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Cutting to the Point of Fiber Lasers

Tue, 05/08/2007 - 11:31am
Precision is of paramount importance in the manufacture of medical devices. Few technologies demonstrate the ability to achieve the necessary degree of accuracy more effectively than laser solutions. This article specifically examines the benefits of using fiber lasers for cutting and welding applications in medical device manufacturing.

By John Tinson and David P. Braman
Technological advancement, a wealthy aging population, and the increasing number of treatable diseases and conditions have created a medical device market that is constantly growing. Combined with this, device size is shrinking, functionality is improving, and the lifetimes of the devices have lengthened—all representative of impressive advancements that have been made in the manufacturing of medical devices.

A nitinol stent cut with an SPI fiber laser.
In recent years, lasers have been at the forefront of this advancement. Specifically, fiber lasers have exhibited favorable capabilities in the manufacturing of medical devices and equipment.
Laser Cutting
Laser cutting has made significant in-roads into the medical device industry. The quality of laser cutting is strongly dependent on several parameters—depth of focus, power stability, cutting speed, and material characteristics.

The cutting capabilities of fiber lasers are illustrated by the ability to prepare fine components. Here a magnified view of a spirally cut ‘Hypo tube’ is presented.
A long depth of focus provides for symmetrical and flat walls of the cut while a stable laser power guarantees these physical aspects over the entire length of the cut. A stable cutting performance is also especially important for thin-walled materials, which is otherwise observed as debris on the underside of the cut.

For a particular thickness of any material, there is a certain cutting speed and average power at which the minimum heat input is achieved. This minimum heat input corresponds directly to the best cutting quality that, in turn, corresponds to minimum dross (or ease of dross removal), minimum discoloration, and minimum cut surface roughness. Additionally, for a particular cutting speed, material thickness, and material type, there is a certain minimum average power required to cut and this average power needs to be determined during the minimum duty cycle.


Medical devices, such as this catheter kit, can benefit from the microwelding and microcutting abilities of the fiber laser equipped FiberStar workstation from Crafford-LaserStar.
Enhancing the Laser Line
Crafford-LaserStar Technologies Corp., a worldwide supplier of laser microwelding, cutting, and marking workstations for industrial applications, introduced its first FiberStar laser welding workstation in 2006 and is already exploring other workstation solutions featuring fiber laser engines.
This addition to the Crafford-LaserStar product range is a direct result of the growing acceptance of fiber lasers for materials processing applications as a cost-effective alternative to conventional laser design. The new welding workstations provide a better quality output combined with improved process yield, reduced running costs, and lower maintenance demands, offering a significant breakthrough in welding performance.The new workstation has been designed with the needs of the precision microwelding and microcutting industry in mind—such as for the manufacture of medical devices—providing a level of accuracy and consistency previously unavailable. This is made possible due to the unique capabilities of the fiber laser engine, including sub 0.5% pulse to pulse energy variation, ±0.5% CW power stability over time, single-mode (TEM00) beam quality, and focused spot sizes down to 10 µm. These features, coupled with high energy efficiency and no optical parts to align or calibrate, make fiber lasers an attractive laser engine for practical shop floor environments.
In the medical industry, fiber lasers are used to cut stents out of thin-walled tubes. With a diameter of 0.8 to 1.2 mm and wall thicknesses below 0.2 mm, these stents are generally prepared out of 304-type stainless steel, but may also be fabricated out of CbCr, Nitinol, or other exotic alloys. Such stents are surgically placed within constricted veins and arteries to help improve blood flow—the smallest being used for blood vessels within the brain and the largest within the thigh. This industry in particular has benefited from the adoption of fiber laser technology, both in terms of reduced production costs and an improved end product.
Laser Welding
Fiber lasers do not exhibit the shortcomings in output power variation, spot size, and focal point caused by thermal effects on the glass rods of traditional YAG lasers. They offer true welding consistency at all power levels, across all pulse sequences. Furthermore, during the entire lifetime of the laser, the laser parameters remain predictable and consistent. The reason for this is that the generation and transport of the laser beam to the workpiece takes place entirely within the confines of a single-mode fiber. The beam shaping provided by this fiber neither degrades over time nor changes with laser power. This also makes the laser exceptionally physically robust and stable, and thus suitable for the most challenging of industrial environments.

A fiber laser can be used for welding the fine wire leads used in medical implants. In this case, the workstation was also used to prepare the end of this 330 µm Pt wire.
Another advantage is that the small spot size and high beam quality translate to high irradiance at the focal point, so workstations equipped with fiber lasers can produce better results at lower power levels. The focused beam consistently affects a very small area of metal, with very little heat generated around the weld point. High quality precision welding can be performed close (0.1 mm) to the most complicated and intricate component parts.

From an economics standpoint, the consistent and improved welding performance means reduced scrap and faster production throughputs, coupled with lower operational running costs and improved laser up-times.
Conclusion
These financial and performance advantages mean that fiber laser technology is now frequently chosen as an upgrade over conventional flash-lamp pumped solid state or even DPSS laser technology in many other laser-based manufacturing segments. In addition, a small footprint and fast ROI open up markets that were previously out of reach for some applications.

The laser is an excellent tool to support the need of the medical device industry to achieve smaller feature sizes and to increase cycle times in the manufacturing process. While Nd:YAG lasers are established and offer great advantages in peak power, new laser types such as fiber lasers are starting to be used for ever finer applications that require high accuracy and repeatability.
ONLINE
For additional information on the technologies and products discussed in this article, see the following websites:
  • www.spilasers.com
  • www.laserstar.net


  • John Tinson is the VP of sales for SPI Lasers UK Ltd. He can be reached at +44-1489-779668 or john.tinson@spilasers.com .

    David P. Braman is the VP of engineering at Crafford-LaserStar Technologies Corp. He can be reached at 401-438-1500 or sales@laserstar.net.

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