Patent ID: 12240056

DETAILED DESCRIPTION

The laser processing machine1shown inFIG.1serves for the butt welding of two planar workpieces2bearing against one another in a butt joint, by a laser beam3. The two workpieces2are formed for example from, e.g., glass, quartz glass, polymer, glass ceramic, in crystalline fashion or from combinations thereof and/or with opaque materials.

The laser processing machine1includes a USP laser4for generating the laser beam3in the form of USP laser pulses5having pulse durations of less than 10 ps, e.g., in the form of femtosecond pulses, a horizontal workpiece table6, on which the two workpieces2to be welded bear next to one another, and a laser processing head8, which is movable in X-Y-directions and is height-positionable in the direction of the double-headed arrow7and has a focusing optical unit9for focusing the laser beam3emerging at the bottom of the laser processing head8. As an alternative or in addition to the laser processing head8that is movable in X-Y-directions, the workpiece table6can also be moved in X-Y-directions.

During the butt welding of the two workpieces2, the laser beam3is directed at right angles onto the workpiece top side10afacing the laser processing head8and is focused into the workpiece material in the region of the common joining surface11of the two workpieces2to locally melt the two workpieces2in the region of the joining surface11. In this case, the laser focus F of the laser beam3is moved in or counter to the beam direction12of the laser beam3to produce in the region of the joining surface11a vertical weld seam13extending in the beam direction12. In this case, the laser focus F of the focused laser beam3is situated at the joining surface11or in proximity to said joining surface11in the volume of one of the two workpieces2. Ideally, the process starts before the laser focus F to allow for power tolerances. Butt welding work is in the vicinity of or in very close proximity to the joining surface11. The vertical weld seam13extends almost over the entire workpiece thickness and ends before the workpiece top side and underside10a,10bsuch that no escape of material arises and a clean process is conducted. This depends on the size of the weld seam13or the welding bubble. Instead of being directed at right angles to the workpiece top side10aas inFIG.1, the laser beam3can also be directed obliquely onto the workpiece top side10a, such that the weld seam produced in the workpiece volume runs obliquely with respect to the workpiece top side10a(e.g.,450welding). The workpiece underside10bof the two workpieces2can for example be coated, e.g., with a highly reflective coating. A plurality of vertical weld seams13can be produced at a distance from one another along the joining line15of the two workpieces. The joining line15can also run non-straight, instead of straight as shown inFIG.1.

FIGS.2A-2Cschematically show different vertical advance movements of the laser focus F in the workpiece volume in the beam direction12, wherein during this vertical advance movement of the laser focus F the laser beam3is stationary relative to the two workpieces2. InFIG.2Athe laser focus F is moved in the beam direction12continuously (e.g., at a vertical advance speed of 20 mm/s) and inFIGS.2B and2C, the laser focus is moved step by step without pauses (FIG.2B) and with a temporal pause (e.g., 2 seconds) between the steps (FIG.2C). As shown inFIGS.2A-2C, the laser beam3can impinge on the workpiece top side10aat right angles or alternatively obliquely.

FIGS.3A-3Care photographs of vertical weld seams13produced by the vertical advance movements of the laser focus F as shown inFIGS.2A2C in a monolithic glass block. As shown inFIGS.3A-3C, both the continuous and the step-by-step movement of the laser focus F in the beam direction12result in a vertical weld seam13which is formed from solidification bubbles (which arise on account of local material densifications) or individual spot welds14and extends in the thickness direction D of the two workpieces2(as shown inFIG.1). It should be emphasized here that an individual spot weld14can also be placed through individual spot welds14that have already been produced beforehand. InFIG.3Bthe respective next individual spot weld14is produced in the material still hot from the preceding individual spot weld14, whereas inFIG.3Cthe respective next individual spot weld14is produced in the material that has already cooled down owing to the temporal delay with respect to the preceding individual spot weld14. No appreciable difference can be ascertained between the weld seam13in material processed hot (FIG.3B) and in cooled-down material (FIG.3C). As a result, the continuous movement and the step-by-step movement of the laser focus F in the beam direction12give rise to a vertical weld seam13. In this case, bubbles14arise during the solidification of the weld seam13on account of rapid expansion and cooling. The bubbles14are not desired, but are difficult to prevent.

FIGS.4A-4Cschematically show different vertical advance movements of the laser focus F in the workpiece volume counter to the beam direction12, wherein during this vertical advance movement of the laser focus F, the laser beam3is stationary relative to the two workpieces2. InFIG.4Athe laser focus F is moved counter to the beam direction12continuously (e.g., at a vertical advance speed of 20 mm/s) and inFIGS.4B,4Csaid laser focus is moved step by step without pauses (FIG.4B) and with a temporal pause (e.g., 2 seconds) between the steps (FIG.4C).

FIGS.5A-5Care photographs of vertical weld seams13produced by the vertical advance movements of the laser focus F as shown inFIGS.4A-4Cin a monolithic glass block. As shown inFIG.5A, the continuous movement of the laser focus F counter to the beam direction12results in a continuous, vertical weld seam13without discernible solidification bubbles or individual spot welds. InFIG.5Bwelding occurs in material still hot from the preceding step, and inFIG.5Cwelding occurs in material that has already cooled down due to the temporal delay with respect to the preceding step.FIGS.5B and5Ceach show a vertical weld seam13interrupted by solidification bubbles14with distinct cracks along the entire weld seam13. As a result, only the continuous movement of the laser focus F counter to the beam direction12gives rise to a continuous, crack-free vertical weld seam13extending in the thickness direction D of the two workpieces2.

During the vertical advance movement of the laser focus F in or counter to the beam direction12, the laser beam3can also be moved relative to the two workpieces2in an advance direction running parallel or transversely with respect to the joining line15, e.g., by the laser processing head8being correspondingly moved in the X-direction and Y-direction. In this case, however, the focus speed at which the laser focus F is moved in or counter to the beam direction12should be greater than the advance speed at which the laser beam3is moved in the advance direction.

By the butt welding methods described above, for example, individual mirror elements2(e.g., for a linear optical system) can be joined together to form a large mirror by one or more vertical weld seams being placed along the joining line. Moreover, poor horizontal weld seams can be corrected by vertical weld seams that are placed through a horizontal weld seam. The weld seam can also have a circular shape or other freeform contour. It is also possible to weld slightly curved surfaces with slight movement in the X-direction during Z-welding.

Other Embodiments

A number of embodiments of the present disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the present disclosure. Accordingly, other embodiments are within the scope of the following claims.