WO2020254639A1

WO2020254639A1 - Method and device for processing a workpiece with a processing beam composed of at least two beam profiles

Info

Publication number: WO2020254639A1
Application number: PCT/EP2020/067209
Authority: WO
Inventors: Malte Kumkar; Felix Zimmermann
Original assignee: Trumpf Laser- Und Systemtechnik Gmbh
Priority date: 2019-06-21
Filing date: 2020-06-19
Publication date: 2020-12-24
Also published as: DE112020002981A5

Abstract

The invention relates to a method for processing at least one workpiece (10, 12), preferably for welding two workpieces (10, 12), having the step of supplying a processing zone (4) of the at least one workpiece (10, 12) with a processing beam (3), which is provided by a pulsed laser beam (2), preferably an ultrashort pulse laser beam, wherein the processing beam (3) is composed of at least two beam profiles (30, 32, 34) in the processing zone (4).

Description

METHOD AND DEVICE FOR MACHINING A WORKPIECE WITH COMPOSITION OF THE MACHINING BEAM FROM AT LEAST TWO BEAM PROFILES

Technical area

The present invention relates to a method for processing at least one workpiece, preferably for welding two workpieces, by means of short laser pulses and in particular by means of an ultra-short pulse laser beam. The method can be used to carry out processing steps known per se in the processing of workpieces, for example for cutting or for welding or for local heating or for introducing others

Modifications in the material of the workpiece or the workpieces. The method is also particularly suitable for machining at least one workpiece from one

transparent or partially transparent material such as a workpiece made of glass.

State of the art

For processing workpieces and in particular for welding two workpieces together, it is known to place the respective workpieces in a process zone by means of a

To apply the laser beam in order to generate a melt in the process zone acted upon by the laser beam by energy absorption, which forms a weld seam between the two workpieces after the melt has solidified.

It is known to place the process zone between the two workpieces to produce a weld between a transparent workpiece and a non-transparent workpiece or to weld two transparent workpieces. This is achieved by focusing the processing laser beam into the process zone in such a way that the energy input is highest in the area of the process zone, in order to generate a corresponding melt between the two workpieces in the process zone and then provide a weld seam accordingly after solidification. In this case, the processing laser beam passes through one of the transparent workpieces and is, for example, only focused into the process zone on the side of the workpiece opposite the entry area. The processing laser beam is focused into the material of one of the workpieces, into both workpieces and / or into the area of an interface between the two adjacent workpieces by means of appropriate optics and the associated beam shaping, in order to then form the respective process zone in this area.

When machining workpieces and especially when welding two workpieces together, the strong local energy input from the focused laser beam results in high temperatures in the process zone, which in the surrounding areas

Material areas are not available. Correspondingly, the heat required in the process zone for processing - for example for producing a weld seam - is supplied

Temperature stresses in relation to the surrounding material areas. Correspondingly, there can be tensions and / or cracks in the material in the area of the weld seam, which can result in a reduction in the quality of the joined materials.

This also applies to other local machining processes in which local volume or surface modifications are carried out. Even with these others

Machining method is the shape and size of the local volume or

Surface modifications limited by the permissible, from the registered

Stresses and cracks introduced by temperature gradients.

The temperature stresses that occur, in particular during the actual heat input, have a correspondingly limiting effect on the size and shape of the modification to be introduced in the process zone. In other words, the known welding processes are limited by the fact that the temperature stresses introduced by the local heat input should not exceed a certain level, which could lead to a structural change in the material, to cracks or to a poor quality of the weld seam or the workpieces joined together.

In addition, more complex components comprising several joining partners cannot be joined in a single pass with a simple standard focus. Presentation of the invention

Based on the known prior art, it is an object of the present invention to provide a method and a device for processing at least one workpiece, by means of which an improvement in the properties just described can be achieved.

The object is achieved by a method with the features of claim 1 and by a

Performing with the features of the independent device claim solved. Advantageous further developments result from the subclaims, the description and the figures.

Correspondingly, a method for machining at least one workpiece, preferably for welding two workpieces, is proposed, comprising the application of one

Process zone of at least one workpiece with a processing beam provided by a pulsed laser beam, preferably by an ultrashort pulse laser beam. According to the invention, the processing beam in the process zone is composed of at least two beam profiles.

The process zone is defined here by the area that is heated by the at least two beam profiles in the workpiece to such an extent that ultimately one in the process zone

Material modification, such as melting the material, is achieved.

For example, in a welding process in which at least two workpieces are to be joined to one another, the material melts in the process zone, so that after the melts have been joined and then solidified, a weld seam is formed accordingly in the area of the previous process zone. In the case of a temperature-induced material modification in the material of a workpiece, this also takes place in the process zone, so that the material modification remains in the workpiece in the area of the previous process zone.

Because the processing beam in the process zone is composed of at least two beam profiles, improved processing of the at least one workpiece can be achieved.

For example, a material processing with a higher

Focal position tolerance possible, so that a simpler alignment of the machining beam can be achieved, this being less sensitive to fluctuations in the geometry of the workpieces, to the flatness of workpieces at an interface or the precision of a

Feed device reacts. The movement of the feed device defines a Feed trajectory in the at least one workpiece that is to be traversed with the process zone.

Furthermore, processing, for example welding, on several interfaces of (partially) transparent materials can be achieved simultaneously in this way.

In other words, a higher throughput can thus be achieved in the machining process compared to, for example, welding only with a single spot, as was conventionally known.

Furthermore, gaps that are formed, for example, at an interface between two materials to be joined with one another, can be better bridged by the proposed method, so that the overall quality of the joining is improved. In particular, the proposed method enables some connections in the first place

Material combinations or processing qualities are made possible.

For example, transparent materials, such as aluminosilicate glasses, can be joined without cracks and with high strength using the proposed method.

With the proposed method, transparent materials with high thermal expansion, for example calcium fluoride, can also be joined particularly advantageously. This also applies particularly when there is a large gap of, for example, 5 to 10 μm between the individual workpieces, which gap must be bridged by means of the melt.

The other known advantages of joining with an ultrashort pulse laser, such as providing gas-tightness of the respective weld seam, good long-term stability of the machining result, and high optical quality of workpieces that include transparent materials, can also be achieved by the proposed method.

