Laser-Based Method and System for Marking a Workpiece

Abstract

A method and system for marking a workpiece at a marking location by infusing colorant into targeted surface material within a region of the workpiece via laser-induced chemical etching are disclosed. The system includes a laser subsystem for generating a pulsed laser output and a transport subsystem including a medium containing the colorant mounted immediately adjacent the marking location to transfer the colorant to the targeted surface material upon impact by the pulsed laser output. The system also includes a delivery subsystem for irradiating the medium and the targeted surface material with the pulsed laser output to melt the targeted surface material to obtain molten material and to transfer the colorant from the medium to the molten material. The molten material allows the transferred colorant to thermally diffuse into and chemically bond to the molten material. Each laser pulse creates a microtextured colorized spot of material on the workpiece.

Claims

1-6. (canceled)

7. A system for marking a workpiece at a marking location by infusing colorant into targeted surface material within a region of the workpiece via laser-induced chemical etching, the system comprising: a laser subsystem for generating a pulsed laser output having a plurality of laser pulses; a transport subsystem including a medium containing the colorant mounted immediately adjacent the marking location to transfer the colorant from the medium to the targeted surface material of the workpiece upon impact by the pulsed laser output; and a delivery subsystem for irradiating the medium and the targeted surface material in the region with the pulsed laser output to melt the targeted surface material to obtain molten material and to transfer the colorant from the medium to the molten material in a predetermined pattern, the molten material allowing the transferred colorant to thermally diffuse into and chemically bond to the molten material wherein each laser pulse creates a microtextured colorized spot of material on the workpiece and wherein the microtextured colorized spots of material create a marked region of the workpiece.

8. The system as claimed in claim 7, wherein the colorant is an ink.

9. The system as claimed in claim 8, wherein the medium is a ribbon of ink-bearing material.

10. The system as claimed in claim 7, wherein the transport subsystem includes a pair of spaced reels including a drive reel and an actuator assembly for rotatably driving the drive reel to advance the medium.

11. The system as claimed in claim 7, wherein the targeted surface material is a metal layer.

12. The system as claimed in claim 7, wherein the workpiece is a metal plate.

13. A system for marking a workpiece having a specular metal surface at a marking location by infusing colorant into targeted surface material within a region of the workpiece via laser-induced chemical etching, the system comprising: a laser subsystem for generating a pulsed laser output having a plurality of laser pulses; a transport subsystem including a medium containing the colorant mounted immediately adjacent the marking location to transfer the colorant from the medium to the targeted surface material of the workpiece upon impact by the pulsed laser output; and a delivery subsystem for irradiating the medium and the targeted surface material in the region with the pulsed laser output to melt the targeted surface material to obtain molten material and to transfer the colorant from the medium to the molten material in a predetermined pattern, the molten material allowing the transferred colorant to thermally diffuse into and chemically bond to the molten material wherein each laser pulse creates a microtextured colorized spot of material on the specular metal surface of the workpiece and wherein the microtextured colorized spots create a marked region which shows significant roughness and eliminates at least strong reflection components.

14. The system as claimed in claim 13, wherein the colorant is an ink.

15. The system as claimed in claim 14, wherein the medium is a ribbon of ink-bearing material.

16. The system as claimed in claim 13, wherein the transport subsystem includes a pair of spaced reels including a drive reel and an actuator assembly for rotatably driving the drive reel to advance the medium.

17. The system as claimed in claim 13, wherein the targeted surface material is a metal layer.

18. The system as claimed in claim 13, wherein the workpiece is a metal plate.

19. A system for marking a workpiece at a marking location by infusing colorant into targeted surface material having a thermal diffusivity within a region of the workpiece via laser-induced chemical etching, the system comprising: a laser subsystem for generating a pulsed laser output having a plurality of laser pulses, each of the pulses having a pulse width; a transport subsystem including a medium containing the colorant mounted immediately adjacent the marking location to transfer the colorant from the medium to the targeted surface material of the workpiece upon impact by the pulsed laser output; and a delivery subsystem for irradiating the medium and the targeted surface material in the region with the pulsed laser output to melt the targeted surface material to obtain molten material and to transfer the colorant from the medium to the molten material, the molten material allowing the transferred colorant to thermally diffuse into and chemically bond to the molten material wherein each laser pulse creates a microtextured colorized spot of material on the workpiece and wherein the microtextured colorized spots of material create a marked region of the workpiece and wherein energy from the laser pulses is transferred to the area around each of the spots via thermal diffusion and wherein the thermal diffusion is based on the pulse width of the pulses and the thermal diffusivity of the surface material.

