Benefits of One-Piece Flow
When you try to attain one-piece flow, you are also setting in motion numerous activities to eliminate all muda (wastes). Let’s take a closer look at a few of the benefits of flow.
- Builds in Quality. It is much easier to build in quality in one-piece flow. Every operator is an inspector and works to fix any problems in station before passing them on. But if defects do get missed and passed on, they will be detected very quickly and the problem can be immediately diagnosed and corrected.
- Creates Real Flexibility. If we dedicate equipment to a product line, we have less flexibility in scheduling it for other purposes. But if the lead time to make a product is very short, we have more flexibility to respond and make what the customer really wants. Instead of putting a new order into the system and waiting weeks to get that product out, if lead times are a matter of mere hours we can fill a new order in a few hours. And changing over to a different product mix to accommodate changes in customer demand can be almost immediate.
- Creates Higher Productivity. The reason it appears that productivity is highest when your operation is organized by department is because each department is measured by equipment utilization and people utilization. But in fact it is hard to determine how many people are needed to produce a certain number of units in a large batch operation because productivity is not measured in terms of value-added work. Who knows how much productivity is lost when people are “utilized” to overproduce parts, which then have to be moved to storage. How much time is lost tracking down defective parts and components and repairing finished products? In a one-piece-flow cell, there is very little non-value-added activity like moving materials around. You quickly see who is too busy and who is idle. It is easy to calculate the value-added work and then figure out how many people are needed to reach a certain production rate. In every case of the Toyota Supplier Support Center, when they changed a mass-producing supplier to a TPS-style line, they achieved at least a 100% improvement in labor productivity.
- Frees up Floor Space. When equipment is organized by department, there is a lot of bits of space between equipment that are wasted, but most of the space is wasted by inventory—piles and piles of it. In a cell, everything is pushed close together and there is very little space wasted by inventory. By making greater use of the floor space you often eliminate the need to build more capacity.
- Improves Safety. Wiremold Corporation, one of the early adopters of TPS in America, has an exemplary safety record, winning a number of state safety awards. Yet when they worked to transform their large-batch-process company to one-piece flow, they decided not to put in place a special safety program. Art Byrne, the former president and a student of TPS, led the transformation and knew that one-piece flow would naturally improve safety, because smaller batches of material would be moved in the factory. Smaller batches meant getting rid of forklift trucks, which are a major cause of accidents. It meant lifting and moving smaller containers of material, so accidents relating to lifting went away. Safety was getting better because of a focus on flow—even without focusing on safety.
- Improves Morale. Wiremold, in its lean transformation, also found its morale improved in every year of the transformation. Before the transformation, only 60% of employees agreed with various responses about the company being a good place to work. That went up each year, to over 70% by the fourth year of transformation (Emiliani, 2002). In one-piece flow, people do much more value-added work and can immediately see the results of that work, giving them both a sense of accomplishment and job satisfaction.
- Reduces Cost of Inventory. You free up capital to invest elsewhere when it’s not invested in inventory sitting on the floor. And companies do not have to pay the carrying costs of the capital they free up. Also your inventory obsolescence goes down.
Illustrates a traditional shop with machines grouped by type. One tool you can use for charting the path of materials is a spaghetti diagram. When we chart the flow of material through this facility, it ends up looking like a randomly tossed bowl of spaghetti, as in Figure 8-3. Product is moving everywhere. There is no coordination of the product across departments. No amount of sched uling can control the inherent variation in the system when that system causes materials to move every which way.
The equipment is organized to follow the flow of material as it is being transformed into a product. It is organized in a U shape, which is a particularly good way for efficient movement of people and materials and good communication. You can also arrange a cell to be a straight line or an L. In this case, we show the paths of two people working in the cell. What if demand is cut in half? Put one person in the cell. What do we do if demand doubles? Put four people in the cell. Of course, people need to be multi-skilled to work across different manufacturing processes, a requirement in Toyota plants.