Going Lean With One-Piece Flow

The goal of one-piece flow is to have a single item or unit of product flow from process to process with no delays or bottlenecks in between.

Mnet 206945 Low Waste
Jesse AllredJesse Allred

In the 1930s, Toyota worked feverishly to duplicate the six-cylinder engine from a competing car manufacturer. Production was difficult; many of the engines were defective. Kiichiro Toyoda knew continuing this batch method of production was far too costly, and so he decided each piece needed to be thoroughly inspected before moving down the production line. That action changed everything.

One-piece flow, also called continuous flow manufacturing or repetitive-flow manufacturing, is a Lean production method that aims to reduce waste by balancing the production line. Simply speaking, the goal of one-piece flow is to have a single item or unit of product flow from process to process with no delays or bottlenecks in between.

The continuous flow approach contrasts with batch production and mass manufacturing. In batch production, units are moved from process to process as a batch. Facilities often operate under batch production when small production runs are necessary or when they need to produce a variety of different products. However, batch production is not a continuous system and inefficiencies can quickly arise between batches.

Mass production shares characteristics with batch production, but this method operates by manufacturing a mass quantity of products at one time. a great approach for companies looking to create a large amount of the same product, mass production does not offer much product flexibility, and introducing variety into the method is difficult.

The traditional approach of batch and mass production are typically inefficient. Both approaches usually result in longer lead times for the consumer, excessive inventory, an accumulation of WIP, and a high number of defective products.

In contrast, single-flow manufacturing works to reduce the amount of goods produced at once by manufacturing products only as they are requested. By moving one piece at a time or in a very small batch, products move from process to process quickly. This approach borrows from just-in-time manufacturing while integrating all the elements of the production system.

The idea of this Lean approach to production is to only produce what the customer wants, in the quantity it is demanded, and deliver the finished product on time. This will greatly reduce will significantly scale down the amount of inventory needed on-hand, freeing up valuable storage space. Having a smaller lot size will help you cut down on wastes and dramatically improve the performance of your manufacturing system.

In order to effectively and successfully implement one-piece flow, your workplace needs to be primed for it. The first step and most intensive step is to create a cellular layout that supports the continuous flow of production. This will require time and effort to plan out work cells and entirely change the design of the facility but is essential for one-piece flow.

When designing your work cells, spend time to lay out the facility in the order of processes in order to limit the space between processes. This will prevent excessive WIP piling up between operations while eliminating the waste of motion as the product doesn’t need to travel as far to the next process. After the cells have been determined, use the lean methodology of 5S to ensure cells are optimized for production. Remove the unnecessary items from the area and so each cell contains only the equipment, machines, and tools necessary to production. Arrange the cell in a logical manner. For instance, place frequently used tools in a place that is easy for workers tor each, and line up the machines in the order they are used.

After the cellular layout has been designed and implemented, the next step is to calculate Takt time. This will help you pace your production to meet customer demand. Simply measure the production time by timing each step that goes into production and use the lowest repeatable time. You will then divide that number by customer demand, how much your facility will need to produce in a week or month to meet demand. The outcome is the Takt time, the amount of time needed to manufacture one part that is free from defects. Using this number, you can scale processes in order to effectively meet demands. You will want to ensure the equipment and machines necessary to production are capable of meeting the identified Takt time as well as having the right number of operators for the given process.

Changeovers are considered a waste in manufacturing. The traditional approach to solving this problem was to minimize the number of changeovers, but that typically resulted in the costly waste of overproduction. Use SMED (Single Minute Exchange of Die) to ensure changeovers as fast as possible. When implementing SMED, you will be making changes to the production process to standardize manufacturing and ensure changeovers are quick. SMED will increase machine work rates and further inventory reductions, giving you a strong foundation for creating smaller lot sizes. 

Your facility is nearly ready to begin one-piece flow. Finish the implementation process by introducing a pull system into your facility. This controlled system is the essence of one-piece flow and ensures supplies and products are smartly stocked to avoid the need to store an excessive amount of inventory. Using a Lean tool like Kanban cards, you can create a visual system that will trigger an action (like restocking or beginning a new process) only when needed. Finally, create a schedule and divide work among operators. Split work evenly between operators and ensure your work cells are balanced and work is being completed efficiently.

One-piece flow is critical to operating as a Lean facility and the system will promote continuous improvement in the workplace. You will find employees feel more empowered in their jobs and take responsibility for integrating quality into their work. This approach will also drastically increase flexibility of the manufacturing line and will allow you to start production of a new item or halt production if necessary, with little to no waste. IT will be simpler to order materials and stock, reduce the amount of costly inventory all while improving productivity.

Jesse Allred is a content outreach assistant at Creative Safety Supply.

More in Industry 4.0