Electromagnetic (EM) forming is a high-speed forming process that uses the forces induced on a conductive workpiece by a transient high frequency current to form the workpiece into a desired shape. This thesis presents the results of an experimental and numerical study carried out to determine whether an EM forming process could be used to sharpen the radius of part pre-formed using a stamping process. Two processes were studied; a single step EM forming operation and a “hybrid forming” operation consisting of a conventional pre-forming step and an EM corner fill, both considering aluminum alloy AA 5754. The single step EM process proved unable to form acceptable samples due to excessive sample distortion, but was used to gain insight into the EM forming process. The hybrid operation consisted of pre-forming 1 mm AA 5754 sheet into a v-shape with a 20 mm outer radius using a conventional stamping operation and then reducing or “sharpening” the radius to 5 mm using EM forming. Sharpening the radius to 5 mm using conventional stamping was not achievable. The hybrid operation proved successful in forming the 5 mm radius, thus demonstrating that the material could be formed beyond its conventional formability limit using the hybrid operation. Numerical models were used to gain insight into the processes and the challenges involved in their numerical simulation. The numerical simulations showed that EM corner fill operation produces very high strain rates (10,000- 100,000 s-1) and complex three dimensional stress and strain states. The effect of the high strain rates could not be properly assessed, since no constitutive data was available for such high strain rates. The predicted stress states show that the process was not plane stress and that large through-thickness compressive stresses are produced that are favorable to damage suppression and through-thickness shear strains that increase ductility. The high strain rates and the complex stress and strain states are considered the likely causes for the observed increase in formability. The models provided valuable insight, but did not predict the final shape exactly and the possible reasons behind this are analyzed. The research indicates that features that are not achievable using traditional stamping techniques can be obtained with the hybrid EM forming process.

Electromagnetic (EM) forming is a high-speed forming process that uses the forces induced on a conductive workpiece by a transient high frequency current to form the workpiece into a desired shape. This thesis presents the results of an experimental and numerical study carried out to determine whether an EM forming process could be used to sharpen the radius of part pre-formed using a stamping process. Two processes were studied; a single step EM forming operation and a “hybrid forming” operation consisting of a conventional pre-forming step and an EM corner fill, both considering aluminum alloy AA 5754. The single step EM process proved unable to form acceptable samples due to excessive sample distortion, but was used to gain insight into the EM forming process. The hybrid operation consisted of pre-forming 1 mm AA 5754 sheet into a v-shape with a 20 mm outer radius using a conventional stamping operation and then reducing or “sharpening” the radius to 5 mm using EM forming. Sharpening the radius to 5 mm using conventional stamping was not achievable. The hybrid operation proved successful in forming the 5 mm radius, thus demonstrating that the material could be formed beyond its conventional formability limit using the hybrid operation. Numerical models were used to gain insight into the processes and the challenges involved in their numerical simulation. The numerical simulations showed that EM corner fill operation produces very high strain rates (10,000- 100,000 s-1) and complex three dimensional stress and strain states. The effect of the high strain rates could not be properly assessed, since no constitutive data was available for such high strain rates. The predicted stress states show that the process was not plane stress and that large through-thickness compressive stresses are produced that are favorable to damage suppression and through-thickness shear strains that increase ductility. The high strain rates and the complex stress and strain states are considered the likely causes for the observed increase in formability. The models provided valuable insight, but did not predict the final shape exactly and the possible reasons behind this are analyzed. The research indicates that features that are not achievable using traditional stamping techniques can be obtained with the hybrid EM forming process.

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No description available.

