Process Capability Studies in Heat Treatment

Abstract

Process capability, which is an important concept within statistical process control (SPC), describes the ability of a process i.e. a thermal process to produce components within the tolerance limits. The purpose of this study was to identify possible methods for how to perform process capability study and temperature uniformity survey. In this essay the capability of the case hardening at continuous furnaces have been studied, considering a number of quality parameters. The outcome form these parameters described how well the process could produce components within the tolerances. The parameters of interest were case depth, core hardness, surface hardness, and surface carbon content. Practical work was done at Volvo Construction Equipment (VCE), Eskilstuna and Getrag All Wheel Drive AB, Köping. The parameters were measured from dummy test specimens in Getrag All Wheel Drive AB, and were analyzed by statistical software Minitab version 16. Temperature uniformity surveys (TUSs) were studied for both companies according to standard AMS 2750 D. However, it was not written in it how to make analysis of temperature data. In TUSs, a datapaq with ten thermocouples where used during production from which the temperature could be logged at different positions of the stacking trays and over the entire cross-section of the furnaces. The furnace temperature was within the specified tolerances; however, the significant differences within each track from each of the furnaces were recorded. One of the furnaces was constructed with two parallel tracks while the other was constructed with three parallel tracks. It’s related with the ratio of production capacity for the actual furnace, it will also give information of how the degree of production capacity is influenced by temperature uniformity. The author recommends that both companies perform the same test next year. It is also recommended that further research should be carried out by the methodology that was utilized in this essay.