Explain the process details on the quality of product in SLA and SGC.
Stereolithography (SLA) and Solid Ground Curing (SGC) are both photopolymerization-based additive manufacturing processes, but they utilize different methods for curing and part support, which leads to significant differences in the quality of the final product.
Quality of Product in Stereolithography (SLA)
SLA is a widely used technology known for its ability to produce parts with a high degree of accuracy and a superior surface finish.
Process Details Affecting Quality:
Laser and Scanning: The use of a highly focused UV laser and a precision galvanometer scanning system is the primary factor in SLA's quality. The small laser spot size allows for very fine details and tight dimensional tolerances, often in the range of ±0.1 mm or better. The precise scanning system ensures that the cross-section of each layer is traced with high fidelity to the CAD model.
Layer Thickness: SLA can achieve very thin layer thicknesses, often as low as 25 micrometers. This fine resolution in the Z-axis minimizes the "stair-stepping" effect on curved and inclined surfaces, resulting in a remarkably smooth final product that requires minimal post-processing for aesthetic applications.
Support Structures: SLA requires the use of support structures to build overhangs and prevent warping. While necessary, these supports must be removed during post-processing. This can leave small marks or surface imperfections where they were attached, which may require sanding or other finishing steps.
Post-Curing: SLA parts are often "green" or partially cured when they come out of the printer. They need a final UV post-curing step in a special chamber to fully solidify the resin and achieve their final mechanical properties, such as tensile strength and durability. Without proper post-curing, the parts may be brittle or have suboptimal strength.
Anisotropy: While SLA parts are generally considered more isotropic than FDM parts, there can still be some variation in mechanical properties between the build direction (Z-axis) and the in-plane directions (X-Y plane).
Quality of Product in Solid Ground Curing (SGC)
SGC was a more complex and now largely obsolete technology, but it had unique features that resulted in a different set of quality characteristics.
Process Details Affecting Quality:
Photomask and UV Flash: Instead of a scanning laser, SGC used a digital photomask and a powerful UV flash to cure an entire layer at once. This method made the build time independent of the part's complexity, allowing for high throughput. However, the resolution was limited by the resolution of the photomask itself.
Milling and Layer Flatness: A key feature of SGC was the milling step after each layer was cured and filled with wax. A milling head would precisely flatten the surface of the new layer to a very tight tolerance. This process ensured exceptional dimensional accuracy in the Z-axis, which was one of SGC's primary advantages.
Wax Support System: The use of liquid wax to fill the voids and support the part was a fundamental aspect of SGC. This full support system meant that complex geometries, internal features, and severe overhangs could be built without the need for dedicated support structures. This eliminated the post-processing steps and potential surface defects associated with support removal.
Part Strength and Brittleness: The process of fully curing an entire layer at once, combined with the stress-relieving properties of the surrounding wax, often resulted in parts with higher structural stability and less brittleness compared to SLA parts from the same era. There was also no need for a final post-curing step.
Surface Finish: While the surface finish was generally good, it was often not as smooth as a post-processed SLA part, especially on vertical walls, due to the planarization step. The main challenge was the thorough removal of the wax after the build was complete, which was a messy and time-consuming process.
