In-Die Micropin Insertion

By: Brad Kuvin

Saturday, April 1, 2017

In-die fastener installation eliminates secondary operations that add labor costs, diminish quality and restrict throughput. While in-die insertion finds widespread use throughout the metalforming industry primarily for larger fasteners in the M8 to M10 range, a recent atypical application, using microfasteners, illustrates how creativity and custom engineering can allow the process to be scaled down to the most precise of applications.

Die-Matic runs the micropin in-die insertion job on a 200-ton Minster mechanical press. To downsize the standard PennEngineering in-die feed setup, engineer Ashok Patil reduced the size of the system cart (shown) and redesigned the bowl-feed and shuttle setup to singulate and deliver the pins to the die. The feed tube is fixed to the press ram, and runs underneath the light curtain and loops back up to the stripper plate. To minimize cycle time, Die-Matic shortened the tube (to about 15 ft.) and positioned it to, as much as possible, get gravity on its side.
The project: Insert two 1.57-mm-dia. by 11-mm-long micropins into a stamped aluminum part running in a progressive die at 35 strokes/min., with tolerances of ±0.2 mm on perpendicularity and 0.3 mm on location. The metalformer that took on this challenging process: Die-Matic Corp., Cleveland, OH, with assistance from in-die installation-system provider PennEngineering, Danboro, PA.

“We are a project-driven company that strives to run projects more efficiently,” says Die-Matic president Jerry Zeitler. “For this automotive part, we built the die about 2 yr. ago and have had it in production for 18 months, running more than 1 million parts/yr. with the potential to escalate to 3 million/yr. While we’ve been employing in-die processing (tapping, staking and clinching) for more than 10 yr., this project took in-die insertion to a new level, and Penn-Engineering worked seamlessly with our automation team to help ensure that we met our customer’s expectations regarding throughput and quality.”

A Slew of Sensors

The stamped part is of aluminum type 5052-O and measures approximately 2 by 3.5 in. Die-Matic runs it on a 200-ton Minster mechanical press in a very complex 19-station die. Explains project engineer Jim Mahnic:

“One of the key aspects of the die, and most challenging, was being able to detect the presence of the prepierced holes to accept each inserted micropin, and also to ensure the presence of each pin in the injector head before it fires. The die also includes sensors for short and long feed, stripper leveling, pin presence and part-out.”

To ensure that parts meet quality specs, the press operator periodically inserts completed parts into an attribute gauge that checks pin perpendicularity and location.

PennEngineering did a great job scaling down the feed system to work seamlessly with our die and accommodate all of the required sensors,” Mahnic says. “That included customizing the bowl feeder and its track, and the setup used to deliver the pins from the feeder through the feed tube and into the die.”

Scaling Down

A custom system for in-die insertion of micropins allows Die-Matic to eliminate costly and time-consuming secondary operations, but getting there was no small challenge, even for a company with more than a decade of in-die-process experience. “This project took in-die insertion to a new level,” explains Jerry Zeitler, Die-Matic president. Among their other duties related to feed length, part-out and more, sensors work to detect not only prepierced holes that will receive the tiny pins, but also the presence of those pins. In addition, the press operator periodically inserts completed parts into an attribution gauge to verify pin perpendicularity and location.
Leading the PennEngineering team on this project was in-die project engineer Ashok Patil, who explains how he was able to retrofit the company’s existing technology and custom-develop and build new tooling suited to the tiny pins. To scale the system down from a standard PennEngineering setup, Patil reduced the size of the cart and redesigned the bowl-feed and shuttle setup that orients and singulates the micropins, and delivers them to the die.

“We had to find a way to fit all of the insertion tooling—pin-capturing assembly (injector head), punch guide and punch driver, and the anvil and anvil pin—in one die station,” Patil says, “and we had to satisfy five specific performance criteria, including 100-percent verification of micropin installation, with a 100-percent foolproof system. So, we built in sensoring to ensure that if, with each stroke, any pins are not properly installed, we signal the press control to stop the press and the micropin feed system. And, there’s a pin-presence sensor in the shuttle that fires the pins —if a pin fails to travel successfully from the bowl feeder to the insertion head, the press stops.”

Also, an anvil assembly is positioned opposite the injector head on the bottom half of the die. On the down stroke, the micropin depresses the anvil pin; when the ram reaches bottom dead center, the pin is clinched into the workpiece.

“A sensor in the anvil assembly,” Patil explains, “reads the position of the anvil pin to signal the press control that it was successfully installed. Programmed in conjunction with the flag sensors, the system knows that the insertion occurred and that it occurred at the correct time in the press cycle.”

Vibration Isolation

Patil then describes another significant challenge to designing the micropin feed setup: isolating the vibrating feed bowl from the rest of the circuit. So that only one pin feeds at a time through the 15-ft. line from the cart to the die, the setup features a shuttle that delivers one pin at a time from the bowl to injector-head assembly.

“To isolate the vibratory bowl from the shuttle,” Patil says, “there’s a 1-mm gap that each pin must pass over. Typically, this interface would be at 90 deg. to the feed axis. However, due to the small diameter of the fastener head, as the fastener moved across this gap the fastener head tended tip into the gap and get caught. To alleviate this issue, we cut the interface between the shuttle track and the bowl track at 45 deg. so that the leading edge of the fastener head transitions onto the shuttle track before it leaves the bowl track.”

Each micropin shoots into the injector head immediately after the retracting punch clears the fastener feed bore in the injector chamber of the head, Patil explains. The pin then enters the nosepiece, which captures and aligns the fastener, staging it for insertion.

“As the die begins to close and the stock strip is registered,” he explains, “the anvil pin protrudes up through the hole in the stock strip. As the punch descends and contacts the top of the fastener, the fastener becomes sandwiched between the punch face and the anvil pin, thus maintaining perpendicularity and alignment to the prepierced hole in the stock strip just prior to insertion. As the die reaches bottom dead center, the fastener passes through the prepierced hole and is clinched into the stock strip. Inserting and clinching in this sequence assures the micropin is installed within the required tolerances.”

Reliability and Repeatability

…always are concerns with any stamping operation, but perhaps more so with this setup. Mahnic explains.

“When we first launched the tool, we dialed it down to about 25 strokes/ min. In a month or so we ramped up to 35 strokes/min., fine-tuning air-flow regulation and the layout of the feed tube. The feed tube is fixed to the press ram, and runs underneath the light curtain and loops back up to the stripper plate. We shortened the tube (to about 15 ft.) and positioned it to, as much as possible, get gravity on our side.”

Slug management also played a critical role in the project’s success. The bottom die half includes a specially designed slug-management system that uses a continuous vacuum to suck slugs out of the tool. “The ‘slug sucker,’ says Mahnic, “is tied to press actuation with its own channel on the Wintriss press control—the press won’t cycle unless that airline is hooked up and running.”

The final quality-control step in the process: periodic push-out tests to ensure the strength of each pin-to-stamping connection.

“We have to meet a 200-N strength requirement,” Mahnic says. “Initially, the specified diameter of the pre-pierced hole was too large to meet this requirement. We reengineered the hole and gained approval from the customer. Since then it’s been smooth sailing.

“If we were to run this process with the pin insertion as a secondary process, we could probably run the press at 60 strokes/min., Mahnic adds. “However, the customer understands well that the payoff for the extra cost of the in-die insertion equipment, and for running the press more slowly, comes quickly when accounting for improved quality control and efficiency of eliminating the secondary operation.” MF


See also: Nidec Press & Automation, PennEngineering

Related Enterprise Zones: Sensing/Electronics, Tool & Die

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