Method for manufacturing an extrusion die

Abstract

Method for producing an extrusion die having a functional surface for metal extrusion material, comprising the following steps: providing a die support body, depositing a weldable substance containing cobalt and/or nickel onto a subsection of the die support body by means of an effective bonding application process to produce an inseparable deposition layer, machining the deposition layer in a chipping and/or material removal process to form the functional surface of the extrusion die, and carrying out a CVD coating process with a reaction gas at least on the functional surface.

Claims

1. Method for producing metal extrusion die having a functional surface for metal extrusion material, comprising the following steps: providing (10) a die support body (50) comprising hot work steel, depositing (14) a weldable substance containing cobalt and/or nickel onto a subsection of the die support body by means of an effective bonding application process to produce an inseparable deposition layer (52), machining (20) the deposition layer in a chipping and/or material removal process to form the functional surface (54) of the extrusion die, and carrying out a CVD coating process (22) with a reaction gas at least on the functional surface.

2. Method according to claim 1, wherein the effective bonding application process has the form of single- or multilayer build-up welding (14).

3. Method according to claim 1, wherein the die support body with the applied deposition layer undergoes heat treatment (16).

4. Method according to claim 3, wherein the heat treatment process reduces internal stresses before the machining operation for chipping and/or material removal.

5. Method according to claim 1, wherein the machining operation for chipping and/or material removal is carried out by milling or eroding in a spark erosion process (20).

6. Method according to claim 1, wherein a preliminary forming and/or preliminary chipping operation (12) is carried out on the die support body in the area of the subsection, before the deposition layer is created.

7. Method according to claim 1, wherein the die support body undergoes a preheating step, to a temperature between 400 C. and 700 C. and/or to an annealing temperature of the hot work steel before the deposition layer is created.

8. Method according to claim 1, wherein the die support body is preheated before the cobalt-containing material is applied and/or the die support body furnished with the deposition layer undergoes a stress relief heat treatment.

9. Method according to claim 1, wherein the welding material is a non-ferrous alloy having a cobalt base and/or a nickel base.

10. Method according to claim 9, wherein the cobalt base is a cobalt-chromium base.

11. Method according to claim 1, further comprising a heat treatment (24) of the die support body after the CVD coating process at an annealing temperature.

12. Method according to claim 1, wherein the CVD coating process is carried out as a medium-temperature process at a coating temperature in a range between 700 C. and 950 C.

13. Method according to claim 1, wherein the CVD coating process is carried out at a coating temperature above 1000 C.

14. Method according to claim 1, wherein the extrusion die is produced as a tool comprising two parts, having a mandrel part and a die plate and the inseparable application layer is applied to at least sections of both the mandrel part and the die plate.

15. Method according to claim 1, wherein the functional surface is created as the delimiting wall of the extrusion die defining a guide and/or flow channel for the ductile extrusion substance.

16. Method according to claim 1, wherein the CVD coating process is carried out as a medium-temperature process at a coating temperature in a range between 700 C. and 950 C., followed by a high-temperature process at a coating temperature above 950 C., in order to create a covering layer on top of a CVD coating that is produced by the medium-temperature process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Additional advantages, features and particularities of the invention will be evident from the following description of preferred embodiments and with reference to the drawing, in which:

(2) FIG. 1: is a schematic flowchart showing the process steps of the method for producing an extrusion die according to a preferred embodiment of the invention;

(3) FIG. 2: is a perspective view of an extrusion die after the process of depositing a cobalt-containing substance according to the method of FIG. 1;

(4) FIG. 3: is a perspective view of the extrusion die of FIG. 2 after the machining removal process of the cobalt-containing substance deposited according to FIG. 2;

(5) FIG. 4: is a schematic side view of a test device for conducting a wear test for extrusion dies produced according to the present invention.

DETAILED DESCRIPTION

(6) In the following, the method according to a first preferred embodiment of the invention for producing an extrusion die having a functional surface for metal extrusion material will be described with reference to FIGS. 1 to 3; FIG. 1 indicates the sequence of process steps 10 to 24.

