Investigation of optimum condition in laser cutting of alloy steel 1.4571 using air assist gas.
Cekic, Ahmet ; Kulenovic, Malik ; Begic, Derzija 等
1. INTRODUCTION
Today, the laser cutting is an important industrial process, used
for cutting all types of material. Laser cutting has wide application in
the field of automobile industry. Practically all bodywork components in
the car sectors cut by using lasers (hood, instrumental panels, roofs,
etc.). The basic advantage is to eliminate a very complex punching tool
whose working life with regular maintenance is relatively small. The
production is simpler, faster and cheaper. Also, using laser cutting
technology used less material consumption, short manufacturing time and
greater accuracy of the product. The AISI is forecasting a dramatic
increase in the use of high alloy steels with increased content alloying
elements especially Cr and Ni in the car industry (Lamikez et al.,
2005). Because imposed the need to research the application of laser in
processing alloy steels. The exothermal reactions of iron and other
alloying elements are complex. These steels have a high content of
alloying elements that can lead to differences with regard to the
cutting of common steels. So the cutting conditions of these steels
cannot be comparing with the cutting of common steels.
There are many types of lasers, only the continuous wave (CW)
C[O.sub.2] and pulsed Nd:YAG lasers are commonly found in industrial
applications (Avanish and Vinod, 2008). Although the interaction of
laser beam- material is better at the ND: YAG laser, but C[O.sub.2]
lasers are the most used. In laser beam cutting process, the thermal
energy of laser beam is used for melting and vaporizing of undesirable
material. The molten material is removed by using suitable assist gas at
high pressure. Researches with the aim of optimization the laser cutting
parameters, which are very comprehensive and complex due to the
existence of a large number of influential factors on the results of
processing are the subject of many research works. The performance of
laser beam cutting mainly depends on appropriate selection of input
process parameters (Rajaram et al., 2003).
In addition to material thickness, the performance of laser systems
(wavelength laser beams, the type and diameter of nozzles, operation
mode and etc.) and the selected assist gas, the most important are the
laser power, cutting speed, focus position, working distance and assist
gas pressure during laser cutting process. These parameters are set to
obtain a minimum kerf width and the minimum size of heat affected zone
with achieving the projected surface quality (Al-Sulaiman et al., 2008).
2. EXPERIMENTAL PROCEDURE
Experimental investigations are conducted at University of Applied
Science Jena, Germany. The experiments are carried out on 2000 W
continuous wave C[O.sub.2] laser system with CNC work table. Laser
cutting experiments are carried out using 4 mm alloy steel 1.4571 sheets
to investigate the effect of laser cutting parameters on the cut
quality. Chemical composition of the examined material (HB
[approximately equal to] 220 hardness) is given in table 1. The sample
geometry and schematic illustration of various cut quality attributes is
illustrated in figure 1.
The beam profile is nearly Gaussian ([TEM.sub.00]) with beam
quality k[approximately equal to] 0.95. The following process parameters
are kept constant during performing the experiments: the laser power of
2000 W, mode of operation--CW, the focal length of lens of 127 mm,
focused spot size of 0.20mm, the nozzle diameter of 2 mm, conical design
of gas jet nozzle and air as assist gas. Previous experiments, optimal
working distance of 1 mm is obtained. The experimental values are shown
that the kerf width and the size of heat affected zone decrease with
decreasing laser power, but the possible cutting speed reduces. The
minimum possible laser power for cutting of this examined material of 4
mm thick is 1500 W and the maximum cutting speed of 1250 mm/min.
Values of parameters that were varied during performing the
experiments are:
--Cutting speed from 250 mm/min to 2750 mm/min by increment of 250
mm/min
--Focus position of -1.5 mm, 0 mm and +1.5 mm,
--Air assisting gas pressure from 5 bar to 12.5 bar by increment of
2.5 bar.
For evaluation of the cut quality, surface roughness was measured
according to DIN 2310 standard, using a Taylor Hobson stylus instrument.
Mean deviation Ra was measured on the 18 different places along the
length of cut and then mathematically calculated average value (Cekic et
al., 2008). The kerf width was measured using a Stemi microscope fitted
with a video camera and a zoom lens. It was also used for measuring size
of heat affected zone.
[FIGURE 1 OMITTED]
3. RESULTS AND DISCUSSION
The effect the focus position and the cutting speed on the kerf
width at the assist gas pressure of 10 bars is illustrated in figure 2.
In fact, experimental research has determined the optimal assist gas
pressure of 10 bars at which it is possible to perform cutting with
higher cutting speeds up to 2750 mm / min.
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
During laser cutting of examined steel, the larger size of heat
affected zone from the bottom side of samples is observed. So that the
effect of the focus position and cutting speed at the constant pressure
of 10 bars on the size of heat affected zone from the bottom side of
samples is shown in figure 3. This was also observed at the other varied
values of assist gas pressure. The effect of the cutting speed and focus
position on the surface roughness at the constant assist gas pressure of
10 bars is shown in figure 4.
4. CONCLUSION
Experimental investigations were carried out during C[O.sub.2]
laser cutting of alloy steel 1.4571 sheets of 4 mm thick to investigate
the effect of process parameters on the cut quality using air as assist
gas. Some interesting conclusions can be drawn from this study:
* Maximum deviation of the kerf width to 0.275 mm and size of heat
affected zone to 2.161 is obtained during these experimental
investigations;
* The kerf width decreases by increasing cutting speed and the
minimum value obtained when the following conditions: pressure of 10
bar, cutting speed of 2250 mm/min and focus position 0 mm;
* The size of heat affected zone decreases with increasing cutting
speed and the minimum value is achieved by the conditions: pressure of
10 bar, cutting speed of 2250 mm/min and focus position 0 mm;
* Small variation of gas pressure does not change the essential
quality of cut. The pressure is in the function of other process
parameters such as laser power, cutting speed, focus position, etc. So
that the minimum value of Ra is achieved by the conditions: pressure of
5 bar, cutting speed of 2750 mm/min and focus position -1.5 mm;
Laser cutting of high alloy steels for the special purpose will be
considered. These process parameters will be optimized with
consideration of multi-performances characteristics of the cut.
5. ACKNOWLEDGEMENT
The authors gratefully acknowledge the support of the Department of
Laser and Opto-Technologies at the University of Applied Science Jena,
Germany for this work.
6. REFERENCES
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Tab. 1. Chemical composition of the examined material
Chemical composition of X6CrNiMoTi17-12-2 (1.4571) steel
C Cr Ni Si Mn S P
Min [greater than or 16,5 10,8 1,0 ... 0,0 15 0,045
equal to] 0,08
Max 18,5 13,5 ... 2,0 ... ...
