In the meantime, 3D printers can print out almost anything they want: small household plastic particles that no longer exist on the market, pawns, entire houses, real food, and even weapons. A recent episode of the US television series “Good Wife” (broadcast in July 2016) is concerned with the weapons issue, which is considered extremely sensitive: The material is plastic and therefore by metal detectors cannot be tracked, the blueprints are available as free files on the net. How does the magic work called 3D printing work?
The essential operation of 3D printers
- As a template for 3D printing is not a text file as with ordinary printers, but a 3D template, as it can be designed with CAD software.
- The most common file types are STL (Standard Triangulation Language), VRML (Virtual Reality Modeling Language), and X3D (Extensible 3D).
- These templates “feed” the 3D printer. The model is then built up from fusible materials, powder, or even from a particular liquid.
- All three common 3D printer types apply thin layers that are cured individually.
3D printing process
Of course, the chances of being able to make any part yourself with a 3D printer are incredibly tempting. Therefore, the possibilities arouse great interest, especially since the required devices are so cheap that they are of interest to private users. But the process is by no means entirely new; it has only been in the spotlight of the general public for several years.
The industry has been using 3D printing for a long time to develop their prototypes and also for small batches. But it was a long time costly, only recently it was exciting as a playground for hobbyists. And still, it seems relatively complicated, which often scares off interested parties away from the cost of a 3D printer. Important to know: There is no single 3D printing process.
3D printing is a collective term for several production techniques according to different principles. Each of these techniques requires particular materials. The only common denominator is the production of three-dimensional objects through the layered construction of equipment. These are additive (adding) methods, as opposed to the subtractive (removal) methods of water-jet milling, planing, sawing, drilling or separation.
3D Printing Method Fused Deposition Modeling
The so-called FDM processes materials that are softened by heat and thus malleable, i.e., thermoplastics such as PLA or ABS, as well as modeling wax and chocolate for the 3D printing of food. The printhead of an FDM machine is a hot nozzle. In this, the solid raw material is pressed in, it liquefies and emerges as a thin, soft thread. The printhead thus records layers of the desired object. Outer contours are modeled as a bounding line; the surfaces are hatchings. When a layer is finished, the head draws the next layer.
FDM 3D printers are relatively inexpensive and dominate the craft market, using filament (plastic wire) in thicknesses of 1.75 or 3.0 mm as raw material. The cable is fixed in the initial state, so there is also the name FFF printer for “Fused Filament Fabrication.” The relatively simple system takes time because plastic does not freeze immediately.
The structures must first be supported, so the software adds grid structures from the plastic, which the user finally breaks off and also loops away. There are also soluble or other support structures. The finished parts you can see the process; they are fluted, which does not necessarily disturb.
- It uses materials that become liquid or malleable under heat – for example, thermoplastics such as PVA, PET, and nylon, but also chocolate and wax.
- The material is heated in a nozzle and liquefied. Afterward, it is – in a similar way to traditional printing – applied to one level at specific points and then cooled so that it hardens.
- Thus, as with the other methods, one layer after the other.
- Again, there is a disadvantage that the model does not fully cure immediately. Therefore support structures may have to be planned.
- For printer and materials are relatively cheap, so they are also suitable for home users.
Selective Laser Melting: powder and light for 3D printing
The industry uses harder materials for their prototypes, namely steel, titanium, or polyamide in powdered form. The powder is blown out and then solidified by the print head in the desired shape. A laser beam does this and pinpoints granules for granules, which gave the process the name SLM for Selective Laser Melting or SLS for Selective Laser Sintering.
Even colors can be added; the color also serves as an adhesive between the powder granules. In contrast to the FDM process, there are no overhangs on the finished object; fresh powder falls. The surfaces of such prints are rough and resemble fine sandpaper; the objects are robust, elastic, and also very filigree. Color printers using SLM technology can be used to produce very realistic miniatures.
- In laser sintering, not only one tank is used, but two tanks arranged side by side, each with one lifting platform.
- In a basin, the powder is used as the starting material (in the picture on the left).
- A roller picks up the powder and rolls it over the lift in the adjacent basin, which is at the top at the beginning.
- A laser melts or sinters (in the case of ceramics) the powder so that it bonds and hardens. The first layer of the object is created with it.
- The lift in the powder tank moves a bit upwards, the one in the object tank sinks off a bit.
- The roller applies the next layer of powder to the first cured layer of the object and the laser restarts to cure.
