Mapping KSs. Heuristic rules are used to reason out a set of stamping operation objects from a set of stamping feature objects through feature-operation mapping; examples of some mapping KS rules are given below.

(a) Piloting KS rules

Rule Piloting101: If a hole can be used as a pilot hole, then it should be circular in shape, should not have very low tolerance in diameter, and should be greater than three times the thickness of the stamped part. (Below is its corresponding source code in CLIPS.)

(defrule Piloting101 Line 1

(declare (salience 30)) Line 2

?Hole <- (Hole (Type THROUGH) (Shape CIRCULAR) (Piloting NO)(Tolerance-range ?Tol-r&:

(> ?Tol-r ?*Tolerance-threshold*))

(Diameter ?Dia&:

(> ?Dia (* 3 ?*Part-thickness*)))) Line 3

=>

(modify ?Hole (Piloting CANDIDATE)) Line 4

)

Line 1 is the rule name. In Line 2, a salience of 30 is de- clared in this rule. This property is used to set the order of rule execution. Line 3 denotes the left-hand side (hypothesis) of the rule, indicating that a desired hole feature constrained in shape, diameter, and tolerance range as above, is needed to fire the rule. Line 4 denotes the right-hand side (conclusion) of the rule, indicating that the hole feature is then selected as a piloting candidate.

Rule Piloting102: If a hole is selected for piloting purpose, then it should be stamped in a single step of piercing operation. (For conciseness, the CLIPS source codes of this rule and other rules introduced later are omitted in this paper.)

Rule Piloting103: If no suitable hole exists for piloting purposes, then piercing operations are required to stamp two pilot holes in the scrap sections and on the opposite sides of the stamped part.

(b) Piercing KS rules

Rule Piercing201: If a hole requires a very low roughness of surface, then it can be stamped by two steps of piercing and trimming operations, or a single step of high precision piercing operation.

(c) Bending KS rules

Rule Bending301: If a bend has a bending angle between 90  ∼

135◦ , then it needs a two-step bending operation.

Rule Bending302: If two bends have 90◦ angles and form a “U”

type channel, then they can be stamped by a single U-bending operation.

Staging KS. Heuristics rules are used to derive the sequence of stamping operation objects automatically by creating stamping operation relations. Examples of some staging KS rules are as follows.

Rule Staging401: The piercing operations to stamp two pilot holes should be staged together in the first station.

Rule Staging402: When embosses exist, if possible they are em- bossed in the first station to prevent deformation of other stamp- ing features.

Rule Staging403: If holes (except pilot holes) and scraps (that don’t accommodate indirect pilot holes) cannot be stamped sim- ultaneously in a same station, the process sequence is as follows: piercing operations precede notching operations.

Rule Staging404: If holes to be pierced are not close to each other, and the distance among them has a high precision require- ment, then the holes should be pierced simultaneously at the same die station.

Rule Staging405: A bending operation is not staged unless all the scraps surrounding the bending flat have been notched by notch- ing operations.

Rule Staging406: If possible, the cut-off operations on scraps that accommodate pilot holes should be staged in the final station.

3.2.2 Object-oriented knowledge organization of KSs