20. The system as claimed in claim 19, wherein the colorant is an ink.

21. The system as claimed in claim 20, wherein the medium is a ribbon of ink-bearing material.

22. The system as claimed in claim 19, wherein the transport subsystem includes a pair of spaced reels including a drive reel and an actuator assembly for rotatably driving the drive reel to advance the medium.

23. The system as claimed in claim 19, wherein the targeted surface material is a metal layer.

24. The system as claimed in claim 19, wherein the workpiece is a metal plate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG. 1 is a side, schematic view of a prior art laser-marked surface;

[0050] FIG. 2 is a table showing various marking mechanisms and methods using an excimer laser;

[0051] FIGS. 3 and 4 are schematics illustrating, by way of example, a mark is the form of a microtextured colorized spot formed on a specular metal surface using at least one embodiment of the present invention;

[0052] FIG. 5 is a schematic block diagram showing some of the elements of a laser-based marking system constructed in accordance with at least one embodiment of the present invention; and

[0053] FIG. 6 shows graphs of temperature versus depth into metal which illustrates the effect of thermal diffusion with a 10 nanosecond laser pulse.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE PRESENT INVENTION

[0054] As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

[0055] Turning to FIG. 5, there is illustrated a representation of a general embodiment of a laser marking system, generally indicated at 10, for marking via etching, a metal workpiece 12 using a focused pulsed laser beam generated by a laser subsystem including a laser 14, such as Q-switched pulsed laser. The pulsed laser beam not only liquefies or melts a spot of material (i.e., FIG. 3) on the workpiece 12 but also transfers a colorant such as ink to the molten material. After solidification, a microtextured colorized spot of material remains on the workpiece 12.

[0056] A clear advantage of using the pulsed laser 14 versus using CW laser with modulation lies in the total average laser power needed for the process. For example, for a dose 0.1 μj with 20-ns pulse duration, it requires a 5-watt CW laser. For the same dose at 50 KHz, it requires only a 5-mw pulsed laser, a reduction of 1,000 times in average power. A milli-watt level laser can easily be air-cooled while a multi-watt laser may have to be water-cooled. The footprint of a milli-watt level laser is also much smaller than that of a multi-watt level laser.

[0057] U.S. Patent Document No. 2006/0000814 is hereby incorporated by reference in its entirety herein especially for its discussion of the various laser subsystems and delivery subsystems for use in the laser-based marking system constructed in accordance with at least one embodiment of the present invention. FIGS. 12 and 13 of the above-noted patent document are reproduced herein as drawing FIGS. 3 and 4. FIGS. 3 and 4 are schematics illustrating, by way of example, a colorized mark formed on the specular surface 24 of the workpiece 12 using a system of the present invention. The pulsed laser 14 may be picosecond laser producing a pulsed output with total energy density (in one or more pulses) sufficient to initiate ablation within a portion of a spot area on the workpiece surface 24. The resulting microtextured surface has surface height variations from tens to hundreds of nanometers. The marked region generally shows significant roughness and eliminates at least strong reflection components.

[0058] Contributing to the marking process are at least the following parameters: laser beam spot size, laser beam profile, location of the laser beam on the marking area (and its accuracy), number of the laser pulses, laser pulse energy, laser pulse width and laser pulse shape (temporal profile).

[0059] The workpiece 12 may be placed on a positioning table or X-Y stage and may be subjected to an application of a focused laser pulse which is produced by the laser 14. The laser pulses are directed to and focused on the workpiece 12 by using a delivery subsystem in the form of a machining head and/or objective lens 16. Alternatively, the table or stage may be stationary and the head or lens 16 may move in two or three dimensions.

