Biomedical Engineering Reference
In-Depth Information
4.2.2.5 Laser machining
Laser machining is a localized, noncontact machining technique. Machining applications of laser
include drilling, cutting, engraving, marking, and texturing. Almost all types of materials, such as
metals, ceramics, plastics, and wood, can be used with laser machining. Most significantly, laser
machining can remove materials in small amounts with a small heat-affected zone. Micromachining
with controlled accuracy can be achieved. A further attractive advantage of laser machining compared
to other micromachining techniques is the possibility of low-cost rapid prototyping. The disadvantage
of laser machining is the re-deposition of substrate material, which makes the quality control of the
machined surfaces difficult.
UV lasers were used to realize microstructures in polymers. Although UV laser is a good choice for
laser ablation, its cost is much higher than that of CO
2
laser. CO
2
laser has a relatively long charac-
teristic wavelength of 10.6
m. Thus, the ablation process is determined by the thermal energy of the
laser beam. Therefore, the cross-section of the microchannel depends on the energy distribution of
the laser beam, its moving speed, the laser power, and the thermal diffusivity of substrate material. The
energy of the laser beam has a Gaussian distribution; thus, the cross-section of the channel also has
a Gaussian shape (
Fig. 4.17
). Three types of lasers are commonly used for laser micromachining:
m
Excimer lasers with ultraviolet wavelengths (351, 308, 248, 193 nm);
Nd:YAG lasers with near-infrared (1,067 nm), visible (533 nm), and UV wavelengths (355 nm,
266 nm); and
CO
2
lasers with deep-infrared wavelength (10.6
m
m).
The two major parameters of laser micromachining are wavelength and laser power. The choice of
wavelength depends on the minimum structure size and the optical properties of the substrate material,
FIGURE 4.17
Typical cross-sections of microchannels fabricated by CO
2
laser.
Search WWH ::
Custom Search