- Make a good promise
- Plan supply in a JIT fashion to keep that promise
- Alert you to when you’re at risk of not keeping your promise so you can fix the issue
The role of Advanced Planning and Scheduling
A key point to understand is that APS strives to match the production plan to the demand plan and then match the procurement plan to the production plan.
The APS lean philosophy is based on:
- Getting a good demand plan
- Creating a just-in-time production plan to meet that demand plan
- Creating a just-in-time procurement plan to meet that production plan
When those three plans are in harmony, you don’t release orders unless you need them to supply the demand. And you don’t release them until you need to. You release orders in the quantities and on the dates APS has orchestrated.
Planning is the process of harmonizing supply with external demand. External demand for any given site can include:
- Customer orders
- Forecasts of future customer orders
- Safety stock
- Transfer orders from other sites
We meet those demands with quantities that are not yet allocated from:
- On-hand inventory
- Expected deliveries (active work orders, purchase orders, transfer orders; and planned orders)
- New planned orders (to make, buy, or transfer items)
- The way APS matches supply with demand is to:
- Plan each order separately
- With up to three planning passes per order
- Creating new planned orders only when there are no supplies
Here’s a summary of the method.
The THREE PASSES with material constraints. The diagram below shows the shifts for three resources. The dark areas are off-shift time.
An order is received with a due date midway through day 3. The item has three operations in its BOM (10, 20, 30) with the same setup and run times. APS checks to see if there are any unallocated quantities in on-hand inventory or on existing orders that could meet the demand. If it finds available quantities, it will allocate them and be done planning that demand. If it doesn’t find enough, it will need to plan supply to meet the demand.
Pass 1: Backward planning
APS starts at the requested due date and looks to see if there is enough on-shift time to meet the times specified on the BOM and if we can get the materials required for each operation. The plan in this example would look like this.
Pass 2: Forward planning
For example, what if we cannot get material for operation 20 until very late on day 2 as shown below?
If we cannot get material, then the first planning pass fails, and APS will forward plan starting with the date it believes is the current date to see when it can feasibly ship supply to meet the demand. Notice that we can get the materials for operation 10 immediately and so that operation is planned to start immediately. We cannot get the materials for operation 20 until almost the end of day 2, and so APS plans operation 20 to start at the end of day 2 when those materials are available and finish on day 3. It also plans operation 30 to start after that and finish on day 3. We now have a projected date APS thinks is feasible. Notice it’s planning the exact same amount of time for each operation; it’s simply planning that time based on material availability.
Pass 3: Backward planning
The purpose of the forward plan is to arrive at a feasible projected date. Because APS is built to implement lean principles, it seeks to utilize resources and materials only when it needs them. So after the forward plan, APS will perform a final backward plan to implement JIT principles based on order priority. APS will always return a projected date that was arrived at using backwards, lean planning. In our example, APS would remove the slack in operation 10 as shown below.
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