CDM Manufacture Report

By: Geoffrey Neale & James Gilchrist

1. Moulding and Finishing Methods The customer has specified that Prepreg is the only acceptable form for the raw composite material. Disregarding this design requirement, prepregs are still the preferable fabrication material for the following reasons:

Easier manipulation – natural tackiness provides adhesion to the curved geometry of cores or tooling.

Lesser need for complex layup tools – e.g. automatic filament winding requires larger initial investment in machinery and staff training;

Greater consistency in resin matrix – resin application to dry fibres is done by a machine providing controlled and even amounts of resin per ply;

Prepregs more appropriate for manufacturing larger parts (e.g. wing) – infusion or wet layup of larger components time and labour intensive.

HexPly® M913 [1]aerospace grade prepreg is selected for its good mechanical properties and availability in both unidirectional (UD) and woven (WV) forms in glass and carbon fibre.

Wrap Core cutting is outsourced to an external supplier to reduce initial investment (machinery and staff training) required to own and operate a 3-axis cutter. This machinery ensures consistency and conformity to specifications and provides better geometric tolerances. The foam is cut to the aerofoil shape (NACA 23015) from foam blocks. Post-cutting, the foam is sanded using a disc sander to provide a smooth surface over which to lay the adhesive film and wrap. Adhesive film is manually draped onto the core surface, providing the bond between the skin and the core. Scotch-Weld™ Structural Adhesive Film AF555, designed for co-curing between laminates and core structures, is selected for its excellent shop handling qualities and its ability to be co-cured with composite under high pressure and temperature. Plies are cut by an automated ply cutter then manually draped onto the adhesive film surface in accordance with the Manufacture Instruction Sheet attached. The component is encased in an exterior aluminium mould, onto which a gel coat and wax have been previously applied (Figure 3 in MIS_1). Gel coat is applied to provide a high-quality surface finish and a smooth aerodynamic profile and wax to facilitate easy de-moulding. An exterior mould is used as opposed to bagging to avoid the inevitable surface wrinkles produced from vacuum bagging. The aluminium exterior mould tooling is manufactured from a steel master model. The design requires that the wing has a 50% empty volume interior. During cure, a solid or hollow foam interior may collapse under the pressure of the autoclave. To avoid this, the required foam volume is hollowed out post curing and the pressure of the autoclave is reduced to 5 bar. After curing and de-moulding, any resin overflow is trimmed and the seams are sanded by hand, then polished to provide a smooth and glossy finish.

Spar & Rib

Figure 1: Spar moulding diagram

Prepreg sheets are similarly draped over male glass fibre composite moulds for both the spar (Figure 1) and rib. Glass fibre moulds are preferred for these female components because there is no male backing mould to prevent distortion (spring back) form the mismatch in thermal expansion between a composite component and metal tool. Small surface wrinkles are acceptable (non-aerodynamic surfaces; smoothness not necessary) and can be sanded away during component finishing processes. Release agent is applied to the mould surfaces pre-draping. Both layup assemblies are then vacuum bagged (nylon bagging material) according to manufacturer’s instructions and cured in an autoclave at 7bar, 180°C for ~120 minutes.

2. Inspection, NDT & Quality Assurance

Process Control On-receipt inspection - outsourced material, such as the foam, is sampled and tested on receipt. This verifies material quality and identifies material property trends. The material sample is visually inspected and mechanical, physical and chemical testing is conducted, with levels of scrutiny determined by the confidence in the supplier [2]. Storage and shelf life monitoring - materials are stored according to manufacturer specifications and in accordance with shelf life restrictions.

Environmental control - Humidity, temperature, dust particle count, temperature and excessive air movement are monitored and recorded throughout manufacturing. Production is halted if allowable limits are exceeded. Manufacturing controls - Records are kept which document the material and detail manufacture including both the process and the persons who performed it. Individual items are recorded along with its batch number and its inspection and testing results at each stage of manufacture. Temperature sensors are placed in the component during cure to ensure accurate internal temperatures and hence a full cure.

Foam Core

Post-cutting, the component is compared to a certified template to ensure correct core geometry before assembly. Inconsistent components are either manually modified or scrapped.

TOOLING

Laminate

Bagging materials (breather + nylon bag)

Spar profile

71mm

50mm flange

Final Inspection

Glass fibre wrap layer makes it possible to detect through thickness defects via visual inspection methods because of the translucency of the laminate. Thermography, x-ray and shearography are not totally suitable as these methods are more suited to detecting in-service and environmental damage. The ultrasonic method is able to detect similar manufacturing defects to previously mentioned methods with increased sensitivity and better inspection of the core-laminate bond.

