Method for embossing microgrooves in light-reflecting thin sheet metal

Abstract

The invention relates to a method for producing grooved, stable thin sheet metal with an at least partially grooved upper surface. The grooving runs in the longitudinal direction of the rolled strip and is embossed as the strip passes between one or more pairs of rollers. The embossing process on the thin sheet metal is carried out on the smooth roller. The embossing is formed using a thin, elastic and / or plastic synthetic layer, which is placed beneath the thin sheet metal, on a smooth roller that is less elastic and / or hard, so that the elastic and / or plastic synthetic layer is squeezed in the region of the groove edges and the squeezed elastic or plastic synthetic layer is squeezed between the groove edges and, due to the squeezing of the elastic and / or plastic synthetic layer, the thin sheet metal is form-fittingly pressed into the groove valleys of the grooved roller, and thus a thin sheet metal with grooves on both sides can be produced using only one grooved roller and one smooth counter-pressure roller.

Description

[0001] Process for embossing microgrooves into light-reflecting sheet metal

[0002] The invention relates to a continuous process for embossing groove-shaped microstructures into thin-walled sheet metal between two rollers, wherein one roller has a groove-shaped contour and the counter-pressure roller has a substantially smooth surface, primarily as a precursor for use as a Venetian blind slat with Fresnel optics.

[0003] An embossing process is typically understood as the impression of an embossed structure into a soft material, such as paper or leather. During the embossing process, the soft material is pressed against a smooth surface, creating a depression in the workpiece. The underside of the embossed material remains flat, without embossing. This is possible because the embossed surface is hard and the workpiece to be embossed is soft and thick enough to provide sufficient penetration.

[0004] This process is also used to emboss grooves on aluminum sheets with an initial thickness of 0.55 mm. The aluminum strips are grooved on one side by an embossing roller, and the counterpressure roller is hard and smooth, so that only the upper side is grooved. The depth of the groove is then, at best, 0.4 mm, less than the material thickness. The raised groove tips increase by 0.1 mm, resulting in a total thickness of 0.65 mm after embossing. The groove is created by a so-called kneading process in the strip material. Plastic deformation takes place.

[0005] The disadvantage of this embossing process between two hard rollers is the need for a thick sheet to create a deep embossed impression in the material. This requires a lot of material and can sometimes cause weight problems later on. It is only suitable for very soft materials that can be plastically deformed.

[0006] DE102018209927 A1 also discloses the double-sided grooving of thin sheet metal strips for Venetian blind slats using two profiled rollers. The strip is driven between two grooved rollers. The strip is stretched between the tips of the rollers and formed into a sawtooth-like contour, with one tooth arranged next to the other. The result can be seen in a photo in Fig. 1 at a scale of 20:1. The surfaces of the folds are no longer suitable for directed reflection.

[0007] Here, the forming process involves stretching the material between roller tips. This induces stresses in the material that, at least in the case of alloyed aluminum, are not released in subsequent straightening processes because the material has hardened. During this forming process, a narrow strip bends and / or twists due to the stresses embedded in the material structure during forming (corkscrew effect). Furthermore, the tooth contour cannot be precisely molded, and anodized pre-material cannot be processed. The anodized surface cracks and loses its mirror finish.

[0008] DE 10 2021 206846.4 discloses forcing a strip through the roll gap between two grooved rolls with a precise roller contour, which has the desired contour of the grooved sheet to be formed. Here, the peaks and valleys in the tool must be exactly opposite each other to avoid introducing asymmetrical stress into the material to be grooved. In reality, it turns out that, due to bearing tolerances, it is technically almost impossible to adjust the tools precisely enough to ensure that the material emerges from the rolling process stress-free, straight, and without twisting. For further development of this innovation, it is crucial to design the process in such a way that asymmetrical force application in the groove formation is prevented.

[0009] Swiss patent specification 461 411 and EPO 900 131 D1 also disclose the rotary stamping of strip material into dents in a soft cushion using individual, distributed stamping dies. The resulting contours stiffen the strip material. The contour of the stamping is left to the self-organization of the workpiece, without ensuring precise molding accuracy. The soft cushion yields to pressure but does not enclose the stamping dies, resulting in a landscape of dents on the sheet metal rather than a precise impression.

[0010] In US 4,059,000, elongated stamp impressions are embossed transversely to the band, so that the soft cushion is only pressed in at certain points and the soft cushion is relieved between the stamp impressions.

