Patent Application
20210354232
The disclosure relates to methods for the determination of the influence of a laser processing parameter on a laser processing operation by a laser beam as well as to laser processing machines suitable for carrying out the methods and to computer program products.
When cutting by a laser beam, deterioration of the cutting quality to the extent of a cutting interruption may occur. Causes are usually deviations in the laser beam profile. Consequences are long machine down times and unsatisfied customers. There is currently no possibility of tracing the fault causes by using a machine, but instead the laser processing machine must be stopped so that an employee qualified therefor can take care of the problem. Currently, different methods, which rely on subjective evaluation, are used for adjusting or checking the optical setpoint status of the laser processing machine. Furthermore, expensive measurement means, large time expenditure and special knowhow are required in order to determine, for example, a power-dependent focal shift, a power loss, a focal diameter variation, etc.
The present disclosure provides simple and economical methods to determine the influence of a laser processing parameter on the laser processing operation, e.g., in an automated fashion. For example, optimal laser processing parameter values and the cause of laser processing parameter changes can be found in the shortest possible time.
These advantages are achieved by methods for the determination, e.g., for the automated determination, of the influence of a laser processing parameter on a laser processing operation by a laser beam, having the following steps:
According to the disclosure, either a sensor unit (for example a photodiode in the laser beam generator or a surface welding depth sensor (OCT)) fully automatically (unmanned) detects, or a human operator detects, a processing interruption caused by the laser processing process as a function of a laser processing parameter. The evaluation is carried out fully automatically (unmanned) by a machine controller of the laser processing machine or by the operator. The laser processing parameter can be a laser beam-related parameter (wavelength, beam quality, intensity distribution, focal position of the laser beam in the beam direction (z focal position), focal diameter of the laser beam, or the laser cable, or the laser power) and/or a gas-dynamic parameter for a predetermined gas composition, which, e.g., is determined by nozzle type, nozzle diameter, distance of the nozzle, and/or the workpiece.
Starting from an initial rate of advance, acceleration is always carried out in the same way, for example continuously or stepwise, to a final rate of advance with the laser beam turned on. The laser-related sensor unit fully automatically and in an unmanned fashion detects the laser processing time between the start of laser processing and an interruption of the respective laser processing. Because of the acceleration always being the same, the laser processing time is representative of the respective laser processing length for the respective value of the laser processing parameter. As an alternative, the machine controller may also establish the speed of advance existing at the time of the interruption as an interruption speed and assign it to the respective value of the laser processing parameter; in this case, the laser processing speed does not always have to be accelerated in the same way, but may be accelerated in any desired way. In the manual variant, the laser processing length is measured by the operator and assigned to the respective value of the laser processing parameter.
In another embodiment, the influence of a cutting parameter on a workpiece processing operation by the laser beam is determined, e.g., determined in an automated fashion, by the following steps:
In another embodiment, the influence of a welding parameter on a workpiece processing operation by the laser beam is determined, e.g., determined in an automated fashion, by the following steps:
Variations in the laser beam, for example because of contamination of the optics, may be identified by the propagation distance in the machine, and detrimental effects on the welding outcome may be prevented or reduced promptly. By contamination of the welding optics (e.g., by splashes), a part of the laser power is absorbed by the optical components and is absent from the process on the workpiece. The penetration welding threshold is correspondingly reached earlier (since a part of the energy is missing), and the penetration welding distance is correspondingly shortened. This may be detected by the proposed methods. To diagnose the laser beam properties by the welding process in laser beam welding, the so-called penetration welding threshold is used. This is the transition from the surface welding process to the penetration welding process, or vice versa. At the penetration welding threshold, the radiation energy is thus just sufficient to melt the material over the entire sheet-metal thickness. The speed is increased continuously, with otherwise constant parameterization. Initially, penetration welding of the sheet metal takes place with a power excess. If the speed increases further, the aforementioned penetration welding threshold is reached, which is used here as a criterion for the evaluation. With a further increase of the rate of advance, the energy is not sufficient for penetration welding, so that surface welding or an interruption of the penetration welding takes place thereafter. If, for example, the focal position is then varied in the next step, the rate of advance of the penetration welding threshold changes and occurs earlier if the weld seam is wider, or later if the weld seam width is less. By means of the variation of the focal positions, the longest distance on the lower side of the sheet metal may either be measured manually or detected automatically by a sensor unit (for example a surface welding depth sensor (OCT) or a diode internal to the laser instrument). In this way, it is possible to check laser-related properties and reflect them in the condition monitoring of the machine, and to recommend handling recommendations if a threshold is violated.
