Control charts

Control Charts Control Charts are use to distinguishes between specializes or common-cause of variation that Is present In a process. There are two basic types of control charts:- Variables Quantitative data (Measured) Attributes Qualitative data (Counted) Variable Control Charts Use actual measurements for charting Types:- Average & Range charts Median & Range charts Average & Standard deviation charts Individual & Moving Range charts Run Charts Attribute Control Charts use pass/fall or go/no-go Judgment Type improvement.To determine the process capability. For decisions In regard to product specifications. For current decisions in regard to recently produced items. Average & Range charts (0 and R) Guidelines for subgroup sizes (n):- As n increases the CLC become closer to central line. 2. As n increases the inspection cost per subgroup increases. 3. Distributions for averages of subgroups are nearly normal for n = 4 4. If n = 10 use the s -chart instead of R-chart . N = 5 commonly being used in industry 6.The percentage of product that falls within any pair of values may be predicted with the highest degree of assurance. It permits the consumer to use the producer's data The operator is performing satisfactorily from a quality viewpoint. PROCESS IN CONTROL (Natural pattern of variation) About 34% of the plotted points in an imaginary band between one standard deviation on both sides of the central line About 13. 5% of the plotted points in an imaginary band About 2. 5% of the plotted points in an imaginary band