Digital Twins and Operational Excellence presentation from the Institute of Industrial & Systems Engineers Annual Conference in 2012. Deals with intelligent scheduling, digital twins, network theory, and operational excellence for outsized, large scale improvements in manufacturing systems.

1. Authors
David Prestin
Nathan Bingman
Manufacturing Flow Time
Reduction Utilizing Digital Twins,
Network Analysis and Critical
Chain

2. 2
AGENDA
 INTRODUCTION
 COMPLEXITY
 PRODUCTION SYSTEM DIGITAL TWINS
 NETWORK THEORY
 CONSTRAINT BASED SCHEDULING AND CRITICAL CHAIN
 PRIORITIZED IMPROVEMENT METHODS
 CLOSING

3. 3
AGENDA
 INTRODUCTION
 COMPLEXITY
 PRODUCTION SYSTEM DIGITAL TWINS
 NETWORK THEORY
 CONSTRAINT BASED SCHEDULING AND CRITICAL CHAIN
 PRIORITIZED IMPROVEMENT METHODS
 CLOSING

4. 4
Introduction
Early program – large aircraft production presents unique challenges to
execution management and production improvement given the
relatively high levels of uncertainty and variability that are exhibited in
these types of production systems early in the program lifecycle.
The purpose of this presentation is to:
1) Describe characteristics of complexity and complicatedness of these
production systems and the resulting challenge they present to targeted
improvement activities.
2) Describe execution management methods, tools, and techniques
currently employed in Boeing.
3) Describe extensions of these execution management techniques for
targeted improvement activities.

5. 5
AGENDA
 INTRODUCTION
 COMPLEXITY
 PRODUCTION SYSTEM DIGITAL TWINS
 NETWORK THEORY
 CONSTRAINT BASED SCHEDULING AND CRITICAL CHAIN
 PRIORITIZED IMPROVEMENT METHODS
 CLOSING

6. 6
Complexity and Complicatedness in Aircraft
Production
Author Melanie Mitchell of Complexity: A
Guided Tour described complexity in a
recent interview as:
A system with large numbers of
interacting components, in which
the components are relatively
simple compared with the system
as a whole, in which there is no
central control or global
communication among the
components, and in which the
interactions among the
components gives rise to complex
behavior.

7. 7
Complexity and Complicatedness in Aircraft
Production
Industry Day Briefing
META
Novel Methods for Design & Verification of Complex Systems
Paul Eremenko
Tactical Technology Office
Defense Advanced Research Projects Agency
(571) 214-2436
paul.eremenko@darpa.mil
22 December 2009
APPROVED FORPUBLIC DISTRIBUTION LIMITED.
Source
 Aerospace industry
complexity grows but so
do cost and schedule
 Other industry’s don’t
seem to have this effect
occurring
 Material and performance
requirements continue to
grow in number and
complexity
 Design and Systems
Engineering manage product
design and development

8. 8
AGENDA
 INTRODUCTION
 COMPLEXITY
 PRODUCTION SYSTEM DIGITAL TWINS
 NETWORK THEORY
 CONSTRAINT BASED SCHEDULING AND CRITICAL CHAIN
 PRIORITIZED IMPROVEMENT METHODS
 CLOSING

9. 9
In Aircraft production, there are several diagrams (models) that are useful for
the Industrial Engineer to design, manage, and improve these complicated
production systems. For purposes of this presentation, we will make a
distinction between two:
Materials Flow Diagrams:
1. Materials Flow Diagrams map the movement of materials and indicate larger
quantities through more profound flow paths.
2. Materials Processing Diagrams map the processing (transformation) of materials and
provide a pictorial of processing equipment within a Production System.
3. Value Stream Maps are used to trace and measure the flow (transformation) of
materials and information within a Production System.
Co2 Emissions Melamine Production Fabrication, Assembly & Test
Aircraft Production Digital Twins
Source: Richard Elliott, 2011 IIE Annual Conference
Presentation “Production System Diagrams”

