Metal substrate provided with tailored surface textures and method for applying such textures on metal substrates

Abstract

A metal substrate provided with surface textures wherein different texture patterns are provided over predefined surface areas of the metal substrate and wherein the different texture patterns are tailored to predefined surface properties of a product which is to be made out of the metal substrate as well as to a method for applying such surface textures on the metal substrate.

Claims

1. A metal substrate, provided with different texture patterns over the surface area of the metal substrate, wherein each said texture pattern comprises dimples which are recesses with a diameter in a range of 25-60 μm, a depth in a range of 2-6 μm and a density in a range of 180-600 dimples per square millimetre, wherein each said dimple in each texture pattern is spaced from each other said dimple to provide surface coverage of 30% to 80%; wherein the dimples respectively have a shape selected from the group consisting of round shape and oval shape; wherein the textures of said different texture patterns differ with respect to each other in at least one of diameter of the dimples, the depth of the dimples, number of dimples per surface area, positioning of the dimples, and spacing of the dimples with respect to each other.

2. The metal substrate according to claim 1, wherein the dimples having the round shape have a perimeter of a circle and the dimples having the oval shape have an oval perimeter.

3. The metal substrate according to claim 1, wherein between first and second texture patterns a transition texture pattern is applied to provide a transition between the first and second texture patterns, wherein the first texture transition pattern has a first said diameter of the dimples, a first said depth of the dimples, and a first said density of dimples per square millimeter of surface area that gradually change from the first diameter of the dimples, the first depth of the dimples, and the first density of dimples per surface area of the first texture pattern at a first portion of the transition texture pattern adjacent the first texture pattern to a second said diameter of the dimples, a second said depth of the dimples, and a second said density of dimples per square millimeter of the second texture pattern at a second portion of the transition texture pattern adjacent the second texture pattern.

4. The metal substrate according to claim 1, wherein the different texture patterns over the surface area of the metal substrate have a roughness Ra in a range of 0.2-3 μm, a peak count RPc in a range of 30-190 per centimetre and an arithmetic mean waviness Wsa of at most 0.35 μm.

5. The metal substrate according to claim 1, wherein the dimples respectively have the round shape with a perimeter of a circle.

6. The metal substrate according to claim 1, wherein the metal substrate is a blank or a strip.

7. The metal substrate according to claim 1, wherein the metal substrate is steel coated with a coating selected from the group consisting of Zn coating, ZnAl coating, ZnMg coating, ZnAlMg coating, Cr coating, Cr alloy coating, Sn coating, and Sn alloy coating.

8. The metal substrate according to claim 7, wherein the diameter of each dimple of said texture pattern is in a range of 30-60 μm.

9. The metal substrate according to claim 7, wherein the metal substrate comprises steel, wherein at least one said texture pattern has a roughness Ra in a range of 0.2-3 μm, a peak count RPc in a range of 30-190 per centimetre and an arithmetic mean waviness Wsa of at most 0.29 μm and wherein the dimples of the different texture patterns each have diameter in a range of 35-60 μm and depth in a range of 3-5 μm and density in a range of 180-500 per square millimetre.

10. The metal substrate according to claim 7, wherein the metal substrate is steel, wherein the steel comprises Interstitial Free steel or Bake Hardening steel.

11. The metal substrate according to claim 1, wherein the metal substrate is tinplate.

12. The metal substrate according to claim 1, wherein at least one of said texture patterns has a roughness Ra in a range of 0.8-1.4 μm, a peak count RPc in a range of 75-110 per centimetre and an arithmetic mean waviness Wsa of at most 0.29 μm.

13. The metal substrate according to claim 1, wherein the different texture patterns comprise dimples with the diameter in the range of 25-60 μm, depth in a range of 2-5 μm and the density in a range of 180 to 600 per square millimetre.

14. The metal substrate according to claim 1, wherein the different texture patterns comprise dimples with diameter in a range of 35-60 μm, depth in a range of 3-5 μm and density in a range of 180-500 per square millimetre.

