Patent ID: 12194563

DETAILED DESCRIPTION OF THE INVENTION

As used throughout the present disclosure, unless specifically stated otherwise, the term. “or” encompasses all possible combinations, except where infeasible. For example, the expression “A or B” shall mean A alone, B alone, or A and B together. If it is stated that a component includes “A, B, or C”, then, unless specifically stated otherwise or infeasible, the component may include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C. Expressions such as “at least one of” do not necessarily modify an entirety of the following list and do not necessarily modify each member of the list, such that “at least one of “A, B, and C” should be understood as including only one of A, on one of B, only one of C, or any combination of and C.

The machining apparatus according to the embodiments of the invention are described below, inter alia, by way of examples with a machining head, without limiting the invention thereto. The machining apparatus and the method according to the embodiments of the invention can also be realised without a machining head.

The term. “a focus of the illumination laser beam and a focus of the machining laser beam axially apart from one another” in the embodiments means that the two focuses are axially apart from one another in the direction of irradiation towards the workpiece, i.e. are axially apart from one another along an optical axis with which the machining laser and illumination laser beams extend coaxially.

Furthermore, where value ranges are described here, the specification of a broad range with narrower alternative or preferred ranges is also considered to disclose ranges that may be formed by any combination of specified lower range limits and specified upper range limits.

FIG.1schematically represents a first example of a machining apparatus10for laser machining a workpiece according to the embodiments of the invention.

The machining apparatus10has a machining laser source10afor generating a machining laser beam14. Furthermore, an illumination laser source10bfor generating an illumination laser beam16is provided. In addition, in the machining apparatus10, there is an outlet opening10cfor the machining laser beam14and the illumination laser beam16. Furthermore, a laser beam guiding device is provided. The laser beam guiding device is designed in such a way that the machining laser beam14and the illumination laser beam16are conducted coaxially through the outlet opening10c. In the present example, the laser beam guiding device includes a transport fibre17to which the machining laser source10aand the illumination laser source10bare coupled. The machining laser source10ahas a power of about 6 kW and generates the machining laser beam in a spectral range which includes a wavelength of 1070 nm. The illumination laser source10bhas a power of about 300 mW and generates the illumination laser beam16with a central wavelength in a spectral range of 973 to 979 nm, with a wavelength band of 6 nm.

For machining a workpiece11made of stainless steel, the machining laser source10aand the illumination laser source10bare put into operation with the powers and spectral ranges described above. The machining laser and illumination laser beams14and16produced thereby are passed through the laser beam guiding device17and finally coaxially through the outlet opening10c, thus being directed coaxially towards the workpiece11. In this way, the workpiece is machined in a machining region11aby the machining laser beam14so that a self-emission of the workpiece is generated. In addition, the machining region11ais illuminated by the illumination laser beam16, so that laser machining of the workpiece11can be observed.

The self-emission in the laser machining is thermal, i.e. the self-emission of the workpiece is proportional to Planck's radiation spectrum shown inFIG.2. The process temperature of the laser machining of stainless steel is in the range of its melting temperature. Stainless steel, as well as other metals which are processed using lasers, for example on flatbed cutting systems, typically have a melting temperature below 3000 K. This means that the maximum thermal emission of these metals in the near-infrared region is 760 to 2500 nm, including stainless steel.

The power of the illumination laser source10band the spectral range of the illumination laser beam16are selected with the above-described ranges such that the illumination by the illumination laser beam16is brighter than the self-emission of the workpiece in the machining region11aduring laser machining.

Compared to the wavelength of the maximum self-emission of the stainless steel in the near-infrared region, i.e. larger than 1000 nm wavelength, it can be illuminated and observed at smaller wavelengths. Therefore, a lower illumination intensity is required for the selected spectral range of the illumination laser beam16than for illumination in the wavelength range of the maximum stainless steel self-emission. In this way, the self-emission of the workpiece11is less bright compared to the illumination in the observed spectral range, so the machining region11acan be observed with a lower self-emission of the workpiece.

