Automatic minimal partitioning method guaranteeing machining efficiency of free-form surfaces using a toroidal tool

Toolpath planning to machine free-form surfaces on a 3-axis CNC machine remains a complex issue. Research work has proven the relative effectiveness of toroidal tools in material removal rates as compared with spherical tools. However, this efficiency has only been confirmed and maximised for a specific feed direction, i.e. the one with the steepest slope. Since the optimal direction for the use of toroidal tools varies on the surface to be machined, more recent works have proposed surface partitioning methods where the surface to be machined is divided into zones, each machined in an optimal direction. The planning of machining toolpaths for free-form surfaces nowadays involves choosing the number of zones when cutting the surface to be machined: too coarse a partitioning will not guarantee the efficiency of using a toroidal tool, while too fine a partitioning will lead to increased travel times between the zones and frequent changes in direction, impairing productivity. The present article therefore proposes a minimum partitioning method for free-form surfaces guaranteeing the efficiency of a toroidal tool. A first section recalls the state of the art in the matter and the issues involved. The next section introduces the parameters needed to define a strategy. In the third section, an efficiency coefficient to quantify the benefits of using a toroidal tool is introduced. The fourth section describes a surface cutting strategy to ensure the efficiency of the tool at any point machined. The fifth section is dedicated to validating the results on machined and simulated parts in different configurations. Analysis of the results confirms the benefits of this new method.