FG Hybride Fertigung
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The Wire Arc Direct Energy Deposition (WA-DED) process is highly
regarded as part of additive manufacturing. Compared to other additive manufacturing
processes, it is characterized above all by its high deposition rate and low
system costs. Despite many years of experience in the build-up welding process,
WA-DED still holds a number of challenges in terms of process stability. This
article analyses the interactions in the WA-DED process. To this end, the process
was visualized and described with the help of Structured Analysis and Design
Technique (SADT). Building on this, a process Failure Mode and Effects Analysis
(FMEA) was presented to identify and priorities risks. Finally, the results of
the Taguchi tests were analyzed and visualized. The results illustrate the strong
interactions between the influencing factors. These have a material-specific effect
on the production results. Each new material composition therefore requires a
systematic analysis in order to determine quantitative correlations. In future, these
can be supported by machine learning approaches.
New technologies have enabled additive manufacturing to construct components layer by layer using 3D model data. Machinery requirements for this are minimal, entailing only a welding device for energy input and a guiding machine to shape the component. Though there are clear benefits to the process, such as the cost-effective technology and high deposition rates, the complex interactions involved must receive due consideration.
Die Dauerschwingfestigkeit ist eine wichtige sowie für die Auslegung von zyklisch belasteten Bauteilen in Umformmaschinen notwendige Materialkenngröße. Diese Kenngröße ist nicht nur material- sondern auch fertigungsprozessabhängig.
Aufgrund der rapiden Entwicklung von additiven Fertigungsanlagen und Werkstoffen mangelt es an hinreichenden Erfahrungswerten zu den Betriebseigenschaften von additiv gefertigten Bauteilen.
Daher ist es wichtig, die Eignung von additiv gefertigten Bauteilen für Umformmaschinen im Vorfeld technologisch und wissenschaftlich zu untersuchen. Die Ermittlung der Dauerschwingfestigkeit von additiv gefertigten Komponenten für Umformmaschinen liefert außerdem einen Mehrwert für die konstruktive Auslegung anderer AM-Bauteile mit einem vergleichbaren Belastungskollektiv und
ermöglicht eine Topologieoptimierung von Komponenten von Umformmaschinen.
Im Rahmen dieses Forschungsvorhabens wurde die Dauerschwingfestigkeit additiv gefertigter Bauteile in Abhängigkeit von der Gesamtheit der Herstellungsparameter eines WAAM-Prozesses sowie diverser Nachbehandlungsmethoden erfolgreich anhand des Fallbeispiels
Pleuel ermittelt.
Außerdem wurde die Anwendbarkeit von WAAM-Prozessen zur Herstellung von individuellen Anlagenbauteilen für den Bereich Umformmaschinen erfolgreich belegt. Mit den ermittelten Dauerschwingfestigkeitswerten konnte eine Grundlage zur Auslegung weiterer AM-Bauteile mit vergleichbaren Belastungskollektiv sowie Topologieoptimierung genannter Bauteile geschaffen werden.
Die Untersuchungen erfolgten an Laborproben geeigneter Geometrie in Bezug auf das Realbauteil und unter Gewährleistung der thermischen Übertragbarkeit auf Realbauteile. Abschließend ist mittels eines skalierten Demonstratorbauteils die Machbarkeit nachgewiesen worden.
Deformation-induced martensite has been observed in the incremental sheet forming of metastable austenitic stainless steels (MASS). The presence of martensite improves the characteristics of the springs. Martensite transformation usually occurs at low temperatures (<70 ℃). Depending on the tool speed, incremental forming of disk springs requires between 3 to 5 min. The forming time needs to be short to increase the process output in industrial settings. However, accelerating the process leads to high temperatures above the martensite transformation temperature that suppress martensite formation, necessitating temperature control during forming. It is suggested to enhance the martensite content of the blank by cooling during the forming operation. In this contribution, two-point incremental sheet forming is conducted to determine the influence of process temperature on the phase content of MASS disk springs. A temperature-dependent phase change material model that includes the strain rate effect is implemented in finite element (FE) simulations to predict the martensite content. FE simulations are performed to investigate the convection coefficients and cooling time leading to process temperatures below 70 ℃. The framework can be used to control and speed up the incremental forming of disk springs while maintaining a high martensite content.
The development of new materials or material systems is always accompanied by the development of processing technologies suitable for the material. The reduction of process steps, the saving of material and the optimization of material properties are aims of forming processes. The basis for this is the comprehensive characterisation of the thermos-physical and thermos-mechanical technologically relevant material behaviour, taking into account the real process conditions. In the present work, the material-specific process limits were determined by means of experimental simulation and used in the numerical simulation in order, on the one hand, to identify the forming steps for optimizing the manufacturing conditions and, on the other hand, to be able to set the final material properties. It was essential to homogenize the casting microstructure for the forming processes and to adjust it to globulitical grains by solution annealing. The previously limited forming behaviour of the cast AlSi9Mg alloy with 20 vol.-% SiC could be increased thus to forging-relevant plastic strains without occurring damages. Based on the comprehensive temperature-dependent material data, a one-step and resource-efficient manufacturing process for AMC materials by hot forming could be developed with the help of the FE software Simufact Forming and validated in reality under near-industrial conditions.
With a view of sustainability and the rising energy costs currently, manufacturing processes of metals are becoming increasingly focused on optimizing process parameters such as energy and time consumption. A conventional hot-forming process route currently involves casting an ingot, letting it cool down, and heating it up again for the hot-forming process (see Fig. 1a). In order to implement the combination of casting and forging, avoiding the reheating cycle and using less energy, by utilizing the casting heat (see Fig. 1b), a methodology was developed within the present work to quantify the influence of the resulting microstructure as a function of the cooling rate on the forming and recrystallization behavior (see Fig. 1c).
For this purpose, AISI 301 austenitic stainless-steel cast samples with different cast cooling rates were generated. An in-situ high-temperature microscope is used to determine the holding time and the heating rate. Dilatometer tests are performed to characterize the interaction between initial microstructure and the flow curves to verify the determination method (see Fig. 1d). The aim was to demonstrate whether the microstructure evolution and mechanical behavior is affected by the initial microstructure. The flow curves and the post-forming microstructure show a higher degree of recrystallization in fast-cooled microstructure than slow-cooled microstructure. Hence, it was found that the initial microstructure and the associated temperature history does have an impact on the mechanical properties.
Classic forming technologies can make a difference to a climate-neutral economy. This also applies to the production of innovative hydrogen coolers (recuperators). To improve the efficiency of hydrogen coolers, heat transfer and heat flux can be increased by tube structures made by pressing spherical elements on their surface. Hydrogen is passed through the tubes of the recuperators and the cooling medium flows across it (Figure 1a). The tube serves as an atmosphere separator. Structured tubes can increase the power den-sity with the same dimensions. Figure 1b shows a process for introducing the structure into the pipe using radially and symmetrically arranged tools. Sheet metal forming usually involves pressing with structural tools, bending into a tube, and longitudinally welding. However, producing small tube diameters in the range of one inch presents a technical challenge. The challenge considered in this paper is to develop a new structuring process while maintaining the structural integrity and wall thickness of the tubes. This study aims to determine the feasibility of a multi-stage vault structuring process for recuperator tubes us-ing heat-resistant semi-finished products.