Rapid Prototyping or Layered Manufacturing (LM) is more than a mainstream technology in engineering product development. Yes, it enables engineers to create a prototype part from a new design before entering final production. Now, it also allows the Center for Visualization Prototypes (CVP) to create 3D visualization hardcopies, collaborating with scientists to enhance data understanding. In 10 years, the CVP has made more than 1,000 models for scientists around the world, helping to visualize data in areas ranging from mathematics to engineering. Along the way, we have learned about using physical hardcopy for understanding science and about turning various types of data into physical form.

Different uses for visualization hardcopy. From top-to-bottom, left-to-right: brushfire visualization,
USA map, Anthrax, molecular docking.

Typical large-scale manufacturing is characterized by subtractive processes, for example, starting with a block of material and then removing pieces of it until only the desired part remains. Layered Manufacturing, on the other hand, is characterized by additive manufacturing processes. They start with nothing, and add material layer-by-layer until the 3D part is completed.

Advantages for scientific visualization include:

• Extremely complex parts can be handled.

• Parts can be started and let run to completion without further intervention.

• Topologically impossible 3D parts can be made. Geometry that is topologically impossible in 3D is often feasible in LM.

• Already-assembled interlocking parts, such as chains and ball-in-socket joints, can be produced.

The de facto standard for all LM machines is the STL file format. An STL file describes 3D solids by listing the triangles that bound them. The STL format is often described as a “bucket of triangles,” because, while this is an easy format to create and to write, it lacks much of the robustness that geometric modeling practitioners have come to expect. For example, we found that many STL files which originate from robust solid modeling CAD systems are not always correct. STL files that are generated from scientific research software are even less likely to be correct. Thus, before fabrication technology can be used productively, better ways had to be found to deal with the STL file format.

The CVP project developed a program to preview and repair STL files. We found it useful to be able to:

• Import ASCII and binary STL files

• Import color STL files using a CVP ASCII color STL extension

• Interactively transform in 3D to inspect the part

• Display the part as points, lines, reduced lines, shaded surfaces, or shrunk triangles

• Scale and re-orient parts

• Detect and fix model cracks and reversed triangles

• Use color to show difficulty of mold creation in different orientations

• Display parts using 3D ChromaDepth

• Export parts in STL, color STL, or PLY (used by the color Z Corp machine)

The most important aspect of this effort was to turn the “bucket of triangles” into a robust data structure.

Link:

See Dr. Bailey’s full manuscript at http://web.engr.oregonstate.edu/~mjb/WebMjb/Papers/cvpcacm.pdf

MPF