EP3887321A1

EP3887321A1 - Butt-joint welding method using a ukp laser beam, and optical element assembled from individual parts

Info

Publication number: EP3887321A1
Application number: EP19801844.2A
Authority: EP
Inventors: Dominik Bauer; Helge Höck; Michael Scharun; Manuel Schindler
Original assignee: Trumpf Laser GmbH
Current assignee: Trumpf Laser GmbH
Priority date: 2018-11-28
Filing date: 2019-11-09
Publication date: 2021-10-06
Also published as: US20210276128A1; DE102018220447A1; CN113227002A; WO2020108960A1

Abstract

The invention relates to a method for butt-joint welding two workpieces (2), in particular panel-shaped workpieces, which are made of glass, in particular quartz glass, using a pulsed laser beam (3), in particular a UKP laser beam, which is emitted into the workpiece material parallel to the joint surface (11) of the two workpieces (2) and which is focused into the workpiece material in the region of the joint surface (11) in order to locally melt the two workpieces (2) in the region of the workpiece joint surface (11). According to the invention, the laser focus (F) of the laser beam (3) focused into the workpiece material is moved in or opposite the beam direction (12) of the laser beam (3) in order to produce a weld seam (13) which extends along the beam direction (12) in the region of the joint surface (11).

Description

Process for butt welding using a UKP laser beam and an optical element assembled from individual parts

The invention relates to a method for butt welding two, in particular plate-shaped, workpieces made of glass, in particular quartz glass, by means of a pulsed laser beam, in particular UKP laser beam, which is irradiated into the workpiece material parallel to the joining surface of the two workpieces and which is in the area of the common joining surface is focused into the workpiece material, to locally melt the two workpieces in the area of their common joining surface, as well as an optical element assembled from several laser-welded individual parts

Ultra-short pulsed (UKP) laser radiation with pulse durations of less than 500 ps, especially in the femtosecond range, is increasingly being used for material processing. The special feature of material processing with UKP laser radiation is the high peak power / peak intensity of the laser radiation with the workpiece. As a result, extreme thermal imbalances can be generated in the solid, e.g. between electrons and atom / ion hulls, which then lead to unique removal or formation mechanisms.

The laser welding of laser-transparent glasses or other materials that are transparent, partially transparent or scattering for the laser beam by means of ultra-short laser pulses enables a stable connection without the use of additional materials, but is limited by laser-induced transient and permanent voltages. For butt-jointing two laser-transparent workpieces, e.g. glasses or crystals, a e.g. UKP laser beam focused in the center of the volume of the two workpieces is moved along the joining line in order to locally melt the two workpieces in the area of their interface and thereby produce a particularly continuous horizontal weld seam in the volume of the two workpieces. The weld seam is characterized by an from the outside

Sweat bladder recognizable melting zone is formed, which starts from the laser focus and extends in the form of a drop against the direction of the incident laser beam, that is, it tapers into the laser focus on the side facing the laser focus and terminates in a hemispherical manner on the side away from the laser focus. To increase the connection area, several weld seams are placed next to each other in strips. This known type of welding enables gas-tight weld seams and joining connections with high strength and is used for joining protective glasses, for example

The background is the local melting of the material using ultra-short laser pulses. If you focus ultra-short laser pulses in the volume of glass, e.g.

Quartz glass, the high intensity present in the laser focus leads to non-linear Absorption processes, which, depending on the laser parameters, can induce various material modifications. Through these non-linear absorption processes, free charge carriers are generated, which absorb quasi linearly as a result. This creates a local plasma that forms the melting zone. If you place the modification in the area of the interface between two glasses, the cooling melt generates a stable connection between the two glasses. Due to the very local joining process, the laser-induced stresses are typically low, which means that very different glasses can also be welded in terms of their thermal properties. Other transparent materials such as crystals with partially even more deviating thermal and mechanical properties can also be welded to one another or to glasses.

In contrast, the object of the present invention is to develop a butt butt welding process of the type mentioned at the outset in such a way that laser-transparent workpieces can be joined together with the least possible visual impairment.

