operation engine II operations scheduling chapter book reference norman gaither and greg frazier

1. Operation Engine II
Session IV
Operations Scheduling
Fatima Aliza
Assistant Professor
IILMAHL

2. Process Focused Manufacturing
 These types of factories are called Job-
Shops.
 A job shop in an organization in which the
work centers or departments are organized
around similar types of functions or
departmental specialties , such as forging,
milling, turning, heat treating, drilling and
assembly.
 Jobs are usually processed in batches, with
the batch size based either on the customer
order size or some economical quantity.

3. Master production
schedule(MPS)
Material
requirements
plan(MRP)
Capacity
requirements
plan(CRP)
Planned order
releases report
Work center
loading and
overtime plan
Engineering the
product designs &
processing plans
Order
processing or
routing plans
Assignment of
orders to work
centers

4. Shop Floor Planning and Control
 Assigning a priority to each order.
 Issuing dispatching lists to each work centers.
 Keeping the WIP inventory updated.
 Providing input- output control on all work
centers.
 Measuring the efficiency , utilization and
productivity of workers and machines at each
work center.

5. Input- Output Control
 This is a key activity that allows operations managers
to identify such problems as insufficient capacity,
excessive capacity and production difficulties among
a group of connected workstations.
 From such reports operations managers can
determine if the amount of work flowing to a work
center is the planned amount and if the capacity of
the work center is according to plan.

6. Gantt Charts
 Gantt Charts can be used to visually display the workloads in each
work center in a department.
 It is used to compare the weekly schedule for five work centers in a
model shop.
 The jobs scheduled to be worked on during the week are displayed
with their code names or numbers ( A,B,C, etc.) , beginning times ,
and ending times, which are represented by an open bar. As work
progresses on a job, a solid bar shows how the work center is
performing to the schedule.
 Machine changeovers , maintenance and other planned
nonproduction work are indicated by an X. Blank spaces indicate
planned idle time at the work center.
 Gantt charts are very useful for coordinating a diversity of
schedules of work teams, work centers and activities of projects.

7. Finite & Infinite Loading
 Infinite approach is used when jobs are assigned to work centers
without considering the capacities of the work centers. This
approach abandons CRP & its loading schedules. Unless a company
has excessive production capacity, unacceptable queues of waiting
jobs occur at work centers.
 Finite approach is used when the capacities of work centers are
allocated among a list of jobs. By using a computer simulation
model or other means each work center’s capacity is allocated to
jobs hour by hour by varying the start and completion times of the
jobs. The end result of this approach is scheduled to a work center
during any hour than the capacity of the work center. This approach
is integral to CRP and is used by many companies today.

8. Forward & Backward Scheduling
 There are two ways to determine to which time slots jobs are
assigned within work centers.
 In forward scheduling , jobs are assigned to the earliest
unassigned time slots in work centers. This approach assumes
that customers want their jobs delivered as soon as possible.
Although simple to use , excessive in process inventories
usually result because jobs tend to sit and wait for their next
work center assignments.

9. Order Sequencing Problems
 In order sequencing problems we want to
determine the sequence in which we will
produce a group of waiting orders at a
work center. We analyze these problems
by discussing the various sequencing
rules , the criteria for evaluating the
sequencing rules, a comparison of
sequencing rules , the control of
changeover costs , and the minimization
of production costs.

10. Sequencing rules
 First come first serve (FCFS): The next job to be produced is
the one that arrived first among the waiting jobs.
 Shortest Processing time(SPT): The next job to be produced
is the one with the shortest processing time among the waiting
jobs.
 Earliest Due Date(EDD): the next job to be produced is the one
with the earliest due date among the waiting jobs.
 Least slack(LS): The next job to be produced is the one with
the least slack ( time to due date minus total remaining
production time) among the waiting jobs.
 Critical Ratio(CR): The next job to be produced is the one with
the least critical ratio ( time to due date divided by total
remaining production time) among the waiting jobs.
 Least changeover cost(LCC): Since some jobs logically follow
each other because of ease of changeovers, the sequence of
waiting jobs is determined by analyzing the total cost of making
all of the machine changeovers between jobs.

11. Criteria for evaluating sequencing
rules
 Average flow time: the average amount of
time jobs spend in the shop.
 Average number of jobs in the system:
The average number of jobs in the shop.
 Average job lateness: The average amount
of time that a job’s completion date exceeds
its promised delivery date.
 Changeover cost: The total cost of making
all the machine changeovers in a group of
jobs.

12. Controlling changeover costs
 Changeover costs are the costs of
changing a processing step in a
production system over from one job to
another. They include costs for such
things as changing machine settings,
getting job instructions, and changing
materials and tools. Usually , jobs should
be produced in the sequence that
minimizes the cost of these changeovers.

13. Scheduling product – focused
manufacturing
 There are two general types of product focused production
: Batch & Continuous
 Batch production is often called a Flow shop because
products follow along direct linear routes. Large batches of
several standardized products are produced in the same
production products are produced in batches , the
production system must be changed over when a different
product is to be produced.
 In Continuous production, a few highly standardized
products are produced continuously in very large volumes
and changeovers are rare. The products may be discrete
such as plastic molded products , or they may be
continuous , such as gasoline.

14. Batch Scheduling
 In product focused systems that produce
products in batches, a key issue is the
size of batches. Two approaches to this
issue will be discussed here:
 EOQ for production lots
 Run out method

15. EOQ for production lots
 The production lot size problem is solved
using the following formula:
 EOQ=√ (2DS/C) (p/(p-d)

16. Run – Out method
 Various deficiencies of the EOQ in
planning production lot sizes have led to
the development of the run–out method.
 This method attempts to use the total
production capacity available in each time
period to produce just enough of each
product so that if all production stops, the
finished goods inventory for each product
runs out at the same time.

17. Delivery schedules : Line of
Balance method
 Some production systems often commit to
delivery schedules for their products that
stipulate how many products must be
delivered to customers in each future week.
If it is important that actual product
deliveries match with the planned delivery
schedule, a system must be devised to
schedule and control all the production steps.
To avoid any delays and corrective actions
line of balance (LOB) has been used to
schedule and control upstream production
steps.