EP3223970B1 - Surface texturing of deforming tools - Google Patents

Description

Technical area

The invention relates to a method for producing a forming tool, which has a structured embossing surface which can be brought into contact with the surface of a substrate for the plastic deformation of a substrate. Furthermore, the invention relates to such a forming tool.

Background of the invention

In plastic forming processes often embossing surfaces, such as the surface of a work roll in the rolling mill, are used with a particularly structured surface texture. The goal is to impress a stamping of the surface structure of the embossing surface in the relevant surface of the substrate by plastic deformation. Such an embossment, which superimposes any existing material and / or process-related near-surface roughness structure, may be motivated by optical, tribological, material-technical, joining-technical or by a combination of these reasons.

An example process flow for the surface embossing of sheet metal in the so-called skin-pass method is to be briefly outlined: During cold rolling, rolls with a defined roughness are used to fulfill gripping conditions and lubrication conditions for the forming. For example, it is known to roughen the last pair of rollers of the cold rolling mill, so that the surfaces of the individual turns of a coil do not stick together during annealing. During the rolling process, the roughness of the rolls is impressed on the sheet. After cold rolling, the sheets are annealed to produce the required formability for subsequent deep drawing. Out For procedural reasons, changes in surface structures during annealing are difficult to avoid. After annealing, the sheet also has a pronounced yield strength, which can lead to flow patterns during forming. By the subsequent rolling of the sheet in the skin pass mill, these mostly undesirable effects can be reduced or eliminated. At the same time, re-rolling is used to produce the final surface texture. The structure through the temper rolling superimposed on the structure applied by the cold rolling and annealing.

Various methods are available for producing the embossing structure, especially on the temper rolling mill; these include Shot Blast Texturing (SBT), Electrical Discharge Texturing (EDT), Laser Texturing (LT), Electron Beam Texturing (EBT), Pretex.

During the deformation of the substrate for structuring the surface, a plastic deformation takes place not only in the vicinity of the surface, but this process requires a flow of material along at least one other main direction. In order to stay with the example of the rolling process, in this case, a decrease in thickness of the substrate takes place, which leads primarily to an elongation. The elongation is usually wanted and also unavoidable. It leads to a stretching of the material in the rolling direction. An extension transverse to the rolling direction does not take place or hardly occurs.

The elongation, or more generally the deformation along one or more principal directions, has the consequence that a structure applied to the surface or applied to the surface corresponds to the degree of deformation along the main directions (when rolling according to the degree of reduction in thickness or elongation) is distorted geometrically. An originally circular structure, for example, is deformed to an ellipse whose major axis is parallel to the rolling direction.

The quality of the impression can be significantly affected by this process-related distortion. As a rule, an undistorted image is desired, but this is only the case if a deformation along such directions, which do not belong to the texturing, ie along the above-mentioned main directions, is avoided. A significant conflict of objectives in the plastic forming with surface texturing is thus that a high quality of the embossing precludes a high degree of deformation. A high degree of deformation along one or more main directions, such as a strong reduction of the material at constant mass flow, in turn, promotes productivity. In this respect, an increase in productivity also precludes the quality of the desired surface texture.

Although the above problem of surface texturing has been presented primarily in the image of a rolling process as an exemplary plastic working process, the difficulties also occur in other plastomechanical forming processes and discontinuous processes, including forging, embossing, stamping, plating and others.

Presentation of the invention

An object of the invention is to provide a forming tool and a method for producing the same, with which a high degree of deformation can be achieved with improved quality of embossing.

The object is achieved by a method having the features of claim 1 and a forming tool having the features of claim 10. Advantageous developments follow from the dependent claims, the following

The JP H05 92283 A describes a method and an apparatus for processing a surface of a work roll by means of a laser.

Presentation of the invention and the description of preferred embodiments.

The method according to the invention serves to produce a forming tool that has a structured embossing surface. The structured embossing surface can be brought into contact with the surface of a substrate for plastic deformation of a substrate. In the case of the preferred rolling process, the substrate is, for example, a metal sheet to be rolled, and the embossing surface is preferably the peripheral surface of a work roll, such as a temper rolling. However, the invention is also suitable for other forming processes, such as forging, stamping, stamping or plating.

