Automobil- und Maschinenbau
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Hybrid manufacturing of titanium Ti-6Al-4V combining laser metal deposition and cryogenic milling
(2020)
Hybrid manufacturing, which, e.g., combines additive manufacturing with conventional machining processes, can be a way of overcoming limitations currently encountered in additive manufacturing. Cryogenic milling might be a viable option for hard-to-cut materials, as it leaves a contamination-free surface and can increase surface quality and tool life compared to conventional cooling concepts. In this study, the influence of cryogenic milling with carbon dioxide on titanium Ti-6Al-4V specimens manufactured with laser metal deposition (LMD) was investigated regarding tool wear and surface integrity in comparison to dry machining and machining with cooling lubricants. Moreover, additional layers of material were deposited on top of conventionally and cryogenically machined surfaces by means of LMD. The interface zone was then examined for defects. The milling process was closely monitored by means of thermal and high-speed imaging. Optical and tactile surface analysis provided evidence that lower roughness values and improved surface qualities could be obtained with cryogenic machining in comparison to dry machining. Moreover, significantly less tool wear was observed when a cryogenic cooling medium was applied. Although the utilization of conventional cooling lubricants resulted in satisfying surface qualities, substantial residual contamination on the milled surface was detected by means of fluorescence analysis. These contaminants are suspected to cause defects when the next layer of material is deposited. This is supported by the fact that pores were found in the weld bead applied on top of the milled specimens by means of LMD. Conversely, cryogenic machining resulted in very clean surfaces due to the residue-free evaporation of the coolant. Hence, a good metallurgical bonding between the weld bead and the milled substrate could be achieved. The results indicate the great potential of cryogenic milling in hybrid manufacturing, especially in terms of intermediate machining, as it provides residue-free surfaces for subsequent material deposition without an additional cleaning step and can significantly prolongate tool life.
Dissipation energy based parameter identification of anisotropic linear viscoelastic composites
(2020)
The current work presents a relaxation analysis based procedure to identify effective material parameters of the multiaxial generalized Maxwell model (GMM) by a numerical homogenization of the microscopic dissipation energy density for anisotropic linear viscoelastic composites. The employed GMM enables the derivation of a thermodynamically consistent constitutive law and a function of the dissipation energy density for direction‐dependent viscoelastic materials. The identity of this energy function to the microstructure's homogenized dissipation energy density is utilized for the identification of effective relaxation times. Furthermore, the identified relaxation times enable a simple determination of the remaining stiffness parameters. Finally, the presented procedure is demonstrated and evaluated for a randomly endless fibre‐reinforced plastic with a polymer matrix exhibiting a significant viscoelastic behaviour.
Hypotrochoidal profile contours have been produced in industrial applications in recent years using two-spindle processes, and they are considered effective high-quality solutions for form-fit shaft and hub connections. This study mainly concerns analytical approaches to determine the stresses and deformations in hypotrochoidal profile shafts due to pure bending loads. The formulation was developed according to bending principles using the mathematical theory of elasticity and conformal mappings. The loading was further used to investigate the rotating bending behaviour. The stress factors for the classical calculation of maximum bending stresses were also determined for all those profiles presented and compiled in the German standard DIN3689-1 for practical applications. The results were also compared with the corresponding numerical and experimental results, and very good agreement was observed. Additionally, based on previous work, the stress factor was determined for the case of torsional loading to calculate the maximum torsional stresses in the standardised profiles, and the results are listed in a table. This study contributes to the further refinement of the current DIN3689 standard.
Beim Presshärten von Mangan-Bor-Stählen handelt es sich um eine Verfahrenskombination aus Umformen und martensitischen Härten, welche sich in den vergangenen Jahren als wegweisende Leichtbaustrategie in der Automobilindustrie etabliert hat. Hierfür werden Stahlplatinen in einem Rollenherdofen austenitisiert und anschließend in einem wassergekühlten Umformwerkzeug, umgeformt und abgekühlt. Durch ungünstige Überlagerungen thermischer und mechanischer Spannungen sowie nicht konturnaher Kühlkanalgeometrien, kommt es regelmäßig zum Produktionsstillstand aufgrund von Rissen im Werkzeug. Neben einem kostenintensiven Stillstand der Anlage geht damit ein aufwendiger Instandhaltungsprozess einher.
