Control Charts

Control Charts

1. Plot attribute data or variable data

   • Attribute
     • n=samples
     • Fraction defective
     • np= n constant
     • p= n is not constant
     • Quality characteristics is symbolized by number
     • c=defects per group
     • c= n constant
     • u= defects per subgroup
     • N= n is not constant
   • Variable
     • X chart
       • Individual, mesuared value
     • Xbar-R
       • Average value an range
     • Xbar-R Chart(samples)
       • Control & analyze process
     • X Chart (Individuals)
       • Obtained over extended time intervals

2. Zone Rules(Western Electric)

   • Designed to detect process instability and the presence of assignable causes
   • Unnatural patterns from natural patterns based on criteria
     • Absences of point near the center line(mixtures)
     • Absence of points near the control (stratification)
     • Presence of points outside the control limits(instability)
     • Systematic, repetitions, trend pattterns
   • How the Zone rules work?
     • Divided the control chart into zones
       • Zone A( 2σ-3σ)
       • Zone B(1σ-2σ)
       • Zone C(1σ)
   • Zone Rules Nª
     • 1.- Any point falls outside the 3σ center line(upper or lower of the control limit)
     • 3.-Four or five points fall beyond 1 σ(zone B)
     • 2.- Two or three points fall beyond 2 σ(zone A)
     • 4.-Seven or more points fall beyond 3 σ
     • Results of applying zone rules
       • Change in the process
       • Reduce 3σ

Bilder und Dateien der Mindmap