Stress analysis on a spur gear using ANSYS software.

Abstract

Gears are power transmission components used to transfer power from a drive like a motor to where it is required. Gears fail in operation when they experience loads that exceed what they are designed to carry. They typically experience failure due to two types of stresses i.e., bending stress and contact stress. Design standards like those provided by the American Gear Manufacturing Association, (AGMA) can be used to determine gear stresses in the design process. These formulae are able to determine the failure stress values to a high degree of accuracy but the process is very lengthy because of all the factors to consider that lead to gear failure. This also makes the formulae tiresome to use, especially because many iterations that are required throughout the design process to ascertain that the designed gear will perform as expected. An efficient design process is dependent on how much knowledge and understanding a designer has about the design and operation of gears in that particular field. With further developments of machinery, stronger and more accurate gear designs are demanded of gear manufacturers. Therefore, if a designer fails to consider any of the numerous factors during the stress analysis or does not have an understanding of the significance of the different factors in the formula, the designed gear can undergo catastrophic failure injuring lives as well as damaging other components of the machinery. The lack of information about the behavior of the rest of the gear other than the failure point makes manufacturers fail to make targeted improvements that can save costs in gear manufacturing. The use of the Finite Element Analysis (FEA) to obtain numerical solutions for equations is an alternate way to obtain the failure values for spur gears. FEA software is able to provide information about how the stress within a body under study is distributed and give visual information on the failure. ANSYS software was used to study the behavior of a gear design used in machine application. A model was created in SolidWorks software, saved as a step file and imported into ANSYS for analysis. Initial analysis for a loaded pinion of the gear set was carried out and the stress values obtained from the software were compared against theoretical calculation for the pinion. This process was repeated for a number of different load values within both the software and using formulae for gears of two different gear ratios. Analysis was also done to determine the best material choice for the gear under study. From AGMA analysis as well as from the software, the gear was seen to exhibit failure when the factor of safety was below 1. This is in agreement with the existing literature on stress analysis. The software was used to determine that a pinion made of Gray Cast Iron was the best to withstand bending stresses and one made of Aluminum alloy was the best to withstand contact stresses when in both cases when paired with a gear made of Structural steel. From analysis, it was observed that higher gear ratios have bigger errors. A limitation was that the software was not able to be used to automatically adjust the gear ratio and analyze that new design.