In other embodiments, the influence of a fusion parameter during the fusion of metal powder by the laser beam is determined, e.g., determined in an automated fashion, by the following steps:
Changes of the optical setup with process powder input in the LMD (Laser Metal Deposition) process, for example because of contamination of the optics, may be identified by the propagation distance in the machine, and detrimental effects on the fusion outcome may be prevented or reduced promptly. By linear variation of one manipulated variable with stepwise variation of a further manipulated variable, the longest fusion track that occurs for a given energy input by interaction with the powder, or a powder jet, can be determined. The longest melting track is evaluated in an automated fashion by laser-related sensors of the machine. The energy of the laser beam is converted with different efficiencies for the melting and fusion of metal powder as a function of the laser beam waist position. The interaction length between the laser beam and the powder, which leads to a particular fusion rate, is to be regarded as an effect variable. The fusion rate may be used for process diagnosis to carry out an assessment of the machine status in a horizontal, tilted, or vertical arrangement of the LMD process.
If, for a given interaction length, the speed of advance increases and a limit speed is reached beyond which the fusion no longer takes place sufficiently because of an energy input that is too low, the interaction length is too short, and no binding of the liquefied powder to the workpiece surface takes place. The maximum melting track length is therefore set up at the limit speed. Above this limit speed, the powder absorbs the laser radiation but no longer binds to the carrier material. The determination of the melting track lengths is carried out for example by evaluating the process-related scattered light, a variation of the emission taking place when the melt binds to the carrier substance. The time from the instant of the start of the process to the signal change may be determined and the limit speed or interruption speed may therefore be calculated. The determination of the maximum melting track length may also be carried out by triangulation- or OCT-based methods.
The methods are suitable both for CW operation and for pulsed operation, so long as the energy is sufficient to separate and melt or fuse the material.
In some embodiments, the laser beam is turned off when reaching the processing interruption, for example, by a laser-related sensor unit in the beam source or by a sensor unit outside the beam source.
In another embodiment, that parameter value for which the processing length, or the associated processing time, or the associated interruption speed of the laser processing operations is maximal is determined, e.g., determined in an automated fashion, as the optimal parameter value. In this case, the optimal parameter value may be determined by interpolation of the measured processing lengths, of the measured processing times, or of the interruption speeds established. In the fully automatic case, the machine may then adjust itself to this optimal parameter value. The optimal parameter values deviate from one another so little in different laser processing machines that subjective evaluation is inapplicable.
If the optimal parameter value to be determined is an optimal z focal position of the laser beam, the laser processing operations are carried out with different z focal positions of the laser beam in step (a). When the optimal z focal position of the laser beam has respectively been determined for different laser powers, a power-dependent focal shift may be determined therefrom.
If the optimal parameter value to be determined is an optimal focal diameter of the laser beam, the laser processing operations are carried out with different focal diameters of the laser beam in step (a).
To be able to establish a power loss occurring in the course of time or a beam expansion occurring in the course of time, with a nominally equal laser power and nominally equal focal diameter, steps (a) and (b) are carried out, e.g., carried out in an automated fashion, for different values of the laser processing parameter “z focal position” at two different instants. The two relationships (curves) respectively determined in this case between the processing lengths of the laser processing operations, the associated processing times, or the interruption speeds of the laser processing parameter “z focal position” are compared with one another so as to establish a power loss or a beam expansion. In the case of a power loss, there is a decrease (negative offset) of the respective processing lengths, processing times or interruption speeds over the entire value range of the laser processing parameter “z focal position” for the subsequently determined curve. In the case of a beam expansion, on the other hand, the two curves respectively intersect at a high focal position and a low focal position, and the subsequently recorded curve has a negative offset in the region between the two points of intersection and respectively a positive offset outside this region.
In another aspect, the present disclosure also relates to laser processing machines having a laser beam generator for generating a laser beam, having a laser processing head, from which the laser beam emerges, and a workpiece base or powder base, both of which are movable relative to one another, and having a machine controller that is programmed to increase the speed of advance in the laser processing operations of a workpiece at least to such an extent that a processing interruption occurs.
In one embodiment, the laser processing machine comprises an interruption detector for detecting a processing interruption and a data memory in which the processing length, the processing time, or the interruption speed, as well as the associated value of the laser processing parameter, are stored while being assigned to one another.