An ultrashort pulse laser provides laser pulses in the picosecond range or femtosecond range. The method can also be carried out with a short pulse laser, which provides pulses in the nanosecond range.

By composing the processing beam in the process zone from at least two beam profiles, it can also be achieved, for example, that the connection cross-section is enlarged and thus also an improved tolerance with regard to the position of the respective foci can be reached.

At least one of the beam profiles of the processing beam can be provided as a Gaussian beam profile, so that the beam profiles can be provided in a simple manner.

Depending on the application, the machining of at least one workpiece with a simple Gaussian beam profile is limited in terms of the focus position tolerance. In other words, the area in which the focus position can be varied is still a reliable one

Machining the workpiece, for example to produce a dense high-strength

Weld seam that can be generated is limited. The use of a Gaussian beam profile is thus limited to certain applications, also with regard to the strength of the resulting weld to be achieved. These advantageous applications are abandoned, for example, when the workpieces to be joined no longer lie almost perfectly flat on top of one another in the area of the desired weld seam and there is thus a gap between the workpieces.

In addition to Gaussian rays, other types of rays, in particular quasi non-diffractive rays, can also be used. Non-diffractive rays must satisfy the Helmholtz equation:

V ² U (x, y, z) + k ² U (x, y, z) = 0 and a clear separability into a transverse and a longitudinal dependence of the shape

U (x, y, z) = U _t (x, y) exp (ikzz). Here k = oo / c is the wave vector with its transverse and longitudinal ones

Components k ² = k _z ² + kt ² and Ut (x, y) any complex-valued function that depends only on the transversal coordinates x, y. The z-dependence in the direction of beam propagation in U (x, y, z) leads to a pure phase modulation, so that the associated intensity I of the solution

propagation-invariant or non-diffractive is: l (x, y, z) = | U (x, y, z) | ² = l (x, y, 0).

This approach provides different classes of solutions in different coordinate systems, such as Mathieu rays in elliptical-cylindrical coordinates or Bessel rays in circular-cylindrical coordinates. A large number of non-diffractive rays in good approximation, i.e. quasi non-diffractive rays, can be implemented experimentally. In contrast to the theoretical construct, these only lead to a finite performance. The length L of the propagation invariance of these quasi non-diffracting rays is also finite.

The focus diameter d ^GF o of a Gaussian beam, the Gaussian focus, or the diameter of the Gaussian steel or the Gaussian profile is determined by the second moments, i.e. the variance of the Gaussian curve, and the associated characteristic length, the Rayleigh length Z _R = TT (d ^GF o) ² / 4A, as the distance starting from the focus position at which the beam cross section has increased by a factor of 2.

Furthermore, we define the transverse dimensions of local intensity maxima as the shortest distance from directly adjacent, opposite ones as the transverse focus diameter or as the diameter of the beam profile in the case of quasi non-diffractive beams d ^ND o

Intensity minima.

The longitudinal expansion in the direction of beam propagation of these almost propagation-invariant intensity maxima indicates the characteristic length L of the quasi non-diffractive beam. This is defined by the intensity drop to 50%, starting from the local intensity maximum in the positive and negative z-direction, i.e. in the direction of propagation.

A quasi non-diffractive beam is present if, for d ^ND o = d ^GF o, i.e. similar transverse dimensions, the characteristic length L clearly exceeds the Rayleigh length of the associated Gaussian focus, for example if L> 10 ZR.

As a subset of the quasi non-diffractive rays, quasi-Bessel rays or Bessel-like rays, also called Bessel rays here, are known. Here, the transverse field distribution Ut (x, y) in the vicinity of the optical axis obeys a Bessel function of the first type of order n to a good approximation. The Bessel-Gaussian rays represent a further subset of this class of rays Generation are widespread. The illumination of an axicon in a refractive, diffractive or reflective design with a collimated Gaussian beam enables the Bessel-Gaussian beam to be formed. The associated transverse field distribution in the vicinity of the optical axis obeys to a good approximation a Bessel function of the first type of order 0, which is enveloped by a Gaussian distribution. As a result, a significantly greater focus position tolerance can be generated during welding. This reduces the influence of local waviness in the glass and the focus adjustment. Correspondingly, it can be advantageous to use a quasi non-diffractive beam, in particular a Bessel beam, for material modification, since this allows, among other things, larger gaps to be bridged and thus the focus position tolerance increases. The proposed method can thus be used in a further area of application - for example, even if the workpieces to be joined do not lie perfectly flat on one another in the area of the desired weld seam and there is accordingly a gap between the workpieces.

Furthermore, the welding of two workpieces made of transparent materials is simplified if the workpieces each have at least one at the respective boundary surfaces

Have transmission loss (without Fresnel losses) of less than 10%. In the case of glass, particularly silica glass, this is the case if the surface roughness is Ra <20 nm.

By assembling the beam profiles within the process zone to the

The machining beam can also ensure that the local energy input is distributed over a larger volume of material, so that the modifications induced in the material become less dependent on the surrounding material areas that are not exposed to the laser beam, which can lead to the material stresses induced in the materials be reduced or redistributed and thereby the quality of the processing and the quality and / or strength of the workpiece is improved.

The beam profiles are preferably present in the process zone at an angle to one another. By aligning the beam profiles at an angle in the process zone, better adaptation to the geometry of a workpiece interface to be machined can be achieved. Furthermore, by aligning the beam profile at an angle, it can be achieved that both a greater lateral exposure of the material volume with laser intensity is achieved and the beam profiles arranged at an angle can be aligned in such a way that overlapping is avoided and the energy input changes accordingly to a bigger one

Material volume distributed.

The present beam profiles can preferably be characterized by at least two different

Laser beams are introduced into the process zone, the laser beams being aligned at an angle to the surface normal of the workpiece, preferably at an angle between 0 ° and 45 °, particularly preferably between 5 ° and 40 °, very particularly preferably between 10 ° and 35 ° to Surface normals of the workpiece. This can be used laterally and / or Generate longitudinally shifted beam profiles, which are correspondingly in the

Process zone ensure that the connection cross-section and the focus position tolerance are increased. In particular, the beam profiles can be offset from one another in the feed direction, so that a point lying on the feed trajectory is swept at least twice in succession by the two laser beams arriving one after the other.