This object is achieved according to the invention in that the laser focus of the laser beam focused in the workpiece material is moved in or against the beam direction of the laser beam in order to produce a weld seam extending along the beam direction in the region of the joining surface. The UKP laser beam preferably has laser radiation with pulse durations of less than 50 ps, preferably less than 1 ps, in particular in the femtosecond range.

According to the invention, weld seams can also be produced by advancing the laser focus in or against the beam direction. This advance movement of the laser focus can take place, for example, by a movement of the laser processing head in or against the beam direction of the laser beam and / or by a feed movement of the optical fiber and perforated element in or against the beam direction of the laser beam, but also a change in the focal length of the Focusing optics are possible. It was found that what has already been welded can be welded, which corrections wrong welds possible. According to the invention, it is also possible to weld curved or slightly curved surfaces with slight movement in the X direction during the Z weld. The advancing movement of the laser focus in or against the beam direction preferably takes place continuously, but can also take place step by step with or without pauses between the individual steps. In the latter case, welding without breaks leads to welding in the material still hot from the previous step, and welding with breaks leads to welding in material that has already cooled down due to the time delay to the previous step. As tests have shown, continuous laser welding against the beam direction in particular leads to a crack-free, continuous weld. In the case of a feed against the direction of incidence of the beam, a continuous feed in the range from 0.5 mm / s to 100 mm / s, preferably 5 mm / s to 30 mm / s, particularly preferably at approximately 20 mm / s, is preferred. worked.

Preferably, a weld seam with a seam diameter of 5-500 gm, preferably 50 gm to 100 gm, is produced during the welding.

In order to enlarge the tolerance range, a transverse displacement (xy displacement) of the laser focus is preferably superimposed on the feed direction of the laser focus in or against the radiation direction of the laser beam (so-called wobbling).

It is possible to work with single pulses during welding. When welding, pulse packets are preferably used which have several individual pulses. A pulse train consists of many individual pulses, the individual pulses in the pulse train having a single pulse repetition rate from pulse to pulse. Pulse packets consist of at least two individual pulses. There is also a single pulse repetition rate here. There is also a pulse packet-to-pulse packet repetition rate. The individual pulses in a pulse packet are preferably the same. The number of individual pulses in a pulse packet is, for example, between 2 and 20, preferably about 5. For example, the pulse packet-to-pulse packet repetition rates can be 50-200 kHz, preferably approximately 125 kHz, and the average pulse power can be 1-20 W, preferably approximately 10 W. The single pulse repetition rate in the pulse packet is typically several MHz.

The laser beam can be directed obliquely or, which is preferred, at right angles to the workpiece side facing the laser beam. In both cases, the weld seam extends in the thickness direction of the workpieces. For a reliable joint connection, several weld seams can be created spaced apart along the joining line of the two workpieces.

In a preferred method variant, the laser beam is not moved further relative to the two workpieces during the movement of the laser focus in or against the beam direction. In the event of a feed movement of the laser focus in the beam direction, welding is carried out using previously welded material, which, as tests have shown, is possible without any problems.

In another method variant, during the movement of the laser focus in or against the beam direction, the laser beam is moved relative to the two workpieces in a feed direction running parallel or transverse to the joining line of the two workpieces. The focus speed at which the laser focus is moved in or against the beam direction should advantageously be greater than the feed speed at which the laser beam is moved parallel or transverse to the joining line.

The two workpieces are preferably formed from glass, in particular quartz glass, from polymer, glass ceramic, crystals or combinations thereof and / or with opaque materials.

In a further aspect, the invention also relates to an optical element made of glass, in particular quartz glass, assembled with the butt-butt welding according to the invention from at least two individual parts, two individual parts being are laser-welded to one another by means of at least one weld seam extending in the thickness direction of the two individual parts. The weld seam can extend at right angles or also obliquely to a surface of the optical element and have a length of at least 50 mm, in particular of at least 1 mm. In this case, the weld seam can be designed as a continuous line or as an interrupted line consisting of spaced-apart individual welding points or sections. The weld seam preferably extends almost over the entire workpiece thickness and ends in front of the two workpiece sides in such a way that no material escapes and a clean process is carried out. This depends on the size of the weld or weld bladder. A plurality of weld seams extending in the thickness direction of the two individual parts are preferably arranged at a distance from one another along the joining line of the two individual parts.

