LASER BEAM PROCESSING DEVICE COMPRISING A COUPLING DEVICE FOR COUPLING A FOCUSED LASER BEAM INTO A FLUID JET

Abstract

Disclosed is a laser beam processing device, the main part of which is a coupling device (1) for coupling a focused laser beam (2) into a fluid jet (3) of a defined cross-section. The coupling device (1) comprises a housing (4), in which a fluid nozzle is configured for forming the fluid jet (3). In addition, an outlet opening (6) is provided in the housing, through which the fluid jet (3) exits from the housing (4) and the cross-section of which is larger than the cross-section of the fluid jet (3). A passage chamber is provided between the fluid nozzle (5) and the outlet opening (6) for the fluid jet (3). According to the invention, a throttle bore is provided, which connects the passage chamber (7) to the pressure chamber and is dimensioned in relation to the outlet opening so that, in the region of the passage chamber which is arranged about the fluid nozzle (5), there is a pressure that is smaller than the pressure in the pressure chamber so that an overpressure does not form in the passage chamber with respect to the pressure in the pressure chamber. In addition, a method is disclosed for setting a pressure in the passage chamber (7) in a coupling device of this type, in which the pressure does not exceed the pressure in the pressure chamber.

Claims

1. A laser beam processing device comprising a fluid nozzle producing a fluid jet, a coupling device (1) for coupling a laser beam (2), which is focused with a lens, into the fluid jet (3) of a defined cross section and a supply of gas which is introduced into a housing into a pressure chamber for producing a gas jet, which is configured annularly and surrounds but does not touch the fluid jet, with such a kinetic energy that, at the processing location of the laser beam on the workpiece itself, in the cavities present in the workpiece, the fluid which has accumulated there can be kept away from the processing location of the laser beam, wherein the fluid nozzle (5) for forming the fluid jet (3) is arranged in the housing (4); and an outlet opening (6) which is arranged in the housing (4) is provided through which the fluid jet (3) emerges from the housing (4) and the cross section of which is larger than the cross section of the fluid jet (3); and a passage chamber (7) for the fluid jet (3), which is arranged between the fluid nozzle (5) and the outlet opening (6); characterized in that at least one throttle bore (8) is provided which is connected in terms of flow to the passage chamber (7), which is separated from the pressure chamber, and to the pressure chamber (1) and has such a small flow cross section A.sub.8 that, in the event of the gas pressure of the supply of gas that is present on the side of said throttle bore that faces away from the passage chamber being greater than in the passage chamber (7), in addition to a throttling action, pressure equalization of precisely such a magnitude can be realized that, in the passage chamber, the pressure does not drop as far as a critical pressure at which the fluid jet breaks up, wherein a resulting outlet opening cross section A.sub.6, which is formed from the cross section of the outlet opening (6) configured as an aperture reduced by the cross section of the fluid jet (3), which does not have any sheathing by an auxiliary gas, with respect to the throttle bore (8) and an output cross section A.sub.11 formed at the emergence of the gas from the pressure chamber (9) at the end lying opposite the throttle bore (8) are dimensioned with respect to each other in such a manner that both A.sub.11 and A.sub.6 are larger than A.sub.8, and A.sub.11 is larger than A.sub.6.

2. The device as claimed in claim 1, characterized in that the gas emerges from the housing (4) via a passage region, which is separated off from the passage chamber (7) by means of an insert (10) arranged in the housing (4), outside the outlet opening (6)surrounding the fluid jet (3)in the manner of an air jet.

3. The device as claimed in claim 1, characterized in that the resulting outlet opening cross section A.sub.6 is double the size of the cross section A.sub.8 of the at least one throttle bore (8).

4. The device as claimed in claim 1, characterized in that there are four throttle bores (8), in particular of identical cross section.

5. The device as claimed in claim 2, characterized in that the pressure chamber (9) has a gas outlet nozzle (11) configured concentrically with respect to the outlet opening (6) in the insert (10).

