Laser cutting has been a widely accepted fabrication method since the invention of lasers in the 1960s. It is now a popular manufacturing technique used to cut a wide range of materials, especially difficult-to-cut ones. Laser cutting is currently holding the largest market share in laser material processing.
Laser cutting can take several forms, including fusion cutting, sublimation cutting, thermal stress cracking, scribing, and photochemical ablation (cold cutting). It can be accomplished through different techniques that involve different laser types (pulsed or CW at different wavelengths), energy levels, and the use or non-use of an assist gas. The advantage of laser cutting over the classical mechanical and thermal methods comes from the strong spatial and temporal localization of laser-matter interaction, which confines the energy deposition into a very small volume and thus provides very large heating and cooling rates, which offer the best possible resolution and accuracy as shown in Fig. 1 [1] and Fig. 2 [2]. A number of the advantages are listed below:
- Non-contact process and requires no clamping for the workpiece, thus avoiding material contamination and mechanical damage from the clamping and avoiding tool wear and associated costs.
- Ease of automation with computer numerical control (CNC) and robotic processing, capable of cutting complex shapes.
- Small spot size (narrow kerf) and minimum heat-affected zone that offers high geometry accuracy.
- A high cutting speed yields a higher production rate.
- Capable of cutting almost all kinds of materials.
- A quiet, clean process compared to traditional methods. In some cases, no post-processing procedures are required.
Many of these advantages are particularly useful for the manufacture of medical materials such as coronary stents (see Fig. 3 [3]). The laser cutting system is now one of the key fabrication technologies used for coronary stent manufacture. Actually, it is the most effective method for processing stents compared to traditional methods. Stents are devices introduced into clinical practice to create a larger lumen within the lesion, providing smooth blood flow rather than removing the muscle cells that build up in the blood vessel. The typical sizes of stents used in clinical practice are 2.5 to 4.0 mm in diameter and 8 to 38 mm in length. The wall thickness is 80-100 µm, and the strut width is 80 µm, as shown in Fig. 4 [4]. Therefore, high accuracy is essential for stent manufacture, and dimensional accuracy is a critical factor for integrating a stent-cutting platform.
Many types of lasers, such as Nd:YAG, fiber, and disk lasers, can be used in stent manufacturing. Lasers with long pulse duration have a long laser-matter interaction time, resulting in a large heat-affected zone. While short-pulse lasers, such as picosecond and femtosecond lasers, produce a no- or minimal-heat-affected zone, offering the best quality in stent manufacture. Stent cutting is a very delicate process due to the intricate design of the miniature stent. Lasers with shorter pulse duration and high beam quality, and stages with high resolution and accuracy are the best options. High-quality stent products should comprise the following features:
- Narrow and consistent kerf width
- Absence of heat heat-affected zone and back-wall damage
- Smooth and clean cut edges with no dross and recast layers
- High geometry accuracy
The production of human coronary artery stents requires not only high geometric precision but also high-quality surface finishes. Therefore, post-processing procedures such as electropolishing, acid pickling, and soft etching are required.
Current-generation laser cutting machines offer high versatility. These integrated systems can use multiple laser sources, including high-performance fiber lasers, picosecond lasers, and femtosecond lasers. They also support multiple types of laser cutting heads and widths, and can perform dry and wet cutting. These machines can be used to cut metals, semiconductors, and dielectrics. The versatility of these machines makes them very cost-effective options. They also come with a variety of safety mechanisms, including safety interlock doors and emergency stops.
The machines are user-friendly and are easy to set up. Many include touch screens and joysticks for manual control. They are designed with intuitive interfaces and can be customized to the user's specifications. Most systems are equipped with user-friendly software that supports a wide range of industrial data formats. Some are even equipped with autofocus.
To summarize, laser cutting technology is a cutting-edge, highly versatile, and cost-effective method of material processing. Laser cutting machines can achieve greater precision than traditional mechanical cutting machines and reduce the risk of contamination. Laser cutting systems have been widely used for decades, and advances in the technology have increased their effectiveness and precision in recent years, making them a top-of-the-line manufacturing tool.
Reference:
[1]. https://www.laserfocusworld.com/articles/2012/06/femtosecond-laser-micromachining-a-back-to-basics-primer.html
[2]. https://optics.org/article/39899
[3]. https://www.sciencedirect.com
[4]. Chen et. al., Material Transactions 53, 2023 (2012).