Flipped 3D printer 25.03.2015

To invent something really new in a technology that has been around for years, you often need to look at it from the opposite side. Most likely, for this you will even have to turn everything upside down or turn it inside out. Thus, internal combustion engines supplanted external combustion engines, although engineers of the century before last predicted the future dominance of steam engines.

Now steam engines have remained only in the fantastic stories of the steampunk genre. True, gasoline engines already have every chance of remaining only on the pages of history, giving way to electric ones. There are many such examples, take the same computer mice that have evolved from ball mice with a cable tail to laser and wireless ones. Now, such a radical transformation may affect 3D printing technology, which has recently become widely available.

There are several different XNUMXD printing technologies, the essence of which is the layer-by-layer creation of an object of the desired shape. One of the widely used methods is laser stereolithography. How does it work? The product is created from a liquid photopolymer - a special substance that hardens under the action of an ultraviolet laser. The laser beam runs around the contour of the part, the areas illuminated by it become solid, and the unexposed areas remain liquid. The product being created is immersed layer by layer in a bath of liquid polymer. When the process is over, the finished part is removed from the bath, the unreacted polymer is removed and the final processing is carried out. The technology is well developed and used all over the world. But she has one drawback - the speed, which does not exceed a few millimeters per hour. After all, you always want to get the finished result as quickly as possible, and not wait half a day or longer, when it will finally be printed there.

What's so slow about 3D printing? It turned out that the slowest stage in the whole process is the curing of the polymer. And the point here is not in the laser or the polymer itself, but in the oxygen of the air. Molecules of this gas dissolve in the upper layer of the liquid polymer and slow down its hardening. Laser radiation creates active molecules that begin to bind the molecules of the polymer material to each other so that it becomes solid. Oxygen, on the other hand, actively interferes with this process, as a result of which the polymer hardens much longer than it could.

Of course, you can put a 3D printer in a sealed chamber, which will contain, say, nitrogen instead of oxygen, but this will completely ruin one of the main advantages of XNUMXD printing - ease of use. However, chemists, together with engineers, came up with a way to direct the "harmful" activity of oxygen molecules into a channel useful for technology, and were able to increase the printing speed by a hundred times. For this, it was just necessary to turn everything upside down.

How to prevent oxygen from reaching active polymer molecules? Since the option with a sealed chamber disappears at the very beginning, another one remains: what if printing is carried out not on the surface of a bath with liquid photopolymer, but at a depth where not a single oxygen molecule can reach from the surface? For example, make a bathtub with a transparent bottom and shine with a laser not from above, but from below. Then it would be possible to print the part, gradually pulling it out from under the layer of liquid polymer. The option is good, except for one thing - the polymer will begin to harden right at the point of contact with the transparent bottom, and the part being created will simply stick to the bath. This is where all the know-how of the invention lies. The developer managed to make sure that the manufactured part does not "burn" to the surface of the bath. And helped them in this, oddly enough, the same "bad" oxygen.

The bottom of the liquid polymer bath was made of a special Teflon material, through which oxygen molecules can almost freely penetrate, but at the same time it is transparent to ultraviolet laser radiation. What happens? Oxygen molecules penetrate such a membrane and dissolve in the near-bottom liquid layer. A laser beam shining through the membrane activates the photopolymer molecules, and they begin to bind to each other, but a thin layer saturated with oxygen prevents them from sticking to the bottom. The thickness of such a "non-stick" coating is only a few tens of micrometers - about the same as a human hair. By balancing the permeability of the membrane, the properties of the photopolymer, and the power of the laser, the entire 3D printing process can be made remarkably fast.

In their experiments, the developers of the technology have achieved a speed of 500 millimeters per hour, which is a hundred times faster than the printing speed using conventional laser stereolithography. And the printed product emerges spectacularly from a bath filled with liquid polymer.