flowchart LR P[Plan] --> D[Do] D --> C[Check] C --> A[Act] A -. cycle .-> P style P fill:#E3F2FD,stroke:#1565C0 style A fill:#E8F5E9,stroke:#2E7D32
78 Quality Management and Six Sigma
78.1 What is Quality?
There is no single definition of quality. Five classical perspectives are used in textbooks (Garvin, 1988) (garvin1988?):
TipGarvin’s Five Approaches to Defining Quality
| Approach | Definition |
|---|---|
| Transcendent | Quality = excellence; you know it when you see it |
| Product-based | Quality = inherent attributes (more or better features) |
| User-based | Quality = fitness for use (customer view) |
| Manufacturing-based | Quality = conformance to specifications |
| Value-based | Quality = best value at a given price |
Modern quality management converges on two anchors — conformance to specifications + fitness for customer use.
78.2 Quality Gurus and Their Big Ideas
TipThe Quality Gurus
| Guru | Big idea | Famous concept |
|---|---|---|
| W. Edwards Deming | Quality is the responsibility of management; reduce variation | 14 Points; PDCA cycle; 85/15 rule |
| Joseph Juran | Quality is fitness for use | Juran’s trilogy — Plan, Control, Improve |
| Philip Crosby | Quality is conformance to requirements | Zero defects; “Quality is free”; 4 Absolutes |
| Kaoru Ishikawa | Quality is customer-centric | Ishikawa diagram (fishbone); seven QC tools; quality circles |
| Genichi Taguchi | Reduce variation; quality loss is a continuous quadratic function | Taguchi loss function; robust design |
| Armand Feigenbaum | Total Quality Control | TQC; cost of quality |
| Shigeo Shingo | Eliminate defects at source | Poka-Yoke (mistake-proofing); SMED |
78.2.1 Deming’s PDCA Cycle
The continuous-improvement loop — also called the Shewhart cycle:
TipDeming’s PDCA Cycle
| Step | Activity |
|---|---|
| Plan | Identify the problem and plan the change |
| Do | Implement on a small scale |
| Check | Measure and compare to expectation |
| Act | Standardise the change or revise |
78.2.2 Juran’s Trilogy
TipJuran’s Quality Trilogy
| Process | Activity |
|---|---|
| Quality Planning | Set quality goals; design products/processes |
| Quality Control | Monitor performance; fix deviations |
| Quality Improvement | Breakthrough projects |
78.2.3 Crosby’s Four Absolutes
TipCrosby’s Four Absolutes of Quality Management
| # | Absolute |
|---|---|
| 1 | Quality is conformance to requirements |
| 2 | The system of quality is prevention, not appraisal |
| 3 | The performance standard is zero defects |
| 4 | The measurement of quality is the price of non-conformance |
78.3 Total Quality Management (TQM)
TQM is an organisation-wide approach in which everyone is committed to continuous improvement of all aspects of the business that affect quality. Eight principles (ISO 9001):
TipEight Principles of TQM (ISO 9001 family)
| Principle | What it captures |
|---|---|
| Customer focus | Understand and meet customer needs |
| Leadership | Top management drives quality |
| Engagement of people | All employees |
| Process approach | Manage activities as processes |
| Improvement | Continuous improvement |
| Evidence-based decisions | Data-driven |
| Relationship management | Suppliers and partners |
| System approach | Interrelated processes as a system |
78.4 Statistical Process Control (SPC)
SPC uses statistical tools to monitor and control quality. Walter Shewhart’s control chart (1924) is the foundational tool (shewhart1939?):
TipCommon Control Charts
| Chart | Used for | Variable type |
|---|---|---|
| X̄ chart | Mean | Variable (continuous) |
| R chart | Range | Variable |
| s chart | Standard deviation | Variable |
| p chart | Proportion defective | Attribute |
| np chart | Number of defectives | Attribute |
| c chart | Count of defects per unit | Attribute |
| u chart | Defects per unit (variable sample size) | Attribute |
A process is in control when only common-cause variation is present (within control limits); out of control when special-cause variation appears.
78.5 Process Capability
TipProcess Capability Indices
| Index | Formula | Interpretation |
|---|---|---|
| Cp | (USL − LSL) ÷ 6σ | Process capability (centred) |
| Cpk | min[(USL − μ), (μ − LSL)] ÷ 3σ | Process capability (off-centre allowed) |
A capable process has Cp ≥ 1.33 typically; Six Sigma processes have Cp ≥ 2.
78.6 Six Sigma
Motorola pioneered Six Sigma in 1986 as a structured methodology to reduce defects to 3.4 per million opportunities (DPMO) — the level corresponding to ±6σ from the mean (harry2000?). Jack Welch made it a strategic priority at GE in the 1990s.
