Superplastic Forming/diffusion Bonding Research Articles

The superplastic forming/diffusion bonding of TA7 titanium alloy for manufacturing hollow structure with stiffeners

The superplastic forming/diffusion bonding (SPF/DB) process has been proved to be an effective way to fabricate multi-layer integrated structures. During this study, a hollow structure with two stiffeners was manufactured by SPF/DB process using TA7 titanium alloy. The tensile behavior of the alloy was investigated by undertaking uni-axial tensile tests at high temperature, with results showing that the maximum elongation was 199.8% at 870 °C/0.001 s−1. Diffusion bonding experiments utilizing TA7 titanium alloy were conducted at different temperatures. The shear strength of DB joints at 880 °C and 900 °C were 568.4 MPa and 569.1 MPa, respectively. Based on the superplastic properties, a finite element simulation of the hollow structure was carried out, with results showing that this could be fabricated by the DB/SPF process. Finally, fabrication of this hollow structure was successfully demonstrated by DB at 880 °C/2 MPa/1 h and SPF at 870 °C with a target strain rate of 0.001 s−1. Thickness measurements indicated that the maximum reduction in thickness was approximately 10% and occurred at the short stiffener. The experimental result was less than the predicted reduction from the finite element simulation. When comparing the tensile strength and elongation of the initial material, the reduction in the manufactured material was 9.4% and 0.4%, respectively. The microstructure was characterized and the average grain size was measured to increase from 7.5 μm to 14.8 μm.

The parameter optimization and mechanical property of the honeycomb structure for Ti2AlNb based alloy

In this paper, the parameter optimization and the mechanical property of the honeycomb structure fabricated by superplastic forming/diffusion bonding (SPF/DB) process for Ti 2 AlNb based alloy were investigated. The uni-axial tensile test was carried out at different temperatures and strain rates. The results showed that the maximum elongation was 236 % at 970℃/0.0003s −1 and the strain rate sensitivity coefficient was 0.3. The mechanical model of the face sheet and core sheet forming was established and the forming process of the structure was analyzed by the finite element method(FEM). The FEM results showed that the grooves on the surface of the honeycomb structure gradually faded and disappeared with the width of the bonding joints increasing. And the honeycomb structure with the bonding width of 10mm was flexible and successfully fabricated. Finally, the thickness distribution of the structure was measured and it was consistent with the FEM results. The obvious microstructure evolution resulted in the reduction of tensile property. The compressive property of this structure in experiment and in FEM was investigated. The compressive strength of experimental test was 7.7MPa and that of the FEM was 6.6MPa, respectively.

The superplastic forming/diffusion bonding and mechanical property of TA15 alloy for four‐layer hollow structure with squad grid

The superplastic forming/diffusion bonding (SPF/DB) process has been widely applied to manufacture the multi-layer components. In this paper, a four-layer hollow structure with squad grid was fabricated by SPF/DB process. The superplastic behavior of TA15 alloy was investigated by the uni-axial tensile tests at high temperature, and the maximum elongation of 911 % was obtained at 920 °C/0.001 s− 1. The finite element method (FEM) of the four-layer structure was conducted, and the results showed that TA15 alloy was appropriate for fabricating this complex-shaped structure. Then the four-layer hollow structure was successfully fabricated by SPF/DB process at 920 °C with the target strain rate of 0.001 s− 1. Finally, the microstructure, thickness distribution and mechanical property of the four-layer hollow structure were investigated. The grain size increased from 5 μm to 10 μm and the sound bonding interface was achieved. The thickness distribution was symmetrical in height direction. The compressive strength and the maximum bending load of the four-layer hollow structure was 50 MPa and 64.4 kN, respectively.

Study of Macroscopic Defects of Four-Layer Structure of Ti–6Al–4V During Superplastic Forming/Diffusion Bonding

Superplastic forming/ diffusion bonding (SPF/DB) is a key technology for preparation of light-weight and integrated multi-layer structures as superplastic deformation and diffusion joints can be achieved in one heat cycle. However, groove defects and inhomogeneous sheets thickness distribution usually appear during SPF/DB, which decreases the mechanical properties of multi-layer structures. In this study, numerical models of four-layer honeycomb and hollow blade structure are established and the effects of forming parameters (thickness ratio, strain rate, DB distance and width) on groove defect and thickness distribution are analyzed. The results show that groove defect for honeycomb structure can be eliminated under proper thickness ratio between face sheet to core sheet. The groove defect decreases with increasing DB distance and decreasing DB width. Insufficient deformation of vertical stiffener is the main problem for hollow blade structure and it can be improved by adjustment of the sheets thickness and the strain rate. Experiments are conducted on the basis of optimized parameters from simulation and agree with results from FEM. This study provides guidance for parameters selection for manufacturing of Ti–6Al–4V multi-layer structure.

