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© 2011 Lockheed Martin Corporation

Concept Development of an Automated Shim Cell

for

F-35 Forward Fuselage Outer Mold Line Control

by

Jamie Smith

A Research Paper Submitted in Partial Fulfillment of the

Requirements for the Master of Science Degree

in

Manufacturing Engineering

Approved: 3 Semester Credits

The Graduate School

University of Wisconsin-Stout

December 2011

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The Graduate School

University of Wisconsin-Stout

Menomonie, WI

Author: Smith, Jamie M.

Title: Concept Development of an Automated Shim Cell for F-35 Forward

Fuselage Outer Mold Line Control

Graduate Degree/ Major: MS Manufacturing Engineering

Research Adviser: Annamalai Pandian D. Eng

Month/Year: December 2011

Number of Pages: 84

Style Manual Used: American Psychological Association, 6th

edition

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Abstract

The F-35 Joint Strike Fighter, produced by Lockheed Martin Aeronautics, requires

precision control of the designed-in shim gap between the forward fuselage understructure and

the mating skin. The current manual shimming method results in excessive time and material

waste which makes it impossible to support a peak production rate of one aircraft a day. The

purpose of this study was to develop a concept for an efficient, automated liquid shimming

system and to verify the feasibility of specific components of the system. A team was assembled

to gather requirements for a production-ready shimming system, develop a shim cell concept,

and complete a cost benefit analysis to justify the need for an automated system. Gage

repeatability/reproducibility and accuracy tests were completed to verify that a non-contact

metrology system could meet requirements for structure location and surface profile verification.

Tests were performed to identify various material options and release agents for an outer mold

line (OML) control tool, and a sub-scale OML control test tool was designed and fabricated. The

results of this study provided Lockheed Martin Aeronautics the necessary foundation to verify

system feasibility and validate system components in order to begin specification development

for the procurement of an automated shim cell for F-35 forward fuselage outer mold line control.

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The Graduate School

University of Wisconsin Stout

Menomonie, WI

Acknowledgments

I would like to thank my husband, Dale, for all of his support, love, and encouragement

throughout this degree process. I would also like to thank David Fly for his advice and guidance,

especially for distance learners. Finally, I would like to thank my field project advisor, Dr.

Pandian, for his valuable time, timely feedback, and improvement suggestions with completing

this paper.

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Table of Contents

.................................................................................................................................................... Page

Abstract ............................................................................................................................................3

List of Tables ...................................................................................................................................8

List of Figures ..................................................................................................................................9

Chapter I: Introduction ..................................................................................................................10

Statement of the Problem ...................................................................................................14

Purpose of the Study ..........................................................................................................15

Assumptions of the Study ..................................................................................................16

Definition of Terms............................................................................................................16

Limitations of the Study.....................................................................................................18

Methodology ......................................................................................................................18

Chapter II: Literature Review ........................................................................................................20

Shimming in the Aerospace Industry .................................................................................20

Shim description ....................................................................................................20

Purpose of shims ....................................................................................................21

Industrial Automation Considerations ...............................................................................22

Automation descriptions ........................................................................................22

The benefits of robotic automation ........................................................................23

Uses of robots ........................................................................................................24

Metrology Enhances Automation Capabilities ..................................................................25

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Types of metrology ................................................................................................26

Metrology and automation for assembly processes ...............................................27

Conclusion .........................................................................................................................30

Chapter III: Shimming Methodology.............................................................................................32

Concept Development ........................................................................................................32

Establish a development team ................................................................................33

Baseline the process ...............................................................................................33

Investigate existing technologies in the industry ..................................................33

Complete a CBA ....................................................................................................34

Verify System Component Feasibility ...............................................................................35

Structure location and surface verification ............................................................35

Shimmed surface profile control feasibility ...........................................................40

Summary ............................................................................................................................41

Chapter IV: Results ........................................................................................................................43

Baseline of Process ............................................................................................................44

Ideal State Process .............................................................................................................45

CBA Results.......................................................................................................................50

Structure Location and Surface Verification Results.........................................................51

Shimmed Surface Profile Control Feasibility Results .......................................................54

Summary ............................................................................................................................59

Chapter V: Discussion ...................................................................................................................60

Significance of the New Automated Shimming System Concept .....................................60

Non-Contact Measurement Systems for Structure Location and Surface Verification .....61

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Release Agent and Shimmed Surface Profile Control .......................................................62

Conclusions ........................................................................................................................62

Recommendations ..............................................................................................................63

References ......................................................................................................................................64

Appendix A: Detailed Release Agent Test Instructions ...............................................................67

Appendix B: Automated Shimming System Design Requirements .............................................70

Appendix C: Supplier Selection....................................................................................................76

Appendix D: Summary of Supplier Responses from RFI Conference .........................................77

Appendix E: Detailed Gage R&R Results ....................................................................................78

Appendix F: OML Control Tool Test Fixture Details ..................................................................81

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List of Tables

.................................................................................................................................................... Page

Table 1: Summary of deliverables and methods ...........................................................................43

Table 2: Manual vs. automated process span time comparison ....................................................50

Table 3: Summary of automated shimming system CBA ............................................................51

Table 4: Non-contact metrology gage R&R results ......................................................................52

Table 5: Non-contact metrology accuracy test results ..................................................................52

Table 6: Metrology system time test results .................................................................................53

Table 7: Release agent pull test results - Tensile stress at max load ............................................55

Table 8: Cured shim surface profile measurements on Teflon pull test coupons .........................57

Table 9: OML control tool potential material and surface finish cost study summary ................57

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List of Figures

.................................................................................................................................................... Page

Figure 1: F-35 Forward fuselage understructure and skins ..........................................................10

Figure 2: F-35 Forward fuselage designed-in shim gap ...............................................................11

Figure 3: Forward fuselage shimmed surfaces .............................................................................11

Figure 4: Manual application of liquid shim.................................................................................13

Figure 5: Problems with overpress method of shim application...................................................14

Figure 6: Accuracy and gage R&R test article .............................................................................36

Figure 7: Nikon Laser Radar MV330 ...........................................................................................37

Figure 8: Hexagon Cognitens WLS400M white light scanner .....................................................38

Figure 9: GOM ATOS Triple Scan ...............................................................................................39

Figure 10: Production forward fuselage used for large-scale time tests .......................................40

Figure 11: Release agent testing setup ..........................................................................................41

Figure 12: Baseline process flow diagram with span times ..........................................................45

Figure 13: Automated system concept layout ...............................................................................46

Figure 14: Automated system process flow diagram with estimated span times .........................49

Figure 15: Surface points collected on forward fuselage for time test .........................................53

Figure 16: Release agent pull test coupons ...................................................................................54

Figure 17: Release agent pull test results ......................................................................................56

Figure 18: OML control tool design .............................................................................................58

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Chapter I: Introduction

The F-35 Joint Strike Fighter is a fifth generation multi-role fighter jet that is dependent

on stealth technology for mission success. To meet design specifications, its manufacturing

processes require precision control of the outer mold line (OML). The F-35 forward fuselage is

produced at Lockheed Martin Aeronautics in Fort Worth, Texas. The design of the forward

fuselage requires a shim gap between the assembled metallic understructure and the mating inner

mold line (IML) machined composite skins. The forward fuselage assembled understructure and

skins are shown in Figure 1. The designed-in shim gap shown in Figure 2 can vary based on the

assembly tolerances of the understructure.

Figure 1. F-35 Forward fuselage understructure and skins

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Figure 2. F-35 Forward fuselage designed-in shim gap

The current method for shimming the forward fuselage requires the bonding of hard

shims to the flanges around the perimeter of the right-hand and left-hand sides of the structure,

while liquid shim is bonded to the flanges in the middle section shown in Figure 3. The hard

shims are made of composite and are necessary in specific areas for wear and load requirements.

The liquid shim is a Hysol EA9377 product referred to as moldable plastic shim (MPS). Both

the hard and liquid shims are bonded to the assembled forward fuselage understructure thicker

than the profile requirement, and the entire assembly is taken to a large precision milling

machine (PMM) where the surface profile is machined to very tight tolerances to match the

mating skins.

Figure 3. Forward fuselage shimmed surfaces

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The problem with this shimming process is that it is very time consuming and subject to

quality issues. The liquid shimming process itself can consume over 60 manufacturing hours per

aircraft since it is completely manual. Initially, mechanics applied the liquid shim to the

understructure and manually spread it with Popsicle sticks to cover the surface. This method,

shown on the left side of Figure 4, proved difficult to maintain a constant thickness of cured

shim. The process was messy and required extensive rework in many cases. A new method for

controlling the cured thickness of the MPS, shown on the right side of Figure 4, was

implemented during the F-35 system design and development (SDD) phase. This patented

process uses stereolithography overpresses which utilize standoff nubs to control the cured

thickness of the MPS. In this method, the MPS is applied to the overpress, the overpress is

applied to the structure, and the mechanic secures the overpress to the structure with C-clamps

and cleans up the liquid shim squeeze out. The MPS is allowed to cure for eight hours and the

overpresses are removed. The mechanic then back fills the indentations produced by the

thickness control standoffs with additional liquid shim and allows for another eight hour cure

prior to sending the entire structure to the PMM. Often, after machining the shimmed surfaces,

air gaps are exposed and additional rework is required to fill the voids and hand sand the surfaces

to the correct profile.

