Feeding Nuts and Unconventional Fasteners
Custom design and advanced technology enable feeders to handle a wide range of threaded, nonthreaded and odd-shaped fasteners.
Screws aren’t the only fasteners that can be fed to fully or semiautomatic installation tools. Nuts, setscrews and other fasteners—both threaded and unthreaded—can be fed automatically, too.
For one European Tier 1 supplier, the challenge was feeding and installing plates and pins—along with screws—in door hinge assemblies. The company tried manual assembly for a while before switching to a DEPRAG Schulz GmbH & Co. system based on a rotary indexing dial.
In operation since August 2013, the system assembles the door hinge in less than 15 seconds. After an operator places three preassembled hinge components into a fixture, two Minimat-EC electronic screwdrivers tighten two sets of screws to a specific torque.
The assembly is then moved to a station where two plates are installed with a press. Before installation, the plates are fed from a vibratory bowl onto a conveyor that aligns and places them opposite one another. A dual gripper picks up the plates and positions them for the press, which inserts them with a force of 200 newtons.
After this, the plates are secured with two screws each using two pneumatic Minimat screwdrivers. The plates are necessary to adjust the hinge during final vehicle assembly.
Finally, two threaded pins are installed with another pneumatic screwdriver. The pins are blow-fed into position through a tube.
To ensure that no incorrectly assembled hinge reaches the packaging department, each workstation transmits an “OK” or “not OK” signal to the system’s master control unit. All bad hinges are transported to workstation one, where the operator places them aside.
Systems like this one represent a clean break from the past—when manufacturers were forced to have assemblers manually position and install nuts, setscrews, expander plugs and other unconventional fasteners. Today’s advanced technology makes feeding them easier than ever.
Manual vs. Automated
Although more prevalent today, fully automated feeding of unconventional fasteners is not an automatic choice for all applications. Manual or semiautomatic feeding (using hand-operated tools) may be best, depending on production volume and part size.
“Many types of odd-shaped components being fed today were not fed before,” claims Lori Logan, marketing manager for DEPRAG Inc. “Bigger parts can be placed manually, but it takes much more time for a person to place smaller parts, which are increasingly common.”
Cost is another factor. Unconventional fasteners tend to require a dedicated feeder that only handles parts within a very small width or length range. Plus, these feeders’ escapements (which singulate and release each fastener) are not interchangeable.
Today’s feeders feature advanced technologies. For example, Weber Screwdriving Systems Inc. offers several stepfeeders that generate vibration with a piezo crystal and angular flat springs rather than electromagnetic coils. Jim Graham, president of Weber Screwdriving, says these stepfeeders provide continuous and reliable feeding of pins, clips and other fasteners. They also are very quiet, with a noise level of only 64 decibels.
“Vibration is controlled by applying a voltage across the crystal, which oscillates and generates linear motion,” explains Graham. “Its high-frequency range of 140 to 400 hertz is less abrasive than the traditional 60 to 120 hertz from coils, and it offers more control of micro pins, clips and nuts.”
Most suppliers offer standard and custom escapements to handle fasteners of various shapes and lengths. DEPRAG also offers two types of escapements (called separators), which have different delivery mechanisms. The slide type captures a fastener between two blocks, while the profile blade encases a fastener within a block and delivers it for installation.
Dixon Automatic Tool makes the ES-16 escapement for use on its 100 Series Track-Fed products. The escapement is for applications where it needs to retract out from under a placement head after placing a fastener in the jaws of the tool.
Visumatic Industrial Products makes five basic escapements, including a Siamese unit that feeds separate spindles. They do not have external springs.
Kevin Buckner, director of engineering for Design Tool Inc., says advances in robotics and CAD software make it easier for suppliers to develop custom feeding and driving systems for unconventional fasteners. Equally important, advances in pneumatic technology enable greater control and more accurate assembly with these fasteners.
All Nuts Allowed
White goods manufacturers are increasingly turning to automated nut feeders to increase production and improve quality and precision. However, manufacturers in the auto industry remain the primary users of these feeders.
For the past three years, a Tier 1 auto supplier has been using custom feeders from Dixon to quicken the assembly of plastic-molded interior and exterior parts. Dixon developed a series of workcells, each of which has a six-axis robot, a part-holding fixture and feeders to handle a variety of odd-shaped fasteners. These include Christmas tree clips with foam washers, A-shaped clips and nonstandard nuts with plastic molded around the outside.
Depending on the part being assembled, the robot retrieves and installs clips and nuts as needed. Nuts are track-fed to custom tooling mounted on the robot, which then anchors the nut inside the plastic part. Bare clips are blow-fed to tooling, but clips with a foam backing are track-fed.
“We customized the tooling for each fastener, but made the fixtures interchangeable,” explains Brian Droy, vice president of sales for Dixon Automatic Tool. “This enables the company to manufacture multiple parts on the same machine.”
Dixon’s SD-2000 series blow-fed drivers handle standard and flanged nuts as wide as M12. Droy says that a different Tier 1 supplier uses the SD-2040 to drive an M8 hex nut onto a compressor assembly. The driver’s pneumatic centering pin and socket drive the nut with 17 newton-meters of torque.
