JPH08144032A - Production of two-way shape memory alloy coil spring - Google Patents

Abstract

PURPOSE: To easily produce a compact two-way shape memory alloy coil spring excellent in corrosion resistance. CONSTITUTION: An NiTi shape memory alloy pipe is cold-formed into a coil spring, then shape memory treatment is applied to obtain a pipe-shaped shape memory alloy coil spring 1, and a wire 2 consisting of elastic material is inserted into the spring and then firmly attached to the spring. Otherwise, a composite wire made of the shape memory alloy and bias spring is prepared, the composite wire is cold-formed into a coil spring, and then shape memory treatment is applied. Alternatively, the composite wire is hot-formed into a coil spring, the coil spring is shot-peened, and then shape memory treatment is applied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a bidirectional shape memory alloy coil spring which is compact and has excellent corrosion resistance.

[0002]

2. Description of the Related Art Shape memory alloys are alloys that have the property of recovering their shape by heating even if they are cooled after shape memory treatment and deformed in the martensite phase state to the extent that slippage does not occur. Usually, the material that has been subjected to the above treatment does not show any change in its shape when cooled, and is therefore called one-way shape memory. By performing a special treatment, it is possible to give a two-way shape memory effect that recovers the memorized shape not only during heating but also during cooling, but it is difficult to control the generated force and shape, Almost never used Also in the shape memory alloy coil spring, the one-way shape memory alloy spring and the bias spring are often used in combination (bias method), rather than being used by imparting bidirectionality to the shape memory alloy itself as described above.

However, in the bias method, since a shape memory alloy coil spring and a bias spring such as a normal spring steel are combined, a certain amount of space is structurally required, and there is a limit to size reduction. It is also known that NiTi-based alloys have good corrosion resistance, but the current bias method makes it unsuitable for use in an environment where the bias spring material is corroded even if the NiTi-based alloy is not corroded. Possible, NiT
The characteristics of i-based alloys have not been fully utilized. Therefore, a coil spring with a double structure in which a bias spring is inserted inside the shape memory alloy pipe is conceivable. However, if the structure is simply a double structure, the shape memory alloy pipe and the bias spring are repeatedly operated by repeated operation at high temperature and low temperature. There is a risk that slippage may occur at the interface of the coil spring, the dynamic characteristics of the coil spring may be reduced, and sufficient bidirectional operation may be hindered. The NiTi alloy is
Since it is not a material with good workability such as hot and cold,
There is a problem that manufacture of a pipe-shaped coil spring is not easy.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made as a result of studying the above-mentioned problems. A NiTi type shape memory alloy pipe is located outside and a bias spring is arranged inside the pipe structure to form a coil spring having a composite structure. This is to develop a manufacturing method that can easily obtain an excellent operating characteristic.

[0005]

According to the present invention, a pipe-shaped shape memory alloy coil spring is formed by cold forming a NiTi type shape memory alloy pipe into a coil spring shape and then performing a memory treatment, and is made of an elastic material. A method of manufacturing a bidirectional shape memory alloy coil spring, comprising inserting a wire into the pipe-shaped shape memory alloy coil spring, and then subjecting it to an adhesion process. After inserting a wire made of an elastic material, hot working and cold working are performed to produce a double structure composite wire, and then the composite wire is cold formed into a coil spring shape, and then a memory treatment is performed. A method for manufacturing a bidirectional shape memory alloy coil spring, which is characterized in that: a wire rod made of an elastic material is inserted into a NiTi-based shape memory alloy pipe, and then hot working,
Cold working is performed to produce a double-structured composite wire, and then the composite wire is hot formed into the shape of a coil spring, shot peening is performed on the surface of the coil spring, and then a memory treatment is performed. A method for manufacturing a bidirectional shape memory alloy coil spring according to claim 3 is characterized in that.

[0006]

That is, according to the invention of claim 1, as described above,
A bias spring made of spring steel or the like is inserted into the iTi-based shape memory alloy pipe to form a coil spring having a double structure,
The outer pipe and the inner bias spring are made by closely processing the NiTi-based shape memory alloy pipe and the inner bias spring so that slippage does not occur at the interface during high temperature and low temperature operation. During operation,
This prevents the occurrence of slippage at the interface between the pipe-shaped shape memory alloy spring and the bias spring inside the pipe-shaped shape memory alloy spring, and maintains good operating characteristics as a coil spring. As a method of this contact processing, a method of mechanically crimping both ends of the coil spring, a method of welding, or a method of joining with an adhesive can be applied.

