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One piece flow is simply a methodology for manufacturing components in a cellular environment (an area where everything that is needed to process the part is within easy reach, and no part is allowed to go to the next operation until the previous operation has been completed). 

Haven learned about the basics of One Piece Flow; the following are the major steps to implementing One-Piece flow:

  • Equality of Number of Units

The number of units you produce should equal the number of items your customers order. In other words, your selling cycle time should equal your manufacturing cycle time.

  • Decide Products or Products Families

This involves deciding which products or product families will go into the cells, and determining the type of cell - Product-focused or mixed model. For product focused cells to work correctly, demand needs to be high enough for an individual product. For mixed model cells to work changeover times must be kept short; a general rule of thumb is that changeover time must be less than one tact time.

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  • Calculate Tact Time

The next step is to calculate tact time for the set of products that will go into the cell. Tact time is a measure of customer demand expressed in units of time. It is calculated as follows:

Takt time = Available work-time per shift / Customer demand per shift

  • Determine the work elements and time required for making one piece

In greater detail, each step and its associated time should be listed. Each step should be timed separately several times with the lowest repeatable time used.

  • Determine if the equipment to be used within the cell can meet tact time

Changeover time, load and unload times, and downtime should all be considered.

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  • Create a lean layout

Design a layout using the principles of 5S which involves eliminating items that are not needed and locating all items/equipment/materials that are needed at their points of use in the proper sequence. Very limited space between processes within a one-piece flow cell is needed to eliminate motion waste and to prevent unwanted WIP accumulation. U shaped cells are generally best; however, if this is impossible due to factory floor limitations, other shapes will also suffice.

  • Balance the cell and create standardized work for each operator within the cell

This can be done by determining how many operators are needed to meet tact time and then split the work between operators. The formula below can be used:

Number of operators = Total work content / Tact time

In most cases, an “inconvenient” remainder term will result (e.g., you will end up with Number of Operators = 4.4 or 2.3 or 3.6 instead of 2.0, 3.0, or 4.0). If there is a remainder term, you may consider applying kaizen techniques to the process and reducing the work content. You may also consider moving operations to the supplying process to balance the line.

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About the Author

Adebayo is a thought leader in continuous process improvement and manufacturing excellence. He is a Certified Six Sigma Master Black Belt (CSSMBB) Professional and Management Systems Lead Auditor (ISO 9001, 45001, ISO 22000/FSSC 22000 etc.) with strong experience leading various continuous improvement initiative in top manufacturing organizations. 

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