Method and apparatus for piercing into a workpiece by means of a laser beam

Abstract

According to the present law a method is described by means of a laser beam piercing into a workpiece, comprising: irradiating a pulsed laser beam (10) onto a workpiece (1) for forming a piercing (9), wherein the average pulse power (P mittel ) of the irradiation of the pulsed laser beam (10) is reduced during piercing.

Description

Technical Field

[0001] The present invention relates to a method and apparatus for penetrating a workpiece by means of a laser beam, and more particularly to a method and apparatus for controlling the penetration process in laser-processed materials. Background Technology

[0002] In equipment used for material processing with lasers, such as in a laser processing head for laser cutting, a laser beam emitted from a laser source or one end of a laser-guiding optical fiber is focused or concentrated onto the workpiece to be processed by beam guiding and focusing optics. Standards use laser processing heads with collimating and focusing optics, wherein the laser is supplied via an optical fiber (also called a laser source).

[0003] Within the realm of laser processing materials, particularly in laser cutting, a penetration process can be achieved using a laser beam into a workpiece. This penetration process precedes the actual cutting process during laser cutting. In this process, an initial hole, or piercing portion, is created in the workpiece, serving as the starting point for the cutting process. Therefore, the penetration process, or piercing into the workpiece, can also be called the piercing process or piercing the workpiece. Since, for example, the subsequent laser cutting process cannot begin without a piercing portion, successfully piercing the workpiece plays a crucial role in laser cutting. The duration, quality, and stability of the penetration process depend on several process parameters. Primarily, the duration of the penetration process—the time between activating the processing beam and piercing the material or workpiece (also known as the piercing time or penetration duration)—is a key factor for process efficiency. The duration of the penetration process depends on the rate of change of penetration depth over time. This rate of change of penetration depth over time is referred to below as the penetration rate and also reflects process efficiency.

[0004] Prior art describes various piercing methods in which the pulse frequency or average laser power is increased during the piercing process up to penetration, in order to minimize the piercing duration or penetration time for a given material thickness. US 5,434,383A describes a piercing method with a shortened duration, in which the pulse frequency and pulse duty cycle are gradually increased during piercing. Similarly, DE 11,2009,001,200 B4 describes a laser processing method for piercing and subsequent cutting, in which piercing begins at a first frequency and continues at a second frequency greater than the first frequency. Conversely, in US 6,693,256 B2, the maximum laser power is gradually increased during piercing.

[0005] The trend toward higher laser power and greater plate or workpiece thickness makes the piercing process more difficult, resulting not only in longer piercing times but also in more frequent piercing stops, at which point the piercing rate approaches zero and piercing fails. Summary of the Invention

[0006] One objective of this invention is to describe a method and apparatus for inserting a laser beam (also known as a processing beam) into a workpiece, wherein the method and apparatus can optimize the insertion process, particularly for inserting into thicker materials or thicker workpieces, for example having a thickness greater than 10 mm or even greater than 20 mm.

[0007] Another objective of this invention is to describe a method and apparatus for penetrating a workpiece using a laser beam, wherein the penetration duration can be minimized or the penetration rate can be maximized.

[0008] Another objective of this invention is to describe a method and apparatus for penetrating a workpiece using a laser beam, which ensures reliable penetration and prevents penetration from stopping.

[0009] These tasks are addressed by the features of the independent claims. Features of preferred embodiments are given in the dependent claims.

[0010] This invention is based on the understanding that the piercing process can be optimized by selectively or controlledly inputting the energy of a laser beam into the processing area, particularly by selectively or controlledly reducing the average pulse power of the laser beam irradiating the processing area during the piercing process. Here, the energy input can be controlled according to at least one of the following process parameters and boundary conditions: material thickness, material type, instantaneous or current piercing time, instantaneous or current piercing depth, process gas type, process gas pressure, focal position, imaging ratio of the optical system, nozzle type, nozzle diameter, laser beam intensity distribution, focal diameter, and nozzle distance to the upper side of the workpiece. Based on the aforementioned parameters, the energy input to the piercing hole or processing area can be adapted according to the current piercing time and / or piercing depth via pulse on-time, pulse off-time, and / or pulse peak power.

