Stringing along a grinding application

It’s not a terribly complicated part – a 0.45" round, hollow disk on top with a collar underneath roughly half the diameter of the larger section. An automotive powertrain supplier approached grinding machine manufacturer Glebar with two challenges in making the part – the need for 3,000 pieces per hour and figuring out a feed mechanism for the non-symmetrical component.

The two challenges are related. The high feed rate demanded to hit volume targets required an automated solution. Hand placement or robotic pick-and-place systems would never be fast enough to get a part facing the grinding wheels every 1.2 seconds. However, the lopsided geometry of the parts meant that simply standing them on their sides to face the machine wouldn’t work, because the unbalanced parts would topple over.

“If you didn’t have a feature on the part, you could feed them back-to-back, and they would support each other going through the machine,” says Glebar President John Bannayan. “With the shoulder, we needed a different approach.”

Beaded necklace

Thankfully, the valve seat components were hollow, so Glebar engineers could develop a feed system that deposited the parts onto a wire. A vibratory bowl feeder sorts the parts so they drop onto the wire wide-side first (the bowl kicks parts back into the bowl if they try to enter the feed system narrow-side first). On the wire, parts align wide end to narrow end, creating a gap-free string of parts that feed into the grinder.

Imagine a beaded necklace – the parts line up on the string, creating a constant feed into the grinder without requiring direct manipulation of any workpiece. As the parts go through the machine, the grinding wheels finish them to a ±0.0002" tolerance.

The results – 5,000 parts-per-hour or a part ground every 0.7 seconds, beating part-production requirements by 66%.

“Whenever there’s a feature in the part that can be leveraged for support, such as a center hole, wire feeding is an approach we consider,” Bannayan says, adding that Glebar engineers first developed wire-feeding techniques more than a decade ago for a Chrysler transmission component. “Ideally, you don’t want to use a wire. It adds setup complexity to the whole package. But sometimes, it’s the best option. We’ve been exposed to a lot of different ways of loading parts; we use a lot of 6-axis robots for part loading and are very comfortable with that. And we implement a lot of vibratory bowl feeding. It really depends on the part geometry.”

Measurement, inspection

While solving the feed challenge was the biggest enabler for the high system throughput, Bannayan says Glebar engineers used other systems to ensure process capabilities as well. Laser scanners measure the valve seat components at various steps of the process to track grinding wheels’ performances. The system uses that data to adjust process parameters and keep production going.

“We perform on-the-fly diameter compensation on the parts as they’re going through the machine,” Bannayan explains. “We are taking diameter readings and crunching the data stream in real time. That processed data goes right into the controller for automatic size compensation.”

Sample parts are also taken off the machine to undergo more thorough roundness testing, something that can’t be done practically on the machine, Bannayan says, because the parts need to be rotated on a fixture to get full roundness measurement.

Engineers do compare the laser diameter measurements against the roundness tests to verify process data, and Bannayan says engineers use that comparative data to adjust and improve the system’s process capability.

“The customer could have gone to anybody for a through-feed grinding machine. The through-feed grinding operation was relatively simple, there was nothing magical about it,” Bannayan states. “The value we were able to provide was data gathering and processing, a unique part-feeding process, and the ability to automatically adjust size on the machine.”

About the author: Robert Schoenberger is the editor of TMV and can be reached at 216.393.0271 or rschoenberger@gie.net.