6. The device as claimed in claim 1, characterized in that the at least one throttle bore (8) and the resulting outlet opening cross section A.sub.6 are dimensioned in such a manner that no negative pressure prevails in relation to the external pressure in the passage chamber (7).

7. The device as claimed in claim 1, characterized in that the at least one throttle bore (8) and the resulting outlet opening cross section A.sub.6 are dimensioned in such a manner that a negative pressure which does not fall below the defined critical pressure prevails in the passage chamber (7).

8. A method for setting a pressure in a passage chamber (7), which is arranged between a fluid nozzle (5) for producing a fluid jet (3) and an outlet opening (6) on the housing (4), for the fluid jet (3) of a laser beam processing device with the features as claimed in claim 1, in which a laser beam (2) serving for the processing on a workpiece surface (14) is coupled into the fluid jet (3), which does not have any sheathing by an auxiliary gas, wherein at least one throttle bore (8), which connects a pressure chamber to the passage chamber (7) in terms of flow, is provided of such a small diameter that, in the event of the gas pressure that is present in the pressure chamber on the side of said throttle bore that faces away from the passage chamber being greater than in the passage chamber, in addition to a throttling action, pressure equalization of precisely such a magnitude is realized that, in the passage chamber, the pressure does not drop as far as a critical pressure at which the fluid jet breaks up, and, on the side facing away from the pressure chamber, is acted upon with the gas in the pressure chamber (9) having the positive pressure present in relation to the pressure in the passage chamber (7), and the passage chamber (7) is bounded by an outlet opening (6) for the fluid jet (3), the outlet opening cross section A.sub.6 of which is larger than the cross section of the fluid jet (3), wherein the pressure p.sub.7 in the passage chamber (7) when the pressure p.sub.9 in the pressure chamber (9) is higher in comparison thereto is set, in particular adjusted, in such a manner that a positive pressure arises therein in relation to the external pressure p.sub.a.

9. The method as claimed in claim 8, characterized in that the pressure in the passage chamber (7) is set by changing the gas pressure in the pressure chamber (9).

10. The method as claimed in claim 8, characterized in that the pressure in the passage chamber (7) is set by changing the cross section of the throttle bore (8) and/or of the outlet opening cross section.

11. The method as claimed in claim 8, characterized in that the pressure in the passage chamber (7) is set by changing the viscosity of the gas in the pressure chamber (9).

Description

[0027] Further advantages, use possibilities and details of the present invention will now become clear with reference to the description of the figures. In the drawing:

[0028] FIG. 1 shows a simplified schematic view of a coupling device for a laser beam processing device according to the prior art;

[0029] FIG. 2 shows a schematic section view of a coupling device according to the invention;

[0030] FIG. 3 shows a coupling device according to the invention according to FIG. 2 during the processing of a workpiece surface in a cavity;

[0031] FIG. 4a) shows the coupling device according to the invention according to FIG. 2, but without an air jet and with a longer laminar length of the fluid jet;

[0032] FIG. 4b) shows the coupling device according to the invention according to FIG. 2 with a shorter laminar length of the fluid jet and an air jet; and

[0033] FIG. 5 shows the coupling device according to the invention according to FIG. 2 with an enlarged illustration of fluid nozzles and insert with indication of the fluid flows.

