Stamping tool, casting mold and methods for structuring a surface of a work piece

BACKGROUND OF THE INVENTION

[0002] Field of the Invention

[0003] The present invention relates to a stamping tool having a structured stamping surface, a casting mold, a method for producing a stamping tool or a casting mold having a structured stamping surface, and methods for structuring a surface of a workpiece.

[0004] Stamping constitutes a non-cutting manufacturing method for producing a relief-like or structured surface on a workpiece. A stamping tool with a profiled or structured stamping surface is used for this. The stamping surface is pressed with such a stamping force onto the surface to be structured of the workpiece or rolled on this, so that the workpiece becomes plastic and flows into depressions in the stamping tool or the stamping surface. Due to the considerable stamping forces employed, the stamping tool and the stamping surface are usually made of metal.

[0005] Further, molding is known. A casting mold with a structured molding face can be used for producing a cast workpiece with a structured surface by casting.

[0006] In the present invention nanometer range is understood to mean profiling or structuring with structural widths <1000 nm, especially <500 nm. The structural width designates the dimension by which individual structural elements, such as bumps, are repeated, that is, for example the average distance of adjacent bumps from one another or of depressions from one another.

[0007] 2. Description of Related Art

[0008] It is very expensive to manufacture a stamping tool with a very finely structured or profiled stamping surface. To create a so-called “moth eye structure”—evenly arranged, egg carton-like bumps—or fine grooves in the nanometer range, it is known from practice to use a lighting pattern with periodic intensity modulation for illuminating photo-sensitive material via two interfering laser beams. After the illuminated material develops, a periodic surface structure results, which is molded into other materials using various replication methods and finally into nickel, for example, by electroforming. This type of manufacturing is very expensive and is suited only for structuring even surfaces.

[0009] In the nanometer range lithographic methods for structuring a stamping surface of a stamping tool can still only be used in a limited way. It should be noted here that the wavelength of the visible light alone is already 400 to 750 nm. In each case lithographic methods are very costly.

[0010] German Patent DE 197 27 132 C2 discloses the manufacturing of a stamping tool by means of electrolytic machining. During electrolytic machining a metallic stamping surface of the stamping tool is treated electrolytically, wherein, being an anode in a fast-flowing electrolyte, the metal of the stamping surface is located at a minimal distance opposite a cathode and is dissolved in surface terms. The metal or the stamping surface contains the structure determined by the form of the cathode, and the cathode thus forms a recipient vessel that is shaped electrochemically. DE 197 27 132 C2 also provides the use of a cylindrical rotation electrode, whose covering surface presents a negative form of the desired stamping structure. Here, too, there is considerable expense involved and structuring in the nanometer range is at least only partly possible.

[0011] The use of anodically oxidised surface layers made of aluminium or magnesium in casting molds to increase resistance is known from Swiss Patent CH 251 451. However, the forming of hollow chambers by oxidation for structuring a molded article in the nanometer range is not disclosed.

[0012] Forming hollow chambers with anodic oxidation of aluminium is described in published European Patent Application EP 0 931 859 A1, for example.

[0013] However, the related art does not provide a cost-effective solution to produce a workpiece, like a stamped piece, or casting with a surface structered in the nanometer range.

[0014] Consequently, there is a need for a stamping tool, a casting mold, a method for manufacturing a stamping tool or a casting mold, a method for structuring a surface of a workpiece and a method for using a surface layer provided with open hollow chambers, wherein structuring in the nanometer range is enabled in a simple and cost-effective manner.

SUMMARY OF INVENTION

[0015] Object of the present invention is to provide a stamping tool, a casting mold, a method for manufacturing a stamping tool or a casting mold, a method for structuring a surface of a workpiece and a method for using a surface layer provided with open hollow chambers, wherein structuring in the nanometer range is enabled in a simple and cost-effective manner.

[0016] One aspect of the present invention is to use a porous oxide layer and especially a surface layer, formed via anodic oxidation and provided with open hollow chambers, as stamping surface of a stamping tool. This leads to several advantages.

[0017] First, an oxide layer, especially the preferably provided aluminium oxide, is relatively hard. With respect to the often very high stamping forces this is an advantage for being able to stamp workpieces of various materials and for achieving a long tool life of the stamping tool.

