An assembly for material processing using a laser beam, particularly laser drilling

Abstract

The present invention relates to an assembly for material processing using a laser beam, in particular laser drilling, comprising a dynamic deflection device AE for a laser beam LS and an optical assembly for focusing the laser beam LS emerging from the deflection device AE onto a work surface W. Along an optical axis, the optical assembly comprises a first optical system OS1 and a second optical system OS2, which are designed and arranged in such a way that the laser beam LS forms an intermediate focus ZF between the first optical system OS1 and the second optical system OS2 and intersects the optical axis between the second optical system OS2 and the work surface W when it is incident on the first optical system OS1 at an angle to and a distance from the optical axis. The proposed assembly has a simple and stable structure, which allows efficient ablation of large and deep boreholes or cutouts in a workpiece.

Description

Technical Field

[0001] The present invention relates to an assembly for material processing using a laser beam, in particular for laser drilling, which is designed to deflect a laser beam in two directions extending perpendicular to each other, and an optical assembly capable of focusing the laser beam emitted from the deflection device onto a processing surface.

Background Art

[0002] In material processing techniques using short laser pulses and ultrashort laser pulses for laser beam cutting or laser drilling, it is not possible to create a steep wall angle using typical processing parameters by perpendicular irradiation. The achievable wall angle of the ablation side is typically within a maximum range of 85 degrees. This is due to the reduction of the pulse intensity when projected onto the inclined ablation side, resulting in the ablation stopping after the critical angle. However, this is not desirable in many applications because, for example, a vertically cut side is not possible or only a conical borehole is possible. In deep ablation, cutting or drilling, the achievable aspect ratio (ablation depth relative to the diameter on the surface) is also limited by the limited wall angle.

[0003] For drilling and precision cutting using a laser beam, special optical devices are available, and with these optical devices, various procedures can be carried out to adjust the position of the laser beam so that a cylindrical borehole or even a negative conical borehole can be created. Using these optical devices, the wall angle created by the perpendicularly incident beam is compensated by the incidence of the laser beam on the workpiece. In the case of precision cutting, the relative movement between the optical system and the workpiece is further initiated during drilling, thereby creating a cut section having the same width as the borehole diameter. The available optical devices can be divided into two groups according to the functional principle of the method used to guide the laser beam. In the first group, the beam is guided using a rotating optical element, such as a rotating prism, a cylindrical lens, or an optical wedge. The second group uses a mirror that can be rotated for complete beam guidance, i.e., for offset, incidence, and deflection.

[0004] One conventional application area of laser drilling is to create extremely accurate micro-boreholes having a diameter of about 10 μm to 100 μm in thin foils that usually have a thickness significantly less than 1 mm. Since ablation is not performed in many cases where drilling is carried out in a multi-pass cutting process along the borehole wall, the drilling optical system is often designed for a maximum borehole diameter of about 1 mm. The larger the drilling diameter, the larger the size of the rotatable optical element has to be, and the deflection speed decreases non-linearly.

[0005] Patent Document 1 discloses an optical device that performs drilling using a laser beam, and the approach angle and the deflection angle can be adjusted separately from each other to define the trepanning machining radius. The assembly has a deflection device having two deflection mirrors, and using this deflection device, the optical distance of at least one of the deflection mirrors can be changed parallel to the optical axis with respect to the focusing optical component. Thereby, it becomes possible to direct the laser beam at different angles to the focusing optical component, and different approach angles are generated according to the positioning of the deflection mirror. The focusing optical component in this assembly is formed by a focusing lens, and through this focusing lens, the laser beam is focused on the machining surface. In this mechanism, the approach angle cannot be larger than the deflection angle of the deflection device. As a result, a large approach angle can be realized only for a large contour.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to provide an assembly for performing material processing using a laser beam, which can produce a large and deep borehole or cutout using a simple, inexpensive, and stable structure, and can also enable a relatively small borehole having a large approach angle.

Means for Solving the Problems

[0008] The above object is solved by the assembly according to claim 1. Advantageous modifications of the assembly are the subject matter of the dependent claims or can be understood from the following description and the exemplary embodiments.

