Riveting expertise permits light-weight magnesium fasteners for gas effectivity

PNNL’s new Rotating Hammer Riveting expertise permits light-weight magnesium rivets for use with out preheating the rivets. The method can be sooner than standard riveting. Credit score: Andrea Starr | Pacific Northwest Nationwide Laboratory

If Rosie the Riveter had entry to a brand new riveting expertise, the character of WWII fame may have labored sooner and made lighter merchandise. As we speak, a newly patented riveting method developed by Pacific Northwest Nationwide Laboratory (PNNL) makes light-weight magnesium simpler to kind and reduces the time wanted to affix every rivet.

Magnesium is likely one of the lightest metals—making it ultimate for higher gas financial system in automobiles. Nevertheless it trails behind aluminum and metal in industrial use as a result of it is generally brittle and troublesome to form into structural elements. The brand new friction-based riveting expertise, referred to as Rotating Hammer Riveting (RHR), avoids the necessity to pre-heat the metallic to kind the rivet and improves the fastening joint. It additionally works on aluminum rivets, that are utilized in airplane development. The processing technique can be considerably sooner, which may save money and time in airplane and car development.

Making an previous course of new

Riveting is likely one of the oldest identified methods for becoming a member of totally different supplies. The traditional Egyptians used picket rivets to affix metallic handles to clay jars. Riveting then handed down by way of ages and throughout civilizations and might be seen in Roman constructions, Viking ships, Medieval armor, and different historic gadgets.

With the arrival of recent supplies within the nineteenth and twentieth centuries, metal riveting turned ubiquitous throughout an enormous array of structural purposes starting from buildings to bridges and battleships to airplanes. However the riveting course of remained nearly unchanged. Take a cylindrical piece of metallic with a mushroom formed cap on one finish, slip the shank or stem by way of holes within the two supplies you need to be part of, then beat on one finish of the shank with a hammer to kind a second head that clinches the 2 supplies collectively.

Strive to try this with a magnesium rivet and it will most likely shatter. Whereas a magnesium alloy has excessive energy for its gentle weight, magnesium tends to be brittle at room temperature. So sometimes, magnesium alloy rivets are heated to get them mushy sufficient to hammer and bend with out breaking.

Heating every rivet is sluggish and costly, so magnesium rivets are not often used though they’re 30% lighter than the aluminum rivets which are used to affix magnesium sheet metallic.

Hammering a brand new type of riveting expertise

The RHR expertise, developed by PNNL, doesn’t require pre-heating the magnesium rivets. The method, described within the Journal of Magnesium and Alloys, makes use of magnesium rivets with out pre-heating. And it does so 4 to 12 occasions sooner, whereas additionally eliminating the time it takes to pre-heat rivets in standard influence riveting and delivering added advantages of enhanced energy and corrosion prevention properties.

RHR is an offshoot of friction stir welding. The method makes use of a small rotating instrument, referred to as a hammer. The rotational drive generates warmth through friction and deformation, which softens the magnesium sufficient to kind the rivet head whereas additionally mixing the underside of the rivet’s head to metallurgically bond with the underlying metallic sheet. This merging of metals kinds a steady bond that wards off corrosion.

“It took many makes an attempt to search out the appropriate stability between the rotational velocity of the hammer and the velocity at which we plunged it into the rivet,” stated lead researcher Tianhao Wang. “However we finally discovered a candy spot within the processing vary the place the rivet head didn’t adhere to the instrument, nor crack through the RHR course of.”

The newly patented course of deforms the metallic such that its crystalline construction is altered. Utilizing high-powered microscopes, researchers have been capable of see how the grains have been refined and reoriented to make the magnesium extra formable and stronger.

Riveting options for plane manufacturing

Corresponding creator Scott Whalen notes that RHR works on aluminum rivets as effectively, like these utilized in plane. With a whole lot of 1000’s of rivets on each business airplane—largely created from aluminum alloy 2024—Whalen says the method may scale back prices and enhance effectivity on the manufacturing line.

Rivets made from aluminum alloy 2024 are too robust to rivet if saved at room temperature. So, they have to be annealed, or softened, after which saved in a freezer to maintain them mushy earlier than riveting.

“As soon as on the manufacturing line, these “ice field rivets” have to be utilized in lower than 15–half-hour, in any other case they develop into too onerous to rivet,” stated Whalen. “Nonetheless, RHR can rivet aluminum 2024 rivets after they’re within the totally hardened state, so chilly storage is just not wanted. This implies rivets would now not have to be saved in a freezer, riveting is just not time delicate, and unused rivets now not have to be re-heat handled and re-placed into chilly storage.”

Quicker friction-based riveting expertise

RHR processing of aluminum is extraordinarily quick. Typical riveting takes between 1–3 seconds per rivet, whereas RHR requires simply 0.25 seconds. That point financial savings may translate into 40 hours saved per 100,000 rivets. “That will imply one full week much less spent riveting on only a fraction of 1 business airliner if RHR have been adopted,” stated Whalen.

RHR is only one of a collection of disruptive manufacturing applied sciences to course of metallic alloys and composites being developed by PNNL. These Stable Section Processing methods contain deforming supplies with out melting to warmth, combine, fabricate, and be part of metals and different supplies. The ensuing supplies have extraordinary properties in comparison with these produced by standard manufacturing strategies.


System bonds metallic and plastic inside seconds


Extra data:
Tianhao Wang et al, Friction-based riveting method for AZ31 magnesium alloy, Journal of Magnesium and Alloys (2021). DOI: 10.1016/j.jma.2021.06.004

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Pacific Northwest Nationwide Laboratory


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