JP5495266B2 - Method of shearing painted steel sheet - Google Patents

Description

  The present invention relates to a method for shearing a coated steel sheet in which the generation of enamel hair is suppressed.

In recent years, products made of coated steel sheets have been widely used as home appliances and automobile parts. In particular, a coated stainless steel plate having a stainless steel plate as a base plate and a clear coating on the surface thereof is frequently used in home appliances aimed at high design.
In addition, from the viewpoint of omitting the process and reducing the cost, a pre-painted steel sheet is used after being pressed into a desired product shape.
In the process of processing a coated steel sheet into a home appliance or an automobile part, shearing by a press machine is often performed. And in the case of a shear process, an enamel hair (coating peeling of an end surface) tends to generate | occur | produce on a shear end surface.

When enamel hair occurs on the shear end face, not only the appearance is deteriorated and the quality of the product is deteriorated, but if it occurs in the process of processing household appliances and automobile parts, it causes a dent and also decreases the yield. Connected.
Therefore, when the coated steel sheet is sheared, the coating film at the shearing portion is cut in advance, or the shear clearance is extremely reduced to reduce sagging, thereby preventing the occurrence of enamel hair. This is because, when the original plate of the coated steel plate is a surface-treated steel plate, if the sag is large, the elongation of the plating layer between the original plate and the coating film is small, so that the portion is easily broken and enamel hair is easily generated.

Specifically, Patent Document 1 proposes that after cutting the film thickness of the coating film in the sheared portion in advance, the punch and die clearance is punched at 5% or more and 10% or less of the plate thickness.
Further, when the original plate is a stainless steel plate, there is no small stretch layer such as a plating layer between the coating film and the original plate, and it is directly coated on the original plate. Therefore, since the size of the adhesion between the original plate and the coating film is directly related to the generation of enamel hair, to prevent the generation of enamel hair, increase the adhesion between the coating film and the original plate, or reduce the thickness of the coating film as much as possible. It is necessary to make it thinner.

Japanese Patent Laid-Open No. 9-3000295

In the method proposed in Patent Document 1, a film portion is cut in advance in the coating film at the shearing portion. For this reason, the shearing process itself is complicated and the productivity is lowered.
In addition, in the case of a coated stainless steel sheet in which a clear coating film is formed on a stainless steel sheet, a thick coating film is required when trying to express a desired high design. As the thickness increases, enamel hair is more likely to occur. And when enamel hair occurs, the workability is very poor, such as the need to remove after processing.

  The present invention has been devised to solve such problems. When shearing is applied to a coated steel sheet, enamel hair is generated even if the processed sheet is a coated steel sheet having a relatively thick coating film. An object of the present invention is to provide a shearing method that suppresses the above.

In order to achieve the purpose of the shearing method of the coated steel sheet according to the present invention, when the punch is pushed into the coated steel sheet placed on the die and shearing is performed, a preliminary punch having a corner R attached to the tip is pressed. In this case, the shearing punch is pushed in after the coating thickness at the shearing portion is reduced.
In the case of shearing to remove the inner side of the material, a concave part is added to the flat part at the tip and a preliminary punch with a corner R attached to the edge part is pressed to reduce the coating thickness at the sheared part. Push in the punch. At this time, it is preferable to use a shear punch having a concave portion on the flat end portion.
In any case, it is preferable to process the coated steel plate placed on the die while being pressed by a plate press.

In the method for shearing a coated steel sheet according to the present invention, the occurrence of enamel hair is suppressed by pressing a preliminary punch having a corner R at the tip to reduce the coating thickness of the sheared portion and then performing the shearing process. For this reason, even when processing a coated steel sheet having a thick coating film, it can be sheared without generating enamel hair.
Therefore, according to the present invention, it is not necessary to perform the removal work of enamel hair after processing as before, and workability is improved.

Diagram explaining the generation mechanism of enamel hair during shearing Diagram explaining the effect of coating thickness on the generation of enamel hair Diagram explaining the method for preventing enamel hair (in case of shearing) Illustration explaining the enamel hair prevention processing method (when shearing the inside of the material)

The inventors of the present invention have intensively studied the cause of enamel hair that occurs when shearing is applied to a coated steel sheet, particularly a coated stainless steel sheet that has been subjected to clear coating, and countermeasures thereof.
First, looking at the cause of enamel hair generation, the generation of enamel hair at the shear end face is presumed to be a phenomenon in which the coating film peels off at the interface with the original plate.
This phenomenon will be described with reference to the drawings.

  As shown in FIG. 1, when the coated steel plate 3 placed on the die 1 is subjected to a shearing process using the punch 2 (a), the cutting edge of the punch 2 first bites into the coating film 5 and the coating film is sheared. (B). Thereafter, the cutting edge of the punch 2 bites into the original plate 4 which is the material, the original plate is sheared (c), and separated into a punching residue and a punching die (d). When the cutting residue is separated and shearing ends, the punch is pulled upward and the cutting edge is detached from the material (e), the coating film end face and the cutting edge side face slide with high surface pressure, and the coating film 5 Force acts in the direction of peeling from the original plate 4. And it is estimated that the coating-film edge peeled off when the blade edge | part separated from the material will detach | leave from a main-body part, and will become enamel hair.

