Production of two-material micro-assemblies by two-component powder injection molding and sinter-joining

In the field of micro-technology the production of metallic and ceramic micro-components by powder injection molding (PIM) has become a more and more established fabrication method. But in order to fulfill the demand for more complex-shaped high-precision micro-components further development work has to be performed. This is especially true if more efficient production routes for multi-component-micro-assemblies consisting of different materials or sub-components are envisaged. To meet these challenges, investigations are performed to realize and to establish two primary shape micro-processes. These are two-component micro-injection molding (2C-MicroPIM) and sinter-joining. The realization of these technologies will lead to a markedly reduction of the efforts for handling, adjustment, and assembling of metallic and ceramic micro-assemblies. Furthermore, an increased integration level and functionality can be yielded. For an effective transfer of scientific results to industrial applications the whole process chain must be considered, from development and construction of the tooling as well as of the components to the quality assurance and determination of the properties of the assemblies after sintering. These primary shape processes shall enable the mutual processing of different materials within the fabrication process, so avoiding separate mounting or assembling steps. Additionally fixed and loose junctions between at least two components shall be realized. The progress in research and development will be demonstrated especially by the implementation of shaft-to-collar connections between micro-gearwheels and corresponding shafts. Regarding two-component micro-injection molding, the tool construction for shaft-to-collar connections will be presented as well as first experimental results on the properties of selected ceramic powders and feedstocks for the special requirements of the 2C-MicroPIM process. With the assembly step being performed outside the injection molding tool before sinter-joining different parts and geometries can be combined quite easily. The presented article gives an overview on the concept and on preliminary testing results for the fabrication of a shaft-to-collar-connection. Additionally, a solution for an automated assembly of a shaft and a toothed wheel outside the injection molding tool is presented.     

Replication of LIGA structures using microcasting

Microcasting with a gold base alloy and an Al-bronze as a replication technique for LIGA structures is shown. A LIGA mold insert for injection molding is used to produce PMMA patterns as lost wax models in the microcasting process. Although there are several steps of replication the accuracy of the process is high and allows the fast manufacturing of middle size batches of microstructured parts. The mechanical properties can be varied within a wide range by choosing different casting alloys or cooling rates. Additionally the influence of the investment on the surface roughness is presented as well as results of flowlength tests showing maximal achievable aspect ratios with the gold base alloy and the Al-bronze.The funding of this work within Collaborative Research Center SFB 499 by Deutsche Forschungsgemeinschaft (DFG) is gratefully acknowledged. Thanks also to the colleagues in the SFB 499 for good collaboration, especially to S. Rath for providing special investments for microcasting.     

Signal evaluation for high-speed confocal measurements

The confocal-detection principle is open especially for use in medical applications. For inspection systems applications for technical objects in reflection confocal setups are of growing importance. For such applications the confocal measurements need to have a very short measuring time. A fast detection system is needed and to satisfy this requirement only a small number of height levels are measured and a fast-evaluation algorithm is used. Drawbacks of the reduction of height levels are a greater influence of noise and additional systematic errors on the measured heights. Study the effects of the reduction are calculated, different evaluation algorithms are analyzed, and the optimization of the parameters is discussed.     

Development of a micro annular gear pump by micro powder injection molding

Scaling down devices from the macroscopic world to microsystems presents various problems since tolerances decrease down to the range of the surface roughness. Consequently, the problems assembling such systems increase and any wear has an extreme impact on the function of microsystems. Recently, most microparts are made of thermoplastics or in brittle materials like silicon by deep etching. The mechanical properties of these materials, however, are not favorable for microparts subjected to mechanical wear. To meet the obvious demand for wear resistant microparts made of metals and ceramics, the development of Micro-Metal Injection Molding (Micro-MIM)/Micro-Ceramic Injection Molding (Micro-CIM) was started at Forschungszentrum Karlsruhe a few years ago. The article describes special distinctions between Micro-Powder Injection Molding (-PIM) and normal PIM as well as the arising process variations.However, one has to keep in mind the shrinkage during the PIM-route that makes it very difficult to meet the small tolerances required.In this paper the results of a demonstrator development of a micro annular gear pump and the adaptation for micro ceramic injection molding (Micro-CIM) are reported. For CIM, mold inserts made by LIGA were used. The quality of the molds was evaluated by SEM and micro injection molding in PMMA. Subsequently, Micro-CIM was carried out using zirconia feedstocks. The microparts were separated from the substrate, debound, sintered and surface finished. The surface roughness was evaluated and the processes were optimized.     

The charged region of Hsp90 modulates the function of the N-terminal domain

Hsp90, an abundant heat shock protein that is highly expressed even under physiological conditions, is involved in the folding of key molecules of the cellular signal transduction system such as kinases and steroid receptors. It seems to contain two chaperone sites differing in substrate specificity. Binding of ATP or the antitumor drug geldanamycin alters the substrate affinity of the N-terminal chaperone site, whereas both substances show no influence on the C-terminal one. In wild-type Hsp90 the fragments containing the chaperone sites are connected by a highly charged linker of various lengths in different organisms. As this linker region represents the most striking difference between bacterial and eukaryotic Hsp90s, it may be involved in a gain of function of eukaryotic Hsp90s. Here, we have analyzed a fragment of yeast Hsp90 consisting of the N-terminal domain and the charged region (N272) in comparison with the isolated N-terminal domain (N210). We show that the charged region causes an increase in the affinity of the N-terminal domain for nonnative protein and establishes a crosstalk between peptide and ATP binding. Thus, the binding of peptide to N272 decreases its affinity for ATP and geldanamycin, whereas the ATP-binding properties of the monomeric N-terminal domain N210 are not influenced by peptide binding. We propose that the charged region connecting the two chaperone domains plays an important role in regulating chaperone function of Hsp90.     

The elusive role of the N-terminal extension of {beta}A3- and {beta}Al-crystallin

ß-Crystallins are structural lens proteins with aconserved two-domain structure and variable N- and C-terminalextensions. These extensions are assumed to be involved in quaternaryinteractions within the ß-crystallin oligomers orwith other lens proteins. Therefore, the production of ßA3-and ßAl-crystallin from the single ßA3/A1mRNA by dual translation initiation is of interest. These crystallinsare identical, except that ßAl has a much shorterN-terminal extension than ßA3. This rare mechanismhas been conserved for over 250 million years during the evolutionof the ßA3/A1 gene, suggesting that the generationof different N-terminal extensions confers a selective advantage.We therefore compared the stability and association behaviourof recombinant ßA3- and ßAl-crystallin.Both proteins are equally stable in urea- and pH-induced denaturationexperiments. Gel filtration and analytical ultracentrifugationestablished that ßA3 and ßA1 both form homodimers.In the water-soluble proteins of bovine lens, ßA3and ßA1 are present in the same molecular weight fractions,indicating that they oligomerize equally with other ß-crystallins.¹H-NMR spectroscopy showed that residues Met1 to Asn22 of theN-terminal extension of ßA3 have great flexibilityand are solvent exposed, excluding them from protein interactionsin the homodimer. These results indicate that the differentN-terminal extensions of ßA3 and ßA1 donot affect their homo- or heteromeric interactions.