DE102015001466A1 - Method and device for determining a three-dimensional geometric energy distribution of a laser beam - Google Patents

Abstract

The invention relates to a method for determining a three - dimensional geometric energy distribution of a laser beam (3) comprising the following steps: providing a test volume (5) which has at least one test material (7) sensitive to a laser beam (3) to be tested; Irradiating the test volume (5) with the laser beam (3) to be tested, and evaluating the test material (7) in the test volume (5) with regard to a three-dimensional geometric energy distribution of the laser beam (3).

Description

The invention relates to a method and a device for determining a three-dimensional geometric energy distribution of a laser beam.

In particular, in laser welding and especially in the welding of plastics, in particular of polymer components, an essential process variable for influencing the quality of a locally introduced into the parts to be welded energy and their geometric distribution. This introduced energy depends on a variety of parameters such as wavelength, irradiation time, materials and geometry. In the process development of a laser welding application, it is advantageous for influencing the quality to determine the energy introduced by the laser as accurately as possible quantitatively locally at the welding site in order to set up the process.

From the German patent application DE 10 2007 051 688 A1 a method for monitoring of workpieces, in particular in the laser plastic welding of two joining partners is known, comprising the following features: irradiating a lying in a workpiece test zone, in particular a weld, with a laser radiation to produce a heat source, detection of direct heat radiation of the heat source in the test zone by means of a thermal sensor through the workpiece at a first time, detection of the heat source from the heat source to the surface of the workpiece transported and there radiated at a later time indirect heat radiation by means of the thermal sensor, and evaluation of the time offset between the two times to determine a to be monitored parameters.

From the German patent application DE 10 2007 021 715 A1 is a feedback control system for controlling a laser source known. This includes a laser source which emits laser energy and an optical sensor which detects the laser energy. The optical sensor outputs a measured signal in response to a measured contribution of the laser energy. The system further includes an optical device that receives the laser energy and guides it to a predetermined location. The optical device reflects a first portion of the laser energy toward the optical sensor. A controller receives the measured signal from the optical sensor and calculates the amount of the first portion of the laser energy. The controller then adjusts the laser source to correct for the losses associated with the reflection of the first portion of the laser energy from the optical device such that a predetermined amount of the laser energy is obtained at the predetermined location. The disadvantage is that the known methods and devices are very complex and complex.

The invention is therefore based on the object to provide a method and an apparatus which do not have the disadvantages mentioned, wherein they are particularly simple and suitable for industrial applications.

The object is achieved by providing the subject matters of the independent claims. Advantageous embodiments emerge from the subclaims.

The object is achieved in particular by providing a method for determining a three-dimensional geometric energy distribution of a laser beam with the following steps: A test volume is provided which has at least one material sensitive to a laser beam to be tested. The test volume is irradiated with the laser beam to be tested, and the test material is evaluated in the test volume with respect to a three-dimensional energy distribution of the laser beam. The provision of the test volume with the material sensitive to the laser beam is simple and extremely cost-effective. By providing and irradiating a test volume, its three-dimensional energy distribution can be determined in an extremely simple and cost-effective manner by examining the test material after irradiation with the laser beam, without the need for elaborate and expensive sensors or evaluation or control mechanisms. In addition, due to the three-dimensional design of the test volume, complete information about the energy distribution of the laser beam in all three spatial directions is possible. Due to the fast three-dimensional determination of the energy distribution, especially in a welding area, set-up times for a laser welding process are shortened, and a process stability and weld quality can be increased. In addition, there is no need or only a significantly reduced production of micrographs for quality control and a significantly reduced accompanying examination of the weld quality, the total set-up costs associated with such a laser process can be reduced.

The fact that the test material is sensitive to the laser beam to be tested means, in particular, that the test material changes during the interaction with the laser beam or under the action of the laser beam. At least one physical and / or chemical property of the test material changes. In particular, it is possible that the test material reacts under the action of the laser beam, in particular chemically reacted, preferably with ambient gases, for example oxygen, that the test material melts, that it crystallizes, and / or that it exhibits an exposure reaction, in particular a color change and / or undergoes a change in its absorption and / or transmission properties. These changes, which the test material experiences locally under the action of the laser beam-in particular depending on a local intensity or energy distribution of the laser beam-can be evaluated after the irradiation of the test volume with the laser beam in order to determine its three-dimensional geometric energy distribution.

Thus, local changes in the test material for evaluating the same are preferably determined, the local changes being inferred from the three-dimensional geometric energy distribution of the laser beam.