In another embodiment, the machine controller is programmed to determine the relationship between the processing lengths, the associated processing times, or the associated interruption speeds and the laser processing parameter in an automated fashion with the aid of the stored data, and to compare with one another and evaluate, in an automated fashion, a plurality of relationships that have been determined.
In another aspect, the disclosure relates to computer program products, e.g., computer readable media, including one or more computer programs configured to carry out all steps of the methods described herein, when the computer programs are run on a machine controller of a laser processing machine.
Further advantages and advantageous configurations of the subject matter of the invention may be found in the description, the claims, and the drawing. Likewise, the features referred to above and those yet to be mentioned below may respectively be used independently or jointly in any desired combinations. The embodiments shown and described are not to be understood as an exhaustive list, but rather have an exemplary nature for the presentation of the invention. In the drawings:
The laser processing machine 1 represented in perspective in
With the energy of the laser beam 5, a particular melt volume, or a particular melting rate, may be produced in the workpiece 6. If the energy of the laser beam 5 is increasingly deposited transversely with respect to the direction of advance of the laser beam 5 during the laser cutting, for example because of a larger focal diameter or beam diameter on the workpiece 6, the maximum possible cutting speed decreases.
To determine the influence of a cutting parameter, for example, the cutting parameter “z focal position F of the laser beam 5,” during the laser cutting of the workpiece 6, the following procedure is adopted:
As shown in
Subsequently—while being controlled in a fully automated fashion by the machine controller 11—the relationship between the cutting lengths L of the laser cuts 12, the associated cutting times t or the associated cutting interruption speeds vA and the cutting parameter is determined with the aid of the measured cutting lengths L1 to L5, the associated cutting times t1 to t5 or the associated cutting interruption speeds vA,1 to vA,5 of the laser cuts 12.
By the variation of the z focal position, different amounts of energy are deposited transversely with respect to the direction of advance, which leads to different cutting interruption speeds, i.e., the laser cuts 12 or the cutting times t are of different length. The cutting times t between the start of cutting and the cutting interruption are detected with the aid of the interruption detector 14. As an alternative, the cutting speed existing at the instant of the cutting interruption may be established by the machine controller 11 as a cutting interruption speed vA and assigned to the respective value of the cutting parameter.
If, as shown in
To be able to establish a power loss occurring in the course of time or a beam expansion occurring in the course of time, with a nominally equal laser power and nominally equal focal diameter, the relationships between the cutting lengths L/cutting times t/cutting interruption speeds vA and the z focal position F of the laser beam 5 are determined at two different instants. The curves determined are compared with one another to establish either a power loss or a beam expansion with the aid of the different curve profiles of
The machine implementation may, for example, be carried out as follows:
As a result, the described method makes it possible to collect digitized data by means of a cutting pattern, whereupon the laser processing machine 1 adjusts itself independently where possible.
In order to determine the influence of a welding parameter, for example the welding parameter “z focal position F of the laser beam 5”, during the laser welding of the workpiece 6, the following procedure is adopted:
As shown in
Subsequently—while being controlled in a fully automated fashion by the machine controller 11—the relationship between the penetration welding lengths L of the laser penetration welds 22, the associated welding times t or the associated penetration welding interruption speeds vA and the welding parameter is determined with the aid of the measured penetration welding lengths L1 to L5, the associated welding times t1 to t5 or the associated penetration welding interruption speeds vA,1 to vA,5 of the laser penetration welds 22.
To determine the influence of a fusion parameter in the LMD process, for example the fusion parameter “z focal position F of the laser beam 5,” during the fusion of metal powder by the laser beam 5, the following procedure is adopted:
As shown in
Subsequently—while being controlled in a fully automated fashion by the machine controller 11—the relationship between the melting track lengths L of the melting tracks 32, the associated fusion times t or the associated melting track interruption speeds vA and the fusion parameter is determined with the aid of the measured melting track lengths L1 to L5, the associated fusion times t1 to t5 or the associated melting track interruption speeds vA,1 to vA,5 of the melting tracks 32.
It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102019201033.4 | Jan 2019 | DE | national |
This application is a continuation of and claims priority under 35 U.S.C. § 120 from PCT Application No. PCT/EP2020/052016, filed on Jan. 28, 2020, which claims priority from German Application No. 10 2019 201 033.4, filed on Jan. 28, 2019. The entire contents of each of these priority applications are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2020/052016 | Jan 2020 | US |
| Child | 17443722 | US |