The present beam profiles and / or the workpieces can also be rotated during the advance so that the rotation results in a symmetrization of the connection cross-section, in particular with respect to the advance direction. The beam cross-sections can be rotated by rotating a beam-shaping unit. For example, with a fixed beam profile and a curved feed trajectory, connection cross-sections of different widths can occur, similar to the effect of calligraphy. If the feed direction is, for example, perpendicular in the process plane to a narrow axis of the beam profile, then the connection cross-section is small. If the feed direction is, for example, perpendicular to a broad axis of the beam profile, then the connection cross-section is large. This asymmetry can lead to different machining geometries and thus, for example, to differently fixed welded connections. By rotating the beam cross-section and / or the workpiece, connecting cross-sections of the same size can be generated over the entire length of the feed trajectory, even with curved feed trajectories. This makes it possible to introduce a material modification that is homogeneous in all directions.

The beam profiles can also be introduced in addition to the feed trajectory. A lateral offset means an offset in the plane whose surface normal coincides with the surface normal. A longitudinal offset means an offset along the

Surface normals, i.e. into the material of the workpiece.

At least two beam profiles with a lateral offset to one another and / or with a longitudinal offset to one another are preferably provided in the process zone. It can thus be achieved that the volume of the process zone is increased in order to also improve the connection cross-section and the focal position tolerance of the method in this way.

Preferably, the laser beam in the form of a Gaussian beam or a quasi non-diffractive beam, in particular one, can be used to adapt the beam shape to the respective geometrical configuration or requirements of the processing as well as to the material of the respective workpieces

Bessel beam are provided and / or at least one beam profile as a Gaussian

Beam profile or as a profile of a quasi non-diffractive beam, in particular as a Bessel profile to be provided. It is also possible to use longitudinally modulated beams, for example so-called bottle-shaped beams (“bottle beams”).

In a preferred development, the lateral offset between two beam profiles is greater than the transverse extent of the respective beam profiles involved, that is to say, in particular, greater than the diameter of the respective beam profiles.

In a preferred development, the longitudinal offset between two beam profiles is greater than the characteristic lengths of the respective beam profiles involved. The characteristic length serves here as a measure for the longitudinal extent of the focus area or the focus zone of the respective beam profile in the direction of beam propagation.

This ensures that the beam profiles overlap in the area of the

Process zone does not or hardly takes place, but an overlap of the melted area of the individual beam profiles in the process zone can take place. This ensures that the areas in which the energy of the pulsed machining beam is absorbed in the process zone are spatially separated from one another in the process zone.

The resulting melt volume, which is formed in the process zone, preferably includes all jet profiles. In other words, the energy input takes place locally distributed within the process zone in order to provide an enlarged process zone and thus also an enlarged connection cross-section, which leads to an improvement in the

Machining process can lead. For example, a larger connection cross-section can lead to greater strength.

In a preferred embodiment, the pulse energy of the laser pulses is modulated over time. The local energy input in the respective beam profiles can be modulated via the temporal modulation of the pulse energy of the laser pulses in order to reduce or avoid an excessive local input of energy in order to simultaneously prevent excessive stresses from occurring in the material.

At least two beam profiles can preferably be introduced into the process zone at the same time. It is particularly preferable for all beam profiles to be introduced into the process zone at the same time.

The beam profiles can also be modulated alternately so that the spatial

Energy input is modulated. This spatial modulation can also take place with a constant input power. Accordingly, it is not a sequential one Scanning the process zone through the individual beam profiles, but rather to provide a processing beam in the process zone, which is composed of (simultaneously) irradiated beam profiles.

According to a preferred exemplary embodiment, the same pulse energy is radiated into the process zone for each laser pulse as with an individually focused laser beam. According to the

However, according to the proposed method, this energy is distributed locally to different positions within the process zone in such a way that the absorption behavior of the material is better utilized and, on the other hand, it is prevented that an excessively high local energy input causes material changes or damage to the material lying outside the process zone.

In a preferred embodiment, at least two pulsed laser beams are provided for generating at least one beam profile each, which is used to assemble the

Processing beam can be introduced into the process zone at the same time. It can thus be achieved that differently pulsed for at least two different beam profiles

Laser beams are used so that, for example, the frequency and the energy of the respective pulsed laser beam and the wavelength of the incident light can be adapted to the geometry and the material of the respective workpiece.

A first laser beam for generating a first beam profile is preferably introduced into the process zone from a first direction with respect to a workpiece, and a second laser beam is introduced into the process zone from a second direction with respect to the workpiece to generate a second

Beam profile introduced in the process zone. The first laser beam and the second laser beam are preferably introduced into the process zone from essentially opposite directions, for example the first laser beam is introduced through the first workpiece and the second laser beam is introduced into the process zone through the second workpiece. The essentially opposite directions also include the fact that the laser beams do not run parallel to one another, but rather at an angle to one another.

The above-mentioned object is also achieved by a device for processing at least one workpiece having the features of claim 11. Advantageous further developments result from the dependent claims, the description and the figures.

Accordingly, a device for processing at least one workpiece, preferably for welding two workpieces, is proposed, comprising a beam source for provision a pulsed laser beam, preferably a beam of an ultrashort pulse laser, and an optical system for providing a machining beam in a process zone of at least one workpiece. According to the invention, the optics are set up and designed such that the processing beam in the process zone is composed of at least two beam profiles.

In this way, the advantages already described above for the method can be achieved, in particular the implementation of a particularly efficient method for processing workpieces, which can result, for example, in joining two or more workpieces, the connection cross-section and the focal position tolerance being improved here.

Correspondingly, an overall improved joining result can be achieved.

To form, adapt and adjust the position and alignment of the beam profiles, the optics preferably include a beam-shaping unit, preferably a spatial light modulator and / or a diffractive optical element and / or an acousto-optical deflector (AOD). Particularly in the case of the configuration with an active optical element such as an acousto-optical deflector, it is possible to easily and quickly adapt a material to the respective combination of materials of the workpieces or to the respective geometry of the workpieces to be joined

Adjustment of the machining beam can be achieved.

The device can also comprise a workpiece holder for receiving a workpiece, as well as at least one positioning system for positioning the laser and / or the workpieces.

In particular, the positioning of the laser and workpiece can also take place relative to one another and also during a movement.

