X-bar and R charts - Purdue University If the R-chart is in control, i e , stable and predictable, then any shifts in the mean of the process come from Special Cause If the X-bar chart indicates the process is “out of control”, i e , that Special Cause is present
PRODUCTIONS OPERATIONS MANAGEMENT X-bar and R Control Charts Attribute Data Data that is discrete Discrete data is based on “counts ” Assumes integer values Number of defective units Number of customers who are “very satisfied” Number of defects Variables Data X-bar and R chart is used to monitor mean and variance of a process when quality characteristic is continuous
Quality control - University of Kentucky Statistical process control methods Control charts for variables: process characteristics are measured on a continuous scale, e g , weight, volume, width Mean (X-bar) chart Range (R) chart Control charts for attributes: process characteristics are counted on a discrete scale, e g , number of defects, number of scratches Proportion (P) chart Count (C) chart Process capability ratio and index
Slide 1 Solve problem bring process back to ‘under-control’ Process Control Charts: example Piston rings manufacturing Critical dimension: inside diameter Mfg process designed for: mean diameter = 74mm, s = 0 01 mm Measure random sample of 5 rings in each hour Record mean value of the inside diameter Plot Process Control Charts example: X-bar
PowerPoint Presentation X bar charts Range control charts Used to monitor the process dispersion R charts Variables generate data that are measured 10-* Mean and Range Charts UCL LCL UCL LCL R-chart x-Chart Detects shift Does not detect shift Figure 10 10A (process mean is shifting upward) Sampling Distribution 10-* x-Chart UCL Does not reveal increase Mean and Range
Control Charts - The Elsmar Cove Quality Forum Determine if your process is capable by looking at your results and determining if your process needs changes What to do after you design the chart and look at the results Make the chart work for you Like it help your company improve quality Summary, the control chart can greatly improve your company’s profits and process capability
Statistical Process Control - WordPress. com Figure S6 7 Process Capability The natural variation of a process should be small enough to produce products that meet the standards required A process in statistical control does not necessarily meet the design specifications Process capability is a measure of the relationship between the natural variation of the process and the design