For small, delicate part applications, lasers deliver stable, accurate energy for cutting, marking, and welding

Doctors are understandably sensitive about the tools they use-every dimension, joint, or mark can add to or detract from performance, depending on how well the tool features are made. So for medical devices, the pinpoint precision of lasers is valuable for cutting, welding, or marking the smallest of devices.

Lot sizes and part styles for medical parts can vary wildly, from customized implants to relatively mass-produced tools and devices. “Nonetheless, every single instrument is subject to the highest quality standards,” says Alexander Knitsch, application specialist for Trumpf Laser (Farmington, CT). For implants in particular, the main priorities include long lifecycles and biocompatibility.

“Medical devices are especially suited to laser processing, because they require extremely tight tolerances and advanced materials processing,” says Larry Green, industrial product manager, Spiricon Inc. (of Ophir Optronics Ltd., Logan, UT). “It’s also evident that the laser performance must be well characterized for the process to be repeatable, robust, and profitable.”

The key to laser-machining small medical applications is to use a laser beam with a narrow, stable, and focused energy profile, even for laser spot diameters under 100 µ More stringent requirements for stents, pacemakers, implants, catheters, and other medical products require better beam profiling and delivery tools, adds Green. Along with added quality and capability, such tools can improve device manufacturers’ cost profile through reduced downtime.

Some problems can be fixed just by checking the beam profile with real-time diagnostics and re-adjusting the laser. Green points to a medical-device manufacturer (the company requested that its name not be used) that laser-marks its product with a logo whose edges were no longer acceptable to the customer. “Since an illegibly marked product cannot be sold, they were discarding perfectly good product because of the poor identification of the part.” Here, laser-beam profiling showed that at certain power settings the beam profile had more than one peak, instead of a single peak at the center of its spot. “Readjusting the laser power settings to eliminate the multiple peaks solved the problem.”

In another case, a medical manufacturer (which, again, does not wish to be named) traced poor welds to a laser beam spot whose focus location varied randomly over time, causing spots of varying size on the product, says Green. The solution was to change the beamdelivery system from “hard” laser optics to fiber delivery-a common trend in laser/medical applications, as we’ll see below.

Bone screws and other medical hardware may look simple, but their manufacturing processes use the most advanced laser technologies. The laser, motion control, part positioning, and even vision software for beam delivery come together to create the small features that doctors need for stabilizing damaged bone or fixing other problems.

“The medical devices industry is now looking for a new generation of lasers that can offer better value and additional functionality over their existing laser technology,” says Linda McIntosh, product manager for Virtek Laser Systems North America Inc. (Waterloo, Ontario). This applies to marking lasers, which have been used for years for writing identifying information and other marks on metal and plastic medical tools.

“Laser marking on metals creates a very high quality, permanent mark, and it does not require inks, solvents, etc.-which means lower operational costs.” Lasers avoid the FDA-approval issues involved with ink, and they can mark surfaces without creating crevices, a feature to avoid on implants, McIntosh adds.

To improve the marking of bone screws, Virtek’s laser-marking systems integrator, FOBA Technology + Service GmbH (Ludenscheid, Germany) integrates a vision system called Intelligent Mark Positioning (IMP). The system is integrated with the laser system’s lens, feeding back data to reduce position errors when marking 0.5-mm characters on 3-mm-diam screw heads. Essentially, the system “puts eyes and intelligence” in the laser, says McIntosh, comparing a model of the part with what it sees for proper positioning. This capability reduces scrapped parts, minimizes fixture costs and laser setup time, and improves machine-to-machine consistency.

Tools used to create the holes for bone screws also require detailed marking, such as depth gaging on the shaft to guide the surgeon. Since these marks must go around a drill or tap’s shaft, the tools must be rotated while being marked, a complicated task better suited for automation, according to system supplier Telesis Technologies Inc. (Circleville, OH). The company’s system incorporates a six-axis robot for handling, a 100-W Nd:YAG laser, and Telesis software. The system “takes a pallet of 100 parts at a time through the complicated marking cycles in a matter of minutes,” says the company’s Ralph Villiotti.