The optics preferably comprise an axicon for forming a quasi non-diffractive beam profile, for example a Bessel profile, with at least one beam profile in the process zone being designed as a quasi non-diffractive beam profile, for example as a Bessel profile. By designing a beam profile as a Bessel profile, it can be achieved that a desired energy distribution is achieved in the material, which supports the joining or a desired geometry is provided for the beam profile which supports the joining of the workpieces to one another.

The optics preferably comprise focusing optics and the laser beam is introduced into the focusing optics offset with respect to the optical axis of the focusing optics in order to bring the beam profiles of the processing beam into the process zone at an angle. In order to achieve rapid adaptation of the optical configuration to the respective method, it is preferred that the optics be a beam-shaping unit, preferably a spatial unit

Light modulator and / or a diffractive optical element and / or an acousto-optical deflector (AOD), in order to provide the beam offset of the laser beam to the optical axis of the focusing optics.

The beam offset is in particular the offset of the beam axes in position and / or angle, which determines the angular and spatial offset of the beam profiles in the process zone. In particular, the laser beam with the focusing optics can be passed through several and separate elements in such a way that the laser beam is only absorbed in the desired process zone.

Furthermore, an aberration correction is provided, in particular for large angles of incidence, which can be designed as part of the focusing optics or the beam-shaping unit. The angle of incidence is understood here as the angle between the beam axis of the respective partial beam and the surface normal. An angle can be considered large if it is greater than 0.5 °, for example 1 °.

For example, an aberration correction may be necessary if a Gaussian beam with a large numerical aperture hits the material surface perpendicularly. It can be the case here, for example, that the aberrations also increase as the numerical aperture increases. For example, aberration correction may also be necessary if a Gaussian beam with a small numerical aperture does not strike the surface of the material perpendicularly.

For example, an aberration correction may also be necessary if a quasi non-diffractive beam, for example a Bessel beam, does not strike the material surface perpendicularly.

For example, aberration correction may be necessary if the material has a

has location-dependent variation of the refractive index. This can be the case with graded index lenses, for example. For example, aberration correction may not be necessary if a quasi non-diffractive beam hits the material surface perpendicularly.

The surface of the material to be processed can be curved, as is the case, for example, with a round, cylindrical or spherical material, so that an aberration correction analogous to the above examples may be necessary here too. In this way it can be achieved that an aberration of the laser beams due to large angles of incidence is prevented and this is pre-compensated, and the laser beam continues to be focused into the process zone as intended. For example, the aberration correction can also be used in such a way that a different one for one laser beam or a partial beam

Focusing plane is reached than for a different laser beam or partial beam.

In particular, the aberration correction can be carried out by a diffractive optical element (DOE). A DOE allows the laser beam to be spatially fanned out to a given geometry by means of diffraction structures. Because the diffraction

is wavelength-dependent, a DOE is suitable for minimizing aberration effects in an optical system, in particular a refractive lens system.

It is also possible for the individual laser beams or partial beams to fall through separate optical elements. In this way it can be achieved that the individual laser beams or partial beams can be focused independently of one another. In addition, the

Adjustment effort for the overall structure.

Brief description of the figures

Preferred further embodiments of the invention are illustrated by the following

Description of the figures explained in more detail. Show:

Figure 1 is a schematic representation of two workpieces, which at an interface

are placed against each other and in which a processing beam is introduced into a process zone, which is composed of three beam profiles,

FIG. 2 shows a schematic representation of three workpieces which are placed against one another at two interfaces and in which a machining beam is introduced into a process zone, by means of which the three workpieces can be joined together at their respective interfaces at the same time,

FIG. 3 shows a schematic representation of two workpieces into which two beam profiles are introduced, a first beam profile being introduced from a first side of the first workpiece and a second beam profile being introduced from a second side of the second workpiece,

Figure 4 A, B, C schematic representations of devices for processing at least one workpiece with feed, FIG. 5 microscope images of a process zone after a modification has been introduced into a

Workpiece with a processing beam which is composed of a beam profile, three beam profiles, five beam profiles and nine beam profiles, and

FIG. 6 shows a schematic comparison between Gaussian and quasi non-diffractive rays

Rays.

Detailed description of preferred exemplary embodiments

Preferred exemplary embodiments are described below with reference to the figures. Identical, similar or identically acting elements are provided with identical reference numerals in the different figures, and a repeated description of these elements is partially dispensed with in order to avoid redundancies.

In FIG. 1, the arrangement of two workpieces 10, 12 is shown schematically, which rest against one another at a common interface 14. In other words, the lower side of the upper workpiece 10 rests on the upper side of the lower workpiece 12. The interface 14 is correspondingly formed directly by the two workpieces 10, 12 resting on one another.

In order to join the two workpieces 10, 12 to one another at their common interface 14 and in particular to weld them to one another, a modification is made in the material of the workpieces 10, 12 by means of the energy of a pulsed laser beam 2.

The pulsed laser beam 2 is provided in the workpieces 10, 12 as a processing beam 3, which is composed of three different beam profiles 30, 32, 34 which are introduced into the material of the workpieces 10, 12 in a process zone 4.

The beam profiles 30, 32, 34 correspondingly jointly form the processing beam 3 in the process zone 4, by means of which the actual processing of the material of the workpiece 10, 12 is carried out in the process zone 4. In particular, the beam profiles 30, 32, 34 shown here are schematic illustrations of the corresponding Gaussian caustics of the Gaussian beams.

The three beam profiles 30, 32, 34 are formed and shown in FIG. 1 by the respective beams of the individual laser spots. The three beam profiles 30, 32, 34 are aligned with one another at an angle a1, a2. The angular alignment results from the configuration of an optical system not shown in FIG.

In other words, the beam profiles 30, 32, 34 are aligned at an angle a1, a2 to one another. The beam profiles 30, 32, 34 are therefore also inclined at an angle β1, β2, β3 with respect to the surface normal 110 of the workpiece 10. The surface normal 110 perpendicular to the plane which is formed by the surface 100 of the workpiece 10.

In particular, the angles a1 = 0 and a2 = 0, so that the rays run parallel to one another. If the angles ß1 = 0, ß2 = 0 and ß3 = 0, it is a normal incidence, i.e. an incidence of the laser parallel to the surface normal.

