Many aerospace components are complex but relatively weak structurally or have reference surfaces that can easily distort. Traditionally, these parts are held by encapsulating them in a low melting alloy. This provides a solid robust structure with clearly defined and rigid location surfaces. However, the mounting and dismounting processes are expensive and add no processing value to the part. With the move toward lower stock levels and the lower Q for grinding and its associated forces, end users are implementing hard-point mounting methods where the part is supported on its reference datum points with hardened steel or carbide-tipped pneumatic or hydraulic clamps.
Hard-point mounting increases the processing options available to the end user. The following includes several that are not practical with encapsulation. For example: [6]
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FIGURE 16.27 Single part fixture.
surfaces in turn to the wheel. The wheel or wheel “pack” (multiple wheel assembly) is designed with a range of diameters and profiles to achieve the clearance to reach and generate the various forms on the part. The design of the fixture is pivotal to the whole process and often extremely complex (Figure 16.29). It can be readily seen that the size of the machine, wheel design, dresser design, and coolant delivery can only be defined once the fixturing is designed. Several companies have specialized in this type of fixturing, working closely with OEMs and wheel makers for turnkey operations.
• Several components can be mounted in a single fixture to present a series of different grind stages. The components are moved progressively from stage to stage taking off one finished blade each time at the final stage and adding one at the initial stage. This approach is most suited to small, easy-to-handle blades on 4- or 5-axis grinders. Fixture design is again critical. For these types of operations in combination with near net shape components, the need for high stock removal rates becomes less critical, as the majority of the cycle time is used for machine indexing. This makes the approach particularly suited to processing using small CBN wheels.