JEC COMPOSITES MAGAZINE - Issue #105 - June 2016 - 47

While the use of lasers
for CFRP machining is
in its early stages, lasers
have been successfully
adopted in the manufacturing industry
for machining various
metals. Lasers provide
the advantages of a
non-contact process
and ease of automation in manufacturing
environments. Laser
machining also elimFig. 2: The Spectra-Physics logo and other fea- inates tool wear and
tures machined in a ~1-mm-thick CFRP plate
reduces operating costs
in general, while eliminating the gradual degradation in quality associated with mechanical techniques due to tool wear. In
addition, the use of lasers for CFRP machining can reduce or
eliminate fibre damage and material delamination. However,
laser machining of CFRP involves a major challenge, which is
to machine the material with both high throughput and minimal heat-affected zone (HAZ) formation in the material.
The most fundamental challenge for laser machining of CFRP
stems from the fact that they are a non-homogeneous combination of carbon fibres and an organic polymer matrix. The
optical and thermal properties of fibre and polymer are vastly
different and hence the interaction of each material with the
laser is very different. To make things more challenging, the
optical and thermal properties of carbon fibre are anisotropic
and vary widely both along and perpendicular to the fibre
axes. These fundamental material properties create a challenge
to define a set of laser parameters that can provide good-quality high-speed machining of CFRP in all directions.

The right laser
High-power continuous-wave infrared wavelength lasers with
multi-kilowatt power levels can machine CFRP at higher
speeds but leave the material with unacceptably large heat-affected zone (HAZ)[3-5]. One way to reduce large HAZ is
to add delay time intervals between machining steps, but
this adds to the overall processing time and hence reduces
throughput. On the other hand, ultrashort pulse lasers with
pulse widths in the picosecond and femtosecond range can
provide low HAZ but usually machine materials at slow
speeds [6-8]. To improve machining speed, very high power
ultrashort pulse lasers are needed. While research to develop
higher power ultrashort lasers is ongoing, it will take some
time to come up with a source that is cost effective and practical for a manufacturing use. So, the current challenge is to
find a laser source and process that can deliver a good balance
of speed and quality. Pulsed nanosecond lasers thus far have

shown moderate processing speeds with reasonable quality,
with the wavelength often having a significant impact on the
results achieved. In particular, the stronger absorption at ultraviolet (UV) wavelength results in good-quality machining.
The machining results achieved with a nanosecond pulsed UV
laser strongly depend on the average laser power, pulse width,
and pulse repetition frequency (PRF). Higher average power
and PRF help achieve higher machining speeds, while a lower
pulse width helps achieve higher quality machining.
Traditional diode-pumped solid-state (DPSS) Q-switched
pulsed UV nanosecond lasers typically have a constant,
non-adjustable pulse width. While PRFs on such lasers are
adjustable, an increase in the PRF will greatly decrease output
power and increase pulse width. Typically, higher power and
shorter pulse widths are available only at lower PRFs. This significantly limits the ability of the laser to be operated at higher
PRF, thus affecting the micromachining speed, feature size,
accuracy and quality achieved. Moreover, typical Q-switched
lasers do not have pulse shaping and pulse splitting capabilities that could help improve the micromachining quality and
throughput. To overcome these limitations, Spectra-Physics
introduced in 2013 Quasar® 355-40, a breakthrough new 355
nm wavelength UV pulsed hybrid fibre laser. This laser offers a
unique combination of higher power and shorter pulse width
available at higher PRF. Quasar also offers TimeShift™ technology for a wide variety of software-adjustable energy and
intensity manipulations of pulses in the time domain, such as
pulse shaping, pulse splitting and burst mode operation. The
current model, Quasar 355-60, with an output power of
>60 W at 300 kHz PRF, offers the highest power available
today in the market at higher repetition rates with single-mode
beam quality.
Spectra-Physics studied the benefits of higher power, higher PRF, shorter pulse width and other advanced features of
the Quasar 355-60 laser when machining CFRPs. This study
focuses on characterizing Quasar's cutting edge TimeShift
technology for CFRP machining in terms of quality and
throughput for three common machining processes used in
CFRP parts: cutting, drilling, and surface texturing.

CFRP cutting
To demonstrate the capability of Quasar UV laser cutting,
Spectra-Physics' team machined a 250-µm-thick PAN-based
CFRP plate material. The team varied the pulse width, power,
repetition rate and scanning speed. The burst machining capability provided by Quasar's TimeShift technology was also
tested. The cutting speed and heat-affected zone (HAZ), here
defined as the average length of exposed fibres along the cut
line, were characterized for various conditions.
The results in figure 1 show that both speed and quality are
achieved using a Quasar laser. The smallest HAZ of ~15µm
was achieved using 2-ns pulses. This is an average HAZ over a
No105 June 2016 /

jec composites magazine 47

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #105 - June 2016