Deformation behavior and mechanical properties of periodic topological Ti structures fabricated by superplastic forming/diffusion bonding

A variety of topological structures, including hollow warren structure (cross warren, diamond warren, triangular warren, four layer warren), 2D lattice structure (hexagonal honeycomb, tetragonal honeycomb), closed-cell foam structure (hexagonal foam, tetragonal foam), open-cell foam structure (multi-layer egg box), and three-dimensional lattice structure (pyramid, tetrahedron, X), were fabricated using the Superplastic Forming/Diffusion Bonding (SPF/DB) process. Finite element simulation was employed to investigate the forming process and mechanical behavior of different topological structures. Extensive analysis was carried out on deformation behavior and corresponding gas loading curves. In addition, the efficiency and the load-bearing features of different topological structures were also investigated. The future development of multifunctional topological structure was prospected.

Simulation and Experiment Investigation on Superplastic Forming/Diffusion Bonding Process of a Ti-6Al-4V Alloy Rear Fuselage Part

Superplastic forming/diffusion bonding (SPF/DB) process is widely used in aviation titanium alloy parts forming. PAM-STAMP was utilized to simulate the SPF/DB process of a Ti-6Al-4V double layer structure part in rear fuselage at 920°C and reach the thickness distribution of the part. Then the part was formed based on simulation. The thickness distribution of the practical part was measured and compared with the simulation result. The results show that the thickness distributions of practical and simulated part fit well with each other.

An investigation on adaptively machining the leading and tailing edges of an SPF/DB titanium hollow blade using free-form deformation

Titanium hollow blades are characterized with lightweight and high structural strength, which are widely used in advanced aircraft engines nowadays. Superplastic forming/diffusion bonding (SPF/DB) combined with numerical control (NC) milling is a major solution for manufacturing titanium hollow blades. Due to the shape deviation caused by multiple heat and pressure cycles in the SPF/DB process, it is hard to manufacture the leading and tailing edges by the milling process. This paper presents a new adaptive machining approach using free-form deformation to solve this problem. The actual SPF/DB shape of a hollow blade was firstly inspected by an on-machine measurement method. The measured point data were matched to the nominal SPF/DB shape with an improved ICP algorithm afterwards, by which the point-pairs between the measurement points and their corresponding points on the nominal SPF/DB shape were established, and the maximum modification amount of the final nominal shape was constrained. Based on the displacements between the point-pairs, an accurate FFD volume was iteratively calculated. By embedding the final nominal shape in the deformation space, a new final shape of the hollow blade was built. Finally, a series of measurement and machining tests was performed, the results of which validated the feasibility of the proposed adaptive machining approach.

A Study of Titanium Alloy Integral Control Surface Based on Superplastic Forming/Diffusion Bonding

A study of titanium alloy integral control surface based on superplastic forming/diffusion bonding(SPF/DB) has been performed by targeting on some supersonic aircraft control surface with the characteristics such as small size, high demanding for aerodynamic configuration, heat resistance, mass coefficient, strength and stiffness, etc. The structure is optimized by using APDL to obtain the best grid size and wall thickness. Due to the specific characteristics of part shape and internal structure, the combination of superplastic forming/diffusion bonding (SPF/DB) is applied to achieve the development of the part. The test results show that the best process parameters of control surface forming by employing TC4 titanium alloy four-layer panel are: forming temperature 910°C, outer pressure 1.5MPa maintained for 80min~100min; inner pressure 1.5MPa~2.0MPa maintained for 15min. By part testing, it is found that the bonding rate of diffusion bonding position reaches over 90%, no pits in the cavity, and the formed control surface after machining and edge-trimming inconformity with the design configuration. In addition, thermal and mechanical test shows that the structure meets the requirements of heat resistance, strength and stiffness.

