Laser decoating of coated metal sheets

Abstract

Methods, devices and systems for laser decoating of coated metal sheets, in particular for removing a metal protective layer from a metal sheet by a laser beam. The laser beam is directed onto a surface of a metal sheet coated with a metal protective layer, such that the laser beam strikes the surface of the metal sheet at a laser spot and melts material of the metal protective layer. A gas is directed by a plurality of nozzles at a pressure of at least 3 bar and at an acute angle with respect to the laser beam onto the laser spot. The nozzles are arranged around the laser beam such that the gas directed from the nozzles blows away the melted material of the metal protective layer from the metal sheet.

Claims

1. A method of laser decoating a coated metal sheet, the method comprising: directing a laser beam onto a surface of a metal sheet coated with a metal protective layer, such that the laser beam strikes the surface of the metal sheet at a laser spot and melts material of the metal protective layer; and directing multiple gas flows, from a plurality of nozzles at a pressure of at least 3 bar and at an acute angle with respect to the laser beam onto the laser spot, the nozzles being arranged around the laser beam such that the gas flows directed from the nozzles intersect with each other on the surface of the workpiece at the laser spot and blow away the melted material of the metal protective layer from the metal sheet.

2. The method of claim 1, further comprising: moving the laser beam relative to the metal sheet in an advance direction and at an advance speed over the metal sheet, to remove material of the metal protective layer from the metal sheet along the advance direction.

3. The method of claim 2, wherein at least one of the nozzles directs the gas onto the laser spot exclusively with flow components in the direction of the laser beam and in the advance direction.

4. The method of claim 2, wherein directing the gas comprises directing the gas onto the laser spot from at least three nozzles, the gas from each nozzle exiting from a pressure of at least 3 bar and at an acute angle with respect to the laser beam, and wherein only a central nozzle of the nozzles directs the gas onto the laser spot exclusively with flow components in the direction of the laser beam and in the advance direction of the laser beam.

5. The method of claim 4, wherein two outer nozzles of the nozzles each direct the gas onto the laser spot symmetrically with respect to a plane defined by the laser beam and the advance direction.

6. The method of claim 5, wherein the two outer nozzles each direct the gas onto the laser spot in an angularly offset manner through approximately 45 degrees with respect to the gas flowing out of the central nozzle.

7. The method of claim 2, further comprising: adjusting the advance speed of moving the laser beam to control a depth of melt of the protective layer.

8. The method of claim 7, further comprising: determining, based on a thickness of the metal protection layer after the melted material has been blown away, whether an intermetallic phase between a coating material and a carrier material of the metal protective layer has been removed.

9. The method of claim 1, further comprising: drawing the gas by a suction device connected to a suction channel located below a workpiece support for the coated metal sheet.

10. The method of claim 1, wherein the nozzles are each spaced from the surface of the metal sheet no more than about 5 to 8 mm.

11. The method of claim 1, wherein the laser beam strikes the surface of the metal sheet perpendicularly.

12. The method of claim 1, wherein the metal protective layer includes at least one of aluminum/silicon protective coating and zinc protective coating.

13. The method of claim 1, wherein the gas is either compressed air or an inert gas.

14. The method of claim 1, wherein the nozzles have an opening diameter of no more than about 2.5 mm, from which the gas is discharged at the pressure of at least 3 bar.

15. A laser decoating device, comprising: a laser beam generation unit for generating a laser beam; and a laser processing head, from which the laser beam is emitted, wherein the laser processing head has a plurality of nozzles arranged around the emitted laser beam and whose nozzle axes are each directed at an acute angle with respect to the laser beam and configured to direct a gas to intersect with the emitted laser beam at a surface of a workpiece coated with a protective layer, wherein the laser processing head is configured to direct the laser beam to strike the surface of the workpiece at a laser spot and melts material of the protective layer, and wherein the plurality of nozzles is configured to direct the gas at a pressure of at least 3 bar onto the laser spot such that the gas directed from the nozzles blows away the melted material of the protective layer from the workpiece.

16. The laser decoating device of claim 15, wherein the plurality of nozzles are arranged on a common nozzle member.

17. The laser decoating device of claim 15, wherein the laser processing head has at least three nozzles, the two outer nozzles being arranged in a mirror-symmetrical manner relative to each other with respect to a plane defined by the laser beam and the nozzle axis of the central nozzle.

