Cutting force and chatter stability analysis for PKM-based helical milling operation

In order to enhance the manufacturing productivity, mobile machining with industrial robots is proposed as a cost-effective and portable manufacturing alternative to large-scale CNC machine tools in aircraft part machining. Combing the advantages of helical milling and parallel robot, the cutting forces and chatter stability of a novel 5-DOF hybrid PKM (named TriMule)-based helical milling process are first investigated in this paper. The cutting force and dynamic model of PKM-based helical milling operation are proposed, and the chatter stability diagrams at the seven representative machining positions are obtained based on the complete discretization scheme with Euler's method approach. The predicted cutting forces and chatter stability diagrams are experimentally validated by the PKM-based titanium alloy helical milling. It can be found that the PKM machining position has a great influence on the corresponding limit stable axial depth of cut in the helical milling operation. Meanwhile, it was indicated that the spindle speed is an important factor affecting the helical milling stability difference at different machining positions. Meanwhile, it was found that the helical milling stability is only determined by second-, third-, and fourth-order modes of TriMule when the spindle speed is higher than 1000 rpm with the first 4 modes of the cutting system considered. The research results are expected to provide a basis for the helical milling parameter optimization and reasonable robot machining position selection.