Transcript Manufacturing Planning and Control

Manufacturing
Planning and Control
MPC 6th Edition
Chapter 8
McGraw-Hill/Irwin
Copyright © 2011 by The McGraw-Hill Companies, Inc. All rights reserved.
Production Activity Control
Production Activity Control (PAC) concerns
the execution of material plans.
A number of MPC activities, including
Shop-floor Scheduling and Control
(SFC), Vendor Scheduling and Followup, Order Release, and Purchasing fall
partly or completely within the realm of
Production Activity Control.
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Agenda
Production Activity Control–An Overview
Manufacturing Planning and Control Linkages
Production Activity Control Techniques
Theory of Constraints
Vendor Scheduling
Principles
8-3
Production Activity Control in
the MPC System
Resource
planning
Sales and operations
planning
Demand
management
Master production
scheduling
Detailed capacity
planning
Detailed material
planning
Material and
capacity plans
Order release
Shop-floor scheduling
and control (SFC)
Purchasing
Production
activity
control
Vendor scheduling
and follow-up
8-4
System Links–MPC and
Production Activity Control
PAC System
Detailed Capacity
Planning
Detailed Material
Planning
• Planning information to
PAC
• Feedback from PAC –
status and warnings
• Planning information to
PAC
• Feedback from PAC –
status and warnings
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Just-in-Time (JIT) Effect on
PAC


Formal systems for shop-floor control are largely
unnecessary under JIT
PAC functions are simplified





Order release through kanbans or other pull system
Limited work-in-process inventories
Detailed scheduling is not needed
No data collection or monitoring requirements–only raw
material and finished goods inventories
Vendor scheduling may be more complex under JIT
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Production Activity Control
and Company Environment
The primary PAC objective is managing
material flows to meet MPC plans
 Other objectives may pertain to efficient use
of capacity, labor, tools, time, or materials
 Under JIT the objective is material velocity
 PAC objectives reflect the firm’s strategy and
competitive position

8-7
Production Activity Control
Techniques
Production Activity Control
Gantt Charts
• Provides graphic
representation of
the system
Priority
Sequencing
Rules
Theory of
Constraints
Scheduling
• Selecting the
order of job
processing
• Scheduling to
minimize impact
of bottleneck
resources
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Basic Shop Floor Concepts

Routing and lead-time data are essential
inputs
Routing specifies the operation, its duration,
and the work center performing the work
 Lead times typically consist of four elements

•
•
•
•
Run time
Setup time
Move time
Queue time
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Operation Setback Chart
Part D has three
operations
Sub-Assembly
Finished Product
Component parts
8-10
Lead-Time Management
The four elements of lead time (run, setup,
move, and queue) can be compressed with
good PAC management
 A basic principle of MPC systems is to
substitute information for inventory


The knowledge of when an order will arrive at
a work center replaces the need to WIP
inventory feeding the work center
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Gantt Charts

Gantt charts show a schedule
Each step listed separately
 Relationship between steps portrayed visually

8-12
Priority Sequencing Rules
Determine which job to run next at a particular
work center
 When a job is near completion, the available
jobs in the queue are evaluated

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Priority Sequencing Rules

Common rules
Order slack–work on the job with the least total
slack
 Slack per operation–divide total slack by the
number of remaining operations, then work on
job with least slack
 Critical ratio–calculate (time remaining)/(work
remaining) and work on job with lowest ratio
 Shortest operation next–work on the job that can
be completed most quickly

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Theory of Constraints (TOC)

TOC focuses effort on bottleneck resources

Bottlenecks limit the capacity of the entire
plant
Objective is to maximize throughput
 Bottlenecks may be constraints other than
work centers
 Constraints are identified, buffered with
inventory, and their importance is stressed to
the entire factory

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Theory of Constraints
Scheduling

Drum-Buffer-Rope
Drum–bottleneck work centers which control the
tempo of workflow through the plant
 Buffer–inventory and/or scheduling activities to
protect the throughput at bottlenecks from
random variation
 Rope–use of pull scheduling at non-bottleneck
resources


Material moves through non-bottleneck
resources as quickly as possible, bottlenecks
are managed for maximum efficiency
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TOC Scheduling
Potential bottlenecks are
identified using rough-cut
capacity planning
Scheduling is completed
according to the work
center type
8-17
Capacity Utilization Chart
Work centers over a
capacity threshold (80%)
are considered bottlenecks
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Buffers

TOC uses both safety stock and safety lead
time at bottleneck operations
Safety lead time is introduced between
sequential orders at the bottleneck
 Safety stock of completed parts from
preceding, non-bottleneck operations is held in
front of the bottleneck to prevent shortages

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TOC and Lot Sizing

Lot sizes are calculated differently for
bottleneck and non-bottleneck resources
For the same finished item, lot sizes at
different operations may be different
 TOC splits orders at non-bottleneck resources
and combines orders at bottlenecks


This maintains supply of non-bottleneck parts
while reducing setup time and/or increasing
efficiency at the bottleneck
8-20
Managing the TOC
Schedule

Schedule new orders on the bottleneck operations (drums)


Exploiting the drums


Release raw materials to non-bottlenecks only when scheduled
Proactive management of buffers


If necessary, add capacity to drums by moving work or outsourcing
Material release–ropes


Finite backward scheduling
Ensure that bottleneck resources are not starved for orders
Elevating the drum

Increase capacity at the bottlenecks to allow the organization to grow
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TOC Contributions
A feasible master
schedule
Less WIP, shorter lead
times, greater material
velocity
Eliminates the conflict
between MRP and finite
scheduling
8-22
TOC Implementation Issues

Requires a major shift in manufacturing
mindset (paradigm shift)


Its OK to not work (at a non-bottleneck) if
there are no orders
Firm needs sound systems, education, topmanagement support, and willingness to
change
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Vendor Scheduling and
Follow-Up
Objective–align orders with due dates
 Vendor must have continually updated
information concerning priorities
 Contractual agreements may limit the type
and degree of change the vendor must
accommodate
 Use of the Internet can enhance the speed
and efficiency of information exchange

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Principles



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Production activity control system design must be in
concert with the firm’s needs.
Vendor capacities should be planned and
scheduled with as much diligence as internal
resources.
Lead times must be managed.
Feedback from the PAC should provide both status
and early warning information to other MPC
modules
8-25
Principles




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E-based systems can improve communication
between customer and vendor, reducing lead time
and overhead.
TOC scheduling provides improved performance by
focusing on the constraining resources.
TOC implementation requires a change in culture.
Traditional priority rules can play a role in
scheduling non-bottleneck resources.
Stability in manufacturing loads and capacity plans
facilitates shop-floor execution.
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Quiz – Chapter 8


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Production activity control (PAC) actions take place mainly in
which section of the MPC system?
The shop-floor control system is kept current on changes in
material plans by the MRP system? (True/False)
Formal shop-floor control systems are unnecessary under
JIT? (True/False)
A visual representation of the scheduling process can be
provided by _________ charts.
The TOC scheduling process is called ______-__________________.
In TOC scheduling, buffers are maintained before and after
_____________ resources.
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