JP5178129B2 - Overhang processing method of metal plate - Google Patents

Description

  The present invention relates to a metal plate overhanging method capable of increasing the forming limit.

As a method for manufacturing automobile parts and home appliance parts, a method of pressing a thin metal plate material is often used. Among the press working methods, there are (1) a drawing method and (2) an overhanging method.
Drawing is a plastic working that draws the outer periphery of the blank material into a die while drawing it into the die, and generally has a case of up to about 2 to 2.5 times the punch size even if the size of the blank is large. It is used for forming a shape with little or no flange after forming.
The overhanging process is a plastic process in which the size of the blank is considerably larger than the size of the punch, the flange hardly moves into the die during molding, and processing is performed only by elongation deformation of the material in the region where the punch is projected.

In press processing, formability is improved by traditionally performing inching molding that stops the slide in the middle of processing, or repeated stroke molding that molds to the bottom dead center while repeatedly raising and lowering the slide several times during processing. It is known.
The former improves the formability by performing an inching operation so that distortion occurs in a portion different from the portion where the strain is once concentrated.
The latter is a method that is possible with a type that allows manual operation of the slide, such as a hydraulic press, for example. In addition to the former effect, oil shortage generated under high surface pressure is eliminated by separating the mold and work material. As a result, the formability is improved as a result of the restoration of the lubricity. When molding is very difficult, the operator may apply lubricant to the material surface after raising the slide.

  For example, in Patent Document 1, press molding is performed while applying minute vibrations to an upper mold or a lower mold of a press molding die, the frictional force between the mold and the material is reduced, the limit drawing ratio is improved, and the moldability is improved. It is described to do. However, the method of Patent Document 1 is practically difficult to apply a desired vibration to a mold because it is a practical press molding machine, regardless of a small experimental apparatus. It was.

  Therefore, as seen in Patent Document 2, in a press molding method in which a metal plate is clamped with a punch and a die, the punch first reaches the stroke end after the punch first contacts the metal plate and molding starts. In the press forming method, the operation of once separating the punch from the metal plate and forming the metal plate again using the punch and the die is performed at least once before the forming is completed. Proposed.

By the way, as a press method of a press machine, conventionally, two methods of a hydraulic press and a mechanical press have been mainstream.
The hydraulic press is suitable for overhanging because it can be molded at low speed, but its productivity is low. On the other hand, the mechanical press has an advantage that it is excellent in productivity because of its high processing speed, but there is also a drawback that cracking tends to occur when the processing speed is high. For this reason, as for the mechanical press, in order to improve the stretch workability, a link motion press in which a link mechanism is attached to slow down the working speed during the stretch forming is also used (for example, see Non-Patent Document 1).

More recently, for example, as can be seen in Patent Document 3, a servo press capable of arbitrarily setting a slide motion using an AC servo motor as a drive source is also used.
JP-A-1-122624 JP 2005-199318 A JP 2002-263742 A Nakada Hiroyasu, “Theory and Practice of Press”, Corona Co., Ltd., February 20, 1973, p.171

So far, in press processing, the lower the slide speed during processing, the better the moldability, so even with link motion etc., the slide speed is slow until the press processing is completed, and the slide speed is increased after passing the bottom dead center. The motion to do was adopted.
Recently, servo presses that are frequently used use an AC servo motor as a drive source, and therefore can perform forward rotation, reverse rotation, stop, speed switching, and the like of a slide arbitrarily. In addition, it can be expected to reduce noise and improve the die life by adjusting the processing speed during press working.

The method proposed in Patent Document 2 is effective from the viewpoint of improving moldability. However, since the timing for once separating the mold in the middle of processing from the metal plate to be processed has not been clarified, if the timing for once separating the mold from the metal plate to be processed is not appropriate, the workability improvement effect cannot be sufficiently obtained. It will be.
The present invention has been devised to solve such a problem, and when the punch is pushed into the workpiece metal plate to perform the overhanging processing, the timing of once separating the punch or the die from the workpiece metal plate is effective. It is an object of the present invention to provide a metal plate overhanging method that is improved in formability by being set at a large time point.

In order to achieve the object, the metal plate overhanging method according to the present invention, when a punch is pushed into a metal plate to be processed fixed by a die and a blank holder, and the material and shape of the die and the punch, Pre - extrusion processing is performed in which the material and shape of the processed metal plate, wrinkle holding force, lubrication conditions and processing speed are the same conditions as the actual overhanging conditions, and forming in one continuous stroke up to the overhanging height at which cracking occurs. After measuring the height from the position of the crack generated in the pre-extrusion processed product to the top of the overhang, after forming to the height from the crack occurrence position to the top of the overhang during the actual overhang processing, It is characterized in that a step of once separating from the processed metal plate is interposed during the forming .

  According to the present invention, the lubricant film is regenerated and the formability is improved by interposing a step of once separating the punch or die from the metal plate to be processed. Moreover, since the timing of once releasing is effective timing for suppressing the concentration of strain at the crack risk site, it can be said that the regeneration effect of the lubricant film effectively acts on the dispersion of strain.