[0034] The coupling device, which is illustrated in FIG. 1, according to the prior art serves for a laser beam processing device, wherein FIG. 1 shows a workpiece surface 14 on which a fluid jet 3 with a laser beam 2 coupled therein strikes for the processing thereof. A protection window 16 is provided in order to separate the dry portion of a laser beam 2 and the fluid portion of a fluid jet 3. A lens (not illustrated) serves to focus the laser beam 2 on the fluid jet. A fluid nozzle 5 is functionally coupled to the protection window 16 leaving a gap for receiving a fluid, e.g. water, from a fluid source or fluid chamber 15. The nozzle 5 has an opening through which the fluid emerges as a fluid jet 3. The nozzle 5 opens in the direction of a passage chamber 7 which serves inter alia for improving the laminar flow of the fluid jet 3. An auxiliary gas flow 21 is supplied from a gas source 20 into the passage chamber via a separate feed line. The auxiliary gas flows in the direction of the fluid jet 3 and sheaths the latter until it emerges from the passage chamber 7. An insert 10 is provided below the nozzle 5, the insert downwardly closing the passage chamber 7 and guiding the fluid jet 3 in the interior. The insert 10 is configured in such a manner that a pressure chamber 9 is formed on its exterior, the pressure chamber serving for forming an air jet or a gas jet 17 and being acted upon in a corresponding manner with this gas from a gas source 19. At the outlet of the housing 4 of the coupling device 1, an annular gap is formed around the lower, protruding end of the insert 10, via which a circular ring-shaped air jet 17 emerges and surrounds the fluid jet at a distance. The air jet 17 is formed parallel here to the fluid jet 14. In the case of this known coupling device, the insert has a physical separation between the gas jet or air jet 17 and the fluid jet 13. This means that the fluid jet 3 and the gas jet 17 leave the coupling device through two different nozzle openings which are separate from each other. By means of the physical separation of the fluid jet from the gas jet, it is possible for an independent control of the gas jet 17 conducted onto the workpiece surface to be conducted, i.e. the parameters of the gas jet can be controlled independently of those of the fluid jet 3. This relates in particular to the pressure and the volumetric flow, and therefore very good conditions for displacing the water present on the workpiece surface or accumulating there can be provided, specifically in such a manner that the gas jet 17 does not enter into negative interaction with the fluid jet 3, into the interior of which the laser jet is coupled for machining the workpiece surface 14. The outer sheath-like surface of the insert 10 extends parallel to the passage direction of the fluid jet 3 in the interior of the insert such that the gas jet, which is configured as an annular jet, runs parallel to the fluid jet 3.

[0035] The passage space 7 in the interior of the coupling device has, in the interior of the insert, a diameter or a cross section which is larger than the direct outlet cross section of the insert through which the fluid jet leaves the insertsheathed with the auxiliary gas supplied from the gas source. The aperture-like diameter d.sub.3 of the outlet opening of the insert is significantly smaller than the inside diameter d.sub.4 of the insert with this part, configured there, of the passage chamber 7.

[0036] This known coupling device is intended to ensure sheathing of the fluid jet 3 by means of the auxiliary gas, which is introduced in addition to the gas jet 17 into the interior of the passage chamber 7 and the interior of the insert 10 and originates from the gas source 20, so that the fluid jet conveys as few as possible if any air molecules on its surface from the passage chamber 7 into the exterior and at the same time is not disadvantageously influenced in relation to the substantially stationary air otherwise surrounding the fluid jet. For this purpose, however, an increased structural outlay for an additional gas source 20 with the corresponding lines, feed lines and insertions into the interior of the coupling device 1, i.e. the interior of the passage chamber 7, is required.

[0037] FIG. 2 illustrates a coupling device 1 according to the invention which avoids the disadvantages of the prior art. In a manner known per se, said coupling device 1 according to a first exemplary embodiment has a housing 4 in which a protection window 16 is provided above a fluid nozzle 5. An intermediate space is provided between the protection window 16 and the fluid nozzle 5, into which intermediate space the fluid, preferably water, is supplied in order to emerge via the fluid nozzle 5 as a fluid jet 3 into the passage chamber 7 below the fluid nozzle 5. A laser beam converging by means of a lens (not illustrated) is inserted into the coupling device 1 in such a manner that the focus thereof lies directly in the fluid nozzle 5 and is coupled as a focused laser beam into the fluid jet 3 in the fluid nozzle 5. Below the fluid nozzle 5, an insert 10 is provided in the interior of the housing 4 of the coupling device 1, the insert separating the passage chamber 7 for the water jet from a pressure chamber 9, which is arranged around the outer sheath surface of the insert 10, for a gas jet 17, which is also referred to as an air jet. The insert 10 projects in relation to the housing and the outer sheath surface of the insert 10 through a gas outlet nozzle 11, and therefore the latter is configured as an annular nozzle around the outer sheath surface of the insert. The pressure chamber 9 is acted upon via a supply of gas, preferably supply of air, inserted into the housing. The gas jet 17, which is of annular configuration, is provided to strike on the workpiece surface (not illustrated in FIG. 2) and there to displace the water conveyed with the fluid jet 3 onto said workpiece surface or the conveyed fluid such that the fluid jet with the laser beam does not first have to penetrate a fluid wall or a fluid layer before the laser beam can pass to the location for the processing of the workpiece surface.