Visual Inspection - Visual examinations inspect for manufacture surface defects such as dry plies, wrinkles, bow waves, mark-off, resin-rich areas, surface porosity and other general surface damage. Possible warpage is also inspected such as wing twist and edge straightness. Simple dimensional checks (e.g. length, width, depth) are conducted using measuring gauges, tapes or templates. Tap testing – Tap testing detects debonding between the core and laminate. Dull sound (as opposed to ringing sound) indicates a region of possible debonding or delamination, where further testing can be carried out. These simple inspection methods help to determine what additional NDT is required and where emphasis during additional testing should be placed.

Table 1: NDT testing method consideration.

Process Advantages Disadvantages

Shearography Fast, accurate

Non-contact

Requires stressing or exciting of component surface

X-ray Real-time imaging Radiation hazard

Thermography

Fast

No radiation

Area testing rather than point testing

Not suitable for thick sections

Ultrasonic Reproducible

Easily presentable

Suitable for thick sections

Not suitable for complex geometry

Requires calibration

Large degree of operator skill needed

Figure 2: Ultrasonic testing double sided approach

Ultrasonic Testing - particularly used to detect composite delamination and debonding between the skin and core, which are easily detected by this method of testing due to its double-sided approach (Figure 2). The deep penetration of the ultrasonic waves makes it suitable for use on the thick sandwich panel structure. The testing method requires access to both sides of the structure for the placement of transducers, which is not infeasible by virtue of the wings dimensions or weight. Component characteristics should allow for immersion testing in a water tank, which produces more accurate results. A breakdown of the advantages and limitations of alternative NDT techniques is given in Table 1. Though this method is more

time consuming than other suitable ultrasonic (water squirter) and NDT methods (x-ray, shearography), the low production rate suggests sufficient time for testing and reworking if necessary. The major disadvantage of this method is the training staff and equipment investment required to employ this method, which increases capital costs, however, by using one comprehensive and reliable method, additional testing is not required.

3. Assembly Interior sections of the foam core are hollowed out post curing to meet the 50% hollow interior design requirement. The core is left fully intact cure, with the exception of two small holes drilled into the tips to allow for fastening to the assembly jig. The laminate is applied to the core as described in the manufacturing instruction sheet.

Core In slightly undersized foam regions, expanding adhesive core splice film (Scotch-Weld™ Core Splice Film AF3090), which provides the bond between the spar and foam, expands between 40% and 90% at a cure temperature of 120°C. This film expands where necessary to fill gaps between the core and the spar. In oversized foam regions, the foam is sanded down to provide a more comfortable fit for the spar. Similar processes are also applicable to uneven foam surfaces under the wrap, switching to the core splice film (Scotch-Weld™ Core Splice Film AF3090) instead of the structural adhesive film (Scotch-Weld™ Structural Adhesive Film AF555), in the case of undersized regions and sanding for oversized regions. The foam is cut to a slightly larger dimensions than specified. This allows for some foam compression during curing in a high-pressure autoclave environment. Post-cure, the ridged skin prevents foam re-expansion to its original size.

Datum Defining a fixed datum position for layup is crucial for ensuring manufacturing consistency in:

Ply placement position;

Cut dimensions;

Dimension measurement etc. Layup ply positioning is determined by laser ply positioning software, which is configured, to the component datum position. Measurements for the positioning of holes and other features are determined from the same material datum assisted by the placement of the wing into an assembly jig. The jig rotates to allow access to both sides during layup.

Holes Boltholes are pre-cut into the lug’s prepreg layers before layup. After prepreg sheets are cut into shape for the lug section, they are fitted to a cutting jig. The lug’s top left corner is used as a datum position for the definition of the hole’s centre point. The measurement is manually made from the corner to the position where the hole should be cut. A cutting die guided by an operator then cuts the hole at the defined position. During layup, the core is fitted into a jig with a dowel at the end where the boltholes should be. The lug layers for both the upper and lower leading edge joints are laid up over this mandrel as to ensure the correct alignment of both the upper and lower lugs. A similar approach is taken for the trailing edge lug attached to the rib.

Wrap, Rail and LE lug integrated layers Wrap, rail and LE lug layers integrated in layup

Refer to LAY/1 in MIS for layup sequence

Refer to Table 2 for layup sequence and Figure 4 for ply drop diagram.