An energy distribution here also means, in particular, an energy density, a power distribution or power density, as well as a geometric positioning of the laser beam-in particular relative to the test volume-in particular the focal position of the laser beam and the spatial extent of the typically tubular focus area being evaluated.

Preferably, the laser beam is aligned relative to the test volume so that the focus area is disposed in the test material or at least at an entrance surface of the laser beam into the test material. This makes it possible to determine the relevant properties of the three-dimensional geometric energy distribution of the laser beam safely, stably and quickly.

An embodiment of the method is also preferred, which is characterized in that a laser beam is tested which is set up and provided for laser welding of polymer components, in particular of a thermoplastic material or of thermoplastic materials. In this case, at least one parameter of the laser beam is tuned for the test for subsequent welding conditions. This means that the laser beam with which the test volume is irradiated, at least with respect to one parameter, is tuned to the subsequent welding conditions, wherein it may, for example, be scaled with respect to the power with a known factor. However, the at least one parameter is particularly preferably chosen to be identical to the subsequent welding conditions, so that the laser beam can be examined exactly as it is later used in laser welding. As a result, particularly realistic information can be obtained when testing the laser beam using the test volume and the test material. Particularly preferably, all parameters of the laser beam are selected to be identical to the conditions or parameters selected later for the laser welding method. The at least one parameter is preferably selected from a group consisting of a laser power, a wavelength of the laser beam, a focal position thereof, a widening, a beam shape, a feed speed along a predetermined displacement path for the laser welding, an irradiation time, in particular a local residence time along the Displacement path, a pulse duration of a pulsed laser and a shutter opening time of a continuous laser (CW laser).

In a particularly preferred embodiment of the method, the test material corresponds to the plastic to be welded in a subsequent welding process or is identical to this. Furthermore, it particularly preferably has an identical geometry. In this case, not only the three-dimensional geometric energy distribution related to the laser beam can be determined, but also directly and directly the energy introduced during the later welding process into the material to be welded can be examined in its three-dimensional distribution on the basis of the test material. It is particularly preferably provided that the laser beam is selected with respect to all parameters identical to the subsequent welding conditions, at the same time the test material corresponds to a plastic to be welded or is identical to the plastic to be welded. In this way, it is possible to gain detailed knowledge about the energy deposited in the material to be welded and its spatial-geometric distribution in an extremely simple and quick manner with extremely high accuracy and certainty.

An embodiment of the method is also preferred, which is characterized in that the laser beam is displaced along a predetermined displacement path relative to the test volume, wherein a change in the three-dimensional energy distribution along the displacement path is examined. Typically, the laser beam is guided along a predetermined displacement path during laser welding to create a weld. It is possible that due to various effects, such as a changing distance between the laser source and the welding material, a changing focus position, optionally depending on the displacement path changing laser energy and / or a variety of other parameters different welding conditions and in particular different energy distributions of the laser beam along the displacement path. This can be realistically, safely, quickly and inexpensively investigated using the proposed embodiment of the method. The predetermined displacement path preferably corresponds exactly to the welding path for laser welding, wherein it is particularly preferably identical to the displacement path which the laser beam takes during laser welding.

An embodiment of the method is preferred, which is characterized in that an amorphous polymer material is used as the test material. Polycarbonate is particularly preferably used as test material. An amorphous polymer material is preferred over a crystalline polymer material, in particular because it typically has a higher transparency. If the test volume with the amorphous polymer material as the test material is irradiated by the laser beam to be tested, structural changes occur in the three-dimensional test material, which are dependent on the local laser power or energy density of the laser beam. These microstructural changes can be examined following irradiation, whereby the geometric distribution of the energy or power in the laser beam, as well as the beam positioning and focusing can be determined.

An embodiment of the method is also preferred, which is characterized in that a fluid, a granular or a gel-like material is used as the test material, in particular of exactly one particular chemical substance. Particularly preferably, a powder, a liquid or a gel is used as the test material, this being preferably embedded in the test volume. In this case, the test material is preferably meltable by the laser beam. In order to obtain as meaningful a measurement as possible, it is preferred that the test material is actually melted by it above a predetermined energy density of the laser beam. Based on the position and the amount of molten test material, the three-dimensional geometric energy distribution of the laser as well as its positioning and focusing can be determined.

