An algorithm for determining the lower confidence limit (NDH) for the minimum value of the hardness of a set of machine parts by calculation is developed. For processing of statistical data of the hardness measurements used a three-parameter Weibull distribution is offered. The transition from sample data to population data is carried out by the graphical method. According to the algorithm, NDH was found for the minimum hardness value with confidence probabilities p=0.9; 0.92;0.93;0.94.

Keywords: hardness, machine parts, sampling, aggregate, lower confidence limit, graphic method, calculation method