🏭 Lean Manufacturing
Definition: A systematic method for waste elimination within a manufacturing system that also takes into account waste created through overburden and unevenness in workloads. Based on the Toyota Production System (TPS).
Coined by: James Womack, Daniel Jones & Daniel Roos — “The Machine That Changed the World” (1990) Origin: Toyota (Taiichi Ohno, Shigeo Shingo) — developed 1950s–80s Key course: HBS TOM, Wharton OIDD
🔑 The Five Lean Principles (Womack & Jones)
- Specify Value: Define value from the customer’s perspective — only what the customer will pay for
- Map the Value Stream: Identify all steps in the production process; separate value-adding from waste
- Create Flow: Eliminate interruptions so the product flows continuously to the customer
- Establish Pull: Only produce what the customer has demanded (vs. push/forecast-based production)
- Seek Perfection: Continuously improve (Kaizen) — perfection is the north star, not the destination
🗑️ The 8 Wastes (DOWNTIME)
Toyota identified Muda (waste) as the enemy of efficiency:
| Waste | Description | Example |
|---|---|---|
| Defects | Products that require rework or scrapping | Wrong assembly requiring teardown |
| Overproduction | Making more than needed right now | Building to forecast, not demand |
| Waiting | Idle time when process stalls | Machine waiting for parts |
| Non-utilized talent | Untapped employee ideas and skills | Operators not in process improvement |
| Transportation | Unnecessary movement of materials | Moving WIP across a large plant |
| Inventory | Excess material or WIP held | Weeks of raw material buffer |
| Motion | Unnecessary human movement | Walking to retrieve tools |
| Extra processing | More work than customer values | 6-coat paint when 3 suffices |
🔧 Core Lean Tools
5S Workplace Organization
| S | Japanese | Meaning |
|---|---|---|
| Sort | Seiri | Remove what’s not needed |
| Set in order | Seiton | Place for everything, everything in its place |
| Shine | Seiso | Clean and inspect |
| Standardize | Seiketsu | Document and make standard |
| Sustain | Shitsuke | Maintain discipline |
Kanban (Visual Pull System)
- Cards or signals authorize production/replenishment
- Nothing is made without a Kanban signal (demand pull)
- WIP is physically limited by card count
- Used by: Toyota, Amazon warehouses, software teams (Jira boards)
Poka-Yoke (Error Proofing)
- Design the process so mistakes are impossible to make
- Examples: USB-A only fits one way (but USB-C doesn’t need to) · ATMs return card before cash to prevent card-forgetting
Value Stream Mapping (VSM)
- Map every step from raw material → customer delivery
- Identify where time is spent (value-add vs. wait)
- Calculate: Process time vs. Lead time (the gap is waste)
Kaizen (Continuous Improvement)
- Small, incremental improvements by frontline workers
- Toyota: Every worker has authority to stop the production line (Andon cord)
- “Kaizen events”: Focused week-long improvement bursts
Takt Time
Takt = “pace” of production to meet demand exactly.
- If customers buy 100 units/shift (8 hrs), takt time = 8 hrs/100 = 4.8 min/unit
- All processes must be designed around takt time
📊 Lean vs. Traditional Manufacturing
| Dimension | Traditional (Push) | Lean (Pull) |
|---|---|---|
| Production trigger | Forecast | Customer order |
| Batch size | Large (economies of scale) | Small (flexibility) |
| Inventory | High buffers | Minimal |
| Quality | Inspect at end | Built into process (jidoka) |
| Layout | Functional (departments) | Flow/cellular |
| Improvement | Top-down engineering | All employees (Kaizen) |
🌍 Beyond Manufacturing: Lean Thinking
Lean has spread far beyond factories:
- Lean Healthcare: Virginia Mason Medical Center reduced OR delays, costs
- Lean Startup: Apply lean principles to startup product development
- Lean Accounting: Match financial reporting to value streams
- Lean Software: Agile is heavily influenced by lean thinking
🔗 Connected Concepts
- Theory of Constraints — Goldratt’s complementary bottleneck approach
- Six Sigma — Quality-focused complement to lean (Lean Six Sigma)
- Supply Chain Management — Lean revolutionized supply chains (JIT)
- Lean Startup — Eric Ries applied lean to startups
← ⚙️ Operations MOC | Related: Theory of Constraints · Six Sigma · Supply Chain Management