The rivet nut is a one-piece, internally threaded, counterbore tubular rivet that can be installed entirely on one side of a panel.
Lock nuts are available in aluminium, steel, stainless steel, monel, and brass.
Using a pull and press tool, the air motor screws the mandrel into the rivet nut. When the fastener is inserted into the workpiece, hydropneumatic pressure is applied to pull the mandrel back. When the set pressure is reached, the air motor turns on again, retracting the mandrel from the nut.
The installation process of cage nuts can be automated. The machine automatically installs rivet nuts into parts lifted by a six-axis robot. Photo courtesy of Fixpal Riveting Systems
Leankeasy is a spacer nut with mating screws pre-tensioned. The installer inserts a two-piece fastener into the hole and installs the nut using a standard pneumatic or electric screwdriver. Crimp the nut and install the counter screw in the same step. Photo credit: Clufix
Rivet nuts are widely used by vehicle manufacturers to fasten parts to structural members.
Automakers are increasingly using hydroformed metal tubes in vehicle designs. Compared to stamped and welded metal parts, hydroformed parts are lighter in weight, lower in cost, and have a higher stiffness to weight ratio.
This is all good as long as the rest of the parts do not need to be attached to the structure using threaded fasteners. Threading tubing may not be possible because the material may not be thick or strong enough. Self-riveting nuts, nut plates or weld nuts are not suitable as installation requires contact with the other side of the metal. Cage nuts are one option, but they require square holes and are difficult to install.
This is where locknuts come in handy. Collar nuts, also known as blind threaded inserts, provide a strong hold for threads in thin panels. These fasteners were originally developed by BF Goodrich decades ago for attaching rubber de-icing boots to aircraft wings. Today, rivet nuts appear in a wide variety of products.
The rivet nut is a one-piece, internally threaded, counterbore tubular rivet that can be installed entirely on one side of a panel. As with traditional blind rivets, the body of the rivet nut is formed on the blind side. The rear flange is large enough to resist pull-out even under eccentric loads. Because the rivet nut can be installed without touching the sides of the panel, these fasteners are ideal for attaching parts to casings, pipes or profiles. These clasps can be installed in all metals, most plastics and even ceramics.
“Rivet nuts are great for plastic because you can’t weld or fasten fasteners,” said Victor Lunni, president of MDS Fastening Systems.
Fasteners are available in aluminium, steel, stainless steel, monel and brass. “The most popular material is galvanized steel, but if you’re particularly concerned about corrosion, you can choose stainless steel,” says Richard J. Kull, product manager for blind rivet nuts at PennEngineering. “Stainless steel rivet nuts are commonly used in solar installations and other outdoor equipment.”
Fasteners of the same size can usually handle a wide range of gripping forces. For example, PennEngineering’s 0.42″ SpinTite rivet nuts provide a clamping range of 0.02″ to 0.08″. The 1.45″ long rivet nut has a clamping range of 0.35″ to 0.5″.
Rivet nuts are available with different head types. The wide front flange provides a large bearing surface. This will strengthen the hole and prevent bursting. Sealant can also be applied under the flange for weather protection. The thick flange can act as a spacer and provide additional push-out strength. Countersunk and low profile heads provide flush or near flush mounting. A wedge or knurl under the head is designed to cut into the mating material and prevent the fastener from turning in the hole.
“Wedge heads are great for soft materials like plastic, fiberglass and aluminium,” Kuhl says. “However, rivet nuts are annealed, so they are relatively soft. Wedges won’t be very effective against steel.”
Rivet nuts also come in a variety of designs. Standard rivet nuts are cylindrical with a smooth surface, but options include slotted, square, and hex bodies. All of these changes are for the same purpose: to prevent the fastener from turning in the hole, especially in softer materials such as aluminum and plastic.
“If the setting is wrong, the round rivet nut can spin in the hole at a high level of torque,” Lunni explains. “With hex clasps, you don’t have that problem.
“The disadvantage of the hex clasp is that it requires a hex hole. For some manufacturers…it’s cheaper to make a round hole than a hexagonal hole.”
Lock nuts are also available in open and closed versions. The latter is ideal for applications such as attachment points on the outside of vehicles where mating screws do not necessarily exist. Thus, the closed end prevents water and dust from entering the assembly.
Rivet nuts can be installed with hand tools or, more commonly, with power tools. The first is similar to a blind rivet setting tool. The latter can be hand-operated or mounted on linear actuators for fully automatic or semi-automatic operation. They can also be installed on six-axis robots.
The simplest power tool for installing rivet nuts is a pneumatic “rotor” tool. Slide the fastener onto the mandrel at the end of the tool. Then the fastener is inserted into the hole in the workpiece. When the tool is activated, the mandrel rotates rapidly and forcefully, pulling the threaded portion of the rivet nut shank toward the blind side of the workpiece and creating a bulge around the unthreaded portion. The protrusion presses on the back side of the panel, creating a clamping force that holds the sheet tightly. Once the rivet nut is securely in place, the mandrel is turned in the opposite direction, unscrewing the threads from the nut and leaving the inner threads of the fastener intact.
