Method For Producing Improved Cold-Forming Tools For High-Strength And Super-High-Strength Steels, And Cold-Forming Tool

Abstract

The invention relates to a method for producing a cold forming tool, particularly for cold forming super-high-strength steels, wherein the cold forming tool is the upper and/or lower tool of a forming tool set, wherein the cold forming tool is made of a metal material and has a forming surface that is designed so that a formed metal sheet has the desired final contour of the component, characterized in that a hard material layer is deposited on the forming surface of the forming tool by means of physical gas-phase deposition, wherein the hard material layer consists of a titanium nitride adhesive layer and alternating layers of aluminum titanium nitride and aluminum chromium nitride deposited thereon, wherein a titanium nitride top layer or alternatively a titanium carbon nitride top layer is deposited as the final layer as the outermost outer surface oriented toward a workpiece that is to be formed.

Claims

1. A method for producing a cold forming tool, particularly for cold forming super-high-strength steels, wherein the cold forming tool is the upper and/or lower tool of a forming tool set, wherein the cold forming tool is made of a metal material (1) and has a forming surface (6) that is designed so that a formed metal sheet has the desired final contour of the component, characterized in that a hard material layer is deposited on the forming surface of the forming tool (6) by means of physical gas-phase deposition, wherein the hard material layer consists of a titanium nitride adhesive layer (2) and alternating layers of aluminum titanium nitride (3) and aluminum chromium nitride (4) deposited thereon, wherein a titanium nitride top layer (5) or titanium carbon nitride top layer is deposited as the final layer as the outermost outer surface oriented toward a workpiece that is to be formed.

2. The method according to claim 1, characterized in that as the first layer of the alternating deposited layers, first an aluminum titanium nitride layer (3) is deposited onto the titanium nitride adhesive layer (2).

3. The method according to one of the preceding claims, characterized in that five to twenty alternating layers are deposited onto the titanium nitride adhesive layer (2) before a final titanium nitride top layer (5) or titanium carbon nitride top layer is deposited.

4. The method according to one of the preceding claims, characterized in that the titanium nitride adhesive layer (2) has a thickness of 0.2 micrometers to 0.9 micrometers, preferably from 0.4 micrometers to 0.7 micrometers.

5. The method according to one of the preceding claims, characterized in that the aluminum titanium nitride layers (3) have a thickness of 0.1 to 0.5 micrometers, preferably from 0.2 to 0.3 micrometers.

6. The method according to one of the preceding claims, characterized in that the aluminum chromium nitride layers (4) have a thickness of 0.1 to 0.5 micrometers, preferably from 0.2 to 0.3 micrometers.

7. The method according to one of the preceding claims, characterized in that the final titanium nitride top layer (5) or a titanium carbon nitride top layer has a thickness of 0.2 to 0.5 micrometers, preferably from 0.2 to 0.3 micrometers.

8. The method according to one of the preceding claims, characterized in that the chemical composition of the layers is as follows: adhesive layer and top layer Ti.sub.2N.sub.1-z, where z=0.4 to 0.6, as an alternative top layer Ti.sub.xC.sub.yN.sub.1-(x+y), where x=44 to 50, y=20 to 23, and the rest is nitrogen, Al.sub.aCr.sub.bN.sub.1-(a+b), where a=30 to 40, b=10 to 20, and the rest is nitrogen, and Al.sub.cTi.sub.dN.sub.1-(c+d), where c=8 to 14, d=30 to 40, and the rest is nitrogen.

9. A cold forming tool with a hard material coating that is particularly deposited using a method according to one of the preceding claims.

10. The cold forming tool according to claim 9, characterized in that the hard material layer is composed of alternating aluminum titanium nitride layers (3) and aluminum chromium nitride layers (4), with a final titanium nitride top layer (5) or a titanium carbon nitride top layer.

11. The cold forming tool according to claim 9 or 10, characterized in that there is a titanium nitride adhesive layer (2) as a first layer on the tool, followed by the aluminum titanium nitride layers (3) and aluminum chromium nitride layers (4) and the final titanium nitride top layer (5) or a titanium carbon nitride top layer.

