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Aircraft Manufacturing and Assembly 51.2 Automated Part Fabrication Systems: Examples 895

goes to the ﬂight ramp for ﬁnal customer acceptance

checks and delivery.

Aircraft manufacturing techniques are well devel-

oped fabrication and assembly processes that follow

a deﬁned sequence, and process parameters for manual

and mechanized/automated manufacturing are precisely

controlled. Process steps are inspected and documented

to meet the established Federal Aviation Administra-

tion quality requirements, ensuring reliable functions

of components, structures, and systems, which result in

dependable aircraft performance.

All activities at aircraft factories are organized

around ﬂow of materials, parts, and structures to the

ﬁnal assembly line. In the early stages of aircraft

manufacturing, detail parts are fabricated (involving

machining, heat treatment, stretch forming, superplastic

forming, chemical treatment, composite material layup,

curing, trimming, etc.), followed by part inspection

(x-ray, ultrasonic, etc.). The next manufacturing steps

focus on the assembly of detail parts into subassemblies

and larger structures using both manual assembly tasks

and automated machinery (C-frame, ring riveters, etc.),

and also moving lines for ﬁnal aircraft assembly.

Due to economic pressures and ergonomic neces-

sities, the majority of manual aircraft manufacturing

has been replaced during past decades by mechanized

and/or automated processes and systems, yielding sig-

niﬁcant process and cost saving improvements; for

example, the productivity of machining processes has

generally improved by a factor of ten, with some highly

automated assembly processes enjoying improvements

in excess of a factor of 15.

51.2 Automated Part Fabrication Systems: Examples

Automated aircraft part fabrication involves a variety

of manufacturing techniques and systems, all tailored

to processing speciﬁc materials and part conﬁgura-

tions, ranging from aluminum and titanium alloys to

carbon-ﬁber epoxy materials, using intelligent automa-

tion to produce strong, lightweight parts at afford-

able/competitive costs.

51.2.1 N/C Machining

of Metallic Components

Process Description

Since the advent of metallic airframe construction,

airplane manufacture has been machining intensive,

largely because the starting material forms (i.e., plate,

extrusion, die forging, etc.) were not available in near-

net shapes. To minimize airplane ﬂy-weight and ensure

good fatigue life, most metallic surfaces are machined

to obtain the ﬁnal component conﬁguration and achieve

a speciﬁed surface ﬁnish. An important expression in

the aerospace machining industry is the buy-to-ﬂy ra-

tio, whichindicates the ratio of excess materialremoved

during a given machining operation versus the remain-

ing material that ﬂies away on the airplane. For an

average commercial aircraft N/C-machined part, this

ratio is about 8 :1.

The machining process usually employs a cutter

mounted in a rotating spindle, where the spindle or part

can be moved relative to one another by a numerical

controller (N/C) using servo motors. The spindle revo-

lutions per minute (RPM) may vary from 0 to 40000,

depending on the material, with the largest wing skin

mills employing multiple spindles with power ratings

up to 200 horsepower (HP). N/C machine tools com-

monly used within the aerospace industry are some

of the largest machine tools in the world, with skin

mill bed sizes ranging up to 24 ft wide by 270ft

long [51.4–8].

Wing Skin Mills

The wing skin mill shown in Fig.51.2 is capable of ma-

chining two wing skins simultaneously. The aluminum

plate from which the wing skins are produced is held

down to the skin mill bed using a vacuum. Typically the

aerodynamic outer wing surface, known as the outside

mold line (OML), is machined ﬁrst. Once completed,

the wing skin is ﬂipped over, the vacuum is reapplied,

and machining on the inside mold line (IML)iscom-

pleted. The IML contains pads and other features which

mate to other wing structure components such as wing

ribs and stringers. In addition, the wing skins, which

are thickest near the fuselage, taper down to approxi-

mately 0.25in thick at the outboard wing tip. Thickness

tolerances for these ﬂight critical components are typ-

ically held to ±0.005in Mammoth gantries (weighing

nearly 30 t) carrying two 200HP machining spindles

over a wing skin move with precision, while holding

the necessary tolerances. Face mill cutters up to 1ft in

diameter are employed to quickly cover the vast ex-

panse of the wing skins, generating a large volume of

Part F 51.2

896 Part F Industrial Automation

Fig. 51.2 Cincinnati milacron wing skin mill and wing skin after machining

aluminum chips, which are collected by a vacuum chip

collection system requiring a 100HP motor.

