Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/03—Observing, e.g. monitoring, the workpiece
  • B23K26/032—Observing, e.g. monitoring, the workpiece using optical means
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K31/00—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups
  • B23K31/12—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups relating to investigating the properties, e.g. the weldability, of materials
  • B23K31/125—Weld quality monitoring
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B11/00—Measuring arrangements characterised by the use of optical techniques
  • G01B11/22—Measuring arrangements characterised by the use of optical techniques for measuring depth

Definitions

• the present invention relates to a method for monitoring a machining process of a workpiece by means of a high-energy machining beam, in particular a laser beam, and a corresponding device and a machining system with the device.
• a known example of such a machining process is a laser welding or laser deep welding process, in which a laser beam is moved over a workpiece surface.
• a measuring light beam for example an optical coherence tomograph, can be directed onto the surface of the workpiece.
• the light reflected from the workpiece surface can be detected by a sensor so that the quality of the welding result can be continuously monitored.
• a surface profile of the workpiece or a depth of a steam capillary which is also referred to as a “keyhole” and is surrounded by liquid melt, can be represented in this way.
• Their depth is related to the weld seam or weld depth and can therefore be used to control the machining process.
• An optical method that can be used for this measurement is, for example, optical coherence tomography (OCT). It enables height differences along the measuring beam axis to be recorded in the micrometer range.
• OCT optical coherence tomography
• measuring light is generated and divided into a measuring beam and a reference beam. The superimposition of the light of the measuring beam reflected on the surface of the workpiece with the reference beam is detected in order to obtain the desired height information.
• OCT optical coherence tomography
• this processing position is the position of the steam capillary. If the machining beam is static relative to the workpiece, ie there is no movement of the machining beam relative to the workpiece, the machining position is concentrated to the point of impact of the machining beam on the workpiece surface or to the position at which the highest power density of the machining beam is achieved. This position can also be referred to as a "tool center point", TCP.
• the optimum working point for process monitoring may not be identical to this static machining position or to the static TCP.
• the optimum working point for the process observation can be referred to as the dynamic processing position or dynamic TCP and can be arranged after the impact point, ie an offset occurs along the path of the processing beam.
• the steam capillary forms with a slight delay and therefore in a position that is shifted into the wake of the point of impact.
• the dynamic processing position e.g. the position of a steam capillary relative to the static machining position can depend on the laser power, the material of the workpiece, the direction and the amount of a speed vector of a feed movement between the workpiece and the machining beam.
• the speed vector, laser power or other parameters can change during the machining process.
• it is essential to determine a current dynamic machining position in order to be able to determine an optimal observation point for the process observation. This is the only way to align an optical measuring light beam to this optimal observation position, for example in order to be able to determine the correct depth of the steam capillary using OCT.
• One way of determining this offset is to determine the dynamic machining position during the machining process with the affected machining system, on which the desired process parameters, such as feed direction, feed speed and power of the machining beam, are set.
• the workpiece machined in this process often has to be discarded as scrap.
• it is generally assumed in the previously known approaches for determining the dynamic machining position that this does not change during a machining process or only changes periodically and in a known manner. Changes
• the measuring process must be carried out again.
• a device for monitoring a laser machining process on a workpiece comprises a computing unit and an observation unit, which is set up to determine at least one monitoring parameter of the laser machining process at a measurement position.
• a monitoring parameter can include parameters that are suitable for monitoring the respective machining process, for example a depth of a steam capillary in a laser welding process.
• the computing unit is set up to determine a current processing position, in particular a current dynamic processing position, relative to a point of incidence of the laser beam.
• the current machining position can correspond to a position of a steam capillary.
• a dynamic machining position can denote a machining position whose position can be changed relative to the point of impact or whose offset with respect to the point of impact, e.g. depending on the current process parameters.
• the computing unit uses a process parameter set of the laser machining process and a model that is based on at least one predefined comparison parameter set and an associated comparison machining position.
• the computing unit and the observation unit can be formed as separate units or can be integrated in one unit.
• the computing unit can be integrated in the observation unit.
• the observation unit can be a Include measuring device with optical coherence tomograph, which also includes the computing unit.
• the process parameter set can comprise at least one process parameter which influences the processing position and whose value is different from that of a corresponding comparison parameter of the comparison parameter set. In other words, there are no previously determined measurement results for the process parameter set.
