Chapter 17 Scheduling. Management 3620Chapter 17 Schedule17-2 Overview of Production Planning Hierarchy Capacity Planning 1. Facility size 2. Equipment

Chapter 17

Scheduling

Management 3620 Chapter 17 Schedule 17-2

Overview of Production Planning Hierarchy

Capacity Planning 1. Facility size 2. Equipment procurement

Aggregate Planning 1. Facility utilization 2. Personnel needs 3. Subcontracting

Master Schedule 1. MRP 2. Disaggregation of master plan

Long-term(Chapter 5)

Intermediate-term(Chapter 14)

Short-term(Chapter 17)

Intermediate-term(Chapters 14 and 15)

Short-term Scheduling 1. Work center loading 2. Job sequencing


The Scheduling Problem• Have the correct amount of

resources at the right time and in the right place

THE CHALLENGEMeet the job’sdue date – customer service

Utilization of theorganization’s resources- productivity


Build A

A Done

Build B

B Done

Build C

C Done

Build D

Ship

JAN FEB MAR APR MAY JUN

On time!

Scheduling Manufacturing Operations

High-volume

Intermediate-volume

Low-volume

Service operations


Work Center #1 Work Center #2 Output

High-Volume Systems• Flow system: High-volume system with

standardized equipment and activities

• Flow-shop scheduling: Scheduling for high-volume flow system– line balancing (Chapter 6)

– design of work systems (Chapter 7)


High-Volume Success Factors

• Process and product design

• Preventive maintenance

• Rapid repair when breakdown occurs

• Optimal product mixes

• Minimization of quality problems

• Reliability and timing of supplies


Intermediate-Volume Systems (1 of 2)

• Outputs are between standardized high-volume systems and made-to-order job shops

• Three basic issues– run size of jobs– timing of jobs– sequence in which jobs should be

processed


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Intermediate-Volume Systems (2 of 2)

• Economic run size

• Base production on a master scheduledeveloped from customer orders and

forecasts of demand


Low-Volume Systems• A variety of unique (customized) jobs arrive

at the shop

• Someone must analyze each job regarding its routing (which work centers it will be required to visit), and the required amount of resources needed at each work center

• Typically the customer is told when the job will be finished (due date)

• The jobs are moved through the required work centers as each becomes available according to a scheduling system


Scheduling Low-Volume Systems

• Loading - assignment of jobs to process centers

• Sequencing - determining the order in which jobs will be processed


Loading Approaches (1 of 2)

• Infinite loading– assumes capacity of a work center is

infinite

– priority sequencing rule then used

– managers may need to respond to capacity overload conditions


Loading Approaches (2 of 2)

• Finite loading – projects the starting and stopping times

of each job at each work center

– takes into account capacities of each work center and the processing times of jobs so that capacity is not exceeded

• In special cases, an algorithm such as the assignment method may be used


Everything is#1 Priority

Sequencing

• Determine the order in which jobs waiting at a work center will be processed

• One approach is to use priority rules (simple heuristics) to select the order in which jobs waiting in line will be processed


Examples of Priority Rules

• FCFS - first come, first served

• SPT- shortest processing time

• DD - due date

• CR - critical ratio


Examples of Performance Measures (1 of 2)

• Job flow time – the length of time a job is in the shop at a particular workstation; includes processing time, wait time, transportation time

• Average job flow time – the sum of the flow time for each job in a group divided by the number of jobs

• Makespan – total time needed to complete a group of jobs


Examples of Performance Measures (2 of 2)

• Job lateness – the length of time the job completion time is expected to exceed the time the job is due

• Average lateness – the sum of the lateness for each job in a group divided by the number of jobs

• Average number of jobs – average work-in-process for a group of jobs; total flow time divided by makespan


Example 2, FCFS

JobDueDate

JobTime

FlowTime Lateness

A 7 2B 16 8C 4 4D 17 10E 15 5F 18 12

Average


Two Work Center Sequencing

• Johnson’s Rule– technique for minimizing completion

time for a group of jobs to be processed on two processes or at two work centers.

– minimizes total idle time of the two processes

• Several conditions must be satisfied


Johnson’s Rule Conditions• Job time must be known and constant

• Job times must be independent of sequence

• Jobs must follow same two-step sequence (flow shop)

• Job priorities cannot be used

• All units must be completed at the first work center before moving to second


Example Problem

Job DataEntry

Verify

A 2.5 1.7

B 3.8 2.6

C 1.9 1.0

D 1.8 3.0

first last


Gantt Chart

• Used as a visual aid for loading and scheduling

• Purpose is to organize and clarify the actual or intended use of resources in a time framework

• Two most commonly used types– load chart– schedule chart


WorkCenter

Mon. Tues. Wed. Thurs. Fri.

1 Job 3 Job 42 Job 3 Job 73 Job 1 Job 6 Job 74 Job 10

Figure 17-2

Gantt Load Chart


Example ProblemJob Data

Entry Verify

A 2.5 1.7

B 3.8 2.6

C 1.9 1.0

D 1.8 3.0

first last

CAD B

DataEntry

Verify

time


Scheduling Approaches

• Forward scheduling– scheduling ahead, from some point in

time

• Backward scheduling– scheduling by working backward from

the job’s due date


Input/Output Control

• Used to manage work flow so that queues and waiting times are kept under control

• Input to a work center is compared to the output of that work center for some time period

• An imbalance indicates management should investigate


Service Operation Problems

• Cannot store or inventory services

• Customer service requests are random

• Scheduling service involves– Customers

– Workforce

– Equipment

Duh! Where’sDilbert?


Scheduling Service Operations

• Appointment systems– Controls customer arrivals for service

• Reservation systems– Estimates demand for service

• Scheduling the workforce– Manages capacity for service

• Scheduling multiple resources– Coordinates use of more than one

resource

Documents

Chapter 17 Scheduling. Management 3620Chapter 17 Schedule17-2 Overview of Production Planning Hierarchy Capacity Planning 1. Facility size 2. Equipment