No additional finishing after curing is required, even for painted or painted parts. Therefore, rivet nuts can be installed at any stage of the production process.
An enhanced version of the Rotate-Rotate tool is the Rotate-Pull tool. As with rotary tools, the air motor turns the arbor into a nut. When the fastener is inserted into the workpiece, hydropneumatic pressure is applied to move the mandrel a predetermined distance. Once the fastener is fastened, the air motor is turned on again, removing the mandrel from the nut.
The third option is the Pull and Pinch tool. It works in the same way as a rotating pull tool, but instead of pulling a predetermined distance, it pulls to a predetermined pressure.
“If you’re bonding soft plastics, it’s best to use a rotary tool,” Lannie says. “Pull and squeeze tools can cause fasteners to get caught in the material. On the other hand, if you’re fastening metal or hard plastics like glass-filled nylon, a pull and squeeze tool will be more reliable.”
The latest development in lock nut setting tools is process monitoring. “It is known that it is very difficult to install rivet nuts correctly,” Lanny says. “Process monitoring technology measures how much force the tool is pulling and how far the fastener is pulled. It also counts the number of fasteners installed per cycle.”
Lock nuts are used in a wide variety of applications across many industries. These fasteners are used in products as diverse as refrigerators, playground equipment, office furniture and bicycles.
In the automotive industry, they are used to connect components to dashboards and firewalls. They are also installed in chassis and body frames to mount radiators, roof racks, spoilers, plastic fenders and instrument panels. The aftermarket Jeep Wrangler hardtop is attached with rivet nuts.
In the aerospace industry, they are used inside aircraft to connect top shelves, armrests, galley and toilet components.
In the defense industry, rivet nuts are used to fasten handles and overhead racks of military equipment. And a manufacturer of temporary shelters is testing fasteners that secure components to a honeycomb composite.
An electrical equipment manufacturer uses rivets to fasten door hinges to large electronic equipment enclosures. Brackets are also installed on floors, ceilings and walls to secure components to enclosures.
While rivet nuts have been around for decades, the technology hasn’t stayed the same. Manufacturers have recently introduced several new designs.
Last fall, French fastener manufacturer Clufix introduced the Leankeasy, a rivet nut pre-assembled with matching screws. As a rule, assembly with flare nuts is a multi-step process that requires special tools. With Leankeasy, assemblers can align parts, insert two-piece fasteners into holes, and install nuts with a standard pneumatic or electric screwdriver. Crimp the nut and install the counter screw in the same step.
Leankeasy is available in size M6 with clamping range (nut side) from 0.5 to 3mm and clamping range (screw head side) from 1 to 5mm.
Since the beginning of 2013, Clufix has tested Leankeasy with 10 customers, including Tier 1 and Tier 2 car suppliers, as well as elevator, tractor and generator manufacturers. According to Eric Masseboeuf, Director of Clufix, Leankeasy has reduced installation costs for these customers by an average of 35%. Tractor manufacturers reported a 33% cost reduction, and elevator manufacturers reported a 70% cost reduction.
Sherex Fastening Solutions LLC recently introduced another new rivet nut. It’s called Riv-Float. Using a standard rivet nut, cut the threads on the body of the rivet. With Riv-Float, the body of the rivet is wrapped around the floating nut. The nut can move 0.003 inches side to side and 0.02 inches radially within the body of the rivet. This allows mating screws to enter at a beveled angle to compensate for misalignment of parts and prevent cross-threading.
Fasteners are available in standard and metric sizes. Standard sizes are grips from 0.027 to 0.15 inches, body diameters from 0.39 to 0.53 inches, and installed lengths from 0.522 to 0.63 inches. Thread sizes 8-32, 10-32 and 1/4-20. Small flange versions are available in head diameters from 0.455″ to 0.595″. Large flange versions are available in head diameters from 0.5″ to 0.685″.
Metric sizes have a grip range of 0.7 to 3.8mm, a case diameter of 9.91 to 13.46mm, and a set length of 13.25 to 16mm. Thread sizes M4, M5 and M6. Small flange versions are available with head diameters from 11.56 to 15.11 mm. Large flange versions are available with head diameters from 13.25 to 16 mm.
Before heading to the showroom, listen to an exclusive panel discussion featuring executives from four of the leading US manufacturing software vendors: Aegis Software, eFlex Systems, Tutelar Technologies Inc. and VKS.
Before heading to the showroom, listen to an exclusive panel discussion featuring executives from four of the leading US manufacturing software vendors (BalTec, Orbitform, Promess and Schmidt).
Post time: Aug-11-2023
