Laser cutting of CFRP sheet by pulsed Nd:YAG

1
Laser cutting of CFRP sheet by pulsed NdYAG
source Influence of pulse energy, pulse duration
and overlapping on kerf geometry and HAZ
Keyword Composites, laser cutting, kerf
geometry, HAZ
2
Composite cutting
Machining of Fibre Reinforced Plastic is very
difficult because of their particulars
properties, specially in cutting and drilling
operations.

• CUTTING METHODS
• Water-jet
• Mechanical (sawing, milling, grinding)
• Punching.

• DRAWBACKS
• Materials are sensitive to mechanical stress.
• Tool wear, delamination and fibre pull out.
• Difficulties for very small or complex shape.

Laser represents a possible alternative to
cutting and drilling composite materials

• DRAWBACKS
• Laser interaction produce heat affected zone
  (HAZ).
• Selection of laser source are required (CO2,
  NdYAG and CW, PM).
• Optimization of process parameters are required.

• ADVANTAGE
• No mechanical force and tool wear.
• Small spot laser beam small cutting width.
• Possibility to realize complex shape too.

3
NdYAG Laser compared to CO2 Laser
The matrix and the fibres are highly absorbing
for the CO2 wavelength of 10.6 µm. NdYAG, in
comparison, have a wavelength 1.064 µm for which
the matrix is highly transparent and the laser
energy is absorbed mainly by the fibers.
The advantages offered by pulsed NdYAG lasers
are

• High beam intensity.
• Better energy distribution (M2) and smaller spot
  beam.
• Possibility to released high pulse energy in
  very short time (Pulse Mode)

The high peak power released in short time
rapidly heats the material and directly leads to
the evaporation and/or plasma, reducing the heat
absorbed by the matrix.
Smaller thermal load, narrow kerf and a smaller
HAZ are obtained.
4
Pulse Mode Cutting parameters
In pulsed laser, cutting is obtained by the
overlapping of single holes produced by each
laser pulse.
So, its very important to define
5
Aim of the work To study the influence of pulse
energy, pulse duration and overlapping percentage
on the kerf geometry and HAZ extension, in
cutting of 1 mm CFRP plates using a lamp pumped
NdYAG laser.
Topics
6
Experimental procedure Laser Equipment
7
Experimental procedures Laser Equipment

• The laser allows to set the parameters
• the pump lamp voltage (V)
• pulse frequency (F)
• pulse duration (D)

The released mean power (Pm), the pulse energy
(E) and the pulse power (Pp) depend on all the
three parameters. The relation is very complex.
8
Experimental procedures Material

• CFRP plates 1 mm thickness
• T400 carbon fibre.
• HMF 934 epoxy resin matrix

• The lay-up was
• 2 external plies of fabric 193 gr/mm2, 50 in
  the warp 50 in the weft directions.
• Eight internal unidirectional plies of 145 g/mm2
  in (452/-452)s.

9
Experimental procedures Testing Conditions

• Four different duration.
• (0.05, 0.10, 0.15 and 0.20 ms).
• Different Pulse energy.
• (between 0.05 J and 0.5 J).
• Different Pulse frequency.
• (between 185 Hz and 2000 Hz).
• Mean Power costant 95 W

• Assist gas Nitrogen
• Pressure 10 bar.
• Gas flow 30 l/min.

• For each process condition, the maximum cutting
  speed was determined.

• Starting from this value, the cutting speed was
  decreased until a spot overlap value of about 98
  was achieved.

10
Experimental procedures Profile Measure
Wt - Kerf top width Wb - Kerf bottom width Ta -
Taper angle HAZ Heat Affected Zone

• At least fifteen cuts and profiles were analyzed
  for each test condition.
• On each cut, three measurements of the kerf
  geometry parameters were carried out.

Measure according to ISO 9013 (Thermal cutting
-- Classification of thermal cuts -- Geometrical
product specification and quality tolerances )
11
Experimental Results Cutting Region
In a previous work , it was found that the
maximum cutting speed linearly depends on the
mean power, while the minimum spot overlapping
depends on pulse energy.
Compared the results, in the present case,
despite the use of a mean power of about 95 W,
the maximum cutting speed varies within a large
value range (from 4 to 10 mm/s).
When large variations in pulse energy occur
(between 0.05 J and 0.5 J), it is not possible to
predict the maximum cutting speed by using the
mean power.
C.Leone, N.Pagano, V.Lopresto, I.De Iorio
Solid state NdYAG laser cutting of CFRP sheet
influence of process parameters on kerf geometry
and HAZ. Proc of 17th Int. Conf. on Composite
Materials - ICCM-17, 27 Jul 2009 - 31 Jul 2009,
Edinburgh UK, 2009, pp. 1-10.
12
Experimental Results Cutting Region
Cutting region
The spot overlap is plotted against pulse energy,
for different values of pulse energy and pulse
duration.
No Cutting region

• The minimum spot overlap decreases with the
  increase of the pulse energy (linear relationship
  between the two).

