JPS59218214A - Manufacture of tapered rod - Google Patents

Abstract

PURPOSE:To manufacture a tapered rod with a high productivity in a very short time by prescribing a distortion speed of a metallic base material within a prescribed range with regard to the minimum diameter part, when forming a tapered part whose diameter is varied in the axial direction by giving a temperature gradient in the axial direction to the metallic base material and applying a tensile force. CONSTITUTION:A prescribed temperature gradient is given in the aial direction to a metallic base material such as an iron and steel wire rod, etc. by a well-known heating means such as direct electric conduction heating method, a high frequency induction method, etc. Subsequently, by applying a tensile force of the axial direction to the metallic base material of this state, the diameter is varied in the axial direction in accordance with a pattern of said temperature gradient, and a desired tapered shape is obtained. In this case, it is necessary to control a distortion speed (working distortion speed) of the metallic base material in case of said drawing operation as follows; that is the base material part corresponding to the minimum diameter part (uniform maximum narrowed part) of a tapered rod is drawn and deformed so that the working distortion speed (i) in the maximum heating temperature part generally becomes 0.5- 1,000%/ sec. As a result, a tapered rod of an object shape can be manufactured efficiently without causing such a problem as breakdown, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a tapered rod, and more particularly to an improvement in a method for manufacturing a tapered rod whose diameter changes in the axial direction from a predetermined metal material without material loss and with high productivity. be.

In recent years, tapered coil springs that use tapered rods and have non-linear characteristics have become popular in place of conventional coil springs with a constant wire diameter to improve the riding comfort of automobiles and railway vehicles. A tapered rod used in such a tapered coil spring has a large wire diameter portion in the center in the axial direction and a tapered portion where the wire diameter continuously decreases toward both ends. This provides a spring characteristic that allows for non-linear height changes, which greatly contributes to the aforementioned improvement in riding comfort.

By the way, taper rods used in tapered coil springs and the like that exhibit such excellent properties have traditionally been manufactured by cutting a metal material such as a wire or bar into a desired tapered shape using a cutting method. However, because it involves cutting metal materials, it is inevitable that there will be a large amount of material loss (approximately 15%), and the cutting process will take a long time, reducing productivity. This has significantly worsened the situation. In addition, a manufacturing method using a hot forging method called the rotary swaging method using a swaging machine is also used in some cases, but although this method also has the advantage of reducing material loss, However, the problem of long processing time still remained unsolved.

For this reason, the present inventors conducted various studies in an attempt to resolve the problems in the conventional methods of manufacturing such tapered rods, and as a result, the inventors of the present invention have developed a method for producing a predetermined tapered rod by tensile deformation in the axial direction of a metal material to which a temperature gradient has been applied. We discovered a new method that could be manufactured in a short time and filed a patent application for this in Japanese Patent Application No. 3,4345/1983. According to this patented method, a desired taper can be formed by applying a temperature gradient in a predetermined pattern only to the part of the metal material where the taper is to be formed and by tensioning it. There is no need for material loss or time-consuming cutting work as in the cutting method, and there is no need for complex, long and inefficient forging work as in the hot forging method, allowing taper forming to be performed in an extremely short time. This could significantly increase the productivity and, in turn, effectively reduce the manufacturing cost of such tapered rods.

As a result of further studies on the previously filed method which has such excellent features, the present inventors found that when a metal material is tensilely deformed in its axial direction, the strain rate of the deformed part, that is, the unit The rate of deformation of the cross section of the material per time is important, and it is necessary to cause tensile deformation so that it is within a predetermined range at the smallest diameter part.
It has been found that a desired tapered rod can be effectively manufactured by this method.

That is, the present invention was completed based on this knowledge, and its feature is that by applying a tensile force to a metal material by creating a temperature gradient in its axial direction, the temperature gradient is Accordingly, when forming a tapered portion of the metal material whose diameter changes in the axial direction, the strain rate of the metal material is 0.5%/sec at the minimum diameter portion.
The tensile deformation is performed within the range of c to 1000%/sec, and this allows the desired tapered rod to be formed in accordance with a predetermined temperature gradient to avoid problems such as breakage due to local shrinkage. This means that it can be manufactured efficiently and easily without creating sticky notes.