[0009] The proposed assembly comprises a dynamic deflection device for a laser beam, designed to deflect the laser beam in two directions perpendicular to each other, and an optical assembly between the deflection device and the machining surface, which focuses the laser beam emerging from the deflection device onto the machining surface. The dynamic deflection device can be, for example, a two-dimensional galvanometric scanner. Of course, other types of such deflection devices for the laser beam may be used. The optical assembly that focuses the laser beam emerging from the deflection device onto the machining surface comprises at least two optical systems along the optical axis of the optical assembly. In this context, an optical system is understood to be an assembly of one or more beam guiding and / or beam shaping optical elements, for example one or more lenses. The optical axis represents the axis of symmetry of the optical assembly through which the incident laser beam passes without deflection. In the proposed assembly, the first optical system and the second optical system are designed and arranged such that the laser beam focused on the machining surface forms an intermediate focus between the first optical system and the second optical system and intersects the optical axis between the second optical system and the machining surface when it enters the optical system at an angle (≠ 0 degrees) with respect to the optical axis and at a distance from the optical axis. The entry of the laser beam at an angle with respect to the optical axis and at a distance from the optical axis into the optical system is caused by the dynamic deflection device and represents the desired operating mode of the assembly for creating a cutout or a borehole in the workpiece, where the surface area to be machined is arranged on the machining surface so as to achieve an incidence of the laser beam on the surface area of the workpiece at an angle greater than 0 degrees with respect to the surface normal. In this patent application, the entry of a laser or a laser beam at an angle with respect to the optical axis and at a distance from the optical axis and the intersection of the optical axis by the laser beam are understood in a known manner to mean that the beam axis of the laser beam extends at an angle with respect to the optical axis and at a distance from the optical axis or intersects the optical axis.

[0010] In the proposed assembly, an angular offset of the optical axis of the optical assembly is created by the dynamic deflection device. Thus, the laser is incident on the first optical system at an angle to the optical axis and at a distance from the optical axis, and is focused by the first optical system at an intermediate focus between the first optical system and the second optical system. The laser beam diverges after the intermediate focus and is then focused by the second optical system onto the machining surface or the workpiece surface. In the proposed assembly, the offset of the laser beam from the optical axis leads to the incidence of a laser beam having a helical point above the machining surface or the focus. In this way, the irradiation direction suitable for creating the intended steep wall angle of the borehole is realized within the machining surface or on the surface of the workpiece. Using the proposed optical structure, therefore, the angular deflection of the laser beam is divided into an offset and an incident angle or irradiation angle. The angle of incidence is proportional to the offset from the optical axis, and the proportionality factor depends in each case on the optical structure and / or the dimensions of the optical structure. It is also possible to create small boreholes with a large angle of incidence by means of helical points at which the laser beam intersects the respective optical axis above the machining surface.

[0011] Unlike the known use of relay systems, in the proposed assembly, by using two optical systems having a defined distance therebetween, the laser irradiation is already focused on the machining surface, whereby when the laser beam enters the first optical system at an angle to the optical axis and at a distance from the optical axis, it intersects the optical axis between the second optical system and the machining surface.

[0012] In contrast thereto, a relay system simply images the deflection surface on a plane behind the optical system. Subsequently, focusing of the laser irradiation can be achieved via additional focusing optics at which the entrance pupil is positioned on the imaged deflection surface. This corresponds to a conventional structure consisting of a deflection device and a focusing lens, and the optical axis is not intersected between the focusing optics and the machining surface. In this case, the relay system simply serves to spatially separate the deflection device and the focusing optics from each other, or to insert a spatial filter at the intermediate focus.

[0013] The diameter of the borehole produced and the scanning speed are determined by the deflection speed and the rotation speed of the dynamic deflection device. Both the proportionality coefficient and the focal diameter are set or defined based on the distance between the two optical systems, the distance between the deflection device and the first optical system, and the distance between the second optical system and the machining surface or the focusing surface, and the selection of the focal lengths of the respective optical systems. The borehole can be produced by either cutting or full ablation using the proposed assembly. Thus, the laser beam can be induced by the corresponding operation of the dynamic deflection device to move along the contour of the borehole and remove material layer by layer in a plurality of passes. This multi-pass cutting of the borehole corresponds to a typical method in trepanning machining optics. On the other hand, layer ablation of the entire borehole surface, i.e., full ablation, can also be performed by scanning the cross-sectional surface of the borehole in different scanning movements. In this process, the surface can be scanned in various ways, for example, by the corresponding operation of the dynamic deflection device in a concentric or spiral motion. Other scan paths are also possible for this full ablation.

[0014] Using the proposed assembly, it is possible to create positive conical, cylindrical, or negative conical boreholes with diameters up to several millimeters. By full ablation, it is possible to advance the focusing surface into the borehole without the laser irradiation being hidden in the process. Furthermore, it is also possible to create three-dimensionally formed boreholes, i.e., boreholes having a non-cylindrical shape. Examples include the production of a drilling funnel, the production of a constricted borehole like an hourglass, or the production of a borehole having a Laval nozzle shape. By using the movement of the workpiece with respect to the proposed assembly, the assembly can also be used for spiral cutting. In addition, this enables vertical ablation side surfaces or even surface ablation with undercuts in the case of microstructuring.

