Reinforced ceramic dies for superplastic forming operations

Ceramic dies have been developed to meet the need for a dimensionally stable tool, which can withstand the temperatures (425 to 950 °C) and high forming pressures (up to 7 MPa) that are required for superplastic forming (SPF), superplastic forming with diffusion bonding (SPF/DB), and hot sizing of metal parts. With the improvements that have been made to strengthen fused silica based ceramics, the performance of ceramic tools is slowly closing in on meeting the same forming complexity as corrosion-resistant steel (CRES) dies can achieve. Boeing has successfully superplastically formed jet engine wide chord fan blades using ceramic dies, and many production aircraft parts are being built with Boeing’s patented ceramic die technology. This paper was presented at the International Symposium on Superplasticity and Superplastic Forming, sponsored by the Manufacturing Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle WA. The symposium was organized by Daniel G. Sanders, The Boeing Company.     

Examination of superplastic forming combined with diffusion bonding for titanium: Perspective from experience

Superplastic forming (SPF) combined with diffusion bonding (DB) has been used successfully for the fabrication of titanium aerospace hardware. Many of these applications have been for military aircraft, whereby a complex built-up structure has been replaced with monolithic parts. Several methods for applying the two- and four-sheet titanium SPF/DB processes have been devised, including the welding of sheets prior to forming and the use of silk-screened stop-off (yttria) to prevent bonding where it is undesirable. Very little progress has been made in the past few years toward understanding and modeling the SPF/DB process using constitutive equations and data by laboratory testing. Concerns that engineers face in designing for fatigue life, acceptable design loads, and damage tolerance are currently being studied, but the database is very limited. This is a summary of past work found in the literature and forms the foundation for additional research. This paper was presented at the International Symposium on Superplasticity and Superplastic Forming sponsored by the Manufacturing Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium was organized by Daniel G. Sanders, The Boeing Company.     

Finite element modeling and optimization of superplastic forming using variable strain rate approach

Detailed finite element simulations were carried out to model and optimize the superplastic blow forming process using a microstructure-based constitutive model and a multiscale deformation stability criterion that accounts for both geometrical instabilities and microstructural features. Optimum strain rate forming paths were derived from the multiscale stability analysis and used to develop a variable strain rate forming control scheme. It is shown that the proposed optimization approach captures the characteristics of deformation and failure during superplastic forming and is capable of significantly reducing the forming time without compromising the uniformity of deformation. In addition, the effects of grain evolution and cavitation on the superplastic forming process were investigated, and the results clearly highlight the importance of accounting for these features to prevent premature failure. This paper was presented at the International Symposium on Superplasticity and Superplastic Forming sponsored by the Manufacturing Critical Sector at the ASM International AeroMat 2004 Conference and Exposition, June 8–9, 2004, in Seattle, WA. The symposium was organized by Daniel G. Sanders, The Boeing Company.     

Commercial Airplane Applications of Superplastically Formed AA5083 Aluminum Sheet

This article discusses some of the advances that have been made at Boeing Commercial Airplanes during the manufacture of superplastically formed (SPF) AA5083 aluminum components for aircraft applications. This specially processed material is the lowest cost aluminum alloy that exhibits superplastic properties. Therefore, the use of 5083 would be beneficial to aircraft in forming complicated configurations. Since this aluminum alloy is non-heat treatable and therefore low strength, it is not typically considered a material for use on commercial airplanes. However, applications have been found on the Boeing Commercial fleet that provide lower cost hardware which, in some cases, is lighter weight. Design Engineers have been able to take advantage of the benefits of using SPF sheet metal hardware fabricated from AA5083 in areas where failure of the component during flight would not cause loss of the aircraft. SPF AA5083 components have replaced aluminum castings, fiberglass assemblies, and components fabricated by SPF from other aluminum alloys. Since this alloy is non-heat treatable, the cost of heat treating, quenching, and aging is avoided. Also, there is no contour distortion to straighten due to the solution heat treating and quenching process. Therefore, the quality of the hardware being delivered to the customer is greatly improved. This article was presented at the AeroMat Conference, International Symposium on Superplasticity and Superplastic Forming (SPF) held in Seattle, WA, June 6-9, 2005.     

Determination and application of stress-based forming limit diagram in aluminum tube hydroforming

The stress-based forming limit diagram（FLSD） established with limit stress is independent of the strain paths. Compared with traditional strain-based forming limit diagram（FLD）, it is more convenient and practical to use as the criterion of forming limit under complex strain paths. The forming limit of 3A21 aluminum alloy sheet was tested and its forming limit diagram（FLD） was determined. Then the FLSD of 3A21 was constituted by transformation formulas between limit strain and limit stress. This FLSD was used in conjunction with LS-DYNA finite element simulations to predict the onset of fracture and limit forming pressure in tube hydroforming. The results indicate that the fracture often occurs in the transition region between corner and straight side of the tube, and the limit forming pressure is 46.4 MPa. The simulation result agrees with the experimental result, and the FLSD is able to predict the forming limit of tube hydroforming with remarkable accuracy.     

Determination of forming limit of a structural aluminum tube in rubber pad bending

Rubber pad bending is a novel technique for producing space frame to reduce the weight of automobiles because it can produce bent profiles with various curvatures in a single production set-up. As in other bending processes, cross-section of the aluminum tube deforms during the process. Such a deformed geometry diminishes bending rigidity, making it inappropriate for a structural use in some cases. Thus, it is important to determine a minimum radius of curvature with sufficient bending resistance. In this study, experimental set-up was developed to investigate deformation characteristics of an extruded rectangular aluminum tube in rubber pad bending. For better understanding of the effect of process parameters such as the material property of rubber and roller diameter, finite element (FE) analyses were also conducted. The ratio of the second moment of inertia of the initial and deformed cross-sections of the tube was introduced as a measure of cross-sectional deformation to represent the variation of bending rigidity of the bent tube. In result, a critical value of sectional deformation and minimum formable radius of curvature with maintaining suitable sectional bending rigidity were, respectively, determined under the present process conditions investigated.     

Developments in investment casting process—A review

Investment casting has been used to manufacture weapons, jewellery and art castings during the ancient civilization. Today, its applications include jewellery/art castings, turbine blades and many more industrial/scientific components. The present paper reviews various investigations made by researchers in different stages of investment casting and highlights their importance. The paper initially highlights the investigations made on pattern wax properties, effects of blending, additives and fillers. Different ways through which pattern properties (like surface finish, dimensional accuracy, etc.) could be enhanced by properly controlling the injection processing parameters are thoroughly discussed. The paper also looks into the investigations made to enhance the strength, surface finish, etc. of ceramic shell for ferrous alloys/non-ferrous alloys as well as superalloys in investment casting. Investigations made on incorporation of nylon fibers and polymer additions confirm that a ceramic shell reinforced with nylon fibers attains additional permeability compared to the one with polymer additions.