Maschinenbau, Umwelt- und Gebäudetechnik
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This study examines the effect of elevated printing speeds (100–600 mm/s) on the dimensional accuracy and tensile strength of PLA components fabricated via fused deposition modeling (FDM). To isolate the influence of printing speed, all other parameters were kept constant, and two filament variants—natural (unpigmented) and black PLA—were analyzed. ISO 527-2 type 1A specimens were produced and tested for dimensional deviations and ultimate tensile strength (UTS). The results indicate that printing speed has a marked impact on both geometric precision and mechanical performance. The optimal speed of 300 mm/s provided the best compromise between dimensional accuracy and tensile strength for both filaments. At speeds below 300 mm/s, under-extrusion caused weak layer bonding and air gaps, while speeds above 300 mm/s led to over-extrusion and structural defects due to thermal stress and rapid cooling. Black PLA yielded better dimensional accuracy at higher speeds, with cross-sectional deviations between 2.76% and 5.33%, while natural PLA showed larger deviations of up to 8.63%. However, natural PLA exhibited superior tensile strength, reaching up to 46.59 MPa, with black PLA showing up to 13.16% lower UTS values. The findings emphasize the importance of speed tuning and material selection for achieving high-quality, reliable, and efficient FDM prints.
Many components in industry are subjected to high loads during operation and therefore often do not reach their intended service life. Conventional steels frequently do not provide sufficient protection against wear and corrosion. One solution is to coat these components using methods like thermal spraying to apply cermet coatings such as Cr3C2-NiCr or WC-Co-Cr. In light of increasingly strict environmental regulations, more eco-friendly alternatives are needed, especially ones that use little or no Cr, Ni, Co, or W. Another alternative is the recycling of powder materials, which is the focus of this research project. This study investigated whether filter dust from an HVOF system could be used to develop a new coating suitable for use in applications requiring resistance to wear and corrosion. This is challenging as the filter dusts have heterogeneous compositions and irregular particle sizes. Nevertheless, this recycled material, referred to as “Green Cermets” (GCs), offers previously untapped potential that may also be of ecological interest. An established WC-Co-Cr coating served as a reference. In addition to friction wear and corrosion resistance, the study also examined particle size distribution, hardness, microstructure, and susceptibility to crack formation at the interface and inside the coating. Even though the results revealed a diminished performance of the GC coatings relative to the conventional WC-CoCr, they may still be applicable in various industrial applications.
High-entropy alloys are known for their promising mechanical properties, wear and corrosion resistance, which are maintained across a wide range of temperatures. In this study, a CoCrFeNiCu-based high-entropy alloy, distinguished from conventional CoCrFeNi systems by the addition of Cu, which is known to enhance toughness and wear resistance, was investigated to better understand the effects of compositional modification on processability and performance. The influence of key process parameters, specifically laser power and scan speed, on the processability of CoCrFeNiCu-based high-entropy alloys produced by laser powder bed fusion additive manufacturing was investigated, with a focus of low laser power, which is critical for minimizing defects and improving the resulting microstructure and mechanical performance. The printed sample density gradually increases with higher volumetric energy density, achieving densities exceeding 99.0%. However, at higher energy densities, the samples exhibit susceptibility to hot cracking, an issue that cannot be mitigated by adjusting the process parameters. Mechanical properties under optimized parameters were further evaluated using Charpy impact and (in situ) tensile tests. These evaluations were supplemented by in situ tensile experiments conducted within a scanning electron microscope to gain insights into the behavior of defects, such as hot cracks, during tensile testing. Despite the sensitivity to hot cracking, the samples exhibited a respectable ultimate tensile strength of 662 MPa, comparable to fine-grained steels like S500MC (070XLK). These findings underscore the potential of CoCrFeNiCu-based high-entropy alloys for advanced applications. However, they also highlight the necessity for developing strategies to ensure stable and reliable processing methods that can mitigate the susceptibility to hot cracking.
Abstract
This study signifies the development and characterization of a composite material with a metallic matrix of aluminum reinforced with a steel mesh, utilizing centrifugal casting technology. An evaluation was conducted to ascertain the influence of the formulation process and the presence of the insert on the mechanical behavior with regard to tensile strength. The aluminum matrix was obtained from commercial and scrap alloys, elaborated by advanced methods of degassing and chemical modification. Meanwhile, the steel mesh reinforcement was cleaned, copper plated, and preheated to optimize wetting and, consequently, adhesion. The structural characterization was performed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy analyses (EDX), which highlighted a well-defined interface and uniform copper distribution. The composite was produced by means of horizontal-axis centrifugal casting in a fiberglass mold, followed by cold rolling to obtain flat specimens. A total of eight tensile specimens were examined, with measured ultimate tensile strengths ranging from 78.5 to 119.8 (MPa). A thorough examination of the fractured specimens revealed a brittle fracture mechanism, devoid of substantial plastic deformation. The onset of failures was frequently observed at the interface between the aluminum matrix and the steel mesh. The use of SEM and EDX investigations led to the confirmation of the uniformity of the copper coating and the absence of significant porosity or interfacial defects. A bimodal distribution of tensile strength values was observed, a phenomenon that is likely attributable to variations in mesh positioning and local differences in solidification. A correlation was established between the experimental results and an analytical polynomial model, thereby confirming a reasonable fit. In sum, the present study provides a substantial foundation for the development of metal matrix composites with enhanced performance, specifically designed for challenging structural applications. This method also demonstrates potential for recycling aluminum scrap into high-performance composites with controlled microstructure and mechanical integrity.
