A common practice in the manufacturing environment is to use different measuring tools for inspecting engineering products. These measuring tools range from hand held tools (manual) such as venire caliper, to manufactured inspection gages, and general purpose coordinate metrology based inspection tools such as: Coordinate Measuring Machine (CMM). Selecting the correct measuring tool is critical to measure the variation resulting from a manufacturing process. Three experiments have been conducted to evaluate the effect of this decision on the process capability index (Cpk), and the Statistical Process Control (SPC) control limits. It was found that the data collected from the CMM tends to be clustered around the process mean, while it is more spread for the other inspection tools. This situation leads to higher process capability index when the data is collected from a CMM compared with the other measuring tools. It also leads to variation in the calculations of the SPC control limits. This may cause in-consistency, confusion, and may result in unnecessary false alarms. A standard deviation monitoring graph has been suggested to monitor the capability of the measuring system to ensure the integrity of the interpretation of the output of the SPC system.
- Manufacturing Engineering Division
Comparison of Process Capability Index and SPC Control Limits Calculations When Using Different Inspection Tools
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Gadalla, MA, & Popielarczyk, M. "Comparison of Process Capability Index and SPC Control Limits Calculations When Using Different Inspection Tools." Proceedings of the ASME 2011 International Manufacturing Science and Engineering Conference. ASME 2011 International Manufacturing Science and Engineering Conference, Volume 2. Corvallis, Oregon, USA. June 13–17, 2011. pp. 15-22. ASME. https://doi.org/10.1115/MSEC2011-50007
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