Um die Stillstandszeiten sowie den Instandhaltungsaufwand zukünftig dezimieren zu können, wird die Verwendung einer neuen Fertigungstechnologie untersuch und beleuchtet. Hierfür wird ein Teil des Werkzeugs (auch Umformeinsatz genannt), durch Elektronenstahlschmelzen aus einem pulverförmigen Werkstoff, additiv gefertigt und dessen Einsatz unter Serienbedingungen erforscht. Dabei werden die Einhaltung der vom Kunden geforderten Qualitätsmerkmale, die Standzeit sowie die Anwendung der im Unternehmen etablierten Instandhaltungsmaßnahmen am additiv gefertigten Umformeinsatz näher untersucht. Zur Einschätzung der Wirtschaftlichkeit erfolgt ein Vergleich der konventionell und additiv gefertigten Version hinsichtlich der eben genannten Parameter.
Die vorliegende Masterarbeit befasst sich mit dem Aufbau, der Funktionsweise und der Optimierung eines bestehenden Traceability-Systems im Automobilbereich. Dazu wird zu Beginn der Begriff Traceability erläutert und die Grundlagen der Rückverfolgbarkeit dargelegt. Danach folgt eine kurze Beschreibung zum Aufbau des aktuellen Traceability-Systems im betrachteten Unternehmen.
Im weiteren Verlauf werden die Anforderungen an die Rückverfolgbarkeit der im Unternehmen gefertigten Produkte zusammengestellt. Dabei werden behördliche, branchenspezifische und interne Vorgaben berücksichtigt.
An einem ausgewählten Fertigungsprozess erfolgt anschließend eine kritische Ist-Zustand-Analyse. Aus der Analyse gehen Optimierungspotenziale hervor, mit denen sich Lücken im Traceability-System schließen lassen.
Ausgehend von der Ist-Zustand-Analyse werden Konzepte entwickelt, die unter Berücksichtigung der Rahmenbedingungen eine nachhaltige Verbesserung des Traceability-Systems zur Folge haben sollen. Die Konzepte zielen auf eine Optimierung der Produkt-Traceability ab.
Zum Schluss werden die entwickelten Konzepte einer kritischen Betrachtung unterzogen und daraus Empfehlungen für deren Umsetzung abgeleitet.
This paper presents an analytical method for determining the bending stresses and deformations in prismatic, noncircular profile shafts with trochoidal cross sections. The so-called higher trochoids can be used as form-fit shaft-hub connections. Hybrid (mixed) higher trochoids (M-profiles) were developed for the special application as a profile contour for the form-fit shaft and hub connections in an earlier work by the author. M-profiles combine the advantages of the two standardised polygonal and spline contours, which are used as shaft-hub connections for the transmission of high torques. In this study, the geometric and mechanical properties of the higher hybrid trochoids were investigated using complex functions to simplify the calculations. The pure bending stress and shaft deflection were determined for M-profiles using bending theory based on the theory of mathematical elasticity. The loading cases consisted of static and rotating bends. Analytical, numerical, and experimental results agreed well. The calculation formulas developed in this work enable reliable and low-cost dimensioning with regard to the stresses and elastic deformations of profile shafts subjected to bending loads.
Nichteisenmetalle
(2022)
A novel approach to consider triaxial tensile stresses within the framework of a failure criterion
(2022)
For use in micromechanical simulations of continuous fiber reinforced polymers, a more general form of the paraboloid failure criterion by Stassi‐D'Alia for matrix failure was developed with explicit consideration of the hydrostatic tension strength. Regarding polymers, limits for hydrostatic tensile strength based on isotropic linear elasticity could be derived. The comparison of the newly developed extended paraboloid criterion with experimental data for yielding as well as for material separation (fracture) shows good agreement.
