Ensuring product quality is an important task in a competitive market. It is impossible to ensure the release of quality products without available quality technology. In engineering, the main indicator of quality is the accuracy of parts manufacturing. The operational characteristics of the manufactured machines depend on the accuracy of the size of the manufactured parts. Processing of machine parts can be carried out using various technologies, but each of them provides a different quality. High quality is accompanied by an increase in costs, which in competitive conditions is not always suitable for product manufacturers.
The article considers the issues of assessing the quality of processing technology taking into account gradation, which is based on quality intervals (high, medium, low). This allows determining the technology that provides the desired quality, and evaluating how the process runs in time.
In the course of solving the problem, the theoretical apparatus of probability theory and mathematical statistics was used. The use of a general model of the distribution density of the linear dimensions of parts is proposed. It is proved that this model has three different forms of distribution density with the same estimates of its parameters, such as: lower and upper bounds on the size, modal value. These forms identify the quality of technology based on its gradation.
Based on the application of the calculation of size dispersion, as an indicator of the accuracy of the technological process of processing parts, an assessment of its quality is carried out. The use of the obtained analytical expressions of the dispersion of sizes for technologies that provide the selected quality (high, medium and low) allows us to evaluate the accuracy and predict the number of parts that are within the tolerance of linear size during production.