JPH067856A - Press forming method - Google Patents

Abstract

PURPOSE:To prevent generation of crack by melting through argon inner gas arc the part where stress concentration is generated at the time of press forming and then forming a solidified molten part. CONSTITUTION:A metal plate is blanked in a prescribed shape by blanking, and a blanked plate is formed. The part where stress concentration is generated in the blanked plate 1 at the time of press forming is melted by the arc discharge 8 generated from the tip end of a tungsten electrode 7 and by the inner gas arc of the surrounding inner gas reservoir 9, and then solidified to form the molten part 10 on an end face 2. The molten part 10 is composed of curved surface without edge. Because of the existence of the molten part 10, crack is not generated when bending is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention This application relates to a press molding method, and more particularly to a method for preventing cracks during press molding.

[0002]

2. Description of the Related Art Each of FIGS. 1 to 3B shows a conventional press forming method. As shown in FIG. 3B, a blank plate shown in FIG. Mold 1. In addition, in this figure, a part of the blank plate 1 is shown in a rotational cross section, and a shear surface 3 and a cutting surface 4 are formed on both sides of the end surface 2. Next, the end surface 2 is coined and sanded to smooth the cut surface 4 and the like, and then predetermined press working such as draw working is performed. FIG. 2B shows a state in which 180 ° bending is performed as the press working, and countless cracks 5 are generated on the end face 2.

[0003]

According to the conventional method,
In order to prevent the generation of the crack 5 shown in FIG. 2B, a coining process, a sanding process or the like is performed prior to the press process. Although it is possible to prevent cracks from occurring to some extent by these processes, it is possible to prevent the occurrence of cracks as shown in FIG.
Under harsh conditions such as 0 ° bending, deep drawing, and piercing, where stress concentration is large, cracks 5 that are visible are inevitably generated. Therefore, the present application provides a method capable of preventing the occurrence of cracks even under such severe processing conditions.

[0004]

In order to solve the above-mentioned problems, the invention of claim 1 forms a blank plate by a blanking step, and a portion of the blank plate where stress concentration occurs during press working is an inner gas arc. Is melted and then solidified to form a melted portion (hereinafter, this melting method is simply referred to as inner gas arc melting), and then the blank plate on which the melted portion is formed is pressed.

The invention of claim 2 uses argon gas as the inner gas of claim 1.

The invention of claim 3 is characterized in that the press molding of claim 1 is drawing.

According to the invention of claim 1, the press molding of claim 1 is piercing, and a molten portion by inner gas arc melting is formed in advance at a piercing target location.

[0008]

According to the first aspect of the invention, the inner gas arc is melted at a predetermined location in the blank plate where stress concentration occurs during press working, so that the surface of the melting portion becomes a curved surface and the metal structure is thermally deformed. Therefore, even if the blank plate is subsequently pressed, cracks are less likely to occur in the melted portion, so that efficient press molding can be performed.

According to the second aspect of the present invention, the use of the argon gas makes it possible to use the generally used TIG welding apparatus.

According to the third aspect of the present invention, cracking is unlikely to occur in the melted portion even when drawing is performed, so the degree of deep drawing can be increased.

According to the fourth aspect of the present invention, even if the piercing is performed, the melted portion is formed in advance in this processed portion, so that cracks are unlikely to occur on the end surface around the piercing hole.

[0012]

EXAMPLE An example will be described with reference to FIGS. First, (A) of FIG. 3 shows a step of press molding in the present application. First, a blank plate having a predetermined shape is formed by a blank step, and then inner gas arc melting is performed at a predetermined position of the blank plate to form a melting portion. Form. Next, the blank plate is pressed. This pressing includes drawing, drawing and bending such as bending, and piercing.

1A and 2A show an example of 180 ° bending of a test piece by this process. First, in FIG. 1 (A), a strip-shaped test piece (15
A blank plate 1 (0 mm × 30 mm) is formed, and then the end face 2 is subjected to inner gas arc melting. Note that FIG.
In (A), a part of the blank plate 1 is shown in a rotational cross section.

The blank plate 1 used in this embodiment is a high-strength steel (KFR440EP manufactured by Kawasaki Steel Co., Ltd.) having a thickness of 4.5 mm and containing niobium (Nb). On both sides of this end face 2, as is apparent from the rotating cross section in FIG. 1 (A), a shearing face 3 and a cutting face 4 are formed by a blank.

The inner gas arc melting apparatus comprises a torch 6
The melting point 10 is formed on the end face 2 by the arc discharge 8 generated from the tip of the tungsten electrode 7 and the inner gas arc of the inner gas layer 9 (argon gas is used in this embodiment) around it. It

As this melting apparatus, a known TIG welding apparatus can be used as it is. The processing conditions are as follows. Current: 20 to 500 amperes (A) Argon amount: 3 to 25 liters / minute Melting degree: Until the edges disappear visually

As is clear from the rotational cross section shown in FIG. 1A, the melting portion 10 has a curved surface without edges by being solidified after melting. This point is the end face 2 in the same cross-section as shown in the conventional example of FIG.
This is clear when compared with the fact that the edge part is formed.

