Lean Production Simplified: A Plain-Language Guide to the World's Most Powerful Production System. Pascal Dennis, John Shook. Productivity Press Inc (August 1, 2002)

What is Lean?

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The term "lean" was popularized in the book, The Machine That Changed the World, written by James Womack, et al., published in 1990. This book detailed the Toyota Production System, comparing and contrasting it to other, then prevalent, approaches to automotive manufacturing. Womack’s description of lean includes identifying customer
value, understanding how it is delivered, maintaining flow, applying pull and assuring system transparency. The authors offered this definition of lean manufacturing:

A systematic approach to identifying and eliminating waste through continuous improvement, flowing the product at the pull of the customer in pursuit of perfection.

Although this definition is brief, it is packed with information. First, the approach to becoming lean must be systematic. You can try to improve certain areas of the business and have some degree of success, but to truly realize the benefits of lean, you must start with an overall strategy and put it into place in the right order.

Second, a lean strategy focuses on eliminating waste. Lean strategies allow manufacturers to systematically eliminate the waste that results from inefficient processes, which can include inventory, over production, waiting, transportation, motion, over processing and defective products. Third, note the phrases "continuous improvement and pursuit of perfection." Perfection can never be achieved, but each step closer increases the profitability and viability of your company. The process of developing a lean enterprise never ends. Lean is not a destination but a journey. There is always something else that you can do to reduce waste or improve a process.

The Principles of Lean Manufacturing
Lean principles are fundamentally customer value driven and they are suitable for many manufacturing environments. There are five basic principles of lean manufacturing:

1. Understanding Customer Value—Value must be externally focused. Only what your customers perceive as value is important.
   
   
2. Value Stream Analysis—Once you understand the value that you deliver to your customers, you need to analyze all the steps in your business processes to determine which ones actually add value. If an action does not add value, you should consider changing it or removing it from the process.
   
   
3. Flow—Instead of moving the product from one work center to the next in large batches, production should flow continuously from raw materials to finished goods in dedicated production cells.
   
   
4. Pull—Rather than building goods to stock, customer demand pulls finished goods through the system. Work is not performed unless the part is required downstream.
   
   
5. Perfection—As you eliminate waste from your processes and flow product continuously according to the demands of your customers, you will realize that there is no end to reducing time, cost, space, mistakes and effort.

These five lean principles work together and are fundamental to the elimination of waste. You can revisit each of them as improvements in one provide an opportunity for improvements in another.

With the passage of time, lean has become a generic term for systems designed around these principles. Unlike mass or craft systems that aim to optimize each activity, lean aims to maximize total system performance from concept to customer delivery. Striving to better meet each of the five objectives results in continuous improvement. In lean systems, inventory is produced in small batches and only advanced by a pull from the next station when it is ready. Pull systems do not rely on central control to “push” resources forward based on some plan prepared and maintained remote from the work force. The resulting production system reduces work in process, increases throughput and is highly responsive to change a lean manufacturing system.