• the process parameter set and / or the comparison parameter set can comprise at least one parameter of: a speed vector of a feed movement of the laser beam relative to the workpiece, an amount of a feed speed, a direction of a feed movement, an output of the laser beam, and one or more material parameters of the workpiece.
• Several sets of comparison parameters can be specified, which differ at least in one parameter.
• the monitoring parameter can include a depth of a steam capillary, a distance to the workpiece or a topography at the dynamic processing position, a temperature and / or a wavelength of light reflected at the dynamic processing position.
• the observation unit can comprise an optical coherence tomograph and can be set up to direct an optical measurement light beam onto the dynamic processing position.
• the observation unit can also be a deflection unit, e.g. a scanner unit or the like, which is set up to direct the optical measuring light beam to a desired position, i.e. to the current machining position.
• the at least one predetermined comparison processing position can include at least one static processing position with a feed rate of the laser beam relative to the workpiece equal to zero and at least one dynamic processing position with a feed rate greater than zero.
• the at least one predetermined comparison processing position can comprise two dynamic processing positions with equal and opposite speed vectors of a feed movement and / or two dynamic processing positions with mutually perpendicular speed vectors of a feed movement.
• the device can further comprise at least one sensor that is set up to determine at least one current process parameter of the process parameter set of the machining process.
• the device can include an interface through which the sensor is connected to the computing unit for transferring the determined current process parameter of the machining process to the computing unit.
• a laser processing system comprises a laser processing head, which is configured to direct a laser beam onto a workpiece, and a device according to one of the preceding examples.
• the laser processing system can include an interface through which the laser processing system is connected to the computing unit for transferring at least one current process parameter of the processing process to the computing unit.
• the laser processing system can include a control device that is set up to specify at least one current process parameter for the Processing process and to control the laser processing system based on this current process parameter.
• the laser processing system can also include an interface through which the control device is connected to the computing unit for transferring the current process parameter to the computing unit.
• the laser processing system can comprise a human-machine interface, a device for inputting and / or selecting at least one process parameter of the processing process and for transferring the same to the computing unit.
• a method for monitoring a laser machining process on a workpiece comprises the steps: determining a current machining position, in particular a current dynamic machining position, relative to a point of incidence of the laser beam for a process parameter set of the laser machining process by means of a model based on at least one predefined comparison parameter set and an associated comparison processing position, and determining at least one monitoring parameter of the laser processing process at the dynamic processing position.
• the associated comparison processing position can be determined for each predetermined comparison parameter set in a setup process.
• the setup process several comparison processing positions can be determined, the at least one static processing position relative to a feed rate of the laser beam to the workpiece is zero and include at least one dynamic machining position with a feed rate greater than zero.
• a corresponding feed rate can be constant during the determination of the dynamic machining position.
• the static machining position can be determined from two dynamic machining positions with equal and opposite speed vectors of the feed movements.
• the machining process can be preceded by an setup process in which at least one comparison machining position is determined relative to a point of impact of the machining beam.
• the at least one comparison processing position can, however, also be predetermined or, for example, stored.
• This comparison processing position can be assigned a comparison parameter set that contains a number of process parameters, such as laser power of the processing beam, direction and speed of the relative movement between the processing beam and the workpiece.
• the respective comparison processing positions can thus be determined as a function of the comparison parameter sets.
• further processing positions can be calculated for specific process parameter sets of a subsequent processing process, and also for those process parameter sets for which no measurements are available.
• the measuring position of the measuring light beam can then be aligned with a calculated machining position during the machining process.
• the invention is based on the assumption that a specific machining position can basically be represented as a function of the process parameters.
• the size of the dynamic offset of a keyhole relative to the instantaneous point of impact of the machining beam depends on the relative speed between the workpiece and the machining beam, the power of the machining beam and, if appropriate, other parameters.
• This function i.e. the relationship between the process parameters and the resulting machining positions, can be represented in a mathematical model that can be used to calculate the machining positions. With the help of such a model, a large number of machining positions can thus be generated from a comparatively small number of measurement or comparison data. If the process parameters change, the dynamic processing positions do not necessarily have to be measured again, as is conventionally the case. Rather, these machining positions can be calculated for a machining process with changed parameters.
