The following article appears in the journal JOM, 52 (3) (2000), pp. 24-28.

Advanced Materials: Featured Overview

Reducing Costs in Aircraft: The Metals Affordability Initiative Consortium

Emerging metallic materials, processing, and manufacturing technologies offer an important opportunity to meet current aircraft-airframe and jet-engine affordability goals, due to their inherent low material costs and excellent producibility characteristics. But to successfully meet systems goals within this new affordability-driven scenario, a consolidation of industry and military-agency development resources and technology-implementation activities is necessary to positively impact the military-aircraft production and sustainment infrastructure. To address this need, a consortium of aircraft and engine manufacturers and key material- and component-supplier companies has been formed to identify critical affordable metal technologies, develop a strategic roadmap for accelerated development and insertion of these technologies, and oversee execution of development activities by integrated industry teams. The goal of the Metals Affordability Initiative is to reduce the cost of metallic components by 50 percent while accelerating the implementation time for these components.

INTRODUCTION

Metallic materials and processing technologies are critical in meeting the near-term affordability objectives of military and commercial aircraft systems. Until recently, system-performance objectives related to range, acceleration, velocity, maneuverability, and low observability were the primary objectives during system-concept development stages of aircraft programs. Achieving these performance goals was often accomplished at the expense of life-cycle cost economy.

The escalation in system costs, despite efficiency improvements in engineering and manufacturing operations at contractor facilities, can be attributed primarily to the increased use of more expensive structural components and assemblies; the trend in aircraft production has been a growing use of high-cost composites and titanium components to maximize weight efficiency (Figures 1a and 1b). Figure 1b highlights where the largest cost factors exist at the system level. Typically, the engine(s) represent 20-25 percent of the acquisition cost of a jet aircraft; the largest cost factor is related to the engineering, fabrication, and assembly of airframe structure. Metal alloys account for 80% of jet-engine components due to the severe operating environment and the need for excellent fabricability to accommodate component complexity within a limited volume. Although the use of organic matrix composites for wing and fuselage skins has been steadily increasing to minimize airframe weight, structural metals still account for at least two-thirds of airframe weight. With the continued widespread use of metallic materials for engine components and for the fabrication of airframe assemblies, applying state-of-the-art metals processing technology and advanced structural design concepts can provide breakthrough cost savings for military aircraft systems.

Figure 1. (a-left) Material usage and (b-right) typicl system cost distribution trends for fighter aircraft.

To meet this goal, a team comprising aircraft and jet-engine manufacturers, aircraft-component suppliers, and material suppliers has been formed to select, consolidate, streamline, and leverage ongoing and future industry activities for affordable metal-technology development. Under the direction of the U.S. Air Force Research Laboratory's (AFRL's) Materials and Manufacturing Directorate, the Metals Affordability Initiative Consortium's (MAIC's) goal is to reduce the cost of metallic components by 50% while accelerating implementation time. The MAIC team-Boeing, Lockheed-Martin Corporation, Pratt & Whitney Aircraft, General Electric Company, Honeywell, Rolls Royce-Allison, Howmet Corporation, Brush-Wellman, Ladish Company, Allegheny-Teledyne, and Carpenter Technologies-has the resources, experience, and coverage of the entire metals-supply chain to successfully develop, demonstrate, and implement metals technologies and manufacturing processes that can provide revolutionary cost savings to military aircraft.

Figure 2. The MAIC roadmap.

The accurate measurement of specific cost reductions associated with changing any given approach to producing airframe structure or jet-engine hardware has been problematic when attempting to prioritize development activities. To address this issue, the MAIC industry team utilized a systematic pairwise assessment method (ExpertChoice^TM software) to prioritize and select metal-technology topics that offer the greatest cost-reduction impact for aircraft and jet engines. Rather than selecting program activities based on individual projected business cases, programs that offer the best combination of rapid implementation, efficient planning, manageable technical risk, effective teaming, and insertion viability are being conducted. The MAIC has developed weighted affordability objectives, identified and ranked the technical challenges related to meeting these objectives, and produced scores for various metal-technologies topics that address the technical challenges. Based on these planning activities, a roadmap was generated to guide the investment of MAIC funding and the selection of affordable metal-technology development projects (Figure 2).

COST IMPACT

A structured development, demonstration, and implementation strategy is necessary for measurable and pervasive cost savings. The MAIC conducted a "top down" approach to determining development paths that provide the framework necessary to ensure maximum payoff from technology tasks that achieve the affordability objectives of the program. The initial step in this approach is determining the key technical challenges in aircraft design and production that most significantly impact system life-cycle costs. The MAIC reviewed traditional materials, design, and manufacturing approaches utilized for aircraft and engine production.

