FINAL ASSEMBLY SCHEDULINGBrian Willcox CFPIM of Action MRPII |
| Last year I held a class for the CPIM Master Planning examination which covers forecasting, top management production planning, master production scheduling and final assembly scheduling. I find that very few understand what final assembly scheduling is, what it can do, or where it is applicable, so I thought it was time to explain this approach. |
| APICS define the final assembly schedule (FAS) as a schedule of end items either to replenish finished goods inventory or to finish the product for specific customers' orders in a "make-to-order" or "assemble-to-order" environment. |
| The
objectives of the final assembly schedule is to keep inventory to a
minimum whilst providing maximum flexibility to our customers. It
aims at providing short lead times to meet customer's needs quickly and
provides the means to simplify the control of complex assemblies which
have a large number of possible configurations.
The final assembly schedule is often compared to the master production schedule. The MPS is the anticipated build schedule whereas the FAS is the actual build schedule. In practice the FAS is made up of
actual customer's orders received, whereas the MPS is a plan for
manufacturing created from the company executives production plan.
The MPS provides stock of major assemblies to be used on the final
assembly schedule. To explain this, I will use as an example an
office desk. This desk is sold in six desk top sizes (A to F).
There are three drawer configurations to choose from which can be fitted
on either the left or right hand side, and the customer has the choice of
not having a drawer unit on one or both sides.. This gives 96
possible configurations (6 sizes x 4 left hand choices x 4 right hand
choices - a choice of three drawer units or not having one). To MPS
and stock all 96 configurations would be very expensive in inventory and
space. Also, how would marketing forecast which possible
configurations people would need. If a person came in and required
two of one sort, the forecast could easily be blown. The only way to
handle this problem is by using a percentage bill with a total marketing
forecast of sales. A percentage bill is created from historical
information of past sales of each option. |
| ________ | _______ | _______ | _______ | _______ | _______ | _______ | _______ | _______ |
| | | | | | | | | | | | | | | | | | |
| Desk A | Desk B | Desk C | Desk D | Desk E | Desk F | Drawer Unit A | Drawer Unit B | Drawer Unit C |
| 6% | 20% | 15% | 15% | 28% | 16% | 80% | 40% | 30% |
| .06 | .2 | .15 | .15 | .28 | .16 | .8 | .4 | .3 |
| When looking at this bill, it will be seen that it is not a bill that can be used for manufacturing. It is a planning bill. To build one desk with 6% of one desk size, 20% of another, 15% of a third, etc. is obviously impossible. This percentage bill is used for organising the supply of purchased material and the manufacturing of the lower level sub-assemblies in preparation for the customer's orders being received. It will be seen that the drawer units add up to 150%. This is because there are two possible positions to fit a drawer unit should one be needed, so the maximum possible number of drawer units is 200%. By applying the total sales forecast of, for example, 1 000 desks to this bill, it is easy to calculate how many desks of each size are needed and how many of each drawer unit are required. 160 of desk “A” and 400 of drawer unit type “B” for example. By stocking these nine items, it is possible to make up any of the 96 configurations very quickly. The result is a saving in inventory holding and a quick response to our customer requirements. The master scheduler produces these main assemblies for stock. |
| Customers orders are received not for a configured desk, but for a desk of a certain size and specifying which drawer units are required on the left and right hand side. The customer actually specifies the configuration and not the finished product part number. The final assembly schedule is constrained by the availability of the main assemblies produced from the MPS and by the final assembly capacity. The FAS lead time should be kept to the absolute minimum. The final assembly schedule is typically found to be used for configuring major mechanical assemblies such as cars, and forklifts to the more complex problems of aircraft manufacture. In the make-to-stock environment, the same approach can be used and is often called a filling or packing schedule, and is applicable to products such as paint or tablets which can be used to fill various can or pack sizes. |
| When a company uses a final assembly schedule it should be controlled by the master scheduler who should also co-ordinate the order entry and order promising activity. The MPS will provide an available to promise figure for each choice of each option as that is the level master scheduled and not the final configured product. The approach that I have discussed is very simple and can be used to simplify complex configuration problems. In certain cases, it is necessary to organise modular bills of material to group the associated parts together for material planning purposes |
| June 1998 |
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