[0011] According to one aspect, a method for penetrating a workpiece using a laser beam (also known as a processing beam) is described. The method includes: irradiating the workpiece with a pulsed laser beam to form a puncture, wherein the average pulse power of the irradiation by the pulsed laser beam decreases during the penetration period or during the penetration time, for example, at least once. The penetration time can here represent the duration of the penetration or puncture process, i.e., the time period from when the laser beam is switched on or first irradiated until the workpiece is punctured. In other words, the method for penetrating a workpiece using a pulsed laser beam includes: a first penetration step, wherein a pulsed laser beam having a first average pulse power is aligned or irradiated onto the workpiece; a second penetration step, wherein a pulsed laser beam having a second average pulse power is aligned or irradiated onto the workpiece, wherein the first average pulse power is greater than the second average pulse power. Preferably, the average pulse power of the irradiation decreases at least once during the penetration period or during the penetration time. The average pulse power of the irradiation can decrease discretely, i.e., gradually or continuously, or it can also decrease in any combination of discrete and continuous variations. The average pulse power of the irradiation decreases multiple times during the penetration period or during the penetration time. Therefore, more than two piercing steps can be performed, each with a different average pulse power, and each lower than the average pulse power in the previous piercing step. The average pulse power of the irradiation can be constant during the piercing steps. The average pulse power of the irradiation by the pulsed laser beam can decrease monotonically or strictly monotonically during piercing. The average pulse power of the irradiation by the pulsed laser beam at the beginning of the piercing or penetration time can be greater than the average pulse power at the time of penetration, i.e., at the end of the piercing or penetration time. Preferably, during the penetration time, i.e., from the beginning of piercing until penetration, the fitted or regressive line of the average pulse power of the irradiation has a negative slope. The average pulse power of the irradiation by the pulsed laser beam can be reduced by at least one of the following adjustments or changes: extending the pulse off-time, reducing the pulse peak power, shortening the pulse on-time, reducing the pulse frequency, and reducing the pulse duty cycle. In particular, the average pulse power of the irradiation can be reduced by changing the pulse on-time and pulse off-time: for example, if the pulse on-time is extended less than the pulse off-time, the pulse off-time and pulse on-time can be extended. In another example, if the pulse on-time is shortened more than the pulse off-time, the pulse off-time and pulse on-time can be shortened. In another example, if the pulse on-time is shortened, the pulse off-time can remain constant. If the average pulse power of the irradiation is reduced by extending the pulse off-time, the peak pulse power and / or pulse on-time and / or pulse energy can remain constant during the insertion or penetration period. In one embodiment, the method may have at least two insertion steps, wherein in a first insertion step, a first average pulse power is greater than or equal to an average limiting pulse power, and in a second insertion step, a second average pulse power is less than the first average pulse power and / or greater than the average limiting pulse power.Optionally, the method may include a third insertion step, wherein the third average pulse power is less than the second average pulse power. The average limiting pulse power may represent the average pulse power when the insertion rate approaches zero, insertion stops, or saturation occurs during insertion. The average limiting pulse power may be pre-given based on the material and / or thickness of the workpiece.

[0012] According to another aspect, a method for penetrating a workpiece using a laser beam (also known as a processing beam) is described. The method includes: irradiating the workpiece with a pulsed laser beam to form a puncture, wherein the pulse-off time of the pulsed laser beam is reduced during the penetration or penetration time, for example, reduced at least once. The penetration time can here represent the duration of the penetration or puncture process, i.e., the time period from the first activation of the laser beam until the workpiece is punctured. In other words, the method for penetrating a workpiece using a pulsed laser beam includes: a first penetration step, wherein a pulsed laser beam having a first pulse-off time is aligned or irradiated onto the workpiece; and a second penetration step, wherein a pulsed laser beam having a second pulse-off time is aligned or irradiated onto the workpiece, wherein the first pulse-off time is less than the second pulse-off time. Preferably, the pulse-off time is reduced at least once during the penetration or penetration time. The pulse-off time of the pulsed laser beam can be discretely extended, i.e., gradually or continuously extended, or can also be extended in any combination of discrete and continuous variations. The pulse-off time can be reduced multiple times during the penetration or penetration time. Therefore, more than two piercing steps can be performed, each with a different pulse off-time and each longer than the pulse off-time in the previous piercing step. The pulse off-time can be constant during the piercing steps. The pulse off-time can increase monotonically or strictly monotonically during piercing. The pulse off-time of the pulsed laser beam can be less at the start of the piercing or penetration time than at the end of the penetration time, i.e., at the end of the piercing or penetration time. Preferably, during the penetration time, i.e., from the start of piercing until penetration, the fitted or regressive line of the pulse off-time has a positive slope. The pulse off-time of the pulsed laser beam can be extended by reducing the pulse frequency and decreasing the pulse duty cycle. The pulse peak power and / or pulse on-time and / or pulse energy can remain constant during piercing or during the penetration time. In one embodiment, the method can have at least two piercing steps, wherein in the first piercing step, the first pulse off-time is less than or equal to the limiting pulse off-time, and in the second piercing step, the second pulse off-time is greater than the first pulse off-time and / or greater than the limiting pulse off-time. Optionally, the method may include a third insertion step, wherein the third pulse shut-off time is greater than the second pulse shut-off time. The limiting pulse shut-off time can represent the pulse shut-off time at which the insertion rate approaches zero, insertion stops, or saturation occurs during insertion. The limiting pulse shut-off time can be pre-defined based on the workpiece material and / or thickness.

