JP3557092B2 - Method for manufacturing NiTi alloy pipe - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a pipe made of a NiTi alloy known to have shape memory properties or superelastic properties.
[0002]
[Prior art]
A typical NiTi alloy as a shape memory alloy is also known as a superelastic alloy. This alloy is processed into various shapes according to its use, but NiTi alloy is generally known as a material that is not easy to process.
[0003]
[Problems to be solved by the invention]
Since the NiTi alloy is a difficult-to-process material, it is difficult to use an existing drilling method used for a steel material, an aluminum material, or the like, for example, when processing into a pipe shape. Conventionally, drilling of NiTi alloys has often been performed by a BT method using a special gun drill (a device in which the drill head and junk are cylindrical) and having excellent straightness. .
[0004]
Even in the case of using the BT method as described above, since the NiTi alloy is a difficult-to-process material, it is necessary to extremely reduce the cutting speed as compared with the case of a normal metal material. For this reason, the processing time is very long, and the processing cost is very large.
[0005]
As a method of processing into a pipe shape, there is a pipe extrusion method used for ordinary materials such as steel, but the application of NiTi alloy is not easy because it is a difficult-to-process material.
[0006]
[Means for Solving the Problems]
The present invention has been made in view of the above-described problems, and has as its object to provide a method for producing an NiTi alloy pipe at an excellent cost by achieving efficient pipe extrusion with a reduced processing time.
That is, in the method for manufacturing a NiTi alloy pipe of the present invention, the NiTi alloy billet is heated to a temperature of 650 to 850 ° C., the billet is housed in a container in which a die is arranged in front, and the tip of the billet is placed in the container. This is a manufacturing method by front-to-back extrusion, in which a pipe portion is extruded by a backward extrusion method using a mandrel while extruding a die forward.
[0007]
Solid materials may be used as billets in the above method. It is desirable to use a die having an approach angle of 90 to 55 °. It is preferable to use a mandrel made of high speed steel (SKH).
[0008]
The NiTi alloy contains, in addition to the binary alloy of Ni and Ti, a total of 10% by weight or less of one or more elements selected from Cu, V, Fe, Al, Cr, Nb, and Co. It may be.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
A method for manufacturing a NiTi alloy pipe of the present invention will be described with reference to FIG. First, a billet of a NiTi alloy to be processed is prepared and heated to 650 to 800 ° C. Then, the billet (reference numeral 1 in the figure indicates a NiTi alloy) is set in a container 22 (a sleeve or the like is omitted) of the extruder as shown in FIG. Next, the mandrel 20 is lowered to perform piercing (drilling) on the NiTi alloy 1. At this time, the process is performed while extruding a small amount of the NiTi alloy 1 forward from the die 23 (see FIG. 1A).
[0010]
Although the tip of the NiTi alloy 1 shown in FIG. 1A does not penetrate, the shape is a pipe shape. According to such pipe extrusion, the processing time can be shortened and the yield can be improved as compared with the case where the above-described conventional BT method is used, so that a NiTi alloy pipe can be manufactured at a low manufacturing cost.
[0011]
The inner diameter of the pipe to be manufactured can be changed by changing the diameter of the mandrel 20. Therefore, it is possible to easily cope with the production of pipes of various sizes only by replacing the mandrel 20.
[0012]
The approach angle and hole diameter of the die 23 may be selected according to the diameter of the mandrel 20 and the like, but the approach angle is preferably about 90 to 55 °. The temperature of the NiTi alloy 1 at the time of pipe extrusion is preferably set to 600 to 850 ° C. If the temperature is lower than 600 ° C., the deformation resistance is too large, and a very high pressing pressure is required. Therefore, the mandrel 20 is liable to be damaged such as deformation. On the other hand, also in the case of the NiTi alloy 1 heated at a temperature exceeding 850 ° C., the temperature is too high, and the problem such as deformation of the mandrel 20 easily occurs. For these reasons, the temperature of the NiTi alloy 1 is suitably from 600 to 850C. Particularly, about 700 to 750 ° C. is desirable.