[0038] An outlet opening 6, which corresponds in FIG. 2 to the inner diameter of the insert for the fluid jet 3, is provided at the lower outlet end of the insert 10. Said inner diameter of the insert is configured to be significantly larger than the fluid jet 3 itself, which is configured to be hair thin. A collar-like flange, in which throttle bores 8 are present, is provided in the upper region, pointing toward the fluid nozzle 5, of the insert 10. The throttle bores 8 have a very small diameter, i.e. a very small cross-sectional area, and connect the pressure chamber 9 to the passage chamber 7. In this exemplary embodiment, the throttle bores are oriented parallel to the longitudinal axis of the insert.

[0039] During operation of the laser beam processing device, the fluid jet, which emerges at high speed from the fluid nozzle 5 and is conducted through the passage chamber 7, continuously entrains air molecules. Despite the laminarity of the fluid jet, the latter has a certain roughness on its surface, as a result of which the air molecules are entrained. During the operation, it may therefore happen that the pressure in the passage chamber 7 drops due to the discharge of air molecules. If the pressure reaches a defined critical value here, i.e. a negative pressure, there is the risk of the fluid jet fanning out, i.e. merging into a spray-like form, which is also referred to as a critical jet evaporation point. In this exemplary embodiment according to the invention of the coupling device 1 in the collar-like flange of the insert, the formation of throttle bores 8 is therefore provided. Said throttle bores make it possible to equalize the possibly resulting negative pressure in the passage chamber 7 in relation to the gas pressure in the pressure chamber 9. The relatively large diameter of the inner passage region of the insert 10, which extends as far as the outlet opening 6 for the fluid jet 3, equally serves to provide for a certain pressure equalization at any rate at the outlet region from the passage chamber 7. However, said larger diameter has the disadvantage that, during a possible flow back into the interior of the passage chamber 7, dirt particles are conveyed in at the same time which may accumulate on the nozzle and therefore, after a certain operating time, lead to an interruption in the reliable operation of the coupling device and require cleaning of the latter. The gas jet 17 which emerges via the annular gas outlet nozzle 11 is spaced apart from the fluid jet 3, and, although it surrounds the latter annularly, it initially does not have any direct contact with the fluid jet. The gas jet 17 serves to displace the fluid conveyed with the fluid jet 3 onto the workpiece surface, which is not illustrated in FIG. 2, and therefore the laser beam 2 which is coupled into the fluid jet 3 can strike directly and without obstruction against the workpiece surface. Above all, the annular gas jet 17 also serves to displace fluid which possibly accumulates in a cavity present in the workpiece surface, and therefore the device according to the invention can also be used to process workpiece surfaces which lie within a cavity and which would only be able to be processed to a limited extent at most without a gas jet for displacing said fluid.

[0040] According to the invention, the passage cross section of the throttle bores 8 is now dimensioned relative to the cross section of the outlet opening 6 and therefore of the passage region of the fluid jet 3 by the insert according to this exemplary embodiment. This dimensioning is carried out in such a manner that the outlet opening cross section of the outlet opening 6 is larger than the cross section of the throttle bores. Said cross section is preferably twice the size of that of the throttle bores. As the outlet opening cross section, the resulting outlet opening cross section which arises from the cross section of the inner diameter of the insert 10 reduced by the cross section of the fluid jet 3 is appropriate here for the dimensioning.

