WO2023138961A1

WO2023138961A1 - Method for laser drilling a drilled hole into a workpiece at first and second mean beam intensities, and corresponding laser drilling device

Info

Publication number: WO2023138961A1
Application number: PCT/EP2023/050511
Authority: WO
Inventors: Oliver BOCKSROCKER; Nicolai Speker; Tim Hesse
Original assignee: Trumpf Laser- Und Systemtechnik Gmbh
Priority date: 2022-01-18
Filing date: 2023-01-11
Publication date: 2023-07-27
Also published as: DE102022101094A1

Abstract

The invention relates to a method for laser drilling a drilled hole into a workpiece (10), wherein at least one laser beam (20) is used for the laser drilling, wherein a laser beam cross section (30) of the at least one laser beam (20) has a central area (31) with a first laser beam profile (32) having a first mean beam intensity and an outer edge area (33), surrounding the central area (31), with a second laser beam profile (34) having a second mean beam intensity, wherein the second mean beam intensity is greater than the first mean beam intensity.

Description

Title : METHOD FOR LASER DRILLING A HOLE IN A WORKPIECE WITH FIRST AND SECOND MEDIUM BEAM INTENSITIES, AND RELATIVE LASER DRILLING DEVICE

Description

The invention relates to a method for laser drilling a hole in a workpiece according to the preamble of claim 1 and a corresponding laser drilling device.

Various methods for laser drilling holes in workpieces are known from the prior art. Figures 1a, 1b and 1c each show a cross-sectional view through a workpiece 10 of three known methods in use.

In the fig. la becomes a also known as percussion drilling

Method used in which the bore 11 in the workpiece 10 is generated by means of a plurality of laser pulses 21 of a laser beam 20 aligned along the z-coordinate shown, with the z-coordinate in depth or Thickness direction of the workpiece 10 runs.

In the fig. 1b, a method also known as trepanning is used, in which the bore 11 is also produced by a plurality of laser pulses 21 of a laser beam 20, the laser beam 20 also being moved or projected along the trajectory 22 shown. is rotated to expand the bore 11 in the x-y plane of the x,y,z coordinate system shown. In the fig. la and fig . 1b shows, by way of example, that a region 12 of the bore 11 still has material from the workpiece 10 and still has to be drilled through.

In the fig. 1c, a method also known as single-shot drilling is used, in which the hole 11 is drilled by a single laser pulse 21 of a laser beam 20 of high intensity along the entire spot surface of the laser beam 20 on the workpiece 10.

Like the method of FIG. 1c associated Figures 2a and 2b show, as well as in the method of FIG. 1a, 1b, the material of the workpiece 10 is almost completely melted and/or evaporated. The outer region 13 of the bore 11 has the melted zene or. melt liquid material. The melt 14 shown is expelled from the bore 11 by the steam pressure. The material of the workpiece 10 has evaporated in the area 15 surrounded by the outer area 13 . This is how it appears in Fig. 2b shown workpiece 10 with the bore 11 . Compared to the known methods, it is desirable that

To increase precision and process efficiency in laser drilling.

The object of the invention is to propose an improved method and an improved laser drilling device for laser drilling a hole in a workpiece, which in particular allow more precise laser drilling with increased process efficiency.

The object is achieved by a method according to claim 1. Accordingly, a method for laser drilling a hole in a workpiece is proposed, wherein at least one laser beam is used for the laser drilling. The laser beam cross-section of the at least one laser beam has a central surface with a first laser beam profile having a first mean beam intensity and an outer edge surface surrounding the central surface with a second laser beam profile having a second mean beam intensity, with the second mean beam intensity being greater than the first mean beam intensity.

