AGMA 17FTM23 PDF

To achieve the requested quality, most gears today are ground. The usual grinding process is treating the gear flank but disengaging before reaching the root rounding area. If the gear is premanufactured with a tool without protuberance, then at the position where the grinding tool retracts from the flank, a grinding notch in the tooth root area is produced. Such a notch may increase the bending stresses in the root area, reducing the strength rating.

The AGMA 2001 standard does not address this topic, but in ISO 6336-3, a rule to consider the stressincrease due to a grinding notch is documented. The formulas presented are based on research done by Wirth in the 1970s. A recent discussion in the ISO Workgroup responsible for the development of this standard, showed that a review of the formulas is necessary. As it is, the method can be interpreted in two ways.

Modern FEM tools are well-adapted to calculate the stress in the root area, so it is possible to perform an FEM-based parametric study to compare the grinding notch effect as calculated by FEM with the formulas of the standard. Additionally, in Wirth’s work, some factors are given, which are currently not considered in the standard. This is an additional topic of this investigation.

To make such a study possible, an option to call an external FEM-software was introduced in a calculation software for strength analysis, according to ISO 6336. The necessary data, such as the exact tooth form and the load at the highest point of single tooth contact, is transferred to the pre-processor, which automatically generates the mesh and calls the solver and the post-processor. The main results are the stress at the 30° (60° for internal gears) tangent point and the maximum stress found in the overall root area. The maximum stress is typically located at the position of the grinding notch.

For helical gears, according to the procedure given in ISO 6336-3, the tooth form of the equivalent spur gear is generated and used for the analysis. An additional topic of interest is the following: if a 3D-FEM analysis is useful for helical gears, how well will the results of the FEM correspond to the equivalent spur gear model used by ISO 6336? This is currently under investigation and will be published later.

In the parameter study for different gear geometries, the grinding allowance, the tip radius of the grinding wheel, the grinding process (generating and form grinding), and the grinding depth were varied. The results give a good overview of the accuracy of the outcome of the two interpretation-variants of the ISO method for the influence of the grinding notch compared to FEM results. Based on the study, the best variant can be demonstrated. The formula used to obtain the grinding notch depth used in the ISO method is deduced and will be presented. The position of the notch on the tooth has an important influence, which can now be much better considered.