In the past few years, I have noticed an increasing number of medical device applications requiring the stripping of outer layers of polymers from small diameter wire to expose the underlying metal conductor. Some applications that spring to mind include cardiac rhythm management, and neurological and radio frequency ablation products.
The laser is well suited for this delicate material removal task – unlike the most common manual process, which entails dipping each wire individually into a solvent, and then manually scraping any remaining coating material deposits with a sharp knife. I call this “the X-ACTO method.”
Moving away from X-ACTO wielding technicians to automated laser equipment increases production process control, ensures quality, and increases throughput. As an added bonus, it also improves worker safety and supports a company’s ISO 14001 sustainability program.
Lasers well suited for wire stripping
Since the laser imparts no physical force on the wire during the process, delicate wires with diameters as small as 50 microns can be stripped. Material is removed by directing a focused beam (around 25 microns in diameter) at the part which is steered in a set path by galvanometers, enabling highly tailored removal.
A good example comes from a large medical device company that recently transitioned from a manual to a laser process for producing stainless steel guidewires used in intravascular interventional devices. The wire, which has a diameter similar to that of a human hair, is coated with an organic material that makes it compatible for use in humans. This organic coating must be stripped away from the microscopic metal core wire to enable connection to the guidewire’s distal end.
The new laser process consistently and precisely strips away the organic material coating from the component’s metal core wire, enabling other subsequent downstream assembly operations. The new process takes only seconds to complete, whereas the legacy process took about eight minutes. Throughput rose by 250 percent, with an additional increase in yield. In addition, the process eliminated the use of chemicals, improving safety and reducing chemical handling and disposal costs.
Picking the right laser
A number of different lasers can be used for wire stripping, depending upon the particular wire diameter, insulation material, and feature requirements. Table 1 shows the most commonly used lasers.
The sealed CO2 laser should always be considered first. With a wavelength of 10604 nanometers (nm), the CO2 beam is readily absorbed by every polymer, so it will work to a certain degree no matter what insulation material is used. Figure 1 shows a polyimide wire that has been stripped using a CO2 laser.
If a CO2 laser cannot be used for reasons of heat input control, a nanosecond laser should be considered next, specifically those with 532nm and 355nm wavelengths.
When extreme quality or minimal heat input is needed, consider are the ultra-short pulse picosecond and femtosecond lasers. These two laser families produce pulse widths that are so short that the material does not have time to conduct any heat from the process area into the surrounding material. However, these best quality results come with a steep price.
Laser wire stripping systems
In medical device manufacturing, the wires are typically part of a production line, processed in either a manual or automated load machine that handles the wire pieces one at a time at the required length.
Figure 2 shows a laser ablation system recently developed by Amada Miyachi America, which includes high speed galvo beam steering, and a custom wire feed and rotating mechanism that achieves accurate and repeatable wire positioning. Also included are several proprietary features needed to manage heat balance in the part. The approach also includes a self-cleaning mechanism – a high-tech “toothbrush” if you will – that removes sticky debris from the ablation process area so it won’t contaminate tooling.
Easily automated, the laser transforms a key step in the manufacturing process to a lean operation, reducing and optimizing human-dependent processes, providing consistent part quality.
Figure 2 – Laser ablation system for wire stripping
To make the right decision on which laser source and removal methodology works best, be sure to test possible options in an application laboratory with a range of lasers so you can optimize both process and implementation. Interested in giving it a try? Amada Miyachi will test your parts FREE.