Improving manufacturing costs and lead times with quality-oriented operating curves

The attainment of products conforming to demanded specifications requires appropriate manufacturing processes. The most widely adopted measure of process adequacy to hold the tolerances is the process capability. This characteristic value describes the relationship between measured variations of a product’s features turned out by the process and its assigned tolerances. The process capability has a great effect on the portion of rework and scrap. The network structure of a job shop production leads to complex interactions between the individual manufacturing processes and inspections. Therefore, the effects of process capability on the quality of products on one hand, and especially on manufacturing costs and lead times on the other hand are difficult to evaluate. Since an analytical approach is not possible, simulation is used to model manufacturing processes and inspections and to investigate the effects. To visualize the complex interactions between quality, manufacturing costs, and lead times quality-oriented operating curves have been developed and are presented in this paper. By means of these operating curves the production planning engineer can choose from among competing processes that one, which is most appropriate for meeting the global economic objectives of high quality, low manufacturing costs as well as low lead times.