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University ofTechnology, Inst. for High Power Beam Technology 2University Erlangen, Inst. for Manufacturing Technology AB STRACTIn the laser cutting process the gas flow is of main importance to remove molten material from the cut kerf. Changes in nozzle geometry, gas supply pressure and nozzle workpiece stand-.offdistance have a strong influence on the cut quality.The aim of the investigation is the numerical simulation of supersonic gas flow.Supersonic nozzles for laser applications are designed Which can be manufactured more easily and cost effective than conventionally used Laval nozzles. For the simulation wall friction is regarded and the flow field is calculated two dimensional and assumed turbulent. Normal jet impingement for the designed nozzles and underexpanded conic-cylindrical nozzles is compared at various nozzle stand-off distances and shows a more constant pressure on the workpiece for the designed nozzles.Furthermore supersonic effects in the cut kerf are investigated and compared with results from Schlieren photographs. The nonlinear pressure distribution inside the kerf indicates both the shock formation and detachment ofthe gas flow.In the presence of shock waves the existing equations in finite volume form have been modified, as they lead to wrong predictions both in the shock location and strength due to an incorrect inertia term in the momentum equations.

The influence of Si-doping on the growth and material characteristics of InAs nanowires deposited by metal-organic vapor phase epitaxy (MOVPE) was investigated. It was observed that above a certain partial pressure ratio, doping has an influence on the morphology. The nanowires exhibit better uniformity but lower height vs. diameter aspect ratio as the supply of the dopant increases. It was consistantly found that the specific conductance of the nanowires also increases. Moreover the electrical measurements showed a transition from semiconducting to metallic behavior in the case of highly doped nanowires.

The big amount (20%) of a marble block becomes marble dust waste during production and manufacturing operations in our country (which has approximately 40% marble reserves of the world). The aim of our research is creating an opportunity to evaluate these waste materials to gain better possibilities in our own scientific, economic, technological and environmental conditions. In this study, pioneering works of our Scientific and Technological Research (TUBITAK) Project which titled " A research on novel nano composites prepared with marble powder: composite synthesis, structural analysis, mechanical and antimicrobial properties" has been done. To examine the realization of this project, we communicated with an organization which is producing kitchen building materials defined by polymer-based micro marble powder composites. The different nanocomposites (including 3%, 5%, 10% zirconium and titanium nano powders) have been prepared in the workshop of this organization operating in Eskişehir-Turkey. Thus, the non-toxic and mechanically advanced metarials have been tried to compose. Suitable, cylindrical molds for mechanical tests were prepared and mechanical tests (Strain -Stress measurements) were made in Geology Department of our University. Already used, pre-manufactured kitchen sink parts, the materials which are used in the preparing process and different marble dusts were examined by using SWAXS methods. Beside of the nanostructural analysis, FT-IR and XRF studies were also carried out to explain the molecular structures of the samples' contents. At last, the correlation between the identified mechanical properties and structural information has been investigated. The more systematical and detailed researches will be done in the content of the above mentioned Project.

In typical optical sensor setups for CO2 laser material processing there are scraper mirrors or beam selectors used to allow sensor positions, which have an coaxial path for both the laser beam and the monitored visible or near-infrared signal. For the monitoring and controlling of the laser welding process it is of interest to get information on the plasma stability. A two color photodiode sensor which has been successftully tested for quality monitoring ofboth cutting and ablation has been used for welding in order to find correlations between the sensor signal and the quality ofthe weld seam. Results and comparisions between cutting and welding will be presented.