Superplastic Forming Research Papers - Academia.edu (original) (raw)

In turbofan engines, most of the thrust is produced by bypassing the air that passes through a large diameter fan located at the front of the engine. The fan consists of multiple blades that rotate at high speeds around an axis to push the air backward into the engine. To achieve this crucial function, it is important for the fan blades component to be manufactured with appropriate materials.

This paper reviews the numerical simulation of the superplastic forming of thin sheet from early attempts with simplified geometries through to general finite element techniques. A summary of the classical finite flow formulation of the problem is presented together with a detailed exposition of the incremental flow formulation. Pressure cycle control and contact algorithms are formulated in detail and a number of applications presented. Finally some practical simulation issues are discussed followed by brief conclusions.

- by Rajab Said
- •
- Engineering, Finite Element, Finite Element Analysis, Numerical Simulation

Excellent superplasticity (elongation $720%) is observed in a novel multi-component (Mn-S-Cr-Al alloyed) ultrahigh carbon steel during tensile testing at a strain rate of 2 Â 10 À3 s À1 and a temperature of 1053 K (just above the equilibrium austenite-pearlite transformation temperature). In order to understand superplasticity in this material and its strong Al dependence, the deformationinduced microstructure evolution is characterized at various length scales down to atomic resolution, using X-ray diffraction, scanning electron microscopy, electron backscatter diffraction, energy-dispersive X-ray spectroscopy and atom probe tomography. The results reveal that 1 wt.% Al addition influences various microprocesses during deformation, e.g. it impedes Ostwald ripening of carbides, carbide dissolution, austenite nucleation and growth and void growth. As a result, the size of the austenite grains and voids remains relatively fine (<10 lm) during superplastic deformation, and fine-grained superplasticity is enabled without premature failure.

- by Dirk Ponge
- •
- Materials Engineering, Mechanical Engineering, Superplasticity, Interface Design

High-strength (1.2–1.5) C–(2–2.5) Mn–(1.5–2) Si–(0.8–1.5) Cr steels (mass%) consisting of martensite and carbides exhibit excellent superplastic properties (eg strain rate sensitivity m≈ 0.5, elongation≈ 900% at 1023K). A homogeneous martensitic starting microstructure is obtained through thermomechanical processing (austenitization plus 1.2 true strain, followed by quenching). Superplastic forming leads to a duplex structure consisting of ferrite and spherical micro-carbides.

—Superplastic forming of metals and alloys is known as a technological process of deformation, of those materials which are characterized by a structure well defined and uniform as grain size around of 10 micrometers, at medium temperature, and with very low strain rate. All of these conditions makes the process unattractive, but the benefits are quite major and valuable. The complexity of shapes deformed and obtained, the large and uniform dimension of parts, are some of these major benefits of this kind of deformation process. Although of these benefits, the superplastic forming process is quite difficult for simulating and analysis process. The finite element method comes to facilitate the analysis and simulation of the flow and forming process. The present work is focused on this objective: to show a method for simulation and finite element analysis of superplastic forming, using the unconventional software ANSYS. Keywords—Superplastic Forming(SPF), finite element analysis, strain rate sensitivity exponent, strain hardening exponent, constitutive material equations.

In late 1964 Backofen, Turner & Avery, at MIT, published a paper in which they described the ''extraordinary formability'' exhibited when fine-grain zinc-aluminum eutectoid (Zn 22 Al) was subjected to bulge testing under appropriate conditions. They concluded their research findings with the following insightful comment ''even more appealing is the thought of applying to superplastic metals forming techniques borrowed from polymer and glass processing.'' Since then their insightful thought has become a substantial reality with thousands of tons of metallic sheet materials now being superplastically formed each year. This paper reviews the significant advances that have taken place over the past 40 years including alloy developments, improved forming techniques and equipment, and an ever increasing number of commercial applications. Current and likely future trends are discussed including; applications in the aerospace and automotive markets, faster-forming techniques to improve productivity, the increasing importance of computer modeling and simulation in tool design and process optimization and new alloy developments including superplastic magnesium alloys.

