Source: Williambeke / CC BY-SA 4.0

Ultra-hard metals and thin-walled metallic tubular structures present machining challenges to medical device manufacturers. Traditionally, a vast array of manufacturing techniques were used to achieve surgical precision edges, contours and patterns, including lasers, electric discharge machining (EDM), water-jet machining, chemical machining and grinding. Even when compared to other laser machining methods, fiber lasers have gained wide appeal as recent developments have allowed for advanced capabilities that produce superior edge quality.

Advantages of Laser Cutting

Laser machining is a non-contact process that is ideally suited for complex machining operations and intricate shapes. Precision cuts on thin materials less than 0.02 inches can be performed in a single pass and focal points finer than 0.001 inches are used to produce superior edge quality with minimal post-processing required.

Fiber Lasers

Fiber laser cutting technology has evolved to achieve finer focal points and deliver higher power. They are being incorporated into turnkey systems with multi-axis motion capabilities and at a lower cost of ownership when compared to competing technologies like pulsed Nd: YAG (neodymium-doped yttrium aluminum garnet) lasers. They are becoming the method of choice for thin metal precision cutting.

Fiber lasers offer exceptional control over pulse width, power and focus spot size and are being offered with a variety of wavelengths across the electromagnet spectrum. These advanced features are used to perform a number of operations from cutting, drilling, ablating, scribing, micro marking to texturing on a wide range of materials, including polymers, metals, glass and ceramics.

Medical device manufacturers are benefitting from a lower cost of ownership when compared to other laser machining equipment. The efficiency of the laser and lower maintenance costs are accompanied by greater cutting speeds that all work to lower the overhead.

Laser-material interactions outside the cutting zone are also minimized as higher repetition rates with femtosecond pulsed fiber laser almost eliminate thermal absorption. These next-generation lasers deliver high peak laser intensity that extends the machining capabilities while the lower photon energy, due to ultrashort laser pulses and higher repetition rates, allows for higher detail.

Fusion Cutting

Endoscopic, arthroscopic and other surgical instrument applications are benefitting from gas assisted operations, known as fusion cutting. In these applications, the laser cutting zone is assisted by a coaxial gas flow, typically oxygen (O2), which further increases the cutting speed and edge quality.

Gas flow serves two purposes, to remove molten metal and to deliver more heat to the cutting area. Around 30 percent to 50 percent more thermal energy is delivered for both on-axis and off-axis cutting operations. Dimensional accuracy is extremely precise within +- 0.0005 inches, although process control is paramount.

An intense laser source is required as the melting point must be reached quickly as the gas flow removes the cut Kerf in unison. Single mode fiber lasers with an average power of 200 watts or greater are ideally suited while the cut quality, heat affected zone and cut speed are only achieved when the process is optimized for each operation.

The technique is well suited for precision cutting of stainless steel, nickel, titanium, Nitinol and other gray metals for fabrication of arthroscopic and endoscopic tubular devices.

Fine Melt Ejection

In some applications, fine melt ejection is preferred and offers considerable costs savings. Fine melt ejection incorporates a short pulse fiber laser with 20 or more watts of average power. It requires multiple passes to make an incision and does not achieve the same accuracy as in gas assisted fusion cutting, but is well suited for two-axis cutting of reflective metals such as gold or copper.

This method is also used for drilling small diameter holes at a high rate of throughput. It delivers minimal thermal energy, which helps minimize the heat affected zone, although the primary benefit of using the fine melt ejection method is that the system costs significantly less than a multi-axis CNC fusion cutting system.

Conclusion

Competing non-laser processes such as wire EDM, water jet cutting and electrochemical grinding (ECM) are still used as equipment cost is significantly less. Cutting speed, edge quality and precision are sacrificed in these methods and part fixturing and process times are elongated. Turnkey laser cutting systems offer numerous benefits to medical device manufacturers explicitly when complex geometries and precision cutting of thin metal tubular structures are required although the success of laser machining often hinges on process design and optimization.

Resources:

Precision Cutting for Medical Devices