# Manufacturing Processes of Integral Blade Rotors for Turbomachinery, Processes and New Approaches
## 2 Monolithic Components: Manufacturing Processes
### Conventional Machining Process: 5-Axis Milling
#### 2.5.1 Cutting Tools and Tool Holders  
One of the main advantages of the conventional milling process is the great adaptability for a huge variety of geometries and range of tool size and form that could be found in the market for many different applications. Usually, solid coated carbide mills are the tool types recommended for blisk and impeller manufacturing processes. Solid carbide mills are standardized in a range of diameters from 2-16 mm; moreover, carbide tools present good tenacity and heat resistance for machining Ti and Ni superalloys [45]. Besides that, indexable milling cutters are an economical alternative for some specific operations, concretely roughing operations, though their use is not very extended for these components manufacturing. Furthermore, coatings (TiAlN, TiN, AlCrN, AlCr and CrN) add real advantages to these cutting tools improving the resistance to friction, temperature, oxidation and corrosion. Finally, General Electric patented an alternative for roughing curved slots using indexable milling cutters instead of solid carbide tools [46].  
From the tool forms point of view, frontal, frontal with corner radius and spherical are the most popular for IBRs manufacturing (Figure 9). Frontal mill is indicated for roughing because the cutting speed depends on the tool diameter, so in this case, it does not decrease at the tool tip. Frontal tools with corner radius are one alternative to be used in order to avoid the excessive wear suffered by cutting edges in 5-axis milling movements. Moreover, these corner radiuses are also adaptable to the blades blend, making them an option for semifinishing operations. Conical tools are normally selected for semifinishing and finishing operations; more specifically, they access the entire cutting length in those cases when the surfaces are ruled. Spherical tools are used for finishing strategies. Moreover, in some cases that present concave surfaces with small curvature radius, spherical tools are the only feasible solution. Finally, there is a new trend to barrel shaped tools; some studies around this form led to the conclusion that they are a real alternative for semifinishing and finishing non-extremely curved blades [47]. The main advantage of this cutting tool form resides in the curvature radius that allows reducing the number of passes, and the machining time [48].  
Figure 8: High pressure compressor generic blisk specifications [4] and Ti and Ni alloys material removal rates and cutting conditions [21].  
In addition to the foregoing, the adequate choice of the tool holder also influences the milling process. On the one hand, each holder type presents different characteristics in terms of accuracy, clamping forces or lubricooling systems. On the other hand, milling strategies closer to blade blends require a holder with smaller body to avoid collisions. Hence, thermal tool holders fit with these requirements.  
IBRs and blisk manufacturing will be reducing time meanwhile new cutting tools experimentation would be performed. Superalloy machining is a hot topic today, both in performance aspects [48; 49] and in the effect on final residual stress and surface integrity [50]. Sintered carbide tools are in rapid evolution, along with coatings [49; 51; 52]. However, the introduction of Gamma TiAl in this business [53] is not expected, due to extreme fragility of the aluminides, which only can be produced with enough reliability with ECM.