Expert system-supported optimization of laser welding of additively manufactured thermoplastic components

Laser transmission welding (LTW) is a known technique to join conventionally produced thermoplastic parts, e.g. injected molded parts. When using LTW for additively manufactured parts (usually prototypes, small series), this technique has to be evolved to overcome the difficulties in the part composition resulted in the additive manufacturing process itself. In this paper, a method is presented to enhance the weld seam quality of laser welded additively manufactured parts assisted by a neural network-based expert system. To validate the expert system, specimens are additively manufactured from polylactide. The parameters of the additive manufacturing process, the transmissivity, and the LTW process parameters are used to predict the shear tensile force with the neural network. The transparent samples are welded to black absorbent samples in overlap configuration and shear tensile tests are performed. In this work, the prediction of the shear tensile force with an accuracy of 88.1% of the neuronal network based expert system is demonstrated

Temperature distribution during laser based heat conduction welding of CFRP

For the implementation of carbon fiber reinforced (CFRP) parts, these need to be assembled to more complex structures. Therefore, laser transmission welding was transferred to heat conduction welding for joining thermoplastic CFRP to itself. The goal of these investigations was to determine the influence of the focal point geometry and the main fiber orientation within the CFRP on the temperature distribution at the upper joining member. A set-up was chosen consisting of two thermo cameras in order to measure the process temperatures on top and underneath the upper joining member. Furthermore, the heat affected width was determined and correlated to the process temperatures

Finite Element Simulation and Experimental Assessment of Laser Cutting Unidirectional CFRP at Cutting Angles of 45° and 90°

Laser cutting of carbon fibre-reinforced plastics (CFRP) is a promising alternative to traditional manufacturing methods due to its non-contact nature and high automation potential. To establish the process for an industrial application, it is necessary to predict the temperature fields arising as a result of the laser energy input. Elevated temperatures during the cutting process can lead to damage in the composite’s matrix material, resulting in local changes in the structural properties and reduced material strength. To address this, a three-dimensional finite element model is developed to predict the temporal and spatial temperature evolution during laser cutting. Experimental values are compared with simulated temperatures, and the cutting kerf geometry is examined. Experiments are conducted at 45° and 90° cutting angles relative to the main fibre orientation using a 1.1 mm thick epoxy-based laminate. The simulation accurately captures the overall temperature field expansion caused by multiple laser beam passes over the workpiece. The influence of fibre orientation is evident, with deviations in specific temperature data indicating differences between the estimated and real material properties. The model tends to overestimate the ablation rate in the kerf geometry, attributed to mesh resolution limitations. Within the parameters investigated, hardly any expansion of a heat affected zone (HAZ) is visible, which is confirmed by the simulation results

Macroscopic simulation model for laser cutting of carbon fibre reinforced plastics

Laser cutting of carbon fibre reinforced plastics (CFRP) has shown promising potential as an alternative to conventional manufacturing processes. Laser cutting has major benefits of contactless and therefore wear-free machining and high automation potential. The main challenge is to reduce the heat input into the material during the process. Excessive temperatures cause damage within the surrounding matrix material and could locally modify the structural properties of the CFRP. For industrial use it is necessary to be able to predict the resulting temperature fields. To gain knowledge of the temperature distribution during the process, a three-dimensional macroscopic finite element model is developed using ANSYS simulation software. Transient-thermal analyses are performed and the material removal process is implemented via the element-death technique. Simulations are run for a unidirectional composite structure and different cutting speeds. The resulting temperatures are compared to experimental data

Gcn5 facilitates Pol II progression, rather than recruitment to nucleosome-depleted stress promoters, in Schizosaccharomyces pombe

In the fission yeast, the MAP kinase Sty1 and the transcription factor Atf1 regulate up to 400 genes in response to environmental signals, and both proteins have been shown to bind to their promoters in a stress-dependent manner. In a genetic search, we have isolated the histone H3 acetyltransferase Gcn5, a component of the SAGA complex, as being essential for oxidative stress survival and activation of those genes. Upon stress, Gcn5 is recruited to promoters and coding sequences of stress genes in a Sty1- and Atf1-dependent manner, causing both an enhanced acetylation of histone H3 and nucleosome eviction. Unexpectedly, recruitment of RNA polymerase II (Pol II) is not impaired in Δgcn5 cells. We show here that stress genes display a 400-bp long nucleosome depleted region upstream of the transcription start site even prior to activation. Stress treatment does not alter promoter nucleosome architecture, but induces eviction of the downstream nucleosomes at stress genes, which is not observed in Δgcn5 cells. We conclude that, while Pol II is recruited to nucleosome-free stress promoters in a transcription factor dependent manner, Gcn5 mediates eviction of nucleosomes positioned downstream of promoters, allowing efficient Pol II progression along the genes

Nucleosomes in gene regulation: theoretical approaches

This work reviews current theoretical approaches of biophysics and bioinformatics for the description of nucleosome arrangements in chromatin and transcription factor binding to nucleosomal organized DNA. The role of nucleosomes in gene regulation is discussed from molecular-mechanistic and biological point of view. In addition to classical problems of this field, actual questions of epigenetic regulation are discussed. The authors selected for discussion what seem to be the most interesting concepts and hypotheses. Mathematical approaches are described in a simplified language to attract attention to the most important directions of this field

