DE102019219651A1 - Sheet metal with a deterministic surface structure and process for the production of a formed and painted sheet metal component - Google Patents

Abstract

The invention relates to a metal sheet (1) with a deterministic surface structure (2), the surface structure (2) being embossed into the metal sheet (1), the surface structure (2) at least one mountain area (1.1) and at least one valley area (1.2) having, wherein the mountain area (1.1) and the valley area (1.2) are connected by a flank area (1.3). The invention also relates to a method for producing a formed and painted sheet metal component.

Description

The invention relates to a metal sheet with a deterministic surface structure, the surface structure being embossed into the metal sheet, the surface structure having at least one mountain region and at least one valley region, the mountain region and the valley region being connected by a flank region. The invention also relates to a method for producing a formed and painted sheet metal component.

Zinc phosphate layers are used to refine the surface of coated (galvanized, hot-dip aluminized) and uncoated metal sheets in order to significantly improve surface-relevant properties. Above all, this includes increasing corrosion resistance and improving formability and paint adhesion. Zinc phosphate layers are inorganic crystalline metal phosphate layers that are deposited from an aqueous phase. These are not closed layers, but an accumulation of individual zinc phosphate crystals, the position, size, distribution, composition and chemical and mechanical properties of which depend on a number of production factors. Above all, this includes the composition of the phosphating solution, the preparation of the substrate and the process parameters during the phosphating. The phosphating process is a multi-stage process which, in addition to multi-stage rinsing steps, is primarily composed of a pretreatment step, an activation step and at least one phosphating step.

The applied zinc phosphate crystals result in a significant increase in the surface area, which leads to improved forming properties (improved oil retention capacity and more homogeneous oil distribution). The crystals also serve as an ideal primer for paints.

The zinc phosphating of metal surfaces has a high technical system (multi-stage process = cleaning, activating, phosphating and rinsing; monitoring) and energetic (the individual process baths are several to many cubic meters in size and have to be kept in constant motion and sometimes up to 60 ° C) be tempered) associated with effort. With standard zinc phosphating, there is a very large consumption of chemicals (including disposal costs, maintenance) and the use of the heavy metals manganese and especially nickel (trication phosphating to increase the temperature and alkali resistance as well as to refine the grain and to adjust the color tone). Accordingly, the automotive industry is very interested in replacing the zinc phosphating process with a more environmentally friendly and process-reliable alternative. Examples of this are nickel-free phosphating or silane-based systems.

When generating zinc phosphate layers, sensitive process management must be ensured during activation and phosphating, for example to prevent carry-over or aging process baths, which can have a negative effect on the phosphating process and to phosphating disorders, in particular to non-closed, surface-covering zinc phosphate layers and / or to impaired paint adhesion lead to avoid. Furthermore, the activation can react sensitively to surfaces that have not been optimally cleaned, so that phosphating spots with large and small crystals lead to optical differences in the phosphating image (dark / light) and non-phosphated areas arise. Dehydration at high temperatures can also have a disadvantage, e.g. when baking a paint, and thus lead to a deterioration in paint adhesion.

The object of the invention is therefore to specify a sheet metal and a method for producing a formed and painted sheet metal component with which a reduced or no zinc phosphating effort is possible compared to the prior art, the surface having essentially comparable properties to a conventionally zinc phosphated surface having.

The provision of a defined surface structure on a dressed sheet metal is essential for further processes, especially in the processing industry for the manufacture of sheet metal components in the automotive industry. In the course of component production, in particular in forming processes, it is advantageous if the process media used, such as oil and / or lubricants, are available in a homogeneous manner and in the required amount at points relevant to the forming process. In order to be able to set a surface roughness that is as advantageous as possible on sheet metal for later processing, the sheet metal is subjected to a rolling process (skin pass), in which, among other things. a roughness is set on the metal sheet using textured skin pass rollers. For example, strip waves can also be eliminated and / or compensated for by skin-pass if the sheet metal has been subjected to a thermal treatment (annealing, etc.) in particular beforehand. The skin pass also causes a decrease in thickness and / or elongation between the incoming and outgoing sheet metal / strip (skin pass degree), so that among other things. the mechanical properties of the sheet metal can also be adjusted in a targeted manner.