[0013] According to another aspect, a method for penetrating a workpiece using a laser beam (also known as a processing beam) is described. The method includes: irradiating the workpiece with a pulsed laser beam to form a puncture, wherein the pulse frequency of the pulsed laser beam decreases during the penetration or penetration time, for example, at least once. The penetration time can here represent the duration of the penetration or penetration process, i.e., the time period from the first activation of the laser beam until the workpiece is penetrated. In other words, the method for penetrating a workpiece using a pulsed laser beam includes: a first penetration step, wherein a pulsed laser beam having a first pulse frequency is aligned or irradiated onto the workpiece; and a second penetration step, wherein a pulsed laser beam having a second pulse frequency is aligned or irradiated onto the workpiece, wherein the first pulse frequency is greater than the second pulse frequency. Preferably, the pulse frequency decreases at least once during the penetration or penetration time. The pulse frequency of the pulsed laser beam can be discretely extended, i.e., progressively or continuously extended, or can also be extended in any combination of discrete and continuous variations. The pulse frequency can decrease multiple times during the penetration or penetration time. Therefore, more than two piercing steps can be performed, each with a different pulse frequency and each less than the pulse frequency in the preceding piercing step. The pulse frequency can be constant during the piercing steps. The pulse frequency can decrease monotonically or strictly monotonically during piercing. The pulse frequency of the pulsed laser beam can be greater at the start of the piercing or penetration time than at the end of the piercing or penetration time. Preferably, during the penetration time, i.e., from the start of piercing until penetration, the fitted or regressive line of the pulse frequency has a negative slope. The pulse frequency of the pulsed laser beam can be reduced by extending the pulse off time. The pulse peak power and / or pulse on time and / or pulse energy can remain constant during piercing or during the penetration time. In one embodiment, the method can have at least two piercing steps, wherein in the first piercing step, the first pulse frequency is greater than or equal to the limiting pulse frequency, and in the second piercing step, the second pulse frequency is less than the first pulse frequency and / or less than the limiting pulse frequency. Optionally, the method can include a third piercing step, wherein the third pulse frequency is less than the second pulse frequency. The limiting pulse frequency can represent the pulse frequency at which the penetration rate approaches zero, penetration stops, or saturation occurs during penetration. The limiting pulse frequency can be pre-defined based on the workpiece material and / or thickness.

[0014] Each of these aspects may have one or more of the following characteristics: Pulse parameters may include average pulse power, pulse off time, pulse on time, pulse frequency, pulse period, pulse duty cycle, and / or pulse peak power. At least one pulse parameter selected from the group consisting of average pulse power, pulse off time, pulse on time, pulse frequency, pulse duty cycle, and pulse peak power may be adjusted according to the workpiece material and / or thickness (also referred to as material thickness) and / or instantaneous insertion time and / or instantaneous insertion depth. In particular, the first pulse frequency, first average pulse power, and / or first pulse off time may be selected according to the workpiece material and / or thickness. The pulse frequency, average pulse power, and / or pulse off time may be adjusted based on the instantaneous insertion time and / or instantaneous insertion depth, especially in insertion steps immediately following the first insertion step. In particular, at least one pulse parameter selected from the group consisting of average pulse power of irradiation, pulse off time, pulse on time, pulse frequency, pulse duty cycle and pulse peak power is based on workpiece thickness, workpiece material, process gas type, process gas pressure, focal position, imaging ratio of optical system or laser processing head, focal diameter and nozzle distance to the upper side of workpiece and is varied according to current penetration time and / or penetration depth.

[0015] Preferably, the pulse on-time is constant during insertion or puncture. The pulse on-time can be adjusted according to the material or thickness of the workpiece.

[0016] Preferably, the peak pulse power is constant during the insertion or puncture time. The peak pulse power can be adjusted according to the material or thickness of the workpiece.

[0017] Preferably, the pulse energy is constant during the insertion or puncture time. In other words, the product of the pulse peak power and the pulse on-time can be adjusted to be constant. The pulse energy can be adjusted according to the material or thickness of the workpiece. Optionally, the minimum value of the pulse energy can be adjusted according to the material or thickness of the workpiece.

[0018] Preferably, the durations of each insertion step have different lengths. For example, the duration of the first insertion step may be longer than the duration of subsequent, such as the second or third insertion step. Furthermore, when the average pulse power, pulse off-time, and / or pulse frequency vary discretely or progressively, the first variation, i.e., the variation from the first insertion step to the second insertion step, may be greater than the second variation, i.e., the variation from the second insertion step to the third insertion step.

[0019] In one embodiment, the pulse frequency used at the start of insertion and / or during the first insertion step may be greater than or equal to the limiting pulse frequency. The limiting pulse frequency may be pre-defined based on the material and / or thickness of the workpiece.

[0020] In one embodiment, the pulse shut-off time used at the start of insertion and / or during the first insertion step can be greater than or equal to the limiting pulse shut-off time. The limiting pulse shut-off time can be pre-defined based on the material and / or thickness of the workpiece.

[0021] Preferably, the pulse on-time, for example during the puncture duration, is in the range of 0.01 ms to 100 ms (0.01 ms ≤ t). an ≤100ms), especially between 0.1ms and 10ms (0.1ms ≤ t an ≤10ms). Preferably, the pulse off time, for example during the puncture duration, is in the range of 0.01ms to 100ms (0.01ms ≤ t). aus ≤100ms), especially between 0.1ms and 10ms (0.1ms ≤ t aus ≤10ms).

