Evaluating the Accuracy of the Reverse Engineering Process of Worn, Non-Standard Spur Gears—Pilot Studies

Abstract

For years, gears have been self-made by many industrial plants as substitutes (custom spare parts) for original parts from the manufacturer. This common practice uses a process called reverse engineering (RE). However, in the available scientific database, it is difficult to find articles about the accuracy of such a process. And while it is obvious that in order to obtain the most accurate quality of such a process, modern measurement techniques (coordinate, optical) should be used, most companies cannot afford to purchase such equipment. Reproducing gear geometry is difficult. But the issue of RE of non-standard gears seems to be even more difficult. This is why the authors undertook pilot studies to assess the accuracy of the RE process of worn, non-standard spur gears using conventional techniques and measuring instruments. Eight gears were tested, the module of which ranges from 1.020 to 4.98 mm. The key parameter was selected to estimate the accuracy of the process—the base pitch. The goal is to determine the value of the profile angle. Eleven models were proposed to estimate the nominal tolerance field, using various types of random data distribution. The tested gears were made in IT grade: 6, 7, 8, and 9 according to DIN 3961. Vernier disk micrometers were used for research. It has been shown that the nominal module does not have to be treated as a random variable in the population. Equation of identity was developed, allowing conversion of any gear with specific values of geometric parameters into an identical gear with alternative values of these parameters. The most effective estimating model was selected taking into account the symmetric Student–Fisher distribution with a confidence level of 60%. However, it is not possible to correctly reproduce the geometry of the gear wheel in that way. The following aspects should be taken into account: type and degree of mode of failure, number of load cycles, rotational speed, direction of rotation, material, type of thermochemical treatment, and torque. A simulation using FEM should be performed to determine the fatigue plastic deformations and diagnose their impact on the geometric dimensions of the gear wheel.

Keywords

• spur gears
• gear reverse engineering
• gear measuring
• equation of identical gears
• compatibility equation
• interchangeability