Downsized and complex micro-machining structures have to meet quality requirements concerning geometry and convince through increasing functionality. The development and use of cutting tools in the sub-millimeter range can meet these demands and contribute to the production of intelligent components in biomedical technology, optics or electronics. This article addresses the development of double-edged micro-cutters, which consist of a two-part system of cutter head and shaft. The cutting diameters are between 50 and 200 μm. The silicon carbide cutting heads are manufactured from the solid material using microsystem technology. The substrate used can be structured uniformly via photolithography, which means that 5200 homogeneous micro-milling heads can be produced simultaneously. This novel batch approach represents a contrast to conventionally manufactured micro-milling cutters. The imprint is taken by means of reactive ion etching using a mask made of electroplated nickel. Within this dry etching process, characteristic values such as the etch rate and flank angle of the structures are critical and will be compared in a parameter analysis. At optimal parameters, an anisotropy factor of 0.8 and an etching rate of 0.34 µm/min of the silicon carbide are generated. Finally, the milling heads are diced and joined. In the final machining tests, the functionality is investigated and any signs of wear are evaluated. A tool life of 1500 mm in various materials could be achieved. This and the milling quality achieved are in the range of conventional micro-milling cutters, which gives a positive outlook for further development.
As copper is a rather difficult material to machine due to its ductility compared to aluminium, this study presents the approach of oxidizing the surface to improve the results of the grinding process. Therefore, batch manufactured flexible micro-grinding tools are used for grinding of copper and oxidized copper surfaces to machine microstructure or local areas of functional surfaces. Besides, we show a comparison of the performance of an abrasive layer made of silicon carbide (SiC) and cubic boron nitride (cBN). The tools are made of a polyimide-based abrasive layer and silicon as substrate and are fabricated by photolithography and deep reactive ion etching. The oxidation of copper surfaces is done by electrochemical processes and are directly machined with grinding tools. The surface quality is evaluated concerning the surface roughness by optical measurements with confocal microscopy. Lower roughness values are achieved on both, the pure copper and the oxidized copper by using SiC grinding tools. On pure copper this is reflected in a reduction of the arithmetical mean roughness value Ra to 0.04 µm. The unprocessed reference surface shows an Ra of 0.24 µm. In addition, the machined oxidized surfaces show a reduction of the mean roughness depth Rz from 7,60 µm to 1.10 µm, which is an optimization of factor 2 compared to the machined non-oxidized copper surfaces (2.32 µm). The machining of copper with cBN micro-grinding tools also shows improved roughness values, but in comparison to the SiC tools these are 50 % higher for machined copper surfaces and similar for machined oxidized copper surfaces. While the oxidation of the copper surface has a positive effect on the surface quality, no effect on tool wear can be observed.
Precision machining is becoming more and more important with the increasing demands on surface quality for various components. This applies, for example, to mirror components in micro-optics or cooling components in microelectronics. Copper is a frequently used material for this purpose, but its mechanical properties make it difficult to machine. In this study, a process strategy for finishing copper surfaces with batch-manufactured micro-grinding tools in an electrochemically assisted grinding process is demonstrated. The tool heads are manufactured from a polyimide-abrasive-suspension and silicon as a carrier substrate using microsystems technology. The matching shafts are milled from aluminium. The tools are then used on pure copper and oxidised copper surfaces. By using finer abrasives grains (1.6–2.4 µm instead of 4–6 µm) than previously, similar surface roughness values could be achieved (Ra = 0.09 ± 0.02 µm, Rz = 1.94 ± 0.73 µm) with the same grinding process. An optimised grinding process that combines the use of rough and fine tools, on the other hand, achieves significantly better surface finishes in just four grinding iterations (Ra = 0.02 ± 0.01 µm, Rz = 0.83 ± 0.21 µm). In order to achieve a further increase in surface quality, this optimised grinding process is combined with the anodic oxidation of the copper workpieces. The surface modification is done to increase the machinability of the surface by creating an oxide layer. This is confirmed by the results of scratch tests carried out, which showed less force acting on the tool during machining with the oxide layer than with a pure copper surface. To realise this within the machine tool, an electrochemical cell is shown that can be integrated into the machine so that the oxidation can be carried out immediately before the grinding process. The copper layers produced inside the electrochemical cell in the machine tool show similar characteristics to the samples produced outside. Processing the oxidised samples with the optimised grinding process led to a further reduction of about 17% in the Rz values (Ra = 0.03 ± 0.01 µm, Rz = 0.69 ± 0.20 µm). The combination of the shown grinding process and the integration of anodic oxidation within the machine tool for the surface modification of copper workpieces seems to be promising to achieve high surface finishes.
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