The structural design and superplastic forming/diffusion bonding of Ti2AlNb based alloy for four-layer structure

The multilayer structure of Ti2AlNb based alloy was fabricated based on the superplastic forming/diffusion bonding (SPF/DB) in this paper. The properties of superplasticity and diffusion bonding of Ti-22Al-27Nb alloy were investigated. The uni-axial tensile experiment showed that the tensile elongation reached up to 236% at the temperature of 970°C with the strain rate of 3×10−4s−1. Based on the superplasticity, the finite element analysis of structural design was carried out and the results showed that the honeycomb structure was flexible. And the diffusion bonding experiment was carried out at the temperature of 950°C and 970°C. Combining the microstructure of bonding interface with shear strength of different joints, the diffusion bonding parameter for present alloy was: 970°C/10MPa/2h. The thickness distribution of the final structure was uniform and consistent with that of the FEA result, and the mechanical properties after SPF/DB reduced and the compressive strength of this structure behavior was about 7.7MPa.

Superplastic forming and diffusion bonding: Progress and trends

This paper summarized recent progress in metal superplasticity and the application of Superplastic Forming/Diffusion Bonding (SPF/DB) or SPF/Welding in typical structures. Various aerospace components such as three dimensional lattice structures made by SPF/DB have been demonstrated. In addition, some newly developed technologies, such as melt droplet spreading/thermo-mechanical forming (MDS/TMF), were also included. Finally, the future potential of SPF/DB technology was predicted.

Three Dimensional FEM Simulation of Titanium Hollow Blade Forming Process

With the introduction of high by-pass turbofan engines into both commercial and military aircraft industries, the fabrication of large size fan blade through superplastic forming/diffusion bonding (SPF/DB) has become a pivotal technique of turbine fan engine. There are three key steps to form a hollow blade: twisting, hot forming and SPF. In this study, a three dimensional finite element method (FEM) model is established to simulate the forming process of titanium fan blade, in which the mechanical behavior of TC4 obeys Backofen's equation. Based on the numerical modeling, the influences of key factors such as the twisting rate, descending velocity, frictional coefficient, strain rate, the sheet thickness ratio of core sheet to face sheet on the forming force were studied. The results show that with increasing of the twisting rate, descending velocity, strain rate, the sheet thickness ratio of core sheet to face sheet, the forming forces increase; however the frictional coefficient has little influence on the forming force.

초소성/확산접합 기술을 이용한 티타늄 샌드위치 경량구조물 제작

In the present study, design and forming process of fabricating titianium lightweight components are developed with applicaton of superplastic forming and diffusion bonding technology. SPF/DB(Superplastic forming/Diffusion bonding) technology is one of the advanced technologies to reduce production cost and weight and currently applied to aircrafts and space launchers in foreign countries. The present study constructs an analysis model to predict superplastic forming behavior of titanium alloy, which is well known for its resistance to deform. The experimental results show the forming of titanium lightweight sandwich structure is successfully performed from 3 sheets of Ti-6Al-4V. The results demonstrate that the developed technology to process design of SPF/DB by the finite element method can be applied to various types of components.

단계적 가압을 이용한 초소성 성형/확산접합의 공정설계

Superplastic forming/diffusion bonding(SPF/DB) has been widely used in the automotive and aerospace industry since it has great advantages to produce very light and strong components. Finite element method(FEM) is used to model the SPF/DB process of 3-sheet sandwich panel to predict the pressure-time curve and to analyze the process parameters. In order to eliminate defects of the part, a new pressurization scheme is proposed. Contrary to the conventional one-step pressurization, which causes the folding at the DB joint, two-step pressurization can eliminate the folding. Effect of pressurization cycle was investigated by using FE analysis and proper pressurization cycle is proposed.

계층적 접촉 탐색방법을 이용한 3-D 초소성 성형/확산접합의 공정설계(I)

Superplastic forming/diffusion bonding (SPF/DB) processes were analyzed using a 3-D rigid visco-plastic finite element method. A constant-triangular element based on membrane approximation and an incremental theory of plasticity are employed for the formulation. The coulomb friction law is used for interface friction between tool and material. Pressure-time relationship for a given optimal strain rate is calculated by stress and pressure values at the previous iteration step. In order to improve the contact searching, hierarchical search algorithm has been applied and implemented into the code. Various geometries including sandwich panel and 3 sheet shape for 3-D SPF/DB model are analyzed using the developed program. The validity fer the analysis is verified by comparison between analysis and results in the literature.

실험계획법을 이용한 초소성 성형/확산접합의 공정설계

The superplastic forming/diffusion bonding(SPF/DB) is widely used in the automotive and aerospace industry because it has great advantage to produce complex, light and strong parts. But the superplastic forming process requires much forming time and generates excessive thinning in the thickness distribution of formed part. It is necessary to minimize trial and error for SPF/DB Process. Finite element analysis using orthogonal may table of Taguchi method for 3-Sheet D/B process is carried out. Through the study, effect of process parameters, such as DH region size, thickness and friction coefficient, is evaluated and the optimum condition is derived.