Determination of thermic unstable and nonvolatile pesticide residues in vegetable food

Ziel der vorliegenden Arbeit war es, Methoden zu entwickeln, mit denen Rückstände thermo-labiler und nichtflüchtiger Pflanzenschutzmittel in pflanzlichen Lebensmitteln identifiziert und quantifiziert werden können. Für die Aufarbeitung der Lebensmittelproben wurde die DFG-Methode S19 und die Methode S19-Online eingesetzt. Diese Methoden wurden für die ausgewählten Pestizide, die Benzoyl-harnstoffe, Iprodion und basische Fungizide, optimiert. Zur Aufreinigung der pflanzlichen Lebensmittelextrakte wurden die Festphasenextraktion an Kieselgel und an Umkehrphasen eingesetzt. Zur weiteren Aufreinigung der Probenextrakte diente die analytische und die präparative GPC. Die chromatographische Trennung erfolgte mittels Hochleistungsdünnschichtchromato-graphie mit automatischer Mehrfachentwicklung (HPTLC / AMD) teilweise mit der Online-Kopplung zur Hochleistungsflüssigchromatographie (HPLC). Mit diesen Verfahren ist eine Trennung von Matrixkomponenten und Analyten ohne Hitzeeinwirkung möglich. Zunächst wurde die Eignung dieser chromatographischen Analysentechniken erfolgreich geprüft. Basierend auf den erhaltenen Ergebnissen wurden Analysenmethoden für ausgewählte Pestizide, die Benzoylharnstoffe, Iprodion und basische Fungizide, entwickelt. Zusätzlich wurden als Alternativmethoden die GC nach Pentafluorbenzylierung und LC / MS für die Analytik der ausgewählten Pestizide entwickelt. Für die Benzoylharnstoffe erwies sich die LC / MS und für Carbendazim und Thiabendazol erwies sich die GC / MS nach Penta-fluorbenzylierung als geeignet. Aufgrund von Matrixeffekten wird eine Quantifizierung mittels Standardadditionskalibrierung empfohlen. Aus der Summe der Ergebnisse konnte geschlossen werden, dass die Online-Kopplung der HPLC mit der HPTLC / AMD die Bestimmung von Pestizid-Rückständen oberhalb einer Konzentration von 0,1 mg/kg ohne aufwendige Aufreinigung erlaubt. Durch die Verbesserung der Empfindlichkeit bzw. der Spezifität der Rückstandsbestimmung, wie sie durch Bioauto-graphie mit Schimmelpilzen oder eine chemischen Derivatisierung erzielt werden kann, konnte eine aufwendige Aufreinigung auch unterhalb dieser Konzentration unterbleiben. Bei optimaler Aufreinigung konnten die untersuchten Pestizide bei einer Konzentration von 0,01 mg/kg bestimmt werden. Anhand der Charakterisierung von Whisky-Inhaltsstoffen mittels der HPTLC / AMD und ihrer Online-Kopplung mit der HPLC konnte der große Anwendungsbereich dieser chromato-graphischen Verfahren gezeigt werden.This thesis was aimed to develop methods to identify and quantify thermically unstable and nonvolatile pesticide residues in vegetable foodstuffs. Sample preparation was performed according to both the DFG Method S19 as well as the Method S19-Online . These methods were optimised for the selected pesticides: benzoylureas, iprodione and basic fungicides. The vegetable food extracts were purified via Solid Phase Extraction using normal (Silicagel) and reversed phases Further clean up of the sample extracts was carried out via analytical and preparative GPC. The chromatographic separation was performed by High Performance Thin Layer Chromatography with Automatic Multiple Development (HPTLC/AMD) or on-line coupling of High Performance Liquid Chromatography (HPLC) with HPTLC/AMD. These procedures allow the separation of matrix components and analytes without heat exposure. Initially, the suitability of these chromatographic analysis techniques was successfully examined. Based on the results obtained, analysis methods for the selected pesticides, benzoylureas, iprodione and basic fungicides, were developed. Additionally, GC after derivatization with pentafluorobenzyl bromide and LC-MS were developed as alternative analysis methods for the selected pesticides. The LC-MS proved suitable for the Benzoylureas and the GC-MS of pentafluorobenzyl derivatives proved suitable for carbendazim and thiabendazole. Due to matrix effects, quantification is recommended by standard addition calibration. The results demonstrate that on-line coupling of HPLC with HPTLC/AMD permits the determination of pesticide residues above a concentration of 0,1 mg/kg without elaborated clean up. Elaborate clean up may be omitted below this concentration upon improvement of the sensitivity and/or the specificity e.g. by using bioautography with mold fungi or a chemical derivatisation. The analysed pesticides could be determined at a concentration of 0,01 mg/kg after optimal clean up. The wide application range of HPTLC/AMD and its on-line coupling with the HPLC could be demonstrated exemplary to characterise whisky ingredients