Furthermore, in the exemplary embodiment shown, the beam profiles 30, 32, 34 are also arranged laterally offset from one another in addition to their angular alignment. In this case, there is preferably no or only an insignificant overlap between the individual beam profiles 30, 32, 34.

The angular alignment and the lateral offset of the individual beam profiles 30, 32, 34 achieve an expansion of the volume of the process zone 4, so that a correspondingly enlarged connection cross-section is achieved. The melt volume is in the

Process zone 4 and defines the connection cross-section. It can also be achieved that due to the increased volume of the process zone 4, a more reliable processing of the workpieces 10, 12 can be achieved and in particular a more reliable weld seam can be provided between the workpieces 10, 12, since the increase in the process zone 4 also increases the melt volume increased in process zone 4. This can be of particular importance if the two joining partners, for example the two workpieces 10, 12, have poor flatness at their interface 14 or have gaps which have to be bridged. As a result of the larger process zone, more melt can be generated in order to bridge the gaps between the workpieces 10, 12 or it can be ensured that melt can also be provided to bridge a larger gap between the two workpieces to be connected.

At the same time, the enlargement of the process zone 4 ensures that the temperature input through the absorption of the machining beam 3 in the material of the workpieces 10, 12 is distributed over a larger volume and, accordingly, the temperature load of the process zone 4 surrounding areas can be reduced, since the respective temperature gradients are lower.

At the same time, by distributing the energy provided via the laser beam 2 to a larger volume of material within the workpieces 10, 12, excessive heating of a small area within the process zone 4 is avoided and a larger material area is heated instead. In this way, stresses that arise in the areas around the process zone 4, in particular stresses that result from temperature gradients to the surrounding material during processing (transient stresses) or that result from different cooling rates of the workpieces (remaining residual stress), can be the workpieces 10, 12 are reduced.

The individual beam profiles 30, 32 shown here are, in addition to their lateral offset, as can be seen from FIG. 1, also shifted longitudinally to one another. Correspondingly, a corresponding focus position tolerance can be achieved, which enables easier process control, since an exact alignment and tracking of the foci of the processing beam 3 in the process zone 4 is not necessary or is not necessary to the extent that is necessary when using a conventional individual focus would.

To introduce the laser energy into the workpieces 10, 12 in the area of the interface 14, the workpieces 10, 12 are preferably transparent or partially transparent for the light of the laser beam 2. Accordingly, a modification of the material of the workpiece 10, 12 can also be made within the respective material lying areas or on one of the

Surface 100 of the workpiece 10, which here serves as an entry surface for the laser beam 2, can be carried out on the side facing away from the workpiece 10. In other words, the energy input can be carried out through the beam profiles 30, 32, 34 within the material or between the workpieces 10, 12, in particular also at the interface 14. This allows the two workpieces 10, 12 to be welded together - virtually through the workpiece 10 through - can be achieved.

In the exemplary embodiment shown, the beam profiles 30, 32, 34 are each Gaussian profiles. Depending on the desired area of application, the beam profiles 30, 32, 34 can, however, also have other beam shapes and are designed, for example, as quasi-non-diffractive beam profiles, for example as Bessel profiles. The individual Gaussian beam profiles 30, 32, 34 are so far apart from one another in the process zone 4 that the beam profiles do not or hardly overlap.

In particular, the distance between the beam profiles 30, 32, 34 is preferably greater than their lateral extent and in particular the diameter of the beam waist.

The three beam profiles 30, 32, 34 can preferably have a lateral offset to one another which is greater than the beam waist.

The three beam profiles 30, 32, 34 can also preferably have a longitudinal offset to one another which is greater than the Rayleigh length of the respective beam profiles.

The offset between the beam profiles 30, 32, 34 is to be seen as the absolute distance between the individual beam profiles 30, 32, 34, which is determined accordingly between the positions of the respective beam waist.

For example, in the case of a vertical alignment of the beam profiles 30, 32, 34 in the direction of the surface normal 1 10 of the workpiece 10, the distance can be determined in a plane which is perpendicular to the surface normal 1 10 and thus also perpendicular to the direction of irradiation of the respective, the Machining beam 3 making up laser beam 2 lies.

If, on the other hand, the Gaussian beam profiles 30, 32, 34 are arranged at an angle to one another, the distance is determined by a straight connecting line between the respective geometric focal points or the focal zones. This connecting line does not necessarily lie in one that is predetermined by the respective Cartesian coordinate system

Main level. In other words, the connecting line for determining the distance between the individual beam profiles 30, 32, 34 can lie in any orientation within the volume of the respective workpiece 10, 12.

The beam profiles 30, 32, 34 can in particular have an offset, in particular a lateral offset, which is arranged in both lateral dimensions, i.e. within a plane perpendicular to the direction of incidence of the laser beam 2 or the processing beam 3. In particular, it is also possible, for example, to generate rotationally symmetrical beam profiles - for example, by forming beam profiles that are concentrically arranged and spaced apart from one another. Correspondingly, the three beam profiles 30, 32, 34 in the process zone 4 are offset from one another, which can be pronounced laterally and / or longitudinally, in such a way that the distance between the beam profiles 30, 32, 34 is so large that an overlap is not or only takes place insignificantly - based on the energy input into the process zone 4.

In other words, the beam profiles 30, 32, 34 are arranged in the process zone 4 in such a way that the respective absorption areas of the processing beam 3 for the individual beam profiles 30, 32, 34 do not overlap. The in the process zone 4 by the absorption of the energy of the

By contrast, the melting zone produced by the ultrashort pulse laser 2, which in this exemplary embodiment essentially corresponds to the volume of the process zone 4, is designed in such a way that it encompasses all absorption areas (that is to say all beam profiles) of the processing beam 3.

Correspondingly, energy is introduced through the absorption of the individual pulses

Ultrashort pulse laser in the process zone 4 in different, non-overlapping local volumes of the process zone 4 instead. The one resulting from the energy input

However, an increase in temperature, which ultimately leads to the modification of the material present in the process zone 4, in particular to its melting, is present in an area which comprises at least two beam profiles 30, 32, 34, preferably all beam profiles 30, 32, 34. The connection of the energy introduced into the individual absorption areas of the beam profiles 30, 32, 34 to a common modification area or to the process zone 4 is achieved via heat diffusion processes within the material of the workpieces 10, 12.

