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UV 3D Printing: An Innovative Application of Photocuring Technology

Release time:

2024-03-23 14:44

UV 3D Printing: An Innovative Application of Photocuring Technology

Light-curing 3D printing, a cutting-edge manufacturing technology, has become a major driving force in the manufacturing industry thanks to its high precision and efficiency. The fundamental principle behind light-curing 3D printing is the use of liquid photopolymer materials that, under the irradiation of a specific light source, undergo a photopolymerization process and solidify layer by layer, thereby building three-dimensional physical models. This technology boasts high precision and efficiency, enabling the production of complex and intricate parts and models, and opening up unprecedented opportunities for innovation across numerous industries.

I. Working Principle

Light-curing 3D printing is a technology that uses ultraviolet light and light-curable resins to fabricate 3D-printed models. It employs a layer-by-layer curing process: First, a three-dimensional model is designed using specialized software. Then, combined with a 3D printer, a computer program is used to determine the scanning path of the light source. The program follows the pre-designed scanning path, directing the light source onto specific areas of the liquid photosensitive resin, causing the resin on the surface to solidify into a thin, solid layer. Afterward, the platform rises or falls by a certain distance, and the next layer is cured on top of the previously solidified resin. This process is repeated layer by layer, ultimately forming a complete 3D-printed model.

II. Composition and Functions of the Materials

Currently, light-curing 3D printing has undergone technological improvements, introducing a combination that uses photosensitive resin as the forming material and wax as the support material, enabling 3D-printed products to achieve even better results.

1. Molding material

The photosensitive resin used for light-curing 3D printing mainly consists of oligomers, Active monomer It consists of three main components—photoinitiators—and a small amount of other additives. Under ultraviolet light irradiation, it undergoes a polymerization reaction, rapidly curing and forming a finished product with high hardness and excellent gloss, while virtually eliminating solvent volatilization.

Among these, oligomers—also known as dimers or trimers—are low-molecular-weight polymers containing unsaturated functional groups. They represent the largest and most fundamental component in the formulation of photosensitive resins. It is the oligomer that determines the processing properties of the photosensitive resin as well as the basic performance characteristics of the photo-cured products, such as viscosity, hardness, and elongation at break. Therefore, in the formulation system of photosensitive resins, selecting an appropriate oligomer is a critically important step.

There are various types of photosensitive resins available to meet the needs of different fields. For example, general-purpose resins are suitable for a wide range of applications, while tough resins offer greater flexibility and impact resistance, making them ideal for manufacturing components that need to withstand certain external forces. In addition, there are specialized types such as high-temperature-resistant resins, which are used to produce components designed to operate in high-temperature environments.

2. Supporting materials

The primary function of support materials is to fill in cavities or overhanging areas in the printed part, providing structural support. During the 3D printing process, certain parts may have cavities and overhanging sections due to their shape or structural complexity. These areas remain unstable during printing, which could lead to deformation and compromise the final product’s shape. Therefore, these areas need to be filled with support materials to maintain their shape and stability, ensuring a smooth printing process and high product accuracy.

Support materials can be broadly categorized into three types: wax-based, phase-change, and light-curing. The choice among these depends on the specific application scenario and requirements.

III. Types of 3D Printers

According to their exposure method, light-curing 3D printing technologies can be divided into two major types: top exposure and bottom exposure. These can also be referred to as "pull-up" and "push-down" methods, respectively—top exposure is the push-down type, while bottom exposure is the pull-up type.

1. Sunken

In a submerged photopolymerization 3D printing system, a liquid photosensitive resin is contained in a resin reservoir. Ultraviolet light, controlled by a computerized device, scans across the surface of the photosensitive resin or exposes the entire surface according to the layered information provided. The resin exposed to the UV light undergoes a photopolymerization reaction, causing localized areas to solidify and forming a thin layer. Once one layer has been fully cured, the build platform precisely moves downward by a fixed distance, allowing a fresh layer of liquid resin to be applied onto the cured resin surface. A blade then levels the resin surface before the next layer is irradiated and cured. The newly cured layer bonds firmly to the previous layer, and this process is repeated iteratively until the entire part is completed.

2. Pull-up type

In an upward-pull stereolithography 3D printing system, a liquid photopolymer resin is housed in a resin reservoir. The bottom surface of the reservoir is made of high-transmittance optical glass. Ultraviolet light, positioned beneath the liquid, passes through the transparent bottom glass and irradiates the resin on the bottom surface, causing specific areas to solidify and form a thin layer. Once one layer has been cured, the build platform rises by a fixed distance, simultaneously lifting the previously cured resin layer with it. As the platform moves, fresh liquid resin naturally flows in to fill the gaps created by the movement, after which the next layer is cured. The newly cured layer bonds firmly to the previous layer, and this process continues until the entire part is completed.

IV. Advantages and Disadvantages of Printing Methods

1. Sunken

Advantages:

(1) High manufacturing precision: Submerged photopolymerization 3D printing typically employs laser scanning or DLP projection technology, enabling highly precise curing of photosensitive resins. This process allows the creation of models with complex structures and fine details, meeting the demands of high-precision manufacturing.

(2) Excellent Quality: Since submerged printing is non-contact, models produced by submerged photopolymerization 3D printing typically have smoother and finer surfaces. The printed products are virtually free of deformation or defects.

Disadvantages:

(1) High costs: Since this is a submerged printing process, the resin tank must be large enough to fully immerse the entire finished part. As a result, the tank is relatively large and deep, requiring a substantial amount of resin material, which significantly increases costs.

(2) Long printing time: Submerged photopolymerization 3D printing typically requires a longer printing time. Especially when constructing structures such as steep slopes and overhangs, additional support structures may be needed, further extending the printing time.

2. Pull-up type

Advantages:

(1) Easy to operate: The pull-up printer has a low technical barrier, allowing users to quickly get started without requiring complex training—making it the preferred choice for individual consumers and start-up enterprises.

(2) Strong versatility: Since top-loading printers typically feature a larger printing space that can accommodate models of greater size, they are suitable for a wide range of application scenarios.

Disadvantages:

(1) Complex support structure: During the pull-up printing process, the model is subjected to an upward pulling force from the build platform as well as its own gravitational force. Therefore, the support structure must be sufficiently robust or thick, which increases the difficulty of both support design and post-processing work.

(2) Limited printing accuracy: During the lifting process, the model is subjected to forces that can easily cause surface defects or overall deformation, thereby affecting printing accuracy and aesthetic appeal.

Both pull-up and pull-down photopolymer 3D printing technologies have their own advantages and disadvantages. When making a choice, users need to consider their specific requirements, budget, and intended application scenarios. For individual consumers and small businesses, a pull-up printer may be a more economical and convenient option; whereas for large enterprises that require high-precision printing and mass production, a pull-down printer might be a better fit.

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