GB2233114A

GB2233114A - Protecting laser focusing system from particles using a vortex

Info

Publication number: GB2233114A
Application number: GB9012412A
Authority: GB
Inventors: Konrad Kinkelin
Original assignee: INST NAT SCIENCES APPLIQ; Institut National des Sciences Appliquees INSA
Current assignee: INST NAT SCIENCES APPLIQ; Institut National des Sciences Appliquees INSA
Priority date: 1989-06-06
Filing date: 1990-06-04
Publication date: 1991-01-02
Also published as: CH681708A5; IT1247412B; IT9083400A0; FR2648737A1; IT9083400A1; DE3918363A1; GB9012412D0

Abstract

A power laser assembly includes an optical focusing system 12 for generating an output laser beam, and a trap 13 between the focusing system and a workpiece so as to prevent particles from the workpiece from damaging the focusing system. The trap 13 includes means for generating a vortex 23 centred on the axis 11 of the laser beam and deflects particles travelling along that axis. <IMAGE>

Description

DEVICE FOR A POWER LASER The invention relates to a device according to

the preamble of the main claim. Such lasers are in most cases C02 lasers having an output power of a few kilowatts. They are used, above all, in the welding, severing or application of materials. The light beam emerging from the laser is collected in front of the workpiece by a converging lens, which has, for example, a f ocal length of 17 cm. The diameter of the 10 lens is in the region of, for example, 30 to 50 mm. The lenses consist, for example, of ZN/Se. They cost approximately 3000 to 6000 French francs. As is also known otherwise from welding, severing, application or the like, hot splashes proceed out in all directions is in the f orm of a shower of sparks from the workpiece. The process is of the explosive type. If, for example, aluminum is welded or severed, then below the aluminum oxide layer a melt covered over by this layer is formed. In the interval of time until this layer rup20 tures, a considerable pressure is developed below it, until the liquid aluminum then sprays out in an explosive manner.

In the above indicated working steps, not only the concentrated laser beam but also gases are required. In this case, these may be protective gases i 2 such as, f or example, argon or nitrogen, which cover over the processing site or the gas concerned may also be, for example, oxygen, which can intensify the action of the laser beam on the workpiece.

The Zn/Se converging lenses exhibit high light transmittance. If a splash strikes this lens in the course of the abovementioned working steps, then this region of the lens absorbs so much energy from the laser beam that the lens is very rapidly destroyed.

This has a whole series of disadvantages: it is necessary to expend the costs of a new lens. Furthermore, the tool is stationary during the exchange. A stop is not favorable for the processing in so far as it is then seen later on the tool where is the interruption of working took place. A person skilled in the art is familiar with further disadvantages.

According to the preamble of the main claim, it is known to provide a trap for the particles spraying up. In some cases, in the trap baffles are provided, on which particles shooting up are intended to impinge. Furthermore, in the prior art gas has been blown into the cavity of the trap in a radial direction, which gas is then caused to flow to the

3 coaxial recess and to further noncoaxial recesses in the trap and has there left the trap. However, it has become evident that the radial gas jet and also the gas flowing to the coaxial recess cannot prevent the 5 damaging of the converging lens.

The object of the invention is to provide a solution in which it is ruled out, entirely or to a statistically substantially greater extent, that the particles thrown through the recess toward the lens can strike the latter.

According to the invention, this protective action is achieved by the features evident from the defining clause.

For this purpose, a spinning flow is thus is generated. As is known, this vortex theoretically has the speed of rotation without limit along the geometric longitudinal axis. In the vortex, this speed decreases in an outward direction, in accordance with the angular momentum law, and at the outside it 20 rotates most slowly. An infinitely high speed of rotation along the geometric longitudinal axis is, of course, in reality not achieved, and indeed on account of the internal friction. Nevertheless, the high speed i 4 of rotation is itself sufficient to deflect outwardly away from the axis by centrifugal f orces particles which f ly along the geometric longitudinal axis. Even if they have initially flown precisely along the geometric longitudinal axis, the imbalance and the asymmetry of their design then bring about a situation in which they are also then deflected outwards. There, they can be caught by baffles, soft walled claddings or the like.

By the features of claim 2, it is achieved that the inlet nozzle excites the vortex with the predominant part of the gas energy.

The features of claim 3 achieve a particularly good excitation of the vortex, in particular in is circumstances in which the inlet nozzle is effectively disposed tangentially.

