What is lean manufacturing?

Key facts

• Origin: the Toyota Production System, developed at Toyota from the late 1940s to the 1970s, mainly by Taiichi Ohno.
• Name: "lean production" was coined by John Krafcik in 1988 and made famous by The Machine That Changed the World (Womack, Jones and Roos, 1990).
• Goal: shorter lead time, higher quality and lower cost by removing waste rather than by working harder.
• Core idea: every step either adds value the customer would pay for or it is waste to be reduced.
• Used in: automotive, food and beverage, pharmaceuticals, mineral processing, packaging, metal fabrication and, beyond the factory, healthcare and logistics.

Where did lean manufacturing come from?

Lean manufacturing is the Western name for the Toyota Production System. After the Second World War Toyota could not afford the large batches, big inventories and dedicated lines of American mass production, so it learned to make many models in small quantities on the same equipment. The answer was just-in-time (make only what is needed, when it is needed) and jidoka (stop and fix a problem the moment it appears). MIT researchers studying car plants around the world in the late 1980s found Toyota needed far less effort, space and inventory per car, and called the approach lean.

What are the five principles of lean manufacturing?

Womack and Jones set out five lean principles in Lean Thinking (1996):

1. Value: define what the customer actually values and will pay for.
2. Value stream: map every step from order to delivery and see which ones add value.
3. Flow: make the value-adding steps run in sequence without waiting, batching or rework.
4. Pull: produce only when the next process or the customer signals demand.
5. Perfection: repeat the cycle, because each improvement exposes the next waste.

What are the 8 wastes in lean manufacturing?

Waste (muda) is anything that adds time or cost without adding value. The eight wastes of lean are often remembered as DOWNTIME:

Lean also targets unevenness and overburden (muda, mura and muri), because an uneven schedule and overloaded people and machines create waste downstream.

What tools are used in lean manufacturing?

The most widely used lean manufacturing tools are:

• 5S to organise the workplace so abnormalities are visible.
• Standard work to set the current best way of doing a job, the baseline for improvement.
• Kanban and takt time to pace production to demand and run pull.
• SMED to cut changeover time so small batches are economic.
• Total productive maintenance and OEE to keep equipment available and measure losses.
• Poka-yoke and andon to prevent defects and signal problems immediately.
• Value stream mapping to see the whole flow and where lead time is lost.
• Kaizen, PDCA and A3 reports to solve problems at their root cause.
• Lean Six Sigma for the harder problems where output varies and the cause is not obvious, run as data-led DMAIC projects.

Why do lean manufacturing programmes fail?

The tools are well documented; the usual failure is adopting them without the management system that keeps them alive. A plant runs a 5S blitz and a few kaizen events, results improve, then attention moves on and the area slides back within a year. The plants that sustain lean add daily routines: tiered daily meetings that review safety, quality, delivery, cost and people against target, leader standard work and gemba walks that put leaders on the floor on a schedule, audits that check standards are still being followed, and a clear path for problems to rise to whoever can fix them. This is the difference between lean tools and lean management.

The other common failure is that sincere, thorough problem solving never happens. Problems are contained, a quick fix goes in, and the root cause is never found or solved, so the same problems keep coming back despite all the effort. It can be argued that every lean tool and method, from 5S and visual management to standard work and tier meetings, exists to expose problems so they can be seen clearly and solved on facts. Exposing a problem is only half the job: unless it is followed by structured root cause analysis and a countermeasure that is checked to work, lean becomes a way of finding the same problems again and again.

Lean manufacturing example

A packaging line in a food plant was missing its daily output target three shifts in five. The team put up a simple tier board recording hourly output against plan and the reason for every miss. Within two weeks the board showed that most lost time came from format changeovers, averaging 70 minutes. A three-day SMED workshop separated the tasks that could be done while the line was running, pre-staged the change parts on a shadow board and standardised the sequence in a one-page work instruction. Changeovers fell to around 30 minutes, the line could run smaller batches, finished-goods inventory dropped and the daily target was met consistently. The standard was then checked weekly in a layered audit so the gain held. (Illustrative example: the figures are typical, not from one named site.)

How do you start lean manufacturing?

1. Pick one value stream with a visible problem the business cares about, such as late delivery or high scrap.
2. Walk it and map it with the people who do the work, measuring lead time, inventory and where work waits.
3. Make performance visible on a board at the line, with a short daily meeting at a fixed time.
4. Stabilise the basics with 5S, standard work and reliable equipment before chasing flow.
5. Solve the biggest loss with a structured method such as PDCA or an A3, and standardise the fix.
6. Hold the gain with leader standard work and regular audits, then move to the next loss.

Sources

• Womack, J. P., Jones, D. T. and Roos, D., The Machine That Changed the World (1990).
• Womack, J. P. and Jones, D. T., Lean Thinking (1996).
• Ohno, T., Toyota Production System: Beyond Large-Scale Production (English edition 1988).
• Lean Enterprise Institute, lean.org, "What is Lean?"