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Additive Fertigungsverfahren zeichnen sich durch eine hohe erreichbare Komplexität der zu erzeugenden Geometrien, bei gleichzeitig kaum steigendem Fertigungsaufwand, aus. Dies wird durch den schichtweisen Aufbau additiver Fertigungsverfahren erreicht, bei dem die zu fertigende Geometrie zunächst in einzelne Bauteilquerschnitte aufgeteilt und anschließend durch Fügen dieser Querschnitte aufgebaut wird. Ein etabliertes additives Fertigungsverfahren ist das selektive Laserschmelzen, bei dem die zu erzeugende Geometrie durch Aufschmelzen von Metallpulver mittels eines Lasers in einem Pulverbett erzeugt wird. Die durch selektives Laserschmelzen generierten Oberflächen müssen zur Erzeugung von Funktionsflächen spanend endbearbeitet werden, wobei die charakteristische Anisotropie additiv erzeugter Werkstoffe berücksichtigt werden muss. Diese Arbeit beschäftigt sich mit den Wirkmechanismen additiv-subtraktiver Prozessketten bei der spanenden Bearbeitung von Edelstahl 1.4404, wobei zunächst beide Prozesskettenteile getrennt voneinander analysiert werden. Es werden unterschiedliche Wirkzusammenhänge der Prozessparameter der additiven Fertigung und Pulvereigenschaften auf den erzeugten Werkstoff identifizert. Weiter werden durch den Einsatz des Mikrofräsens als Bearbeitungsverfahren (Werkzeugdurchmesser < 50 µm) Wechselwirkungen zwischen anisotropem Werkstoff sowie Prozess- und Prozessergebnisgrößen der spanenden Bearbeitung besonders deutlich. Die Untersuchungen ergaben, dass prozesskettenübergreifende Wirkmechanismen zwischen additiven und subtraktiven Prozesskettenteilen beim selektiven Laserschmelzen und Mikrofräsen von Edelstahl 1.4404 bestehen.
Additive manufacturing (AM) enables the production of components with a high degree of individualization at constant manufacturing effort, which is why additive manufacturing is increasingly applied in industrial processes. However, additively produced surfaces do not meet the requirements for functional surfaces, which is why subsequent machining is mandatory for most of AM-workpieces. Further, the performance of many functional surfaces can be enhanced by microstructuring. The combination of both AM and subtractive processes is referred to as hybrid manufacturing. In this paper, the hybrid manufacturing of AISI 316L is investigated. The two AM technologies laser-based powder bed fusion (L-PBF) and high-speed laser directed energy deposition (HS L-DED) are used to produce workpieces which are subsequently machined by micro milling (tool diameter d = 100 µm). The machining results were evaluated based on tool wear, burr formation, process forces and the generated topography. Those indicated differences in the machinability of materials produced by L-PBF and HS L-DED which were attributed to different microstructural properties.
In selective laser melting (SLM) the variation of process parameters significantly impacts the resulting workpiece characteristics. In this study, AISI 316L was manufactured by SLM with varying laser power, layer thickness, and hatch spacing. Contrary to most studies, the input energy density was kept constant for all variations by adjusting the scanning speed. The varied parameters were evaluated at two different input energy densities. The investigations reveal that a constant energy density with varying laser parameters results into considerable differences of the workpieces’ roughness, density, and microhardness. The density and the microhardness of the manufactured components can be improved by selecting appropriate parameters of the laser power, the layer thickness, and the hatch spacing. For this reason, the input energy density alone is no indicator for the resulting workpiece characteristics, but rather the ratio of scanning speed, layer thickness, or hatch spacing to laser power. Furthermore, it was found that the microhardness of an additively manufactured material correlates with its relative density. In the parameter study presented in this paper, relative densities of the additively manufactured workpieces of up to 99.9% were achieved.
In the field of metal additive manufacturing (AM), one of the most used methods is selective laser melting (SLM)—building components layer by layer in a powder bed via laser. The process of SLM is defined by several parameters like laser power, laser scanning speed, hatch spacing, or layer thickness. The manufacturing of small components via AM is very difficult as it sets high demands on the powder to be used and on the SLM process in general. Hence, SLM with subsequent micromilling is a suitable method for the production of microstructured, additively manufactured components. One application for this kind of components is microstructured implants which are typically unique and therefore well suited for additive manufacturing. In order to enable the micromachining of additively manufactured materials, the influence of the special properties of the additive manufactured material on micromilling processes needs to be investigated. In this research, a detailed characterization of additive manufactured workpieces made of AISI 316L is shown. Further, the impact of the process parameters and the build-up direction defined during SLM on the workpiece properties is investigated. The resulting impact of the workpiece properties on micromilling is analyzed and rated on the basis of process forces, burr formation, surface roughness, and tool wear. Significant differences in the results of micromilling were found depending on the geometry of the melt paths generated during SLM.
Laser-based powder bed fusion (L-PBF) is a promising technology for the production of near net–shaped metallic components. The high surface roughness and the comparatively low-dimensional accuracy of such components, however, usually require a finishing by a subtractive process such as milling or grinding in order to meet the requirements of the application. Materials manufactured via L-PBF are characterized by a unique microstructure and anisotropic material properties. These specific properties could also affect the subtractive processes themselves. In this paper, the effect of L-PBF on the machinability of the aluminum alloy AlSi10Mg is explored when milling. The chips, the process forces, the surface morphology, the microhardness, and the burr formation are analyzed in dependence on the manufacturing parameter settings used for L-PBF and the direction of feed motion of the end mill relative to the build-up direction of the parts. The results are compared with a conventionally cast AlSi10Mg. The analysis shows that L-PBF influences the machinability. Differences between the reference and the L-PBF AlSi10Mg were observed in the chip form, the process forces, the surface morphology, and the burr formation. The initial manufacturing method of the part thus needs to be considered during the design of the finishing process to achieve suitable results.
As additive manufacturing offers only low surface quality, a subsequent machining of functional and highly loaded areas is required. Thus, a sound knowledge of the interrelation between the additive and subtractive manufacturing process as well as the resulting mechanical properties is indispensable. In this work, specimens were manufactured by using laser-based powder bed fusion (L-PBF) with substantially different sets of process parameters as well as subsequent grinding (G) or milling (M). Despite the substantially different surface topographies, the fatigue tests revealed only a slight influence of the subtractive manufacturing on the fatigue behavior, whereas the different laser-based powder bed fusion process parameters led to pronounced changes in fatigue strength. In contrast, a significant influence of subtractive finishing on the fatigue properties of the defect-free continuously cast (CC) reference specimens was observed. This can be explained by a dominating influence of process-induced defects in laser-based powder bed fusion material, which overruled the influence of surface machining. However, although both laser-based powder bed fusion parameter sets resulted in substantial defects, one set yielded similar fatigue strength compared to continuously cast specimens.