H.-G. Enkler

A Contribution to the Simulation of Molded Micro Components and Systems With Regard to the Grain Structure

Experimental work for characterizing materials’ properties as well as components’ and systems’ behaviors have to be supplemented by numerical analyses when regarding micro components and systems. In order to accomplish a complete possibilities’ overview for micro machines these analyses should cover both component and system issues. On a component level, established macroscopic approaches are extended by methods that allow the consideration of components’ grain structures influence, including possible superficial and internal defects. Because of technological restrictions, especially when applying miniaturized conventional manufacturing techniques, shape and material deviations cannot be scaled down in the same dimensions like micro parts. Thus, high tolerances accepted for the individual components and their effects on the expected transfer behavior of the whole system are taken primarily into account. This paper presents approaches for the simulation of micro components and systems using the Finite Element Method and Multi Body Simulation. Methods to overcome the above mentioned issues will be shown, as well as the effects of grain structure on the stress distribution in the individual components. Some effects over the system’s behavior of this inhomogeneous stress distribution are also discussed.Copyright

Simulation of Molded Micro Components and Systems With Regard to the Grain Structure

Miniaturization of macroscopic mechanical systems enables the opening of new areas of application for micro technological systems. Because of actual technological restrictions, especially when applying miniaturized conventional manufacturing techniques, shape and material deviations can not be decreased as strong as the dimensions of the micro parts are reduced. A long-term objective in the development of such systems is to ensure functional capability by adoption of appropriate design measures that compensate these deviations. This work presents methods based on computer simulation that contribute to achieve this objective. One method is based on the utilization of ad-hoc modified and simplified Finite Element Analysis techniques, which now regards some issues of interest from Multi Body Simulation. The introduction of this method also allows studying the behavior of the components and the system with regard to the component’s internal grain structure. When the focus is directed to the robustness or the reliability of the system, another method is presented that is based on a hybrid FEA-MBS solver. It shows better performance both on parameters modeling capability and computational efficiency. Methods to overcome the above mentioned issues, as well as the effects of grain structure on the stress distribution in the individual components will be presented. Some effects affecting the system’s behavior because of this inhomogeneous stress distribution are also discussed. Finally, an investigation about the consequences of having internal defects within individual components is conducted.Copyright

Dealing with Uncertainty of Micro Gears - Integration of Dimensional Measurement, Virtual and Physical Testing

Design and quality assurance of micro gear wheels and involute gear wheels involve multiple challenges regarding prediction of functionality and life cycle performance of complex and wear-resistant micromechanical systems. First of all, this is due to the fact that up to now no tolerance system for micro dimension has been defined. In second place, most measurement strategies for the dimensional characterization of involute micro gears cannot be brought forward from the macro world just as they are. There is few knowledge about the relevant quality characteristics for these micro systems, optical sensors’ precision is affected by fuzzy edges detection and no tactile scanning modes for relevant features smaller than 100 μm exist, which is the scale normally applied in macroscopic dimensions. Simulation methods for analyzing the influence on the whole system of different components’ geometrical deviations are very valuable to supplement the knowledge based on real tests. Furthermore, it could be also necessary to consider the material’s anisotropy caused by the not negligible grain structure to evaluate the stress field correctly. Therefore, a new approach for design and quality assurance needs to be developed, in order to assure the functionality and long-term performance of molded micro systems. This work uses a planetary gear train as a demonstrator. A validation of the entire product functionality test chain has to be conducted to come closer to an integrated robust design approach for mechanical micro systems — from simulation in the early design stages to test and to quality assurance of large series production. This paper outlines a threefold methodological approach integrating dimensional measurement, virtual tests based on real geometry and physical tests of real gears. The measurement of the micro systems components both in disassembled as in assembled state is conducted using multisensory coordinate measurement machines. Based on the measured contours of real gears, virtual gears are derived and meshed for its subsequent use in adequate FEA model. Simultaneously, the gears are mounted and tested on a micro gear test rig. Both simulation and test rig conduct a radial composite inspection adapted to the micro scale; results are then compared. Micro gears molded of zirconium oxide were selected as a demonstrator for the presented methodology. These 12 teeth gears, with a diameter of approximately 2.0 mm and a modulus of 169 μm, are produced within Collaborative Research Center (CRC) 499 “Development, Production and Quality Assurance of Primary-Shaped Micro Parts made of Metallic and Ceramic Materials” of the German Research Foundation (DFG).Copyright

Methods for the Simulation of Micro Components With Respect to the Grain Structure

