AGMA 05FTM15-2005 pdf free download.Repair of Helicopter Gears.
The MFI process is a vibratory honing process. The hardness and texture of the abrasive media can be controlled to achieve any desired surface finish, down to a bright mirror finish (0.02 micro-inches Ra). With proper media selection, thin coatings can be polished without being removed. This is a time consuming operation. The Extrude Hone process involves honing the surface of the part with putty like media charged with abrasive particles. This is a cutting process rather than a burnishing/honing process. The surface finish that can be achieved is a function of the surface finish before processing with the functional limit for finest finish is approximately in the 4 to 6 micro-inches Ra range. This method requires tooling specific to each part to ensure uniform stock removal. The REM Chemicals process is a chemically accelerated vibratory finishing technology. A mildly acidic phosphate solution produces a soft conversion coating, which is easily removed by the rubbing of the non-abrasive media. he exact blend of chemicals and the size and shape of the media are selected on the basis of the material being processed, the size and shape of the part, and the desired final surface finish.
The MFI process requires long process time to produce fine finishes. The Extrude Hone process requires special tooling to ensure uniform stock removal, and can produce only a moderately fine finish. Thus, of the three processes evaluated, the REM Chemicals process offers the best advantage in producing a fine finish (1-2 micro-inches Ra range), rapid processing time, and controlled, minimalt stock removal. Based on this analysis (a detailed analysis was not considered a part of the effort) and considerable experience with the REM Chemical’s process for superfinishing gears(1 .2.3), I was selected for this effort.
Pre-Finishing Evaluations
Two Sun Gears and two Input Pin ions that had been scrapped due to major FOD were provided for examination. These gears also exhibited minor FOD (edge not detectable with the point of a sharp probe, atypical example is shown in Figure 1) and early pitting (gray staining, a typical example is shown in Figure 2) was detected on the Input Pinions, making these gears good candidates to investigate repair procedures.
Metallurgical Characterization Pre-Suoerfinishing
A metallurgical section was cut from one of the sun gears through an area with minor FOD damage. This section was polished, and examined for evidence of sub-surface cracking resulting from the dislocation when the foreign object passed through the mesh. A high magnification photomicrograph of this section is shown in Figure 3. No evidence of sub—surface cracking could be detected. Thus, damage of this limited magnitude is a satisfactory candidate for remediation by superfinishing the surface.AGMA 05FTM15 pdf download.