590:, the melt layer flow and melt expulsion can be modeled using hydrodynamic equations (Ganesh et al.,1997). Melt expulsion occurs when the vapor pressure is applied on the liquid free surface which in turn pushes the melt away in the radial direction. In order to achieve fine melt expulsion, the melt flow pattern needs to be predicted very precisely, especially the melt flow velocity at the hole's edge. Thus, a 2-D
1943:
424:
601:
Ganesh's model for melt ejection is comprehensive and can be used for different stages of the hole drilling process. However, the calculation is very time consuming and Solana, et al. (2001), presented a simplified time dependent model that assumes that the melt expulsion velocity is only along the
197:
In early work (Körner, et al., 1996), the proportion of material removed by melt expulsion was found to increase as intensity increased. More recent work (Voisey, et al., 2000) shows that the fraction of the material removed by melt expulsion, referred to as melt ejection fraction (MEF), drops when
77:
Incremental improvements in laser process and control technologies have led to substantial increases in the number of cooling holes used in turbine engines. Fundamental to these improvements and increased use of laser drilled holes is an understanding of the relationship between process parameters
22:
is the process of creating thru-holes, referred to as “popped” holes or “percussion drilled” holes, by repeatedly pulsing focused laser energy on a material. The diameter of these holes can be as small as 0.002” (~50 μm). If larger holes are required, the laser is moved around the circumference of
201:
A better finish can be achieved if the melt is ejected in fine droplets. Generally speaking, droplet size decreases with increasing pulse intensity. This is due to the increased vaporization rate and thus a thinner molten layer. For the longer pulse duration, the greater total energy input helps
827:
Grad and Mozina (1998) further demonstrated the effect of pulse shapes. A 12 ns spike was added at the beginning, middle, and the end of a 5 ms pulse. When the 12 ns spike was added to the beginning of the long laser pulse, where no melt had been produced, no significant effect on removal was
215:
incorporate solid, fluid, temperature, and pressure during laser drilling, but it is computationally demanding. Yao, et al. (2001) developed a 2-D transient model, in which a
Knudsen layer is considered at the melt-vapor front, and the model is suited for shorter pulse and high peak power
214:
hole drilling and the drilling process is transient. Kar and
Mazumder (1990) extended the model to 2-D, but melt expulsion was not explicitly considered. A more rigorous treatment of melt expulsion has been presented by Ganesh, et al. (1997), which is a 2-D transient generalized model to
823:
Roos (1980) showed that a 200 ÎĽs train consisting of 0.5 ÎĽs pulses produced superior results for drilling metals than a 200 ÎĽs flat shaped pulse. Anisimov, et al. (1984) discovered that process efficiency improved by accelerating the melt during the pulse.
743:
124:
duration and energy playing an important role. Generally speaking, ablation dominates when a Q-switched Nd:YAG laser is used. On the other hand, melt expulsion, the means by which a hole is created through melting the material, dominates when a
605:
The liquid will move upwards with velocity u as a consequence of the pressure gradient along the vertical walls, which is given in turn by the difference between the ablation pressure and the surface tension divided by the penetration depth
567:
is assumed to exist at the melt-vapor front where the state variables undergo discontinuous changes across the layer. By considering the discontinuity across the
Knudsen layer, Yao, et al. (2001) simulated the surface recess velocity
233:
198:
laser energy further increases. The initial increase in melt expulsion on raising the beam power has been tentatively attributed to an increase in the pressure and pressure gradient generated within the hole by vaporization.
1404:
Solana, Pablo; Kapadia, Phiroze; Dowden, John; Rodden, William S.O.; Kudesia, Sean S.; Hand, Duncan P.; Jones, Julian D.C. (2001). "Time dependent ablation and liquid ejection processes during the laser drilling of metals".