[0018] Second, model-free oxidation is very easy and cost-effective to carry out. In particular, producing hollow chambers is (quasi) independent of the form and configuration of the cathodes employed, so a model or negative form is not required, as in electrolytic machining.

[0019] Third, the provided model-free forming of open hollow chambers via anodic oxidation enables structures to be manufactured in the nanometer range very easily and cost-effectively. In particular, structural widths of 500 nm and less, even 100 nm and less are possible.

[0020] Fourth, depending on choice of procedural conditions the configuration—regular or irregular—and the surface density of the hollow chambers can be varied as required.

[0021] Fifth, by likewise simply varying the procedural conditions—especially by variation of the voltage during anodising—the form of the hollow chambers and thus the structure of the stamping surface can be adjusted and varied.

[0022] Sixth, the anodically oxidised surface layer can be used directly, thus without further molding, as the stamping surface of a stamping tool.

[0023] A further aspect of the present invention is to use a porous oxide layer and especially a surface layer with open hollow chambers, formed by anodic oxidation directly or model-free, thus independent of a cathode form, as molding face or inner face of a casting mold. This has a number of advantages.

[0024] First, an oxide layer, especially the preferably provided aluminium oxide, is relatively hard. With respect to the often very high forces utilised in casting or molding this is an advantage for being able to produce workpieces of various materials and for achieving a long shelf life of the casting mold.

[0025] Second, the model-free oxidation is very easy and cost-effective to carry out. Producing hollow chambers is (quasi) independent on the form and configuration of the cathodes used, and a model or negative form is therefore not required.

[0026] Third, the model-free forming of open hollow chambers as provided via anodic oxidation enables structures to be manufactured in the nanometer range very easily and cost-effectively. In particular, structural widths of 500 nm and less, even 100 nm and less are possible.

[0027] Fourth, depending on choice of procedural conditions the configuration—regular or irregular—and the surface density of the hollow chambers can be varied as required.

[0028] Fifth, by likewise simply varying the procedural conditions—especially by variation of the voltage during anodising—the form of the hollow chambers and thus the structure of the surface can be adjusted and varied.

[0029] Sixth, the anodically oxidised surface layer can be used directly, thus without further molding, as the surface of a casting mold.

[0030] Further advantages, properties, features and goals of the present invention will emerge from the following description of preferred embodiments with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]
FIG. 1 shows a very schematic sectional elevation of a proposed stamping tool and a workpiece structured therewith according to a first embodiment; and

[0032]
FIG. 2 shows a very schematic sectional elevation of a proposed casting mold and a workpiece structured therewith according to an second embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0033] In a highly simplified sectional elevation, FIG. 1 shows a proposed stamping tool 1 with a structured, i.e. profiled or relief-like stamping surface 2. The stamping surface 2 is formed by a flat side of a surface layer 3, which is provided with open hollow chambers 4 produced by anodic oxidation.

[0034] In the illustrative example, the surface layer is applied to a support 5 of the stamping tool 1. For example, the surface layer 3 is applied to the support 5 by plasma coating. But the surface layer 3 can also be formed directly by the support 5, and thus be a surface area of the support 5.

[0035] It is understood that the surface layer 3 can also be deposited on the support 5 using other methods.

[0036] In the illustrative example the surface layer 3 preferably consists of aluminium which is applied to the support 5 especially via plasma coating and adheres well to the support 5 preferably made of metal, especially iron or steel.

[0037] The surface layer 3 is oxidised anodically at least partially in the illustrative example to the depth of a covering layer 6, whereby the hollow chambers 4 are formed in the surface layer 3. The hollow chambers 4 are formed immediately and/or without any model or pattern, i.e. the arrangement, distribution, form and the like of the hollow chambers 4—as opposed to electrolytic machining—is, thus, at least essentially independent of the surface shape and the proximity of the cathode (not shown) used in oxidation. Moreover, according to the invention, the “valve effect”, namely the occurring, independent formation of hollow chambers 4 during oxidation or anodisation of the surface layer 3,—at least in particular in the so-called valve metals—is used. This immediate or undefined formation of the hollow chambers 4 does not preclude an additional (before or after) formation or structuring of the stamping surface 2 or the hollow chambers 4 by means of a negative form.

