A simulation system for improving machining accuracy in milling

The end milling process is used extensively in a variety of manufacturing areas, especially in the aerospace industry, where many of the machined parts are pockets and thin webs. Many of the end milling applications involve machining of thin webs using long and flexible cutters. This leads to the fundamental problem of surface accuracy in milling. The superposition of the tool and the workpiece deflections, which is known as effective system deflection, will cause dimensional errors and irregularities on the finished surface.In the case of thin web machining, using conventional cutting speeds (i.e. 30 to 60 m/min) the surface generation is mainly influenced by the workpiece vibration and to a lesser extent by the tool deflection. The severity of these vibrations depend on the cutting conditions used, as well as material and geometry of the workpiece being cut. In this paper, a simulation system for finish milling of flexible structures is developed. This system includes an improved model for the prediction of the cutting force. This enhanced dynamic model takes into account the deflections of the tool and the workpiece in the calculation of the chip load. A dynamic, 3-D finite element model of the workpiece, which takes into account the effect of material removal, is used in the simulation. An Automatic Mesh Generation program is developed to simulate the material removal during cutting.The simulation results are then compared with the experimental results obtained on a vertical milling machine. Several finishing cuts are performed and the resulting workpiece surface dimensions are compared with the predicted errors.