by Cassandra Balentine
The use of UV and UV LED curing is particularly relevant to some areas of three-dimensional (3D) printing, additive manufacturing (AM) processes. UV and UV LED come into play for AM methods that work with resins, specifically photopolymerization-based processes like stereolithography (SLA), digital light processing (DLP), and multi-jet printing (MJP).
Final pieces and parts produced with resin-based AM and then UV cured range from medical instruments and medical implants to engineering prototypes, jewelry, footwear, and automotive parts.
“The power of UV curing lies in its ability to catalyze the transformation of liquid photopolymers into solid, 3D components. This pivotal technology is employed across a spectrum of AM methods,” shares Eugene Mikhaylichenko, director of sales and marketing, Uvitron International, Inc.
Stacy Hoge, marketing communications manager, Phoseon Technology, points out that UV LED curing presents a stable process that increases the strength, durability, and chemical resistance of 3D/AM printed parts on a commercial scale. “Reliable UV LED curing equipment benefits the 3D printing industry by providing fast, consistent, and reliable curing every time.”
UV curing in AM offers high reaction rate; small footprint—especially UV LED; low emissions as formulations are 100 percent reactive; unique performance properties like toughness; process flexibility and consistency; higher first time quality as the product can be handled immediately after forming; as well as less waste,” according to Colin Bergs, technical sales engineer, AMS Spectral UV, a Baldwin Company.
UV curing proves its merits in many ways. “Primarily, the materials that are UV-curable bring to the table superior mechanical properties. They span an impressive spectrum, offering everything from extreme flexibility to lasting durability, effectively imitating materials as diverse as rubber and glass,” explains Mikhaylichenko.
This type of versatility opens the door to additional applications, ranging from the creation of prototypes to the production of parts meant for end use.
Another attribute of UV curing is its exceptional speed and efficiency. “In an industry where each tick of the clock represents potential profits, the rapid curing times offered by UV light significantly expedite production timelines and cut down on costs,” notes Mikhaylichenko.
Along with speed, Mikhaylichenko says UV curing also ensures precision and sustainability. “It facilitates layer-by-layer curing, providing the ability to create complex geometries, intricate details, and internal features that are difficult to achieve with conventional manufacturing techniques. Moreover, UV curing contributes to the ‘green’ revolution in AM. By utilizing just the right amount of material, it minimizes waste, and the materials it employs are frequently more eco-friendly compared to those used in other manufacturing methods.”
UV Curing Process in AM
UV curing in AM generally begins with a digital design of the object, which is usually created with 3D modeling software. “This design is then sliced into very thin layers by a specialized software program, preparing it for the AM process,” explains Mikhaylichenko.
Depending on the specific AM method used, steps typically include a layer-by-layer construction, UV curing, and post processing.
The process starts in a UV-curable resin tank and the 3D printer constructs the object layer by layer. This is followed by UV curing. “The key role of UV curing in this process is to harden or cure the UV-reactive resin. When exposed to UV light, the resin undergoes a chemical reaction known as photopolymerization,” explains Mikhaylichenko.
Following the completion of the printing process, Mikhaylichenko says it’s often necessary for the printed object to undergo further treatments. “This might include steps such as cleaning of uncured material residue, an additional UV curing stage to improve hardening and reduce surface tack, and occasionally some finalizing procedures to ensure the object’s surface is sleek and immaculate.”
Bergs adds that each layer of 3D printed material is cured with UV light absorbed by photoinitiators (PIs), which are formulated to match the required peak wavelength to cure the product instantly. “The outcome is a product that is ready to use and does not require a secondary cure.”
“AM processes that require a long printing cycle or use heat-sensitive materials benefit the most from UV LED curing,” comments Hoge.
Mikhaylichenko points out that for SLA, UV curing systems create objects by focusing a UV laser onto a vat of photopolymer resin. As the laser traces a pre-defined design, the photopolymer hardens, building the object layer by layer. “Post-processing UV curing systems play a crucial role in solidifying these intricate designs and adding a polished finish,” he shares.
When it comes to DLP, it follows a similar path to SLA, but with a digital projector screen to expose the entire layer of resin at once, rather than a UV laser tracing the design. “This simultaneous exposure and curing by UV light expedites the process, and post-processing UV curing systems are instrumental in enhancing the speed and efficiency of this method,” notes Mikhaylichenko.