The development of smaller and smaller micro components and systems is an ongoing process. Effects coming along with this process have to be investigated. A polycrystalline material consists of grains with different orientations. Therefore, a micromechanical model of a polycrystalline material for a Finite Element analysis should consider the grain structure. Studies show that with decreasing size of a micro component its grain structure and material anisotropy gain more and more influence on its stress, strain and flow of forces. In order to ensure a reliable dimensioning of micro components the influence of the grain structure and material’s anisotropy upon the stress and stress distribution has to be investigated. For this purpose, experimental work for characterizing materials’ properties is supplemented by numerical analyses. On the one hand, these analyses allow examining specific influences on the mechanical stress. On the other hand, micromechanical modeling has potential to increase the understanding of material behavior. Methods for modeling two- and three-dimensional micro components with complex grain structures including defects such as pores are presented and compared. The consideration of effects coming along with the grain structure makes a contribution to a reliable dimensioning of micro components with distinct grain structures.© 2007 ASME

A Two Layered Process for Early Design Activities Using Evolutionary Strategies

Especially in system and conceptual design activities designers resort to already existing components that are combined and arranged to a new system which has to fulfill a predefined set of requirements. Designers have to deal with requirements and constraints that are changing during the development process. General goal is an automatic generation of compatible conceptual design proposals that meet the predefined requirements such as design space, EMC, etc. To this, libraries containing standardized data on components have to be developed. These libraries include component specific characteristics and data such as CAx models or efficiency factors. In an iterative process compatible systems are configured and evaluated by means of CAx based analyses. Afterwards an optimization system based on genetic algorithms accesses these data to find optimal configurations. By combining the optimization algorithm with a CAD system, design proposals are directly visualized and can be processed by the designer in the further product development process.

Ein Verfahren zur Standortbestimmung und Strategiebildung von Fakultäten und Universitäten

Im Zusammenhang mit der Exzellenzinitiative der Bundesregierung in den Jahren 2006 und 2007 mit der Kurung von 9 „Eliteuniversitaten“ wurde eine breite Diskussion angestosen, wie Exzellenz, sei es einer Universitat, einer Fakultat oder eines Studiengangs, moglichst objektiv beurteilt und gemessen werden kann. Schon im Jahre 2003 formierte sich auf Initiative der Fakultat fur Maschinenbau der Universitat Karlsruhe (TH) eine Gruppe von neun Maschinenbaufakultaten aus den Universitaten Aachen, Berlin, Braunschweig, Darmstadt, Dresden, Hannover, Karlsruhe, Munchen und Stuttgart, die bereit war, sich gegenseitig einer kennzahlenbasierten Evaluation zu stellen. Der hier vorgestellte von den Autoren entwickelte Balanced-Score-Card Ansatz mit gewichteter Kennzahlenbildung auf der Basis objektivierter Grunddaten wurde masgeblich durch gemeinsame Workshops in der Gruppe und auch engagierte Beschaffung von Daten aus den beteiligten Fakultaten validiert und in seiner Aussagekraft gepruft. Damit steht ein Kennzahlensystem zur Verfugung, mit dem die wesentlichen Leistungspotentiale in Forschung und Lehre erhoben und verglichen werden konnen. Die Auswertung und intensive Diskussion der Daten fuhrte weiterhin zur gemeinsamen Definition von Schwellenwerten bzw. Zielkorridoren fur die einzelnen Kennzahlen, deren Erreichung als Mas fur die „Gute“ der Fakultat unter den betrachteten Aspekten von Forschung und Lehre gelten kann. Vom Fakultatentag fur Maschinenbau und Verfahrenstechnik (FTMV) wurde das Verfahren nach intensiver Diskussion aufgenommen und erweitert mit dem Ziel, fur die Mitgliedsfakultaten ein Qualitats- bzw. Gutesiegel zu definieren und zu vergeben. Mit diesem Verfahren ist es nun moglich auf der Basis nachvollziehbarer und objektiver Daten die Leistungspotentiale von ingenieurwissenschaftlichen Fakultaten darzustellen und zu kommunizieren. Gleichzeitig konnen die teilnehmenden Fakultaten die Ergebnisse zur eigenen Standortbestimmung, Strategiebildung und Zukunftsplanung nutzen. Letztlich kann das Verfahren auch in der Diskussion in den Medien um Rankings in Forschung und Lehre zu einer objektiveren und vor allem substanziell begrundeten Informationsbasis beitragen. Durch Anpassung und Erganzung der Kennwerte kann das vorgestellte Verfahren auf Fakultaten anderer Fachrichtung angepasst werden, ohne die methodische Basis neu erstellen zu mussen. Das Verfahren bietet ein strategisch orientiertes Konzept zur Qualitatssicherung und -entwicklung, das uber die eher an Mindeststandards orientierten Akkreditierungsverfahren weit hinaus geht und auch ein moglicher Baustein eines aus der jeweiligen Universitat heraus getriebenen Qualitatssicherungsprozesses im Rahmen der Prozess-Akkreditierung sein kann.