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The hot extrusion process can effectively refine the coarse grains of metastable β titanium alloy billet, thereby enhancing the material's internal microstructure and mechanical properties. This study explored the hot deformation behavior of as-cast Ti-6554 samples at temperatures ranging from 900 °C to 1150 °C and strain rates between 0.001 s-1 and 1 s-1 by a Gleeble-3500 tester. The Arrhenius constitutive model was established to simulated the hot extrusion process. Parameters such as the degree of deformation (x), metal plastic flow (μ), and deformation temperature (θ) were introduced to quantify the uniformity of distribution under various processes. Based on the simulation results, the optimal extrusion conditions were determined to be an extrusion ratio of 10, an extrusion angle of 60°, an extrusion velocity of 40 mm/s, a preheating temperature of 1100 °C, and an extrusion load of 2500 tf. Examination of the microstructure of the hot-extruded bar revealed that grain sizes consistently decreased from the centers towards the edges. The grains were refined from 2000~5000 μm to 100~200 μm after extrusion, demonstrating that the deformation degree, plastic flow and deformation temperature were well coordinated under these conditions. [ABSTRACT FROM AUTHOR]

Electromagnetic incremental forming (EMIF) is employed for forming large-sized parts of aluminum. The basic characteristic of EMIF is multi-electromagnetic forming (EMF). The forming uniformity of a multi-EMF is the key to the success of an EMIF method. In this study, first, several important parameters affecting the forming uniformity of single EMF are studied using orthogonal experimental research scheme. In order to conduct a comparative study on the forming uniformity of the multi-EMF, two-coil moving strategy is selected. Thereafter, the effect of overlap ratio on the forming uniformity of the multi-EMF is studied using the coil sequence moving strategy. The effect of shaping voltage is also investigated using the coil spaced moving strategy. Based on the findings, the optimum conditions of forming uniformity of the multi-EMF are obtained. An experimental verification of the simulation results is also conducted. The obtained results present a viable method and guidance for EMIF of large-sized aluminum alloy sheet metal parts. [ABSTRACT FROM AUTHOR]

Discharge coil is the core component of the traditional electromagnetic forming technology. However, the machining of discharge coil is difficult, and the manufacturing cost is expensive. The durability of the coil is also challenged due to the effect of temperature rise, and accumulated coil deformation leads to a change in coil parameters during multiple discharges, which seriously restricts the industrial application of electromagnetic forming. This paper proposes a new electromagnetic forming method, named direct pulse current electromagnetic forming (DPCEMF). The traditional electromagnetic forming method loads the current to the coil, and then, an eddy is inducted on the surface of the workpiece conductor near the coil. However, the new method is a reverse approach, that is, the workpiece is directly loaded with a pulse current, and the surface of the high-conductivity metal block near the workpiece induces an opposite eddy and produces a repulsive electromagnetic force, which in turn causes the high-speed deformation of the workpiece. The discharge coil of conventional electromagnetic forming is replaced with a high-conductivity metal block, which greatly improves the strength, service life, and reliability of the forming system. The DPCEMF process is thermoplastic electromagnetic forming in which heating and electromagnetic forming are conducted simultaneously and completed in microseconds. The method has been well verified by experiments to overcome the forming of a difficult-to-form material, taking a solid step toward realizing the industrial application of electromagnetic forming. [ABSTRACT FROM AUTHOR]

Adhesively bonded sandwich structure with dissimilar materials becomes an important means of lightweight for the next generation of autobody closure panels. However, during the baking process, the complicated change of physical properties of the adhesive can lead to structural mismatch deformation. In this paper, a multi-physics coupling numerical model of the curing process is proposed to reveal the deformation mechanism of adhesively bonded sandwich structures quantitatively. The material constitutive model of the one-component hemming adhesive hemming adhesive is established, considering evolution of curing properties. The curing process of typical aluminum alloy and steel-bonded sandwich structure is simulated in COMSOL Multiphysics. The predicted surface deformation of the component is verified by experiment using Digital Image Correlation (DIC) technique, which captures the full-field displacement in a non-intrusive manner. Then, the development process of surface deformation of the outer panel and residual internal stress of the adhesive layer is analyzed, and the influence of temperature cycle on the maximum deformation of the component is discussed. The results show that at the beginning of holding stage, the deformed component slightly rebounds, which is related to the chemical shrinkage. Mechanical strain caused by the coefficient of thermal expansion (CTE) and stiffness difference of the inner and outer panels is dominant in the adhesive layer. Reducing the curing rate and maximum holding temperature can reduce the overall deformation of the structure. [ABSTRACT FROM AUTHOR]

