Determination of the necessary volume of measurements when controlling the quality parameters of gear wheels on a coordinate measuring machine

This article deals with the issue of determining the required amount of measurement, in particular the number of points to be measured on the lateral surface of gears when using the coordinate method with the use of coordinate measuring machines (CMMs). Recommendations and requirements of normative documents concerning the determination of the number of controllable points of the lateral surface of toothed wheels are considered. For the control of geometric parameters of the gear wheel it is proposed to consider the strategy of arrangement of control points in the form of a grid. Determination of the number of control points required for adequate evaluation of control results is carried out on the basis of an experiment to assess the reproducibility of measurement results obtained when controlling the recommended list of geometric parameters on the CMM, taking into account the different volume of measurement information. The scheme of experimentation on estimation of reproducibility of measurement results is offered, including measurements of side surfaces of gear wheels on different number of control points, determination of arithmetic mean values of control results, calculation of normative of operational control of reproducibility, comparison of results of reproducibility indicators with normative value. On the example of a specific gear wheel the scheme of arrangement of controlled side surfaces of the part in determining the list of geometric parameters recommended for CMM inspection, the principle of approximation of control points, embedded in the methodology of measurement results processing and determination of deviation values of controlled geometric parameters on the basis of the obtained measurement information are considered. The reproducibility index for the measurement results obtained at different number of control points is estimated. In accordance with the obtained data the conclusions about insufficiency of control of the side surface of the gear wheel on the control grid of small sizes, due to unsatisfactory data of reproducibility indexes of measurement results are formulated. Recommendations are given for selecting the optimum number of inspection points in the grid, taking into account reproducibility and time spent on inspection of one gear wheel on the list of geometric parameters recommended for control on the CMM.