Is it important to you how faithfully your designs can be created when weighing rapid prototyping or digital manufacturing options? Then you will want to learn about Fineline’s Technology Comparator, a standard test part with a variety of demanding surfaces created to evaluate RP alternatives.
The Comparator has upfacing and downfacing sides… vertical and horizontal knife edges….sidewall detail. By producing it on a variety of different digital manufacturing systems, we can demonstrate how each can produce different complex shapes with demanding surface features. Then you can choose the features that are most important to you and specify the process accordingly. No process reproduces all types of surface flawlessly, but if you understand the relative strengths and weaknesses of the different processes, it’s easier to choose what will work best for the parts you need to produce. With this in mind, here is a look into the principles of RP technologies that drive precision, resolution and surface finish.
• No single operating principle tells the whole story on detail capability, surface finish or precision.
• No one technology can “do it all.”
• Knowing the principles behind any given technology can allow you to extrapolate its performance onto your parts.
Competitive RP systems
Fused Deposition Modeling (FDM) has been around almost as long as stereolithography. FDM is also a layered process, but uses a filament of actual thermoplastic that is melted and extruded through a tiny nozzle. The nozzle drives down a “road” all around the part’s 2D cross-section, and then crisscrosses inside to fill in the volume. FDM’s strength is…well, strength! Since you are working with an engineering thermoplastic, you can get better material properties than with many other RP processes. However, due to voids and imperfections in interlayer adhesion, it does not match the strength of the base engineering resin. FDM has a weakness—resolution and accuracy of small features.
Selective Laser Sintering (SLS) is a layer-based process, but instead of using a liquid or extrusion, it works with a bed of thermoplastic powder. Each layer of fresh powder is sintered (slightly melted) together using a high-power laser. Then a fresh layer of powder is rolled onto the surface so that the process can be repeated for the next cross-section. The imaging is vector-based, so it can be quite accurate. SLS parts are typically very strong, and exhibit material properties that come close to the base material. They are an excellent choice for parts requiring strength and toughness. The weaknesses of SLS are its inability to do fine details and its surface roughness.
Stereolithography SLA5000 belongs to the previous generation of large machines from 3D Systems, Inc. It has been replaced by the Viper Pro, but there are still a large number of these machines and the similar SLA-7000 at work producing parts around the world. While similarly fast as compared to the Viper Pro, these machines do not produce at nearly as high a quality level because of their optical configuration. Sidewalls are rougher and details are not as crisp, since they use a laser focus that draws with roughly a 0.015-in. line versus the 0.003-0.005-in. line of the Viper Pro.
Stereolithography Viper Pro does for large parts what the Viper did for small parts—it represents a significant step up in quality and resolution. The ‘Pro uses a Viper-HR-like 0.005-in. laser beam diameter for the borders–the outsides of the parts that you see, feel, and measure–and a thicker, 0.030-in. diameter beam for the insides of the part to image it much faster. It is set apart from the older large machines by its advanced imaging system, which allows the beam path to be shorter, leading to better control over vector drawing.
3D Printing InVision SR, by 3D Systems, Inc., is in the class of 3D printers that use multiple jets imaging in raster fashion to deposit UV-curable liquid. The fully computer-generated supports are wax and are melted away to reveal the parts. It has a well-balanced X, Y, and Z resolution, so parts look largely the same in any orientation. Detail is crisp, with similar surface roughness to the PolyJet. It is a fast-building machine, intended for quick concept models.
3D Printing Z Corporation technology is another in the class of 3D printers for concept modeling. It uses a raster-based imaging style with multiple jets for good throughput. The print heads jet out a binder onto a bed of powder in multiple layers to form 3D parts. One unique feature of some of the Z Corp machines is their ability to make multi-colored parts directly in the machine using colored binders. This technology is not known for fine details, but with the recent introduction of a high-definition machine, it does pretty well. With post-build infiltration of hardening and strengthening agents, Z Corp parts can attain remarkable toughness.
3D Printing PolyJet technology, invented and patented by Objet Geometries, is gaining ground
rapidly for concept modeling applications. It is in the class of 3D printers that use multiple jets imaging in raster fashion to deposit UV-curable liquid. The supports are gelatinous and can be torn and jetted away with reasonable effort. Available systems use a remarkably thin layer thickness, which gives them great Z-axis resolution, but the X and Y resolution is significantly lower. Also, since they are raster-based, the parts have a slightly rough surface finish.