Method for joining workpieces arranged at least partially one above the other by means of at least one laser beam from at least one laser

Abstract

Method for joining workpieces (1, 2) arranged at least partially one above the other with different melting, boiling and / or decomposition temperatures or temperature-sensitive workpieces (1, 2), wherein at least one workpiece is a hot crack-sensitive workpiece, by means of at least one laser radiation (3) of at least one laser, comprising the following steps: - producing at least one depression (4) breaking through the first workpiece (1) by complete removal from the solid phase in the first temperature-sensitive or hot-crack-sensitive workpiece (1) facing the laser radiation (3) and - melting the second workpiece (2) arranged beneath the first workpiece (1) and made of a material which is less sensitive to temperature than the material of the first workpiece (1) by reducing the intensity with increasing distance from the laser focus and the partial scattering and absorption in the region of the depression (4) breaking through the first workpiece, wherein a targeted partial boiling of the molten material of the second workpiece (2) coupled with a defined scanning speed of the laser drives the melt against the feed direction into the depression (4) above, the first workpiece (1) is wetted in the depression (4), the melt solidifies upon contact with the wall of the depression (4), so that a wall material which is partially melted on the surface and interlocked with the solidified melt is present and a solid and / or tight joint (7) is formed.

Description

The invention relates to a method for connecting workpieces arranged at least in regions one above the other with different melting, boiling and / or decomposition temperatures or temperature-sensitive workpieces, wherein at least one workpiece is a heat-crack-sensitive workpiece, by means of at least one laser radiation.Methods for joining with laser radiation are already known.Carbon dioxide lasers, for example, are used for welding workpieces. In this case, a high heat input takes place with a long action time, so that these lasers are not very suitable for joining workpieces made of brittle-hard or other hot-crack-sensitive materials. Only by an additional thermal treatment of the workpiece can it be welded without cracks.The publication DE 197 51 195 C1 discloses a method and a device for welding by means of laser radiation, which is suitable in particular for deep welding of a wide variety of materials. For this purpose, at least one laser beam is used, which simultaneously has two regions of different intensity by suitable beam shaping. The region of higher intensity is used for melting and that with lower intensity for enlarging the melted region. The irradiation of the workpieces with lower intensity furthermore leads to reduced temperature gradients and thus to a reduced cooling rate of the melt. Thermal stresses and a crack formation resulting therefrom cannot be ruled out.The publication DE 10 2009 051 336 A1 discloses a device and a use of brilliant laser radiation for welding, for glazing or both for welding and for glazing workpieces made of brittle-hard or other materials sensitive to hot cracks. For this purpose, a brilliant fiber or disk laser with a power greater than 50 W is used as the laser, wherein the laser radiation of the laser has a wavelength in the range equal to / greater than 0.5 μm and less than / equal to 2 μm. Furthermore, the optics or the scanner is connected to a control device in such a way that the laser radiation is moved with a focus of less than 75 μm and at a speed of 10 m / min to 300 m / min over the machining point for crack-free welding, glazing or welding and glazing, wherein no thermal post-treatment is necessary. A specific method for joining workpieces having different melting, boiling and / or decomposition temperatures, temperature sensitive workpieces or workpieces, wherein at least one workpiece is a hot crack sensitive workpiece, is not disclosed.Document EP 0 628 376 A1 discloses a method for connecting a metal element and a semiconductor element, wherein the metal element has a hole. A semiconductor element is positioned adjacent to the hole of the metal element. By supplying a controlled amount of heat, an amount of the semiconductor material that flows into the hole and reacts with the metal material melts. The formation of the hole in the metal member and the supply of the controlled amount of heat may be performed with a single laser beam.The document JP 2007-287 991 A includes a method for semiconductor production with a connection of a metal element to a semiconductor element, wherein the semiconductor material is melted.The document JP H08-332 582 A discloses a laser welding method, wherein parts made of copper and aluminum are connected to one another, for example.JP S57-91 895 A discloses a welding method with a laser beam, wherein an additional material is used in an opening of one of the workpieces for connecting two workpieces. The energy density of the laser beam is reduced with the filler material.The publication DE 10 2013 109 588 A1 contains a melting-on connecting method of two workpieces, wherein one of the workpiece regions is melted zone by zone, the corresponding, melted material flows around the other workpiece region and thus holds it firmly by form locking.The invention specified in claim 1 is based on the object of easily joining workpieces of different materials by means of laser radiation.This object is achieved with the features set out in claim 1.The method for connecting workpieces arranged at least in regions one above the other with different melting, boiling and / or decomposition temperatures or temperature-sensitive workpieces, wherein at least one workpiece is a workpiece sensitive to hot cracks, by means of at least one laser radiation of at least one laser is characterized in particular in that the workpieces are easily connectable to one another and connected thereto.The following steps are carried out for this purpose:generating at least one depression piercing the first workpiece by complete removal from the solid phase in the first temperature-sensitive or hot-crack-sensitive workpiece facing the laser radiation, andmelting the second workpiece arranged under the first workpiece from a material that is more temperature-insensitive than the material of the first workpiece by reducing the intensity with increasing distance from the laser