Referring to Fig. 1, the planning solution is partitioned into four different object levels: stamping part, stamping features, stamping operations, and stamping process plan, each represent- ing initial input or different partial solutions posted on the black- board by the specialist KSs. They are described as follows.

3.1.1 Input data to the blackboard

Input data to the blackboard mainly includes the part and press ob- jects. The generic declaration of a part object includes the basic attributes such as part type, part dimensions, weight, surface treat- ments, blank thickness, blank material, annual production, blank dimensions, etc., and points to its constituent stamping feature ob- jects that will be elaborated later on. The press object contains the attributes such as press type, press tonnage, bolster dimensions, bed open dimensions, shut height, number of strokes, etc.

3.1.2 Object-oriented feature modeling to stamped metal parts

Since traditional geometric modeling techniques do not capture design intent (e.g., design for manufacturing), they are in gen- eral unable to support sophisticated and intelligent reasoning capabilities, e.g., knowledge-based process planning. Recently, the concept of machining features has been introduced to cre- ate a direct link between design and manufacturing [23]. Feature modeling is a relatively new way of storing design and manu- facturing information in CAD/CAM/CAPP systems. Similarly, stamping features of a stamped metal part can enable stamping process planning tasks to be performed directly from the geo- metric model. Stamping features are information carriers that are used to model a stamped part with a set of design and manu- facturing information including geometric and non-geometric at- tributes. Each of these stamping features can be   manufactured

with a specific stamping operation or a combination of stamping operations.

Using the hierarchical classification structure of general de- sign features by Chen et al. [24], a stamped metal part can be modeled with four categories of stamping features:

Primary features: flat, drawing, etc.;

Positive secondary features: tab, curl, emboss, hem, bead, flange, etc.;

Negative secondary features: hole, extrusion hole, profile, de- form, slot, step, etc.; and

Connective secondary features: bend, blend, etc.

In this work, the object-oriented feature representation is em- ployed to encapsulate design and manufacturing information in a stamping feature object. For example, a hole feature object contains the basic attributes such as feature type, feature ID, pri- mary feature ID, position, orientation, depth, diameter, precision, roughness, etc., and methods to calculate perimeter.

Besides  representation   of   inpidual   stamping features, a comprehensive representation of feature relations guarantees that all the stamping features associated with stamping process planning are considered. In addition, the data on feature relations are useful for determining the sequence of stamping operations and sometimes the stamping operations themselves. Four criti- cal types of relations among stamping features – “is-in”, “is-on”, “adjacent-to” and “precision-associated” are identified, which have been elaborated in our previous work [25] and won’t be repeated in this paper for conciseness. For example, a precision- associated relation represents design constraints that arise when a stamping feature does not directly connect to, but is associ- ated with, another stamping feature by a toleranced dimension. The feature relation data is also included in the feature object for more complete feature modeling.

3.1.3 Stamping operation objects mapped from stamping feature objects