First, a target structure to be fabricated on the substrate, which is also called a texture, is determined. This is the desired surface profile to be produced by means of plastic deformation. For example, the target structure could be clearly represented as a two-dimensional function, a mountain and valley profile depending on the position on the surface. Preferably, the target structure is isotropic, i. at least in some respects direction-independent, designed. The definition of the target structure may also include a measure of roughness (average roughness, squared roughness, average roughness, peak number, etc.). Unintentional distortion of the target structure was particularly evident in the past in structures of high roughness or high degrees of deformation. This problem is solved by the invention, and insofar it is particularly suitable for target structures of this type.

The target structure is then geometrically distorted, resulting in a structure that will be referred to herein as a mintage mapping structure. The geometric distortion includes, in particular, upsetting and stretching of the target structure. The purpose of this transformation is to create an indispensable and usually desired deformation of the substrate along one or several main directions. The main direction is a direction that is not determined by the profiling or texturing along which, nonetheless, a plastic deformation of the substrate takes place during profiling. For example, if the forming process is the above-mentioned rolling process, the said main direction corresponds to the rolling direction; because along the rolling direction, a stretching or elongation of the material takes place, which comes about through the rolling action, but not through the actual structure. An elongation transversely to the rolling direction (in the plane of the substrate), however, does not take place, or at least scarcely, so that in the rolling process a deformation along only one main direction can be assumed. In other words, this means: A planar deformation takes place in the length and thickness direction, but not in the width direction, so that with respect to the surface the deformation only appears in one main direction, namely in the direction of the length. Generally speaking, however, the transformation can take place along several main directions. The geometric transformation thus compensates for the elongation of the substrate in the rolling direction in the case of rolling. For example, if the target structure consists of a plurality of circles, they are consciously and intentionally compressed into ellipses within the geometric distortion, their main axes being transverse to the rolling direction.

The embossing image structure is then inverted, thereby obtaining a structure called an embossed structure. The embossing surface of the forming tool is then manufactured according to the embossing structure thus obtained. In other words, the embossing structure is the structure with which the embossing surface of the forming tool is to be provided.

The invention allows a high degree of embossment from the tool to the substrate without creating unintentional distortions on the target texture. It can be realized high roughness, without such a negative the quality of the target structure. In particular, regular and / or isotropic structures with a high degree of deformation can be produced with the method presented here. In contrast to more stochastic structures, where a distortion is to be considered directly. To increase the quality in the past large roll diameters, low degrees of deformation and / or other disadvantageous technical solutions were required. These problems are solved by the invention. In particular, it contributes to improving the surface quality in terms of optical, tribological, material engineering, joining technology and / or a combination of these or other properties. All of this can be achieved in conjunction with extremely high deformation or embossing degrees, whereby an increase in productivity without structural change in the forming plant is achieved. Thus, the invention with little modifications to the tool can be realized.

The target structure is preferably described by a transfer function whose parameters or arguments contain the embossed structure and one or more process parameters. The process parameters describe the forming behavior of the substrate during the plastic deformation along one or more main directions. The term "process parameters" is generally understood herein and includes parameters of the substrate to be processed as well as those parameters that describe properties of the forming tool. For example, the deformation along a main direction may depend on the substrate thickness, for example the sheet thickness or strip thickness during rolling. Furthermore, the formability may depend on the yield stress of the material. A geometric size, in the rolling process about the diameter of the roller, can also influence the forming behavior of the substrate. The larger the roll diameter, the smaller the elongation in the rolling direction. Other parameters that may play a role in this regard are the embossing speed, for example the rolling speed in the rolling process, the tension along one or more main directions during forming, a coefficient of friction between Embossing tool and substrate and / or another measure for the extension of the material.

Preferably, the embossing pattern has an anisotropic geometric property whose counterpart is isotropic in the target structure. Here, the embossing structure in its entirety may be anisotropic, i. Depending on the direction (analogous to the target structure in its entirety isotropic, i.e. direction-independent), or only one or more geometric properties of the structure can be provided anisotropically or isotropically. For example, if the target structure is made up of a plurality of circles, then these circles may be anisotropically distributed. Nonetheless, the structure would have a corresponding isotropic property - the circles. In the embossed structure these circles would be compressed to ellipses.