MJP jets photopolymer materials onto a build platform, which are immediately cured by UV light to solidify them. This method is renowned for its high resolution, precision, and ability to print in multiple materials and colors simultaneously. “UV curing systems here in the post-processing stage ensure that high standards of precision are maintained while offering a tack-free and smooth finish to the printed objects,” adds Mikhaylichenko.
Material jetting is a popular technology used for 3D printing, which can be UV cured. “PolyJet belongs to the family of material jetting AM processes. The PolyJet 3D printer sprays photo-sensitive resin material layer by layer onto the print tray until the parts are completed. Each layer of material is cured with UV light while being sprayed and can be taken out and used immediately without secondary curing. It can realize the combination of color and multi-materials in a single printing to produce a prototype close to the real product. It is also used to print quick molds and verify product designs. Full color, multi-material 3D printers can mix six materials at the same time to achieve 500,000 colors, different textures, transparency, and softness. Products are widely used in medicine, education, and engineering models,” shares Hoge.
Each of these processes benefit from UV curing, not only because of the high resolution, fine detail, and smooth surface finish that can be achieved, but also due to the variety of materials utilized and the rapid production times possible, according to Mikhaylichenko.
With a reliable UV LED light source, Hoge says customers can run a stable process for a long time, with some printing cycles reaching over 48 hours. The UV LED printing process offers the highest efficiency, printing accuracy, and most yield to fulfill the end customer’s stringent requirements. LED technology allows users to cure heat-sensitive materials offering new revenue opportunities for printers.
“The final outcome of this process is a 3D object created from a digital design, exhibiting high resolution and detail. The object can be as strong and durable as the UV-curable material allows,” shares Mikhaylichenko. “This gives UV curing a significant advantage over other 3D printing technologies as it can produce parts that are not just prototypes but are also strong enough for end-use applications in various industries.”
Material Considerations
The use of UV curing in AM is recognized for resin-based processes.
Bergs points out that formulations that can be UV cured must be specifically created to do so. “There is a specific chemical class of PIs that absorb UV energy and then transform to a compound that is highly reactive to start the polymerization process.”
Therefore, Bergs explains that UV curing in AM works very well with resins, which aid in enhancing the material properties. “Through the use of UV curing, AM processes are quicker with higher quality product as a final result.”
For the most part, Hoge says LED cured AM materials are acrylate-based, which is the same as what is seen in inks, adhesives, and coatings—i.e. monomers, oligomers, and PIs. “It is likely that some 3D printers are using other atypical chemistries with LED high UVA wavelength energy to cure,” she notes.
In addition to photopolymer, other substances are tailored to respond to UV light. UV-curable inks, coatings, and adhesives are common examples that are employed across various industries. “These substances contain PIs—compounds that react to UV light to trigger hardening or curing. In the realm of AM, efforts are underway to widen the array of UV-curable materials, beyond just photopolymer resins,” says Mikhaylichenko.
UV and UV LED Trends in AM
Experts expect an increase in use of UV curing within certain AM technologies.
Hoge specifically sees growth with UV LED curing technology because it offers a consistent, reliable process that runs on a wide range of heat-sensitive materials for a long period of time.
Bergs predicts growth will come as companies try to move away from conventional UV, which is not as energy efficient as UV LED. “As more formulators make products with LED UV curing capability the market use will increase significantly. LED UV is the future for sustainable curing in almost every industry that uses UV in their processes.”
A primary driving force is the continuous advancement in UV curing and AM technologies. “The constant innovation we are observing in UV light sources, photopolymers, and 3D printing hardware and software ensures a bright future for this sector. As these technologies mature, they create an effective synergy, further enhancing the efficiency and capabilities of UV-cured AM,” comments Mikhaylichenko.
Another compelling factor is the increasing adoption of AM across an array of industries. “Whether it’s aerospace or healthcare, automotive or consumer goods, companies leverage AM for rapid prototyping, customization, and in some areas such as the dental industry, even large-scale production. As more sectors uncover the unique benefits of UV-cured 3D printing—namely, high resolution, superb mechanical properties, and rapid production times—we see continued growth in the demand for UV curing within AM,” states Mikhaylichenko.
