Pablo Leslabay

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

Modelling, Sensitivity Analysis and Optimization of Mechanisms Made of Micro-Molded Components

The miniaturization of metallic and ceramic molded components is limited by technological restrictions in conventional manufacturing techniques. Thus shape and material deviations cannot be scaled down in the same proportion as the micro parts. Systems including such components should be designed to accommodate the individual component’s wide geometrical variation and usually require large clearance. A study of the effects introduced thereby is needed to understand the system’s limits and to be able to forecast their output’s performance. To save time and resources, costly prototypes and test runs should be avoided in favour of computer simulation. The method proposed by the authors is exemplified on a micro technology demonstrator system developed by the Collaborative Research Center 499. It consists of a one stage planetary gear train in a sun-planet-ring configuration. The simulation procedure relies on ordinary Multi Body Simulation methods and subsequently adds other techniques to further investigate details of the system’s behaviour and to predict it’s response. In order to quantify the variability and to reveal the most critical points of the system, a whole-mechanism Sensitivity Analysis is performed. A reduced set of relevant parameters could be derived for further investigation and to feed a final optimization process, whether as optimization parameters or as external perturbation collective. The lack of previous knowledge about the system forced different DOE methods, involving small and large amount of experiments, to be tested. In this particular case the parameter space can be divided into two well defined groups, one of them containing the gear’s profile information and the other the components’ spatial location. This has been exploited to explore the different DOE techniques more promptly. Comparison and an analysis of the most successful DOE methods is included. In a final optimization step, the 10 most relevant perturbation factors and 4 to 6 prospective target parameters are included in a new, simplified model. All of these, and the objective functions, are affected by the production variability and the problem becomes an optimization of the system’s robustness and reliability exercise. Different techniques are discussed with examples. The study shows a first step in the development path of methods for designing and optimizing complex micro mechanisms composed of wide tolerated elements, accounting for the robustness and reliability of the systems’ output.Copyright

Electrolytic Reactors for High Pressure Hydrogen Generation: Design and Simulation

The implementation of hydrogen as a mass scale energy vector requires the development of simple, cheap and efficient technologies for its production, storage and transportation. Generating hydrogen through electrolysis of alkali solution directly under pressures up to 700bar without the intervention of any mechanical gas compression systems and the direct storage of the gases in appropriate tanks is a viable example of such a technology. The present study introduces the advantages of this production scheme and the major technical difficulties to be overcame on the design of a high pressure operating electrolytic reactor. In order to study the general system’s behavior, a numerical simulation method that includes all the relevant components is developed. To reduce the complexity of the initial model, the details of the electrochemical reaction taking place on each electrolytic cell is not covered and its effect is replaced with an energy efficiency curve derived from experimental observations. Despite this simplification, the characteristics of the system remain very complex and require the use of multi-physics simulation tools to describe the interactions between solids, liquid and gas, the temperature distribution and pressure, and the production of gas and heat in the reactor. In spite of the multiple coupling possibilities within the multiphysics software, the interaction of the modules proved challenging and required the manual introduction of further differential equations and physical expressions, along with auxiliary routines, to allow the convergence of the solution. The simulation method developed is validated by modeling a test reactor designed and constructed in the Instituto Tecnologico de Buenos Aires for its installation in the Argentinean Antarctic, for which different test-run results are available for comparison.Copyright