4M Knowledge base - papers

Prof. Dr.-Ing. Dr.-Ing. E.h. Walter Michaeli, Dipl.-Ing. Dirk Opfermann
Institute of Plastics Processing (IKV) at RWTH Aachen University, 52062 Aachen, Germany

Abstract

The miniaturisation of technical products becomes more important in many technological areas. Many functions can be optimised by the use of micro systems. On less space more functions can be integrated. In the field of medical technology miniaturisation means also new methods of treatment with fewer side effects on the patient. New cures are being developed as a result of the miniaturisation of medical instruments, such as the key hole surgery. Polymers are spread widely in the field of medical applications. Since plastics are a relatively cheap material and polymer parts can easily be reproduced in high series and accuracy, for examples by injection moulding, their use as disposable articles is predetermined. Polymer materials offer a wide range of properties that can be chosen according to the functional necessities.

W. Michaeli, M. Bussmann, B. Renner
Institute of Plastics Processing (IKV), Department of Injection moulding,
RWTH Aachen University, 52062 Aachen, Germany

Abstract

Beside melt flow simulation in injection moulding the prediction of arising internal properties is essential to forecast final part properties. Crystallisation e.g. causes anisotropic structure set-ups in a moulded cross-section and affects the resulting global mechanical part behaviour.

Nucleation and spherulite growth are complex processes going on during the cooling-down of semi-crystalline polymer melts. The knowledge of the final local structure set-ups and the degree of crystallinity is essential to predict the resulting mechanical part properties in future. Within the scope of the special research centre 370 (SFB 370) at RWTH Aachen University the software SphaeroSim was developed. It allows the online calculation of spherulite growth processes during the cooling of quiescent melts under injection moulding conditions. At present the software is operating two-dimensional using the Cellular Automata Method.

In the past, only part cross-sections with different shapes were focused for simulation, but now it is also possible to consider micro-sized parts with a more complex geometry through a higher resolution of the geometry. Thus it is possible to visualise the going on crystallisation processes by the newly modified software considering new boundary conditions. In this paper simulation results are shown and interpretations to micro-parts properties will be pointed out.

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.

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.

R. Jurischka(a), A. Schoth(a), C. Müller(a), C. Baggi(b), R. Gallera(b), H. Reinecke(a)
a: Department of Microsystems Engineering IMTEK, Laboratory for Process Technology University of Freiburg, 79110 Freiburg, Germany
b: Sarix SA, Micro EDM Technology, 6616 Losone, Switzerland

Abstract

Microfluidic devices are becoming more and more important in life science, chemical analytic, and medical areas. For these applications disposable and low cost articles are highly convenient. Polymers are ideally suited for these applications due to their material properties and their applicability for high volume production with high accuracy.

In this study, we combine the CNC-milling technology with a optimized μEDM-milling process to fabricate mould inserts made from steel, including micro and macro fluidic structures. The microfluidic structures have channel dimensions down to 18μm, aspect ratios of up to 4 and a surface roughness Ra 70 nm. Additionally, demoulding drafts of 2-6 degrees have been achieved, resulting in low demoulding forces. These tools were characterized and polymer parts were reproduced by injection moulding. The main advantage of the combination of CNC- and μEDMmilling technology is the rapid and direct structuring of tool steel for mould inserts with a 3D geometry and a long tool life time. These tools are used as mould inserts for injection moulding, enabling flexible prototyping as well as the high volume replication of polymers.