Reducing lateral stair-stepping defects in liquid crystal display-based vat photopolymerization by defocusing the image pattern

Abstract

Vat photopolymerization-based additive manufacturing (AM) technology has emerging success in efficiently fabricating complex and high-resolution objects. However, the lateral and vertical stair-stepping defects limit vat photopolymerization in manufacturing smooth surfaces, such as optical components. Vertical stair-stepping was mitigated by thinner layer thickness or layer-less fabrication. It is still challenging to reduce the lateral stair-stepping defects caused by the pixelated projection pattern, especially for Liquid Crystal Display (LCD) projection whose pixels are disconnected. To tackle this lateral stair-stepping issue, we propose to defocus the curing image pattern by increasing the gap between the LCD screen and the resin vat. This gap intentionally blurs the disconnected pixels to create a continuous and smooth projection pattern. Experiments verified that the smoothened LCD pattern led to an average 81.2% reduction in surface roughness, which was much more effective than grayscale pixels. The gap between the LCD screen and the resin vat also enabled blowing air to dissipate the heat from LCD and the resin polymerization, reducing the part distortion and printing failure due to the thermal stress. The present approach improved the surface roughness and paved the way for vat photopolymerization in fabricating smooth micro-optics, microfluidic channels, and functional curved surfaces.