Beitz Steffen, Uerlich Roland, Bokelmann Tjorben, Diener Alexander, Vietor Thomas, Kwade Arno
Institute for Particle Technology, TU Braunschweig, 38104 Braunschweig, Germany.
Institute for Engineering Design, TU Braunschweig, 38106 Braunschweig, Germany.
Materials (Basel). 2019 Jan 18;12(2):297. doi: 10.3390/ma12020297.
Three-dimensional printing used to be a rapid prototyping process, but nowadays it is establishing as an additive manufacturing (AM) process. One of these AM techniques is selective laser sintering (SLS), which most often involves partial melting of the particles and therefore belongs to the category of powder bed fusion processes. Much progress has been made in this field by research on process parameters like laser power, hatch distance, and scanning speed while still lacking a fundamental understanding of the powder deposition and its influence on parts. A critical issue for economic manufacturing is the building time of parts with good mechanical properties, which can be reduced by lower surface roughness due to less or missing post processing. Therefore, the influence of three blade shapes on powder bed surface roughness has been evaluated for PA12 powder with three different grain size distributions by using advanced X-ray micro computed tomography (XMT) and a confocal laser scanning microscope (LSM). Along with those methods, new techniques for powder characterization were tested and compared. Lowest roughness has been achieved with a flat blade, based on a higher compression due to a larger contact zone between blade and powder bed. Furthermore, an anisotropic effect of the mechanical properties resulting from different building directions has been detected which can be explained by varying amounts of solid contact paths through the powder bed depending on powder application direction. In addition, an optimal combination of process parameters with an even compression of the powder bed leads to low surface roughness, complementing the advantages of additive manufacturing.
三维打印曾经是一种快速成型工艺，但如今它正确立为一种增材制造（AM）工艺。这些增材制造技术之一是选择性激光烧结（SLS），它最常涉及颗粒的部分熔化，因此属于粉末床熔融工艺类别。通过对激光功率、扫描间距和扫描速度等工艺参数的研究，该领域已取得很大进展，但对粉末沉积及其对零件的影响仍缺乏基本了解。经济制造的一个关键问题是具有良好机械性能的零件的制造时间，由于较少或无需后处理而降低的表面粗糙度可以缩短制造时间。因此，通过使用先进的X射线显微计算机断层扫描（XMT）和共聚焦激光扫描显微镜（LSM），评估了三种叶片形状对具有三种不同粒度分布的PA12粉末的粉末床表面粗糙度的影响。除了这些方法外，还对粉末表征的新技术进行了测试和比较。基于叶片与粉末床之间较大的接触区域导致的更高压缩，使用扁平叶片可实现最低粗糙度。此外，还检测到不同构建方向导致的机械性能的各向异性效应，这可以通过取决于粉末施加方向的穿过粉末床的固体接触路径数量的变化来解释。此外，工艺参数的最佳组合与粉末床的均匀压缩导致低表面粗糙度，补充了增材制造的优势。
