An inexact subgraph matching algorithm for subpart retrieval in NC process reuse

With the wide application of CAD/CAM technology, huge amounts of process data are generated each year, which are valuable to be referred to and reused. For the reuse of these historical process data, the retrieval of the subpart model is the key, as similar structures usually correspond to similar NC processes. However, the existing subpart retrieval methods are only practical to the parts with simple structures or fixed geometry. This research proposes a subpart model retrieval method based on inexact subgraph matching, which can be used for parts of arbitrary complexity. By representing the part model as an attribute graph, the task is first transformed into an inexact subgraph matching task where some degree of matching difference is accepted to retrieve similar subparts. Next, this research proposes VF3-light-N, an inexact subgraph matching algorithm that operates on attribute graphs. The idea of VF3-light-N is to quantify the mismatch of both nodes and edges based on matching error first. Then use the empty map to remove the nodes that cannot be matched, so that the remaining nodes and edges can be matched exactly. Thus, VF3-light-N can search out all the matched subgraphs within a certain noise threshold. A case study based on aircraft structural parts is carried out, and the result shows that the proposed method can efficiently retrieve subparts from complex part models. Furthermore, it is believed that VF3-light-N can be also used in other inexact subgraph matching applications, such as feature recognition.