This results in a spatially separate distribution of the individual

Energy absorption of the irradiated ultrashort pulse laser 2 within the process zone 4, but the resulting melting range is designed to be coherent.

The beam profiles 30, 32, 34 can also be provided in the form of a quasi non-diffractive beam profile, for example a Bessel profile. For this purpose, the incoming laser beam 2 or the processing beam 3 is processed via appropriate optical elements, for example by providing an axicon, which can lead to the formation of quasi non-diffractive beam profiles, for example Bessel profiles, in the process zone 4.

By providing the at least two beam profiles 30, 32, 34 in the process zone 4 when an ultrashort pulse laser is used, the material of the respective workpiece 10, 12 is melted locally in the area of the process zone. In other words, by bringing in the ultrashort laser pulses in the process zone 4 and the respective absorption of pulsed laser energy in the process zone 4, a modification of the material is written.

If, for example, ultrashort laser pulses are focused in the material volume of glass, for example quartz glass, the high energy present in the respective focus leads to non-linear absorption processes, whereby the corresponding material modifications - depending on the respective laser parameters - a corresponding material modification can be induced in the material.

If the time interval between the individual ultrashort laser pulses is shorter than the typical heat diffusion time of the respective material in the process zone 4, and in particular of the respective glass material, the temperature in the area of the focus increases by a

corresponding heat accumulation from pulse to pulse. With an appropriate dimensioning, this increase in temperature can lead to a local melting of the material in the area of the process zone 4. If the modification mentioned, i.e. the melting of the material in the area of the process zone 4, is arranged in the interface 14 between the two workpieces 10, 12 or is induced in the area of the interface 14, after the material has melted and the melt subsequently cooled , a stable connection between the workpieces 10,12 can be achieved.

When welding transparent workpieces 10, 12 or when welding an (upper) transparent workpiece 10 with an underlying opaque workpiece 12, welding takes place through the upper joining partner, i.e. the transparent workpiece 10, with a focus in the interface 14 between the two workpieces 10.12 takes place.

In the course of the heat accumulation of the laser pulses from pulse to pulse, the

Absorption zone due to the melting of the material in the process zone 4 in the direction of the beam incidence of the ultrashort pulse laser, so that in a conventional welding process a weld seam elongated longitudinally in the direction of the beam incidence of the ultrashort pulse laser results.

Due to the composition of the processing beam 3 in the process zone 4 proposed here from at least two beam profiles 30, 32, 34, which have a lateral offset and / or a longitudinal offset and / or an angular alignment to one another, whereby instead of a conventional Gaussian profile, a quasi non- diffractive beam profile, for example a Bessel profile, can be used, the formation of such a (dynamically) longitudinally elongated weld seam can be reduced.

The proposed composition of the machining beam 3 from at least two beam profiles 30, 32, 34, which are offset laterally and / or longitudinally and / or at an angle to one another, the connection cross-section can be increased accordingly, whereby the strength of the joint can be improved.

At the same time, from a procedural point of view, the focus position tolerance can advantageously be improved. In particular, it can be achieved that even if one does not plan completely

At the interface 14 between the workpieces 10, 12 a reliable formation of a weld seam is achieved.

A method is shown schematically in FIG. 2 in which three workpieces 10, 12, 16 are to be joined together. The workpieces 10, 12, 16 are arranged one on top of the other, with an interface 14 between the workpiece 10 and the workpiece 12 below and a further interface 18 between the workpiece 12 and the workpiece 16 below. Correspondingly, the respective workpieces 10, 12, 16 lie on top of one another at the boundary surfaces 14 and 18.

In the exemplary embodiment shown, the process zone 4 extends in such a way that it spans the two boundary surfaces 14, 18. A first beam profile 30 and a second beam profile 32 are provided in the process zone 4. For the sake of clarity, no further beam profiles have been drawn in in this schematic representation. However, more than the two beam profiles shown can be provided in order to be composed as

Processing beam 3 in the process zone 4 to introduce a modification into the material accordingly.

In the exemplary embodiment shown, a beam profile 30 is arranged in the process zone 4 such that its focus lies essentially in the plane of the interface 14. In this way, a corresponding modification can be introduced into the material of the adjacent workpieces 10, 12 in the area of the interface 14, which, for example, can lead to the melting of the material of the workpieces 10, 12 such that finally a weld seam between the workpiece 10 and the workpiece 12 is provided in the area of the interface 14. In this exemplary embodiment, a second beam profile 32 is arranged in the process zone 4 in such a way that its focus lies essentially in the plane of the interface 18 between the second workpiece 12 and the third workpiece 16. Correspondingly, by absorbing the energy of the machining beam 3 and in particular by absorbing the energy introduced in the region of the focus of the beam profile 32 in the region of the interface 18, the material of the second workpiece 12 and the third workpiece 16 can be melted.

In the exemplary embodiment specifically shown here, the first beam profile 30 and the second beam profile 32 have a longitudinal offset LO which essentially corresponds to the distance between the planes defined by the boundary surfaces 14 and 18.

The energy input of the beam profiles 30, 32 in the area of the process zone 4 takes place

Accordingly, a modification of the material and in particular a melting of the material in the process zone 4 takes place, which bridges the two interfaces 14, 18.

In the exemplary embodiment shown in FIG. 2, the beam profiles 30, 32 are also at an angle β1 and β2 with respect to the surface normal 110, so that here, at the same time as the lateral offset LA and the longitudinal offset LO, there is also an angular offset between the two beam profiles 30, 32 is present in order to achieve an advantageous introduction of energy into the process zone 4 in this way.

With the method shown, it is accordingly possible to join more than two joining partners together at the same time. In the embodiment shown, for example, three

Workpieces 10, 12, 16 are joined to one another at their respective interfaces 14, 18.

Of course, the method is not limited to joining three workpieces 10, 12, 16, but a larger number of workpieces can also be joined together.

Correspondingly, in a single processing pass through the radiation of the

Processing beam 3 into the process zone 4, wherein the processing beam 3 is composed of at least two beam profiles 30, 32, 34, a simultaneous joining of several workpieces can be achieved.