According to the invention, large optics that were previously expensive to produce from a large substrate can now be joined inexpensively from individual parts that are laser-welded to one another via several vertical welds. In contrast to horizontal weld seams, vertical weld seams do not adversely affect the appearance, but only selectively. The extent of the weld seam in the optical element is small and thus the risk of changing the optical properties of the optics is minimized.

Further advantages and advantageous configurations of the object of the invention result from the description, the claims and the drawing. Likewise, the features mentioned above and those listed further can be used individually or in combination in any combination. The embodiments shown and described are not to be understood as an exhaustive list, but rather have an exemplary character for the description of the invention. Show it:

1 shows schematically a laser processing machine for butt-butt welding two laser-transparent workpieces according to the invention by means of a laser beam, one of the two workpieces being shown broken away in the area of vertical weld seams; Fig. 2a-2c schematically different vertical feed movements of the laser focus in the beam direction of the laser beam during butt welding according to the invention in order to produce a weld seam, in a sectional view along the joining surface of the two laser-welded workpieces;

Fig. 3a-3c photos of vertical welds made in a monolithic

Glass block with the in fig. 2a-2c, vertical feed movements of the laser focus were generated;

Fig. 4a-4c schematically different vertical feed movements of the

Laser focus against the beam direction of the laser beam in butt welding according to the invention to produce a vertical weld seam, in a sectional view along the joining surface of the two laser-welded workpieces; and

Fig. 5a-5c Photos of vertical welds made in a monolithic

Glass block with the in fig. 4a-4c, vertical feed movements of the laser focus were generated.

The laser processing machine 1 shown in FIG. 1 is used for butt butt welding two plate-shaped workpieces 2 which abut one another in the butt joint by means of a laser beam 3. The two workpieces 2 are made, for example, of glass, in particular quartz glass, of polymer, glass ceramic, crystalline or of combinations thereof and / or formed with opaque materials.

The laser processing machine 1 comprises a UKP laser 4 for generating the laser beam 3 in the form of UKP laser pulses 5 with pulse durations of less than 10 ps, in particular in the form of femtosecond pulses, a horizontal workpiece table 6 on which the two workpieces 2 to be welded side by side rest, as well as a laser processing head 8 movable in the XY direction and vertically displaceable in the direction of the double arrow 7 with focusing optics 9 for focusing the laser beam 3 emerging from the laser processing head 8 below. Alternatively or in addition to the laser beam movable in the XY direction machining head 8, the workpiece table 6 can also be moved in the XY direction. When the two workpieces 2 are butt-welded, the laser beam 3 is directed at right angles to the upper side 10a of the workpiece facing the laser processing head 8 and is focused into the workpiece material in the area of the joint surface 11 of the two workpieces 2, so that the two workpieces 2 in the area of the

Melt joint surface 11 locally. The laser focus F of the laser beam 3 is moved in or against the beam direction 12 of the laser beam 3 in order to produce a vertical weld seam 13 extending in the beam direction 12 in the region of the joining surface 11. The laser focus F of the focused laser beam 3 is located on the joining surface 11 or close to this joining surface 11 in the volume of one of the two workpieces 2. Ideally, the process starts before the laser focus F in order to have a performance tolerance. In butt welding, it is preferred to work in the vicinity or very close to the joining surface 11. The vertical weld seam 13 preferably extends almost over the entire workpiece thickness and thus ends in front of the workpiece top and bottom 10a,

