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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 representing initial input or different partial solutions posted on the blackboard by the specialist KSs. They are described as follows.
Fig.1. Blackboard framework for stamping process planning
3.1.1 Input data to the blackboard
Input data to the blackboard mainly includes the part and press objects. The generic declaration of a part object includes the basic attributes such as part type, part dimensions, weight, surface treatments, blank thickness, blank material, annual production, blank dimensions, etc., and points to its constituent stamping feature objects 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 general unable to support sophisticated and intelligent reasoning capabilities, e.g., knowledge-based process planning. Recently, the concept of machining features has been introduced to create a direct link between design and manufacturing [23]. Feature modeling is a relatively new way of storing design and manufacturing 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 geometric model. Stamping features are information carriers that are used to model a stamped part with a set of design and manufacturing information including geometric and non-geometric attributes. 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 design 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, deform, slot, step, etc.; and
Connective secondary features: bend, blend, etc.
In this work, the object-oriented feature representation is employed 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, primary 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 critical 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.
3.1.3 Stamping operation objects mapped from stamping feature objects
On the blackboard, the stamping operation objects are in a lower level than the stamping feature objects, and are used to define the manufacturing process from metal strip to the formed metal part. Stamping features constitute a stamped part, while stamping operations are selected as elements of a stamping process plan. Essentially, the stamping process planning task is to transform a set of stamping features into a set of stamping operations, and to describe the relations between these. The generic declaration of a stamping operation object includes stamping operation type, geometric shapes, geometric constraints, precision, roughness, relationships with stamping features, control parameters, etc. Typical stamping operation objects include piercing, notching, cut-off, blanking, lancing, shaving, drawing, embossing, coining, trimming, and other miscellaneous forming operations. A stamping feature may be manufactured with a specific stamping operation (one-to-one mapping) or a combination of stamping operations (one-to-many mapping). Several stamping features may also be manufactured with a single stamping operation (many-to-one mapping).