Lean Manufacturing and Six Sigma

(1) What is lean manufacturing?
Currently there are two premier approaches to improving manufacturing operations. One is lean manufacturing (hereinafter referred to as “lean”) and the other is Six Sigma.
Lean evaluates the entire operation of a factory and restructures the manufacturing method to reduce wasteful activities like waiting, transportation, material hand-offs,inventory, and over-production. It reduces variation associated with manufacturing routings, material handling, storage, lack of communication, batch production and so forth. Six Sigma tools, on the other hand, commonly focus on specific part numbers and processes to reduce variation. The combination of the two approaches represents a formidable opponent to variation in that it includes both layout of the factory and a focus on specific part numbers and processes.
Lean and Six Sigma are promoted as different approaches and different thought processes. Yet, upon close inspection, both approaches attack the same enemy and behave like two links within a chain – that is, they are dependent on each other for success. They both battle variation, but from two different points of view. The integration of Lean and Six Sigma takes two powerful problem-solving techniques and bundles them into a powerful package. The two approaches should be viewed as complements to each other rather than as equiva
lents of or replacements for each other (Pyzdek, 2000). In practice, manufacturers that have widely adopted lean practices record performance metrics superior to those achieved by plants that have not adopted lean practices. Those practices cited as lean in a recent industrial survey (Jusko, 1999) include
• quick changeover techniques to reduce setup time;
• adoption of manufacturing cells in which equipment and workstations are arranged sequentially to facilitate small-lot, continuous-flow production;
• just-in-time (JIT) continuous-flow production techniques to reduce lot sizes, setup time, and cycle time; and,
• JIT supplier delivery in which parts and materials are delivered to the shop floor on a frequent and as-needed basis.
(2) Differences between Lean and Six Sigma
There are some differences between Lean and Six Sigma as noted below.
• Lean focuses on improving manufacturing operations in variation, quality and productivity. However, Six Sigma focuses not only on manufacturing operations, but also on all possible processes including R&D and service areas.
• Generally speaking, a Lean approach attacks variation differently than a Six Sigma system does (Denecke, 1998) as shown in Figure 5.4. Lean tackles the most common form of process noise by aligning the organization in such a way that it can begin working as a coherent whole instead of as separate units. Lean seeks to co-locate, in sequential order, all the processes required to produce a product. Instead of focusing on the part number, Lean focuses on product flow and on the operator. Setup time, machine maintenance and routing of processes are important measures in Lean. However, Six Sigma focuses on defective rates and costs of poor quality due to part variation and process variation based on measured data.
• The data-driven nature of Six Sigma problem-solving lends itself well to lean standardization and the physical rearrangement of the factory. Lean provides a solid foundation for Six Sigma problem-solving where the system is measured by deviation from and improvements to the standard.
• While Lean emphasizes standardization and productivity, Six Sigma can be more effective at tackling process noise and cost of poor quality.