69:
and machined components. Their ability to drill holes at shallow angles to the surface at rates of between 0.3 and 3 holes per second has enabled new designs incorporating film-cooling holes for improved
1491:
Anisimov, V. N.; Arutyunyan, R. V.; Baranov, V. Yu.; Bolshov, L. A.; Velikhov, E. P.; et al. (1984-01-01). "Materials processing by high-repetition-rate pulsed excimer and carbon dioxide lasers".
149:, peak power in the order of sub MW/cm, and material removal rate of ten to hundreds of micrometers per pulse. For machining processes by each laser, ablation and melt expulsion typically coexist.
813:
623:
491:
171:
The "best of both worlds" is a single system capable of both "fine" and "coarse" melt expulsion. "Fine" melt expulsion produces features with excellent wall definition and small
117:
The energy required to remove material by melting is about 25% of that needed to vaporize the same volume, so a process that removes material by melting is often favored.
1113:
Körner, C.; Mayerhofer, R.; Hartmann, M.; Bergmann, H. W. (1996). "Physical and material aspects in using visible laser pulses of nanosecond duration for ablation".
419:{\displaystyle I_{abs}+k\left({\frac {\partial T}{\partial z}}+r{\frac {\partial T}{\partial r}}\right)+\rho _{l}\nu _{i}L_{v}-\rho _{v}\nu _{v}(c_{p}T_{i}+E_{v})=0}
90:
Following is a summary of technical insights about the laser drilling process and the relationship between process parameters and hole quality and drilling speed.
909:
227:
At the melt-vapor front, the Stefan boundary condition is normally applied to describe the laser energy absorption (Kar and
Mazumda, 1990; Yao, et al., 2001).
572:
distribution, along the radial direction at different times, which indicates the material ablation rate is changing significantly across the
Knudsen layer.
1318:
Ganesh, R.K.; Faghri, A.; Hahn, Y. (1997). "A generalized thermal modeling for laser drilling process—I. Mathematical modeling and numerical methodology".
1232:
Chan, C. L.; Mazumder, J. (1987). "One-dimensional steady-state model for damage by vaporization and liquid expulsion due to laser-material interaction".
210:
Chan and
Mazumder (1987) developed a 1-D steady state model to incorporate liquid expulsion consideration but the 1-D assumption is not suited for high
1903:
190:
for which the recoil and surface tension forces are equal is the critical temperature for liquid expulsion. For instance, liquid expulsion from
839:
Forsman, et al. (2007) demonstrated that a double pulse stream produced increased drilling and cutting rates with significantly cleaner holes.
31:
Laser drilling is one of the few techniques for producing high-aspect-ratio holes—holes with a depth-to-diameter ratio much greater than 10:1.
1035:
Kestenbaum, A.; D'Amico, J.F.; Blumenstock, B.J.; DeAngelo, M.A. (1990). "Laser drilling of microvias in epoxy-glass printed circuit boards".
1216:
1275:
Kar, A.; Mazumder, J. (1990-10-15). "Two-dimensional model for material damage due to melting and vaporization during laser irradiation".
1019:
828:
observed. On the other hand, when the spike was added at the middle and the end of the long pulse, the improvement of the drilling
1642:
617:
of liquid motion on the vertical wall is a good approximation to model the melt expulsion after the initial stage of drilling.
832:
was 80 and 90%, respectively. The effect of inter-pulse shaping has also been investigated. Low and Li (2001) showed that a
1812:
1581:
Low, D.K.Y; Li, L; Byrd, P.J (2001). "The influence of temporal pulse train modulation during laser percussion drilling".
1868:
781:
1672:
35:
1164:
Voisey, K.T.; Cheng, C.F.; Clyne, T.W. (2000). "Quantification of Melt
Ejection Phenomena During Laser Drilling".
738:{\displaystyle \rho {\frac {\partial u(r,t)}{\partial t}}=P(t)+\mu {\frac {\partial ^{2}u(r,t)}{\partial r^{2}}}}
435:
1542:
Grad, Ladislav; MoĹľina, Janez (1998). "Laser pulse shape influence on optically induced dynamic processes".