15. The metal substrate according to claim 1, wherein at least one of the different texture patterns comprises a texture pattern tailored for friction properties that has a roughness Ra in a range of 0.2-3 μm, a peak count RPc in a range of 30-190 per centimetre and an arithmetic mean waviness Wsa of at most 0.35 μm and with dimples with diameter in the range of 25-60 μm and depth in the range of 2-6 μm and dimple density in a range of 180-360 per square millimetre.

16. The metal substrate according to claim 1, wherein the texture pattern has a surface coverage of 39.3% to 80%.

17. The metal substrate according to claim 1, wherein the distance between the dimples in the texture pattern in an area of the metal substrate intended for elongation in a later forming operation is adapted to the elongation to arrive at the shape of an automotive outer part by being decreased in predetermined directions in a range of 5-30% to compensate for the elongation relative to distance in corresponding predetermined directions between the dimples in the texture pattern in an area of the metal substrate not intended for elongation.

18. An elongated metal substrate comprising the metal substrate according to claim 1 provided with the different texture patterns elongated 0.5-2% as a result of temper rolling the metal substrate after the metal substrate has been provided with the different texture patterns.

19. A method for making the metal substrate provided with different texture patterns of claim 1, comprising applying surface textures on the metal substrate wherein the method comprises the steps of: collecting data concerning dimensions, shape, forming operation and predefined surface properties of a product which is to be made out of the metal substrate, applying one or more texture patterns on the metal substrate wherein the texture patterns are applied on basis of the collected data such that the product has the predefined surface properties.

20. A metal substrate, provided with different texture patterns over the surface area of the metal substrate, wherein each said texture pattern comprises dimples which are recesses with a diameter in a range of 25-60 μm, a depth in a range of 2-6 μm and a density in a range of 180-600 dimples per square millimetre, wherein each said dimple in each texture pattern is spaced from each other said dimple to provide surface coverage of 30% to 80%; wherein the textures of said different texture patterns differ with respect to each other in at least one of diameter of the dimples, the depth of the dimples, number of dimples per surface area, positioning of the dimples, and spacing of the dimples with respect to each other, wherein the spacing between dimples is quasi deterministic.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be further explained on hand of the example shown in the drawing and experimental results, in which:

(2) FIGS. 1A-C shows schematically a metal strip with a product that is to be made out of the strip and a number of textures applied on the strip.

(3) FIGS. 2A-E shows schematically a similar metal strip as in FIG. 1 with the product made out of such strip and the applied textures,

(4) FIGS. 3A,B shows schematically a product made out of a strip and a texture applied at a high elongation area, and

(5) FIGS. 4A-C shows schematically a metal strip subdivided in areas with different textures for different specifications.

(6) FIG. 5 shows a 3D representation of a texture pattern

(7) FIG. 6 shows a surface texture profile from two different texture patterns

(8) FIGS. 7-9 show data for samples according to the invention

DETAILED DESCRIPTION OF THE DRAWINGS

(9) In FIG. 1A schematically a metal strip 1 is shown which is divided in sections 2 indicated with a broken line 3. The broken line 3 represents reference points provided on the strip. Furthermore each section 2, or blank when cut from the strip, is provided with a unique identification code to be able to track the section 2 or blank at both the metal manufacturer and the manufacturer of the product that is made from the blank.

(10) In the figure an imaginary representation of a product 4 is shown that will be made out of a section 2 which in this case is an outer door panel for a vehicle.

(11) In the enlargement of a section 2 the product is indicated with broken lines which represent the product after forming the product from the blank, which typically is after forming the product in a press device. Also schematically shown in the enlargement are the different textures applied on the surface of the blank which are respectively a texture 5 optimised visual appearance of the product with paint applied and compensated for elongation (FIG. 1B) and a texture 6 optimised for reduced galling in press device (FIG. 1C).

(12) The texture as shown in FIG. 1B is optimised for paint appearance has small dimples of little depth and with a larger density than those optimised for press performance as shown in FIG. 1C. In this example the diameter of the dimples is 30 μm, the depth is 4 μm and the density is 500/mm2. Furthermore, in order to compensate for elongation of the metal during forming of the product the spacing between the dimples is adjusted to compensate for the elongation. This means that in areas of substantial elongation the spacing between the dimples is adjusted such that after forming the spacing in the area of elongation is the same or is in the same range as that of the dimples in areas that have not undergone any elongation.

