Solid Imaging

Solid Imaging is a component of Rapid Prototyping which uses a database to translate three-dimensional geometry into physical models or parts using a variety of resins and other materials. The file formats used by Alias to output files for Rapid Prototyping are the STL and SLC.

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.

Tip:

Consult with the operator of the solid imaging machine to optimize the transfer of data.

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.

SLC header information

The header section of the .slc file is an ASCII character string (up to 2048 bytes) containing global information about the model.

The output in the header provides the following information:

• SLC file format version number (-SLCVER2.0)
• Output units (-UNITS<INCH/MM>
• Type of model (-TYPE<PART/SUPPORT/WEB>)
• Vendor package and version number (which produce the SLC file (-PACKAGE ALIAS V2010)
• Calculations and sets from SLC output x,y,z extends of the model (-EXTENTS mx,Mx,my,My, mz,Mz)

Header keywords (CHORDDEV, ARCRES, SURFTOL, GAPTOL, MAXGAPFOUNS, EXTLWC, STHICK, STARD and ENDD) are set to 0.0.

SAT ACIS

Save ACIS Text (SAT) allows you to import and export ACIS options of curves, surfaces, and shells data from and to Spatial's ACIS 3D toolkit SAT format.

SAT Requirements

• Export all surfaces as NURBS.
• Alias.

Workflow

1. Choose File > Save > Save as  to open the Save All Options window.

   Or choose File > Save > Active as  to open the Save Active Options window.

2. Set File Formats to SAT, and then set the SAT Options.
3. Click Save and enter a filename in the File Browser.

Functionality of TC VisProducts

The following sections provide detailed descriptions of the functionality available in Alias's TC Direct Connect translator. At a high level, there are two interfaces available in TC Direct Connect. The software is offered either as a stand-alone command-line driven tool, or it can be launched from within Alias via the File > Save As  > TC VisProducts menu. The TC software is designed to operate in one direction, converting Alias data to TC DirectModel files. (For import into Alias, please see the JT import translator.)

How the TC translator works

Hierarchy in Alias is represented by DAG node objects. The basic parent/child relationship is reflected through the group node, which refers to a list of child DAG nodes. This type of DAG node allows the hierarchical grouping of DAG nodes. A group node can share its list of children with another sibling group node.

The translator works by converting each DAG node object into the equivalent DirectModel node object. DirectModel can represent many of the same types of nodes that Alias supports. For example, Alias surfaces are individually tessellated into unique DirectModel parts. There should be a 1:1 correspondence between Alias surface names and DirectModel part names. If surfaces are grouped in Alias, they will also be grouped in DirectModel.

The TC translator is controlled through several possible methods. You have the choice of either an Alias plug-in, accessed within the File > Save As  > TC VisProducts menu, or batch mode driven by a command-line. This gives you control over various tessellation parameters and other important options.