Improvement of machined accuracy under constant feed speed at milling point with a five axis controlled machining center considering approach path

Abstract

We suggested a novel method to maintain a machined surface quality of a curved surface shape by synchronous motion between two linear axes and a rotary axis with the five-axis machining center. It was demonstrated that the proposed method made it feasible to prevent a machined error due to the quadrant glitch caused by friction of the ball screw and linear guide of feed drive system by the method. Moreover, in the previous report, we discussed the influence of servo characteristic difference between linear axis and rotary axis on the machined shape error to improve machined surface quality and suggested a method to reduce shape error of machined workpiece with an advanced control. However, we have not discussed the errors that influence the shape with this method and suggested an improved method based on non-machining motion. In the present report, we focused on using this method to develop a motion for cutting a circular shape, including approach path during actual machining. First, we developed a model formula for the shape error based on the predicted causes of error. Second, we validated our model based on NC data from an actual end-mill tool. We then determined the most appropriate processing method by comparing cutting results. The causes of error were identified as a circle radius decrement due to the circular interpolation motion of the two linear axes, relative angle difference between the linear and rotary axes, and eccentricity of the circular interpolation motion of the two linear axes because of the outside approach path of the machining tool. Finally, we confirmed an effect on reducing the shape error of the machined workpiece considering differences in the servo characteristics of the three axes by monitoring the cutting force with a wireless tool holder during machining. The results showed that the proposed method greatly decreased the shape error.