Page 282 - DMGT206_PRODUCTION_AND_OPERATIONS_MANAGEMENT

Unit 14: Operations Scheduling

14.1.2 Hard Ceilings Notes

Hard ceilings are where the capacity is extremely difficult to flex.

Example: A major piece of capital equipment which runs at a fixed rate such as a heat
treatment process, where process times are fixed, or production line where the track rate is fixed.
In this case, all you can do is maximize utilization, avoid breakdowns and quality problems, and
ensure that it is always working to customer needs. Or a hard ceiling may be due to a job
requiring a scarce skill that is difficult to train, such as is often encountered in tool making or
maintenance.
There is a limit to how much overtime can be worked to meet demand, and the training program
to reach basic skills is protracted. In both cases, it is difficult to increase output above a given
level and sub-contracting is not practicable for quality reasons, or lack of availability of suitable
sources.

14.1.3 Soft Ceilings

Soft ceilings can be flexed by scheduling manpower, buying additional inexpensive plant
machinery, recruiting unskilled or semiskilled staff, or sub-contracting, or overtime. The essential
differences between the two types of capacity constraint are cost and lead time, which need to be
built into the calculations.
In addition, we also need to define the rules that are to be used to assign work to the resources
(schedule) in the model. These rules could be very simple such as:

 Select the task that is due the soonest (earliest due date).
 Select the task that requires the least amount of time to complete (shortest processing
time).

 Select the task that requires the least amount of set up time or clean up time or travel time.
In the real world, it is usually the case that the rules are not very simple. These could also be very
complex such as:

 Select the task that is due the soonest unless there are any tasks to be completed for
Customer A, in which case all tasks for Customer A should be completed first.
 Select the task that uses the same tooling, has the same colour, and the same due date as the
last task completed by a particular resource.
 Select the task that allows the resource used to be completed or prepared for another task
by a certain time.

 Select the resource that best meets all skill requirements to complete the specific task (i.e.,
allocate repairmen to service calls where each service call will require a certain skill set
and the repairman will have that skill set).
Complex rules are very often just a combination of – or exceptions to – the simple rules. These
combinations and exceptions make planning and scheduling a difficult task. Scheduling models
can be broadly classified into two categories—continuous or intermittent conversion processes.
A continuous or assembly type system is one where a large number or indefinite numbers of
homogenous units are produced. On the other hand, an intermittent system produces a variety
of products either one at a time or in batches. Some processes have the characteristics of both
these types of systems, they are neither strictly continuous nor intermittent.

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