In general, in the overhanging process, distortion concentrates on the punch shoulder and cracks occur at that portion. Usually, the punch shoulder radius is expanded or the lubricating oil is highly lubricated to avoid cracking.
However, the enlargement of the punch shoulder radius requires a change in the shape of the overhang processed product, and the higher lubrication of the lubricating oil leads to an increase in cost.

Therefore, the present inventors refer to the metal sheet press forming method described in Patent Document 2 and use a servo press capable of freely setting the motion of the slide, thereby allowing the stretch workability to be performed. The effect of the timing of mold release on the process was investigated.
As a result, it has been found that the stretch formability is improved by once separating the punch or die from the metal plate to be processed after forming from the crack occurrence position to the height of the stretch top.
Details will be described below.

First, a SUS430 stainless steel plate having a thickness of 0.8 mm was used as a test material, and a spherical overhanging process with a punch diameter of φ100 mm was performed using a blank cut to 300 × 300 mm. The dice corner R (Rd) was 2 mm. The punch is a spherical head having a corner R (Rp) of 50 mm. A 10-fold diluted solution of α soap was used as the press oil, and overhanging was performed at a wrinkle holding force: 400 kN, slide speed: 200 mm / second.
In this overhanging process, when the overhang height reached 25 mm, a crack occurred at a position 10 mm above the top of the spherical surface.

Next, the overhanging process was performed again under the same conditions. Here, under the condition of sandwiching the process of once separating the punch from the workpiece metal plate at a height of 5 mm, and the condition of sandwiching the process of once separating the punch from the workpiece metal plate at a height of 15 mm I tried two types of overhanging.
In the former, it was possible to mold to an overhang height of 25 mm exactly as in the case of continuous one-stroke slide movement (cracking occurred at an overhang height of 25 mm). On the other hand, in the latter, it was possible to mold to an overhang height of 35 mm (cracking occurred at an overhang height of 35 mm).

  In this way, as shown in FIG. 1B, the step of once separating the punch from the metal plate to be processed is interposed after forming from the crack occurrence position to the height of the overhang in the overhang processing of only one step. As a result, the stretch formability can be greatly improved. FIG. 1A shows a situation during the overhanging process. Details will be given in the description of the example, but under exactly the same conditions, the molding height reaches the height H (see FIG. 2 (a)) from the crack occurrence position to the top of the overhang processed product. It has been found that it is effective to intervene a step of once separating the punch from the workpiece metal plate after the time (see FIG. 2B).

  In the overhanging process, cracks occur at sites where strain is concentrated and the amount of deformation is large. The position where the strain concentrates changes depending on the shape of the punch, the characteristics of the material, the lubrication conditions, the processing speed, and the like. For example, in the above-described SUS430 stainless steel sheet overhanging process, it is considered that the position at a height of 10 mm from the overhanging top where the crack is generated corresponds to the part where the distortion is concentrated and the amount of deformation is large. Accordingly, it can be said that the most effective timing for improving the moldability is to once remove the punch or die from the material and restore the lubricity when the strain is concentrated at the site where the oil shortage has occurred. On the other hand, even if the punch or die is once separated from the material before it contacts the portion where the punch strain is concentrated, the effect of improving the formability is hardly recognized.

When the overhanging process is performed by pressing the punch against the workpiece metal plate by continuous one-stroke slide movement, the surface of the workpiece metal plate and the punch surface slide while being pressed against each other. In the process of forming, the lubricant film that exists between the punch surface and the surface of the metal plate to be processed becomes thin at the start of forming, and when the film breaks, the metals are in direct contact with each other. become.
As a result, the coefficient of friction between the surface of the metal plate to be processed and the punch surface is increased, the lubricity is lowered, and the metal plate to be processed is cracked.
And the crack occurs in the part where distortion tends to concentrate most.

Therefore, it is considered that the stretch formability can be improved by grasping in advance the portion where distortion is most likely to concentrate and improving the lubricity of the portion during the stretch processing.
First, as means for improving lubricity, means for once separating the punch from the metal plate to be processed is adopted. When the punch is separated from the workpiece metal plate, the strain is generated in a portion different from the portion where the strain is once concentrated, and a high pressure is applied in the fine recess on the punch surface or in the minute recess on the workpiece metal plate surface. It is considered that the lubricant confined in the step appears on the surface, regenerates the lubricant film, and the moldability is improved by the effect of improving the lubricity.

The part where the strain is most likely to be concentrated can be known by measuring the height from the top of the overhang to the position where the crack has occurred when the overhanging process is performed by a continuous one-stroke slide movement.
The reason why it is preferable to interpose a step of once separating the punch from the work metal plate after forming it to the height from the crack occurrence position to the top of the overhang when performing overhang processing by continuous one-stroke slide movement is as follows: When overhanging is performed with a continuous one-stroke slide movement, the height from the cracking position to the top of the overhang and the position where the strain concentrates are almost the same, and when the strain has concentrated at the site where oil shortage has occurred It is conceivable that the moldability is most effectively improved by once removing the punch or die from the material to restore the lubricity.

