“Factory scheduling should be signed off by all parties at the beginning of a production cycle”
There are 2 very important concepts that were alluded to in part 1 of the article that need further discussion and these are buffers and cycle times. In this discussion, we aren’t talking about Safety stock in the warehouse, but buffers used to protect the process and ensure continuity of flow. These are very important in trying to keep product moving through the factory continually when life does get in the way.
Firstly, lets chat about Cycle times. Everything we do in operations takes a certain amount of time to complete. We measure these to create standards for each operation. Each step of the value chain should be measured for each product produced. While there are many ways to approach this so that we don’t get bogged down in analysis paralysis, the objective is to group like products together and create a standard for each group. An example of a manual process can be bulk picking of materials in preparation for production – These can be grouped according to the number of stock items that comprise the formula, if you need more detail, sub divide between the bulk materials and the minor materials that need to be dispensed.
If we are looking at an automated process, let’s say a liquid filling line where we are filling 200ml bottles, the equipment handbook is the starting point to identify the theoretical rated line speed. If you have information on prior production runs, then compare to 80% of the RLS, select the higher of the 2 and use this as the starting point and measure runs for this product configuration going forward. You should periodically take a snap shot of the actual line speed, and compare this to the average line speed based on throughput over time. These measures will clearly show continuous improvement.The diagram above shows cycle times for a single group of products, your average production schedule could have 20 or more of these groups, depending on the size of your operation, so you can imagine the balancing act needed to optimise capacity.
This is where buffers enter the equation. Think of this single example above as a chain. If you pull the chain at either end until it breaks, it will only ever break in 1 place, the weakest link. The same principle holds for the work centre that is the slowest of the 6 shown above, it will determine the throughput for this product. This is where you need to focus your attention to optimise throughput. To do this, we place a buffer ahead of the work centre, the size of which is determined by the “level of weakness”. Again, imagine the 20 different product groups each having their own weakest link. You will now see that a number of buffers are required across the process in order to keep it running as smoothly as possible throughout the week. We need to instill the discipline of measurement in the same way we control our batch documents because this is how to control your operating costs and also ensure that working capital isn’t tied up unnecessarily.
Finally, over sized buffers will create congestion and undersized will lead to stoppages, both impact on delivering that product into the warehouse in time for the sale.