Electromagnetic impaction forming of 5052 aluminium alloy sheets using a V-shaped die and a conical die was performed. The conventional quasi-static forming limit curve (QS-FLC) is obtained according to the linear loading condition, which can only describe linear strain paths. However, it cannot accurately evaluate the formability of electromagnetic impaction forming, especially strain paths that have become highly non-linear. In this study, the formability of electromagnetic impaction forming, which considers a bilinear strain path and a continuous highly non-linear strain path, was investigated. The conventional QS-FLC is no longer suitable to evaluate the formability of electromagnetic impaction forming. Therefore, modified FLCs were established in strain space that follow bilinear strain paths and continuous non-linear strain paths. The actual formability improvement was compared with the modified FLC. The maximum safe strain of bilinear strain paths near the sidewall of V-shaped specimens increased in formability by approximately 30% at the discharge voltage of 20 kV compared with conventional QS forming. The maximum safe strains near the apex of the conical specimens increased in formability by approximately 100% at the same discharge energy. It should be noted that the increase in formability above the modified FLC is a conservative estimate, because the limit strains at the necking location were not known in the electromagnetic impaction forming. The influencing factors of the formability improvement of 5052 aluminium alloy sheet in electromagnetic impaction forming were also discussed. [ABSTRACT FROM AUTHOR]

Electromagnetic blanking (EMB) based on force-free region deformation is proposed to meet the no burr forming requirement of diaphragm parts for carrier rockets in the aerospace field. Deformation behaviors of the part were revealed along with the effects of key process parameters on the forming quality investigated. During the EMB process, the electromagnetic force, effective stress, and plastic strain were distributed in a rather uniform annular region and peaked near the edge of the die. High-speed deformation coupled tension and bending were evidenced. With the increase in discharge voltage, the diameter of the part reduced slightly, and the filling degree of the trimmed edge section reduced remarkably, while the thickness uniformity was improved. It was found that the filling degree was dependent on the deformation degree and the interaction between two different regions. Similar effects of initial blank diameter and discharge voltage were observed. The interaction was notable at a larger initial blank diameter, causing the sharper drop in the filling degree. The forming quality could be improved by using a blank holder, but an undesirable extra deformation zone would appear. In a word, the proposed EMB process is capable of forming no burr diaphragm part with high quality. [ABSTRACT FROM AUTHOR]

Aiming to the precise control of forming quality in electromagnetic incremental forming (EMIF), deformation behaviors of a spherical crown-shaped thin-walled workpiece during a single layer forming of EMIF are analyzed by means of numerical simulation. The influences of the coil overlap ratio, coil moving strategy, and discharge voltage combination on the forming uniformity of the workpiece are revealed. The maximum electromagnetic force and forming depth represent a "dramatic decrease–long-term steady–moderate decrease" variation over the increase of discharge time for forming a single layer by sequential discharging. The difficult-to-deform region located outside the overlap region of coil positions deforms insufficiently, leading to poor overall uniformity. Better uniformity and higher forming efficiency are achieved by sequential discharging compared with interval discharging. With an increase in the coil overlap ratio, the circumferential uniformity of the workpiece is improved because the transition deformation region is reduced and the active deformation region subjected to electromagnetic force is increased. In addition, the forming uniformity of the workpiece can be improved significantly by an optimized discharge voltage combination with properly decreased first discharge voltage and increased last discharge voltage, respectively. A forming scheme for a spherical crown-shaped thin-walled workpiece is proposed based on the forming principles and a workpiece with high precision and good uniformity is obtained. Therefore, EMIF is demonstrated as capable to form high precision large-size thin-walled parts. [ABSTRACT FROM AUTHOR]

