Electromagnetic forming (EM forming or magneforming) is a type of high-velocity, cold forming process for electrically conductive metals, most commonly copper and aluminium. The workpiece is reshaped by high-intensity pulsed magnetic fields that induce a current in the workpiece and a corresponding repulsive magnetic field, rapidly repelling portions of the workpiece. The workpiece can be reshaped without any contact from a tool, although in some instances the piece may be pressed against a die or former. The technique is sometimes called high-velocity forming or electromagnetic pulse technology.
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Transcription
Hello. My name is John Coffey, and I am currently an undergraduate researcher within the Impulse Manufacturing Laboratory. This video gives a short description of the Openable electromagnetic actuator. First, however, let's start off with an overview of Electromagnetic forming. Electromagnetic forming is a process that utilizes a solenoid coil, a capacitor bank, and a workpiece. The workpiece is placed around the coil and it is attached to the capacitor bank. The following short clip is of an electromagnetic ring expansion. Energy is then gathered in the bank and released. This current flows through the coil thereby inducing an opposing current within the conductive workpiece. Due to the opposing nature of the currents, the magnetic fields created are also opposing. Due to the resulting repulsive force between the ring and the coil, the ring expands. Within this short animation the red arrows are symbolizing the current that is sent through the actuator assembly, and the green arrows are symbolizing the induced current within the workpiece. This process is the same with a tubular expansion even though a ring expansion is shown. This process is capable of a few different operations such as expansion (as just shown), and compression , as well as propulsion of a flat workpiece toward a die where the workpiece can be formed, sheared, embossed, or welded. One of the neat applications of this technology is that semi-finished pieces can be formed due to the lack of direct contact between the workpiece and the actuator. This particular Openable-Actuator (O-Actuator) is used for compression. A piece of hexagonal 1018 steel rod is placed within the 6061 T6 annealed Aluminum tube after being cleaned. The tube was annealed at 525 for an hour. A piece of tape is then wrapped around the end of the steel so that the steel is centered within the aluminum tube (the tube is formed beneath the tape, so that the interlayer does not affect the results). There could be other and better ways of positioning the tube and the rod concentrically, but for the sake of this demonstration we used tape. The workpiece is placed within the assembly and secured with three c-clamps that are insulated from the aluminum enclosure. The charge is then released through the coil. The Openable actuator uses tertiarily induced currents to form the workpiece. The coil induces a current within the aluminum enclosure. Then, due to the currents within the aluminum enclosure, a current is induced within the aluminum tube. Due to the compressive force on it, the aluminum tube crimps onto the steel rod. As you can see, the voltage (the blue line) and the current (the green line) are traced while the experiment is being performed. They are shown on the monitor to the left. This allows us to see the time that it took the experiment to be performed, as well as giving us some information about the individual experiment so that calculations can be preformed. This was done at three energy levels. As we see here, the conformance decreases with the decrease in energy level from 8 kJ to 4 kJ. Unfortunately, the tertiary currents are incredibly diminished in comparison to those released by the capacitor bank. We ran a comparative test using non-annealed T6 Aluminum at 6 kj with a disposable electromagnetic actuator The disposable coil, within the disposable electromagnetic actuator, uses the primary current to induce currents within the workpiece. Leading to greater overall efficiency However, the coil that was used is destroyed in the process. This is the conformal joint formed using T6 aluminum tube (that was not annealed) at 6 kJ. The joint formed is comparable to the 8 kj joint in the o-actuator. However, the disposible coil shows weld like deformation at the end of the aluminium tube. Where as the 8 kJ one does not. Even though the O-Actuator is relatively inefficient, no waste is formed in the process so this would be ideal for clean room processes. So thank you very much for watching. If you would like to learn more about o-actuators or the impulse manufacturing laboratory please check out our webpage and subscribe.
Explanation
A special coil is placed near the metallic workpiece, replacing the pusher in traditional forming. When the system releases its intense magnetic pulse, the coil generates a magnetic field which in turn accelerates the workpiece to hyper speed[quantify] and onto the die. The magnetic pulse and the extreme deformation speed transforms the metal into a visco-plastic state – increasing formability without affecting the native strength of the material. See the magnetic pulse forming illustration for a visualization.