FIG. 3 shows a further schematic representation of a method in which a processing beam 3 is again composed in a process zone 4 from at least two beam profiles 30, 32. The beam profiles 30, 32 each lie, for example, in one of the two workpieces 10, 12 resting against one another at an interface 14. In the exemplary embodiment shown, the provision of the first beam profile 30 takes place via a first laser beam 2, which is irradiated from outside the first workpiece 10. The second beam profile 32 is provided by a second laser beam 2 ′, which is irradiated from outside the second workpiece 12.

In other words, the first laser beam 2 and the second laser beam 2 ‘in this

Embodiment arranged so that they radiate into the two workpieces 10, 12 from different directions.

In this way it can be achieved that the respective beam profile 30, 32 introduced into the process zone 4 can be adapted, for example, to the respective material properties of the workpiece 10, 12. Furthermore, it is easily possible in this way to provide the beam profiles 30, 32 with different energies.

FIG. 4A shows a schematic representation of an apparatus 1 for processing at least two workpieces 10, 12.

The device 1 comprises a beam source 200 for generating a laser beam 2, which is guided onto and into the workpieces 10, 12 via an optical system 5.

The optics 5 here include a schematically indicated capacitor 50 for conditioning the beam quality of the laser beam 2, a schematically indicated beam-shaping unit 52 and a schematically illustrated focusing optics 54.

The focusing optics 54 are used to provide those provided by the beam-shaping unit 52

To focus beam pattern in the workpieces 10, 12 in order to in this way the

to provide different beam profiles 30, 32 within the process zone 4 in the workpieces 10, 12. The beam profiles 30, 32 are each shown in the two shown in FIG

Partial beams arranged. In these areas, energy is introduced into the material of the workpieces 10, 12.

By means of the beam-shaping elements 52, the corresponding beam pattern, which ultimately leads to the generation of the beam profiles 30, 32 composing the machining beam 3 in the workpieces 10, 12, can be generated.

If the beam-shaping unit 52 can be actively controlled, for example in the form of an acousto-optical deflector (AOD), the position, alignment and intensity of the beam profiles 30, 32 in FIG the workpieces 10,12 are set dynamically or to the respective

Material properties of the workpieces 10,12 are adapted. This can be done, for example, by using the beam-shaping unit 52 to set an offset of partial beams with respect to the optical axis of the focusing optics 54 in such a way that the beam profiles 30, 32 are shifted accordingly, for example in a lateral offset and / or a longitudinal offset and / or an angular offset between the individual beam profiles results.

A beam-shaping unit 52 can, however, also be used to compensate or precompensate the aberrations of the partial beams in such a way that different focus points are achieved for the various partial beams with the focusing unit 54.

An axicon 56 can be provided in order to provide a quasi non-diffractive beam, for example a Bessel beam, by means of the optics 5.

The parameters of the beam source 200 and the optics 5 can be selected as follows, for example:

Wavelength between 200 nm and 5000 nm

- Repetition rate between 100 Hz and 50 MHz (optional bursts where the repetition rate of the pulses in the burst can be between 1 MHz and 50 GHz)

- Laser pulse duration between 10 fs and 50 ps

- Focusing so that fluence in the beam profiles> 0.01 J / cm2 (modification threshold in the volume typically between 1-5 J / cm2)

- Relative advance of the work piece (s) to the machining beam between 0.01 and 1000 mm / s

- Angle at which the partial processing beams hit a workpiece between 0 ° and 45 ° (in air).

In FIG. 4B, analogously to FIG. 4A, there is a device 1 for processing at least one

Workpiece shown. In contrast to the device 1 from FIG. 4A, the device 1 in FIG. 4B has separate focusing optics 54 which focus the beam pattern provided by the beam-shaping unit 52 into the workpieces 10, 12. Due to the separate focusing optics for the partial beams from the beam-shaping unit 52, it is possible to focus the partial beams separately from one another. For example, the partial beams can be focused in different planes. In addition, the adjustment effort for the overall structure is reduced, while at the same time allowing more flexible focusing.

With the structures of FIGS. 4 A, B, the present beam profiles and / or the workpieces can also be rotated during feed, so that the rotation results in a symmetrization of the connection cross section, in particular with regard to the feed direction. By rotating the beam cross-section and / or the workpiece, you can also use the curved

Feed trajectories of the same size connection cross-sections over the entire length of the

Feed trajectory are generated. For example, the feed can be implemented via an xy table on the workpiece, while mirror optics rotate the beam profile. If, for example, a beam is particularly extended in one direction, that is to say in particular oval or elliptical, then the long axis of the beam can always be kept perpendicular to the feed trajectory, whereby the connection cross-section becomes large. Conversely, the short axis can always be kept perpendicular to the feed trajectory, which makes the connection cross-section particularly small.

FIG. 4C shows the effects of the rotation of the beam profile during the advance. The short axis of the beam profile 30 is always kept perpendicular to the feed trajectory V. This results in a homogeneous connection cross-section. For example, the extension of the connection cross-section orthogonal to the feed trajectory is always the same.

In FIG. 5, four different results are schematically shown in a microscope image

Machining process shown in which the number of beam profiles in the process zone, which are introduced into the respective workpiece or the workpieces, are varied.

With ordinal number 1, only a single beam profile was introduced into the process zone. This corresponds to the conventional welding process with a single beam profile focused into the workpiece.

In the microscope image with the order numbers 3, 5 and 9, 3, 5 or 9 beam profiles have been focussed into the respective process zone

Have composed the machining beam in the process zone. It can be seen that the volume of the process zone 4 increases with the number of beam profiles introduced, which is symbolized here schematically by an inscribed rectangle. This also immediately shows that, for example, the connection cross-section and the focus position tolerance increase due to the increase in the number of beam profiles in the process zone.

FIG. 6 shows a comparison of the propagation behavior of a Gaussian beam in FIG. 6A and two quasi non-diffractive beams in FIGS. 6B, C. The self-drawn arrows mark the diameter or the length of the beam profile.

The longitudinal expansion in the direction of beam propagation of the Bessel beam from FIG. 6B is shown in FIG. 6E. The almost propagation-invariant intensity maximum shows a

characteristic length L, which is defined by the intensity drop to 50%, starting from the local intensity maximum in the positive and negative z-direction. The associated

characteristic length L can easily exceed 1 mm

The transverse intensity distribution associated with FIG. 6B is shown in FIG. 6D. In the vicinity of the beam axis, the intensity distribution obeys a good approximation of a Bessel function of the first kind of order 0, which is enveloped by a Gaussian distribution. Typical Bessel-Gauss rays, which can be used for processing transparent materials, show

for example, the diameter of the central intensity maximum on the optical axis of d ^ND o = 2.5pm.

