Maximum number of parts that can be accurately counted using a weighing scale

Many factors may influence the accuracy of part count by weight, but one of the most ubiquitous and often overlooked causes is part variability. In this work, experiments were performed to quantify the weight variation of injection molded parts and to measure the maximum number of those parts that could be accurately counted by weight. A model and working equations that account for tolerances of both the mold cavity and plastic were derived to estimate how part variability affects the weight counting of a single set of parts. Within experimental uncertainty, the model gave estimates that agreed with the actual part counts.