The use of SLA technology to manufacture prototypes requires fast and accurate, strict requirements for the accuracy and performance of the parts, and easy operation in the forming process.
SLA performance requirements are special, and generally meet the following requirements:
The viscosity, and photosensitivity properties of the resin before curing, and the accuracy and mechanical properties of the material after curing.
Therefore, this material must have the following characteristics:
(1) The performance before curing is stable, easy to transport and store, and no dark reaction occurs
The photosensitive resin used for SLA is usually not removed once injected into the resin tank and is later added as it continues to be consumed in use.
Therefore, the use time of resin is generally very long, that is, the resin is required to not undergo thermal polymerization under normal circumstances, and it should also have high stability to visible light. To ensure the stable performance of the resin during the long-term molding process.
(2) Low viscosity
The SLA manufacturing process is shaped layer by layer, and when the layer is made, the liquid surface tension makes it difficult for the resin to automatically cover the surface of the cured layer.
Therefore, after making a layer, it is necessary to use an automatic scraper to scrape and coat the resin liquid surface once, and only after the liquid level is stable can it be scanned, otherwise the part will produce defects.
Therefore, the viscosity of the resin becomes an important performance indicator, and the smaller the viscosity of the resin in the case of other unchanged properties, the better, which can not only shorten the production time but also facilitate the addition of resin and the cleaning of waste liquid.
(3) Small curing shrinkage
The main problem of SLA is manufacturing accuracy, and shrinkage during forming will not only reduce the accuracy of the part but more importantly, it will also lead to warpage, deformation, cracking, etc. of the part.
In severe cases, the parts will be moved by the scraper during the forming process, resulting in complete failure of forming. Therefore, the resin used for SLA should be used as much as possible to use a material with less shrinkage.
(4) High degree of one-time curing
Some SLA resins cannot be directly applied after being made into parts, and need to be post-cured in the ultraviolet light box, but it is impossible to ensure that the light intensity received in all directions and faces is the same during the curing process.
(5) Small swelling
During the molding process, the cured product is infiltrated in the liquid resin, and if the cured product swells, it will not only affect the strength of the part but also expand the cured part, resulting in overflow, which seriously affects the accuracy.
There are more uncured resins on the surface of the formed parts that need to be cleaned with solvents, and it is hoped that only the uncured part will be removed during washing without affecting the surface of the parts, so it is hoped that the cured products have better solvent resistance.
(6) Fast curing speed
It has large absorption and fast response speed for light with a wavelength of 355 nm.
SLA generally uses ultraviolet lasers, and the energy concentration of the laser can ensure that the parts have high accuracy, but the scanning speed of the laser is fast, generally greater than 1m/s. Therefore, the time for light to act on the resin is extremely short, and the resin can only be quickly cured if the light in this band has a large absorption and a faster response speed.
(7) Semi-finished products have high strength
To ensure that the parts do not deform, expand, bubble, and layer separation during the post-curing process.
(8) The cured product has good mechanical properties
Such as high breaking strength, impact strength, hardness, chemical resistance, ease of washing and drying, and good thermal stability.
Among them, precision and strength are the two most important indicators of rapid prototyping, the strength of rapid prototyping parts is generally not high, especially SLA parts, which were generally brittle before, and difficult to meet the requirements of functional parts, but in recent years, some companies have also introduced materials with higher toughness and strength.
(9) Low toxicity
The use of toxic oligomers, monomers, and photoinitiators should be avoided as much as possible to protect the health of operators and avoid environmental pollution.
Future rapid prototyping can be done in the office, so there is even more consideration when designing recipes.
The above 9 points are the characteristics that well-formed 3D printing photosensitive resin materials should have.