A rapidly changing magnetic field induces a circulating electric current within a nearby conductor through electromagnetic induction. The induced current creates a corresponding magnetic field around the conductor (see Pinch (plasma physics)). Because of Lenz's Law, the magnetic fields created within the conductor and work coil strongly repel each other.
In practice the metal workpiece to be fabricated is placed in proximity to a heavily constructed coil of wire (called the work coil). A huge pulse of current is forced through the work coil by rapidly discharging a high-voltage capacitor bank using an ignitron or a spark gap as a switch. This creates a rapidly oscillating, ultra strong electromagnetic field around the work coil.
The high work coil current (typically tens or hundreds of thousands of amperes) creates ultra strong magnetic forces that easily overcome the yield strength of the metal work piece, causing permanent deformation. The metal forming process occurs extremely quickly (typically tens of microseconds) and, because of the large forces, portions of the workpiece undergo high acceleration reaching velocities of up to 300 m/s.
Applications
The forming process is most often used to shrink or expand cylindrical tubing, but it can also form sheet metal by repelling the work piece onto a shaped die at a high velocity. High-quality joints can be formed, either by electromagnetic pulse crimping with a mechanical interlock or by electromagnetic pulse welding with a true metallurgical weld. Since the forming operation involves high acceleration and deceleration, mass of the work piece plays a critical role during the forming process. The process works best with good electrical conductors such as copper or aluminum, but it can be adapted to work with poorer conductors such as steel.
Comparison with mechanical forming
Electromagnetic forming has a number of advantages and disadvantages compared to conventional mechanical forming techniques.
Some of the advantages are;
- Improved formability (the amount of stretch available without tearing)
- Wrinkling can be greatly suppressed
- Forming can be combined with joining and assembling with dissimilar components including glass, plastic, composites and other metals.
- Close tolerances are possible as springback can be significantly reduced.
- Single-sided dies are sufficient, which can reduce tooling costs
- Lubricants are reduced or are unnecessary, so forming can be used in clean-room conditions
- Mechanical contact with the workpiece is not required; this avoids surface contamination and tooling marks. As a result, a surface finish can be applied to the workpiece before forming.
The principle disadvantages are;
- Non-conductive materials cannot be formed directly, but can be formed using a conductive drive plate
- The high voltages and currents involved require careful safety considerations
References
- "Materials and Manufacturing: Electromagnetic Forming of Aluminum Sheet" (PDF). Pacific Northwest National Laboratory. Archived from the original (PDF) on 2005-12-18. Retrieved 2006-06-09.
- "Electromagnetic Hemming Machine And Method For Joining Sheet Metal Layers". US Patent and Trademark Office. Archived from the original on 2018-05-18. Retrieved 2005-09-02.
- "Resources on Electromagnetic and High Velocity Forming". Department of Materials Science and Engineering, Ohio State University. Archived from the original on 2005-12-19. Retrieved 2006-04-06.
- "Electromagnetic Metal Forming Handbook". An English translation of the Russian book by Belyy, Fertik, and Khimenko. Archived from the original on 2006-09-05. Retrieved 2006-08-06.
- "FEA of electromagnetic forming using a new coupling algorithm". Ali M. Abdelhafeez, M.M. Nemat-Alla and M.G. El-Sebaie. Retrieved 2013-01-15.[1]
External links
- "Industrial Application of the Electromagnetic Pulse Technology" (PDF). PSTproducts GmbH. Archived from the original (PDF) on 2011-07-15. Retrieved 2010-08-01.
- "Electromagnetic Forming of Cylindrical Components". Magnet-Physik. Archived from the original on 2005-12-14. Retrieved 2006-06-06.
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- ^ Abdelhafeez, Ali M.; Nemat-Alla, M.M.; El-Sebaie, M.G. (2013-03-05). "FEA of electromagnetic forming using a new coupling algorithm". International Journal of Applied Electromagnetics and Mechanics. 42 (2): 157–169. doi:10.3233/JAE-131653.
This page was last edited on 27 October 2023, at 22:51