Customized Long-Bed Gantry-Style

Milling Machines

Dedicated long-bed purpose-designed gantry-style

milling machines have been the traditional choice for

machining major wing structural components (i.e.,

stringers, spar chords, and channel vents). These

machines employ multiple high-power (112kW), low-

RPM spindles, each capable of high material removal

rates (MRR). Each wing component (upper chord,

lower chord, stringers, and channel vents) for each

airplane model has a dedicated part holding ﬁxture.

Large-diameter cutters mounted in steep-taper tool

holders experience high cutting forces and bending mo-

Fig. 51.3 Dedicated spar mill gantry with typical cross section and machined part

ments. This technology is still appropriate when high

MRR is required for long extruded parts of adequate

stiffness. These machines have been regarded as the

aerospace machining standard for 50years.

The right side of Fig.51.3 shows a typical 110 ft-

long completed part after machining and a typical cross

section of the extrusion that makes this part. The cross-

sectional area reduction is evident in this illustration.

Approximately 12 kg of material is machined away for

each (1 kg) of ﬂyaway part. When buy-to-ﬂy ratios for

various manufacturing methods are compounded by the

sheer size of commercial airplanes, it becomes obvi-

ous how an airframe manufacturer can produce over

35million pounds (16 Gg) of aluminum chips annually.

This is roughly equivalent to the airframe weight of 100

Boeing 747 aircraft.

Part F 51.2

Aircraft Manufacturing and Assembly 51.2 Automated Part Fabrication Systems: Examples 897

High-Performance Machining

As future airframe designs are considered, more em-

phasis will be placed on component producibility and

manufacturing costs. Traditional built-up assemblies

are being replaced by monolithic designs. Contrary to

popular belief, the value for the airframe producer to

utilize high-speed machining techniques does not lie

solely in reduced machining cycle times. Economies

of scale are gained not by machining cycle time re-

duction alone, but by conversion of multiple-piece

assemblies to monolithic components. This ensures

a more accurate ﬁnal part and the elimination of assem-

bly tooling, labor, equipment, and facilities previously

required by built-up designs. High-performance ma-

chining provides designers a manufacturing process to

produce thin-wall monolithic parts quickly with min-

imal distortion.

However, monolithic designs are placing new bur-

dens on high-performance machining technology. Such

designs often require more material be removed dur-

ing the machining process than previously required

for built-up or assembled sheet metal components.

It is difﬁcult to use extrusions or die forgings for

monolithic airplane components that are long with

signiﬁcant cross-sectional changes. Components up to

110ft (35 m) with a tapering cross-section must either

be produced from multiple die forgings that are joined

or machined from plate stock (if they are designed

as a monolithic part). This requires removing large

amounts of material, as depicted in Fig.51.3. Increased

buy-to-ﬂy ratios will necessitate that more emphasis

be placed on maximizing material removal rates in the

future.

Technical data

• Stretch forming of large contoured fuselage skins

• Machine size: L = 20m; W = 4m; H = 3m

• Sheet size max. t = 6mm; W = 2.5m; L = 12m

• Articulating jaws stretch force = 1500 tons

• Articulating jaws min. radius: longitudinal axis = 10m

• Articulating jaws min. radius: transverse axis = 2m

• Stretch die table max force = 1000 tons

• CNC controller

• All machine motions can be actuated manually or

controlled by program

Fig. 51.4 Stretch-forming machine for skins

51.2.2 Stretch Forming Machine

for Aluminum Skins

Machine Description

The machine depicted in Fig.51.4 is capable of stretch-

forming large contoured fuselage skins. The major

machine components are:

1. A die table for supporting and moving stretch form

dies (dies contain the conﬁguration of the ﬁnal skin

and are placed on the table) vertically during the

stretch forming process.

2. Two articulating jaws (one on each side of the

table), consisting of multiple jaw segments, en-

abling articulation of each jaw around longitudinal

and transversal axis to accommodate the contoured

skin geometry. Jaw segments have built-in hydraulic

clamps which ﬁrmly clamp the metallic sheets prior

to the stretch-forming process. During the forming

process each jaw moves longitudinally away from

the die table.

