3D Printing 101
A short introduction to 3D Printing
3D Printing opens up new opportunities in a wide range of applications. However, 3D printing isn’t just a term for a single technology; it is a collective term for numerous and sometimes completely different technologies in additive manufacturing.
We provide an overview here of the various technologies and materials used, to make it easier for you to choose the most suitable ones for your project.
Topics: 3D Models | 3D Printing Technologies | Differentiating Factors of the technologies | Support in choosing a material and technology
Digital model of a 3D figure
Digital 3D models form the basis of 3D printing, and these are necessary to print the component. The files are like digital photos; the only difference is that the picture elements are three-dimensional, whereas photos are only two-dimensional. This makes it easier to imagine what the model will look like after printing.
The file formats used are often .stp, .stl or .obj, although there are many more formats which are specific to certain software packages. These formats differ in terms of the information they contain.
- STP (Step) data are often used by engineers, since they contain parameters which can control changes in model dimensions.
- STL data are standard in 3D printing, since these only contain information which is necessary for 3D printing.
- OBJ, PLY or WRL (VRML) data contain additional information to that found in STL; they also contain details of colors in the form of a ‘texture’.
One aspect that all these formats have in common is that the model must be dissected into horizontal layers before it can be printed. This is done with a specific software package known as a slicer; the data can then be sent to the printer.
The Most Important 3D Printing Technologies
After the creation of a model, the question of which technology and material to choose needs to be considered. 3D printing is a collective term for numerous technologies. In contrast to machining technologies, 3D printing technologies all have one thing in common: models are built up layer by layer.
In the same way as the technologies, the characteristics of the materials used may also vary widely. The same applies to the costs of 3D printing; costs can vary from a few Euros for plastics to five-figure amounts for precious metals.
In general, several methods are possible for printing any component, and its intended use and the costs involved therefore have to be assessed.
Some basic information on the most widely used 3D printing procedures:
- Colorjet (also Colorjet CJP, full-color Print or 3DP) uses plaster powder for printing. An adhesive colorant is applied in layers, using an inkjet printhead with a colored plaster in powder form, the model is thus directly printed in color. This technology is especially suitable for architectural models, 3D figures, design objects and -prototypes.
- In Polyjet printing, a printhead applies tiny droplets of photopolymer onto a printer bed. The liquid is then hardened immediately under a strong UV lamp. This offers the possibility of combining several materials; for example, a smooth material and a solid material can be combined in the finished object (e.g., a holder can be made in a smooth material and the corresponding fitment in a solid one). This combination can be made place before hardening takes place, so that materials with new characteristics can be developed, which are known as digital materials. Thus, you can select a Shore hardness of between approximately A20–A90 by mixing smooth and solid materials. This technology is generally used for prototypes.
- The basic principle of Stereolithography (SLA) is the selective curing of a liquid resin (epoxy resin or acrylic) using a UV laser. There are two types of SLA machines: one prints the model upwards (‘bottom-up’; these are mostly professional machines), and the other prints the model downwards (‘top-down’; these are generally desktop SLA printers). This technology is very precise, and gives good surface qualities; it is typically used for prototypes and design objects.
- Laser Sintering (SLS) also works with a laser. While printing, it heats up (‘sinters’) the powdered plastics (often Polyamide or TPU) and fuses adjacent areas together in layers. Polyamide is mechanically very resistant, and is popular for prototype constructions and small batch series of smaller pieces.
- Direct metal 3D printing (SLM) is similar to laser sintering. One difference is that metal (generally aluminum) is used in this technology. The other difference is in the process used. While laser sintering heats the material to below the melting point (‘sintering’), direct metal 3D printing melts the metal directly with a laser. The cost of this process is therefore higher since the laser used is much stronger. This technology is used for metal prototyping.
- In FDM, plastic threads are melted and then applied on a printing bed with the aid of a small nozzle. Most home printers work on this principle. In addition to these machines which are available for a few hundred euros, there are also expensive professional ones. The technology is mostly used in the hobby sector or for designs at a very early stage. Professional printers are typically used when ABS is needed for a prototype.
- Material Characteristics: The choice of materials usually depends on or is influenced by the technology used. For example, polyamide is one of the few materials which can be used by two technologies (FDM and SLS). The characteristics of these two processes differ, since FDM melts the material and SLS sinters it. Furthermore, a wide range of materials is available, including rubber-like ones (Polyjet), transparent plastic (Polyjet, SLA) and metals (SLM).
Examples of solid and smooth material
- Supporting Structures: Some of these technologies (Color Jet, laser sintering and direct 3D metal printing) take place in a powder bed. This means that the bounding box is completely filled with powder. In all the other methods, the overhanging structures are loose, either hovering (FDM, Polyjet) or in a liquid (SLA). Supporting structures are sometimes used to prevent these overhanging structures from falling down or breaking, but these have certain disadvantages. More material is needed, meaning higher costs, and the surface areas on which these supporting structures are placed are often slightly affected.
Example of Supporting Structures. Picture: Wikipedia.
- Costs of 3D Printing: Costs depend on the technology, printer and material used. For example, the printers required for laser melting are very expensive (about EUR 500,000) since the laser has to be very strong in order to fuse aluminum at approximately 660°C. On the other hand, a simple FDM printer can be acquired for several hundred euros, whereas in SLM, costs can run from few hundred to a thousand euros.
Example costs FDM (right) few euros, SLM (left) approx. EUR 80,-
- Surface Characteristics: The quality of the surface also depends on the procedure used. In FDM, for example, melted plastic is applied using a round nozzle, and the finished object has clearly visible grooves. With Polyjet, in contrast, the applied droplets aggregate in a layer only about 16 μm thick, and the surface is consequently very smooth and detailed. Colorjet and Laser Sintering are based on the use of powder, and thus the surface is slightly ‘corned’. In Stereolithography, a laser is used to harden a liquid, and this method is therefore very precise.
Beispiel Oberfläche PolyJet (links) mit annähernd Spritzgussqualität und FDM (rechts) mit relativ unebenen Oberflächen.
Which is the right technology for my project?
Unfortunately, there aren’t any general rules for when to use a certain technology, and the selection must be made on a case-by-case basis. Listed below are some examples illustrating when the use of each technology is likely to be appropriate:
- Case 1: You just need a rough first draft and tolerances are not important. Here, FDM can be used; the surface is rough but the process is very cost efficient.
- Case 2: You have a developed design that you want to use for a provisional prototype. In this case, Stereolithography or Laser Sintering are suitable. For complex geometries with many overhangs, the latter is recommended, since no support structures are required. For low tolerances or challenging surface properties, Stereolithography should be chosen, although usually, both methods are possible. The differences in price are low, although Stereolithography is often a little more cost-intensive.
- Case 3: You are planning a prototype, which is on the brink of batch serial production. Polyjet would be a suitable method, since the surface properties are outstanding. In general, Stereolithography and Laser Sintering are also possible choices, depending on the geometry, desired properties, size and functions of the project.
- Case 4: You are planning a design or art object. Here, Color Jet should be your first choice, since full-color printing is possible. If the project is single-colored, the choice will depend on the properties required. Stereolithography is likely to be most suitable, and Laser Sintering is also possible. Stereolithography is often used in the design sector, since a transparent material can be used.
- Case 5: You need a combination of materials within a component or have special requirements for the material. Polyjet is the only method with which you can use multiple materials in a single object. In addition, Polyjet offers a choice of many specialist materials, such as biocompatible or rubber-like ones.
- Case 6: If you want to print a metal object, Laser Melting (SLM) is likely to be the right procedure. Other methods can produce a metal object, although these will require certain adjustments.
Share this page