Now, the metal materials used in the present invention are generally in the form of wires or bars, and are usually made of steel, but may be made of other non-ferrous metal materials. It doesn't make any difference. However, in order to obtain a tapered rod that can be suitably used in a tapered coil spring,
The metal material contains 0.35 to 1.10% carbon (C) by weight, and if necessary, 2.5% or less silicon (Si), 1.5% or less manganese (Mn), 3.0
% or less copper (Cu), 3.0% or less nickel (Ni)
, 5.0% or less chromium (Cr), 1.0% or less molybdenum (Mo), 1.0% or less vanadium (V)
, 0°05% or less boron (B), 0.1% or less aluminum (Aβ), and 0.5% or less each of titanium (Ti), niobium (Nb), zirconium (Zr),
It is desirable to use a steel wire containing tantalum (Ta), tungsten (W), and hafnium (Hf), with the remainder being iron.

The reason for determining the content range of each component in such a preferable steel wire is as follows.

C: If it is less than 0.35%, quenching roughness will occur during heat treatment after coil forming, and sufficient spring properties will not be obtained. In addition, if it exceeds 1.10%, the pro-eutectoid carbide becomes huge and deteriorates the fatigue life, so it is preferable.St:Si is a preferable element because the more it is, the more it improves the fatigue resistance of the spring. S if it exceeds 2.5%
This is not preferable because the segregation of t becomes large and pro-eutectoid ferrite remains during quenching and heating, which deteriorates fatigue life.

Mn: Mn is a preferable element because it is a deoxidizing element and improves hardenability. However, if it exceeds 1.5%, it tends to cause burn cracks during the hardening operation. The following are desirable.

Cu: Cu is an element that increases weather resistance and is effective in preventing decarburization during hot heating, but if it exceeds 3%, it causes red brittleness and inhibits hot workability, so its upper limit should not be exceeded. 3%.

Ni: Ni is an effective element for increasing hardenability and whipping properties, but if it exceeds 3%, retained austenite will be generated during the hardening operation, resulting in a decrease in yield strength. The upper limit was set at 3%.

Cr: Cr not only increases hardenability but also increases temper softening resistance, so it is possible to temper at a higher temperature to obtain the same strength, and therefore the yield strength ratio can be increased. , the design stress of the spring can be increased. However, if it exceeds 5%, cracks are likely to occur during cooling after hot rolling, so the upper limit is set at 5%.

Mo: Mo is a preferable element because it increases both hardenability and temper softening resistance, but it tends to cause cracks during cooling after hot rolling, so the upper limit is set to 1%.

(2): (2) is a preferable element because it refines crystal grains and improves whipping properties, and it also improves high-temperature strength properties, so it is effective in heat-resistant applications. However, if it exceeds 1%, the effect is saturated, so the upper limit is set at 1%.

BIB is an effective element because it significantly increases hardenability even when added in a small amount. However, if excessively added, Fe5
13 and causes red heat brittleness, the upper limit is set at 0.05%.
shall be.

A6 - This element reduces oxygen in steel as a deoxidizer,
Since it reduces specific metal inclusions, it is effective in improving fatigue life, and it also refines the grain size and lowers the impact transition temperature. However, if it exceeds 0.1%, the whipping properties will deteriorate, so
The upper limit is set to 0.1%.

Ti, Nb, Zr, Ta, W, Hf: These elements form fine carbides and increase tempering resistance, so they are preferable elements, but if they exceed 0.5%, they impair whipping properties, so each The upper limit is set at 0.5%.

In addition to these elements, phosphorus, sulfur, arsenic, and
There is no problem even if trace impurity elements such as tin, antimony, zinc, and selenium are included in the steel wire. Further, among the above-mentioned elements, in addition to C being essentially included in the steel wire rod, other elements may be contained within a predetermined amount range as necessary depending on the performance required of the target Taber Rond. The result is that

