The constantly increasing economical and ecological concerns in the automotive and aerospace industries have resulted in high demand for improved fuel economy and greater vehicle performance. Lightweight construction is critical for reducing inertial and rolling resistance losses to increase the product performance while maintaining safety and functional requirements. This will open a wide variety of opportunities to implement materials with high strength-to-weight ratios, such as aluminum, magnesium, stainless steel and titanium alloys. However, when using conventional forming processes, these light materials bring about processing challenges: low formability, high yield strength and low strain hardening coefficients. Electrically-Assisted Forming (EAF) is a method of overcoming these limitations. Specifically, EAF is a novel forming process where electricity, AC or DC, is applied to the metallic workpiece through the dies during deformation. Previous experimental investigations have shown that EAF can lead to reductions in flow stress and power consumption, increase in formability through larger achievable strains, the ability to reduce/eliminate springback, and improved precision. This study investigates the influence of electricity on the different lubrication mechanisms by evaluating lubricant performance in an EAF process and identifying potential lubricant candidates for EAF. The tribological conditions have a significant influence on the frictional forces occurring at the die/workpiece interface, thus on the forming load, part quality, and achievable form. When electricity is applied, besides the changes due to surface expansion at the interface occurring in conventional processes, the lubricant is exposed to high localized temperatures and current fields. To analyze this, electrically-assisted ring compression tests are conducted and the performance characteristics of several lubricants are studied. By combining the experiments and finite element simulation results, friction coefficients can be estimated, and the effect of electric current flow on friction characteristics quantified. One goal of this study is to identify possible lubricant candidates to be used in EAF processes.

Pressure welding technology is a solid state bonding process and generally involves heating the metal surfaces and then applying a suitable amount of axial pressure. In this state the metal components being joined undergo only microscopic deformation and the joining region is homogeneous and complete metallurgical bonding is possible without secondary materials or liquid phases. In the present work, pressure welding of titanium alloys has been investigated to fabricate several aerospace components with various complex configure. The result shows that the pressure welding method has been successfully applied with blow forming for near net shape forming of aerospace components, including high pressure tank for attitude control of spacecraft, and other lightweight structural panels.

It was recently demonstrated that significant increases in formability in tube hydroforming (THF) can be achieved if the load is applied in a pulsed, as opposed to the monotonic, manner. The frequency of such loading is of the order of 1 Hz, and the benefits can be observed in the case of free inflation of a tube (i.e., without a die), as well. Hence the mechanism of such improvements is not related to enhanced tribological conditions between the tube and the die, as is the case in the ultrasonic THF. In an effort to understand if and how the pulsed application of the load affects the material ductility, specimens from stainless steel 304 were subjected to uniaxial tension, with the load applied in a pulsed manner. The results of these experiments were compared to the corresponding monotonic cases under the same strain rates. Significant increases in ductility can be noted between the two types of loadings. Subsequently, further experiments described in the paper revealed that the deformation-induced heating of the stainless steel is often responsible for this behavior. However, if the loading is rather slow, the ductility enhancement is still observed, but cannot be attributed to the specimen heating.

In Electrical-Assisted Forming (EAF), current is passed through the material during the deformation process, which results in a decrease in the required flow stress for the material. While resistive heating occurs, the flow stress reductions are beyond what can be explained by temperature effects alone. Hypotheses for this effect relate to the current affecting dislocation generation and aiding dislocation motion through the lattice structure. If the latter was the case, then materials with higher dislocation densities from severe deformation should have more pronounced benefits from EAF. In this research, Equal Channel Angular Extrusion (ECAE) was used to induce severe plastic deformation into the material. Subsequent EAF compression experiments with the ECAE specimens and as-received material with comparable grain sizes were conducted. As expected, the EAF process reduced the flow stress value substantially more, e.g., 224MPa versus 115MPa at a strain of 0.8 for the ECAE specimens compared to the as-received specimens respectively. These flow stress reductions were from a case with no current applied to a case where an initial current density of 250A/mm 2 was applied. EAF may particularly be beneficial at the microscale to address size effects as the current required to achieve an elevated current density is more viable.