3. A computerized numerical control (CNC)ma-

chine controller, which executes stretch-forming

programs by activating/moving machine compo-

nents [51.1–3].

Heat-Treat and Stretch-Forming Processes

Common structural materials used for fuselage skins,

fuselage frames, and stringers are the high-performance

aluminum alloys, namely the2000series and 7000series

aluminum alloys (i.e., 2024, 7075). Both of these alu-

minum alloys are heat-treatable for strength, toughness,

and corrosion resistance. To achieve high strength,

Part F 51.2

898 Part F Industrial Automation

the 2024 alloy, commonly used for fuselage skins, is

heat-treated in furnaces up to 496

◦

C. A quenching

process from these elevated temperatures dissolves the

alloy constituents (i. e., such as copper) in a solid state

in the solid aluminum alloy. After quenching, room-

temperature aging occurs, causing copper constituents

to precipitate along the grain boundaries and along slip

planes of the alloy. This action distorts the crystal lat-

tice interferes with any smooth slip process, resulting

in increased strength of the material. Immediately af-

ter quenching, the material is relatively soft and can be

formed as in as-quenched (AQ) tempering. However af-

ter about 20min the alloy will start room-temperature

aging and strengthen to the T4temper condition. Room-

temperature aging is also referred to as natural aging.

The ﬁnal T4 strength obtained is about 96h.

Alloy sheets are moved from the quenching sys-

tem/equipment to the stretch-forming machine and laid

up on the stretch die, then both ends of the sheets are

pushed into the jaws and jaw segment clamps are ac-

tivated, clamping onto sheet ends. Jaw segments are

conﬁgured around the longitudinal axis to accommo-

date skin shape, dictated by the stretch die geometry,

and longitudinal forces are applied to the sheet by driv-

ing jaws away from the table. At a certain point, the

table isactivated, moving thestretch die vertically while

the jaws rotate around the transversal axis, pulling the

sheet and forcing it to comply to the stretch die ge-

ometry. After sufﬁcient stretch (plastic deformation) is

achieved, the jaws and table reverse direction, relieving

tension on the sheet once it has attained the desired skin

geometry (and allowing for some spring-back). Ideally,

aluminum skin stretch form dies are built with spring-

back compensation. This is especially important for

large contoured skins. Software for stretch die design

tools are readily available and have proven very useful.

For many decades, the stretch forming process was

(and partially still is) a black art. It requires very ex-

perienced personnel to drive machine elements (table,

jaws) in linear and rotational axes while observing the

skin during stretch-forming operations. Variations in

skin and stretching behavior result from changes in ma-

terial properties during the incubation time and make

it difﬁcult to establish precise process parameters. Af-

ter years of experimentation, and collecting empirical

data (required degree of stretch, etc.), the majority of

skin form operations can be computer controlled or

at least semi-automated, whereby the operator observ-

ing the skin behavior can make slight adjustments to

the degree of stretch to compensate for material prop-

erty variations. Programs can be generated ofﬂine, or

recorded/stored in the teach mode on the machine dur-

ing the stretch-forming process.

51.2.3 Chemical Milling and Trimming

Systems for Aluminum Skins

System Description

Chemical milling is a material removing process using

chemical reaction to dissolve material in certain loca-

tions to produce contoured skins with variation in cross

sections (thickness), accommodating changing design

load conditions along the fuselage. This process in-

volves several subsystems:

1. Galvanic treatment tanks for cleaning and surface

preparation of stretch-formed skins

2. A ﬁve-degree-of-freedom (DOF) robotic system ap-

plying a mask to the skin surface

3. A ﬁve-DOF gantry robotic system and ﬂexible pogo

ﬁxture using a carbon-dioxide laser to scribe the

mask, enabling mask removal in certain skin loca-

tions

4. Chemical milling and galvanic treatment tanks to

perform metal removal (chemical milling)

5. A ﬁve-DOF CNCgantry systemwith a ﬂexible pogo

table to trim and drill skins [51.1–3].

Process Description

Stretch-formed skins have to be cleaned and surface

prepared for the application of the chemical milling

mask. A robotic system under program control auto-

matically applies the mask of deﬁned thickness to both

Fig. 51.5 Skin with scribed mask

Part F 51.2

Aircraft Manufacturing and Assembly 51.2 Automated Part Fabrication Systems: Examples 899

sides of the skin, moving a spray nozzle along opti-

mized patterns to achieve homogeneous mask coverage

thickness and to minimize overspray. After the mask

is sufﬁciently dry, skins are positioned onto the ﬂexi-

ble pogo table, stabilized with suction cups to pogos.

