Variable-depth multi-pass tool path generation on mesh surfaces

In a typical multi-pass machining process of freeform surfaces, especially at the roughing stage, the constant Z level strategy is typically used. Under this strategy, the inevitably formed islands where the tool has to travel between increase the machining time as the tool has to air-cut between them. Moreover, the uneven intermediate geometry left on the islands leads to sharp changing of chip load and jeopardizes the finish surface quality. To avoid the staircase-like intermediate geometry of the islands and most of all for the ultimate goal of maximizing the machining efficiency, in this paper we present a method of variable-depth of cut multi-pass tool path generation for multi-axis machining of mesh surfaces. By parameterizing the cut volume to a unit uvw cubic parametric domain, the multi-pass process planning task turns to finding an optimal sequence of w level parameters. To solve the optimization problem, we introduce a machining efficiency indicator—the average material removal rate (AMRR). The w level parameters are obtained by iteratively solving the maximization problem regarding AMRR. The preliminary computer simulation and real physical cutting experiments show that substantial savings in total machining time could be achieved by the proposed method as compared to the traditional constant Z level method.