[0038] Depending on how completely or how deeply the surface layer 3 is oxidised, or whether the surface layer 3 is formed directly by the support 5, the surface layer 3 can correspond to the oxidised covering layer 6. In this case, for example, the intermediate layer 7, which is comprised of aluminium in the illustrative example and which promotes very good adhesion between the covering layer 6 and the support 5, can be omitted.

[0039] For example, according to an alternative embodiment, the uncoated support 5 can be oxidised anodically on its surface forming the stamping surface 2 by formation of a porous oxide layer or hollow chambers 4. This is possible for example for a support 5 made of iron or steel, especially stainless steel. In this case the surface layer 3 then corresponds to the covering layer 6, i.e. the oxidised layer.

[0040] Aluminium and iron or steel, especially stainless steel, have already been named as particularly preferred material, used at least substantially for forming the anodically oxidised surface layer 3 or the covering layer 6. However, silicon and titanium as well as other valve metals for example can also be used.

[0041] In the illustrative example the proportions in size are not presented true to scale.

[0042] The stamping tool 1 or its stamping surface 2 preferably has a structural width S in the nanometer range, especially from 30 to 600 nm and preferably from 50 to 200 nm.

[0043] The hollow chambers 4 or their openings have an average diameter D of essentially 10 to 500 nm, preferably 15 to 200 nm and especially 20 to 100 nm.

[0044] In the illustrative example the hollow chambers 4 are designed essentially lengthwise, wherein their depth T is preferably at least approximately 0.5 times the above-mentioned, average diameter D and especially approximately 1.0 to 10 times the diameter D.

[0045] The hollow chambers 4 are designed here at least substantially similarly in shape. In particular, the hollow chambers 4 are designed substantially cylindrically. But the hollow chambers 4 can also present a form deviating therefrom, for example they can be designed substantially conically.

[0046] In general, the hollow chambers 4 can also have a cross-section varying in its depth T in form and/or diameter. In addition to this, the hollow chambers 4 can be designed substantially conically as a rough structure for example, and provided along their walls with many fine depressions (small hollow chambers) to form a fine structure in each case.

[0047] The hollow chambers 4 are preferably distributed at least substantially uniformly over the surface of the surface layer 3 or over the stamping surface 2. However, uneven distribution is also feasible.

[0048] The hollow chambers or their openings are preferably distributed over the stamping surface 2 with a surface density of 109 to 1011/cm2. In the illustrative example the surface density is substantially constant over the stamping surface 2. But the surface density can also vary partially on the stamping surface 2 as required.

[0049] The area of the openings of the hollow chambers 4 is, at the most, preferably 50% of the extension area of the stamping surface 2. A sufficiently high stability or carrying capacity of the stamping surface 2 or the surface layer 3/covering layer 6 is hereby achieved with respect to the high stresses arising during the stamping.

[0050] In general, the form, configuration, surface density and the like of the hollow chambers 4 can be controlled by corresponding choice of the procedural conditions during anodic oxidation. For example, with oxidation of aluminium under potentiostatic conditions—with at least substantially constant voltage—an at least substantially even cross-section of the hollow chambers 4 is achieved over their depth T, i.e. an at least substantially cylindrical form. Accordingly, the form of the hollow chambers 4 can be influenced by varying the voltage. For example, galvanostatic oxidation—i.e. at an at least substantially constant current—leads to a somewhat conical or hill-like form of the hollow chambers 4, so that a type of “moth eye structure” or the like can be formed in this way. The surface density of the hollow chambers 4, i.e., the number of hollow chambers 4 per surface unit the stamping surface 2, depends inter alia on the voltage and the current during anodising.

[0051] As required, the hollow chambers 4 can vary in their form, depth and/or surface density over the stamping surface 2, especially partially, and/or be designed only partly on the stamping surface 2.

[0052] And, if required, the stamping surface 2 can also be modified before and/or after oxidation—creation of the hollow chambers 4—for example via a lithographic process, etching and/or other, preferably material-stripping methods, for example to create a rough structure in the form of paths, ridges, areas with or without hollow chambers 4, large-surface bumps or depressions and the like on the stamping surface 2.

