C.Soutis Progress in Aerospace Sciences 41 (2005)143-151 147 aerodynamic performance.This tailoring can involve intensive hand lay-up techniques to those requiring high adopting laminate configurations that allow the cross- capital investment in automatic tape layers (ATLs). coupling of flexure and torsion such that wing twist can Tape-laying machines operating under numerical con- result from bending and vice versa.FE analysis allows trol are currently limited in production applications to this process of aeroelastic tailoring,along with strength flat lay-up and significant effort is being directed by and dynamic stiffness (flutter)requirements to be machine manufacturers at overcoming these problems performed automatically with a minimum of post- associated with laying on contoured surfaces.The width analysis engineering yielding a minimum mass solution. of UD tape applied varies considerably from about Early composite designs were replicas of those that 150mm down to a single tow for complex structures. employed metallic materials,and as a result the high The cost of machinery is high and deposition rates low. material cost and man-hour-intensive laminate produc- In 1988,the first Cincinnati tape layer was installed in tion jeopardised their acceptance.This was compounded the Phantom Works and in 1995 a seven-axis Ingersol by the increase in assembly costs due to initial difficulties fibre placement machine was installed.This gave the of machining and hole production.The cost is directly capability to steer fibres within an envelope of 40ft x proportional to the number of parts in the assembly and, 20ft with a 32-tow capability.An overwing panel had as a consequence,designs and manufacture techniques been manufactured where it was able to steer around had to be modified to integrate parts,thereby reducing cut-outs.Collaboration with DASA on global optimisa- the number of associated fasteners.A number of tion software was to be completed at the end of 1998. avenues are available for reducing the parts count, This software is claimed to have produced a 13%weight amongst which are the use of integrally stiffened saving.Other applications include an engine cowling structures,co-curing or co-bonding of substructures door,ducting with a complex structure,FA18 E/F and onto lift surfaces such as wings and stabilisers and the T45 horizontal stabiliser skins.Its capacity was extended use of honeycomb sandwich panels.Hand lay-up to take a 6-in wide tape and Boeing 777 has been techniques and conventional assembly results in manu- converted from hand lay-up to fibre placed (back to facturing costs 60%higher than the datum and only back then split)spars with a saving $5000 per set.Bell with the progressive introduction of automated lay-up Textron has a 10-axis Ingersol,contoured automatic and advanced assembly techniques composites compete tape laying machine for the B609 skin lay-up,which is with their metallic counterparts.Also,the introduction placing a 6-in wide T300 tape onto an inner mould line of virtual reality and virtual manufacturing will play an Invar tool with pre-installed hat stringers.Fibre place- enormous role in further reducing the overall cost.The ment and filament winding technologies are also being use of virtual reality models in engineering prior to used to manufacture components for the V22 [7]. manufacture to identify potential problems is relatively Once the component is laid-up on,the mould is new but has already demonstrated great potential.Bell enclosed in a flexible bag tailored approximately to the Textron in the USA made a significant use of IT during desired shape and the assembly is enclosed usually in an the product definition phase (for the V22 Osprey Tilt- autoclave,a pressure vessel designed to contain a gas at rotor,Fig.1)to ensure 'right first time'approach. pressures generally up to 1.5 MPa and fitted with a Other manufacturing tools that can reduce produc- means of raising the internal temperature to that tion cost and make composites more attractive are required to cure the resin.The flexible bag is first Virtual Fabrication(creating parts from raw materials), evacuated,thereby removing trapped air and organic Virtual Assembly (creation of assembly from parts), vapours from the composite,after which the chamber is Virtual Factory (evaluation of the shop floor).Virtual pressurised to provide additional consolidation during manufacturing validates the product definition and cure.The process produces structures of low porosity, optimises the product cost;it reduces rework and less than 1%and high mechanical integrity.Large improves learning. autoclaves have been installed in the aircraft industry capable of housing complete wing or tail sections. Alternatively.low-cost non-autoclave processing 3.Manufacture methods [21]can be used like vacuum moulding (VM), RTM,Fig.2,vacuum-assisted RTM (VARTM)and The largest proportion of carbon fibre composites RFI.The vacuum moulding process makes use of used on primary class-one structures is fabricated by atmospheric pressure to consolidate the material while placing layer upon layer of unidirectional (UD)material curing.thereby obviating the need for an autoclave or a to the designer's requirement in terms of ply profile and hydraulic press.The laminate in the form of pre- fibre orientation.On less critical items.woven fabrics impregnated fibres or fabric is placed on a single mould very often replace the prime unidirectional form.A surface and is overlaid by a flexible membrane,which is number of techniques have been developed for the sealed around the edges of the mould by a suitable accurate placement of the material,ranging from labour clamping arrangement.The space between the mouldaerodynamic performance. This