Photomask technology is a rapid prototyping method developed by Cubital, an Israeli company. Similar to the SLA (Stereolithography) process, this system also utilizes ultraviolet (UV) light to cure photosensitive resin. However, unlike SLA, the light source and specific process method differ significantly. The exposure in Photomask technology uses optical mask techniques, where an electronic imaging system first generates a static electrostatic latent image on a special glass plate, representing the cross-sectional shape. This latent image attracts carbon powder to form a negative image of the section. The resulting “film” is then used for UV exposure and curing of the photosensitive resin layer. Excess resin is removed, and the gaps in the cross-section are filled with paraffin wax. This process continues layer by layer to create the prototype.

Compared to SLA, Photomask (SGC) technology is more efficient, as each layer’s curing is instantaneous. Additionally, the working space is larger, allowing for multiple parts to be created at once or for single, larger parts (e.g., up to 500mm x 350mm x 500mm).

Specific Process Steps:

1. 3D Model Creation and Slicing: The part’s 3D model is created, and slicing software is used to divide the model into layers. Before starting each layer, a uniform layer of photosensitive resin is applied to the working plane.
2. Photomask Printing: Each layer is exposed using Cubital’s patented photomask printing technology.
3. UV Exposure: A strong UV lamp (2kW) is used to expose the photosensitive resin. The exposed resin is cured in one pass.
4. Resin Removal and Recycling: After each layer is cured, any unexposed resin is vacuumed away for reuse. The cured resin is subjected to a second UV exposure (4kW) for further hardening.
5. Wax Filling: The vacuumed areas are filled with wax. The wax is then cooled and hardened to serve as support material, eliminating the need for additional support structures.
6. Layer Flattening: The wax and resin layers are flattened to prepare for the next layer’s creation.
7. Finishing the Model: Once the part is complete, the wax is removed, and the part is polished to achieve the final prototype without requiring further post-processing.

Advantages of Photomask Rapid Prototyping:

1. No Need for Support Structures: The use of wax as support material means there’s no need to design additional support structures for the model, simplifying the process.
2. High Speed and Efficiency: The layer curing process is fast since the resin is exposed instantaneously, with an entire layer being formed in one step. This makes the process especially efficient, with speed not being affected by the complexity of the part.
3. High Precision: The technology offers excellent accuracy, with a relative precision of approximately 0.1%, making it suitable for creating highly detailed models.
4. Ideal for Multiple Prototypes: Photomask technology is ideal for making multiple prototypes simultaneously. The printing order of different parts can be changed freely during production. If a part is not completed, another part can be printed first, and the unfinished one can be resumed later.
5. Low Internal Stress and Minimal Deformation: This method minimizes internal stress and deformation, making it suitable for producing large parts with a high degree of precision.
6. Error Correction Capability: If a layer is found to have errors during production, it can be milled off and remade without affecting the rest of the model. This flexibility in error correction is a significant advantage over other prototyping methods.

Disadvantages of Photomask Rapid Prototyping:

1. High Material Waste: The process involves considerable waste of resin and wax, making it less material-efficient compared to other rapid prototyping methods.
2. Complex Process: The procedure is more intricate, involving multiple steps and precise handling, which can make it more time-consuming and labor-intensive.
3. Large Equipment Footprint and High Maintenance Costs: The machines required for Photomask rapid prototyping are large and require significant space. Additionally, the equipment can be noisy, and maintenance costs are typically high.
4. Limited Material Selection: The choice of materials is restricted, and the resin and wax used in the process can be toxic, requiring special storage and handling conditions, such as light-sealing and safety precautions.
5. Potential Overexposure Issues: If the resin is overexposed to UV light, it can degrade and lose its ability to cure properly, leading to material failure.
6. Wax Removal Post-Processing: After the model is finished, the wax support material needs to be removed, adding an additional post-processing step to the workflow.

Conclusion

Photomask rapid prototyping technology offers a unique set of advantages, including high speed, high precision, and the ability to produce multiple parts simultaneously. While it may not be as widely used as other methods like SLA or SLS, its ability to handle larger parts with minimal deformation and internal stress makes it a strong contender for certain applications. However, the challenges associated with material waste, limited material selection, and high maintenance costs must be carefully considered when deciding if this technology is the right fit for a particular project.

As with all prototyping methods, choosing the right technology depends on the specific requirements of the project, including the size, complexity, and material properties needed for the final part.