A quality inspector took five samples, each with four observations (n = 4), of the length of time for glue to dry. All values are in minutes. Use this information to obtain three-sigma (ie, z= 3) control limits. Construct three sigma mean and range charts. Determine corrective action is needed. SAMPLE 3 5 Observation 12.11 12.10 1211 1200 1215 1212 121 1211 12.09 12.09 1211 1215 4 1212 1210 1206 12.10 1209 1214 1213 1212 Chapter 10 Glue Drying Problem - Answer Sheet X double bar R bar UCL x bar Show calculation: LCL x bar Show calculation: UCL R Show calculation: LCL R Show calculation: Using X bar, is the process in control If not, what is the problem Using R, is the process in control If not, what is the problem Steps for X bar and R Determine # of sample Periods/Times Determine how many observations per Sample Period. This # will be used in Three sigma table Determine the mean (average) of the observations per Sample Period= X bar Average the means (x bar) of each sample period = X (double bar) or grand mean. Calculate the dispersion (high vs low) for each sample period Range Average the Ranges (dispersions) to get R bar. Go to Table and using # of observations get A2, D3, and D4. Graph UCL and LCL and plot X barmeans and R dispersions to see if in control O . Table - Three sigma control limits 13 TABLE 10.3 Faclors for three-sigma control limits for and R tharts FACTORS FOR CHATS Number of Observations Factor for Lower Upper if Sihgtonpi. F Chart, Control Limit Control limit. D D. LES 3.82 an3 098 0.48 0.62 0.37 0.34 0.31 129 327 2.57 2.25 2.11 200 1.92 LAS 1.62 0.08 0.14 022 0.28 L74 1.72 021 0.28 15 10 11 12 13 14 15 18 n 18 19 025 0.24 022 0.21 020 019 19 0.16 0.31 0.3 06 0.36 038 020 0.40 L32 165 IBA 1.52 1.51 1.00 1.99 20 Instructor Slides