• FIG. 1 shows a schematic sectional view of a workpiece (top) for illustrating a steam capillary and a measuring light beam during laser welding according to embodiments of the present disclosure
• FIGS. 2A to 2C are schematic representations for explaining a set-up process according to a preferred embodiment of the method according to the invention.
• FIG. 3 is a schematic representation for explaining a determination of a current processing position according to a preferred embodiment of the method according to the invention;
• FIG. 4 is a schematic representation of a device according to a preferred embodiment of the invention.
• FIG. 5 is a schematic illustration of a laser processing system in accordance with a preferred embodiment of the invention.
• FIG. 1 shows a schematic sectional view of a workpiece for illustrating a steam capillary and a measurement light beam during laser welding in accordance with embodiments of the present disclosure.
• a steam capillary KH which is also called a keyhole, is formed during the welding process during a welding process along the beam axis of the laser beam 1 and is surrounded by liquid melt 2.
• the depth Td of the Steam capillary is related to the weld seam or weld depth Te and can therefore represent a monitoring parameter for monitoring the machining process.
• the solidified melt 4 is located behind the liquid melt 2.
• a measuring light beam 3 of an optical coherence tomograph can be directed into the steam capillary KH parallel to or coaxially with the laser beam 1.
• the incident light hits the bottom or the end of the steam capillary KH, is partially reflected there and returns to the optical coherence tomograph, with the help of which the depth Td of the steam capillary KH can be measured with high precision.
• the machining process is a laser welding process by means of a laser beam 1 on the workpiece.
• the beam axis is perpendicular to the drawing plane, while the drawing plane itself coincides with the plane of the workpiece surface WB.
• the spatial directions X and Y shown thus extend perpendicular to one another on the surface of the workpiece, while the beam axis of the laser beam runs perpendicularly thereto.
• a steam capillary KH is generated in the workpiece surface WB by the laser beam and is surrounded by a melt.
• the steam capillary is also referred to as a “keyhole” and extends into the workpiece from the surface of the workpiece to a certain depth Td.
• the depth of the steam capillary generated is of crucial importance for the result of the laser welding process. For this reason, the depth of the steam capillary during the machining process can be determined as a monitoring parameter by an observation unit 17 for monitoring the machining process.
• the observation unit 17 can, for example, comprise an optical coherence tomograph and be set up to direct a measurement light beam 3 to a measurement position on the surface of the workpiece.
• the light of the measurement light beam which is reflected by the surface of the workpiece, can be observed by the observation unit 17 to capture. A distance from the surface of the workpiece at the measuring position can in turn be determined from this.
• the position at which the steam capillary KH is formed according to the present embodiment is that position of the workpiece surface at which the desired modification of the workpiece is currently taking place due to the absorption of the power of the laser beam. This position is referred to below as the processing position TCP.
• An optimal measuring position for determining the depth of the steam capillary is therefore the current processing position.
• FIG. 2A illustrates a situation in which the laser beam 1 is not moved relative to the surface of the workpiece WB, that is to say the laser beam stands statically on the workpiece surface and falls on the workpiece surface at an impact point AP.
• This point of impact AP can be regarded as the origin of a coordinate system at which the axes of the spatial directions X and Y intersect. Due to the static position of the laser beam relative to the surface of the workpiece, the point of impact AP coincides with the machining position TCP, that is, the static machining position TCPs. The vapor capillary is thus also formed at this point.
• Fig. 2B a situation is shown in which the fiber beam and the surface of the workpiece move relative to each other at a feed speed with speed vector vi. Because of this movement, the processing position TCP no longer coincides with the instantaneous point of impact AP of the fiber beam, but rather lies in the wake of the point of impact AP. In this case, the processing position is referred to as the dynamic processing position TCPi. This creates an offset between the point of impact AP and the processing position TCPi. This is because the vapor capillary formed during fiber welding can form in the workpiece surface with a slight delay, while the point of impact AP of the fiber beam has already moved further over the workpiece surface.
• the measuring position of the observation unit matches the current machining position TCP as exactly as possible.
• the offset between the point of impact AP of the fiber beam and the processing position TCP, or the current dynamic processing position TCPi relative to the point of impact AP must therefore be determined as precisely as possible.
• the measuring position of the observation unit is aligned with a current machining position that has been calculated beforehand and from the process parameters of the machining process, such as, for example, the amount and direction of a speed vector of the feed movement of the laser beam relative to the workpiece, the laser power and, if appropriate, further process parameters, is dependent.