The inventors have found that metal sheets can be produced with a deterministic surface structure, which not only combines the aforementioned advantages, but can also at least partially or completely replace conventional zinc phosphating by creating an artificial enlargement of the surface in such a way that the mountain area and / or the valley area has a substructure which is designed in such a way that the substructure has a surface area that is at least 3% larger than a planar projection area of the mountain area and / or the valley area or an Sdr value of at least 3%. According to the invention, the increase in surface area is no longer produced by zinc phosphating or by zinc phosphate crystals, but rather by a larger surface that can be set in a targeted manner. The specifically adjusted surface enlargement not only serves as an optimal primer for a lacquer coating, but can also promote the adhesion suitability by providing a larger interface, in that the adhesive can be offered a corresponding reaction surface.

The substructure in particular has a surface that is at least 7%, preferably at least 10%, preferably at least 15%, preferably at least 20% larger surface compared to the planar projection surface of the mountain area and / or valley area, in particular determined by atomic force microscopy (AFM), which enables a resolution with an area of up to 90 x 90 µm ^{2, for example.} Depending on the surface structure to be measured, a resolution in the order of magnitude, for example, of a valley region or part of a valley region or a mountain region or part of a mountain region can be selected, which can also have an area smaller than 90 × 90 μm ² , for example.

A planar projection surface of the mountain region or valley region is to be understood as a flat surface which is visible and / or determinable in plan view, parallel to the sheet metal plane. The larger surface area created by the substructure in the mountain area or valley area corresponds to the actual, determinable three-dimensional (upper) area.

The Sdr value relates to a developed limit value ratio or is also a measure for the surface enlargement, which indicates the percentage of the additional area of a definition area that can be traced back to a texture (substructure) compared to the absolutely flat definition area, wherein the definition area (resolution) can be directed to a part of the valley area or to a valley area and / or to a part of the mountain area or to a mountain area. The substructure in particular has an Sdr value of at least 7%, preferably of at least 10%, preferably of at least 15%, preferably of at least 20%. A plane surface would have an Sdr value of 0. The Sdr value can also be determined, for example, by or by means of atomic force microscopy (AFM).

Under deterministic surface structure are to be understood recurring structures (at least one valley area or valley areas and at least one mountain area) which have a defined shape and / or design, cf. EP 2 892 663 B1 . In particular, this also includes surfaces with a (quasi-) stochastic appearance, which, however, are applied using a deterministic texturing process and are thus composed of deterministic form elements. In particular, a continuous mountain area with several recurring valley areas, which are each connected to the mountain area by flank areas, is designed as a surface structure.

Metal sheet is to be understood in general as a flat metal product which can be provided in sheet form or in the form of a plate or in the form of a strip.

Further advantageous configurations and developments emerge from the following description. One or more features from the claims, the description and also the drawing can be combined with one or more other features from them to form further embodiments of the invention. One or more features from the independent claims can also be linked by one or more other features.

According to one embodiment of the metal sheet according to the invention, the substructure is formed like a crystal in the mountain area and / or in the valley area. The crystal-like design can be elongated and / or spherical and / or oval as an elevation and / or depression in the mountain area and / or valley area, with a length, width or diameter of the crystal-like design between 0.5 and 20 μm, in particular between 0 , 9 and 15 µm, preferably between 1.2 and 10 µm.

According to one embodiment of the metal sheet according to the invention, the metal sheet is coated with a metallic coating. The metal sheet can be coated with a zinc-based coating which is applied by hot-dip coating. In particular, the metal sheet is a steel sheet. Preferably, the coating can besides Zinc and unavoidable impurities contain additional elements such as aluminum with a content of up to 5% by weight and / or magnesium with a content of up to 5% by weight in the coating. Steel sheets with a zinc-based coating have very good cathodic corrosion protection, which has been used in automotive engineering for years. If improved corrosion protection is provided, the coating additionally has magnesium with a content of at least 0.5% by weight, in particular of at least 0.6% by weight, preferably of at least 0.9% by weight. As an alternative or in addition to magnesium, aluminum can be present with a content of at least 0.5 wt To prevent steel sheet essentially so that the positive corrosion properties are retained.

A thickness of the coating can be between 1 and 15 μm, in particular between 2 and 12 μm, preferably between 5 and 10 μm. Below the minimum limit, no adequate cathodic corrosion protection can be guaranteed and above the maximum limit, joining problems can occur when joining the steel sheet according to the invention or a component made from it to another component; in particular, if the maximum limit specified is exceeded, no stable process during thermal joining or joining can occur. Welding can be ensured. In hot-melt exchange coating, the steel sheets are first coated with an appropriate coating and then passed to the skin pass. The skin pass takes place after the hot-dip coating of the steel sheet.