A Gaussian focus with d ^ND o = d ^GF o = 2.5 pm, on the other hand, is characterized by a focus length in air of only Z _R = 5 pm at A = 1 pm, see FIG. 6A. In these cases relevant to material processing, L »10ZR can even apply.

As far as applicable, all the individual features that are shown in the exemplary embodiments can be combined with one another and / or exchanged without departing from the scope of the invention. Reference list

1 device for machining a workpiece

10 workpiece

12 workpiece

14 interface

16 workpiece

18 interface

100 surface of the workpiece

1 10 surface normals

2 laser beam

200 beam source

3 machining beam

30 beam profile

32 beam profile

34 Beam profile

4 process zone

5 optics

50 capacitor

52 beam-shaping unit

54 Focusing Optics

LA lateral offset

LO longitudinal offset

a1 angle between beam profiles

a2 angle between beam profiles

ß1 angle of a beam profile to the surface normal ß2 angle of a beam profile to the surface normal ß3 angle of a beam profile to the surface normal V feed trajectory

Claims

Expectations

1 . A method for processing at least one workpiece (10, 12), preferably for welding two workpieces (10, 12), comprising exposing a process zone (4) to at least one workpiece (10, 12) with a pulsed laser beam (2), preferably processing beam (3) provided by an ultrashort pulse laser beam, characterized in that the processing beam (3) in the process zone (4) is composed of at least two beam profiles (30, 32, 34).

2. The method according to claim 1, characterized in that the individual

Beam profiles (30, 32, 34) in the process zone (4) are aligned at an angle (cd, a2) to one another.

3. The method according to claim 1 or 2, characterized in that the present in the process zone beam profiles (30, 32, 34) at an angle (ß1, ß2, ß3) to the surface normal (1 10) of the workpiece (10, 12) aligned are preferably at an angle (β1, β2, β3) between 0 ° and 45 °, preferably between 5 ° and 40 °, particularly preferably between 10 ° and 35 °, to the surface normal (1 10) of the workpiece (30, 32, 34).

4. The method according to any one of the preceding claims, characterized in that at least two beam profiles (30, 32, 34) with a lateral offset (LA1, LA2) to one another and / or with a longitudinal offset (L01, L02) to one another in the process zone ( 4) be aligned.

5. The method according to any one of the preceding claims, characterized in that the laser beam (2) is provided in the form of a Gaussian beam or a quasi non-diffractive beam, preferably a Bessel beam or a bottle beam, and / or at least one beam profile (30, 32, 34) is provided as a Gaussian profile or as a quasi non-diffractive beam profile, preferably as a Bessel profile or as a bottle beam.

6. The method according to any one of the preceding claims, characterized in that the beam profiles (30, 32, 34) have a longitudinal offset (L01, L02) to one another which is greater than the respective characteristic length of the beam profiles and preferably greater than the Rayleigh length of Gaussian beam profiles or greater than the length at which quasi non-diffractive beams, preferably Bessel beams, only have 50% of the intensity in the central main intensity maximum in the longitudinal extent.

7. The method according to any one of the preceding claims, characterized in that the beam profiles (30, 32, 34) have a lateral offset (LA1, LA2) to one another which is greater than the lateral extent of the respective one

Beam profiles (30, 32, 34) and is preferably larger than the beam tales of Gaussian beam profiles or the diameter of quasi non-diffractive beams, preferably Bessel beams.

8. The method according to any one of the preceding claims, characterized in that at least two beam profiles (30, 32, 34) are introduced simultaneously into the process zone (4).

9. The method according to any one of the preceding claims, characterized in that at least two pulsed laser beams (2, 2 ‘) for generating at least one beam profile (30, 32) are provided, which for

Composition of the processing beam (3) can be introduced into the process zone (4) at the same time.

10. The method according to any one of the preceding claims, characterized in that a first laser beam (2) for generating a first beam profile (30) from a first direction with respect to a workpiece (10) is introduced into the process zone (4) and a second laser beam ( 2 ') is introduced from a second direction with respect to the workpiece (10) in order to generate a second beam profile (32) in the process zone (4), the first laser beam (2) and the second laser beam (2') preferably from different, preferably from essentially opposite directions, are introduced into the process zone (4).

11. Device for processing at least one workpiece (10, 12, 16), preferably for welding two workpieces (10, 12, 16), comprising a beam source for Provision of a pulsed laser beam (2, 2 '), preferably one

Ultrashort pulse laser beam and an optical system (5) for providing a

Processing beam (3) in a process zone (4) of at least one workpiece (10, 12, 16), characterized in that the optics (5) are set up and designed in such a way that the processing beam (3) emerges in the process zone (4) at least two beam profiles (30, 32, 34)

composed.

12. The device according to claim 11, characterized in that the device is a workpiece holder and / or at least one positioning system

Positioning the laser beam and / or the workpieces includes.

13. Device according to one of claims 11 to 12, characterized in that the optics (5) have a beam-shaping unit (52), preferably a spatial one

Light modulator and / or a diffractive optical element and / or an acousto-optical deflector (AOD).

14. Device according to one of claims 11 to 13, characterized in that the optics (5) comprises an axicon (56) for forming a quasi non-diffractive beam, preferably a Bessel beam or a bottle beam, wherein at least one beam profile ( 30, 32, 34) in the process zone (4) is designed as a quasi non-diffractive beam profile, preferably as a Bessel profile or as a bottle beam.

15. Device according to one of claims 11 to 14, characterized in that the optics (5) comprise focusing optics (54) and the laser beam (2, 2 ') offset with respect to the optical axis of the focusing optics (54) into the focusing optics (54) ) is introduced in order to bring the beam profiles (30, 32, 34) of the processing beam (3) into the process zone (4) at an angle, the optics (5) preferably being a beam-shaping unit (52), preferably a spatial light modulator and / or a diffractive optical element and / or an acousto-optical deflector (AOD), in order to provide the beam offset of the laser beam (2, 2 ') to the optical axis of the focusing optics (54).