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Laser Cutting


Picosecond Lasers Showing Promise Many lasers currently deployed are either CO2


With fusion-cut stents, cutting kerfs typically are 10-20 µm, or fiber


lasers, with fiber gaining converts in recent years as prices for fiber lasers have fallen. Both these types of lasers use a fusion cut that melts metals efficiently while using nozzles to deliver a gas, either oxygen, nitrogen, or even shop air, to blow away particles from the cutting area. A newer class of extremely short-pulse picosecond lasers also is starting to be employed, particularly for cutting stents, with a cold process where the laser vaporizes the material instead of melting it. Te manufacturing of stents is an important area in medi-


cal device manufacturing, notes Sascha Weiler, program manager, Micro Processing, Trumpf Inc. (Farmington, CT), but lasers are used in many aspects of medical manufacturing. “You can divide that into three applications: welding, marking, and cutting. Tese can include welding of pacemaker hous- ings, endoscopes, parts that require clean and smooth welds, which go into the human body. And marking, it’s the same story, marking pacemakers, surgical instruments, or hearing aids, which are made of many materials.”


he notes. Trumpf offers fiber lasers, as well as newer short- pulse picosecond lasers in the green wavelength specifically aimed at cutting stents, which have relatively thin walls and don’t require higher power lasers. “For stent cutting, we typically use a green picosecond


laser. Te reason is because it’s more versatile—it can cut a metal stent as well as polymer and nonmetal stents,” Weiler states. “Tis is very different from the fusion cut. Picosecond pulses are so short that the material is not molten, like with the fusion cut, it’s vaporized. So now we don’t have any metal, we just have vapor, so we just need some kind of nozzle to blow away the vapor—people call it ‘cold cut’ or a cold process, and that eliminates any residual heat in the material, which results in perfect edge quality, and especially for the nonmetal- lic stents, they cannot be cut with a fusion cut at all, the cutter would just melt the whole thing.” Picosecond lasers like the Trumpf TruMicro Series 5000 la-


ser line can vaporize metal or nonmetals using 50W of power and a pulse energy rated at up to 250 microjoules. Tese short pulses of less than 10 picoseconds vaporize the material so fast that no heat-affected zone (HAZ) can be detected. Micropro- cessing applications for the TruMicro 5000 line include cut- ting, structuring, ablation and drilling. “Tat’s a short pulse, actually high intensity, because in the peak of the pulse, you’ve got the power of multiple tens of megawatts,” Weiler observes. “It’s like a very tiny, but powerful hammer. And you’ve got like 800,000 of those hammers a second. Tis is how it works, this is how you get the productivity.” Trumpf, which launched its first picosecond lasers in


early 2008, is now offering its second-generation picosecond lasers for microprocessing applications. “I’d say for the cutting nonmetals in medical, truly it’s an enabling technology. You couldn’t do that before, with this kind of quality. “At the beginning, it was a testing element—no one was


The multiaxis Sigma Laser Tube Cutter fiber system from Miyachi Unitek offers users flexible, noncontact cutting of small tubes for medical device components.


In stent cutting, the state-of-the-art cutting method still is


the fusion cut with mostly 100 to 200-W fiber lasers, Weiler adds. “Tis works well for stainless steel, maybe for Nitinol, because here and there you can allow some postprocessing, and you need the postprocessing because it’s a fusion cut, where the laser melts the metal and you have gas nozzles that blow the metal out of the cutting surface.”


80 Medical Manufacturing 2013


sure it was going to take off,” Weiler recalls of picosecond lasers. Te technology is used not only in medical, but for a wide variety of applications, he adds, including semicon- ductors. Key to the success of these short-pulse lasers is the quality of the cut. “If the quality isn’t there, it means it must be somehow post-processed, and believe it or not, it’s done manually. Tere are guys sitting there with a microscope and checking if they see anything on the stent, and then they do sandblasting or brushing, and check again. And it is very time-consuming and a lot of labor.” Hand finishing of stents involves small sandblaster tools


used with microscopes to spot any imperfections in the stent, he notes. “Camera vision is literally impossible to implement. Te human eye, you can teach it. You have to somehow hold the stent under the microscope and play with it, and then you see the obstacles. You can do it manually, but it’s very difficult, and a lot of stents are made out of Nitinol, which is 50% nickel


Image courtesy Miyachi Unitek Corp.


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