Alternatively or additionally to the spectral range of the illumination laser beam16, the illumination power is adjusted according to requirements or the task, e.g. according to the surface structure, the material and/or the shape, e.g. the thickness, of the workpiece, and/or according to the requested illumination. Furthermore, the power of the illumination laser source can be adjusted according to the outlet opening of the machining apparatus, e.g. the optionally irradiated nozzle of a machining head. Furthermore, adjusting the power of the illumination laser source can promote safety for the operator of the machining apparatus, in particular eye safety. This may be advantageous in particular when servicing the open machining apparatus or an open machining head. For example, in such a situation or in a similar situation, the illumination laser source can be reduced to less than 1 mW power with a power of at least 50 mW, for example, so that the illumination laser source is substantially safe for the eyes.

If an illumination laser source with a power of at least 50 mW is used, in addition to an adjustment of the power, similar safety precautions can be taken to protect the eyes of an operator as with the machining laser. One possibility is to integrate the illumination laser in the safety circuit of the machining laser. The safety circuit allows the illumination laser source to be turned on only when a laser release is acknowledged and/or the machine enclosure is closed. Alternatively, care can be taken, in particular during servicing of the (open) laser head/machine interior, for the illumination laser not to be switched on without eye safety precautions, such as safety glasses.

In a modification of the first example, the power of the illumination laser source10ais about 50 mW, and the generated illumination laser beam16has a central wavelength in a range of about 486 to 490 nm. Even with this power of the illumination laser source and/or with this spectral range of the illumination laser beam, the self-emission of the stainless steel workpiece in said spectral range is less bright compared to the illumination, so the machining region11amay be observed with reduced or suppressed self-emission. The spectral range of the illumination laser beam is selected as a wavelength band of 4 nm. This narrow band helps to suppress or reduce the self-emission of the workpiece during the machining process. Furthermore, less power is needed because of the shorter wavelength selected compared to the first example of illumination.

Another modification of the first example relates to the transport fibre17. Here, the transport fibre17is designed so as to have an inner fibre core17a, an outer fibre core17benclosing the inner fibre core17aand a fibre cladding17cenclosing the outer fibre core17b. The transport fibre17is shown inFIG.3ain a cross-sectional view along the transport fibre17and inFIG.3bin a cross-sectional view transverse to the transport fibre17.FIG.3cshows the refractive index profile of the transport fibre corresponding to the cross section ofFIG.3b. The machining laser source10aand the illumination laser source10bare coupled to the transport fibre17such that the machining laser beam14is guided by the inner fibre core17aand the illumination laser beam16is also partially guided by the outer fibre core17b. This configuration causes the illuminated region of the workpiece to be substantially at least 1.5 times larger than the machining region11aof the workpiece. Furthermore, the illumination laser beam16can additionally be guided through the fibre cladding17c, wherein likewise the illuminated region of the workpiece is larger than the machining region. In all of these cases, the machining laser beam14and the illumination laser beam16are guided coaxially by means of the transport fibre17.

It should be noted that some fibres are configured without an outer core and the (inner) core is directly surrounded by the cladding. In this case too, the illumination laser beam can be guided through the fibre cladding. In such an example, the fibre core can have a diameter of 100 μm, and the fibre cladding surrounding the core can have a diameter of 150 or 360 μm.

If, as in the example ofFIGS.3ato3c, the illumination laser beam16is conducted via the outer fibre core17bor additionally via the fibre cladding17cof the transport fibre17, then the illumination laser beam16is wider than the machining laser beam14. The latter is guided only by the inner, clearly smaller fibre core17a; seeFIGS.3aand3b. Since the machining region11aof the workpiece11is within the region of extension of the machining laser beam16, the machining region11ais thus smaller than the illumination region. The diameter of the outer core17bor of the fibre cladding17ccan in principle be selected during fibre design. Depending on the desired extension of the illumination region, a correspondingly large fibre cladding or outer core diameter can be chosen. This measure, which ensures that the illuminated region around the machining region11ais sufficiently large, is independent of the focal position of the machining and illumination laser beams14and16. The size ratio of the machining region11aand the illumination region is particularly dependent on the diameter of the outer core17b. The design of the fibre is different and can be selected depending on the manufacturer of the fibre17; for example, the diameter of the inner fibre core can be 100 μm, and the outer fibre core150or 360 μm (from the centre of the fibre).

