Method for manufacturing a skinning roller, skinning roller and method for skinning a hot-dip coated steel strip

Abstract

According to claim 1, the invention relates to a method for manufacturing a skinning roller, wherein the skinning roller is clamped in a rotary device and set into rotation at a rotational speed w, wherein a surface of the skinning roller to be processed is treated during rotation by means of laser pulses via at least one pulsed laser or an optic coupled to a pulsed laser, wherein the laser is operated with a repetition rate f, with a maximum laser power P, with a pulse radius r and a pulse duration t, wherein the laser pulses are directed overlappingly onto the surface and thereby create overlapping cup-shaped depressions in the surface, wherein the laser pulses have a pulse spacing d between 0.6 and 1.4 of a pulse radius r, wherein the laser is controlled and / or regulated by means of a process computer, characterized in thatthat a stochastic structure is generated on the surface of the skinning roller, wherein the surface of the skinning roller to be processed is divided by a program into a pixel pattern with n × m pixels, wherein each pixel of the pixel pattern has a resolution of up to p steps with respect to a pulse energy, wherein the pixel pattern is generated normally distributed with at least one Gaussian curve or uniformly distributed numerically, and the pixel pattern generated thereby is implemented in a process computer for the control and / or regulation of the laser for processing the surface of the skinning roller.

Description

[0001] The invention relates to a method for manufacturing a dressing roller, a dressing roller and a method for dressing a hot-dip coated steel strip.

[0002] In current technology, rollers with an EDT surface are used for steel production. These rollers feature stochastic structures to adjust the surface properties of the thin steel sheets. The arithmetic mean roughness (Ra) and the peak count (RPc) are linked in this process. A higher arithmetic mean roughness results in a lower peak count. This contradicts the general requirements of automotive manufacturers, significantly limiting the usable parameter space.

[0003] These parameters can be freely adjusted using non-stochastic, so-called deterministic structures, which can be introduced into the rollers, particularly through laser texturing. Deterministic structures have the disadvantage of being sensitive to optical disturbances or surface defects. The slightest changes in a regular pattern (deterministic structure) are perceived by the human eye as errors and are considered disruptive. With a random distribution, such as noise, these errors cannot be perceived.

[0004] Methods for producing laser-textured rollers, in particular with a random (stochastic) texture, are described by way of example in EP 2 794 178 B1 and in JP 2004-106 015 A. Furthermore, a generic method for texturing the surfaces of temper rollers is known from DE 10 2020 107 858 A1. Reference is also made to DE 10 2012 017 703 A1 as further prior art.

[0005] The object of the present invention is to provide a method for manufacturing a skin-coating roller with which a parameter space encompassing topographic characteristics such as arithmetic mean roughness Ra and peak number RPc can be significantly expanded. Furthermore, it is an object of the present invention to provide a skin-coating roller and a method for skin-coating a hot-dip coated steel strip, with which an advantageous surface for the manufacture of vehicle components can be provided.

[0006] This problem of manufacturing a tempering roller is solved by a method with the features of claim 1, for a tempering roller is solved by the features of claim 7, and for tempering a hot-dip coated steel strip is solved by a method with the features of claim 8. Further embodiments are described in the dependent claims.

[0007] The first teaching relates to a method for manufacturing a skinning roller, wherein the skinning roller is clamped in a rotary device and set into rotation at a rotational speed w, wherein a surface of the skinning roller to be processed is treated during rotation by means of laser pulses via at least one pulsed laser or an optic coupled with a pulsed laser, wherein the laser is operated with a repetition rate f, with a maximum laser power P, with a pulse radius r and a pulse duration t, wherein the laser pulses are directed overlappingly onto the surface and thereby create overlapping cup-shaped depressions in the surface, wherein the laser pulses have a pulse spacing d between 0.6 and 1.4 of a pulse radius r, wherein the laser is controlled and / or regulated by means of a process computer, wherein a stochastic structure is created on the surface of the skinning roller.

