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Electromagnetic Pulse Metalworking

The Basics

The sketch at the right gives the basic idea of how electromagnetic metal forming works. A very brief and intense current is delivered from the capacitor bank through the solenoid (also called an actuator coil). This develops an intense transient magnetic field that induces a current in anything conductive that is nearby. The mutual repulsion of these fields can, for example, launch the ring around the solenoid at very high velocities (100 m/s; and higher). This launch can be done without making physical contact with the ring. This basic process can be carried out with a wide variety of sample and actuator geometries.  This is a central idea that is detailed in many other places on this website.Electromagnetic expansionThe above gif represents the general ring expansion process. Red Arrows are conventional current, the green arrows are induced current, and the purple arrows are the force created by the two opposing electric fields. The first step is the charging step, the capacitor bank charges until the target voltage is reached. Once the target voltage is achieved the second switch closes and sends the current through the system. Next an induced current (moving in the reverse direction to the solenoid) is formed in the ring specimen due to the current moving through the solenoid. The two currents then create opposing electric fields which force the ring specimen away from the solenoid. Because the process occurs very quickly, the plastic deformation limit of the ring is surpassed by the force and the ring expands.








Axisymmetric Direct Induction Expansion and Compression Coils

These use simple helical coils to couple to typically cylindrical workpieces. These have high efficiency but limited versatility.


Axisymmetric Expansion and Compression Actuators with Field Shapers

The most complete reference and use of these actuators is the Electromagnetic Forming Handbook by Belyy and co. Also, Peihui Zhang of EWI has used modern numerical tools to perform a quantitative analysis of the coupling between the primary coils field shaper and workpiece.


The Uniform Pressure Actuator

This is a development from the Impulse Manufacturing Laboratory. It is relatively efficient, versatile and permits a large variety of operations to be performed involving the forming, embossing, micro forming or shearing of relatively thin sheets of conductive materials (aluminum and copper primarily, however the process works for other metals such as stainless steels, titanium, etc.) with the use of a driver sheet.


The Path Actuator

There are very versatile ways of producing pressure of velocity along a given path. This can be used for flanging, hemming, shearing, or forming discrete features. There is a simple design methodology that accompanies the use of this kind of coil.


Open-able Coils

These are field shapers that allow for the electromagnetic actuator coil to be placed within a steel enclosure separated from the workpiece. This steel enclosure is split so that the coil and the workpiece can be removed once the workpiece has been compressed. The two pieces of steel (for the enclosure) are insulated from each other so that the field produced is around the work piece and the induced current does not short circuit. The field created induces an opposing current within the steel enclosure. The steel enclosure then induces a current within the workpiece because the currents within the workpiece and the steel enclosure are opposing they repel each other. This repulsion collapses the workpiece inward on itself thereby electromagnetically forming the workpiece.


Related Links:

-Conformal Joining

-Openable Electromagnetic Actuator