Jump Motion Planning for Shrouded Blisks Multi-Axis EDM with Short Line Segments

Abstract

As key components of aero and rocket engines, shrouded blisks are made of difficult-to-cut materials and have complex structures. Multi-axis electrical discharge machining (EDM) which involves rotary axes is an effective approach for machining shrouded blisks. Most EDM machines provide only linear or circular interpolations. To machine a workpiece with a complex structure, a large number of short line segments are used to represent a feeding path for EDM, which is expressed in terms of G01 codes in a machine coordinate system (MCS). Discontinuities along a feeding path consisting of short line segments can cause feedrate fluctuations in jump motions. To eliminate velocity discontinuities, smoothening a multi-axis jump path which involves rotary axes needs to be addressed. In this paper, a transition algorithm and a jump motion velocity planning for multi-axis EDM of shrouded blisks are proposed to smoothen multi-axis jump paths. Considering the differences between translational and rotational movements, one multi-axis jump path can be divided into two subpaths: a linear subpath and a rotary subpath. For each subpath, a parametric spline curve is used to smoothen adjacent short line segments. Depending on the computer aided design (CAD) models of both an electrode and a shrouded blisk, approximation error constraints for corner smoothening in the MCS can be converted into the approximation error constraints in the workpiece coordinate system (WCS). When designing a transition curve, discharge gap is used as the approximation error tolerance in WCS for jump motions, and the multi-axis jump path can be smoothened. Then, a jerk-limited S-shaped feedrate planning algorithm is used for jump motion planning. Simulation results show that the velocity profile of the proposed motion planning is smoother.