Electromagnetic-assisted forming (EMAF) combining quasi-static stamping and electromagnetic forming (EMF) is a potential method for controlling the springback of aluminium alloy materials. In this study, to further promote the application of EMAF in the high-precision forming of aluminium alloy sheet parts, the springback during electromagnetic-assisted bending of aluminium alloy sheet was investigated using a custom-designed U-shaped bending tool with the optimised curved spiral coils. Two types of conditions to control springback were designed: gapless and gap conditions, and the springback under these conditions was studied both experimentally and using numerical simulations. In addition, the effects of the discharge parameters on springback were analysed. Finally, the mechanism for controlling springback under different forming conditions was revealed. The results showed that the efficiency of springback control was significantly higher under gap conditions compared with gapless condition. With increasing gap, the springback angle decreased, but negative springback easily occurred when using excessively wide gaps. As the discharge voltage or number of discharges increased, the tangential stress of the fillet area decreased, thereby reducing the springback angle. Stress oscillations under the gapless condition reduced the tangential stress of the fillet area to a certain extent, while inertial motions under gap conditions greatly reduced the tangential stress, which were the essential mechanism for the observed springback reduction. [ABSTRACT FROM AUTHOR]

For the manufacturing of large-scale sheet parts, traditional stamping, spinning, and single-point incremental forming are limited by the rupture prone and severe springback of the formed parts and the requirement of large-scale forming equipment. In this paper, the method of electromagnetic incremental forming (EMIF) based on dual coil was creatively proposed to solve the manufacturing problem of large-scale parts of aluminum alloy. The forming results of EMIF based on single coil and EMIF based on dual coil are compared by finite element simulation. The effect of the two moving strategies on uniformity in EMIF based on dual coil was researched. In addition, the effect of the shaping voltage on uniformity in EMIF based on dual coil with the interval moving strategy was studied. It was observed that the forming quality of EMIF with dual coil was better than that of EMIF with single coil. For EMIF based on dual coil, the interval moving strategy is better than the sequential moving strategy in achieving better forming quality. For the first layer of EMIF based on dual coil with the interval moving strategy, the optimized forming voltage and shaping voltage were 12 kV and 18 kV, respectively. For the second layer of EMIF based on dual coil with interval moving strategy, the optimized forming voltage and shaping voltage were 18 kV and 27 kV, respectively. The shaping voltage was 1.5 times of forming voltage for both layers so that better forming uniformity was achieved. Then, the method of EMIF based on dual coil with interval moving strategy by multilayers is proposed to fabricate large-scale sheet parts. Finally, experiments were performed to confirm the feasibility of EMIF with dual coil, and the experiment results show good agreement with the simulation results. The findings of this work could provide guidance on deform large-scale parts of aluminum alloy by the EMIF method. [ABSTRACT FROM AUTHOR]

In the forming process of rib-web parts, which are widely used in automobiles and aircrafts, severe streamline disorder often occurs because of unreasonable metal flow. In this study, a back-pressure-controlled forming method that can control the direction of metal flow was introduced. The effects of key parameters on metal flow were investigated, including the back-pressure value, loading mode, and back-pressure distance. The results showed that streamline defects can be avoided and the final forming load can be reduced by reasonably controlling the back-pressure parameters. The constant back-pressure mode was more conducive to achieving good forming quality compared with the linear-increased back-pressure mode. From the stress analysis of metal flow, it was demonstrated that the stress state in the rib root is changed by the back pressure, which makes the metal flow more easily along either the tangential or the radial direction. The advantages of the back-pressure-controlled forming method were confirmed by applying it to a compressor scroll rotor. [ABSTRACT FROM AUTHOR]