Alternatively, the metal sheet can be coated with a metallic coating, in particular a zinc-based coating, which is applied by electrolytic coating. The thickness of the coating can be between 1 and 10 μm, in particular between 1.5 and 8 μm, preferably between 2 and 5 μm. In comparison to hot-dip coating, the steel sheet can first be skin-passed and then electrolytically coated. Depending on the thickness of the coating, the roughness in the flank area can essentially be retained even after the electrolytic coating. Alternatively, an electrolytic coating with subsequent skin-passing is also conceivable.

It is also conceivable that no coating, for example no metallic coating, is provided. It is also conceivable that the metal sheet is / is coated with a non-metallic coating, for example in a coil coating system, the metal sheet being coated with a non-metallic coating before or after the coating.

According to one embodiment of the metal sheet according to the invention, the metal sheet is coated with a phosphate coating or a silane-based coating, the thickness of the phosphate coating or silane-based coating in particular being less than 500 nm. In order to retain the advantages of a (phosphate) coating, in particular with regard to the wetting behavior and / or as a primer for paint coatings and / or adhesive systems, and to be able to continue to use existing process routes that have been designed for phosphated metal sheets, the metal sheet can be coated with a phosphate coating be coated or with a silane-based coating. The thickness of the phosphate coating or silane-based coating can be set to less than 500 nm, in particular less than 200 nm, preferably less than 100 nm, preferably less than 50 nm, particularly preferably less than 25 nm. Conventional zinc phosphating forms a coating with a thickness of at least 500 nm on the surface of a metal sheet, which is insulating, electrically non-conductive and can thus interfere with the process in a welding process, in particular in a resistance welding process. A reduction of an insulating, electrically non-conductive phosphate coating or a silane-based coating to a thickness below 500 nm does not represent a process-disruptive factor.

• - Bereitstellen eines Metallblechs mit einer deterministischen Oberflächenstruktur, wobei die Oberflächenstruktur in das Metallblech mittels einer Dressierwalze eingeprägt worden ist, wobei die Oberflächenstruktur mindestens einen Bergbereich und mindestens einen Talbereich aufweist, wobei der Bergbereich und der Talbereich durch einen Flankenbereich verbunden sind,
• - Umformen des Metallblechs zu einem Blechbauteil,
• - Lackieren des umgeformten Blechbauteils.

According to a second aspect, the invention relates to a method for producing a formed and painted sheet metal component, the method comprising the following steps:

• - Provision of a metal sheet with a deterministic surface structure, the surface structure having been embossed into the metal sheet by means of a skin pass roller, the surface structure having at least one mountain area and at least one valley area, the mountain area and the valley area being connected by a flank area,
• - Forming the sheet metal into a sheet metal component,
• - Painting the formed sheet metal component.

According to the invention, the skin pass roller, with which the surface structure was embossed into the sheet metal, generated a substructure during the embossing in the mountain area and / or in the valley area such that a substructure with a surface area that is at least 3% larger than a planar projection area Mountain range and / or the valley area or with an Sdr value of at least 3%.

Depending on the sheet metal component to be produced, in particular a corresponding sheet metal is provided, which is cut before, during and / or after the deformation. Depending on the design, the forming takes place with conventional tools.

The formed sheet metal component is painted in a conventional manner.

In order to avoid repetition, reference is made in each case to the statements relating to the metal sheet according to the invention.

On a skin pass roller, at least one valley area can be designed as an open structure. Mountain areas on the skin-pass roller thus define local and recurring bumps on the surface of the skin-pass roller. By corresponding action of the skin pass roller on a surface of a sheet metal, the mountain areas of the skin pass roll are stamped into the surface of the sheet metal and form a surface structure with an essentially closed structure (closed volume). The mountain areas of the skin pass roller thus produce pocket-like structures on the surface of the sheet metal. The closed volume, the so-called empty volume, can accommodate a process medium, for example forming oil, which is applied for later processing, in particular by means of a forming process. In addition, in the at least one valley area and / or in the mountain area or mountain area of the skin pass roller, a (negative) substructure is formed which, by acting on the surface of the sheet metal, creates a (positive) substructure with a surface that is at least 3% larger than a planar one Projection area of the mountain area and / or the valley area or with an Sdr value of at least 3%.

The generation of a deterministic surface topography with at least one mountain area or mountain area and at least one valley area including (negative) substructure on the surface of the skin pass roller can be carried out in a targeted manner by means of a laser texturing process, cf. EP 2 892 663 B1 .