• The dashed line represents the boundary between
  the cut regime and the no-cut regime.

• The minimum spot overlap is 80 that
  corresponding a cutting speed of 11 mm/s .

13
Experimental Results Width Kerf
The mean values of the top and the bottom kerf
width are plotted against the spot overlap, for
different values of pulse energy and pulse
duration.

• The data distribution do not allow any
  particular observation about the influence of the
  different values of pulse energy and pulse
  duration.

• Only observation is that visible reduction of
  the bottom kerf width occur for the lowest pulse
  energy.

• The top kerf width varies between 160260 µm.

• The bottom kerf width vary in the range 68119 µm
  (high pulse energy), while vary in the range
  3575 µm (low pulse energy).

14
Experimental Results Taper angle
The mean values of the taper angle is plotted
against the spot overlap, for different values of
pulse energy and pulse duration.

• The taper angle is very small, with values in
  the range of 1 4.5 degree.

• The maximum value is obtained in correspondence
  of low pulse energy

15
Experimental Results Defects (matrix burning,
fibre pull out, bridging)
From the optical microscopy analysis, the typical
composites thermal damage observed are
However these defects are very limited.
16
Experimental Results Defects (Heat Affected Zone)
The HAZ appears as matrix burning with or without
the presence of inconsistent fibres and a width
larger than the external visible damage.
The HAZ is strongly dependent by the process
parameters and it is clearly visible by different
light reflection.
High pulse repetition Low Cutting Speed
Low pulse repetition High Cutting Speed
17
Experimental Results HAZ extension
The inner extension of the HAZ was measured and
reported against the spot overlapping for the
different process conditions
All the points converge to two different curves
that could be represented by an exponential low
(in agreement with )

• The first one corresponding to the high pulse
  energy and low pulse repetition conditions.

• The second one corresponding to the low pulse
  energy and high pulse repetition conditions.

C.Leone, N.Pagano, V.Lopresto, I.De Iorio
Solid state NdYAG laser cutting of CFRP sheet
influence of process parameters on kerf geometry
and HAZ. Proc of 17th Int. Conf. on Composite
Materials - ICCM-17, 27 Jul 2009 - 31 Jul 2009,
Edinburgh UK, 2009, pp. 1-10.
18
Experimental Results HAZ extension
The HAZ depends on the energy released and how
this energy is released.
19
Experimental Results HAZ extension
The inner extension of the HAZ was reported
against the K-parameters and compared with the
data from .

• Its possible an unique formulation for the
  prevision of the HAZ although the different
  assistance gas

nitrogen (black line)
and oxigen (red line).

• Despite the different process condition, all the
  data converge to a single logarithmic curve.

C.Leone, N.Pagano, V.Lopresto, I.De Iorio
Solid state NdYAG laser cutting of CFRP sheet
influence of process parameters on kerf geometry
and HAZ. Proc of 17th Int. Conf. on Composite
Materials - ICCM-17, 27 Jul 2009 - 31 Jul 2009,
Edinburgh UK, 2009, pp. 1-10.
20
Conclusions

• A pulsed NdYAG can be used to cut 1-mm thick
  CFRP plates, with a cutting speed of about 11
  mm/s and a mean power of about 95 W

• Processing regimes for laser cutting can be
  established considering the pulse energy and the
  spot overlapping.

• The kerf width (Top and Bottom) is almost
  insensitive to variations of the process
  parameters within the considered range.

• The external thermal damage is very limited.

• The HAZ extension is related to the spot overlap
  through an exponential law.

• A unique formulation for the prevision of the
  HAZ was found. The relation binds the HAZ to the
  process parameters Pm, S, F and D.

• To obtain a high productivity and high quality
  cuts, high speed, high pulse energy and a short
  duration are needed.

21
Acknowledgements
The authors are particularly grateful to the
CIRTIBS Research Centre, for providing the
equipments and financial support to develop the
present research work.
22
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