Operations Notes – Quality

Quality is a multi-faceted concept. It is not a constraint but an objective that needs to be continuously improved.

Key Quality Contributors

• W.E. Deming and Shewart (Statistical Process Control – SPC)
• J. Juran (Strategic Quality Management, Cost of Quality)
• P. Crosby (Top Management Involvement, “Quality is Free”)
• G. Taguchi (Designing Quality In)

Common and Special Causes of Variation in Quality

• Common causes are from a combination of small, purely random fluctuations. These are common to everyone in the system and are inherently a part of the process
  • responsibility of management
• Special causes arise from specific circumstances
  • can be responsibility of workers or management
• Use Control Charts to determine if problem is common or special
  • if process measurements fall within control limits and doesn’t fall on one side of the limit too often (no “runs”), it is said to be in statistical control – only common causes afflict the process (stable)
  • If a measurement falls outside the control limit, then with a high degree of probability, it’s a special cause that must be investigated.

Capability is meeting customer specifications – a large % of data points must fall within specification limits

Process capability index (C_p) is given by: C_p = USL – LSL
                                                                         6σ

If C_p = 1 then you have a 3-sigma process; If C_p = 2 you have a six-sigma process (0.002 defects per million)

Total Quality Management (TQM)

• Customer satisfaction, a must for long-term success, arises from consistently meeting/exceeding customer expectations.
• Processes focus is preferred to “individual focus”
• Processes must be optimized, standardized, and documented.
• Decisions are better left to workers closer to the customer.

TQM Plan, Do, Check, Act (PDCA) Cycle

Step 1 – Analyze Situation
Step 2 – Develop Solution
Step 3 – Develop Action Plan
Step 4 – Implement & Evaluate

Key Take-Aways

• Quality attitudes should not be defensive.
• Quality can be a competitive weapon.
• A capable process is one whose variability is significantly smaller than customer specified variability limits. Six-sigma programs attempt to accomplish this.
• Due to assembly stackups, quality of a composite system is significantly less than the quality of its components.