GCD Accessibility and Tool Orientations
When aPriori analyzes a part’s geometry, it analyzes the nature of each GCD’s accessibility from each direction from which a tool might usefully approach, and represents the results as Is Accessible From relations. (See GCD Relations in the Geometric Cost Drivers pane.) The following types of accessibility are possible:
• Parallel: a tool oriented parallel to the GCD could approach from the specified direction without obstruction. In this case the tool orientation is parallel (un-obstructed) to the GCD.
• Parallel obstructed: a tool oriented parallel to the GCD could approach from the specified direction, but would be somewhat obstructed. In this case some tools may be able to access the GCD despite the obstruction, or the GCD may be accessible using combination of different tool orientations (see
Multiple Approach Surface Finishing).
• Normal: a tool oriented normal to the GCD could approach from the specified direction without obstruction. In this case the tool orientation is normal (un-obstructed) to the GCD.
• Normal obstructed: a tool oriented normal to the GCD could approach from the specified direction, but would be somewhat obstructed. In this case some tools may be able to access the GCD despite the obstruction, or the GCD may be accessible using combination of different tool orientations (see
Multiple Approach Surface Finishing).
• Oblique: a tool oriented oblique to the GCD could approach from the specified direction without obstruction. In this case the tool orientation is oblique (un-obstructed) to the GCD.
• Oblique obstructed: a tool oriented oblique to the GCD could approach from the specified direction, but would be somewhat obstructed. In this case some tools may be able to access the GCD despite the obstruction.
A GCD is at least partially accessible from the direction specified by a tool orientation if there exists an Is Accessible From relation whose value for first is the GCD and whose value for second is the tool orientation (setup axis). The type of accessibility (parallel, parallel obstructed, normal, etc.) is specified by the Direction Type attribute of the Is Accessible From relation.
Different operations require different types of accessibility. For example, a facing operation on a planar face requires that there is a tool orientation that is normal (unobstructed) to the planar face (but see also
Multiple Approach Surface Finishing). The table below shows the general requirements for some basic types of machining operations:
Tool orientation/GCD relationship | Facing | Side Milling | Contouring | Hole Making |
Planar Face | Normal (unobstructed) | Parallel (unobstructed) | Oblique (unobstructed) | |
Curved Wall | | Parallel (unobstructed) | Oblique (unobstructed) | |
Curved Surface | | | Oblique (unobstructed) | |
Hole | | | | Parallel (unobstructed) or Parallel obstructed |
Note that parallel, normal, and oblique are defined as follows for different GCD types:
• Parallel
o Planar face: a setup axis is parallel to a planar face if some line segment in the planar face runs along the direction specified by the setup axis.
o Curved wall: a setup axis is parallel to a curved wall if the rules of the wall run along the direction specified by the setup axis. (A curved wall can be thought of as described by the motion of a line segment, or rule, translated--and not rotated--through space along a smooth curve.)
o Ruled curved surface: a setup axis is parallel to a ruled curved surface if the average direction of the rules is the same as the direction specified by the setup axis. (A ruled curved surface can be thought of as generated by the motion of a line segment, or rule, translated and rotated through space.)
o Unruled curved surface: a setup axis is parallel to an unruled curved surface if the average direction of normals to the surface is the same as the direction specified by the setup axis.
o Axisymmetric GCD: a setup axis is parallel to an axisymmetric GCD if its axis of symmetry runs along the same direction as that specified by the setup axis.
• Normal
o Planar face: a setup axis is normal to a planar face if it is normal to every line segment in the planar face.
o Curved wall: a setup axis is normal to a curved wall if it is normal to the rules of the curved wall.
o Ruled curved surface: a setup axis is normal to a ruled curved surface if it is normal to the average direction of the rules of the curved surface.
o Unruled curved surface: a setup axis is normal to an unruled curved surface if it is normal to the average direction of normals to the surface.
o Axisymmetric GCD: a setup axis is normal to an axisymmetric GCD if it is normal to the GCD’s axis of symmetry.
• Oblique: s setup axis is oblique to a GCD if it is neither parallel nor normal to it.