| In many ways, an Advanced Planning System (APS) is counter-intuitive to the whole Lean philosophy. One of the basic elements of Lean, and not a small reason for its popularity, is that it does not depend on a great deal of advanced planning for its operational purposes. APS essentially creates plans for meeting both forecasted and actual demand, by calculating and comparing product Bill of Materials against actual operational resources and constraints. It then dynamically reschedules the receipt of materials and use of capacity within production to meet stated promise dates. This approach requires detail reporting and monitoring of every operation, which is all good if the manufacturing effort requires tight control of the various elements involved. However, inevitably something, or rather, a lot of things change from the time the manufacturing effort begins to the time when it is completed. Inventory can get damaged or delayed; personnel may not be available; equipment may need repair, etc. Every time something changes that affects the effort, the APS needs to perform a transaction to compute the impact of this change on production. Depending on the APS, this more than likely is a very intensive process that takes a long time. Factors on the ground might have already changed again by the time the APS has completed the first transaction. And with each transactional change, various operators need to re-assess how those changes impact their operations. So while the APS provides a handle on how well the manufacturing effort adheres to the plan, or vice versa, it is optimally deployed in a manufacturing mode where a lot of changes are not expected to occur. Lean takes a different approach. There isn?t a master plan that drives each operation within the plant as with APS. Instead there is a schedule set for a pacemaker operation in the plant based on current (often actual) demand for the week. The pacemaker operation is generally a final assembly operation. The schedule sets the pace and sequence of production based on tact (demand) and target inventory levels, so that the pacemaker and upstream operations can operate with level schedules during the week and avoid disruptive over and under-loading loading. In addition, a signaling system is used by operators who have a greater degree of responsibility for what happens in their cells, and the flexibility to respond to changes as they occur. So, a change in production does not tend to be as disruptive. At the end of the run, a backflush is performed to determine what has been utilized and what needs to be replenished. It?s less compute-intensive, requires less work-in-process inventory and creates a more dynamic, flexible manufacturing environment. |