Edge cracking is one of the major issues for stamping Advanced High Strength Steel (AHSS). This type of cracking is influenced by three major factors: the material property, the die condition and the shearing/blanking process. The current shearing/blanking process has been applied to traditional mild steels for years and has not been modified for shearing AHSS. Other than the high energy laser cutting process, the traditional die cutting process would generate a rough edge (burr) with micro cracks in shearing/blanking edges for AHSS, which could serve as the crack initiation during forming. This study is to investigate the effects of shear edge conditions on edge cracking for AHSS. A special hole shearing process has been developed on a laboratory hydraulic press. Different shearing parameters, including die clearance, cutting angle and material orientations, were investigated in terms of shear edge conditions. The hole expansion test was conducted to evaluate the effects of shear edge conditions on the material edge stretchability. Results showed that an optimal selection of die clearance and shearing angle can greatly increase the edge stretchability for AHSS.

A new bending technique was presented for forming very thin metal tubes, which is characterized by ball filler in the tube as force-transferring media during bending process. Due to the good flow capacity and non-uniform pressure, ball filler is considered as an alternative filler to bend very thin tubes. The experiments of ball filler push bending were carried out for very thin copper tubes. The results indicate that the back pressure and lubrication condition have great effects on the forming quality of the tubes. As the back pressure increases and/or lubrication condition improves, the tube surface quality is improved. The ovality of the bent tube is small, and the intrados and extrados wall thickness are both thickened and changed uniformly, which indicates that the new process applied to form the very thin tubes is feasible.

Tube Hydroforming (THF) is a metal-forming process that uses a pressurized fluid in place of a hard tool to plastically deform a given tube into a desired shape. In addition to the internal pressure, the tube material is fed axially toward the die cavity. This process has various applications in the automotive, aerospace, and bicycle industries. Accurate coordination of the fluid pressure and axial feed, collectively referred to as a loading path, is critical to THF. Workable loading paths are currently determined by trial and error, which can be time consuming. This paper discusses an innovative technique for developing an interactive, real-time database that would be able to predict loading paths for typical classes of THF products and hence, reduce the computational time required. By classifying most of the commercial THF parts into families, parameters such as material properties, part geometry, and tribological factors were simulated by category and stored in the database. Multidimensional cubic spline interpolation was implemented to enable an end user to request from the database a loading path for a wide range of conditions. Test results from the database for different THF families were shown to approximate the simulated results. In addition, by reducing the computation time, the use of interpolation techniques eliminates the need for carrying out multiple simulations for similar THF parts.

The paper is presented a dynamic installation used for determination the elastic characteristics of gypsum materials, such as elasticity modulus-E, rigidity modulus-G, etc. This dynamic installation is composed from: mechanical device for application of axial force, cylindrical gypsum samples on which are fixed 2 strain gages, 2 bridges circuit type “Switch & Balance Unite SB-10 with digital Strain Indicator-P3500, A/D board and PC. As the samples are used two cylinders with differently gypsum compositions: gypsum of dressing and light orthopedic corsets, and from gypsum with sonic absorbent and thermal isolator properties. The acquisition and the interpretation of data with MATLAB program is realized, by used two original programs: “Daquest-2m” for acquisition data, and “Evaluation-1m” for calculation and plot diagram of shock wave time. By determination of shock propagation time passing through the gypsum sample can be calculated the wave velocity and the elasticity modulus of gypsum tested. For building materials on base of gypsum with special applications in medicine, and panels with sonic absorbent and thermal isolator properties are demand to determine the elastic characteristics to enhance the manufacturing process and usefully.

Traditional tube flaring processes focuses on expanding one end of the tube without changing its cross-sectional shape. This paper presents a new two-step tube flaring process for expanding one end of a titanium alloy microtube while simultaneously changing its cross-sectional shape from circular to elliptical. Experiments were performed to investigate and verify this process. Furthermore, an analytical model was developed to analyze the forming process and investigate the relationship between punch feed and maximum plastic strain during the flaring process. The analysis shows that the two-step flaring process used is effective in expanding the circular cross section to an elliptical cross section without failure. It is also shown that the developed analytical model can predict the fracture of the tube end during the flaring process approximately. Finally, a FEM simulation was performed to further investigate the two-step flaring process.

In the present study, the loading path with constant internal fluid pressure during axial feeding to hydroform an automotive structural part with higher expansion ratio was investigated. The axial feedings employed at various internal fluid pressures were simulated by the finite element method. It is found that the axial feeding applied at a favorable internal fluid pressure, the production part with higher expansion ratio still could be made. Compared with other loading paths published in literature, which are mainly linear paths, the proposed loading path provides a simple approach to achieve better performance in the hydroforming process. The factors causing wrinkling fin the hydroforming process were also studied by analyzing the relationship between the die face shape and the material flow in the die cavity. An optimum die face design that avoided pinching at the die closing process was then proposed. The actual hydroforming process for manufacturing the automotive structural part was conducted as well in the present study to validate the proposed loading path and the optimum die face design. The consistent agreement between the production part and the finite element simulation results confirms not only the proposed loading path and die face design, but also the effectiveness of the finite element analysis employed in the tube-hydroforming process.