A predetermined temperature gradient is then applied to the metal material such as the steel wire in its axial direction.
The pattern of the temperature gradient varies depending on the material, dimensions, heating temperature, tensile conditions, etc. of the material, and the desired taper shape, and cannot be unambiguously limited, and depends on each specific case. A decision will be made as appropriate. However, in general, the hot portion of the metal material becomes thinner due to subsequent stretching operations, while the cold portion becomes less thin than the hot portion. Therefore, when forming a tapered material that has a minimum diameter portion at the center and has tapered portions on both sides of the minimum diameter portion whose diameter gradually increases as the distance from the minimum diameter portion increases, the center in the axial direction of the metal material is A temperature gradient with a chevron-shaped pattern in which the temperature is high in the central part and the temperature decreases as the distance from the central part decreases is suitably adopted. However, when providing such a temperature gradient, the maximum heating temperature of the metal material is 60°C.
It is desirable that the temperature be within the range of 0 to 1000°C. If the maximum heating temperature is less than 600°C, the elongation at break of the metal material will be low (for example, the elongation at break of the above-mentioned steel wire will be 40% or less), and local drawing will be required before forming into the desired final tapered shape. If the maximum heating temperature exceeds 1000°C, oxidation and decarburization of the surface of the material will become significant, causing fatigue when it is finally made into products such as springs. This causes undesirable phenomena such as a decrease in service life.

In addition, heating methods for metal materials to impart a predetermined pattern of temperature gradient include direct current heating, high-frequency induction heating, gas heating, infrared heating, and indirect heating using an electric furnace. Any known heating method may be employed, and an appropriate heating means is appropriately selected from among them. The method of applying a predetermined temperature gradient using this selected heating method is generally (1)
(2) A method of heating a metal material so that a predetermined temperature gradient is formed in the axial direction of the metal material, and (2) a method of heating the metal material so that a predetermined temperature gradient is formed in the axial direction. A method of adjusting the temperature by cooling so as to form a temperature gradient is preferably employed. More specifically, in order to impart a predetermined temperature gradient to the metal material within the heating region, the amount of heating or cooling at each position in the axial direction of the material is changed according to the desired taper shape. For example, the degree of cooling can be changed by increasing or decreasing the amount of air blown at each divided position from the center of the formed taper part to both ends (both sides), or by high-frequency induction heating. In this method, the coil diameter or pitch at each position in the material's axial direction is changed, or in gas heating, the gas flow rate at each location in the material's axial direction is changed,
Methods such as adjusting the electrical input of multiple rows of resistive heating elements may be used to advantage.

Next, a tensile force in the axial direction of the metal material is applied to the metal material to which the predetermined temperature gradient has been applied, causing the material to change its diameter in the axial direction according to the pattern of the temperature gradient. At the very least, the desired tapered shape is formed. That is, the hotter portion generally has a smaller diameter, and the colder portion does not vary significantly in diameter.

Note that this tensile force generally depends on the material, shape, and
The temperature gradient is applied to the metal material to which a predetermined strain rate is applied depending on the desired taper shape. In order to efficiently obtain a tapered rod shape, it is important to control the strain rate (processing strain rate) of the metal material during this tensile operation. It became clear that it was necessary to control the diameter portion (uniform maximum aperture portion) within a predetermined range.

Therefore, in the present invention, the metal material portion corresponding to the minimum diameter portion (uniform maximum drawing portion) of the tapered rod generally has a processing strain rate (2) of 0.5%/sec to 0.5%/sec at the highest heating temperature portion. The tapered rod can be tensilely deformed at a rate of 1000%/sec, and as a result, a tapered rod of the desired shape can be obtained efficiently and easily without causing problems such as breakage. Note that if the strain rate is low, less than 0.5%/sec, the temperature gradient applied in the axial direction becomes flattened, and the desired taper shape becomes a solid piece. The lower limit of the speed needs to be 0.5%l sec or more. In addition, the strain rate is 1000%/sec
If it exceeds this, the heat generated by plastic deformation will increase, causing local heat generation, causing local shrinkage and breaking, so the upper limit needs to be 1000%/sec. . Here, the strain rate (ε) refers to the amount of deformation per unit time at the minimum diameter portion, more specifically, the amount of change in the cross-sectional box, and is generally determined according to the following equation.