By the features of claim 4, it is possible to excite the vortex at a plurality of positions, f or example offset by 1800, offset by 1200, offset by 900 20 and so on. However - depending upon the particular operating problem - it is also possible to supply only one inlet nozzle or however also two inlet nozzles and so on with gas. It would then be possible to operate all inlet nozzles in circumstances in which very many particles are spraying.

By the features of claim 5, it is achieved that the vortex is developed uniformly and moreover it is then possible to produce the inlet nozzle with an improved design, for example in an inlet nozzle ring.

By the features of claim 6, it is achieved that at the same gas pressure it is possible to generate angular momenta of the vortex which differ in magnitude, depending upon the activation of specific inlet nozzles.

The features of claim 7 give a particularly simple production and a vortex exhibiting a particularly ideal form.

By the features of claim 8, it is achieved that the tip of the vortex rotates particularly strongly and thus the splashes are thrown outwards equally from the outset.

By the features of claim 9, no special gas source is required for the vortex.

6 By the features of claim 10, adaptation is made to the types of gas employed in most cases.

By the features of claim 11, parameters are obtained such as they have successfully been tested in practice.

By the features of claim 12, the device itself remains sufficiently cool and it is possible to advance with it close to a workpiece.

The f eatures of claim 13 give a trap which does not cause obstruction when it is necessary to operate to a large extent in corners or other positions of poor accessibility.

By the features of claim 14, the gas remains longer in that region of the workpiece which is to be processed.

By the features of claim 15, it is possible to change over the trap very rapidly, depending upon which trap is suitable f or which mode of operation. The trap according to claim 13 is then, so to speak, the basic structure.

1 7 The features of claim 16 give a particularly simple mode of securing without disturbing that region in which the inlet nozzles are provided.

The features of claim 17 give, in addition, also a further positive connection between the flat base wall and the conical base wall.

By the features of claim 18, the spacing from the workpiece does not alter, irrespective of whether the conical base wall or the flat base wall is used.

The invention is now described with reference to preferred illustrative embodiments. In the drawing:

Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 shows a diagrammatic side elevation of a trap with vortex and lens, shows the plan view of Fig. 1, but without the lens. shows a radial cross section through a first part of a trap, shows the top view of Fig. 3, shows a cross section along the line 5-5 in Fig. 6 through a nozzle ring, shows a cross section along the line 6-6 from Fig. 5, Fig. 7 Fig. 8 Fig. 9 8 shows the plan view of a cover ring, shows a radial cross section through a part of a trap with a conical base wall, shows an axial cross section through a part, which can be screwed on, with a flat base.

Along a geometric longitudinal axis 11 a beam (not shown) of a power laser (not shown) emerges. The beam is concentrated by a lens 12. The focus is situated on the geometric longitudinal axis 11 below a trap 13. The lens 12 is situated in the region 14 above the trap. The trap 13 is substantially rotationally symmetrical in relation to the geometric longitudinal axis 11. It has a circular- cylindrical casing wall 16 of brass and a base wall 17 which extends radially to the geometric longitudinal axis 11. Both are made in one piece. Below the upper region 14, near the lens 12, a gas conduit 18 is provided, which receives compressed gas from a gas source (not shown). The mouth 19 of the gas conduit leads into the internal space 21 of the trap 13 and is disposed, together with the gas conduit 18, at least in its region close to the casing wall 16, in such a manner that gas flows in tangentially into the upper region of the internal space 21. Coaxially with the geometric longitudinal axis 11, the base wall 17 has a circular- 1 9 cylindrical recess 22, the diameter of which is, however, substantially smaller than the internal diameter of the casing wall 16. The result of this arrangement is that in operation a vortex 23 is developed, the flow paths of which are diagrammatically represented in Figs. 1 and 2. The vortex 23 is of the angular momentum type. The greater the spacing of a gas particle from the geometric longitudinal axis 11, the more slowly does that particle fly. In the region of the geometric longitudinal axis 11, the speed of rotation is thus greatest. Should a splash try to climb upwards through the recess 22 along the geometric longitudinal axis 11, then there is already in the recess 22 or is closely thereabove the greatest probability that it will be forced, by imbalance, centrifugal forces or the like, to adopt a trajectory leading away from the longitudinal axis 11 and the splash will then be deflected very rapidly outwards, so that it impinges on the internal surface of the casing wall 16. It is not shown that this casing wall 16 can be equipped internally with baffles and/or baffle plates. Furthermore, the internal wall 16 can be softly cladded, for example with metal wool, in order to absorb impinging particles. Where baffles are present, these can likewise be equipped with a thin layer of energy-absorbing material, so that the splashes cannot rebound of f again, but are retained firmly at the point where they impinge.

