Additive Manufacturing Requires More Than Scanning to a Point Cloud

After scanning to a point cloud, additive manufacturing requires some part design features not common in subtractive manufacturing.

Language: So necessary for communication; so often the cause of miscommunication. Miscommunication, even simple misinterpretations, can be costly: assembled parts don’t fit, scrap and rework increases, mechatronic systems have unintended bleed-throughs, life and death are at stake.

Scanning parts to create data clouds is a key process in metrology and additive manufacturing (AM; aka, 3D printing). But “most scanning software is pretty basic,” explains Chris Strong, president of Rapid Scan 3D (rapidscan3d.com), a distributor of metrology and reverse engineering hardware and software. “You scan the part. You collect the data. You create a mesh. There’s no clean-up.” There’s not much else the software can do.

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This is why getting the right tool for the job is crucial—even software tools. Take metrology software, for example, which finds and compares measurements. Metrology software can capture a scanned part for AM, but the software must do more. It has to be “AM aware.”

Design for additive manufacturing
AM design software is basically a mash-up of computer-aided design (CAD), computer-aided engineering (CAE), finite element analysis (FEA), and simulation—plus functions to prepare scanned geometry for AM. For instance, the software has to be able to generate internal support structures to minimize manufacturing stresses during the build, strengthen the finished part, and, for metal, provide adequate heat transfer. The software also needs to be capable of orientating parts and designing external supports for the build. Both of these factors are constrained by a variety of properties beyond the need for adequate workholding, such as build envelop and the mechanical properties of the build material.

The software also must create a watertight mesh (i.e., a mesh with no holes, voids, or intersecting geometry) from the scanned data. Better is AM software that can also optimize the mesh, such as fill voids that meet certain parameters; ensure the flatness of “level” surfaces; remove scratches, dents and other surface imperfections in the scanned object; and, says Strong, correct inverted vertices that wind up in the scanned data, but that cause errors when printing the part.

Last, for lightweighting, the software needs to generate lattices. “An ideal design for additive would be a very organic, dynamic structure, with millions of faces, which is just a bear to measure,” says Bryan Hodgson, aerospace applications leader for 3D Systems  (3Dsystems.com). Likewise, manipulating these lattices inside a part is compute-intensive. 

Scan to print
Artec Studio 3D (artec3d.com) scanning and data processing software handles reverse engineering (e.g., AM) and quality control inspection. Manufacturers can scan objects directly to Artec Studio, then export the resulting geometry file to any AM machine or CAD system.

The software controls how the scanner captures data and with what level of precision. There’s no need to prepare an object in advance; just point the 3D scanner and shoot. Tracking algorithms handle texture and geometry; advanced algorithms automatically map texture where data is missing. Smart base removal automatically eliminates the surface on which the object is standing, even if that surface is curved. Also, the software lets users compare scans and 3D CAD models with heat distance maps.

Artec Studio Version 12 can optimize the size of the final file by reducing the number of polygons from millions to thousands while maintaining a high-quality mesh. A revised Global Registration algorithm, a resource-intensive operation to convert all the scanned data to a single coordinate system, works up to 20 times faster than in previous versions.

Metal or plastic?
3D Systems has two primary AM-centric design software packages: 3D Sprint and 3DXpert. 3D Sprint is for plastics AM; 3DXpert, for metal. Both, says Hodgson, “fill a big void in the marketplace: How do you take geometry and manipulate and build it for additive?” Both import part data, position the part, optimize the geometry and lattice creation, set printing strategies, calculate the scan-path, arrange the build platform, and send the optimized scan path to the printer.

3DXpert offers an array of options for build support. Hodgson says it also has “about a dozen different styles of lattices for all sorts of support, lightweighting and cooling applications. It allows you to build these crazy, funky cool lattices the way you really want without overwhelming your computer.” The lattice tool within 3DXpert analyzes structural strength, such as whether a part’s internal lattice structure and overall wall thicknesses can withstand the forces applied to the part. While users can see the lattice on the screen, 3DXpert is not crunching all the detailed calculations to form that lattice. Instead, the software does those calculations once the user prints the part.

3DXpert also comes with 3DXpert Build Simulation, a simulator combined with the analysis tools to design parts that won’t fail to build. The simulator can predict part stresses, support failures, warpage and other deformations, heat distribution, material failure due to plasticity and other factors leading to robust parts, minimized wasted material, shortened printing time and lower overall AM cost. The simulator can even predict the effects of post-processing, such as the displacement created after cutting a part off the plate, and displacements and stress after removing supports.

3DXpert also includes a form of local revision control because, Hodgson jokes, “3D printers aren’t Star Trek replicators.”  The software lets designers add material that will later go through post machining to compensate for the vagaries in every AM machine, according to Hodgson. 

Ultimately, selecting AM software is a matter of basics. Concludes Hodgson, “Laser sintering plastics means you have 20 minutes of scan work. But if you have poor software, you may have two days of adding fillets and radii.” He suggests the software choice “really boils down to how user-friendly it is, how much it’s geared toward your engineers, and what you need to do.” Which is probably the case even for subtractive manufacturing software, too.