Further, he says the emphasis on sustainability in the manufacturing industry also contributes to this upward trend. UV-cured AM presents a “greener” alternative to traditional manufacturing methods, minimizing waste through efficient material usage and reducing the carbon footprint by consuming less energy. As the shift towards environmentally friendly manufacturing solutions gains momentum with more countries introducing expanding environmental regulations, UV-cured AM is likely to generate increasing attention.
Mikhaylichenko believes the recent COVID-19 pandemic with its supply chain issues underscored the value of AM in fulfilling urgent, large-scale requirements, such as the production of medical equipment and personal protective gear. “This realization may result in more industries incorporating AM as a dependable contingency strategy, thereby broadening the scope for UV curing applications.”
Advantages to AM
UV and UV LED curing bring certain benefits to AM, including faster print speeds, increased durability, consistent curing over time, and reduced environmental impact compared to traditional methods, lists Hoge.
Mikhaylichenko says in its work specializing in the post-processing stage of AM, Uvitron found UV curing systems to be instrumental in enhancing the quality and efficiency of the final product. A few key advantages he’s observed include speed and efficiency, exceptional detail, versatility and robustness, and sustainability.
In terms of speed, UV curing systems rapidly solidify each layer of the product, thereby significantly reducing production times. This increase in speed allows companies to expedite their production cycles, enhancing overall productivity and reducing the time-to-market of their products, according to Mikhaylichenko.
When it comes to detail, Mikhaylichenko feels that the advantage of UV curing systems lies in their capacity to yield high-detail results. “They allow for the creation of intricate designs and complex geometries, which might be difficult or even impossible to achieve with other manufacturing methods.”
Versatility comes with the ability of UV curing systems to be employed with a wide and continuously expanding array of UV-curable materials. It enables the creation of easily customized products with varying properties, rendering UV curing relevant across a range of industries, according to Mikhaylichenko.
And for sustainability, UV curing systems contribute to a more environmentally conscious manufacturing process. They efficiently utilize materials, curing only what’s necessary, and typically consume less energy than other techniques. “This aspect can help reduce the overall environmental impact of the manufacturing process,” says Mikhaylichenko.
Future of UV and AM
The future is bright for 3D printing and AM, and UV is along for the ride.
“As more research and development is done to push the performance of UV-cured resins, the future will offer the ability to print on a wider range of materials and substrates enabling new applications,” predicts Hoge.
Mikhaylichenko anticipates several developments that will influence its specialization in the post-processing stage of AM. “Firstly, we foresee a wider range of UV-curable materials. Today, photopolymer resins are primarily used, but ongoing research aims to bring UV-curable ceramics, composites, and even metals into the fold. This progression would expand the scope of UV-cured AM, paving the way for more diverse end products and broader industrial applications.”
Mikhaylichenko also foresees improvements in UV light sources, which are crucial for post curing. For instance, LED technology advancements offer lower energy consumption and extended operational life, promising to significantly improve UV curing efficiency. “More precise control over wavelength and intensity could also unlock a new level of curing precision and expand material options.”
The fusion of UV curing with other emerging technologies is another exciting prospect. “Integrating artificial intelligence and machine learning, for example, could optimize the curing process, reducing errors and enhancing efficiency. Pairing UV curing with 3D scanning technologies may also facilitate real-time monitoring and quality control during the AM process,” comments Mikhaylichenko.
Lastly, the exploration of functional UV-curable materials holds immense potential. “The incorporation of additives or nanoparticles into UV-curable formulations could introduce specific properties like conductivity, thermal resistance, or antimicrobial characteristics. Such advancements would open new opportunities for producing electronic components, heat-resistant parts, or even biomedical devices through UV curing,” shares Mikhaylichenko.
“With more industries utilizing this technology there will be an even larger demand for UV curing,” advises Bergs.
Expanding UV
UV-curable materials are utilized in resin-based processes, most commonly SLA, DLP, and MJP. The use of UV and UV curing is expected to expand into the future.
“In our efforts to drive innovation in the AM industry, we are focused on exploring and expanding the possibilities of UV curing,” says Mikhaylichenko. “Integrating these technologies is key to reaching new avenues for fast prototyping and mass customization across various sectors such as automotive, aerospace, healthcare, and consumer goods. As we move ahead, our commitment is to deliver reliable and efficient UV curing systems that fuel the future of AM.”
Sep2023, Industrial Print Magazine