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Figure 4. Manual applications of liquid shim

A. Manual application without using overpresses

B. Manual application using the overpress method

The overpress method of shim application was not designed for F-35 full rate production

(FRP) which has a goal of one aircraft per day. Rate problems with the current overpress method

include:

• The extensive cost and storage for rate quantities of 40 overpresses and 260 C-clamps

per ship set.

• The cost and time to procure replacement overpresses which often break during their

removal from the structure.

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• The thickness control standoffs, shown in Figure 5, result in a second cure time.

• The MPS surface requires expensive PMM machine time.

• Entrapped air exposed after PMM machining, shown in Figure 5, results in rework

and a third cure time.

• The thick application of MPS and operator dependency results in excessive material

waste.

Figure 5. Problems with overpress method of shim application

This chapter will present the problem statement, objectives, and significance of the study.

Statement of the Problem

The current F-35 forward fuselage shimming method results in excessive span time,

extensive manual labor, extreme material waste, and quality issues which make it impossible to

support a peak production rate of one aircraft a day.

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Purpose of the Study

The purpose of this study was to develop a concept for an efficient, automated F-35

forward fuselage liquid shimming system and to verify the feasibility of specific components of

the system. The deliverables of this study were to:

1. Establish the inefficiencies in the current shimming process and outline an ideal state

process.

2. Document F-35 automated system and shimming requirements.

3. Identify existing automated technologies related to liquid shim, sealant, or adhesive

dispense and other associated shimming tasks.

4. Identify potential system solutions for incorporation into a specification.

5. Determine the feasibility to use non-contact metrology technology to locate the

structure and validate the surface profile before and after shim installation.

6. Identify various material options and release agents for an OML control tool, and

design and fabricate a single piece sub-scale OML control tool which could later be

used to evaluate the tool’s ability to release from the structure after the shim has

cured, tool locating techniques, and OML control tolerances achievable with no

additional processing of the cured shim.

Automated dispense systems are not a new technology; however, compared to the

automotive industry, the tight tolerances, expensive and delicate parts and assemblies, and lower

manufacturing rates of the aerospace industry require special considerations. The automated

shimming system needs to apply liquid shim as well as aid in OML control processes that must

meet stringent tolerance requirements. This study provides Lockheed Martin Aeronautics the

necessary foundation to verify system feasibility and validate system components in order to

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begin specification development for the procurement of an automated shim cell for F-35 forward

fuselage OML control.

Assumptions of the Study

This study builds on existing automated dispense and robotic technology; therefore, the

research assumes technology suppliers will work cooperatively with Lockheed Martin

Aeronautics when examining existing technology and proposing a system to meet the

requirements.

Definition of Terms

F-35: The F-35 Lightning II, or the Joint Strike Fighter, is a state-of-the-art fighter jet currently

in low rate production at the Lockheed Martin Aeronautics final assembly plant in Fort Worth,

Texas. This Department of Defense program is aimed at “defining affordable next generation

strike aircraft weapon systems for the Navy, Air Force, Marines, and our allies” (“The F-35,”

n.d., para. 1).

Coordinate Measuring Machine (CMM): The CMM is “a sophisticated measuring instrument

with a flat polished table and a suspended probe that measures parts in three-dimensional space”

(“Basics,” 2011, para. 3).

Gage Repeatability & Reproducibility (R&R): A gage R&R study measures the sources of

variation in a measurement and determines if the gage is “acceptable for its intended use” (Sloop,

2009, p. 44).

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Inner mold line (IML): For the F-35, IML refers to inner surfaces of parts that are measured

and controlled in order to maintain the outer mold line surfaces.

Metrology: Metrology is “the science of measurement” (“Metrology,” n.d., para. 1).

Outer mold line (OML): For the F-35, the OML refers to the outer surface of the aircraft or the

outer surface of a part or assembly in a specific portion of the fabrication process.

Overpress: The overpresses designed to aid in manual liquid shim application for the F-35

forward fuselage have a surface that mimics the profile of the forward structure (Hestness, 2006).

That surface contains thickness control standoff nubs to provide a constant thickness of cured

shim to be machined. The overpress is removed after the shim has cured and before it is

machined.

Request for information (RFI): The RFI is a process used to gather general information about

the capabilities of potential suppliers, future steps that need to occur, product offerings, and

pricing options. The data is used for further product definition and comparative purposes

(“Request,” n.d.).

Shim: A shim is a material that is used to fill space between things (“Shim,” n.d.).

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Structured improvement activity (SIA): An SIA is tool used by Lockheed Martin to determine

the problems with or inefficiencies in a design or process and document solutions for it. The SIA

is typically a multi-day meeting involving all stakeholders and utilizing other lean six sigma

tools.

System design and development (SDD) phase: During the SDD phase of the F-35, the entire

aircraft system, including the manufacturing process, is developed and tested (“F-35," n.d.).

Limitations of the Study

This study is limited to the investigation of existing technologies. This research built on

those technologies to meet the requirements of the F-35 forward fuselage liquid shimming

process. Budget and time restrictions limit the ability to develop something completely

revolutionary.

Methodology

The remainder of this paper will review previous research related to aerospace fabrication

and assembly challenges as well as present studies supporting the feasibility of addressing these

challenges. This paper summarizes the methods used by this research to create a concept for an

automated liquid shimming system to address the current manual shimming challenges used on

the F-35 forward fuselage. This research completed tasks to address the deliverables of this

project, including automated system concept development, non-contact metrology testing,

release agent pull testing, and OML control tool design. The results and analysis completed by

this research are presented in the following sections. The paper discusses the significance of the

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new shim cell concept and the results of the component feasibility testing as well as suggests

opportunities for further development.

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Chapter II: Literature Review

The focus of this literature review is to summarize topic areas related to aerospace

fabrication and assembly challenges, as well as to present studies supporting the feasibility of

addressing these challenges. The review describes what shimming is and the purpose of

shimming, benefits of automation, various uses for automation in industry, types of metrology,

and studies related to uses of metrology in coordination with automation.

Shimming in the Aerospace Industry

Shimming in the aerospace industry is very common. Components and assemblies are

typically built to much tighter tolerances than other industries because of the functions of the

manufactured parts. Lockheed Martin design engineer, Dan Heap, describes that fabrication of

parts with certain materials, such as composites, also results in unknown surfaces and tolerance

stack-ups that require shims to be designed in to the components. Shims are also used to keep

finished assembly weight to a minimum. The following sections will discuss what shims are and

why they are used.

Shim description

A shim is a material that is used to fill space between things (“Shim,” n.d.). Shims can

be made from a variety of different materials depending on the application. In the aerospace or

automotive industries, shim materials can include metallic laminated shim stock, nonmetallic

laminated shim stock, metallic solid shim stock, composite solid shim stock, and moldable

plastic shim (MPS) (Graydon, 2006). Solid shims are typically bonded to a surface with an

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adhesive, while MPS is a liquid shim that is directly applied to the surface where it cures and

bonds. Shims can either be machined to the proper dimensions prior to bond, or they can be

bonded to the structure and either molded or machined to the correct profile. The surface must

be prepared prior to bond, and shims are usually located with some sort of hard tooling or shop

aids (Graydon, 2006).

Purpose of shims

Shims fulfill many purposes in manufactured products. Shims carry loads, adjust

surfaces to decrease mismatch, provide wear resistance, or ensure a proper fit between mating

parts or adjoining surfaces (“Shim,” n.d.). In aerospace, shims are typically designed into the

manufacturing plan to account for a tolerance stack up in final assembly. A tolerance stack up

analysis can be completed to determine the tolerance value of the whole assembly or a specific

gap of the assembly when the tolerances of each part in the assembly are known. According to

Foster (1994), a tolerance is the total amount that a specific dimension may vary. The tolerance

is the difference between the maximum and minimum dimensions that the part can be accepted.

Every manufactured part has a tolerance associated with it. Those parts outside the tolerance are

usually discarded. Tighter tolerances are more difficult to meet, very expensive, and increase the

number of failed parts. Shims allow for more lenient tolerances. It would be impossible to

produce every part perfectly; no two parts are the same (Morey, 2011). Shims can be employed

to overcome manufacturing uncertainty.

