AGMA 92FTM12-1992 pdf free.Noise Reduction in a Plastic and Powder Metal Gear Set Through Control of“Mean Involute Slope”.
5.1. P/U Pinion. With steel powder metal parts, the profile shape will be primarily determined by the shap. of the tool. There lint much net change in shape of the part as it is removed from the cavity and is sintered. There usually is a very slight increase in size as the part expands when leaving the cavity, which ii largely offset by the slight shrLnkage in sintering. Therefore, obtaining the proper tooth shape depends on getting the cavity developed right in the first place. It isn’t possible to play with other process variables such as temperature to change part geometry.
5.2. bIded Plastic Gear. Molded plastic gears are another story. The cavity size has to be determined by accurately knowing the shrink rate of the material being used. Typical gear materials night have a shrink rate that varies Iron .OOS”/jnch to .030/lnch, depending on material as well as fillers such as glass fibers. This has to be taken into account when designing the size of the cavity. Other process variables such as temperature and pressure will also affect the shrink rate and therefore the resulting part size and profile shape.
6.0. REDESION OF UOLD CAVITY (Plastic Gears).
6.1. Keasurement of Parts from First Cavity. Molded plastic parts. made of unreinforced material, generally shrink at a nearly unifor, rate. In this case, the material was an acetal (DeIrin 500). The original cavity was designed for a specific shrink rate. The resulting parts were measured for various diameters such as OD. root dis., tin dia., and hub dia. The teeth were also measured for involute by adjusting the base diameter until the MiS was near zero. This showed that the base diameter shrunk at nearly the same rate as all the other diameters. The mold cavity was also measured for these various diameters. From these measurements, It was determined that the .rtglnal parts shrunk more than expected. This resulted in the gears having a higher pressure angle than desired.
6.2. Cavity Redesign. A new cavity was designed and made to the new actual shrink rate (or the material and process being used. This resulted in parts that were closer to the desired specification.
7.0. EVALUATION OF FINAL PRODUCTION PARTS.
7.1. Final Involute Tests. Involute results of the new parts are shown in Figure 10 1 11. The 1115 for both mating parts are within .0002”. meaning that they are nearly conjugate.
7.2. Final Noise Test. Noise tests of the final parts show little indication of gear noise in the spectrum. Gear related peaks are no worse than peaks from other sources such as timing pulley and fan. Figure 12 shows these results.
8.0. PROCESS CONTROL OF MOLDED GEAR PROFILE.AGMA 92FTM12 pdf download.