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Fig. 13. Possible parting directions for one surfaces set and the pocket.
corresponding parting direction, the fragment f t is rearranged to the same mold piece region as the fragment f e.
As shown in Fig. 14, the fragment f e is obscured by other surfaces when viewed from infinity along direction −d3 . Thus, it is an exact fragment that only belongs to the mold piece associated with parting direction d5 . Conversely, f t is a tentative fragment that is visible in both directions −d3 and −d5 ; hence, it can belong to either mold pieces associated with d3 or d5 . However, the mold piece containing f e will pass through f t if it is withdrawn along direction d5 . Therefore, f t is rearranged into the same region as f e. To check whether a tentative fragment f t is passed through by the mold piece of the exact fragment f e, we create extrusion surfaces from edges of f e along the parting direction. If the interior
its accessibility to the surfaces of each set Si must be analyzed. If
of f t
intersects with the extrusion surfaces, f t
e
is considered to be
all surfaces of Si are accessible by the APD, the surfaces of Si are grouped with the surfaces of the undercut feature to create a new surface set associated with the APD. This process ensures that the
passed through by the mold piece of f .
Criterion 2. When a tentative fragment f t
e
is adjacent to several
number of mold pieces is reduced to a minimum.
exact fragments f
of several mold-piece regions, the tentative
4.4. Formation of regions for mold pieces
fragment is rearranged into the mold-piece region having the most
exact fragments adjacent to f t .
As shown in Fig. 15, fragments f e and f e are exact fragments
1 2
The regions for mold pieces are determined using all visible-
moldable surfaces of each set Si associated with direction di. These
of the mold-piece region associated with parting direction d5 . Fragment f t e
regions are groups of adjacent surfaces connected together to form f e
1 is a tentative fragment adjacent to both f1 and
a united region. In the proposed algorithm, a region of a mold piece is called ‘mold-piece region’, and is denoted by Ri. Inpidual
2 . Moreover, there are no exact fragments of other mold-piece regions adjacent to f t . Thus, f t is rearranged into the same mold-
1 1
piece region as f e and f e.
1 2
visible-moldable surfaces and surface regions pided from dual
moldable surfaces or pided from partially obscured surfaces are generally called ‘fragments’. In reality, a fragment of surface sets Si may either belong to exactly one mold-piece region associated with one parting direction di (in which case it is an ‘exact fragment’,
Criterion 3. A tentative fragment f t is rearranged into the mold- piece region associated with the parting direction along which the withdraw distance of f t is minimal.
t
denoted by f e), or to several mold-piece regions associated with
The withdraw distance of a tentative fragment f
is measured by
t
several parting directions (in which case it is a ‘tentative fragment’, denoted by f t ). Rearrangement of tentative fragments in surface sets Si into appropriate regions is the most important process in the formation of mold-piece regions. Three criteria are proposed for this work.