(7) According to the embodiment described, in step 10 a hot work steel is provided, and in step 12 a tool form is produced in a material removal process; for this purpose, the embodiment of FIGS. 2 and 3 shows a mandrel tool that is constructed in cooperation with a matrix tool (not shown) for extruding an aluminium profile. The hot work steel is type 1.2344 steel; a maximum diameter of the tool shown in various stages of production in FIGS. 2 and 3 is approximately 45 mm.

(8) The material removal machining (step 12) is followed by multilayer build-up welding with a cobalt-containing material of type Stellite 6, available commercially from the company Kennametal, for example.

(9) This multilayer build-up welding is typically carried out at a temperature of 650 C., wherein the build-up welding (not shown in the workflow diagram in FIG. 1) may be preceded by a heat treatment step, at a temperature of 550 C.-700 C. for an hour, for example.

(10) FIG. 2 shows the result after depositing of the cobalt-containing material, designated with reference sign 52, and joined inseparably to the underlying tool body (die support body) 50 made from hot work steel by build-up welding.

(11) In the subsequent step 16, stress relief heat treatment of the configuration shown in FIG. 2 at 550 C.-700 C. is carried out over a period of about two hours. This is followed by a further heat treatment step 18, for annealing (at a typical annealing temperature) of about 580 C. to 600 C. for example. This heat treatment step 18 is advantageous, but is not essential for obtaining the advantages of the invention.

(12) These treatment steps are followed by the chipping or material removal processing of deposition layer 52 in functional surfaces 54, as shown in FIG. 3. In this embodiment according to the invention, this process has the form of spark erosion with the objective of forming the functional surface according to desired contour or actual structure (in the embodiment shown, for producing intermediate ribs in an extrusion product). The result of this material removal step is shown in FIG. 3.

(13) In the context of the embodiment according to the invention, this is followed by a CVD coating step, process step 22, which is applied at least to area 54 where the material was applied and subsequently removed in a chipping or material removal process, in practical terms this being the entire die. In otherwise known manner, as disclosed in the referenced prior art of EP 1 011 885 B1 for example, Al.sub.2O.sub.3 for example is deposited from the gas phase at a typical high temperature CVD coating temperature of 1050 C., and thus creates a coating on the functional surface or the die. Subsequent annealing (step 24) to a typical annealing temperature in the range of about 500 C.-600 C. completes the production process and delivers the finished extrusion die.

(14) In practice, it has proven favourably that compared with tools according to EP 1 011 885 B1 that have undergone CVD coating and are otherwise of identical construction, wear resistance results may be improved by 30% to 50%, which is reflected in a correspondingly longer operating and service life of the tool.

(15) In order to obtain such comparative data, it has proven preferable to use a device such as is illustrated diagrammatically in FIG. 4, which serves to generate wear data, particularly of extrusion dies coated in a CVD process and enables assessments of wear resistance properties to be made for comparison purposes. Specifically for this purpose, as shown schematically in the left part of FIG. 4, a sample 60 (produced from a hot work steel and treated with the subsequent process steps 12 to 24 according to the invention) is fixed in non-rotating manner and brought into contact with a friction partner 62 made from an aluminium alloy and secured in a carrier unit 64, which is rotated under pressure by a rotary drive unit 66 and brought into contact with sample 60 to produce the friction. In the present case, the interaction takes place at rotating speeds between 40 and 100 rpm and under a contact pressure of about 2 to 8 bar; in this configuration, care must be taken to ensure that the temperature of friction partner 62 (which has the form of an interior cone corresponding to the cone-shaped contour of sample 60) does not exceed an operating temperature of about 300 C., which might result in the friction partner melting or otherwise becoming unusable.

(16) Now, if test readings are taken after various periods, and a point in time is determined at which the tool (sample 60) reaches the wear limit (because pieces of the tool or support body become detached, for example), a value becomes available that can be used under comparable test conditions to evaluate the advantages of the present invention in relative measurement readings with respect to the extrusion dies coated by species-related CVD coating methods.

(17) Independent protection is claimed within the scope of the present invention for the method of carrying out such a comparative wear test and an arrangement of the kind illustrated in FIG. 4.