The part where strain is most likely to concentrate depends on the physical properties of the material, including the mechanical properties of the material, the surface condition, etc., the mold characteristics including the surface condition of the punch, the usage status of the lubricant, or the processing speed. It changes a lot.
Therefore, a preliminary experiment was performed in which the metal plate, die, lubricant to be used, and working speed that are actually subjected to overhang processing were made the same, and from the crack occurrence position to the top of the overhang according to the conditions. It is necessary to grasp the height H in advance.

  With a conventional mechanical press, it is difficult to release the mold once from the material during molding, and even with a hydraulic press, it is difficult to automatically perform such repeated stroke motion. Therefore, if the servo press is capable of setting the slide motion arbitrarily using an AC servo motor as the drive source, the mold can be temporarily separated from the material during molding, which is effective in improving moldability. It is possible to perform an operation of once separating the mold from the material at a proper timing (after forming from the crack occurrence position to the top of the overhang when the overhang is performed by continuous one-stroke slide movement).

Example 1;
Using a SUS430 stainless steel plate having a thickness of 0.8 mm as a test material and using a blank cut to 300 × 300 mm, spherical overhanging with a punch diameter of φ100 mm was performed. The dice corner R (Rd) was 2 mm. The punch is a spherical head having a corner R (Rp) of 50 mm. A 10-fold diluted solution of α soap was used as the press oil, and overhanging was performed at a wrinkle holding force: 400 kN, slide speed: 200 mm / second.
In this overhanging process, when the overhang height reached 25 mm, a crack occurred at a position 10 mm above the top of the spherical surface.

Next, the overhanging process was performed again under the same conditions. However, when the overhang height reached the height shown in Table 1, a step of once separating the punch from the workpiece metal plate was sandwiched. And the overhanging process was finished when the crack occurred. Thereafter, the overhang height was measured, and the height from the crack occurrence position to the overhang top was measured.
The results are also shown in Table 1.
From the result shown in Table 1, after finishing the overhanging process to a height position exceeding the height from the crack occurrence position to the overhanging top (in the case of this example, after the overhanging process to a height of 10 mm), the punch It is understood that it is effective to intervene a step of once separating from the workpiece metal plate (in the case of the present embodiment, at least one operation of separating at a position where the overhang height exceeds 10 mm).

Example 2;
Extrusion processing was performed under the same conditions as in Example 1 except that a SUS304 stainless steel plate having a thickness of 0.8 mm was used as a test material.
First, in the spherical overhanging process by continuous one-stroke slide movement, overhang molding was possible up to a spherical height of 40 mm. At this time, a crack occurred at a position 18 mm high from the top of the spherical surface.
Next, as in Example 1, overhanging was performed again under the same conditions. However, when the overhang height reached the height shown in Table 2, a step of once separating the punch from the metal plate to be processed was sandwiched. And the overhanging process was finished when the crack occurred. Thereafter, the overhang height was measured, and the height from the crack occurrence position to the overhang top was measured.
The results are also shown in Table 2.

  Also from the results shown in Table 2, after finishing overhanging to a height position exceeding the height from the crack occurrence position to the top of the overhang (in this example, after overhanging to a height of 18 mm), It is understood that it is effective to intervene a step of once separating the punch from the workpiece metal plate (in the case of this embodiment, at least one separation operation at a position exceeding the overhang height of 18 mm).

  In the above embodiment, the punch is separated from the workpiece metal plate, but in many cases, a die is attached to the slide in a normal press, so the die is once separated from the workpiece metal plate. Similarly, it is possible to improve the stretch formability by taking a step of once separating the die from the workpiece metal plate at the time after the height position where the crack is generated when the stretch process is performed by continuous one-stroke slide movement. confirmed. Since the die presses the material on the crease and presses the material against the punch, once the die is released, the contact pressure between the punch and the material is released, and the punch is once released from the workpiece metal plate. The same effect was obtained.

Figure explaining how to apply metal sheet to a metal plate, (a) During normal overhang processing, (b) When the punch is separated from the metal plate to be processed (A) The figure explaining the cross-sectional shape of the molded product after preliminary overhang processing, (b) The figure explaining the timing which separates a punch from a processed metal plate

Claims (1)

When pushing and punching a punched metal plate fixed by a die and a blank holder, the material and shape of the die and punch, the material and shape of the metal plate to be processed, the wrinkle holding force, the lubrication conditions, and the processing speed Pre - extrusion processing is performed in which the conditions are the same as the actual overhanging conditions and molding is performed in one continuous stroke up to the overhanging height at which cracking occurs, and the height from the position of the crack generated in the pre-extruding product to the top of the overhanging After measuring the above, at the time of the actual overhanging process, after forming to the height from the crack occurrence position to the overhanging top part, a step of once separating the punch or die from the work metal plate is interposed in the middle of the forming A metal plate overhang processing method.

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