Typically, when we think about forming metal parts, we think about beating them with hammers, or squeezing them with big hydraulic presses. But what if magnets could do the squeezing? As it turns out—Grumman Aerospace discovered they can, several decades ago! Even better, they summed up this technique in a great educational video which we’ve placed below the break.
The video concerns the development of the Grumman EMF Torque Tube. The parts are essentially tubes with gear-like fittings mounted in either end, which are fixed with electromagnetic forming techniques instead of riveting or crimping. Right away, we’re told the key benefits—torque tubes built this way are “stronger, lighter, and more fatigue resistant” than those built with conventional techniques. Grumman used these torque tubes in such famous aircraft as the F-14 Tomcat, highlighting their performance and reliability.
The video goes on to explain the basics of the EMF torque tube production process. A tube is placed inside a coil, with the end fitting then installed inside. A capacitor bank dumps current through the coil to generate a strong electromagnetic field. This field is opposed by a secondary field generated by eddy currents. The two forces result in an explosive force which drives the tube inwards, gripping into the grooves of the end fitting, and destroys the coil in the process. Grumman notes that it specifically optimized a grooving profile for bonding tubes with end fittings, which maximised the strength of these EMF-produced joints.
This tip was sent in by [irox]. The video itself was posted by [Greg Benoit], who notes his father Robert Benoit was intimately involved with the development of the technique. Indeed, it was useful enough that the technology was licensed to Boeing, generating many millions of dollars for Grumman.
We feature all kinds of machining and forming techniques here, but this sort of forming isn’t something we see a lot of around these parts. Still, we’re sure someone will be Kickstarting a home EMF forming machine before the end of next week.
Very cool, indeed… but are we just going to ignore hydroforming?
Heard about this ca. 1965 when I happened to be working for a company that used large capacitors. Worked fine on some aluminum tubing, so I thought it would be fun to crush the electrodes in a vacuum tube while leaving the envelope intact. Turns out it doesn’t work very well for ferrous metals.
Sounds a lot like using EMF to shrink quarters. Capturedlightning dot com goes into the process with photos.
So can crushing and Quarter shrinking actually just came from an older idea?
cool.
makes can crushing look like cargo cult, doesn’t it.
I do wonder whether the mandrel they envisioned needed to be non-conductive at larger diameters.
When a glider disintegrated after a lightning strike in 1999, Al control rods behind the instructor’s head were shrunk by the currents. Both pilots (one on his first flight!) parachuted to safety.
The glider was extensively examined by the AAIB at Farnborough, and the findings changed the construction of modern composite airliners.
https://asn.flightsafety.org/wikibase/146762 and there is a 10minute BBC programme on the accident.
Fascinating!! Thank you for sharing.
To see the process, skip the first 5 minutes.
If you see it from the start, then try to count how many times the narrator says this stuff is (was) patented (60 years ago).
I wonder where in the automotive industry this is used?