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Introduction to Statistical Quality Control

Introduction to Statistical Quality Control. What is Statistical Quality Control?. S tatistical Q uality C ontrol Statistical Quality Control - SQC. “Statistical”. What does the term statistical imply?. “Control”. What does the term control imply?. What is Quality?. What is Quality?.

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Introduction to Statistical Quality Control

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  1. Introduction to Statistical Quality Control

  2. What is Statistical Quality Control? • Statistical • Quality • Control • Statistical Quality Control - SQC

  3. “Statistical” • What does the term statistical imply?

  4. “Control” • What does the term control imply?

  5. What is Quality?

  6. What is Quality? • Traditional definition of Quality: • Product focused • Fitness of use - products must meet the requirements of users.

  7. Dimensions of Quality (Products) • Performance – Will the product do the intended job? • Reliability – How often does the product fail? • Durability - How long does the product last? • Serviceability – How easy is it to repair the product? • Aesthetics – What does the product look like? • Features – What does the product do?

  8. Dimensions of Quality • In addition to products there is quality of: • Dimensions

  9. Two Aspects of “Fitness for Use” • Quality of design – • Products are designed to be in various grades of quality. (e.g., Autos differ with respect to size, options, speed, etc.) • Service systems are designed for different grades of quality • Quality of conformance – • How well the product conforms to specifications. (e.g., If diameter of a drilled hole is within specifications then it has good quality.) • Does the service representative follow guidelines?

  10. A General Definition of Quality • Quality can viewed in multiple ways • To study quality and develop quality analysis approaches, a more general definition is needed

  11. A General Definition of Quality • Quality is inversely proportional to Variability • If the variability of an important product characteristic decreases  quality of product increases • Quality Improvement – • Reduction of variability in processes and products.

  12. Examples

  13. A General Definition of Quality • Characterizing variability is generally quantitative and data driven. • Reducing variability in some product/service characteristic forces more in depth exploration and knowledge of the design and production or delivery processes.

  14. Summary • SPC embodies statistical methods focusing on monitoring and reducing variability. • Our initial focus will be on basic statistical concepts and analysis methods.

  15. Quality in Industry • Terminology • Where quality control is applied • Six-Sigma

  16. Terminology • Quality Engineering – • Set of operational, managerial, and engineering activities that a company uses to ensure that quality characteristics of a product/service are at nominal levels • Quality planning • Quality assurance • Quality control and improvement

  17. Terminology • Quality planning • Strategic: Customers and their needs, products, measures,… • Quality assurance • Policies, procedures, work instructions, specifications, records, etc. for making sure products meet desired quality levels • Quality control and improvement • Monitoring specific results and identifying ways to eliminate causes of unsatisfactory results (reduce variability)

  18. Where Quality Control is Applied • “An ounce of prevention is worth a pound of cure”

  19. Acceptance Sampling • Sample from lot to determine acceptance • More efficient than 100% inspection • Reduces bad product sent to consumer • Dodge & Romig 1930s • No feedback, prevention or improvement

  20. On-Line Process Control • Monitoring of manufacturing process measures with control charts • Shewhart 1920s • Sample & stop process if necessary • No improvement, but maintains current process

  21. Off-Line Improvement • Designed experiments • Taguchi & Classical Statistics 1980s • Continuous improvement of product designs and manufacturing processes • Identification of “leverage” relative to improvement • Optimization of process parameters

  22. Statistical Methods for Quality Control & Improvement • Method - Relative Savings • Acceptance Sampling ($1) • On-Line Process Control ($10) • Off-Line Process Improvement ($100)

  23. Six Sigma - Motorola • Six Sigma = 2 defects per billion opportunities! • Applied ubiquitously (originally production focused) • identify problem; • develop measurement; • set goal; • close gap • Utilizes statistical methods • Training levels defined for personnel

  24. DMAIC – Chapter 2 • DMAIC is a structured problem-solving technique consisting of the following steps: • Define • Measure • Analyze • Improve • Control • DMAIC is usually associated with six sigma.

  25. Reading • Text coverage of the introductory material • Chapter 1 • Chapter 2 • Reading assignment • Chapter 3 – see syllabus • Reminder: • There is a lab this week.

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