[0011] These processes differ fundamentally from the innovative task of creating a continuous groove pattern in the longitudinal direction parallel to the edges of the strip material. The problem with continuous grooving is that the soft rubber cushion builds up in front of the roll gap like a "bow wave" due to the uninterrupted pressure and leads to the destruction of the soft cushion on the roll. High pressures are required to achieve precise molding of the embossed contour in the strip material. Experience shows that the thicker rubber layer, as can be seen from the prior art, is torn off the roll due to the material buildup in front of the roll gap according to US 4,059,00, CH 461411, EP 0900131 D1 or the rubber cushion is quickly worn out. It is technically impossible to achieve process reliability in continuous groove molding based on the prior art model.

[0012] The object of the invention is to introduce a precise, groove-shaped contour into a thin slit strip made of steel or aluminum with a high molding accuracy of the embossing roller in the longitudinal direction of a slit strip, without the rubber pad of the counter-pressure roller accumulating in front of the roll gap and without creating corkscrew effects and furthermore without destroying the mirror surface.

[0013] The task is, among other things, to produce a raw material for Venetian blind slats from surface-treated sheet metal, e.g. from anodized strip. The concave cross-sectional contour of the grooved slit strip is intended to create Venetian blind slats with a Fresnel optic at the end, which reflect incoming sunlight back into the sky. This requires a high degree of molding accuracy for prismatically shaped grooves. The aim is to emboss V-shaped grooves into the slit strip, whereby the sides of the grooves must be very smooth in order to precisely reflect the incident sunlight. The angles of the V-shaped grooves must also be reproduced as precisely as possible in order to be able to focus the radiation using the groove flanks. A further aim is to produce the raised tips of the groove structure with sharp edges so that the edges do not dazzle interior occupants behind a blind or cause diffuse light scattering.The primary goal is to produce stable blind slats or a pre-product for blind production.

[0014] In summary, the task is to achieve high process reliability and high forming accuracy for a grooved roll without introducing stresses into the material during the forming process that could lead to cupping or twisting of the embossed slit strip. In particular, the raised tips of the resulting mirror prisms are to be formed with as sharp edges as possible, and the V-shaped groove flanks are to be formed as smoothly as possible. The solution to this problem follows the main claim.

[0015] The claim teaches how precision molding can be realized:

[0016] - is embossed between two hard rollers, whereby

[0017] - there is a soft, elastic and / or plastic layer between the hard rollers into which the embossing takes place and by displacing the material in the soft intermediate layer a counter pressure is generated which pushes the raised peaks of the creasing upwards on the back.

[0018] - The elastic and / or plastic layer is, for example, a rubber skin on the counter-pressure roller and / or a foil arranged on the underside of the slit strip to be embossed.

[0019] This foil and / or the rubber skin on the roller is squeezed at the embossing points. The material displaced by the squeezing deflects sideways and presses the slit strip into the grooves on the underside, resulting in V-shaped grooves that are as form-fitting as possible on both sides.

[0020] This process requires the counterpressure roller to be hard relative to a soft embossing substrate. The counterpressure roller can be made of steel, provided the foil is thick enough to push the grooves on the underside upward into the groove contour of the embossing rollers. A rubber pad on the counterpressure roller supports the pressure on the foil.

[0021] The innovative process is particularly suitable for thin, soft slit strip, e.g. from a deep-drawable steel strip with a yield strength of < 300 N / mm 2 or deep-drawable aluminum with a yield strength < 180 N / mm 2 , especially pure aluminum with a yield strength < 150 N / mm 2The wall thicknesses used for the slit strip are 0.3 mm, preferably between 0.2 and 0.1 mm, or even thinner for alloyed materials or steel. The foils applied to the back can be permanently applied to the slit strip either as a protective or sacrificial foil or as a composite foil.

[0022] The crushed sacrificial foil or the composite foil overlay beneath the sheet to be embossed should be thin. Its dimensions are adapted to the depth of the groove embossing. Preferred foil thicknesses are 0.02 to 0.5 mm, even down to 0.1 mm. This also ensures that the foil does not build up in front of the roll gap or form a "bow wave" that leads to peeling off the sheet. In the case of a hard counter-pressure roller covered with an additional rubber skin, the foil creates a two-layer pressure cushion of different hardness and properties. While the foil performs the greater deformation work, the hard rubber overlay on the counter-pressure roller only serves to press down, without a "bow wave" building up in front of the roll gap and without the tips of the grooves digging deeply into the rubber overlay. The crushed sacrificial foil thus also protects the hard rubber overlay of the counter-pressure roller.

