52 (3) (2000), pp. 24-28.
TABLE OF CONTENTS
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.
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
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,
Pratt & Whitney Aircraft,
General Electric Company, Honeywell,
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 (ExpertChoiceTM 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).
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.
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
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.
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.
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.
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
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
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
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.
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.Bibliography
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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 email@example.com.
Direct questions about this or any other JOM page to firstname.lastname@example.org.
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