[0008] For example, the melt dynamics during laser processing are used to treat the surface of the temper roller. This contrasts with so-called laser polishing, in which a constant melt film is created that smooths the surface and thus influences the arithmetic mean roughness Ra, particularly by reducing it. Laser processing is an ablation process in which the resulting vapor pressure is used to introduce "unrest" into the melt. This can lead to a targeted arithmetic mean roughness. The strength of the ablation, and thus the amount of melt and the resulting vapor pressure, can be adjusted via the maximum laser power P in conjunction with the pulse radius r. The laser pulse duration t determines the ratio of melt to vaporized material, and thus the strength of the vapor pressure and the penetration depth of the melt.During processing, the point-to-point distance (pitch), line spacing, and laser pulse duration can be kept constant. A constant pulse duration allows for a lower system complexity and the use of a commercially available pulsed laser. These lasers typically have a constant repetition rate. A combination of rotational speed w and repetition rate f results in a preferably constant pitch on the surface. This is largely subject to natural fluctuations in the rotational speed of the skinning rollers and is negligible for this application. The axial line spacing is determined by the traverse speed v of the laser or the optics coupled to the laser. The traverse speed is preferably kept constant during processing. Ideally, the pitch and line spacing are equal.

[0009] A point density resulting from the combination of pitch and line spacing can generate heat accumulation, which increases the heat penetration depth and thus in turn can influence the amount of melt and vapor pressure.

[0010] According to the invention, the surface of the skinning roller to be processed is considered as a developed area. A pixel pattern for laser processing is derived from the pitch and line spacing, which can, for example, correspond to the pulse spacing. Each pixel represents a laser shot and the associated pulse energy. Depending on the system, the pulse energy is also divided into steps. Typically, 8 bits (256 values) are used, although in individual cases 16 bits or, if required, more than 16 bits can be used. The pixel pattern can be numerically generated with a fixed value, a normal distribution and at least one Gaussian curve, or a uniform distribution. The resulting pixel pattern can then be implemented in a process computer for regulating and / or controlling the laser for processing the surface of the skinning roller.A fixed value can be understood, for example, as the ability to generate each pixel with a constant pulse energy.

[0011] It is known to use random number generators to numerically generate a random, or stochastic, pattern. Suitable programs are available on the market, such as Matlab. In this program, the surface of a skinning roller to be processed can be transformed into a developed area and divided into n x m pixels. Thus, the developed area is divided into n pixels per row and m pixels per column, where n and m are integers. n and m can also be equal. Each pixel is preferably chosen to be the same size, or its size can vary depending on the developed area or surface.

[0012] By selectively adjusting the aforementioned parameters on the laser using the control and / or regulation system, topography parameters Ra and peak count RPc on the surface of the dressing roller can be specifically or positively influenced.

[0013] According to one implementation, the pixel pattern can be numerically generated using a normal distribution with at least two Gaussian curves. Typically, a program numerically generates one pixel pattern at a time using a normal distribution with a Gaussian curve. For example, at least two pixel patterns, each with a normal distribution and a Gaussian curve, can be numerically generated, and these two distinct pixel patterns can be combined. This means, for instance, that the even-numbered pixels in pixel pattern 1 are used and the odd-numbered pixels in pixel pattern 1 are discarded, and the odd-numbered pixels in pixel pattern 2 are used and the even-numbered pixels in pixel pattern 2 are discarded. The combination of pixel patterns 1 and 2 then generates a "new" pixel pattern. Thus, by combining two pixel patterns, a "new" pixel pattern can be created by alternately combining the individual pixels.Preferably, pixel patterns are numerically generated with a normal distribution using (exactly) two Gaussian curves. This allows for targeted influence on the topography values, and in particular, higher Ra values, for example greater than 3.0 µm, preferably greater than 4.0 µm, preferably greater than 5.0 µm, and lower RPc values, for example less than 100 1 / cm, preferably less than 80 1 / cm, preferably less than 60 1 / cm.

[0014] According to one embodiment, a repetition rate f between 10 and 8000 kHz can be used or set. In particular, the repetition rate f can be between 50 and 2000 kHz.

[0015] According to one embodiment, a maximum laser power P between 10 and 1000 W can be used or set. The maximum laser power can be, in particular, at least 15 W, preferably at least 20 W. The maximum laser power can be, in particular, a maximum of 700 W, preferably a maximum of 300 W. Preferably, the pulse energy can be varied to control the ablation depending on the maximum laser power.

[0016] According to one embodiment, a pulse radius r between 10 and 80 µm can be used or set. The pulse radius can, in particular, be at least 12 µm. The pulse radius can, in particular, be a maximum of 65 µm, preferably a maximum of 55 µm.

[0017] According to one embodiment, a pulse duration t between 300 fs and 500 ns can be used or set.

[0018] A distance L between 20 and 300 mm can be used or set.

[0019] A rotational speed w typically corresponds to the product of pitch and repetition rate.

[0020] A traverse speed v is determined in particular as a function of rotational speed, line spacing and roller circumference.