10. 10
Aircraft Production Digital Twins
In Aircraft production, there are several diagrams (models) that are useful
for the Industrial Engineer to design, manage, and improve these
complicated production systems. For purposes of this presentation, we
will make a distinction between two:
Workflow Diagrams:
1. A workflow diagram consists of a sequence of operational tasks necessary
to produce an end product.
2. More abstractly, a workflow is a pattern of activity enabled by a
systematic organization of resources, energy, and information flows that
can be documented, learned, and repeated.
Precedence Network Diagram
w/ Critical Path in red
PERT Diagram
and related Gantt Chart
Quality Assurance (4800 min)
Standard Operations
(Daily Operating Plan)
for
Ares I Upper Stage Reaction Control
System (ReCS) and First Stage Roll
Control System (RoCS)
2 Positions with 2 Units in Flow
3 Technicians and 1 Quality Assurance
Shift 1
January 4, 2010
Mfg Day 14769
Flow Day 1
6:00 AM 2:30 PM
SHIFT
CUM 0
0 Shift 1
January 5, 2010
Mfg Day 14770
Flow Day 2
6:00 AM 2:30 PM
SHIFT
CUM 0
0 Shift 1
January 6, 2010
Mfg Day 14771
Flow Day 3
6:00 AM 2:30 PM
SHIFT
CUM 0
0 Shift 1
January 7, 2010
Mfg Day 14772
Flow Day 4
6:00 AM 2:30 PM
SHIFT
CUM 0
0 Shift 1
January 8, 2010
Mfg Day 14773
Flow Day 5
6:00 AM 2:30 PM
SHIFT
CUM 0
0 Shift 1
January 11, 2010
Mfg Day 14774
Flow Day 6
6:00 AM 2:30 PM
SHIFT
CUM 0
0 Shift 1
January 12, 2010
Mfg Day 14775
Flow Day 7
6:00 AM 2:30 PM
SHIFT
CUM 0
0 Shift 1
January 13, 2010
Mfg Day 14776
Flow Day 8
6:00 AM 2:30 PM
SHIFT
CUM 0
0
A Tech #1
3
1
2
B L46BF ??
3
1
2
C Tech #2
3
1
2
D Tech #3
3
1
2
E QA #1
3
1
2
Takt Time (4956 min)
SOP 2 X-Ray (POS 2) (240 min)
SOP 1 Assembly Manifold (POS 1 Bench) (2160 min) SOP 3 Proof & Clean (POS 2) (240 min) SOP 4 Weld Surge Arrestors to Manifold (POS 2) (600 min) SOP 8A Dry Fit Manifold to Module (POS 1) (360 min)
SOP 9 Weld/ASSY Manifold to Structure
(POS 1) (270 min)
SOP 10A Install Purge Lines (POS 1) (285 min)
SOP 11A Install
Pneumatic Lines
(POS 1) (90 min)
SOP 12 X-Ray (POS 2) (180 min) SOP 13 Proof & Clean (POS 2) (240 min)
SOP 14 Install Instrumentation (POS 3) (360 min) SOP 15 Route, Bundle, & Clamp wires (POS 3) (480 min) SOP 16A Pin-out wires & Tension Test (POS 3) (720 min)
SOP 17 Install Top
Infrastructure (POS 3)
(120 min)
SOP 18 Perform TCV Functional Test (POS 3) (2160 min) SOP 19A Install Fairing & Close-Outs (POS 3) (420 min) SOP 20A Bag, Purge & Prep for Shipping (POS 3) (280 min)
SOP 16B Pin-out wires & Tension Test (POS 3) (720 min) SOP 6 Recieving: Visual Inspect & Hydrazine Sniff Thruster (POS 1) (360 min) SOP 5 Module Structure Build-Up (POS 1) (960 min) SOP 7 Align & Install Thrusters (POS 1) (360 min) SOP 8B Assist Dry Fit Manifold to Module (POS 1) (360 min)
SOP 19B Assist Install
Fairing & Close-Outs
(POS 3) (120 min)
SOP 10B Assist Install Purge Lines
(POS 1) (195 min)
SOP 11B Assist Install
Pneumatic Lines
(POS 1) (90 min)
SOP 20B Assist Bag, Purge & Prep for
Shipping (POS 3) (200 min)
Report to Supervisor (261 min)
Report to Supervisor (840 min) Report to Supervisor (354 min)
Report to Supervisor (240 min)
Shift 1
January 14, 2010
Mfg Day 14777
Flow Day 9
6:00 AM 2:30 PM
SHIFT
CUM 0
0 Shift 1
January 15, 2010
Mfg Day 14778
Flow Day 10
6:00 AM 2:30 PM
SHIFT
CUM 0
0
Report to Supervisor (135 min)
SOP 1 Quality Assurance
Assembly Manifold (POS 1
Bench) (120 min)
SOP 4 Quality
Assurance Weld Surge
Arrestors to Manifold
(POS 2) (120 min)
SOP 5 Quality Assurance
Module Structure Build-Up
(POS 1) (120 min)
SOP 6 Quality Assurance
Recieving: Visual Inspect
& Hydrazine Sniff Thruster
(POS 1) (120 min)
SOP 7 Quality Assurance
Align & Install Thrusters
(POS 1) (120 min)
SOP 8 Quality Assurance
Dry Fit Manifold to Module
(POS 1) (120 min)
SOP 9 Quality Assurance
Weld/ASSY Manifold to
Structure
(POS 1) (120 min)
SOP 10 Quality
Assurance Install
Purge Lines (POS 1)
(120 min)
SOP 11 Quality
Assurance Install
Pneumatic Lines
(POS 1) (68 min)
SOP 18 Perform TCV
Functional Test (POS 3)
(120 min)
SOP 19 Quality Assurance
Install Fairing & Close-
Outs (POS 3) (120 min)
SOP 20 Quality
Assurance Bag, Purge &
Prep for Shipping (POS
3) (113 min)
Resource assigned Barchart of Parallel Workflows
Source: Richard Elliott, 2011 IIE Annual Conference
Presentation “Production System Diagrams”