The electromagnetic forming (EMF) process is an attractive high-speed manufacturing technique that is appropriate for aluminium alloys. This paper outlines experimental work conducted to determine the influence of different process parameters, such as the discharge voltage, lubrication, blank holder force and two-step EMF process, on the dome height, diameter, maximum major/minor strains, strain distribution and thickness distribution of AA 5052 and AA 5754 sheets through the process of electromagnetic free forming. The results show that the dome height and the maximum strain of specimens exhibit linear positive correlations with the discharge voltage. Maximum major strains on the order of 35-45% emerge at the sidewall near the top of the domes, which is also the main area for the thickness reduction, indicating that the inertia effect plays a key role in the EMF process. Increasing lubrication levels or decreasing the blank holder force can augment the deformation height, reduce the major strains and promote material flow. When discharge occurs at the same location, the two-step EMF process does not increase the forming height but can obviously improve the flow of material compared to one-step forming. Furthermore, an appropriate follow-up discharge voltage can thicken the area of the specimen at which necking most easily emerges and reduce the major strains, thereby improving sheet formability. [ABSTRACT FROM AUTHOR]

The ANSYS software was used to establish an electromagnetic-structural coupling model and simulate the electromagnetic tube bulging process. Compared to the experimental results, the maximum simulation error was approximately 4 % at the longitudinal center of the tube. Then, the simulation method was used to analyze the effects of multidirectional magnetic force on the tube bulging process. The results indicate that an axial magnetic force can be generated at the tube end by setting the coil at the end of the tube. The values of material flow, stress, plastic strain, and thickness in different forming processes were compared. Compared to traditional forming processes, electromagnetic tube bulging with multidirectional magnetic pressure can significantly increase the axial feeding, decrease the tensile stress, and reduce the thickness at the easily broken position. Therefore, a higher bulging height can be obtained by the new method. [ABSTRACT FROM AUTHOR]

In the conventional drawing process, the predominant failure modes of a sheet metal are wrinkling and fracture. Wrinkling during the forming process can often be treated as a recoverable defect as it can be eliminated though the appropriate control of the blank holding force. Fracture, however, is a fatal flaw. When the fracture occurs, the drawing process cannot continue. We propose a new forming method that can handle large height/diameter ratios. The new method uses electromagnetic pulse-assisted incremental drawing (EMPAID) together with radial magnetic force and a suitable auxiliary coil structure and size. Both the calculated and experimental results indicate that the magnetic force generated by the auxiliary coils can increase the flange material flow and significantly improve the ability of the sheet metal to resist fracture. When only the auxiliary coil is used in the experiment, the drawing depth increases by 21.8 % (with respect to conventional drawing) if the auxiliary coils discharge once. The drawing depth can be increased by as much as 36.7 % when multiple discharges are applied. When the auxiliary coil is used in combination with other electromagnetic forming coils in the experiment, the maximum drawing height of the cylinder cup increases by 141.6 %, after multiple discharges. [ABSTRACT FROM AUTHOR]

In this article, we report a new method to test the formability of low conductive metal sheet under electromagnetic forming using a single planar spiral coil. Proposed novel design of test articles can produce the biaxial tensile strain state, uniaxial tensile strain state, and plane strain state, respectively. The three strain states created by the novel specimen designs were then verified by simulations. Finally, the forming limits of Ti-6Al-4V sheet metal in three different stain states during electromagnetic forming were determined by corresponding experiments using the novel specimen designs. The results indicate that the new method is reasonable and reliable. Formability of Ti-6Al-4V titanium alloy experienced significant improvement when compared with that in quasi-static condition. The extent of improvement was greatest in the plane strain state, reaching 73.65 %. The proposed specimen designs can also be used to test the formability of sheet metal under quasi-static conditionse. [ABSTRACT FROM AUTHOR]

