Manufacturing Master Schedule




On the surface, Company A appears to be a nicely bundled continuous-flow operation. All component parts except hardware are molded in-house on the press line. Some parts go to the assembly area to be built into truck hoods or truck tops. The truck hoods are painted with primer and share a paint line with the tops that are painted in multiple colors to a finished state. Other molded components go directly from the press line to a second paint line that paints primer only. In all cases after painting, the products are packaged for shipment. It would appear that one bill of material per end item, with a routing from start to finish would be appropriate. In utilizing this single-thread concept, the end items would be master-scheduled, leaving all lower levels to be planned in an MRP fashion. A typical BOM would look like this:

Bill of Material—Truck Tops

Finished Top (MPS Item) Shipping Bags Painted Top Assembled Top Molded Top Panel Molded Right Side Panel Molded Left Side Panel Molded Rear Panel

• Molding Compound #9024, 85#

• • Fiberglass Roving, 15#

• • • • • R & H Resin, 65#

• • • • • Calcium Carbonate, 5#

• • • Hardware

• • • Rubber Seals

• • Paint

• • Spatter Coat

As "clean" as this sounds, the approach leaves something to be desired. In order to understand the weaknesses we need to examine the resources:

1. The Paint Primer Line is near 100% capacity on two shifts, but can process any amount that the presses can provide. A consideration for the primer line is that they must run things in batches that use the same type of primer.

2. The hood and top assembly line is under capacity on its two-shift operation.

3. The presses are overloaded. Certain presses are working three shifts per day. Additionally, the tools to make certain component parts cannot be placed in just any press. Due to size and pressure requirements tools are limited to use in certain presses.

Because of these constraints, top-level master scheduling will not provide control over the critical resources, the presses. Also, scheduling by end item does not provide the controls needed at the primer line. Clearly, the objective is to maximize control over the resources that control the output of the plant. To do so, MPS and BOM changes are required.

Scheduling Company A

The Press Line is the first candidate for master schedule control, but only for those presses that are regulating throughput (bottle­necks). The presses that do not control the throughput of the follow-on resources are left to MRP. The bottleneck presses require a good deal of attention. After all, by definition, they are regulating the flow of product through the entire process. With these thoughts in mind we must develop a schedule for the bottleneck presses that maximizes their output. This maximization is accomplished through the application of any number of tech­niques such as batch splitting, minimizing down time by sched­uling preventive maintenance, reducing setup times, maximizing the quality of incoming material to the presses and improving molding processes to el iminate scrap at the presses. After applying the techniques and maximizing the presses' output, we have produced a schedule that can be used to drive the other resources. We now use the press schedule to backward-schedule the Com­pound Room (upstream activity), and to forward-schedule the downstream activities (Figure 1).

By master-scheduling the bottleneck presses, we are assured of maximizing the total system's output. It would not be logical to assume that all of our planning considerations could be accom­modated by back-scheduling the presses from an end-item explo­sion, in a typical MRP fashion.

Once the MPS is completed, the BOM must be created, or adjusted, to provide the ability to execute the schedule. In this case, since the MPS is in midstream of the product flow, multiple bills must be created. Conceptually, the outcome we have created is the scheduling of the actual resources, the presses. But, in application we must produce a schedule for those parts that run over those resources. Each of the MPS items must have a BOM to develop requirements for the Compound Room. One of those bills might look like this:

Top Level 13768a

Level 01 Molding Compound #9024, 85#

Level 02 Fiberglass Roving, 15#

Level 02 R & H Resin, 65#

Level 02 Calcium Carbonate, 5#

The demand on the Compound Room is the projected output plan for the bottleneck presses. We can input that demand schedule to MRP and let it do the balance of the planning for the Compound Room.

There is another resource we should consider for master sched­uling; the Paint Primer Line. The reason for master scheduling this resource is that it must be scheduled in accordance with whatever is produced from the presses. The actual and planned output from the presses becomes the demand that is loaded into the primer line MPS. Now the primer line can be scheduled in accordance with its peculiar requirements. And, in a fashion identical to the press line, bills of material must be developed for the primer line's MPS items.

By scheduling Company A as has been described, several advan­tages are achieved:

1. The critical, or bottleneck, resources are maximized, and subsequently the output of the total system.

2. Inventories can be controlled better because both push and pull techniques are employed.

To be Continued


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