The Analysis of Fiber and CO 2 Laser Cutting Accuracy

Abstract

The aim of the conducted research was to compare the functional properties and the cutting accuracy of items produced using Fiber lasers in comparison with CO2 lasers. The object of 6 mm thick sheet plates made of S235JR steel cut with the two different laser types were analyzed. The tests covered dimensional accuracy (in accordance with the PN EN 22768-fH standard) and the surface after cutting (in accordance with the PN-EN ISO 9013: 2017-04). The results of the analysis have demonstrated that for the same welding linear energy, more accurate cutting surface is obtained using Fiber laser cutting.

Full text

The Analysis of Fiber and CO2 Laser Cutting
Accuracy
Robert Sołtysiak1*, Piotr Wasilewski2, Agnieszka Sołtysiak1, Adam Troszyński1
,
and Paweł
Maćkowiak1
1UTP University of Science and Technology, al. prof. S. Kaliskiego 7, 85-796 Bydgoszcz, Poland
2Zakład Produkcyjno-Handlowo-Usługowy TEMIROL Mirosław Łachacz, Gutkowo 81A,
11-041 Olsztyn, Poland
Abstract The aim of the conducted research was to compare the
functional properties and the cutting accuracy of items produced using
Fiber lasers in comparison with CO2 lasers. The object of 6 mm thick sheet
plates made of S235JR steel cut with the two different laser types were
analyzed. The tests covered dimensional accuracy (in accordance with the
PN EN 22768-fH standard) and the surface after cutting (in accordance
with the PN-
EN ISO 9013: 2017
-04). The results of the analysis have
demonstrated that for the same welding linear energy, more accurate
cutting surface is obtained using Fiber laser cutting.
1 Introduction
The laser technology was applied for the first time for cutting of steel sheets using CO2
laser. It took place in 1967 [1]. Thanks to advancements in the design of laser devices the
laser cutting technology has become one of the basic technologies of cutting engineering
materials
[2]. CO2 lasers have been used for a long time for laser cutting, but recently Fiber
lasers have become more and more popular [3-4].
List of basic parameters of CO2 and Fiber lasers is shown in the Table 1. Fiber lasers are
characterized by significantly lower BPP (Beam Parameter Product). The most favorable
BPP value for Fiber lasers is achieved for the power of up to about 3
-4 kW. Above this
value of power BPP starts to increase (i.e. the beam quality decreases). However, for
cutting with a power of about 1 kW, the BPP is characterized by about 50% better value for
Fiber lasers as compared to CO2 lasers.
Fiber lasers emit about 10 times shorter wavelengths than CO2 lasers. Shorter
wavelength improves the laser beam absorption coefficient. Thanks to the lower BPP and
shorter wavelengths, cutting with Fiber lasers can be faster and more accurate [2]. As
a result of the increase in the laser beam absorption, through the use of a laser that emits
a shorter wavelength laser beam, the scope of cut materials is also broadened by e.g.
copper, nickel and its alloys, as well as composite materials such as Kevlar coated sheet
metal [2].
* Corresponding author: robert.soltysiak@utp.edu.pl
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Fiber lasers do not require such frequent servicing. From the list presented in Table 1 it
follows that Fiber lasers can operate without the need for servicing 5 times longer. This
solution reduces machine downtime as well as lowers service costs.
The downside of Fiber lasers is their higher purchase cost, which can be more than
twice as high as for CO2 type lasers. However, thanks to high energy efficiency (about
30%), high quality of the beam when cutting with power of up to 4 kW and other
advantages of the aforementioned Fiber lasers,
the demand for them on the market and the
interest in their use is growing.
The aforementioned advantages of Fiber lasers as compared to CO2 lasers result also in
the possibility to obtain better quality of the cut surface. It should be borne in mind that
better surface quality obtained after laser cutting can contribute to the elimination of the
need for additional machining. The quality of the surface is also of great importance for the
surface preparation for various types of connections, for example adhesive ones [5-6] as
well as f
or preparation of various types of s
pecimens, e.g. for destructive tests [7].
Table 1. Comparison of basic physical properties and technical parameters of CO2 and Fiber lasers [2]
Laser
type
Laser
source
Length of
emitted
wave, µm
Beam transfer
Laser
mobility
Output
power,
kW
Energy
efficiency,
%
CO2
gas
mixture
10.6
mirrors, lenses
low
up to 50
5-8
Fiber
admixtured
fiber
1.07
fiber, lenses
high
up to 50
20-
30
Laser
type
The BPP
for laser
power of
1.0 kW,
mm/mrad
The BPP
at max.
laser
power,
mm/mrad
Required
frequency of
periodic
inspections of
the equipment,
in h
Approximate
cost of the
laser per 1.0
kW of power,
1000 USD
Surface
area
occupied
by the
device
Typical
diameter of
transporting
fiber, μm
CO2
3.7 3.7
2 000
60
very high
-
Fiber
1.8 12
10 000 130-
150
low
100-
200
Studies available in the professional literature
concerning
tests on surfaces obtained
using various types of lasers demonstrate that the accuracy of the cut depends mainly on the
roughness. In the study [8] on the surface quality after cutting with Nd-YAG laser, it was
shown that the surface roughness increases with the increase of the cutting speed.
