30.2 SCHEDULING

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We often know well in advance what has to be produced

We can use computer programs to come up with a `near perfect' schedule for all jobs, ahead of time.

These methods at the present time are not well enough developed to handle sudden disruptions on the shop floor (See next section on Shop Floor Control).

Schedules are often made up weekly

*************** ADD DETAILS FOR MRP I and MRP II

30.2.1 Material Requirements Planning (MRP)

This is one very popular approach to planning

Uses Master Production Schedules to determine how much of each product should be produced within given periods. Master Production Schedules are based on customer, or projected demand.

The elements used by MRP to plan are,

- Master Production Plan (Schedule)

- On-hand inventories

- Bill of Materials

- Current of Purchased and Manufactured Orders

- Rules for each part produced (including WIP)

The rules about each step in production include,

- Lead time

- Order quantity per final part

- Scrap rate

- Buffer stock quantity

- etc.

MRP then tries to determine quantities required using the data input from the users, and a set of rules, such as,

- Fixed Order Quantity - Product are produced as required using a prespecified lot size.

- Economic Order Quantity - The cost of carrying inventory is weighed off against the cost of setup for one production run.

- Lot for lot - Lots are produced as required, any batch size.

- Fixed-period Order Quantity - Produce parts to cover more than a single order.

Lot sizes required are subtracted from available stocks.

The required production quantities are used to order from suppliers, etc, while considering lead times, and delays.

You should note that this approach is concerned more with inventory minimization than with utilization of machines.

While this system can lead to easy production scheduling, it is susceptible to errors in BOMs, routings, etc.

Advantages,

- improved Customer Service

- better Scheduling

- reduced inventory

- reduced component shortages

- reduced manufacturing costs

- reduced lead times

- higher production quality

- less scrap, and rework

- higher morale in production

- improved communication

- improved plant efficiency

- improved competitive position

- improved coordination of marketing and finance

MRP II (Manufacturing Resources Planning) - A closed-loop MRP system that, at a minimum, includes detailed capacity analysis (see next section). Some MRP II systems include the business plan in the closed-loop system.

30.2.2 Capacity Planning

While MRP is concerned with determining how much should be produced, it is not concerned with how to produce it.

Capacity planners attempt to determine how to assign jobs to machines, people, etc.

Information used by capacity planners includes,

- Planned orders (from MRP)

- Orders in process (order status)

- Routings, including setup and run time (from process plans)

- Available facilities

- Workforce availability

- Subcontracting potential

There are some strategies used by the Capacity Planner to Assign jobs to machines,

- Splitting of lots (batches) across identical machines

- Splitting of lots to expedite a smaller quantity

- Sequencing of lots to minimize setup times

- Alternative routings that require different resources

- Loading a facility by weight, volume, etc. (eg. heat treating)

After jobs have been assigned to machines, the capacity of the machines must be considered.