GCD Extraction
aPriori extracts the geometry of a CAD model in the form of geometric cost drivers (GCDs) that include Bends, Ends, and Forms, as well as Holes, Rings, Surfaces, and CrossSections. As usual, there is a special GCD, Component, that represents the part as a whole. Below are some of the important properties of each of these GCD types. Each GCD’s units are shown in metric.
• Component:
o Volume (mm3)
o Surface Area (mm2)
o Length, Width, and Height (millimeters)
o Number of Surfaces
o Min Thickness, Max Thickness, and Avg Thickness (millimeters)
o Length Direction, Width Direction, and Height Direction: each of these is a unit vector, two of whose components are 0 (the other component is 1 or -1). These vectors can be compared with the Direction vector of another GCD (such as a Perimeter or Setup Axis) in order to determine whether the GCD’s direction is aligned with the part’s length, width, or height.
• Cross Section:
o Area (mm2)
o Height (millimeters)
o Inside Diameter (millimeters)
o Outside Diameter (millimeters)
o Perimeter (millimeters)
o Thickness (millimeters)
o Width (millimeters)
o Sheet Width (millimeters)
• Surfaces (Curved Surface, Curved Wall, and Planar Face):
o Finished Area (mm2)
o Bend Diameter (millimeters)
o Perimeter (millimeters)
o SER Length and SER Width (smallest enclosing rectangle dimensions in millimeters)
o Corner Diameter (millimeters)
o Inside Diameter (millimeters)
o Number of Surfaces
o Fillet Min Angle and Fillet Max Angle (degrees)
o Round Radius (millimeters)
o Round Length (millimeters)
surfaces.jpg
• Simple Hole, Multistep Hole:
o Diameter (millimeters),
o Length and Depth (millimeters)
o Volume (mm3)
o Surface Area (mm2)
o Maximum diameter and Minimum diameter (millimeters—for multistep holes)
o Step count (for multistep holes)
o Hole type (THROUGH or BLIND)
o Blind, Sleeve Pin, Threaded, Countersunk, and Flanged (TRUE or FALSE)
o Accessibility (THROUGH, OBSCURED, SIDE_A, SIDE_ B, or UNDERCUT--determines operation sequence and tooling requirements.)
 
o
 
• Ring:
o Depth (millimeters)
o Min Wall Thickness (millimeters)
o Volume (mm3)
o Axial Section Area (millimeters)
 
 
• Bending/Forming (Bends, Ends, Forms):
o Area (mm2)
o Bar Position (millimeters)
o Max Cut Angle (degrees)
o Outer Perimeter (millimeters)
o Bend Angle (degrees)
o Min Bend Radius (millimeters)
o Neutral Bend Radius (millimeters)
o Is Circular (Boolean, Bends only)
o Is Planar (Boolean, Bends only)
o SER Length (millimeters)
o SER Width (millimeters)
end_bend_form.jpg
See also Extrusion GCDs.
Extrusion GCDs
If you have licensed the Extrusions cost model, aPriori attempts to recognize parts that can be manufactured from extruded stock with punching, bending, and/or light-to-moderate machining. In order to do this, aPriori determines the geometry of the workpiece in an unbent state, with holes and cutouts filled in. For the workpiece in that state, if there is a direction along which the cross-sections are all the same, the part is recognized as an extrusion.
Note: Extrusions are recognized by default in starting point VPEs. To disable extrusion recognition, set the site variable enableGenericExtrusions to false.
Note: For heavily machined, extruded parts, use 2-model machining.
Important GCDs for extrusions include the following:
• CrossSection GCD. Important properties include:
o Shape: for extrusions, this is set to GENERIC_EXTRUSION.
o Outside Diameter: diameter of the CrossSection’s smallest enclosing circle
o Max Thickness: maximum thickness of the part
o Perimeter: perimeter of the CrossSection
• CrossSectionHollow GCD: region of a CrossSection such that one of the following holds:
o Fully hollow CrossSectionHollow: region is bounded by an internal contour.
o Semi-hollow CrossSectionHollow: region is not occupied by the part and is surrounded, except for a small gap, by part of the part’s external contour. A gap is considered small if the square of its length is less than two and half times the hollow area.
The cross sections shown below have fully hollow regions:
A close up of a window Description automatically generated
The cross sections shown below have semi-hollow regions:
Important properties include:
o Gap Length: length of the gap in the contour surrounding the hollow. This is 0 for fully hollow CrossSectionHollow GCDs.
o Area: area of the hollow.
o Symmetric: true if the hollow is symmetric with respect to a line extending from the gap midpoint.
• Cutout GCD: represents a volume of material that is removed either interior to the part or adjacent to an end of the part. For parts made from custom extrusion profiles, these are extracted instead of ComplexHole GCDs (which provide less information about accessibility and applicable tool sizes). Cutout GCDs may either be machined with a 3-Axis or 5-Axis CNC Router, or may be punched with a Tube Laser.