Impact of different milling strategies on surface properties and productivity in turbine blade machining

Turbine blade production through 3- and 5-axis CNC machines is a challenging process. Planning and realizing an entire turbine blade is the goal of this project. Besides, it is fundamental to experiment alternative machining strategies and find the best one, after defining clear and useful performance criteria. The focus is put on the blade's airfoil finishing. In order to reach this goal, four different machining strategies have been implemented. Among them, there are three 3-axis strategies and one 5-axis one. The starting raw workpiece is an aluminium cylinder. The chosen CNC machine is the GMX 250 linear by Gildemeister and is a 5-axis one. The used tools are a 52 mm diameter toroidal mill, a 16 mm diameter ball end mill and a 20 mm diameter toroidal mill. In order to create the desired machining strategies, a core role is played by the CAD/CAM softwares used to obtain the tool paths corresponding to each implemented machining strategy. The used softwares are: VANC; Gib-CAM; Tebis. The core of the thesis project consists of: complete description of the entire turbine blade machining process; description of the four airfoil's finishing strategies; analysis of these strategies in order to find the best one. The performance criteria chosen to judge the different finishing operations are surface roughness (as quality representative) and machining time (as productivity equivalent). All the four finishing strategies have been set in order to give as result a workpiece with about the same surface roughness. Once this is proved, it is possible to establish which finishing operation is the fastest one, the most productive. What is expected and obtained, after implementing the different finishing operations, is that with 5-axis machining there is a large time reduction compared to each 3-axis machining time.