Assessing Process Capability

1. Assessing Process Capability • Please contact DaRon Huffaker at jdhuffaker@micron.com or (208) 368-1879 for an electronic copy of the presentation. • Presentation Outline : Assessing Process Capability       • Definition of process capability • Estimating Process capability • Understanding the formulas • Assumptions and verifying them • One-sided and two-sided spec limits • Process capability indices versus DPM levels (6 sigma methodology) • Cpk versus Ppk (the automobile industry’s spin on process capability indices) • Estimating short-term versus long-term variation • Estimating correct short-term variation • Process capability indices for non-Normal data • Using quantiles, other parametric distributions, and JMP’s nonparametric density • These capability indices do not equate to the same DPM levels as capability indices based on the Normal distribution • Calculating an equivalent capability index for non-normal data that can be compared to capability indices based on the Normal distribution (i.e., they mean the same thing with regards to DPM levels) • Process capability index confidence intervals • Capability indices are based on sample statistics (average and stdev) that have a margin of error. Therefore, process capability indices also have a margin of error. • Examples using JMP software