The 3D printer is the object of desire for many people now … but how does a 3D printer work? What can you do with this tool? Our guide wants to treat the 3D printer in all respects, from functioning to finishing materials.

INTRODUCTION

The 3D printer can be considered a natural evolution of a 2D printer, then laser or inkjet (the common office printers). The main difference lies in the type of “ink” and the support used. Obviously, while traditional printers use paper material as a support and print texts and images by depositing layers of liquid ink or toner powder (for laser models), the 3D printer uses a filament of plastic material that is deposited layer on layer until you get the object in 3 dimensions. As we will see later, there are various methods of printing. The case just examined is the FDM (fused deposition modeling), cited because it is the easiest to explain to all those people who are approaching this new world.

3D printers differ from CNC milling machines because they use subtractive techniques, while the former use additive technology. Modern 3D printers are having considerable success on the market because they are the fastest and most effective tool for creating three-dimensional objects with additive technology.

Another substantial difference compared to other tools is that, unlike inkjet or laser printers where there is a sort of oligopoly in the market, 3D printer manufacturers are dozens (if not hundreds now) and their number is soaring every month. This number of manufacturers in the 3D printer market can only be good for the end user who, by now, can buy a 3D printer (even if small) at a price very similar to that of a 2D printer. Another factor that marked the price drop (and the invasion of the market by many companies) lies in the fact that the patent for the FDM technique, developed by 3D SYSTEM, expired in 2005.

WHAT ARE THEY FOR?

The field of action of 3D printers was from the beginning the industrial one.This type of machine can in fact be used for prototyping relatively quickly and inexpensively. This allows engineers and designers to touch their creations with no need to start a real production process. Consider, for example, the mechanical sector, where the components of an engine or any other equipment can be printed for in-depth analysis, rather than being observed exclusively on the monitor during the design phase.

Things have changed a bit in recent years. 3D printing is no longer an exclusive of large companies, but has also reached the domestic environment .To get an idea of the trend, the popular Swedish portal The Pirate Bay opened at the beginning of 2012 a section dedicated to sharing files to be fed to this type of printer, to create models of any kind: from toys to models, passing through logos, representations of paintings in three dimensions and much more.

In other words, the only limits are dictated by the imagination and the size of the printer. He had the “Liberator” affair discussed, a real do-it-yourself gun, whose files ended up last year on P2P circuits to be downloaded by thousands of users in just a few hours.

There are those who have chosen to use this technology as an expressive means for their art: this is the case of the Dutch designer Iris van Harpen, who has dressed the models with a collection of catwalk dresses entirely printed in three dimensions.

Even medicine is looking with increasing interest to these technologies: we have already spoken several times about the possibility of printing prostheses or even entire organs, with research already started also on the reproduction of tissues and blood vessels to be implanted in patients where traditional techniques do not they should prove to be effective.

Not to mention the space projects are in fact, studying new technologies to bring 3D printers on other planets, where they can independently print the components needed to build space bases, without the direct human intervention.

OPERATION AND PRINTING METHOD

To make an object through 3D printing there is more than one technique. The queen technology (due precisely to low cost) is certainly the fused deposition modeling (FDM). Other printing techniques are the SLS – selective laser sintering, the Digital Light Processing – DLP, as well as other methods used for the realization of objects in metal alloys and other materials. Now we will analyze some of the most common methods.

FDM – fusion method – fused deposition modeling. It is a technology developed by Stratasys, a leading company in the market, which uses traditional rapid prototyping. This process requires that a filament made of polymers (of different diameters, among which the most used and available on the market are 3 mm and 1.75 mm) heated by a resistance (up to temperatures of 250 ° C) is passed through a nozzle, which layer it layer by layer to give shape to the object. Currently there are many materials that support this technique, in fact it is widely used in the consumer market. The most common are:
PLA (organic derivation – corn), ABS, Laywood (PLA mixed with wood sawdust), PVA, HIPS, rubber materials like Ninja flex. Month after month new 3D printers are introduced onto the market that use this technique because it is the one that allows to have the lowest selling price. With the increasing diffusion of these economical 3D printers, there is a flourishing of new materials suitable for the most disparate purposes. The 4DOITaly 3D printers work like this.





SLA – Stereolithography: Patented by Chuck Hull in 1986, stereolithography uses a photopolymerization process to solidify a liquid resin. Similar to DLP, this technique varies only for the type of light, which in this case is a laser. The main limits are determined by the scarce availability, potential toxicity and high cost of photosensitive resins; the lack of mechanical resistance of the prototypes and the tendency of the latter to deform with relative rapidity over time due to the action of ambient light.

DLP – digital light processing: Depending on the type of light used to selectively solidify the material, it is called SLA, which generally uses a laser source, or DLP, which employs LED or LCD projectors to polymerise, generally from below, a layer in a tank containing the liquid photopolymer. This polymer is exposed to the light of a DLP projector in inattinic light conditions, so the exposed liquid hardens, the construction plate moves up a few tenths of a millimeter and the liquid polymer is again exposed to light. The process is repeated until the model is finished. This technology, originally used to create professional and industrial printers with particularly high costs, is now experiencing a process of democratization and promises the advent of high-resolution printers with popular prices in the market.

