa de eliminacion de material. Los modelos en frecuencia que se utilizan en la actualidad no consideran la influencia del angulo de helice y el retardo que produce en las fuerzas generadas entre las distintas secciones de la fresa helicoidal. En el presente trabajo este efecto ha sido considerado extendiendo el modelo multifrecuencia al caso de las fresas helicoidales. Los resultados obtenidos han sido validados con simulaciones de estabilidad obtenidas mediante otras vias como el metodo de la semi-discretizacion, simulaciones temporales y finalmente mediante pruebas experimentales. Los resultados han demostrado que la helice influye decisivamente en los lobulos adicionales (flip bifurcation) que aparecen especialmente en las zonas de alta velocidad, mientras que la influencia sobre los lobulos tradicionales (Hopf Bifurcation) es despreciable. Se ha demostrado que los lobulos adicionales flip se convierten en una serie de curvas cerradas que pueden estar aisladas de las zonas de inestabilidad tradicionales. Estas islas quedan separadas por lineas horizontales en las que la profundidad de corte coincide con multiplos de paso de la fresa helicoidal.
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Several methods exist for the analysis of the dynamic stability of milling processes. The methods based on the time domain analysis have been developed for systems with natural modes parallel to the coordinate system of the machine, that... more
Several methods exist for the analysis of the dynamic stability of milling processes. The methods based on the time domain analysis have been developed for systems with natural modes parallel to the coordinate system of the machine, that is, axes defined by the spindle (Z), the feed direction (X), and perpendicular to both (Y). For finishing operations, at which the main flexibility comes from the spindle / tool side, the approach is acceptable, but for roughing operations, or for any process in which the structural modes of the machine are involved, the method can not be applied for the analysis of the stability against chatter vibration. The paper shows a modification of the method of Semi-discreti zation based on a modal content approach. The new method allows to include in the simulation modes in any spatial direction, and further is not limited to a maximum number of three modes, as the previous developments. A com parison of the results with the methods of Semi-discretization and Multi-frequency Analysis is performed, showing excellent agreement.
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ABSTRACT Automatic detection and diagnosis systems have always attracted considerable interest in control engineering due to their positive effects of increasing safety and product quality in machinery condition monitoring and maintenance... more
ABSTRACT Automatic detection and diagnosis systems have always attracted considerable interest in control engineering due to their positive effects of increasing safety and product quality in machinery condition monitoring and maintenance applications. Implementing automated detection and diagnosis has always been a challenge in rotating machines. In this article, we present the development of a strategy to detect and diagnose faulty bearings in a heavy-duty milling machine tool's spindle head and its implementation in a real machine. First, a comparison study of advanced methods for ball bearing fault detection in machine tool spindle heads is presented. Then, two automatic diagnosis procedures are compared: a fuzzy classifier and a neural network, which deal with different implementation questions involving the use of a priori knowledge, the computation cost, and the decision making process. The challenge is not only to be capable of diagnosing automatically but also to generalize the process regardless of the measured signals. Two actions are taken to achieve some kind of generalization of the application target: the use of normalized signals and the study of the Basis Pursuit feature extraction procedure. Finally, automatic monitoring system implementation on a real milling machine tool is presented.