focus and the partial scattering and absorption in the region of the depression piercing the first workpiece, wherein by a specifically generated partial boiling of the molten material of the second workpiece paired with a defined scanning speed of the laser the melt is driven counter to the feed direction into the depression lying above, the first workpiece is wetted in the depression, the melt solidifies on contact with the wall of the depression, so that a wall material partially fused on the surface and interlocked with the solidified melt is present and a solid and / or dense joint connection forms.In contrast to the known laser welding methods as heat-conducting welding or deep welding, no attempt is made in this joining process to establish a molten phase in both joining partners, since this inevitably leads, for example in the case of materials sensitive to hot cracks, to the breakage of the temperature-sensitive joining partner as a result of thermal stresses or volume changes in the case of solid phase transitions of various modifications of the base material. Rather, it is the basis here to remove the temperature-sensitive joining partner from the solid phase by means of suitable laser parameters with the lowest possible thermal load and to remove it completely along a defined structure / geometry as far as the underlying material more insensitive to temperature. During the subsequent entry of laser radiation into the underlying material, only this material is melted due to the reduction of the intensity with increasing distance from the laser focus and the partial scattering and absorption in the region of the depression penetrating the first workpiece. A selectively generated partial boiling of the molten subsurface material paired with a defined scanning speed of the laser drives the melt counter to the feed direction into the depression lying above and wets the first workpiece in the depression. The melt solidifies on contact with the wall of the depression. This leads to a wall material which is partly melted on the surface and interlocked with the solidified melt and / or to a formation of a surface alloy and / or transition phase of the materials of the workpieces. A tight and / or loadable connection is formed between the workpieces without stress cracks.The method is thus suitable, for example, for joining workpieces made of materials that are difficult to join, such as are metal and ceramic, for example, or for joining two materials of the same type, wherein a joining partner is temperature-sensitive. Ceramic sensors, for example pressure sensors for reactive atmospheres, can thus be joined to a base body made of solid ceramic by means of a thin-walled and easily brittle cover.In the connection, for this purpose, the first workpiece has at least one depression which is produced by removal by means of laser radiation of at least one laser and penetrates the first workpiece. Furthermore, the second workpiece has solidified melt in the depression, wherein the melt caused by exposure of the second workpiece in the region of the depression to laser radiation of the laser or of a further laser is present, such that the connection is formed by toothing of the workpieces and / or by forming a surface alloy from the materials of the workpieces and / or by forming a transition phase from the materials of the workpieces in the depression.The first workpiece and the second workpiece preferably form an overlap joint connection.Advantageous embodiments of the invention are specified in patent claims 2 to 12.The second step can take place according to the development of claim 2 directly after the first step or temporally after the first step. The melting of the second workpiece can thus take place directly after the removal of the first workpiece or temporally after the removal.Between the first step and the second step, according to the further development of claim 3, a means for improving the wetting is introduced into the depression piercing the first workpiece. In this way, in particular the surface tension of the melt can be reduced, so that the flowability of the melt is increased.According to the further development of claim 4, the laser radiation of a laser is used for forming the depression as a perforation of the first workpiece and for subsequent melting of the second workpiece in the perforation.According to the development of claim 5, the laser radiation of a first laser is used to form the depression as a perforation of the first workpiece and the laser radiation of a second laser is used to melt the second workpiece in the perforation.According to the further development of claim 6, a trench or hole is produced in the first workpiece as a depression penetrating the first workpiece, so that a linear or point-like joint connection is present.A plurality of joining connections arranged at a distance from one another are produced according to the development of claim 7. The workpieces are connected to one another by a sequence of linear and / or point-like joint connections.A plurality of first joining connections arranged at a distance from one another are produced according to the development of claim 8. Furthermore, at least one second joint is produced between the first joint connections in each case in such a way that the first joint connections and the further joint connections overlap in regions. A linear, tight joint connection is produced.According to the further development of claim 9, at least one joint connection having a sinusoidal, rectangular, triangular or saw-tooth shape and at least one linear joint connection are produced in such a way that the joint connections intersect. The tightness of the joint connection is thus increased. Randomly occurring joining defects are thereby insulated in islands between the joining connections.According to the further development of claim 10, at least two joint connections are each produced with a sinusoidal, rectangular, triangular, sawtooth-shaped form or a combination thereof such that the maxima and minima of the oscillations at least touch one another or the oscillations intersect one another. The tightness of the joint connection is thus increased. Randomly occurring joining defects are thereby insulated in islands between the joining connections.According to the further development of claim 11, after passing through the depression penetrating the first workpiece, the intensity of the applied brilliant laser radiation is so low that the material of the