JP2015157314A - PUNCHING METHOD OF Zn BASED GALVANIZED STEEL SHEET - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a punching method of a Zn-Al-Mg based galvanized steel sheet, capable of suppressing degradation of corrosion resistance at a punching end surface of a punching process product.SOLUTION: In a punching process method of a Zn-Al-Mg based galvanized steel sheet, a punching process is performed by using a metal die in which any shoulder part R of a die and a punch is given a curvature radius calculated from a formula (1), such that a clearance between the die and the punch is 10% or less of thickness of the steel sheet. 0.1×((P/S)×t/t)×t≤R≤0.5×((P/S)×t/t)×t)..(1) Here, Pis hardness of galvanized metal, Sis hardness of base steel sheet, t is thickness of galvanized steel sheet, and tis thickness of base steel sheet, with 0.1-0.5 being a coefficient.

Description

The present invention relates to a method for suppressing a decrease in corrosion resistance of a punched end face that occurs when a Zn-based plated steel sheet coated with a plated metal containing Zn is cut by punching.

Conventionally, plastic processed products such as automobile parts and household appliance parts are generally manufactured by plastic processing of cold-rolled steel sheets to form a shape with a predetermined dimension, and then applying Zn plating (post Zn plating). However, in recent years, for the purpose of improving the corrosion resistance and durability of parts and reducing costs by omitting processes, Zn-plated steel sheets coated with Zn or Zn alloy on the steel sheet surface are used as the material, and the steel sheets are made plastic. Increasingly, parts are manufactured by processing. In the present specification, a steel plate obtained by plating Zn or an alloy containing Zn on the surface of the steel plate is referred to as a Zn-based plated steel plate. Among the plastic processing of Zn-based plated steel sheets, drawing, overhanging, and bending processes are subject to damage such as cracking and peeling in the plating layer. This damage can be avoided or suppressed. However, in a process that cuts the Zn-based plated steel sheet into an arbitrary shape, such as removing the flange in order to obtain the final product shape, the cut end surface is in a state in which no plated metal is present or partly absent. turn into. In this way, if there is a region where there is no plating metal on the cut end face, red rust is likely to be generated from that region, and the red rust expands to the flat part where the plating metal exists, deteriorating the appearance and strength of the product. Problems come out.
As a method for cutting a Zn-based plated steel sheet, punching with a punch and a die is usually performed. And as a method of improving the rust prevention capability of this punching end face, for example, as shown in Patent Document 1, manufacture of a metal plate part in which a surface treatment agent (rust preventive agent) is applied to all or part of the punching end face The method is known. Or
As shown in Patent Document 2, a method has been proposed in which a punched end surface is covered with a covering member made of Al, a Zn-based plated steel plate, or the like. Further, in Patent Document 3, in a Zn-based plated steel sheet having a thickness of 2 mm or less, the shoulder of either the punch or the die has a curvature radius of 0.1 to 0.5 times the thickness of the Zn-based plated steel sheet. There has also been proposed a method in which punching is performed using a set die, the shearing surface ratio of the punched end face after punching is 90% or more, and the zinc coverage of the shearing surface is 50% or more. This technique is intended to utilize the sacrificial anticorrosive action that Zn-based plating has on steel sheets.

JP 2006-315052 A JP 2000-34586 A Japanese Patent No. 5272518

As described above, in the methods proposed in Patent Document 1 and Patent Document 2, it is necessary to separately apply a surface treatment agent (rust preventive agent) and manufacture a covering member. The cost associated with the material and manufacture of the covering member increases, resulting in a problem that the cost of the punching process itself increases.
Further, in the method for cutting a Zn-based plated steel sheet of Patent Document 3, the rust prevention ability is improved in any environment as long as the plated metal is present in the entire cut end face, but the zinc coverage of the shear plane is 50%. In this case, since the coated zinc is 50% or less of the entire punched end face, the sacrificial anticorrosive action is insufficient due to the environment in which the product is placed and red rust is generated, which may not be applicable.

Therefore, an object of the present invention is to provide a method for suppressing the increase in cost and suppressing the occurrence of red rust on the punched end face, with respect to the method for cutting a Zn-based plated steel sheet.

In order to achieve the object, the processing method of the present invention is a method of punching a Zn—Al—Mg based steel sheet using a die comprising a die, a punch and a plate presser, Punching is performed by setting the curvature radius R of any shoulder within the range of the value calculated from the following formula (1) and setting the clearance between the die and the punch to 10% or less of the plate thickness of the steel plate. It is characterized by that.
_{0.1 × ((P HV / S} HV) × t S /t)×t≦R≦0.5×((P HV / S HV) × t S / t) × t) ·· (1)
_{Here, P HV:} hardness of the plated _{metal, S HV:} a base steel sheet Hardness, t: plate thickness of the plated steel sheet, _{t S} is the thickness of the base steel sheet.