11. 11
Aircraft Production Digital Twins
In Aircraft production, there are several diagrams (models) that are useful
for the Industrial Engineer to design, manage, and improve these
complicated production systems. For purposes of this presentation, we
will make a distinction between two:
The Point Is:
 Use advanced tools and methods to move what seems complex
(knowable, maybe after the fact with analysis), into something more
of a complicated nature (knowable – able to analyze, sense, then
respond)
 We focus on the workflow modeling, and employ advanced tools
and methods to both manage production execution and also to
analyze and facilitate improvement in this complicated environment

12. 12
Aircraft Workflow Modeling
Modeling Parameters
In the Past:
 Workflow modeling and thus scheduling were manual or utilized early
stage computing power often leading to sub-optimal results
 Most algorithms and tools could not handle complicated workflow
models with thousands of tasks and cross conflicting resources
Presently:
 There are tools available that utilize the increased processing speeds
on PC’s as well as much more advanced network theory algorithms
coupled with Artificial Intelligence to produce “more optimal” solutions
 These now allow us to perform what we call Constraint Based
Scheduling

13. 13
AGENDA
 INTRODUCTION
 COMPLEXITY
 PRODUCTION SYSTEM DIGITAL TWINS
 NETWORK THEORY
 CONSTRAINT BASED SCHEDULING AND CRITICAL CHAIN
 PRIORITIZED IMPROVEMENT METHODS
 CLOSING

14. 14
Aircraft Production Digital Twins
Applied Network Theory
A workflow model can be contextualized into Network Theory terminology
and is pertinent to follow on slides in this presentation:
A workflow model is an acyclic – directed network of causally linked task
events.
A directed network is a network in which each edge has a direction,
pointing from one vertex to another.
An acyclic network is one in which there are no cycles or in other words,
closed loops of edges with the arrows on each of the edges pointing the
same way around the loop.
Source: Networks: An Introduction, M.J. Newman
Oxford University Press, Copyright 2010
A B
A B
C
A B
C

