EP1268864A1

EP1268864A1 - Production of an embossing tool and use of the same

Info

Publication number: EP1268864A1
Application number: EP01911329A
Authority: EP
Inventors: Kurt Steinhoff; Nathalie Schuleit
Original assignee: RUAG Components AG; SM Schweizerische Munitionsunternehmung AG
Current assignee: RUAG Components AG
Priority date: 2000-03-21
Filing date: 2001-03-21
Publication date: 2003-01-02
Also published as: AU2001240411A1; WO2001071048A1; EP1136574A1

Abstract

The displacement of lubricant as a result of dynamic and static processes is a problem in forming procedures but also in bearings. Specific crater-shaped recesses (2) formed in the surface of a tool (1) using heat allow the formation of deterministically located lubricant pockets with raised edges (9). When the tool surface is embossed on the workpiece, tribologically advantageous lubricant pockets are formed. Said pockets reduce wear during subsequent forming, hereby increasing the endurance of the tools. A texture obtained in this way is also advantageous for fixing subsequent coatings.

Description

Manufacture of an embossing tool and its application

The present invention relates to a method according to claim 1 and to a lubrication pocket according to claim 6 and to a preferred application of the method according to claim 10.

A method according to the preamble of claim 1 was proposed in PCT / CH99 / 00451 and, for the purpose, has to form workpiece surfaces with different physical / technical and / or chemical properties and to reduce wear on surfaces subject to high stress. This also has a beneficial effect on the tribological properties of the surfaces.

Processes for producing defined microstructures on tool surfaces and on workpieces have been known for some years (including DE-AI-195 29 429) and are used in particular in forming processes. During the plastic forming process, the texture (micro-geometry) of the tool surface is embossed on the workpiece surface; this stamping has a positive effect on the tool life in subsequent processes. An analysis of the functions of a surface provided with microstructures shows the following:

1. Improvement of the tribological conditions for subsequent shapes.

2. Improvement of the tribological conditions in assemblies and systems such as plain bearings. 3. Improvement of the adhesion and the aesthetic appearance after a painting (bodies).

4. Simplification and improvement of coating processes, in particular improvement of the layer adhesion of primers and claddings.

An indirect structuring of workpiece surfaces is particularly recommended for high numbers of pieces; The necessary, defined structure in the workpiece usually requires several shaping steps, whereby the surface structure that is tribologically suitable for each subsequent step must be provided.

Such methods are known in the production of thin sheets, in deep drawing, inter alia also in reducing cold rolling with subsequent re-rolling. It has been shown that structures have a disadvantageous effect, in which the lubrication pockets formed have been created by embossing a raised structural component caused by volume displacement. The inevitable connection of a raised structural part with a recess results in a tribologically unfavorable material rearrangement, which is removed in a post-processing, usually by a grinding process. This means that such a lubrication bag loses its wear resistance and its edge seal. Thus, only very limited lubricant reserves can be formed, which are also either spooled out by dynamic processes during the shaping process and / or removed by squeezing the lubricant out of the zones with the highest contact voltages. It is therefore an object of the present invention to provide methods for producing an improved, optimized lubrication pocket geometry which has the following properties:

1. The microstructure of the tool surface, in particular its raised structural components, should have a high wear resistance.

2. The design of raised and deepened structural areas should be in a non-disadvantageous relationship and should therefore be largely free to design.

3. The completion of the lubrication pocket as a prerequisite for a hydrostatic pressure build-up should take place in the earliest possible process phase and at the same time ensure a supply of lubricants during the entire process. The contact angles of the lubrication pockets should also be able to be adjusted favorably to the way the lubricant flows out.

This object can be achieved by means of an embossing tool which was produced by the method according to the features of claim 1; the resulting lubrication pockets meet the features of claim 6.

According to PCT / CH99 / 00451, the entry of carbide particles mentioned in patent claim 1 can take place by means of a slurry applied to the tool surface before the thermal treatment, by adhesive strips covered with carbide powder or by carbide particles which are introduced into the melt. The latter is used in the coating of Metal surfaces and similar technologies are frequently used and are considered to be the usual method known per se.

The amount of carbide particle entry is determined empirically and has to compensate for the material losses in the tool surface caused by sublimation evaporation, solidification shrinkage and by the plasma shock wave, i.e. the level of the tool surface - its topography - should be as unchanged as possible after the local melting, but at least reproducible and should only vary in the micro range.

