Novel testing device and routine to characterise the spreadability of powders for powder bed fusion processes – a problem-oriented approach

Abstract

Currently there is considerable interest in understanding and quantifying the powder characteristics that affect the quality of the top spread powder layer for processes such as powder bed fusion and binder jetting. For this purpose, a new testing device has been developed in order to assess several aspects of this top spread powder layer. Using different measurement procedures, the roughness of the top layer, the surface coverage of a single spread powder layer and the powder bed density of an entire spreading experiment can be determined. Since the tester is freely programmable, the individual process steps of spreading a single powder layer can also be varied. Using these methods, the influence of different process parameters such as e.g. the spreading velocity or the distance between the blade and the building platform, which is also referred to as gap size in general, on the quality of the top or only a single spread layer and on the powder bed packing density can be examined. This study presents the new test device as well as the corresponding measurement procedures mentioned, the reproducibility of the results, which, depending on the measurement method and the measured parameter, range between 0.24 and 4.81%, and the influence of the spreading strategy, which defines the chronological order of the single steps during spreading.

Effect of reuse times on H13 powder properties processed by selective electron beam melting

“…The relative packing density of the powder bed can directly affect the quality of the AM products [25]. A loose and uneven powder bed will make the melting of the powder worse, and then cause defects such as balling and pores and so on.…”

Experimental metrics of the powder layer quality in the selective laser sintering process

“…Several recent works have been focused on the experimental assessment of the quality of spread powder layers [7,10,[26][27][28][29]. A first qualitative visual analysis of the surface quality and the layer density was proposed by Van den Eynde et al [26].…”

“…More recently, a step forward was put using a shadowgraphy technique to highlight the surface roughness and the linear defects along the direction of spreading [28]. A promising algorithm based on single-particle detection was recently proposed by Mitterlehner et al [29].…”

Powder spreading testbed for studying the powder spreading process in powder bed fusion machines

“…Mitterlehner et al developed a spreading testbed to investigate the influence of powder moisture on its spreadability [30]. Their testbed is a smaller version of commercial PBF machines including a vertically moving feeder, build platform, and overflow bins at each end and a belt-driven moving blade as the spreader.…”