FIG. 2A shows a state in which the blank plate 1 after the melt processing is bent by 180 °. Due to the presence of the fusion zone 10, cracks 5 as shown in FIG. 2B do not occur even by this bending process. Table 1 shows the comparison results when the sample of FIG. 1B manufactured using the same material by the conventional method is processed as shown in FIG. 2B. Moreover, even if it is melted by a normal carbon dioxide gas arc that does not use acetylene gas or inner gas, the effect as in this example cannot be obtained. These are also described as reference examples.

The reason why cracks are not generated by this method has not been clarified. However, compared with the conventional processing by machining such as coining and sanding, it is possible to eliminate surface roughness more delicately, and the inner gas arc melting using a high temperature and inert gas causes the structure of the melting portion to be modified, It is considered that various properties required for press molding such as ductility are improved.

[0020]

4 to 10 show an example of drawing such as drawing, foaming and bending as press working, and FIG. 4 shows inner gas arc melting at predetermined positions a to d of the blank plate 1 after blank working. Indicates the status. In the figure, reference numeral 11 is a flange portion, 12 is a shaft member mounting hole, 13 is an adjustment hole for wall extension, 14, 15 and 16 are mounting portions, and 17 is a curved portion.

The material of the blank plate 1 and the method of inner gas arc melting are the same as in the previous embodiment. Also, a
The positions of ~ d are set at the locations where the stress concentration is greatest during the next press working.

FIGS. 5 to 9 show a pressed product obtained by bending the blank plate 1 of FIG. 4 along a dotted line and drawing it. FIG. 5 is a plan view, FIG. 6 is a side view, and FIG. 7 is FIG. A-
It is an A line cross section. Further, FIG. 8 shows the direction of the arrow R in FIG. 6, and FIG. 9 shows the direction of the arrow L in FIG.

As is clear from these figures, the fusion zone 10
The parts a to d provided with are extremely harsh molding condition parts in which elongation and bending act in a complicated manner, and in ordinary drawing processing, visible cracks occur not only on the cut surface but also on the sheared surface. . However, according to the present embodiment, since the melted portion 10 is formed in each of these portions a to d, no crack occurs.

A comparison of a conventional product produced by subjecting only the fusion zone 10 to conventional coining and sanding under the same conditions as the product of this embodiment, as shown in the following Table 2, the effect of this embodiment is obvious. Was recognized. The non-defective product ratio (the number of non-defective products / the number of samples × 100%) is the same as in Table 1. Also,
Also in the case of melting using acetylene gas or carbon dioxide arc, the results were the same as in Table 1.

[0026]

Reference numerals 18 to 21 in the drawings are pierce holes formed by subsequent processing. Inner gas arc melting may be performed in advance at these processing locations, and in this case, machining of the end surface after piercing may be omitted. Such pretreatment of the piercing portion can be applied when forming the adjustment hole 13. Reference numeral 22 in FIG. 6 is a bolt attached to the piercing hole 21.

10A and 10B are photographs of the structure of the fusion zone 10 in the section d of FIG. 4 taken with a 20 × microscope. FIG. 10A shows the present embodiment, and FIG. 10B shows a conventional blank plate with sander and coining. Here is an example: As is clear from FIG. 10A, in this embodiment, the coarse crystal layer 23, the modified layer 24, the intermediate layer 25 made of medium-sized crystals, and the heat-affected layer are arranged in order from the curved surface to the inside. 26 and the base material layer 27. The heat-affected layer 26 is formed with a depth of about 2 mm from the surface, and reaches about 3-4 mm depending on the location. Note that the other abc parts also had the same organizational structure. On the other hand, as is apparent from FIG. 10B, in the conventional example, there is only the heat-affected layer 26 formed on the surface side at the time of machining and having a maximum depth of about 0.8 mm.

The inner gas used in the invention of the present application may be an inert gas other than argon (for example, helium gas).

[Brief description of drawings]

FIG. 1A is a diagram showing a melting process of an example, and FIG. 1B is a diagram showing a sander scoring.

FIG. 2A shows a 180 ° bent state of the example product,
(B) is a diagram showing the same state of the conventional product

3A is a process diagram of the present invention, and FIG. 3B is a process diagram of a conventional example.

FIG. 4 is a plan view of the blank plate after the melting process of the example.

FIG. 5 is a plan view of an example product after press working.

FIG. 6 is a side view of the same.

7 is a sectional view taken along the line AA of FIG.

FIG. 8 is a direction view of arrow R in FIG.

FIG. 9 is a direction view of arrow L in FIG.

FIG. 10 (A) is a micrograph of the structure of the fusion zone in the d part of FIG.

[Explanation of symbols]

 1 blank plate 2 end face 10 fusion zone

Claims (4)

[Claims] 1. A blank step of punching a flat metal plate into a predetermined shape, and a portion of the blank plate where stress concentration occurs during press working is melted by an inner gas arc and then solidified to form a molten portion. Melting process,
And a press step of pressing the blank plate on which the fused portion is formed. 2. The press molding method according to claim 1, wherein the inner gas is argon. 3. The press molding method according to claim 1, wherein the press molding is drawing. 4. The press-molding method according to claim 1, wherein the press-molding is piercing, and a melted portion by an inner gas arc is previously formed in a portion to be pierced.