In airframe construction, the center and aft fuselages represent the highest costs on a dollar per pound basis. This is primarily attributed to factors such as high part count and the use of titanium components needed to construct highly-loaded assemblies (e.g., tightly spaced frame assemblies and titanium bulkhead components). Airframe construction has traditionally relied on the built-up mechanical assembly of machined hogouts, sheet metal, and forged/machined components to build aircraft assemblies. This philosophy currently represents the lowest risk approach since there is a historical knowledge base. Design and analysis activities can be segmented to small subassembly levels with individual load cases, and airframe-component manufacturing can be rapid, flexible, and straightforward since part details are relatively simple in geometry. The disadvantage of the current design and manufacturing philosophy is that part count is high, resulting in excessive engineering logistics costs. Also, material efficiency can be poor, component assembly is often problematic due to part distortion and tolerance build-up, and modularity is difficult at the system level. The disadvantage in relying heavily on traditional titanium components is that the costs of manufactured components are increasing due to reduced availability, escalating material costs, and the relative difficulty in machining and forming component geometries. The largest percentage of airframe costs is touch labor; other costs accounted for about 25% of costs, followed by procured hardware and raw materials.

Although no specific jet-engine subsystem stands alone in relative cost inefficiency, a review determined that the nozzles, high-pressure compressor, and high-pressure turbine sections represent the best opportunity to maximize cost benefits resulting from metals-development activities. In simple terms, the escalating cost of purchased parts (e.g. airfoils/cases and forged disks), reduced component-quantity requirements, and a continued increase in performance demands are primary factors contributing to poor cost efficiency. Performance-driven jet-engine design is less reliant on mechanical fastening as compared to airframe construction due to the severe knockdown in component life associated with localized stress concentration and the unique volume and geometrical considerations of turbofan engines. These issues, combined with the high raw-material cost of the alloys needed for severe temperature environments, have already driven manufacturing philosophies toward near-net-shape forging and casting. Materials and process-development activities have included near-net-shape processing improvements, but have primarily focused on alloy development for improved high-temperature properties and weight efficiency. Disadvantages identified with the current approach range from the high costs associated with the extensive list of specialized and limited volume metal alloys and specifications, resulting in an escalation of supplier costs, to an inefficient supplier-prime infrastructure, causing inflated final-component costs.

Figure 3. Operation and support cost distributions from life-cycle costs.

In addition to acquisition-related costs, operation and support (O&S) costs for aircraft in service typically represent nearly half of the overall life-cycle cost of military aircraft (Figure 3). Most of the O&S costs are related to personnel and material used to support scheduled and unscheduled maintenance actions, so reduction in aircraft-support costs through application of advanced metal technologies has been identified as a primary affordability target. The elimination of premature failures in the field, efficient inspection techniques, reduced maintenance actions, and rapid toolless production of spare parts are areas identified as having significant cost impact.

Other critical factors related to cost impact have been identified that are generic to all metal components and assemblies, regardless of specific systems and applications. These factors are related to quality cost, which is often not accounted for during initial cost projections when selecting materials, designs, and manufacturing concepts for aerospace hardware. Examples are the imposition of specific inspection requirements that result in very poor material efficiency (e.g., excess forging stock for sonic inspection), high realization factors due to excessive inspection labor hours, and manufacturing and geometric design approaches that require excessive machining and cause distortion during subsequent manufacturing operations. These critical factors can be resolved by the application of analytical simulation and design tools to support robust component production and advanced inspection techniques that streamline component qualification steps.

Another factor that bears emphasis is the high cost associated with the use of organic matrix composites for high-performance, lightweight components on aircraft systems. The performance gains achieved through the use of these materials has sacrificed affordability. Advanced metallic materials are substitution candidates for composites due to comparable performance characteristics. By maintaining the inherent affordability characteristics of metal, they can provide substantial cost savings to aircraft. Thus, it is imperative to continually improve the efficiencies of manufacturing and maintain and/or increase the yield of emerging advanced metallic materials.

In addition to the key factors that have been identified, the selection of development activities must also take into account the changing nature of the aerospace industry. Production quantities in the military sector are diminishing, and new-generation aircraft acquisitions are rare. As a result, high nonrecurring costs associated with a new material or processing approach can be prohibitive due to undesirable break-even analyses. New metallic materials and processes that can forego high up-front investments during component implementation (e.g., tooling) are necessary. For this reason, a critical enabling factor related to reduced nonrecurring airframe and engine costs is a primary consideration in determining which technologies offer the greatest opportunity for meeting the affordability objectives of this program.

