1.2 SCHEDULING

 

• 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

 

 

 

1.2.1 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.

 

 

1.2.2 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.