- So the model is built layer by layer from bottom to top.
- The advantage of the process is the versatile selection of materials. Also, no supports must be arranged, since the powder is cured immediately load-bearing.
- In contrast to stereolithography, the objects have a rough surface during laser sintering. The printers are also costly and, therefore, more developed for the industry.
Stereolithography (SLA) is the third 3D printing process in which the workpiece is shaped in a basin full of liquid synthetic resin. The level is slightly increased for the layers, while the liquid cures selectively under UV light. For the forms, either a laser or a projector are used. With stereolithography, the most delicate details can be modeled in 3D, but they are fragile, which also depends on the synthetic resin used. This can also age visibly.
Stereolithography has been around since the 1980s, making it the oldest 3D printing technology. Relevant 3D forums frequently cite a 1989 broadcast of “Good Morning America,” in which a stereolithography 3D printer recreated the announcer’s hairstyle.
- The starting material is liquid epoxy resin, which is located in a basin.
- In the basin is a lift that can be moved up and down. On this, the 3D model is created.
- At the beginning of printing, the lift is just below the surface of the synthetic resin – about 0.05 to 0.25 mm.
- A laser mounted above the pool cures the first layer of the model.
- Now the lift moves down a bit. Depending on the printer type and decoration of the model, the layers are 0.05 to 0.25 mm thick. The epoxy resin coalesces over the first, already cured layer.
- Now the next layer of the object is cured and blends seamlessly with the first underlying layer.
- Thus, the 3D model is built layer by layer from bottom to top.
- The advantage of the SLA process is the smooth surface of the model. However, the fluid does not carry overhanging parts unless they are fully cured. Therefore support structures may have to be used.
A kit for a 3D printer
Since the 3D printers in the FDM version still cost four-digit prices, interested parties can also order a 3D printer kit. He makes plastic parts, decorations, small toys, and accessories, is home-made to the printer, and is RepRap-compatible. This means that freely available 3D CAM programs are sufficient for operation. The software is available as open-source for free. With online model data, 3D artists can design their models.
As a rule, models can be produced by 20 × 20 × 20 cm, the resolution in the XY direction is 0.015 mm. This makes the printer fast (300 mm / s) and also very precise. The kit includes, for example, a sturdy aluminum frame, processed ABS and PLA filament in ø 3.0 mm. The extrusion nozzle has a diameter of 0.5 mm, the construction of the entire printer should be completed in five to eight hours. Such a 3D printer kit includes a Windows, Mac, or Linux computer for software processing.
Templates for 3D printing
For the operation of the printer, particular file types are available (usually in STL file format). Free, open-source programs include OpenSCAD, FreeCAD, Blender, SketchUp, or Wings3D. Some of the programs are available for download, others (3dtin.com, Tinkercad) as a web-based browser version. Anyone who has created a 3D model on the PC can save it in various formats such as STL, OBJ, or PLY. But not every hobby 3D hobbyist wants to create his models. Therefore, there are also databases with templates for 3D printing, which are offered in most cases for free.
The most common format is STL, the file is loaded into the printer software, the printout can begin. Interested parties will find free software and model templates on relevant 3D model platforms, are offered a lot of gadgets, but also complicated jewelry or even R / C models. If you load and use something for free, you have to assume that everything is not fit for purpose: the technical characteristics should be checked in advance so that the 3D model works as it was initially intended.
Individual variants for 3D printing
For the sake of completeness, we would like to point out a few unique variants with which 3D printing is also possible. There are printers – such as the Stratasys Objet series – that use PolyJet technology to print the resin in droplets and then immediately cure with UV light. By several parallel operating nozzles and heads, it is possible in this more complicated process to process different materials simultaneously to an object. Other 3D printers also mix plastics that have very different, freely selectable elasticities and hardnesses.
Even the 3D printing of gold and silver is possible, whereby it takes place indirectly: The model is printed in 3D from modeling wax, then the melting of the precious metal conventionally takes place in the lost wax process. Last but not least, there is 3D printing with paper, which can be colored in advance with an inkjet head. For the durability of the paper sheets with each other liquid glue is used. The finished paper object is usually soaked in synthetic resin to make it haptic pleasant. The surface then shines silky.
Conclusion for 3D printing
The rapid progress of 3D printers cannot be stopped. Experts expect prices to fall sharply by 2020 so that current forecasts point to the fact that many people probably operate a 3D printer at home in a few years – just like today’s standard laser or inkjet printer.