In the central carbide-containing zone, these occur in the form of dispersed particles, but also as alloy components in metal carbides, which form during the local melting and cooling.

The presence of a vertically oriented “end ring” in the workpiece surface is characteristic of a texture produced with an embossing tool according to the invention. This causes a mechanical delimitation, that is, a closed lubrication pocket during the first contact phase with the, for example, shaping tool.This enables a hydrodynamic pressure build-up, which activates the lubricant supply, even if no actual form locking between tool and workpiece has yet taken place , Due to the resulting small contact surfaces, an empty volume is formed above the surface surrounding the lubrication pockets, through which lubricant is led into the contact zones of high stress. This results in a considerably reinforced hydrodynamic lubrication film compared to lubrication based on pure surface wetting high load capacity. If the surface leveling progressively, the "squeezing away" of the lubricant is inevitable, but this can be compensated for by increasing (oversizing) the lubrication pocket volume to such an extent that, for example, the shaping process can be carried out even after a long service life, without any major wear.

Due to the previously usual requirement of an approximate volume constancy in the conventional manufacturing processes for lubrication pockets, modified (smaller) play between the tools is possible with tool surfaces manufactured according to the invention, i.e. tighter dimensional tolerances can also be maintained when texturing surfaces.

The local thermal U-melting of the tool surface mentioned in the patent claim makes such a high one

Energy is introduced into the material (substrate) so that sublimation evaporation takes place and therefore there is almost no material rearrangement controlled carbide powder can be controlled.

Claim 1 describes the melting of a surface covered with carbide particles, which is particularly simple and can be carried out on numerous known systems.

Surprisingly, after a notoriously known, non-cutting removal process on the tool surface - at the location of the heat treatment - a structure arises, which is ideal for stamping and creates ideal lubrication pockets in the workpiece surface.

The lubrication pocket according to the invention is characterized by its relatively voluminous crater-shaped depression and a circumferential edge closure of low height.

Preferred developments of the subject matter of the invention are characterized in dependent claims.

The method-specific use of a pulsed Nd: YAG laser is particularly economical and efficient.

In principle, the focal spot of the laser beam can be set within wide limits by means of notoriously known, cooled focusing lenses, so that crater-shaped depressions of any size and contact angle can be achieved even with the same beam power.

A very simple and economical definition and refinement of the raised parts of the surface, in particular their rounding and smoothing, is carried out by means of a beam processing. Loose or poorly adhering carbide and / or alloy components are removed at the same time.

Mechanical blasting is favorable in terms of system technology, since the corresponding devices are relatively small and can be easily integrated into the manufacturing process. However, it is also conceivable to use other radiation sources and fluids under high pressure, but also brushing and thus grinding off zones of lower hardness. At the same time Verschleissgradient let through the beam processing the workpiece and this Zwi ^¬ rule set the tool and the workpiece in which the carbide layer is reduced to the desired degree.

Depending on the size of the tool and the available technical facilities, chemical ablation can also be advantageous. Of course, the removal ^method chosen must be adapted to the hardness of the substrate, ie the tool surface, so that its mass and surface quality do not change disadvantageously; Multi-stage deduction procedures are also possible.

The original carbide layer - before the thermal melting - can be applied particularly simply in the form of a slick to the desired locations on the surface of the tool; have also retains carbide powder with Kar ^¬ coated tape.

The actual design of the lubrication pockets can be varied within wide limits, which allows adaptation to the tool geometry, the local load and the lubricant used, as well as the resulting abrasion. The shape of the lubrication pockets is not restricted to rotationally symmetrical craters, elongated craters can also be formed if this appears to make tribological sense. In any case, it is important to have edge closures that have a slope that, ^¬ due to the usually relatively high cohesion of lubricants, prevent them from being pulled or pressed out of the crater. These criteria result in the preferred dimensions claimed, which can be individually optimized are. Preferred pitch angles for the edge seals are shown in further dependent claims, with liquid lubricants of medium viscosity being used.

Stamping rolls (= tools) for thin sheet production manufactured in accordance with the process together with the sheet to be rolled (= workpiece) form lubrication pockets during the rolling process, which have a favorable effect on the wear of the stamping roll. In subsequent forming processes, the lubrication pockets embossed in the sheet metal ensure a longer service life for the usually very expensive tool shapes.