In the punching method of the Zn-based plated steel sheet according to the present invention, as shown by the formula (1), the die or punch is formed based on the ratio between the hardness of the plated metal and the hardness of the base steel sheet and the thickness of the base steel sheet. The curvature radius R of the shoulder is determined. In other words, the ratio between the hardness of the plated metal and the hardness of the base steel sheet is an item that takes into account the level of deformation of the plated metal, and the thickness of the base steel sheet takes into account the area where the plated metal wraps around the punched end face. ing. All of these items place emphasis on the wrapping of the plated metal around the punched end face. By using a mold having a curvature radius R of the shoulder determined in consideration of these items, plating is performed. It is possible to increase the plating coating area on the punched end surface due to metal wrapping.
In addition, as the material to be punched, Zn-Al-Mg-based plated steel sheet is used, and since the anticorrosion function of the punched end face is higher than other Zn-based plated steel sheets, the entire surface of the punched end face is not coated with plated metal. However, relatively high corrosion resistance of the punched end face can be ensured.

FIG. 2 is a schematic diagram for explaining a punching method in which a shoulder portion R is provided on a die in an embodiment of the punching method of the present invention; and (b) a schematic diagram for explaining a punching method in which a shoulder portion R is provided on a punch. Figure

Embodiments of the present invention will be described below.
The Zn—Al—Mg based plated steel sheet that is the subject of the present invention is obtained by coating the surface of a base steel sheet with a Zn alloy containing Al and Mg as a plating metal. When punching is performed without imparting a radius of curvature R to the shoulder of the die or punch, the plated metal wraps around and coats a part of the punched end surface. From this coated plated metal, Zn, Al, and Mg are coated. The protective film composed of the eluted metal is formed in the portion which is eluted and is not covered with the plating metal. As a result, the corrosion resistance of the punched end face is relatively higher than that of other Zn-based plated steel sheets, and the corrosion resistance of the component itself is improved. Further, the corrosion resistance of the flat portion other than the punched end face is superior to other Zn-based plated steel sheets. The base steel plate of the Zn—Al—Mg plated steel plate is not particularly limited, and for example, low carbon steel, medium carbon steel, high carbon steel, alloy steel, or the like can be used. Further, when good press formability is required, a steel sheet for deep drawing made of low carbon Ti-added steel, low carbon Nb-added steel, or the like is preferable as the base steel plate.

