In the beginning before Rapid Prototyping….there was the evolution of 3D CAD.CAD was first developed over 20 years ago with the development of personal computers. The first company to become a leader in the CAD world was Autodesk with a product called AutoCAD. This was the first software product that allowed the user to produce 2-dimensional drawings on the computer and take advantage of the efficiencies that software can provide (copy, templates, etc.). It is important to note that at this time in the product development world, all products were designed and developed from 2-dimensional drawings. These 2D drawings fully represented all appropriate views of the part or product. While this was a standard method of product design, it did require the learned ability to “visualize” what the part would look like in 3-dimensions (or in the “real” world). Since this was a subjective requirement, communication regarding the part was subject to misinterpretation. This also required parts to be designed much simpler than our products today. With 2D design, it was very difficult and expensive to develop parts that were highly contoured or with complex surfaces. This is the reason products of this era were more “blocky” and simple. Think of the cars of the 60′s and 70′s. It was not until the late 1980′s that software began evolving to render solid models and true 3-dimensional representations of the parts or products. Software was finally developed that could completely represent the part in 3-dimensional space so the designer did not have to imagine how the part would look.Once the 3D CAD became available, this lead to the development of rapid prototyping and 3D printing. Now additive fabrication is becoming mainstream. It has been great to see over the past 20+ years.
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Standard Tessellation Language (STL) is a file format native to the Stereolithography software created by 3D Systems. This file format is supported by many CAD software packages and is widely used for rapid prototyping and computer-aided manufacturing (CAM).STL is a facet-based representation that approximates surface and solid entities only with triangles (i.e., STL files describe only the surface geometry of a three dimensional object). Entities such as points, lines, curves, and attributes such as layer and color, in the CAD systems will be ignored during the output process.An STL file consists of a list of facet data. Each facet is uniquely identified by a unit normal (a line perpendicular to the triangle and with a length of 1.0) and by three vertices (corners). The normal and each vertex are specified by three coordinates each, so there is a total of 12 numbers stored for each facet. This data is used by a slicing algorithm to determine the cross sections of the three-dimensional shape to be built. This format approximates the surfaces of a solid model with triangles. With creating STL files, there are some common errors that will lead to poor part build or delayed leadtimes because the files are unusable. Some of the errors are:
Manifold (Leaks)
Although it is not explicitly specified in the STL data standard, all facets in a STL data file should construct one or more closed volume entities. If a file is not ‘water-tight’, it is said to contain ‘leaks’. When a ‘leaky’ STL file is processed by slicing algorithms, the algorithms may not correctly detect the error, and as a result produce slice boundaries that are not fully closed. When the erroneous slices are used in the rapid prototyping process, the laser beam, cutter or whatever tools that generate the slice will ‘escape’ from the openings of the boundaries. Some recent pre-processing software such as 3D LightYear by 3DSystems, will try to correct the error by adding extra segments to link up broken boundaries.Degenerated Triangles Degenerated triangles are very thin triangular facets in the tessellated solid whose three defining vertices almost lie in a single line. The sides of degenerated triangles could create extra vectors in a given layer. These are usually the result of the design application’s attempt to tessellate a complex geometry.
Narrow or Wide Gaps
Violations of the Gapless Exterior Rule, narrow or wide gaps are empty spaces between defined triangular facets in the tessellated solid. These are also typically the result of the design application’s attempt to tessellate a complex geometry.
Inverted Triangles (Incorrect Normals)
Inverted triangles are a violation of the Right-Hand Rule for the formation of valid STL files. These are triangular facets in the tessellated solid whose normal vector (based on the order in which the vertices of the triangle are listed in the STL file) appears to be oriented in the opposite direction of the normal vectors of adjacent triangles. In other words, when examining the continuity of a region’s exterior surface, these triangles (based on the respective directions of their normals) appear to be oriented such that their exterior surfaces are facing inward.
Unmatched Triangle Sides
Unmatched triangle sides are a violation of the Vertex-to-Vertex Rule for the formation of valid STL files. These are triangles whose vertices touch the edges rather than the vertices of adjacent triangles.These are just some of the issues that arise from the creation of STL files. In the end, it is best to consult an expert during the file creation process if you experience any issues. Most issues can be solved pretty quickly…you just need to know what to look for.