[0013]
【Example】
Example 1
Example 1 of the present invention will be described with reference to FIG.
The prepared NiTi alloy billet has a diameter of 50 mm and a length of 70 mm. The NiTi alloy billet (corresponding to the reference numeral 1 in FIG. 1A) was coated with a carbon-based lubricant and then heated in an electric furnace heated to 800 ° C. for 20 to 30 minutes. Next, the NiTi alloy billet was set in the container 22. At this time, the temperature of the NiTi alloy billet was approximately 700 to 750 ° C. Reference numeral 24 in the figure is a container receiving stand.
[0014]
After setting the NiTi alloy billet in the container 22, the mandrel 20 was lowered to extrude the NiTi alloy 1 by pipe. The mandrel 20 has a cylindrical shape with a diameter of 31 mm and is made of SKD-61. In this figure, the mandrel 20 is attached to the mandrel holder 21, but in the first embodiment, the mandrel holder 21 and the mandrel 20 are used integrally.
[0015]
The die 23 arranged in front of the container 22 has a hole diameter of 41 mm and an approach angle (corresponding to θ in the die 230 shown in FIG. 2) of 60 °. When the mandrel 20 is lowered to extrude the NiTi alloy 1 into a pipe, the NiTi alloy 1 is extruded little by little from the die 23. By doing so, the press pressure at the time of this pipe extrusion can be greatly reduced, the deformation of the mandrel 20 and the like can be suppressed, and good pipe extrusion can be achieved.
[0016]
Comparative Example 1 will be described with reference to FIG. The difference from the above-described present invention example 1 is that a container 27 having a bottom without a die is used below the NiTi alloy 1, and the mandrel 25 and the mandrel holder 26 are the same as those of the above-described first embodiment of the present invention. is there. In this comparative example as well, the mandrel 25 was lowered and the NiTi alloy 1 was extruded in the same manner as in Example 1 of the present invention. However, the press pressure was significantly higher than in the case of Example 1 of the present invention described above. After the pipe was extruded, the mandrel 25 could not be removed from the NiTi alloy 1, so when it was cut and examined, it was found that the tip of the mandrel 25 was greatly deformed. This is because the press pressure became very large. If the mandrel 25 is deformed in this way, there are problems such as the inability to pull out the mandrel 25, or even if the mandrel 25 can be pulled out, a NiTi alloy pipe of sufficient quality cannot be manufactured.
[0017]
Next, Example 2 of the present invention will be described. FIG. 4 is an explanatory view showing a mandrel. The mandrel 30 shown in FIG. 4A has a mandrel holder portion and a mandrel portion integrated with each other. On the other hand, the example of FIG. Numeral 310 is attached to the mandrel holder 311. The mandrel 310 and the mandrel holder 311 are fixed to each other by screwing as shown, or by a joining method such as shrink fitting or brazing. According to the screw fixing as shown in FIG. 4A, the replacement of the mandrel 310 is easy, so that it is practical.
[0018]
Now, pipe extrusion similar to that of Example 1 described above was performed using various materials of the mandrel 310 shown in FIG. FIG. 5 is a diagram showing the number of extrusions and the change in the tip diameter of the mandrel 310 when the material of the mandrel 310 is HSS (SKH-51) and when the material of the mandrel 310 is hot tool steel (SKD-61). Note that the initial diameters of the tip portions of these two types of mandrels are slightly different. The material of the mandrel holder 311 was hot tool steel (SKD-61).
[0019]
In FIG. 5, points indicated by black diamonds indicate changes in the diameter of the tip of the mandrel when the mandrel 310 made of SKD-61 is used. The points indicated by black squares indicate changes in the diameter of the tip portion of the mandrel 310 when the mandrel 310 made of SKH-51 is used. As can be seen from this graph, when the mandrel 310 made of SKD-61 is used, the tip diameter greatly increases each time with respect to the initial tip diameter (diameter when the number of extrusions is 0). ing. Since the tip diameter increased by 0.15 mm or more by the number of extrusions three times, the extrusion after the fourth time was stopped. On the other hand, when the mandrel 310 made of SKH-51 was used, it was found that the increase in the tip diameter of the mandrel 310 was relatively small even when the number of extrusions was six.
