Automatic Reasoning for Defining Lathe Operations for Mill-Turn Parts: A Tolerance Based Approach

With the increase in computer-controlled hybrid machining (e.g., mill-turn machining), one needs to discern what features of a part are created during turning (i.e., with a lathe cutter) versus those created by milling. Given a generic part, it is desirable to extract the turnable and nonturnable features in order to obtain feasible machining plans. A novel approach for automating this division and for defining the resulting turning operations in a hybrid process is proposed in this paper. Given a mill-turn part, the algorithm first identifies the dominant rotational-axis in order to quickly generate the axisymmetric “as-lathed” model. This model is then subtracted from the original part to isolate the nonturnable features. Next, the as-lathed model is translated to a label-rich graph, which is fed into a grammar reasoning algorithm to produce feasible turning sequences. During the turning process planning, the knowledge encapsulated in the design tolerances is used to guide the generation of feasible turning sequences. Two case studies are provided to explain the details of our algorithm. One of the suggested turning plans is compared with a manually proposed plan from an expert machinist and the results show the optimality of our plan in satisfying the prescribed tolerances.