JPH07303919A - How to remove residual strain - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to an improvement in a method for removing residual strain generated during press molding. [Structure] A residual current is removed by applying a direct current or an alternating current to a bent portion B of a press-formed product W in a direction substantially perpendicular to the acting direction of residual stress that causes residual stress. At this time, the energization direction may be a direction along the ridge of the bent portion B, or a plurality of spots may be energized along the bent portion B at predetermined intervals in the plate thickness direction. The method of flowing in the thickness direction can remove the strain with smaller power.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method for removing residual strain generated during press molding.

[0002]

2. Description of the Related Art Conventionally, when press-molding a press-molded product, as a measure against residual strain such that the shape of the molded product taken out of the mold slightly returns, for example, in consideration of the restored portion, a bending angle larger than the desired shape is used. There is known a method in which the residual stress is removed by molding or by partially heating.

[0003]

However, in the method of preliminarily deforming excessively, the number of steps is increased by an extra processing amount, and moreover, the press-formed product has a plurality of press-formed products, which is usually used alone. Despite the fact that they are often used integrally by welding or the like, residual stress remains, so there is a problem that the residual stress is released by heat during welding or baking during painting, causing deformation or cracking. It was

Further, in the case of the method of removing residual stress by heating, it is necessary to heat the iron-based material to about 150 to 200 ° C., generally to about 500 ° C. or more and hold it for several tens of minutes to several hours. However, there is a problem that processing time is required and cost is increased due to processing equipment.

Therefore, there has been a demand for a removing method which can easily remove the residual strain and has a short processing time.

[0006]

In order to solve the above problems, the present invention provides a method for removing residual strain generated during the molding of a press-molded product, in which a residual strain is left in the press-molded product. The residual strain was removed by passing a direct current or an alternating current in a direction substantially perpendicular to the acting direction of the residual stress that causes the strain.

The energization direction is set to be substantially perpendicular to the plate thickness direction of the press-formed product.

Further, a plurality of current-carrying points are provided at predetermined intervals along the line where the residual strain is generated.

[0009]

The residual stress that causes the residual strain is caused by the deviation of the regular lattice positions of the atoms of the material.

[0010] In other words, when looking at the molded portion in the case of bending and forming at a micro level, the original lattice spacing of atoms is wider on the front side of bending, and the original lattice spacing of atoms is narrower on the back side of bending. Residual stress acts in the direction in which the lattice spacing is normally returned.

[0011] And, the additional elements contained in the material,
Due to lattice defects, the types of constituent atoms, and the like, a so-called metastable state is obtained in which the positions of the atoms balance with each other at a predetermined distance from the normal position.

Therefore, in order to remove the residual stress, it is sufficient to destroy the metastable state and return the misaligned atoms to the normal position so that the residual stress becomes zero.

[0013] For example, the conventional removal of residual strain by heat treatment or high-frequency heating is to add thermal energy from the outside to destroy the metastable state. However, in order to destroy the metastable state, it is not limited to the thermal energy. Alternatively, other means such as light, electric current, microwave, wave of electromagnetic wave, or the like may be used.

However, for example, in the case of light, the wavelength must be extremely shortened for irradiation, and in the case of wave, the frequency must be increased, which causes a problem in equipment.

Therefore, the present inventors have paid attention to the electric current. In other words, electric current is a flow of electrons, and when electrons move, a magnetic field is also generated.Therefore, by directly energizing the place where residual strain occurs, the vibration energy of atoms in the metastable state is increased, and the metastable state is increased. The residual strain is removed by shifting from the state to the stable state.

Further, it is considered that the electrons collide with the atoms when a current is passed and the vibrations of the atoms are increased by the collisions. Therefore, it is desirable that the current flow in the direction in which the collisions occur at the highest frequency.

Therefore, electrons can be made to collide with misaligned atoms with the highest frequency by energizing in a direction substantially perpendicular to the acting direction of the residual stress that causes residual strain.