The atomizing gas dynamics and the applied process energy have a significant influence on the produced particles. The melting process of the two wires can be influenced by current modulation. As for arc welding processes, more and more electronic and software-controlled machines are being used for arc spraying and will have replaced conventional power sources in the future. Due to the highly dynamic, fast regulating computing technology in the latest energy source, technology arcs can be operated with different current forms and types. The modern machines allow process-stable, reproducible variation of the particles and heat input into the substrate. Constant and pulsed current can be used as current forms. Usable current types are direct current (DC) and alternating current (AC). The electrical parameters must be analyzed to evaluate the process behavior. The consumable used is a wire-shaped iron-based alloy with a diameter of 1.6 mm. Relevant process parameters such as basic current Iground, pulse current Ipulse, pulse duration tpulse, impulse frequency fpulse, and alternating current frequency, fAC, are varied and recorded using appropriate measurement technology. The aim is to change the process performance and thereby the particle formation in a broad band. High-speed images are used to observe the arc and the deposition process. In addition, particle sizes are determined.
Traffic calming is introduced to minimise the negative results of motor vehicle use, for example, low safety level or quality of life, high noise and pollution. It can be implemented through the introduction of road infrastructure reducing the velocity and the traffic volume. In this paper, we studied how traffic-calming influences the traffic assignment. For the research, a traffic-calming measure of speed cushions on the Stachiewicza street in Krakow was taken. A method of extracting trajectories from aerial footage was shown, and it was used to build a model. For a given example, through driving characteristics research and microscopic modelling, volume–delay BPR functions were estimated—for a street with and without traffic calming. Later, a toy network of two roads of the same length, connecting the same origin and destination, was simulated using an equilibrium traffic assignment method. Simulations were conducted both with the use of PTV Vissim and Visum software and through individual calculations. According to the results of this paper, there was a difference in traffic volume according to the equilibrium traffic assignment in the aforementioned toy network as a function of total network traffic volume.
Lewis–Mogridge Points: A Nonarbitrary Method to Include Induced Traffic in Cost-Benefit Analyses
(2020)
We propose a new method to estimate benefits of road network improvements, which allows to include the induced demand without arbitrary assumptions. Instead of estimating induced demand (which is nontrivial and hardly possible in practice), we search for demand induction where initial benefits are mitigated to zero. Such approach allows to formulate a dual measure of benefit, covering both the potential benefits and the likelihood of consuming them by the induced traffic. We first estimate benefits of road network improvement assuming that traffic demand is fixed. Consequently, we find demand model configurations at which the benefits of the new investment become null, i.e., all the initial benefits are consumed by the traffic demand growth. We call such states of induced demand the Lewis–Mogridge points of the analysed improvement. We select the most probable of such points and use it to calculate the proposed novel indicator μ, for which the initial benefits (obtained under a fixed-demand assumption) are multiplied with a demand increase rate needed to consume them. We believe that such measure allows to include the critical phenomena of induced traffic and, at the same time, to overcome problems associated with reliable estimation of induced demand. As we illustrate with the case of two alternative road improvement schemes in Kraków, Poland, the proposed method allows to estimate maximal threshold of induced traffic and to select scenario more resilient to induced traffic.
Effect of acoustic excitation on fiber-reinforced polypropylene and the influence on melt viscosity
(2021)
The paper describes a novel technological approach to influencing the rheological properties of thermoplastic materials exposed to acoustic energy. The flow behavior of polypropylene with different mass percentages of glass fibers is investigated in a parallel plate rheometer under high-frequency longitudinal excitation. The influence of oscillation frequency on the melt viscosity is explained by means of shear thinning criteria. The dependence of the oscillation shape using sinusoidal excitation on shear thinning as a function of different fiber reinforcement percentages is also investigated. A phenomenological view describes the mutually influencing parameters with regard to different material compositions and different excitation frequencies over the time course of the rheometric measurement. Interacting relationships are analyzed and discussed and the potential of the actuator system to influence the plastic melt is worked out. Based on this, a technological approach follows which describes the transfer of an oscillating mold surface to plastics processing methods, which, especially in the case of energy-intensive injection molding technology, leads to the expectation of possible resource efficiency in energy and material.