- by Anthony Barnes
- •
- Materials Engineering, Process Optimization, Superplastic Forming
- by Michel Bellet
- •
- Viscoplasticity, Modeling, Superplasticity, Finite element method

Superplastic forming has been considered as an attractive process in the automotive and aerospace industries. However, the disadvantages of slow forming rate, high-temperature requirement, poor thickness distribution, and expensive base material have hindered its widespread use for high production volume. In this paper, the non-superplastic grade of 5083 aluminum alloy (AA5083) sheets with thickness of 3 mm was employed in a superplastic-like forming process, which is a combination of drawing (mechanical pre-forming) and superplastic forming (blow forming). Experimental trials were conducted to verify the possibility of improving the forming rate and lowering the process temperature. The blank was firstly pre-formed during the mechanical pre-forming phase. As a result, some part of material along the flange area was introduced inside the deformation cavity in advance of the blow forming phase. Secondly, argon gas was applied on the sheet, which would be deformed to come into contact with the inner die surface at the end of pressure cycle. It took only 8 min for the blow forming phase, and the process achieved an almost fully formed part at 400°C. The minimum thickness occurred at the inward corners, and the maximum thinning of the formed part was 54%. Grain growth and cavitation were found from the microstructure observations.

- by Ming-Jen Tan
- •
- Engineering, Materials Engineering, Mathematical Sciences, Grain Growth

A 7475-aluminum alloy was subjected to a thermomechanical heat treatment that resulted in a final recrystallized grain size on the order of 10 µm. Tensile specimens of dimensions 10 × 4 × 2.3 mm were machined such that the tensile axis was parallel to the rolling direction. Tensile tests were carried out at high temperatures in the range of 773 to 803 K at different cross-head speeds corresponding to initial strain rates in the range of 10−4 to 10−2 s−1. Elongations of several hundred percent were observed at strain rates of −3 s−1. The correlation between flow stress and strain rate suggests that the strain rate sensitivity m is close to 0.5 at the lower strain rates. The value of m decreases to ≈0.2 at high strain rates. The decrease in m suggests a transition in the rate-controlling process from superplastic deformation (m ≈ 0.5) to dislocation creep (m ≈ 0.2) with increasing strain rate. The calculated activation energies in the two deformation regions are consistent with the suggested rate-controlling processes.

- by Mahmoud Soliman
- •
- Superplastic Forming

Objectives: The study examined the setting and thermal expansions of seven dental casting investments intended for use in the superplastic forming (SPF) of Ti6A14V for dental implant superstructures. The total expansion is compared with the coef®cient of thermal expansion of the alloy. Methods: The unrestricted setting expansion of the investment was measured at room temperature using a lined brass trough and dial gauge. The thermal expansion was measured at a heating rate of 58C/min up to 9008C. The thermal expansion of Ti6A14V was measured at a heating rate of 158C/min. Results: The Selevest investment had a small shrinkage on setting. The largest setting expansions were observed with Rema Exakt and Fujivest. Selevest DM and Fujivest had the greatest thermal expansions. Rema Exakt had the greatest overall expansion. The total expansion of Rematitan most closely matched the thermal expansion of Ti6A14V when the manufacturer's recommended special liquid to water ratio for crowns and bridges was used. Signi®cance: SPF is a novel technique which is being applied to the manufacture of dental prostheses. As dental casting investments are used to make the dies used for SPF the dimensional changes associated with these materials should be matched to the dimensional changes of the Ti6A14V alloy used in order to achieve a passive ®t. This study has identi®ed Rematitan as an investment whose total expansion may enable an accurately ®tting SPF implant superstructure to be made.