Further, even when the current is applied in the plate thickness direction even in the direction substantially perpendicular to the acting direction of the residual stress, a small electric power is required, and the residual stress can be effectively removed.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The residual strain removing method of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a configuration example of an electrode arrangement for energizing along a ridgeline direction of a bent portion, (A) is a perspective view,
(B) is an enlarged view of the X part of (A), FIG. 2 is a perspective view showing a configuration example of an electrode arrangement for energizing in the plate thickness direction, and FIG. 3 is an explanatory view showing various aspects of the energizing direction.

When a molded product is subjected to bending by press working, when the molded product is taken out of the mold, residual stress acts on the bent portion and residual strain occurs in the direction of decreasing the bending angle. It is considered that this residual stress occurs because the position of the atom deviates from the normal position as described above.

Therefore, in the residual strain removing method of the present invention, an electric current is applied to the bent portion of a press-formed product which has been press-molded to increase the vibrational energy of atoms in the bent portion to normalize the positions of the atoms and reduce residual strain. I tried to remove it.

At this time, as a general energizing direction, as shown in FIG. 3 (A), a case where a current is made to flow along the ridgeline of the bending portion of the molded product and a case shown in (B) are shown. To
There are a case where a current is applied as a spot in a direction substantially perpendicular to the plate thickness direction and a case where the current is applied along the direction of action of residual stress that causes residual strain as shown in (C). In the case of, in order to increase the frequency of electron collisions with the atoms of the bent portion, a method of energizing in a direction substantially perpendicular to the acting direction of the residual stress that causes residual strain, that is, the methods of (A) and (B) It was adopted.

FIG. 1 shows a concrete example of the arrangement of electrodes in the energizing method corresponding to FIG. 3A, and FIG.
It is a structural example of a concrete electrode arrangement of the energization method corresponding to (B).

First, as Example 1, an experiment was conducted in the energizing direction shown in FIG.

That is, the plate thickness 0.8 as shown in Table 1 below.
mm and 1.4 mm of cold-rolled steel sheet, hot-rolled steel sheet, and hot-dip galvanized steel sheet as the test materials to be bent and formed into a press-formed product W as shown in FIG. A sandwiching jig 1 such as an alligator clip as shown in FIG. 2 was attached to the corner of the bent portion B of the product W, and a direct current was passed along the ridgeline of the bent portion B.

[0026]

[Table 1]

At this time, the bending radius of the bent portion B is R5,
After bending at 90 degrees, it was released from the mold and spring back was still generated, but this spring back amount was about 20 degrees in various test materials.

The energization time was set to 6/50 seconds at which the temperature of the work did not rise, and the minimum current at which the strain was completely released and the springback became almost 0 was measured.

As a result, the energizing current was 35 to 46 A as shown in Table 1 above, and the bending angle after energizing was 91 to 93.
It was degree.

On the other hand, the comparative example in which the cold rolled steel sheet and the hot rolled steel sheet having a plate thickness of 0.8 mm in the lower two steps of Table 1 above are used as test materials is based on the conventional idea and is shown in FIG. It is intended to remove strain by heat energy in the energizing direction.

In this case, when the energization time is set to 6/50 seconds, the springback is not sufficiently removed even if the current is increased to 3000 A. Therefore, the energization time is extended to 1 second to give the necessary thermal energy. I did it.

As a result, the minimum current value at which springback is almost eliminated is 400 A or 5 as shown in the same column.
It was 00A.

That is, it can be seen that Example 1 is extremely energy-friendly, with a current value of 1/10 or less and an energization time of 6/50 as compared with the comparative example based on thermal energy.

Next, in Example 2, as shown in Table 2 below, the same test material as in Example 1 was used, and as shown in FIG.
Direct current and alternating current were applied in the directions indicated by (A) to (C).

[0035]

[Table 2]

In this case, the test material to be tested was a work having the same size as in Example 1, which was bent and formed to 90 degrees with a bending radius R5. In the case of the energizing method shown in FIGS. Electricity is applied in the generated state, and in the case of the energization method of FIG. 3 (B), the electrodes provided in the die as shown in FIG. 2 are used to energize in the die.