4. Manufacturing Instruction Sheet For the purposes of keeping to the word count limit, the Manufacturing Instruction Sheet (MIS) is simplified and emits the non-crucial parts of the fabrication process e.g. material disposal and re-storage, inspection

techniques, detailed layer by layer instructions, integration of rail, wrap and lug layers. Only the MIS for the Final wrap assembly onto the core is provided, again in an effort to keep to the document word count. Separate MIS should be created for the spar and rib fabrication as well as the removal of the core foam cavities and the inclusion of ribs to the wing assembly.

Document Number: MIS_1 Manufacturing procedure for the wing skin & LE root lug Material Requirements: 2× 50x500mm ±0,90° UDHSCFEP [KIT/1] 2× 600x1500mm ±0,90° WVHSCFEP [KIT/2] 2× 67x1500mm ±0,90° WVEGEP [KIT/3] 8× 667x750mm ±45° WVHSCFEP [KIT/4] 16× 471.6x471.7×667mm triangular ±45° UDHSCFEP [KIT/5] Tooling Requirements: Wing section mould tools WA/1 and WA/2 should be used for this procedure alongside the foam core. Lay-up Template Requirements: Lay-up template LAY/1 should be applied. Latex gloves should be used at all times to avoid contamination of the composite. Heat resistant gloves should be used when removing components from ovens or autoclaves. Process Sequence:

1 Remove prepreg rolls from the freezer and allow defrosting for 24 hours for the material to reach room temperature. Reject any material with moisture formed inside the bag and notify shop managers.

2

Unravel the prepreg roll onto the working surface of the automatic cutter, simultaneously checking

the prepreg surface for defects or damage and the ply cutter for cleanliness. Check ply cutter datum

corresponds to material datum Run the ply cutter program according to KIT/1 - KIT/5.

3

Place cut plies, flat (avoid curling up), into a bag along with silica gel condensation sacs and seal using a hot press. Mark the bag with an identification code/number and a “use by” date. Record batch number; “use by” date and material state. Sheets have a tack life of 10-15 days and an out life of up to 42 days at room temperature. If material exceeds this time frame notify shop managers.

4 Open the bag and remove the prepreg sheets required for manufacture; ensure that surfaces are

free from contamination or defects. Record batch number on manufacture log.

5 Fasten the pre-cut foam into the assembly jig JIG/1.

6 Apply adhesive film to the surfaces of the spar (pre-fabricated) smoothing out with rollers and

spatulas. Insert the spar into the pre-cut slot in the root end of the foam.

7

Remove the resin film from the ply 0 (according to LAY/1 and LUG/1), inspecting for wavy edges,

then drape it onto the mould placing according to the laser ply positioning software for layer 0,

using rollers to help smooth it into place and remove wrinkles or bridging.

8 Debulk at room temperature for 20 minutes at -1bar gauge pressure after applying the layer 0 to the mould. Repeat debulking after the draping of every ply.

9

Remove the backing paper of the layer 0. Check for wrinkles or handling damage. Repeat this ply layering procedure according to LAY/1 using the laser ply positioning software to determine ply placement. Where small rework is necessary, lift the ply edge and re-drape the local region by heating with heat gun and document areas of reworking.

10

In a separate clean room, apply a coating of wax and gel coat to the interior surfaces of the wing

mould. These moulds are cleaned and inspected for damage (scratches etc.) and possible

contamination before the application of these demoulding and finishing products.

11 Remove the wing from the assembly jig and place it into the lower-half mould. Place the upper-half

mould onto the wing assembly and clamp the two moulds together.

12

Place assembly into the autoclave, connect the vacuum hoses, seal the door and set the cure cycle

as per the prepreg manufacturer’s instructions described in CURE/1. However to reduce the

pressure on the foam core during cure, set cure pressure to 5bar rather than 7bar.

13 Post cure, remove the component from the autoclave; carefully remove bagging, demould and de-

flash.

14

Measure the correct profile according to schematic and trim approximately 10mm from root and tip

edges as well as from around the lug edges. Check the shave off amounts before trimming checking

the dimensions with suitable gauges of rulers.

15 Record the component weight in the log and stamp with an identification number for record

keeping.

