After more than three years of R&D, Structo has developed a truly unique method of SLA printing for the industrial 3D printing market. Structo’s proprietary liquid crystal mask technology (MSLA) is what allows their printers to be much faster than competing 3D printers, especially when printing large objects. This paper outlines the limitations with current SLA machines and how Structo’s MSLA technology is able to overcome these limitations.
Innovation on a conceptual level
All inkjet- or laser based AM machines are inherently difficult to scale without sacrificing printing speed, because they employ moving parts in the XY plane. These types of printers always require a number of passes or motions along a path to print a single layer, which means that it takes a proportionally longer time to print larger objects as compared to smaller ones. For example, laser-based SLA printers utilize one or more laser beams that can be directed to illuminate desired patterns in a layer of photocurable resin. If the complexity or size of the desired object is increased, the laser beams will take a proportionally longer time to trace the required path to illuminate all areas required to form the layer of that object.
Naturally, all 3D printer OEM’s are working on ways to increase printing speed, but generally only incremental improvements are made by adding more nozzles, print heads or laser beams. Structo’s founding team has reinvented stereolithography with a fundamentally different approach; drawing inspiration from mask lithography used in IC manufacturing, Structo’s technology utilizes a panel light source array and a liquid crystal film mask to control which regions in the printing plane are illuminated by the light source.
This process allows all features in the XY plane to be cured in a single exposure, and although the same is achievable with micromirror-based illumination technologies, Structo’s method is uniquely capable of being scaled to industrial dimensions without sacrificing light intensity per unit surface area and thereby printing speed.
Inside Structo’s print engine, a light source of the appropriate wavelength emits uniform and collimated light toward the liquid crystal layer, which is capable of being either transparent or opaque to the incident light. Wherever the liquid crystal panel permits light to pass through it, the light will travel onward and strike photocurable resin, immediately curing it. The central processing unit in the printer sends new mask patterns to the liquid crystal panel for each layer of the desired object, and in this way layer-by-layer printing is accomplished.
Each layer of an object can be cured in a mere 2-5 seconds regardless of the size and complexity, which can be qualified as relatively fast by anyone versed in using conventional SLA printers. Structo has matched the emission wavelength of the light source to the peak absorption wavelength of its resin formulations, this optimizing the speed of printing by the fastest possible curing process.
DMD (DLP) vs LCD
A competing method of achieving high speed layer-by-layer printing utilizes a digital micromirror device for the projection of layer images. The DMD stereolithographic printers, generally known as DLP printers, which use this technology have been in the market for several years and have found wide adoption across a range of industries.
The key difference between DLP-based printers and Structo’s MSLA technology is that the latter utilizes an array of hundreds of individual emitters, rather than a single point emitter light source like a laser diode or DLP bulb. The light source array can be scaled to virtually any size by adding more emitter units, without reducing the intensity per unit surface area, and thereby enabling the same per-layer exposure time at virtually any size for which a liquid crystal film mask can be manufactured.
DLP printers utilize an array of microreflectors to project an image onto a layer of resin, but the size of the image is restricted by the resolution of the array, which means that with DLP technology there will always be a trade-off between the build size surface area and XY resolution: printing larger objects requires sacrificing print quality, whereas liquid crystal mask panels can be manufactured to virtually any size and resolution (pixel density).
A further disadvantage of DLP printers is that the very nature of the single-point emitter (bulb light source) causes unequal exposure between the centre and the edges/corners of the print area. Even with lenses and other optics, DLP-based printers typically have higher intensity light near the centre of the build area than near the edges. This means that at any given setting, either objects at the centre are being overexposed (therefore inaccurate), or objects near the edges are failing to print due to underexposure. Structo’s MSLA technology resolves this issue as the array lightsource provides uniform and equal light intensity across the entire print area to achieve the consistent and accurate printing of laser-based machines, at speeds exceeding even the fastest DLP-based printers.
Structo is currently transitioning from the R&D phase to technology commercialization, and is running beta-tests with their patented technology for selected users across a variety of end-use applications. The industrial-scale RapidForm printer is targeted at service bureaus, who require high throughput 3D printers to match their growing demand. The smaller OmniForm is an office friendly printer targeted primarily at product designers as well as architectural, engineering and healthcare industries. Given the uniqueness of the orthodontic market for high volume customized manufacturing Structo’s OrthoForm printer was specifically designed to meet dental clinics’ and labs’ need for high printing throughput in clean office, clinic and laboratory environments.