Die Optimierung mechanischer Bauteile nimmt in der Entwicklung technischer Produkte einen immer größer werdenden Stellenwert ein. Ziel dieses Prozesses ist herauszufinden, welche Form und Topologie eine Struktur besitzen muss, um die an sie gestellte Konstruktionsaufgabe besonders gut zu erfüllen. Damit die optimierten Strukturen auch herstellbar sind, ist das Bestreben aktueller Forschung, Informationen über die Fertigungsprozesse direkt in die entsprechenden Optimierungsverfahren in Form von Fertigungsrestriktionen zu integrieren. In dieser Arbeit wird eine Methodik zur Integration von Fertigungsrestriktionen bei 3D-Fräsverfahren in die Topologieoptimierung mit der Level-Set-Methode entwickelt. Berücksichtigt werden dabei die Gewährleistung der Werkzeugzugänglichkeit aller Bearbeitungspunkte sowie die Einhaltung einer Mindestwandstärke. Die Methodik basiert auf der Induktion eines Strukturwachstums in Bereichen, die entweder unzugänglich oder zu dünn sind. Um diese Bereiche zu identifizieren, wird ein Verfahren entwickelt, bei dem die Level-Set-Funktion entlang der Außenkonturen realistischer Werkzeuggeometrien interpoliert wird. Zur Induktion des Strukturwachstums wird regelmäßig ein Potential definiert. Dieses besitzt innerhalb der Struktur größere Werte als außerhalb und ändert sich normal zum Strukturrand linear. Eine Minimierung des auf dem Strukturrand vorliegenden Potentials wird in ein Strukturwachstum überführt. Dazu werden die Sensitivitäten des Potentials bezüglich Verschiebungen des Strukturrandes ermittelt und mit den Entwicklungsgeschwindigkeiten der Level-Set-Funktion gekoppelt. Dadurch werden beide Fertigungsrestriktionen in eine gemeinsame mathematische Restriktion überführt und schließlich explizit in das Optimierungsproblem integriert.
Abstract
Considering the significant health risks posed by hard chrome plating during its application, thermally sprayed Cr3C2-NiCr cermet coatings represent a suitable alternative. Incorporating hexagonal boron nitride (hBN) as a dry lubricant into the feedstock powder can further enhance wear resistance and thermal conductivity, crucial for preventing premature failure caused by inadequate lubrication. In this study, the mass fraction of hBN was varied between 0 and 15 wt.% to assess its influence on the tribological performance of the coatings using pin-on-disk tests. The coating’s hardness was measured via the Vickers method, and its cracking tendency at the coating/substrate interface was evaluated. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to analyze the microstructure and phase composition, while thermal diffusivity was determined using the laser flash method. The findings revealed that the inclusion of hBN, at concentrations of up to 10 wt.%, leads to an improvement in thermal diffusivity and a reduction in the coefficient of friction. However, exceeding this threshold leads to a decrease in hardness and increased crack formation tendency, highlighting the trade-off between frictional and mechanical properties.
The feed-in of electricity from renewable energies, such as wind or solar power, fluctuates based on weather conditions. This unpredictability due to volatile feed-in can lead to sudden changes in energy generation so that solutions ensuring grid stability need to be implemented. The cooling sector offers the opportunity to create flexibilities for such balancing, with this study focusing on the thermal flexibilities that can be provided by cooling applications. Various cooling-demand profiles are investigated with respect to their load profile and their impact on flexibility is analysed. In addition to the cooling demand, scenarios of different storage dimensions are considered. As a result, it shows that an increasing base-load level and increasing operating-load duration have a negative effect on flexibility, while an increasing full-load duration is beneficial for flexibility. Storage size also has a strong impact as higher storage capacity and storage performance indicate higher flexibility, whereas above a certain size they only provide little added value.
Integrity Assessment of Electron-Beam-Welded Joints of Additively Manufactured AlSi10Mg Components
(2023)
Abstract
Laser-based powder bed fusion of metals (PBF-LB/M) is found to be a promising
processing method for the fabrication of components with no limits of complexity
by adding layers upon layers of material. However, drawbacks such as pro-
ductivity and dimension limitations adversely affect the employment of com-
ponents processed by additive manufacturing (AM) in envisaged applications.
This brings welding and joining techniques into play to integrate AM metal parts
into larger assemblies. In the present study, electron beam welding is used to join
the AlSi10Mg specimens, fabricated via two different manufacturing processes,
that is, PBF-LB/M and casting. The main focus is to study the quasistatic and
fatigue behavior of similar and dissimilar welded joints in different combinations,
namely AM–AM, AM–cast, and cast–cast, alongside thorough microstructure
analysis, to investigate the correlation between the microscopic and macroscopic
properties. Dissimilar welded joints demonstrate inferior material strength. This
fact can be attributed to the inherent coarse microstructure of the cast material.
Although similar welded joints of AM components suffer from high porosity in
the weld zone, they are characterized by a better fatigue life, which can be
attributed to the equiaxed eutectic microstructure in the welded area.
Abstract
In this work, we develop an approach for the level set based topology optimization of millable 3D structures. We focus on the 3-axis machining with realistic formed milling tools. The basis of the method lies in the identification of surface areas that cannot be reached by a given milling tool during optimization. For this purpose, we present an interpolation method that identifies these areas by an interpolation of the level set function along the outer contours of realistic milling tools, considering available machining directions. To minimize inaccessible surfaces, we define a potential field whose values decrease linearly into the outer normal direction of the structure. The inaccessible boundaries are pushed outward by minimizing their respective potential and therefore become accessible. Manufacturability is integrated into the optimization problem as an explicit constraint.