(13) The texture as shown in FIG. 1C which is optimised for reduced galling in the press device also has small dimples but with a lower density than those of the texture optimised for paint appearance. In this example the diameter of the dimples is 30 μm, the depth is 2-4 μm and the density is 180/mm2.

(14) The area or areas of the section 2 or blank outside the applied optimised textures have a texture 8 resulting from temper rolling of the strip 1.

(15) All together by providing a differentiated surface texture which is in line with geometrical product specifications and forming specifications an optimum in paint appearance and press performance is realised.

(16) In FIG. 2A another example of a strip 1 is shown divided in sections 2 indicated with a broken line 3 and with an imaginary representation of a product 4. The product in this example is one piece front-left fender including part of a bonnet and wheel arch. FIG. 2B shows the product after forming and trimming of the edges of the blank. The area around the imaginary representation of product 4 again is provided with a texture 9 optimised for reduced galling in the press device. The more or less horizontal and vertical parts of the formed product are provided with textures optimised for paint appearance properties. The more or less horizontal top part of the product is provided with a homogeneous texture 10 optimized for visual appearance on horizontal surfaces, see FIG. 2E. In FIG. 2D a texture 11 is shown for the more or less vertical part of the product 4 which has an optimized ratio between vertical and horizontal dimple spacing to reduce sagging of applied paint on vertical surfaces. With these more or less vertical parts the dimple spacing in a direction perpendicular to the gravitational direction is usually reduced in a range of 5-30%, which in this example is about 20%. Both textures 10 and 11 are also optimised for elongation resulting from forming the product 4. The area outside the optimised textures has a texture 8 resulting from temper rolling of the strip 1.

(17) FIG. 3A shows schematically a formed product 12, in this case a part of a transmission tunnel, which does not need to have optimised textures for paint appearance since it is a part that normally will remain out of sight. The product 12 has a complex geometrical shape with a critical area in corner area 13 where large elongations of the metal are required to be able to form the product from a single blank. These large elongations can only be realized if the metal can sufficiently move between the die and punch and/or the clamps of the press device used for forming the product 4 to get the necessary material flow. For that reason the area surrounding the corner area is provided with a texture 14 (FIG. 3B) optimised for low friction and improved material flow. In this example the diameter of the dimples is 30 μm, the depth is 2-4 μm and the density is 180/mm2. The remaining surface area does not need to have a specially optimised texture and has a texture 8 resulting from temper rolling of the strip 1 which is sufficient for the purpose.

(18) FIG. 4A shows a strip 1 which is divided in sections 15, 16, 17, 18, 19 both in the length direction of the strip and in a transverse direction indicated respectively with broken lines 20, 21. The broken lines 20, 21 represent reference points provided on the strip which together define the sections. Furthermore each section is provided with a unique identification code to be able to track the sections.

(19) The sections 15, 16, 17, 18 are provided with textures according to customer specification which could be a single texture for a section but also several textures per section or a subdivision of a section in sub-sections with product optimised textures for each sub-section. Because of the laser applied textures a strip can easily be subdivided in sections of different lengths and widths over the length and width of a strip. This allows to manufacture very cost efficient low volume orders for niche markets, which otherwise would not have been possible or only against high costs. For example, this can be interesting for food and beverage packaging cans which are only made in small volume for special occasions. In order to deliver such low volume orders within a short period of time these low volume orders are preferably not first accumulated in order to be able to cover a complete length of strip, but rather short lengths of large standard strip coils with a general texture are used. The short lengths are preferably at the end or beginning of a large strip coil so that sufficient length of strip remains for the customer with high volume orders for strip with a general texture.

(20) In the example section 15 is a product X for customer A and has a length of 0.8 km over the total width of the strip, section 16 is a product Y for customer B and has a length of 2.9 km over a limited width of the strip, section 17 is a product Z for customer A and has a length of 0.8 km over the total width of the strip and section 18, the remainder of the strip is for a bulk product K with a general texture for customer C. The general texture is typically applied by temper rolling but could of course also be applied by laser texturing.

