How to Use Single-Piece Flow

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How to Use Single-Piece Flow

Single-Piece Flow is the Cornerstone of Lean Manufacturing.

With single-piece methodology,  you want the initial process to produce products in the smallest batch-sizes possible and then this next process should pass these small batches on to the next process, and have that next process convert that small batch as quickly as possible too. You never want work-in-process product to sit stagnant between processes. Ideally, with single-piece flow methodology, this small batch-size is literally only one-piece. In this case every process is handing off just one-piece to the next process and everyone is working at the customer order Takt-Time.

In a hand assembly cell, true single-piece flow is usually easily obtained. An assembly operator can install a few screws and pass on one part to the next person who installs a cover and  then they pass it on to another person who puts on product tags and packages the product. In this case you want everyone's process time to be equal across all process steps so no one waits for product to process. . Waiting time is considered lean waste or MUDA.

Single-piece flow gets a little more difficult with machine production because machine output is so fast. So the best way to connect machine processes is through the use of a Kanban system between the processes. You will want processes working in small batches and producing to Takt-Time. This method is a really simple and effective method to keep inventories low and keep your customers happy by achieving high rates of on-time-delivery.

TOP TIP: If the work area is cluttered and disorganized, start with a 5S Project.

Often, software-based systems can’t compete with Lean when it comes to managing production flow and WIP inventory. However, note that in a job-shop where product is made custom, let’s say kitchen cabinets, whereas each cabinet is a different size, color and configuration, this gets a little more difficult to apply, but Kanbans can be implemented for common components like screws, glues, hinges and sliders.

It's easy to reduce batch-sizes and to implement Kanbans between the processes. Start by running a trial and see how "low you can go" with batch sizes. You may find a little trouble if your process changeovers take a long time. If this is the case, then you will want to initiate a SMED or quick changeover project in conjunction with the batch size reductions. As you reduce changeover times, you can further reduce batch sizes. 

Single-piece flow is the ultimate goal of lean manufacturing. All of the other lean tools pivot around this one, but as you know, lean is about continuous improvement. You may not be able to achieve absolute single-piece flow, but you can continually reduce batch-size. Start with a goal of reducing in-process batch-sizes by 50% and once you achieve that, then try for another 50% reduction (aka continue to improve).  

Are you interested in learning more about manufacturing? Be sure to checkout Tools for the Trenches!

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