Lean Inventory Tools – One-piece Flow – definition | implementation | why
Lean Inventory Tools – One-piece Flow
Every practice in lean manufacturing is intended to support a just in time inventory strategy, which means you move inventory only when it is needed. One of the building blocks of lean inventory management is the concept of one-piece flow. Now don’t let the name fool you. Most people define one-piece flow as processing one item at a time throughout the factory from start to finish.
That certainly is the ideal situation, and some industries like chip makers have been working on this goal for many years. But some companies define the term one as one customer order rather than one unit of product. That’s a good measure because lean teaches us that all our activities should be based on actual demand from our customers. No matter how you define one piece, the idea is that products should move continuously through the factory from one work station to the next.
In fact, one-piece flow is often referred to as continuous flow manufacturing. In other words, there is no batching of products. With batching, a machine will produce a certain number of products before sending work to the next work station. For example, if the company sells products by the case, material will move from one work station to the next in batches of 12 units. This means that each unit of inventory sits at each work station until the entire batch is processed. With batching, inventory begins to accumulate throughout the factory. With continuous flow, each item or each order moves as soon as it is completed, which keeps inventory from building up between work stations.
From an inventory management view, this is a very important benefit. One-piece flow also helps to reduce muda, the Japanese word for any waste that is created by having non-value-added process steps. With one-piece flow, employees don’t waste time waiting for a new batch to arrive or transporting large batches unnecessarily. But one-piece flow is not for everyone. There are certain requirements for implementing this lean practice.
First, your processes must be stable. If you have many quality issues, your production line will be constantly shut down. With one-piece flow, this means you will miss customer delivery dates. Second, your process times must be consistent. A lot of variation between work stations means some stations will be storing inventory while other stations are waiting for work to arrive. Third, your equipment must be reliable. Machine breakdowns will interrupt the flow of material and cause late customer deliveries. Last, your process times must match the rate of customer demand. This is called take time, and it is key to implementing continuous flow. For example, if your company is selling 10 units per day, your factory should be able to produce 10 units per day. Matching these two rates as closely as possible is vital to success.
Is one-piece flow right for your operation? It’s worth your time to investigate this. Because lean focuses on customer demand, looking into take time is a good place to begin. What’s the rate of customer orders at your factory? What’s the rate of making finished products? If these two rates are closely matched, you may be a good candidate for continuous flow manufacturing.