[0053] Chemical sizing, especially by partial etching of oxide material, can also be carried out to modify the stamping surface 2 or the hollow chambers 4. In this way the surface ratio of the opening surfaces of the hollow chambers 4 to the extension area of the stamping surface 2 can be varied or increased. It is understood that other modifications of the stamping surface 2 or of the hollow chambers 4 can also be made, depending on reaction time and intensity.

[0054] A particular advantage of the proposed solution is that the stamping surface 2 can also be designed in a curved manner—for example cylindrically—or bulged—for example lenticular or hemispherical. In particular the stamping surface 2 can have practically any shape at all. Compared to the prior art it is thus not necessary that the stamping surface 2 or the surface of the surface layer 3/covering layer 6 is at least substantially even.

[0055] The figure also shows a workpiece 8, likewise in a highly simplified, not true-to-scale sectional diagram, in the already stamped state, i.e. with a surface 9 already structured by the stamping tool 1. Stamping takes places especially by the stamping tool 1 being pressed with a corresponding stamping force onto the surface 9 of the workpiece 8 to be structured, so that the material of the workpiece 8 flows at least partially into the hollow chambers 4. Here it is not necessary that the workpiece 8, as illustrated diagrammatically in the figure, is designed in a monoblock manner. Instead, the workpiece 8 can also present another type of surface layer or surface coating or the like, not illustrated here, which forms the surface 9 and is structured or designed in a relief-like manner by means of the stamping tool 1.

[0056] Instead of the stamp-like embossing the stamping tool 1 can be unrolled with corresponding shaping/form of the stamping surface 2 and/or the surface 9 to be structured. By way of example the stamping surface 2 and/or the surface 9 to be structured can be designed in a curved manner—for example cylindrically—or in a bulged manner to enable reciprocal unrolling for structuring the surface 9.

[0057] Both a die stamping process and also a rolling stamp process can be realized with the proposed solution.

[0058] Furthermore, the proposed solution can be used for embossing as well as closed-die coining or coining. A corresponding abutment for the workpiece 8 or a corresponding countertool is not illustrated for clarification purposes.

[0059] The proposed stamping tool 1 allows very fine structuring of the workpiece 8 or its surface 9. If needed the workpiece 8 or the surface 9 can also be profiled or structured repeatedly, first with a rough structured stamping tool—optionally manufactured also in customary fashion—and then with the finer structured proposed stamping tool 1. A lower stamping force is employed, especially during the second stamping procedure using the finer stamping tool 1 and/or, in an intermediate step, the surface 9 is hardened in order not to fully neutralise the rough structure produced at first stamping, but to achieve superposition from the rough structure and the fine structure of both stamping tools. Thus, it is possible, for example, to create on the surface 9 relatively large bumps of the order of 0.1 to 50 μm each with several, relatively small protrusions, for example of the order of 10 to 400 nm, on the surface 9 of the workpiece 8.

[0060] The proposed solution very easily and cost-effectively enables very fine structuring of the surface 9. Accordingly, there is a very broad area of application. For example, such especially very fine structuring can be utilised in anti-reflex layers, for altering radiation emission of structured surfaces, in sensory analysis, in catalysis, in self-cleaning surfaces, in improving surface wetability and the like. In particular, the proposed solution also extends to the use of workpieces 8 with structured surfaces 9 that have been structured by use of the proposed stamping tool 1 for the purposes mentioned hereinabove.

[0061] In particular the proposed solution is suited for stamping synthetic materials—for example PMMA (polymethyl methacrylates), Teflon or the like, metals—for example gold, silver, platinum, lead, idium, cadmium, zinc or the like, polymer coatings—for example paints, dyes or the like, and inorganic coating systems etc.

[0062] Expressed in general terms, an essential aspect of the present invention according to the first embodiment is using a surface layer with hollow chambers formed by anodic oxidation as bottom die or upper die, to enable surface structuring in the nanometer range.

[0063] Now, the second embodiment of the present invention is discussed with reference to FIG. 2.

[0064] In a highly simplified partial sectional elevation, FIG. 2 shows a proposed casting mold 11 with an at least partially structured, thus profiled or relief-like inner face or molding face 12. The face 12 is formed by a top or flat side of a surface layer 13 that is provided with open hollow chambers 14 produced by anodic oxidation.

