Production Production and Operationsand OperationsManagement:Management:Manufacturing and Manufacturing and ServicesServices

PowerPoint Presentation for Chapter 17PowerPoint Presentation for Chapter 17

Operations SchedulingOperations Scheduling

ChaseChaseAquilanoAquilano

JacobsJacobs

Eighth EditionEighth Edition

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Work Center

Area in a business in which productive resources are organized and work is completed.

May be a single machine, a group of machines, or an area where a particular type of work is done. – Job shop (by function)– Flow (product)– Assembly line– GT cell

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Typical Scheduling and Control Functions

Allocating orders, equipment, and personnel

Determining the sequence of order performance

Initiating performance of the scheduled work

Shop-floor control

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Work-Center Scheduling Objectives

Meet due dates

Minimize lead time

Minimize setup time or cost

Minimize work-in-process inventory

Maximize machine utilization

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Priority Rules for Job Sequencing

1. First-come, first-served (FCFS)

2. Shortest operating time

3. Earliest due date first

4. Earliest start date first (due date-lead time)

5. Least slack time remaining first

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Priority Rules for Job Sequencing

6. Least slack time remaining (per operation as opposed to per job) first

7. Smallest critical ratio first(due date-current date)/(number of days remaining)

8. Smallest queue ratio first(slack time remaining in schedule)/(planned remaining queue time)

9. Last come, first served

10. Random order

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Schedule Performance Measures

Meeting due dates of customers or downstream operations.

Minimizing the flow time (the time a job spends in the process).

Minimizing work-in-process inventory.

Minimizing idle time of machines or workers.

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Job Sequencing ExampleFirst-Come First-Served

Jobs (in order Processing Due Date Flow Timeof arrival) Time (days) (days hence) (days)

A 4 5 4B 7 10 11C 3 6 14D 1 4 15

FCFS Schedule

Late?On-Time?

Orders submittedat beginning of week

Jobs (in order Processing Due Dateof arrival) Time (days) (days hence)

A 4 5B 7 10C 3 6D 1 4 n-jobs on one machine

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Job Sequencing ExampleShortest Operating Time

Orders submittedat beginning of week

Jobs (in order Processing Due Dateof arrival) Time (days) (days hence)

A 4 5B 7 10C 3 6D 1 4

Shortest Operating Time Schedule

Jobs (in order Processing Due Date Flow Timeof arrival) Time (days) (days hence) (days)

D 1 4 1C 3 6 4A 4 5 8B 7 10 15

Late?On-Time?

n-jobs on one machine

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Job Sequencing ExampleLast-Come First-Served

Orders submittedat beginning of week

Jobs (in order Processing Due Dateof arrival) Time (days) (days hence)

A 4 5B 7 10C 3 6D 1 4 n-jobs on one machine

Last-Come First-Served ScheduleJobs (in order Processing Due Date Flow Time

of arrival) Time (days) (days hence) (days)D 1 4 1C 3 6 4B 7 10 11A 4 5 15

Late?On-Time?

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Job Sequencing ExampleEarliest Due Date First

Orders submittedat beginning of week

Jobs (in order Processing Due Dateof arrival) Time (days) (days hence)

A 4 5B 7 10C 3 6D 1 4

Earliest Due Date First

Jobs (in order Processing Due Date Flow Timeof arrival) Time (days) (days hence) (days)

D 1 4 1A 4 5 5C 3 6 8B 7 10 15

Late?On-Time?

n-jobs on one machine

n/1 Example

21E

96D

72C

64B

53A

Due date (days hence)

Processing time (Days)

Job (in order of arrival)

FCFS

21E

96D

72C

64B

53A

Due date (days hence)

Processing time (Days)

Job (in order of arrival)

15 + 1 = 16

9 + 6 = 15

7 + 2 = 9

3 + 4 = 7

0 + 3 = 3

Flow Time (days)

Total flow time

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Shop-Floor ControlMajor Functions

1. Assigning priority of each shop order

2. Maintaining work-in-process quantity information

3. Conveying shop-order status information to the office

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Shop-Floor ControlMajor Functions

4. Providing actual output data for capacity control purposes

5. Providing quantity by location by shop order for WIP inventory and accounting purposes

6. Providing measurement of efficiency, utilization, and productivity of manpower and machines

Capacityrequirements

planning

Routingsand

work centers

Shop-floor

dispatching

Work-in-process

control

Input/output

analysis

Prioritizedqueuelists

Standardproduction

costs

Labor andequipment

requirements

Work orders

Work orderscheduling

Work ordertracking

Hewlett-Packard’sShop-Floor ControlSystem

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Input/Output Control

Input Output

Planned input should never exceed planned output

Focuses attention on bottleneck work centers

WorkCenter

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Principles of Work-Center Scheduling

1. There is a direct equivalence between work flow and cash flow.

2. The effectiveness of any job shop should be measured by speed of flow through the shop.

3. Schedule jobs as a string, with process steps back to back.

4. A job once started should not be interrupted.

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Principles of Job Shop Scheduling

5. Speed of flow is most efficiently achieved by focusing on bottleneck work centers and jobs.

6. Reschedule every day.

7. Obtain feedback each day on jobs that are not completed at each work center.

8. Match work center input information to what the worker can actually do.

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Principles of Job Shop Scheduling

9. When seeking improvement in output, look for incompatibility between engineering design and process execution.

10. Certainty of standards, routings, and so forth is not possible in a job shop, but always work towards achieving it.

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Personnel Scheduling in Services

Scheduling consecutive days off

Scheduling daily work times

Scheduling hourly work times