In further modifications of the first example, the laser beam guiding device includes the transport fibre17or no transport fibre17, and includes at least one element selected from the following group (not shown inFIG.1): at least one optical unit for focusing the machining laser beam and/or the illumination laser beam, e.g. a focusing lens; and at least one unit for at least partially deflecting the illumination laser beam and/or the machining laser beam, in particular a dichroic mirror. In each case, the laser beam guiding device causes the machining laser beam and the illumination laser beam to be coaxially guided.

If, in the present example and its modifications, the machining laser beam and the illumination laser beam are guided coaxially by means of the transport fibre17, a cost-intensively designed illumination laser source that is awkward to mount on the machining apparatus, in particular on a machining head of a machining apparatus, is not required. In addition, the machining apparatus or machining head does not become more complex or heavier because of an illumination laser source additionally mounted thereon.

Another modification of the first example comprises a video camera as a detector device (not shown inFIG.1) for detecting the illumination laser beam reflected from the workpiece, wherein a spectral range of the detector device is selected or adjustable such that it at least partially coincides with the spectral range of the illumination laser beam, in particular the reflected illumination laser beam. In this case, an element selected from the power of the illumination laser source and the spectral range of the illumination laser beam can be selected such that the detected self-emission is smaller in the detected spectral range than the power of the illumination laser beam reflected and detected by the workpiece. The detected spectral range of the detector device can be selected as a wavelength band having a width of less than 20 nm, preferably less than 10 nm, more preferably less than 5 nm. Furthermore, the detected spectral range can be in the spectral range of the illumination laser beam or substantially detect it or substantially coincide with it. For example, a video camera can be used as a detector device which records the observation region coaxially. In this way, the machining region is monitored by video camera. Instead of a two-dimensional, spatially resolved detection unit, such as a camera, a one-dimensional detector array can also be used, its orientation being provided transversely to the cutting direction. Using the cutting direction, the spatial resolution can be found in the direction perpendicular to the array.

FIGS.5and6show recordings from a coaxial video camera in a laser cutting process of a stainless steel workpiece, with a machining apparatus according to the above modification of the first example. The machined workpiece is thermally emitted during the laser cutting process, i.e. broadband over a large spectral range. If detected only in a narrow spectral band, the detected power of the self-emission of the workpiece is correspondingly much lower. A laser is inherently narrowband. All the power of a laser will only be present in the narrow spectral band. If narrowband is detected, preferably exclusively in the spectral band in which the laser emits, significantly less illumination power is needed in order to provide brighter illumination compared to the brightness of the self-emission. In the present case, the visual impression is particularly important.

FIG.5shows a camera recording of the laser cutting process without illumination. Essentially, the self-emission of the process can be seen. InFIG.6, the illumination laser is additionally turned on in the cutting process. For the recording fromFIG.6, a significantly shorter camera exposure time is required than without illumination. The self-emission is strongly suppressed (you can still see it weakly in the middle of the kerf gap); however, the environment of the cutting gap is clearly visible.

In a further modification, the laser beam guiding device or single or a plurality of elements thereof at least partially have an outer coating for reducing a reflection of the illumination laser beam. The coating is matched to the selected illumination and observation spectrum. This causes the largest possible part of the reflected illumination laser beam16to be observed and as few irritating reflections of the optical units as possible to occur. In particular, it is advantageous in this way to avoid reflections from planar optical units. In this modification, at the wavelength(s) of the illumination laser beam16, the dichroic mirror has a reflection-to-transmission ratio of about 50%, for example. All other optical elements are substantially 100% transmissive at the illumination wavelength(s).

FIG.4schematically shows a second example of a machining apparatus100for laser machining a workpiece according to the embodiments of the invention.

In the example ofFIG.4, the transport fibre17is coupled laterally to a machining head12of the machining apparatus100. Furthermore, a dichroic mirror13is provided, which reflects the machining laser beam14and the illumination laser beam16and is at least partially transparent to radiation reflected by the workpiece11in the wavelength range of the illumination. The dichroic mirror13is oriented within the machining head12such that the machining laser beam14and the illumination laser beam16are deflected towards the outlet opening10c. In addition, between the dichroic mirror13and the outlet opening10cis an optical unit, which is designed in the present example as a focusing lens18. Furthermore, a detector device in the form of a video camera15is provided. The dichroic mirror13is disposed between the focusing lens18and the video camera15. This makes it possible for the illumination beam14reflected by the workpiece to impinge on the video camera15at least partially through the focusing lens18and the dichroic mirror13.