- by Richard Curtis
- •
- Engineering, Algorithms, Thermodynamics, Dental Materials

In this work, the forming behaviour of a commercial sheet of AZ31B magnesium alloy at elevated temperatures is investigated and reported. The experimental activity is performed in two phases. The first phase consists in free bulging test and the second one in analysing the ability of the sheet in filling a closed die. Different pressure and temperature levels are applied. In free bulging tests, the specimen dome height is used as characterizing parameter; in the same test, the strain rate sensitivity index is calculated using an analytical approach. Thus, appropriate forming parameters, such as temperature and pressure, are individuated and used for subsequent forming tests. In the second phase, forming tests in closed die with a prismatic shape cavity are performed. The influence of relevant process parameters concerning forming results in terms of cavity filling, fillet radii on the final specimen profile are analysed. Closed die forming tests put in evidence how the examined commercial magnesium sheet can successfully be formed in complicated geometries if process parameters are adequately chosen.

- by Gianfranco Palumbo
- •
- Modeling, Magnesium, Inflation, Material Characterization

This paper presents the numerical results obtained from the finite element analyses of the superplastic forming (SPF) of AlTi alloys. The models are used to optimise the process and predict forming times in terms of deformed shapes,... more

- by Clayton Adam
- •
- Materials Engineering, Mechanical Engineering, Superplasticity, Finite Element

A new optimization approach for superplastic forming of Mg AZ31 alloy is presented and experimentally validated. The proposed new optimization approach is based on a multiscale failure criterion that takes into account both geometrical necking and microstructural evolution, yielding a variable strain rate forming path instead of the commonly used constant strain rate approach. Uniaxial tensile tests and free bulge forming experiments, in conjunction with finite element analysis, are used to evaluate the proposed optimization approach. Significant reduction in forming time is achieved when following the proposed optimization approach, without compromising the uniformity of deformation.

Over the past thirty years Superform has been a pioneer in the SPF arena, having developed a keen understanding of the process and a range of unique forming techniques to meet varying market needs. SuperformÕs high-profile list of customers includes Boeing, Airbus, Aston Martin, Ford, and Rolls Royce. One of the more recent additions to SuperformÕs technical know-how is finite element modeling and simulation. Finite element modeling is a powerful numerical technique which when applied to SPF provides a host of benefits including accurate prediction of strain levels in a part, presence of wrinkles and predicting pressure cycles optimized for time and part thickness. This paper outlines a brief history of finite element modeling applied to SPF and then reviews some of the modeling tools and techniques that Superform have applied and continue to do so to successfully superplastically form complex-shaped parts. The advantages of employing modeling at the design stage are discussed and illustrated with real-world examples.

- by Anthony Barnes
- •
- Materials Engineering, Finite Element Model, Superplastic Forming, Simulation Tool

Superplastic forming (SPF) has been considered a process for improving the formability of aluminum alloys for the production of automotive body panels. In order to accurately simulate the SPF process, elevated temperature, uniaxial tension tests are used to develop the material flow model. Due to the high temperature and large degree of deformation in these tests, strain is typically calculated using crosshead displacement rather than with an extensometer. This approach requires the assumption of a constant material volume in the gage section to calculate the uniform strain. It has been observed that a significant amount of material flows from the grips into the gage section during testing which results in inaccuracies in the material model. This article presents a numerical tool that accounts for material flow from the grips and produces a more accurate constitutive equation. Experimental and numerical validations of the results of the developed tool are presented.

This work examined the effect of multiaxial stress on deformation characteristics of a superplastic aluminum alloy 8090 by deforming the sheet into a die with a cylindrical cavity. Several interrupted tests were performed to bulge the sheets to various depths for different strain rates, the formed parts were utilized to evaluate the deformation status, thickness distribution, local strain states, and cavitation. It was found that evolution of cavity volume fraction with forming time could be related to the thinning behavior of the deformed sheet during forming. Decrease in cavity volume fraction at the central region was observed in the later stage of forming as the thickness of the deformed sheet remained constant for all test forming rates.

