Operation management 10e heizer render chapter 15

Operations
Management
Chapter 15 –
Short-Term Scheduling
PowerPoint presentation to accompany
Heizer/Render
Principles of Operations Management, 7e
Operations Management, 9e
© 2008 Prentice Hall, Inc.

15 – 1


Outline
 Global Company Profile:
Delta Air Lines
 The Strategic Importance of ShortTerm Scheduling
 Scheduling Issues
 Forward and Backward Scheduling
 Scheduling Criteria

© 2008 Prentice Hall, Inc.

15 – 2


Outline – Continued
 Scheduling Process-Focused
Facilities
 Loading Jobs
 Input-Output Control

 Gantt Charts
 Assignment Method

© 2008 Prentice Hall, Inc.

15 – 3


Outline – Continued
 Sequencing Jobs
 Priority Rules for Dispatching Jobs
 Critical Ratio
 Sequencing N Jobs on Two
Machines: Johnson’s Rule
 Limitations of Rule-Based
Dispatching Systems

 Finite Capacity Scheduling (FCS)
© 2008 Prentice Hall, Inc.

15 – 4


Outline – Continued
 Theory of Constraints
 Bottlenecks
 Drum, Buffer, Rope

 Scheduling Repetitive Facilities
 Scheduling Services

 Scheduling Service Employees with
Cyclical Scheduling

© 2008 Prentice Hall, Inc.

15 – 5


Learning Objectives
When you complete this chapter you
should be able to:
1. Explain the relationship between shortterm scheduling, capacity planning,
aggregate planning, and a master
schedule
2. Draw Gantt loading and scheduling
charts
3. Apply the assignment method for
loading jobs
© 2008 Prentice Hall, Inc.

15 – 6


Learning Objectives
When you complete this chapter you
should be able to:
4. Name and describe each of the priority
sequencing rules
5. Use Johnson’s rule
6. Define finite capacity scheduling

7. List the steps in the theory of
constraints
8. Use the cyclical scheduling technique
© 2008 Prentice Hall, Inc.

15 – 7


Delta Airlines
 About 10% of Delta’s flights are
disrupted per year, half because of
weather
 Cost is $440 million in lost revenue,
overtime pay, food and lodging
vouchers
 The $33 million Operations Control
Center adjusts to changes and keeps
flights flowing
 Saves Delta $35 million per year
© 2008 Prentice Hall, Inc.

15 – 8


Strategic Importance of
Short-Term Scheduling
 Effective and efficient scheduling
can be a competitive advantage
 Faster movement of goods through a
facility means better use of assets

and lower costs
 Additional capacity resulting from
faster throughput improves customer
service through faster delivery
 Good schedules result in more
dependable deliveries
© 2008 Prentice Hall, Inc.

15 – 9


Scheduling Issues
 Scheduling deals with the timing of
operations
 The task is the allocation and
prioritization of demand
 Significant issues are
 The type of scheduling, forward or
backward
 The criteria for priorities
© 2008 Prentice Hall, Inc.

15 – 10


Scheduling Decisions
Organization

Managers Must Schedule the Following

Arnold Palmer
Hospital

Operating room use
Patient admissions
Nursing, security, maintenance staffs
Outpatient treatments

University of
Missouri

Classrooms and audiovisual equipment
Student and instructor schedules
Graduate and undergraduate courses

Lockheed Martin
factory

Production of goods
Purchases of materials
Workers

Hard Rock Cafe

Chef, waiters, bartenders
Delivery of fresh foods
Entertainers
Opening of dining areas

Delta Air Lines

Maintenance of aircraft
Departure timetables
Flight crews, catering, gate, ticketing personnel

Table 15.1
© 2008 Prentice Hall, Inc.

15 – 11


Scheduling
Flow

Figure 15.1

© 2008 Prentice Hall, Inc.

15 – 12


Forward and Backward
Scheduling
 Forward scheduling starts as soon
as the requirements are known
 Produces a feasible schedule
though it may not meet due dates
 Frequently results in
buildup of work-inprocess inventory
Now

© 2008 Prentice Hall, Inc.

Due
Date
15 – 13


Forward and Backward
Scheduling
 Backward scheduling begins with
the due date and schedules the final
operation first
 Schedule is produced by working
backwards though the processes
 Resources may not
be available to
accomplish the
Due
Now
Date
schedule
© 2008 Prentice Hall, Inc.

