A double-NURBS approach to the generation of trochoidal tool path

Abstract

Trochoidal milling becomes a popular strategy in high-speed rough milling, thanks to its advantages in lowering cutting force (and tool wear) and increasing tool life. However, it also suffers from the disadvantages of low cutting efficiency and prolonged machining time due to its reduced cutter-workpiece engagement in the cutting area and the idle tool path in the non-cutting area. In this paper, a new trochoidal tool path generation method is proposed based on a double-NURBS curve. Unlike traditional circular trochoidal tool path that combines circular and linear paths to approximate the trochoidal path, the double-NURBS tool path can truly represent a trochoidal path with C2 continuity throughout the entire tool path. In the front cutting area, the control points of the NURBS are modified to increase the cutter-workpiece engagement angles; in the rear non-active area, the NURBS curve is modified to shorten the non-cutting distance and the machining time. Degree elevation of the NURBS circle from 2 to 3 maintains C2 continuity to ensure the machining is smooth throughout all transitions. Cutting force simulations and pocket machining experiments are carried out to validate that the proposed double-NURBS approach deliver the expected result and performance.