1. Manufacturing Planning and Control
MPC 6th Edition
Chapter 8a

2. Advanced Scheduling
Detailed scheduling of individual jobs through work centers in a shop has been the focus of numerous researchers. Focusing on some basic concepts and results and relating them to some newer manufacturing approaches can show how to apply results in different operating situations.

3. Agenda Overview of Scheduling Research Basic Scheduling Research
Advanced Procedures

4. Scheduling Research Framework
A schedule is a plan for the sequence of time allotted for and operations necessary to complete an item
The schedule has several inputs
Sequential constraints
Time estimates for each operation
Required resources for each operation

5. Basic Scheduling Research
The One-Machine Case
The Two-Machine Case
Dispatching Approaches
Sequencing Rules

6. The One-Machine Case
Problem of how to best schedule a fixed set of jobs through a single machine
All jobs are available at the start of the period
Setup times are independent of the sequence
Objectives
Minimize total time–all sequences are equal
Minimize average time–process shortest jobs first
Minimize average number of jobs in the system–process shortest jobs first

7. The Two-Machine Case More complex than the one-machine case
Must consider job routings
Minimum total time (make span) depends upon sequencing
Two-machine case can be used as an approximation of the M-machine problem (where M > 2)

8. Dispatching Approaches
Dispatching approaches allow analysis of dynamic problems (where randomness in inter-arrival times and service times are considered)
Uses logic rules to guide the prioritizing of jobs at a work center (sequencing rules)
Often uses simulation methodology to study realistic problems

9. Sequencing Rules
Sequencing rules provide guidelines to the wide range of possible sequencing options
With n jobs and m machines, there are (n!)m possible ways to schedule the system

10. Sequencing Rules
Random–pick any job with equal probability. Used as a benchmark for other rules.
First-come/first-served–jobs are processed in the order they arrive
Shortest processing time–reduces work-in-process, average completion time, and average lateness
Earliest due date–often works well to reduce job lateness
Least work remaining–considers all remaining processing time
Least setup–minimizes changeover time on the machine and maximizes capacity utilization

11. Due Date-Setting Procedures Dynamic Due Dates
Labor-Limited Systems
Group Scheduling and Transfer Batches
Advanced Procedures

12. Due Date-Setting Procedures
Establishing order release and due dates is critical in many firms
Due dates often must be set at the time of order entry
Estimating manufacturing time is a key function
Calculating lead times on the basis of total work content is often best

13. Dynamic Due Dates
Maintaining valid due dates as system parameters change is also important
Dynamic due dates allow updating of open order due dates
May lead to system “nervousness”
Can cause shop floor employees to distrust the system
Can improve customer service and reduce total inventory

14. Labor-Limited Systems
Useful when labor is the bottleneck resource
Three major elements for controlling workflow
Determining which job to do next at the work center
Determining when a person is available for transfer to another work center
Determining the work center to which an available person is to be assigned
Research shows the importance of cross-training and labor assignment flexibility
Both labor and job dispatching can have a major impact in controlling work flow

15. Group Scheduling and Transfer Batches
Theory of Constraints scheduling uses different batch sizes for bottleneck and non-bottleneck work centers
Repetitive lots concept–original order quantities released to the floor can be split into smaller transfer batches
Gives work centers the flexibility to start producing an order before the previous work center is completely done with the job
Reduces flow times, improves utilization, cuts setup times, and smoothes work flow

16. Principles
It is important to determine the objective(s) of scheduling before selecting an approach.
Shortest processing time sequencing rule can provide effective performance and should be considered a standard in designing shop-floor systems.
Flexibility is introduced into scheduling through alternative routings, labor assignment adjustments, the use of transfer batches, and overlap scheduling. Flexibility can lead to great improvements.
Setting and managing due dates is an important scheduling activity.
Due date filtering procedures should be used to reduce shop-floor nervousness.

17. Quiz – Chapter 8a
In the one-machine case, the order of job processing is not an important factor in performance? (True/False)
The shortest processing time (SPT) sequencing rule performs well to minimize overall job lateness? (True/False)
One means of evaluating the effectiveness of due date-setting is _________ __________ _____________.
In TOC, original orders may be divided into smaller quantities called _____________ batches.