METHOD FOR INTRODUCING A PERFORATION LINE INTO AN AIRBAG COVER

Description

[0001] The invention relates to a method for introducing a perforation line into an airbag cover, in which a residual wall thickness of the airbag cover is determined and a processing beam source is controlled depending on the residual wall thickness.

[0002] A method for processing a workpiece, which can in particular be a plate-like material for the deployment of an airbag (airbag cover), is known from DE 10 2018 002 300 A1. For area attenuation, an attenuation laser beam is emitted by an attenuation laser, which is guided overlapping, parallel, or corresponding to a measurement laser beam, wherein the measurement laser beam has a wavelength that differs from the wavelength of the attenuation laser beam. An area to be attenuated exhibits a higher transmission for the wavelength of the measurement laser beam than for the wavelength of the attenuation laser beam. The attenuated areas can be arranged next to each other in a tooth-like row.The current power of the measuring laser beam is measured by a detection sensor, and a residual wall thickness is indirectly determined from this power using a predefined measuring laser-attenuating laser relative path ratio. Based on the determined residual wall thickness, the laser power and / or the laser duration of the attenuating laser are adjusted. In the disclosed method, laser radiation must always be transmitted through the workpiece to determine the residual wall thickness and consequently to adjust the parameters of the attenuating laser. This means that only very small residual wall thicknesses can be determined, and the method is only suitable for certain workpiece materials with corresponding optical properties.

[0003] Another method for laser material processing of a workpiece is disclosed by WO 2014 / 138939 A1. This method comprises the emission of a material processing beam and one or more imaging beams. A phase change region of the workpiece is illuminated with the material processing beam and at least one imaging beam. The imaging beams are used to perform measurements at at least one point in the phase change region using low-coherence interferometry. For this purpose, the components of the imaging beams reflected by the workpiece are combined with other components, for example, from a reference arm, to generate an interferometric output based on a path length difference. Subsequently, the interferometric output is processed to determine at least one characteristic of the phase change region, such as the depth of a blind hole.Based on at least one specific characteristic of the phase change range, at least one parameter of the machining process can be controlled.

[0004] DE 10 2018 129 407 A1 discloses a method for cutting a workpiece using a laser beam. In this method, a cutting slit is created on the workpiece with the laser beam emitted by a laser device. Simultaneously, the cutting slit is illuminated by a measuring beam emitted from a light source of a coherence tomograph. The coherence tomograph has a reference arm from which coupled light is made to interfere with the reflected measuring beam. The measuring beam is deflected to measure the cutting slit, and an interference response is detected to determine at least one geometric property of the cutting slit. Based on the at least one detected property of the cutting slit, a process parameter of the cutting process, in particular the parameters of the laser device, can be controlled.

[0005] A disadvantage of the two aforementioned methods is that the reference arm is independent of the workpiece. This means that unevenness of the support surface on which the workpiece rests, unevenness of the workpiece surface, or variations in the workpiece thickness are not taken into account, leading to an incorrect determination of the remaining wall thickness.

[0006] WO 01 / 70445 A1 discloses a device for introducing a predetermined breaking line into an airbag cover, comprising two sensors directed towards the processing point from opposite sides. The remaining wall thickness is derived from a combination of the signals from the two sensors.

[0007] EP 1 977 850 B1 discloses a machining device for processing workpieces with a high-energy machining beam. The machining head is associated with at least one scanning device designed as an optical coherence tomograph, with which the workpiece surface can be scanned in one, two, or three dimensions. Scanning is carried out using a measuring beam emitted by the coherence tomograph and reflected from the workpiece surface. The reflected measuring beam is directed, at least partially, together with a reference light beam onto a detector.

[0008] DE 103 55 931 A1 (disclosing the preamble of claim 1) describes a method for laser drilling and a device for carrying out a method for laser drilling in a plate-shaped component. Before the drilling process, the component thickness is determined in the drilling area using at least one measuring instrument, which is defined by the distance between the two component surfaces. During the drilling process, the drilling depth of the borehole is recorded using a second measuring instrument.

[0009] The object of the invention is to find a method for introducing a perforation line into an airbag cover in which a remaining residual wall thickness can be determined without errors, regardless of unevenness or thickness variations, and with which a flawless determination of the remaining residual wall thickness is possible for a workpiece that is opaque in the area of ​​a measuring radiation.