It depends also on the frequency of the pulse as well as on its length. In other studies [9]
authors observed that the surface roughness after cutting with Slab type CO2 gas lasers was
sometimes increasing and sometimes was falling with the increase of the cutting power.
Other researchers [10] determined optimal cutting parameters without roughness
measurement. However, the standard [11] clearly states that the mean height of the profile
Rz5 and the value of the perpendicularity tolerance of the surface after cutting „u” are used
to qualify the cutting accuracy.
The authors of this paper compared the functional properties and the accuracy of cutting
using F
iber lasers in comparison with CO
2 lasers. Surfaces of 6 mm thick sheet metal plates
made of S235JR steel were analyzed after cutting. The tests included the analysis of the
manufacturing accuracy in terms of dimensional tolerance (based on the PN EN 22768-fH
standard) and surface quality after cutting (based on PN-EN ISO 9013: 2017-04).
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2 Research object
In order to conduct a comparative analysis, Figure 1 was prepared, on the basis of which
two items were cut from S235JR steel. One was cut with CO2 laser and the other with Fiber
laser. The cutting parameters (Table 2) were selected so that the linear energy in both cases
was 55.4 kJ/m. Figure 2 shows photos of the item produced. The item is 6 mm thick.
Table 2. Cutting parameters used for cutting accuracy tests.
Fig. 1. Detailed drawing of the item
3
Results and discussion
3.1 Measurement of main dimensions after cutting operation
The main geometrical dimensions indicated in Figure 1 were analyzed. Measured radii were
marked with R1 to R10 symbols, the lengths with 1 to 6 numbers, angles with <1 to <4
symbols and one diameter was marked as ø60. The tolerance of perpendicularity and
parallelism with regard to A and C bases indicated in Figure 1 was also measured. The tests
were carried out using Quick Scope CNC machine tools of QS and CRYSTA-APEX S
series manufactured by Mitutoyo. Nominal dimensions and actual dimensions of items cut
with CO2 and Fiber laser are listed in Table 3. This table also includes the difference
between the nominal dimension N and the actual dimension R and the dimensional
tolerances determined in accordance with PN EN 22768-fH standard. The dimensions
obtained were compared with the most accurate class provided in the PN EN 22768 series
standards [12-13].
Power, kW
Focus, mm
Pressure, bar
Cutting speed, m/s
CO2
2.0
Auto
0.8
0.03667
Fiber
2.0
- 1.6
0.6
0.03667
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Table 3. Nominal and actual dimensions of measured parameters.
Ite
m
Symbol
in the
drawing
Nominal
dimensio
n
N
Actual value - R
Difference = N - R
Tolerance
CO2
Fiber
CO2
Fiber
PN EN
22768-
fH
1
R1
10M
10.135 mm
10.061 mm
-0.135
-0.061
± 0.100 mm
2
R2
20 mm
19.937 mm
20.076 mm
0.063
-0.076
± 0.100 mm
3
R3
40 mm
40.129 mm
39.964 mm
-0.129
0.036
± 0.150 mm
4
R4
15 mm
15.134 mm
15.075 mm
-0.134
-0.075
± 0.100 mm
5
R5
3 mm
3.280 mm
2.936 mm
-0.280
0.064
± 0.050 mm
6
R6
5 mm
5.046 mm
5.017 mm
-0.046
-0.017
± 0.050 mm
7
R7
7 mm
7.242 mm
7.005 mm
-0.242
-0.005
± 0.100 mm
8
R8
9 mm
9.122 mm
9.033 mm
-0.122
-0.033
± 0.100 mm
9
R9
11 mm
11.109 mm
11.033 mm
-0.109
-0.033
± 0.100 mm
10
R10
15 mm
15.270 mm
15.168 mm
-0.270
-0.168
± 0.100 mm
11
1
30 mm
30.145 mm
30.044 mm
-0.145
-0.044
± 0.100 mm
12
2
50 mm
50.030 mm
49.961 mm
-0.030
0.039
± 0.150 mm
13
3
30 mm
30.177 mm
30.157 mm
-0.177
-0.157
± 0.100 mm
14
4
60 mm
60.201 mm
60.182 mm
-0.201
-0.182
± 0.150 mm
15
5
140 mm
139.893 mm
139.962 mm
0.107
0.038
± 0.200 mm
16
6
60 mm
60.024 mm
59.988 mm
-0.024
0.012
± 0.150 mm
17
<0
120°
119°56’09”
119°58’39”
0.064°
0.022°
± 0.500°
18
<1
120°
120°01’52”
120°00’36”
-0.031°
-0.010°
± 0.500°
19
<2
5°
4°57’03”
4°59’02”
0.049°
0.016°
± 0.333°
20
<3
10°
9°59’11”
9°57’08”
0.014°
0.048°
± 0.333°
21
<4
5°
5°01’18”
4°59’18”
-0.022°
0.012°
± 0.333°
22
Ø60
60 mm
60.063 mm
60.074
-0.063
-0.074
± 0.150 mm
23
A
-
0.403 mm
0.443 mm
-
-
0.200 mm
24
// A
-
0.016 mm
0.015 mm
-
-
0.200 mm
25
// C
-
0.089 mm
0.023 mm
-
-
0.200 mm
The tests show that for 25 measurements taken for the object cut with the CO2 laser, 11
of them do not fall within the range of the selected tolerance specified in the standards
[12,13]. However, in the case of an object cut with the Fiber laser, only 5 measurement
results are outside the tolerance. It is clearly observed that deviations from the nominal
dimension for the object being cut with the Fiber laser are lower than in the case of those
cut with CO2 laser.