For the production of the embossing surface are the so-called "Shot Blast Texturing" (SBT), "Electrical Discharge Texturing" (EDT), "Laser Texturing" (LT), "Electron Beam Texturing" (EBT), Pretex. In shot blast texturing, macroscopic particles are accelerated by a blast wheel onto the embossing surface. When hitting the embossing surface, the particles plastically deform the surface and possibly knock out material. The roughness can be adjusted by the speed of the blast wheel, the blasting medium, the hardness of the embossing surface, the abrasive throughput and / or the processing time. In "Electrical Discharge Texturing", electrodes are moved to the preferably moving embossing surface (for example to the rotating roll surface) without touching it. A high-voltage pulse of the electric generator produces a sufficiently high electric field strength between electrode and substrate, so that a spark discharge occurs in the dielectric between the two poles. The fuel flow flows in the plasma of the forming arc.

A small area of the embossing surface is melted. In the dielectric gas bubbles form. When you turn off the Erodierimpulses implode the Gas bubbles and the molten material is ejected. The roughness can be adjusted in addition to the hardness of the embossing surface on parameters such as voltage, current, control times and distance of the electrodes. Compared to SBT, EDT can produce higher peak numbers and lower roughness with higher reproducibility. Laser texturing focuses a laser beam onto the embossing surface and melts a small area of the surface. A chopper wheel or a suitable electronic control interrupts the jet, and the melt is blown out by the pressure of the plasma and an inert gas. The melt either collects around a bead around the edge of the crater or is piled up on one side of the crater and solidifies there. To adjust the roughness about the laser power, the feed of the laser beam, the chopper speed and the inert gas are used. In "Electron Beam Texturing", an electron beam is used to melt the material of the embossing surface. Part of the molten material vaporizes so that the vapor pressure accumulates the melt into a ring around the crater. In the "Pretex" process, the embossing surface is electrolytically hard-chrome plated. The control of the voltage between the anode and the embossing surface serving as a cathode results in the formation of spherical-segment-shaped structural elements on the surface.

The invention further relates to a forming tool having the features of claim 10.

Although the present invention is used in the technical environment of tools for plastic deformation and structuring, in particular work rolls or temper rolling, the invention can also be implemented in other areas if necessary. In addition, other advantages and features of the present invention will become apparent from the following description of preferred embodiments. The features described therein may be implemented alone or in combination with one or more of the features mentioned above insofar as the features are not contradictory. The following description of preferred embodiments is made with reference to the accompanying drawings.

Brief description of the figure

The FIG. 1 schematically shows the sequence of a Nachwalzprozesses in which by means of a structured embossing surface of a work roll a metal strip a structure is plastically impressed.

Detailed description of preferred embodiments

Hereinafter, exemplary embodiments of the invention will be described in detail with reference to the drawings. It should be understood that the embodiments described herein are not intended to limit the invention but to serve to explain the invention, and the features or combinations of features of the embodiments may not always be essential to the invention.

The FIG. 1 schematically shows a process of re-rolling a metal strip 1, which is an example of the more general term "substrate". The reference numeral 1 denotes not only a metal strip, but also indicates its surface structure, such as before re-rolling, on Bandeinlauf the rolling mill 2 could be present. The metal strip 1 has at this point in addition to the surface structure, which is referred to below as OE, a strip thickness h and a yield stress kf.

By means of the rolling mill 2, a suitable geometric structure or texture is applied to one or both surfaces of the metal strip 1 in a combined embossing and thickness reduction process. In other words, not only does the embossing of a structure into the surface of the metal strip take place in the rolling plant 2, but the strip also experiences an elongation, which is associated with a reduction in thickness. In addition to the actual texturing, there is thus a deformation along another skin direction, in the present case the longitudinal and transport direction of the band 1. By performing these two process steps (elongation and structuring) together, the productivity of the processing process can be increased. In addition, surface textures of high degrees of conversion or high roughness can be realized, which would not be feasible without such accompanying deformation along one or more main directions or only at great expense, such as with a considerable increase in the roll diameter. In the present example, the work roll 3, that is to say that roll which has the embossing surface with a specific surface structure and impresses it into the substrate 1, has a diameter of only approximately 400 mm. Other diameters are of course also possible. For example, experiments have been successfully carried out with a roll diameter of about 230 mm. It is important to realize that embossing with rolls of comparatively small diameter is possible, with an embossing quality that was previously reserved for larger rolls. The diameter of the work roll is denoted by D. It should also be noted that embossing by means of several work rolls is possible if both sides of the strip are to be embossed or the pattern to be produced requires several embossing steps.