The skin surface pointing to the outside of the air-

craft is positioned onto pogos and does not require any

chemical milling. A gantry robot moves the head with

a carbon-dioxide laser in ﬁve DOFs across the inner

surface of the skin, scribing (cutting) mask along cer-

tain patterns to facilitate peeling off of the mask. After

all patterns are cut (Fig.51.5) skins are processed using

computer-controlled cranes to move skins through the

chemical milling tanks. First, the mask is removed in ar-

eas which will lead to the thinnest skin cross-sections.

Skin is dipped into the chemical milling tank, allowing

NaOH chemical (kept at elevated temperatures) to etch

exposed aluminum surface long enough to achieve the

desired remaining cross section. Etching velocity de-

pends on the NaOH concentration (which is controlled

daily). The etching velocity is used as an input param-

eter to the crane controller, which pulls the skin out

of the tank at a predetermined time automatically. If

measurement of the desired aluminum skin thickness is

veriﬁed, the next mask area is peeled off, and the next

chemical milling process is repeated, until all required

skin areas are processed. The last skin processing step

involves trimming of boundaries and drilling of tool-

ing and determinant assembly holes. These tasks are

accomplished on theﬁve-axis trimming anddrilling ma-

chine (Fig. 51.6). Pogosof the ﬂexiblemachine table are

driven in three linear DOFs to positions dictated by the

skin conﬁguration, and swiveling suction cups on top of

pogos stabilizethe skinduring thetrimming and drilling

operations. Mechanical cutters and chip extraction noz-

Fig. 51.6 CNC trimming and drilling system

zles surrounding the cutter are used. Net trimmed skins

with tooling and determinant assembly holes are now

ready for assembly.

All crane movements in the galvanic process line

and the robotic chemical mask application process are

controlled by a simple program. For mask scribing, the

laser gantry robot, and the trimming/drilling robotic

system, computer-aided design (CAD) skin geome-

try data is imported into the process simulation and

a semi-automated program creation system generates

processing programs.

51.2.4 Superplastic Forming (SPF)

and Superplastic Forming/

Diffusion Bonding (SPF/DB)

Process Description

The SPF process is an elevated-temperature process

where ﬁne-grain material, such as alpha-beta titanium

(Ti-6Al-4V is most common) and certain aluminum

alloys (7475, 2004, and 5083), can be formed into com-

plexshapes usinggas pressure.The processtemperature

depends on the material and alloy being formed: tita-

nium (774–927

◦

C aluminum (454–510

◦

C). SPF parts,

such as those shown in Fig. 51.7, are produced with

typical elongations up to 300% [51.4–8].

The basic principles of the superplastic forming pro-

cess are illustrated in Fig.51.8, typically using heat and

gas pressure to fully form aluminum or titanium part

blanks to match the tool’s contour.

Fig. 51.7 Parts fabricated using super plastic forming

(SPF)

Part F 51.2

900 Part F Industrial Automation

• Elevated temperature

• Superplastic material

• Computer-controlled gas

pressure forms the part

into the cavity at a

constant strain rate

Part

Gas

Fig. 51.8 SPF process principles

The SPF/DB process combines an SPF operation

with a diffusion bonding (DB) process, whereby two or

more sheets of titanium are used to create an integrally

stiffened panel structure. For DB to occur, the titanium

sheets must contact each other in an inert atmosphere

at controlled temperatures and pressures for a speci-

ﬁed time. Several methods can be used to achieve these

conditions. The one shown in Fig.51.9 uses a heated

press and tool pressure to bring the sheets together.

Another method uses gas pressure inside the welded ti-

tanium pack to force the sheets into contact with each

other. Diffusion bonding is a solid-state process and

no melting occurs at the bond line. Once the individ-

ual grains on the surface touch each other, they start

growing across the interface of the two sheets. This pro-

cess continues until the sheets are completely diffusion

bonded to each other and there is no evidence micro-

scopically of there having been two, or more, pieces of

material.

The typical hot (up to 982

◦

C) shuttle table press,

showninFig.51.9, produces SPF and SPF/DB alu-

minum and titanium parts and has computer-controlled

heating, pressure, and gas systems.