With the method according to the invention, an increased process efficiency and thus also a reduced cycle time can be achieved during laser drilling, because the material of the workpiece is processed particularly intensively, in particular evaporated and/or melted, only in an edge area of the bore that essentially corresponds to the outer edge surface of the laser beam cross section (locally by the generated laser spot of the laser beam), and the material lying within the edge area is less edited or is heated, in particular can remain in a solid state. In other words, more power of the laser radiation is targeted to the surface of the periphery of the bore rather than to the surface of the interior of the bore, thereby enabling the machining at the periphery that ultimately enables the creation of the borehole. In this way, the area or Central area are punched out by the at least one laser beam. With this optimized laser intensity distribution in relation to the laser beam cross section, the hole diameter of the bore can be set particularly precisely and a more precise roundness and cylindricity of the bore can be achieved than is the case with the methods known from the prior art, in which the beam intensity typically decreases from the inside to the outside, as shown in FIG. 2a can be removed.

Workpieces of different materials, for example metallic materials, ceramic materials, polymer-based materials or materials with combinations of the aforementioned materials, can be drilled with the method according to the invention. The workpiece can be designed in one layer or with several layers made of the same or different materials, in particular different of the aforementioned materials.

In principle, the laser drilling can be carried out with a fluence H<500 kJ/mm ² , in particular with a fluence H<100 kJ/mm ² , of the at least one laser beam. For the Total intensity of the entire at least one laser beam and/or the second average beam intensity can in particular have an intensity I of the at least one laser beam of I<15. 000 kW/mm ² , especially from I < 6 . 500 kW/mm ² can be used.

Under the radiation intensity or Radiation intensity is understood here as that energy of the laser beam that is transported in a specific time through the laser beam cross section, ie an area perpendicular to the direction of propagation of the at least one laser beam. Thus, radiation intensity is energy per time per area and can be expressed in W/mm ² . The radiation power Radiant power refers to the radiated energy over time, which can be given in watts. In other words, the beam intensity is the beam power in relation to the laser beam cross section. The first average radiation intensity consequently means the radiation intensity averaged over the central area. The second average radiation intensity correspondingly means the radiation intensity averaged over the outer edge surface. So if the radiation intensity varies across the central area or the outer edge area, it can be averaged over the entire central area, so that the first or second average radiation intensity is obtained, which can also be specified in W/mm ² . The central surface and the outer edge surface surrounding it preferably together form the entire laser beam cross section of the laser beam. With the outer edge surface is therefore meant in particular that the outer edge surface on the outside of the

Laser beam cross-section is located and in particular the central area completely surrounds. It is advantageous if the outer edge surface and the central surface are in a certain size relation to each other. Thus, the outer edge surface can preferably have a maximum diameter which is at least 1, 2 times, at least 1, 5 times or at least 2 times the maximum diameter of the central surface. Again, a maximum diameter of the outer edge surface can preferably be at most 5 times, very particularly at most 4 times the maximum diameter of the central surface.

It is particularly advantageous if the material of the workpiece is only visible in an edge region of the borehole or of the borehole is melted and/or evaporated. Correspondingly, the material in a central area of the hole corresponding to the central surface of the laser beam cross-section (locally due to the generated laser spot of the laser beam) is not melted or melted. vaporize . As a result, the power of the laser device used for laser drilling can be used entirely for process-efficient laser drilling in the edge area of the hole, which also means that greater precision can be achieved during laser drilling.

The laser drilling of the hole can be done by one or more laser pulses of the at least one laser beam. The methods described above, in particular single-shot drilling, i.e. laser drilling with just a single

Laser pulse or percussion drilling, i.e. laser drilling with several consecutive laser pulses, are used. Here, a pulse duration of a laser pulse in the range of 5 ps to 1. 000 ms , especially in the range from 10 ps to 1 . 000 hp , lie . A pulse duration of a laser pulse can particularly preferably be in the range from 5 ps to 200 ps. In the ranges mentioned, high pulse energies of more than 50 mJ enable sufficient vaporization and melt ejection. In addition, short interaction times in this pulse duration range ensure that there is a need-based melting or Heating and removal of the material with little heat input at the edges of the hole.