[0022] Preferably, the pulse on-time or pulse period of the pulsed laser beam, for example during the piercing duration, is in the range of microseconds or milliseconds. In this case, piercing can be achieved primarily by melting the workpiece. Fiber lasers, disk lasers, or direct diode lasers can be used. The wavelength of the pulsed laser beam is preferably in the range of 800 nm to 1300 nm.

[0023] Preferably, the pulse frequency is adjusted according to the thickness of the workpiece. For workpiece thicknesses of 10mm to 15mm, the pulse frequency, for example during the puncture duration, can be between 400Hz and 3000Hz (400Hz ≤ f ≤ 3000Hz), particularly between 600Hz and 1500Hz (600Hz ≤ f ≤ 1500Hz). Here, the pulse frequency can be changed at least once during puncture. For workpiece thicknesses of 15mm to 20mm, the pulse frequency, for example during the puncture duration, can be between 300Hz and 2000Hz (300Hz ≤ f ≤ 2000Hz), particularly between 400Hz and 900Hz (400Hz ≤ f ≤ 900Hz). Here, the pulse frequency can be changed at least once during puncture. For workpiece thicknesses of 20mm to 25mm, the pulse frequency, for example during the puncture duration, can be between 300Hz and 1500Hz (300Hz ≤ f ≤ 1500Hz), particularly between 400Hz and 800Hz (400Hz ≤ f ≤ 800Hz). Here, the pulse frequency can be changed at least twice during puncture. For workpiece thicknesses greater than 25mm, the pulse frequency, for example during the puncture duration, can be between 200Hz and 1000Hz (200Hz ≤ f ≤ 1000Hz), particularly between 400Hz and 700Hz (400Hz ≤ f ≤ 700Hz). Here, the pulse frequency can be changed at least twice during puncture.

[0024] The method can be used to penetrate workpieces with a thickness of at least 10 mm, particularly at least 20 mm, such as 30 mm. The peak power of the pulsed laser beam during penetration is preferably at least 4 kW and particularly greater than or equal to 6 kW.

[0025] The material can be a metal workpiece. The workpiece can be made of metal or may include metal. The workpiece can include or be sheet metal. Furthermore, the material of the workpiece or sheet metal can include or be structural steel alloys, stainless steel alloys, aluminum alloys, copper alloys, brass alloys, structural steel, stainless steel, aluminum, copper, and brass.

[0026] Preferably, during insertion, an inert process gas, such as nitrogen or argon, is directed at the workpiece. The process gas can act on the workpiece coaxially with the laser beam.

[0027] The method for piercing can be used to prepare a method for laser cutting. In other words, the method may also include cutting the workpiece from the piercing portion using a laser. Therefore, according to one embodiment of the invention, a method for laser cutting is also described, comprising the method for piercing according to one embodiment of the invention, and cutting from the piercing portion using a laser beam. During or during the piercing method, the laser beam (also called the processing beam) may be pulsed. It is preferable to use the laser beam continuously during laser cutting. Of course, the same laser beam, which may have different parameters, can be used for both laser cutting and piercing. In other words, the laser beam for piercing and the laser beam for laser cutting may originate from the same laser source.

[0028] According to another aspect, an apparatus for laser processing materials on a workpiece is described. The apparatus includes a laser source for generating a laser beam; a laser processing head for irradiating the workpiece with the laser beam; and a control device configured to control the apparatus, particularly the laser source and / or the laser processing head, to perform a method for insertion according to one of the embodiments described herein.

[0029] Within the scope of this invention, the pulse off time can be defined as the time of the pulse period, wherein the irradiation power is below a predetermined threshold, for example, below 30%, 20%, or 10% of the maximum laser power or the peak pulse power. In other words, within the scope of this invention, the pulse on time can be defined as the time of the pulse period, wherein the irradiation power is above a predetermined threshold, for example, above 30%, 20%, or 10% of the maximum laser power or the peak pulse power.

[0030] Furthermore, within the scope of this invention, pulse parameters, such as the average pulse power, peak pulse power, pulse frequency, pulse period, pulse off time, pulse on time, pulse duty cycle, and / or pulse energy, are within ±0.2 or ±0.1 times the average value of the pulse parameters, rather than being constant. Attached Figure Description

[0031] Embodiments of the invention are shown in the accompanying drawings and described in more detail below. The drawings show: Figure 1 : A schematic structure of an apparatus for laser processing materials according to an embodiment of the present invention. Figure 2 : A schematic diagram of pulse parameters Figure 3A A graph showing the puncture time based on measured pulse frequency for different workpiece thicknesses. Figure 3B Microscopic images of the insertion process into a 30mm thick stainless steel sheet with different pulse frequencies. Figure 4A A schematic diagram of the insertion process with a limiting pulse frequency at the first time point. Figure 4B : The second time point after the puncture stops Figure 4A A diagram illustrating the insertion process. Figure 5 A schematic diagram of the pulse frequency according to the insertion time during a method for insertion at a progressively decreasing pulse frequency, according to an embodiment of the present invention. Figure 6 A schematic diagram of the irradiation laser power or irradiation pulse sequence based on the piercing time during a method for piercing with a gradually decreasing pulse frequency, according to an embodiment of the present invention, under the condition of a constant pulse on-time. Figures 7A to 7D :exist Figure 6 A schematic diagram illustrating the correlation between pulse frequency and insertion depth during the insertion method. Figure 8 A schematic diagram of the pulse frequency according to the insertion time during a method for insertion with progressively decreasing pulse frequencies, according to an embodiment of the present invention, and Figure 9 A schematic diagram of the pulse frequency according to the insertion time during an insertion method for a pulse frequency that decreases with a fitted line according to an embodiment of the present invention.