16 Inspect for defects and demoulding damage using visual, tap and ultrasonic methods.

Manufacturing Record Sheet for: MIS_1 Moulding Number: __________________________________________ Date of Manufacture: ________________________________________ Person Responsible for Manufacture: ___________________________ Signature: _________________________________Date_________________

Action Sign off Comments

1. ________________ WVHSCFEP Batch Number: _________________

2. ________________

3. ________________

4. ________________

5. ________________

6. ________________

7. ________________

8. ________________

9. ________________

10. ________________

11. ________________

12. ________________

13. ________________

14. ________________

15. ________________

16. ________________

17. ________________ Cure Time: ____________________________

18. ________________

19. ________________ Weight: ______________________________

20. ________________ Inspection Result: ______________________

General Comments: _________________________________________________________________________________ Corrective actions required in case of inspection reject: _________________________________________________________________________________ WA/1 & WA/2

Figure 3: Diagram depicting WA/1 and WA/2 moulding tools for wing assembly

Layup Template LAY/ 2 for use with MIS_2 Padding up layers in blue; original integrated wrap/rail layers in red. Cross out each layer as it is laid onto spar Table 2: LAY/1

Orientation WEAVE/UD Material

±45 WEAVE GLASS FIBRE

0,90 WEAVE CARBON FIBRE

0,90 WEAVE CARBON FIBRE

0,90 WEAVE CARBON FIBRE

0,90 WEAVE CARBON FIBRE

0,90 WEAVE CARBON FIBRE

±45 WEAVE CARBON FIBRE

0 UD CARBON FIBRE

0,90 WEAVE GLASS FIBRE

0 UD CARBON FIBRE

±45 WEAVE CARBON FIBRE

0,90 WEAVE CARBON FIBRE

0,90 WEAVE CARBON FIBRE

0,90 WEAVE CARBON FIBRE

0,90 WEAVE CARBON FIBRE

Foam core Upper mould

Lower mould

Laminate

WA/1

WA/2

0,90 WEAVE CARBON FIBRE

±45 WEAVE GLASS FIBRE

Figure 4: LUG/1 - Ply Drop Scheme

Figure 5: CURE/1

Figure 6: KIT/1, KIT/2, KIT/3, KIT/4, and KIT/5 in order

Figure 7: JIG/1

5. Geometric Tolerances & Acceptance Criteria

Defect Allowances

Some defects can be accepted “as is” or the component can be reworked to allow for acceptance. Table 3 list the defect allowances for “as is” or reworking acceptance. Table 3: Defect allowance table.

Stage Defect

Lay-up Poor release agent application; inadequate vacuum level; wrinkling of layup; inadequate bagging; wrong bagging materials

Cure Dwell time too long; cure time too short

Moulding Inspection and Finishing

Demoulding damage; fibre bridging or wrinkling; flanges too wide/thin; dry fibres; resin rich areas

Drill and Machine Undersized holes; holes out of round; countersink too deep; oversized holes; holes tapered; countersink too shallow; countersink eccentric

Paint Shop Wrong material used; drips, runs, orange peel; holes filled or dimensions compromised

Acceptance Criteria

Foam Core

Dents and Scrapes - ≤1mm width and depth acceptable Surface smoothness - smooth to the human touch

Skin, Ribs & Spar (composite components) Surface scratches - Surface resin scratches acceptable once scratches do to cut fibres

Surface depressions or raised regions - small depressions acceptable once NDT shows no sufficient surface-core debonding; raised regions acceptable once NDT shows no sufficient surface-core debonding and no material inclusion.

Delaminations or voids - small delaminations or voids acceptable once sufficiently removed from edges, holes or other regions of stress concentrations and within acceptance criteria for ultrasonic testing.

Warpage – acceptable once fitting possible with light pressure Radius bridging - acceptable once it does not result in the formation of voids. Material inclusions - Not acceptable for any component or in final assembly. Wrinkles - small patches of wrinkles are acceptable on interior facing surfaces as are wrinkles

transferred from release films. Not acceptable on aerodynamic surfaces and requires refinishing. Cure cycle – cure at elevated temperatures as per manufacturer specification (± 5°C); checked with

thermocouple inserted into mould. Debulking – Debulking at -1±0.1bar (gauge pressure) measured with pressure gauge Dimensional – component thickness within ±5% of defined laminate thickness (typical airbus data

[3]);

Assembly

Visual Inspection – No visual material inclusions or noticed twisting checked with levellers. Tap Testing - ringing sound acceptable as it represents good consolidation and lack of pores or core

debonding; dull sound requires further NDT method application to determine component acceptability.