That is, FIG. 3 (B) shows a structure in which electricity is applied at a plurality of positions at a predetermined interval along the bending portion B of the molded product W in a direction substantially perpendicular to the plate thickness direction. As shown in FIG. 2, upper electrodes 4a and 4 provided on the upper mold 2 are provided.
b, 4c (6a, ..., 8a, ..., 10a, ...) and lower mold 3
Lower electrodes 5a, 5b, 5c (7a ..., 9a ..., 1) provided on the
The bent portions B, ... Are sandwiched by 1a ...), and electricity is applied spotwise in the plate thickness direction.

An insulating member 12 is interposed between each of the upper and lower molds 2 and 3 and the upper and lower electrodes 4 to 11 so that they are independent of each other and the circuits are arranged in parallel.

Also, the electrodes 4a, 4b along the bent portion B,
The interval is 10 mm, the size of the electrode itself is 1 mm, and in the embodiment, ten electrodes 4a, 4b, ... Are arranged on a line.

In the plate thickness direction, when a direct current and an alternating current are passed by the device having the structure shown in FIG.
The results of applying direct current and alternating current with the device shown in
It is as shown in Table 2. Here, the energization time was 6/50 seconds as in Example 1.

The direction of energization when using heat is
Energize according to the procedure shown in Fig. 3 (C). At this time, the energizing time is 6/5.
When it was set to 0 second, a sufficient effect could not be obtained even if several thousand A was passed, so the time was increased to 1 second. Then, the current value is gradually increased during this energization time, and the current value at which the generated springback is substantially corrected is shown in Table 2 above. By the way, when the springback is corrected, the bending angle is 84 to 9
The time was 6 degrees.

From these results, compared with the current value and energization time when the springback is corrected by heat, the current value is 1/10 or less and the energization time is 6/50.
It turns out that it is advantageous in terms of energy.

It is also clear that the current value is more advantageous when the current is applied substantially perpendicularly to the plate thickness direction than when the current is applied along the ridgeline of the bent portion B.

Here, in terms of energy, current × current ×
Since resistance x time, for example, hot dip galvanized steel sheet 0.
Taking 8t as an example,
Comparing the case of energizing in the direction substantially perpendicular to the plate thickness of the present invention, if the resistance is the same, 20/500 × 20
/500×6/50=0.000192, about 50
It turns out that energy close to 1/00 is enough.

It should be noted that in the case of an actual work, it becomes larger, and it seems that a longer energization time and a higher current than those of the above-mentioned test material are required, but it is much easier to deal with than the conventional method. Further, the present invention can be similarly applied to an aluminum alloy material as a material other than the embodiment.

[0046]

As described above, the residual strain removing method of the present invention increases the vibration energy of atoms by directly applying a direct current or an alternating current to the place where residual strain occurs, and normalizes the position of atoms. Since the residual stress is removed by removing the residual stress, the residual strain can be easily removed with inexpensive equipment.
At this time, electrons can be made to collide with the atom with the highest frequency with respect to the misaligned atom by energizing in a direction substantially perpendicular to the acting direction of the residual stress that causes the residual strain. Further, even if the current is applied in the plate thickness direction even in the direction substantially perpendicular to the acting direction of the residual stress, a small amount of electric power is required and the residual stress can be effectively removed.

[Brief description of drawings]

FIG. 1 is a configuration example of an electrode arrangement for energizing along a ridge line direction of a bent portion, (A) is a perspective view, and (B) is an enlarged view of an X portion of (A).

FIG. 2 is a perspective view showing a configuration example of an electrode arrangement for energizing in a plate thickness direction.

FIG. 3 is an explanatory diagram showing various modes of the energization direction.

[Explanation of symbols]

 1 Clamping jig 2 Upper mold 3 Lower mold W Press-formed product B Bending part

Claims (3)

[Claims] 1. A method for removing residual strain generated during the molding of a press-molded product, wherein the residual strain of the press-molded product is approximately equal to the direction of action of the residual stress that causes the residual strain. A method for removing residual strain, which comprises applying a direct current or an alternating current in a vertical direction to remove residual strain. 2. The residual strain removing method according to claim 1, wherein the energizing direction is substantially perpendicular to a plate thickness direction of the press-formed product. 3. The residual strain removing method according to claim 2, wherein a plurality of the energized portions are provided at predetermined intervals along a line in which the residual strain is generated.