[0032] Unless otherwise emphasized, the same reference numerals are used for elements that have the same or the same function. Detailed Implementation

[0033] Figure 1 A schematic diagram of an apparatus for laser processing materials according to an embodiment of the present invention is shown. The apparatus may include a laser processing head 100, particularly a laser cutting head, for irradiating a laser beam 10 onto a workpiece 1, a laser source 200 for generating the laser beam 10, and a control device 300. The control device 300 is provided or configured for controlling the apparatus, particularly according to a method corresponding to one of the embodiments described herein.

[0034] Laser source 200 emits laser beam 10, also known as a processing beam, which is guided and focused onto workpiece 1 by processing optics. The processing optics and / or laser source 200 are connected to control device 300. In addition to control functions, control device 300 may also have analysis, evaluation, and / or calculation functions. The processing optics may have transmission and / or reflection optical elements for beam guiding and beam shaping. Furthermore, the equipment for laser processing materials may have a gas supply device for supplying process gases to the processing zone on workpiece 1.

[0035] During insertion, the laser beam is pulsed 10 times and aligned with workpiece 1. Figure 2 The diagram shows a schematic overview of the pulse parameters. The pulse period, or pulse period T, is determined by the pulse on-time t. an and pulse off time t aus Conclusion: T=t an +t aus Pulse on time t an This represents the time period during which the laser pulse irradiates workpiece 1 with energy. Correspondingly, the pulse off-time t... aus This represents the time period during which no or almost no energy is irradiated onto workpiece 1. The reciprocal of the pulse period T is called the pulse frequency: f = 1 / T. Therefore, the pulse frequency depends not only on the pulse on-time but also on the pulse off-time. The ratio between the pulse on-time and the pulse period is called the pulse duty cycle R: R = t an / T. Pulse peak power P peak This corresponds to the maximum laser power provided by the laser source 200, hereinafter referred to as the maximum laser power P. max The irradiation energy during the pulse, also known as the pulse energy, is calculated by multiplying the peak pulse power by the pulse on-time. E Puls =P peak t an Therefore, the average pulse power of the irradiation is calculated by the product of the duty cycle and the peak pulse power, or by the product of the peak pulse power, the pulse on-time, and the pulse frequency. P mittel =P peak R=P peak t an f=P peak (1-t aus / (t an +t aus )) In the context of this invention, not only can the pulse cycle time during periods without energy irradiation be considered the pulse off-time, but also the pulse cycle time during periods when the irradiation energy or power remains below a threshold can be considered the pulse off-time. Figure 2 In the diagram, this threshold for irradiation power is plotted as P. SW,aus That is, once the power currently irradiating the workpiece is lower than this threshold P... SW,aus This results in a pulse off-time. For example, the threshold can be 30% of the maximum laser power (P).SW,aus =0.3 P max (or 20% of the maximum laser power or even 10% of the maximum laser power.)

[0036] According to the present invention, the control device 300 is configured to control the energy input to the processing zone or workpiece 1 based on one or more of the following process parameters and boundary conditions: material thickness or workpiece thickness, workpiece material, current insertion time, current insertion depth, process gas type, process gas pressure, focal position, imaging ratio of the optical system, focal diameter, and nozzle distance to the upper side of the workpiece. Based on at least one of these parameters, the energy input can be controlled by the pulse on-time (t). an ), pulse off time (t) aus ) and / or pulse peak power (P peak It is controlled based on the current insertion time or depth. By understanding the relationships within the process zone, process parameters can be tailored to improve process efficiency.

[0037] Typically, the penetration rate (the change in penetration depth per unit time) decreases as the penetration depth increases, while the puncture time, i.e. the time from when the laser beam first irradiates the workpiece until it is punctured, increases as the penetration depth s increases. Figure 3A This diagram shows the puncture time (in seconds) for different material or workpiece thicknesses (in millimeters) based on the selected pulse frequency (in Hertz). Here, the pulse frequency is constant throughout the puncture process. As the pulse frequency decreases, the puncture time increases disproportionately. This is primarily due to the increased resolidification of the molten material on the walls of the puncture hole. As a result, the puncture rate decreases and the process efficiency declines. Furthermore, the saturation region, where depth removal ceases, is depicted by shading, along with the so-called limiting pulse frequency related to material thickness. The limiting pulse frequency describes a pulse frequency threshold from which reliable puncture can no longer be achieved under given process parameters and boundary conditions. As the material thickness increases, the limiting pulse frequency shifts towards smaller pulse frequencies.

