Comparing major manufacturing improvement methods — Part 2

EDITOR'S NOTE: The past decade has seen the development of a number of manufacturing management concepts. Chief among them are: lean manufacturing, Six Sigma, supply chain management, total productive maintenance (TPM), and reliability centered maintenance (RCM). While these names are well known, they are not well understood.

10/01/2001



Lean Manufacturing

Lean Manufacturing is more a philosophy or condition than it is a process. For example, when you're lean, you minimize waste in all its forms by:

  • Having minimal inventory, work in process, and raw material

  • Having high on-time delivery performance

  • Operating in a "pull" mode; that is, you make only enough to fill near-term demand

  • Making more smaller batches and having fewer longer runs (a bit counter-intuitive)

  • Minimizing delay times and system cycle times.

    • And you use techniques such as:

      • One-piece flow, quick changeover, takt time, and mistake proofing (Takt time is the pace at which the plant operates to meet market demand—and no more.)

      • Measuring system cycle times and delay times, and managing them effectively

      • Minimizing the variability of your processes

      • Having very reliable equipment through proactive maintenance.

        • Process plants tend to be inherently leaner than batch and discrete plants — they don't or can't carry a lot of intermediate stocks to compensate for disruptions. But they also tend to "push" production more so than batch and discrete plants. This tendency to push generally relates to a lesser ability to operate efficiently at production rates below design. Process manufacturers generally also have better reliability, better operating and maintenance practices, and better plant management support in the application of these principles.

          Batch/discrete manufacturers tend to carry more intermediate stocks to handle production and equipment disruptions. They also tend to be less reliable, having poorer operating and maintenance practices.

          But, they can more effectively operate in a pull mode, due in large measure to a greater tendency to have manufacturing "cells" that can operate relatively autonomously without sacrificing the efficiency of the total operation.

          If you don't have reliable processes and equipment, it will be very difficult to be lean. You need that extra "stuff" (buffer stocks, spare parts, spare equipment, etc.) to manage your unreliability and still meet customer demands. You must have the basics of good reliability practices in place to assure lean manufacturing performance.

          Further, good reliability is not just about maintenance. Superb reliability requires excellence in design, procurement, operations, and maintenance. MCP Consulting, in its work with the Dept. of Trade and Industry in the United Kingdom, observed that some 40-50% of equipment breakdowns were related to poor operating practices; 30-40% were related to poor equipment design or condition, and 10-30% were related to poor maintenance practices.

          Several Fortune 500 manufacturers have also reported that two-thirds of equipment downtime is a result of poor operating or design practices, not poor maintenance, and that some two-thirds of all production losses, as measured against ideal, are not related to equipment downtime.

          Clearly, if you want reliability, the first order of business is to ensure excellence in operating practice, then over the longer term excellence in design practices. Of course excellence in maintenance is always a plus.

          Six Sigma

          Six Sigma is a statistical term that characterizes quality as having less than 3.4 defects per million for a given product or process specification. However, Six Sigma has also become the name for a methodology for reducing the variability of processes such that the result is greater quality and consistency. It stresses simultaneously achieving seemingly contrary objectives: