JPH0671354A - Production of high tension sheet steel parts of postheat treatment type by detonating pressure - Google Patents

Abstract

PURPOSE:To repeatedly operate safely and in short time and to manufacture high tension sheet steel parts of postheat treatment by the high pressure of detonation. CONSTITUTION:A combustion chamber 1 is so designed that the cross section gradually decreases from one end 1A as flame progresses, a convergence part having the smallest cross section is formed in the other end 1B, and the end face of a pressure medium in a pressure chamber 12 is faced at the opening of the other end 1B. Pressure is raised because the cross section of the combustion chamber becomes smaller as the flame inside the combustion chamber 1 progresses, and the pressure becomes extremely high at the other end 1B. This high pressure is converted to the pressure medium inside the pressure chamber 12. On a die 16, a high tension sheet steel which is made to have a high strength in a heat treatment after receiving a primary forming is arranged, and the high tension sheet steel P is pressed with the die 16 through the pressure medium and is formed (straightened) into the final prescribed shape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing post-heat treatment type high strength steel plate parts such as automobile strength parts utilizing the excellent shape correcting effect of convergent detonation molding.

[0002]

2. Description of the Related Art Conventionally, cold-rolled steel sheets have been widely used as sheet materials for forming and processing of automobile strength parts and the like, but in recent years, there has been an increasing demand for weight reduction for improving fuel efficiency of automobiles, and in order to meet those demands. High-strength steel plates are used for automobile strength parts.

Since the elongation of a high-tensile steel plate decreases as the strength increases, compared with a soft cold-rolled steel plate for general press forming, shape defects due to forming cracks and spring back are more likely to occur, and the press formability is much reduced. To do. Therefore, in actual press forming, what is commonly used today is the most tensile strength 60 kg / mm ² blind.

[0004]

In order to realize further weight reduction, a method for producing a high strength steel plate part having a tensile strength of 60 kg / mm ² or more is desired.

Generally, the higher the strength of the material, the smaller the elongation and the worse the press formability. Therefore, there is an upper limit on the strength level of the material to be formed, and the tensile strength of 60 is currently applied to general automobile strength parts. ~ 80 kgf / mm ² is considered the upper limit. Therefore, if the strength can be further improved by heat treatment such as quenching after forming a material of 60 to 80 kgf / mm ² or less, it is possible to manufacture a strength component far higher than the current level as a product, and further The weight of the vehicle can be reduced. But,
Large residual stress is inevitably present in hydraulically or press-molded parts, and it is difficult to avoid deformation of parts due to changes in residual stress in subsequent heat treatment. It is necessary to correct the shape of this deformed part and commercialize it. Before molding, even if the strength level is as low as 80 kgf / mm ² or less, 10
When the tensile strength is 0 kgf / mm ² or more, it cannot be easily straightened by the conventional straightening technique.

Therefore, although a method of manufacturing a product by improving the strength and the like by heat treatment after press molding has been considered so far, it was realized because there was no effective straightening technology for high strength materials. Not not. However, by utilizing the strong straightening effect of the convergent detonation, even a very strong component can be sufficiently straightened, and the product can be manufactured by such post-press heat treatment.

There are some conceivable impact molding methods used for such shape correction other than the convergent detonation method, but none of them is suitable. This point will be described below.

First, a liquid or a medium equivalent thereto is preferable as the medium for transmitting the impact force. This is because the shape of the part before correction has a large difference in springback characteristics depending on the material strength, so there is a large difference, so it is important to adapt the shape easily and transmit the impact force.

Several methods are known as the impact hydraulic method. For example, firstly, a bullet is driven into a liquid such as water for pressurization to generate an impact hydraulic pressure in the liquid, and the pressure is applied to a member to be molded such as a plate material and the member is applied to a mold. An impact hydraulic pressure generating device that presses into a three-dimensional forming screw
It is proposed in 157725.

Secondly, there is also known an explosive molding apparatus for generating an impact water pressure by burning explosives in water and pressing a thin plate as a member to be molded into a mold by the pressure to perform three-dimensional molding. ing. This device is mainly used for molding large parts.

Further, as a third aspect, an impact hydraulic pressure is generated by causing a piston accelerated at high speed by gas pressure to collide with the liquid surface of the pressurizing liquid contained in the container,
There is also known a device in which the member to be molded is pressed by a hydraulic pressure into a mold. The device is used for molding relatively small parts.

However, although it is possible to apply the method of molding by impact hydraulic pressure by the above-mentioned first to third devices to shape correction, there are common or unique problems as follows. . Use dangerous and expensive explosives. There is a risk that there are restrictions on the installation location. It is difficult to significantly change the ultimate pressure. Not suitable for repeated operation in a short time. Large-scale equipment is required. It is necessary to replace moving parts such as pistons. Due to the complicated structure of the device, maintenance and inspections are difficult to perform.

The present invention solves the above-mentioned problems of the conventional method, and provides a method for producing a post-heat treatment type high strength steel plate part which is safe, can be repeatedly operated in a short time, and has a high detonation pressure. That is the purpose.

[0014]

According to the present invention, the above object is to provide a method for forming a post-heat treatment type high-tensile steel plate component on a mold, and then forming the steel plate by hydraulic forming or press forming, Heat treatment is applied to improve the strength, and then the steel sheet is placed on a mold, and the detonation wave generated by igniting a combustible air-fuel mixture is converged as it progresses, and the high pressure obtained at the converging portion is converted into a liquid. Alternatively, it is achieved by transmitting to an elastic body to convert into hydraulic pressure or elastic pressure, and pressing the steel plate against the mold by the hydraulic pressure or elastic pressure.

[0015]

In the present invention, the molding heat treatment and the shape correction are performed as follows.

First, since the high-strength steel sheet has a tensile strength of 60 to 80 kgf / mm ² or less at the time of press forming, it has sufficient ductility. Such a steel sheet is pressed with a shape free from forming cracks, with the forming depth slightly smaller than a predetermined value.

Next, the molded part is heated to an austenite temperature range and then quenched in water or the like to form a bainite or martensite structure alone or a mixed structure with a ferrite structure to increase the strength. At this time, the shape is distorted due to a large residual stress during pressing.

The quenched part is set on a mold having a regular product shape in the convergent detonation generator.

Thereafter, the combustible chamber, the guide passage and the ignition chamber in the convergent detonation generator which are in communication with each other are filled with a combustible gas mixture having a substantially theoretical mixing ratio.

Next, ignition is performed in the ignition chamber.

When ignited, the flame advances in the combustion chamber through the taxiway due to the detonation. that time,
Since the guide paths have the same path length, each guide path flame reaches one end of the combustion chamber at the same time.

In the combustion chamber, the flame propagates toward the other end, but since the cross-sectional area of the combustion chamber decreases toward the other end, the flame pressure rises and reaches the maximum value at the other end. .
Since the pressure chamber is connected to the opening at the other end, the pressure is transmitted to the pressure medium (liquid or elastic body) in the pressure chamber.

The pressure in the pressure chamber is corrected to a predetermined product shape by pressing the steel plate, which is the member to be molded, into the mold through the film body or directly.

[0024]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a vertical sectional view of the apparatus of this embodiment. In the figure, reference numeral 1 denotes a combustion chamber, which has a conical shape facing downward and has a maximum cross-sectional area at the upper end 1A and a minimum at the lower end 1B to form a converging portion.

The inner wall of the upper end portion 1A of the combustion chamber 1 is curved slightly upward, and a plurality of hole-shaped guide passages 2 communicate therewith. The plurality of guide paths 2 are focused on a disk-shaped dispersion chamber 3 at the top. An ignition chamber 4 extending upward is connected to the dispersion chamber 3 so as to communicate therewith. An ignition plug 5 that is operated by an ignition device 6 is provided above the ignition chamber 4, and a fuel supply source 9 and an oxidant supply source 10 are connected via flowmeters 7 and 8, respectively. . In addition, 11 is a pressure gauge for confirming the pressure in the ignition chamber 4.

The lower end portion 1B of the combustion chamber 1 is opened, and the pressure chamber 12 is connected thereto. The pressure chamber 12
An elastic body or a liquid is contained therein as a pressure medium. In the case shown, an example of an elastic body is shown. A molding device 13 is provided immediately below it. The pressure chamber 1
In FIG. 2, an elastic body is accommodated as a pressure medium in the case of the drawing, but a strong and easily deformable film body even if its upper end surface directly faces the lower end portion 1B of the combustion chamber 1 as shown in the drawing. You may form the intervening surface. A pipe 14 for bleeding air is connected to the pressure chamber 12 via a valve, and a liquid supply device 15 such as water for hydraulic pressure is connected via a valve when the pressure medium is a liquid.

The molding apparatus 13 accommodates a mold 16 of which the upper surface has a predetermined three-dimensional shape and has a predetermined shape in a replaceable manner. If necessary, the forming device 13 can hold the peripheral edge of the steel plate P to be subjected to forming between the pressure chamber 12 and, for example, both flanges. A vacuum pump device 17 is connected to the molding device 13 so as to penetrate the mold 16 and communicate with the upper space thereof to form a vacuum in the space. The vacuum pump device 17 is also connected to the ignition chamber 4 described above.

In the apparatus of this embodiment, generation of high-pressure liquid pressure or elastic pressure and molding utilizing this are performed as follows.

First, a high-strength steel sheet is press-formed with a shape free from forming cracks and the forming depth is slightly smaller than a predetermined value.

Next, the steel sheet that has undergone such forming is heat treated to improve its strength.

Then, the steel plate P is set on the mold 16 having a predetermined shape.

Next, the vacuum pump device 17 brings the ignition chamber 4, the dispersion chamber 3, the guide passage 2 and the combustion chamber 1 to a predetermined vacuum degree. At the same time, the mold 16 and the plate P
Similarly, the space between and is also suctioned so as to have a predetermined degree of vacuum.

After that, when the pressure medium is a liquid, for example, water is filled in the pressure chamber 12, and the ignition chamber 4, the dispersion chamber 3, the guide passage 2 and the combustion chamber 1 have substantially the same theoretical mixing ratio. The combustible gas is filled by the fuel supply source 9 and the oxidant supply source 10.

After completion of such setting, the ignition device 6 operates the spark plug 5. Detonation occurs due to ignition in the ignition chamber 4, and the flame is propagated to the upper end 1A of the combustion chamber 1 through the dispersion chamber 3 and the guide passage 2. At this time, since the path lengths of the plurality of guideways 2 are set to be equal to each other, the flames of the plurality of guideways 2 simultaneously reach the upper end portion 1A.

In the combustion chamber 1, the flame progresses from the upper end portion 1A to the lower end portion 1B, but since the cross-sectional area of the combustion chamber 1 gradually decreases downward, its pressure rises and at the lower end portion 1B. It becomes extremely high pressure.

Since the liquid surface of the liquid in the pressure chamber 12 or the end surface of the elastic body faces the opening of the lower end portion 1 B of the combustion chamber 1, the high pressure is applied to the liquid surface or the end surface from the liquid surface or the elastic surface. Propagated into the body, the steel plate P is a mold 16
Then, it is pressed with an equal pressure to form (correction) the final predetermined shape.

Next, a concrete example performed by the apparatus of the embodiment of the present invention will be shown by numerical values.

<Specific Example 1> Many channel components having a hat cross section as shown in FIG. 2 are used as strength components for automobiles. Therefore, in general, a hat cross section channel is often used in a model test for evaluating the shape correction effect.

Therefore, a manufacturing experiment of a channel component having a hat cross section was conducted. First, plate thickness 1.6 mm, tensile strength 65
Alloy composition of 0.1% C, 0.5% Si, which is kgf / mm ² ,
A 1.6% Mn, 0.5% Cr steel plate was press-molded into a channel having a cross section of a hat having a length of 200 mm with a mold shown in FIG. 3 to obtain a primary molded product. Next, this was heated to 850 ° C. and then water-quenched. Then, the tensile strength is 123kgf / mm
^{Although the} strength was increased to ^2, there was a large amount of dimensional difference with the mold due to distortion and deformation. The dimensional accuracy of this was evaluated according to the procedure shown in FIG. That is, the wall warpage ρ and bending angle changes θ _p and θ _d shown in FIG. 4 and the twist angle θ _T shown in FIG. 5 were measured. The measurement results after water quenching are wall warpage ρ = 0.72 mm, bending angle change θ _p = 108 °, θ _d = 86 °, and twist angle θ
_T = 5.5 °.

Next, the rubber having the shape shown in FIG. 6 was used as a medium for transmitting a shock wave by convergent detonation to correct the shape of the primary molded product. FIG. 7 shows a part of a device for correcting the shape of a hat cross section channel by convergent detonation. The shock wave generated by the convergent detonation is concentrated in the A part, and the shock wave is propagated from the upper part to the lower part of the rubber cone to apply a very high shock pressure to the inside of the channel part. Then, 1mm deeper than the primary molded product 40
Molded to mm. At that time, the side wall B is subjected to a tensile force and a high surface pressure, and its shape is corrected. The measurement result of dimensional accuracy is wall warpage ρ = 0.02 mm, bending angle change θ _p = 91 °, θ _d =
91 ° and the twist angle θ _T = 0.2 °, which is a very small amount that does not pose a problem in practical use.

On the other hand, instead of correcting the shape of the primary molded product by convergent detonation, as a comparative example, restriking was performed as a shape correcting method using a press which is usually used. In this case, the condition for the wrinkle holding force is 75 tons, which is close to the breaking limit, and 40 to 40 mm from the height of 39 mm before restriking.
Processed to mm.

As a result, the wall warp ρ = 0.25 mm, the die shoulder angle θ _d = 88 °, and the punch shoulder angle θ _p = 95.
However, although it was considerably corrected compared to before correction, it was a practically acceptable level (ρ <0.10 mm, θ _d <2
°, θ _p <2 °) has not been reached. On the other hand, straightening by convergent detonation clears these allowable levels, and it can be seen that even a high-strength steel sheet having a tensile strength of 120 kgf / mm ² can be sufficiently straightened.

<Specific Example 2> As automobile panel parts, there are many square tube-shaped parts having a curvature in only one direction of the panel bottom, so-called kamaboko-shaped parts. Therefore, generally, a kamaboko-shaped component is often used in a model test for evaluating the shape correction effect.

The following tests were carried out for the purpose of evaluating the shape freezing effect of convergent detonation. First, 0.3mm
A tin plate on a (thickness) × 130 mm (diameter) disk was press-formed into a kamaboko-shaped panel as shown in FIG. 8 under the conditions of a wrinkle holding force of 2.4 tons and a forming height of 8 mm. Next, this kamaboko-shaped panel is set in the convergent detonation generator. FIG. 9 shows a part of a shape-correcting device for a kamaboko-shaped panel by convergent detonation. The shock wave generated by the convergent detonation is concentrated on the portion A, the shock wave is propagated from the upper part to the lower part of the rubber cone, and a very high shock pressure is applied to the inside of the kamaboko-shaped panel. Then, a very high surface pressure is applied and the shape is frozen in the shape of the mold. A method for measuring dimensional accuracy will be described with reference to FIG. Using a gauge with a dial gauge in the center and a span of 20 mm, the span 20 in the direction of the radius of curvature 240 mm in the center of the kamaboko-shaped panel is used.
The deviation height ΔH from the horizontal position in mm was measured. The result is shown in FIG. When the combustion gas filling pressure is increased, that is, the detonation pressure is increased, ΔH is 0.03 mm.
It can be lowered sufficiently to the following. This value has almost cleared the practically acceptable level, and the tensile strength is 120 kgf / mm ²
Sufficient shape freezing was obtained even with the high-strength steel sheet with the above strength.

[0046]

As described above, if the convergent detonation forming is performed using the post-forming heat treated high-strength steel sheet of the present invention, high strength and shape dimensional accuracy can be secured, and a very high strength of the same shape as a general steel sheet can be secured. It will be possible to manufacture lightweight automobile strength parts, etc.

Further, according to the present invention, unlike the conventional bullet driving type and explosive type, since no explosive is used, the device is not restricted by the setting, and the impact pressure can be continuously generated. The effect is that it can be converted to a mass production system.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing the shape of a hat cross-section channel in Specific Example 1 used for molding in the apparatus shown in FIG.

FIG. 3 is a cross-sectional view showing a mold used for press molding of the channel of FIG.

FIG. 4 is a diagram showing an evaluation procedure of dimensional accuracy of the hat cross-section channel component of FIG. 2.

FIG. 5 is a diagram showing another dimensional accuracy evaluation procedure of the hat cross-section channel component of FIG. 2;

6 is a diagram showing the shape of the pressure medium used in the convergent detonation device for straightening the channel of FIG. 2 after heat treatment.

FIG. 7 is an enlarged view showing a processing chamber of the apparatus shown in FIG.

FIG. 8 is a partially cutaway perspective view of a kamaboko-shaped part that is a molded product as specific example 2.

9 is a partial cross-sectional view of an apparatus used for press molding of FIG.

10 is a diagram showing an evaluation procedure of dimensional accuracy of the kamaboko-shaped part of FIG.

11 is a diagram showing a result of the evaluation shown in FIG.

[Explanation of symbols]

 1 Combustion Chamber 1B Converging Part (Lower End) 12 Pressure Medium (Liquid, Elastic Body) 16 Mold P High Tensile Steel Plate

Claims (1)

[Claims] 1. A method for forming a post-heat treatment type high-strength steel sheet component on a die for forming, wherein the steel sheet is hydraulically or press-formed and then heat-treated to improve its strength. Is placed on the mold, the detonation wave generated by igniting the combustible mixture is converged as it progresses, and the high pressure obtained at the converging part is transmitted to the liquid or elastic body and converted into hydraulic pressure or elastic pressure. A method for producing a post-heat treatment type high-strength steel plate component by detonation pressure, which comprises pressing the steel plate into a mold with the liquid pressure or elastic pressure.