15 – 14


Forward and Backward
Scheduling
 Backward scheduling begins with
re

a
the due date and
schedules
the
final
s
e
h
c
f
f
roa trade-o
p
p
a
operation
a
sefirst
e
p
nd
h
o
t
a
l
e
e
n
l

v
e
u
t
d
de
Of
e
o
h
t
c
d
s
le
ne
i
b
i
b
 Schedule
s
tes by working
m
is
produced
a
a
e
f

d
co
a
e
u
n
d
e
r
e
e
w
t
m
be
backwards
custo though the processes
 Resources may not
be available to
accomplish the
Due
Now
Date
schedule
© 2008 Prentice Hall, Inc.

15 – 15


Different Processes/

Different Approaches
Process-focused
facilities

Forward-looking schedules
MRP due dates
Finite capacity scheduling

Work cells

Forward-looking schedules
MRP due dates
Detailed schedule done using work cell
priority rules

Repetitive facilities

Forward-looking schedule with a
balanced line
Pull techniques for scheduling

Product-focused
facilities

Forward-looking schedule with stable
demand and fixed capacity
Capacity, set-up, and run times known
Capacity limited by long-term capital
investment

Table 15.2
© 2008 Prentice Hall, Inc.

15 – 16


Scheduling Criteria
1. Minimize completion time
2. Maximize utilization of facilities
3. Minimize work-in-process (WIP)
inventory
4. Minimize customer waiting time
Optimize the use of resources so
that production objectives are met
© 2008 Prentice Hall, Inc.

15 – 17


Scheduling ProcessFocused Facilities
1. Schedule incoming orders without
violating capacity constraints
2. Check availability of tools and materials
before releasing an order
3. Establish due dates for each job and
check progress
4. Check work in progress
5. Provide feedback
6. Provide work efficiency statistics and
monitor times

© 2008 Prentice Hall, Inc.

15 – 18


Planning and Control Files
Planning Files
1. An item master file contains information about
each component
2. A routing file indicates each component’s flow
through the shop
3. A work-center master file contains information
about the work center

Control Files
Track the actual progress made against
the plan
© 2008 Prentice Hall, Inc.

15 – 19


Loading Jobs
 Assign jobs so that costs, idle
time, or completion time are
minimized
 Two forms of loading
 Capacity oriented
 Assigning specific jobs to work
centers

© 2008 Prentice Hall, Inc.

15 – 20


Input-Output Control
 Identifies overloading and
underloading conditions
 Prompts managerial action to
resolve scheduling problems
 Can be maintained using ConWIP
cards that control the scheduling
of batches

© 2008 Prentice Hall, Inc.

15 – 21


Input-Output Control
Example
Work Center DNC Milling (in standard hours)
Week Ending

6/6

6/13

6/20

6/27

7/4

7/11

Planned Input

280

280

280

280

280

Actual Input

270

250

280

285

280

Cumulative Deviation

–10

–40

–40

–35

Planned Output

320

320

320

320

Actual Output

270

270

270

270

Cumulative Deviation

–50

–100

–150

–200

0

–20

–10

+5

Cumulative Change
in Backlog

Figure 15.2
© 2008 Prentice Hall, Inc.

15 – 22


Input-Output Control
Example

Work Center DNC Milling (in standard hours)
Week Ending

6/6

6/13

6/20

6/27

7/4

7/11

Planned Input

280

280

280

280

280

Actual Input

270

250

280

285

280

Cumulative Deviation

–10

–40

–40

–35

Planned Output

320

320

320

320 Explanation:

270

270

270

–50

–100

–150

0

–20

–10

Explanation:
Actual Output
270 input,
270 output implies
Cumulative Deviation
0 change
Cumulative Change
in Backlog

250 input,

270 270 output implies
–200 –20 change

+5

Figure 15.2
© 2008 Prentice Hall, Inc.

15 – 23


Input-Output Control
Example
Options available to operations
personnel include:
1. Correcting performances
2. Increasing capacity
3. Increasing or reducing input to
the work center

© 2008 Prentice Hall, Inc.

15 – 24


Gantt Charts
 Load chart shows the loading and
idle times of departments, machines,
or facilities
 Displays relative workloads over
time
 Schedule chart monitors jobs in
process

 All Gantt charts need to be updated
frequently to account for changes
© 2008 Prentice Hall, Inc.

15 – 25