Solid Imaging Requirements

NURBS surfaces must be translated into either the .stl or .slc format before reading the file into the solid imaging machine software.

Workflow

Alias wire files exist as NURBS data. To use that data to create physical models using solid imaging technologies, you must translate the NURBS to either the .stl or .slc format so that the geometry can be read by the solid imaging machine’s software. Included in the list of solid imaging technologies is SLA (Stereolithography), SLS (Selective Laser Sintering), LOM (Laminated Object Manufacturing), SGC (Solid Ground Curing), FDM (Fused Deposition Modeling) and others.

Converting the Alias geometry to the .stl format or the .slc format can be done from within Alias.

STL Format

An.stl file is a tessellated file (binary or ASCII), which means the NURBS surface is described by a series of triangles. The resolution of this polygonized data base is defined in Alias by the subdivision characteristics of the original NURBS surface. Once the tessellated geometry is sent to the Solid Imaging technology, the geometry is sliced, and then those slices are used to describe the physical model that will be produced.

With STL as the transfer format, you can send geometry to most Solid Imaging technologies while controlling the resolution of the finished model.

The STL file exported from Alias conforms to 3D systems file format version 2.0. When you export a model as an STL file, Alias displays:

• A solid check is run-on the model and the results are displayed at the prompt line. This tessellation check determines if it is a valid solid watertight model or if it has any gaps indicating topological errors. This allows the Alias user to determine if the data being transferred can be used by the operator of the solid imaging (for example SLA) machine to build the part.

  If gaps are found, the user receives a warning indicating that it is an illegal solid and the number of free edges in the model. When you view the model, edges with gaps are highlighted in red so that you can easily identify where gaps are and then repair the surface model.

• Stitch and tessellation tolerances options allow you to set the merge vertices tolerance, the maximum distance at which two vertices will be merged together into one.
• During tessellation, degenerate triangles (with two or more equal vertices) are removed and the normals of the triangles are recalculated.

SLC format

An.slc file (StereoLithography Contour) cuts 2D contours of the 3D data base. These contour lines are polylines. The advantage to using this file format is that the NURBs geometry description in Alias is directly sliced and therefore fewer iterations are required between the original geometry and the data sent to the Solid Imaging machine to be built.