[0010] This problem is solved according to the invention for a method for introducing a perforation line into an airbag cover, in which the airbag cover is guided along an imaginary line relative to a tool with a processing beam source and a first measuring beam source, a processing beam is emitted with the processing beam source, a first measuring beam is emitted with the first measuring beam source and a second measuring beam is emitted with a second measuring beam source, a processing location located on a side of the airbag cover facing the processing beam source is illuminated with the processing beam and the first measuring beam along an illumination axis, wherein material removal occurs at the processing location by the illumination with the processing beam, and a measuring location is illuminated with a second measuring beam.A first path length of the first measurement beam and a second path length of the second measurement beam are determined, the first path length and the second path length are evaluated, the first path length and the second path length are used to determine a remaining residual wall thickness, and the processing beam source is controlled depending on the determined remaining residual wall thickness, solved by using as the measurement location a location on a side of the airbag cover facing away from the processing beam source, which is located on the illumination axis.The second measuring beam is applied. Before the airbag cover is positioned, the distance between the first and second measuring beam sources is determined. The remaining wall thickness is then calculated from the difference between the distances between the first and second measuring beam sources and the sum of the path lengths of the first and second beams. The distance between the first and second measuring beam sources is determined by a reflecting element of a defined thickness, which is positioned at the processing location.

[0011] Advantageously, the first and / or second measurement beam source is each the measurement beam source of a coherence tomograph, and the first path length and / or the second path length is determined using optical coherence tomography. To perform the optical coherence tomography, the first and / or second measurement beam can be partially reflected or partially transmitted into a reference arm by a beam splitter located in the respective beam path before being directed onto the target. The portion of the respective measurement beam that passes through the reference arm is then superimposed or made to interfere with the portion of the respective measurement beam reflected by the airbag cover, and an interference response is detected by a detector. The first and / or second path length can be determined from the interference response.

[0012] The airbag cover can rest on a support surface throughout the entire procedure. This support surface can be transparent or partially transparent to the second measurement beam, allowing it to be transmitted through the surface before impact on the measurement location. Alternatively, the support surface can have cutouts to allow the second measurement beam to be transmitted through these cutouts before impact on the measurement location.

[0013] The first measurement radiation can be advantageously guided at least sectionally parallel or overlapping with the processing radiation before and after the measurement point is exposed.

[0014] It is advantageous if the processing radiation has a first wavelength and the first measurement radiation has a second wavelength. The first wavelength can differ from the second wavelength. Alternatively, the first measurement radiation can be white light.

[0015] The first measurement beam is particularly suitable when implemented as a laser beam from a fiber laser.

[0016] The processing radiation of a CO2 laser beam is advantageous. Equally advantageous is the processing beam source of another pulsed laser whose pulse energy, pulse duration, repetition rate and / or emission spectrum are controlled depending on the determined residual wall thickness.

[0017] The invention will be described in more detail below by means of exemplary embodiments with reference to drawings. The drawings show: Fig. 1 A side view of an arrangement for carrying out the method, comprising a tool, an airbag cover, a support surface and a second measuring beam source, Fig. 2 A side view of the beam paths of processing radiation, first measuring radiation and second measuring radiation for determining a residual wall thickness of the airbag cover, Fig. 3 A side view of the beam paths of first measuring radiation and second measuring radiation with a reflecting element at the processing location, for determining the distance between the first measuring beam source and the second measuring beam source, Fig. 4 A side view of the beam paths of processing radiation, first measuring radiation and second measuring radiation in an advantageous embodiment of the method and Fig. 5 A side view of the beam paths of processing radiation, first measuring radiation and second measuring radiation in a further advantageous embodiment of the method.

[0018] An arrangement for carrying out a procedure for introducing a perforation line into an airbag cover 1 is in Fig. 1 schematically represented. During the process, the airbag cover 1 is guided along an imaginary line L relative to a tool 2, thereby creating blind holes BO at several machining locations, which form a perforation line in the airbag cover 1. Throughout the entire machining process, the airbag cover 1 either rests on a support surface 9 or is held by a robot arm (not shown).

[0019] The tool 2 comprises a processing beam source 3 and a first measuring beam source 4. The processing beam source 3 is aligned along an illumination axis BA, which is essentially perpendicular to one side 6 of the airbag cover 1 facing the processing beam source 3. A second measuring beam source 5 is arranged on a side 7 of the airbag cover 1 facing away from the processing beam source 3 throughout the entire process.

