Fachbereich Maschinenbau und Mechatronik
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Improving the Mechanical Strength of Dental Applications and Lattice Structures SLM Processed
(2020)
To manufacture custom medical parts or scaffolds with reduced defects and high mechanical characteristics, new research on optimizing the selective laser melting (SLM) parameters are needed. In this work, a biocompatible powder, 316L stainless steel, is characterized to understand the particle size, distribution, shape and flowability. Examination revealed that the 316L particles are smooth, nearly spherical, their mean diameter is 39.09 μm and just 10% of them hold a diameter less than 21.18 μm. SLM parameters under consideration include laser power up to 200 W, 250–1500 mm/s scanning speed, 80 μm hatch spacing, 35 μm layer thickness and a preheated platform. The effect of these on processability is evaluated. More than 100 samples are SLM-manufactured with different process parameters. The tensile results show that is possible to raise the ultimate tensile strength up to 840 MPa, adapting the SLM parameters for a stable processability, avoiding the technological defects caused by residual stress. Correlating with other recent studies on SLM technology, the tensile strength is 20% improved. To validate the SLM parameters and conditions established, complex bioengineering applications such as dental bridges and macro-porous grafts are SLM-processed, demonstrating the potential to manufacture medical products with increased mechanical resistance made of 316L.
Tribological performance of biodegradable lubricants under different surface roughness of tools
(2019)
The fourth industrial revolution introduces disruptive technologies to production environments. One of these technologies are multi-agent systems (MASs), where agents virtualize machines. However, the agent's actual performances in production environments can hardly be estimated as most research has been focusing on isolated projects and specific scenarios. We address this gap by implementing a highly connected and configurable reference model with quantifiable key performance indicators (KPIs) for production scheduling and routing in single-piece workflows. Furthermore, we propose an algorithm to optimize the search of extrema in highly connected distributed systems. The benefits, limits, and drawbacks of MASs and their performances are evaluated extensively by event-based simulations against the introduced model, which acts as a benchmark. Even though the performance of the proposed MAS is, on average, slightly lower than the reference system, the increased flexibility allows it to find new solutions and deliver improved factory-planning outcomes. Our MAS shows an emerging behavior by using flexible production techniques to correct errors and compensate for bottlenecks. This increased flexibility offers substantial improvement potential. The general model in this paper allows the transfer of the results to estimate real systems or other models.
Chromatography is the workhorse of biopharmaceutical downstream processing because it can selectively enrich a target product while removing impurities from complex feed streams. This is achieved by exploiting differences in molecular properties, such as size, charge and hydrophobicity (alone or in different combinations). Accordingly, many parameters must be tested during process development in order to maximize product purity and recovery, including resin and ligand types, conductivity, pH, gradient profiles, and the sequence of separation operations. The number of possible experimental conditions quickly becomes unmanageable. Although the range of suitable conditions can be narrowed based on experience, the time and cost of the work remain high even when using high-throughput laboratory automation. In contrast, chromatography modeling using inexpensive, parallelized computer hardware can provide expert knowledge, predicting conditions that achieve high purity and efficient recovery. The prediction of suitable conditions in silico reduces the number of empirical tests required and provides in-depth process understanding, which is recommended by regulatory authorities. In this article, we discuss the benefits and specific challenges of chromatography modeling. We describe the experimental characterization of chromatography devices and settings prior to modeling, such as the determination of column porosity. We also consider the challenges that must be overcome when models are set up and calibrated, including the cross-validation and verification of data-driven and hybrid (combined data-driven and mechanistic) models. This review will therefore support researchers intending to establish a chromatography modeling workflow in their laboratory.
We prove characterizations of the existence of perfect ƒ-matchings in uniform mengerian and perfect hypergraphs. Moreover, we investigate the ƒ-factor problem in balanced hypergraphs. For uniform balanced hypergraphs we prove two existence theorems with purely combinatorial arguments, whereas for non-uniform balanced hypergraphs we show that the ƒ-factor problem is NP-hard.
