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International Scientific Conference
PRO-TECH-MA ’16
PROGRESSIVE TECHNOLOGIES AND MATERIALS
LASER BEAM MILLING OF ALUMINA CERAMIC AND THE
IMPACT ON MACHINED SURFACE MORPHOLOGY
Peter ŠUGÁR1, Martin FRNČÍK2, Jana ŠUGÁROVÁ3, Miroslav SAHUL4
Keywords: laser, machining, ceramics, material removal rate (MRR), surface topography
A variety of ceramic materials such as alumina (Al2O3), zirconia (ZrO2), magnesia
(MgO), silicon carbide (SiC), and silicon nitride (Si3N4) are widely used in
microelectronics, automotive, medical and biotechnological applications. Despite superior
mechanical and physical properties, these materials have some limitations toward
machining into desirable components using conventional machining techniques [1, 2]. An
innovative and potential tool for bulk material removal and fabrication of complex
structures of ceramics is laser machining. Optimal selection of process parameters is highly
critical for successful material removal and high machined surface quality. A combination
of short pulse laser with short wavelengths usually leads to the best results in laser machining of ceramics, but thermal stresses during machining can result in cracking, so optimized
process parameters should be set to keep the heat input to the bulk material low and thus to
avoid cracks formation. Micromachining with longer pulse lasers (micro- and millisecond
regime) includes melting in material removal mechanism. This method promises processing
with very high removal rates but causes a creation of glassy layer that is often considered as
the source of micro-cracks [3, 4].
In this paper the influence of laser beam milling parameters on the machined surface
morphology is experimentally studied applying the nanosecond pulse fibre laser and alumina ceramics as working material. The influence of pulse energy, pulse repetition rate,
scanning speed and step size on material removal rate and the quality of machined surface
was examined via Taguchi method (L27 orthogonal matrix was used) in preliminary
experiment.
1
[email protected], 2 [email protected], 3 [email protected],
[email protected]
Slovak University of Technology, Faculty of Materials Science and Technology, Institute
of Production Technologies, Paulínska 16, 917 24 Trnava, Slovakia
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International Scientific Conference
PRO-TECH-MA ’16
PROGRESSIVE TECHNOLOGIES AND MATERIALS
Experimental results revealed that the laser pulse energy (heavily dependent on the laser
power and repetition rate) and scanning speed affect the studied material removal rate significantly. Material ablation has taken part in laser micro-machining process only if the
pulse energy values are higher than 0.9 ± 0.1 mJ. Machined surface quality is affected by
the scanning speed, pulse repetition rate and laser tracks distance significantly. This preliminary experiment confirmed difficult machinability of alumina ceramics and defined main
process parameters: pulse energy and scanning speed. Therefore, another two experiments
were carried out in order to the influence of pulse energy and scanning speed was analyzed
in more detailed way, parameters and its levels are listed in Tab. 1 and Tab. 2.
Table 1 Input parameters in experiment No. 2
Table 2 Input parameters in experiment No.3
Factors
Power I
Factors
Scanning speed
Repetition rate PRR
Scanning speed vs
Laser tracks distance s
20.8 ÷ 52 W
(2.08 W increment)
50 kHz
1500 mm.s-1
10 μm
Repetition rate PRR
Power I
Laser tracks distance s
1000 ÷ 2800 mm.s-1
(200 mm.s-1 increment)
50 kHz
52 W
10 μm
In the experiment No. 2, laser beam power as the input parameter was recalculated into
the pulse energy which varies in the interval from 0.42 to 1.04 mJ. Experimental results
shown that with an increasing value of pulse energy the MRR value raises as well, while
the correlation of these parameters is severely linear. Raised values of pulse energy affect
the quality of machined surface in positive way also, because a minimization of machined
surface maximal profile height with raising pulse energy was observed.
In the experiment No. 3, the effect of scanning speed on the MRR and the quality of
machined surface was analyzed. MRR values decrease with the increasing values of scanning speed only minimally, while this correlation is slightly linear. Optimal value of MRR
is maximal (4.282 mm3.min-1) using a scanning speed of 1600 mm.s-1. Scanning speed
influence analysis on the quality of machined surface shown fine uniform pore structure
using a scanning speed no higher than 1400 mm.s-1 with the material clusters from 30 to 50
μm long, using a higher scanning speed the material clusters quantity and dimensions were
increasing and the machined surface quality was considerably worse.
Acknowledgment
This research was supported by an international research project under the MANUNET
2014 call, entitled: Innovative methods of sheet metal forming tools surfaces improvement R&D (2014/11283), VEGA project No. 1/0669/15 and SUT SZR project No. 1350/16.
References:
[1] Samant A. and Dahotre N. Laser machining of structural ceramics – a review. Journal
of European Ceramic Society, 29 (2009), pp. 969–93.
[2] Hitesh D. Vora et all. Evolution of surface topography in one-dimensional laser
machining of structural alumina. Journal of the European Ceramic Society 32 (2012),
pp. 4205–4218.
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International Scientific Conference
PRO-TECH-MA ’16
PROGRESSIVE TECHNOLOGIES AND MATERIALS
[3] Dahotre N. and Samant A. Laser Machining of Advanced Materials. Leiden: CRC
Press, 2011.
[4] Rihakova L. and Chmelickova H: Advances in Materials Science and Engineering
2015, pp. 1 – 6
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