Another finish option available for the stereolithography (SLA) process and additive manufactured processes in general is to have parts nickel plated after fabrication. The process of adding a metal coating over an SLA model enhances the stiffness of the model. In addition, it improves the overall strength of the part. The strong stiff metal layer deposited on the outer surfaces creates a metal resin composite where the reinforcing materials can most effectively influence the bending moment of the part. The process works by taking a standard SLA part and painting it with conductive paint. Then a coating of copper is applied via an electroplating process and finally a coating of nickel is applied via the electroplating process. The plating adds .0035″ of thickness to the part and increases its strength 200% at 3% strain. The stiffness is increased by over 500%. Another great benefit to the nickel plating finish is that the parts become virtually waterproof. Water and moisture is typically the kryptonite to all rapid prototyping materials in their uncoated state. With the nickel plating of an SLA, the testing has shown that the parts remained dimensionally stable while being submerged for over two weeks. An uncoated part on the other hand, increased in size by 2% over that same period of time. The last benefit of nickel plating is that the parts become electrically conductive. Since the coating material contains copper, it allows for the part to be highly conductive. This benefit enables the parts to provide an EMF shielding in the end application. Nickel plating is another option in the long list of finishes available for rapid prototypes and SLA parts in particular. Learn more about the rapid prototyping processes and finishes at http://www.quickparts.com
Rapid prototypes are used for a number of different applications; functional testing, marketing show models, trade show models, etc. With such wide number of end uses, the type of finish used on the stereolithography (SLA) model becomes very critical. One of the often overlooked finish option categories is the WaterClear/QuickClear finishes. These finishes allow the parts to be clear – to a point of being able to see and read text while looking through the material. The finishes offer great functionality to engineers wanting to see what the components look like inside of an enclosure. For instance, an engineer could create WaterClear SLA models for a cell phone housing and assemble the boards internally. At that point, the engineer could see how the boards assemble together and how the internal components of the unit functions. In addition, other engineers have used WaterClear SLA’s to view liquid flowing through a channel. The difference between the WaterClear finish and the QuickClear finish are minor. When performing a WaterClear finish, all the support structures are removed, a 420 grit paper is used to remove all build layers and then a clear coat finish is applied. With QuickClear, all the support structures are removed, a 320 grit paper is used to rough sand the part and then a clear coat finish is applied. You can see examples of both stereolithography finishes at: http://www.quickparts.com/english_quickparts_2.aspx?Page=/LowvolumePrototypes/ProcessDetails.aspxIn closing, the WaterClear and QuickClear finishes are tools in the engineering tool kit that can provide great solutions to some of the more difficult challenges faced during the product development phase.
One of the technologies out there that been gaining momentum in the additive fabrication space is Selective Laser Sintering (SLS). Over the past few years this process has transitioned from being looked at strictly as a rapid prototyping solution to now being considered for rapid prototyping and final end use production. The aerospace and industrial product industries started using parts manufactured from this process as final end use production parts. One of the main drivers for this transition is the materials that are offered. The Duraform materials are nylon based and can also contain glass adders. This enables the material to withstand up to 300 degree temperatures and gives the parts great durability features. In additional, the parts can be coated to help improve their durability and moisture resistance. (Moisture is an enemy of SLS parts)To find out more on the exact material properties and the various materials offered, click on the following link: http://www.quickparts.com/english_Quickparts_2.aspx?Page=/LowVolumePrototypes/SLS.aspxYou will find material spec sheets and other important information on build requirements and tolerances.
Developing advanced biocompatible stereolithography (SL) resins for the medical industry is becoming increasingly important. According to Wohler’s Report 2008, the medical/dental industry is the third largest industry for additive manufacturing after consumer products/electronics and automotive, but growing at a faster rate than either. Somos WaterShed® XC 11122 rapid prototyping resin is a clear, water-resistant material that is already widely used in the medical device industry. The classification officially approves the rapid prototyping resin for use in a wide range of biomedical or skin contact applications.United States Pharmacopeia (USP) XIX biological tests are designed to provide information on potential biological effects of polymer materials. One of six different classes (I-VI) are assigned to a material, depending on its performance in biological tests. The higher the material class, the more severe and stringent are the tests. WaterShed® XC 11122 has passed the most severe test requirements in order to be qualified as a USP XIX Class VI material. Special cleaning procedures must be used for the parts used in USP Class VI applications.
The latest addition to the Fused Deposition Modeling (FDM) process is the ability to offer Ultem as a material choice. This is a high end, engineering grade material that is used by many industries including the medical and aerospace industries. The Ultem 9085 offered through the FDM process is certified for use on commercial aircrafts and has proven to be successful for electric / electrical components, microwave applications, pump and valve parts, and marine and automotive manufacturers. This is a huge advancement for the rapid prototyping industry and the FDM process overall because it now adds a mainstream engineering grade material option to the offering. As many are aware, ABS and PC materials have been offered for quite a while through the process. But one of the main limitations keeping the additive technologies from becoming a mainstream manufacturing process has been the limited material options. This material addition definitely helps overcome those barriers and allows product development engineers a new option for product development and production manufacturing. To learn more about the material properties of Ultem material for the FDM process you can check it out here: http://www.quickparts.com/english_Quickparts_2.aspx?Page=/LowVolumePrototypes/FDM/MaterialProperties.aspx
Recently Huntsman Corporation launched a new Black stereolithography material for the rapid prototyping industry. This is a major milestone for the stereolithography material market. As many will probably remember, the original rapid prototyping materials were an amber/clear material that looked bad. Then there was an advancement made to offer a white stereolithography material. For the most part, the physical characteristics did not change but the visual appearance was a huge improvement. Now after years of trying by many companies, black material is offered to customers. So with the option of white, gray or black stereolithography material, what more can a person want. We have tripled the options that Ford offered with the Model T…
