ARRANGEMENT FOR MATERIAL PROCESSING WITH A LASER BEAM, IN PARTICULAR FOR LASER BEAM DRILLING

Description

Technical application area

[0001] The present invention relates to an arrangement for material processing with a laser beam, in particular for laser beam drilling, with a dynamic deflection device for the laser beam, which is designed to deflect the laser beam in two mutually perpendicular directions, and an optical arrangement with which a laser beam emerging from the deflection device can be focused onto a processing plane.

[0002] In material processing using short and ultrashort laser pulses for laser cutting or laser drilling, steep wall angles cannot be achieved with typical processing parameters and vertical irradiation. The achievable wall angle of the removal flanks is typically in the range of 85° at most. This is due to the reduction in pulse intensity when projected onto the inclined removal flank, as a result of which removal stops at a critical angle. For many applications, however, this is undesirable because, for example, no vertical cutting flanks or only conical holes are possible. In deep removal, cutting, or drilling, the limitation of the wall angle also leads to a limitation in the achievable aspect ratio (removal depth to surface diameter). State of the art

[0003] Special optics are available for drilling and fine cutting using laser beams. These can be used in various ways to angle the laser beam to create a cylindrical or even negatively conical hole. With these optics, the wall angle that occurs with normal incidence is compensated for by angled the laser beam relative to the workpiece. During fine cutting, a relative movement is initiated between the optics and the workpiece during drilling, creating a cut with the width of the hole diameter. The available optics can be divided into two groups depending on the principle of how the laser beam is angled. In the first group, the beam is guided using rotating optical elements such as rotating prisms, cylindrical lenses or wedge plates. The second group uses rotating mirrors for the entire beam guidance, i.e. for offset, angle and deflection.

[0004] A classic application for laser drilling is the creation of precise micro-drilling holes with diameters of a few 10 to 100 µm in thin films, usually well below 1 mm thick. Drilling is often performed using multi-pass cutting along the borehole wall, meaning there is no complete removal. The drilling optics are often designed for a maximum borehole diameter in the order of 1 mm. For larger borehole diameters, the size of the rotatable optical elements must be increased, which results in a nonlinear reduction in the deflection speed.

[0005] DE 10 2018 208752 A1 (basis for the preamble of claim 1) discloses an arrangement for material processing with a laser beam, which comprises a relay system consisting of a first and a second relay optical group. Following this relay system, an additional focusing unit is required to focus the laser beam onto the focal or processing plane.

[0006] From DE 100 54 853 A1 a device and a method for making a micro-hole in a workpiece with a laser beam are known, in which the laser beam is focused on the workpiece and the focus is continuously moved along a circular path concentric with the hole axis.

[0007] EP 1 082 883 A1 describes a method and device for drilling microvias into electrical circuit carriers or substrates using a laser beam. In this method, the vias are drilled with a specific, e.g., annular intensity distribution of the laser beam, which is generated using steel forming elements.

[0008] EP 1 188 509 B1 discloses an optical device for drilling using a laser beam, in which the angle of attack and deflection for defining a trepanning radius can be adjusted separately. The arrangement has a deflection device with two deflection mirrors, in which the optical distance of at least one of the deflection mirrors relative to the focusing optics can be changed parallel to the main optical axis. This allows the laser beam to be directed at different angles onto the focusing optics, resulting in different angles of attack depending on the position of the deflection mirror. The focusing optics in this arrangement is formed by a focusing lens, through which the laser beam is focused onto the processing plane. In this embodiment, the angle of attack can be as large as the deflection angle of the deflection device. Large angles of attack can therefore only be achieved for large contours. Description of the invention

[0009] The object of the present invention is to provide an arrangement for material processing with a laser beam, with which large and deep bores or cuts can be produced with a simple and thus very inexpensive and stable structure and which also enables comparatively small bores with a large angle of attack.

[0010] The object is achieved by the arrangement according to patent claim 1. Advantageous embodiments of the arrangement are the subject of the dependent patent claims or can be derived from the following description and the exemplary embodiment.

