Metrology and Quality Control - Mechanical Engineering (MCQ) questions and answers for Q. 4976

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• Sravanthi   -Posted on 27 Oct 15
  A pattern is described by points plotted on control charts. Different patterns for assignable causes are:
  
  1) Trend pattern: Continuous movement of points in upward or downward direction is called a trend. The downward trend indicates initial improvement and upward trend indicates gradual wearing of parts, slackening of control etc.
  
  2) Shift pattern: Change in position of the sample readings relative to the control limits is indicated by a shift. A shift is caused due to change in machine setting, change in operator and inspection method, etc
  
  3) Extreme variation pattern: Points within upper and lower control limits indicate statistical control of process on the chart. An assignable cause is noticed if the sample point falls out of control limits. Vibrations, fixture malfunctioning, etc are the common causes of these sudden vibrations.
  

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