Papers by Keyword: Super Plastic Forming (SPF)

Abstract: In this paper, mould configurations are studied by finite element simulation for superplastic blow forming of combustion chamber outer jacket. One concave and two convex mould configurations are basically considered to determine which type would be advantageous in terms of forming time and thickness distribution. For the simulation, the flow stress equation of duplex stainless steel was determined from free bulging test. The simulation results showed that the concave type was quit a bit different from the other two cases. The concave mould configuration produced shorter forming time and thicker thickness distribution than the others, and it seems to be more effective for superplastic forming of outer jacket. The obtained pressure profile for the concave mould configuration was employed in actual forming and the thickness distribution was compared for the verification.

Abstract: Fine-grained AA5083 aluminum-magnesium alloy sheet can be formed into complex closure components with the Quick Plastic Forming process at high temperature (450oC). Material models that account for both the deformation mechanisms active during forming and the effect of stress state on material response are required to accurately predict final sheet thickness profiles, the locations of potential forming defects and forming cycle time. This study compares Finite Element (FE) predictions for forming of an automobile decklid inner panel in fine-grained AA5083 using two different material models. These are: the no-threshold, two-mechanism (NTTM) model and the Zhao. The effect of sheet/die friction is evaluated with five different sheet/die friction coefficients. Comparisons of predicted sheet thickness profiles with those obtained from a formed AA5083 panel shows that the NTTM model provides the most accurate predictions.

Abstract: Accurate numerical simulation capability is critical to the development and implementation of hot forming technologies. Numerical simulations were developed for gas-pressure forming of commercial, fine-grained aluminum-magnesium (AA5083) material into deep pan shapes at 450°C. These simulations utilize a material constitutive model recently developed for fine-grained AA5083 materials as a user-defined routine in commercial Finite Element Method (FEM) software. Results from simulations are compared against data from gas-pressure forming experiments, which used the same forming conditions and die geometries. Specifically, local sheet thinning and radius of curvature in edges and corners are compared between simulation and experiment. Numerical simulations are in good agreement with experiments for local sheet thinning of up to 50%. For locations where sheet thinning exceeds 50%, simulations predict less thinning and larger formed radii than observed in experiments. It is likely that cavitation, which is not accounted for in simulations, plays a significant role in causing a decrease in simulation prediction accuracy for thinning values greater than 50%. This study demonstrates a simulation capability that is potentially of significant practical use for predicting the hot gas-pressure forming of fine-grained AA5083 material.

Abstract: Most of the work done on superplastic forming is related to sheet metal forming. Very limited studies have been directed toward investigating the superplastic tube forming process. In this work, Finite Element (FE) simulations are carried out in order to simulate the superplastic tube forming process. The analysis is conducted for the superplastic magnesium alloy AZ31 at 400°C. The results clearly demonstrate that there is a significant difference between tube forming and sheet metal forming in terms of forming pressure profiles. In addition, the effects of tube radius, free forming length, and contact on the tube forming process are investigated.

Abstract: Friction Stir Welding of Ti-6Al-4V was performed on 5 mm thickness plate in order to assess the affect of welding conditions on the resulting microstructure and superplastic forming behavior of the joints. A variety of welding conditions were tested and all welds were subsequently Superplastically formed. It was found that the weld parameters do influence the microstructure and degree of superplastic performance of the joints. Spindle speed was found to have the most dominant affect on the resulting microstructure and superplastic forming behavior. Low spindle speed welds lead to fine grained microstructures and highly superplastic welds, relative to the base material, while high spindle speed welds larger grained microstructures and less superplastic welds.

Abstract: In friction stir welding (FSW), the semi-circular shaped FSW pin tool feed marks that are left behind varied in depth and shape which are detrimental not only in fatigue performance but also in further processing such as superplastic forming (SPF). Experimental investigation was conducted to determine the effects of changes to the FSW process parameters on the surface roughness of the weld of fine grain 2 mm thick titanium alloy, Ti- 6Al-4V. In addition to optimizing the surface texture of the welds, the superplastic performance of the weld nugget was made to be equal to the superplasticity of the parent metal by altering the spindle speed and feed rate used during FSW to identify the quality in terms of cold weld or hot weld. FSW process conditions of spindle speed of 500 RPM and a feed rate of 150 mm/min was found to produce a uniform deformation in both weld and parent metal when the joint was superplastc formed.

