Multiple Materials

From the previous section, color is one of the clearest examples of multiple material products that AM is capable of producing. As described in other chapters, parts can be made using AM from composite materials, with varying porosity rates or with regions containing discretely various materials. For many of these new AM technologies, STL is starting to become an obstacle. Because the STL description is for surface data only, it is therefore presumed that the solid material between these surfaces is homogeneous. This may not be the case, as we can see from the above. Although considerable consideration has been given to the issue of representations for heterogeneous solid modeling, there is still a great deal to consider until we can arrive at a standard to supersede STL for future AM technology.

Use of STL for Machining

STL is used for applications beyond transforming CAD to additive manufacturing input. Reverse engineering packages can also be used to convert point cloud data directly to STL files without the need for CAD. Such technology, which is directly connected to AM, could conceivably form the basis for a 3D fax machine. Subtractive manufacturing is another technology that can easily make use of STL files. Subtractive manufacturing systems can easily use the surface data described in the STL to assess the machining boundaries. With some additional knowledge on

FIGURE 2.14 DeskProto software is used to extract machine tool paths from the STL file data to shape a mold to create a motorcycle windscreen.

the sizes of the starting block of material, tool, machining center, etc., it is possible to calculate machining strategies for the creation of a 3D surface model.

As stated earlier, it is likely that complex geometries cannot be completely machined due to undercutting features, internal features, etc., but there is no reason why STL files cannot be used to build computer-aided manufacturing (CAM) profiles for machining centers. For several years now, Delft Spline has been using STL files to create CAM profiles. Figure 2.14 shows the progress of the model to the tool used to manufacture the final product using their DeskProto software. The SRP (subtractive rapid prototyping) technique developed by Roland for their desktop milling machines is another technology that uses a combination of subtractive and additive processes to produce parts.