Gas Blow Forming Research Articles

Gas Blow Forming of Nanocrystalline Ni Foil Assisted by Two-Dimensional Pulse Current

Gas Blow Forming of Nanocrystalline Ni Foil Assisted by Two-Dimensional Pulse Current

THE EFFECT OF METAL ALLOY MICROSTRUCTURE
 ON THE THICKNESS DISTRIBUTION IN THE CIRCULAR PLATE UNDER THE SUPERPLASTIC BLOW-FORMING

The gas-blow forming of sheet specimens under the superplastic conditions is the widespread and intensive developing technological method for metal-forming of modern alloys (mainly on the aluminium and titanium base). The investigation of evolution of the microstructure parameters in the deformation process is necessary to obtain the defect-free constructions with required mechanical properties. In thepresent paper the blow-forming process of the thin circular plate to the hemispherical form is modelled. The stress-strain relations used include the parameters of the grain size and of the hardening depending on theaccumulated plastic strain. It is shown that taking into account the evolution of the microstructure parameters in the superplastic deformation can significantly improve the estimation of the optimal characteristics of the manufacturing process and eventually can provide the most thickness-uniform engineering product.

Thermomechanical Modeling of Amorphous Glassy Polymer Undergoing Large Viscoplastic Deformation: 3-Points Bending and Gas-Blow Forming.

Polymeric products are mostly manufactured by warm mechanical processes, wherein large viscoplastic deformation and the thermomechanical coupling effect are highly involved. To capture such intricate behavior of the amorphous glassy polymers, this paper develops a finite-strain and thermomechanically-coupled constitutive model, which is based on a tripartite decomposition of the deformation gradient into elastic, viscoplastic, and thermal components. Constitutive equations are formulated with respect to the spatial configuration in terms of the Eulerian Hencky strain rate and the Jaumann rate of Kirchhoff stress. Hyperelasticity, the viscoplastic flow rule, strain softening and hardening, the criterion for viscoplasticity, and temperature evolution are derived within the finite-strain framework. Experimental data obtained in uniaxial tensile tests and three-point bending tests of polycarbonates are used to validate the numerical efficiency and stability of the model. Finally, the proposed model is used to simulate the gas-blow forming process of a polycarbonate sheet. Simulation results demonstrate well the capability of the model to represent large viscoplastic deformation and the thermomechanical coupling effect of amorphous glassy polymers.

A finite-strain thermomechanical model for severe superplastic deformation of Ti-6Al-4V at elevated temperature

This paper presents a new finite-strain and thermomechanically-coupled constitutive model for severe superplastic deformation of Ti-6Al-4V at elevated temperature. The kinematic hypothesis of this model is a multiplicative decomposition of the deformation gradient into elastic, superplastic and thermal components, allowing the model to simultaneously take into account the large superplastic flowing deformation, the evident thermal expansion and the local temperature evolution. The model begins with the establishment of a thermodynamically consistent framework, including the Helmholtz free energy function, the entropy inequality and the heat production, from which constitutive equations are derived. The strain rate and temperature dependent material behavior is formulated by using a bilinear interpolation scheme and an exponential function. The ABAQUS/Explicit user-defined material subroutine VUMAT is employed to realize the numerical implementation of the model. The model is validated against the experimental data obtained in tensile tests on Ti-6Al-4V specimens. Finite element simulation of the superplastic gas-blow forming of Ti-6Al-4V sheet well demonstrates the model capabilities of accurately describing large superplastic deformation of Ti-6Al-4V at elevated temperature.

Multiphase Gas Blow Forming of AA2017

Abstract This study describes a gas blow forming process used to produce metal components from aluminum AA2017 alloy. With regards to producing an axisymmetric metal component by means of a multiphase gas blow forming process, it is possible to optimize thickness distribution in terms of thickness uniformity and obtain forming times that are suited to high volume production.