[0060] The marking system 10 generally includes the laser subsystem, the delivery subsystem, and an ink tape or transport subsystem, which cooperate and are coordinated to operate together via a system controller to permanently apply colorized indicium or marks upon the workpiece 12. The laser subsystem, as described above, is provided for heating selected portions of a colorant such as ink via laser pulses in a predetermined pattern to help create the indium by transforming ink to the workpiece 12. In the present embodiment, ink is provided via the ink tape subsystem. The ink tape subsystem includes a pair of reels 18 and 20 disposed on opposite sides of the laser 14. A first reel 18 of the pair of reels 18 and 20 is adapted to carry unused ink tape 22 and the other reel 20 of the pair of reels 18 and 20 is adapted to carry used ink tape 22. The ink tape 22 spans across and is immediately adjacent the upper surface 24 of the metal workpiece 12 adjacent an area to be marked. The ink tape 22 may be held in this position adjacent the area to be marked using a retaining member (not shown). Ideally, the retaining member is held in contact with ink tape 22 to hold the ink tape 22 generally flat and in contact with the surface 24 of the workpiece 12.

[0061] The reel 20 is a drive reel 20 of the tape subsystem and is driven by an actuator or rotary motor assembly under control of the system controller to rotatably drive the drive reel 20 to advance the tape 22.

[0062] The laser 14 is actuated under control of the system controller to heat selected portions of the ink tape 22 which causes those exposed portions of ink tape 22 to deposit or transfer the ink onto the molten metal of the workpiece 12 after it too is irradiated with the laser beam pulse. The laser beam is only directed to those portions of the ink tape 22 whose ink is to be infused or diffused into the molten metal. It should be appreciated that the system controller, the laser 14 and the delivery system are capable of creating any one of an infinite number of designs, which may include names, logos, serial numbers, bar codes, data matrices, and the like. As each indicium is formed, used ink tape may be advanced, either manually or automatically, via the actuator assembly to provide a “fresh” portion of unused ink tape.

[0063] Heat Affected Zone (HAZ) is a three Dimensional Effect

[0064] When a laser pulse hits a spot on the metal workpiece 12, the electrons in the workpiece 12 absorb the laser energy very quickly (less than pico seconds). The energy is then transferred to the area surrounding the spot via electron-lattice interaction, generally called “thermal diffusion.”

[0065] This diffusion effect is three dimensional, i.e., the energy will transfer in all directions (not only in the lateral x and y plane, but in the z direction as well). The dimension z of the thermal diffusion can be estimated by the square root of the product of pulse width, t.sub.p, and material diffusivity, D.

[0066] The curves of FIG. 6 illustrates the effect of thermal diffusion with a 10 nano-second laser pulse interacting with copper and aluminum (they both have similar thermal diffusivity).

[0067] Thermal diffusivity of selected metals and other materials are given by the following table:

TABLE-US-00001 Thermal Thermal diffusivity diffusivity Material (m.sup.2/s) (mm.sup.2/s) Pyrolytic graphite, parallel to layers 1.22 × 10.sup.−3 1220 Silver, pure (99.9%) 1.6563 × 10.sup.−4  165.63 Gold 1.27 × 10.sup.−4 127 Copper at 25° C. 1.11 10.sup.−4 111 Aluminum  9.7 × 10.sup.−5 97 Al—10Si—Mn—Mg (Silafont 36) at 74.2 × 10.sup.−6 74.2 20° C. Aluminum 6061-T6 Alloy  6.4 × 10.sup.−5 64 Al—5Mg—2Si—Mn (Magsimal-59) at  4.4 × 10.sup.−5 44.0 20° C. Steel, AISI 1010 (0.1% carbon) 1.88 × 10.sup.−5 18.8 Steel, 1% carbon 1.172 × 10.sup.−5  11.72 Steel, stainless 304A at 27° C.  4.2 × 10.sup.−6 4.2 Steel, stainless 310 at 25° 3.352 × 10.sup.−6  3.352 Inconel 600 at 25° C. 3.428 × 10.sup.−6  3.428 Molybdenum (99.95%) at 25° C. 54.3 × 10.sup.−6 54.3 Iron  2.3 × 10.sup.−5 23

[0068] In at least one embodiment of the present invention, a method of iteratively, selectively and accurately marking by etching with a colorant such as ink is done by diffusion of colorant. The method includes: directing a focused pulsed laser source to a selected area of the ink tape and the workpiece to irradiate them, and applying a laser pulse from the focused pulsed laser source thereto. The laser pulse melts the selected area thereby allowing the diffusion or infusion of colorant into and chemically bond to the molten material. The method also includes allowing the melted selected area to solidify. Each laser pulse creates a microtextured colorized spot of material (i.e., FIGS. 3 and 4) on the workpiece 12.

[0069] While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.