Utilizing proper geometric dimensioning and tolerancing is essential for cost-effective

manufacturing and dependable metrology, assembly, and part operation (Tandler, 2010). If the

final assembled part has very loose tolerances, shims may not be needed to account for the

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individual part variation or the assembly variation. For instance, the assembly of a bookshelf

does not require tight tolerances. The bookshelf only needs to be somewhat level to the eye, but

it would still perform the same function if there were small gaps between the shelves and the

structure walls or even if the shelves were tilted at a small angle. According to Lockheed Martin

applications engineer, Jeff Langevin, aircraft assembly requires extremely tight tolerances, to the

order of thousandths of an inch; therefore, shims must be used to fill gaps resulting from

manufacturing and assembly tolerances.

Industrial Automation Considerations

Automating a process can significantly reduce the amount of time that process takes and

the amount of inconsistency associated with manually performing that process (Hensley, 2008).

Automation is not right for everything; the application must be carefully considered in order to

determine if automating the process is cost-effective. Automation must provide cost savings to

justify the capital investment needed to develop and implement the process. The following

sections will discuss what automation is as well as the benefits and uses for robotic automation.

Automation descriptions

Industry is using more computer-based automation due to the desire for increased

productivity and the delivery of quality products (Fu, Gonzalez, & Lee, 1987). Many automated

manufacturing tasks are completed by hard automation systems designed to perform

predetermined functions. The inflexibility and relatively high cost of these machines have led to

a lot of interest in the use of robots, which are a type of automation capable of performing

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various manufacturing functions in a more flexible working environment and at lower production

costs.

“A robot is a reprogrammable general-purpose manipulator with external sensors that can

perform various assembly tasks” (Fu et al., 1987, p. 1). The key words are reprogrammable and

variety. A robot is a type of automation, but hard automation is not a type of robot because it is

built for a single purpose and rarely adaptable for another job.

An industrial robot is a general-purpose, computer-controlled manipulator consisting of

several rigid links connected in series by revolute or prismatic joints. One end of the

chain is attached to a supporting base, while the other end is free and equipped with a tool

to manipulate objects or perform assembly tasks (Fu et al., 1987, p. 1).

The benefits of robotic automation

Typically, the aerospace industry has steered clear of robots. Before an aircraft part

enters an automated process, it normally requires a lot of manual work. Many automated

machines for the fabrication and assembly of aircraft components are specifically designed for a

single function (Webb, Eastwood, Jayaweera, & Chen, 2005). Unlike the automotive industry,

military fighter aircraft are produced at much lower rates, and tolerance requirements are often

tighter than robotic processes can control. However, for specific process, robots may provide a

solution that is more flexible than a dedicated machine. According to Teresko (2008), robots can

be programmed to perform a variety of tasks, and they are repeatable. Robots are also good at

performing tasks that are redundant or that exist in environments that are dangerous for humans.

The automotive industry has gained a lot of benefits from the integration of robots into various

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manufacturing processes (Teresko, 2008). Robotic automation can help reduce direct labor

costs, free up skilled labor, and increase quality (Hensley, 2008).

Robotic automation for specific manufacturing processes can be economical. The typical

six-axis robot is more affordable than and can be just as effective as a custom-built machine

(Hensley, 2008). Robotic automation is also much simpler to deploy than setting up customized

machines. Robots are flexible for various applications and various work envelopes. In addition,

robots can endure repetitive, time consuming, and tedious tasks. Allowing robots to do these

types of tasks frees up operators to perform other tasks, allowing productivity to increase without

adding additional labor. Robotic automation is not just appropriate for high volumes. With the

use of special software, robots can be programmed offline to avoid expensive setup time in order

to be cost effective for low-volume production (Brown, 2009). Finally, automation can improve

quality metrics (Hensley, 2008). Process flaws are exposed much more quickly in an automated

process because machines do exactly the same thing every time, unlike humans.

Uses of robots

Industrial robots are widely used in manufacturing and assembly tasks including material

handling, spot/arc welding, parts assembly, paint spraying, loading and unloading numerically

controlled machines, space and undersea exploration, prosthetic arm research, and in handling

hazardous materials (Fu et al., 1987). According to Paul Graham, one of the managers at the

Arlington, TX General Motors manufacturing plant, the auto industry employs robots to

assemble major auto body parts, perform welding tasks, apply adhesives and sealants, install

windshields and other components, and check parts. (P. Graham, personal communication, June

27, 2011). These applications can be used in aircraft production with minor adjustments.

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Other industries use robots for packaging and palletizing (Langnau, 2005). Robotic

palletizing is on the rise. Palletizers are large, hard to maintain, expensive, and take up a lot of

floor space. Using a robot with custom end effectors to palletize allows for much more delicate

handling of materials than palletizers and much more efficiency than humans. Robots also allow

for flexibility and minimized changeover and setup time for multiple stacking patterns. Robotic

palletizing requires less area and power consumption and can handle multiple products

simultaneously.

Bombardier Aerospace is gearing up to use robots to help assemble the cockpit and

fuselage of its CSeries aircraft (“Bombardier,” 2011). Because this aircraft is larger than any

Bombardier has ever built, the previous manual assembly methods would be ergonomically

challenging. Using a robot to join the fuselage sections will eliminate many hours of manual

labor including assembly of scaffolding to reach the top of the plane.

Metrology Enhances Automation Capabilities

Various kinds of measurement instruments exist to ensure manufactured parts comply

with engineering design. The correct measurement instrument must be selected for the

appropriate application. Non-contact metrology systems are being used more and more in the

aerospace industry for many inspection applications, especially as tolerances tighten and rate

increases. Research shows that these systems can also be used to enhance fabrication and

assembly processes as well (Jamshidi et al., 2010; Jayaweera & Webb, 2007; Noruk, 2011;

Webb et al., 2005). The following sections will discuss various types of metrology and how it

has been used in coordination with automated systems to improve the system capabilities for

assembly processes.

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Types of metrology

Metrology is “the science of measurement” (“Metrology,” n.d., para. 1). Applied

metrology has to do with the application of measurement science to manufacturing processes to

make sure the appropriate measurement instruments are used in order to ensure the accuracy of

the measurements. There are various types of metrology used in the aerospace industry.

Coordinate measuring machines (CMMs), which can take up a lot of floor space and can

be very expensive, were developed over 60 years ago in order to measure precision military

components (O’Rourke, 2011). The aerospace industry considers these types of touch probe

inspections very accurate; touch probe and manual gauge inspections are used as the baseline

process in most cases. However, the need for inspections with better resolution, faster processes,

and reduced capital costs is always increasing, especially as parts become more complex and

difficult to inspect (O’Rourke, 2011). Because of this, many non-contact metrology systems

have been developed. One example is a laser scanner. Laser scanning allows three-dimensional

data to be collected in order to create a computer aided design (CAD) model of the as-built part

so that it can be compared to the nominal CAD model of the part (O’Rourke, 2011). By using a

laser line to scan the part surface, thousands or even millions of data points can be quickly

collected and processed to create the part geometry.

Laser trackers are also very popular in the aerospace industry (Morey, 2011). A laser

beam produced by the tracker reflects off a spherical mounted retroreflector (SMR). Distance is

calculated by measuring two angles and the length to the SMR. Although most laser trackers are

manually operated, there is a continuing trend toward integrating them into automated systems as

control sensors.

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It is challenging and sometimes impossible with touch probes to measure free-form

surfaces that require a large density of points. Unlike laser trackers, laser radars do not require a

reflector target (Morey, 2011). Laser radars are easily automated because they do not require an

operator to touch the part, and hundreds or thousands of points can be collected per second.

Another system that is useful for free-form part measurement is structured white or blue

light systems (Morey, 2011). These systems use a light source and imaging cameras to calculate

locations in space for various surfaces or part features. With all of these alternate metrology

options, choosing with right one for the application can be a challenge. There are some

restrictions with non-contact measurement devices. It is difficult to collect data on shiny or

translucent surfaces, and large parts require data to be digitally stitched together. Part vibration

during measurement is also a concern.

Metrology and automation for assembly processes

Using robotics to fabricate and assemble large structures that have tight tolerances has

been limited by size and accuracy requirements of the components involved. Variation is a basic

component of the manufacturing process of these structures because of inconsistencies in

materials, tools, factory environments, and human intervention (Jamshidi, Kayani, Iravani,

Maropoulos, & Summers, 2010). Because of the tight tolerances required to fabricate and

assemble these components, simple robotic approaches cannot be used due to the inherent

dimensional variability in the parts. Several case-studies and tests have been performed to help

solve this problem by using non-contact metrology systems in coordination with automated

processes to measure part deformation and misalignment in real time (Jamshidi et al., 2010;

Jayaweera & Webb, 2007; Noruk, 2011; Webb et al., 2005). “Metrology is becoming a major

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contributor to being able to predict, in real time, the automated assembly problems related to the

dimensional variation of parts and assemblies” (Jamshidi et al., 2010, p. 25).

