Issue34

A. Riemer et alii, Frattura ed Integrità Strutturale, 34 (2015) 437-446; DOI: 10.3221/IGF-ESIS.34.49 438 For all AM-processes is common that part production is based on the CAD model which has to be designed or obtained using 3D-scans in the step before manufacturing. The AM process is characterized by material efficiency and a short time for marketing of AM components. The reasons for these advantages may be found in the following points:  Material efficiency is realized by part manufacturing only in solid areas corresponding to the CAD model. In some AM processes like SLM the excess and unfused powder material may be sieved following part manufacturing and reused in subsequent process operations. Thus, the amount of waste material is reduced to a minimum.  Using the direct manufacturing of parts from a CAD model, there is no need for the development and manufacturing of tools and casting molds. Consequently, the time for marketing is decreased. Figure 1 : Basic steps of SLM-process. The additive manufacturing process Selective Laser Melting is characterized by transition of powdered material into solid part following being irradiated by the laser source. The melt pool within this process is extended only in a small local area. Hence, layer-by-layer manufacturing of complex and delicate components becomes possible. The fabrication of parts by SLM is an iterative process that is divided into three consecutive steps, Fig. 1, as follows:  Recoating: This step in the process involves the deposition of powder; either directly on the building platform within the first recoating step or on the previously deposited and irradiated powdered material in each subsequent step.  Irradiation: Here, the powdered material becomes locally melted by the laser energy and bonded with the subjacent – already solidified – material. The irradiated regions here correspond to the volume areas of the CAD model. The SLM process includes various exposure strategies which have strong impact on the evolution of the material condition (i.e. residual stresses and porosity) [5,6].  Lowering: This step characterizes the lowering process of the building platform and thus of the entire powder bed. The lowering value here corresponds to the thickness value of one layer selected for the fabrication. The space resulting from the lowering of the platform and the powder bed may be used in the next step for powder deposition. Despite numerous advantages and unique features of the SLM process, the success and implementation of this technology depends mainly on its behaviour under loading. Thus, there is a real need to examine SLM materials and to optimise them. For that reason crack growth analyses on titanium alloy Ti-6-4 and stainless steel 316L were carried out. S AMPLE MANUFACTURING or the production of Ti-6-4 and 316L samples the Selective Laser Melting machine SLM250 HL (SLM Solutions) was used. The mounted laser is an ytterbium fiber laser with a maximum power of 400 watts. The data file preparation for the selective melting machine was realized by the commercial software SLM AutoFab (Marcam F