Defining a transition zone between a shell and lattice cell array in a three-dimensional printing system

1. An apparatus for manufacturing a three-dimensional article formed by additive manufacturing, the apparatus comprising a processor and a memory for storing executable instructions that in response to execution by the processor cause the apparatus to at least:

receive initial data defining the three-dimensional article having an outer surface;

define a shell having the outer surface of the three-dimensional article and an opposing inner surface that defines an inner cavity;

define a transition zone between the inner surface of the shell and a boundary that is inside the inner cavity and generally follows the inner surface of the shell;

define a lattice of arrayed unit cells that fill the inside of the boundary, the lattice is defined by connected lattice segments;

define transition segments that couple the lattice to the inner surface of the shell, the transition segments are generally oriented more toward a normal to the inner surface of the shell relative to the lattice segments; and

define a mesh cage at the boundary between the transition zone and the lattice, the mesh cage couples to the lattice and to the transition segments.

2. The apparatus of claim 1 wherein defining the shell includes offsetting the outer surface of the shell inwardly to define the inner surface of the shell.

3. The apparatus of claim 1 wherein the unit cells are individually one of cubic, hexagonal, rhombohedral, triclinic, monoclinic, tetrahedral, and shortened tetrahedral.

4. The apparatus of claim 1 wherein the lattice segments are individually defined by a pair of intersecting sheets.

5. The apparatus of claim 1 wherein the transition segments directly couple to the lattice.

6. The apparatus of claim 1 , further comprising identifying an unsupported contour and then defining a transition segment to couple the unsupported contour to the lattice.

7. A computer-readable storage medium for defining a supported shell for manufacturing a three-dimensional article by additive manufacturing, the computer-readable storage medium being non-transitory and having computer-readable program code portions stored therein that in response to execution by a processor cause an apparatus to at least:

receive initial data defining the three-dimensional article having an outer surface;

define a shell having the outer surface of the three-dimensional article and an opposing inner surface that defines an inner cavity;

define a transition zone between the inner surface of the shell and a boundary that is inside the inner cavity and generally follows the inner surface of the shell;

define a lattice of arrayed unit cells that fill the inside of the boundary, the lattice is defined by connected lattice segments;

define transition segments that couple the lattice to the inner surface of the shell, the transition segments are generally oriented more toward a normal to the inner surface of the shell relative to the lattice segments; and

define a mesh cage at the boundary between the transition zone and the lattice, the mesh cage couples to the lattice and to the transition segments.

8. The computer-readable storage medium of claim 7 wherein defining the shell includes offsetting the outer surface of the shell inwardly to define the inner surface of the shell.

9. The computer-readable storage medium of claim 8 wherein the unit cells are individually one of cubic, hexagonal, rhombohedral, triclinic, monoclinic, tetrahedral, and shortened tetrahedral.

10. The computer-readable storage medium of claim 8 wherein the lattice segments are individually defined by a pair of crossed sheets.

11. The computer-readable storage medium of claim 8 wherein the transition segments directly couple to the lattice.

12. The computer-readable storage medium of claim 8 further comprising identifying an unsupported contour and then defining a transition segment to couple the unsupported contour to the lattice.