The collected information was used to support the comparison of factors related to aircraft and engine costs and the weighting of technical challenges. The results of studies conducted by the MAIC identified several key technical challenges that have the most significant impact on airframe and engine costs of military aircraft. Scoring the effect that various metal-technology topics have on meeting the identified technical challenges provides a guideline on technologies that are critical to meeting affordability objectives. Using the results of cost-impact studies produced by ExpertChoice, a quantified assessment of high cost-impact metal technologies illustrated in Figure 2 was developed.

INITIAL MAIC PROJECT ACTIVITIES

	SPF/DB Provided Part Reduction 726 Part Details Eliminated 10,000 Fewer Fastners
Figure 4. The use of superplastic forming-diffusion bonding to reduce the fuselage part count in F-15E aft fuselage (blats SPF-DB) showing (a-left) before and (b-right) after SPF-DF.

Some recent initiatives aimed at reducing aircraft weight have also demonstrated the feasibility of incorporating output from the MAIC to achieve affordability goals. For example, the F-15E has implemented a superplastically formed and diffusion-bonded (SPF/DB) Ti-6Al-4V airframe structure as a replacement for built-up assemblies used in earlier models. This initiative has resulted in a dramatic part count reduction and demonstrated the successful use of unitized construction in service (Figure 4). Another historical example of utilizing an advanced metals technology for weight reduction that also addresses a technical challenge related to cost reduction is the incorporation of high-speed machined aluminum components on the F/A-18E/F airframe. This initiative resulted in the elimination of 1,600 part details in the forward fuselage as compared to earlier models. The widespread implementation of structural titanium castings (Figure 5) during the transition from the YF-22 to the F-22 aircraft for applications such as flapperon hinge fittings, aileron hinge fittings, canopy decks, wing side-of-body joints, rudder-hinge fittings, rudder-actuator supports, APU inlet door frames, canted bulkheads, and aileron bay strongbacks, is another example. By conducting such initiatives within the framework of the MAIC, greater resources will be available to effectively resolve technical issues for risk mitigation and more rapidly transition the technology to other systems.

Figure 5. A cast titanium side-of-body for military aircraft.

Under the sponsorship of the AFRL and the Dual Use Science and Technology Office, the MAIC is initiating technical activities based on the output of MAIC cost-impact studies and technology assessments. These activities began in August 1999 and are directed toward the pervasive technical challenges of efficient manufacturing processes, collaborative design and manufacturing, and part-count reduction. The topics selected for immediate development are deemed to have sufficient technical maturity and directly address the selection criteria outlined by the MAIC.

Metal-product technologies that are currently under development can have a dramatic impact on the cost of aircraft components by reducing buy-to-fly material costs and eliminating manufacturing steps. An illustration of how some of these selected process technologies can be applied to aircraft components to meet the affordability objectives outlined by the MAIC is shown in Figure 6. These technologies include the following.

• Direct production of high-quality, titanium-alloy slabs using advanced melting techniques will streamline the production of plate product used to manufacture engine and aircraft components, allowing the use of a higher percentage of low-cost meltstock (recycled titanium) and eliminating ingot-breakdown steps.
• Laser forming, a process currently being commercialized by AeroMet, produces titanium components by using localized deposition of alloyed titanium, driven by an electronic-component description, to build up component features on a generic, wrought, titanium workpiece. This process offers an alternative to machined titanium-plate hogouts and forgings that have poor material utilization and high machining costs.
• Vacuum-die casting of titanium components is an emerging process technology that has the potential to shorten casting lead times, improve product quality, and further reduce casting costs. Developing and implementing this advanced casting technique will broaden the application base for castings in critical structural applications and provide widespread cost savings.
• Advanced wrought aluminum-beryllium products possess a unique combination of extremely low-density and high-structural properties. Successful development and demonstration of this class of metals will provide a low-cost, weight-equivalent replacement for organic matrix composites currently used for lightweight structural skins.
• Development of a streamlined processing route for powder-metallurgy superalloy components will have a substantial effect on final product costs. Establishing the acceptability of ultrasonic inspection of pancake forgings will eliminate expensive forging and machining steps.
• Direct production of high-quality powder-metallurgy superalloy billets will eliminate deformation processing steps needed for producing manufactured components. By developing a modified powder-atomization technique, billet quality will be sufficient to allow direct machining of component geometries to provide significant reductions in cost.
• Roll forming turbine-engine components uses novel metal-spinning and shear-forming techniques to produce near-net-shape nickel and titanium geometries. Successful development and implementation of this processing technology will increase material-utilization factors and eliminate costly machining steps.
• Modeling distortion that occurs when machining forged products by quantifying residual stresses that exist and using analytical tools to simulate the elastic response caused by material removal can increase cost efficiency by optimizing forging geometry and machining sequences.
• Metallurgically joining titanium castings can combine the affordability of near-net-shape castings and unitized construction to maximize cost savings. By demonstrating and qualifying the novel approach to producing titanium assemblies, pervasive cost savings for aircraft systems will be achieved.
  