It is particularly advantageous if the first laser beam profile and/or the second laser beam profile is changed during a laser pulse. Such a change can be sudden or continuous. This makes it possible, in particular, to change the bore diameter continuously in the drilling direction. In particular, the entire laser beam profile of the at least one laser beam, i.e. the first and second laser beam profile together, or the first or second laser beam profile in each case can be changed in such a way that a laser beam profile is switched between a Gauss-like, top-hat-like and/or ring-like laser beam profile. It can also be provided that there is a gradual switchover between intermediate stages between two or all three of the aforementioned laser beam profiles.

Alternatively or additionally, it can advantageously be provided that a diameter of the at least one laser beam is changed during a laser pulse. Such a change can be sudden or continuous. Also this makes it possible to change the borehole diameter in particular continuously in the drilling direction.

It is also advantageous if a pulse shape of a laser pulse is rectangular, triangular, sinusoidal or a combination of at least two of the aforementioned shapes. In this way, improved coupling of the laser beam and targeted vaporization and targeted expulsion of molten material from the workpiece can be achieved.

The second mean radiation intensity is preferably at least 10% greater, particularly at least 20% greater and also particularly at least 50% greater than the first mean radiation intensity. It has been shown that the drilling precision is particularly high with such an average radiation intensity distribution.

It is also advantageous if an intensity gradient of the second laser beam profile is greater than an intensity gradient of the first laser beam profile. Accordingly, a standardized intensity gradient of AI>50 kW/(mm ² *dw) with beam diameter dw can be deliberately deviated from. The beam diameter is in particular the 86% diameter of the laser beam, ie the diameter of the part of the laser beam that is at least 86% of the total energy of the beam contains . This allows the size and extent of the melted area to be reproduced, even with different surface qualities on the workpieces, and the drill hole diameter can also be set very precisely. In particular, it is possible for the at least one laser beam to have a minimum radiation intensity in the central area. In other words, the beam intensity can have its minimum over the entire laser beam cross section in the central area. The radiation intensity minimum can very particularly lie in or near the center of area of the laser beam cross section. As a result, it can be avoided to a particular extent that material lying inside the bore is heated less and is therefore preferably not melted and/or not evaporated.

The beam intensity minimum can preferably propagate in the laser beam propagation direction of the at least one laser beam. This means in particular that the beam intensity minimum continues over a distance of the order of magnitude of a Rayleigh length or more along the laser beam propagation direction. This property can be generated via an optical fiber in which a near-diffraction-limited laser beam is guided by exerting a mechanical force on this optical fiber. Alternatively, beam-shaping elements can be used that impose a vortex-shaped phase distribution, such as e.g. B. Vortex mirrors or vortex phase plates. As a result, a high tolerance width can be achieved in the direction of the optical axis of the laser beam.

The outer edge surface can preferably have a ring shape, a square shape or a polygon shape. The polygon shape can have any number of corners, for example three, five, six or more, for example twelve.

It is also advantageous if an extension of the outer Edge surface in a plane of the laser beam cross-section in the two spatial directions spanning the plane is essentially identical over essentially the entire outer edge surface.

It is also advantageous if the second laser beam profile consists of several, in particular azimuthal (to the workpiece) arranged or oriented , laser beams is generated . This makes it possible for all of the multiple (individual) laser beams to be variable in their beam power independently of one another.

It is also advantageous if the second laser beam profile is essentially homogeneous with regard to its beam intensity. Essentially homogeneous includes technically caused deviations or Tolerances from a mathematically perfectly homogeneous beam intensity distribution over the outer edge surface, which in reality hardly or not at all. is very difficult to achieve. The homogeneous beam profile can be created, for example, by an appropriate beam-shaping element, e.g. a di f fractive optical element in the laser drilling device, in particular its optics, can be achieved.