Description

[0051] The invention will be explained by way of example based on the drawings. In the drawings:

[0052] FIG. 1 shows a sample layer structure with a titanium nitride adhesive layer 2 on a substrate 1 containing 15 layers each of alternating aluminum titanium nitride layers 3 and aluminum chromium nitride layers 4 and a titanium nitride top layer 5 in a first embodiment;

[0053] FIG. 2 shows an abstract calotte grinding, i.e. a top view in which the individual layers are visible;

[0054] FIG. 3 shows a metallographic comparison of sample layers by means of a calotte grinding, which were deposited onto a specimen using two different systems;

[0055] FIG. 1 shows a sample layer construction with a titanium nitride adhesive layer 2 on a substrate 1 containing 15 layers each of alternating aluminum titanium nitride layers 3 and aluminum chromium nitride layers 4 and a titanium nitride top layer 5 in a first embodiment, wherein the titanium nitride adhesive layer 2 is followed directly by an aluminum titanium nitride layer 3.

[0056] FIG. 2 shows an abstract calotte grinding. In the calotte grinding, a ball grinds a calotte (spherical cap) into the surface. If the multilayer structure is ground through to the substrate, then the substrate is visible in the innermost circle. The sample layer structures are visible. First, the substrate 1 has a titanium nitride adhesive layer 2 applied to it, which improves the adhesion between the subsequent layers and the substrate 1. The titanium nitride adhesive layer 2 is advantageously followed directly by an aluminum titanium nitride layer 3. Then come alternating aluminum titanium nitride layers 3 and aluminum chromium nitride layers 4; these layers are deposited 15 times each and finally, a titanium nitride top layer 5 is deposited.

[0057] FIG. 3 shows the metallographic calotte grindings of two sample layer structures, which have been deposited onto a cylindrical test specimen composed of the corresponding steel material. The layer structure is the same as in FIG. 2. The coating system on the left was applied using an alpha 400P coating system produced by the applicant and the coating system on the right was applied using an alpha 900P coating system produced by the applicant.

[0058] The figures do not depict an exemplary use of a titanium carbon nitride top layer instead of a titanium nitride top layer.

[0059] The invention will be explained below based on a specific example:

[0060] The chemical composition of the layers in the example consists of approx. 45 at % titanium and approx. 55 at % nitrogen in the titanium nitride, approx. 35 at % aluminum, approx. 15 at % chromium, and approx. 50 at % nitrogen in the aluminum chromium nitride, whereas approx. 11 at % aluminum, 35 at % titanium, and 45 at % nitrogen are contained in the aluminum titanium nitride.

[0061] A coating for cold forming tools is produced in the form of a multilayer hard material coating, which, starting from the substrate 1 (tool base material, metal material) and using PVD-ARC technology, is deposited as a sequence of a TiN adhesive layer 2, an AlTiN—AlCrN multilayer system (15 individual layers of each), and a TiN top layer 5 and is able to improve the service life of the cold forming tool. The optimization of the tool service life is achieved in that the PVD arc-based AlTiN—AlCrN multilayer system, because of its mechanical and thermal properties, produces wear-minimizing and local thermal effects with respect to the extreme contact stresses in the normal direction during forming. The additional thin TiN top layer 5 benefits the break-in behavior of the layer and reduces the friction in comparison to the underlying harder AlTiN—AlCrN multilayer structure.

[0062] The 0.5 μm-thick TiN adhesive layer 2 is deposited with an increasing substrate temperature ramp from 400 to 450° C., a decreasing substrate bias voltage of 600-220 V, and a vaporizer current of 60 A with the aid of the reaction gas N.sub.2 at 1.2*10.sup.−2 mbar. The composition of the TiN adhesive layer 2 is as follows, within the measurement uncertainty: 45 at % Ti and 55 at % Al.

