When a cutter traverses a region local to the singularity in 5-axis machining, the stability of machine tool motion may be violated and inevitably lead to a reduction in machining quality and accuracy. In this paper, the underlying cause of the singular machine behaviors is first investigated by differentiating tool path motions, on the basis of the tool path motion expressions in part and machine coordinate systems. A further investigation indicates abrupt kinematic changes to be inevitable when the rotary axes approach a singularity. To eliminate such possible singular risks in 5-axis machining, a local tool path modification method is proposed by adjusting the two rotary axes out of a singular configuration. The critical kinematics smoothing and the consequent gouging concerns resulting from reorientation are comprehensively incorporated in the process of singularity avoidance, by means of a novel tool orientation optimization model. Specifically, the algorithm starts with the determination of an appropriate adjustment range in a simple yet effective manner, and then the primary rotary axis is adjusted in a constrained region away from zero, so as to avoid singularity. After that, the second rotary axis is accordingly adjusted, with no gouging requirements being violated. In this way, singularity problems in 5-axis machining are solved, and both the machine axes kinematics and surface gouging errors are under control. Machining simulation and laboratory experiments were conducted to validate the effectiveness of the proposed method.

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