	Low Cost Ti Plate has Strong Cost Impact
	Al-Be Can Reduce Cost and Survive Higher Temps @ Equivalent Weight
	VDC Titanium is Lower Cost than Complex Machined Forging
	Laserforming of Flanges Eliminates Material Waste from Machining Ti Plate
Figure 6. Examples of cost-reduction opportunities by implementing metal-process technologies. (a-upper left) Machined titanium frames, (b-upper right) composite pylon skins, (c-lower left) titanium hinge forgings, and (d-lower right) machined titanium support ribs.

In addition to the systematic approach to selecting affordable technology topics, the MAIC is positioned to ensure that all performance standards are met, and that insertion paths are established to support widespread implementation in supplier facilities and production aircraft programs. Execution of the technical projects will emphasize the use of advanced analytical tools for process optimization and integrated design and manufacturing to ensure maximum cost efficiency. Additional technology topics were selected by the MAIC to increase coverage of the technical challenges that have been identified; these projects are being initated in April under the sponsorship of the Materials and Manufacturing Directorate.

FUTURE MAIC PROJECT ACTIVITIES

As additional resources are identified, the MAIC will continue to launch development activities that provide a foundation for a metals-development infrastructure that addresses the broad spectrum of technical challenges in meeting goals for breakthrough system affordability. The MAIC consortium has established the Executive Steering Committee, composed of high-level managers from each of the member companies, to define how the consortium will operate and to identify and distribute the resources necessary for supporting technical activities. The Technical Oversight Committee, composed of managers from the member companies, has also been established to identify the primary cost drivers, develop the metals-development infrastructure plan, and select and oversee metal-development activities. The selected projects will be led by Activity Integrated Product Teams that will consist of companies ranging from the supply chain through system integrators.

Figure 7. The MAIC management structure.

The management approach for the MAIC is illustrated in Figure 7. Although the development of the Metals Affordability Initiative has been the result of the efforts of the 11 charter company members working with the AFRL Materials and Manufacturing Directorate, the membership of the MAIC may be broadened. The AFRL Materials and Manufacturing Directorate will manage the size and composition of the MAIC. Further, it will be required that resource flow be established such that interested companies not part of the MAIC can also participate; this is most easily accomplished by teaming with an MAIC member on individual projects and programs.

Project selection and initiation will be based on a project's criticality in addressing high-cost-impact needs for a responsive metals-development industry infrastructure. The MAIC has adopted a task/gate process that will maximize progress and allow go/no-go decisions. This is a risk-minimization plan based on business decision-making methods used by industries that make significant investments in technology. The plan will structure all MAIC projects in a task-gate process in which the selection, development, and implementation process are divided into tasks that represent a step-wise progression of development and gate reviews at critical points to assess plan progress, test the proposed economics, and approve continuation into the next task. This process is schematically summarized in Figure 8. There are five gates, from Task 1 (concept) to Task 6 (full production). The gate reviews are designed to allow the process owners, customers, and Technical Oversight Committee members to assess the technical progress and economic benefit of a project. The gates are the primary cost-control mechanism for the management of the program.

Figure 8. The task-gate approach to project development.

CONCLUSIONS

It is the belief of the MAIC that the timing for revitalizing the metals-development infrastructure is excellent due to the overwhelming need to address affordability needs in the military-aircraft industry. The coordination of the entire metal-product-supplier chain has been accomplished, and the potential for reviving and elevating the opportunity for dramatic and widespread change within the aerospace metals-development community can now be realized. As the momentum of the MAIC grows, it is anticipated that the investment of industry and government resources will increase, and the resulting high-level improvement in aircraft-system affordability will be realized through efficient development and application of advanced metals technologies.

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Rick Martin is manager of metallic processes development at Boeing-Phantom Works. Daniel Evans is metals technology development leader with the Air Force Research Laboratory-Materials and Manufacturing Directorate.

For more information, contact R. Martin, Boeing-Phantom Works, MC 276-1240, P.O. Box 516, St. Louis, Missouri 63166; (314) 233-0258; fax (314) 234-5410; e-mail ricky.l.martin@boeing.com.