[0038] exist Figure 3B The image shows a microscopic image of a 30mm thick stainless steel workpiece penetrated by a pulse peak power of 6kW (see [link]). Figure 3A The top curve in the image). At a pulse frequency of 350 Hz (constant), the puncture time is 3.6 s (…). Figure 3B (First image from left in the middle) At a pulse frequency of 400Hz (constant), the puncture time is 2.5s (in... Figure 3B (Second image from left in the middle) At a pulse frequency of 500Hz (constant), the puncture time was 1.7s (in... Figure 3B(Third image from left in the middle). At a pulse frequency of 588Hz (constant), puncture stopped (no penetration occurred). Figure 3B (Right side of the middle)

[0039] exist Figure 4A and 4B The diagram schematically illustrates the insertion hole 3 at two different time points when piercing at the limiting pulse frequency. Starting from a determined insertion depth s, the time between each pulse (pulse shut-off time) is too short or the pulse frequency is too high, preventing sufficient molten material from being expelled from the insertion hole 3, thus causing insertion to stop. Another reason for insertion stopping is that as the insertion depth s increases, the path that the molten material must travel before leaving the insertion hole 3 also increases (see [reference]). Figure 4A The coupling energy of the laser beam 10 at the insertion bottom 5 decreases. As the insertion depth increases, the irradiation energy increasingly heats the sides of the insertion hole 3, potentially leading to cavitation-like melting. In cases of thicker material, such as greater than 20 mm, saturation of the insertion process may occur (see...). Figure 4B If the pulse frequency is arbitrarily large or greater than the corresponding limiting pulse frequency, the penetration rate approaches 0 (penetration stops). Residual melt in the penetration hole 3 and subsequent pulses cause the heating of the processing zone to increase pulse by pulse. This results in heat accumulation in the penetration hole (pulse-to-pulse mechanism), causing a defined area of ​​material to melt transversely to the penetration direction, and the bottom of the penetration 5 is always refilled with material. The previously achieved penetration depth s decreases, and thus a limiting penetration depth s appears. grenz (See) Figure 4B and 3B (Right side). Safe penetration cannot be achieved (insertion stops along the direction of penetration).

[0040] To avoid stopping the puncture and simultaneously shorten the puncture time, the average pulse power irradiated onto the workpiece during puncture is reduced according to the present invention. This maximizes the puncture rate along the puncture depth while ensuring puncture penetration. Several embodiments of the puncture method according to the present invention are described below.

[0041] The following describes a method for inserting into a workpiece and an apparatus for laser processing materials, the apparatus having a control device configured to perform the method. According to the embodiment, the average pulse power of the irradiation is reduced by decreasing the pulse frequency during insertion. However, the invention is not limited thereto. Alternatively, the average pulse power of the irradiation can be reduced, for example, by extending the pulse off-time and / or shortening the pulse on-time and / or reducing the duty cycle.

[0042] exist Figure 5In the illustrated embodiment, the pulse frequency decreases progressively, gradually, or discretely. For example, the pulse frequency decreases at least once during the puncture time, preferably at least twice. In this case, the method for puncture may include at least a first puncture step (step 1) with a first pulse frequency f1 and a second puncture step (step 2) with a second pulse frequency f2, wherein the first pulse frequency f1 is greater than the second pulse frequency f2. Thus, the first puncture step (step 1) occurs at the start of puncture, while the second puncture step (step 2) occurs after the first puncture step (step 1). However, the method may also have any number of puncture steps, for example, n, wherein the pulse frequency of each puncture step is lower than the pulse frequency of the previous puncture step. The pulse rate may be constant during the puncture steps. Alternatively, as follows... Figure 9 As described above, the pulse frequency during the insertion step can be the average pulse frequency f of the nth insertion step. n The content is between 80% and 120%, preferably between 90% and 110% (i.e., f). n ±0.2 f n or f n ±0.1 f n The pulse frequency change between insertion steps, i.e., Δf 1,2 They can be the same or different. Preferably, the first change, i.e., ΔΔf 1,2 Greater than the second change, i.e., Δf 2,3 Similarly, the duration of each insertion step can be the same or different. Preferably, the first insertion step has the longest duration.

[0043] Alternatively, for a gradual or discrete reduction, the pulse frequency can be decreased during the puncture time by any combination of discrete and continuous reductions (see also...). Figure 8 ).

[0044] about Figure 5 At least one change or decrease in the pulse frequency (f2 < f1) is described. This refers to the pulse frequency at the start of insertion or at the start of penetration time f1 and / or the pulse frequency f2 to f1 during subsequent insertion steps. n It can be adjusted according to the thickness of the workpiece and / or the instantaneous insertion time and / or the instantaneous insertion depth.

[0045] In one embodiment, insertion with a variable pulse frequency can be achieved by two variations of the pulse frequency. Preferably, the pulse frequency at the start of insertion and / or in the first insertion step is greater than or equal to a limiting pulse frequency for the workpiece, which may depend on the workpiece thickness and workpiece material.

[0046] exist Figure 6schematically shows another embodiment. As in Figure 5 , the pulse frequency is reduced in n piercing steps until piercing is achieved. Furthermore, in the embodiment shown in Figure 6 , the pulse on-time t an remains constant or nearly constant throughout the entire piercing process. In the latter case, the pulse on-time can deviate by ±20% or ±10% from the average pulse on-time during the piercing period. In other words, the nearly constant pulse on-time can lie in the band range from 0.8 t an to 1.2 t an or from 0.9 t an to 1.1 t an .