If the texture obtained is regularly distributed on the sheet metal surface, it also serves as an ideal primer for later coatings, which is particularly desirable in car body construction.

Exemplary embodiments of the subject matter of the invention are explained in more detail below with the aid of drawings. Show it:

Fig. 1 is a schematic sectional view showing the carbide layer after the thermal processing of the tool surface, the for

Machining used lasers and the beam angle are indicated,

2 shows a characteristic shape of an individual crater, produced by stamping with a tool manufactured according to the method, with registered dimensions, 3 as a function of the radius r, zones which can be ascertained and which have arisen as a result of thermal processing, in a standardized, enlarged representation,

4 shows the zones according to FIG. 2 in a top view of the crater,

5 shows a possible deterministic arrangement of the thermally implanted working points according to FIGS. 1 to 3, in a simplified, partial / enlarged enlargement on a tool surface,

6a shows a real tool surface structure measured interferometrically in the abscissa direction,

6b the embossing of the surface structure Fig. 6a in the workpiece,

7a shows a real tool surface structure measured interferometrically in the ordinate direction and

Fig. 7b the embossing of the surface structure Fig. 6a in the workpiece.

In FIG. 1, 1 denotes a cross section through part of a tool. The surface 1 'of the tool 1 is a substrate for a coating with carbide powder 3 which has been applied with an organic binder. The tool itself consists of a commercially available cold work steel 1.2601 (standard DIN 17350).

Above this is a commercially available pulse laser system (Nd: YAG laser) 100 with a focusing lens 10; the emerging laser beam is designated 5 and dis- - lo ¬

carbide 3 is gated in an implantation zone 6. Due to the high point energy, part of the steel 1 sublimes and alloys or is remelted in an edge zone 7. A crater 2 remains, which is filled with dispersed and alloyed carbides 4. The transition between the edge zone 7 and the substrate of the tool 1 is designated 8 and relates to a solid phase in which only a structural change has taken place.

If such a type of prepared tool surface 1 'is then subjected to a removal process, for example by sandblasting, the hard, carbide-containing layers remain almost unchanged, while the softer remelting zones are removed and form annular recesses. By embossing such a topography, lubrication pockets can be formed.

The simplified form of an ideal lubrication pocket produced in this way can be seen in FIG. 2, with the annular edge termination being designated by 9 here. A main level HE is also entered, which is identical to the tool surface in the area of the crater.

Furthermore, the outer ring diameter is shown with d _a , the inner ring diameter d _x, the maximum depression of the crater with respect to the main plane HE with t [ _< and the elevation opposite it with h _s . The total dimension is R _t ; the tangential angle characterizing the flank slope in crater 2 is β and is usually 15 ° to 45 °. An examination of the melting carried out according to FIG. 1 shows the layer structure typical of FIG. 3 after mechanical removal:

From the center of the crater 2 in the radial direction r, see FIG. 4, one encounters the first layer ZI, the dispersed / alloyed layer which was created by the thermally performed liquid phase processing. This is followed by a somewhat thinner layer, a remelting zone Z2, which has also been remelted but is carbide-free. The next layer is a conversion zone Z3, which phase in the hard ^¬ is formed by the action of heat. The substrate, the tool steel 1, is located on the outside.

The relative hardness is denoted by H in the ordinate.

A tool surface created according to the invention with a uniform grid is shown in FIG. 5. The distances between the individual craters 2 are varied depending on the local load, but for practical reasons this is done line by line (in columns).

The following characteristic data, for example, was obtained on the implemented tool by an interferometric surface measurement:

Max. Diameter d _{a of} the edge seal 9 = 300 μm inner diameter d * _. at the edge 9 = 230 μm tangential angle (flank angle) ß = 10 ° maximum depression t * .- = 6 μm maximum elevation h _s = 4μm full depth of lubricant R _t = 10 μm The following laser parameters were used:

Pulse energy (spot energy) = 1 joule pulse frequency = 10 Hz pulse power = 400 W power density = 1.4 x 10 ⁵ W / cm ²

A tool surface with the above data has an interferometric profile in the abscissa direction according to FIG. 6a.