An embodiment of the method is also preferred which is characterized in that a preferably homogeneous mixture of energy-selectively selectively different materials sensitive to the laser beam is used as the test material. These materials are preferably in the form of small particles, in particular in the form of - preferably coated with colored beads - which react energy-dependent with the laser beam, wherein the particles of different, mixed materials are characterized in terms of their energy-dependent interaction with the laser beam. For this purpose, for example, a color code can be selected, for example such that at lower energy density melting particles are colored blue, with melting at higher energy density melting particles are red, with gradations with respect to the specific energy density at which the particles melt first, can be provided. The particles are preferably homogeneously mixed, with a spatial resolution of the method being predefined in particular by a region in which at least one particle from each type of material used occurs. On the fine granularity or the particle size of the materials used and the homogeneity of the mixing so the spatial resolution of the process can be adjusted. If the material is irradiated with the laser beam, locally melt those beads which are melted at and below the local prevailing energy density of the laser beam, whereby those particles which are melted only above the local prevailing energy density, do not melt. Based on the identity of the locally selectively interacting with the laser beam particles can then be determined in a next step, the three-dimensional geometric distribution of the energy density of the laser, its positioning and focusing. In this case, the particles of the different materials can also be distinguished from one another in a different way than by their color, for example based on their density.

An embodiment of the method is also preferred, which is characterized in that a plurality of layers of the test material is used as the test volume, as viewed in the propagation direction of the laser beam. It is possible that different layers in the form of films or plates are present, which are preferably stacked on top of each other. It is possible that the layers are laminated together.

In particular, in this case, but also in other cases, it is possible that the layers exposed simultaneously, so are irradiated at the same time with the laser beam. Alternatively, it is possible that the individual layers are sequentially irradiated, thus sequentially. In this case, for example, first a first layer of the test material is irradiated. This is then taken away, and it is irradiated a second, arranged underneath layer. This is then taken away again, and it is a third, arranged underneath layer irradiated. This is continued until all layers of the test material, arranged one below the other in the direction of propagation of the laser, have been sequentially irradiated successively. The irradiated layers can be evaluated to reflect the change from one layer to the next To determine three-dimensional geometric energy distribution of the laser beam.

In a preferred embodiment of the method it is provided that the different layers have exactly one particular chemical substance, so that the test material is formed as a single-substance system. Alternatively, it is possible that the test material used is a known structure having mutually different materials, in particular with energy-dependent selectively different materials sensitive to the laser beam. In this case, in particular the individual layers are selectively sensitive to the laser beam depending on the energy. Based on the identity of the selectively reacting laser-active materials can then - as explained above - three-dimensional geometric energy of the laser beam can be determined.

Particularly preferred is an embodiment of the method in which a block with a plurality of layers of photo paper is used as the test volume. This block of photo paper is exposed two-dimensionally in layers from top to bottom. After exposure of a first, uppermost layer in a first step, for example, in a second step, the uppermost layer is removed, and in a third step, the next, second layer is exposed. This will continue until all layers of the block have been exposed. Finally, the three-dimensional energy distribution in the laser beam and in particular the three-dimensional laser focusing can be determined on the basis of the change of the two-dimensional exposure pattern from one layer to the next layer.

The object is also achieved by providing a device for determining a three-dimensional geometric energy distribution of a laser beam which has a test volume which has at least one material sensitive to a laser beam to be tested. In connection with the device, the advantages that have already been explained in connection with the method result.

The test material preferably comprises or consists of an amorphous polymer material. In a preferred embodiment, the amorphous polymer material is polycarbonate.

Alternatively or additionally, it is provided that the test material comprises a fluid, granular or gel-like material, or consists of a fluid, granular or gel-like material, in particular of exactly one particular chemical substance. In particular, it is preferably a powder, a liquid or a gel. The material is preferably fusible by the laser, more preferably a predetermined energy density exists above which the material is fusible by the laser beam.

Alternatively or additionally, the test material comprises a - preferably homogeneous - mixture of energy-dependent selectively differently sensitive to the laser beam materials or consists of such a mixture.

Alternatively or additionally, the test volume - seen in the direction of propagation of the laser beam - a plurality of layers of the test material, which can preferably be irradiated successively, in particular irradiated layers can be removed so that underlying layers can be irradiated. Particularly preferably, the test volume has a block with a plurality of layers of photo paper.

It is also preferred an embodiment of the device that is characterized in that the test volume comprises a vessel or a frame in which the test material is arranged.

In a plane perpendicular to the propagation direction of the laser beam, the test volume preferably has an extent which is at least as great as the largest diameter of the laser beam to be examined by means of the test volume. In this way it is possible to obtain complete information about a region of interest of the laser beam.

