Abstract
Die Fußgänger‐ und Fahrradbrücke über die Broye (Schweiz) bindet das neue Wohnviertel Rives de la Broye an die in der Nähe gelegene Stadt Payerne an. Der Überbau der 36 m langen Trogbrücke ...besteht aus 26 t wetterfestem Stahl. Die Ausführung als Stahltrog stellt sicher, dass sich der Brückenüberbau oberhalb des Hochwasserpegels befindet. Die Stege und die Oberflansche des Trogs haben dabei nicht nur eine statische Funktion, sondern sind gleichzeitig die Geländer bzw. Handläufe der Brücke. Die Stege sind von einem Lochmuster durchzogen, welches am Computer generiert und mittels einer CNC‐Lasermaschine ausgeschnitten wurde. Die Lochverteilung wurde in Abhängigkeit von den Kraftverläufen in den Stegen gewählt. Das verbleibende Material folgt den Spannungstrajektorien in den Stegen. Die jeweilige Lochgröße richtet sich dabei nach der lokalen Beanspruchung der Stege. Das Muster lässt die Brücke nicht nur transparenter und optisch leichter erscheinen, sondern trägt auch zur Gewichtsreduktion und Materialersparnis bei. Der Überbau der Brücke wurde vollständig im Werk vorfabriziert und anschließend innerhalb weniger Stunden mithilfe eines Autokrans auf die Widerlager gesetzt. An den Widerlagern wird jeweils durch ein Druck‐ und ein Zugauflager eine Einspannwirkung erzeugt, welche sich positiv auf die Durchbiegung in Feldmitte und die dynamischen Eigenschaften des Überbaus auswirkt. Die Lager sind in Lagerebene verschieblich, um Temperaturunterschiede auszugleichen.
Abstract
Trough bridge over the river Broye – a pedestrian and cycling bridge made of weathering steel with laser‐cut webs
The pedestrian and cycling bridge over the river Broye (Switzerland) connects the new residential area Rives de la Broye to the nearby town Payerne. The superstructure of the 36 m span trough bridge is made of 26 t of weathering steel. Due to the trough cross‐section, the full superstructure is above flood level. Webs and upper flanges do not only have structural purpose but also function as railings and handrails. The webs have a perforated pattern, which was generated computer‐aided and CNC‐laser cut. The pattern was chosen according to the stress distribution in the webs. The remaining material follows the stress trajectories and the seizes of the perforations depend on the local stresses. The pattern does not only make the superstructure look more transparent and lighter, but also reduces the total weight and saves material. The bridge superstructure was completely prefabricated and installed within hours using a mobile crane. At the abutments a restraining effect is achieved by a combination of a tension and a compression bearing, which positively affect the maximum deflection in mid‐span and the dynamic bahaviour. The bearings can move at bearing level to allow for temperature differences.
This article deals with the laser cutting of wood and wood composites. The laser cutting of wood and wood composites is widely accepted and used by the wood industry (due to its many advantages ...compared to, e.g., saw cutting). The goal of this research was to optimize the cutting parameters of spruce wood (Pices abies L.) by a low-power CO2 laser. The influence of three factors was investigated, namely, the effect of the laser power (100 and 150 W), cutting speed (3, 6, and 9 mm·s−1), and number of annual rings (3–11) on the width of the cutting kerf on the top board, on the width of the cutting kerf on the bottom board, on the ratio of the cutting kerf width on the top and bottom of the board, on the width of the heat-affected area on both sides of the cutting kerf (this applies to the top and bottom of the board), and on the degree of charring. Analysis of variance (ANOVA) and correlation and regression analysis were used for developing a linear regression model without interactions and a quadratic regression model with quadratic interactions. Based on the developed models, the optimization of parameter settings of the investigated process was performed in order to achieve the final kerf quality. The improvement in the quality of the part ranged from 3% to more than 30%. The results were compared with other research dealing with the laser cutting of wood and wood composites.