[0023] A rubber coating of the flat counter-pressure roller is also advantageous so that the tips of the contour roller do not hit the steel of the counter-pressure roller when the embossed strip runs out of the tool, since the rollers sit without a gap or are even lower when the strip is very thin.

[0024] However, the innovation is not limited to the two-layer pressure pad. A multi-layer foil overlay or even embossing without an intermediate foil layer into a suitable rubber overlay is also possible. It is crucial that no "bow wave" builds up in front of the roll gap. The advantage of the soft foil, which is combined with the slit strip as a sacrificial foil or composite foil, is that - because the foil is very thin - no "bow wave" can form.

[0025] Furthermore, the risk of a "bow wave" increases with the mechanical pressure and the depth of the grooving, as well as with the increasing material hardness of the slit strip. The grooving depth should therefore be < 1 mm, preferably < 0.5 mm.

[0026] Ideally, the structure would be as follows:

[0027] Thin sheet slit strip < 0.3 mm with an adhesive sacrificial foil overlay > 0.2 mm for embossing V-shaped grooves with a depth of preferably < 0.5 mm and a rubberized counter-pressure roller with 70-80 Shore A hardness. In order to create sharp-edged prismatic groove tips, the mirror side is coated with a sacrificial foil, while the textured roller embosses the slit strip from the back. This process not only protects the mirror surface, it also increases the mirror gloss. It is also possible to emboss the mirror surface to better shape the groove depression. A particularly good result is achieved if the embossing is carried out in two consecutive passes, with the grooved roller and the counter-pressure roller being offset in the first and second pass, so that embossing occurs first from one side and then from the other.During the forming process, the sheet metal is essentially subjected to a load perpendicular to the surface. Experience shows that this allows the strip to exit the tool without twisting or corkscrewing.

[0028] Unlike a traditional embossing process, which applies pressure to the material from only one direction, this innovative process embosses from two sides simultaneously. The idea behind the invention is that the squeezed plastic deforms under pressure into an embossing die!

[0029] While traditional embossing only compresses the workpiece at the embossing point, the innovative two-sided embossing also stretches the material. In contrast to the prior art from DE 10 2018 209927A1, the forming process is not carried out by tensile forces between the roll tips, but, according to the invention, exclusively by compressive forces.

[0030] The underlying plastic bed into which the embossing takes place is preferably made of silicone rubber, rubber, an elastomer, or even PTFE. The sacrificial foil is softer, and the roller surface is harder.

[0031] It can be observed that an anodized strip material embossed with the innovative process is less brittle on the anodized surface and has fewer hairline cracks in the mirror surface compared to the forming process according to DE10 2018 209927A1 with two grooved rollers.

[0032] The purpose of anodizing is to protect the surface and, in the case of bright anodizing, to enhance the mirror effect of the raw material. Hairline cracks in the surface of the stretched material, according to the current technology, cause the surface to lose its shine, become dull, and fail to deliver the desired mirror effect and oxidation protection.

[0033] Thanks to the innovative embossing process, the anodized surface nestles into the tool contour without losing its mirror finish. Especially with vapor-deposited additional coatings or sputtered layers, the gloss of the originally smooth surface is retained even on the embossed surface contour, as the vapor-deposited layer is extremely smooth and acts like a lubricant in the tool. The surface is obviously stretched, but cannot visibly crack under the simultaneous pressure applied to the surface. The mirror finish is retained. This is a major advantage of the innovation for the specific production of mirror blades with special optics. Therefore, already surface-finished products can be used as starting material for the innovative manufacturing process.

[0034] If embossing is carried out on a very thin sheet, it is necessary to stabilize the strip by means of coextrusion, whereby the grooved sheet is lined with plastic in an extrusion tool after the sacrificial foil has been removed.

[0035] They show:

[0036] Fig. 1 the 20-fold magnification of a grooved thin sheet according to the state of the art Fig. 2 the layer structure of a thin sheet in combination with an elastic / plastic layer

[0037] Fig. 3 Ideal contour of an embossed composite film during tool passage

[0038] Fig. 4 a blind slat with one slat half grooved on the top

[0039] Fig. 5 the optical system on a blade with a grooved blade half and a non-grooved blade half

[0040] Fig. 6 a concave / convex lamella with a smooth underside and an irregularly embossed groove structure on the upper side.

[0041] Fig. 7, 8 shows a lamella with central grooving and surfaces without grooving on the long sides.