second workpiece is not predominantly removed.The fluence or the line energy of the applied brilliant laser radiation is, after passing through the depression piercing the first workpiece, according to the development of claim 12, so great that the material of the second workpiece is melted and driven into the depression piercing the first workpiece.An exemplary embodiment of the invention is in each case illustrated in principle in the drawings and is described in more detail below.The following are shown: FIG. 1 shows two workpieces which are connected to one another by the action of laser radiation, FIG. 2 shows a joint connection having the form of a sinusoidal oscillation and a linear joint connection, and FIG. 3 shows two joining connections each having the form of a sinusoidal oscillation.In a method for connecting workpieces 1, 2 arranged at least in regions one above the other with different melting, boiling and / or decomposition temperatures or temperature-sensitive workpieces 1, 2, wherein at least one workpiece is a heat-crack-sensitive workpiece, at least one depression 4 piercing the first workpiece 1 is produced in a first step by means of at least one laser radiation 3 of at least one laser, and in a second step the second workpiece 2 arranged under the first workpiece 1 is melted in the region of the depression 4. The connection is thus based on a cutting welding method.FIG. 1 shows two workpieces 1, 2 which are connected to one another by the action of laser radiation 3 in a basic illustration.Contrary to known laser welding methods such as heat-conducting welding or deep welding, a molten phase is not attempted to be established in both joining partners during cutting welding. In the case of a connection of very thin-walled functional ceramic to ceramic housing parts, for example, this would lead to the breakage of the temperature-sensitive joining partner as a result of thermal stresses or volume changes in the case of solid phase transitions of various modifications of the base material. In the case of an easy-to-join metal and ceramic, in which, owing to the greatly different melting and boiling or decomposition temperatures, it is frequently not possible to achieve a mixed phase of molten material of both joining partners, there is no common melting phase.Rather, the method is based on the fact that the temperature-sensitive joining partner is ablated from the solid phase by means of suitable laser parameters as short interaction times in the case of high-intensity pulses with the lowest possible thermal load and is completely removed from a material that is more temperature-insensitive along a defined structure / geometry as far as the second workpiece 2 lying below. Upon the subsequent entry of the laser radiation 3 into the underlying and more temperature-sensitive material of the second workpiece 2, the latter is only melted as a result of the reduction of the intensity with increasing distance from the laser focus, which is located at a suitable distance from the joining partners, and the partial scattering in the underlying material and in the depression 4 primarily piercing the overlying first workpiece 1. The distance can result from the thickness of the first workpiece 1. A targeted partial boiling with the generation of a vapor 6 of the molten subsurface material paired with a defined scanning speed of the laser drives the melt 5 counter to the feed direction into the depression lying above and wets it. The melt 5 solidifies upon contact with the wall of the depression 4. This leads to a wall material which is mechanically interlocked or melted on the surface and interlocked with the solidified melt 5 and thus to a tight and durable connection between the workpieces 1, 2 without stress cracks.In a first embodiment, workpieces 1, 2 made of 99% aluminum oxide ceramic and 96% aluminum oxide ceramic are thus joined to one another in an overlap.The first workpiece 1 made of aluminum oxide ceramic 99% is a membrane having a thickness of 300 μm, which is joined to the second workpiece 2 as a base body made of aluminum oxide ceramic 96%. The intensity of the applied brilliant laser radiation pulses is so high and the pulse duration is so short that the material of the membrane is predominantly ablated. The pulse duration can be 30 ns and the intensity 1.5*10 9 W / cm 2. However, the intensity is again attenuated so much after passing through the membrane that the base material is only predominantly melted and forced into the joining gap. The average power of the pulsed laser is preferably 300 W at a scanning speed of 3 to 9 m / min and a focus diameter of 20 μm. By means of the laser radiation 3, solid joining regions are thus produced which are spaced apart. By means of a plurality of irradiations, the joining regions are filled up in such a way that overlapping occurs. A continuous, firm and tight joint connection 7 is produced.In a second embodiment, workpieces 1, 2 made of aluminum oxide ceramic 96% and metal are thus joined to one another. The first workpiece 1 made of aluminum oxide ceramic 96% is a membrane having a thickness of 300 μm, which is joined to the second workpiece 2 as a base body. The base body consists of stainless steel. The intensity of the applied brilliant laser radiation 3 is so high and the stretching energy is so low that the first workpiece 1 made of ceramic located above is predominantly ablated. After passing through the membrane as the first body 1, however, the intensity is again so low that the base body made of stainless steel is only predominantly melted and driven into the joining gap. The melt wets the piercing depression 4 of the membrane and a continuous, firm and tight joint connection 7 is produced.FIG. 2 shows a joint connection having the form of a sinusoidal oscillation 7 aand a linear joint connection 7 bin a principal plan view.In a further embodiment, a joint 7 awith the shape of the sinusoidal oscillation and a linear joint 7 bintersecure.FIG. 3 shows two joining connections 7 a, 7 c, each having the form of a sinusoidal oscillation, in a principal plan view.In a further embodiment, the maxima and minima of sinusoidal oscillations of the joining connections 7 a, 7 ccontact one another. Of course, the joining connections 7 a, 7 cmay also be formed and thus be such that the oscillations intersect.Randomly occurring joining defects are thereby insulated in islands between the joining connections 7. The joint connection 7 has a statistically increased tightness.