According to a second aspect of the present invention, a wire made of a material such as spring steel is inserted as an elastic material into the NiTi-based shape memory alloy pipe, and this is subjected to hot working such as extrusion and an annealing step. Cold working such as drawing is performed to produce a double-structured composite wire, and the composite wire is cold-formed into the shape of a coil spring, and then subjected to a memory treatment. According to this method, the NiTi-based shape memory alloy pipe on the outside and the bias spring such as the spring steel on the inside are intimately combined and brought into contact with each other by the working steps such as hot working, cold working and annealing. There is no slippage at the interface when operating as a spring, and it works well.

Next, a third aspect of the present invention is to insert a wire made of a material such as spring steel as an elastic material into a NiTi-based shape memory alloy pipe, and hot-work such as extruding and annealing. Cold working such as drawing was performed to produce a double-structured composite wire, the composite wire was hot formed into the shape of a coil spring, and shot peening was performed on the surface of this coil spring. After that, a storage process is performed. According to this method, similarly to the above, the interface between the pipe and the bias spring is in intimate contact, so there is no slippage at the interface when operating as a spring, and it works well, As for the recovery of strain upon molding, the shape memory recovery rate can be increased by introducing strain again by cold working by shot peening.

Next, the NiTi-based shape memory alloy applicable to the present invention is a NiTi alloy consisting of at 49% to 52% Ni at the balance and the balance Ti, or a part of the above Ni or / and Ti, Fe, Cr, Al, V, Pd, Mn,
Any one of Co, Nb, and Cu, or two or more of them can be used as 0.
A NiTi-based alloy substituted in the range of 01 to 2% can be applied. And the above-mentioned NiTi-based shape memory alloy pipe is
These alloys are melt-cast, hot extruded at 700 to 1000 ° C. to produce a pipe, and finished to a predetermined size by repeated cold drawing including an annealing step at 600 to 800 ° C. A composite wire having a double structure is 700 to 100 after a wire material such as spring steel is inserted inside a shape memory alloy pipe.
A composite wire is formed by hot extrusion at 0 ° C.
Finished to a predetermined size by repeated cold drawing with an annealing step of 0 to 800 ° C. Further, the shape memory treatment can be applied to the treatment which is usually performed at 400 to 500 ° C. for 30 minutes to 2 hours.

The coil spring is roughly classified into a tension spring used by applying a tensile force and a compression spring used by applying a compressive force, and the present invention can be applied to both. In the case of a tension spring, NiTi stored in the shape of the tension coil spring (shape that shrinks at high temperature) at a temperature of Af or higher
A bias coil spring is arranged inside the system shape memory alloy pipe. Since the shape memory alloy spring is stretched by the load of the bias spring at a low temperature below the Ms point, this spring is stretched as a whole. Ni at high temperatures above the Af point
Since the Ti-based alloy recovers its shape and compresses the bias spring, the spring as a whole contracts as compared to when the temperature is low. Therefore, this double structure spring is a bidirectional shape memory alloy coil spring that has the characteristic of expanding at low temperature and contracting at high temperature.

In the case of the compression spring, contrary to the case of the above-mentioned tension coil spring, a bias is applied to the inside of the NiTi type shape memory alloy pipe stored in the shape of the compression coil spring (the shape pulled at high temperature) at a temperature of Af point or higher. Place the coil spring.
Since the shape memory alloy spring is contracted by the load of the bias spring at a low temperature below the Ms point, this coil spring is contracted as a whole, but at a high temperature above the Af point it is N.
The iTi-based alloy recovers its shape and stretches the bias spring, so that it is elongated as a whole as compared with the case of low temperature. Therefore, the bidirectional shape memory alloy coil spring has a characteristic of contracting at low temperature and expanding at high temperature.

The two-way shape memory coil spring having the above dual structure has theoretically equivalent load-deformation characteristics to the two-way shape memory coil spring in which the shape memory alloy coil spring and the bias coil spring are connected in parallel or in series. Indicates. In these two-way shape memory alloy coil springs, only the surface of the NiTi alloy is in contact with the outside, and the good corrosion resistance of the NiTi alloy can be utilized. Further, since the pipe has a higher torsional rigidity than the solid line of the same cross-sectional area, the cross-sectional area for obtaining the same spring characteristics is small, and the material can be saved. Further, since the bias coil spring is incorporated inside the NiTi-based shape memory alloy pipe coil spring, the size is smaller than that of a normal two-way shape memory coil spring in which the bias coil spring and the shape memory alloy coil spring are connected in series. become.

