1. Operations Management Short-Term Scheduling

2. Strategic Implications of Short-Term Scheduling
By scheduling effectively, companies use assets more effectively and create greater capacity per dollar invested, which, in turn, lowers cost
This added capacity and related flexibility provides faster delivery and therefore better customer service
Good scheduling is a competitive advantage through dependable delivery

3. Short-Term Scheduling
Deals with timing of operations
Short run focus: Hourly, daily, weekly
Types
Forward Scheduling
Backward Scheduling B E B E
Today
Due Date
Today
Due Date

4. Short-Term Scheduling Examples
Hospital
Outpatient treatments
Operating rooms
University
Instructors
Classrooms
Factory
Production
Purchases
© T/Maker Co.

5. Scheduling Decisions Organization Managers Must Schedule
Mount Sinai Hospital
Indiana University
???
Delta Airlines
Operating room use
Patient admission
Nursing, security, maintenance staffs
Outpatient treatments
Classrooms and audiovisual equipment
Student and instructor schedules
Graduate and undergraduate courses
Production of goods
Purchase of materials
Workers
Maintenance of aircraft
Departure timetables
Flight crews, catering, gate, and ticketing personnel

6. Short-term Scheduling
Capacity Planning, Aggregate Planning, Master Schedule, and Short-Term Scheduling
Capacity Planning
1. Facility size
2. Equipment procurement
Long-term
Aggregate Planning
1. Facility utilization
2. Personnel needs
3. Subcontracting
Intermediate-term
Master Schedule
1. MRP
2. Disaggregation of
master plan
Intermediate-term
Short-term
Short-term Scheduling
1. Work center loading
2. Job sequencing

7. Forward and Backward Scheduling
Forward scheduling: begins the schedule as soon as the requirements are known
jobs performed to customer order
schedule can be accomplished even if due date is missed
often causes buildup of WIP
Backward scheduling: begins with the due date of the final operation; schedules jobs in reverse order
used in many manufacturing environments, catering, scheduling surgery

8. The Goals of Short-Term Scheduling
minimize completion time
minimize WIP inventory (keep inventory levels low)
maximize utilization (make effective use of personnel and equipment)
minimize customer wait time

9. Choosing a Scheduling Method
Qualitative factors
Number and variety of jobs
Complexity of jobs
Nature of operations
Quantitative criteria
Average completion time
Utilization (% of time facility is used)
WIP inventory (average # jobs in system)
Customer waiting time (average lateness)

10. Scheduling Methods Differ by Process
Process-Focused
Repetitive-Focused
Product-Focused
Variety of Methods
Level Use Methods

11. A Production Planning and Control System Should
Schedule incoming orders without violating capacity constraints of individual work centers
Check availability of tools and materials before releasing an order to a department
Establish due dates for each job and check progress against need dates and order lead times
Check work in progress as jobs move through the shop
Provide feedback on plant and production activities
Provide work efficiency statistics and monitor operator times for payroll and labor distribution analyses

12. Types of Planning Files
Item master file - containing information about each component the firm produces or purchases
Routing file - indicates each component’s flow through the shop
Work center master file - containing information about the work center such as capacity and efficiency

13. Process-Focused Work Centers
High variety, low volume systems
Products made to order
Products need different materials and processing
Complex production planning and control
Production planning aspects
Shop loading
Job sequencing

14. Process-Focused Planning System
Forecast &
Firm Orders
Material
Requirements
Planning
Aggregate
Production
Resource
Availability
Master
Scheduling
Shop
Floor
Schedules
Capacity
Realistic?
Yes
No, modify CRP, MRP, or MPS

15. Shop Loading Assigning jobs to work centers Considerations Approaches
Job priority (e.g., due date)
Capacity
Work center hours available
Hours needed for job
Approaches
Gantt charts (load & scheduling)
Assignment method

16. Order Release Begins Shop Loading
Release Order 1 2 3
Gross Requirements
Yes
Scheduled Receipts
100
Priority & Capacity OK?
Available
Net Requirements
Planned Order Rec. No
100
Hold Release
Planned Order Rel.

17. Options for Managing Facility Work Flow
Correcting performance
Increasing capacity
Increasing or reducing input to the work center by:
routing work to or from other work centers
increasing or decreasing subcontracting
producing less (or more)

18. Gantt Load Chart Shows relative workload in facility Disadvantages
Does not account for unexpected events
Must be updated regularly

19. Gantt Load Chart Shows relative workload in facility Disadvantages
Does not account for unexpected events
Must be updated regularly
Work Center M T W Th F
Sht. Metal
Job A
Job F
Mechanical
Job D
Job G
Electrical
Job B
Job H
Painting
Job C
Job E
Job I

20. Gantt Scheduling Chart
Used to monitor job progress S M T W F
Day
Job
Job A
Job B
Job C
Repair
Today

21. Assignment Method Assigns tasks or jobs to resources
Type of linear programming model
Objective
Minimize total cost, time etc.
Constraints
1 job per resource (e.g., machine)
1 resource (e.g., machine) per job

22. Assignment Method - Four Steps
Subtract the smallest number in each row from every number in that row; then subtract the smallest number in every column from every number in that column
Draw the minimum number of vertical and horizontal straight lines necessary to cover all zeros in the table
If the number of lines equals either the number of rows or the number of columns, then you can make an optimal assignment (Step 4)
Otherwise:
Subtract the smallest number not covered by a line from every other uncovered number. Add the same number to any number(s) lying at the intersection of any two lines. Return to Step 2
Optimal assignments will always be at the zero locations of the table