[0015] In a preferred variant, the first optical system and the second optical system are each composed of a lens or a lens mechanism. Not only the distance between the lenses or the optical systems, but also the distance of the lens or the optical system from the deflection device and the machining surface can be fixedly specified in this regard. In an advantageous variant, one or more of these distances can also be made adjustable by suitable mechanical positioning elements or displacement mechanisms on one or both of the optical systems and / or the deflection device.

[0016] Further components for beam guidance and / or beam shaping can also be arranged in the beam path of the laser beam, in addition to the deflection device and the optical assembly adjacent to the deflection device. Thus, for example, the proposed assembly can be provided with a telescope in front of the deflection device in the beam path, and this telescope can be used to adapt the beam diameter and the focal diameter of the laser beam also at the machining surface. In order to also enable the adaptation of the focal diameter at the machining surface, an optical device for pre-focusing the laser beam can also be installed in front of the deflection device. Also, as is known from assemblies for performing spiral drilling using laser irradiation, it is also possible to rotate the laser beam while machining the material using a suitable rotating optical element, for example, a double prism that rotates about its own longitudinal axis.

[0017] In a further advantageous variant, one or more suitable positioning elements are provided to enable the focusing plane to be shifted or adjusted perpendicular to the optical assembly during machining. Such a Z shift of the focusing plane can be achieved by mechanical z-axis movement or by shifting the optical elements of the first optical system and / or the second optical system along the optical axis of the optical assembly. In the proposed assembly, an element for generating linearly polarized, circularly polarized or statistically distributed polarized light of the laser irradiation can also be installed in the beam path of the laser beam. In any case, it is possible to rotate the polarization simultaneously using suitable optical elements such as λ / 2 waveplates, λ / 4 waveplates, double prisms (synchronous, asynchronous), etc.

[0018] When performing material processing using the proposed assembly, one or more processing and / or laser parameters can be adapted to the process workflow during the process. In the case of laser parameters, this applies to pulse energy, pulse duration (pulse width) and repetition rate, and for process parameters, it applies to scan geometry, scan speed, Z-shift speed, Z-shift path and the waiting time between individual processing steps. In addition, a process gas such as air, an inert gas or an active gas can be used during processing in a known manner, for example through the use of a cross jet or a coaxial nozzle, to improve the removal of ablation particles from the interaction region with the laser irradiation.

[0019] Using the proposed method, large and deep boreholes or cutouts can be made with a very inexpensive and stable structure. The proposed assembly can be retrofitted to many existing processing and structuring systems. This assembly enables full ablation or cutting of the borehole cross-section by means of a helical or circular cross-section, each with an adapted approach angle. In the simplest case, the optical assembly has only two lenses, resulting in only minor losses in the optical beam path. Since no moving parts are arranged in the optical assembly, the proposed assembly has a simple, stable and inexpensive structure. The size of the borehole that can be drilled using this assembly is limited only by the diameter of the two optical systems. When the cut is helical, the cutting depth can also be made larger due to the larger cutting kerf. The proposed assembly can be used for drilling in, for example, turbomachine construction, electronic component manufacturing or semiconductor technology, and for helical cutting in, for example, precision mechanics, semiconductor technology or tool making and aircraft assembly.

[0020] In the following text, the proposed assembly will be described in more detail again, in connection with the drawings, with reference to exemplary embodiments.

Brief Description of the Drawings

[0021]