The geometric configuration (size and depth) of the deterministic surface topography in the form of at least one mountain area or mountain area and at least one valley area including (negative) substructure can be set individually by using a pulsed laser as a result of material removal on the surface of the skin-pass roller. In particular, targeted control of the energy and the pulse duration of a laser beam acting on the surface of the skin-pass roller can have a positive influence on the design of the structure (s). The interaction time between the laser beam and the skin-pass roller surface increases with a longer or longer pulse duration, and more material can be removed from the surface of the skin-pass roller. A pulse leaves an essentially circular, in particular concave, crater on the skin-pass roller surface, which after skin-pass treatment depicts the surface of the steel sheet. A reduction in the pulse duration has an influence on the formation of a crater; in particular, the diameter of the crater can be reduced. By reducing the pulse duration, in particular when using short or ultra-short pulse lasers, it is possible to set the geometric structure on the surface of a skin-pass roller in such a way that a sheet steel surface can be functionally textured. This is achieved, for example, if the pulse duration of the laser with which the surface of the skin pass roller is textured is reduced and the geometric structure on the roller can thus be generated with a higher resolution.

According to one embodiment of the method according to the invention, no zinc phosphating has been carried out before the metal sheet is formed. With the invention, the laborious step of conventional zinc phosphating to generate a larger surface area using zinc phosphate crystals can essentially be omitted.

According to one embodiment of the method according to the invention, the metal sheet has been coated with a phosphate coating or a silane-based coating before the metal sheet is provided, the thickness of the coating being in particular less than 500 nm. As a result, the advantages of a phosphate layer can be retained and, in particular, by reducing the coating thickness, resistance welding, preferably resistance welding, can be implemented reliably. The phosphating includes, in particular, a deposition / separation of surfactants, a conversion chemistry or a pickling, for example with phosphoric acid.

According to one embodiment of the method according to the invention, the metal sheet has been treated with an acidic solution before or after the introduction of the surface structure. The use of an “acidic” solution, which has a pH value less than 3, in particular less than 2, preferably less than 1, is preferably used to clean the surface and / or to remove oxide deposits (oxide layer) on the surface of the metal sheet.

According to one embodiment of the method according to the invention, the sheet metal component is an outer skin part of a vehicle. Outer skin parts in particular are subject to strict requirements for suitability for forming and the appearance of paint. Corresponding outer skin parts can be produced inexpensively by the invention.

According to an alternative embodiment of the method according to the invention, the sheet metal component is a structural part of a vehicle.

In the following, specific embodiments of the invention are explained in more detail with reference to the drawing. The drawing and accompanying description of the resulting features are not to be read in a restrictive manner to the respective configurations, but serve to illustrate exemplary configurations. Furthermore, the respective features can be used with one another as well as with features of the above description for possible further developments and improvements of the invention, especially in the case of additional configurations which are not shown. The same parts are always provided with the same reference numerals.

• 1) eine schematische Teilschnittansicht einer Ausführungsform aus dem Stand der Technik,
• 2) eine schematische Teilschnittansicht einer Ausführungsform gemäß der Erfindung,
• 3) eine schematische Teilschnittansicht einer weiteren Ausführungsform gemäß der Erfindung und
• 4) eine schematische Abfolge einer Ausführungsform gemäß einem erfindungsgemäßen Verfahren.

The drawing shows in

• 1 ) a schematic partial sectional view of an embodiment from the prior art,
• 2 ) a schematic partial sectional view of an embodiment according to the invention,
• 3 ) a schematic partial sectional view of a further embodiment according to the invention and
• 4th ) a schematic sequence of an embodiment according to a method according to the invention.

In 1 is a schematic partial sectional view of an embodiment from the prior art. The execution can, for example, the execution according to the EP 2 892 663 B1 correspond. A metal sheet is shown ( 1 ) with a deterministic surface structure ( 2 ), where the surface structure ( 2 ) into the metal sheet ( 1 ) is embossed, whereby the surface structure ( 2 ) at least one mountain area ( 1.1 ) and at least one valley area ( 1.2 ), the mountain area ( 1.1 ) and the valley area ( 1.2 ) by a flank area ( 1.3 ) are connected. The sheet metal ( 1 ) is preferably a steel sheet.

