STL format input (DIEGEO) The STL format represents a surface by a series of three sided facets. This format may be created from almost all commercial solid modeling packages from a either a solid model or a surface model. For very simple shapes, such as a cube, very few facets may be used to provide an excellent representation of the shape. In the case of an extrusion die where the facets are used to model a curved surface, many facets may be required in order to give the object a smooth representation or to render small details in a geometry. An economy of the number of facets used to represent a geometry is recommended in order to minimize the size of the database file. As more facets are used, the size of each step in the database file will increase. The increase in the time for the contact calculations is negligible with the increase of the number of facets in the die geometries. Upon inputing an STL file into the Pre-processor, the user is immediately prompted for a error tolerance value. This value is the snapping distance between the points in the STL file. Since the facets are not dependent on each other, the points in which adjacent facets share may not be represented exactly the same way in an STL file. Since they were meant to be the same point, the Preprocessor assumes some error tolerance where the points are merged into representing the same point. The default value of 1e-005 is usually a good starting value. If there are small cracks in the die geometry, they may closed by increasing the error tolerance value and hoping that the cracks are snapped 79 closed. This is not a very controlled manner in which to close any cracks and should be used with extreme caution. After using this method, the geometry should be carefully checked to ensure that no holes are introduced or important features are lost. The file format for STL files may be either ASCII or binary format. DEFORM can both read and write ASCII and binary versions of the STL file. The facets are all defined independently of each other, so the danger of there being folds, holes, overlapping facets, or invalid facet orientations is possible. After reading an STL file, it is strongly recommended to check the geometry to make sure that there are no folds, holes or other problems. If there are geometry problems in a deforming body, problems may occur upon meshing the object. If there are geometry problems in a rigid die, problems may occur during the simulation where nodes get trapped and severely compromise the integrity of the deforming body. This can be very problematic since problems in die geometries may not occur until well into a simulation. The manner in which to best determine if a die geometry is well defined or not is to try to apply a mesh to it. If a mesh can be generated on geometry, then it is a well defined geometry, however, if the meshing fails, then it is possible that there is a problem with the geometry definition.