4 How Inventory Hides Problems
The more WIP inventory a production system has, the more likely it is that the system will neglect the operational issues. Let’s have another look at our batching simulation.
Simulation Part 4 – Batch Production Hides Problems
In this simulation, we have received an order to produce one hundred badges. As you will see, workstations keep processing items in batches of ten without any waiting time. At batch number 4, a worker notices that one item does not meet the design specifications, sets it aside, and completes the batch with nine items. Thus, our order is shipped with one missing badge, and the customer is invoiced for 99 badges instead of 100. The system moves on to the next order, which is possibly already late, leaving the defective part to be dealt with at some other time.
Credit: Batch Production Hides Problems by Fatih Yegul and Conestoga College, CC-BY-NC-SA 4.0
Using the batching approach, it is possible that badges will continue to be shipped to customers with 1 unit less than the quantity ordered. It may take a long time for the engineers to find an opening in their schedule to analyze the cutting workstation and look for the root cause of the issue that creates the defects.
Now let’s look at how the same problem would be handled in the one-piece flow scenario.
Simulation Part 5 – One-Piece Flow Reveals Problems
In this simulation, we have received an order to produce one hundred badges. As you will see, workstations keep processing items one at a time. Moving fast forward, a worker notices that one item does not meet the design specifications, which means it cannot be processed. The defective item is set aside, and the following station is supposed to wait for the arrival of the next good item to continue production. The situation will also force stamping to wait for one part. Because it is one-piece flow, the order can be shipped once one hundred badges are produced. In this case, the defective part that was set aside is not hidden beneath the WIP inventory and is easily noticeable.
Credit: One-Piece Flow Reveals Problems by Fatih Yegul and Conestoga College, CC-BY-NC-SA 4.0
In a one-piece flow production system, it is not easy to look the other way when you have defective parts lying around: Each defect causes the line to pause and wait for the next good piece. Thus, the managers perceive each defect as a critical problem for the whole system that needs to be solved, leading them to look for root causes and solutions immediately. This approach plays a vital role in making the continuous improvement mentality part of the organizational culture.
