Rodion Groll

GrindBall: an advanced micro-grinding tool

Small machine tools and inherent miniaturized components are persistent development topics in scientific research. Miniaturization usually requires not only reproducing existing systems at a smaller scale, but also a complex integration of various functions into one single element. This concept is presented here by means of a miniature spherical grinding module (GrindBall). It combines a specifically developed magnetic bearing with fluid dynamic propulsion, thus enabling novel grinding kinematics and the possibility of integration in small machine tools. In this paper, the requirements of micro-grinding processes are introduced and the manufacture as well as performance of grinding spheres are discussed; the design of the magnetic bearing is presented and its functionality validated in experiments. Finally, results from numerical simulations leading up to the development of the propulsion system as well as its geometric layout are reported.

NUMERICAL SIMULATION AND EXPERIMENTAL VALIDATION OF A HYPERSONIC FLOW FOR

The subject of interest is the validation of a 3-D numerical computer model of a hypersonic fl ow around double cone geometry. The double cone geometry represents a generic space vehicle which enters the atmosphere at extremely high velocity. This leads to complex fl ow phenomena around the space vehicle. In this paper the fl ow-fi eld around the space vehicle is investigated. Experimental data is obtained for different double-cone geometries mounted inside a hypersonic wind-tunnel. During the experiments the Mach number is equal to 9. Three different geometries and four different operating conditions are the subject of this study. Because of the short test period of less than 200 ms a measurement of temperatures and local velocities is not possible during test. Therefore, the computational model is used. The numerical solver is based on the compressible Navier‐Stokes equations and implements an adaptive meshing tool. This solver is used for fl ow-fi eld simulations of re-entry phenomena. The cell refi nement tool adapts the local cell length to the density gradient. In this way, all shock-waves receive higher resolution than the remaining mesh and the solver shows good agreement with the experimental results while minimizing computational cost and time. For this purpose of this study a basic open source solver is used and modifi ed and solutions are validated on experimental data. The aim of this paper is to show a good agreement of experimental pressure measurements and numerical results and to estimate results of the temperature fi eld, the velocity fi eld and the local Mach number using the numerical model.

SHEAR FORCE ANALYSIS OF AN OIL-DRIVEN GRINDING TOOL

The main goal of the present grinding concept GrindBall is to develop a manufacturing process to machine micro structures [1] on hard and brittle materials, using a spherical and shaftless grinding tool. Thereby the negative effect of cutting speed variation caused by fixed rotational axes of conventional grinding pins is reduced. Spherical tools require new technologies for contactless tool drive and positioning [2] that are able to be miniaturised to a compact machining module and fit in the workspace of small machine tools [3]. Therefore, a fluidic drive and an electromagnetic bearing system were chosen for the GrindBall module as practically contactless technologies for power transmission [4].

GrindBall—A Novel Drive and Bearing Concept for Micro Grinding Tools

Small machine tools and their components are persistent topics of research. Effective miniaturisation usually requires a complex integration of various functions into a reduced number of components. The concept presented here constitutes a highly miniaturised grinding module named GrindBall. This concept combines a three-dimensional magnetic bearing with a fluidic drive system to embody a micro grinding module with contactless tool positioning and drive. The grinding tool consists of a sphere with an abrasive surface that is able to perform a shaftless micro machining, allowing novel grinding kinematics on hard and brittle materials, such as glass and ceramics. Due to its size and working principles, this concept is specifically developed for micro grinding applications in small machine tools.

Computational Multi-component Modelling Of Electron Transport And Ohmic Heating Inside A Micro Arc-jet Thruster

Fuel mass is one of the main economical and technical restrictions while designing space propulsion systems. Given the high costs related to the transport of mass into space, the necessary fuel mass for accomplishment of the mission should be minimised. For an optimum “thrust/fuel consumption ratio” the gas exit velocity must be maximised. In this research this is achieved through the heating of the micro gas flow by an electrical arc inside the sub-sonic region of the propulsion system. The electrical arc induces a partial ionisation of the propellant gas. Because of the very low mass flow, the gap of the plasma channel has a width of just a few hundred microns. The electrical arc consists of electrons being accelerated through this small gap by the charged walls of the microchannel. The electrons move in a cross flow compared to the propellant gas. The computational results are validated with the experimental data. Through this investigation a very efficient form of electrodynamic heating-modelling is developed. The very good results show the quality of the present method and encourage further utilisation and development. For this reason this model will be used for the optimisation and the computational engineering pre-development of future thermo-electric propulsion systems.