[0063] The 0.2 to 0.3 μm-thick AlTiN layer 3 of the AlTiN—AlCrN multilayer system starts with an AlTiN layer with a high Ti concentration, which is deposited at a substrate temperature of 450° C. and a substrate bias voltage of 200 V, with a simultaneous deposition of AlTi cathodes at 55 A and Ti cathodes at 60 A with the aid of the reaction gas N.sub.2 at 2*10.sup.−2 mbar. The composition of the AlTiN individual layer is as follows, within the measurement uncertainty: 11 at % Al, 35 at % Ti, and 54 at % N.

[0064] The overlying 0.2 to 0.3 μm-thick AlCrN layer 4 of the AlTiN—AlCrN multilayer system is deposited at a substrate temperature of 450° C., a substrate bias voltage of 80 V, and an AlCr cathode current of 105 A with the aid of the reaction gas N.sub.2 at 2*10.sup.−2 mbar. The composition of the AlCrN individual layer 4 is as follows, within the measurement uncertainty: 35 at % Al, 15 at % Ti, and 50 at % N.

[0065] The individual layers of AITiN 3 and AlCrN 4 are applied 15 times one after another and produce the above-mentioned AlTiN—AlCrN multilayer system.

[0066] The 0.2 μm-thick TiN top layer 5 is deposited with an increasing substrate temperature of 450° C., a substrate bias voltage of 80 V, and a Ti cathode current of 60 A with the aid of the reaction gas N.sub.2 at 2*10.sup.−2 mbar. The composition of the TiN top layer 5 is as follows, within the measurement uncertainty: 45 at % Ti and 55 at % Al.

[0067] The layer thickness of the overall layer composite in the example is 5-7 μm. The forming surface 6 is the tool surface that is oriented toward the workpiece.

[0068] The layer properties relating to tool service life were determined on a stamping tool since stamping tests and the parameters associated with them are better defined than forming tests. All of the stamping tests were performed on an eccentric press (four pillar eccentric press, 15,000 kg). A respective stamping tool was coated that was made of cold work steel (with 0.7 wt % carbon, 5 wt % chromium, 2.3 wt % Mo, 0.5 wt % vanadium, and 0.5 wt % manganese, 0.2 wt % Si, with a hardness of 60 to 61 HRc). It was used to stamp a 1.5 mm-thick sheet composed of super-high-strength steel with a tensile strength of 1400 MPa without additional lubrication.

[0069] Stamping Parameters:

[0070] Stroke rate: 160-170 strokes/minute

[0071] Feed rate (with 1.5 mm-thick steel sheet): 8 m/min

[0072] Pressure: 72,500-74,000 N

[0073] The service life was measured in comparison to an aluminum titanium nitride-based reference layer and tool failure or the burr height on the stamped workpiece/component was used as an abort criterion. In other words, if tool failure occurs, then the wear in the edge regions of the tool is high enough that a critical burr height is reached on the workpiece/steel sheet. In this case, the aluminum titanium nitride-based reference layer reached a critical burr height at 65,000 strokes and the tool that is coated according to the invention reached the critical burr height only after 365,000 strokes. This corresponds to extending the service life by a factor of 5.

[0074] Instead of the TiN top layer, it is also possible to use a TiCN top layer. The 0.2 μm-thick TiCN top layer can be deposited with an increasing substrate temperature of 450° C., a falling substrate bias voltage from 150 V to 50 V, and a falling Ti cathode current from 60 A to 42 A with the aid of the reaction gases N.sub.2 and CH.sub.4 at 1.2*10.sup.−2 mbar. The composition of the TiCN top layer is as follows, within the measurement uncertainty: 20 to 23 at % C, 30-33 atomic percent N.sub.2, and 44-50 at % Ti.

[0075] With the invention, it has been advantageously possible to significantly increase the service life of a tool with the multilayer structure according to the invention.

REFERENCE NUMERAL LIST

[0076] 1 metal material, substrate (tool to be coated) [0077] 2 titanium nitride adhesive layer (TiN adhesive layer) [0078] 3 aluminum titanium nitride layers (AITiN layer) [0079] 4 aluminum chromium nitride layers (AlCrN layer) [0080] 5 titanium nitride top layer (TiN top layer) [0081] 6 forming surface