It can be discerned from the angular momentum law together with Figs. 1 and 2, that the speed of rotation is extremely high, quite substantially higher than the speed of the gas flowing in through the gas conduit 18.

According to Figures 3 and 4, which are represented to the scale 1:1, the casing wall 24 has a design coaxial with the geometric longitudinal axis 11. At the bottom, the base wall 26 is radial to the longitudinal axis 11. For reasons of good heat conduction, both walls have a considerable thickness, the dimensions of which can be discerned from the figures. The recess 27 is again coaxial and has at the top a counter sink 28, which promotes the penetration of the tip of the vortex into the recess 27. The lower surface 29 of the base wall 26 extends radially and is flat, so that the vortex which emerges at the bottom from the recess 27 and broadens out again can broaden out between the lower surface 29 and the upper surface of the workpiece 31. Figure 3 shows that by the invention, for example, blowing into the welding bed 32 11 does not take place to such a great extent as would be the case if gas with a purely axial direction of movement were to flow out of the recess 27 parallel to the geometric longitudinal axis 11. Thus, the welding bed 32 remains, by the invention, even in its liquid condition in a more undisturbed manner; this is of great importance as regards the quality of the weld seam.

At the top of the casing wall 24 a radial, circular securing flange 33 is provided, in which three securing holes 34 offset by 1200 are provided.

The nozzle ring 36 shown in Figures 5 and 6 to a scale of 1:1 is likewise made of metal. Its internal through bore 37 has an internal diameter in accordance with the internal diameter of the casing wall 24. It has three securing holes 37 corresponding to the securing holes 34, so that the two parts can be connected to one another by screws. Bores 39, 41, 42, 43 extending linearly open tangentially to the internal wall 38 of the securing hole 37. They become progressively larger in diameter ' and specifically the bore 39 has a diameter of 2 mm, the bore 41 a diameter of 3 mn, the bore 42 of 4 mm and the bore 43 of 5 mm. At the outer end region, the bores 39, 43 merge into 12 similarly designed stepped bores 44 with internal thread 46. Flexible gas hoses coming from a gas source can be screwed therein. In order that any complementary nuts present should find a flat bearing surface, millings 47 are provided perpendicular to the longitudinal extent of the bores 39. 41, 42, 43. The nozzle ring 36 f its in a gastight manner on to the securing flange 33. On to the securing flange 33 there fits in turn a retaining f lange 48, which is shown to a scale of 1: 1, is made of metal and the function of which is selfevident.

Figure 8, which is drawn to a scale of 1:1, shows the lower part of a trap without retaining flange and nozzle ring. It is coaxial with the geometric is longitudinal axis 11. The nozzle ring (not shown) fits on to a bead 49. A securing f lange 5.1 already serves for the purposes mentioned. Below the securing f lange 51 a short, circular side wall 52 is provided, which a conical base wall 53 extending at an angle of 340 adjoins from below. An external thread 54 is cut into the upper region of the base wall 53 and into the side wall 52. The base wall 53 does not terminate precisely as the vertex of a cone. Rather, a radial internal surface and a radial external surface 57 are provided, which are traversed by the coaxial recess 58. The base 13 wall 53 in this angular setting provides little obstruction to the outer zones of the vortex 23 which forms in operation, and thus permits a greater intensity of the vortex in its central region.

According to Figure 9, a cap is provided for the device according to Figure 8. The cap 59 has a coaxial rim 61, which has at its upper internal region an internal thread 62, which can be screwed on to the external thread 54. In other respects, the rim 61 in the screwed-on condition does not anywhere contact the base wall 53 in its obliquely extending region. In a downward direction, the rim 61 merges into a radial base 63, the lower surface 64 of which is likewise radial to the geometric longitudinal axis 11. A recess 66 has a frustoconical design with an angle of 340 corresponding to that angle at which the outer surface of the base wall 53 also extends. Moreover, in the screwed-in condition, the lower surface 64 is in alignment with the outer surface 57. Cooling bores 67 are provided in the relatively thick base 63, and cooling conduits 68 are provided on the base 63 outside the 340 cone angle.

The base wall 53 facing the workpiece 31 is coated with a thermal protection 69 made of suitable 14 material, such as graphite. The graphite is sprayed on to the base wall.

In the hitherto known designs, the lens 12 and its mount are a component per se, and likewise the trap 13.

