Download Statistical Quality Control - Study Guide for Exam 2 | OM 300 and more Exams Production and Operations Management in PDF only on Docsity! Ch. 6 Statistical quality control Descriptive Statistics – used to describe quality characteristics and relationships. Included stats = mean, standard deviation, range, and measure of the distribution data. Statistical process control – methods employ descriptive statistics to monitor the quality of the product and process. Point is to determine the amount of variation that is common. And to make sure the process is in a ‘stat of control’. Control charts are mainly used. Control charts – have a Upper and Lower control limits and a center line VARIABLE control chart – used to monitor characteristics that can be measured and have a continuum of values. Examples - height, weight, or volume. Mean (X-BAR) chart – (x1 +x2+x3..xk) / k …. X – average of the sample… k – number of samples UCL – x(double bar) + (std dev)*(std/SQRT(sample)) LCL - x(double bar) - (std dev)*(std/SQRT(sample)) RANGE CHART – CenterLine – average range… UCL – D4(average range)…. LCL – D3(average range) ___on table 6-1___ ATTRIBUTE control chart – used to monitor characteristics that have discrete values and can be counted. Often they can be evaluated with a simple yes or no decision. Examples – color, taste, smell. P Chart- used to measure the proportion that is defective in a sample. UCL – average proportion + (std dev)*(std dev of average proportion defective) LCL - average proportion - (std dev)*(std dev of average proportion defective) Std dev of avg prop. = √ p(1−p) n n = sample size C Chart –used to monitor the number of defects per unit. Examples – the number of returned meals in a rest., the number of trucks that exceed their weight limit in a month, the # of discolorations on a square foot of carpet UCL = average defects + (std dev)√ (average defects) Process Capability – Cp = specification width / process width = USL – LSL / 6(sigma) Cp = 1.. the process variability just meets the specifications ……. Cp ≤1 = process variability is outside the range of specs…. Cp ≥ 1 = process variability is tighter than specifications and the process exceeds minimal capability Process variation and mean Cpk = min( USL−u 3(sigma) , u−LSL 3(sigma) ) more commonly used than Cp CH 9 Facility Location Xcg = SUM(load*(Load*x)) / SUM (load) Ycg = SUM(load*(load*y)) / SUM(load)