A new method of incremental forming was introduced and investigated, which used a tool with multiple heads turning around holding mandrels freely. In order to investigate the advantages of this method, experiment and forming analysis were done. In this process, some truncated components were made from thin Al2024-O Aluminium plate with inward tool path. An analysis model of tool path was created with geometric method. A calculation of strain and stress distribution was developed and compared with experimental results. And an investigation of forming limit was made by experiments with truncated pyramid and strip shape. The results agreed with each other. It has been shown that this method can easily improve the forming efficiency and surface roughness.

This paper describes the development and implementation of closed-loop control for an oval stamp forming die using Matlab ® ’s Simulink ® and the dSPACE ® ControlDesk ® . A traditional PID controller was used for the blank holder pressure and an advanced controller utilizing fuzzy logic combining a Linear Quadratic Gauss controller and a Bang-Bang controller. The draw beads were used to control local forces near the draw beads. The blank holder pressures were used to control both wrinkling and local forces during forces. It was demonstrated that a complex, advanced controller could be modeled using Matlab’s Simulink and implemented in dSPACE ControlDesk. The resulting control systems for blank holder pressures and draw beads were used to control simultaneously local punch forces and wrinkling during the forming operation resulting in a complex control strategy that could be used to improve the robustness of stamp forming dies.

Hydro and pneumatic sheet metal forming operations are commonly carried out at warm and elevated temperature; hence for modelling the behaviours of the formed materials, testing at such temperatures is necessary. The uniaxial tensile test is the most universally-adopted mechanical testing procedure for material characterisation purposes; yet in spite of its simplicity and standardisation for room temperature testing, the test is problematic at higher than-ambient-temperatures. Perhaps that explains the disagreements between different researchers in the field on some of the most critical aspects of the test. Crucially, any inaccuracies in warm and elevated temperature tensile testing have direct impact on the accuracy of the constitutive models and finite element simulations, which we rely on in running and optimising hydro/pneumatic forming operations. This work presents a comprehensive testing methodology that aims at resolving the most critical of issues encountered in this unique type of testing. The methodology is centred about quick-mount grips that tackle the thermal issues by facilitating mounting the test specimen in a very short time. A testing procedure is devised accordingly, and preliminary testing results are presented to demonstrate the impact of the methodology on the accuracy of the results. In addition, the effect of the specimen geometry on the test outcome is investigated using a wide variety of geometries; an optimised geometry is derived based on the obtained experimental results. The methodology is validated by testing AZ31B-H24 magnesium alloy specimens at different temperatures and strain rates.

Servo presses are recently introduced metal forming machinery and they are in many ways, a hybrid of mechanical and hydraulic presses. They are designed to combine the strengths of conventional mechanical and hydraulic presses, and at the same time to minimize their constraints. The advantages of servo presses in metal forming technology are discussed briefly. Advantages they offer in warm forming are discussed more in detail and demonstrated experimentally. By using the flexibility that the servo press offers, the effect of contact pressure on temperature change and surface roughness of aluminum and magnesium sheet is experimentally investigated. Non-isothermal warm forming is introduced and studied experimentally. Combined advantages of the non-isothermal approach and the servo motor controlled press are demonstrated by introducing a variable forming speed concept. As a result, 60% savings in cup drawing time is achieved experimentally. Measured temperature curves were used in FEA to determine heat transfer coefficients. Effect of the determined heat transfer coefficients on deep drawing was analyzed using FEA and good agreement were obtained between FEA predictions and experimental measurements.

A common manufacturing process typically used to create large surface contours in sheet metal is stretch forming. With this process, the ability to create geometrically accurate parts and smooth surfaces is achievable, yet there are certain limits when considering the achievable elongation of the material and the inability to produce sharp contours in the sheet metal. Present research using Electrically-Assisted Manufacturing (EAM) has shown that applying direct electrical current to the workpiece during the forming process can increase the formability and reduce springback of the material, while also lowering the required forming forces. Seeing the advantageous qualities of EAM, this study examines the use of EAM for a simple stretch forming process. Specifically, this research examines this stretch forming process with regards to how the location where the electrical current is applied to the material affects the process, the achievable forming depth without fracture, and the application direction of the current. Overall results displayed that the directional flow of electrical current and the application location did not affect the obtained forming forces or forming depths using EAM.