[0020] First, the airbag cover 1 is prepared, into which a perforation line is to be made. To create the blind holes or the perforation line in the airbag cover 1, the processing beam source 3 emits a processing beam 3.1, which is applied to a processing point BO located on the side 6 of the airbag cover 1 facing the processing beam source 3. The application of the processing beam 3.1 results in an energy input at processing point BO, causing material removal. At processing point BO, the airbag cover 1 has a residual wall thickness RWS after application of the processing beam 3.1, which is equal to the thickness of the airbag cover 1 at processing point BO minus the depth of the blind hole. The residual wall thickness RWS is determined simultaneously with the processing of the airbag cover 1.

[0021] To determine the residual wall thickness RWS, the first measuring beam source 4 emits a first measuring beam 4.1, which is applied to the processing point BO. The first measuring beam 4.1, diffusely reflected from the processing point BO, is detected by a detector (not shown). By applying the first measuring beam 4.1, a first path length a is determined, which corresponds to the distance from the first measuring beam source 4 to the processing point BO. The second measuring beam source 5 emits a second measuring beam 5.1, which is applied to a measuring point MO located on a side 7 of the airbag cover 1 facing away from the processing beam source 3 on the illumination axis BA. The second measuring beam 5.1, reflected from the measuring point MO, is detected by another detector (also not shown). By applying the second measuring beam 5.A second path length b is thus determined, which corresponds to the distance from the first measuring beam source 5 to the measuring point MO. These distances are not to be understood as spatial distances, but rather as optical distances or path lengths along the beam paths. Using the first path length a and the second path length b, the remaining residual wall thickness RWS is then to be determined. The processing beam source 3 is controlled depending on the remaining residual wall thickness RWS. In order to determine the residual wall thickness RWS using the first path length a and the second path length b, it is advantageous to know the positions of the first measuring beam source 4 and the second measuring beam source 5 relative to the airbag cover 1, and thus their relative position to each other, or at least their distance from each other.

[0022] In Fig. 2 The beam paths of the processing radiation 3.1, the first measurement radiation 4.1, and the second measurement radiation 5.1 are shown. Additionally, the first path length a, the second path length b, and a distance c between the first measurement source 4 and the second measurement source 5 are indicated. The processing radiation 3.1 and the first measurement radiation 4.1 can be, as shown in Fig. 2 The first measurement radiation 4.1 is shown to run across the beam. However, it may not run along the illumination axis BA. In particular, the first measurement radiation 4.1 may run parallel to the beam or at least partially parallel to the illumination axis BA.

[0023] Before the airbag cover 1 is deployed, the distance c between the first measuring beam source 4 and the second measuring beam source 5 can be determined in order to calculate the remaining residual wall thickness RWS from the difference between the distance c and the sum of the first path length a and the second path length b. Fig. 3 An arrangement for determining the distance c is shown. The distance c is determined by inserting a reflective element 8 with a defined thickness d. If the thickness d of the reflective element 8 along the illumination axis BA is known, the distance c can be determined by determining the first path length a and the second path length b. This distance is the sum of the first path length a, the second path length b, and the thickness d of the reflective element 8. The first path length a and the second path length b can also be determined using optical coherence tomography. The distance c between the first measuring beam source 4 and the second measuring beam source 5 can also be determined by determining the position of the measuring beam sources or by using a reflective coating on one of the measuring beam sources. Fig. 3 The detector for the second measuring beam source 5 is shown, which is arranged opposite a reference arm behind a beam splitter.

[0024] The first path length a and / or the second path length b can be determined using optical coherence tomography. For this purpose, a beam splitter is present in the respective measurement beam path, which partially reflects or partially transmits the light coming from the measurement beam source into a reference arm. A mirror is arranged in the reference arm, which reflects the portion of the measurement radiation reflected into the reference arm back to the beam splitter. At the measurement location MO and / or the processing location BO, a portion of the incident measurement radiation is also reflected and combined again at the beam splitter with the portion of the measurement radiation reflected into the reference arm. The two components of the measurement radiation interfere with each other, and a path length difference between the portion of the measurement radiation reflected into the reference arm and the transmitted portion can be determined from an interference response detected by a detector.From this difference in path lengths, the first path length a and / or the second path length b can then be determined. In . Fig. 4 A reference arm including beam splitter and flat mirror for the first measuring beam source 4 is shown.

[0025] If the airbag cover 1 rests on a support surface 9 throughout the entire procedure, it always does so with the side 7 facing away from the processing radiation 3.1. The first measurement radiation 4.1 can, as also described in Fig. 4 The second measurement radiation 5.1, as shown, can also be guided only partially overlapping the processing radiation 3.1. In order to determine the residual wall thickness RWS, the second measurement radiation 5.1 emitted by the second measurement beam source 5 must be able to pass through the support surface 9 to the measurement location MO. For this purpose, the support surface 9 can be at least partially transparent to the second measurement radiation 5.1. This has the advantage that each processing location BO, and thus each measurement location MO, can be chosen arbitrarily.

