Influence of the recoating parameters on resin topography in stereolithography

The recoating step in stereolithography (SL) is one of the principal sources of inaccuracies. The liquid layer deposition on top of irregular topography leads to a non-uniform layer thickness which eventually results in a poor quality of the final product. To compensate the unevenness of the underlying geometry, an approach where the recoating parameters are (continuously) changed during the recoating step might be used. The main reason for the absence of advanced control systems in modern SL equipment is the lack of understanding of the fluid dynamics during the resin deposition process. This paper is focused on the recoating step implementation over a rectangular cavity as a prototypical roughness element. The impact of the recoater speed, recoater width, and the vertical position of the recoater on the resin surface topography is considered. By means of an analytical relation based on a simple Couette-Poiseuille flow we qualitatively estimate the influence of these parameters. For a more detailed flow analysis, 2D numerical simulations are carried out. In addition, numerical and analytical results are compared with the experiment. This study shows that the blade width and the blade speed have the same effect on the resin thickness, namely, increase of these parameters leads to a thinner liquid layer. Depending on the underlying geometry and within a representative range of the recoating parameters, doubling of the blade speed or its width results typically in 5–10 % decrease of the layer thickness. Additionally, the mechanism of the development of the resin surface imperfection above a deep-to-shallow underlying geometry transition is described. It is also shown that for small values of the gap between the blade and the cured layer the increase of the gap results in lowering of the resin level. This trend continues until a certain critical gap size. When the gap increases further the resin level starts to increase. For too large values of the gap the resin level becomes independent of the gap and remains constant.