Der Konstruktionsbereich ist zu einem neuen Schwerpunkt der allgemeinen Rationalisierungsbemühungen geworden. Zunehmend führt man organisatorische Hilfsmittel, technische Hilfsmittel (EDVA) und neue Konstruktionsmethoden in der Konstruktion ein. Der vorliegende Beitrag analysiert zunächst die Ursachen dieser Entwicklung und zeigt im weiteren einige heute bereits eingesetzte Hilfsmittel an Hand von Beispielen auf und diskutiert die Anwendungsmöglichkeiten.
Der Konstruktionsbereich ist zu einem neuen Schwerpunkt der allgemeinen Rationalisierungsbemühungen geworden. Zunehmend führt man organisatorische Hilfsmittel, technische Hilfsmittel (EDVA) und neue Konstruktionsmethoden in der Konstruktion ein. Der vorliegende Beitrag analysiert zunächst die Ursachen dieser Entwicklung und zeigt im weiteren einige heute bereits eingesetzte Hilfsmittel an Hand von Beispielen auf und diskutiert die Anwendungsmöglichkeiten.
In den letzten Jahren hat der Einsatz von graphischen Datenverarbeitungsanlagen auf dem technischen, naturwissenschaftlichen und kommerziellen Sektor immer mehr an allgemeinem Interesse und Bedeutung gewonnen. Diese Entwicklung hat neue Aspekte und Probleme in bezug auf Anwendungsmöglichkeiten, Programmierung, Datenstrukturen sowie der Hard- und Software dieser Anlagen hervorgerufen. Zur Zeit werden von verschiedenen Institutionen die Einsatzmöglichkeiten graphischer Datenverarbeitungsanlagen in den Funktionsbereichen Konstruktion und Arbeitsvorbereitung untersucht. Der folgende Beitrag zeigt eine kurze Übersicht über die verschiedenen programmiertechnischen Probleme sowie eine Auswahl von Programmbeispielen, die am Laboratorium für Werkzeugmaschinen und Betriebslehre der RWTH Aachen entwickelt wurden. Bei den Bildschirmsystemen wird zwischen zwei Arten unterschieden. Aktive Bildschirmeinheiten besitzen als äußeres Merkmal einen Lichtstift und eine Funktionstastatur zur Programmverzweigung. Passive Bildschirmeinheiten lassen demgegenüber einen Eingriff in das Programm in der oben aufgeführten Form nicht zu. Zwischen diesen extremen Formen gibt es noch eine Reihe Mischformen. Die in Aachen zur Verfügung stehende Anlage arbeitet aktiv und wird im nachfolgenden Kapitel näher beschrieben.
Die technischen und wirtschaftlichen Anforderungen, die heutzutage an moderne Maschinen, Geräte und Apparate gestellt werden, steigen ständig. Immer häufiger sehen sich die Konstrukteure gezwungen, geforderte Funktionen mit Hilfe zugekaufter Normeinzelteile, Bauelemente und Funktionsgruppen zu erfüllen. Bei dieser Entwicklung vergrößert sich die Zahl der von den Spezialherstellern angebotenen Zukaufteile überproportional, in gleichem Maße geht dem Anwender die Übersicht über das Zukaufteilespektrum verloren. Zunächst wird in diesem Bericht diese Entwicklung anhand einer im allgemeinen Maschinenbau durchgeführten Befragung aufgezeigt. Anschließend soll darauf aufbauend ein Ordnungssystem vorgestellt werden, welches jedem Unternehmen wieder eine Übersicht über das am Markt angebotene Zukaufteilespektrum ermöglicht.
