Minimum Feature Size and Detail Fidelity Design Guidelines for SLA Process

Precision capabilities and limitations of the SLA process

The SLA (stereolithography) process is one of the most precise 3D printing processes. Its XY direction accuracy can reach 25-50μm, and the Z direction layer thickness can reach 25μm. This high precision enables SLA to manufacture fine features and intricate details, making it widely used in jewelry, dentistry, precision prototyping, and more. However, there is a difference between theoretical accuracy and actual manufacturable features. Minimum feature size is determined not only by the resolution of the device, but also by material strength, cure shrinkage, support requirements and post-processing feasibility. These factors need to be taken into consideration during design to ensure that the designed features can be successfully printed and meet the usage requirements.

Minimum wall thickness and minimum column size design

Wall thickness and column size are the most basic minimum characteristic parameters in SLA design. The recommended minimum wall thickness for standard resin materials is 0.4mm, and high-performance engineering resins can reach 0.3mm. The wall thickness design needs to consider the size of the parts, and the wall thickness of large-sized parts should be appropriately increased. The minimum diameter of independent columnar features is 0.5-0.8mm. Thin columns with a diameter less than 0.5mm are easy to break during printing or post-processing. The minimum thickness of ribs and bosses attached to the body may be slightly less than the free-standing wall thickness, subject to evaluation of load-bearing requirements. Fillet transitions should be used where wall thickness changes to avoid stress concentration.

Minimum size of holes and notches

The minimum size of holes and notches depends on depth and location. The minimum diameter of through holes is 0.5mm and the minimum diameter of blind holes is 0.8mm. The diameter of the deep hole needs to increase as the depth increases, and the ratio of diameter to depth is recommended to be no less than 1:10. The width and depth of the notch need to match, the minimum width is 0.4mm, and the depth should not exceed 5 times the width. The layout of holes needs to consider support removal. Supports in deep holes and blind holes are difficult to remove. It is recommended to design through holes accessible from the surface. The edges of the holes should be chamfered or rounded to avoid damage to sharp edges when supports are removed.

Detail fidelity and surface quality

Detail fidelity refers to the degree to which design details are restored by the print. The SLA process can achieve micron-level details, but the actual discernibility of details is limited by the viewing distance and the resolution of the human eye. When designing details, their purpose should be clear: functional details (such as mating surfaces, positioning features) need to be manufactured accurately; decorative details (such as textures, text) need to consider visual recognition. The minimum line width of text and graphics is 0.3mm, and the minimum height is 0.5mm. The depth of the bas-relief is recommended to be no less than 0.2mm. The unit size of the surface texture is recommended to be no less than 0.5mm×0.5mm.

The impact and compensation of post-processing on details

The post-processing of SLA parts will affect the detailed features. Support removal of details that may damage the supporting surface, it is recommended to arrange important details on the non-supporting surface. Cleaning may soften and deform tiny features, so cleaning time and solvent concentration need to be controlled. Grinding will reduce the feature size, so a grinding allowance needs to be reserved during design. Spraying and coatings increase feature size and coating thickness needs to be considered in the design. For details with strict dimensional requirements, it is recommended to measure and trim after post-processing. Post-processing effects can be pre-compensated in the CAD model during design to ensure that the final dimensions meet the requirements.