Cavitation Behavior in Superplastic AZ31 Magnesium Alloy During Pulse Current Auxiliary Gas Blow Forming

During the gas blow forming of AZ31 magnesium alloy, the heavy pulse current was applied. The effects of pulse current on the cavitation during superplastic forming were examined. Scanning electronic microscopy (SEM) was employed to observe the cavities and topography of the forming samples. Theoretical analysis and experimental results show that the pulse current flowing through the cavity tip will form a local high-temperature zone and local compressive stress area near the vicinity. It is helpful to heal the cavity and avoid the further growth; at the same time, the non-thermal effect of pulse current will also affect the cavity nucleation and growth, thereby changing the morphology and distribution of cavities. It delayed the appearing of large size cavity to some extent, avoiding the material premature fracture and helping to improve the forming limit of the material during the superplastic deformation.

Finite Element Simulation of High-Speed Blow Forming of an Automotive Component

High-speed blow forming (HSBF) is a new technology for producing components with complex geometries made of high strength aluminum alloy sheets. HSBF is considered a hybrid-superplastic forming method, which combines crash forming and gas blow forming. Due to its novelty, optimization of the deformation process parameters is essential. In this study, using the finite element (FE) code ABAQUS, thinning of an aluminum component produced by HSBF under different strain rates was investigated. The impact of element size, variation of friction coefficient, and material constitutive model on thinning predictions were determined and quantified. The performance of the FE simulations was validated through forming of industrial size parts with a complex geometry for the three investigated strain rates. The results indicated that the predictions are sensitive to the element size and the coefficient of friction. Remarkably, compared to a conventional power law model, the variable m-value viscoplastic (VmV) model could precisely predict the thickness variation of the industrial size component.

The effects of pressure control technique on hot gas blow forming of Mg AZ31 sheets

The forming pressure-time schedule is critically important in high temperature gas blow forming of sheet materials. Forming pressure controls the strain rate that influences necking and thickness distribution uniformity in the formed component. In this work, the effects of forming pressure control technique; constant pressure versus constant strain rate, on the superplastic forming of Mg AZ31-H24 sheets at 400 °C are investigated. Experiments and detailed finite element simulations that incorporate a phenomenological microstructure based constitutive model for forming a cylindrical cup are conducted. Sheet thickness distribution across the formed part and the deformation progress are examined in details. The results clearly reveal that for the same forming time required to fully form the cup, the constant forming pressure control technique acts as a variable strain rate forming procedure that yields to a more uniform thickness distribution when compared to the constant strain rate control technique. However, it should be noted that the initial strain rates for forming at constant pressure are of extreme importance as high initial strain rates that exceed 10−2 s−1 might cause rupture.

Gas Blow Forming in AA2017 Aluminium Alloy

In this paper the hot behaviour of AA2017 aluminium alloy sheet was analyzed through gas blow forming tests. The material, heated and kept at a constant temperature, was subjected to gas blow forming tests under a constant pressure. Specimens with a thickness of 1.00 mm and 0.55 mm were employed. The study defines a reference value for the forming temperature as well as the hardness of the finished component. In addition, the hardness was also measured following tests conducted in several steps of the forming process.

Coarse-grained superplasticity and gas blow forming of commercial AZ31 magnesium alloy sheet

Superplasticity of commercial AZ31 magnesium alloy sheet has been investigated at strain rate range of 0·7 × 10−3–1·4 × 10−1 s−1 and temperature range of 523–673 K. Hot uniaxial and equi-biaxial tensile tests are carried out. The maximum elongation of 362% has been obtained at the temperature of 673 K and strain rate of 0·7 × 10−3 s−1. The calculation of activation energy Q and examination of microstructures show that the deformation mechanism of commercial AZ31 magnesium alloy is dissimilar at different conditions. With the decreasing of temperature and increasing of strain rate, the deformation mechanism is converted from grain boundary sliding controlled by grain boundary diffusion to the mix of grain boundary sliding and plastic or/and creep deformation controlled by lattice diffusion. In the free bulging tests, the hemisphere has been formed successfully and for the components, the failure reason is the growing and connecting of the cavities.