Fig. 51.9 Hot press, tool, and SPF part

SPF Beneﬁts.

The beneﬁts of the SPF process are that:

•

It replaces multipiece assemblies with one mono-

lithic component, saving cost, weight, and tool-

ing.

•

It can produce complex geometry and sharp radii.

•

Components contain very little, if any, residual

stress (no spring-back).

•

Less assembly is required (lower cost, lighter

weight, and better dimensional accuracy).

•

Titanium parts are corrosion resistant.

SPF/DB Beneﬁt. The beneﬁt of the SPF/DB process is

that:

•

It reduces assembly, producing an integral structure,

with no fasteners needed to attach inner structure to

outer skin.

51.2.5 Automated Composite Cutting

Systems

Ultrasonic Cutting Machine

Uncured unidirectional and fabric carbon ﬁber, glass

ﬁber, Kevlar, prepreg, and honeycomb materials can be

cut into various shapes or forms (preforms) prior to

hand placement. Automated computer-controlled ultra-

sonic cutting machines precisely perform this task with

minimal waste of these expensive materials due to ad-

vanced computer nesting programs. Up to ten plies of

prepreg can be cut at the same time by a carbide ul-

trasonic knife, which translates up and down at 30000

strokes per second to provide a clean cut.

The prepreg material, which includes a backing

ﬁlm, is pulled off a roll at the end of the cutting ma-

chine bed (Fig.51.10) and is laid down on a rubber

table. A disposable bag is then placed over the prepreg

material and any wrinkles are smoothed out. Vacuum

is turned on in the table, which pulls the bag down

on top of the prepreg material and stabilizes it dur-

ing the cutting operation. The two-axis N/C machine

accurately positions the ultrasonic knife along a prepro-

grammed path to achieve the desired shape. Once the

cutting operation is complete, the vacuum is released

and the vacuum bag is removed. Then the preforms and

scrap material are manually removed from the machine

bed [51.9–15].

Abrasive Water Jet

Cured graphite–epoxy composite structure has very

strong ﬁbers in a softer matrix, so trimming them with

Part F 51.2

Aircraft Manufacturing and Assembly 51.2 Automated Part Fabrication Systems: Examples 901

Technical data

• Typical configuration: flat bed two-axis gantry

• Work zone: up to 10 ft × 100 ft

• Cutting speed: up to 1000 in/min

• Rapid traverse speed: 2000 in/min

• Positioning accuracy: 0.002 in/ft–0.015 in overall

• Knife: 20000–30000 strokes/s

Fig. 51.10 Two-dimensional ultrasonic cutting machine

Insert shows a 60000 psi waterjet

stream cutting a part

Technical data

• Precision multiaxis overhead gantry, 5 up to 11 axes

• Work zone: up to 20 ft × 50 ft × 5 ft

• Cutting speed: up to 250 in/min

• Rapid traverse speed: 1200 in/min

• Positioning accuracy: 0.002 in/ft–0.015 in overall

• Thin stream: 0.020 to 0.050 in dia.

Fig. 51.11 Gantry abrasive water jet with pogostick tooling

conventional machining techniques does not work very

well, since heat and the abrasive nature of compos-

ites tend to wear out cutters rapidly and delaminate

or pull ﬁbers out of the adhesive matrix. Abrasive

water jets are being used extensively to trim, and in

some cases drill, holes in these materials due to the

clean cut, low ﬁber pull out, and little or no de-

lamination. The majority of water-jet systems used in

aerospace are high-pressure (60 000–87000psi) gar-

net or aluminum-oxide grain abrasive water-jet units

(Fig.51.11).

An N/C machine positions a high-pressure abrasive

water jet near the periphery of a composite part that is

held in the correct contour by a series of headers or po-

gos (Fig.51.11). The computer program drives the N/C

machine in a very accurate path at various speeds to cut

off the excess material and provide the ﬁnished edge of

the part.

51.2.6 Automated Tape Layup Machine

Automated tape layup (AT L) is an additive process used

to construct large structures from composite prepreg

tape material. It is primarily used in the aerospace in-

dustry. Machines typically have a ﬁve-axis precision

overhead gantry and an application head that is sus-

pended from a cross rail. The machine motion and

head functions are controlled by a computer with spe-

cialized programming. Prepreg tape is typically more

than 3 in wide, which is suited to ﬂat or mild contours

(Fig.51.12).