Carbon fibre reinforced plastic (CFRP) composites are found to be cut satisfactorily by a pulsed Nd:YAG laser at the optimum process parameter ranges. Predictive models have been developed based on ...important process parameters, viz. cutting speed, pulse energy, pulse duration, pulse repetition rate and gas pressure. The responses considered are the heat-affected zone (HAZ) and the taper of the cut surface. The optimisation of process parameters was done using response surface methodology (RSM). The thermal properties of the constituent material and the volume fraction of the fibres are the principal factors that control the cutting performance. The effect of the process parameters on the output responses is also discussed.
The laser cutting of rock has been popular recently because of its advantages over traditional rock cutting methods. Several types of research were performed to replace traditional rock cutting ...techniques with laser cutting. The purpose of this experiment is to observe cutting quality for intrusive igneous rocks using a high-power multimode fiber laser. The cutting quality, in terms of kerf width and penetration depth, resulted from different scanning speeds and was studied and compared. The specimens used in this study were gabbro, granite, and diorite, which are widely applied in the construction industry because of their high compressive strength and beautiful textures. Energy-dispersive X-ray Spectroscopy (EDX) analyses were conducted to observe the chemical content of three different areas, the melting area, the burnt area, and a non-processed area, for each rock specimen. The study of the compositional changes in each area will also go over the cutting quality of each rock specimen at different scanning speeds. According to the experimental results, the kerf widths of the specimens gradually decrease as the scanning speeds increase. The penetration depths into the specimens sharply decrease as scanning speeds increase. From a study of their compositional changes, it is found that the cutting quality for each rock depends on their silica content. This study summarizes that the cutting quality for a rock specimen greatly depends on the scanning speed of the laser cutting.
The technology of laser cutting is widely used in various industries for processing materials. However, it generates a substantial amount of harmful dust, smoke, and aerosols, which pose a threat to ...the environment and endanger the health of workers. One potential method that has emerged to monitor the cutting process and identify materials in real-time is speckle sensing. This paper presents a novel material classification technique that employs a new deep-learning model architecture designed for speckle pattern images to classify materials according to the speckle patterns of the material's surface. The proposed approach involves training a convolutional neural network (CNN) on a large dataset of laser speckle patterns to recognize various material types for safe and efficient cutting. Material classification using speckle sensing enhances the process, reducing the time required to train the speckle images and the inference time for predicting the material from the speckle images. Experimental results demonstrate that the suggested method achieves high precision in categorizing materials, particularly hazardous ones. The model was evaluated on a test dataset of 3,000 new images, achieving an F1-score of 0.9781. The utilization of speckle sensing enables the proposed method to offer a fast, reliable, and accurate approach to material-aware laser cutting while mitigating the potential risks associated with the process.
•The 3D mathematical model of the laser cutting of current collectors is developed.•Penetration time, depth, width, and absorptivity, are analyzed with selected laser parameters.•Melt pool flow, melt ...pool geometry and temperature distribution are investigated.•The transition from partial to full penetration modes and crest are observed for copper.•Not only the crest, but also two deep penetration holes are observed for aluminum.
One of the challenges of the lithium-ion battery manufacturing process is the sizing of electrodes with good cut surface quality. Poor cut surface quality results in internal short circuits in the cells and significant heat generation. One of the solutions that may improve the cut quality with a high cutting speed is laser cutting due to its high energy concentration, fast processing time, high precision, small heat affected zone, flexible range of laser power and contact free process. In order to utilize the advantages of laser electrode cutting, understanding the physical phenomena for each material is crucial. Thus, this study focuses on the laser cutting of current collectors, such as pure copper and aluminum. A 3D self-consistent mathematical model for the laser cutting, including fluid flow, heat transfer, recoil pressure, multiple reflections, capillary and thermo-capillary forces, and phase changes, is presented and solved numerically. Simulation results for the laser cutting are analyzed in terms of penetration time, depth, width, and absorptivity, based on these selected laser parameters. In addition, melt pool flow, melt pool geometry and temperature distribution are investigated.