[0042] Fig. 9,10 shows a lamella with grooving over the entire cross-section.

[0043] Fig. 2 shows a greatly enlarged section of a typical pre-product for introducing grooves. It consists of a thin sheet 10 with a thickness di and a protective film 11. The thickness d2 of the protective or sacrificial film can be thicker or thinner di. The thickness d2 also depends on the intended groove depth. The thin sheet preferably has a thickness di of < 0.3 to 0.05 mm. The film 11 is either removable (sacrificial film) or forms a permanent bond with the thin sheet 10. The thin sheet 10 can be an alloyed aluminum strip, ultra-pure aluminum or even a steel strip. Deep-drawable sheets are preferably used. Figures 2 and 3 show an enlarged view of a thin sheet with a thickness of 0.2 mm and a protective film with a thickness of 0.4 mm.

[0044] The V-shaped groove can be split in large working widths > 1 m and in a subsequent work step or it can be embossed in narrower lamella widths.

[0045] Fig. 3 shows a section of an idealized representation of a V-shaped grooved pattern with isosceles grooves at a 90° angle between a pair of rollers. The grooved pressure roller 17, which engages from above in the figure, has embossed the thin sheet on the upper side in the area of ​​valleys 12, 13. By displacing the soft, plastic plastic film between the valleys, the plastic in areas 14, 15 presses the raised peaks of the thin sheet upward into the valleys on the underside of the grooved roller. The smooth counterpressure roller 16 is made of steel.

[0046] The grooving process results in extreme compression of the plastic at the groove edges. These exert strong deformation pressure in the opposite direction to that of the grooving rollers. The cleverness of the process lies in the fact that compressive forces are the primary force. With a symmetrical groove pattern, the load is applied exactly symmetrically to the grooves, ensuring that the strip warps less or not at all after the tool exits. The depth of the groove imprint is H.

[0047] The thin sheet, surface-finished with anodizing, PVD, or paint, can be coated with a protective film either on the good side or on the reverse side, with the embossing roller embossing from the opposite side of the film coating. Embossing occurs either into the flat strip or, in the case of a concave / convex grooved roller with a concave / convex counterpressure roller, into a concave / convex contour. Figures 1 and 2 show flat rollers.

[0048] Fig. 4 and 5 show the final product of a 50 mm wide retro-blind slat. The incoming sidelight is focused by the concave bulge on the retroreflector 20 and redirected in the direction of incidence. The parallel section 21 directs the light in the opposite direction. This illustration serves to understand the requirements for the grooved product. The V-shaped grooves have an opening angle of preferably 90° ± 10° in the flat, grooved sheet metal strip. In this case, the grooved sheet metal is stabilized on the underside by coextrusion. ABS or PVC, for example, is used for this purpose. The innovative manufacturing process for producing stable light-directing slats involves coextrusion, which is preferably carried out online by prior grooving. The grooved sheet metal then serves only as a reflective surface for the plastic slat.

[0049] Fig. 5 uses ray tracing to illustrate the complex optics and beam guidance achieved by grooving. The ray tracing clearly shows that the mirror optics require a high degree of molding accuracy from the microstructured roller tools, which cannot be achieved with a rolling process according to the state of the art.

[0050] Fig. 6 shows a grooved sheet with a partially irregular groove structure produced using the innovative process. The grooved sheet is joined to a support profile 22 by coextrusion. To prevent a bimetallic effect, the underside can be additionally covered with a smooth sheet.

[0051] Fig. 7 and 8 show a concave-convex slat with only central grooving. The strip is not grooved along the longitudinal edges 25 and 26. Fig. 8 shows the slat reinforced with a plastic injection molding 23. This is necessary when the strip material is too thin to be used as a Venetian blind slat without plastic injection molding.

[0052] Fig. 9 and 10 show a concave-convex lamella with a groove across its entire cross-section. In Fig. 10, the lamella is again injected with plastic 24. The concave-convex contour can either be subsequently formed into a flat, grooved strip or the groove can be embossed into a concave-convex roller.

[0053] The advantage of the subsequent concave-Z-convex forming is that the strips can be grooved in large widths in order to split them into lamella widths in a further work step and only then to bring them into a concave-Z-convex shape.

[0054] The concave-convex shape stabilizes the slat's straightness. The sheet hardens during the forming process and tends to curl after rolling. These stresses can be released from the rolled strip through a subsequent straightening process. It is particularly advantageous to form the strips into a concave-convex final contour after rolling and / or straightening. Due to their hardness, the resulting strips can be rewound despite the grooved stiffening. When the strips are later unwound from the winding roll in Venetian blind machines, they spring back into a straight slat.

