Where lean comes from
Lean manufacturing is a way of organising work around one question: what does the customer value, and which of our activities do not contribute to it? Its roots are usually traced to the Toyota Production System, developed at Toyota in Japan over several decades after the Second World War. The word “lean” was popularised later, in the West, to describe this family of ideas.
Lean is better understood as a way of thinking than as a fixed toolkit. Different organisations apply it differently, and the same vocabulary is sometimes used to mean different things. What follows are the core ideas in their most common form.
Value and waste
In lean, value is what the customer would be willing to pay for. Anything in the process that consumes time, effort or material without adding value is waste. Lean teaching often lists seven types, using Japanese terminology in some sources. A common English version is:
- Overproduction: making more, or sooner, than is needed.
- Waiting: people or parts idle while something else finishes.
- Transport: moving items further or more often than necessary.
- Over-processing: doing more work than the customer requires, such as tolerances tighter than needed.
- Inventory: stock and work in progress that sits unused.
- Motion: unnecessary movement by people, such as searching for tools.
- Defects: errors that require rework or scrap.
Some lists add an eighth, the unused skills and ideas of the people doing the work. The categories are a prompt for observation, not a rigid classification. If you find a wasteful activity that fits none of them neatly, that does not matter.
Not all non-value-adding activity can simply be removed. Safety checks, legally required records and some inspection steps do not add value in the customer’s eyes but are still necessary. Lean asks you to question such activities and keep them where there is a real reason.
Value streams
A value stream is the full sequence of steps, from request to delivery, that turns an input into something the customer receives. Value stream mapping is the practice of drawing these steps, usually with the time each takes and the time work spends waiting between steps.
A simple illustration, with invented numbers: suppose an item takes 10 minutes of actual work in total but spends 5 days moving between queues. The map makes it obvious that the delay, not the work, dominates the time. Teams often find this surprising, and it points them towards the queues instead of towards making people work faster.
Flow
Flow means work moves steadily from step to step without stopping and waiting in piles. Large batches tend to work against flow: every item waits for the whole batch to finish before moving on. Smaller batches generally shorten the wait, though they may increase the number of changeovers, so there is a trade-off to understand rather than a rule to follow blindly.
Bottlenecks matter here. The slowest step limits the output of the whole line, so improving a step that is not the bottleneck often changes little. Finding the actual constraint first avoids effort in the wrong place.
Pull
In a push system, work is started according to a forecast or schedule and pushed forward whether or not the next step is ready. In a pull system, work is started only when downstream demand signals that it is needed. Kanban, a card or signal system, is a well-known way of implementing pull: a step produces more only when it receives a signal that stock has been used.
Pull tends to limit inventory and expose problems, because there is less buffer to hide them. That is also why it can feel uncomfortable at first.
Beyond the factory
The ideas travel because every field has queues, handoffs, rework and unnecessary steps.
- Software teams often talk about work in progress limits, small batches, and delays between code being written and being reviewed. Teams using agile methods will recognise some of the overlap.
- Offices and services can map how a request moves through approvals and where it waits.
- Laboratories and maintenance teams can look at how long samples or repairs sit unattended compared with the time spent working on them.
- Documentation and engineering change processes often have long waiting periods for sign-off.
In each case the method is the same: observe the real process, find the waits and rework, and test a change.
Common misuses
- Lean as cost cutting. Treating lean as a headcount reduction programme tends to destroy the cooperation it depends on. Lean aims to remove waste from the process, not to take people out of it.
- Tool collecting. Adopting kanban boards or mapping templates without understanding the problem they are meant to solve.
- Removing buffers blindly. Cutting inventory or spare capacity in a fragile process can cause shortages and stress without improving anything. Safety-related margins in particular should not be reduced for the sake of leanness.
- Ignoring quality. Speed without attention to defects only moves problems around. Lean is closely tied to building quality in, and to using quality control and quality assurance practices rather than replacing them.
- Top-down only. The people doing the work usually know where the waste is. Improvements imposed without their input often do not last.
Connection to improvement
Lean works best when it becomes a habit rather than a project. Small, regular changes, tested and measured, accumulate; this is the idea behind continuous improvement, which is covered in its own article. Root cause analysis is often used when a recurring defect or delay shows up on a value stream map.
A practical way to start
Pick one process you know well. Write down each step, estimate the working time and the waiting time, and mark any steps that involve rework or searching. Choose one wait or one repeated error and try a small change for a few weeks. Measure the result before deciding whether to keep it. This is a modest start, and results will vary with your context.
This article is general educational information. Practices differ between industries and organisations, and where safety or regulation is involved you should follow the standards and professionals that apply to you.