tailoring can involve adopting laminate configurations that allow the cross￾coupling of flexure and torsion suchthat wing twist can result from bending and vice versa. FE analysis allows this process of aeroelastic tailoring, along with strength and dynamic stiffness (flutter) requirements to be performed automatically witha minimum of post￾analysis engineering yielding a minimum mass solution. Early composite designs were replicas of those that employed metallic materials, and as a result the high material cost and man-hour-intensive laminate produc￾tion jeopardised their acceptance. This was compounded by the increase in assembly costs due to initial difficulties of machining and hole production. The cost is directly proportional to the number of parts in the assembly and, as a consequence, designs and manufacture techniques had to be modified to integrate parts, thereby reducing the number of associated fasteners. A number of avenues are available for reducing the parts count, amongst which are the use of integrally stiffened structures, co-curing or co-bonding of substructures onto lift surfaces suchas wings and stabilisers and the use of honeycomb sandwich panels. Hand lay-up techniques and conventional assembly results in manu￾facturing costs 60% higher than the datum and only withthe progressive introduction of automated lay-up and advanced assembly techniques composites compete with their metallic counterparts. Also, the introduction of virtual reality and virtual manufacturing will play an enormous role in further reducing the overall cost. The use of virtual reality models in engineering prior to manufacture to identify potential problems is relatively new but has already demonstrated great potential. Bell Textron in the USA made a significant use of IT during the product definition phase (for the V22 Osprey Tilt￾rotor, Fig. 1) to ensure ‘right first time’ approach. Other manufacturing tools that can reduce produc￾tion cost and make composites more attractive are Virtual Fabrication (creating parts from raw materials), Virtual Assembly (creation of assembly from parts), Virtual Factory (evaluation of the shop floor). Virtual manufacturing validates the product definition and optimises the product cost; it reduces rework and improves learning. 3. Manufacture The largest proportion of carbon fibre composites used on primary class-one structures is fabricated by placing layer upon layer of unidirectional (UD) material to the designer’s requirement in terms of ply profile and fibre orientation. On less critical items, woven fabrics very often replace the prime unidirectional form. A number of techniques have been developed for the accurate placement of the material, ranging from labour intensive hand lay-up techniques to those requiring high capital investment in automatic tape layers (ATLs). Tape-laying machines operating under numerical con￾trol are currently limited in production applications to flat lay-up and significant effort is being directed by machine manufacturers at overcoming these problems associated withlaying on contoured surfaces. The width of UD tape applied varies considerably from about 150 mm down to a single tow for complex structures. The cost of machinery is high and deposition rates low. In 1988, the first Cincinnati tape layer was installed in the Phantom Works and in 1995 a seven-axis Ingersol fibre placement machine was installed. This gave the capability to steer fibres within an envelope of 40 ft  20 ft witha 32-tow capability. An overwing panel had been manufactured where it was able to steer around cut-outs. Collaboration withDASA on global optimisa￾tion software was to be completed at the end of 1998. This software is claimed to have produced a 13% weight saving. Other applications include an engine cowling door, ducting witha complex structure, FA18 E/F and T45 horizontal stabiliser skins. Its capacity was extended to take a 6-in wide tape and Boeing 777 has been converted from hand lay-up to fibre placed (back to back then split) spars with a saving $5000 per set. Bell Textron has a 10-axis Ingersol, contoured automatic tape laying machine for the B609 skin lay-up, which is placing a 6-in wide T300 tape onto an inner mould line Invar tool withpre-installed hat stringers. Fibre place￾ment and filament winding technologies are also being used to manufacture components for the V22 [7]. Once the component is laid-up on, the mould is enclosed in a flexible bag tailored approximately to the desired shape and the assembly is enclosed usually in an autoclave, a pressure vessel designed to contain a gas at pressures generally up to 1.5 MPa and fitted witha means of raising the internal temperature to that required to cure the resin. The flexible bag is first evacuated, thereby removing trapped air and organic vapours from the composite, after which the chamber is pressurised to provide additional consolidation during cure. The process produces structures of low porosity, less than 1% and high mechanical integrity. Large autoclaves have been installed in the aircraft industry capable of housing complete wing or tail sections. Alternatively, low-cost non-autoclave processing methods [21] can be used like vacuum moulding (VM), RTM, Fig. 2, vacuum-assisted RTM (VARTM) and RFI. The vacuum moulding process makes use of atmospheric pressure to consolidate the material while curing, thereby obviating the need for an autoclave or a hydraulic press. The laminate in the form of pre￾impregnated fibres or fabric is placed on a single mould surface and is overlaid by a flexible membrane, which is sealed around the edges of the mould by a suitable clamping arrangement. The space between the mould ARTICLE IN PRESS C. Soutis / Progress in Aerospace Sciences 41 (2005) 143–151 147