According to an illustrative embodiment of the invention, it is, however, possible to combine the two, as is diagrammatically shown by Figure 1 and the gas then cools at least also the lower surface of the lens 12, so that the latter does not require any special cooling gas supply. In this case, the gas then has a lower cooling temperature, known to the expert world.

It is, however, also possible, by modifications within the scope of the invention, to achieve a situation in which the upper surface of the lens 12 is likewise cooled, such as, for example, by a second connecting socket. The rotary movement of the gas gives an improved, more gradient-free cooling than the previously employed transverse flow.

The lens 12 can also be replaced by any other device which collects the laser beam, such as, for example, one or more appropriately curved mirrors. Any focusing system can be employed.

t 1 16

Claims

CLAIMS:

1. A device f or a power laser which exhibits an optical focusing system at the exit, which device deflects the laser beam along a geometric longitudinal axis, having a trap, connected downstream of the focusing system, for particles spraying from the workpiece towards the focusing system, which trap is substantially coaxial with the longitudinal axis, exhibits a casing wall and a base wall, exhibits an inlet nozzle for gas and exhibits in the base wall a coaxial recess for the exit of the laser beam and of the gas, wherein the inlet nozzle together with the casing wall is an angular momentum generator.

2.

3.

The device as claimed in claim 1, wherein the inlet nozzle is disposed predominantly tangentially to the casing wall.

The device as claimed in claim 2, wherein the inlet nozzle is disposed from tangentially to + 20o.

4. The device as claimed in claim 1, wherein a plurality of inlet nozzles are provided.

17

5. The device as claimed in claim 4, wherein the inlet nozzles are disposed at the same height.

6. The device as claimed in claim 4, wherein all inlet nozzles have a different diameter.

The device as claimed in claim 4, wherein all inlet nozzles have the same diameter.

8. The device as claimed in claim 1, wherein the coaxial recess is the sole outlet for a vortex generated by the angular momentum generator.

The device as claimed in claim 1, wherein a gas source is connected to the inlet nozzle, which gas source emits a gas which is in any event required on the workpiece in the course of the operation of the laser.

10. The device as claimed in claim 1, wherein the gas is an inert gas and/or oxygen.

11. The device as claimed in one or more of the preceding claims, wherein the speed of the gas emerging from the inlet nozzle is in the 18 decameter range/sec., wherein the characteristic internal diameter of the trap is in the decacentimeter range, and wherein the gas throughput is in the deci-m3/h range to the lower M3/h range.

12. The device as claimed in claim 1, wherein the base wall exhibits a cooling device.

13. The device as claimed in claim 1, wherein the trap exhibits a coaxial, circular-conical base wall.

14. The device as claimed in claim 1, wherein the trap exhibits a coaxial substantially flat base wall.

15. The device as claimed in claim 13 and 14, wherein the flat base wall exhibits a coaxial mount rim, which can encompass the conical base wall and is detachably secured in the region thereof.

16. The device as claimed in claim 15, wherein the trap exhibiting the conical base wall exhibits in the region of its casing wall an external thread on to which the mount rim can be screwed by its 19 internal thread.

17. The device as claimed in claim 16, wherein the tip region of the conical base wall is fittingly received by a conical counter sink in the flat base wall.

18. The device as claimed in one or more of the preceding claims, wherein the tip of the conical base wall is flat perpendicular to the geometric longitudinal axis and, when the mount rim has been screwed on, is in alignment with the lower surface of the flat base wall.

19. The device as claimed in claim 10, wherein where a single inlet nozzle is present the gas is supplied in the form of a mixture.

20. The device as claimed in claim 10, wherein where a plurality of inlet nozzles are present each gas is supplied separately.

2 1. The device as claimed in claim 1, wherein the base wall is covered, on its side facing the workpiece, with a heat protection layer.

22. The device as claimed in claim 1, wherein the focusing system and the inlet nozzle have a position such that the gas also cools the focusing system at the same time.

23.

A power laser assembly including an optical focusing system for providing an output laser beam along an axis, and means f or generating a vortex around said axis so as to deflect particles travelling toward the focusing system.

24. A device for a power laser, the device being substantially as herein described with reference to the accompanying drawings.

Published 19910 at T.liePacrtOffice.State House.66 71 High Holborn, London WC 1R 4TP. Further copies maybe obtained from The PatentOffice. Sales Branch, St Mary Cray, Orpington. Kent BRS 3RD. Printed by Multiplex techniques ltd, St Maxy Cray, Kent. Con. l.87