The method according to the invention can be used in a particularly advantageous manner to produce a bore with a bore depth of <3 mm, in particular <500 μm, and/or with an aspect ratio of bore depth to minimum width of the bore (11) of <1:100, in particular <1:10.

The task mentioned above is also achieved by a

Laser drilling device for laser drilling a hole in a Workpiece, wherein the laser drilling device has a laser beam device for emitting at least one laser beam and an optical system for aligning the at least one laser beam onto the workpiece in such a way that a laser beam cross section of the at least one laser beam has a central surface with a first laser beam profile having a first average radiation intensity and an outer edge surface surrounding the central surface with a second laser beam profile having a second average radiation intensity, the second average radiation intensity being greater than the first average radiation intensity.

The features described herein in relation to the method according to the invention can of course also be used in relation to the laser drilling device according to the invention, and vice versa. In particular, the laser drilling device can be set up to carry out the method according to the invention.

For example, scanner optics, ie optics with one or more movable mirrors for deflecting the laser beam, can be used as the optics. The scanner optics can, for example, have an imaging ratio in the range from 1:1 to 5:1, in particular in the range from 1.5:1 to 2:1. For example, the scanner optics sold by TRUMPF under the designation FPO33-2 can be used.

The laser beam device of the laser drilling device can be, for example, a quasi-continuous wave laser or a VIS laser, i.e. a laser with a visible wavelength of the Laser light works. Alternatively, a different laser beam device and/or, in principle, the use of flying optics, in particular with the same imaging ratios, is also possible, for example such as is marketed by TRUMPF under the name BEO.

A single-mode laser, for example a laser sold by TRUMPF under the name TruFiber (pulse) 500-2000, or a multimode laser, for example a disk laser sold by TRUMPF under the name TruDisk (pulse) 2000-5000, can be used as a quasi-continuous-wave laser. It is also possible to use the laser sold by TRUMPF under the name variMODE Pro, which is characterized by a single-core fiber on which mechanical pressure is exerted so that a ring-like beam profile is generated from a Gaussian-like beam profile. It is also possible to use the laser sold by TRUMPF under the name variMODE Star, which is characterized by a ring fiber that is fed from several laser modules.

It is also possible that a beam parameter product SPP of the at least one laser beam is in the range from 0.3 mm*mrad to 34 mm*mrad, in particular in the range from 0.38 mm*mrad to 32 mm*mrad. When using a single-mode laser, an SPP of 0.6 mm*rad or less has proven particularly advantageous. When using a multimode laser, an SPP of 4 mm*rad or less is particularly advantageous.

With regard to process management, it is advantageous if a

Beam diameter of the at least one laser beam in the area from 10 gm to 800 gm, in particular in the range from 20 gm to 200 gm. When using a single-mode laser, a beam diameter in the range from 20 gm to 50 gm has proven advantageous, and when using a multimode laser, a beam diameter in the range from 50 gm to 200 gm has proven advantageous.

When using a laser beam source in the form of a

Infrared lasers in the laser beam device, it has proven to be advantageous if a wavelength of the at least one laser beam is in the range from 800 nm to 1200 nm, in particular in the range from 1030 nm to 1070 nm.

Again, when using a laser beam source in the form of a VIS laser in the laser beam device, it has proven to be advantageous if a wavelength of the at least one laser beam is in the range from 380 nm to 530 nm, particularly in the range from 400 nm to 515 nm or in the range from 400 nm to 450 nm (blue light) including 515 nm (green light).

The average laser power Pav can be in the range of 2 W to 2 . 000 W, especially in the range of 50 W to 700 W. When using laser pulses, the pulse peak power Ppeak can also be in the aforementioned ranges. A pulse frequency in the range from 25 to 50 . 000 Hz, especially in the range from 250 to 5. 000 Hz , can be used . A switching frequency with respect to the changing or Switching the laser beam profile can be greater than the pulse frequency f out . Further details and advantageous configurations of the invention can be found in the following description, on the basis of which exemplary embodiments of the invention are described and explained in more detail.