The merits of warm and elevated temperature hydro/pneumatic sheet metal forming operations, most prominently superplastic and quick plastic forming, have been ever counteracted by two major drawbacks: slow forming rates and non-uniform thickness distribution with potentially severe thinning. Trying to resolve one of the two issues has generally led to escalating the other, so a compromise based on the nature of the part being formed is often targeted. To tackle the latter of the two issues, imposing a pre-thinning reverse bulging step has been shown to ease the problem with specific part geometries that involve large plastic strains and intricate details. The aerospace industry, however, is the prime sector that is able to afford the “seemingly” prolonged forming times associated with this approach. Yet with the lack of adequate details on the implications of utilising reverse bulging, this effort explores some of the hidden merits of the approach. A recently-developed simple monitoring technique for providing a direct feedback on the sheet’s advancement during pneumatic forming operations, coupled with an interrupted testing methodology, are utilised to have a closer look at the process. The results reveal significant time-savings that can be achieved with the proper use of reverse bulging, for both simple and complex part geometries.

A fuzzy inference system with an associated database was developed in order to determine the forming conditions required to obtain the objective height of a drawn cup using magnesium alloy sheet. The results from both experimental and finite element analyses (FEA) have been used for constructing the database which contains information on the forming conditions used and the resultant height of the drawn cup. A case study utilizing circular-cup deep-drawing was used to test the inference system, whereby experimental results for the height of the drawn cup using specific forming conditions (temperature, blank size and blank holding force) agreed with those predicted using the inference system. This confirms the validity of the inference system. Furthermore, a learning method was developed in order to improve the system using further experimental results, the FEA results and a fuzzy algorithm. The experimental analysis showed good agreement between the required objective height and the experimentally measured height of the drawn cup.

The marriage of the Tube HydroForming (THF) process with metal foams is interesting for different reasons: a) THF parts are naturally suited as cases to be filled by an internal metallic foam reinforcement and therefore for structural applications; b) the possibility to increase the mechanical strength of hydroformed parts allows to plan the THF process more freely and flexibly. These components, made of an outer hollow thin compact metal skin and a cellular lightweight core may find several applications in different industrial fields. In order to allow for an efficient and effective product/process design with a concurrent engineering approach, the structural performance of these composite parts must be predicted by means of FEM calculation. The optimal combination of tube and metal foam properties must be found. While FEM simulation of bending and hydroforming is state of the art, the accurate FEM simulation of the mechanical behavior of metal foams cannot be considered fully established. In the first part of this paper the foam-filling production cycle of a simple hydroformed aluminum part is shown, in order to discuss some of the design and manufacturing issues that can be faced in FEM based product/process analysis, concerning the thermal effects on the tube materials, the ability of completely filling the tube, the foam/tube interface conditions, the uniformity of cell distribution. A few potential applications of foam-filled hydroformed tubes are also presented. In the second part of the paper, the common methods and formulations for FEM simulation of foam based structures are discussed, and a new and very promising method is proposed.

The variable thickness tube drawing is a new modification in the tube drawing methods which enables production of axially variable thickness tubes faster and easier in comparison with other similar methods like radial forging or indentation forging. The production of this type of tubes can be used in optimum design of mechanical parts which do not necessarily need constant thickness along the axis of tube and this method can strikingly reduce the overall weight of parts and mechanical assemblies like cars. In this paper, the variable thickness tube drawing were parameterized in a MATLAB code and optimized with the Ls-Opt software as an optimization engine and Ls-Dyna as a FE solver. The final objective of this optimization study is to determine the minimum thickness which can be produced in one step by this method with various tube dimensions (tube thickness and outer diameter). For verification of results, some experiments were performed in the tube drawing machine which was fabricated by this research group and acceptable correspondence was observed between numerical and experimental results.

This paper proposes a novel thin shell curved surface forming method by dieless single point forming technology embodying the thought of the parallel running for both design and manufacture. And a sheet metal superplastic forming prototype system with a heterogeneous master-slave manipulator by force-reflecting control has been developed. The system mainly consists of mechanical transmission components, servo system, online optical scaler for the measurement and the path planning of the forming tool. The final ideal forming experiment has physically testified the feasibility of the mutual forming method for the shell sample of a panda model. This paper brings up the tentative idea of real object modification with the use of heptic force-feedback.