Laser technology offers the surgical precision required for medical tools

February 2011 - Fine laser cutting is an ideal technology for specialized cutting requirements found in the manufacturing of medical tube tools and components because of the need for sharp edges, contours and patterns.

From surgical instruments used in cutting and biopsy to needles containing unusual tips and side-wall openings, laser cutting provides higher precision, quality and speed than traditional cutting techniques. It is ideal for working on small tubes that must be cut to high dimensional accuracy because the laser light used does not have any physical presence and makes no contact with the material. It does not push, drag or impart force that might bend a part or cause flex that would have a negative impact on process control.

It also offers minimal thermal input, with fine control over how hot the work area gets. This is important because small parts heat up quickly and might otherwise overheat or deform.

Laser cutting with gas assist produces the highest cut quality and high-resolution cut paths. Dimensional accuracy is key to measuring cut quality: does the part match the print? Other considerations include surface roughness and the absence of thermal damage.

Cut width can be extremely small with laser cutting, less than 0.001 in., and dimensional accuracy is extremely precise, at about ± 0.0005-in. This accuracy is very useful for producing the jagged teeth used in some cutting tools. Dross or burr left on the underside of the cut is minimized or eliminated. This significantly reduces the amount of post-processing needed. The recast level layer is less than 0.0005 in.

Other technologies
Laser cutting's speed and precision compares favorably with that of electro discharge machining. To obtain the same quality cut as a laser cutting machine, EDM requires up to four passes, which slows down processes considerably. On the plus side, EDM allows multiple parts to be processed at once.

The width of cuts produced by a laser cutter is as small as 0.001 in., while that of EDM is around 0.004 in. The EDM process also is limited because it works best with certain geometries, for example, tubes with a symmetrical profile. If there is a hole in a tube that does not go through both sides, it can create problems.

Another technology available is electro chemical grinding, which removes electrically conductive material by grinding with a negatively charged abrasive grinding wheel, an electrolyte fluid and a positively charged workpiece. ECM is a fast cutting method that gets quality similar to EDM. With ECM, the electrolyte used must be disposed in accordance with OSHA as hazardous waste, and some electrolytes produce hexavalent chrome when cutting steels.

A third available technology is waterjet cutting, which offers restricted cut geometry. This technology can only create symmetrical through-features or end cuts. The explosion of non-invasive surgery tools gives rise to some unique and innovative shapes. This in turn requires motion packages that offer a new level of cutting geometry. The ability to keep a part in a machine and make intricate cuts gives designers freedom, enabling them to cut more challenging geometries in one pass.

Miyachi Unitek Corp., Monrovia, Calif., offers a five-axis laser cutting system. Software controls the laser and the motion together, and the integration of these two aspects provides a rigid structure, free from vibration.

The five-axis motion consists of three linear axes and two rotary axes. The unique set-up allows system engineers great flexibility to choose the best axis configuration for a particular cut, not limited to where they are on the part. Engineers can mix and match and set combinations that make it more efficient for a process. For example, designers might place four axes on the part and one on the focus head or switch them around according to the best solution for the application. FFJ