Untersuchungen zum thermodynamischen Verhalten des Sauerstoffs in Kupfer-Wismut-Schmelzen bei 1200°C
(1982)
Feinbleche schweißen : die Temperaturverteilung in dünnen Stahlblechplatten beim Lichtbogenschweißen
(1971)
This paper aims to evaluate the formability of tailor welded blanks of dual phase (DP600)/transformation induced plasticity (TRIP700) steel sheets. In this work, bead on plate butt joints of 2·5 mm DP600 and 1·2 mm TRIP700 steel sheets were performed using CO2 laser beam welding. Microhardness measurements and transverse tensile testing were carried out to characterise the welds. The formability of base metals and welds were investigated by standard Erichsen test. In a perpendicular tensile test to the weld line, all specimens were fractured at the TRIP base metal, and the strengths were somewhat higher than those of base metal. There was a significant reduction in formability caused by welding of the DP600/TRIP700 steel sheets, and the formability increased with increasing welding speed.
Thermohydrodynamic analysis of thrust-bearing with circular pads running on bubbly oil (BTHD-theory)
(1985)
Traditional vulcanization mold manufacturing is complex, costly, and under pressure due to shorter product lifecycles and diverse variations. Additive manufacturing using Fused Filament Fabrication and high-performance polymers like PEEK offer a promising future in this industry. This study assesses the compressive strength of various infill structures (honeycomb, grid, triangle, cubic, and gyroid) when considering two distinct build directions (Z, XY) to enhance PEEK’s economic and resource efficiency in rapid tooling. A comparison with PETG samples shows the behavior of the infill strategies. Additionally, a proof of concept illustrates the application of a PEEK mold in vulcanization. A peak compressive strength of 135.6 MPa was attained in specimens that were 100% solid and subjected to thermal post-treatment. This corresponds to a 20% strength improvement in the Z direction. In terms of time and mechanical properties, the anisotropic grid and isotropic cubic infill have emerged for use in rapid tooling. Furthermore, the study highlights that reducing the layer thickness from 0.15 mm to 0.1 mm can result in a 15% strength increase. The study unveils the successful utilization of a room-temperature FFF-printed PEEK mold in vulcanization injection molding. The parameters and infill strategies identified in this research enable the resource-efficient FFF printing of PEEK without compromising its strength properties. Using PEEK in rapid tooling allows a cost reduction of up to 70% in tool production.
In times of short product life cycles, additive manufacturing and rapid tooling are important methods to make tool development and manufacturing more efficient. High-performance polymers are the key to mold production for prototypes and small series. However, the high temperatures during vulcanization injection molding cause thermal aging and can impair service life. The extent to which the thermal stress over the entire process chain stresses the material and whether it leads to irreversible material aging is evaluated. To this end, a mold made of PEEK is fabricated using fused filament fabrication and examined for its potential application. The mold is heated to 200 ◦C, filled with rubber, and cured. A differential scanning calorimetry analysis of each process step illustrates the crystallization behavior and first indicates the material resistance. It shows distinct cold crystallization regions at a build chamber temperature of 90 ◦C. At an ambient temperature above Tg, crystallization of 30% is achieved, and cold crystallization no longer occurs. Additional tensile tests show a decrease in tensile strength after ten days of thermal aging. The steady decrease in recrystallization temperature indicates degradation of the additives. However, the tensile tests reveal steady embrittlement of the material due to increasing crosslinking.
Establishing high-performance polymers in additive manufacturing opens up new industrial applications. Polyetheretherketone (PEEK) was initially used in aerospace but is now widely applied in automotive, electronics, and medical industries. This study focuses on developing applications using PEEK and Fused Filament Fabrication for cost-efficient vulcanization injection mold production. A proof of concept confirms PEEK’s suitability for AM mold making, withstanding vulcanization conditions. Printing PEEK above its glass transition temperature of 145 °C is preferable due to its narrow process window. A new process strategy at room temperature is discussed, with micrographs showing improved inter-layer bonding at 410°C nozzle temperature and 0.1 mm layer thickness. Minimizing the layer thickness from 0.15 mm to 0.1 mm improves tensile strength by 16%.