Glass blasting with commercially available, spherical glass beads with a diameter of 25 - 50 μm under a pressure of 4.0 bar has proven particularly effective for the removal process.

Also suitable for this is an etchant called "V3A Stain", which consists of 100 parts of distilled water, 100 parts of hydrochloric acid (37%), 10 parts of nitric acid (65%) and 0.3 part of commercially available "Stain"

(Dr. Vogels Sparbeize, No. 1830/170014, Wirtz-Buehler GmbH, D-40599 Düsseldorf).

The embossing produced in an aluminum workpiece (99.5% Al) with a pressure of 25 bar shows the profile inverse to FIG. 6a according to FIG. 6b.

Analogous are the recordings in the ordinate direction Fig. 7a and Fig. 7b, which in turn show the good embossing behavior and recommend the system not only because of its tribological advantages, but also because of the ideal texturing of the workpiece for subsequent coatings (body panels, etc.). The considerations carried out with the aid of a tool and a workpiece to be machined can of course also be applied to sliding surfaces in which, in one or - with shorter sliding paths - the lubrication pocket according to the invention is alternately provided in both sliding surfaces at locations of high stress.

For economic reasons, the process is based on commercially available carbides; however, other materials can also be implanted or alloyed according to the invention.

Claims

Patent claims

1.Procedure for producing a stamping tool for the texturing of workpieces by a targeted partial change in the physical / technical properties, with deterministic microstructures of the workpiece to be provided with a texture being adapted to the intended tribological conditions by local thermal melting on the tool surface Grids, m defined geometrical distances between the grids, are attached, carbide particles being introduced into the microstructures during the melting, characterized in that a central, carbide-containing zone (ZI) is higher due to the thermal melting of the tool surface (1 ') Hardness is produced such that a remelting zone (Z2) which is jacket-shaped or coaxial to the central region (ZI) and has a lower hardness than the central region and another outer transformation zone (Z3) surrounding the remelting zone (Z2) are forms which have a relation to the U - schschmelzzone (Z2) and the WerkΣeugoberflache (l ¹⁾ has a lower hardness, the power fed into thermal energy mix is adjusted such that the To ^¬ pographie of the tool in the micro range remains at least approximately unchanged and that after the tool has cooled down, it is subjected to a uniform removal process, which the three zones (ZI to Z3) correspond to in their hard profile High and the transitions between the zones (ZI to Z3) and the tool surface (1 ') smoothes.

2. The method according to claim 1, characterized in that a pulsed Nd: YAG laser is used for the thermal melting of the tool surface.

3. The method according to claim 1 or 2, characterized in that the zones (ZI to Z3) are set by a beam processing.

4. The method according to claim 3, characterized in that the blasting is carried out mechanically, in particular by sandblasting, steel shot peening or shot peening.

5. The method according to claim 1 or 2, characterized in that the zones (ZI to Z3) are set by a chemical treatment, in particular by etching.

6. Lubrication pockets in workpiece surfaces which are produced by embossing with a tool produced according to claims 1 to 5, characterized in that these one from the workpiece surface

Have (1 ') projecting, arc-shaped circumferential edge distance circuit (9) that is viewed inside the edge termination (9) has a crater-shaped depression (2) in front ^¬, and that the lubrication pockets in one of the local loading of the workpiece (1) adapted grid at defined geometric distances between the individual grids, on the workpiece top area (l ¹ ) and / or are distributed according to a predetermined texture.

7. Lubrication pockets according to claim 6, characterized in that they are rounded and smoothed and that a tangential angle (β) is provided in the range between 5 ° and 15 ° between the tool surface (HE) and the inside of the edge closure (9) ,

8. Lubrication pockets according to claim 6 or 7, characterized in that the outer diameter (d _{a) of} the

Edge termination (9) <500 μm and> 150 μm is that the maximum depression (t _κ ) is> 2 μm and <20 μm and that the elevation (h _s ) of the edge termination (9) relative to the workpiece surface (HE) <5 μm and> l μm.

9. Lubrication pockets according to claim 8, characterized in that the tangential angle (β) is selected according to the lubricant to be received in the recess (2) or according to its viscosity at working temperature.

10. Application of the method according to claim 1, for the generation ^¬ supply forming lubrication pockets of embossing rolls for finish rolling and texturing of sheet metal.