We had a chat with Charles Bibas, the CEO of Tecnica, a producer of a SLS 3D printer with a very unusual light engine.
SLS, or “Selective Laser Sintering” is a process in which a laser melts portions of a flat bed of thermoplastic powder in successive layers to gradually build up an object. It’s one of the most well-regarded 3D printing processes as it has the ability to produce objects with high resolution and without the need for support material (the surrounding unfused powder provides support automatically).
However, SLS is not without its issues.
SLS 3D Printing Issues
Typical light engine on an SLS 3D printer [Source: Tecnica]
Most of the SLS systems seen today use a galvanometric mechanism for aiming the laser at the powder bed. Basically, the heavy and powerful laser is mounted in a static position, and it fires at a mirror. The mirror can precisely tilt to aim the laser beam at the correct spot on the powder bed.
At first, you’d think this is an effective system, but there’s a problem: as the laser beam is tilted further and further towards the edges of the powder bed, the angle of the beam results in a distorted melt spot. A perfectly vertical beam would generate a perfectly round laser dot, but on the edges it would be an ellipse.
The misshapen laser dot results in less energy per area, causing complications in achieving constant print quality throughout the build. Also, the speed of the dot can increase as it gets further from vertical, if the mirror rotates at a constant rate. This can also decrease the energy per area per time.
Some systems attempt to solve this dilemma with an f-theta lens system. However, the presence of a lens in the light path means that it is subject to the same energy intended to hit the powder bed, and thus causes constraints on how powerful the laser can be.
Finally, scaling up this type of system is challenging because in order to minimize the laser dot ellipse problem, the mirror must be mounted ever-higher. This is why you often see rather tall powder bed / laser systems, and we wrote about this issue a two years ago.
Tecnica began in 2013 when the founders attempted to use 3D printers of the day for another project, and found them problematic. They set out to redesign the SLS process to make it more efficient and effective. The result was a new concept for SLS light engines.
Tecnica’s advanced SLS light engine concept [Source: Tecnica]
Tecnica’s solution is quite elegant. Instead of using a galvanometer to quickly tilt a mirror to and fro, they use a fixed concave mirror and a constantly rotating mirror.
As the rotating mirror turns, it sweeps the laser beam along the concave mirror where it is reflected downward in a perfectly straight manner. No lens system is required to make adjustments to the beam.
You can see how this works in Tecnica’s animation video:
Of course, Tecnica has patented all of this concept in a number of patents, which they display prominently on all of their material. For those interested, they are:
There are multiple advantages to this approach:
No lenses are used, thus the laser energy can be ramped up to higher levels
Increased laser power means printing can take place much faster
Eliminates the possibility of light aberrations caused by lenses
Laser impact energy is identical regardless of the location on the powder surface
The mirror’s constant rotation provides a smoother and more consistent position than a tilting mirror that must respond to arbitrary directional changes
The concept can be scaled up significantly
The Tecnical’s concept might result in a doubling of 3D print speed with higher quality prints.
I asked Bibas how the concept could be scaled, and he suggested that with their existing access to third party components, a single linear actuator could produce a build volume of 6 x 2 x 1 meters. With two actuators, 6 x 6 x 1 meters. That’s quite large, as large as any of the largest 3D printers you can find today.
“Because we solved the nonlinearity issue we moved the burden to third party vendors/manufacturers. If someone wants to get the benefit of speed then they need a higher power laser to accommodate for higher energy delivery at high speed. If someone wants a large printer then they will turn to the actuators company to deliver a long actuator with small repeating error (error in micrometer when the actuators need to go back to a set point). Similarly, a third party vendor can improve on the Z and get it to be more than 1 meter in depth.”
One thought I had was that the powder bed / laser concept is used for not only thermoplastic materials, but also for metal powder. In fact, most of today’s metal 3D printers use a light engine very similar in concept to those used in SLS systems. Could the Tecnica concept be used for metal powder?
Bibas explained that their current device, the CASA and CASA Pro, are intended for use as SLS systems with thermoplastic powders. However, their next generation device, the upcoming Optima machine, will be able to 3D print in metal powder.
Tecnica 3D Printer Specifications
The CASA and CASA Pro will both offer a modest build volume of 92 x 120 x 140 mm. The base CASA machine has a resolution of 0.2mm with a beam diameter of 0.2mm. The CASA Pro has slightly better resolution.
However, the most interesting feature could be the price point for these machines. The CASA is priced at only US$18,000, and the CASA Pro at US$24,000. That is substantially less than commercial SLS systems, albeit the build volume on the CASA is a bit smaller.
Based on this price level, it’s likely the larger systems Tecnica will eventually build and sell will cause a price shift in the commercial SLS market.
Can you buy a CASA? Yes and no. At this stage they have only a proof-of-concept machine (shown at top) and are in the process of building ten “pilot” devices. If you’re interested in trying out this concept, Tecnica will sell you one of the ten units for only US$12,000 and provide “unlimited support and handholding for a year.”
I’m quite interested to see how this technology unfolds over the next few years.