WO1998017433A2 - Procede de traitement d'une partie d'une surface a l'aide d'un faisceau laser de lecture - Google Patents

Procede de traitement d'une partie d'une surface a l'aide d'un faisceau laser de lecture Download PDF

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Publication number
WO1998017433A2
WO1998017433A2 PCT/IB1997/001142 IB9701142W WO9817433A2 WO 1998017433 A2 WO1998017433 A2 WO 1998017433A2 IB 9701142 W IB9701142 W IB 9701142W WO 9817433 A2 WO9817433 A2 WO 9817433A2
Authority
WO
WIPO (PCT)
Prior art keywords
pulses
light beam
different
laser
surfacial
Prior art date
Application number
PCT/IB1997/001142
Other languages
English (en)
Other versions
WO1998017433A3 (fr
Inventor
Martijn Adriaan De Keijzer
Hans Kuiper
Anton Mark Bootsma
Original Assignee
Philips Electronics N.V.
Philips Norden Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Philips Electronics N.V., Philips Norden Ab filed Critical Philips Electronics N.V.
Publication of WO1998017433A2 publication Critical patent/WO1998017433A2/fr
Publication of WO1998017433A3 publication Critical patent/WO1998017433A3/fr

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/064—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms
    • B23K26/0643—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms comprising mirrors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/064—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms

Definitions

  • the invention relates to a method of treating a surface of a body, whereby light beam pulses from a Q-switched laser are fired sequentially at the surface according to a surfacial pattern.
  • treating is here intended to encompass such actions as marking, etching, engraving, ablating, texturing, coloring, etc. , whereby absorption of energy from the laser beam is exploited so as to produce a localized chemical or physical reaction, resulting in a localized change in some characteristic (such as color, texture or profile) of the irradiated surface.
  • Q-switched laser should be interpreted as referring to any laser (e.g. solid state or gas) which contains a Q-switch (e.g. mechanical, electro-optical or acousto-optical).
  • a method as stated in the opening paragraph can be used to treat the surfaces of all sorts of materials, including plastics, semiconductors, ceramics, metals and vitreous materials. Since modern lasers are becoming increasingly powerful, irradiation of such materials with a continuous laser beam will often result in excessive energy transfer, causing, for example, unwanted damage to the material, or difficulty in localizing the desired surfacial treatment (due to leaked thermal (conductive) energy within the material). Consequently, use is preferably made of a Q-switched laser, which produces short pulses of radiative energy — typically of the order of a few hundred nanoseconds in duration, and with a frequency of the order of a kilohertz.
  • a common application of the said method is in the marking of surfaces with, for example, numerals, letters, bar-codes, emblems and other symbols; close inspection of such surfacial markings then reveals that, what appears from a distance to be a smooth line is in fact a collection of dots in close mutual proximity.
  • Another application of the method is in the creation of rastered surfacial pictures, whereby use is made of dithering effects to create the illusion of different shades. Both such applications exploit materials which change color (e.g. blacken) upon irradiation with the laser beam.
  • the new method should allow the realization of new and useful surfacial marking effects.
  • the inventive measure allows the energy-content of the laser beam to be varied on a per-pulse basis. This opens up a whole range of possibilities, as will be elucidated on the basis of a number of specific embodiments herebelow.
  • the value of E p can be varied as required by driving the Q-switch with a voltage wave which has an appropriately varied duty cycle.
  • Q-switches are generally driven by a high-frequency sinusoidal voltage (frequency of the order of 25 MHz) which is amplitude-modulated by a low-frequency wave (e.g. a square wave, sine wave, sawtooth, etc. , typically having a frequency of the order of about 5 kHz); the accompanying laser then emits radiation pulses with a frequency equal to that of the low-frequency wave.
  • the inventors have found that, by varying the duty cycle D of the low-frequency wave, the value of E p can be correspondingly varied: for a given light pulse, the value of E p scales inversely with D. Each radiation pulse in a sequential array can thus be endowed with a different, predetermined value of E p , by appropriate choice of the duty cycle of the corresponding portion of the low-frequency driving wave.
  • D and E p for a given laser apparatus
  • a particular embodiment of the method according to the invention whereby the light beam pulses cause localized discoloration of the surface, is characterized in that E p is altered to as to achieve different shades of surface discoloration for different pulses.
  • E p is altered to as to achieve different shades of surface discoloration for different pulses.
  • plastics such as POM (polyoxymethylene) and ABS (acrylonitrile butadiene styrene), which are intrinsically dark in color but can be caused to turn whitish upon irradiation.
  • POM polyoxymethylene
  • ABS acrylonitrile butadiene styrene
  • E p is altered so as to achieve different surface colors for different pulses.
  • materials typically comprise common plastics, such as ABS, which are doped with special organic chemicals.
  • the energy output E p of each pulse can be altered on a real-time basis, so that each individual pulse can produce a different, pre-determined color on the irradiated surface; such a procedure is thus very considerably faster than the alternative discussed above.
  • , E p is continually adjusted in such a manner that: a decrease in
  • Such a method avoids over-exposure to laser energy in those regions of a linear pattern wherein a line undergoes a sudden change in direction, since changes in
  • a particular embodiment of the method according to the invention is characterized in that the Q-switch is acousto-optical.
  • the Q-switch is acousto-optical.
  • an acoustic wave is used to modulate the optical properties of a medium, producing periodic variations in its scattering behaviour.
  • the frequency of such acoustic waves is typically of the order of about 5 kHz, which lends itself to application in most laser machining applications.
  • Figure 1 depicts apparatus for enaction of a particular embodiment of the method according to the invention
  • Figure 2 shows a waveform with which the Q-switch in Figure 1 may be modulated according to the invention
  • Figure 3 is a calibration graph in which relative energy per laser pulse is plotted against Q-switch duty cycle for a number of different laser specifications
  • Figure 4 shows two pulses of laser radiation having different values of E p .
  • Figure 1 depicts apparatus with which it is possible to enact a particular embodiment of the method according to the invention.
  • the apparatus comprises a laser 1 which includes the following internal components: - A lasing source 3;
  • the laser 1 produces a pulsed beam 15 which impinges upon, and is reflected by, a rotatable mirror 17.
  • the reflected beam 15' then impinges on a surface 19' of a body 19.
  • the reflected beam 15' can be caused to move (scan) in the direction 23, thereby tracing out a linear marking 25 on the surface 19'.
  • the mirror 17 If the mirror 17 is rotated from rest, then, because of its inertia, it will require a certain finite time to reach a given end velocity. As a result, the beam 15' will spend relatively more time traversing the start 25 s of the linear path 25 than it will traversing the rest 25r of that path 25, and, consequently, the start 25s of the path 25 will receive relatively more light pulses. In the absence of the inventive measure, this would result in over-exposure of the start 25s relative to the rest 25r, causing the marking 25 to have a blotchy, non-uniform appearance.
  • the driving input 13 of the Q-switch 11 is supplied with a low-frequency modulating square wave having a variable duty cycle D.
  • a low-frequency modulating square wave having a variable duty cycle D.
  • FIG. 2 An example of such a square wave is shown in Figure 2.
  • the wave comprises a sequential array of cycles C with a constant period T.
  • the "high" blocks 31 ,32,33,... are numbered in the order in which they are supplied to the input 13.
  • the amplitude of the square wave is 5 volts, for example (TTL standard). Inspection of Figure 2 makes it clear that the value of t 3 starts relatively high, but is then progressively decreased. This behaviour is chosen to counter the behaviour of the surfacial velocity of the beam 15' , which starts at zero, steadily increases in the region 25s, and then levels off in the region 25r. For those regions of the linear marking 25 where the constituent laser pulses impinge in relatively close proximity to one another (e.g. region 25s), the "high" blocks are thus relatively long (i.e. t 3 is relatively large), resulting in relatively low-energy pulses; on the other hand, for those regions where the pulses impinge relatively far away from one another (e.g.
  • the "high" blocks are relatively short (i.e. t 3 is relatively small), resulting in relatively high-energy pulses. Consequently, "over- exposure” in the region 25s is prevented.
  • Embodiment 2 is destined to fail: since such a light source 5 typically has a reaction time of the order of a few seconds, it cannot possibly be modulated on a per-pulse basis.
  • Figure 3 graphically depicts the (empirical) relationship between relative radiative energy per pulse E pr and Q-switch duty cycle D for various different lasers.
  • the lines through the data points are intended to serve as guides to the eye.
  • the three data sets all relate to a HAAS 532 LTM frequency-doubled Nd:YAG laser, but pertain to different values of the Q-switch frequency f Q (low-frequency modulation) and/or electrical current rating I, as follows:
  • the data points are based on calibration experiments performed using an acousto-optical Q- switch subject to square-wave low-frequency modulation.
  • D is defined hereabove in Embodiment 1
  • E pr for a given data set is defined as E p /E pm , in which E pm is the maximum attained value of E p for that data set.
  • FIG 4 depicts two different laser pulses 50,50' produced by a Q- switched laser light source such as the laser 1 in Figure 1.
  • the pulses 50,50' correspond to different cycles C of a driving waveform such as that depicted in Figure 2; for example, the pulses 50,50' correspond respectively to the block-sets 31,41 and 34,44.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Mechanical Engineering (AREA)
  • Laser Beam Processing (AREA)
  • Lasers (AREA)

