ether-ether-ketone) is possible, and the resulting structure has been implemented
for embossing PMMA, PC and PS and COC. However, the technique is restricted
by the amount of removed PEEK material, and only negative polarity features up to
10 μm in height are feasible [ 4 ].
The CAD file is converted in to a format that is suitable for the machine interface
that one uses. Epilog series are compatible with files processed in Illustrator (.AI) or
Corel Draw (.CDR). Lasers from Synrad in contrast use their own 2D CAD
software to control the movements of the laser head. Despite the different file
formats, all lasers have similar setting parameters that define the translation from
2D drawing into 3D feature onto the substrate. The amount of energy that is
dissipated by the laser head is determined by the power of the laser. But the
absorbed energy is equal to the product of the absorption coefficientα, the incident
powerPinand the irradiation timeΔt:
Qin¼αPinΔt, where Δt¼L=vThe irradiation time is related to the cutting speed (v) and the effective spot size
along the scanning directionLas illustrated in Fig.3.8. This model is suggested by
Romoli et al. [ 16 ] who assume the irradiated area to be rectangular and the
irradiance distribution of the nearly-Gaussian beam to be triangular, L is
represented by half of the groove widthW. In the same paper authors assume that
the removed materialmis proportional to the amount of heatQavailable to
vaporize the polymer. This heat can be evaluated as the difference between the
absorbed energyQinand the threshold energyQth:
m¼kQ¼kQðÞinQthwhere,kis a constant related to the chemical bond energy of the PMMA polymer
and is generally characterized by a nonlinear dependence on temperature. HereQth,
is cumulative value combining two major loss terms: one is the energy needed to
heat-up the irradiated area prior vaporization starts, the other energy lost into the
surroundings due to conduction.
Fig. 3.8 Geometrical
definition of the groove
profile and irradiated
volume. Reprinted by
permission from Elsevier
[Optics and Lasers in
Engineering] [ 16 ]
98 N. Dimov