[0047] Preferably, the value for the pulse on-time t an is selected according to the workpiece thickness. In this case, the average pulse power or pulse frequency is reduced by increasing the pulse off-time t aus , for example as a function of the piercing time ( Figure 6 ) or as a function of the piercing depth ( Figures 7A-7D ). This ensures that as the piercing depth increases, the melt has sufficient time between pulses to be discharged from the piercing hole, for example by means of the blown-in process gas.

[0048] In the embodiment shown in Figure 6 , instead of a constant pulse on-time, the irradiated pulse energy E Puls , i.e. the product of the pulse peak power and the pulse on-time, can be kept constant, and the other pulse parameters can be selected as in the embodiment shown in Figure 6 . Alternatively, the pulse energy can be set to a minimum value that is dependent on the material and thickness.

[0049] In another embodiment illustrated intuitively in Figures 7A-7D , the workpiece thickness is at least 20 mm, and the pulse peak power is at least 4 kW. The method for piercing has at least three piercing steps with different pulse frequencies. Herein, the piercing process starts with a first pulse frequency that is greater than or equal to the limit pulse frequency associated with the workpiece thickness ( Figure 7A : f grenz ≤f1). This can correspond to step 1 of Figure 5 . After a predefined piercing time and / or piercing depth, the pulse frequency is reduced to a second pulse frequency f2 that is less than the first pulse frequency or the limit pulse frequency ( Figure 7B : f2<f1 or f2<f grenz ≤f1). This can correspond to Figure 5 step 2. After a further predefined penetration time and / or penetration depth, the pulse frequency is reduced to a third pulse frequency f3 that is less than the second pulse frequency f2 ( Figure 7C : f3<f2) and maintained until piercing 9 (see Figure 7D ). In the Figures 3A-3B example of penetrating into a 30 mm thick stainless steel workpiece with a pulse peak power of 6 kW, the piercing time can be reduced by more than 50% by means of this method, namely from 1.7 s at a constant pulse frequency of 500 Hz to 0.8 s. Here, the pulse frequency is changed twice during penetration: from a first pulse frequency f1=588 Hz at the start of penetration to a second pulse frequency f2=400 Hz, and subsequently to a third pulse frequency f3=350 Hz. The first pulse frequency f1 of 588 Hz is greater than the limit pulse frequency (see Figure 3A ). This results in a penetration process that is optimized in terms of short piercing time and safe piercing.

[0050] As described above, the average pulse power or pulse frequency does not have to decrease monotonically or strictly monotonically. Instead, the average pulse power or pulse frequency can be reduced stepwise or stagewise, wherein the average pulse power or pulse frequency can move within a power band or pulse frequency band in each step. That is, during each step, the average pulse power or pulse frequency lies within a band range having a predefined minimum value and a predefined maximum value. The power band can be defined by a deviation of ±20%, in particular ±10% of the average value of the average pulse power during the penetration step (step n). Similarly, the pulse frequency band can be defined by a deviation of ±20%, in particular ±10% of the average pulse frequency f n during the penetration step (step n). Figure 8 shows an exemplary pulse frequency band, wherein the pulse frequency can move during the respective steps 1,...n. The pulse frequency band shifts to smaller values with each step. For example, the pulse frequency band can be reduced stepwise or stagewise. In the Figure 8 , the pulse frequency band is defined as follows: f 1,min =0.8 f1 (or 0.9 f1); f 1,max =1.2 f1 (or 1.1 f1); f 2,min =0.8 f2 (or 0.9 f2); f 2,max =1.2 f2 (or 1.1 f2); f n,min =0.8 f n (or 0.9 f n ) and f n,max =1.2 f n (or 1.1) f n In other words, as long as the pulse frequency decreases with the time average until penetration, a slight increase in the pulse frequency can be ignored. If the average pulse power is to be reduced by changing another pulse parameter, for example by extending the pulse off time, this change can also be made gradually, wherein the pulse parameter is within ±20% of the average value of the pulse parameter in each step, and especially within ±10% of the average value of the pulse parameter in this step.

[0051] Similarly, the average pulse power or pulse frequency can decrease continuously or almost continuously. For this purpose, it is possible to shift the average pulse power or pulse frequency within a band that decreases in value over time (see [link to relevant documentation]). Figure 9 That is, the average pulse power or pulse frequency decreases on an average basis over time. In other words, if the corresponding fitted or regression line ( Figure 9 (The dashed line indicates that) during the puncture time, i.e., from the start of puncture until puncture, the average pulse power or pulse frequency has a negative slope, and thus can be considered to be decreasing. This is because the very short temporal increase in average pulse power or pulse frequency is negligible for the puncture method according to the invention. If the average pulse power is to be reduced by changing another pulse parameter, for example by extending the pulse off-time, this change can also be made continuously or almost continuously, provided that the fitted or regressive line of that pulse parameter has a negative slope during the puncture time.