The description of the device on the one hand and the method on the other hand are to be understood as complementary to each other. Procedural steps that have been described explicitly or implicitly in connection with the device are preferably individually or combined with each other steps of a preferred embodiment of the method. Features of the device that have been described explicitly or implicitly in the context of the method are preferably individually or combined together features of a preferred embodiment of the device. The method is preferably characterized by at least one method step, which is caused by at least one feature of the device. The device is preferably characterized by at least one feature, which is due to at least one method step of a preferred embodiment of the method.

The invention will be explained in more detail below with reference to the drawing.

Showing:

1 A first schematic representation of an embodiment of the method;

2 a second schematic representation of the embodiment of the method with altered irradiation conditions;

3 a schematic representation of a second embodiment of the method, and

4 a schematic representation of a third embodiment of the method.

1 shows a schematic representation of a first embodiment of a method for determining a three-dimensional geometric energy distribution of a laser beam. It is in 1 also an embodiment of a device 1 illustrated, which is adapted to determine the three-dimensional geometric energy distribution of a laser beam schematically illustrated 3 , The device 1 has a test volume 5 on, the at least one on the laser beam to be tested 3 sensitive test material 7 having. The test volume 5 becomes with the laser beam 3 irradiated, with the test material 7 changed not only in the range of a focal point of the laser, but also outside the focal point under the action of laser radiation. This makes it possible, not only the position of the focal point of the laser beam 3 but also to investigate its three-dimensional geometric energy distribution in a volume outside the focal point.

It is possible that the test material 7 under the action of the laser beam 3 a chemical reaction is received, melts, crystallized or generally exposed, so in particular shows a change in color or absorption due to exposure to the laser radiation. After irradiation with the laser beam 3 can be local changes of the test material 7 be determined, which in turn draw conclusions about the spatial-geometric energy distribution in the laser beam 3 allow.

The laser beam 3 is preferably set for laser welding of polymer components, in particular of thermoplastic materials. In doing so, all parameters of the laser beam become 3 in the context of the method preferably chosen as they are also chosen for the laser welding. This applies in particular to the global power of the laser beam 3 , its wavelength, its focal position, its widening and / or beam shape, its feed rate along a predetermined displacement path, its irradiation duration, in particular the pulse duration of a pulsed laser beam or the duty cycle of a continuous laser beam (cw laser beam). Will the later to be welded polymer material as a test material 7 using the method proposed here, not only the three-dimensional geometric energy distribution of the laser beam 3 but also the energy deposited in the polymer material is determined directly in its three-dimensional geometric distribution.

As part of the in 1 illustrated embodiment of the method is the laser beam 3 along a predetermined displacement path relative to the test volume 5 shifted, as is also intended to produce a weld during laser welding. Within the scope of the method, a change in the three-dimensional geometric energy distribution of the laser beam then takes place 3 along the displacement path. The displacement path in the context of the method preferably corresponds to the welding path for a subsequent laser welding with the laser beam 3 ,

In 1 is the relocation route 9 here indicated by a curve, which the trajectory of the focal point of the laser beam 3 equivalent. This representation has been chosen for simplicity, in fact, it comes to every point of the displacement path 9 or the in 1 represented curve starting from this point three-dimensionally extending volume, which is the three-dimensional geometric energy distribution of the laser beam 3 represents.

This volume typically has the shape of an hourglass, in particular it has a constriction at the location of the focus of the laser beam. A corresponding volume is shown schematically and with the reference numeral 11 characterized.

The test material 7 preferably has an energy threshold or a threshold for the energy density, above which it with the laser beam 3 interacts or when irradiated with the laser beam 3 changed. Therefore, in the test volume 5 typically not the entire beam path of the laser beam 3 in the form of a change of the test material 7 but only one - here in the form of the volume 11 indicated - range of the laser beam 3 in which its energy or power density is the threshold of the test material 7 exceeds. The test material 7 However, it is chosen so that this area is not limited to the focal point of the laser beam 3 limited, but a volume - namely the volume 11 - encloses around the focus point.

For the test material 7 it can be an amorphous polymer material, in particular polycarbonate, a fluid, granular or gel-like material, in particular a powder Liquid or a gel to a - preferably homogeneous - mixture of energy-dependent selectively in different ways on the laser beam sensitive materials, or - seen in the direction of propagation of the laser beam - a plurality of layers of test material, in the latter case, the various layers irradiated successively become. In particular, it is possible that the test volume 5 has a plurality of layers of photo paper.

Preferably, the test volume 5 also a vessel 13 in which the test material 7 is arranged.

In the embodiment according to 1 can the vessel 13 be formed as a box completely with the test material 7 is filled. The container 13 but can also be designed as a kind of frame having a hollow wall, which with the test material 7 - along the relocation route 9 - Is filled, wherein a space enclosed by the frame interior can remain empty.