18. The laser decoating device of claim 17, wherein the two outer nozzles are each arranged in a manner offset through an angle of approximately 45 with respect to the central nozzle.

19. The laser decoating device of claim 15, wherein an opening diameter of the nozzles is a maximum of about 2.5 mm.

20. The laser decoating device of claim 15, further comprising a suction device connected to a suction channel located below a workpiece support for a coated metal sheet, the suction device configured to draw the gas through the suction channel during operation of the laser decoating device.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows a laser decoating device for carrying out a laser decoating method according to the invention, and

(2) FIGS. 2a, 2b are a side view (FIG. 2a) and a plan view (FIG. 2b) of three nozzles which are secured to a laser processing head, respectively.

DETAILED DESCRIPTION

(3) A laser decoating device 1 which is illustrated in perspective in FIG. 1 includes a laser, e.g., a CO.sub.2 laser, a fiber laser, a diode laser or solid-state laser, as a laser beam generation unit 2, a movable laser processing head 3, and a workpiece support 4. In the laser beam generation unit 2, a laser beam 5 is generated which is guided by means of a fiber optic cable (not shown) or redirection mirrors (not shown) from the laser 2 to the processing head 3. There is arranged on the workpiece support 4 as a workpiece a metal sheet (tailored blank or hotforming blank) 6 which is coated at both sides with an aluminum/silicon layer 7. The laser beam 5 is directed onto the metal sheet 6 by means of a focusing optics which is arranged in the processing head 3. The laser decoating device 1 is further supplied with compressed air or inert gas 8, for example, nitrogen. Alternatively or in addition, compressed air or application-specific gases may also be provided. The use of the individual gases is dependent on the material of the metal sheet 6 to be processed, on the coating to be removed and on quality requirements. There is further provided a suction device 9, which is connected to a suction channel 10 located below the workpiece support 4.

(4) As shown in FIGS. 2a and 2b, there are secured to the processing head 3 by means of a retention member 11 three nozzles 12.sub.1-12.sub.3 which have an opening diameter of a maximum of 2.5 mm and from which the inert gas 8 is discharged at a high pressure of at least 3 bar. The nozzles 12.sub.1-12.sub.3 are arranged around the emitted laser beam 5, in particular in the form of a quarter-circle with identical angular spacings of 45 degrees, the nozzle axes 13.sub.1-13.sub.3 all being orientated at an acute angle with respect to the laser beam 5 and intersecting the emitted laser beam 5 at the same intersection location 14. The two outer nozzles 12.sub.1, 12.sub.3 are arranged in a mirror-symmetrical manner relative to each other with respect to the plane defined by the laser beam 5 and the nozzle axis 13.sub.2 of the central nozzle 12.sub.2. In the embodiment shown, the nozzles 12.sub.1-12.sub.3 are constructed in a common nozzle member 15, but each with their own gas connection, but they may also have individual nozzle members which are separate from each other.

(5) In order to remove the aluminum/silicon layer 7, the laser beam 5 is moved in an advance direction v over the metal sheet 6, the processing head 3 being located with such spacing from the metal sheet 6 that the intersection location 14 is located on the surface 16 of the metal sheet. Of course, the metal sheet 6 can also equally well be moved relative to the laser beam 5. By means of the nozzles 12.sub.1-12.sub.3 which are arranged around the laser beam 5, the inert gas 8 is in each case directed at a pressure of at least 3 bar and at the acute angle onto the intersection location 14, that is to say, onto the laser spot 14 on the metal sheet surface 16. The central nozzle 12.sub.2 directs the inert gas 8 onto the laser spot 14 exclusively with flow components in the direction of the laser beam 5 and in the advance direction v. The two external nozzles 12.sub.1, 12.sub.3 direct the inert gas 8 onto the laser spot 14 in each case symmetrically relative to the plane defined by the laser beam 5 and the advance direction v. The nozzles 12.sub.1-12.sub.3 are therefore all directed precisely onto the laser spot 14 with a spacing of a few millimeters in order to achieve the most localized and rapid flow possible of the inert gas 8 at the laser spot 14. In the region of the removed aluminum/silicon layer 7, the metal sheet 6 is now made weldable.

(6) A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.