A Reliable and Efficient Approach to Numerically Controlled Programming Optimization for Multiple Largest Tools Cutting Blisks Patch by Patch in the Blisks' Four-Axis Rough Machining

摘要

As an important component of gas turbine engines, a blisk (or an axial compressor) is complex in shape. The pressure and suction surfaces of the blisk blades are designed with free-form surfaces, and the space (or the channel) between two adjacent blades varies significantly. Thus, some blade patches can be machined with large-diameter cutters, and some patches have to be cut with small-diameter cutters. Usually, the blisk's material is high-strength stainless steel, titanium alloy, or difficult-to-cut material. The cutting force and temperature in roughing the blisks are high, and thus, the machine tool should be rigid and the cutters should be as large as possible. Therefore, the best industrial practice of rough-machining the blisks is to use multiple largest solid and indexable end-mills to cut them patch by patch on a four-axis computer numerically controlled (CNC) machine. The reasons are (a) four-axis CNC machines are more rigid than five-axis CNC machines, (b) multiple largest cutters are used for higher cutting speeds and feed rates and for less machining time and longer tool life, and (c) if indexable end-mills can be used, the tooling costs are further reduced. For the blisk finishing, a small cutter is often used on a five-axis CNC machine, which is not a topic of this work. However, due to complex shape of the blades, it is quite difficult to automatically optimize the blade surface partition so that each surface patch can be cut with a largest cutter in four-axis blisk rough machining. In the conventional way, numerically controlled (NC) programmers often employ small-diameter solid end-mills and plan their paths to cut the blades layer by layer in four-axis milling. Unfortunately, the machining efficiency of this way is low, and the end-mills wear out quickly. This work establishes a theoretical and completed solution. A simplified optimization model of the largest allowable diameter of the theoretical cutter at a cutter contact (CC) point is established, and an efficient and reliable solver is proposed. The blade surfaces are automated partitioned for largest cutters to the surfaces patch by patch in four-axis rough machining. This approach is efficient and reliable, and it is viable in theory and practical in industry.