[0055] Fig. 7 shows strips that are grooved only in their cross-section center and are smooth and curved or slightly angled at the edges 25 and 26. This is only possible because the grooves are very fine and shallow, so that no large stress differences arise in the slit strip. The present process is particularly suitable for producing mirror optics.

[0056] All groove representations in the figures represent ideal contours with sharp groove tips and precisely formed groove valleys. The patent relates to a process for approximating these ideal contours. Depending on the raw material quality, pressure buildup between the rollers, and Shore hardness of the embossing, the material appears differently under the microscope. Radii inevitably arise at the groove tips and especially in the groove valleys, which are not specified here and are not part of the manufacturing process.

Claims

Patent claims Claim 1 Method for producing grooved, stable thin sheet, preferably for producing Venetian blind slats with at least partially metallically reflective and at least partially grooved upper sides for light deflection, wherein - the grooving is produced by V-shaped grooves running in the longitudinal direction of the rolled strip and - the creasing is to be embossed in the passage between one or more pairs of rollers, whereby - the embossing in thin sheet metal strips is carried out by arranging a thin, elastic and / or plastic layer of plastic beyond the embossing side, so that embossing takes place through the thin sheet into this soft plastic layer and whereby - the counter-pressure roller has a smooth, elastic, but harder or hard surface, so that - the thin, elastic and / or plastic layer is squeezed more strongly in the area of ​​the groove edges and - the squeezed, elastic and / or plastic plastic layer squeezes into the groove valleys between the groove edges, so that - by squeezing the elastic and / or plastic layer at the groove edges, the thin sheet supports a positive forming in the groove valleys of the grooved roller as a result of displacement and - a sheet grooved on both sides can be produced using a smooth counter-pressure roller without grooves. Claim 2 Method for producing grooved, stable sheet metal according to claim 1, characterized in that the sheet metal is deep-drawable and that the sheet metal has a yield strength in the case of steel < 300 N / mm 2 and in the case of aluminium or an aluminium alloy < 180 N / mm 2 or pure aluminum < 150 N / mm 2 has. Claim 3 Method for producing grooved, stable thin sheet according to claim 1, characterized in that the elastic and / or plastic plastic layer consists of a single-layer or multi-layer film, wherein the film is either firmly combined with the thin sheet as a composite film or the film is removed after grooving. Claim 4 Method for producing grooved, stable thin sheet according to claim 1 or 3, characterized in that a hard rubber pad is arranged on the hard counter-pressure roller and the rubber pad has a Shore hardness of preferably 70 to 80 A. Claim 5 Method for producing grooved, stable thin sheet according to claim 1, characterized in that the elastic and / or plastic plastic layer (11) has at least the thickness of the groove depth. Claim 6 Method for producing grooved, stable thin sheet according to claim 1, characterized in that the thin sheet (10) has a material thickness of < 0.3 mm, in particular from 0.05 to 0.2 mm and the groove depth H is 0.03 to 1 mm and the thickness of the film is 0.05 to 1.0 mm. Claim 7 Method for producing grooved, stable thin sheet according to claim 1, characterized in that the grooved roller is formed concavely or convexly and that the smooth counter-pressure roller is formed correspondingly convexly or concavely, or behind the grooving in the flat sheet, one or more pairs of rollers for concave-convex shaping are arranged so that a stable, straight lamella can be produced. Claim 8 Method for producing grooved, stable thin sheet according to claim 1 and / or 7, characterized in that the groove contour is introduced into a very thin thin sheet, preferably with a thickness of < 0.2 mm, and is injected under it in a stabilizing manner using a plastic online in a co-extrusion process, so that a smooth underside results after grooving. Claim 9 Method for producing grooved, stable thin sheet according to claim 8, characterized in that the smooth underside is laminated with a metallic thin sheet. Claim 10 Use of grooved, stable thin sheet according to claim 1 or 8 or 9, characterized in that the groove-shaped embossed thin sheet has, at least on its upper side, at least partially a tooth-shaped cross-section with grooves open at 90° ±10° and wherein at least individual V-shaped grooves consist essentially of isosceles flanks and have groove spacings of a maximum of 2 mm, preferably < 1 mm and the cleavage product serves as a lamella precursor for an optical mirror system of a lamella curtain.

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