During operation, the machining laser beam16and the illumination laser beam14are directed laterally into the machining head12via the transport fibre17, deflected at the dichroic mirror13towards the workpiece11and focused by the focusing lens18onto the workpiece11. The illumination laser beam14is at least partially reflected back into the machining head12through the outlet opening10c, is transmitted through the focusing lens18and the dichroic mirror13and impinges on the video camera15. In this way, the machining region11aof the workpiece11machined by the machining laser14is illuminated by the illumination laser beam16and observed by means of the illumination laser beam reflected at least partially on the video camera15.

In modifications of the second example, at least one element selected from the focusing lens18, the machining laser source10aand the illumination laser source10bis designed or can be adjusted such that a focus of the illumination laser beam16and a focus of the machining laser beam14are axially apart from one another, in particular on the optical axis. This design promotes illumination of a sufficiently large area around the machining region11a. In particular, the illumination region can be larger, for example at least 1.5 times as large, preferably twice as large, as the machining region11a, also referred to as the process interaction zone.

According to a particular modification, the machining laser source10aand the illumination laser source10bare designed or can be adjusted such that the spectral ranges of the laser beams generated by them differ, and the focusing lens18is designed to be dispersive.

In the above modification of the second example, the focus of the illumination laser beam16and the focus of the machining laser beam14do not coincide, but are apart from one another axially on the optical axis. This is achieved by the fact that the wavelengths of the machining laser beam14and the illumination laser beam16are divergent and the optical unit, in the present modification the focusing lens18, is designed to be dispersive, i.e. has a wavelength-dependent refractive index. The latter is the case with substantially all known optical materials.

With the known lens focal length formula, there is a difference Δf=f2−f1in the focal lengths of the two wavelengths of the machining laser beam14and of the illumination laser beam16.

Δ⁢f≈r1⁢r2r1+r2⁢Δ⁢n(n1-1)⁢(n2-1)

wherein the refractive indices of the two wavelengths are denoted by n1and n2, and Δn=n2−n1is used. Δf is advantageously large when large radii r1and r2of the imaging optical unit, here the focusing lens18, are used and Δn is large. With a machining laser beam14, which also has a wavelength of 1070 nm in the present example, illumination laser beams16having a wavelength of less than 1070 nm, in particular wavelengths of the blue spectral range, are therefore to be preferred.

According to another modification of the second example, a further improvement in illumination is achieved by means of beamforming. In this case, the laser beam guiding device comprises a unit for selective beamforming of the illumination laser beam, for example a modified focusing lens18, which is designed such that the illuminated region of the workpiece11is larger than the machining region of the workpiece11, in particular at least 1.5 times as large, preferably twice as large as the machining region11a. This beamforming acts only on the illumination laser beam16and not on the machining laser beam14.

An example of said selective beamforming may be a diffractive optical element that only affects radiation having a wavelength in the range of the illumination laser wavelength and leaves the machining laser beam14unchanged. As a diffractive optical element, a diffractive optical grating can also be used on an (already existing) optical element.

Another example can be a beamforming element for optimal illumination which is implemented and/or designed such that only the illumination laser beam16guided over the outer core of the transport fibre17is affected and the machining laser beam14remains unchanged.

Finally, it should be noted that the description of the invention and the exemplary embodiments are not to be understood as limiting in terms of a particular physical realisation of the invention. All of the features explained and shown in connection with individual embodiments of the invention can be provided in different combinations in the subject matter according to the invention to simultaneously realise their advantageous effects.

The scope of protection of the present invention is given by the claims and is not limited by the features illustrated in the description or shown in the figures.

It is particularly obvious to a person skilled in the art that the invention can be used not only for laser machining systems, but also for other devices comprising lasers. Furthermore, the components of the machining apparatus for laser machining workpieces can be produced so as to be distributed over several physical products.