The highly specialized head can precisely lay any

number of plies of composite ﬁlament tape, in any

desired orientation, assuring consistent part shape,

thickness, and quality. A typical machine draws from

supply reels, then deposits 3, 6 or 12in tape on ﬂat or

mild-contour layup tools. The layup heads can heat the

Part F 51.2

902 Part F Industrial Automation

Technical data

• Precision five-axis overhead

gantry with multifunction head

• Work zone: up to 20 ft × 100 ft

• Feed rate: up to 1200 in/min

• Traverse speed: 2200 in/min

• Positioning accuracy: 0.002

in/ft–0.015 in/overall

• Layup rate: up to 50 unknown

unit lbs/h

Fig. 51.12 Overhead gantry with work piece below and multifunction tape application head

Technical data

• Precision multiaxis platform with horizontal ram

with multifunction head

• Work zone: up to 20 ft dia./times 75 ft

• Working feed rate: 1200 in/min

• Traverse speed: = 2200 in/min

• Positioning accuracy: 0.002 in/ft–0.015 in/overall

• Layup rate: up to 30 unknown unit lbs/h

Fiber placement

head, mounted to

a roll-bend-roll wrist

Headstock

Tailstock

Refrigerated creel

containing bidirectional

tensioners

Fig. 51.13 Automated ﬁber placement machine

tape prior to laying it down, then compact or compress

the tape after it isplaced on the layup tool. Each layer or

ply of tape can be oriented in a direction that optimizes

the speciﬁc desired part characteristics [51.9–15].

51.2.7 Automated Fiber Placement Machine

Automated ﬁber placement (AFP) machines, such as

that shown in Fig. 51.13, combine two technologies

widely used in industry: automated tape layup (ATL)

and ﬁlament winding (FW). The AFP processisusedby

the aerospace industry to construct large-circumference

and complex structures such as fuselage barrels, ducts,

and pressure vessels from composite prepreg materials.

The Boeing 787 fuselage barrel in Fig.51.14 is a pri-

mary example [51.9–15].

Fig. 51.14 Boeing 787 fuselage barrel

Part F 51.2

Aircraft Manufacturing and Assembly 51.3 Automated Part Inspection Systems: Examples 903

Redirect

roller

Compaction roller

Clamp

Restart rollers

Cutters

Controlled head

Individual tow payout

with controlled tension

Fig. 51.15 Automated tape layup process head

This additive process utilizes relatively narrow

strips of unidirectional composite prepreg tape, com-

monly called tow, which have unidirectional ﬁbers

preimpregnated with a thermoset resin that is later

cured. Central to the process is the ﬁber placement ma-

chine, basically a seven-axis manipulator with a head

(Fig.51.15) thatarrays a group of tows side-by-side into

a continuous band and compacts them against the sur-

face of a concave, convex, contoured combined layup

mandrel. The mandrel is mounted on a trunion system

similar to a lathe, so that it can rotate as the manipula-

tor is placing the tow. AFP combines the advantages of

both ﬁlament winding and automated tape layup. The

raw materials used are tow-preg or slit-tape rolls of

aramid, ﬁbreglass or carbon ﬁber, preimpregnated, typ-

ically with epoxy resin. The width of tow or slit-tape

ranges from 3.2mm to 6.4 mm with thicknesses rang-

ing from 0.13mm to 0.35mm. Typical systems permit

the use of 12, 24, or 32 tows simultaneously and can

lay up on the top of a honeycomb core without degrad-

ing it.

51.3 Automated Part Inspection Systems: Examples

The nondestructive inspection (NDI) of aircraft sys-

tems is performed at the very highest level of sensitivity

because of the criticality of the components. X-ray ra-

diography is the primary method for the inspection of

metallic components, particularly welds in tubes and

ducts of titanium and inconel as well as other aerospace

welded joints [51.1, 2]. Ultrasonic inspection is the

primary method for carbon-ﬁber polymer compos-

ites [51.3,4]. Both x-ray and ultrasonics beneﬁt in terms

of quality and value by the implementation of highly

automated systems. Ultrasonic systems have required

major developments in robotics for inspection rate and

sensitivity requirements for both production [51.5–7]

and for ﬁeld in-service inspection operations [51.8, 9].

