2011

Fine Laser Cutting Technology

Laser Cutting vs. Other Technologies

altLaser cutting’s speed and precision compares favorably with that of the chief competing technology, electro discharge machining (EDM). To obtain the same high quality cut as a laser cutting machine, EDM requires up to 4 passes, which slows down processes considerably. On the plus side, EDM allows multiple parts to be processed at once. The widths of cuts produced by a laser cutter is as small as 0.001-inch, while that of EDM is around 0.004-inch. Feature sizes are limited with EDM and sharpness is not as good, compromising cut resolution.

The EDM process is also limited by the fact that it works best with certain geometries, for example tubes with a symmetrical profile. Problems arise if there is a hole in a tube that does not go through both sides. The process is analogous to the ubiquitous cheese cutter that uses a wire to slice through a block of cheese. All is well with a symmetrical, solid shape, but the wire cannot handle any complex geometries.

A final issue is floor space, especially for factories where space is at a premium. A typical EDM machine can be as large as 10 to 12 feet square, while a laser cutting system is 5 to 6 feet square.

Another technology available is electro chemical grinding (ECM), which removes electrically conductive material by grinding with a negatively charged abrasive grinding wheel, an electrolyte fluid, and a positively charged work piece. ECM is a fast cutting method that gets quality similar to EDM. With ECM, the electrolyte used must be disposed of in accordance with OSHA as hazardous waste, and some electrolytes produce hexavalent chrome when cutting steels. Finally, ECM’s use of hard tooling makes it much less flexible than laser cutting.

A third available technology is water jet cutting, which slices into metal using a jet of water at high velocity and pressure, or a mixture of water and an abrasive substance. Water jet cutters offer restricted cut geometry. Only symmetrical through-features or end cuts are possible using this technology.

Figure 3 shows a comparison of the cut quality of EDM and laser. Note the smooth sharp edges in the cute made by the fiber laser equipment.

5-Axis Motion

altThe explosion of new 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.

One technology now being offered is a 5-axis laser cutting system. The control software controls the laser and the motion together, and the integration of these two aspects provides a rigid structure, free from vibration. The 5-axis motion consists of 3 linear axes and 2 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 4 axes on the part and one on the focus head, or switch them around according to the best solution for the application.

The Key to Success

Laser cutting for medical tube tools and components has many benefits, but actually achieving them depends in no small part on successful system integration. Designers need to develop an entire system where the motion, laser, software, and tooling all work properly and are integrated into a whole that supports the desired process flow.

This article was written by Geoff Shannon, Laser Technology Manager, Miyachi Unitek Corporation (Monrovia, CA). For more information, contact Mr. Shannon at Geoff@muc.miyachi.comor, or visit http://info.hotims.com/34459-201.

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