[0065] In the illustrative example, the surface layer 13 is applied to a support 15 of the casting mold 11. For example, the surface layer 13 is applied to the support 15 by plasma coating. But the surface layer 13 can also be formed directly by the support 15, and thus be a surface area of the support 15.

[0066] It is understood that the surface layer 13 can also be deposited on the support 15 using other methods.

[0067] In the illustrative example, the surface layer 13 preferably comprises aluminium, which is applied to the support 15 especially via plasma coating and adheres well to the support 15 preferably made of metal, especially iron or steel.

[0068] The surface layer 13 is oxidised anodically at least partially, in the illustrative example to the depth of a covering layer 16, by means of which the hollow chambers 14 are formed in the surface layer 13 or covering layer 16. The hollow chambers 14 are formed directly or model-free, that is, the configuration, distribution, form and the like of the hollow chambers 14 is, compared to electrolytic machining, therefore at least substantially dependent on the surface shape and proximity of the cathodes (not illustrated here) used during oxidation. Rather, the ‘valve effect’ is made use of here, as per the invention, namely the automatic development of the hollow chambers 14 occurring during oxidation or anodising of the surface layer 13, at least especially with so-called valve metals. Such direct and model-free production of the hollow chambers 14 does not exclude additional (prior or subsequent) forming or structuring of the face 12 or of the hollow chambers 14

[0069]

completely or how deeply the surface layer 13 is oxidised, or whether the surface layer 13 is formed directly by the support 15, the surface layer 13 can correspond to the oxidised covering layer 16. In the illustrative example in this case, for example, the intermediate layer 17, which is comprised of aluminium and which promotes very good adhesion between the covering layer 16 and the support 15, can be omitted.

[0070] For example, according to a design alternative the uncoated support 15 can be oxidised anodically on its surface forming the face 12 by formation of a porous oxide layer or hollow chambers 14. This is possible for example for a support 15 made of iron or steel, especially stainless steel. In this case the surface layer 13 then corresponds to the covering layer 16, i.e., the oxidised layer.

[0071] Aluminium and iron or steel, especially stainless steel, have already been named as particularly preferred material, used at least substantially for forming the anodically oxidised surface layer 13 or the covering layer 16. However, silicon and titanium as well as other valve metals for example can also be used.

[0072] In the illustrative example the proportions in size are not presented true to scale.

[0073] The face 12 preferably has a structural width S in the nanometer range, especially of 130 to 600 nm and preferably of 50 to 200 nm.

[0074] The hollow chambers 14 or their openings have an average diameter D of essentially 10 to 500 nm, preferably 15 to 200 nm and especially 20 to 100 nm.

[0075] In the illustrative example, the hollow chambers 14 are designed essentially lengthwise, wherein their depth T is preferably at least approximately 0.5 times the above-mentioned, average diameter D and especially approximately 1.0 to 10 times the diameter D.

[0076] The hollow chambers 14 are designed here at least substantially identically. In particular the hollow chambers 14 are designed substantially cylindrically. But the hollow chambers 14 can also present a form deviating therefrom, for example they can be designed substantially conically.

[0077] In general the hollow chambers 14 can also have a cross-section varying in its depth T in form and/or diameter. In addition to this, the hollow chambers 14 can be designed substantially conically as a rough structure for example, and provided along their walls with many fine depressions (small hollow chambers) to form a fine structure in each case.

[0078] The hollow chambers 14 are preferably distributed at least substantially uniformly over the surface of the surface layer 13 or over the face 12. However, uneven distribution is also feasible.

[0079] The hollow chambers or their openings are preferably distributed with a surface density of 109 to 1011/cm. In the illustrative example the surface density is substantially constant over the face 12. But the surface density can also vary selectively on the surface 12 as required.

[0080] The area of the openings of the hollow chambers 14 is at the most preferably 50% of the extension area of the face 12. A sufficiently high stability or carrying capacity of the face 12 or the surface layer 13/covering layer 16 is hereby achieved with respect to the high stresses arising partially from molding or casting.