Show it :

FIGS. 1a-1c show cross-sectional views through a workpiece which is drilled using laser drilling methods known from the prior art;

FIGS. 2a, 2b perspective views of the workpiece from FIG. 1c ;

FIGS. 3a, 3b perspective views of a workpiece which is drilled by means of an exemplary embodiment of a laser drilling method according to the invention;

Figure 4 is a schematic cross-sectional view of a

From exemplary embodiment of a laser drilling device according to the invention during laser drilling of the workpiece from FIG. 3a, 3b;

FIGS. 5a, 5b are schematic views of possible laser beam cross sections of the laser drilling device from FIG. 4 laser beam used for laser drilling;

Figures 6a- 6c schematic representations of the

Laser beam cross section of the laser beam Fig. 4 with intensity distribution graphs in a plane of the laser beam cross section; and

Figures 7a-7c schematic representations compared to Figs. 6a-6c alternative laser beam cross section with intensity distribution graphs in the plane of the laser beam cross section.

FIGS. 1a-1c and FIGS. 2a, 2b show the laser drilling methods already explained at the outset in use on the workpiece 10, as are known from the prior art.

In contrast, FIGS. 3a, 3b and 4 show an exemplary embodiment of a method according to the invention for laser drilling the hole 11 in the workpiece 10 by means of a laser drilling device 40 set up according to an exemplary embodiment of the invention.

As Fig . 3a shows, other laser beam profiles 32, 34 (see FIG. 4) are used than are shown in FIG. 3a is the case with the prior art. Instead of operating a central surface 31 with a more intense radiation intensity in the laser beam cross section 30 than in an outer edge surface 33 surrounding it, as in FIG. 4 shows a different beam intensity distribution set on the basis of the laser beam cross section 30 of the laser beam 20 directed by the laser drilling device 40 onto the workpiece 10 with a laser pulse 21 .

In this case, a first average radiation intensity in the

Fig. 4 shown first laser beam profile 32 in the central surface 31 of the laser beam cross section 30 in FIG on the spanned x, y-plane lower, in particular by at least 10% lower and very particularly significantly lower, so that there is an intensity minimum in a centroid of the laser beam cross section 30 than a second average radiation intensity of the second laser beam profile 34 in the edge surface 33 of the laser beam cross section 30 .

As Fig . 3 a shows, this results in a central area 17 in the area of the bore 11 in the workpiece 10 which is not melted and is surrounded by an edge area 16 . The central area 17 corresponds locally essentially to the central area 31 of a laser spot of the laser beam 20 . Equally, the edge region 16 corresponds locally essentially to the edge surface 33 of the laser spot of the laser beam 20 or its laser beam cross section 30 . Consequently, the bore 11 can be drilled very precisely, with the central area 17 being punched out, which, unlike the edge area 16 , has no area 13 with molten material and no area 15 with vaporized material of the workpiece 10 .

As a result of the laser drilling process, what is shown in FIG. 3b obtained workpiece 10 shown, whose bore 11 can be produced very precisely with regard to the desired drilling depth T and minimum width B of the bore 11.

As Fig . 4 shows, the laser drilling device 40 has a laser processing head 41 in which a laser beam device 42 is at least partially arranged, which in turn can be connected to a laser beam source (not shown) or can have this. Furthermore, the Laser processing head 41 has optics 43 , which in particular can be embodied as scanner optics 43 .

Figures 5a, 5b show alternative laser beam cross sections 30, according to which the laser beam 20 can be formed. The outer edge surface 33 in the example of FIG. 5a rectangular, in particular square, instead of ring-shaped, as in FIG. 4 shaped . In the example of FIG. 5b, the laser beam cross-section 30 is shaped as a 12-corner polygon. Correspondingly, a bore 11 with a rectangular or polygonal cross section can be produced with such laser beam cross sections 30 .