[0041] FIG. 3 shows a further exemplary embodiment of a coupling device 1 according to the invention in which the striking of the fluid jet, into which the laser beam 2 is coupled, is directed onto a workpiece surface 14 of a workpiece 12 and strikes there, specifically without the fluid jet 3 having to penetrate through a fluid column because the gas jet 17 strikes against the fluid collecting in the cavity 13 and removes the fluid 18, which is to be displaced, outward over the edge of the cavity. This ensures that the fluid jet strikes directly on the workpiece surface 14, which is to be processed, at the bottom of the cavity. The basic design of the coupling device 1 is very similar to that according to FIG. 2, and therefore the individual components will not be explained once again here. In contrast to FIG. 2, the insert 10, which is provided in this exemplary embodiment, is provided with an outlet opening 6 which is reduced in relation to the inner passage diameter. Said outlet opening 6 is configured in the form of an aperture-like constriction or an aperture-like tapering and ensures that the outlet opening 6 is specifically of such a size that the fluid jet can readily leave the interior of the passage chamber 7 without sheathing with a gas jet, but too great a flow of external air or external gas back through the outlet opening 6 into the interior of the passage chamber 7 is minimized because of a negative pressure which may be formed. This prevents or at least greatly reduces dirt particles entering the interior of the passage chamber 7.

[0042] The dimensioning of the cross sections of the throttle bores and of the resulting outlet opening cross section 6 takes place in such a manner that the pressure in the passage chamber is formed as uniformly as possible and has such a value that, in the passage chamber 7, there is either no positive pressure in relation to the external pressure or at least no positive pressure in relation to the pressure in the pressure chamber 9. With the coupling device 1 according to the invention, it is thereby prevented that, even during longer operation, a negative pressure is formed in the passage chamber 7 that is in the vicinity of a critical negative pressure, from which the fluid jet breaks up and becomes a spray, as a result of which the operation of the coupling device would no longer be ensured. This specifically does not occur in the case of the coupling device according to the invention, specifically without, as is provided in the prior art, an additional auxiliary gas directly enclosing the fluid jet together with corresponding lines, pressure containers, etc., having to be provided. The coupling device according to FIG. 3 is structurally particularly advantageous and simple in comparison to that according to the prior art.

[0043] FIG. 4a) illustrates a coupling device according to FIG. 3, specifically without a gas jet 17 having to be provided. Such an arrangement is possible above all if the workpiece surface to be processed is either convex or at least flat at the processing point from where the water conveyed with the fluid jet to the processing point or the conveyed fluid can flow away. The advantage of processing a workpiece surface with a laser beam 2 coupled in a fluid jet 3 consists in that the laminar length of the fluid jet is greater than if an annular gas jet is present, as is illustrated in FIG. 4b).

[0044] In FIG. 4a), the insertsimilarly as in the exemplary embodiment according to FIG. 3has, in the upper collar region, throttle bores 8 which connect the passage space 7 to the pressure chamber 9 in which external pressure prevails in the present exemplary embodiment. The fluid for the fluid jet 3 passes via a feed line and a fluid chamber 15 to the fluid nozzle 5 from which the fluid jet emerges and in which the laser beam 2 is coupled via a protection window 16.

[0045] FIG. 4b) illustrates a coupling device according to FIG. 4a), in which, however, a gas jet is additionally conveyed into the pressure chamber 9, said gas jet emerging from the pressure chamber in the form of a gas jet 17 of annular configuration from the coupling device 1. The remaining design corresponds to that according to FIG. 4a). Since the annular gas jet after emerging from the annular gas outlet nozzle fans open relatively rapidly, after a defined distance the annular gas jet touches the fluid jet. From this point, the fluid jet 3 is disturbed in respect of its laminarity, and the fluid jet 3 fans out. This is also referred to as an atomization point for the fluid jet 3. It becomes clear from FIGS. 4a) and 4b) that the annular gas jet does indeed have the advantage of displacing fluid accumulating in a cavity of a workpiece to be processed so that the fluid jet can reliably pass with the laser beam directly onto the processing point. However, because of its fanning out, the annular gas jet reduces the laminar length of the fluid jet after the latter has emerged from the outlet opening 6 at the lower end of the insert 10.