[0026] Alternatively, the contact surface can have a recess through which the second measuring radiation 5.1 reaches the airbag cover 1, as shown in Fig. 5 shown. Reference symbol list

[0027] 1 Airbag cover 2 Tool 3 Processing beam source 3.1 Processing radiation 4 First measuring beam source 4.1 First measuring radiation 5 Second measuring beam source 5.1 Second measuring radiation 6 Side facing the processing beam source 7 Side facing away from the processing beam source 8 Reflective element 9 Contact surface a First path length c Second path length c Distance d Thickness BA Illumination axis BO Processing location MO Measuring location RWS Residual wall thickness L Imaginary line

Claims

1. A method for making a perforation line in an airbag cover (1), wherein the airbag cover (1) is guided relative to a tool (2) with a processing beam source (3) and a first measurement beam source (4) along an imaginary line (L), said method comprising the steps of: - providing an airbag cover (1), - emitting a processing beam (3.1) with the processing beam source (3); - emitting a first measurement beam (4.1) with the first measurement beam source (4); - emitting a second measurement beam (5.1) with a second measurement beam source (5); - applying the processing beam (3.1) and the first measurement beam (4.1) along an illumination axis (BA) to a processing location (BO) located on a side (6) of the airbag cover (1) facing the processing beam source (3), wherein the application of the processing beam (3.1) causes material to be removed at the processing location (BO); - applying a second measurement beam (5.1) to a measurement location (MO); - determining a first path length (a) of the first measurement beam (4.1); - determining a second path length (b) of the second measurement beam (5.1); - evaluating the first and second path lengths (a, b), the first and second path lengths (a, b) being used to determine a parameter, and - controlling the processing beam source (3) as a function of the determined parameter, wherein - the parameter is a remaining residual wall thickness (RWS), and - as measurement location (MO), a location on a side (7) of the airbag cover (1) facing away from the processing beam source (3) and located on the illumination axis (BA) is acted upon by the second measurement beam (5.1) and, before the airbag cover (1) is provided, a distance (c) between the first measurement beam source (4) and the second measurement beam source (5) is determined and the remaining residual wall thickness (RWS) is determined from the difference between the distance (c) and the sum of the first path length (a) and the second path length (b), characterized in that the distance (c) of the first measurement beam source (4) and the second measurement beam source (5) is determined, before providing the airbag cover (1), by a reflective element (8) with a defined thickness (d), the reflective element (8) being provided at the processing location (BO).

2. The method for making a perforation line in an airbag cover (1) according to claim 1, characterized in that the first measurement beam source (4) is the measurement beam source of a coherence tomograph and the first path length (a) is determined by means of optical coherence tomography.

3. The method for making a perforation line in an airbag cover (1) according to claim 1 or 2, characterized in that the second measurement beam source (5) is the measurement beam source of a coherence tomograph and the second path length (b) is determined by means of optical coherence tomography.

4. The method for making a perforation line in an airbag cover (1) according to any one of claims 1 to 3, characterized in that the airbag cover (1) rests on a supporting surface (9) during the entire process.

5. The method for making a perforation line in an airbag cover (1) according to claim 4, characterized in that the second measurement beam (5.1) is transmitted through the supporting surface (9) before acting upon the measurement location (MO).

6. The method for making a perforation line in an airbag cover (1) according to claim 4, characterized in that the second measurement beam (5.1) is transmitted through a recess in the supporting surface (9) before acting upon the measurement location (MO).

7. The method for making a perforation line in an airbag cover (1) according to any one of claims 1 to 6, characterized in that the first measurement beam (4.1) is guided, at least in some sections, in a manner parallel to or covering the processing beam (3.1).

8. The method for making a perforation line in an airbag cover (1) according to any one of claims 1 to 7, characterized in that the processing beam (3.1) has a first wavelength, the first measurement beam (4.1) has a second wavelength, and the first wavelength differs from the second wavelength.

9. The method for making a perforation line in an airbag cover (1) according to any one of claims 1 to 8, characterized in that the first measurement beam (4.1) is white light radiation.

10. The method for making a perforation line in an airbag cover (1) according to any one of claims 1 to 9, characterized in that the first measurement beam (4.1) is the laser beam of a fiber laser.

11. The method for making a perforation line in an airbag cover (1) according to any one of claims 1 to 9, characterized in that the processing beam (3.1) is the laser beam of a CO2 laser.