48 Tooth Theta Helical Gear Apparent Hardness Study – January 2009

1. 48 Tooth Theta Helical GearApparent Hardness Study – January 2009

2. 48 Tooth Theta Helical Gear Apparent Hardness Study Test Method A study comparing the apparent hardness obtained from the gear body and the tooth face was performed as follows: Figure 1. • Tooth apparent hardness was collected in accordance with ASTM E18 with the following exception, reference figure 1. It is recommended that the distance between each measured point and the edge of the part must be more than 2 ½ times the diameter of the indent. The available area on this application does not allow conformance to this requirement. The available area will allow a distance of approximately 1 ½ times the diameter of the indent. Recommended Exception Figure 2. • Gear face data was derived from the grove side of the component, reference figure 2.

3. 48 Tooth Theta Helical Gear Apparent Hardness Study Test Method (continued) Figure 3. • Tooth data was also collected from the grove side of the gear. To accurately gather apparent hardness values from this surface, the top and bottom surfaces of the gear were ground to the same OAL as the teeth, reference figure 3. This was necessary to eliminate the possibility of the gear shifting during testing and ultimately negatively influencing the hardness values.

4. 48 Tooth Theta Helical Gear Apparent Hardness Study Results • Fifteen parts were measured for apparent hardness at two locations. Five observations were taken per part at each location. • Body Face Average 82 HRBW • Tooth Surface Average 85 HRBW

5. 500X 1000X 48 Tooth Theta Helical Gear Apparent Hardness Study Results (continued) Metallographic Analysis – The degree of sinter is acceptable with particle-to-particle bonding and pore rounding evident. The microstructure is comprised of a mainly eutectoid or pearlitic structure. Copper is present and in solution with the Fe-C matrix. The combined carbon content is 0.7 – 0.8% noted throughout. Typical microstructure for this material designation. Material Designation: MPIF FC-0208-50

6. 48 Tooth Theta Helical Gear Apparent Hardness Study • Conclusions • Based on the selected material designation and Metaldyne processing parameters, the apparent hardness throughout the gear is similar. The processing conditions do not include any operations that would intentionally alter surface hardness of the gear. • Apparent hardness if a function of the matrix hardness plus the effect of porosity. Because this component is compacted using a single level tool set, the resulting density variation is minimal. Likewise, the uniform microstructure is comprised of a mainly eutectoid or pearlitic structure throughout the entire cross-section which yields consistent micro-indentation hardness. Therefore, all areas such as the body face, tooth, and core will yield comparable hardness values. • The negligible 3 point HRBW variance as seen in the hardness data represented on page 3 may have been caused by a minor variation in density (tooth-to-body face). Work hardening of the tooth material resulting from testing near the compact edge may have also contributed or caused the slightly higher hardness level.

7. 48 Tooth Theta Helical Gear Apparent Hardness Study • Conclusions (continued) • Measuring the apparent hardness of the gear teeth is not a feasible production intent technique due to the significant sample preparation required to obtain accurate test data. It should be noted that although precautions were taken to obtain accurate data, the standard deviation from the tooth area observations was 2.5 times greater than what was recorded for the body area. This may be a result of the exception taken as defined on page 1. • Data collected during this evaluation suggests that measurements obtained at the body face location of the gear are adequate in determining the apparent hardness of the entire component. Unlike the tooth surface, the body face location provides sufficient surface area for accurate testing in accordance with the ASTM E18 specification. Therefore, during production the apparent hardness will be measured at the body face location.