This thesis presents the results of experimental and numerical work carried out to determine if electromagnetic forming (EMF) increases the formability of aluminum alloy sheet and, if so, to determine the mechanisms that play a role in the increased formability. To this end, free form (open cavity) and conical in-die samples were produced to isolate high strain rate constitutive and inertial effects from the effects of the interaction between the die and the sheet. Aluminum alloys AA5754 and AA6111 in the form of 1mm sheet were chosen since they are currently used in automotive production and are candidates for lightweight body panels. The experiments showed significant increases in formability in the conical die samples in areas where significant contact with the tool occurred, with no significant increase recorded for the free-formed samples. This indicates that the tool/sheet interaction is playing the dominant role in the increase in formability observed. Metallographic and fractographic analysis performed on the samples showed evidence of microvoid damage suppression, which may be a contributing factor to the increase in formability. Numerical modeling was undertaken to analyse the details of the forming operation and to determine the mechanisms behind the increased formability. The numerical calculations were performed with an explicit dynamic finite element structural code, using an analytical electromagnetic pressure distribution. Microvoid damage evolution was predicted using a microvoid damage subroutine based on the Gurson-Tvergaard-Needleman constitutive model. From the models it has been determined that the free forming process is essentially a plane-stress process. In contrast, the tool/sheet interaction produced in cone forming makes the process unique. When the sheet makes contact with the tool, it is subject to forces generated due to the impact, and very rapid bending and straightening. These combine to produce complex non-linear stress and strain histories, which render the process non-plane stress and thus make it significantly different from conventional sheet forming processes. Another characteristic of the process is that the majority of the plastic deformation occurs at impact, leading to strain rates on the order of 10,000 s^-1. It is concluded that the rapid impact, bending and straightening that results from the tool/sheet interaction is the main cause of the increased formability observed in EM forming.

This thesis presents the results of experimental and numerical work carried out to determine if electromagnetic forming (EMF) increases the formability of aluminum alloy sheet and, if so, to determine the mechanisms that play a role in the increased formability. To this end, free form (open cavity) and conical in-die samples were produced to isolate high strain rate constitutive and inertial effects from the effects of the interaction between the die and the sheet. Aluminum alloys AA5754 and AA6111 in the form of 1mm sheet were chosen since they are currently used in automotive production and are candidates for lightweight body panels. The experiments showed significant increases in formability in the conical die samples in areas where significant contact with the tool occurred, with no significant increase recorded for the free-formed samples. This indicates that the tool/sheet interaction is playing the dominant role in the increase in formability observed. Metallographic and fractographic analysis performed on the samples showed evidence of microvoid damage suppression, which may be a contributing factor to the increase in formability. Numerical modeling was undertaken to analyse the details of the forming operation and to determine the mechanisms behind the increased formability. The numerical calculations were performed with an explicit dynamic finite element structural code, using an analytical electromagnetic pressure distribution. Microvoid damage evolution was predicted using a microvoid damage subroutine based on the Gurson-Tvergaard-Needleman constitutive model. From the models it has been determined that the free forming process is essentially a plane-stress process. In contrast, the tool/sheet interaction produced in cone forming makes the process unique. When the sheet makes contact with the tool, it is subject to forces generated due to the impact, and very rapid bending and straightening. These combine to produce complex non-linear stress and strain histories, which render the process non-plane stress and thus make it significantly different from conventional sheet forming processes. Another characteristic of the process is that the majority of the plastic deformation occurs at impact, leading to strain rates on the order of 10,000 s^-1. It is concluded that the rapid impact, bending and straightening that results from the tool/sheet interaction is the main cause of the increased formability observed in EM forming.

Flugzeuge sind üblicherweise als Rahmenstrukturen aus Leichtbauwerkstoffen wie faserverstärktem Kunststoff, Titan- oder Aluminiumlegierungen gestaltet. Je nach Anwendungsfall reicht die Tragfähigkeit der eingesetzten Streben von wenigen Kilonewton bis zu mehr als 250 kN. Die Verbindungen der Streben mit Anschlussstücken sind häufig komplex, sodass hohe Kosten für die montierten Bauteile entstehen. Fügen durch elektromagnetische Kompression (EMK) stellt aufgrund der verfahrensspezifischen Vorteile eine vielversprechende Alternative dar, um Verbindungen deutlich einfacher zu realisieren, insbesondere wenn Streben aus Aluminiumrohr eingesetzt werden.

Aircraft are typically designed as frame structures using lightweight materials such as fiber reinforced plastics, titanium or aluminum alloys. Depending on the application, the load capacity of the struts used ranges from a few kilonewtons to more than 250 kN. The connections between the struts and the connectors are often complex, resulting in high costs for the assembled components. Joining by electromagnetic forming (EMF) offers a promising alternative to make connections much simpler, especially when aluminum tube struts are used.

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No description available.