[0052] According to embodiments of the present invention, a method and apparatus for penetrating a workpiece by means of a laser beam are described, thereby minimizing the penetration duration or maximizing the penetration rate while ensuring safe penetration and preventing penetration from stopping.

Claims

1. A method for penetrating a metal workpiece with a thickness of at least 10 mm using a laser beam, comprising: A pulsed laser beam (10) is irradiated onto a metal workpiece (1) with a thickness of at least 10 mm to form a puncture (9). The average pulse power P of the pulsed laser beam (10) is... mittel The pulse is reduced multiple times during insertion until penetration, wherein the pulse closing time t is used. aus The average pulse power P of the irradiation is reduced by extending the pulse frequency f, reducing the pulse duty cycle, or otherwise decreasing the pulse duration. mittel In this process, more than two insertion steps are performed, each with a different average pulse power, and each lower than the average pulse power in the previous insertion step.

2. The method according to claim 1, wherein, The average pulse power P of the irradiation mittel Decrease discretely and / or gradually and / or continuously.

3. The method according to claim 1 or 2, wherein, During the puncture, the average pulse power P of the irradiation mittel The fitted line has a negative slope.

4. The method according to claim 1 or 2, wherein, The average pulse power P of the irradiation mittel It decreases gradually, and during each step it lies within a band with a pre-given minimum and a pre-given maximum value.

5. The method according to claim 1 or 2, wherein, The average pulse power P of the irradiation mittel Furthermore, by shortening the pulse on-time t of the pulsed laser beam (10) an To reduce.

6. The method according to claim 1 or 2, wherein, By extending the pulse off time t aus Reduce the average pulse power P of the irradiation mittel And maintain the peak pulse power P during insertion. Peak and / or pulse on-time t an and / or pulse energy E Puls Constant.

7. The method according to claim 1 or 2, wherein, To avoid stopping the piercing, the average pulse power P of the pulsed laser beam (10) is... mittel The pulse frequency is reduced multiple times during insertion until penetration, wherein, in the first insertion step at the start of insertion, the first pulse frequency f1 is greater than or equal to a predetermined limit pulse frequency, wherein the predetermined limit pulse frequency indicates the pulse frequency at which insertion stops.

8. The method according to claim 1 or 2, wherein, The average pulse power P of the irradiation mittel The reduction occurs in more than two steps, wherein in the first insertion step, the first pulse frequency f1 is greater than or equal to a predetermined limit pulse frequency, and in the second insertion step, the second pulse frequency f2 is less than the predetermined limit pulse frequency, wherein the predetermined limit pulse frequency indicates the pulse frequency at which insertion stops.

9. The method according to claim 7, wherein, The predetermined limiting pulse frequency depends on the thickness and / or material of the workpiece (1).

10. The method according to claim 8, wherein, The predetermined limiting pulse frequency depends on the thickness and / or material of the workpiece (1).

11. The method according to claim 1 or 2, wherein, At least one of the pulse parameters of the pulsed laser beam (10) is adjusted according to the material and / or thickness of the workpiece and / or the instantaneous insertion time and / or the instantaneous insertion depth, and the pulse parameter is selected from the group including the average pulse power of the irradiation, the pulse off time, the pulse on time, the pulse frequency, the pulse duty cycle and the pulse peak power.

12. The method according to claim 1 or 2, wherein, The pulse off time t of the pulsed laser beam (10) aus and / or pulse on-time t an It falls within the range of 0.01ms to 100ms.

13. The method according to claim 12, wherein, The pulse off time t of the pulsed laser beam (10) aus and / or pulse on-time t an It falls within the range of 0.1ms to 10ms.

14. The method according to claim 1 or 2, wherein, The pulse frequency of the pulsed laser beam (10) is in the range of 200Hz to 3000Hz.

15. The method according to claim 14, wherein, The pulse frequency of the pulsed laser beam (10) is in the range of 400Hz to 2000Hz.

16. The method according to claim 1 or 2, wherein, Insertion is performed into a workpiece (1) with a thickness greater than 20 mm.

17. The method according to claim 1 or 2, wherein, The average pulse power P of the irradiation mittel Control is based on at least one of the following parameters: workpiece thickness, workpiece material, current insertion time, current insertion depth, process gas type, process gas pressure, imaging ratio of the optical system of the laser processing head (100), focal position, focal diameter, intensity distribution of the pulsed laser beam (10), nozzle type, nozzle diameter, and distance from the nozzle to the workpiece.

18. The method according to claim 1 or 2, wherein, The insertion occurred in the metal sheet.

19. A method for laser cutting, comprising: A method according to any one of the preceding claims for inserting a laser beam into a metal workpiece having a thickness of at least 10 mm; and Cutting is initiated from the puncture site (9) by a pulsed laser beam (10).

20. An apparatus for laser processing materials for metal workpieces (1) having a thickness of at least 10 mm, comprising: A laser source (200) for generating a pulsed laser beam (10); A laser processing head (100) is used to irradiate the workpiece with the pulsed laser beam (10); and A control device (300) configured to control the device in order to perform the method for insertion according to any one of claims 1 to 18.

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