Laser cutting of nickel-based superalloy sheets, having wide applications in aircraft and rocket industries, is important from the quality of cut point of view. Keeping this in view, a hybrid ...approach of Taguchi method (TM) and principal component analysis (PCA) has been applied for multi-objective optimization (MOO) of pulsed Nd:YAG laser beam cutting (LBC) of nickel-based superalloy (SUPERNI 718) sheet to achieve better cut qualities within existing resources. The three-quality characteristics kerf width, kerf deviation (along the length of cut), and kerf taper have been considered for simultaneous optimization. The input parameters considered are assist gas pressure, pulse width, pulse frequency, and cutting speed. Initially, single-objective optimization has been performed using TM and then the signal-to-noise (S/N) ratios obtained from TM have been further used in PCA for multi-objective optimization. The results of MOO include the prediction of optimum input parameter level and their relative significance on multiple quality characteristics (MQC). The responses at predicted optimum parameter level are in good agreement with the results of confirmation experiments conducted for verification tests.
Laser circular cutting of Inconel 803 alloy is carried out. Temperature and stress fields are predicted in the cutting section using ABAQUS finite element code mimicking the experimental conditions. ...To examine the influence of the hole diameter size on the thermal stress field developed in the cutting section, 2 mm and 10 mm hole diameters are considered in the experiments and analysis. Temperature predictions are validated through the thermocouple data. Morphological and elemental changes in the cutting section are examined incorporating the analytical tools. It is found that laser cut holes are free from large size asperities such as cracks and excessive sideways burnings. However, few small dross attachments are observed at the kerf exit for the small diameter (2 mm) hole. The maximum temperature is higher for small diameter hole than that of the large diameter hole (10 mm) prior to cutting ceases, which is attributed to heat transfer rates from kerf site to its neighborhood. von Mises stress remains low in the region where temperature remains high in the cooling period. This is associated with the elastic modulus of the substrate material, which reduces with increasing temperature. von Mises stress becomes almost same for small and large diameter holes after the cooling period ends and it is in the order of 0.45 GPa.
Compliant mechanism transfers motion or force using the elastic deflection of flexures or the whole mechanism (distributed). Pantograph is a widely proven mechanism which can imitate motion. The ...compliant pantograph models proposed by earlier researcher are limited to use of all circular flexure hinges; with some reporting geometric amplification (GA) around 2. Thus the present research work is an attempt towards using different combinations of flexures viz. circular, elliptical and parabolic deployed (for proposed six models), while developing the compliant pantograph (CP) in order to improve the GA. Also the effect of material Stainless Steel (SS) and Mild Steel (MS) on the performance of CP is presented. The finite element analysis is undertaken and output displacement is estimated for pre-decided range of input motion The maximum GA achieved for one of the combinations (combination no. 4) using SS is 2.57 wherein the flexures considered consist of two Elliptical and four circular flexures. Depending on desirable output range any of the above models can be used in micro stages/slides and many more precision applications.
Efficiently cutting smaller two-dimensional parts from a larger surface area is a recurring challenge in many manufacturing environments. This point falls under the cut-and-pack (C&P) problems. This ...study specifically focused on a specialization of the cut path determination (CPD) known as the laser cutting path planning (LCPP) problem. The LCPP aims to determine a sequence of cutting and sliding movements for the head that minimizes the parts’ separation time. It is important to note that both cutting and glide speeds (moving the head without cutting) can vary depending on the equipment, despite their importance in real-world scenarios. This study investigates an adaptive biased random-key genetic algorithm (ABRKGA) and a heuristic to create improved individuals applied to LCPP. Our focus is on dealing with more meaningful instances that resemble real-world requirements. The experiments in this article used parameter values for typical laser cutting machines to assess the feasibility of the proposed methods compared to an existing strategy. The results demonstrate that solutions based on metaheuristics are competitive and that the inclusion of heuristics in the creation of the initial population benefits the execution of the evolutionary strategy in the treatment of practical problems, achieving better performance in terms of the quality of solutions and computational time.
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