Lean Manufacturing & the Toyota Production System

Delivering value with minimum waste. Learn the five lean principles, the eight wastes (TIMWOODS), value-stream mapping, flow and pull, takt time, kanban and supermarkets, SMED quick changeover, 5S and visual management, jidoka and poka-yoke, standard work, heijunka, kaizen, OEE and TPM — with Python computing OEE and the capacity freed by SMED.

Lean thinking grew from the Toyota Production System (Ohno, Shingo) and was named by Womack and Jones in 'The Machine That Changed the World'. Its core idea: most of the time a product spends in a factory, nothing valuable happens to it — it waits, moves or sits in inventory.

By making work flow in small batches at the pace of customer demand, pulling rather than pushing, and exposing problems so they can be fixed, lean organisations cut lead times, inventory and defects while raising productivity.

An analogy

Inventory is like water in a river hiding the rocks (problems). Lean lowers the water level on purpose so the rocks become visible and can be removed — instead of adding more water to float over them.

Principles and wastes

Lean's five principles: specify value, map the value stream, create flow, establish pull, pursue perfection. The eight wastes (TIMWOODS):

Value-stream mapping, flow and pull

A value-stream map shows material and information flows, inventory, cycle times, changeovers, uptime and lead time from supplier to customer; typically value-added time is < 5% of lead time. The future-state map applies takt time, continuous flow (one-piece flow cells), supermarkets with kanban pull where flow isn't possible, a single pacemaker process, and levelled production (heijunka).

Core lean tools

5S (sort, set in order, shine, standardise, sustain) and visual management make abnormalities obvious; standard work defines the current best method; SMED converts internal to external setup to cut changeovers; jidoka stops the line on defects (andon); poka-yoke prevents mistakes; TPM involves operators in maintenance; kaizen events drive rapid improvement.

Lean beyond the factory

Lean healthcare (patient flow, reducing waits), lean office and services, lean construction (Last Planner), lean software (Kanban, DevOps, value-stream metrics like lead time and deployment frequency), and lean product development. Lean succeeds as a management system — leader standard work, gemba walks, A3 problem solving and respect for people — not just a toolkit.

Formulas

Worked example: Process cycle efficiency

Given: Value-added time 150 s, lead time 11 days (8 h/day)

Find: PCE.

Answer: 0.047% — typical before lean

Worked example: Kanban cards

Given: D = 400/day, L = 0.5 day, safety 10%, container 50

Find: N.

Answer: 4.4 → 5 kanbans

Worked example: Lead time from WIP

Given: WIP 3000 units, throughput 600/day

Find: Lead time.

Answer: 5 days (Little's law)

OEE, takt time and SMED capacity

# Overall equipment effectiveness and takt time
planned = 480            # min per shift
downtime = 47            # breakdowns + changeovers
ideal_cycle = 0.5        # min/unit
total_units, good_units = 780, 757
run = planned - downtime
A = run / planned
P = ideal_cycle * total_units / run
Q = good_units / total_units
print(f"availability {A*100:.1f}%, performance {P*100:.1f}%, quality {Q*100:.1f}% -> OEE {A*P*Q*100:.1f}%")
demand = 700
print(f"takt time = {planned/demand:.3f} min/unit vs ideal cycle {ideal_cycle} min")
# SMED: cutting changeovers from 40 to 10 min (3 changeovers per shift)
freed = 3 * (40 - 10)
print(f"SMED frees {freed} min/shift = {freed/ideal_cycle:.0f} extra units of capacity")
# availability 90.2%, performance 90.1%, quality 97.1% -> OEE 78.9%
# takt time = 0.686 min/unit vs ideal cycle 0.5 min
# SMED frees 90 min/shift = 180 extra units of capacity

OEE ≈ 79% is typical; world class is ~85%. Each loss category points to a lean tool: availability → TPM and SMED, performance → minor-stop elimination, quality → jidoka and poka-yoke. Faster changeovers free capacity or, more importantly, allow smaller batches and shorter lead times.

Common mistakes

Applications

Key takeaways

Going further