The SD-2000 series is also available with vacuum tooling that prevents the nut from dropping should there be an obstacle between the tooling and the target part. A sensor in the driver’s controller monitors the vacuum source for process assurance.
Jarrod Neff, marketing manager for Visumatic Industrial Products, says Tier 1 auto suppliers use the company’s feeders extensively to feed all types of Palnuts, including serrated and spring-loaded. Their feeders also are used by aerospace and military suppliers to feed and drive nuts onto studs in radar and telemetry equipment.
Another nonautomotive customer manufactures sprinklers for golf courses. Each sprinkler has a fluid-control device that requires a ¼-20 nylon locking nut to be mounted on a stud in a recessed area. Five years ago, assemblers were manually installing the nuts with a pneumatic driving tool. They often over- or undertightened the nuts, or positioned them improperly, resulting in cross-threading.
The company replaced the manual system with a Visumatic VNPD-56.6 nut feeder, which automatically advances the nut to the drive position and aligns it with the receiving stud. Neff says the feeder has shortened cycle time, improved quality and eliminated cross-threading. The manufacturer also uses a DC electric tool with torque and angle control to ensure proper tightening. It has since installed two more nut feeders.
Design Tool’s nut feeders can handle both standard hex nut and flange nuts of different thicknesses. Buckner says one customer recently installed a small custom feeding system that drives a hex flange nut onto a carriage bolt in a bracket assembly. The system features a feed mechanism, platen assembly and nest to hold the bracket. Cycle time to drive the nut onto the bolt is 1.5 seconds.
“Correctly orienting the nut and positioning it to the bolt was challenging, but so was designing the nest,” acknowledges Buckner. “It had to ensure alignment of the nut and bolt, as well as permit easy bracket loading and unloading after the nut was driven.”
Graham says customers in the auto industry frequently feed nuts onto studs in the cylinder heads of small engines, and to assemble the discs for disc brakes. He also claims that some manufacturers are testing Weber nut feeders with vision-inspection systems to verify the nut’s diameter and thread height before it’s installed.
In the aerospace industry, manufacturers use the supplier’s feeders to automatically feed and install threaded HI-LOK and HI-LITE collars (nuts) onto mating pins. The collars are made of red-anodized aluminum. Graham says the custom feeders also are designed to vacuum up the collar ends that break off after installation.
In general, feeders can also easily handle square nuts, tee nuts, unfaced nuts (which have a nonmachined surface), Keps nuts (which have a retained washer) and long coupling nuts. More difficult types are slotted nuts and castle nuts, which feature slots in a rounded section above either the threads or the main nut.
So Many Others
Excluding nuts, the list of unconventional fasteners manufacturers need to feed is extensive. It includes setscrews, expander plugs, plates, pins, clips, wooden dowels, brazing rings, O-rings, springs, washers (round or square), bolts, scrivets, brass fittings, rivets and valve cores.
Neff explains that one automotive tubing supplier recently worked with Visumatic to develop an automated machine to feed, lubricate, and install a threaded valve core into vehicle charge port assemblies. The main challenges are preventing bad valves from entering the assembly process and tightening each core to a consistent preset torque.
After an operator places a preassembled charge port into a fixture, sensors close the fixture and verify whether the port is good or bad. Bad ports are retained in the fixture and can only be released when a supervisor enters a password on the machine’s HMI. If the port is deemed good, assembly is initiated.
A valve core is blow-fed from a bowl to the machine’s VPM power module, which then moves the core into position for placement. Aerosolized lubricant is quickly applied to the core, and it is tightened to a preset torque.
Grammer AG of Amberg, Germany, develops and manufactures components for vehicle interiors, as well as driver and passenger seats. Crash-active headrests for front seats are part of the company’s product line. In 2010, Grammer had DEPRAG develop a 14-station turnkey system to make the headrests.
Unconventional fasteners required to assemble each headrest include a lock pin and two grooved pins, according to Boris Baeumler, application engineer for DEPRAG Inc. The grooved pins are blown from a vibratory bowl into a separator, and then pressed into the carrier-CAK (one of the headrest’s main subassemblies) to secure two guide tubes.
Immediately after this, a lock pin is blown from a different vibratory bowl into a separator and then inserted and secured in the headrest’s slide (another subassembly). Cycle time to assemble each headrest is less than 10 seconds, enabling a production rate of more than 360 units per hour. Grammer has since installed three more systems in Mexico and one in Poland.
Fire-sprinkler manufacturers frequently feed and drive setscrews to hold in place the sprinkler head’s glass vial, notes Graham. When a fire occurs, heat buildup causes the chemical liquid in the vial to expand and burst the glass, releasing the sprinkler’s shut-off valve and water.
He says automakers feed plastic clips to assemble door liners and body panels. Medical-device manufacturers feed pins as small as 0.021-inch wide and 0.06-inch long for micro assemblies.
“We’ve made a lot of one-off systems for customers, including one to feed 4-inch dipsticks for a manufacturer of heavy-duty transmission mounts,” notes Neff. “Getting the system just right always requires working closely with the customer and making sure both of us can justify the tooling development expense.”
“Not all unconventional fasteners are designed for automated feeding,” concludes Droy. “Some just can’t be blow-fed because of their shape. They are prone to get stuck in the tube.”