Diffusion monodisperser Zweiphasenströmungen

Ziel ist es, Bewegung und Interaktion von Partikeln bzw. Tropfen innerhalb einer kontinuierlichen Phase zu beschreiben. Um eine Aussage uber globale Zusammenhange einer Zweiphasenstromung treen zu konnen, wird zuerst die Bewegung einzelner Partikel untersucht, bevor eine Aussage uber die Bewegung ganzer Partikelwolken getroen werden kann. Analog zu Transportgleichungen aus der Mechanik einphasiger Stromungen werden physikalische Grosen mehrphasiger Stromungen durch Gleichungen dargestellt, welche physikalische Relationen der zu beschreibenden Grose zu raumlicher Bewegung und/oder zeitlichem Ablauf mittels Dierential- oder Integraloperatoren darstellt.

Diffusion molekularer Strömungen

Wahrend der erste Hauptsatz der Thermodynamik mit seiner Aussage, dass die Energie in einem geschlossenen System konstant ist, allein schon rein subjektiv verstandlich erscheint, verursachte der zweite Hauptsatz schon zu Grunderzeiten der fruhen Thermodynamik zunehmende Skepsis und grose Verwirrung.

Motivation und wissenschaftliche Fragestellung

Die mathematische Modellierung technischer Stromungen kann inzwischen auf eine Jahrhunderte lange Geschichte verweisen. Bereits Leonardo da Vinci (1452-1519) beobachtete Gesetzmasigkeiten bei der Umstromung stumpfer Korper in eineroenen Kanalstromung oder der Druckverteilung um den ausgestreckten Flugel eines Vogels. Daniel Bernoulli (1700-1782) und Leonard Euler (1707-1783) stellten erste Gleichungen auf, um die Anderung physikalischer Transportgroen in einer Stromung vorherzusagen und damit globale Beziehungen in einem solchen System herzuleiten. Im zentralen Fokus steht dabei, dass Orts- und Zeitabhangigkeiten technischer Prozesse durch mathematische Gleichungen beschrieben werden. Dieser Vorgang wird Modellierung genannt. Ziel ist es, durch die Losung einer mathematischen Gleichung, die einen technischen Prozess modelliert, eine Aussage zur Ortsund Zeitabhangigkeit physikalischer Grosen einer technischen Stromung zu gewinnen.

Diffusion eines polydispersen Mehrphasengemischs

Die Vorhersage monodisperser Stromungen wird durch die dominierende Interaktion zwischen disperser Phase und Tragerphase beeinflusst[253, 159, 239]. Fur monodisperse Stromungen verbleibt als einziger einflussnehmender Parameter die Phasendifferenzgeschwindigkeit. Variierende charakteristischer Langenmase oder gar deren Anderung bestimmen in keiner Form die Phaseninteraktion. Ebensowenig spielt die Partikelseparation untereinander eine entscheidende Rolle.

Diffusion einphasiger Kontinua

Die Beschreibung der Stromungsmechanik basiert auf der Beantwortung der essentiellen Frage, wann sich welches durch die vorliegende Stromung transportierte Teilchen wo befindet. Um so einen Ansatz fur die Beschreibung physikalischer Prozesse zu gewinnen, werden Basisgroen wie Raum und Zeit definiert. Aus den Betrachtungsweisen materieller Korper, welche in der Kontinuumsmechanik verwendet werden, resultieren die mathematischen Beschreibungen physikalischer Systeme, auf welche anschliesend aufgebaut wird. So werden Turbulenz, thermische Flusse oder Dichteunterschiede, sofern sie nicht aufgelost werden, als mechanische Spannungen - wie Druckgradienten oder Scherkrafte - und damit als Impulsdiffusionsprozesse modelliert [157, 232, 233].