CHAPTER 6 Control Charts for Variables Quality Control Source: Besterfield, Dale H., Quality Control.
Introduction Variation Axioms or truisms of manufacturing no two objects are ever made exactly alike variation law of nature height of human beings weight of fiber-tipped pens shape of snowflakes precision instruments will show differences measure variation versus control variation
Introduction Variation Categories of variation in production within-piece variation piece-to-piece variation time-to-time variation Sources of variation equipment material environment operator
Introduction Variation Chance causes of variation inevitable numerous reasons relatively small importance difficult to detect or identify Assignable causes of variation large in magnitude readily identified
Introduction The Control Chart Method analysis and presentation of quality indicate when variations are greater than “chance” visualizing “central tendency” visualizing “dispersion” graphical record of the quality one chart per characteristic process stability
Introduction The Control Chart Method
Introduction The Control Chart Method
Introduction The Control Chart Method
Introduction Objectives of Variable Control Charts quality improvement determine process capability quality decisions product specifications production process recently produced items
Control Chart Techniques Introduction Control charts for the average (“X bar”) and the range (R) 1. Select the quality characteristic 2. Choose the rational subgroup subgroup size equal to 1 rational ? subgroup size for destructive testing ? 3. Collect the data 4. Determine the trial central line and control limits 5. Establish the revised central line and control limits 6. Achieve the objective
Control Chart Techniques Collect the Data
Control Chart Techniques Determine the Trial Central Line and Control Limits Theoretical formulas Formulas used in practice based on factors obtained from tables
Control Chart Techniques Determine the Trial Central Line and Control Limits
Control Chart Techniques Determine the Trial Central Line and Control Limits
SME Introduction to Lean Tooling 18 min