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Development of the machining simulation system - ToolSimulation

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Ekrem Oezkaya
added 3 research items
Tapping is the most used process for manufacturing of internal threads and usually the last machining step when producing a workpiece. Asymmetrical tools, core holes with narrow tolerances, tool wear, or incorrectly chosen cutting speeds, cutting materials, cooling lubricants and chucks, quickly result in waste cut or, in the worst case, in tool breakage. In contrast to turning, drilling, or milling, the tapping process and its cutting tool is one of the least understood machining processes. To master a system and to optimize the tool using process parameters, it is necessary to have a basic understanding of machinability. Only by possessing the exact knowledge of cutting data, tool wear, tool life, cutting forces, chip formation and their correlations, a progressive processing of flexible ma-chining systems and machine tools is possible. Due to a lack of basic research, the production of taps – the geometrical construction and their specification – depend on the practical knowledge of manufacturers, which is often passed on verbally and in strict confidence to the next generation. Although simulations based on the finite element method (FEM) are used in almost every manu-facturing process, they cannot be used effectively for the tapping process. The high geometrical complexity of the tools with many cutting edges and different mesh situations represents signifi-cant challenges in the tapping process. For predicting the tool performance, one of the most important parameters of tapping is the torque. In contrast to other geometrically defined cutting edges, the cutting mechanism of tapping is completely different, since the dynamic cutting forces form over the whole chamfer length. The three-dimensional simulation of the tapping process presents great difficulties. Modelling and simulating all the tool variants over the whole chamfer length, to provide a basis for process optimization, would be too time-consuming. In this work, these challenges are met and an FEM-based software system is presented, which allows the three-dimensional simulation of tapping tools. The main focus is laid on the predic-tion of torque with practical computation times. At first, a general concept for this purpose will be described. On this basis, results of experi-mental and simulative investigations executed in metric tap series will be presented. Hereupon, methods and mathematical models to reduce the computing time, as well as a prediction method for the torque using other tool variants follow. The main methods used are the decomposition of the workpiece in partial segments and the interpolation and extrapolation from determined values for selected tool variants. Those methods are incorporated in the FEM-based software system. For the FE-simulation, the engineering software DEFORM 3D is employed. Therefore, an appropriate communicative interface is provided, which allows for the execution of pre- and postprocessor procedure steps as well as some solver options. For an interactive control, a user friendly graphical interface was created which considers the special conditions of the 3D-tapping process. The potential of the solution will be demonstrated by a dynamic system control. High performance taps are often equipped with internal cooling channels to increase productivi-ty and reduce tool wear. The primary objective is to improve the supply of coolant to the cutting edge and secondly to ensure a universal tool design. Effective cooling and lubrication is a part of the process optimization and helps increasing process safety, while simultaneously decreasing production costs. Therefore, CFD analyses have been per-formed in this work, so that physical phenomena of the coolant lubrication flow in tapping processes could be investigated for the first time. The arrangement of the internal cooling channels was analyzed using CFD simulation and the tool was optimized accordingly. In doing so, an optimized tool was obtained on the one hand and on the other hand, the applicability as well as the reliability of the CFD approach have been validated.
The conventional tapping tool development consists of costly investigative experiments. The development time and cost can be significantly reduced, if these test were replaced by virtual analyses, before the tool prototypes are fabricated. Compared to turning, milling and drilling, in which many valid simulative methods have been established, the tapping process has been given rather little research attention. In this paper an approach is presented, which could be used during the design phases, to predict the relative torque, so that resources, energy and cost can be saved. Based on a simulated reference model, which is in good agreement with corresponding experimental results, the problem of a long computing time could be solved by using a proper segmentation method, which offers a process simulation along the whole chamfer length. With an according mathematical model, the discontinuous torque curve could be summarized to a total load cycle.
Werkzeughersteller sind bei der Konstruktion von Gewindewerkzeugen für neue Aufgaben-stellungen auf die variantenreiche Produktion von Testwerkzeugen und deren Feldversuche angewiesen. Allein bei der Schumacher Precision Tools GmbH werden jährlich 3.000 bis 4.000 neue Werkzeuge konstruiert. Für diese ist derzeit bei neuen Einsatzfeldern eine gesi-cherte Aussage über den späteren Einsatzerfolg nur durch zeit- und kostenaufwändige Proto-typen möglich. Da sich dieser Entwicklungsaufwand, für neue Produkte im Bereich aller Res-sourcen vom Materialeinsatz bis zum Energieverbrauch, marktbedingt nicht im Produktpreis wiederspiegelt, ist es notwendig, schlankere Entwicklungsverfahren für neue Präzisionswerk-zeuge zu entwickeln. Mit aktueller Standardsimulationssoftware kann die Werkzeugentwicklung nur in geringem Umfang unterstützt werden, da trotz der Fortschritte der letzten Jahre weiterhin große Unsi-cherheiten hinsichtlich der quantitativen Resultate herrschen. Insbesondere beim Gewinde-bohren ist die Rechenzeit einer Simulation, basierend auf der Finiten Element Methode (FEM), aufgrund der hohen geometrischen Werkzeugkomplexität mit einer Vielzahl an Schneiden mit unterschiedlichen Eingriffssituationen zu lang. Der Anspruch des Präzisionswerkzeugherstellers Schumacher Precision Tools GmbH war es, ein System zu schaffen, mit dem aus ökonomischer Sicht für Werkzeughersteller der KMU-Klasse Wettbewerbsvorteile generierbar sind. In einem Kooperationsprojekt mit dem Institut für spanende Fertigung (ISF) der Technischen Universität Dortmund wurde ein Soft-waremodul entwickelt, welches es dem Konstrukteur ermöglicht, bereits während des Kon-struktionsprozesses Werkzeuggeometrien mit Hilfe eines FEM-basierten Zerspanungsprozes-ses zu testen [1].
Ekrem Oezkaya
added a research item
Dr.-Ing. Ekrem Oezkaya's recent peer-reviewed paper entitled Mathematical model for predicting the torque during tapping using FEM simulation has been recognized by Advances in Engineering as a Key Scientific Article contributing to excellence in engineering, scientific, and industrial research. Advances in Engineering “ensures that the results of excellent scientific research are rapidly disseminated throughout the world, in a fashion that conveys their significance for advancing scientific knowledge and developing innovative technologies for the benefit of mankind.” The website is visited nearly 650,000 times each month. Ekrem Oezkaya's recent paper recognized as Key Scientific Article contributing to excellence in engineering research.