1361:
Zhang, W.; Yao, Y.L.; Chen, K. (2001-09-01). "Modelling and
Analysis of UV Laser Micromachining of Copper".
505:
describes temporal input laser intensity including pulse width, repetition rate, and pulse temporal shape.
120:
Whether melting or vaporization is more dominant in a laser drilling process depends on many factors, with
1842:
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for drilling small (0.3–1 mm diameter typical) cylindrical holes at 15–90° to the surface in cast,
43:
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per pulse. A flash lamp pumped Nd:YAG laser normally has a pulse duration on the order of hundreds of
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pumped Nd:YAG laser is used. A Q-switched Nd:YAG laser normally has pulse duration in the order of
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form a thicker molten layer and results in the expulsion of correspondingly larger droplets.
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Basu, S.; DebRoy, T. (1992-10-15). "Liquid metal expulsion during laser irradiation".
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957:"PCB Laser Technology for Rigid and Flex HDI – Via Formation, Structuring, Routing"
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Laser-drilled high-aspect-ratio holes are used in many applications, including the
1201:
Damage caused during laser drilling of thermal spray TBCs on superalloy substrates
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of linearly increasing magnitude had a significant effect on expulsion processes.
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Assuming that the drilling front is moving at a constant velocity, the following
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acting on the surface due to vaporization must be sufficiently large to overcome
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can take place when the temperature at the center of the hole exceeds 3780 K.
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denote liquid phase, vapor phase and vapor-liquid interface, respectively.
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1043:(4). Institute of Electrical and Electronics Engineers (IEEE): 1055–1062.
563:
If the laser intensity is high and pulse duration is short, the so-called
1512:
1203:. ICALEO 2001. Jacksonville FL: Laser Institute of America. p. 257.
848:
595:
538:
191:
110:") of the workpiece material through absorption of energy from a focused
107:
79:
1006:. Proceedings of 3rd Electronics Packaging Technology Conference. IEEE.
1134:
530:
99:
42:, aerospace turbine-engine cooling holes, laser fusion components, and
1448:
Roos, Sven-Olov (1980). "Laser drilling with different pulse shapes".
1208:
1037:
IEEE Transactions on
Components, Hybrids, and Manufacturing Technology
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1048:
908:
Bovatsek, Jim; Tamhankar, Ashwini; Patel, Rajesh (November 1, 2012).
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hole wall, and can give results with a minimum computational effort.
910:"Ultraviolet lasers: UV lasers improve PCB manufacturing processes"
1651:
62:
160:. For melt expulsion to occur, a molten layer must form and the
885:"Superpulse A nanosecond pulse format to improve laser drilling"
1624:
1199:
Voisey, K. T.; Thompson, J. A.; Clyne, T. W. (14–18 Oct 2001).
1363:
133:, peak power on the order of ten to hundreds of MW/cm, and a
98:
Laser drilling of cylindrical holes generally occurs through
152:
Melt expulsion arises as a result of the rapid build-up of
16:
Process of creating thru-holes using laser cutting methods
1620:
23:
the “popped” hole until the desired diameter is created.
1369:(5). Springer Science and Business Media LLC: 323–331.
1121:(2). Springer Science and Business Media LLC: 123–131.
497:
is the laser absorption coefficient depending on laser
1115:
Applied Physics A: Materials Science & Processing
785:
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236:
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forces and expel the molten material from the hole.
1851:
1798:
1686:
1172:. San Francisco: Cambridge University Press (CUP).
1002:Gan, E.K.W.; Zheng, H.Y.; Lim, G.C. (7 Dec 2000).
807:
737:
485:
418:
182:The recoil force is a strong function of the peak
767:is the pressure gradient along the liquid layer,
525:are distances along axial and radial directions,
74:, reduced noise, and lower NOx and CO emissions.