[0011] The proposed arrangement has a dynamic deflection device for the laser beam, which is designed to deflect the laser beam in two mutually perpendicular directions, and an optical arrangement between the deflection device and a processing plane, with which optical arrangement a laser beam emerging from the deflection device is focused onto the processing plane. The dynamic deflection device can, for example, be a two-dimensional galvanometer scanner. Other types of such deflection devices for laser beams can of course also be used. The optical arrangement for focusing the laser beam emerging from the deflection device onto the processing plane has at least two optical systems along an optical axis of the optical arrangement. The optical system here is an arrangement comprising one or more beam-guiding and / or beam-shaping optical elements, e.g.one or more lenses. The optical axis represents the axis of symmetry of the optical arrangement along which an incoming laser beam passes through the optical arrangement without deflection. In the proposed arrangement, the first and second optical systems are designed and arranged such that the laser beam focused onto the processing plane forms an intermediate focus between the first and second optical systems and, upon entering the optical system, crosses the optical axis at an angle (≠ 0°) to the optical axis and at a distance from this between the second optical system and the processing plane.Entry into the optical system at an angle to the optical axis and at a distance from it is caused by the dynamic deflection device and represents the desired mode of operation of the arrangement for producing a cut or a bore in a workpiece whose surface area to be machined lies in the machining plane, in order to thereby achieve an alignment of the laser beam (angle > 0° to the surface normal) with respect to the surface area of ​​the workpiece. In the present patent application, entry of the laser or laser beam at an angle to the optical axis and at a distance from it, and crossing of the optical axis by the laser beam in a known manner, means that the beam axis of the laser beam runs at an angle to the optical axis and at a distance from it or crosses the optical axis.

[0012] In the proposed arrangement, the dynamic deflection device generates an angular offset relative to the optical axis of the optical arrangement. The laser therefore strikes the first optical system at an angle to the optical axis and at a distance from it and is focused by the first optical system to an intermediate focus between the first and second optical systems. The laser radiation diverging after the intermediate focus is then focused by the second optical system onto the processing plane or the workpiece surface. In the proposed arrangement, the offset of the laser beam relative to the optical axis leads to the laser beam being positioned with a helix point above the processing plane or the focus. In this way, an incident direction suitable for the steep wall angle of a bore to be achieved is achieved in the processing plane or on the surface of the workpiece.With the proposed optical setup, the angular deflection of the laser beam is divided into offset and angle of incidence. The angle of incidence is proportional to the offset from the optical axis, whereby the proportionality factor depends on the selected optical setup and its dimensions. The helix point above the machining plane, where the laser beam crosses the optical axis, allows even small holes to be drilled with a large angle of incidence.

[0013] In contrast to the known use of a relay system, in the proposed arrangement, the laser radiation is already focused on the processing plane by using two optical systems at defined distances from one another, in such a way that the laser beam crosses the optical axis at an angle to the optical axis when entering the first optical system and at a distance from this between the second optical system and the processing plane.

[0014] In contrast, a relay system simply projects the deflection plane onto a plane behind the optical system. The laser beam can then be focused using additional focusing optics, whose entrance pupil is positioned in the imaged deflection plane. This corresponds to a conventional setup consisting of a deflection device and a focusing lens, in which there is no intersection of the optical axis between the focusing optics and the processing plane. In this case, the relay system serves only to spatially separate the deflection device and the focusing optics or to insert spatial filters in the intermediate focus.

[0015] The diameter of a drill hole to be created and the scanning speed are determined by the deflection and rotation rate of the dynamic deflection direction. Both the proportionality factor and the focus diameter are set or determined depending on the distances between the two optical systems, between the deflection device and the first optical system and between the second optical system and the processing or focal plane, and the choice of the respective focal lengths of the optical systems. With the proposed arrangement, holes can be created both by cutting out and by full ablation. Thus, by appropriately controlling the dynamic deflection device, the hole contour can be traversed with the laser beam in several passes and ablated layer by layer. This multi-pass cutting of the holes corresponds to the typical process used in trepanning optics.On the other hand, by scanning the cross-sectional area of ​​the borehole using various scanning movements, a layer-by-layer ablation of the entire borehole surface, i.e., a complete ablation, can be achieved. The area can be scanned in different ways by controlling the dynamic deflection device accordingly, for example, using concentric circles or in a spiral. Other scan paths are also possible for this complete ablation.

[0016] The proposed arrangement can be used to create positively conical, cylindrical, and even negatively conical drill holes with diameters of up to several millimeters. Through full ablation, the focal plane can be pushed into the hole without shielding the laser radiation. Furthermore, three-dimensionally shaped holes, i.e. holes that deviate from a cylindrical shape, can be created. Examples include the creation of drill funnels, the creation of hourglass-shaped holes, or the creation of holes with a Laval nozzle shape. By moving the workpiece relative to the proposed arrangement, the arrangement can also be used for helical cutting. Furthermore, flat ablation with vertical ablation flanks or undercuts can be achieved in microstructuring.

