In the field of additive manufacturing, 3D resin molding technology centers on photosensitive polymerization, transforming liquid resin into a three-dimensional entity with complex geometry and fine surface features through layer-by-layer curing. This process requires not only a deep understanding of photochemical reaction mechanisms but also a high degree of coordination in equipment control, process parameters, and post-processing to ensure stable achievement of molding accuracy, mechanical properties, and surface quality.
The basic principles of photopolymerization lay the foundation for this process. 3D resins contain photolytic photoinitiators and polymerizable olefin monomers or oligomers. Under specific wavelengths of ultraviolet or visible light irradiation, the initiator decomposes to generate free radicals or cations, triggering the opening of double bonds and the formation of a cross-linked network, causing the resin to transform from a liquid to a solid state. This process is characterized by layer-by-layer accumulation, with the thickness of each layer determined by the light source focus and scanning strategy, thus building a complete shape layer by layer. Depending on the light source and projection method, mainstream processes are divided into stereolithography (SLA), digital light processing (DLP), and liquid crystal display (LCD) photopolymerization.
SLA (Surface Mount Laser) technology uses a UV laser beam to scan the resin surface or cured layer at high speed via a galvanometer system, curing point-by-point to form the cross-sectional profile. Its advantages lie in the small laser spot size and precise positioning, achieving extremely high dimensional accuracy and detail reproduction, making it suitable for complex curved surfaces, microstructures, and molds and precision parts with stringent surface quality requirements. The key to this process lies in matching laser power, scanning speed, and overlap ratio, as well as coordinating liquid level control and layer thickness settings to reduce interlayer stress and warpage.
DLP (Digital Micromirror Process) technology utilizes a digital micromirror device (DMD) to project the entire UV image onto the resin tank, curing the entire cross-section in a single pass. Due to simultaneous exposure of the entire layer, its forming speed is significantly higher than SLA, and it offers better interlayer consistency, making it suitable for small to medium batch production and prototype fabrication requiring a uniform surface finish. The key to this process lies in optimizing projection resolution and light source uniformity, as well as precisely controlling exposure time and light intensity to avoid edge burrs and dimensional deviations caused by over-curing or under-curing.
LCD technology uses a high-resolution LCD screen as a mask, combined with ultraviolet backlighting to achieve layer-by-layer exposure. The equipment cost is relatively low and it is easy to popularize. Its resolution is limited by the size of the LCD pixels, but with reasonable parameters, it can still meet the manufacturing needs of most appearance prototypes and medium-precision parts. The process requires special attention to the screen's resistance to ultraviolet aging, the matching of the light source wavelength, and the flatness of the release film to reduce distortion and poor interlayer peeling.
In a general process flow, the model is first sliced and a support is generated, converting the 3D data into layer-by-layer exposure instructions. The equipment then automatically completes cycles of resin coating, leveling, exposure curing, platform lifting, and preparation for the next layer until the entire piece is formed. Layer thickness selection must comprehensively consider accuracy and efficiency: 0.025–0.1 mm layer thickness is commonly used for precision parts, while 0.1–0.2 mm can be increased for ordinary prototypes to speed up the process. Exposure energy is directly related to the curing depth; insufficient energy will result in incompletely cured layers, while excessive energy increases the risk of shrinkage, warping, and post-curing embrittlement.
Post-processing is crucial to the final quality. The initial molded parts need to be cleaned with a solvent (such as isopropanol) to remove uncured resin. This process requires careful control of time and mechanical action to avoid damaging the cured surface. A secondary curing process is then performed in a UV chamber with matched wavelength and dosage to further enhance cross-linking and mechanical properties, but overexposure must be avoided to prevent yellowing or accelerated dimensional shrinkage. Removal of the support structure requires combined cutting, grinding, and polishing processes to achieve the desired surface finish and dimensional accuracy.
Environmental and process control are also crucial. Resin is sensitive to temperature, humidity, and light. The molding environment should be kept at a constant temperature (20℃~28℃), with appropriate dehumidification and light shielding to prevent pre-curing and performance fluctuations. Regarding equipment maintenance, the resin tank needs to be cleaned regularly, the light source intensity and uniformity checked, and the platform level calibrated to ensure long-term stability of layer thickness and positioning accuracy.
Overall, 3D resin molding is a system engineering project integrating photochemistry, precision mechanics, and software algorithms. Different types of processes have their own advantages in terms of accuracy, speed, and applicable scenarios; proper selection and parameter optimization can maximize the material's potential. With advancements in light source technology, resin formulation, and intelligent control, this process will continue to evolve towards higher precision, faster efficiency, and greater functional adaptability, providing solid molding support for fields such as precision manufacturing, cultural and creative industries, and medical models.