[0081] In general the form, configuration, surface density and the like of the hollow chambers 14 can be controlled by corresponding choice of the procedural conditions during anodic oxidation. For example, with oxidation of aluminium under potentiostatic conditions—i.e., at at least a substantially constant voltage—an at least substantially uniform cross-section of the hollow chambers 14 is achieved over their depth T, i.e., an at least substantially cylindrical form. Accordingly, the form of the hollow chambers 14 can be influenced by varying the voltage. For example, galvanostatic oxidation, i.e. at an at least substantially constant current, leads to a somewhat conical or hill-like form of the hollow chambers 14, so that a type of “moth eye structure” or the like can be formed in this way. The area density of the hollow chambers 14, i.e., the number of hollow chambers 14 per area unit on the face 2, depends inter alia on the voltage and the current during anodising.

[0082] As required, the hollow chambers 14 can vary in their form, depth and/or surface density over the face 2, especially partially, and/or be designed only partially on the face 12.

[0083] And, if required, the face 12 can also be modified before and/or after oxidation—thus creation of the hollow chambers 14—for example, via a lithographic process, etching and/or other, preferably material-stripping methods, for example to create a rough structure in the form of paths, ridges, areas with or without hollow chambers 14, large-surface bumps or depressions and the like on the face 12.

[0084] Mechanical processing and/or chemical sizing, especially by partial etching of oxide material, can also be carried out to modify the face 12 or the hollow chambers 14. In this way, the area ratio of the opening areas of the hollow chambers 14 to the extension area of the face 12 can be varied or increased. It is understood that other modifications of the face 12 or of the hollow chambers 14 can also be made, depending on reaction time and intensity.

[0085] A particular advantage of the proposed solution is that the face 12 can also be designed in practically any shape at all.

[0086] The figure also shows a molded article or workpiece 18, likewise in a highly simplified, not true-to-scale, sectional diagram, in the already finished state, i.e., with a surface 19 already structured by the casting mold 11 after casting.

[0087] The proposed casting mold 11 allows very fine structuring of the workpiece 18 or its surface 19. It is possible, for example, to create relatively large bumps of the order of 0.1 to 50 μm each with several, relatively small projections on the surface 19, for example of the order of 10 to 400 nm, on the surface 19 of the workpiece 18.

[0088] The proposed solution very easily and cost-effectively enables very fine structuring of the surface 19. Accordingly, there is a very broad area of application. For example, such especially very fine structuring can be utilised in anti-reflex layers, for altering radiation emission of structured surfaces, in sensory analysis, in catalysis, in self-cleaning surfaces, in improving surface wettability and the like.

[0089] Expressed in general terms, an essential aspect of the present invention is casting or molding a surface layer with hollow chambers formed directly or model-free by anodic oxidation, to enable surface structuring in the nanometer range.

[0090] The present invention is especially not limited to a casting mold 11 in the narrower sense. Rather, the surface layer 13 or covering layer 16 is to be understood as model for a general structuring of a surface, a tool, a workpiece or the like in the nanometer range. In particular, the model may be molded in any way at all. And in particular, no reshaping is required when molding. For example, with the workpiece 18 to be manufactured having a structured surface 19, this can be a cast article, wherein the surface 19 is structured by casting or decanting or any molding of the mold 11.

[0091] In general, the present invention enables a simple, cost-effective stamping or molding in the nanometer range by a surface layer with hollow chambers formed by anodic oxidation being used as matrix or as casting mold.

[0092] Technical Applicability

[0093] The proposed solution very easily and cost-effectively enables very fine structuring of the surface. Accordingly, there is a very broad area of application. For example, such especially very fine structuring can be utilised in anti-reflex layers, for altering radiation emission of structured surfaces, in sensory analysis, in catalysis, in self-cleaning surfaces, in improving surface wetability and the like. In particular, the proposed solution also extends to the use of workpieces with structured surfaces that have been structured by use of the proposed stamping tool for the purposes mentioned hereinabove. Further, the proposed solution can be used for casting with practically any material, since aluminium oxide especially is highly resistant mechanically, thermally and/or chemically.

Number	Date	Country
100 20 877.0	Apr 2000	DE
101 31 513.9	Jul 2001	DE
101 54 756.0	Nov 2001	DE

	Number	Date	Country
Parent	10281376	Oct 2002	US
Child	10778077	Feb 2004	US

Stamping tool, casting mold and methods for structuring a surface of a work piece

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