[0017] In a preferred embodiment, the first optical system and the second optical system are each formed from a lens or a lens arrangement. The distances between the lenses or optical systems and also between the deflection device and the processing plane can be fixed. In an advantageous embodiment, one or more of these distances can also be adjustable by suitable mechanical adjusting elements or adjustment mechanisms on one or both optical systems and / or the deflection device.

[0018] In addition to the deflection device and the optical arrangement connected to the deflection device, further components for beam guidance and / or beam shaping can also be arranged in the beam path of the laser beam. For example, the proposed arrangement can have a telescope in the beam path upstream of the deflection device, with which the beam diameter of the laser beam and thus also the focus diameter in the processing plane can be adjusted. An optical device for pre-focusing the laser beam upstream of the deflection device can also be used in order to also be able to adjust the focus diameter in the processing plane. It is also possible to rotate the laser beam during material processing using suitable rotating optical elements, e.g. a DOVE prism rotating around its longitudinal axis, as is known from arrangements for helical drilling using laser radiation.

[0019] In a further advantageous embodiment, one or more suitable adjusting elements are provided in order to be able to shift or adjust the focal plane perpendicular to the optical axis of the optical arrangement during processing. Such a Z-shift of the focal plane can be achieved by moving a mechanical z-axis or by shifting the optical elements of the first and / or second optical system along the optical axis of the optical arrangement. In the beam path of the laser beam, elements for generating a linear, circular, or statistically distributed polarization of the laser radiation can also be used in the proposed arrangement. Furthermore, it is possible to rotate the polarization using suitable optical elements, such as a λ / 2 plate, λ / 4 plate, or DOVE prism (synchronous, asynchronous).

[0020] When processing materials with the proposed arrangement, one or more process and / or laser parameters can preferably be adapted to the process sequence during the process. For the laser parameters, this concerns the pulse energy, the pulse duration, and the repetition rate; for the process parameters, this concerns the scan geometry, the scan speed, the Z-shift speed, the Z-shift profile, and the waiting times between individual processing phases. In addition, process gases such as air, inert gas, or active gas can be used in a known manner during processing, e.g., by using a crossjet or a coaxial nozzle, in order to achieve improved removal of the ablation particles from the interaction area with the laser radiation.

[0021] The proposed method enables large and deep holes or cuts to be created using a very cost-effective and stable structure. The proposed arrangement can be subsequently integrated into many available machining or structuring systems. The arrangement enables complete removal of the drilled hole cross-section or cutting using spiral or circular movements with an adapted angle of attack. In the simplest case, the optical arrangement has only two lenses, so that only minimal losses occur in the optical beam path. Since there are no moving components in the optical arrangement, the proposed arrangement has a simple, stable, and cost-effective structure. The size of the holes that can be produced with the arrangement is limited only by the diameter of the two optical systems. With spiral cutting, greater cutting depths are also possible due to a larger kerf.The proposed arrangement can be used, for example, for drilling in turbomachinery, electronics manufacturing or semiconductor technology, for spiral cutting, e.g. in precision mechanics or semiconductor technology or also in toolmaking and aircraft construction. Short description of the drawings

[0022] The proposed arrangement is explained in more detail below using an exemplary embodiment in conjunction with the drawing. Here: Fig. 1 an example of a design of the proposed arrangement. Ways to implement the invention

