3D printing technology is constantly evolving, and researchers and businesses are constantly developing new technologies and processes. One such technology, vat photopolymerisation or resin 3D printing, has evolved in this way. This article traces the evolution of resin 3D printing technologies through three generations.
It should be noted that, while resin was the first 3D printing technology, there are different 3D printers available that one can choose from to print parts depending on the material and application requirements.
Resin 3D Printing
Resin 3D printing is a type of 3D printing technology in which the build material is liquid photopolymer resin. It is popular for applications such as jewellery, dental and medical models, figurines, and other small to medium-sized objects due to its high-resolution and detailed prints. Resin 3D printing is well-known for its high surface finish, use of flexible and biocompatible materials, high precision, and even translucent parts.
It is, however, more complex and messier than FDM (Fused Deposition Modelling) and may necessitate more post-processing, such as cleaning and curing, before it can be safely handled.
A light source, typically a UV laser or a projector, is used in resin 3D printing to cure or solidify the resin layer by layer as the build platform is lowered into the resin vat. The 3D model is formed by the cured resin. Curing occurs layer by layer, and after each layer, the build platform moves in the z-axis, and the curing process continues until the entire model is printed.
According to ASTM, there are seven different 3D printer categories, and resin 3D printing is classified as a vat photopolymerization 3D printer.
For good reason, resin 3D printers are more expensive than filament printers. Although the precision equipment used in these printers is costly, the products produced have better strength properties, a better surface finish, greater accuracy and precision, and print faster than filament printers.
The three generations of Resin 3D printers are discussed below:
Evolution of Resin 3D Printing
First Generation: Stereolithography
Stereolithography (SLA) is the first patented and invented 3D printing technology. It began as a rapid prototyping tool but quickly evolved into a manufacturing technology. Because it is a resin 3D printing technology, it employs liquid resin materials, specifically thermosetting plastics, which are cured to form solid objects.
Thermosetting plastics, also known as thermosets, are polymers that solidify and harden permanently when heated. They cannot be melted and reshaped once they have been formed. They have a chemical structure that, once cured, forms cross-links between polymer chains that cannot be undone.
Working of Stereolithography
Stereolithography (SLA) employs a UV laser to cure the resin, resulting in 3D printed parts. Stereolithography is explained in detail below:
- The build platform is initially positioned or dipped in the tank at a height equal to the layer height. The UV laser is then activated and directed to the target on the resin via the scanning mirrors.
- The UV laser traces the design’s X-Y geometry or the cross-sectional area of the model to cure each individual point and thus the entire laser.
- After printing the first layer, the platform is raised and a wiping system sweeps through the bottom of the tank to remove any bubbles, reducing the likelihood of a print failure.
- The UV laser is turned back on to cure the model’s second layer. This procedure is repeated layer by layer until the entire model is constructed.
- After the model has been built, it is removed from the build platform and washed in a water bath before being washed in an isopropyl alcohol (IPA) bath to remove any residue resin that has adhered to the printer part. The part is then placed in a UV curing chamber to cure the resin and harden the model.
- After that, the model is cleaned and post-processed to remove any remaining uncured resin and smooth out any rough edges.
Some of the major disadvantages of the technology include the use of a costly laser, which raises the cost of the printer as well as any subsequent repair and replacement if the laser or galvanometers (Scanning mirrors) fail. Furthermore, because the technology employs a laser, which is a point source, it must trace individual points, slowing the printing speed.
Second Generation: Digital Light Processing
Digital Light Processing (DLP) is a 3D printing technology that falls under the category of Vat Photopolymerisation. This is the second generation of vat photopolymerization technology, which has addressed some of the most serious issues with SLA 3D printers.
With the exception of the light source, the operation of a DLP printer is similar to that of an SLA printer. DLP 3D printers use a light projector instead of a laser source like SLA. The projector prints an entire layer on a single flash by flashing an image of an entire cross-section. This allows for faster printing speeds and represents a significant improvement over traditional SLA printers.
DLP 3D printing technology has several advantages over other 3D printing technologies. One of the most significant advantages is the ability to produce highly detailed and accurate parts with smooth surfaces and high resolution. Furthermore, when compared to other types of 3D printing, DLP 3D printing is relatively fast, with many machines capable of printing a full object in just a few hours. The number of parts on a build plate has no effect on print speed, but it can have an effect on part quality because the limited number of pixels are distributed across the number of parts.
Another benefit of DLP 3D printing technology is the variety of materials that can be used. Photopolymer resins, for example, can be formulated to mimic the properties of a wide range of materials, including rubber, metal, ceramics, and even living tissue.
Carbon’s patented DLS™ (Digital Light Synthesis) technology is one of the most well-known examples of DLP printing technology. The DLS technology cures (hardens) a photosensitive liquid resin held in a vat above an ultraviolet light. The build platform is initially dipped in liquid resin before being drawn upwards to literally pull the 3D object out of the resin.
Third Generation: Masked Stereolithography
Masked Stereolithography (MSLA) is the third generation of resin 3D printers that builds on the first generation, SLA technology. It uses the same principles as traditional Stereolithography (SLA), but adds a mask to selectively cure the liquid resin.
A laser is used in traditional SLA to cure the entire surface of a vat of liquid resin, layer by layer, to create the 3D object. A digital mask is used in MSLA to selectively block light from certain areas of the vat, curing only the resin that is exposed to the light. This gives you more control over the curing process and allows you to produce more precise and detailed parts than a traditional SLA printer.
A computer controls the mask, which is placed between the projector and the resin vat. Because the mask can block certain areas of the projected light, only certain areas of the resin are cured. This allows for greater control over the curing process and the production of parts with greater precision and detail.
One of the primary benefits of MSLA is that it can produce parts with greater accuracy and precision than traditional SLA. Furthermore, MSLA is relatively fast, producing a complete object in a matter of hours. MSLA can also be used with a variety of materials, including photopolymer resins that can mimic the properties of rubber, metal, ceramics, and even living tissue. MSLA, on the other hand, has some limitations.
One of the most significant limitations is that the build volume of MSLA 3D printers is frequently smaller than that of other types of 3D printing. MSLA printers can only be used with bottom-up printers, and the light source must be strong enough to pass through the LCD screen and cure the resin. This high power degrades the LCD screen, which becomes a consumable and must be replaced on a regular basis.
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