Modified male die rapid gas blow forming of fine-grained Mg alloy AZ31B thin sheet

Gas blow forming of a commercial, fine-grained, 0.6-mm-thick Mg alloy AZ31B thin sheets under high strain rates to decrease the forming time was investigated in the present work. An innovative male die rapid gas blow forming method was developed. Using this new method and stepwise pressurization profiles, alloy sheets were successfully deformed to form shallow rectangular pans. Deformation characteristics of rapid gas blow forming were discussed. Results indicated that the proposed process significantly reduces the forming time and that a shallow rectangular pan may be formed under a maximum average strain rate of approximately 10−2 s−1. A 10-mm-high rectangular pan was formed in <109 s. Sheet thinning was improved by modified male die forming. The fillet radius of the rectangular pan was found to be one of the key factors that influence the rapid gas blow forming time. Strain-enhanced grain growth was the major growth mechanism during rapid gas blow forming. Grain growth and cavitation were not serious problems during rapid gas blow forming.

Formability and Grain Size of AZ31 Sheet in Gas Blow Forming Process

Initial microstructural effect on mechanical properties and high temperature formability was investigated by experiments such as uniaxial tensile test at room temperature and 400°C and biaxial gas blow forming at 400°C. To observe distinct microstructural effect, three types of AZ31 alloy sheets which have different average grain size as 16.41μm (type-A), 11.02μm (type-B), and 7.58μm (type-C) were investigated. Among the three types of AZ31 alloy sheets, Type-A and Type-B was the partially hardened specimens containing twins (AZ31-H) and Type-C was fully annealed specimen with equiaxed grains (AZ31-O). At room temperature tensile test, initial microstructural features such as twin density, dislocation density, and grain size affected mechanical properties. However at 400°C tensile test and gas blow forming, only initial grain size affected mechanical properties due to the fact that the original microstructures of AZ31-H alloy sheets evolved into recrystallized microstructures with equiaxed grains. Accordingly, AZ31-H magnesium alloys, which have improved mechanical properties at room temperature, could not affect superplastic formability and mechanical properties of post-superplastic formed microstructures.

Tensile Properties and Shallow Pan Rapid Gas Blow Forming of Commercial Fine-grained Mg Alloy AZ31B Thin Sheet

Tensile tests and gas blow forming were performed to explore the deformation behavior of a fine-grained AZ31B Mg alloy sheet. This work studied the decrease in forming time in gas blow forming using fine-grained Mg alloy AZ31B thin sheet with a thickness of 0.6mm. The stress-strain rate data showed that fine-grained AZ31B thin sheet on testing at 420°C exhibited strain rate sensitivity exponent values of approximately 0.29–0.36 in a strain rate ranging from 4×10-3 and 2×10-2s-1, indicating that the dislocation creep would be a possible deformation mechanism to reduce forming time in gas blow forming. The alloy sheets were successfully deformed into a shallow rectangular pan using constant gas pressure forming. The deformation characteristics of gas blow forming were discussed. As a result, a significant reduction in forming time was achieved, in which a rectangular pan was formed with a height of 10mm in less than 105s at 420°C. Pan forming revealed that the maximum average stain rates of 7.0×10-3 and 8.7×10-3 s-1 were obtained for forming at constant pressures of 2.6 and 3.2MPa, respectively. Fillet radius of the rectangular pan should be one of the key factors influencing forming time on closed die gas blow forming.

Deformation characteristics of fine grained magnesium alloy AZ31B thin sheet during rapid gas blow forming

Decreasing the forming time in gas blow forming using fine grained Mg alloy AZ31B thin sheet with a thickness of 0·6 mm was studied in this work. Tensile tests and gas blow forming using stepwise pressurisation profiles were performed to explore the deformation behaviour of a fine grained AZ31B Mg alloy sheet. The alloy sheets were successfully deformed into hemispherical domes using two proposed stepwise pressurisation profiles during gas blow forming. As a result, significant reduction in forming time was achieved. Maximum effective deformation rates of 1·02 × 10–2 and 1·98 × 10–2 s–1 were obtained at 300 and 370°C respectively. It was feasible to form a hemispherical dome with a height of 20 mm in less than 80 s at 370°C. The results confirmed that the thickness distribution along the centreline of the formed dome was sensitive to the pressurisation profiles. A higher thinning effect was observed at 370°C due to the higher deformation rate imposed during forming. Grain growth was not a serious problem for forming even at 370°C, and static grain growth should be the major factor resulting in grain growth during forming.