(21) The texture as shown in FIG. 4B is a product Y for customer B. In this example the diameter of the dimples is 30 μm, the depth is 3 μm and the density is 500/mm2. Furthermore, the dimples are patterned in a deterministic manner to realize a highly homogeneous dimpled texture.

(22) The texture as shown in FIG. 4C is a product Z for customer A. In this example the diameter of the dimples is 60 μm, the depth is 6 μm and the density is 180/mm2. Furthermore, the dimples are patterned in a pseudo-deterministic manner to reduce any preferred orientation of the dimpled texture.

(23) Section 19 is a small rest section of the standard strip with a general texture, which can re-enter the metal manufacturing process as scrap material.

(24) Several texture patterns were analysed via computational analysis to study the expected paint properties and press performance. The waviness is taken as a predictive feature for paint appearance, wherein a low waviness corresponds to a good paint appearance. The closed void volume is taken as an indication for press performance, wherein a high closed void volume corresponds to good press performance. Variations in dimple density, depth and diameter were analysed on their expected influence on the surface properties of the final sheet. The dimples investigated were either round or oval shaped.

(25) In the simulation a 3D texture pattern was generated based on dimple diameter, dimple depth and dimple density. FIG. 5 shows an example of an inventive surface. This example shows a square spatial distribution of dimples which is tilted 30 degrees relative to the x axis.

(26) The simulated 2D profile from which the roughness (Ra), Peak count (RPc) and Waviness (Wsa) were determined was based on two 2D texture patterns which were superposed. The first texture pattern was based on a measured strip roughness profile where the measured roughness profile height distribution has been scaled to an Ra of 0.2 μm. The measured strip was made by temper rolling with Electro Discharge Textured work rolls. An initial strip roughness (Ra) of 0.2 μm was used in the example as such a roughness preferably arises from the texture pattern obtained after smooth temper rolling. The second texture pattern is a cross section of the 3D height map parallel to the x-axis. In the computational simulation these texture patterns are superposed to generate the computational surface texture. FIG. 6 shows an example of the surface texture, with an overlay of these two different texture patterns. The total length of the computational 2D texture was 65 mm. Roughness and peak count were calculated based on EN10094 (filter cut offs λs=λc/300, λc=2.5 mm), Waviness was calculated based on SEP1941 (filter cut offs λc=1 mm, λf=5 mm).

(27) The computational results are provided in table 1.

(28) Comparative example C1, without dimples, has a low waviness, a low peak count and a low roughness and only one texture pattern obtained from temper rolling.

(29) The inventive examples I1-I7 are according to the invention and have both the texture pattern from temper rolling as well as a texture pattern with dimples. The area with the texture pattern was investigated for its surface properties. It can be seen that varying the diameter, depth and density of the dimples, the waviness, peak count and roughness of the steel strip can be optimized for different purposes.

(30) The inventive examples I1-I7 will all have a good paint appearance (Wsa below 0.05 μm). Samples I1 and I5-I7 will all have both good paint performance and very good press performance (closed void volume above 800 mm{circumflex over ( )}3/m2). Sample I3 will have good paint appearance and acceptable press performance, whereas sample I4 will likely have bad press performance. So, by applying a different surface texture next to the texture obtained from the work roll, the final properties can be tailored to the characteristic desired for the final product. Comparative examples C2-C6 have varying dimple parameters with a relative low density and show a large increase of waviness compared to the inventive examples and will therefore have bad paint appearance. The results are also visualized in FIG. 7 where it is shown that the inventive samples all have the same preferred low waviness equal or less than 0.05 μm similar to the base sample C1 on which the texture was superposed. This indicates that the texture pattern does not increase waviness of the strip while at the same time a wide range of roughness (Ra) can be realized. The comparative samples C2-C6 show a much higher waviness and will have worse paint appearance.

(31) In addition to the computational samples mentioned in table 1, more surface textures were generated and plotted in FIG. 8. The textures were not superposed on the rough strip, therefore the initial waviness was 0 μm and FIG. 8 shows the additional waviness (ΔWsa). For each dimple density samples have been computed with a dimple diameter in the range of 40-80 μm and a dimple depth in the range of 2.5-5.5 μm. It can be observed from the figure that a wide range of roughness (0.4-2.7 μm) can be obtained. Only the computed samples with a dimple density (n) equal or larger than 100, preferably larger than 150, more preferably larger than 180, result in a low additional waviness. The computed samples with an area coverage (Acl)>80% show good waviness but will have a low closed void volume (not shown) due to overlapping dimples and hence a worse press performance.