A robot with vision capabilities has the ability to sense specific environmental factors and

respond to those factors appropriately (Fu et al., 1987). The use of vision is motivated by the

continuing need to meet more difficult manufacturing challenges with the use of inexpensive and

less specialized equipment. Vision uses pattern recognition of video signals to find information,

compare that information to a learned image, and then intelligently interpret that information to

perform appropriate actions (Fu et al., 1987; Ardayfio, 1987). Robot vision systems provide the

most basic automated real-time inspection systems; however, they only provide a means for the

robot to respond to programmed and predicted conditions. A vision system does not generate

any new data like other metrology systems.

Laser vision sensing can play an important role in automated systems like the automated

welding process (Noruk, 2011). One way to achieve a flexible, adaptive welding system and

avoid excessive variability in the parts and fixturing is to use laser vision sensors for joint

finding, joint tracking, and automated weld inspection. Laser vision allows an automated

welding system to begin welding if a joint is in tolerance or to prevent welding if it is out of

tolerance. Laser vision sensing can also compensate for a joint that is within tolerance but still

has too much variability for automated welding without vision.

Laser vision has also been investigated by Jayaweera and Webb (2007) for automated

aircraft assembly. For a manual assembly process, individual parts are located with setup holes

that are machined to a very tight tolerance. In order to be able to use an automated system to

assemble aircraft parts to the same tolerances as a tool-assisted manual process, a metrology

system must be used to locate the individual parts throughout the assembly process (Jayaweera &

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Webb, 2007). A side benefit of laser vision is that it provides a quality assurance check

concurrent with assembly. Often, during part manufacturing and assembly, the structures are

deformed from their original machined shape. Because the part geometry and dimensions

change, the metrology system aids in the alignment process by providing feedback to the

automated system about the as-is part geometry and hole location. If installation cannot be

accomplished within tolerances, the part can be rejected automatically. Jayaweera and Webb

(2007) found that automated assembly could be accomplished within the necessary production

tolerances by using a robot in coordination with a laser vision system.

Jamshidi et al. (2010) performed a case study on an aircraft wing to evaluate the adaptive

control enhancement of a robotic system utilizing metrology systems which provided inputs to

the robot controller to compensate for positioning errors. The measurement and scanning data

was used to guide the robot for manufacturing and assembly processes. The researchers used

three different measurement technologies, including a laser tracker, a laser radar, and a handheld

scanner with a tracking camera. The laser tracker was used to evaluate the fixturing and the

effect of surrounding vibration. Both the laser tracker and the laser radar were using during the

assembly process for inspection purposes. The scanner was used to acquire data for shimmed

surfaces. The researchers found that in some cases, the robot positioning could be corrected

using the adaptive control system; however, the system could not account for deviations in

assembly for loading parts. The assembly tolerance stack-ups made it too difficult to properly

load a part. Jamshidi et al. (2010) determined that for automation to work, metrology systems

should be an integral part of the assembly process. This compensates for assembly discrepancies

and required production assembly tolerances, not just the part positioning process.

30


Webb et al. (2005) developed a flexible robotic rapid assembly cell that was capable of

carrying out several different assembly processes on aero-structure sub-assemblies. Whereas

automotive typically has a robot dedicated to each operation as the structure moves along a flow

line, these researchers used a single robot to reduce the cost of the cell. The conventional

manner to perform the assembly tasks, which utilizes a complex fixture and pre-defined robot

programs, would not be able to achieve the required accuracy and repeatability needed for

aerospace components. The researchers developed a control system that used a CAD model of

the assembly to provide an approximate representation. During the assembly process, several

non-contact metrology systems scan the structure to create an as-is model of the components as

operations are completed and prior to the next operation. By doing this, the robot knows exactly

what the assembled structure looks like at that point in time. Because the structure deforms after

certain assembly operations, the robot has no other way to accurately know where to perform the

next operation unless it has the metrology system telling it where to go. This successful robot

cell shows the potential feasibility of combining non-contact metrology and a cell control system

to assemble structures with tight tolerances and dimensional uncertainty.

Conclusion

While this literature review has discussed several areas related to aerospace fabrication

and assembly challenges, there is still much work to be done to fully address issues with creating

such specialized, low rate parts and assemblies. As aerospace technology complexity increases,

so will the manufacturing difficulties associated with producing these complex engineered parts

and assemblies. This research project was completed to specifically address the production

challenges associated with a manual liquid shimming process used for the fabrication of the F-35

31


forward fuselage. Based on the research completed, technology does exist to potentially meet

the challenges associated with aerospace manufacturing, but specialized systems must be

developed to address each unique challenge. This paper presents a concept solution to the span,

labor, waste, and quality issues associated with the current manual F-35 forward fuselage

shimming method. The solution consists of an automated shimming system which incorporates

robotic automation, 3D metrology technology, and special tooling.

32


Chapter III: Shimming Methodology

The current F-35 forward fuselage shimming method results in excessive span time,

extensive manual labor, extreme material waste, and quality issues which make it impossible to

support a peak production rate of one aircraft a day. The purpose of this study was to develop a

concept for an efficient, automated F-35 forward fuselage liquid shimming system and to verify

the feasibility of specific components of the system. The concept included the new process flow

and equipment requirements for the shim cell. This study was significant because it provides

Lockheed Martin Aeronautics the necessary foundation to verify system feasibility and validate

system components in order to begin specification development for the procurement of an

automated shim cell for F-35 forward fuselage OML control.

Concept Development

The first part of the purpose of this project was to create a concept for an automated

shimming system. The deliverables for this task included:

1. Establish the inefficiencies in the current shimming process and outline an ideal state

process.


3. Identify existing automated technologies related to liquid shim, sealant, or adhesive

dispense and other associated tasks.

4. Identify potential system solutions for incorporation into a specification.

The following sections will discuss the process taken to achieve these deliverables.

33


Establish a development team

To begin the process, a development team was constructed, and a re-occurring weekly

meeting was setup. The purpose of the team was to gain a clear understanding of the

requirements for a production-ready shimming system, develop a shim cell concept for

incorporation into a future specification, and complete a cost benefit analysis (CBA) for capital

justification. Present in these meetings were representatives from all stakeholders, including F-

35 forward fuselage manufacturing engineering, industrial engineering, facilities, forward

fuselage production, forward fuselage design engineering, and manufacturing technology.

Baseline the process

In order to accomplish the goals established by this research project, several tasks were

completed to compare the old manual processes to the concept for an automated process. First,

this research work baselined the current manual process. A structured improvement activity

(SIA) was held to establish the inefficiencies in the current process and outline ideas for an ideal

state process. This research documented a detailed flow of the manual process and performed

time studies which included observing the current process and gathering historical span and labor

data from previously completed F-35 aircrafts. This research also completed a risk analysis for

the development of the new process and built a document summarizing the shimming

requirements and the production needs.

Investigate existing technologies in the industry

As a part of this project, an industry investigation was completed to understand and

evaluate existing automated technologies related to liquid shim, sealant, or adhesive dispense as

34


well as additional associated shimming tasks. Potential system suppliers, integrators, and

industry partners were contacted, and information was requested to be provided to Lockheed

Martin regarding any related experience with designing, integrating, or using similar automated

equipment. The documented industry information was used to determine relevant suppliers and

integrators to invite to a request for information (RFI) conference. The RFI conference was held

with these suppliers to educate them on Lockheed’s current shimming process and its associated

challenges and to describe Lockheed’s requirements for an automated shimming process.

Conference attendees were asked to propose their solution to an automated shimming system.

Potential system solutions and key findings were identified by this research project as a result of

the RFI for incorporation into a future specification.

Complete a CBA

Baseline process data, documented needs and requirements, and RFI responses were used

by this research to create a concept for the new automated process. The concept was compared

to the baseline process to complete a CBA to calculate the hours per unit (HPU) savings and to

calculate a return multiple (RM), which is equal to the total savings divided by the total cost. All

costs, including capital investment, labor, material, and development costs were considered for

the new process. The cost difference between the baseline process and the new process resulted

in the savings which was extrapolated over the documented F-35 aircraft delivery schedule. The

CBA results help justify a need to change the current manual shimming process and integrate the

new automated system.

35


Verify System Component Feasibility

The second part of the purpose of this project was to verify the feasibility of specific

components of the automated shimming system. The deliverables for this task included:

1. Determine the feasibility to use non-contact metrology technology to locate the

structure and validate the surface profile before and after shim installation.

2. Identify various material options and release agents for an OML control tool, and

design and fabricate a single piece sub-scale OML control tool which could later be

used to evaluate the tool’s ability to release from the structure after the shim has

cured, tool locating techniques, and OML control tolerances achievable with no

additional processing of the cured shim.

The following sections will discuss the process taken to achieve these deliverables.