When a large shear force is applied to the interface between the original plate and the coating film, if the adhesion force at the interface is smaller than the breaking force of the coating film (= cross-sectional area x breaking stress of the coating film), the coating film peels from the interface and becomes enamel hair. Conversely, when the adhesion is strong, cracks occur in the coating film. As shown in FIG.
Therefore, the present invention has been devised so that the edge of the coating film is not peeled off or detached from the main body during shearing.
The details will be described below.

As can be seen from the effect of the coating film thickness shown in FIG. 2, when the film thickness increases, the breaking force of the coating film (= cross-sectional area × breaking stress of the coating film) becomes larger than the adhesion force at the interface, and shear processing is performed. Sometimes the edge of the coating tends to peel off from the main body, and conversely, if the film thickness is thin, the breaking force of the coating is smaller than the adhesion at the interface, so the coating edge breaks away from the main body. It becomes difficult to peel.
Therefore, when applying the shearing process, it is assumed that if the coating thickness of the shearing portion is made thin in advance, it is difficult to peel off and generation of enamel hair can be suppressed, and the present invention has been achieved.

First, the enamel hair prevention processing method at the time of carrying out the shearing process which only divides | segments material is demonstrated.
As shown in FIG. 3, (1) a pre-punching with a corner R attached to the tip is pressed against a desired shearing portion of a coated steel sheet placed on a die to crush the coating film at the shearing portion. (2) Thereby, the coating film thickness of a desired shearing part is made thin. After that, (3) a normal shearing punch is pushed in and normal shearing is performed.
Even when processing a coated steel sheet with a large coating thickness, since the coating thickness at the sheared part is thin, the generation of enamel hair is suppressed as in the case where the coating film shown in FIG. 2 is thin. be able to.

Next, an enamel hair prevention processing method when shearing the inside of the material will be described.
As shown in FIG. 4, (1) a pre-punched punch with a corner R attached to its edge is pressed against the desired punched portion of the coated steel sheet placed on the die to crush the coating film at the sheared portion. (2) Thereby, the coating film thickness of a desired shearing part is made thin. At that time, in order to facilitate the escape of the coating film, a punch provided with a recess in the flat portion at the tip is used. After that, (3) a normal shearing punch is pushed in and normal shearing is performed. In addition, like the preliminary punch, the shearing punch preferably has a recess for allowing the coating film to escape at the flat portion at the tip.
Even when processing a coated steel sheet with a large coating thickness, since the coating thickness at the punched portion is thin, the generation of enamel hair is suppressed as in the case where the coating film shown in FIG. 2 is thin. be able to.
When performing the shearing process, if the coated steel sheet placed on the die is pressed with a sheet presser, the coated steel sheet can be processed with high processing accuracy without being deformed.

Next, we introduce an example of applying shear processing to a coated stainless steel sheet with clear coating. The raw material is a SUS430 cold-rolled annealed sheet having a mechanical thickness shown in Table 1 and having a thickness of 0.4 mm, and the surface is subjected to chromium-free pre-coating treatment before 3, 6, 8, 11, and 17 μm. The one with a clear coating of polymer acrylic system was used.
The chromium-free pre-coating treatment is performed using a chemical conversion treatment solution containing a soluble halide or oxyacid salt to which polyvinylphenol is added.
The conditions shown in Table 2 were adopted as the shearing conditions. No processing oil or protective film was used.

First, the five types of coated steel sheets were punched using a punch without a corner R attached to the tip of the blade edge.
The results are shown in Table 3. Enamel hair was generated with a coating thickness of 8 μm or more. When the coating thickness was 6 μm or less, only opening cracks occurred. This situation was all the same regardless of clearance.

Next, the shearing process which applied this invention was given about three types of coated steel plates with the coating-film thickness of 8 micrometers or more which the enamel hair generate | occur | produced.
As a preliminary punch, the diameter shown in Table 4 was 28.0 mm, a corner R of 1.0 mm was attached to the edge thereof, and a concave portion having a diameter of 16.0 mm and a depth of 0.1 mm was provided on the flat portion of the tip. A punch was used.
Further, as a punch and die for shearing, a punch having a diameter of 22.00 mm shown in Table 5 and a concave portion having a diameter of 16.0 mm and a depth of 0.1 mm in a flat portion at the tip and a die having a diameter of 22.06 mm are used. Using.

Using the preliminary punch and the shearing punch, the three kinds of coated steel sheets were subjected to a shearing process according to FIG.
In addition, after prepressing so that the film thickness of a shearing part might become the film thickness shown in Table 6 with a preliminary punch, it punched out with the shearing punch and die | dye.
As a result, as shown in Table 6, any of those subjected to shearing after the coating thickness was reduced to 6 μm or less by preliminary pressing with a preliminary punch could be processed without generating enamel hair.

Claims (3)

  When carrying out shearing by pushing a punch into a coated steel plate placed on a die, press a preliminary punch with a corner R at the tip to reduce the coating thickness at the sheared part and then push the shearing punch. A shearing method for coated steel sheet characterized by   When a punch is pushed into a coated steel plate placed on a die and shearing is performed, a concave portion is given to the flat portion of the tip and a preliminary punch with a corner R attached to the edge is pressed to A method for shearing a coated steel sheet, comprising pressing a shearing punch after reducing the coating thickness.   The method for shearing a coated steel sheet according to claim 2, wherein a shearing punch having a concave portion in the front end flat part is used.

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