23. Sequencing Specifies order jobs will be worked Sequencing rules
First come, first served (FCFS)
Shortest processing time (SPT)
Earliest due date (EDD)
Longest processing time (LPT)
Critical ratio (CR)
Johnson’s rule

24. Sequencing Challenge Production Control Production
Which job do I run next?
Dispatch List
Order Part Due Qty
XYZ
ABC
Job Packet
Job XYZ
Order release

25. Priority Rules for Dispatching Jobs
First come, first served
The first job to arrive at a work center is processed first
Earliest due date
The job with the earliest due date is processed first
Shortest processing time
The job with the shortest processing time is processed first
Longest processing time
The job with the longest processing time is processed first
Critical ratio
The ratio of time remaining to required work time remaining is calculated, and jobs are scheduled in order of increasing ratio.
FCFS
EDD
SPT
LPT CR

26. First Come, First Served Rule
Process first job to arrive at a work center first
Average performance on most scheduling criteria
Appears ‘fair’ & reasonable to customers
Important for service organizations
Example: Restaurants

27. Earliest Due Date Rule Process job with earliest due date first
Widely used by many companies
If due dates important
If MRP used
Due dates updated by each MRP run
Performs poorly on many scheduling criteria

28. Critical Ratio (CR) Ratio of time remaining to work time remaining
Work days
remaining
Due date -
Today'
s date
Work (lead
) time remaining =
Process job with smallest CR first
Performs well on average lateness

29. Advantages of the Critical Ratio Scheduling Rule
Use of the critical ratio can help to:
determine the status of a specific job
establish a relative priority among jobs on a common basis
relate both stock and make-to-order jobs on a common basis
adjust priorities and revise schedules automatically for changes in both demand and job progress
dynamically track job progress and location

30. Criteria to Evaluate Priority Rules
Avg.
completio
n time
Flow time #
Jobs
Utilizatio n
Process ti me
jobs in s
System
Processing
time
job laten
ess =
Late time S S S

31. Johnson’s Rule
Used to sequence N jobs through 2 machines in the same order
Jobs (N = 3)
Saw
Drill
Job A
Job B
Job C
© 1995 Corel Corp.
© 1995 Corel Corp.

32. Johnson's Rule - Scheduling N Jobs on Two Machines
All jobs are to be listed, and the time each requires on a machine shown.
Select the job with the shortest activity time. If the shortest time lies with the first machine, the job is scheduled first; if with the second machine, the job is scheduled last.
Once a job is scheduled, eliminate it.
Apply steps 2-3 to the remaining jobs, working toward the center of the sequence.

33. Johnson’s Rule Steps 2 1 List jobs & activity times Select job with
shortest time
Machine?
Schedule
FIRST
LAST
Eliminate job
from list
Jobs left?
Break
arbitrarily
Ties?
Yes 1 2
Stop No

34. Limitations of Rule-Based Dispatching Systems
Scheduling is dynamic; therefore, rules need to be revised to adjust to changes in process, equipment, product mix, etc.
Rules do not look upstream or downstream; idle resources and bottleneck resources in other departments may not be recognized
Rules do not look beyond due dates

35. Theory of Constraints
Deals with factors limiting company’s ability to achieve goals
Types of constraints
Physical
Example: Machines, raw materials
Non-physical
Example: Morale, training
Limits throughput in operations

36. Theory of Constraints A Five Step Process
Identify the constraints
Develop a plan for overcoming the identified constraints
Focus resources on accomplishing the previous step
Reduce the effects of the constraints by off-loading work or by expanding capability
Once one set of constrains is overcome, return to the first step and identify new constraints

37. Bottleneck Work Centers
Have less capacity than prior or following work centers
Limit production output
Remedies
Increase capacity of bottleneck
Develop other routings or subcontract
Schedule throughput to match bottleneck
© 1995 Corel Corp.

38. Techniques for Dealing With Bottlenecks
Increase capacity of the constraint
Ensuring well-trained and cross-trained employees are available to operate and maintain this constraint
Developing alternate routings, processing procedures, or subcontractors
Moving inspections and tests to a position just before the constraint
Scheduling throughput to match the capacity of the bottleneck

39. Advantages of Level Material Use
Lower inventory levels, releasing capital for other uses
Faster product throughput
Improved component quality and hence improved product quality
Reduced floor space requirements
Improved communication among employees because they are closer together
Smoother production process because large lots have not “hidden” the problems

40. The 10 Commandments for Correct Scheduling
the utilization of a non-bottleneck resource is not determined by its own capacity but by some other constraint in the system
activating a resource is not synonymous with utilizing a resource
an hour lost at a bottleneck is an hour lost of the whole system
an hour saved at a non-bottleneck is a mirage
the transfer batch may not, and many times should not, be equal to the process batch

41. The 10 Commandments for Correct Scheduling
the amount processed should be verifiable and not fixed
capacity and priority need to be considered simultaneously, not sequentially
Damage from unforeseen problems can be isolated and minimized
plant capacity should not be balanced
the sum of the local optimums is not equal to the global optimum

42. The Advantages of Level Material Use
lower inventory levels
faster product throughput
improved component quality and product quality
reduced floor-space requirements
a smoother production process because large lots have not "hidden" the problems