With the continuous development of 3D printing technology, SLA/DLP printing has been widely used in industrial design, dentistry, jewelry casting and other fields. This kind of printing technology usually uses liquid photosensitive resin as the material, which is cured layer by layer by ultraviolet (UV) irradiation. However, after printing, 3D printed parts often need further UV curing treatment-Post-curing to improve the mechanical properties, stability and surface quality of finished products. This paper will introduce in detail how to carry out UV curing on 3D printed parts.

I. Principle of UV curing

Resin materials used in photocurable 3D printing are mainly composed of photoinitiator, monomer and oligomer. In the printing process, the printer irradiates the resin with UV light or laser to initiate a chemical reaction, so that the liquid resin is partially cured and molded. However, due to the limitation of illumination time and intensity in the printing process, the resin inside the printed piece may not be completely cured.
　　UV post-curing is to put the printed parts in a high-intensity ultraviolet light or a special UV curing box, so that they can continue to complete the cross-linking reaction under more uniform and sufficient illumination conditions, thereby improving the hardness, strength and heat resistance of the parts, reducing internal stress and improving dimensional stability.

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Second, the role of UV curing
　　1. Improve mechanical properties: Post-curing can enhance the rigidity and impact resistance of printed parts, making them more suitable for functional applications.

2. Enhance heat resistance and chemical stability: The fully cured resin is more resistant to high temperature and solvent corrosion.

3. improve the appearance quality: the surface that is not completely cured is easy to stick to hands or leave sticky substances, and the surface smoothness can be significantly improved after UV curing.

4. Eliminate internal stress: The unreacted monomer remaining in the printing process will further react in the post-curing process, reducing the risk of deformation or cracking of parts.

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Third, the operation method of UV curing

1. Preparation stage:

-After printing, it is necessary to remove the printed piece from the platform and use alcohol (usually IPA) to clean and remove the uncured resin on the surface.

-After cleaning, it should be dried as much as possible or dried with a hair dryer to avoid residual alcohol affecting the subsequent curing effect.

2. Select a device:

-Special UV curing machine, UV light box or post-curing box with heating function can be used.

-Some equipment also has the function of temperature control, and the curing effect is better under heating conditions.

3. Set parameters:

-Time: It is generally recommended that the curing time is 10-30 minutes, depending on the resin type, the thickness of printed parts and the power of the equipment.

-Temperature: Some high-performance resins are recommended to be cured at 50-70℃ to accelerate the crosslinking reaction.

-Illumination intensity: Ensure that the wavelength of UV lamp (usually 405nm) matches the resin to achieve the best curing effect.

4. Precautions:

-Avoid stacking printed parts or blocking light when curing, and ensure that each surface can be fully irradiated with UV light.

-Wear gloves and goggles when operating, so as to avoid damage to skin and eyes caused by UV light.
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Iv. UV curing requirements of different resins

Different brands and types of photosensitive resins have different chemical compositions, so the requirements for UV curing are also different. For example:

-Standard resin: generally cured under UV lamp for 10-20 minutes.
　　-Engineering resin (such as ABS, heat-resistant resin): it may take longer or heat for post-curing.

-Biocompatible resin (if used in dentistry): the curing time is more strict, and the parameters recommended by the manufacturer should be followed.

It is recommended to read the technical specifications of resin products carefully before use and operate according to the recommended curing conditions.

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V. Summary

UV curing is an indispensable part of photocuring 3D printing process. It not only improves the physical properties and service life of printed parts, but also significantly improves the appearance quality and stability of finished products. For users engaged in professional applications, mastering the correct UV curing method will help to give full play to the advantages of 3D printing and achieve higher quality printing results.

Therefore, after completing 3D printing, it is important not to ignore the key step of UV post-curing, and treat it scientifically and reasonably, so as to truly display the potential of high-quality 3D printed products.