Structure location and surface verification

Testing was performed as part of this study to determine the feasibility to use non-contact

metrology to locate the structure within the shim cell and validate the surface profile before and

after shim installation. To do this, several studies were performed on the test article shown in

Figure 6 to measure accuracy and gage repeatability and reproducibility (R&R) for laser radar,

white light, and blue light non-contact metrology systems. The test article was an aluminum

plate with a contoured primed surface, three 0.5” tooling spheres, and surface points on 1” grid.

Surface profile measurements were collected with each measurement system, including a

baseline CMM measurement, and the data was analyzed using SPC XL software and an ANOVA

analysis to determine if the non-contact metrologies can meet the tolerance and R&R

36


requirements needed for the automated system to perform structure location and surface

verification.

Figure 6. Accuracy and gage R&R test article

This research selected vendors to test each type of metrology system. The tests were a

collaborative effort between the suppliers and Lockheed Martin. For each type of metrology

system, three operators collected the surface profile points multiple times. The following

procedure was used to gather data for the accuracy and gage R&R tests:

1. Measure locations of the three tooling spheres.

2. Best fit to the tool.

3. Measure 21 surface points.

4. Provide an Excel output of X, Y, Z surface points.

5. Change operator and repeat the data collection process until all data has been collected.

The first supplier to perform the tests was Nikon Metrology with their Laser Radar

MV330 shown in Figure 7. This piece of metrology is a frequency modulated IR laser radar that

provides a non-contact measurement. Two angles (elevation and azimuth) are measured from a

37


mirror pointing system. The range is measured by laser radar. The 3D Cartesian coordinates are

calculated by a simple mathematical transformation of the measured spherical coordinates.

Figure 7. Nikon Laser Radar MV330

The second supplier to perform gage R&R and accuracy tests was Hexagon Metrology

with their Cognitens WLS400M white light scanner shown in Figure 8. The sensor projects a

random burst pattern on an object and triggers a simultaneous capture of area of interest by its

cameras. The images are correlated using proprietary algorithms to create a 3D point cloud

representation of area. The system has a fast acquisition time that allows for on-airplane work

and hand-held operation.

38


Figure 8. Hexagon Cognitens WLS400M white light scanner

The third supplier to perform gage testing was Shape Fidelity. This supplier used a GOM

product called the ATOS Triple Scan shown in Figure 9. This system uses blue light to project a

2D fringe pattern on 3D objects. High resolution digital cameras record these distorted images,

and software calculates the distance from the cameras. The triple scan feature allows for better

definition for complex shapes.

http://www.cognitens.com/media/datapool/images/CogniTens/Cognitens_wls400m_435x390_rdax_90.jpg

http://www.cognitens.com/media/datapool/images/CogniTens/Cognitens_wls400m_435x390_rdax_90.jpg

39


Figure 9. GOM ATOS Triple Scan

For this research work, data was also collected with each of the three non-contact

metrology systems on an actual production F-35 forward fuselage shown in Figure 10. This data

was used to understand how each system could collect data on a larger scale and how much time

would be required for data collection. The baseline forward fuselage profile data collection

process utilizes a laser tracker which can take over two hours per side to collect data.

40


Figure 10. Production forward fuselage used for large-scale time tests

Shimmed surface profile control feasibility

Pull tests were completed for this research to identify various material options and release

agents for an OML control tool. Composite, aluminum with a machined finish, and aluminum

with a polished finish coupons were fabricated to simulate potential materials for an OML

control tool. Four release agents, including Zyvax HiVis, McLube 1700R, Teflon tape, and

Zyvax Nano Release were applied to each type of coupon, and a thin layer of liquid shim was

applied between the test coupon and a primed aluminum plate to simulate the forward fuselage

understructure. After the coupons cured for at least eight hours, pull test data was collected with

an Instron machine to determine the force required to release the material from the cured shim.

The pull tests were repeated three times in order to verify results. Detailed test instructions are

described in Appendix A. Figure 11 shows the test setup.

41


Figure 11. Release agent testing setup

As part of this project, a sub-scale OML control test tool for the control of the cured shim

profile was designed and fabricated in coordination with a supplier. The test tool incorporates

two alternate methods for locating the tool to the correct OML position to produce the desired

cured shim profile. This sub-scale tool will be tested in the future to determine if the OML

profile of the shimmed surface mating with the IML profile of the composite skin can be

controlled with a tool without any machining or post processing of the cured shim.

Summary

This research has been carried out to solve the existing problems with the manual

shimming process for the F-35 forward fuselage. A team was assembled to gather requirements

for a production-ready automated shimming system, develop a shim cell concept, and complete a

CBA to justify the need for an automated system. This research work completed gage R&R and

accuracy tests to validate if non-contact metrology systems could be used in the shimming

system to meet requirements for structure location and surface profile verification. Tests were

performed as a part of this study to identify various material options and release agents for an

42


OML control tool, and a sub-scale OML control test tool was designed and fabricated to test the

concept at a later date. The methods used and tests performed in this study provided Lockheed

Martin Aeronautics the necessary foundation and a clear direction to begin specification

development for the procurement of an automated shim cell for F-35 forward fuselage OML

control.

43


Chapter IV: Results

Research and current applications show that technology exists to potentially meet the

challenges associated with aerospace manufacturing, but specialized systems must be developed

to address each unique challenge. The current F-35 forward fuselage shimming method does not

support the peak production rate, so the purpose of this study was to develop a concept for an

efficient, automated F-35 forward fuselage liquid shimming system. The methods used to

accomplish each of the deliverables of this study are discussed in Table 1.

Table 1. Summary of deliverables and methods Item # Deliverable Method


Created the requirements for a production-ready shimming system shown in Appendix B.

2.

Identify existing automated technologies.

Completed an industry investigation of automation

suppliers and integrators as well as automotive and aerospace partners to understand and evaluate existing automated and dispense technologies that could be used in an automated shimming system. The supplier selection list is shown in Appendix C.

3.

Identify potential system solutions.

Planned and executed an automated shim cell RFI

conference to get potential concept solutions from suppliers. A summary of the supplier solutions is shown in Appendix D.

4.

Establish the inefficiencies in the current shimming process and outline an ideal state process in order to quantify the potential savings of an automated system.

Completed a baseline flow and total span of the

current shimming process based on time studies and historical data.

Developed a final automated system concept flow with estimated span times based on RFI responses.

Completed a CBA to justify the need for an automated shimming system.

44


5. Conduct testing to verify the feasibility of various components of an automated system.

Performed gage R&R and accuracy tests on three non-contact metrology technologies to determine if systems can be used to locate the structure and validate the surface profile before and after shim installation.

Completed OML control tool release agent pull tests.

Managed subcontract with supplier to design and fabricate a sub-scale OML control test tool for future concept testing.

Baseline of Process

Below is a summary of the baseline process and a flow diagram shown in Figure 12:

Hard shims around the perimeter of the structure

o Composite and aluminum

o Necessary for wear and load requirements

Liquid shim in the middle section

o Hysol EA9377 – moldable plastic shim (MPS)

o Two-part epoxy in 6 oz. Semkits

Shim is bonded to the assembled understructure thicker than the profile requirement

Entire profile is precision machined to match the mating skins

Total span time is 174.78 hours

45


Figure 12. Baseline process flow diagram with span times

Ideal State Process

Figure 13 shows a model of the automated concept shim cell layout.

46


Figure 13. Automated system concept layout

The future automated system developed in this project will include automated transfer

from the forward fuselage Machine Tool Transfer Line into the shimming cell. The robot will

complete operations for structure location, pre-shim surface profile measurement, surface

preparation, shim application, OML control tool placement, edge cleanup, OML control tool

removal, and post-shim surface profile measurement. The system will be equipped with safety

features and an enclosed work cell. The proposed detailed flow for the new process is below and

is summarized with estimated span times in Figure 14:

1. Manually apply solid shims and move forward fuselage to Machine Tool Transfer

Line.

2. Safety system is activated on service isle. Area scanner is used to confirm that safety

area is cleared.

3. Bridge is opened allowing loading station to move loading position.

47


4. Loading station moves to loading position.

5. Machine Tool Transfer Line brings pallet with the fuselage and leaves it the loading

station.

6. Loading station moves pallet with forward fuselage into the robot cell and robot cell

door is closed.

7. Bridge is closed and safety system deactivated.

8. Robot picks probe from the tool rack and locates fuselage position measuring position

of the tooling spheres on the fixture.

9. Robot changes end effector to 3D camera system.

10. Robot performs scanning operation for one side of the fuselage.

11. Robot changes end effector to spindle motor.

12. Robot performs surface preparation operations. Buffing wheels and abrasive disks

are changed when usage time expires.

13. Robot changes end effector to the first dispensing unit.

14. Robot performs dispensing operations and changes dispensing unit automatically to

next one when needed.

15. Robot changes end effector to pick up OML control tool and precisely places it to

squeeze out liquid shim to correct profile.

