Positioning accuracy improvement in five-axis milling by post processing

Abstract

A five-axis machine is currently one of the most versatile machine tools available. The importance of five-axis milling is easily recognizable when manufacturing moulded and sculptured surfaces; where the tool tip direction and position are controlled simultaneously. The complex structures of the machine tools produce an inaccuracy at the tool tip which is caused by kinematics parameter deviation resulting from manufacturing error, assembly error or quasi-static error. The machines are very sensitive with angular error depending on the tool and pivot distance. In five-axis machine tools, all linear and rotational axes are theoretically perpendicular (dot product, cos90°=0) to each other and directed along or around the X, Y and Z of the Cartesian coordinate system, but in working machines the axes are nearly perpendicular (cos89.9°≠0) because of the reasons mentioned above. This kind of error can be taken into consideration only by the precise description of the actual kinematics of the machine tool. By counting the new axes values using the numerical iteration technique of the defective axes from the cutter location data (CL-data), it may be possible to position the tool tip at the desired position and orientation. The method implemented in a postprocessor makes it possible to perform the kinematics calculations on-line on the machine.