In the punching method of the present invention, emphasis is placed on the wrapping of the plated metal around the punched end face. When punching is performed, after the steel sheet is deformed by pressing the Zn-Al-Mg plated steel sheet with a punch, there is a crack near the die side (opposite side of the punch pressing surface) of the steel sheet. Although it is generated and cut, it is necessary to promote the deformation and movement of the plating metal by the pressurization of the punch in order to make a large amount of the plating metal go around the punched end face.
The deformation of the plated metal increases as the deformability increases, that is, as the hardness decreases. That is, in order to increase the amount of plating metal around the punched end face, it is necessary to consider the hardness of the plating metal and the base steel sheet.
Further, since the corrosion resistance of the end face is lowered unless the plated metal is more widely wrapped around the end face of the base steel plate, the necessary amount of deformation of the plated metal is also a factor for determining the curvature radius R of the shoulder portion of the mold. The required amount of deformation of the plated metal is determined by the thickness of the base steel plate. If the thickness of the plated steel plate is the same, the thickness of the plated metal is also determined when the thickness of the base steel plate is determined. The ratio of the plate thickness of the base steel plate to the plate thickness of the plated steel plate is affected.
However, even if the hardness ratio between the plated metal and the base steel sheet and the plate thickness ratio between the plated steel sheet and the base steel sheet are the same, if the thickness of the plated steel sheet changes, Affects the occurrence of If the curvature radius R of a shoulder part is determined only by said ratio, when the plate | board thickness of a plated steel plate is thin, it will become easy to generate | occur | produce sagging and a burr | flash.
The inventors of the present invention have the shoulder radius of curvature R to ensure the quality of the punched hole by wrapping the plated metal around the punched end surface, the ratio of the hardness of the plated metal to the base steel plate, and the plated steel plate to the base steel plate. The present invention has been completed by grasping that it depends on the thickness ratio and the thickness of the plated steel sheet.
The curvature radius R of the shoulder is determined by the above-described formula (1). However, when the plated metal is harder than the base steel plate, the plated metal is less likely to be deformed. It needs to be bigger. On the contrary, when the hardness of the plated metal is lower than that of the base steel plate, the plated metal is easily deformed. Therefore, the wraparound of the plated metal can be realized even if the radius of curvature R is reduced. The wrapping around the punched end face needs to be realized more widely on the base steel sheet surface of the punched end face. However, the thicker the plated metal thickness and the thinner the base steel sheet, the wider the plated metal surface on the end face steel sheet surface. Therefore, the curvature radius R of the shoulder can be reduced as the plating metal is thicker, that is, when the plate thickness ratio between the plated steel plate and the base steel plate is lower. Conversely, if the thickness of the plated metal is thinner, that is, if the plate thickness ratio between the plated steel plate and the base steel plate is high, the curvature radius R of the shoulder portion needs to be increased.
However, even if the above ratio is the same, when the thickness of the plated steel sheet itself is different, the deformation state of the plated steel sheet when punched is also different. When the plate thickness of the plated steel sheet is reduced, sagging and burrs are likely to occur on the punched end face, and the end face quality is degraded.
As a result of various studies, the present inventors have found that the ratio of the hardness of the plated metal and the base steel sheet, the ratio of the thickness of the plated steel sheet and the base steel sheet, and the plate thickness of the plated steel sheet are coefficients of 0.1 to 0.5. It was found that the shoulder R can be derived by multiplying the value of. When the coefficient is smaller than 0.1, the plating metal is not sufficiently wrapped around, and when it is larger than 0.5, the punched end face is sag.
Furthermore, the clearance between the punch and the die is 10% or less of the plate thickness of the plated steel plate. When the clearance is set to exceed 10%, the sagging of the punched end surface becomes large.
When plating metal is wrapped around the end face of a part punched by pressurization with a punch, shoulder R is applied to the die as shown in Fig. 1 (a), and the plated metal is wrapped around the punched hole. In the case where it is necessary, a shoulder R is provided to the punch as shown in FIG.

  As the Zn-6% Al-3% Mg plated steel sheet 1, a steel sheet with a plated steel sheet thickness, a single-side plated metal thickness and a base steel sheet hardness changed was used. For punching, a punch 2 having a diameter of 9 mm and a die 3 having an inner diameter changed by a clearance are used, and a shoulder R4 is also provided to each of the punch 2 and the die 3. The 3% Mg plated steel sheet 1 was fixed.

  Regarding the state of the punched end face, the cross section of the end face was observed to check the surrounding area of the plated metal and the presence or absence of sagging. The wrapping area of the plating metal was evaluated by the ratio of the wrapping length of the plating metal to the thickness of the end face.

The results are shown in Table 1. No. In No. 10, the clearance between the die and the punch was 15%, which was excessive, and sagging occurred. No. No. 16 has a radius of curvature of the die shoulder R of 0.8 mm, which is a die condition outside the range in the equation (1), and therefore the wrapping ratio of the plated metal to the punched end surface is 70%, 100 % Did not become.
No. In No. 3, the die shoulder R was 0.6 mm, which was a mold condition larger than the range in the formula (1), and sagging occurred.
According to the punching method of the present invention, the plated metal can be made to wrap around the entire area of the punched end face, and no sagging has occurred.

  The punching method according to the present invention is suitable for suppressing deterioration in corrosion resistance of a punched end face of a part manufactured by punching using a Zn-6% Al-3% Mg plated steel sheet as a raw material.

1 Zn-Al-Mg plated steel plate 2 Punch 3 Die 4 Shoulder R
5 Work clamp

Claims (1)

Using a die consisting of a die, punch and plate presser,
A method of punching a Zn—Al—Mg based steel sheet,
The radius of curvature of the shoulder R of either die or punch is within the range of values calculated from equation (1);
A punching method for a Zn-Al-Mg plated steel sheet, wherein the clearance between the die and the punch is 10% or less of the thickness of the Zn-Al-Mg plated steel sheet.
_{0.1 × ((P HV / S} HV) × t S /t)×t≦R≦0.5×((P HV / S HV) × t S / t) × t) ·· (1)
_{Here, P HV:} hardness of the plated _{metal, S HV:} hardness of the base steel sheet, t: plate thickness of the plated steel sheet, _{t S} is the thickness of the base steel sheet, 0.1 to 0.5 is a coefficient.
It is.

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