16. Clamps on tooling activate to hold OML control tool in place.

17. Turntable is turned 180 degrees.

18. Robot performs operation phases 8-16 to the other side.

19. Shim cures for 3 hours.

48


20. Robot picks up end effector to finishing knife and performs finishing operations to

the edges of the shimmed surfaces.


22. Finishing operations are performed on other side.

23. Shim cures for remaining 5 hours.

24. Robot removes OML control tool.

25. Turntable is turned 180 degrees

26. Robot removes OML control tool on other side.

27. Robot changes end effector to 3D camera system.

28. Robot performs scanning operation for one side of the fuselage. Output is the

thickness of the shim.


30. Robot performs scanning operation for other side of the fuselage. Output is the

thickness of the shim.

31. Fuselage is transferred back to Machine Tool Transfer Line.

32. Fuselage moves to precision milling machine to complete machining of hard shims

and drilling operations.

49


Figure 14. Automated system process flow diagram with estimated span times

Table 2 shows a manual process vs. automated process comparison of the span times

associated with the steps necessary to complete shimming operations on the forward fuselage.

50


Table 2. Manual vs. automated process span time comparison Process Step Manual Process Time (Hrs.) Automated Process Time (Hrs.)

Apply hard shims

Use of metrology systems

Complete surface preparation

Apply liquid shim (including cured shim profile/edge control) Cure Repairs PMM machining

34

9.68

3.4

16.9

24

6.8

80

34

1.34

0.5

5.32

8

N/A

76.5

Total span time

% Reduction

174.78

--

125.74

28.1%

CBA Results

As a part of this project, a cost benefit analysis was completed to justify the need for an

automated shimming system. The concept developed by this research project was compared to

the baseline process to calculate the hours per unit (HPU) savings and a return multiple (RM),

which is equal to the total savings divided by the total cost to implement the new system. All

costs, including capital investment, labor, material, and development costs were considered for

the new process. The return multiple for implementing an automated shimming system in 2013

in place of the current manual shimming process is 15.3 with a payback period in 2016. A

summary of the CBA is shown in Table 3.

51


Table 3. Summary of automated shimming system CBA Savings Category F-35 CTOL F-35 STOVL F-35 CV Average

Current HPU (Hrs.) Target HPU (Hrs.)

263.36

199.66

301.36

231.66

307.36

243.66

290.69

224.99

Total HPU savings

per aircraft (Hrs.)

% HPU reduction

per aircraft

63.7

24.2%

69.7

23.1%

63.7

20.7%

65.7

22.7%

Return multiple

Payback period

(year)

--

--

--

--

--

--

Total

15.3

2016

Structure Location and Surface Verification Results

Table 4 shows a summary of the gage R&R results for the three types of non-contact

metrology under evaluation. In order to meet production requirements, the metrology equipment

must have a precision to tolerance ratio of 30% or less. Smaller percentages are better. The goal

is to have a gage R&R of 10%, but up to 30% is acceptable. Detailed test results are shown in

Appendix E.

52


Table 4. Non-contact metrology gage R&R results Metrology System Precision To Tolerance Ratio

Nikon Laser Radar

Cognitens WLS400M

ATOS Triple Scan

55.08%

16.29%

6.45%

Table 5 shows a summary of the accuracy test results for the three types of metrology

under evaluation. In order to be acceptable for production tolerances, the measurement accuracy

must be 0.002” or less.

Table 5. Non-contact metrology accuracy test results Metrology System Measurement Accuracy

Nikon Laser Radar

Cognitens WLS400M

ATOS Triple Scan

0.004”

0.0006”

0.0003”

Based on the test results shown in Tables 4 and 5, both the Cognitens WLS400M and the

ATOS Triple Scan systems are capable of meeting the profile measurement tolerances and the

repeatability and reproducibility requirements for the forward fuselage. Because the ATOS

Triple Scan provided the best results in both categories, this is the metrology system that this

research has selected for the final automated system concept described in this paper.

As a part of this study, each vendor was asked to prove that their system could perform

the profile measurements on a production forward fuselage and document how the system

53


collected the data on this larger scale. During this test, time data was collected with each

metrology system.

The Laser Radar was programmed to measure each point prior to the inspection. All of

the data was gathered in a single setup, so no data stitching was required. For the Cognitens

WLS400M and the ATOS Triple Scan systems, photogrammetry was used prior to the 3D light

scan. The view range of the scanners is limited; therefore, in order to capture large volumes of

data, a stitching process must be used. All three systems were able to capture the necessary data.

The surface points collected for the time test are shown in Figure 15. The results of the

time study are shown in Table 6. All of the metrology systems show a significant time reduction

in data collection compared to the baseline process.

Figure 15. Surface points collected on forward fuselage for time test

Table 6. Metrology system time test results Metrology System Time To Collect Data (Hrs.) % Reduction

Baseline: Laser Tracker

Nikon Laser Radar

Cognitens WLS400M

ATOS Triple Scan

2.42

0.83

0.67

0.75

--

65.7%

72.3%

69.0%

54


Shimmed Surface Profile Control Feasibility Results

Pull tests were completed to identify various material options and release agents for an

OML control tool. Test coupons are shown in Figure 16, and results are shown in Table 7 and

Figure 17.

Figure 16. Release agent pull test coupons

55


Table 7. Release agent pull test results – Tensile stress at max load Release Agent Coupon Material Trial #1 (psi) Trial #2 (psi) Trial #3 (psi)

Nano

Nano

Nano

Teflon

Composite

Machined Aluminum

Polished Aluminum

Composite

2208.77

1194.27

214.97

29.92

1940.79

1476.61

154.48

23.01

373.28

215.28

265.80

36.88

Teflon

Teflon

Machined Aluminum

Polished Aluminum

58.95

N/A*

23.52

31.22

24.86

19.61

1700R

1700R

1700R

Hi Vis

Hi Vis

Composite

Machined Aluminum

Polished Aluminum

Composite

Machined Aluminum

13.98

57.50

57.27

204.13

146.24

73.16

99.35

77.42

249.33

261.19

79.36

97.21

82.89

125.94

231.43

Hi Vis Polished Aluminum 88.00 60.40 148.39

*Not measured because test coupon separated from aluminum bond plate prior to insertion in Instron machine

56


Figure 17. Release agent pull test results

Based on the pull test results, this research determined that Teflon was the best and most

reliable release agent for the OML control tool. The main purpose of the release agent testing

was to determine the best release agent to use in conjunction with the OML control tool. No

release force data was known prior to testing; however, the bonded shim material is rated for

thousands of pounds, so the release forces were expected to be much less once a release agent

was applied. The Nano release and Hi Vis release forces were unacceptable. Teflon provided

the lowest release forces. Surface profile was measured with a profilometer on the Teflon coated

coupons, and the data is shown in Table 8.

57


Table 8. Cured shim surface profile measurements on Teflon pull test coupons Coupon Material Trial #1 (Ra) Trial #2 (Ra) Trial #3 (Ra)

Composite

Machined Aluminum

14

11

26

10

18

13

Polished Aluminum 9 11 7

Based on the results shown in Table 8, this research determined that for the variables

tested, coupon material and surface finish had little effect on the final cured shim surface

roughness. The cured shim surface profile must be 125 Ra or better for production. In the

release agent testing, composite, machined aluminum, and polished aluminum all provided an

extremely good surface finish, therefore all of them were acceptable materials for the OML

control tool. Because of this conclusion, a cost study was performed for this project for the

various material options and surfaces finish combinations. A composite OML control tool would

require an invar cure tool and a trim tool for machining operations, greatly affecting the cost of

the material per square inch. A hand-polished surface more than doubles the cost of aluminum

compared to a machined aluminum surface. The cost summary is shown in Table 9.

Table 9. OML control tool potential material and surface finish cost study summary OML Control Tool Material Cost/in2

Composite

Machined Aluminum (63 Ra)

Polished Aluminum

$304.00

$6.50

$15.50

Based on the cost study and the surface finish results, a machined aluminum material was

selected by this research for the OML control tool.

58


The OML control tool design, shown in Figure 18, incorporates two alternate methods

for locating the tool to the correct position to produce the desired cured shim OML profile. The

first method utilizes the machined hard shim regions at the simulated canopy sill and keel on the

test fixture detailed in Appendix F. The other method utilizes controlled surfaces extending from

the internal tooling. This sub-scale tool will be tested in the future to determine if the OML

profile of the shimmed surface mating with the IML profile of the mating skin can be controlled

with a tool.

Figure 18. OML control tool design

59


Summary

The current manual shimming process is very expensive and time consuming and does

not support a final production rate of one aircraft a day. This research was undertaken to provide

an efficient automated solution to the forward fuselage liquid shimming issues. The results of

the testing conducted for this study are presented in this section.

Based on the literature survey, industry survey results, and based on supplier information,

this research work developed an ideal state process for an automated shimming system. As part

of this study, the baseline process was compared to the automated process to develop the CBA

which shows a 15.3 ratio of total savings to total system implementation costs. Based on the

CBA analysis, an automated liquid shimming system cost is justified.

