Global industrial adoption of laser-based powder bed fusion (LPBF) technology is still limited by the production speed, the size of the build envelope, and therefore the maximum part size that can be produced. The cost of LPBF can be driven down further by improving the build rates without compromising structural integrity. A common approach is that the build rate can be improved by increasing the laser power and beam diameter to instantly melt a large area of powder, thus reducing the scanning time for each layer. The aim of this study was to investigate the aspects of upscaling LPBF processing parameters on the characteristic formation of stable single tracks, which are the primary building blocks for this technology. Two LPBF systems operating independently, using different parameter regimes, were used to produce the single tracks on a solid substrate deposited with a thin powder layer. The results obtained indicate that higher laser power and spot size can be used to produce stable tracks while the linear energy input is increased. It was also shown statistically that the geometrical characteristics of single tracks are mainly affected by the laser power and scanning speed during the scanning of a thin powder layer.
In Selective Laser Melting, the initial units produced are single tracks that overlap to create a single layer; from the sequence of layers, a 3D object is manufactured. The properties of the parts produced by SLM depend heavily on the properties of each single track and each layer formed by these tracks. This study evaluates the effect of processing parameters on the geometrical characteristics of single tracks manufactured from 17-4PH stainless steel powder. A single-mode continuous-wave ytterbium fibre laser was used to manufacture single tracks at laser powers in the range of 100-300 W with a constant spot size of ∼80µm. The single tracks produced were subjected to standard metallographic preparation techniques for further analysis with an optical microscope. Deep molten pool shapes were observed at low scan speeds, while shallow molten pool shapes were observed at high scan speeds. At higher laser power densities, under-cutting and humping effects were also observed. The dimensions of single tracks processed without powder generally decrease with increasing scan speed at constant laser power. However, the geometrical features of the single tracks processed with powder revealed pronounced irregularities believed to be caused by non-homogeneity in the deposited powder layer. OPSOMMINGSelektiewe lasersmelting produseer enkel bane wat mekaar oordek en vorm so ʼn enkele laag. Daaropvolgende lae vorm dan ʼn driedimensionele onderdeel. Die eienskappe van hierdie onderdele word grootliks beïnvloed deur die eienskappe van elke baan en elke laag. Hierdie studie evalueer die effek van die prosesseringsparameters op die geometriese eienskappe van enkel bane wat van 17-4PH vlekvrye staalpoeier vervaardig is. ʼn Enkelmodus kontinuegolf ytterbium vesel laser is gebruik om die enkel bane te vervaardig. Die laser drywing het gewissel van 100 tot 300W met ʼn konstante kolgrootte van ongeveer 80µm. Die enkel bane is dan aan standaard metallografiese voorbereidingstegnieke onderwerp sodat verdere analise met ʼn optiese mikroskoop kon geskied. Diepgesmelte poel vorms is bespeur teen lae skandeersnelhede, terwyl vlakgesmelte poel vorms by hoë skandeersnelhede gewaar is. By hoër laser drywingsdigthede is ondersnyding en hobbelvorming waargeneem. Die dimensies van die enkel bane wat sonder poeier geprosesseer is, het oor die algemeen afgeneem met ʼn toename in skandeersnelheid by konstante laserdrywing. Die geometriese eienskappe van die enkel bane wat wel met poeier geprosesseer is, het noemenswaardige onreëlmatighede aan die lig gebring. Daar word vermoed dat die onreëlmatighede as gevolg van nie-homogene verskynsels in die gedeponeerde poeierlaag is.
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