10b that there is no material leakage and that a clean process is run. This depends on the size of the weld 13 or the weld bladder. Instead of at right angles to the workpiece top 10a as in FIG. 1, the laser beam 3 can also be directed obliquely to the workpiece top 10a so that the weld seam produced in the workpiece volume runs obliquely to the workpiece top 10a (for example 45 ° welding). The workpiece underside 10b of the two workpiece 2 can, for example, be coated, for example with a highly reflective coating. Fig. 2a-2c schematically show different vertical feed movements of the laser focus F in the workpiece volume in the beam direction 12, the laser beam 3 being stationary relative to the two workpieces 2 during this vertical feed movement of the laser focus F. In FIG. 2a the laser focus F is continuous in the beam direction 12 (for example with a vertical feed rate of 20 mm / s) and in FIGS. 2b, 2c step by step without pauses (Fig. 2b) and with a time pause (eg 2 s) between the steps (Fig. 2c). The laser beam 3 can, as in FIGS. 2a-2c shown, impinge at right angles or also obliquely on the workpiece top 10a. FIGS. 3a-3c are photos of vertical weld seams 13 drawn in a monolithic glass block, which are similar to those shown in FIGS. 2a-2c, vertical feed movements of the laser focus F were generated. As in Figs. 3a-3c, both the continuous and the step-wise movement of the laser focus F in the beam direction 12 leads to a vertical weld seam 13, which is formed from solidification bubbles (these arise due to local material densifications) or individual weld spots 14 and which are in one another Direction of thickness D of the two workpieces 2 extends. It should be noted that an individual welding point 14 can also be placed through previously generated individual welding points 14. In FIG. 3b, the next weld-in point 14 is generated in the material still hot from the previous individual weld spot 14, whereas in FIG. 3c the respective next weld-in point 14 is generated in the material that has already cooled due to the time lag to the previous individual weld spot 14. A noteworthy difference between the weld seam 13 in hot-processed material (FIG. 3b) and in cooled material (FIG. 3c) cannot be determined. As a result, the continuous and the stepwise movement of the laser focus F in the beam direction 12 leads to a vertical one Weld seam 13 This creates bubbles (voids) 14 when the weld seam 13 solidifies due to rapid expansion and cooling. These bubbles 14 are actually unwanted, but cannot be prevented.

Fig. 4a-4c schematically show different vertical feed movements of the laser focus F in the workpiece volume counter to the beam direction 12, the laser beam 3 being stationary relative to the two workpieces 2 during this vertical feed movement of the laser focus F, in FIG. 4a the laser focus F becomes continuous against the beam direction 12 (eg with a vertical feed speed of 20 mm / s) and in the fig. 4b, 4c moved step by step without pauses (Fig. 4b) and with a time pause (e.g. 2 s) between the steps (Fig. 4c).

Fig. 5a-5c are photos of vertical weld seams 13 drawn in a monolithic glass block, which are similar to those shown in FIGS. 4a-4c, vertical feed movements of the laser focus F were generated. As shown in FIG. 5 a, the continuous movement of the laser focus F leads against the beam direction 12 a continuous, vertical weld 13 without recognizable solidification bubbles or individual weld spots. In FIG. 5b welding is carried out in the material still hot from the previous step and in FIG. 5c in already cooled material because of the time delay to the previous step. Fig. 5b and 5c each show a vertical weld seam 13, interrupted by solidification bubbles, with clear cracks along the entire weld seam 13. As a result, only the continuous movement of the laser focus F against the beam direction 12 leads to a continuous, crack-free vertical weld seam 13, which is shown in FIG Direction of thickness D of the two workpieces 2 extends.

As shown in FIG. 1, a plurality of vertical weld seams 13 can be produced spaced apart from one another along the joining line 15 of the two workpieces. Instead of straight as shown in FIG. 1, the joining line 15 cannot run straight either.

During the vertical feed movement of the laser focus F in or counter to the beam direction 12, the laser beam 3 can also be moved relative to the two workpieces 2 in a feed direction running parallel or transverse to the joining line 15, e.g. by moving the laser machining head 8 in the X and Y directions accordingly. However, the focus speed at which the laser focus F is moved in or against the beam direction 12 should be greater than the feed speed at which the laser beam 3 is moved in the feed direction.

