DEVICE AND METHOD FOR THE PLASTIC FORMING OF A WORKPIECE MADE OF METAL OR A METAL ALLOY BY MEANS OF ECAP

Abstract

A device for the plastic forming of a workpiece made of metal or a metal alloy by ECAP is described. The device comprises more than two channels, wherein an inlet channel and an outlet channel are provided, wherein these channels indirectly connect to one another and are arranged approximately perpendicularly to one another. Furthermore, a method for the plastic forming of a workpiece made of metal or a metal alloy ECAP is described. The workpiece is pressed once or multiple limes through a device having more than two channels, wherein the workpiece is plastically formed by a single or multiple pressing through an inlet channel and an outlet channel which indirectly connects to the inlet channel and is arranged approximately perpendicularly thereto.

Description

The invention relates to a device for the plastic forming of a workpiece made of metal or a metal alloy by means of ECAP, which device comprises more than two channels.

Furthermore, the invention relates to a method for the plastic forming of a workpiece made of metal or a metal alloy by means of ECAP, wherein the workpiece is pressed once or multiple times through a device having more than two channels.

Devices for the plastic forming of a workpiece, made in particular of a metal alloy, by means of equal channel angular pressing (ECAP) are known from the prior art. Known devices typically comprise two channels, wherein what is referred to as a forming bend is embodied between the channels. Devices or methods of this type are generally suitable for the forming of a workpiece made of a metal alloy, such as a magnesium alloy, wherein good mechanical characteristic values are normally achieved.

Certain magnesium alloys are used, for example, to form bioresorbable stents or osteosynthesis components. A magnesium alloy must thereby satisfy multiple requirements to be able to be used as material for medical implants of this type. Aside from a high biocompatibility and a low decomposition rate, or a decomposition rate adapted to an application, an alloy of this type must also exhibit very good mechanical properties, such as high strength, for example. Known ECAP devices are suitable for the forming of a workpiece made of a magnesium alloy for applications of this type, but even better mechanical properties are desired.

ECAP devices and methods for the plastic forming of a workpiece made of a metal or a metal alloy are known, for example, from the article Principles of equal-channel angular pressing as a processing tool for grain refinement (R. Z. Valiev, T. O. Langedon, Progr. Mat. Sci. 51 (2006) 881).

RU 2 181 314 C2 discloses a device for the plastic forming of a workpiece made of metal. For the production of a workpiece having high strength, the device comprises three channels, Wherein an inlet channel and an outlet channel are arranged parallel to one another. However, even with this device, it does not appear possible to produce a workpiece with the desired mechanical properties.

The object of the invention is to specify a device of the type named at the outset, with which device in particular a workpiece made of a magnesium alloy can be formed in an effective and efficient manner.

Another object is to specify a method of the type named at the outset, with which method a workpiece, made in particular of a magnesium alloy, can be formed with high strength being achieved.

The object is attained according to the invention in that, with a device of the type named at the outset, an inlet channel and an outlet channel are provided, wherein these channels indirectly connect to one another and are arranged approximately perpendicularly to one another.

An advantage obtained by the invention can in particular be seen in that a workpiece made of metal or a metal alloy, in particular a magnesium alloy, can be produced with markedly improved mechanical properties by means of the device. For this purpose, it is provided that extended longitudinal axes of the inlet channel and of the outlet channel intersect approximately at a right angle. In particular, a workpiece having high strength can be produced, wherein the workpiece is preferably pressed through the device multiple times. A forming of the workpiece thus comprises a repeated pressing of the workpiece through the device. Compared to forming devices known from the prior art, a workpiece having a higher strength can be produced with the device according to the invention, which workpiece can, after further processing, be used as a medical implant, for example. In particular, a quantity of the pressing operations through the device to produce a predefined strength is reduced. In addition, a maximum attainable strength of the workpiece is also higher than with plastic forming using an ECAP device known from the prior art.

It is advantageous if at least one additional channel is provided, wherein the inlet channel and the outlet channel are connected to one another by the at least one additional channel. The device is thus embodied for a double forming in each pressing operation. The workpiece is, for the forming of the same, preferably pressed through the device multiple times. Multiple channels can also be arranged between the inlet channel and the outlet channel. It is thereby always provided that the inlet channel is aligned approximately perpendicularly to the outlet channel.