Automated x-ray systems have been slower to be im-

plemented, but progress is being made. The future

direction in aircraft part inspection will be automated

interpretation of the NDI data that is currently being

implemented in higher-production-rate industries.

51.3.1 X-ray Inspection Systems

Figure 51.16 shows a diagram and photograph of

a seven-axis CNC system for digital radiography (DR)

of welds at Boeing Commercial Airplanes Fabrication

Division in Auburn, WA, USA. The CNC manipu-

lator, source, and detector are located in a radiation

vault. A complex welded duct is positioned by the CNC

manipulator at a series of preprogrammed locations be-

tween the x-ray source and digital detector, as shown

in the right-hand image. The insert in the lower right

of the ﬁgure shows the DR image from the opera-

tor’s console display. The system consists of ﬁve major

components: the Siemens controller-based CNC ma-

nipulator, the x-ray source, the digital x-ray detector,

the control computer for the CNC manipulator, and the

image display and analysis system. The system require-

ment is for x-ray image quality indicator sensitivity of

1-1T (1% part thickness with visible hole of 1% part

thickness diameter) in the radiographic image for 100%

coverage of the part. To achieve this image quality an

x-ray spot size of 20μm nominal and a magniﬁcation

of 4.5× is used to create images with greater than ten

line-pairs per millimeter resolution and better than 1%

contrast sensitivity. Position of the weld to be inspected

is critical to achieving the required image quality and

this is accomplished by automated control of the CNC

manipulator. Table 51.1 lists the critical characteristics

of the CNC manipulator system. The CNC manipulator

is programmed to begin a testing session by positioning

and imaging a test standard at the same geometric fac-

tors, exposure parameters, and image display settings

as will be used for the part to be inspected. Once the

operator approves the quality of the inspection for the

Part F 51.3

904 Part F Industrial Automation

–B' (CW)

+B' (CCW)

(back) + (fwd)

C' (tilt)

DR image

of weld

Fig. 51.16 Diagram and photograph of robotic digital radiography system (courtesy of Boeing)

standard, inspection of the part begins. Each part con-

ﬁgurationisprogrammedintheCNC manipulator to

allow the weld to be 100% inspected by a series of ra-

diographic views. The CNC manipulator positions the

part according to the program for an exposure at the

ﬁrst location. Following operator review of the result-

ing radiographic image, the CNC manipulator advances

to the next position in the sequence and the process

repeats until the entire part is inspected. Typical inspec-

tion sequences for the CNC manipulator include 20–50

views, taking approximately 10–20min. Images are re-

viewed by automated sequence of viewing parameters

followed by preset adjustments of the image display

for enhancement of areas of interest for detail review.

Enhancement and measurement features include differ-

ent window/level parameters, digital magniﬁcation, and

contrast enhancement [51.16–28].

Table 51.1 Boeing commercial airplane robotic x-ray system characteristics

Characteristic Values

Robot Type Siemens Simotion seven axis

Range of motion Magniﬁcation axis: ≈1.5m, loading axis: 0.3m, rotation axis: 360

◦

tilting table axis: ±60

◦

Positional accuracy 0.5 mm, angular axis <1

◦

Load-carrying ability 70 kg

X-ray source Model FEINFOCUS, Model: FXE-225, 320W (225kV at 1400mA)

Spot size Less than 20 μm

Detector Model Perkin Elmer 1620

Pixel size/bit depth 200μm/16bit

Weld radiography quality Image quality 1-1T, with >10line pairs/mm at 4.5×

Inspection time 10s per view, 30s to 1min per weld

51.3.2 Ultrasonic Inspection Systems

For carbon-ﬁber polymer composite materials includ-

ing laminate, sandwich structure, and bonds, ultrasound

is the principle inspection method and requires highly

automated scanners to keep up with the production rate.

Sophisticated automation is also needed to handle the

complex contoured geometry of the large composite

assemblies. Ultrasonic scanning systems can be con-

structed in a variety of forms from small portable units

to large gantry systems. Ultrasonic inspection is most

commonly performed with some type of water coupling

of the ultrasonic energy between the piezoelectric trans-

ducer and the test part. Methods include: immersion

where the part is submerged in a water bath with the

transducer; bubbler systems, where the transducer rides

on the surface in a shoe that also has a ﬂow of water;

Part F 51.3