PP – method with powder bed and linkjet heads – Plaster-based 3D Printing:This 3D printing method consists of using an inkjet head which deposits a binder on a bed of powder (gypsum, starch, resins), proceeding with a layer in layer until the completion of the model. The printer creates the model one layer at a time, spreading a layer of powder (gypsum or resins) and printing a binder in the cross section of the part with the ink jet. The process is repeated until each layer is printed. This method also makes it possible to make protrusions, in fact the powder not reached by the binder supports the model, and in this way it is possible to create practically any undercut. It is also recognized as the fastest method. A great advantage of this technique is the possibility of mixing color to the binder, creating objects with real colors. The poor mechanical resistance and the porous appearance of the surfaces of the created models unfortunately represent the limits of this technique. The aesthetics and functionality of the models can be improved with subsequent treatments with waxes and polymers by impregnation.

RESOLUTION:

What’s this? Is it better if it is lower or higher? Many people ask themselves these questions by reading the characteristics of each 3D printer. Yes, because after the print volume, which varies depending on the 3D printer, the other feature that you immediately look at is the resolution. By “resolution” of a 3D printer we mean the minimum thickness of material with which a 3D print can realize an object. Usually expressed in microns, it can range from 100 to 300 microns for a common 3D printer with FDM technique, up to “stratospheric” levels of 10 microns for some models in SLS or DLP. Therefore it is clear that the lower the resolution value, the more the layer of material is up and therefore more defined (the layers are so fine as to make the object appear smooth and uniform). But be careful, because the more the layer is fine the more the times to realize the object will lengthen: as always we must find the right compromise (at least with current technologies). Some technical data sheets also give the possibility to know the XY resolution (therefore on the XY plane which is two-dimensional, whereas the resolution mentioned above is on the Z axis) which, however, can be measured in dpi as for common inkjet or laser printers.

The question arises: is a beautiful / high resolution object automatically accurate? No! The two concepts are unrelated and it is in fact possible to have objects with an incredible resolution and beautiful to see but, when we go to measure them, they turn out to be completely out of tolerance compared to the measures set to CAD. On the contrary, I can have an “ugly” object to look at but very precise in terms of dimensions. I would like to clarify that in these last lines the precise term was used in an unsuitable way because the correct term to use is accurate . If my machine prints a 20×20 mm CAD cube and I measure 20.1X20.1 mm, I can define accurate printing. If I then decide to print several cubes placed on the printing plate, and the measurements taken at the end of the print are very similar to each other, then I can say that my machine is precise and therefore has good repeatability. On the single piece it is easy to stay in tight tolerances: different when the machine has to work on a very large (and perhaps heated) plate where variations in the inclination of the plane or the temperature of it can lead to substantial differences between the various objects printed on its.

Little clarification on the XY resolution: as for the one in Z, this planar resolution allows us to obtain high quality artefacts but it is not said that then they are accurate in terms of size. In particular we can define it as the “ability to reproduce the smallest detail” that is, the smaller the movements of my machine will be and the better / more defined will be the details of a print (the details of a face for example). Thanks to the microstepping of the new print drivers it is possible to obtain really insignificant and almost imperceptible movements to the human eye: therefore you are wondering why FDM filament 3D printers are not used in the field of jewelery or for example miniatures from modeling. The answer is simple: while those used for dental and jewelry use a laser with a 50 micron spot or a DLP projector with a single pixel projection of even 49 microns (which translates into miniscule details perfectly reproduced), in the 3D printing FDM comes into play a component that shuffles all the cards … the NOZZLE or NOZZLE.

We can therefore have the machine with perfect movements, high microstepping, etc., but in the end the least reproducible detail is determined by the nozzle DIAMETER . The filament, in this exact point, passes from its nominal diameter of 1.75 mm (or 3.00 mm) up to 0.4 / 0.35 mm (400/350 micron) on average. As a consequence, very small objects with details below this size are NOT reproduced. To make the difference clearer here is a series of explanatory images:

It is evident that using a much higher nozzle leads to better definition of the object. But this benefit also brings a major disadvantage: print times can even double or even triple. Furthermore, with some materials, in combination with very thin nozzles, there could also be delamination due to poor interlayer adhesion. These will however be topics covered in a separate article.

In the picture above it is possible to notice that with the 0.8 mm nozzle details are lost, or better, the details of the face are as blunt and not very defined. In the case of very small details, these may not even be reproduced.

In summary:

  • Resolution in XY and Z determine how much an object is beautiful, finished and all its details.
  • Accuracy and repeatability / precision help us to understand how much our printed object will be faithful, in dimensional terms, to the computer model

We hope that with this article some doubts about this technology we have found an answer, if not, please contact us for further questions or just for clarification, so as to keep constantly updated this article.
We thank the sources from which parts of the information and images were taken to create this article:

  • http://www.stampa3d-forum.it/
  • http://www.webnews.it/
  • https://help3d.it/