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IENG 350-W01 Statistical Process Control How to use Excel in Statistical Quality Control

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Introduction Why use Excel for Statistical Analysis? 1.Professional statisticians don’t always have powerful software at their disposal. 2.The accompanying diskette in the back of the textbook is for a limited time and has an unfriendly interface. 3.Resourcefulness. Limited budgets and an available application for all students. 4.Limitless. 1.Don’t need to perform nonlinear regression with a custom loss function for maximum possibility. 2.Customized through VBA, and your own ingenuity.

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Shewhart Control Charts Most users can create and format simple charts but many don’t exploit Excel’s capabilities for advanced graphical applications. A basic line chart can easily be turned into a Shewhart control chart quickly. Figure 1. Represents data from a machining operation for the diameter of a metal component.The sample average (n=5) are in column F, and the sample ranges are in column G.

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Shewhart Control Charts Control limits and center lines are obtained for this X-bar chart do the following: 1.Compute the grand average (double bar X) of the data by using the paste function button (f of x). Type the following into cell F27: = AVERAGE(F2:F26). 2.Compute the average range by copying the formula from F27 to G27. 3.In cell I2: type “= $F$27”. Note the use of absolute references, denoted by the dollar signs.(an absolute address means the contents of a cell are used in a formula, even though it is copied to other cells.) 4.To calculate the upper and lower control limits for a x-bar chart, see table d in text.

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5.Use the table d worksheet enclosed in excel file. The sample size is 5, thus A 2 = 0.577. In cell H2, type “ = I2+0.577*$G$27”. 6.For the LCL, in cell J2 type “ = I2- 0.577*$G$27”. 7.All formulas are entered. Copy cells H2:J2 to cells H3:J26 to get control limits and a center line.

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8.To get an x-bar chart of the data, highlight cells F1:F26. 9.For noncontiguous cells use the control Key to select cells H1:J26. 10.Select “Insert” from the pulldown menu, then “Chart”.

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11.You will create a line chart, choose the first of five in the chart sub-type category. Then click “Next”.

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The columns, H,I, and J will display horizontal lines that represent the UCL, Center Line, and LCL. All that is needed is to format the chart after placing within the existing worksheet or on a new worksheet.

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To the left is the chart after editing. Right click on the background of chart and select “Format Chart Area” to eliminate the grey background and the border around the chart.

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Right click on Lines and select “Format Data Series” and the dialogue box in the lower portion of this slide will appear to enable you to change: UCL and LCL to bold dashed lines with no markers.Change the center line to a lighter solid line with no markers. Change the x-bar data series to a bold solid line with large markers. Edit the lables, fonts, axes,headers, margins, etc.

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