WIP Vs Single Piece FlowIn conventional manufacturing, your are safe to make stocks and keep them. All the internal customers of your process are dependent on this stock or Work In Progress to carry out their work continuously. Running out of safety stock is dangerous and immediate actions will be taken to restore the safety stocks. Of cause this manufacturing method works fine and will run your manufacturing process smoothly. Unfortunately though, lean manufacturing treats these stocks as an enemy and aggressively refuses the use of safety stocks to smoothen the production run. Lean manufacturing depends on single piece flow concepts. Therefore every process will depend on each other directly, not on the inventory to run smoothly. This conceptual deference reshaped the process of manufacturing forever. Lean manufacturing interprets large stocks as reflection of imperfections the system has. Lean manufacturing proposes to remove all the safety stocks, which means the system must run perfectly. Think about a machine breakdown in the system. If there is an inventory, the system will run on it without stopping. Meanwhile the process prior to the point where machine breakdown occurred will also run continuously and will increase the WIP. With this example we can understand two things. The system will run without stopping if there is a sufficient level of inventory. Also, the imperfection in the system, which is machine breakdown in this case will accumulate WIP. Therefore if there is a higher WIP we know for sure, there is something wrong in the system. In a lean manufacturing system, if there is a machine breakdown, the whole system will be stopped. Therefore lean manufacturing is demanding for the perfection of the system. This might seems like impossible. But even Toyota has proven that if you have the correct attitude, you will be able to do this with very little effort. It is much easier to have the perfect system rather than relying on a system which is proven to create problems. |
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