• the current processing position TCP can be predicted based on the current process parameters and the measuring position of the observation unit can be adjusted accordingly.
• a set-up process can be carried out before the machining process, which is in particular a test machining of a workpiece.
• at least one comparison processing position is determined relative to an impact point AP of the laser beam as a function of the comparison parameters used.
• an associated comparison processing position TCP n is determined.
• a comparison parameter set can in particular comprise a speed vector, which indicates the amount and direction of a feed movement of the laser beam relative to the workpiece, and a power P of the laser beam.
• the comparison parameter set can also contain further process parameters, such as a material or material parameters of the workpiece.
• a static processing position TCP S is first measured for a laser power Po without a relative movement between the workpiece and the laser beam, as shown in FIG. 2A. Then at least one dynamic processing position TCP di for a laser power Po and a feed rate vi greater than zero is measured (FIG. 2B).
• the feed speed vi is described in the direction and amount by a speed vector v 1 .
• This vector v x is preferably kept constant during the determination of the machining position TCP di .
• the static processing position TCP S and the dynamic processing position TCP di can each be represented as a function of their process parameter sets PPSs and PPS di .
• a model (or regularities) can be derived that allows calculation and thus forecast of dynamic processing positions TCPi for process parameters for which no measurements are available, i.e. which do not correspond directly to a set of comparison parameters.
• the model and the process parameters of the machining process the corresponding current machining position TCPi can be determined.
• two dynamic machining positions TCP di and TCP_ di can also be used, whose parameter sets PPS di and PPS- di have feed speed vectors with identical amounts, but which are directed in opposite directions, ie their directions rotated by 180 ° in relation to one another are.
• a static machining position TCP S can be determined more precisely from two dynamic machining positions TCP di , -TCP di with two opposite speed vectors v x and v 2 , for example as a spatial mean value from the dynamic machining positions TCP di , -TCP di .
• the comparison processing positions TCP n determined in the set-up process can comprise two dynamic processing positions TCP di , TCP d2 , the feed speed vectors v x and v 2 of which are perpendicular to one another, where both speed vectors can have a component perpendicular to the axis of the laser beam.
• a second dynamic processing position TCP d2 for a second process parameter set PPS d2 can be measured with the laser power Po and a second feed speed V2 with the speed vector v 2 .
• the speed vectors v 1 and v 2 are preferably perpendicular to one another and perpendicular to the axis of the machining beam.
• this procedure can be repeated for other PPS n with different laser powers P n and / or different speed vectors v n .
• Fig. 2B shows a situation in which a speed vector » j of the advance movement of the laser beam relative to the workpiece is directed to the right along the horizontal X-axis and the corresponding dynamic machining position TCP di along the X-axis compared to the current impact position AP
• 2C shows another situation in which the speed vector v 2 is directed downwards along the Y-axis, ie perpendicular to the vector v x from FIG. 2B, and the corresponding dynamic processing position TCP d 2 is shifted upwards along the Y axis with respect to the current impact position AP.
• the relationships between the comparison processing positions TCP n and the respective comparison parameter sets PPS n can be used to create a model that predicts the prediction or the calculation of a current dynamic TCPi for any process parameters, such as different speed vectors or laser powers.
• this model can calculate the current dynamic machining position TCPi as a function of a current process parameter set PPSi of the machining process without a dynamic TCP for this process parameter set PPS having to be measured beforehand, for example by interpolation or using models of machine learning, whereby the TCPi are calculated in a neural network.
• a current dynamic machining position on the TCPi calculated by the computing unit for a speed vector v 3 of the feed movement of the laser beam relative to the workpiece is shown, which has been calculated based on the determined machining positions TCP n and the process parameter sets PPS n associated with them, for example basie rend on the comparison processing positions TCP di , TCP d 2, and / or TCP S.
• this calculated machining position TCPi can be used to align the measuring position of the observation unit 17 with it.
• the observation unit 17 can comprise an optical coherence tomograph in order to determine a current depth of the steam capillary or the keyhole KH by means of optical coherence tomography (OCT, Optical Coherence Tomography).
