Rotary bushings are commonly deployed in transfer line tooling applications such as automotive engine block cam and crank boring. A step beyond the more common, and better known common drill bushing, rotary bushings not only facilitate accurate cutting they also eliminate heat, wear and chatter. Their use in production can boost CPK value as well, a calculation that gauges the extent to which a process has met the quality specification limits established by customers.
Although rotary bushings are a small but vital component of high-volume manufacturing, they can also be troublesome. This is due to the design limitations of most boring machines. Past practice involved mounting individual detail parts directly into the machine housing. The line boring bar moves through the bushings’ inner diameter and, with the help of precision bearings, rotates without friction. The design of many machines involves the use of individual parts that comprise the bearing support, and are built into the machine housing.
The limitation of this design is apparent when new guide bushings are installed. It may be necessary to remove the entire housing, rebuild it in the tool room, and then realign it back on the machine. This can further delay production. A delay can also occur when the bearings, seals, or components go bad, and repair or replacement is required. Downtime results in both cases, and the delay can be costly.
A rotary bushing retrofit to a more easily replaceable part, however, can help reduce downtime. To accomplish this task, Gatco, Inc. developed a quick-change, precision cartridge with a self-contained bearing assembly that can be installed quickly, and eliminates the time consuming and expensive replacement of individual detail parts.
These rotary bushings make a machine housing rebuild and realignment unnecessary. Rather than removing worn parts, ordering and installing them, the user simply slips the new cartridge in place and locks it. Additionally, all the quick-change cartridges are factory pre-adjusted to customer specifications.
Downtime Happens
Some amount of downtime will always occur, however, particularly with line boring bar supports. In a typical parts-punishing, high-production application, such as engine block boring, trips to the tool room for repair and replacement are unavoidable and may be required several times per month. This can be a detriment for a U.S. automaker competing with top Asian organizations.
Companies like Toyota, Honda and Hyundai have mastered their production processes through incremental tweaking, and have learned how to transition product from the manufacturing floor to the sales floor with minimal interruption. Learning from the Asian process, American automakers and the industries that serve them are working on concepts that enhance production efficiency one step at a time. A rotary bushing retrofit may prove to be a small, but important, step in that direction.
Successful Rotary Bushing Retrofits
Galaxy Industries of Canton, MI, performs a range of machining work for major equipment manufacturers such as Caterpillar, Inc. and Eaton Corp. Galaxy had used three bushings in an engine block boring to pilot the line boring bar, and in 2005 all three wore out near the end of a Caterpillar job. Though the company had a spare set of bushings on hand, the resolution was not as simple as expected.
“When the bushings wore out we were at the point in the job where we were ready to bore all seven crank journals in the engine block simultaneously,” said plant manager Dale Funk. “We had another set of bushings available but we didn’t realize they were the wrong size until we had completely torn down the existing setup to install them. There had been a change in the crank bar, and it turned out that the bushings we had were too small. It really messed us up.”
The operation came to a halt for 24 hours, and the delay cost the company $150,000, not a penny of it recoverable down the road. Additionally, Galaxy had already invested $25,000 in off-size bushings, plus the time and labor entailed in the disassembly operation.
“We contacted Gatco for a retrofit, and they had whole process wrapped up in just 24 hours,” Funk says. “Had we approached this thing in a different way we would have been looking at something like six weeks to resolve the situation, and who knows what that would’ve cost us.”
Jim Malczewski, a manufacturing engineer at Ford Romeo in Romeo, MI, has a similar story. The Romeo plant builds 4.6 liter engines for pickup trucks, Crown Victorias and other Ford models. In 2002, an order came in to enhance the Mustang Cobra with more horsepower. This operation would require the engines to be beefed-up inside the vehicle’s engine block. More stock would need to be machined, which would shorten the lifespan of the bearings involved to a mere three months. Replacement maintenance cost from deployment to replacement turned out to be exorbitant, and tool repair was becoming a pricey issue as well.
“The job was very rough on our equipment,” Malczewski said. “Old bearings would fail prematurely, and tools were being literally destroyed, creating unwanted scrap cost. We also had to spend a lot of money to replace the busted tooling. When we finally got around to redesigning our tooling we decided to incorporate Gatco retrofit bushing. It turned out to be a wise decision.”
According to Malczewski, prior to the Gatco retrofit, Ford Romeo was replacing bearings on a monthly basis. Since the install, Ford is just now replacing bearings for the first time due to wear.
“The retrofit has already saved us roughly $100,000,” adds Malczewski. “Some of the repairs were costing us $5,000 each and we were making them all the time. The investment we made in Gatco has really paid off. The retrofit has not only secured us a cost advantage but an efficiency advantage as well. You really can’t ask for more than that.”
Gatco, Inc.
734-453-2295
www.gatcobushing.com