Also called lean production, lean enterprise, or simply lean
Lean manufacturing refers to a system of methods that emphasize identifying and eliminating all non-value-adding activities—waste—from a manufacturing or manufacturing support organization. Processes become faster and less expensive. Lean manufacturing is characterized by fast cycle times, just-in-time methods, pull systems, little or no inventory, continuous flow or small lot sizes, production leveling, and reliable quality. Lean organizations are efficient, flex-ible, and highly responsive to customer needs.
History and Applications
Although the principles, concepts, and tools of lean manufacturing are often credited to Taiichi Ohno, an engineer at Toyota, Ohno himself said he learned many of his ideas from Henry Ford and Ford Motor Company. As with Shewhart’s statistical process con-trol, American industry forgot the concepts it had developed and relearned them from the Japanese in the 1980s. The term lean was coined in 1990 by an MIT research team.
The concepts of constraint management (theory of constraints or TOC) and syn-chronous flow manufacturing (SFM) were developed by Dr. Eliyahu Goldratt and pop-ularized through the 1992 book The Goal. These concepts are complementary to lean manufacturing.
The concepts of lean require changes in support functions such as product and process design, purchasing, shipping, and, indeed, throughout the entire supply chain. An organization implementing lean concepts in all these ways is called a lean enterprise.
By addressing waste reduction, lean manufacturing efforts solve problems of cycle time reduction, standardization, flexibility, and quick response to customer needs.
While the concepts of waste reduction could apply anywhere, for waste is certainly present in service industries and office functions as well as in manufacturing, many of the techniques of lean are specific to manufacturing and have to be translated to apply outside manufacturing environments.
Although lean manufacturing has the potential to revitalize manufacturing, its principles, while widely known, are not yet widely applied. Like every other system of organizational improvement, implementation requires difficult organizational and cul-tural change.
Identifying Waste
Waste is much more than scrap and defects. Ohno defined seven forms of waste: defec-tive product (costs of poor quality, including final inspections, scrap, and rework), inventory (both finished product and work-in-process), overproduction, non-value-added processing, transportation of goods (both within and outside the factory), motion (of people, tools, or product), and waiting.
Even value-added activities often have components of waste. How many turns of the wrench are required before the nut is seated? Is the product rotated to be able to reach the bolt? How many times is the tool picked up and put down?
Masaaki Imai says that value is added at brief moments—“Bang!”—and everything else in the process step is waste. Think about the process of firing a gun 300 years ago, when powder, wad, and ball were separately dropped into the gun barrel and rammed with a rod before the gun could finally be fired. Firing the gun was the value-added step;
everything else was waste. Although that process was taken for granted then, today we recognize how wasteful it was of time, motion, materials, and even human lives. Once non-value-added components of any process are recognized, we can begin to think of ways to eliminate them.
Constraint management and synchronous flow manufacturing are approaches that come from Goldratt’s Theory of Constraints but fit beautifully with lean concepts. A constraint is the slowest process step: the bottleneck. Under constraint management, improvement efforts are focused at the constraint, because increasing throughput any-where else will not increase overall throughput. Time lost at other process steps can be made up, but time lost at the constraint is lost forever. Synchronous flow manufacturing modifies just-in-time and pull system approaches so that the constraint sets the pace for the rest of the process. Under the Theory of Constraints, even traditional cost accounting methods used to plan production are turned upside down, so that the true costs of waste-ful processes become clear.
Methods and Tools
Because lean manufacturing starts with identifying waste, tools such as value-added analysis and value stream mapping are used along with the seven QC tools and an
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improvement process such as kaizen. Mistake-proofing is widely used in lean. Because of the emphasis on adding value, linkage of customer needs to process activities is often accomplished through QFD. Lean concepts find their way into product and process design, which is called design for manufacturing (DFM) or design for assem-bly (DFA).
An important tool unique to lean is 5S, named after five Japanese words that roughly translate to sort (seiri), set (seiton), shine (seiso), standardize (seiketsu), and sustain (shitsuke). Sometimes the 5Ss are translated into CANDO: clearing up, arrang-ing, neatness, discipline, and ongoing improvement. One basic idea behind 5S is that waste hides in clutter and dirt. An oil leak is noticeable on an uncluttered, clean, white floor. The other basic idea of 5S is that rooting out waste requires continual, focused attention and commitment.
Many of the tools of lean are techniques or systems that solve common waste prob-lems in manufacturing. Pyzdek2has described lean as offering “a proven, pre-packaged set of solutions” to waste. These include:
• Autonomation, or machines that sense conditions and adjust automatically
• Factory layout variations, such as cellular manufacturing (machines organized around the part), and flexible processes (maneuverable tools that can be quickly reconfigured)
• Just-in-time, in which materials are received and operations performed just before they are needed by downstream processes
• Level loading, which aims to create a consistent, market-sensitive production schedule
• Preventive maintenance, which reduces unplanned downtime through well-functioning equipment
• Pull systems, in which the pace of downstream activities “pulls” work into the beginning of the process
• Quick changeover methods or setup reduction, such as single-minute exchange of die (SMED), which eliminate long machine downtimes between tasks
• Single-unit processing, or at least small lot processing, to eliminate the waste of batch-and-queue operation
• Standardization, to keep waste from creeping back into the process
• Visual controls, such as warning lights or lines on the floor to mark reorder levels