Weldability and microstructure of laser-surface-remelted TiAl intermetallic alloy

Through the combination of superplastic forming/diffusion bonding (SPF/DB) with laser surface processing, a new approach to join TiAl workpieces is proposed. In situ observations of the transformation of laser-surface-remelted TiAl intermetallic alloy (LSMTIA) were carried out during heating. The effect of different temperatures on the rate of dendritic structure refinement and the mechanism of refinement were discussed. The results show that the metastable microstructure of TiAl alloy obtained by laser surface remelting can be transformed into fine, equiaxed grains at certain elevated temperatures, and the structural transformation rate accelerates with the elevation of heating temperature. During continuous heating with a heating rate of 10 °C min−1, the dendritic structure is transformed into fine-grained structure at about 860 °C; the hardness of LSMTIA varies correspondingly. The fine-grained structure and the property variation of LSMTIA offer a good basis to SPF/DB. With significant microstructural refinement achieved by laser treatment of the surface and subsequent heat treatment, SPF/DB at a lower temperature and in a shorter time than conventional SPF/DB was achieved, and the bonding effects brought by temperature, pressure and time were discussed, respectively. The results show that, at the condition of 900 °C and 60 MPa, sound bonds could be obtained in 1 h.

Variation of structure and properties in laser surface melted titanium aluminide during continuous heating

Structural transformation and variation of hardness in laser surface melted TiAl intermetallic alloy (LSMTIA) are studied systematically during continuous heating. The results show that, during continuous heating from 50 to 1000 °C with a heating rate of 10 °C/min, α 2→γ phase transformation takes place at about 750 °C, and the dendritic structure is transformed into fine-grained structure at about 860 °C, at the same time, the hardness of LSMTIA varies correspondingly. This kind of fine-grain structure offers a good basis to superplastic forming/diffusion bonding (SPF/DB).

Fracture Toughness of Superplastic Formed/Diffusion Bonded Interfaces

The present paper is concerned with the interfacial fracture problem of bi-material interfaces of superplastic forming/diffusion bonding (SPF/DB) components. It has been known that the interfacial fracture toughness is a strong function of the mode mixture of crack tip, which is the most important characteristic of interfacial problems. Micromechanical models have been proposed to understand this trend of interfacial toughness curves, based on which a modified criterion for fracture under mixed-mode loading is advanced in this paper to predict phenomenological functional forms of toughness curves. On the ground of linear elastic fracture mechanics (LEFM), mode I and mode II interfacial fracture toughnesses of SPF/DB components formed under different processing conditions have been measured in this paper using the double cantilever beam (DCB) and end-notched flexure (ENF) specimens, respectively. It is found that, just as is the general trend of interfacial fracture toughness curves, the experimental results of mode II toughness values are much greater than those of mode I toughness values, and the fluctuation of mode II toughness values under different processing conditions is much greater than that of mode I toughness values. On the basis of the experimental results, the four basic parameters in the modified criterion are obtained and the interfacial toughness curve of Ti-50A/Ti-6Al-4V SPF/DB components is determined using the modified criterion for fracture under mixed-mode loading. Comparison between the results shows that the agreement between experiment and theory is excellent.

Simulation of superplastic forming/diffusion bonding with finite-element analysis using the convective coordinate system

Abstract Superplastic-forming processes are simulated with finite-element analysis in the convective coordinate system. The finite-element code developed is applied to blow-forming processes for demonstration of its validity by predicting the optimum forming pressure cycle. The numerical results provide the pole height and intermediate deformed shapes with variation of the forming time, as well as thickness distribution. The results are compared with those from the experiment and finite-element analysis with a continuum element. The finite-element code is applied to the analysis of a superplastic-forming/diffusion-bonding (SPF/DB) process of four-sheet sandwich parts. The result shows that the deformed shape with the three-dimensional analysis is different from that with the two-dimensional plane strain because of the end effect, and so is the thickness distribution. The analysis enables accurate prediction of thickness distribution, which is necessary for the good design of multi-sheet sandwich parts such as an aircraft part.

Design of Advanced Titanium Structures

The emergence of new titanium fabrication techniques has opened up new possibilities for achieving high structural efficiency at considerably reduced costs. Superplastic forming/diffusion bonding (SPF/DB), combined with conventional metallurgical joining techniques, has been shown to effect weight reductions in future weapon systems. This paper shows how the basic steps utilized in structural design were altered in the application of SPF/DB to a Mach 2.0 aircraft.