Abstract

L'invention a trait à un procédé de traitement d'une surface (19') d'un corps (19) dans le cadre duquel des impulsions de faisceau lumineux provenant d'un laser à impulsions géantes (1) sont envoyées de manière séquentielle sur ladite surface (19') selon une configuration de surface, le q-switch (11) étant commandé de façon à ce que toutes les impulsions lumineuses n'aient pas la même durée Ep. Dans un mode de réalisation particulier, les impulsions du faisceau lumineux entraînent une décoloration localisée de la surface (19') et Ep est modifiée de manière à obtenir différentes nuances de décoloration de surface pour différentes impulsions. Dans un autre mode de réalisation, les impulsions du faisceau lumineux entraînent une coloration localisée de la surface (19') et Ep est modifiée de manière à obtenir différentes couleurs en surface pour différentes impulsions. Dans un autre mode encore, le faisceau lumineux (15') est promené au-dessus de la surface (19') selon un trajet linéaire (25), la vitesse de surface Vb du faisceau (15') ayant une grandeur variable IVbI, et la valeur de Ep est sans cesse ajustée de façon à ce qu'à une diminution de IVbI corresponde une diminution de Ep et qu'à une augmentation de IVbI corresponde une augmentation de Ep et que, s'il en est autrement, Ep demeure inchangé, de manière à obtenir une fluence laser sensiblement constante au-dessus de la partie balayée (25) de la surface (19').
PCT/IB1997/001142 1996-10-21 1997-09-22 Procede de traitement d'une partie d'une surface a l'aide d'un faisceau laser de lecture WO1998017433A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP96202925.2 1996-10-21
EP96202925 1996-10-21

Publications (2)

Publication Number Publication Date
WO1998017433A2 true WO1998017433A2 (fr) 1998-04-30
WO1998017433A3 WO1998017433A3 (fr) 1998-06-25

Family

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Application Number Title Priority Date Filing Date
PCT/IB1997/001142 WO1998017433A2 (fr) 1996-10-21 1997-09-22 Procede de traitement d'une partie d'une surface a l'aide d'un faisceau laser de lecture

Country Status (1)

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WO (1) WO1998017433A2 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001008733A1 (fr) 1999-07-31 2001-02-08 Glaxo Group Limited Procede de marquage

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994011146A1 (fr) * 1992-11-09 1994-05-26 Partek Cargotec Oy Procede de marquage par laser et surface metallique marquee par ce procede
EP0624421A2 (fr) * 1993-05-13 1994-11-17 Podarok International, Inc. Méthode et appareil pour créer une image par un faisceau laser pulsé, à l'intérieur d'un matériau transparent
DE19542973A1 (de) * 1994-11-17 1996-05-23 Nec Corp Verfahren und Einrichtung zum Markieren von Werkstücken mittels Laserstrahl

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH06237037A (ja) * 1993-02-12 1994-08-23 Fuji Electric Co Ltd レーザ加工装置

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994011146A1 (fr) * 1992-11-09 1994-05-26 Partek Cargotec Oy Procede de marquage par laser et surface metallique marquee par ce procede
EP0624421A2 (fr) * 1993-05-13 1994-11-17 Podarok International, Inc. Méthode et appareil pour créer une image par un faisceau laser pulsé, à l'intérieur d'un matériau transparent
DE19542973A1 (de) * 1994-11-17 1996-05-23 Nec Corp Verfahren und Einrichtung zum Markieren von Werkstücken mittels Laserstrahl

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001008733A1 (fr) 1999-07-31 2001-02-08 Glaxo Group Limited Procede de marquage

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WO1998017433A3 (fr) 1998-06-25

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