Effect of pressurization profile on the deformation characteristics of fine-grained AZ31B Mg alloy sheet during gas blow forming

The deformation characteristics of a 0.6 mm-thick, fine-grained AZ31B Mg alloy sheet were investigated with the intention of reducing forming time during gas blow forming. The sheets were successfully deformed into hemispherical domes at 300, 370, and 420 °C under various pressurization profiles. The results show that the proposed pressurization profiles could achieve the goal of reducing forming time. A stepwise pressurization profile may be a suitable process at lower temperatures, whereas a constant or near constant pressure imposed during forming is a better method at higher temperatures. The pressurization profiles used in this study were not restricted to providing the optimum constant strain rate, which is often used in the traditional superplastic forming. Under the proposed pressurization profiles, maximum stress in the range of 23.5–45.6 MPa and resultant average strain rate in the range of 6.63 × 10 −3 to 1.56 × 10 −2 s −1 were imposed on the deforming sheet at the apex of the dome. The pressurization profile might not be one of the major factors influencing formability at the same forming temperature but it can significantly affect the forming time. Deviation of the bulged shape from the perfect sphere shape increased with increasing forming temperature.

Selection of material models for predicting necking in superplastic forming

The mechanical behaviour of a superplastic alloy is characterised by both the sinh-law, ε ̇ p∝ sinh(βσ) , and power-law, ε ̇ p∝(σ/K) 1/m , constitutive equations together with the hardening variables containing significant physical meanings. The material constants in the power-law equation are determined using two different methods: the genetic algorithm (GA)-based optimization technique and the more recently developed physically-based multiple step method. The two techniques give different values for the material constants and thus result in different magnitudes for the strain rate sensitivity parameter m. Together three SETs of determined unified constitutive equations are obtained and all enable the experimental stress–strain curves and grain growth data of the material to be well captured. In this paper, studies are carried out to investigate the effects of the three determined material models on necking predictions for the superplastic gas-blow forming of a structural component. In addition the predicted gas pressure cycles, required to ensure that the maximum strain rate over the workpiece approximately equals the pre-defined target deformation rate, are compared and analysed for the three cases.

Effects of grain-size gradients on thinning in superplastic gas-blow forming

This paper shows that the mechanical response of superplastic materials is related to their microstructure and that the use of a microstructural gradient approach can improve the evenness in straining during superplastic gas-blow forming. Finite element simulations of the forming process are carried out to investigate the effect of initial grain-size gradients on the non-uniform thinning of a formed structural component.

423 RB/SPFによる中空構造部材の成形加工(OS 溶接・接合)

This paper describes a new method for practical superplastic gas blow forming. The method consists of conventional forming processes except using Gas Generants as apressure source instead of inert or air gas blowing. When the temperature reaches at specific range, Gas Generants can decompose by itself and some gasses come out. Then any increase in temperature up to superplastic range may produce a dilatational work for gas blow forming. Alternative application to making of hollow structural truss components by using Gas Generants and hot roll bonding simultaneously can be illustrated also.

614 ガス発生剤による超塑性成形(オーガナイズドセッション : 超成形・超塑性と材料)

This paper describes a new method for practical superplastic gas blow forming. The method consists of conventional forming processes but using Gas Generants as a pressure source instead of using inert or air gas blowing. When the temperature reaches at specific range, Gas Generants can decompose by itself and some gasses come out. Then any increase in temperature up to superplastic range will produce a dilatational work for gas blow forming. Alternative application to making of hollow structural truss components by using Gas Generants and hot roll bonding simultaneously can be illustrated also.