Claims

Method for connecting workpieces (1, 2) arranged at least in regions one above the other with different melting, boiling and / or decomposition temperatures or temperature-sensitive workpieces (1, 2), wherein at least one workpiece is a heat-crack-sensitive workpiece, by means of at least one laser radiation (3) of at least one laser, having the following steps: - generating at least one depression (4) which penetrates the first workpiece (1) by complete removal from the solid phase in the first temperature-sensitive or heat-crack-sensitive workpiece (1) which points towards the laser radiation (3), and - melting the second workpiece (2) arranged below the first workpiece (1) from a material which is more temperature-insensitive than the material of the first workpiece (1) by reducing the intensity with increasing distance from the laser focus and the partial scattering and absorption in the region of the depression (4) which penetrates the first workpiece, wherein, by means of a specifically generated partial boiling of the molten material of the second workpiece (2) paired with a defined scanning speed of the laser, the melt is forced counter to the feed direction into the depression (4) lying above, the first workpiece (1) is wetted in the depression (4), the melt solidifies on contact with the wall of the depression (4), such that a wall material partially melted on the surface and interlocked with the solidified melt is present and a solid and / or dense joint (7) is formed.Method according to claim 1, characterised in that the second step takes place directly after the first step or that the second step takes place temporally after the first step.Method according to claims 1 and 2, characterised in that between the first step and the second step a means for improving the wetting is introduced into the recess (4) piercing the first workpiece (1).Method according to claim 1, characterised in that the laser radiation (3) of a laser is used for forming the depression as a perforation of the first workpiece (1) and for the subsequent melting of the second workpiece (2) in the perforation (4).Method according to claim 1, characterised in that laser radiation (3) of a first laser is used to form the depression (4) as a perforation of the first workpiece (1) and laser radiation (3) of a second laser is used to melt the second workpiece (2) in the perforation.Method according to claim 1, characterised in that a trench or a hole is produced in the first workpiece (1) as a depression (4) penetrating the first workpiece (1), so that a linear or punctiform joining connection (7) is present.Method according to claim 1, characterised in that a plurality of joining connections (7) arranged at a distance from one another are produced.Method according to claim 1, characterised in that a plurality of first joining connections arranged at a distance from one another are produced and that at least one second joining connection is produced in each case between the first joining connections in such a way that the first joining connections and the further joining connections overlap in regions and a continuous joining connection (7) is present.Method according to claim 1, characterised in that at least one joint connection (7a) having a sinusoidal, rectangular, triangular or saw-tooth shape and at least one linear joint connection (7b) are produced such that the joint connections (7a, 7b) intersect.Method according to claim 1, characterised in that at least two joining connections (7a, 7c) are produced each with a sinusoidal, rectangular, triangular, sawtooth-shaped form or a combination thereof in such a way that the maxima and minima of the oscillations at least touch one another or the oscillations intersect one another.Method according to claim 1, characterised in that the intensity of the applied brilliant laser radiation (3) after passing through the depression (4) piercing the first workpiece (1) is so low that the material of the second workpiece (2) is not predominantly removed.Method according to claim 1, characterised in that the fluence or the stretching energy of the applied brilliant laser radiation (3) after passing through the depression (4) piercing the first workpiece (1) is so great that the material of the second workpiece (2) is melted and driven into the depression (4) piercing the first workpiece (1).

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