[0021] The second teaching of the invention relates to a skinning roller with a laser-processed stochastic texture on the surface, preferably manufactured according to the first teaching, wherein the surface of the skinning roller has a topography with an arithmetic mean roughness Ra between 0.8 and 8.0 µm and with a peak number RPc between 30 and 250 1 / cm, wherein Ra and RPc are determined according to DIN EN 10049:2014-03.

[0022] The surface of the dressing roller can have a surface roughness (Ra) of at least 0.9, 1.0, 1.1, 1.2 µm, preferably at least 1.3, 1.4, 1.5, 1.6 µm, preferably at least 1.7, 1.8, 1.9, 2.0 µm, particularly preferably at least 2.2, 2.5, 2.7, 3.0 µm, and more preferably at least 3.5, 4.0, 4.5, 5.0 µm.

[0023] According to one embodiment, the surface of the dressing roller can have an RPc of at least 30 1 / cm and in particular a maximum of 240, 230, 220, 210 1 / cm, preferably a maximum of 200, 190, 180, 170 1 / cm, preferably a maximum of 160, 150, 140, 130 1 / cm, particularly preferably a maximum of 120, 110, 100, 90 1 / cm, further preferably a maximum of 80, 70, 60, 50 1 / cm.

[0024] According to an alternative embodiment, the surface of the dressing roller can have an RPc of a maximum of 250 1 / cm² and in particular at least 55, 60, 65, 70 1 / cm², preferably at least 75, 80, 85, 90 1 / cm², more preferably at least 95, 100, 105, 110 1 / cm², particularly preferably at least 115, 120, 125, 130 1 / cm², more preferably at least 135, 140, 145, 150 1 / cm².

[0025] According to one embodiment, the surface of the skinning roller can have a surface area (Ra) of at least 0.9, 1.0, 1.1, 1.2 µm, preferably at least 1.3, 1.4, 1.5, 1.6 µm, more preferably at least 1.7, 1.8, 1.9, 2.0 µm, particularly preferably at least 2.2, 2.5, 2.7, 3.0 µm, more preferably at least 3.5, 4.0, 4.5, 5.0 µm and an RPc of at least 30 1 / cm² and in particular a maximum of 240, 230, 220, 210 1 / cm², preferably a maximum of 200, 190, 180, 170 1 / cm², more preferably a maximum of 160, 150, 140, 130 1 / cm², more preferably a maximum of 120, 110, 100, 90 1 / cm, preferably with a maximum of 80, 70, 60, 50 1 / cm.

[0026] According to an alternative embodiment, the surface of the dressing roller can have a surface area (Ra) of at least 0.9, 1.0, 1.1, 1.2 µm, preferably at least 1.3, 1.4, 1.5, 1.6 µm, more preferably at least 1.7, 1.8, 1.9, 2.0 µm, particularly preferably at least 2.2, 2.5, 2.7, 3.0 µm, more preferably at least 3.5, 4.0, 4.5, 5.0 µm and an RPc of at most 250 1 / cm² and in particular at least 55, 60, 65, 70 1 / cm², preferably at least 75, 80, 85, 90 1 / cm², more preferably at least 95, 100, 105, 110 1 / cm², particularly preferably at least 115, 120, 125, 130 1 / cm, preferably at least 135, 140, 145, 150 1 / cm.

[0027] The third teaching of the invention relates to a method for dressing a hot-dip coated steel strip, wherein the hot-dip coated steel strip is passed between two dressing rollers having a stochastic texture and thereby dressed, wherein at least one dressing roller is used according to the second teaching, and in particular is manufactured according to the first teaching.

[0028] Preferably, both dressing rollers conform to the second doctrine and are manufactured in particular according to the first doctrine.

[0029] To avoid repetition, reference is made to the explanations of the first and second doctrines.

[0030] According to one embodiment, the steel sheet comprises a zinc-based coating. In addition to zinc and unavoidable impurities, the coating may contain additional elements such as aluminum with a content of up to 8 wt.%, in particular up to 5 wt.%, and / or magnesium with a content of up to 8 wt.%, in particular up to 5 wt.%. Steel sheets with a zinc-based coating offer very good cathodic corrosion protection and have been used in automotive manufacturing for many years. If improved corrosion protection is required, the coating additionally contains magnesium with a content of at least 0.3 wt.%, in particular at least 0.6 wt.%, preferably at least 0.9 wt.%. Alternatively or additionally, aluminum may be included with magnesium with a content of at least 0.1 wt.%, in particular at least 0.3 wt.%.A certain percentage of the coating must be present to, for example, improve the bond between the coating and the steel sheet and, in particular, to essentially prevent the diffusion of iron from the steel sheet into the coating during heat treatment of the coated steel sheet, thus ensuring, for example, good adhesion. The coating thickness on each side can be between 1.5 and 30 µm, particularly between 2 and 25 µm, preferably between 3 and 20 µm. Below the minimum limit, sufficient cathodic corrosion protection cannot be guaranteed, and above the maximum limit, joining problems can occur when connecting the steel sheet according to the invention, or a component manufactured therefrom, to another component. In particular, if the coating thickness exceeds the specified maximum limit, a stable thermal joining or welding process cannot be ensured.