15. 15
degree
count
0
100
200
300
400
500
0 10 20 30 40 50
Parallelism of Precedence Network Digital Twins
Precedence networks for airplane
manufacturing tend to be highly
parallel
Degree distribution tends to follow a
power law, similar to scale-free or
small-world networks1
1Albert R., Barabási A.-L. (2002). "Statistical mechanics of complex networks". Rev. Mod. Phys. 74: 47–97.
876
.
1
418
.
2050
)
( −
= x
x
f
9759
.
0
2
=
R

16. 16
AGENDA
 INTRODUCTION
 COMPLEXITY
 PRODUCTION SYSTEM DIGITAL TWINS
 NETWORK THEORY
 CONSTRAINT BASED SCHEDULING AND CRITICAL CHAIN
 PRIORITIZED IMPROVEMENT METHODS
 CLOSING

17. Constraint Based Scheduling = Scheduling With:
• All Tasks / Jobs
• The Relationships Between These Tasks / Jobs
• The Durations Of Each Task / Job
• The Resources Required For Each Job (Labor/Tools/Space/Etc.)
Critical
Path Critical
Chain
Constraints
What Is Constraint Based Scheduling?
Critical Path = Shortest pathway of events that define the total flow of a project – the zero slack route
Constraints = what is keeping a system from providing a product or service faster – better - cheaper
Examples: Project Start and End Dates, Labor Headcount, Hangar Space, Aircraft zones, etc.
Critical Chain = Critical Path + Resource Contention

18. 18
Aircraft Workflow Modeling
Modeling Parameters
Global Calendars
Shift Schedules
Project Start/End Dates
Milestones (Control Points)
Local Durations
Safe
Aggressive
Resources
Labor
Zone
Mechanics
Electricians
Functional Test Technicians
1
2
.
.
.
n
Precedence
The parameters listed here
are examples of those that
used in constraint based
scheduling and analysis of
the work flow model.
.
.
.

19. 19
Original Critical Chain vs Dynamic Critical
Chain
Original Critical Chain (OCC) – the critical chain at the onset of the
project. The best path forward from the onset of the project execution
phase.
“How the product wants to get built”
Dynamic Critical Chain (DCC)– the current critical chain at a given time
in the project. This takes into account any deviations from the OCC due
to production system variability.
“How the product is actually being built”

20. 20
Dynamic Critical Chain Over Time
Critical Chain changes as the project is
executed!

21. 21
DCC Occurences
count
0
50
100
150
200
0 5 10 15 20
Occurrences on Dynamic Critical Chain
Number of appearances on dynamic critical chain distribution by
task followed power law, similar to task degree distribution
What does this mean?
A few number of jobs frequent the DCC, primarily constraining flow
Pareto Principle!

22. 22
Percentage of Time on DCC
Number of appearances on dynamic critical chain distribution by
task followed power law, similar to task degree distribution
What does this mean?
A few number of jobs frequent the DCC, primarily constraining flow
Pareto Principle!

23. 23
AGENDA
 INTRODUCTION
 COMPLEXITY
 PRODUCTION SYSTEM DIGITAL TWINS
 NETWORK THEORY AND CONSTRAINT BASED
SCHEDULING
 CRITICAL CHAIN
 PRIORITIZED IMPROVEMENT METHODS
 CLOSING

24. 24
Value Stream Analysis
Early Program production systems are
dynamic  Hard to pin point highest
leverage improvement opportunities
Improve the Dynamic Critical Chain
tasks with this method and the
manufacturing flow is more likely to
decrease
Integrating value stream analysis can
help prioritize supporting flows
associated with the prioritized DCC
tasks

25. 25
Prioritized Improvement
Identifying high leverage tasks is only the first step! Must carry
through actual improvement!
Theory of Constraints – break the constraint! Conduct Industrial
Engineering analysis to reduce flow on the prioritized jobs
Subordinate
Identify
Exploit
Elevate
Repeat
VSM
Methods
Engineering
Standard
Work
Poke-Yoke
PDCA
Kanban
SPC
Work
Sampling

26. 26
Repeatability
Improving the Critical Chain will by consequence likely move it into
another sequence of events.
Must repeat the cycle  Plan, Do, Check, Act!
Identify high-leverage tasks Improve high-leverage tasks
Repeat

27. Thank You
27