[0013]

EXAMPLES An example of the present invention will be described below. (Example 1) A NiTi alloy with Ni of 50.3 at% balance Ti was melt-cast by high-frequency vacuum melting, extruded at a temperature of 900 ° C to form a pipe, which was annealed at 800 ° C and repeatedly drawn by cold drawing. Diameter 1 mm, inner diameter 0.8
mm pipes were made. This was molded into the shape of a compression coil spring and subjected to a memory treatment at 450 ° C. for 1 hour. The coil spring dimensions are: average coil diameter = 10 mm, effective number of turns =
7. Spring height = 40 mm. Then, a stainless steel wire for spring having a wire diameter of 0.7 mm is formed into the same shape as the coil spring, and is inserted into the shape memory alloy pipe spring.
The both ends were welded and the interfaces were brought into close contact with each other to prepare a double-structure coil spring having a shape memory alloy pipe coil spring 1 on the outside and a bias spring 2 on the inside, as shown in FIG. This coil spring is a compression spring that operates to contract at low temperatures and expand at high temperatures.

(Example 2) Ni 50.75 at on the outside
%, Fe0.05 at% balance Ti Ni-based alloy,
A double-structured composite material in which stainless steel for springs is combined inside is made by hot extrusion at 1000 ° C., and cold drawing including an annealing step at 800 ° C. is used to make a shape memory alloy pipe on the outside and a bias spring on the inside. A double-structured composite wire having a diameter of 1 mm was prepared. This wire is cold formed into the shape of a coil spring, fixed in the shape of a tension coil spring, and
A tension spring was manufactured that was subjected to a memory treatment for time, and that extended at low temperature and contracted at high temperature.

(Embodiment 3) A composite wire having a diameter of 1 mm produced in the same manner as in Embodiment 2 is formed into a coil spring at a temperature of 900 ° C., and cold shot peening is performed to form Ni on the outside.
The surface of the Ti alloy coil was subjected to cold working, finally fixed to the shape of the compression coil spring and subjected to a memory treatment at 450 ° C. for 1 hour to produce a compression coil spring that contracts at low temperature and expands at high temperature.

(Comparative Example) Ni 50.3 at with a diameter of 1 mm
%, NiTi alloy wire with the remaining Ti, average coil diameter = 10
mm, effective number of turns = 7, spring height = 40 mm, solid wire coil springs and stainless steel wire coil springs with the same dimensions are connected in series by the conventional bias method, and the bidirectionality of the bias method A shape memory alloy coil spring was produced.

Regarding the shape memory alloy springs of the present invention of Examples 1 to 3 and the coil spring by the bias method of the comparative example, heating to a temperature of Af point or higher (about 60 ° C.) or higher and Ms.
An experiment was performed in which cooling to a temperature not higher than the point + 20 ° C. (Ms point: Ni 50.3 at% was −1.9 ° C., Ni 50.75 at% was 4.4 ° C.) was repeated 5000 times. As a result, the double-structured shape memory alloy coil spring according to the present invention showed the same characteristics as the shape memory alloy coil spring according to the conventional bias method.

[0018]

According to the present invention as described above,
A compact bidirectional shape memory alloy coil spring having the same characteristics as those of the conventional biasing method, excellent in corrosion resistance, and obtained in a relatively easy manner has a remarkable industrial effect.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a bidirectional shape memory alloy coil spring according to an embodiment of the present invention.

[Explanation of symbols]

 1 Shape memory alloy pipe coil spring 2 Bias spring

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsuhiko Ueki 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (3)

[Claims] 1. A NiTi-based shape memory alloy pipe is cold-formed into a coil spring shape, and then subjected to a memory treatment to form a pipe-shaped shape memory alloy coil spring, and a wire made of an elastic material is formed into the pipe-shaped shape. A method for manufacturing a bidirectional shape memory alloy coil spring, which comprises inserting the memory alloy coil spring and then performing a contact process. 2. A wire rod made of an elastic material is inserted into a NiTi-based shape memory alloy pipe, followed by hot working and cold working to produce a double-structured composite wire, and then the composite wire is cold-worked. A method for manufacturing a bidirectional shape memory alloy coil spring, which comprises forming a coil spring into a shape of and then performing a memory treatment. 3. A wire rod made of an elastic material is inserted into a NiTi-based shape memory alloy pipe, and then hot working and cold working are performed to produce a double-structured composite wire, and then the composite wire is hot-worked. 1. A method for manufacturing a bidirectional shape memory alloy coil spring, which is characterized in that the coil spring is formed into a shape of a coil spring, shot peening is performed on the surface of the coil spring, and then a memory treatment is performed.