[0046] In the case of the exemplary embodiment according to FIG. 4a), the laminar length of the fluid jet is particularly large and is, for example, approx. 50 mm. By contrast, the laminar length in the case of the exemplary embodiment according to FIG. 4b) is smaller and is, for example, 30 to 35 mm. However, in both cases, said laminar length is sufficient because the distance between the outlet of the fluid jet and workpiece surface is generally approx. 20 mm. In the case of the exemplary embodiment according to FIG. 4b), a further advantage consists in that the annular air jet has a good protective effect for the fluid jet and therefore the laser beam coupled therein as far as the atomization point. This is of importance, for example, if the laser beam machining device is moved together with the coupling device over the workpiece surface during the processing and the protective effect of the air jet prevents the fluid jet with the laser beam coupled therein from being deflected or deformed.

[0047] Finally, FIG. 5 illustrates a coupling device 1 according to the invention according to FIG. 2, in which, in the enlarged illustration of the detail for the region of fluid nozzle 5, passage space 7 and insert 10, the pressure and flow conditions are indicated. All remaining elements or components correspond to those according to FIG. 2 or else FIG. 3, and therefore this is not discussed again here. In the figure, the letters placed between parentheses mean the following: [0048] (a) gas/air supply with the cross section A1 and the pressure p1, [0049] (b) pressure space with cross section A2 and pressure p2 in the form of a storage space, [0050] (c) throttle bore for equalizing the pressure between passage space 7 for the water jet 3 and the pressure chamber 9 with the cross section A3 and the pressure p3, [0051] (d) outlet opening for the fluid jet from the insert with the cross section A4 and the pressure p4, and [0052] (e) output of the annular gas jet 17 from the gas outlet nozzle 11 with the cross section A5 and the pressure p5.

[0053] For the dimensioning, it now is applicable that A1<A2>A3<A4 and in particular A5>A1. With regard to the pressures, p1>p2<p5. The air flow builds up as follows: the gas or the air flows via the feed line into the pressure chamber 9. The pressure chamber 9 is not a pressure accumulator since the output cross section, which is configured as an annular gap, for the gas is always larger than the cross section of the feed line for the gas or for the air. In particular, the output cross section is double the size of the cross section of the throttle bores 8. The passage space 7 for the fluid jet 3 has a resulting output cross section A4 which is larger than the cross section of the throttle bores A3. As a result, a positive pressure does not arise in the passage space 7. As a result, no air sheathing or gas sheathing to equalize the speed ratios between the fluid jet 3 and its surroundings arises either. On account of this configuration according to the invention of the insert with a defined output cross section 5 and the throttle bores 8, the pressure equalization with a negative pressure otherwise forming in the passage chamber 7 takes place automatically. The average pressure level in the passage space 7 is smaller than or at maximum equal to the external pressure. In many cases, this can be the ambient pressure. However, it is also conceivable for the device according to the invention to be encapsulated and to operate under pressure, wherein a gas may also be used instead of air depending on the requirement conditions.

[0054] Via the dimensioning and the control of the pressure, the temperature and the viscosity of the fluids used, it is therefore possible to regulate the pressure in the passage space 7 of the coupling device according to the invention such that a continuous, permanent and reliable operation of the laser beam processing device can be ensured, wherein the outlay on apparatus is kept lower in comparison to that according to the prior art.

LIST OF REFERENCE SIGNS

[0055] 1 Coupling device [0056] 2 Laser beam [0057] 3 Fluid jet [0058] 4 Housing [0059] 5 Fluid nozzle [0060] 6 Outlet opening [0061] 7 Passage chamber [0062] 8 Throttle bore [0063] 9 Pressure chamber [0064] 10 Insert [0065] 11 Gas outlet nozzle [0066] 12 Workpiece [0067] 13 Cavity [0068] 14 Workpiece surface [0069] 15 Fluid chamber [0070] 16 Protection window [0071] 17 Gas jet/air jet [0072] 18 Fluid to be displaced [0073] 19 Air jet gas source [0074] 20 Auxiliary gas gas source [0075] 21 Auxiliary gas flow