548:the latent heat of vaporization. The subscripts
1320:International Journal of Heat and Mass Transfer
808:{\displaystyle 2\sigma \over {\bar {\delta }}}
175:while "coarse" melt expulsion, such as used in
1004:Laser drilling of micro-vias in PCB substrates
955:Meier, Dieter J.; Schmidt, Stephan H. (2002).
1636:
771:is the difference between the vapor pressure
8:
594:transient model is used and accordingly the
223:Laser energy absorption and melt-vapor front
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156:(recoil force) within a cavity created by
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1546:. 127–129 (1–2). Elsevier BV: 999–1004.
61:have benefited from the productivity of
1904:Multiple-prism grating laser oscillator
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486:{\displaystyle I_{abs}=I(t)^{-\beta z}}
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883:Forsman, A; et al. (June 2007).
7:
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1240:(11). AIP Publishing: 4579–4586.
493:is the absorbed laser intensity,
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1583:Optics and Lasers in Engineering
1456:(9). AIP Publishing: 5061–5063.
1283:(8). AIP Publishing: 3884–3891.
1078:(8). AIP Publishing: 3317–3322.
44:printed circuit board micro-vias
598:and continuity equations used.
1813:Amplified spontaneous emission
1499:(1). The Optical Society: 18.
1326:(14). Elsevier BV: 3351–3360.
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1603:10.1016/s0143-8166(01)00008-2
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1427:10.1016/s0030-4018(01)01072-0
1340:10.1016/s0017-9310(96)00368-7
1413:(1–2). Elsevier BV: 97–112.
962:. LPKF Laser and Electronics
179:, removes material quickly.
1869:Chirped pulse amplification
1589:(3). Elsevier BV: 149–164.
1989:
1673:List of laser applications
1450:Journal of Applied Physics
1277:Journal of Applied Physics
1234:Journal of Applied Physics
1072:Journal of Applied Physics
1937:
1658:
501:and target material, and
1012:10.1109/eptc.2000.906394
778:and the surface tension
1544:Applied Surface Science
1663:List of laser articles
983:Cite journal requires
936:Cite journal requires
859:List of laser articles
809:
739:
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420:
106:(also referred to as "
1407:Optics Communications
1375:10.1007/s001700170056
1178:10.1557/proc-617-j5.6
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755:is the melt density,
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421:
135:material removal rate
78:and hole quality and
1838:Population inversion
1513:10.1364/ao.23.000018
782:
624:
580:After obtaining the
517:is the temperature,
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234:
1889:Laser beam profiler
1808:Active laser medium
1748:Free-electron laser
1668:List of laser types
1595:2001OptLE..35..149L
1552:1998ApSS..127..999G
1505:1984ApOpt..23...18A
1462:1980JAP....51.5061R
1419:2001OptCo.191...97S
1332:1997IJHMT..40.3351G
1289:1990JAP....68.3884K
1246:1987JAP....62.4579C
1127:1996ApPhA..63..123K
1084:1992JAP....72.3317B
890:. Photonics Spectra
177:percussion drilling
55:aircraft propulsion
1135:10.1007/bf01567639
819:Pulse shape effect
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735:
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173:heat-affected zone
162:pressure gradients
94:Physical phenomena
1955:
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1909:Optical amplifier
1758:Solid-state laser
1218:978-0-912035-71-0
1209:10.2351/1.5059872
914:Laser Focus World
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765:P(t)=(ΔP(t)/x(t))
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511:heat conductivity
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49:Manufacturers of
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1919:Optical isolator
1884:Injection seeder
1864:Beam homogenizer
1843:Ultrashort pulse
1833:Lasing threshold
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1897:
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1879:Gaussian beam
1877:
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1859:Beam expander
1857:
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1038:
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1023:
1021:0-7803-6644-1
1017:
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948:
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930:
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854:Laser cutting
852:
850:
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831:
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796:
789:
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583:
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566:
565:Knudsen layer
561:
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547:
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508:
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93:
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68:
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60:
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41:
40:engine blocks
37:
32:
26:
24:
21:
1899:Mode locking
1852:Laser optics
1586:
1582:
1576:
1543:
1537:
1496:
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1453:
1449:
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1410:
1406:
1399:
1366:
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1356:
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1280:
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1194:
1169:
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1118:
1114:
1108:
1075:
1071:
1065:
1040:
1036:
1030:
1003:
997:
976:cite journal
964:. Retrieved
950:
929:cite journal
917:. Retrieved
903:
892:. Retrieved
838:
826:
822:
772:
768:
764:
756:
752:
750:
745:
612:
607:
604:
600:
592:axisymmetric
584:
579:
562:
557:
553:
549:
542:
534:
526:
522:
518:
514:
506:
502:
494:
431:
426:
226:
212:aspect ratio
209:
200:
196:
181:
170:
154:gas pressure
151:
143:microseconds
119:
116:
104:vaporization
97:
89:
76:
48:
33:
30:
27:Applications
19:
18:
1968:Hole making
1929:Q-switching
1790:X-ray laser
1783:Ti-sapphire
1753:Laser diode
1731:Helium–neon
834:pulse train
184:temperature
158:evaporation
147:millisecond
139:micrometers
131:nanoseconds
122:laser pulse
67:sheet metal
36:oil gallery
1962:Categories
894:2014-07-20
865:References
830:efficiency
499:wavelength
112:laser beam
1973:Machining
1894:M squared
1716:Gas laser
1699:Dye laser
1611:0143-8166
1568:0169-4332
1521:0003-6935
1478:0021-8979
1435:0030-4018
1383:0268-3768
1348:0017-9310
1305:0021-8979
1262:0021-8979
1186:0272-9172
1143:0947-8396
1100:0021-8979
1057:0148-6411
800:¯
797:δ
790:σ
761:viscosity
720:∂
691:∂
684:μ
657:∂
634:∂
628:ρ
476:β
473:−
363:ν
353:ρ
349:−
330:ν
320:ρ
302:∂
294:∂
276:∂
268:∂
137:of a few
127:flashtube
1947:Category
1741:Nitrogen
1529:18204507
1391:17600502
1151:97443562
849:Drilling
843:See also
596:momentum
539:velocity
192:titanium
108:ablation
80:drilling
57:and for
38:of some
1726:Excimer
1591:Bibcode
1548:Bibcode
1501:Bibcode
1458:Bibcode
1415:Bibcode
1328:Bibcode
1285:Bibcode
1242:Bibcode
1123:Bibcode
1080:Bibcode
966:20 July
919:20 July
759:is the
531:density
509:is the
100:melting
82:speed.
1768:Nd:YAG
1763:Er:YAG
1704:Bubble
1652:Lasers
1609:
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1527:
1519:
1476:
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1389:
1381:
1346:
1303:
1260:
1215:
1184:
1149:
1141:
1098:
1055:
1018:
751:where
432:where
86:Theory
63:lasers
1773:Raman
1387:S2CID
1147:S2CID
960:(PDF)
888:(PDF)
769:ΔP(t)
145:to a
1778:Ruby
1607:ISSN
1564:ISSN
1525:PMID
1517:ISSN
1474:ISSN
1431:ISSN
1379:ISSN
1344:ISSN
1301:ISSN
1258:ISSN
1213:ISBN
1182:ISSN
1139:ISSN
1096:ISSN
1053:ISSN
1016:ISBN
989:help
968:2014
942:help
921:2014
556:and
537:the
521:and
503:I(t)
102:and
53:for
1736:Ion
1599:doi
1556:doi
1509:doi
1466:doi
1423:doi
1411:191
1371:doi
1336:doi
1293:doi
1250:doi
1205:doi
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1170:617
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