2 shows a second schematic representation of the method. Identical and functionally identical elements are provided with the same reference numerals, so that reference is made to the preceding description. Here is - preferably at increased laser power of the laser beam 3 - The focus widened, resulting in a larger interaction volume 11 in the test material 7 looming. The widening of the focus here is also in the form of compared to 1 thicker curve representing the displacement path 9 features. Based on a comparison of 1 and 2 it becomes clear that with the help of the method the three-dimensional geometric energy distribution of the laser beam 3 can be detected in a simple, faster and safer way.

3 shows a schematic representation of a second embodiment of the method. Identical and functionally identical elements are provided with the same reference numerals, so that reference is made to the preceding description. Here it is shown that the focusing - and preferably also the power density of the laser beam 3 - along the relocation route 9 changed. On the one hand, this is based on the variable thickness of the displacement path 9 recognizable curve along the displacement path, on the other at the two here along the displacement path 9 offset volumes shown 11 . 11 ' , being a second volume 11 ' is greater than a first volume 11 , It thus appears that in the context of the method, in particular, changes in the three-dimensional geometric energy distribution of the laser beam 3 along a predetermined displacement path 9 can be determined.

The 1 to 3 is common that the focus of the laser beam 3 here in the test material 7 is arranged so that an area of the laser beam 3 in the form of volumes 11 . 11 ' above and below - in the propagation direction - the laser beam 3 in the test material 7 in the form of a change of the same.

4 shows a schematic representation of a third embodiment of the method. Identical and functionally identical elements are provided with the same reference numerals, so that reference is made to the preceding description. In this embodiment of the method, the focus of the laser beam is at an entrance surface 15 of the laser beam 3 into the test material 7 arranged. As a result, only one region of the laser beam, arranged below or behind the focus, as viewed in the propagation direction, is distinguished here 3 in the form of a change in the test material 7 from. It shows in comparison to the 1 to 3 thicker, the displacement path 9 indicating curve in 4 that here is the laser power or energy density of the laser beam 3 was particularly high.

Overall, it turns out that by using the method and the device 1 a fast, accurate and three-dimensional determination of the energy distribution of the laser beam 3 can be determined in a welding area, which shortens the setup times for a laser welding process and increases its process stability and the weld quality. In addition, a reduction of set-up costs is achieved by the production of micrographs, and costs associated with accompanying weld quality inspection are reduced.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102007051688 A1 [0003]
• DE 102007021715 A1 [0004]

Claims (9)

Method for determining a three-dimensional geometric energy distribution of a laser beam ( 3 ) comprising the following steps: providing a test volume ( 5 ), the at least one on a laser beam to be tested ( 3 ) sensitive test material ( 7 ) having; - irradiation of the test volume ( 5 ) with the laser beam to be tested ( 3 ), and - evaluation of the test material ( 7 ) in the test volume ( 5 ) with regard to a three-dimensional geometric energy distribution of the laser beam ( 3 ). Method according to claim 1, characterized in that a laser beam ( 3 ) is tested for laser welding of polymer components, in particular of thermoplastic materials, wherein at least one parameter of the laser beam ( 3 ) is selected for the test matched to subsequent welding conditions. Method according to one of the preceding claims, characterized in that the laser beam ( 3 ) along a predetermined displacement path ( 9 ) relative to the test volume ( 5 ), wherein a change in the three-dimensional geometric energy distribution along the displacement path ( 9 ) is examined. Method according to one of the preceding claims, characterized in that as test material ( 7 ) an amorphous polymer material is used. Method according to one of the preceding claims, characterized in that as test material ( 7 ) a fluid, granular or gel material is used. Method according to one of the preceding claims, characterized in that as test material ( 7 ) a - preferably homogeneous - mixture of energy-dependent selectively on the laser beam ( 3 ) sensitive materials is used. Method according to one of the preceding claims, characterized in that the test volume ( 5 ) - in the propagation direction of the laser beam ( 3 ) - a plurality of layers of the test material ( 7 ), which are preferably irradiated successively, using as test volume ( 5 ) preferably a block is used with a plurality of layers of photo paper. Contraption ( 1 ) for determining a three-dimensional geometric energy distribution of a laser beam ( 3 ) with a test volume ( 5 ), the at least one on a laser beam to be tested ( 3 ) sensitive test material ( 7 ) having. Device according to claim 8, characterized in that the test volume ( 5 ) a vessel ( 13 ) or a frame in which the test material ( 7 ) is arranged.

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