OM Test 2 Cheat Sheet (2).docx - QUALITY MANAGEMENT QM...

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QUALITY MANAGEMENT QM: ability of a product or service to consistently meet or exceed customer expectations RANDOM VARIATION: Natural variations in the output of the process created by minor factors (Ex: temp and humidity variations) ASSIGNABLE VARIATION: Source of the variation can be identified usually by a major factor ( tool failure, incorrect processing methods) IN CONTROL: if variability in the process is caused by pure random variations ( Control limits are used to see if the process is in control or not and are computed using a formula) CONTROL CHART : time ordered plot of representative sample stats obtained from an on-going process CENTER LINE: defines the mean value of the samples IN CONTROL: all points are between UCL and LCL OUT OF CONTROL: outlier → stop process and fix TYPE 1 ERROR: process is OUT of control when it actually is IN control TYPE 2 ERROR: process is IN control when it actually is OUT of control Narrow control limits INC Type 1 Errors and DEC Type 2 Errors (good quality but end up rejecting) Wide control limits INC Type 2 Errors and DEC Type 1 Errors (bad quality but accept it anyways) Same size range but increasing mean (X bar chart detects shift, R bar chart does not) Same mean but increasing range (X bar chart = does NOT reveal inc, R bar chart = reveals outlier and inc) X-BAR CHART: n = # of observations per sample (NOT sample number) ***Mean charts are sensitive to shifts in the process mean Find the mean of each sample (x + x + x)/n where n = 3 Find range of each sample (max - min); z = 3 X Bar μ and σ are KNOWN: σ xbar = σ / n UCL = μ + z( σ xbar ) LCL = μ - z( σ xbar ) X Bar μ is UNKNOWN and σ is KNOWN: σ xbar = σ / n UCL = x double bar + z( σ xbar ) LCL = x double bar - z( σ xbar ) X Bar μ and σ are UNKNOWN: UCL = x double bar + A 2 (R bar) LCL = x double bar - A 2 (R bar) ***Use n to find A 2 on table X Bar μ is KNOWN and σ is UNKNOWN: UCL = μ + A 2 (R bar) LCL = μ - A 2 (R bar) μ does NOT = x double bar R-CHART: UCL = D 4 ´ R LCL= D 3 ´ R to MONITOR PROCESS DISPERSION σ ≈ n 3 A 2 ´ R
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