4M Knowledge base - papers

K. Hofmann(a), H. Kück(a)(b) H. Ruoffc, L. Staemmler(b)
a: Institute of Micro- and Precision Engineering (IZFM), University of Stuttgart, 70569 Stuttgart, Germany
b: Hahn-Schickard-Institute for Micro Assembly Technology (HSG-IMAT), 70569 Stuttgart, Germany
c: Institute for Materials Testing, Materials Science and Strength of Materials (IMWF), 70569 Stuttgart, Germany

Abstract

Electrochemical milling with ultra short voltage pulses (ECF) is an innovative technique to machine electrochemically active materials at micrometer feature size, especially very hard materials like steel. The movement of the tool is similar to conventional milling, although it does not rotate. Therefore 3D-forming of the workpiece is possible. The surface of the workpiece is etched by a galvanic current. Due to this neither mechanical forces nor thermal loads are applied to workpiece or tool. The ability to manufacture hard materials like stainless steel at micrometer feature size makes ECF the ideal technique for processing micro moulds. When manufacturing moulds large differences in machining speed and quality of the surface occur. So far possible explanations for this were supposed differences between the machinability of grain boundaries and interior of the grains. But experiments showed no significant influence. Furthermore the dependence of the tool diameter on the working distance was determined. Experiments showed a decreasing working distance with increasing tool diameter. This phenomenon could also be explained theoretically. Finally the influence of the grade of hardness on the ECF process is investigated at the tool steel M 340.

J-F. Charmeux, R. Minev, S. Dimov, E. Minev
Manufacturing Engineering Center, Cardiff University, Cardiff, CF24 3AA, UK

Abstract

Producing micro-castings trough vacuum investment casting is known to be associated with high cooling rates due to small scale of the castings. High cooling rates together with alloy composition might be the main factors affecting the final metallographic structure of castings’ alloys during the solidification process. When using Al-Si-Mg casting alloys, the size of the dendritic structure can be used for a non-destructive test to assess the mechanical properties and overall quality of the castings. Also the ability of the alloys to be structured by different mechanical and energy assisted processes is highly dependant on their metallographic structure. This paper investigates the structural changes occurring when shifting from conventional size castings to micro-castings. An empirical model describing the degree of dendrite cell refinement as a function of micro-castings aspect ratio is proposed. Additionally, the paper reports the changes in porosity and Si particles morphology observed on micro-castings produced with different flask temperatures. MHV measurements were also performed for different aspect ratio of the cast micro-features.

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.