A novel collision-free NC code generation method with fixed tool orientation vector using the geometric decoupling strategy based on the three rotary axes milling head

The superior performance of machining large parts with the free-form surface is demonstrated by a five-axis gantry machine tool composed of a gantry mainframe and a milling head. A turntable is used to adjust the position of the workpiece rather than a linear guideway when machining impellers or integral turbines. Furthermore, collisions between adjacent blades are almost unavoidable in the machining region, which is relatively narrow for milling heads. The majority of existing methods attempt to solve the problem by changing the tool's tilt angle. However, when an end-mill cutter is employed, this method will deteriorate surface quality and reduce efficiency. On the condition that the milling head has three rotary axes (TRA), a novel NC code generation method with a fixed tool orientation vector for narrow space surfaces is proposed in this paper. When the geometrical model, considered a supplementary condition, is combined with the kinematics model, an inverse kinematics solution to a general multi-axis gantry machine tool with a TRA milling head is obtained. The problem of multi-axis coupling in the inverse kinematics model is solved by combining the iteration method and geometrical model. In the narrow space for a milling head, the redundant degree of freedom, provided by a machine tool equipped with a TRA milling head, enables adjusting the posture of the milling head without changing the tool orientation vector. Feature points are extracted by preprocessing points selected from machined parts and the TRA milling head to choose the feasible posture and simulate the machining process. Collisions in the narrow space are successfully avoided throughout the cutting process. The NC code generation method is verified on CAM software and cut experiments, proven effective in this paper.