- by Nihat Akkus
- •
- Materials Engineering, Mechanical Engineering, Modeling, Prediction

Gas pressure forming is the most common and widely practiced method of evaluating practical superplastic forming characteristics. In order to carry out the forming operation under constant strain-rate conditions, a mathematical model is necessary to govern the pressure-time path. In the present analysis, a simple and straightforward equation has been developed relating the required gas pressure to the material parameters such as flow stress, strain rate, and also the sheet and die geometries. Another equation has been derived to predict the thickness variations between the pole and the equator of a hemisphere. The effectiveness of these equations has been validated by monitoring the progress of forming at the different stages of blowing Ti-6.5AI-3.3Mo-l.6Zr alloy hemispheres and thereby measuring the radii of curvature and thicknesses at pole and equator.

- by Abhijit Dutta
- •
- Materials Engineering, Mechanical Engineering, Kinetics, Strain Rate
- by D. Ponge and +1
- •
- Materials Engineering, Mechanical Engineering, Superplasticity, Interface Design

In this study, the twin roll casting process has been utilized to prepare initial as-cast strip of AZ91 alloy that has been further tested in uniaxial tension at 325, 350 and 375 ºC, and at strain rates from 10 -2 to 10 -4 s -1 . The ability of AZ91 strip to undergo superplastic or superplastic-like deformation in longitudinal direction, in transverse direction, and in 45 degrees to longitudinal direction was investigated with no further thermal or thermomechanical processing applied prior to the testing. At temperature 350 ºC and medium strain rate the maximum elongation reached almost 200% in direction parallel to the strip casting, however in the transverse and 45 degrees direction, different temperature, and at higher strain rates the maximum elongation was lower. Based on microstructural investigation by means of OM and SEM it could be seen that continuous dynamic recrystallization of initial coarse dendritic as-cast microstructure during elevated temperature deformation is active and responsible for high elongations. Additional analysis is provided by means of a strain rate sensitivity characterization and its evolution with increased level of strain. Strain rate sensitivity of AZ91alloy increased with increasing level of strain from 0.20 to 0.33.

- by Gaurav Bali
- •
- Superplasticity, Magnesium, Magnesium Alloys, Superplastic Forming

Multi-level modeling adaptive to theoretical treatise of superplastic deformation is proposed not only to make process simulation for superplastic forming but also to describe the microstructural change taking place in materials processing. Use of the unit cell modeling enables us to make theoretical linkage between the macroscopic and the mesoscopic models. The fundamental theory is introduced with some comments on the unit cell model for macro-micro mechanics linkage and the advanced granular modeling for mesoscopic representation of superplasticicty. The sinter-forging process is employed for practical demonstration of the present multi-level modeling.

- by Tatsuhiko Aizawa
- •
- Superplasticity, Finite element method, Homogenization, Forging

Intrinsic difficulty of metal forming in magnesium alloys must be overcome by new processing. Superplatic injection forming is one of the most promising methodologies. Stroke velocity controlled forming system was developed to evaluate the formability of AZ91 at 573 K both in upsetting and backward-extrusion modes. Uniaxial constitutive equation was used together with consideration of grain growth to predict the stress-strain rate and the stress-stroke relations in upsetting experiments. Double flange, thin-walled cup can be superplastically formed from a cylindrical billet.

- by Tatsuhiko Aizawa
- •
- Materials Science, Superplasticity, Strain Rate, Grain Growth

... The forming takes place in the supercooled liquid region, where the viscosity of the BMG permits forming pressures that can be created with the force exerted by the human lung alone. ... Here viscosities down to 10 5 Pa s can be... more

- by Richard Curtis
- •
- Materials Engineering, Mechanical Engineering, Superplastic Forming, Blow Molding

Effect of lubrication on deformation behavior of a superplastic material has relatively been less examined, though it is important for industrial application. In this paper, a superplastic 5083 Al alloy under bi-axial deformation was investigated by deforming the sheet into a rectangular die cavity with and without lubrication. It was found that reducing the interfacial friction by use of a lubricant altered the metal flow after the deformed sheet had made contact with the die surface. Changes of the metal flow during forming not only developed a better thickness distribution of the formed part, but also improved cavitation distribution. The cavitation levels could be effectively reduced for forming with lubrication at a higher strain rate; the maximum cavity volume fraction decreased from 6.75 to 3.33% for forming at a strain rate of 1 × 10 −3 s −1 .