The metrology gage R&R and accuracy test results completed by this research work

show that the most capable piece of metrology is the GOM ATOS Triple Scan for forward

fuselage structure location and surface verification in the automated shim cell. The testing

performed as part of this research proved that the ATOS scanner can meet the repeatability,

reproducibility, and tolerance requirements for the automated shimming system.

Finally, the release agent tests conducted by this research show that the Teflon has the

lowest release forces and is the best release agent to be used on the OML control tool to control

cured shim liquid profile. Based on the test results, surface finish and OML control tool material

had little effect on the cured shim surface roughness, so the least expensive material under

evaluation, machined aluminum, was chosen for the OML control tool. A sub-scale OML

control tool was designed and fabricated based on the release testing performed in this study. It

is recommended to test the OML control tool at a future date to determine if it can be used to

control the shimmed surface profile within production tolerances.

60


Chapter V: Discussion

In order to develop a concept for an automated F-35 forward fuselage liquid shimming

system that will support a peak production rate of one aircraft a day, this research work targeted

to complete the following important things:

1. Justify a need and a return on investment for an automated shimming system.

2. Determine if efficient non-contact measurement systems could be incorporated into

the system design.

3. Execute testing to develop a design for an OML control tool which can be used to

control cured shim profile.

Automated dispense systems are not a new technology; however, compared to the

automotive industry, the tight tolerances, expensive and delicate parts and assemblies, and lower

manufacturing rates of the aerospace industry require special considerations. The automated

shimming system needs to apply liquid shim as well as aid in OML control processes that must

meet stringent tolerance requirements. This study provided Lockheed Martin Aeronautics the

necessary justification, foundation, and clear direction to begin specification development for the

procurement of an automated shim cell for F-35 forward fuselage OML control.

Significance of the New Automated Shimming System Concept

The concept developed by this research project for an automated shimming system has an

estimated 125.74 span hours, a 28.1% reduction when compared to the current manual process

span. Much of the time is wasted with the current process due to the multiple cure times

associated with filling in voids and completing repairs. The new automated process would

61


provide consistent, repeatable shim application eliminating air voids and provide a method to

control OML profile of the cured shim without machining it, reducing machining time on

expensive precision milling machines. The newly developed concept for an automated system

results in an average of 65.7 labor hour savings per aircraft. The new system also eliminates

quality issues related to shimmed surfaces. Capital costs associated with the automated

shimming system are minimal compared to the return on the investment. This study determined

that the ratio of total system savings to automated system costs is 15.3. The cost benefit analysis

shows that the system will pay for itself in 3 years.

Non-Contact Measurement Systems for Structure Location and Surface Verification

The gage R&R and accuracy tests completed as part of this project for the laser radar,

white light, and blue light systems proved that not all of the systems are repeatable and capable

of locating the forward fuselage structure within the shim cell and verifying the surface profile of

the shimmed surfaces before and after shim application. Only the Cognitens WLS400M and the

ATOS Triple Scan systems are capable of meeting the profile measurement tolerances required

for the forward fuselage and the repeatability and reproducibility requirements. All of the

systems are significantly faster than the current method for surface measurement and capable of

measuring volumes as large as the forward fuselage. Based on the gage R&R and accuracy tests

for the non-contact metrology systems, it is recommended that the GOM ATOS Triple Scan is

the most desirable system for an accurate, efficient, automated measurement system.

62


Release Agent and Shimmed Surface Profile Control

As a part of this study, an OML control tool design was completed based on release tests

which incorporated various release agents on potential OML control tool material and surface

finish combinations. Based on the test results, all the materials tested provided an acceptable

surface finish, so due to the lower costs associated with machined aluminum, the sub-scale OML

control test tool was designed and fabricated with machined aluminum finish. The release agent,

Teflon, provided the lowest release forces and will be used as the release agent for the OML

control tool tests.

Conclusions

The current manual F-35 forward fuselage shimming process is not acceptable for a peak

production rate of one aircraft per day. The purpose of this study was to create a concept for an

automated liquid shimming system which would address the manual process issues of excessive

span, labor, and waste. Based on the literature survey and supplier information this research

determined that the capability exists to automate this very specialized, intricate, tight tolerance

process with the use of non-contact metrology and special tooling designed specifically for this

application.

The CBA completed as a result of this study compared the current manual shimming

process to the automated system concept developed by this research project. The return on

investment calculated provided a return multiple of 15.3, which justifies a need for an automated

shimming system.

Three non-contact measurement systems were tested as a part of this project for

repeatability, reproducibility, and accuracy to determine if they could be incorporated into the

63


system design to locate the forward fuselage structure in the shim cell and measure the shimmed

surfaces before and after shim application. This research found that although all three systems

were significantly faster at data collection than the baseline laser tracker method, only the white

light and blue light systems were able to meet R&R and measurement tolerance requirements.

The automated shimming concept developed by this research provided an OML control

tool to control the cured shim surface profile. This type of special tooling has never been used

for controlling cured shim profile at this large of scale. In order to design an OML control test

tool, this research executed release agent testing to determine the best release agent, surface

finish, and tool material for an OML control tool. The release agent, Teflon, provided the lowest

release forces with no dependency on surface finish or test coupon material.

Recommendations

Based on the conclusions of this study, this research recommends that Lockheed Martin

Aeronautics pursue the procurement of an automated shimming system for the F-35 forward

fuselage. Further testing is recommended using the OML control tool to determine how

repeatable it is at providing a cured shim surface profile within production tolerances. Alternate

non-contact metrology system, such as laser scanners, could also be evaluated as potential

metrology solutions. Overall production system specifications should be developed based on the

concept described in this paper.

64


References

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Trademark Office.

65


Jamshidi, J., Kayani, A., Iravani, P., Maropoulos, P. G., & Summers, M. D. (2010).

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Management, 60(2), 39-41.

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0939450753529744%3Av0qd01-tdlq&cof=FORID%3A9&ie=UTF-

8&q=metrology&sa=Search#922.

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Engineering, 146(3), 53-65.

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The Industrial Robot, 32(5), 383-387.

67


Appendix A: Detailed Release Agent Test Instructions

Obtain liquid shim and let it warm to room temperature prior to continuing with prep instructions

Test Sample Preparation

• Wipe surface with clean cloth moistened with approved solvent

• Immediately wipe surface dry with approved cloth

• Let surface dry for a minimum of 15 minutes prior to release application

• Apply release agent and allow to dry 15 minutes

• Apply a minimum of 2 additional coats with a minimum 15 dry time between (Teflon

tape requires only one application and no “dry time”)

– Allow minimum 15 minutes after final coat before next operation

– If applying tape, ensure minimal overlap of strips while maintaining full coverage

of test piece

• Write on top of each test piece the material type, release method, and test number

Base Plate Setup

• Obtain primed base plates, cut in 12” x 3” x 0.25” strips

– Should be able to hold minimum of 3 test pieces each

• Prepare primed surface

– Mask any surrounding areas that may require subsequent painting, sealing, or

bonding

– Clean surface

– Scuff sand primer with Scotchbrite to break surface glaze

– Immediately wipe all surfaces with a clean dry cloth and repeat cleaning

68


– Shim should be applied within 4 hours of cleaning and prepping

• Obtain Teflon tape and apply to fixture

– Should cover base plate surface longitudinally .625” in from EOP on each side,

along with strips covering the ½” space between coupons

MPS Application

• Obtain liquid shim (room temp) and fan tip applicator

• Mix liquid shim per manufacturer’s instructions

• Document “Out-Time” and “Mix-Time” in notebook

• Apply liquid shim directly to prepped (primed side) of base plate

• Carefully spread liquid shim with popsicle stick in thin, consistent layer to avoid air

bubbles

Test Sample Application

• Lay 1.5” x 3” coupon directly on liquid shim, released side down, longitudinally aligned

with base plate

• Try to place correctly the first time to eliminate sliding of test piece in MPS

• Place next coupon on base plate approximately 1” from previous coupon

• Press coupons firmly to base plate, ensuring squeeze-out on all sides

• Wipe excess MPS from sides of coupon

• Once all coupons are on base plate, clamp in place with slide-clamps (do NOT use C-

Clamps since the twist and will move coupon)

• Clamp just tight enough to hold coupon in place

• Document time of completion in notebook and on test fixture

69


Cure Time

• Let liquid shim cure 3 hrs, undisturbed, then carefully remove excess squeeze out with a

blade

• Let liquid shim cure an additional 21 hrs, undisturbed

Post Attachment (for connection to Instrom machine)

• Clean and prep top surface of coupon

• Bond post to center of coupon

• Let cure for 24 hrs

Removal of Test Pieces

• Document time in notebook and on test fixture

• Complete pull tests on Instron machine

• Write force required on the back of the coupon

• Document any visual deformations noticed, quality of MPS surface, and visually inspect

release agent on coupon

• Repeat until all coupons are removed

70


Appendix B: Automated Shimming System Design Requirements

Surface Preparation Requirements

• Mask

• Currently, All Surrounding Areas/Edges Must Be Masked, But The Goal Is To

Eliminate The Masking Step By Having A More Controlled Shim Application.