Fig. 6a once again shows the laser beam cross section 30 from FIG. 4 . These show the Fig. 6b and 6c two intensity distribution graphs of the laser beam intensity I of the laser beam cross section 30, namely once in the x direction and once in the y direction of the x, y plane of the laser beam cross section 30 shown. It can be seen how the second average beam intensity of the second laser beam profile 34 has clear intensity peaks or Intensity maxima 35 , while the first average beam intensity of the first laser beam profile 32 in the central region 31 shows a clear intensity minimum 36 between the two intensity peaks 35 , in particular in or near a centroid of the laser beam cross section 30 .

Fig. 7a shows another laser beam cross section 30 for a possible laser beam 20 with which the laser drilling can be carried out according to the invention. Like the associated intensity distribution graphs in FIG. 7b, 7c show falls the intensity minimum 36 in the central region 31 is not quite as strong as in the laser beam cross section 30 of FIG. 6a, whereby a high process efficiency can still be achieved and the drilling diameter of the bore 11 can be set precisely.

Claims

Method for laser drilling a hole (11) in a workpiece (10), wherein at least one laser beam (20) is used for the laser drilling, characterized in that a laser beam cross section (30) of the at least one laser beam (20) has a central surface (31) with a first laser beam profile (32) having a first mean beam intensity and an outer edge surface (33) surrounding the central surface (31) with a second laser beam profile (34) having a second mean beam intensity, the second mean Radiation intensity is greater than the first average radiation intensity. Method according to claim 1, wherein material of the workpiece

(10) is melted and/or vaporized only in an edge region (16) of the bore (11) corresponding to the outer edge surface (33) of the laser beam cross section (30). Method according to Claim 1 or 2, in which the laser drilling of the bore (11) is carried out by one or more laser pulses (21) of the at least one laser beam (20). Method according to claim 3, wherein the first laser beam profile (32) and/or the second laser beam profile (34) is changed during a laser pulse (21). Method according to claim 3 or 4, wherein a diameter of the at least one laser beam (20) is changed during a laser pulse (21). Method according to one of claims 3 to 5, wherein a pulse shape of a laser pulse (21) is rectangular, triangular, sinusoidal or a combination of at least two of the aforementioned shapes. A method according to any one of the preceding claims, wherein the second mean beam intensity is at least 10% greater than the first mean beam intensity. Method according to one of the preceding claims, wherein an intensity gradient of the second laser beam profile (34) is greater than an intensity gradient of the first laser beam profile (32). Method according to one of the preceding claims, wherein the at least one laser beam (20) has a beam intensity minimum (36) of its beam intensity in the central area (31). Method according to claim 9, wherein the beam intensity minimum (36) propagates in a laser beam propagation direction of the at least one laser beam (20). A method according to any one of the preceding claims, wherein the outer peripheral surface (33) has a ring shape, a square shape or a polygon shape. Method according to one of the preceding claims, wherein the second laser beam profile (34) is generated by a plurality of laser beams (20), in particular arranged azimuthally. Method according to one of the preceding claims, wherein the second laser beam profile (34) is substantially homogeneous. Method according to one of the preceding claims, wherein a bore (11) with a bore depth (T) of <3 mm and/or with an aspect ratio of bore depth (T) to minimum width (B) of the bore (11) of <1:100 is produced. Laser drilling device (40) for laser drilling a hole (11) in a workpiece (10), the laser drilling device (40) having a laser beam device (42) for emitting at least one laser beam (20) and an optical system (43) for aligning the at least one laser beam (20) onto the workpiece (10) in such a way that a laser beam cross section (30) of the at least one laser beam (20) has a central area (31) with a first laser beam profile (32) having a first central beam intensity and an outer edge surface (33) surrounding the central surface (31) with a second laser beam profile (34) having a second mean beam intensity, the second mean beam intensity being greater than the first mean beam intensity.