It is advantageous if two channels are each arranged relative to one another such that they form a forming bend. Angles of consecutive forming bends can be of an equal or different size. Thus, for example, an angle of a forming bend between the inlet channel and an additional channel connecting thereto can be approximately 75° to 135°, in particular approximately 90° to 120°, particularly preferably 90°. An angle of a forming bend between the additional channel and the outlet channel connecting thereto can be equal to the angle of the forming bend between the inlet channel and the additional channel connecting thereto, or can have an angle of a different size. This angle can, for example, be approximately 105° to 135°, in particular approximately 115° to 125°, particularly preferably 120°. it has been shown that such an embodiment of the device is particularly beneficial for producing a workpiece made of a magnesium alloy with particularly high strength. Furthermore, a workpiece having a very fine grain can be produced. If multiple channels are arranged between the inlet channel and the outlet channel, an angle of a forming bend between two consecutive channels can in each case be of an equal or different size.

Expediently, a heating apparatus is provided. The heating apparatus is embodied for heating the device, and thus the workpiece, to a predetermined temperature, wherein the heating apparatus is arranged on the device. In particular, with the heating apparatus it is possible to lower a temperature each time a workpiece, made in particular of a magnesium alloy, is pressed through the device. Thus, for example, the temperature can be set to approximately 270° C. to 380° C., in particular to approximately 300° C. to 350° C., for a first pressing-through of the workpiece, whereas the temperature can be set to approximately 190° C. to 270° C., in particular 220° C. to 240° C., for a last pressing-through. It can also be provided that the heating apparatus lowers the temperature to room temperature by the last pressing-through. Between a first and a last pressing of the workpiece through the device, the workpiece can be pressed through the device as often as desired, wherein a temperature of the heating apparatus is steadily decreased. It generally holds that a device according to the invention requires a lower temperature than known devices, whereby a workpiece can be plastically formed in a more effective manner with the device according to the invention.

The other object is attained if, with a method of the type named at the outset, the workpiece is plastically formed by being pressed once or multiple times through an inlet channel and an outlet channel that indirectly connects to the inlet channel and is arranged approximately perpendicularly thereto.

One advantage thus attained can in particular be seen in that a workpiece having high strength is produced as a result. In addition, a tendency of cracks to form in the workpiece is inhibited by the pressing through multiple channels. The workpiece is plastically formed by means of ECAP, or equal channel angular pressing. One or more additional channels are arranged between the inlet channel and the outlet channel, wherein a forming bend is embodied between each two channels. As a result, the workpiece is formed at least twice each time it is pressed through. The outlet channel is always arranged approximately perpendicularly to the inlet channel.

It is advantageous if, before each introduction into the inlet channel, the workpiece is rotated about a longitudinal axis of the same. The workpiece is thus formed into a workpiece that has a uniform strength and is provided with a uniform fineness of grain. In addition, an attainable strength of the workpiece is increased.

It is beneficial if the workpiece is formed at least twice each time it is pressed through the device. For this purpose, the workpiece is pressed through at least three channels, wherein the inlet channel and the outlet channel are always arranged perpendicularly to one another. In particular, the workpiece is pressed through three channels.

It is advantageous if the workpiece is pressed through multiple channels, wherein a forming bend is provided between each two channels. The forming bends can have angles of an equal or different size. For example, two forming bends can be provided between three channels, wherein a first forming bend can have an angle of approximately 75° to 135°, in particular approximately 90° to 120°, particularly preferably approximately 90°, and a second forming bend can have an angle of an equal size or, for example, an angle of approximately 105° to 135°, in particular approximately 115° to 125°, particularly preferably approximately 120°. In a first forming of the workpiece, a tendency of cracks to form in the workpiece is inhibited by the high hydrostatic pressure as a result of the forming bend, in particular of approximately 90°. If multiple channels are arranged between the inlet channel and the outlet channel, an angle of a forming bend between two consecutive channels can in each case be of an equal or different size.

It is beneficial if the workpiece is heated, wherein a temperature is lowered for each pressing of the workpiece through the device, in order to efficiently form the workpiece. In particular, the workpiece is heated with a heating apparatus. Thus, for a first pressing-through of a workpiece, made in particular of a magnesium alloy, a temperature is set to approximately 270° C. to 380° C., in particular to approximately 300° C. to 350° C., whereas the temperature is set to approximately 190° C. to 270° C., in particular 220° C. to 240° C., for a last pressing-through. The temperature can also be lowered to room temperature by the last pressing-through. Between a first and a last pressing of the workpiece through the device, the workpiece is pressed through the device as often as desired, wherein a temperature of the heating apparatus decreases in the direction of pressing.