[0023] In the proposed arrangement, a laser beam is focused onto a workpiece surface by means of a deflection device via an optical arrangement in order to remove material from this workpiece surface, in particular in order to create drill holes or cuts in the workpiece. Figure 1shows a schematic representation of an example structure of the proposed arrangement. In this representation, collimated laser radiation LS from a laser beam source LA is deflected by the deflection unit AE in two mutually perpendicular directions (X and Y directions). This deflection unit AE can be, for example, a two-dimensional galvanometer scanner. The figure shows three positions of one of the mirrors of the deflection unit AE with the resulting beam path of the laser radiation. In two of the three positions shown, the laser radiation strikes the first optical system OS1, in this example a focusing lens, at an angle to the optical axis. In the middle position of the mirror of the deflection unit AE shown, the laser radiation propagates along the optical axis through the first optical system OS1. An intermediate focus ZF is created at a distance b of the focal length of the first optical system OS1.The diverging laser radiation is then focused onto the workpiece W by the second optical system OS2. In this example, the second optical system OS2 is also formed solely by a focusing lens. The distances a, b, c and d between the deflection unit AE and the first optical system OS1, between the first optical system OS1 and the intermediate focus ZF, between the intermediate focus ZF and the second optical system OS2 and between the second optical system OS2 and the workpiece surface W, which in this example corresponds to the machining plane, are selected such that the laser beam crosses the optical axis before hitting the workpiece surface W. This is shown enlarged in the enlarged view of section A in the right-hand part of the figure. The offset of the laser beam from the center line orThe optical axis, which was created during the passage through the first optical system OS1 with the corresponding mirror position, leads to the laser beam being angled at an angle α and a helix point above the focal plane. The two optical systems OS1 and OS2 image a virtual point including a virtual deflection above the deflection unit AE, thus leading to an angle adjustment in a direction advantageous for the conicity of the desired bore.

[0024] By appropriately dynamically deflecting the laser beam LS with the deflection unit AE, the desired hole can be created. The angle of incidence on the workpiece surface is proportional to the offset of the laser beam between the two optical systems OS1, OS2 from the centerline or optical axis. By changing the distances a, b, c, and d and appropriately selecting the focal lengths of the optical systems OS1, OS2, both the proportionality factor and the focus diameter can be adjusted.

[0025] With the following exemplary configuration, a hole with a diameter of 500 µm can be created in a workpiece made of 5 mm thick nickel-based alloy. A pulse energy of ~1 mJ is used, a focus diameter of 40 µm, and a pulse duration of < 20 ps, ​​and complete removal by spirals takes place. Figure 1 The parameters shown are selected as follows: a = 50 mm b = 500 mm c = 500 mm d = 80 mm Focal length of lens OS1: 500 mm Focal length of lens OS2: 70 mm List of reference symbols

[0026] AEDeflecting unit LALaser beam source LSLaser beam OS1First optical system OS2Second optical system WWorkpiece surface ZFIntermediate focus a - dDistances

Claims

1. Assembly for material processing using a laser beam, in particular for laser drilling, with - a dynamic deflection device (AE) for the laser beam (LS), which is designed to deflect the laser beam (LS) into two directions extending perpendicularly to each other, and - an optical assembly, with which a laser beam exiting the deflection device (AE) is focussed onto a processing plane (W), - wherein the optical assembly includes a first optical system (OS1) and a second optical system (OS2) along an optical axis of the optical assembly, which are designed and arranged such that the laser beam (LS) forms a intermediate focus (ZF) between the first and second optical systems (OS1, OS2), characterized in that the laser beam when entering the first optical system (OS1) at an angle to the optical axis and at a distance therefrom intersects the optical axis between the second optical system (OS2) and the processing plane (W).

2. Assembly according to Claim 1, characterized in that one or more positioning elements are attached to one of the two optical systems (OS1, OS2) or to both optical systems (OS1, OS2), with which a spacing between the two optical systems (OS1, OS2) and / or a spacing between the first optical system (OS1) and the deflection unit (AE), and / or a spacing between the second optical system (OS2) and the processing plane (W) can be set or changed.

3. Assembly according to Claim 1 or 2, characterized in that a telescope is arranged in front of the deflection device (AE) in the beam path of the laser beam (LS), with which a beam diameter of the laser beam (LS) can be changed.

4. Assembly according to Claim 1 or 2, characterized in that an optical device for pre-focussing the laser beam (LS) is arranged in front of the optical assembly or the deflection device (AE) in the beam path of the laser beam (LS).

5. Assembly according to Claim 4, characterized in that the optical device for pre-focussing is designed in such manner that it enables a variable pre-focussing of the laser beam (LS).

6. Assembly according to any one of Claims 1 to 5, characterized in that the optical assembly includes one or more positioning elements, with which a focussing plane of the laser beam (LS) can be shifted along the optical axis of the optical assembly during the material processing.

7. Assembly according to any one of Claims 1 to 6, characterized in that the optical assembly includes at least one element for influencing the polarisation, by which a polarisation advantageous for the material processing can be set.

8. Use of the assembly according to one or more of the preceding claims for creating a borehole by full ablation in layers, in which a laser beam passes over the entire borehole cross section in each case.

9. Use of the assembly according to one or more of the preceding claims for creating a borehole by cutting out a borehole contour by means of spiral or circular traverses with the laser beam.