There are different lasers used in different 3D printing technologies – the CO2 lasers, fiber lasers, LED lasers. You met with that before, that is for sure. But do you know when each of them is used and what is their influence on the whole 3D printing process?
Sintering process main actor: The Factor.
Different kind of laser has a different way of inducing light, so that means that a different factor causes the light to be made. In CO2 laser it is carbon dioxide cloud. But in general, construction of the different lasers is quite similar: there is always the cylinder surrounded by the medium, that shines into the cylinder just. On the bottom and top of the cylinder are two mirrors. And it is needed to illuminate enough light on both to make the pressure of this light and “force” the light to move from mirror to mirror. As a result, this will give us an ordered movement of this light.
Most of SLS 3D printers producers use CO2 lasers, we do it as well. And it is not because they are cheaper than in ex fiber one (if anyone will tell you ever that – please consider that he/ she do not know much about selective laser sintering process and polyamide powders). CO2 laser is used in SLS 3D printing devices because a very big part of power made by that laser is absorbed by polyamide powder, instead of being bounced off powder surface.
As it was already said, almost all producers equip theirs SLS 3D printers in CO2 lasers. And the reason is simple: that kind of power source is the best to work with polyamide powders. The light produced by CO2 lasers (with a length of 10.6 µm) is to a large extent absorbed by powder particles. If we will try to use in laser sintering process in. ex fiber or LED laser, the light would mostly be reflected from the powder, so losses in power will be really significant.
What about the power?
So why some producers use 30 W laser when the others install 60 W or 80 W ones? We hope it will not be surprising, but the power of installed in SLS 3D printer laser is not as important as many think. Crucial here is the right amount of energy pumped into the material in time. So more: If we have a weak laser installed the energy pumped into powder in time will be lower, whole 3D printing process much longer but otherwise it will give usually very nice surface. That means that the smaller the laser means the sintering is slower. But on the other hand, it gives better control over how you sinter. What does it mean?
Each laser is not completely stable. When we put our laser to work with 60% of its power, every laser will have some fluctuation and will give sometimes 55% of full power, sometimes 59% and sometimes 64%. Therefore, with smaller lasers, this deviation has finally a much lower value (5% of 30W). With more powerful lasers, the differences can be much larger (5% of 80W) and significantly affect the quality of the process and the model itself. So despite the long time needed to sinter the model, devices with weak lasers usually give models with a very nice surface. They use 100% of their power (30 W) it is much easier to control constant of the given power and stability of the sintering process. BUT. There is always “A BUT”. On the other hand, the laser constantly used at 100% of its power consumes significantly faster and its lifetime is finally much shorter.
Long-lasting & High Stability 80 W laser in SLS 3D printer? Yes, sure.
In SondaSYS devices we usually use 60 W or 80 W lasers, although the customer can also choose a 100 W laser. To effectively eliminate power fluctuations, this is an HS (high stability) quality laser, which ensures that the power fluctuations are less than 2%. Thanks to that we can use a fast laser with high power but also be sure that the surfaces of final models will be as good as the ones produced using slower, low power lasers. But that is not all. High stability laser allows us to change the laser beam diameter DURING the printing process to get models even faster (we sinter interior using a bigger laser beam and higher laser power and exterior with laser beam changed for smaller and also with lower laser power). The full power of the laser is used only when you need to quickly scan any surface and therefore quickly move the mirrors to fill the surface.
When having the 60 W or 80 W CO2 laser you may be sure that you will not often use it with full power. So even when after several hundred working hours its power will decrease the laser will still have full production ability and stability and power level enough to sinter high-quality models. On the other hand, it is not to achieve with SLS 3D printers that have from the beginning small lasers. Also worth noting is that laser working hours are not the same as the SLS 3D printer working hours. The laser operation time is only counted when it emits a beam. Realistically, during 10-15 seconds scanning the continuous laser operation is about 5 seconds. Usually if building the entire printout took several dozen hours, it is only several minutes of laser work.