[0031] If the coating contains magnesium and aluminum in addition to zinc and unavoidable impurities, it is known in the scientific community as zinc-magnesium, ZM or Zn-Al-Mg.

[0032] In a preferred variant, the aluminium content in the coating is 1.1 to 8 wt.%, in particular 1.2 to 5 wt.%.

[0033] In a preferred variant, the magnesium content in the coating is 1.1 to 8 wt.%, in particular 1.2 to 5 wt.%.

[0034] The coating may also contain only zinc with small amounts of aluminum up to 0.3 wt.% in addition to unavoidable impurities, known in technical circles as "Z".

[0035] Unavoidable impurities, such as elements from the group consisting of silicon, antimony, lead, titanium, calcium, manganese, tin, lanthanum, cerium and chromium, may be present individually or in combination in the coating in amounts up to 0.5 wt.%, in particular up to 0.3 wt.%, preferably up to 0.1 wt.%, preferably up to 0.05 wt.%.

[0036] The steel strip consists of a steel material which, in addition to iron and unavoidable impurities, contains alloying elements such as carbon, silicon, manganese, and aluminum. Other components, such as titanium and chromium, may also be present, either individually or in combination, and can be selected depending on the application and strength class. It is well known in technical circles which steel materials are particularly suitable for the production of cold-formed components in the automotive industry, depending on the application.

[0037] According to a preferred embodiment, the steel strip is a cold-rolled strip. A cold-rolled strip is a cold-rolled steel strip. The production of cold-rolled strips is common practice.

[0038] The invention also includes any combinations of the embodiments and alternatives described above.

[0039] The invention is explained in more detail with reference to the following exemplary embodiments in conjunction with the drawing.

[0040] Standard sizes of skinning rollers have a working surface width between 1200 and 2200 mm and a diameter between 350 and 650 mm. These specifications are entered into the example program Matlab, and based on predefined parameters or by the program itself, a developed surface is divided into a pixel pattern with n x m pixels. Each pixel of the pixel pattern has a rectangular shape, preferably a square shape, with a side length between 5 and 50 µm and a resolution of up to p steps based on the pulse energy.

[0041] In a practical series of tests, 8 different standard dressing rollers were used, each with a surface to be processed or a corresponding area of ​​2200 × 1500 mm. 2Textured. Each skinning roller was clamped in a rotary device and rotated at a constant speed w, calculated as the product of pitch and repetition rate. Optics coupled to a pulsed laser were used to process the surface of the skinning roller during rotation. The laser-coupled optics were moved parallel to the axis of the skinning roller at a constant distance L = 50 mm from the surface, with a traverse speed v dependent on the rotational speed, line spacing, and roller circumference. Using the Matlab program, the surface was divided into a developed area with a pixel pattern of 88,000 (n) x 60,000 (m) pixels, where each pixel of the pixel pattern had a rectangular or square shape with a side length of 25 µm.The pixel pattern was numerically generated using a Gaussian distribution and implemented in a process computer to control the laser for processing the surface of the skinning roller. A commercially available laser from IPG with a repetition rate of 100 kHz and a maximum power of 300 W was used. A stochastic structure was generated on the surface of each skinning roller using laser pulses via optics coupled to the laser. The laser was controlled and / or regulated according to the specifications implemented in the process computer. Further parameters used for laser control, as well as the resulting topography parameters Ra and RPc, are listed in Table 1. In all cases, the ablation was controlled by varying the pulse energy according to the corresponding numerically generated pixel patterns.

