Originally Published January 2000
Bar Feeders Bolster Manufacturing Operation
Lathe add-ons help cut cost of making surgical products
Pressed by a posse of tough competitors, a Texas-based medical device maker has told its machining vendors to hit the trail. The result: Aided by a trio of efficiency-boosting bar feeders, the company's new in-house machining process has reduced manufacturing costs without sacrificing product quality.
Osteomed Corp. (Addison, TX) manufactures a line of precision power tools used in facial and small-bone orthopedic surgery. The company also makes attachments for these toolsdrills, routers, and burrsas well as plates and bone screws used in surgical procedures. All of these small items are manufactured in high volume from hard-to-machine materials such as titanium (for the surgical fasteners) and 17-4 stainless steel (for the power tools and components).
In the past, Osteomed farmed out all of its machining to vendors. But in response to competitive pressures, the company changed course and began to do its own machining. "Bringing the machining operation in-house was a move toward a more cost-effective operation," explains Otis Blackwell, Osteomed's manufacturing manager.
To gear up for the task, Osteomed purchased a vertical machining center and a laser marking system. In addition, the company installed five Citizen Swiss-type turning machines, three of which are hooked up to bar feeders.
"An important part of [our] strategy is to make sure that the in-house operation meets productivity requirements as quickly as possible," Blackwell says. "Maximizing the amount of time the machine tools are making parts is the key to increasing productivity."
The Mini-Rhinobar features a feed tube extension that supports bar stock to eliminate vibration and improve cutting accuracy.
That's where the bar feeders come in. Made by Lexair Inc. (Lexington, KY), the single-tube Mini-Rhinobar bar feeders help keep the Citizen machines running without operator intervention. "Instead of cutting off itsy-bitsy pieces [of metal] and feeding them into the lathe one at a time, the bar feeder automates the lathe," explains Wes Allen, Lexair's vice president of technology. "You can put in a full 12-ft length [of bar], and the bar feeder loads the bar stock as required."
Available Mini-Rhinobar models can handle 6- or 12-ft bar lengths. Designed especially for Swiss-type CNC screw machines, the bar feeder can be equipped with 16 different feed tubes to handle bar diameters from 1/8 to 15/8 in.
At Osteomed, two Citizen L-20 machines are dedicated to titanium screw production. Fed 3/16-in.-diam rod, the machines turn out screws varying in length from about 0.00002 to 1 in. The other Mini-Rhinobar-equipped Citizen, an L-25 turning center with six programmable axes, turns out components for Osteomed's tool product line, including housings, motor shafts, reciprocating shafts, and other small pieces. Bar stock for this operation is 17-4 stainless steel ranging in diameter from 1/4 to 7/8 in.
A Big Wet Noodle
With diameters this small, a 12-ft-long bar rotating at high speeds "is like a big wet noodle," Allen notes. Besides being noisy, the vibration of these bars is transferred to the lathe, where it can spoil the surface finish of manufactured parts.
To reduce bar vibration, the Mini-Rhinobar employs hydrodynamics. Oil fills the gap between bar stock and feed tube, acting as a noise-dampening support. As the bar begins to turn, hydrodynamic forces move it toward the center of the feed tube, with centering forces increasing as bar speed increases.
Three of Osteomed's Citizen turning machines are equipped with the Mini-Rhinobar bar-feed system.
For additional bar support, the Mini-Rhinobar features a feed tube extension equipped with nonrevolving bushings. This support, working with a dynamic bearing-mounted pusher cone that maintains contact with the bar chamfer, allows much higher turning speeds than other bar-feed systems, according to Lexair.
Though it operates according to programmed instructions, the Mini-Rhinobar itself requires no programming. "It's an accessory to the lathea slave," Allen explains. "So you program the lathe only." The advantage of this arrangement? "It's faster," Allen says. "You don't have to save programs for the bar-feeder like you do for the lathe. Your bar feed operation [instructions] are piggybacked on the lathe program, so there's no program coordination involved."
To simplify the bar-loading process, the Mini-Rhinobar system can be operated with a remote pendant. This handheld control box allows workers to control the bar feeder while standing next to the lathe. This means that when a new bar is being loaded, a worker can operate the bar feeder while looking into the lathe to make sure the bar has moved into the correct position. This can save lots of "running back and forth" between lathe and bar feeder, according to Allen.
When the lathe finishes with a bar, an alarm alerts the operator, who pulls out the remnant and loads a new bar. At Osteomed, total bar changeover time is about three minutes, Blackwell estimates.
The single-tube Mini-Rhinobar can handle only one bar at a time. By contrast, so-called magazine bar feeders can hold a number of bars and will automatically load new bars into the lathe. "They're a lot more expensive but not a whole lot faster," Allen says of the magazine systems. A very fast one might load a bar in 30 seconds, he notes, compared with three minutes for the Mini-Rhinobar. On the other hand, he points out, setup of a magazine bar feeder can take 30 minutes when switching to bars of a different diameteragain versus three minutes for the Mini-Rhinobar.
At Osteomed, Blackwell considered magazine bar-feed systems but eventually decided that the single-tube type would be best for his operation. "Magazine bar feeders are appropriate for certain production turning operations, but when I looked at the cost compared with single-tube feeders, I felt that the single-tube approach was the most cost-effective solution to our production needs."
Blackwell was also impressed by the compactness of the Mini-Rhinobar (the 12-ft model used by Osteomed is 17 ft long). "It's a given that manufacturing operations never have enough room, no matter how large an area is available," Blackwell says. "The bar feeders are critical to maintaining high productivity, we have to have them, and the fact that they take up minimum floor space is an added advantage."
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