Comparative study of 3-and 5-axis CNC centers for free-form machining of difficult-to-cut material

This paper examines the cost effectiveness of 3- versus 5-axis machines for the machining of a turbine blade made of alloy steel EN 34CrNiMo6. The acceptable surface finish cannot be achieved when a free surface is machined on a 3-axis CNC center due to the variation of the tool's position in relation to the part's surface. A feed-rate adjustment algorithm is proposed in this paper as a way to compensate for that limitation. To that end, the following two research questions are addressed: (1) if the algorithm is used, can the required surface finish be achieved on a 3-axis CNC center, and (2) which of two alternatives: a 3-axis (assuming the algorithm is executed) or 5-axis CNC center (without the algorithm) will be more cost effective? The study demonstrates that if the algorithm is executed, the finish of the surface machined on a 3-axis center reaches a similar standard as can be achieved on a 5-axis center. Additionally, the machining time is reduced by over 17% when compared to the machining time required on the same 3-axis machine when the NC code is not optimized with the feed-rate adjustment algorithm. The cost effectiveness of the two alternatives is compared using the cost model, which is the research contribution and justifies the application of software technology for the machining of complex geometries on a 3-axis machine. (C) 2014 Elsevier B.V. All rights reserved.