Additional features, advantages and effects of the invention follow from the exemplary embodiment described below. In the drawings which are thereby referenced:

FIG. 1 shows a device according to the invention;

FIG. 2 shows experimental results of a tensile test;

FIG. 3 shows experimental results of a compression test;

FIG. 4 shows additional experimental results of a tensile test;

FIG. 5 shows additional experimental results of a compression test;

FIG. 6 shows experimental results of high strengths.

FIG. 1 shows a device 1 according to the invention for the plastic forming of a workpiece made of metal or a metal alloy by means of ECAP. The device 1 comprises an inlet channel 2 and an outlet channel 3, wherein the inlet channel 2 and the outlet channel 3 are connected by an additional channel 4. The inlet channel 2 and the outlet channel 3, or the longitudinal axes thereof, are arranged approximately perpendicularly to one another. Between the inlet channel 2 and the additional channel 4, a forming bend with an angle a of approximately 90° is provided, Furthermore, between the additional channel 4 and the outlet channel 3, another forming bend is embodied, wherein this forming bend has an angle β of approximately 120°. The device 1 is thus embodied as a double ECAP device.

In general, it can also be beneficial if multiple additional channels 4 are provided between the inlet channel 2 and the outlet channel 3, wherein a forming bend is embodied between each two channels 2, 3, 4.

In FIGS. 2 and 3, experimental results of a tensile test and a compression test are shown. Data A for a workpiece in a starting condition, data B for a workpiece formed using a known ECAP device, and data C for a workpiece formed using the device 1 according to the invention are thereby compared with one another. The workpiece is made of a magnesium alloy and, for data B and data C, is in each case pressed multiple times through a known device and a device 1 according to the invention, respectively. Both the tensile test according to FIG. 2 and also the compression test according to FIG. 3 show that the workpiece produced using the device 1 according to the invention exhibits a significantly higher strength. The workpiece is heated during both the pressing through the known device and also through the device 1 according to the invention, wherein a temperature is lowered from 350° C. to 290° C. between a first pressing-through of the workpiece and a last pressing-through of the same.

Analogous data A, B and C are shown in FIGS. 4 and 5, wherein a workpiece made of a magnesium alloy is once again formed and measured. However, the magnesium alloy differs in its composition from the magnesium alloy according to FIGS. 2 and 3. It is thereby also evident that the workpiece plastically formed using the device 1 according to the invention exhibits a significantly higher strength than a workpiece produced using an ECAP device having two channels. In this case, a temperature is lowered from 300° C. to 220° C., wherein the workpiece is once again pressed multiple times through a known device and a device 1 according to the invention. Data A once again originates from the untreated workpiece.

FIG. 6 shows experimental results of a workpiece 1 made of a magnesium alloy, which workpiece has been produced using a device 1 according to the invention. Extremely high strength levels are achieved. A tensile strength of the workpiece is approximately 468 MPa and an elastic limit of the same is approximately 413 MPa.

With the device 1 according to the invention and the method according to the invention, a workpiece made of a metal or a metal alloy can be produced in an efficient manner, which workpiece exhibits high strength, adequate ductility, high hardness, a uniform fineness of grain, and a low tendency to form cracks. A workpiece of this type is therefore suitable, for example, for the production of a stent or other medical implants.

Claims

1. A device for the plastic forming of a workpiece made of metal or a metal alloy by means of ECAP, which device comprises more than two channels, characterized in that an inlet channel and an outlet channel are provided, wherein these channels indirectly connect to one another and are arranged approximately perpendicularly to one another.

2. The device according to claim 1, characterized in that at least one additional channel is provided, wherein the inlet channel and the outlet channel are connected to one another by the at least one additional channel.

3. The device according to claim 1, characterized in that each two channels are arranged relative to one another such that they form a forming bend.

4. The device according to claim 1, characterized in that a heating apparatus is provided.

5. A method for the plastic forming of a workpiece made of metal or a metal alloy by ECAP, wherein the workpiece is pressed once or multiple times through a device having more than two channels, in particular through a device according to claim 1, characterized in that the workpiece is plastically formed by a single or multiple pressing through an inlet channel and an outlet channel which indirectly connects to the inlet channel and is arranged approximately perpendicularly thereto.

6. The method according to claim 5, characterized in that, before each introduction into the inlet channel, the workpiece is rotated about a longitudinal axis of the same.

7. The method according to claim 5, characterized in that the workpiece is formed at least twice each time it is pressed through the device.

8. The method according to claim 5, characterized in that the workpiece is pressed through multiple channels, wherein a forming bend is provided between each two channels.

9. The method according to claim 5, characterized in that the workpiece is heated, wherein a temperature is lowered each time the workpiece is pressed through the device.