Ultrasonic Testing - Laminate consolidation is characterised by porosity, which increases attenuation during ultrasonic testing. Less than 2% laminate porosity is acceptable. Greater than 4% porosity can result in significant performance reduction from the occurrence of delamination, core debonding and wrinkles.

Dimensions – All dimensions and holes should be in accordance with manufacture drawings, checked with measuring gauges; shimming possible for following gap widths during assembly

o No Shim limit 0.2mm o Liquid Shim limit 0.5mm o Solid Shim limit 1.2mm

6. Production Facility

Figure 8: Factory layout

Figure 8 shows a schematic of the plant design. 50 units (100 wings) are built per year, which is a relatively low production volume; roughly equating to two wings per week. Automated equipment is used throughout the process, not for the purpose of speeding up manufacture but for datum control, quality assurance and consistency and for when tight tolerances are needed. A conveyor type process, like those used in car manufacturing, is avoided, as the production volume does not warrant the need to speed up the process dramatically. Minimising the distance parts have to travel is key to building an efficient manufacturing plant. Figure 8 shows the production path for each main element of the wing; Spar, Foam and Rails + Wrap. Reducing the overall movement of the parts not only increases the efficiency of the plant, it also reduces the likelihood of Foreign Object Damage (FOD) (e.g., from handling tools) occurring as the objects are transported from different areas. The employee entrance is equipped with lockers where workers store items that could cause FOD (e.g. necklaces, wristwatches, etc.). Every area has specially designed tool racks that clearly show when a tool has not been replaced, to encourage the return of tools and thus cleaner and tidier work surfaces which also reduces the probability of FOD. Material storage is located on the north wall of the factory to allow for shipments of materials to be delivered straight to storage, avoiding journeys through the factory. The Prepreg cutting, rail + wrap layup and Spar layup areas will be clean room environments that are controlled to keep temperature, dust level, airflow, etc. inside allowable ranges. The Inspection and NDT area is located in the middle of the plant. This is because parts from many areas need to be inspected and thus to reduce overall movement distance the optimum location for it is in the middle of the plant. It is possible to have separate inspection areas, however, having a centralised area will reduce necessary staff numbers as well as reducing the need for additional inspection equipment which is often very expensive. It also keeps inspection staff together allowing them to easily ask for a second opinion for any problems that may occur.

7. Cost and Mass Contribution

Major Mass and Cost Contributions

The glass fibre layers within the structure provide the greatest mass contribution per unit volume. The wing’s composite components are fabricated from a combination of high strength carbon fibre-reinforced polymer (CFRP) (woven and unidirectional) and glass fibre-reinforced polymer (GFRP) (woven only). The GFRP layers are 20% more dense than the CFRP layers and constitute the majority of the wing’s composite components. Large cost contributions to the assembly are made by the wing’s CFRP components, which are 7- 8 times more expensive than their GFRP counterparts. The lug padding up layers, rail layers, spar and the rib are all fabricated primarily from CFRP. Carbon fibre components account for 37% of the material cost but only 10% of utilized material.

Improving Cost and Mass Reduction Strategy

The selected foam density is based on conservative estimates for structural loading. This density can be reduced to achieve mass savings once the structural requirements of the foam are not compromised. Reducing foam density from 70kg/m3 to 30kg/m3 provides a 24% mass reduction. Provided that these improvements can be achieved, mass savings can be made from material removal and cost savings from both material saving and reduced foam shape complexity. Changing the prepreg system can alter the resin system used while keeping the fibre system consistent with the original. Prepregs which use less dense resins with similar physical properties, can be used to achieve cost and/or mass savings. The case study defined prepregs used in the design process have densities for CFRP and GFRP of 1.5(UD) -1.6 g/cm3 (woven) and 1.85g/cm3 respectively. Using, for example HexPly® M56

prepreg (aerospace grade) reduces those densities to 1.50g/cm3 (UD & woven) and 1.81g/cm3 respectively, reducing component weight marginally. This prepreg system cures out of an autoclave at 180°C between -0.95 and -0.5 bar (gauge pressure) in a vacuum bag. Removing the autoclave from the fabrication process removes the marginally higher costs (electricity, staff training and initial investment) associated with running it.