TipSix Sigma Performance Levels
| Sigma level | DPMO (defects per million opportunities) |
|---|---|
| 2σ | 308,537 |
| 3σ | 66,807 |
| 4σ | 6,210 |
| 5σ | 233 |
| 6σ | 3.4 |
78.6.1 DMAIC and DMADV
TipTwo Six Sigma Methodologies
| Methodology | Use | Phases |
|---|---|---|
| DMAIC | Improve existing process | Define · Measure · Analyse · Improve · Control |
| DMADV / DFSS | Design new product / process | Define · Measure · Analyse · Design · Verify |
78.6.2 Six Sigma Roles (Belt System)
TipSix Sigma Belt Hierarchy
| Role | What it does |
|---|---|
| Champion / Sponsor | Senior leader who supports the project |
| Master Black Belt | Trains and mentors Black Belts |
| Black Belt | Full-time project leader |
| Green Belt | Part-time, leads small projects |
| Yellow / White Belt | Team member; basic training |
78.7 The Seven QC Tools (Ishikawa)
TipIshikawa’s Seven Basic QC Tools
| Tool | What it does |
|---|---|
| Cause-and-Effect (Fishbone, Ishikawa) | Brainstorm causes of a problem |
| Pareto chart | 80/20 — focus on vital few |
| Histogram | Frequency distribution |
| Check sheet | Data collection form |
| Scatter diagram | Bivariate correlation |
| Control chart | SPC |
| Stratification (Flow chart) | Process flow / data segmentation |
78.8 Lean and Other Quality Approaches
TipOther Modern Quality Approaches
| Approach | Idea |
|---|---|
| Lean / TPS | Eliminate the 8 wastes (TIMWOODS) — Transport, Inventory, Motion, Waiting, Overproduction, Over-processing, Defects, Skills |
| Kaizen | Continuous incremental improvement |
| 5S | Sort, Set in order, Shine, Standardise, Sustain |
| Poka-Yoke | Mistake-proofing |
| Lean Six Sigma | Combines lean (waste) and Six Sigma (variation) |
78.9 Indian Quality Awards and Standards
TipIndian Quality Frameworks
| Item | Concerned with |
|---|---|
| Bureau of Indian Standards (BIS) | National standards body; ISI mark |
| FSSAI | Food safety |
| ISO 9001 (Quality Management Systems) | Most-adopted globally |
| Rajiv Gandhi National Quality Award | India’s national quality award |
| CII-EXIM Bank Award | Based on EFQM model |
| Deming Prize / Deming Application Prize | International — many Indian winners |
78.10 Practice Questions
Q 01
Crosby
Easy
"Quality is free" and the "zero defects" performance standard are associated with:
View solution
Correct Option: C
Philip Crosby's Quality is Free (1979) and the four absolutes — including zero defects.
Q 02
PDCA
Medium
The PDCA cycle stands for:
View solution
Correct Option: A
PDCA = Plan-Do-Check-Act (Shewhart-Deming cycle) — the foundational continuous-improvement loop.
Q 03
Six Sigma
Medium
A "Six Sigma" process targets:
View solution
Correct Option: A
Six Sigma → 3.4 DPMO = ±6σ from mean. Pioneered by Motorola in 1986; popularised by GE under Jack Welch.
Q 04
DMAIC
Medium
DMAIC stands for:
View solution
Correct Option: A
DMAIC for improving existing processes; DMADV / DFSS for designing new ones.
Q 05
Ishikawa
Medium
The "fishbone" diagram is also known as:
View solution
Correct Option: B
Kaoru Ishikawa's Cause-and-Effect / Fishbone diagram — visualises potential causes of a problem.
Q 06
Shingo
Medium
"Poka-Yoke" — mistake-proofing — is associated with:
View solution
Correct Option: B
Shigeo Shingo's Poka-Yoke (Japanese for mistake-proofing) — design defects out of the process.
Q 07
5S
Easy
The Japanese "5S" stands for:
View solution
Correct Option: A
5S — Seiri (Sort), Seiton (Set in order), Seiso (Shine), Seiketsu (Standardise), Shitsuke (Sustain).
Q 08
Cp
Medium
A process capability index Cp = 1.0 means the process spread:
View solution
Correct Option: B
Cp = 1 means 6σ spread = USL − LSL — process *just* fits. Capable processes typically have Cp ≥ 1.33; Six Sigma Cp ≥ 2.
ImportantQuick recall
- Garvin’s five approaches to quality. Modern view = conformance + fitness for use.
- Quality gurus: Deming (PDCA, 14 Points), Juran (trilogy), Crosby (4 absolutes, zero defects), Ishikawa (fishbone, 7 QC tools), Taguchi (loss function, robust design), Feigenbaum (TQC), Shingo (poka-yoke).
- TQM eight principles (ISO 9001).
- Shewhart’s control charts — variable (X̄, R, s) vs attribute (p, np, c, u). Common-cause vs special-cause variation.
- Cp / Cpk — process capability indices.
- Six Sigma = 3.4 DPMO. DMAIC for improvement; DMADV / DFSS for design. Belt hierarchy: White → Yellow → Green → Black → Master Black → Champion.
- Seven QC tools (Ishikawa). Lean (8 wastes — TIMWOODS), Kaizen, 5S, Poka-Yoke.
- Indian: BIS, FSSAI, ISO 9001, Rajiv Gandhi National Quality Award, Deming Prize.