3D printing: How does it work?
3D printing is not a technology that works in one and the same way. There are actually a multitude of methods for printing an object in 3D. If the techniques used differ in form, the principle always remains the same. It consists of superimposing layers of materials with a 3D printer according to the XYZ coordinates (width, depth, height) transmitted by a 3D file . The following guide shows how this technology works step by step, as well as the materials used in the 3D printing process.
How a 3D printer works
3D printing works according to several processes, which differ depending on the type of 3D printer used. We can classify these processes in three main groups:
– Material deposition
– Solidification by light
– Agglomeration by bonding
These three processes work according to the same basic principle, ie superimpose layers of materials according to the XYZ coordinates of a 3D file. The difference lies in the way its layers are deposited and processed, as well as the type of material used.
For most of the processes used the user needs:
– a 3D printer
– a consumable (filament, powder, etc.)
– a 3D file (most often in STL or OBJ format )
– a slicing software to slice the file and transmit the indications to the printer
– a computer
The way to export files to the printer differs between brands and models: USB cable, Wi-Fi or SD card.
1. 3D printing by material deposition
The majority of personal 3D printers work on this principle. FDM is the acronym for Fused Deposition Modeling which means “modeling by deposition of molten filament”. This process, which was invented in 1988 by the Stratasys company, is a registered trademark. We also speak of FFF (Fused Filament Fabrication) or even of MPD (Molten Polymer Deposition) which are themselves copyright-free terms. This technique consists in depositing layer by layer a filament of thermoplastic material melted at 200 ° C (on average) which by being superimposed gives shape to the object.
The print head moves according to the X, Y, and Z coordinates (length, width, and height) transmitted by a 3D file corresponding to the 3D model of the object to be printed. Limited for a long time to plastic-type materials such as classic PLA and ABS, 3D printing is seeing the arrival of new composite filaments based on metal (copper, bronze, etc.), carbon fibers, and even wood. More rarely, certain machines use waxes or polycarbonates. Today the food industry and medicine are gradually seizing this technique to print food and cells by adapting the extrusion head.
– Below is a tutorial video that will help you better understand the operation of an FDM 3D printer and the different stages of printing.
2. Solidification by light
Stereolithography is the first 3D printing technique to have been highlighted. If the paternity of this process is often attributed to the American Charles Hull founder of 3D Systems, we in fact owe this invention to three French people (Alain le Méhauté, Olivier de Witte, and Jean Claude André) whose patents although filed for 3 weeks earlier (July 16, 1984), were unfortunately not renewed.
Also called SLA (Apparatus Stereolithography) this technique consists in solidifying a photosensitive liquid by means of an ultraviolet laser beam. SLA-operated printers have four main parts: a tank that can be filled with a photopolymer liquid, a perforated platform that is lowered into the tank, ultraviolet (UV) radiation and a computer controlling the platform and the laser.
Just like the FDM, the printer will first analyze the CAD file, then depending on the shape of the object will add temporary fixings to it to hold some parts that could sag. Then the laser will start by touching and instantly hardening the first layer of the object to be printed. Once the initial layer of the object has hardened, the platform is lowered, then a new surface layer of liquid polymer is exposed. The laser again traces a cross section of the object that instantly sticks to the hardened part below.
This process is repeated over and over again until the entire object is formed and is fully submerged in the tank. The platform will then rise to reveal the finished object in three dimensions. After it has been rinsed with a liquid solvent to rid it of excess resin, the object is baked in an ultraviolet oven to harden the additional plastic.
Objects made according to stereolithography generally have a good quality of finish and detail (0.0005 mm) and very smooth and regular surfaces are obtained. Qualitatively it is one of the best 3D printing techniques currently. The time it takes to create an object with this technique also depends on the size of the machine used. The SLA also has the advantage of being able to produce large parts (several meters). For these objects it will take several days, a few hours for the smallest.
Among these drawbacks, a higher cost than FDM and a more limited range of materials and colors due to the polymers used as raw material. Solvents and polymer liquids also emit toxic vapors during printing, your room must be equipped with an extractor hood for ventilation.
The Polyjet process
This technology, patented by the Israeli-American company Objet Geometries Ltd (bought in 2012 by the American Stratasys), also works on the principle of photopolymerization. Likewise, the object will be modeled in 3D with specialized software ( AutoCAD for example) then its file sent to the 3D printer. The print heads will then drop photosensitive material onto a gel support, according to the coordinates transmitted by the file.
Once the material has been deposited, it will be exposed to an ultraviolet ray which will then harden it instantly. The operation will be repeated until the final object is obtained, then all that remains is to clean it. With an accuracy of around 0.005mm, it is possible to produce objects with a high level of detail and assembly parts that can fit together like gears.
Object Geometries subsequently refined this technique by developing Polyjet Matrix. With 96 tips for each of its printheads, it is possible for the user to combine several different materials, flexible or more rigid. By making it possible to create your own composite, this process offers the possibility of printing more varied and more complex objects.
This technique, created by an American student at a Texas university in 1980, was later developed (2003) by the German company EOS. Also called SLS (Selective Laser Sintering), it is also a laser printing process. This time a very powerful laser beam will merge a powder at very precise points defined by an STL file that your computer communicates to your 3D printer.
The powder particles under the effect of heat will then melt and eventually merge together. A new layer of fine powder is then spread and again hardened by the laser and then connected to the first. This operation is repeated several times until your part is finished. Then your part is lifted from loose powder and the object is brushed then sanded or hand-sanded for finishes.
The powder most often used for this type of printing is polyamide. White in color, this material is actually nylon. It will give your object a porous surface that can also be repainted if you want to give it color. Other components such as glass powder or ceramic can also be used. Often manufacturers use a mixture of two kinds of powders to obtain more successful objects.
On the same principle, we also find DMLS which is the abbreviation of Direct Metal Laser Sintering. This process makes it possible to produce metal objects, this time fusing a powder of fine metal particles. Almost any metal can be used, ranging from cobalt and titanium to steel and alloys like Inconel.
Even if its printing precision is lower than SLA, laser sintering makes it possible to manufacture parts with a fairly high level of detail (0.1mm) and with complex geometry. In addition, the remaining powder which has not been lasered can be reused the next time. Generally, the parts obtained with this process require more finishes (sanding, painting, varnish…) than the SLA because of its somewhat grainy finish.
3. Agglomeration of powder by gluing
Originally developed in 1993 in Massachusetts at the Institute of Technology (MIT) in 1993, 3DP (Three-Dimensional Printing) forms the basis of Z Corporation’s 3D printing process. The process consists of spreading a thin layer of composite powder on a platform. The print head will then deposit fine drops of colored glue on it, which, when combined, make it possible to obtain a wide range of colors. The platform lowers as the powder layers are glued until the final object is obtained.
For the finish, it is necessary to suck off the excess powder, brush and/or sand the part, then heat it to finalize the solidification. 3DP has the advantage of being fast and offering a wide range of colors. Up to 6 times cheaper than an SLA 3D printer, its price is more attractive despite the accuracy and sometimes lower print quality. Among the disadvantages, without post-printing treatment, the parts are more fragile and their surface is rougher.
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