Explain Solid ground curing process with neat sketch and its advantages and disadvantages.
Solid Ground Curing (SGC) Process
Solid Ground Curing (SGC) is a unique and now largely obsolete photopolymer-based additive manufacturing process. It was developed by Cubital Ltd. in the 1980s. Unlike other photopolymerization methods like SLA that use a laser to trace each layer, SGC cures an entire layer at once using a high-powered UV lamp and a specially prepared photomask. The process is notable for its use of a wax filling and milling step to create a solid, fully supported block from which the final part is extracted.
Basic Methodology
The SGC process involves a series of complex and repeated steps for each layer:
Mask Preparation: While the previous layer is being processed, a glass plate is cleaned and prepared. A printer, similar to an electrostatic photocopier, creates a digital photomask of the current layer's cross-section on the glass plate. The parts of the mask representing the solid object are transparent, while the surrounding area is opaque.
Resin Deposition: The build platform is covered with a thin, uniform layer of liquid photopolymer resin.
Curing with Mask: The prepared photomask is positioned over the resin layer. A powerful UV lamp then flashes, curing and hardening the entire layer of resin in the transparent areas defined by the mask.
Excess Resin Removal: An aerodynamic wiper or vacuum removes the excess, uncured liquid resin from the surface, leaving behind only the solid layer.
Wax Filling and Support: The voids left by the removed resin are immediately filled with a layer of melted wax. This wax serves a crucial role by supporting any overhangs or delicate features of the part, eliminating the need for a separate support structure.
Solidification and Milling: A cold plate is applied to quickly solidify the wax. A milling head then trims the top surface of the layer to a precise, flat thickness. This milling step is a key feature, ensuring high dimensional accuracy and flatness for each subsequent layer.
Repetition and Completion: The entire process is repeated for each layer until the object is fully built, surrounded by a block of solidified wax. After the build is complete, the wax is melted away, leaving the final part.
Advantages of SGC
High Speed and Productivity: Since an entire layer is cured at once rather than being traced by a laser, the build time is independent of the layer's complexity. This makes SGC particularly fast for large or intricate parts and for producing multiple parts simultaneously.
High Accuracy: The milling step after each layer ensures a high degree of dimensional accuracy, especially in the Z-direction (layer thickness).
No Support Structures: The wax used to fill voids provides continuous and robust support for all parts of the model, including overhangs and internal features. This eliminates the need for separate, manually-designed support structures, simplifying the design process and post-processing.
Fully Cured Parts: The high-powered UV lamp fully cures each layer, resulting in durable parts that do not require an additional post-curing process.
Minimal Warping: The solid wax surrounding the part provides structural stability throughout the build process, which helps to minimize warping and curling.
Disadvantages of SGC
System Complexity and High Cost: The SGC machine is highly complex, involving multiple subsystems for masking, curing, waxing, cooling, and milling. This complexity leads to very high acquisition and maintenance costs.
High Waste and Environmental Impact: The process generates a significant amount of waste, including the used resin, the wax that is melted away, and the milled material. The wax, in particular, is often not recyclable.
Large Footprint and Noise: SGC machines are typically very large, heavy, and noisy due to the multiple mechanical systems and the large compressor required.
Material Limitations: SGC is restricted to a specific type of photopolymer resin and wax, limiting the material properties of the final parts.
Obsolete Technology: Due to the high cost, complexity, and waste, SGC was not commercially successful and is no longer being produced. Other, more cost-effective and efficient technologies have since surpassed it.