[0020]
From the above results, it is understood that it is desirable to use a mandrel made of high speed steel (SKH-51 or the like) rather than hot tool steel (SKD-61 or the like). The degree of deformation of the mandrel 310 depends on the diameter thereof, the temperature of the NiTi alloy billet, and the like. Therefore, the material of the mandrel may be appropriately selected according to the size of the NiTi alloy pipe to be manufactured.
[0021]
Next, Example 3 of the present invention will be described. Example 3 of the present invention is a case where the same pipe extrusion as that of Example 1 of the present invention described above was performed by changing the approach angle (θ in FIG. 2) of the die 23 in FIG. When the approach angle θ was 90 °, the NiTi alloy 1 was not extruded from the die 23 as shown in FIG. 1A, and the pressing pressure was very large, 200 to 250 ton. Therefore, the result was similar to that of Comparative Example 1 described above. On the other hand, when the approach angle θ was set to 70 ° or 60 °, the press pressure was kept low at 110 to 130 ton, and good pipe extrusion became possible. The same procedure was performed when the approach angle θ was 45 °. In this case, the NiTi alloy 1 was extruded from the die 23 without being extruded from the pipe.
[0022]
As described in detail above, in the method for manufacturing a NiTi alloy pipe of the present invention, deformation of the mandrel is suppressed, and a NiTi alloy pipe having excellent accuracy can be obtained at a lower cost than the conventional method. Also, by changing the diameter of the mandrel, the inner diameter of the manufactured NiTi alloy pipe can be easily changed, which is practical.
[0023]
【The invention's effect】
The method for manufacturing a NiTi alloy pipe according to the present invention is an excellent method for manufacturing a NiTi alloy pipe in terms of manufacturing cost and quality, and enables relatively inexpensive supply of a high-quality NiTi alloy pipe. For this reason, the industrial contribution of the present invention is great, such as encouraging the expansion of its use.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a method for manufacturing a NiTi alloy pipe of the present invention.
FIG. 2 is a diagram illustrating a die used in the method for manufacturing a NiTi alloy pipe of the present invention.
FIG. 3 is a diagram illustrating a die used in a method for manufacturing a NiTi alloy pipe of a comparative example.
FIG. 4 is a diagram illustrating a mandrel used in the method for manufacturing a NiTi alloy pipe of the present invention.
FIG. 5 is a graph showing the degree of deformation of the tip of the mandrel in the example.
[Explanation of symbols]
1 NiTi alloy 20 Mandrel 21 Mandrel holder 22 Container 23 Dice 24 Container cradle 230 Dice 25 Mandrel 26 Mandrel holder 27 Container 30 Mandrel 310 Mandrel 311 Mandrel holder

Claims (5)

The NiTi alloy billet was heated to a temperature of 650 to 850 ° C., the billet was housed in a container in which a die was arranged in the front, and the billet was extruded forward from the die while using a mandrel. A method for producing a NiTi alloy pipe by forward and backward extrusion, wherein the pipe portion is extruded by a backward extrusion method. The method according to claim 1, wherein the billet is a solid material. 3. The method for manufacturing a NiTi alloy pipe according to claim 1, wherein the die has an approach angle of 90 to 55 [deg.]. The method for manufacturing a NiTi alloy pipe according to any one of claims 1 to 3, wherein the mandrel is made of high-speed steel (SKH). 5. The NiTi alloy according to claim 1, wherein the NiTi alloy contains at least 10% by weight of one or more elements selected from Cu, V, Fe, Al, Cr, Nb, and Co. A method for producing the described NiTi alloy pipe.

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