Downloaded from https://www.everyspec.com ADS-43A-HDBK dimensions are the close tolerances of the blade root dovetail or fir tree and the aerodynamic shape, angle, and twist of the blade. The dovetail and fir tree retention is critical from a safety standpoint, and the aerodynamic shape is critical to engine performance. The specific critical dimensions are identified in the manufacturing drawings and/or the STDP. The manufacturing contractor will be furnished an MCC by USAATCOM engineering or must have a MCC certified and serialized by a source approved by USAATCOM engineering. This MCC must be available for the First Article Inspection.
The MCC is used in conjunction with an optical comparator which projects a magnified image of the part profile which is then compared directly with the MCC. The MCC shows, in blown-up form, the allowable tolerances for the blade airfoil or fir tree shape. The size of the MCC image and the magnification and screen size of the optical comparator are normally specified by USAATCOM engineering. The compressor or turbine disks that retain the blades are dimensionally controlled by engineering drawings augmented by MCC or CAD. The fir trees and dovetails that retain the blade are made to close tolerances.
The internal or external bearing or centering journals, splines, and curvic couplings are dimensionally critical. The heat treat, shot peening, machining feeds/speeds, surface finish and other processes may be critical to parts lives. The structural integrity, balance, and performance of these rotating parts make some dimensions critical. The specific critical dimensions are identified on the manufacturing drawings and/or the STDP. Blisks, which combine disks and blades into an integral one-piece cast unit, are dimensionally controlled by drawings, MCC and/or CAD. In the case of a cast piece, the technical expertise is in the design and manufacturing of the die/pattern.
However, the finished casting must be checked for critical characteristics. The structural integrity of the blisk, the aerodynamics of the blade, the close tolerances of bearing or centering journals and curvic couplings, and the rotating balance of the blisk make some dimensions critical. The specific critical dimensions are identified in the manufacturing drawing or the STDP. Low cycle fatigue is a life limiting factor for the compressor, impeller, turbine disks, cooling or sealing plates, and certain other parts.
Some of the factors which contribute to reducing low cycle fatigue life are material properties, material processing, surface finishes, marking components, radii, fillets and comer relief, and other anomalies. It is essential that all identifiable contributors to low cycle fatigue life reduction be eliminated to the greatest extent possible. i. Oil jets are designed to be installed in only one position. To provide an exact aiming point for the jet, the jet hole drill angle is critical and maintained at close tolerance. All oil jets must be flow tested for proper oil quantities at system pressure, proper 1 5