- by Chui-Hung Chiu
- •
- Materials Engineering, Mechanical Engineering, Lubrication, Strain Rate

This paper examines the effect of friction and back pressure on the formability of superplastically formed aluminium alloy AA7475 sheet at the temperature of 517 °C. Several experiments with lubrication and back pressure are performed using a simple box shape tool cavity. The coefficient of Coulomb friction between the formed sheet and tool has been determined indirectly using a finite element model to simulate superplastic forming of the box shape. Typical values determined for all lubricant conditions tested are in the range 0.1 < μ < 0.2. The void growth with strain was determined directly from measurements as a function of back pressure. The results show the application of back pressure at 1 MPa reduces the growth of voids from 7% to 0.3% void volume fraction at a logarithmic thickness strain of 0.65. This paper reports back pressure has a significantly greater role than friction in enhancing the formability of the alloy.

- by Andrzej Rosochowski
- •
- Engineering Design, Lubrication, Superplastic Forming, Back Pressure

A numerical model for solving either elastic-plastic, elastic-viscoplastic or purely viscoplastic deformation of thin sheets is presented, using a membrane mechanical approach. The finite element method is used associated with an incremental procedure. The mechanical equations are the principle of virtual work written in terms of plane stress, which is solved at the end of each increment, and an incremental semi-implicit flow rule obtained by the time integration of the constitutive equations over the increment. These equations are written using curvilinear coordinates, and membrane elements are used to discretize them. The resolution method is the Newton-Raphson algorithm. The contact algorithm is presented and allows for applications to cold stretching and deep-drawing problems and to the superplastic forming of thin sheets.

- by Michel Bellet and +1
- •
- Sheet Metal Forming, Finite element method, Superplastic Forming

Superplastic forming process has been a standard manufacturing process in aircraft industry and its applications in other industries are increasing. Superplasticity is utilised in forming parts which can not be produced technically or economically using materials with ordinary ductility. As superplastic deformation should be carried out under certain strain rate in which m value is maximal, the finite element method is applied to model the forming process in order to optimise the process through generating a pressure-time curve. In this paper, the dynamic explicit solution procedure was taken as an alternative solution due to its efficiency, as most of the current simulations of SPF used static implicit. The material parameters of Aluminium alloy 5083 SPF were first determined and the creep constitutive model was chosen. The finite element analysis results from dynamic explicit were verified with experimental results and then compared with static implicit. The simulation of bulge forming process with the geometry of a cup was conducted. The effects of m value and friction coefficient value were investigated.

: In this paper, reverse superplastic blow forming of a Ti-6Al-4V sheet has been simulated using finite element method in ABAQUS to achieve the optimized control of thickness variations. The deformation process, pressure versus time curve, variation of thickness strain and effect of a change in friction coefficient have been investigated. In addition, simulation of the same structure with non-reverse forming has also been carried out and a detailed comparison has been made between results from different forming processes.

- by Chennakesava Reddy A
- •
- Superplastic Forming

In this work, a set of parametric experiments was conducted on a superplastic material (eutectic tin-lead alloy) with one or more pre-drilled holes in each specimen. The small-sized holes were for simulating microvoids that occur and grow during superplastic forming. All holes were axially aligned with the tensile axis. The results revealed an increase in ductility with the number of holes up to 10 holes and a decrease thereafter. The ductility enhancement was explained based on the m-curve as due to a rise in the strain rate sensitivity locally around the holes. The decrease was explained due to strong void interaction that resulted in shear failure. This was further verified by a separate set of experiments of only two interacting voids with various interspacing. Finally, the void size versus applied strain was fully characterized and the results supported the ductility observations.

- by Mark Horstemeyer
- •
- Materials Engineering, Mechanical Engineering, Civil Engineering, Plasticity