Current frequency is one of the key effect factors on forming efficiency during electromagnetic forming (EMF) process. In the past, many scholars considered that the optimum current frequency corresponds to the skin depth which should be less than workpiece thickness. This is because the magnetic field will greatly lose if the skin depth is larger than workpiece thickness. In this paper, the 2D sequence simulation method is utilized to predict the electromagnetic sheet bulging, and the simulation results are both in agreement with experimental results. It can be found that the larger of the magnetic field losses, the bigger displacement can be obtained in experiments. This is in stark contrast to previous results reported in literature. We also found that the sheet thickness and current damping exponent both have great effects on optimum current frequency if the discharging energy keeps constant, which can cause the skin depth corresponding to the optimum current frequency to be larger than the sheet thickness. Thus, the current frequency is a very complex factor on electromagnetic forming, and it is difficult to choose the optimum current frequency. [ABSTRACT FROM AUTHOR]

The ANSYS software is used to establish the electromagnetic-structural coupling model and predict the electromagnetic sheet forming process. In comparison with experimental result, the maximum simulation error, about 4.5 %, occurs at the sheet center. Then, the simulation method is used to analyze the effect of discharge voltage on thickness distribution. The results indicated that the location of the maximum thickness reduction transfers from sheet center to the region near the sheet center (A region) and then to the region corresponding to the die corner (B region) with the voltage increases, which also cause the first principle strain changed. In addition, lager magnetic force and the material at sheet flange restrained to flow are the two reasons for the thickness reduction at B region. While the direction of material flows changed by inertial effect is the reason for thickness reduction at A region. [ABSTRACT FROM AUTHOR]

Profiled power spinning is a complex metal forming process as there are many factors interrelated. The spinnability plays an important role in predicting fracture and controlling the shape of the profiled component. In this paper, a 3D finite element (FE) model is established so as to investigate on the spinnability of the ellipsoidal power spinning. The variation of the equivalent stress and the equivalent plastic strain are analyzed, and the analysis of variance takes comprehensive influence on the spinnability into consideration. The fracture behaviors of the ellipsoidal components are analyzed with the Johnson-Cook fracture criterion. The results show that the equivalent stress and the equivalent plastic strain increase with the forming time. As for the mono-factor influence, the spinnability is improved when the feed rate of the rollers decreases or the friction coefficient increases. As for the multi-factor influence, the interaction between the feed rate and the friction coefficient has a significant effect on the spinnability. The initial fracture is presented in the fillet part between the blank and the mandrel where the equivalent plastic strain reaches the maximum, the stress triaxiality is the minimum, and the Johnson-Cook damage initiation criterion approach one. The simulation results using the Johnson-Cook fracture criterion are in a good agreement with the experimental results during the ellipsoidal power spinning. [ABSTRACT FROM AUTHOR]

In order to improve energy efficiency, a driver plate made from high-conductivity material is normally used in the electromagnetic forming process of high-strength but low-conductivity sheet metal. The choice of driver plate significantly influences final deformation of the workpiece. In this paper, the electromagnetic free bulging process of Ti-6Al-4V titanium alloy sheet, widely used in aerospace, was studied by both experimental means and numerical simulation. The forming efficiency and quality of the workpiece under different types of driver plates were investigated in detail. The results show that by using high-conductivity and easily deformed materials such as aluminum alloy, with a skin depth in thickness, high efficiency and uniform deformation can be achieved. The results of this study can provide guidance on the choice of process parameters such as the material and thickness of a driver plate. [ABSTRACT FROM AUTHOR]

In the past, many simulation methods for electromagnetic forming (EMF) just consider the effect of the first half current pulse on electromagnetic forming process. And it is deemed that the sequence coupling method has a higher accuracy than loose coupling method because the effect of workpiece deformation on magnetic analysis is considered. In this work, the loose coupling method and sequence coupling method are both used to investigate how the second half current wave affects the simulation result. If the first current pulse is only considered in the simulation process, higher accuracy can be obtained by loose coupling method at 4,366 Hz of discharge current or sequence coupling method at 2,183 Hz of discharge current. If the second current pulse is also considered, the sequential coupling method can obtain more precise results than loose coupling method in the two different current frequencies. With the increase of displacement, the loose coupling method could cause a bigger overestimation than sequential coupling method. Then, the total resistance in EMF system is adjusted to obtain different damping exponent. It is found that the effect of the second current pulse on sheet deformation increases with the increasing of the discharge frequency. [ABSTRACT FROM AUTHOR]