[0042] Using confocal light microscopy, images of the textured surface of the dressing rollers were first taken section by section, and the data acquired were then subjected to filtering operations. Topographic parameters such as Ra and RPc, which are included as standard in the software in accordance with DIN EN 10049:2014-03, could be determined and output using evaluation software, such as MountainsMap from digital surf. Table 1 Dressing roller Pulse spacing [µm] maximum laser power P [W] Laser pulse radius [µm] Pulse duration [µs] Ra [µm] RPc[1 / cm] 1 28,57 33 17 1 0,89 127 2 25 40 17 1 1,8 200 3 28,57 30 17 1 1,3 227 4 40 200 35 1,5 3,4 235 5 33,33 100 25 1,5 3,5 122 6 20 100 25 1,5 6,7 114 7 50 300 50 0,7 2,5 111 8 25 100 17 1 3,3 152

[0043] With the aforementioned settings, high Ra values ​​are sometimes possible with correspondingly high RPc, whereby the maximum laser power determines the maximum pulse energy and this was variably set based on the steps in the numerically generated pixel pattern. Fig.Figure 1 shows an example of a partial view of the dressing roller 5. On the left is the pixel pattern numerically generated using the Matlab program, with a normally distributed depth distribution and a Gaussian curve. On the right is the image evaluated using MountainsMap, after laser processing and with the pixel pattern shown. The partial view of the pixel pattern shown in this case corresponded to a square shape with an area of ​​0.7 × 0.7 mm. 2 Each pixel was square with a side length of 25 µm. A resolution of 8 bits, and thus 256 levels, was chosen based on the (maximum) pulse energy. Level 255 in the Fig.Level 1 on the left shows the brightest point (white) on the scale and thus corresponds to an unprocessed area on the surface of the skinning roller with the lowest pulse energy, and level 0 shows the darkest point (black) on the scale and thus corresponds to a processed area on the surface of the skinning roller with the highest pulse energy. The surface resulting after laser processing is shown in Fig. 1 shown on the right in the partial view, whereby a stochastic structure could be generated by varying the pulse energy depending on the specified pixel pattern, with depths up to 15 µm (negative) and heights up to 10 µm (positive), thus a roughness depth up to 25 µm.

Claims

[1] A method for manufacturing a skinning roller, wherein the skinning roller is clamped in a rotary device and rotated at a rotational speed w, wherein a surface of the skinning roller to be processed is treated during rotation by means of laser pulses via at least one pulsed laser or optics coupled to a pulsed laser, wherein the laser is operated with a repetition rate f, with a maximum laser power P, with a pulse radius r and a pulse duration t, wherein the laser pulses are directed overlappingly onto the surface and thereby create overlapping cup-shaped depressions in the surface, wherein the laser pulses have a pulse spacing d between 0.6 and 1.4 of a pulse radius r, wherein the laser is controlled and / or regulated by means of a process computer, characterized by, that a stochastic structure is generated on the surface of the skinning roller, wherein the surface of the skinning roller to be processed is divided by a program into a pixel pattern with nxm pixels, wherein each pixel of the pixel pattern has a resolution of up to p steps with respect to a pulse energy, wherein the pixel pattern is generated normally distributed with at least one Gaussian curve or uniformly distributed numerically, and the pixel pattern generated thereby is implemented in a process computer for regulating and / or controlling the laser for processing the surface of the skinning roller. [2] Method according to claim 1, wherein the pixel pattern is numerically generated using at least two Gaussian curves and is normally distributed. [3] Method according to any of the preceding claims, wherein a repetition rate f between 10 and 8000 kHz is used or set. [4] Method according to any of the preceding claims, wherein a maximum laser power P between 10 and 1000 W is used or set. [5] Method according to any of the preceding claims, wherein a pulse radius r between 10 and 80 µm is used or set. [6] Method according to any of the preceding claims, wherein a pulse duration t between 300 fs and 500 ns is used or set. [7] Dressing roller with a laser-processed stochastic texture on the surface manufactured according to one of the preceding claims, characterized by , that the surface of the dressing roller has a topography with an arithmetic mean roughness Ra between 0.8 and 8.0 µm and with a peak number RPc between 30 and 250 1 / cm, where Ra and RPc are determined according to DIN EN 10049:2014-03. [8] Method for dressing a hot-dip coated steel strip, wherein the hot-dip coated steel strip is passed between two dressing rollers having a stochastic texture and having a dressing gap, characterized by , that at least one dressing roller according to claim 7 is used. [9] Method according to claim 8, wherein the hot-dip coated steel strip comprises a zinc-based coating. [10] Method according to claim 8 or 9, wherein the hot-dip coated steel strip contains a coating comprising, in addition to zinc and unavoidable impurities, additional elements such as aluminium and magnesium, each with a content of up to 8 wt.%. [11] Method according to any one of claims 8 to 10, wherein the steel strip is a cold-rolled strip.

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