Stereolithography is one of the oldest methods of 3D printing, thanks to Chuck Hull, who first introduced it in 1986. It is one of the most detailed and fastest methods, where an entire layer is printed at once. The projected image cures the resin during the same time interval, regardless of the number of printed parts.
In the early days, stereolithography was unavailable to ordinary users. Expensive 3D printers and material were the main obstacles, and the material was also brittle and prone to rapid aging, making it suitable for prototyping only.
Recently, however, these obstacles have begun to be removed. Thanks to cheap LCD designs, stereolithography printers have spread among the wider public. Nevertheless, the preparation of 3D printing data sometimes remains problematic. However, if the part is correctly oriented, the result is worth it.
But the key question remains: Is it possible to produce functional plastic parts using stereolithography? This article will reveal some of the issues involved in choosing a suitable material and perhaps shed some light on their considerable potential for our future.
Current developments in photopolymers
Thanks to modern organic chemistry, materials for stereolithography have improved significantly in recent years. The original materials were fragile, but the latest generations are significantly more durable and completely replace thermoplastics.
The first generation we started using in 2014 was based on monomers from fossil sources. These monomers were toxic and hazardous both in their uncured form and after curing. Sticky surface and allergic reactions were common problems. Therefore, we recommend that you always view the Hazard statements section and pay attention to the safety pictograms in the document called MSDS - Czech safety data sheet. Many manufacturers still produce these toxic materials today, although they are well aware of their shortcomings. These materials are often cheap and readily available on the market. Their liquid consistency allows for easy printing, but unfortunately they have significant drawbacks. They are fragile and deform relatively quickly, which limits their use for prototyping.
The second generation of materials, based on renewable resources, appeared in 2018. These materials, composed of larger "components" (oligomers), are denser and require heating to be printable. Their significantly longer resistance and UV stability have made it possible to use them in mass production as well. Their durability is comparable to Plexiglas; it does not break even when dropped from two meters. The development of materials that resemble the properties of ABS, PP and the first generation of flexible rubbers has been achieved.
In 2021, a number of patents were approved, which led to the development of the third generation of "monomer free" materials. These materials, based on oligomers and macromers, are natural, highly biocompatible and exhibit high resistance. Printing with these materials on low-end 3D printers can be challenging, but doable with a little effort. In a professional environment, higher class DLP printers, equipped with heating and sensors that monitor the thickness of each layer, provide more reliable results. These materials are extremely durable and can withstand a fall of more than four meters. The result is mechanically resistant materials similar to POM, Nylon, PA12, PEEK and functional abrasion-resistant rubber.
price vs. generation
Industrial use and the issue of durability
While most SLA materials quickly degrade and change their properties, the best quality materials retain their mechanical properties for 5 years or more. There are materials with different properties, including tough, rigid, super hard, flexible rubber, transparent, high temperature resistant, and composites. Modern materials are often similar to conventional plastics such as ABS, PP, POM, Nylon, PA12, PEEK and can achieve resistance similar to thermoplastics.
brittleness - impact strength vs. generation
Some materials contain additives such as ceramics, mineral or carbon fibers, or graphene. There are also special lines, such as self-extinguishing (UL94 V0), electrically conductive or ESD materials, and what the ready-made materials do not offer, can be custom mixed.
Postprocessing is also a big topic, which has a fundamental effect on the mechanical resistance of the parts. Proper cleaning is key to ensuring the toughness and unbreakability of the materials. It is essential to follow the recommended procedures listed in the product sheet or in the IFU (Instructions for Use) document, where manufacturers describe appropriate methods for cleaning and curing printed parts. For example, simply ventilating for one hour after cleaning can increase resistance by up to 30%.
Durability is also affected by the design of the component itself. DLP and LCD stereolithography prints interior angles as sharp as they are defined in the design. These sharp corners can be a weak point, so it is advisable to round them off to prevent them from cracking.
This issue is vast and cannot be fully covered within the scope of this article. We will therefore be happy to share further experiences and findings with you in further publications.
What to look for in a material sheet
For most materials, you would needlessly search for the material sheet. However, some material brands realize that entry into industrial production requires certain guarantees. That is why they offer materials with an elaborate material sheet. This contains not only the basic mechanical properties, but also important information about the purpose of use, resistance, working temperature, absorbency, biocompatibility and electrotechnical properties.
One of the most important factors for users is the change in mechanical properties over time. Some material sheets therefore list aging tests due to heat, weather (sun, temperature fluctuations and humidity) and material behavior in a chemical environment.
Open access to materials
Many 3D printer manufacturers have realized that it is better to fully focus on perfecting their devices rather than trying to be materials manufacturers as well. That's why they opened up their systems and allowed their customers to take advantage of industrial materials from other brands.
BASF offers materials with medium durability that are easily printable even on low-end LCD printers and achieve good resolution. Although they are cheap, they have higher toxicity.
The Loctite brand produces safer materials, which are more expensive, but the result is always worth it. These materials are better printable at a higher temperature and greater light output, which DLP printers in particular have. However, with a little effort, they also work on low-end LCD printers.
Evonik brand materials are very well printable on all types of printers, are highly durable and require additional heat curing.
The Liqcreate brand offers more expensive but environmentally friendly materials with medium durability that can be printed even on low-end LCD printers.
Core Alpha is the most durable material, but requires a demanding 3D printing process and special vacuum heat curing equipment. This material is not easily usable for production.
Conclusion
Materials for stereolithography have been undergoing a renaissance in recent years and offer a number of advantages. Compared to other technologies, they have a much more diverse portfolio of materials, which are described in detail and allow for individual adaptation to our needs.
Even though these materials are more expensive, the technology is compact, has low energy consumption and is highly productive. Investments in a reliable and powerful high-end 3D printer do not exceed a million crowns. These printers have a lifespan of about a decade and require minimal servicing. There is gradual automation, simplification of surface treatment of printed parts and optimization of parts not only by lightening.
In many cases, it is therefore reasonable to consider or start adopting the replacement of conventional production methods with this technology. When putting it into practice, it is important to cooperate with a seller who has experience in production and can guide you through this issue without wasting time and money.
Do you want to bring your idea to life? Contact us for professional advice in SLA 3D printing. We will design the most suitable material, handle the complete production of your product, or deliver and help integrate the manufacturing process, including the technology.
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