Abstract: Ultra high-pressure waterjets (WJ) have gained consideration as a viable alternative to conventional material removal and cleaning methods such as chemical milling, grit blasting, and grinding. Waterjets have often been considered for the stripping of unwanted coatings, but they also exhibit an inherent ability for the controlled milling of metallic materials. The waterjet material removal process poses a secondary benefit – the material erosion occurs due to the repetitive impact of droplets within the waterjet stream, which also serve to induce compressive residual stresses in the shallow sub-surface layers of the work piece. An experimental study was conducted to explore the removal of the alpha case layer on Superplastically Formed conventional and fine grain Ti-6Al-4V specimens. The resulting surface roughness parameters and completeness of alpha layer removal were characterized. Based on the experimental results, waterjet removal processes may serve as an alternate method for the post-processing of Superplastically Formed titanium alloys.

Abstract: Superplastic Diaphragm Forming (SPDF) is applicable when parts are required to be shaped in materials that are either non-superplastic or where limited strain and near constant thickness are demanded. Unique components made in certain thermoplastic composites can be processed via SPDF and so can heavily perforated superplastic blanks. This paper illustrates a range of applications for SPDF used at Superform and provides more detailed case studies, some of which involve computer modeling to evaluate and optimize successful outcomes.

Abstract: In the past, engine aft fairing heat shields have typically been titanium castings. With a current single aisle airplane, these components were converted to sheet metal titanium 6Al-4V details fabricated by hot forming or Superplastic Forming (SPF). This conversion saved approximately 20% in both cost and weight per airplane. When heat shields for a twin aisle airplane were being developed, the engineers were interested in a sheet metal version of their heat shields hoping to achieve similar savings. However, the twin aisle configuration was different from the single aisle and did not allow the details to be simple pieces of formed sheet metal. Instead, these twin aisle heat shields are assemblies of details containing SPF components as well as Superplastically Formed and Diffusion Bonded (SPF/DB) panels. Some of the heat shield components are fabricated using the world's first applications of fine grain 6Al-4V titanium, which was developed to SPF at 775°C, covered by a U.S. patent [1], instead of 900°C, which is used for standard grain material. The SPF/DB technology being used contains innovative process developments that are covered by several patent applications [2-4]. The twin aisle heat shield assemblies were estimated to save approximately 15% in both cost and weight per airplane. Actual weight measurements of the first assembly showed an additional 5% savings over the calculated weight per engine resulting in a total weight savings of approximately 20% per airplane compared to titanium castings.

Abstract: When Superplastic Forming (SPF) was offered as a production process in the mid 70’s, it became the panacea of all processes for sheet metal products designed to be made from Titanium and Aluminium materials. The claims were (1) reduced part count (2) reduced assembly time (3) weight reduction (4) monolithic parts and (5) stronger structures. Following Pearson’s work in the mid 30’s with Lead-Tin and Bismuth-Tin alloys [1], showing higher than 1000% elongation without failure, the Aluminium industry developed SPF alloys and launched into numerous commercial applications. Other research facilities focused on the potential of achieving superplasticity in Titanium alloys. This was demonstrated in the late 60’s using the now well established Ti6Al4V alloy. Considerable funding was allocated, both in the USA & UK, specifically for the development of the process. The USA focused on the military programmes and the UK on the civil (Concord) and some military aircraft. Success in these programmes and the claims made, resulted with a production process. Companies invested in suitable plant and equipment, and designers grasped the process potential and applied SPF to their sheet metal designs expecting to reap the claimed benefits. The claims are valid if applied to correctly chosen components. All too often, the SPF manufacturing choice did not deliver its claims. In many cases cost of material, need to chemical mill and higher energy costs, were either not envisaged or taken into account. Today all processes, material cost and alternative material types have to be assessed before the manufacturing method is chosen. The aerospace industry is attacking the Buy-Fly ratio. Energy and labour cost are at a premium and these have caused the SPF and Hot Forming community to examine ways of producing products (a) from less material (b) by Hot Forming (eliminating the need to apply chemical milling to remove the alpha case) (c) questioning the material choice (CP instead of Ti6Al4V) and (d) by applying modern fabrication methods. The paper will illustrate this change in philosophy; shows today’s choices and demonstrate how the SPF process can be cost effective, and in fact still does have a major role to play in producing airframe and engine structures.