The work roll 3 has an embossing surface, which in the FIG. 1 designated by the reference numeral 4. The embossing surface 4 has a structure which is to be impressed on the substrate 1. The structure of the embossing surface 4 can be described by a function, which will be referred to below as OW.

The resulting surface texture, as that structure which ultimately rests on the substrate 1 at the outlet of the rolling mill 2 and is designated by the reference numeral 5, is not only a function of OW, but depends on further process parameters; for example, the extension ε due to the reduction in thickness by rolling, the rolling speed v, the strip tension at the inlet FE, the strip tension at the outlet FA and the friction μ in the nip. One or more of these parameters determine the elongation of the tape along the transport direction of the tape. This is a deformation which distorts the structure predetermined by the embossing surface 4 of the work roll 3, whereby there is conventionally an unintentional anisotropy of the structure at the strip outlet.

The surface structure 5, which rests after the rolling step, ie at the outlet of the rolling mill 2, is described by a function OA. OA generally has the following form: $$\mathrm{OA}=\mathrm{f}\left(\mathrm{OW};\mathrm{OE}.\mathrm{D}.\mathrm{H}.\mathrm{kf}.\mathrm{\epsilon }.\mathrm{v}.\mathrm{FE}.\mathrm{FA}.\mathrm{\mu }\right)$$

The terms "isotropy" and "anisotropy" in the present text refer to at least one or more geometric properties that can be identified in the embossing surface 4 and in the target structure 5 and compared with each other. If the embossing surface 4 of the work roll 3, for example, has circles which have led on the strip surface 5 at the output of the rolling mill 2 to ellipses with parallel to the transport direction major axis, then the structure OW was anisotropically distorted.

As already mentioned, in order to reduce the degree of anisotropy, in general the distortion during rolling, the diameter of the work roll can be increased or, for example, an increase in the nip friction can be sought. Both possibilities are associated with technical and / or economic disadvantages, such as a structural enlargement of the plant and a greater energy demand.

The technical solution presented below starts elsewhere. In the terminology of the above rolling mill 2, the desired surface texture OA of the aluminum strip 1 is generated by the work roll 3 regardless of the degree of deformation by selecting a compressed, generally distorted, surface texture OW. The distorted, usually anisotropic surface texture 4 of the work roll 3 is selected as the inverse of the transfer function OA and applied to the desired target texture OW. The structure which defines the transfer function OA is referred to herein as an imprint mapping structure. There is a combined embossing and thickness reduction process by the work roll 3 with a suitably geometrically distorted embossing structure, whereby due to the elongation of the tape 1, the desired target structure is obtained. The type and degree of geometric distortion of the pattern on the embossing surface 4 are chosen to correspond to the inverse transfer function OA to the substrate 1: $$\mathrm{OW}={\mathrm{f}}^{-1}\left(\mathrm{OA};\mathrm{OE}.\mathrm{D}.\mathrm{H}.\mathrm{kf}.\mathrm{\epsilon }.\mathrm{v}.\mathrm{FE}.\mathrm{FA}.\mathrm{\mu }\right)$$

Any fine adjustment of the impression characteristics of the work roll 3, or generally of the tool, on the substrate 1 can by changing other process parameters, such as the belt tension at the inlet FE and outlet FA, the extension ε, the rolling speed v and / or the friction in the nip ( Lubrication) μ can be realized.

Embodiment for the transfer function of the simple drawing

mit Faktoren C₁, C₂ >0, die von weiteren Prozessbedingungen wie h und µ abhängig sein können.OA represented by height profile zA (x, y)
OW represented by height profile zW (x, y)
x: rolling direction
y: width direction $$\mathrm{zA}\left(\mathrm{x},\mathrm{y}\right)=-\mathrm{z\; W}\left(\mathrm{x}/\left(1+{\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="imgf0001.png"\; state="\{\{state\}\}">C</figure-callout>}}_2*\mathrm{\epsilon }\right).\mathrm{y}\right)/{\mathrm{C}}_1$$

with factors C ₁ , C ₂ > 0, which may depend on other process conditions such as h and μ.