With the butt-joint welding described above, for example, individual mirror elements 2 (e.g. for a line optics) can be joined together to form a large mirror by placing one or more vertical weld seams along the joining line. Also bad horizontal welds can be corrected by vertical welds by a horizontal one

Welded through. The weld seam can also have a circular shape or other free-form contour. It is also possible to weld slightly curved surfaces with slight movement in the X direction during the Z weld.

Claims

1. Method for butt welding two, in particular plate-shaped, workpieces (2) made of glass, in particular quartz glass, by means of a pulsed laser beam (3), in particular UKP laser beam, which is parallel to the joining surface (11) of the two workpieces (2) into the Workpiece material is blasted in and is focused in the area of the joining surface (11) in the workpiece material in order to locally melt the two workpieces (2) in the area of their joining area (11),

characterized,

that the laser focus (F) of the laser beam (3) focused in the workpiece material is moved in or against the beam direction (12) of the laser beam (3), in order to extend in the area of the joining surface (11) along the beam direction (12) Generate weld seam (13).

2. The method according to claim 1, characterized in that the feed movement of the laser focus (F) in or against the beam direction (12) takes place continuously or stepwise.

3. The method according to claim 2, characterized in that the feed movement of the laser focus (F) against the beam direction (12) continuously with a feed speed of 0.5 mm / s to 100 mm / s, preferably of 5 mm / s to 30 mm / s, particularly preferably approximately 20 mm / s.

4. The method according to any one of the preceding claims, characterized in that a weld seam (13) with a seam diameter of 5 to 500 mm, preferably 50 to 100 mm, is produced.

5. The method according to any one of the preceding claims, characterized in that the advance and movement of the laser focus (F) in or against the radiation direction (12) of the laser beam (3) is also a transverse movement of the laser focus (F) is superimposed.

6. The method according to any one of the preceding claims, characterized in that the pulsed laser beam (3) is designed as a laser pulse packet, which consists of individual pulses.

7. The method according to claim 6, characterized in that the individual pulses in the pulse packet are the same.

8. The method according to any one of the preceding claims, characterized in that the laser beam (3) strikes the workpiece side (10a) facing the laser beam (3) at right angles or at an angle.

9. The method according to any one of the preceding claims, characterized in that a plurality of weld seams (13) are produced at a distance from one another along the joining line (15) of the two workpieces (2).

10. The method according to any one of the preceding claims, characterized in that during the advancing movement of the laser focus (F) in or against the beam direction (12) the laser beam (3) is not moved further relative to the two workpieces (2).

11. The method according to any one of claims 1 to 9, characterized in that during the advancing movement of the laser focus (F) in or against the beam direction (12), the laser beam (3) is parallel to the two workpieces (2) or is moved transversely to the joining line (15) of the two workpieces (2).

12. The method according to claim 11, characterized in that the focus speed at which the laser focus (F) is moved in or against the beam direction (12) is greater than the speed (v) , with which the laser beam (3) is moved parallel or transversely to the joining line (15).

13. The method according to any one of the preceding claims, characterized in that the UKP laser beam has laser radiation with pulse durations of less than 50 ps, preferably less than 1 ps, in particular in the femtosecond range.

14. Optical element made of glass, in particular quartz glass, which is assembled from at least two laser-welded individual parts (2),

characterized,

that two individual parts (2) are laser welded to one another by means of at least one weld seam (13) extending in the thickness direction (D) of the two individual parts (2).

15. Optical element according to claim 14, characterized in that the weld seam (13) extends at right angles or at an angle to a surface (10a) of the optical element.

16. Optical element according to claim 14 or 15, characterized in that the weld seam (13) has a length of at least 50 mm, in particular of at least 1 mm.

17. Optical element according to one of claims 14 to 16, characterized in that the weld seam (13) is designed as a continuous line or as an in particular interrupted line several times.

18. Optical element according to one of claims 14 to 17, characterized in that a plurality of weld seams (13) extending in the thickness direction (D) of the two individual parts (2) are spaced apart from one another along the joining line (15) of the two individual parts (2). are arranged.

19. Optical element according to one of claims 14 to 18, characterized in that the weld seam (13) has a seam diameter of 5 to 500 mm, preferably 50 to 100 mm.