Replication

S. Geißdörfer, U. Engel, M. Geiger
Chair of Manufacturing Technology, University of Erlangen-Nuremberg, 91058 Erlangen, Egerlandstr. 11, Germany

Abstract

At microscale, the large ratio between mean grain size of the material and specimen dimension cause an increasing influence of single grain forming behaviour on the overall forming process. Thus the forming behaviour of these parts can no longer be regarded as to be homogeneous. This leads to a change in the material behaviour resulting in a large scatter of forming results, e.g. varying cup height in a cup backward extrusion process or varying spring-back angles in a micro bending process. Moreover, some correlation between the integral flow stress of the workpiece and the scatter of the process factors on the one hand and the mean grain size and its standard deviation on the other hand has been detected in experiments. Conventional FE-simulation which is by its nature size independent, is not able to consider these effects observed when scaling down processes, in particular represented by a reduction of the flow stress, an increasing scatter of the process factors and a local material flow being different to that obtained in the case of macro parts. Therefore, a new simulation model is being developed in order to take into account the identified effects and to determine the scatter of the process factors. The so-called mesoscopic model provides the discretisation of the simulated material into individual objects which represents the grain structure of the real material. To each object an individual flow curve is assigned, calculated on the basis of metal physics given by Hall-Petch and Ashby’s theory. The computational grain structure generation is based on the theory of a Monte Carlo Potts growth law.

The present paper deals with the theoretical background of the new mesoscopic model, its characteristics like synthetic grain structure generation and the calculation of micro material properties - based on conventional material properties. The verification of the simulation model is done by carrying out various experiments with different mean grain sizes and grain structures but the same geometrical dimensions of the workpiece.

Ph. Imgrund, Dr. A. Rota, L. Kramer
Fraunhofer Institute for Manufacturing and Advanced Materials (IFAM), D-28215 Bremen, Germany

Abstract

Several metals and alloys can be used to enhance mechanical and physical properties of micro parts and components for micromechanical, -chemical or sensor applications. Such parts can be produced in series by the powder metallurgical process of micro metal injection moulding (μ-MIM) that has been developed at IFAM in recent years.

A micro system is usually obtained by assembling a number of parts with different functions, i.e. materials, in difficult packaging or joining operations. This paper describes a novel manufacturing route for metallic multi-material micro components, bi-material micro metal injection moulding (2K-μ-MIM). Similar to “two-colour” injection moulding of plastics, the process allows the integration of multiple functions in a micro part by simultaneously injecting and joining two materials in one mould. Net-shape parts with well-defined, solid material interfaces are obtained. In this paper, the 2K-μ-MIM process is exemplified for the combination of different non-magnetic (316L) and ferromagnetic (17-4PH, Fe) metals. It is shown that intact material interfaces of less than 1x1mm2 can be achieved by careful selection and tailoring of metal powders (powder particle size, chemical composition), injection moulding and co-sintering parameters.

T. Brenner, C. Müller, H. Reinecke, R. Zengerle, and J. Ducrée
IMTEK – University of Freiburg, Georges-Koehler-Allee 106, D-79110 Freiburg, Germany

Abstract

We established an integrated prototyping chain for rapid fabrication of microfluidic chips in polymers comprising fabrication of masters made from elastomers, replication into polymers by soft embossing, surface modification and thermal sealing. Our techniques enable rapid and precise fabrication of fully functionalized microfluidic chips featuring typical minimum lateral dimensions of 50 μm and aspect ratios smaller than one.

R. Jurischka (a), Ch. Blattert (a), I. Tahhan (a), A. Schoth (a), H. Reinecke (a),
a Laboratory for Process Technology, Institute of Microsystem Technology, University of Freiburg, 79110 Freiburg, Germany

Abstract

Present main applications of microfluidic devices are within the life sciences or chemical analysis. Polymers are ideally suited for these applications due to their material properties and their applicability for high volume production. In this study, we developed a rapid manufacturing technology for disposable microfluidic devices using UV-LIGA and injection molding. Exchangeable inserts for the molding tool were fabricated by a modified UV-LIGA technology. The UV-LIGA process is based on a SU-8 lithography with a metal substrate, which allows for a reduction of the nickel electroplating time. These inserts enable a cost effective structuring of polymers. Different prototypes of chips for microfluidic applications with channel dimensions down to 10 μm and aspect ratios of 8 have been fabricated. The electroplated nickel structure has a hardness of 800 Vickers and an excellent top surface roughness of Ra < 20 nm. Taper angles of 3-8 degrees result in low demolding forces. The main advantage of our rapid processing technology is the availability of the geometry, the specific target material and manufacturing technology right from the start of the development to a cost effective high volume production of microfluidic devices.

M. Sahli (a,c), C. Roques-Carmes (a), R. Duffait (b) and C. Khan Malek (c)
a Laboratoire de Microanalyse des Surfaces (LMS), ENSMM, 26 Rue de l’Epitaphe,
b Centre de Transfert des Micro et Nanotechnologies (CTMN), 39 Avenue de l’Observatoire,
c Laboratoire FEMTO-ST, CNRS UMR 6174, Département LPMO, 32 Avenue de l’Observatoire, 25000 Besançon, France.

Abstract

A study of the rheological properties of two types of amorphous polymeric materials (PMMA and COC) was conducted in order to optimize the operating conditions for the hot embossing of the polymers. The glass transition temperature (Tg), the melt flow index (IF), and the viscosity as a function of shear stress were determined. These intrinsic properties were related to the aptitude of the polymers to reproduce the geometrical shape and surface states of a microstructured mould. The flow imposed to the polymeric material in shear or elongational mode was correlated to this rheological approach.