However, A3: original cross-sectional area of the metal material (cn) A: cross-sectional area of the smallest diameter part of the tapered rod (metal material after tension) (cJ) t: tension time (sec) The tapered rod is suitably used as a material for a tapered coil spring as described above, and is also used for various conventionally known purposes. In particular, in order to manufacture a tapered rod for a tapered coil spring, the method of the present invention is applied intermittently to a long continuous wire or bar at predetermined intervals in the axial direction. After forming and processing, by sequentially cutting at the minimum diameter portion of the tapered shape, it is possible to continuously obtain a tapered rod in which both end portions exhibit a tapered shape (the diameter gradually decreases toward the end). .

Examples of the present invention will be shown below to clarify the present invention more specifically, but it goes without saying that the present invention is not limited in any way by the description of these Examples.

Example 1 c: o, 6t%, Si: 2.05%, Mn: 0.81%
A steel cable material (diameter 6.35 mm) obtained by rolling and drawing containing Cr: 0.11% is used, both ends of which are gripped by a water-cooled chuck, and air-cooled with a different amount of air ejected at each position in the axial direction. While using a combination of means, direct electrical heating was carried out so as to form a mountain-shaped temperature gradient having a heating area of about 200° and a temperature of 850° C. at the center.

Thereafter, the strain rate (d) at the minimum diameter portion at the center was varied to cause the steel material having the predetermined temperature gradient to be tensed and deformed. The uniform maximum reduction ratio at each strain rate was determined, and the results are shown in Table 1. Note that the uniform maximum drawing ratio (%) indicates the amount of deformation until constriction (leading to breakage) occurs in the material that is being deformed into a tapered shape, and is calculated by (A3-A) x 100/A3. That is, it is expressed as (cross-sectional area of the material - cross-sectional area of the smallest diameter portion)X100/(cross-sectional area of the material). Also, the results in Table 1 are
As shown in the figure.

As is clear from the results in Table 1 and Figure 1, the maximum uniform drawing ratio is large in the region where the processing strain rate is 0.5 to 1000%/sec, and the maximum part thereof is located. By performing tensile deformation in such a region with a large uniform maximum drawing ratio, it becomes easier to process the material into the desired tapered shape. In other words, the number of processing steps can be reduced.

Table 1 Example 2 A steel material (wire rod) obtained by spheroidizing annealing and drawing containing various chemical components shown in Table 2 was heated by the heating method according to Example 1 (the maximum heating temperature was After heating (as shown in the table) to impart a predetermined temperature gradient, tensile deformation was performed in the same manner as in Example 1 at the processing strain rate (λ) shown in Table 3. The obtained uniform maximum drawing ratio (
%) are also shown in Table 3, and it was found that all steel materials exhibited an excellent uniform maximum drawing rate.

Table 2 Table 3

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the strain rate of the minimum diameter portion determined in Example 1 and the uniform maximum reduction rate. Applicant Daido Steel Co., Ltd.

Claims (4)

[Claims] (1) By applying a tensile force to a metal material by applying a temperature gradient in its axial direction, forming a taper portion whose diameter changes in the axial direction of the material according to the temperature gradient, the metal material 1. A method for manufacturing a tapered rod, which comprises tensilely deforming the tapered rod so that the strain rate at its minimum diameter ranges from 0.5%/sec to 1000%/sec. (2) The metal material is 0.35 to 1.10% by weight
of carbon, and optionally 2.5% or less silicon, 1.5% or less manganese, 3.0% or less copper, 3.0
% or less nickel, 5.0% or less chromium, 1.0% or less molybdenum, 1.0% or less vanadium, 0.05
% or less of boron, 0.1% or less of aluminum, and
2. The method of claim 1, wherein the wire is a steel wire containing 0.5% or less of each of titanium, niobium, zirconium, tantalum, tungsten and hafnium, the balance being iron. (3) When imparting a temperature gradient to the metal material in its axial direction, the maximum heating temperature is 600 to 100.
The method according to claim 1, wherein the temperature is within the range of 0°C. (4) After applying a temperature gradient in the axial direction to the metal material, an operation of applying tensile deformation in the axial direction to form a tapered portion is performed intermittently in the axial direction, and cutting is performed at the minimum diameter portion. 4. The method according to any one of claims 1 to 3, wherein a tapered rod for a tapered coil coil 2 spring having both end portions tapered is obtained by doing so.