8. Material Utilisation The foam core cutting is outsourced. To cut PMA Foam to within acceptable tolerances requires an automated 3-axis cutter device as opposed to cheaper hot wire cutting. Dust created by the process increases the likelihood of contamination of other areas of the shop floor, which is not acceptable for clean room environments. To overcome these challenges, foam cutting is outsourced and transported to the factory in aerofoil profile blocks 1.5m long. Post layup and curing, 57.1% of the foam core is hollowed out in order to provide cavity space for fuel and avionics systems, resulting in 42.9% utilization. For the wrap and the rail a 2D bin-packing algorithm is used to optimise the utilization of the cutting pattern in order to reduce waste; initial estimate is made here. For simplicity the lug is not considered his as it only accounts for 1% of the final material usage. For the rail, two 0° UD HSCF plies are used for 500mm along the wing and are then dropped as the rail returns to the original wrap layup (Figure 4) (wrap is integrated with the specific rail plies). The aerofoil perimeter is 677mm and the ply material provided has a width of 600mm, hence two sheets are needed for the wrap. The joins of these sheets must be displaced by 15mm for every new layer in order to prevent crack propagation. Rail 0 UDHSCEP:

Wrap 90, 0 WVEGEP: (next page)

Wrap 45 WVEGEP:

It is assumed that the company produces other components using similar prepregs and that the majority off waste material is utilized in other fabrication processes.

9. Costing The foam cutting is outsourced to an external fabricator, the reasons for which are discussed in the Material Utilisation section of this report. The costing model applies a bottom up approach to costing bearing in mind that material costs vary between suppliers. The sale price is determined by the cost plus pricing method, adding a 30% mark up to the cost price. The sale price per wing is £1318.20 and thus the unit price is £2636.40. Assumptions:

Company produces other similar composite based products i.e. initial investment in new generalised machinery (autoclave, automated cutter, etc.) or tools (rollers, spatulas) is not necessary

Labour costs relating to staff not directly associated with the fabrication of the wing are absorbed in the labour considerations of the entire company and as such are not included in the wing costing estimation.

Factory rent, financing, utilities are absorbed in the entire company’s considerations and as such are not included in the wing costing estimation.

The required NDT (ultrasonic) equipment is unique to this product and as such is included in the cost estimation.

Table 4: Product costing analysis table

Cost Type Name of Cost Unit Cost Amount Cost

£/Wing Cost £/Yr

Materials Epoxy Glass x 11 rolls 12/m2 660m2 72.9 7,290

Materials Carbon HS x 1 roll (150mm

width) 63.9/m2 60m2 38.38 3,834

Materials PMA Foam Wing

(Outsourced) Outsourced Outsourced 50 5,000

Materials Auxiliary Materials (wax,

coating, foam sealant, etc.) 10 100 10 10,000

Tools Moulds £300 (Average) 4 One Off 1,200

Specialist Equipment

NDT- Ultrasound Equipment + water bath

£24,000 1 One Off 24,000

Staff Technicians £27500/Yr 2 550 55,000

Staff NDT Ultrasound Training £1000 Week

Course 2 One Off 2,000

End of Process

Costs

Certification, Packaging and Shipping cost

£300/wing 100 300 30,000

Total: £1,021.00 £138,324.00

Sale price @ 30% mark up £1318.20

10. Production Volume Change

One Wing per Year Decreasing the production volume to one wing per year warrants no initial investment in any production equipment specialised to its manufacture. Manufacture can be conducted on another production line for a similar component. An example of when this would happen is if a new prototype were to be developed.

1000 Wings per Year Increasing the production volume correlates to approximately 20 wings per week. To cope with increased production, 2 identical productions lanes will be used, so that if there is a break down in one line (i.e., Autoclave 1), production will still be possible on the other while repairs are made. A key production difference will be the use of Automated Tape Laying (ATL) Machine. This will increase the accuracy, repeatability and quality of the wing layup. Automating the layup process will reduce layup time. ATL is preferred over an automated fibre placement (AFP) because it performs well with simple, single curve geometries and is faster than an AFP machine. Using an automated process should mean that the scrap rate for the process, compared to hand layup, will decrease to approximately 10%. The size of the autoclave will be increased, as the wings will be cured in larger batches to hasten fabrication.

To conduct similar quality assurance methods for 10 times the original production rate may prove cost prohibitive. Quicker alternative forms of NDT e.g. shearography should be used as opposed to lengthy ultrasonic inspection.

11. References

[1] Hexcel, HexPly M91 180ºC (350ºF) curing epoxy matrix Product Data and User Guide.

[2] ELSEVIER, Polymer Composites in the Aerospace Industy, Woodhead Publishing.

[3] AIRBUS, Manufacturing Technologies for Carbon Wing Assembly.