In 2 there is shown a schematic partial sectional view of an embodiment according to the invention. In contrast to 1 indicates the mountain area ( 1.1 ) and / or the valley area ( 1.2 ) a substructure ( 1.11 , 1.21 ), which is designed in such a way that the substructure ( 1.11 , 1.21 ) a surface that is at least 3% larger than a flat projection surface (P) of the mountain area ( 1.1 ) and / or the valley area ( 1.2 ) or has an Sdr value of at least 3%. The substructure ( 1.11 , 1.21 ) can be crystal-like in the mountain area ( 1.1 ) and / or in the valley area ( 1.2 ), the crystal-like design being elongated and / or spherical as an elevation and / or depression, shown as a depression in this embodiment, in the mountain area ( 1.1 ) and / or valley area ( 1.2 ), wherein in particular a length, width or diameter of the crystal-like formation can be set between 0.5 and 20 μm.

In 3 is a schematic partial sectional view of a further embodiment according to the invention. Compared to 2 is the sheet metal ( 1 ) with a metallic coating ( 3 ) coated, preferably with a zinc-based coating. Alternatively or preferably in addition, the metal sheet ( 1 ) with a phosphate coating ( 4th ) coated, the thickness of the phosphate coating ( 4th ) can be smaller than 500 nm.

A metal sheet according to the invention ( 1 ), in particular according to the execution in 3 , is provided for the production of a formed and painted sheet metal component (not shown), (A). In the next step, the provided metal sheet is reshaped ( 1 ) to a formed sheet metal component, (B). After forming, the formed sheet metal component is painted, (C). 4th shows schematically a corresponding sequence of the method according to the invention. The formed and painted sheet metal component, not shown, can be used as an outer skin part or a structural part in the vehicle.

As far as technically possible, the individual features can all be combined with one another.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 2892663 B1 [0012, 0027, 0036]

Claims (11)

Sheet metal (1) with a deterministic surface structure (2), the surface structure (2) being embossed into the sheet metal (1), the surface structure (2) having at least one mountain area (1.1) and at least one valley area (1.2), the The mountain region (1.1) and the valley region (1.2) are connected by a flank region (1.3), characterized in that the mountain region (1.1) and / or the valley region (1.2) has a substructure (1.11, 1.21) which is designed in such a way that that the substructure (1.11, 1.21) has a surface that is at least 3% larger than a planar projection area (P) of the mountain area (1.1) and / or the valley area (1.2) or an Sdr value of at least 3%. Sheet metal after Claim 1 , the substructure (1.11, 1.21) having a surface that is at least 7% larger than the planar projection area (P) of the mountain area (1.1) and / or the valley area (1.2) or an Sdr value of at least 7%. Sheet metal according to one of the preceding claims, wherein the substructure (1.11, 1.21) is formed like a crystal in the mountain region (1.1) and / or in the valley region (1.2). Metal sheet according to one of the preceding claims, wherein the metal sheet (1) is coated with a metallic coating (3). Metal sheet according to one of the preceding claims, wherein the metal sheet (1) is coated with a phosphate coating (4) or a silane-based coating, in particular the thickness of the coating (4) being less than 500 nm. A method for producing a formed and painted sheet metal component, the method comprising the following steps: providing a sheet metal (1) with a deterministic surface structure (2), the surface structure (2) having been embossed into the sheet metal (1) by means of a skin pass roller, wherein the surface structure (2) has at least one mountain area (1.1) and at least one valley area (1.2), the mountain area (1.1) and the valley area (1.2) being connected by a flank area (1.3), - forming the sheet metal (1) a sheet metal component, - painting of the formed sheet metal component, characterized in that the skin pass roller with which the surface structure (2) has been embossed into the metal sheet (1), during the embossing in the mountain area (1.1) and / or in the valley area (1.2) a Substructure (1.11, 1.21) generated in such a way that a substructure (1.11, 1.21) with a surface area that is at least 3% larger than that of a plan projection surface (P) of the mountain area (1.1) and / or the valley area (1.2) or with an Sdr value of at least 3%. Method according to a Claim 6 , with no zinc phosphating having been carried out before the metal sheet (1) was formed. Procedure according to Claim 6 or 7th , the metal sheet (1) having been coated with a phosphate coating (4) or a silane-based coating prior to providing the metal sheet (1), the thickness of the coating (4) being in particular less than 500 nm. Method according to one of the Claims 6 to 8th , wherein the metal sheet (1) has been treated with an acidic solution before or after the introduction of the surface structure (2). Method according to one of the Claims 6 to 9 , wherein the sheet metal component is an outer skin part of a vehicle. Method according to one of the Claims 6 to 9 , wherein the sheet metal component is a structural part of a vehicle.

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