3.2 Measurement of surface accuracy after cutting operation
The cut surface accuracy was tested on the basis of
standard [11] titled: Thermal cutting
- Classification of thermal cuts - Geometrical product specification and quality tolerances.
The following parameters were tested: drag - n, perpendicularity tolerance - u, mean height
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of the profile – Rz5 and additionally arithmetic mean deviation of the assessed profile - Ra.
The tests were carried out using Mahr MarSurf GD 120 testing machine.
The "u" and "n" parameters were measured three times on the surface designated in
Figure 1 as the base A. The roughness measurements were made at the height of 1/3a
viewed from the upper surface of the sheet plate (in accordance with [11]) and, as a
comparison, at a height of 2/3a (where : a
-
thickness of the cut sheet plate). The
measurements were carried out three times on the surface A and three times on the surface
for which the parallelism tolerance was determined (Fig. 1). Table 4 presents the results of
mean values of the measurements carried out. A graphical illustration of the Rz5 roughness
measurement results is shown in Figure 2.
Table 4. Measurement results for u, n, Rz5 and Ra parameters
CO
2
Fiber
n, µm
u, µm
n, µm
u, µm
0.084
0.052
0.077
0.051
Base A surface
- 1/3a
Surface II to A
- 1/3a
Base A surface
- 1/3a
Surface II to A
- 1/3a
Rz5, μm
Ra, μm
Rz5, μm
Ra, μm
Rz5, μm
Ra, μm
Rz5, μm
Ra, μm
4.1981
0.7591
8.5201
1.4010
5.0380
0.9566
7.7669
1.5299
Base A surface
- 2/3a
Surface II to A
- 2/3a
Base A surface
- 2/3a
Surface II to A
- 2/3a
Rz5, μm
Ra, μm
Rz5, μm
Ra, μm
Rz5, μm
Ra, μm
Rz5, μm
Ra, μm
128.8031
23.8343
33.3495
6.3180
6.2384
1.2569
4.3192
0.6956
Fig. 2. A graphical illustration of the Rz5 roughness measurement results
Considering the comparison between the value of the drag distances "n" for the CO2
and Fiber laser, it should be noted that the surface obtained after the Fiber laser cutting is
characterized by smaller deviation. The perpendicularity tolerance "u" of surfaces obtained
with CO2 and Fiber laser cutting is comparable. Significant differences are observable for
Rz5 values measured at a height of 2/3a. For example, the Rz5 value of the base surface A
measured at that height is 95% higher for a surface obtained using CO2 laser than for a
surface obtained using Fiber laser. Noteworthy is also the fact that the surface roughness
obtained with the Fiber laser is more repeatable than obtained using t
he CO2 laser.
Better results of deviations from the nominal dimension and accuracy the cut surfaces
were obtained after Fiber laser cutting. This is due to the fact that Fiber lasers are
characterized by the higher energy density as a result of a better beam quality. Furthermore
the Fiber lasers have a higher value of absorptivity when compared with CO2 laser, and
thus is able to reach higher accuracy of the cut surfaces.
Base A surf. – 1/3a Surf II to A. – 1/3a Base A surf. – 2/3a Surf II to A. – 2/3a
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4 Conclusions
When comparing functional properties, frequency of servicing, efficiency of CO2 and Fiber
lasers, it should be concluded that Fiber lasers are a good solution for cutting. The sole
disadvantage of Fiber lasers can only be their purchase price.
The conclusions refer only to the tests carried out with specific cutting parameters. It
was assumed for the tests that the value of linear energy during cutting with both types of
lasers would amount to 55.4 kJ/m. With such assumptions, the comparison of the accuracy
of the surface after cutting with CO2 laser and Fiber laser shows that significantly higher
dimensional accuracy was obtained for Fiber laser. Surfaces cut with Fiber laser were also
characterized by better roughness and high repeatability of roughness results over the entire
cutting height.
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1018 (2010)
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48/issue-04/features/the-state-of-the-art.html
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13. PN-EN 22768-2:1999
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