The inversion is: $$\mathrm{z\; W}\left(\mathrm{x},\mathrm{y}\right)=-\mathrm{C}1*\mathrm{zA}\left(\mathrm{x}*\left(1+\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="imgf0001.png"\; state="\{\{state\}\}">C</figure-callout>}2*\mathrm{\epsilon }\right).\mathrm{y}\right)$$

A fine adjustment, for example via the extension ε and the strip tension FE at the strip inlet would be as follows: $$\mathrm{\Delta OA}=\left[\partial \mathrm{f}\left(\mathrm{OW};\mathrm{OE}.\mathrm{D}.\mathrm{H}.\mathrm{kf}.\mathrm{\epsilon }.\mathrm{v}.\mathrm{FE}.\mathrm{FA}.\mathrm{\mu }\right)/\mathrm{\partial \epsilon }\right]\mathrm{\Delta \epsilon \; +}\left[\mathrm{\partial f}\left(\mathrm{OW};\mathrm{OE}.\mathrm{D}.\mathrm{H}.\mathrm{kf}.\mathrm{\epsilon }.\mathrm{v}.\mathrm{FE}.\mathrm{FA}.\mathrm{\mu }\right)/\mathrm{\partial FE}\right]\mathrm{\Delta FE}$$

After the embossed structure has been determined in this way, the embossing surface can be made. Various techniques are available, such as Shot Blast Texturing (SBT), Electrical Discharge Texturing (EDT), Laser Texturing (LT), Electron Beam Texturing (EBT), Pretex.

Where applicable, all individual features illustrated in the embodiments may be combined and / or interchanged without departing from the scope of the invention.

LIST OF REFERENCE NUMBERS

1. 1 substrate at the tape inlet
2. 2 rolling mill
3. 3 stripper
4. 4 embossing surface
5. 5 substrate with target structure at the belt outlet

Claims (10)

1. Method of producing a deforming tool (2) having a structured embossing surface (4), which for plastic deformation of a substrate (1) can be brought into contact with a surface thereof, wherein the method comprises:

   determining a target structure to be produced on the substrate (1);

   geometrically distorting the target structure, whereby an embossing image structure is obtained;

   inverting the embossing image structure, whereby the embossing structure for the embossing surface (4) is obtained; and

   producing the embossing surface (4) of the deforming tool (2) in accordance with the embossing structure.
2. Method according to claim 1, characterised in that the target structure is described by a transfer function (OA), the parameters of which contain the embossing structure and one or more process parameters.
3. Method according to claim 2, characterised in that one or more of the process parameters describes or describe the deformation behaviour of the substrate (1) during the plastic deformation along one or more main directions.
4. Method according to claim 3, characterised in that the process parameters contain one, more or all of the following parameters; the substrate thickness, the flow tension of the substrate (1), a geometric variable of the embossing surface (4), the elongation of the substrate (1) during deformation along a main direction, the embossing speed, the tension along one or more main directions during deformation and a coefficient of friction between embossing surface (4) and substrate (1).
5. Method according to any one of the preceding claims, characterised in that the deforming tool (2) comprises a working roll (3), preferably a dressing roll.
6. Method according to claim 5, characterised in that the target structure is described by a transfer function, the parameters of which contain the embossing structure and one, more or all of the following process parameters: the substrate thickness, the flow tension, the diameter of the working roll (3), the elongation of the substrate (1) along the rolling direction, the rolling speed, the substrate tension at the entry to the working roll (3), the substrate tension at the exit from the working roll (3) and the friction in the rolling gap.
7. Method according to any one of the preceding claims, characterised in that the substrate (1) is a sheet, preferably a metal sheet.
8. Method according to any one of the preceding claims, characterised in that the embossing structure has an anisotropic characteristic, the pendant of which in the target structure is isotropic.
9. Method according to any one of the preceding claims, characterised in that the embossing structure (4) is produced by one, more or all of the following methods: SBT, EDT, LT, EBT and Pretex.
10. Deforming tool (2) having a structured embossing surface (4), which for plastic deformation of a substrate (1) can be brought into contact with a surface thereof, wherein the deforming tool (2) is produced in accordance with any one of the preceding claims, the deforming tool (2) has a working roll (3), the surface of which has the embossing surface (4), and the structure of the embossing surface (4) has a plurality of elliptical patterns, the main axes of which lie transversely to the rolling direction.

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