• OCT optical coherence tomography
• the measuring light beam 3 To the To be able to determine the keyhole depth correctly, the measuring light beam 3 must strike the current processing position TCPi and thus in the steam capillary KH. For this, the current processing position TCPi must be known in order to be able to align the measuring position, ie the position of the measuring light beam, accordingly.
• the current feed velocity vector can be used by the model to predict the new dynamic machining position TCPi.
• a current dynamic processing position TCPi for a current process parameter set PPSi of the processing process carried out is calculated can.
• a corresponding dynamic processing position TCPi can be predicted based on the current feed movement between the laser beam and workpiece and the laser power present.
• the device can correct the measurement position or the position of the measurement light beam in real time in order to measure the correct keyhole depth.
• the device comprises a computing unit 16 which calculates and applies a current machining position TCPi relative to an impact point AP of the laser beam 1 for a process parameter set PPSi of the laser machining process on the basis of the model the observation unit 17 transmits as the measurement position, and an observation unit 17 for determining at least one monitoring parameter, for example a distance, at the measurement position.
• the computing unit 16 and the observation unit 17 can be coupled wirelessly or wired for mutual data exchange.
• the computing unit 16 can be set up to be connected directly to the respective machine or the respective processing system.
• the computing unit 16 and the observation unit 17 can be embodied together as one unit, or the computing unit 16 can be embodied integrated in the observation unit 17.
• the computing unit 16 is set up to calculate current processing positions TCPi on the basis of the process parameter sets PPSi, which in turn are output to the observation device 17.
• the calculated processing positions TCPi are used to align a measuring position, for example a measuring light beam, of the observation unit 17 with a calculated processing position TCPi. In the case of a laser welding system, this can correspond to the position of a generated steam capillary that is formed in the workpiece surface during the machining process.
• the arithmetic unit 16 calculates these current machining positions TCPi using the model on the basis of the respective process parameter sets PPSi of the machining process as well as predetermined comparison machining positions TCP n and these associated comparison parameter sets PPS n .
• the model can represent a dependency or a connection between the respective machining positions TCPi and the machining parameter sets PPSi. This model can be stored in the computing unit 16 and can be used to calculate the current machining positions TCPi.
• FIG. 5 shows a laser processing system 10, which comprises a laser processing head 12 and the device 15.
• the laser processing system 10 can comprise a PLC control device 14, which is set up to output current process parameter sets PPSi to the laser processing head 12 and in this way to control the processing process, in particular the amount and the direction of a relative advance movement between the laser beam and the workpiece, the power of the laser beam and the like.
• These process parameter sets PPSi can also be output by the PLC control device 14 to the computing unit 16 via a corresponding interface.
• the computing unit 16 can receive the process parameter sets PPSi directly from the laser processing head 12.
• the predicted current processing position TCPi can thus be controlled directly in the process in order to increase the process quality.
• the computing unit 16 can be connected to a human-machine interface 20, which is provided for the input and / or selection of process parameter sets PPSi of the machining process.
• this human-machine interface 20 can comprise a graphical user interface. It goes without saying that other types of input interfaces can also be provided.
• the computing unit 16 preferably calculates a current processing position TCPi taking into account the current process setting, ie based on a current process parameter set PPSi.
• the computing unit 16 can be set up to calculate a current processing position TCPi based on a predetermined process parameter set for a previously defined subprocess. This enables the current processing position TCPi to be calculated if no current process parameter sets are available. For example, different process parameter sets can be selected for different sub-processes of the machining process.
• the laser processing head 12 and / or the device 15 can be equipped with sensors 18 which, for example, make it possible to measure a current feed rate between the laser beam and the workpiece and their direction and / or further parameters, such as the current laser power, for example Temperature, etc.
• sensors 18 may include encoders that are attached to axes of the laser machining head 12. The measured values can be transmitted to the arithmetic unit 16 as current parameters for the process parameter sets of the machining process. The forecast of the current machining positions TCPi can therefore also be carried out on the basis of the process parameter sets PPSi transferred by the sensors 18.

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• Laser Beam Processing (AREA)

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• 2018
  • 2018-10-01 DE DE102018124208.5A patent/DE102018124208B4/de active Active
• 2019
  • 2019-09-16 WO PCT/EP2019/074618 patent/WO2020069840A1/de unknown
  • 2019-09-16 EP EP19773010.4A patent/EP3860796A1/de not_active Withdrawn
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