(32) Samples SC1 and SI1-I5, corresponding to computational experiments C1 and I1-I5 were prepared for further investigation. A standard steel sheet was produced and finished with hot rolling and cold rolling as known to a person skilled in the art, after cold rolling the sheet was annealed and hot dip galvanized with a zinc alloy and finished by temper rolling. As comparative example a steel sheet directly obtained from the zinc bath before temper rolling (SC7) was included, with a texture pattern obtained from the the zinc bath. For the inventive examples, the steel sheet was smooth skin passed and an additional texture pattern was applied by laser as described in WO20217125497. The results from a smooth skin passed steel sheet without a texture pattern applied is provided as comparative example SC1.

(33) It is clear from table 2 that by applying a different texture pattern, on top of the smooth skin passes structure, according to the invention, a variety of roughness can be obtained, all with the same low increase in waviness (less than 0.05 μm) in addition to the waviness of sample SC1. FIG. 9 also underlines this decoupling of waviness and roughness.

(34) When making more complex products, such as the outer door panel for a vehicle of FIG. 1, the flange area (texture 6) could have a surface structure according to sample SI1 with a high closed void volume and hence good press performance and galling properties whereas the panel area (texture 5) could have a surface structure according to sample SI2, having an optimized visual appearance, with a low waviness and roughness, but a medium closed void volume, whereas area 8 could have a surface corresponding to SC1. Hence by applying different surface texture a complex product with tailored properties can be obtained.

(35) TABLE-US-00001 TABLE 1 Computational Samples and their calculated properties I1 I2 I3 I4 I5 I6 I7 Simulation inputs Diameter D μm 55 40 48 32 80 50 25 Depth h μm 5.5 4.5 4.5 2.5 4 4 4 Density n /mm.sup.∧2 240 240 150 150 100 240 800 Initial Ra_in μm 0.2 0.2 0.2 0.2 0.2 0.2 0.2 roughness Simulation results Roughness Ra μm 1.61 0.97 0.90 0.33 1.21 1.17 1.01 Peak count Rpc /cm 106 83 62 37 65 97 164 Waviness Wsa μm 0.05 0.05 0.05 0.05 0.05 0.04 0.05 Area Ac % 57.0% 30.2% 27.1% 12.1% 50.3% 47.1% 39.3% coverage Closed Vcl mm.sup.∧3/m.sup.∧2 1589 690 618 152 1009 951 812 volume C1 C2 C3 C4 C5 C6 Simulation inputs Diameter D μm n/a 80 100 200 60 60 Depth h μm n/a 6 6 5.5 6 10 Density n /mm.sup.∧2 n/a 50 35 10 50 50 Initial Ra_in μm 0.2 0.2 0.2 0.2 0.2 0.2 roughness Simulation results Roughness Ra μm 0.19 1.13 1.23 1.25 0.71 1.16 Peak count Rpc /cm 4 36 30 18 28 28 Waviness Wsa μm 0.04 0.15 0.16 0.285 0.142 0.235 Area Ac % n/a 25.1% 27.5% 31.4% 14.1% 14.1% coverage Closed Vcl mm.sup.∧3/m.sup.∧2 760 829 865 430 733 volume

(36) TABLE-US-00002 TABLE 2 Experimental samples with measured properties Experimental samples SI1 SI2 SI3 SI4 SC1 SC7 Diameter D μm 55 40 48 32 Depth h μm 5.5 4.5 4.5 2.5 Density n /mm.sup.∧2 240 240 150 150 Roughness Ra μm 1.75 1.00 1.29 0.57 0.41 0.49 Peak count Rpc /cm 106 94 71 58 29 13 Waviness Wsa μm 0.18 0.19 0.19 0.19 0.19 0.46 Closed Vcl mm.sup.∧3/m.sup.∧2 1619 765 1065 186 77 109 volume