Figure 1

Mode for Carrying Out the Invention

[0022] With the proposed assembly, a laser beam is focused on the workpiece surface by a deflection device via an optical assembly in order to remove material from the workpiece surface, in particular to create a borehole or cutout in the workpiece. FIG. 1 is a schematic view of an exemplary structure of the proposed assembly. In this figure, a collimated laser beam irradiation LS from a laser beam source LA is deflected by a deflection unit AE in two directions (X direction and Y direction) extending perpendicular to each other. The deflection unit AE can be, for example, a two-dimensional galvanometer scanner. This figure shows three positions of one of the mirrors of the deflection unit AE together with the beam path of the laser irradiation resulting from the deflection unit AE. At two of the three positions shown, the laser irradiation is incident on a first optical system OS1, in this example a single focusing lens, at an angle with respect to the optical axis. At the central position of the mirror shown in the deflection unit AE, the laser irradiation propagates along the optical axis through the first optical system OS1. At a distance b of the focal length of the first optical system OS1, an intermediate focus ZF is realized. Thereafter, the diverging laser irradiation is focused on the workpiece W through a second optical system OS2. The second optical system OS2 in this example is also formed by only a single focusing lens. The distance a between the deflection unit AE and the first optical system OS1, the distance b between the first optical system OS1 and the intermediate focus ZF, the distance c between the intermediate focus ZF and the second optical system OS2, and the distance d between the second optical system OS2 and the workpiece surface W corresponding to the machining surface in this example are selected such that the laser beam intersects the optical axis before it is incident on the workpiece surface W. This is shown enlarged in the enlarged view of section A on the right side of this figure. Due to the offset of the laser beam from the center line or optical axis formed during passage through the first optical system OS1 together with the corresponding mirror position, the laser beam is incident with an angle α and a helical point above the focusing plane. The two optical systems OS1, OS2 map a virtual point having a virtual deflection above the deflection unit AE, so that alignment in a direction advantageous for the conicity of the desired borehole is achieved.

[0023] By the corresponding dynamic deflection of the laser beam LS using the deflection unit AE, it is possible to create a desired borehole. The irradiation angle on the workpiece surface is proportional to the respective offset of the laser beam between the two optical systems OS1 and OS2 from the center line or optical axis. Both the proportionality coefficient and the focal diameter can be adjusted by changing the intervals a, b, c, and d and by appropriately selecting the focal lengths of the optical systems OS1 and OS2.

[0024] With the following exemplary dimensioning of the assembly, it is possible to produce a borehole having a diameter of 500 μm in a workpiece made of, for example, a 5 mm thick nickel-based alloy. In this connection, a pulse energy of about 1 mJ is used with a focal diameter of 40 μm and a pulse duration of less than 20 ps, and full ablation by helical motion occurs. The parameters shown in FIG. 1 in this case 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

Description of Signs

[0025] AE Deflection Unit LA Laser Beam Source LS Laser Beam OS1 First Optical System OS2 Second Optical System W Workpiece Surface ZF Intermediate Focus Intervals a~d

Claims

1. An assembly for performing laser drilling using a laser beam, a dynamic deflection device (AE) of the laser beam (LS) designed to deflect the laser beam (LS) in two directions extending perpendicular to each other, an optical assembly that focuses the laser beam emitted from the deflection device (AE) onto a machining surface (W), comprising: The optical assembly includes a first optical system (OS1) and a second optical system (OS2) along the optical axis of the optical assembly. The first optical system (OS1) and the second optical system (OS2) are such that the laser beam (LS) forms an intermediate focus (ZF) between the first optical system (OS1) and the second optical system (OS2), and when the laser beam (LS) is incident on the first optical system (OS1) at an angle with respect to the optical axis and at a certain distance from the optical axis, the second optical system (OS2) and the machining surface (W) are designed and arranged to intersect the optical axis therebetween. An assembly.

2. One or more positioning elements are attached to one or both of the two optical systems (OS1, OS2). Using the one or more positioning elements, the distance between the two optical systems (OS1, OS2) and / or the distance between the first optical system (OS1) and the deflection device (AE), and / or the distance between the second optical system (OS2) and the machining surface (W) can be set or changed. The assembly according to claim 1, characterized in that.

3. A telescope is arranged in front of the deflection device (AE) in the beam path of the laser beam (LS), and the beam diameter of the laser beam (LS) can be changed using the telescope. The assembly according to claim 1 or 2, characterized in that.

4. An optical device for pre-focusing 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). The assembly according to claim 1 or 2, characterized in that.

5. The optical device for pre-focusing is designed to enable a variable pre-focus of the laser beam (LS). The assembly according to claim 4, characterized in that.

6. The optical assembly comprises one or more positioning elements, and by using the one or more positioning elements, the focusing surface of the laser beam (LS) can be shifted along the optical axis of the optical assembly into the laser drilling, characterized in that the assembly according to any one of claims 1 to 5.

7. The optical assembly comprises at least one element that affects polarization, and by the at least one element, a polarization advantageous for the laser drilling can be set, characterized in that the assembly according to any one of claims 1 to 6.

8. Use of the assembly according to one or more of claims 1 to 7 for creating a borehole in a layer by full ablation, in each case the laser beam passing over the entire cross-section of the borehole.

9. Use of the assembly according to one or more of claims 1 to 7 for creating a borehole by cutting out the borehole profile by a helical or circular cross-section by the laser beam.

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