Originally Published MPMN November 2001

PROFILE

Feed System at the Heart of Pacemaker Production

Equipment reduces vibration to enhance productivity and accuracy

The production of pacemakers, defibrillators, and dental implants requires many small, intricately machined components. For manufacturer MedSource Technologies Inc. (Minneapolis), most of these parts begin as 1/8-in.-diam stock that it machines down to finished products with diameters of 0.030–0.090 in., tolerances of ±0.0001 in., and finishes averaging 32 rms. Today, the company can easily achieve these exacting specifications, but when production first commenced, it ran into a significant problem. Although the firm was able to produce the required parts using its existing equipment, it had difficulty maintaining acceptable production speeds.

After some investigation, MedSource determined that the problem was caused by the gravity feed systems used to supply stock to each of the CNC turning machines and lathes. "With that kind of system, you reach a certain rpm and the bar starts whipping around," explains first operations foreman Dave Thomas. "That inhibits your ability to hold tight tolerances and finishes." The firm approached Lexair Inc. (Lexington, KY) to see if adopting its Mini-Rhinobar hydrodynamic bar feeder might offer a solution.

The Mini-Rhinobar feeder is a single-tube feeding system that uses oil to improve bar stock stability and reduce noise levels. The liquid fills the gap between the bar stock and the feed tube, using hydrodynamic force to center the material as it rotates. As the rotation speed of the bar stock increases, so does the magnitude of this centering force. A front swing-out mechanism with a large barrel clamp helps to further reduce vibration. Each Mini-Rhinobar system can accommodate as many as 16 feed tubes with diameters of 1/8-1 5/8-in and lengths of 6 or 12 ft.

MedSource installed 30 of the Mini-Rhinobar systems over a 2-year period and has noticed dramatic increases in productivity. "The primary benefit that we saw after installing the bar feeders was the stock stability it provided our CNC machines equipped with rotary guide bushings," says Thomas. "The rotary bushing on the machine rotates with the bar, allowing us to increase the rpm, which, of course, increases productivity." Thomas estimates that after installation, operators were able to improve the speed of some of the Swiss machines by as much as 50%, and 30% on average. Overall productivity was said to increase 20%.

But reducing vibration and noise are not the feeding system's only benefits. The unit also features an end-of-bar signal and an automatic retraction feature that allow unattended operation. Bar changeover time is estimated at 3 minutes. The equipment is sized for use in both large and small shops; the model employed by MedSource has a length of 17 ft. While not negligible, the required room is justified, says Thomas. "The floor space that they require is simply an issue that has to be planned in advance."

MedSource says it will continue to use Mini-Rhinobar feed systems in the future. With services spanning prototyping to full production runs, the company can machine complex components with microminiature to 1-in. diameters from stainless steel, titanium, platinum, MP35N alloy, and other materials.

Zachary Turke

Copyright ©2001 Medical Product Manufacturing News