Six Sigma: How Lean/TPS Pull Systems Work

Manufacturing pull systems minimize inventory, improve flexibility, and reduce errors. This video shows why you might be interested in pull systems, and it shows an example of one of our clients learning how to use a pull system. Learn more about how lean/TPS pull systems work in the video below. Have any questions? Leave a comment below!




If you’re learning about Lean or Toyota Production System, you’ll hear about something called a pull system of manufacturing. This video gives a short explanation of why you might care about pull systems and how they operate. There are several advantages to a well-designed pull system including flexibility, efficiency, defect reduction, but in my opinion, one of the largest benefits is the highly effective management of inventory. Excess inventory is evil, whether it is in the form of raw materials, work-in-process, or finished goods. Slashing inventory without compromising customer service levels positively affects the strength of the company and its ability to grow and provide a good work environment. A good pull system minimizes inventory. If you can extend the pull system throughout your supply chain, you’ll have an effective just-in-time system that serves customers well and very effectively controls inventory throughout the chain.

The idea of a Kanban is a key part of pull systems. Now, in Japanese it means poster or billboard and they pronounce it either Kanban or Kanban. In a pull system, a Kanban is a visible signal indicating need. Nothing gets bought moved or assembled without a Kanban. There is no working ahead, no buying ahead, and no building of unnecessary inventory. If there’s no Kanban, there is no action. Kanbans take many forms. We’ll be using one particularly simple form for illustration. I’ll demonstrate a pull system for making a little model cars and the simple Kanban will be a card with the sketch of the assembly required. If the card is covered with an assembly, there is no demand. If the image is visible, there is demand and the assembly should be produced and placed over the image. Our first assembly is the axle kit and this is its Kanban card. That’s just for axles in a fixture here. The next assembly stage is the wheels and washers and that’s just wheels and a washer put on each and this is the Kanban card that represents that step. Finally, we have final assembly and here’s a car on its Kanban card. So if I remove the car from the card, meaning the customers bought it, this card is now showing that it requires something to cover it. So we need to make a new car. Ok, the final assembly Kanban is now covered and shows no demand but my wheel and washer assembly is signaling that it requires attention. So I need to produce something there which means that I’ll draw an axle kit from here. So now this Kanban is covered and there’s no demand showing but this one is now empty, which indicates that I ought to prepare a new one. When you do this with a work cell and this final item is removed, it’s just like somebody had grabbed a great big string that goes clear through the work cell and pulled all that product forward.

Here’s a video clip of one of our clients learning to do this. We started them with no instructions and no pull system that didn’t work very well. Then we did three cycles of building with a pull system. Each time the people in the work cell learn the system a little better and had an opportunity to make improvements in the way the work was done. That’s Kaizen or constant gradual improvement. Watch and note how production became smoother with each cycle.

The payoff is more efficient and effective production and much lower inventory. If you do production the old way, you order a batch of say a hundred sets of parts, build them up, and put them in the warehouse. Then you draw down that inventory as customers buy your product. This requires high levels of raw material, working process, and finished goods and as I said, excess inventory is evil. Just ask your chief financial officer. If you have a pull system that responds perfectly to tact time, which is the drumbeat of the market, and if you’re pull system extends into your suppliers, so parts arrived just as they’re needed and if customers take finished material off your doc just when it’s produced, then inventory levels are very low. Approaching the ideal of single unit flow is a very effective way to manufacture. One good way to think about it is this material should flow through the factory like water through pipes, not like chunks of ice carried around on trucks.

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