• Clean

• Substrate Must Be Wiped With Clean Wipe Cloth (AMS 3819, Grade A, Class 1,

2, Or 3) Moistened With LM Proprietary General Purpose Solvent.

• Surface Must Be Immediately Wiped Dry Using Clean, Dry Approved Wipe

Cloth.

• Solvent Must Dry For A Minimum Of 15 Minutes Prior To Proceeding With

Additional Operations.

• Scuff

• Surface Must Be Abraded To Break Surface Glaze Using 120 Grit Or Finer

Aluminum Oxide Abrasive (Scotchbrite Or Equivalent) Abrasive.

• Surfaces Must Be Immediately Wiped With A Clean Dry Cloth.

• Clean

• Repeat Cleaning As Stated Above.

• Note: MPS Must Be Applied Within Four Hours Of Surface Preparation.

71


Shimming Requirements

• Material

• Required Shim Material Is Hysol EA9377 Moldable Plastic Shim (MPS) Bonded

To Primed Aluminum Structure

• MPS Must Be Kept In Original Unopened Closed Containers, Unmixed At A

Temperature Of Less Than 85°F.

• MPS Has A Working Life Of 100 Minutes For A 50 Gram Kit And 60 Minutes

For A 100 Gram Kit.

• Application / Cure

• MPS Cannot Extend Past 0.010” Of The Edge Of Part (EOP). The Preferred

Application Is To Have The Shim Flush With The Mating EOP. Shim Must Cover

The Entire Flange For Fuel Sealing And Corrosion Requirements.

• Mixed Material Shall Be Applied To The Surfaces To Which It Is To Remain

Adhered.

• Apply The MPS To The Surface In A Sufficient Thickness To Assure Squeeze

Out And/Or Constant Contact During Machining Of MPS.

• MPS Squeeze-out Shall Be Removed Prior To Cure.

• MPS Must Cure For A Minimum Of 8 Hour At Room Temperature.

• Air Voids Must Be Less Than 0.10” X 0.10”.

72


Facilities Requirements

• Work Cell

• The System Must Interface With And Include A Transfer Method To And From

The Machine Tool Transfer Line (MTTL).

• The System Must Fit Into A Maximum Of 24’ x 30’ x 16.6’ High Area. A

Smaller Footprint Is Desired.

• The Work Cell Must Include An Area For MPS Storage.

• The Work Cell Must Have Storage Racks For The OML Control Tool(s) (If

Utilized) And Various End Effectors.

• The Work Cell Must Have An Area For OML Control Tool Prep/Clean Up (If

Utilized).

• The Work Cell Must Safely Contain Any Chemicals.

• The Supplier Must Provide EMCS, Task Lighting, Fire Alarm Interfaces.

• The Work Cell Must Include Safety Guarding As Dictated By Process & LMCO

Requirements.

• LMCO Available Facilities

• Chilled Water, Compressed Air, Industrial Waste, De-ionized Water, Vacuum,

Fire Sprinkler, Natural Gas, 480/277-3ø, 208/120-3ø, Telephone.

73


Automated Equipment Requirements

• Shim Application

• The System Must Have An Effective And Safe Way To Apply MPS.

• The System Must Have A Method To Either Eliminate Or Accommodate

For Air Gaps During MPS Dispense.

• The System Must Have A Working Envelope That Can Apply MPS To

The Understructure Surfaces Plus An Additional 25% In Length (Forward

To Aft) To Accommodate For Any Potential Structural Changes To The

Aircraft Or Other Future Uses.

• The System Must Have A Method To Control Cured Shim Profile

• The System Must Have A Method To Eliminate Or Clean-Up Liquid Shim

Squeeze-Out

• The System Must Be Able To Locate The Structure.

• The System Must Measure The Structure Surface Profile Before And After Shim

Application To Possibly Control Shim Dispense Amount, Safely Complete

Surface Preps Steps, Validate Shim Profile, Etc.

• The System Must Be Able To Perform The Surface Preparation Steps Previously

Detailed

• The System Must Be Able To Handle Multiple End Effectors (Specified By The

Supplier) And An OML Control Tool Weighing Up To 350 Lbs (If Utilized).

74


Control System and Interface Requirements

• Controls

• The System Must Have A Method Of Program Shift For Part Alignment And

MPS Application Accommodating Each New Part.

• The System Must Have A Precision Method For Accurate Dispensing Of MPS,

With Feedback For The Operator.

• The System Must Have Data Retention With A Time And Date Stamp.

• The System Must Read And Display The Material Flow Rate.

• Human Machine Interface (HMI)

• The HMI Must Be User Friendly And Have Few Manual Inputs.

• The HMI Must Have Visual Aids And Feedback For MPS Application.

• The HMI Must Provide Feedback For When Additional MPS Is Needed.

75


General System Design Requirements

• The System Must Complete The Liquid Shimming Process In 15 Hrs (Including Cure

Time).

• The System Shall Accommodate MPS Application To A Forward Fuselage Flange Width

From ~0.85”- 4.25”.

• MPS Must Be Applied To Both Sides Of The Forward Fuselage.

• The System Must Apply MPS So That No Major Rework For Air Bubbles/Voids Is

Required.

• The System Must Apply MPS Properly So That It Does Not Result In Flaking/Chipping

If PMM Milling Is Required.

• The System Must Use As Little MPS As Possible Per Ship.

• The Work Completed Must Flow With The Rest Of The Assembly Process.

76


Appendix C: Supplier Selection

The following table lists information about various dispense and automation suppliers gathered from an industry investigation. Company Notes

Aerobotix

*Response provided with related experience *Robotic mold in place coating project has a lot of transferrable technology (white light, rigid mold tool)

ARM Automation *Develop solutions to automation problems that don’t exist off-the-shelf

Burton Industries *Installed the windshield urethane application cells for Nissan

Durr *LM paint robot integrator

Fastems *Response provided with related experience *LM FF MTTL and Load/Unload/Skin Install (LUSI) station manufacturer

FLX Technologies *Involved in initial robotic shim cell concept testing and demonstration

Fori Automation

*Response provided with related experience *Currently working on an R&D project for robotically applying a two-part sealant onto bulkhead coupons and other airplane sections

Jay Enn *Lockheed tooling and development supplier *Lots of auto industry experience

Kuka *Have bid on several automation projects for LM

Par Systems *LM bulkhead marking machine supplier

RAMPF

*Response provided with related experience *Have demonstrated a small-scale robotic dispensing system to dispense material in an exact amount and vary the amount dispensed in an area if needed. *They can scan the structure, determine the thickness required and dispense the correct amount of material. *Currently working with applications in Europe for a variety of Aerospace applications.

SCA Schucker *Recommended by GM as a leader in robotic dispense

SpenTech *Installed the windshield urethane application cells for Nissan

Waltonen Engineering, Inc *Develop solutions to automation problems that don’t exist off-the-shelf

77


Appendix D: Summary of Supplier Responses from RFI Conference

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78


Appendix E: Detailed Gage R&R Results

Nikon Laser Radar Results

MSA ANOVA Method Results

Gage R&R Surface Profile Measurement SPC Analysis For Nikon Laser Radar

· -

• Th,j;age R&R lfasiJ11acreptable Measurem<ml Varlabo~tV iss 08~1 TMSmalle<1ht> l't'rrentage The &'tl~ Tht> ~o I ~To HoVE' A Gi!Sl' ~R'"< 10% les~ Thap J0'41s AcCl'Ptable

79


Cognitens WLS400M Results


Gage R&R Surface Profile Measurement SPC Analysis For Cognitens WLS400M

! ·-

- -

----- -·- ·-·---~--------------~

• The Gage R&R Has Acceptable Measurement Variability (16,29%). The Smaller The Percentage The Better. The Goal Is To Have A Gage R&R < 10%. Less Than 30% Is Acceptable.

80


ATOS Triple Scan Results


Gage R&R Surface Profile Measurement SPC Analysis For ATOS Triple Scan

!-

• The Gage R&R Has Acceptable Measurement Variability (6.45%). The Smaller The Percentage

The Better. The Goal Is To Have A Gage R&R < 10%. Less Than 30% Is Acceptable.

81


Appendix F: OML Control Tool Test Fixture Details

OML control test fixture fuselage test section

Approximate dimensions of OML control tool test fixture

82


OML Surfaces

Controlled Surface Locations

83


Test fixture modifications to accommodate OML control tool testing

84


OML control tool on modified test fixture

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