PROCESSING APPARATUS, METHOD OF MANUFACTURING METALLIC MEMBER, AND METALLIC MEMBER

A processing apparatus capable of manufacturing a metallic member with improved corrosion resistance at its cut edge surface is provided. A processing apparatus (20) includes a punch (21) and a die (22) to be positioned on one side and the other side of a workpiece constituted by a metal sheet (10), the one and the other sides being arranged in the sheet-thickness direction, each of the punch (21) and the die (22) includes an end face (211), (221) and a side face (212), (222), the punch (21) and the die (22) are positioned such that the end face (211) of the punch (21) and the end face (221) of the die (22) do not overlap in plan view, at least one of the side face (212) of the punch (21) and the side face (222) of the die (22) includes an inclined portion (212a) providing a surface inclined to face the metal sheet (10) and shaped to overlap the other one of the punch (21) and the die (22) in plan view, and the surface provided by the inclined portion (212a) and the sheet-thickness direction form an angle θ not smaller than 15°.

TECHNICAL FIELD

The present invention relates to a processing apparatus, a method of manufacturing a metallic member, and a metallic member.

BACKGROUND ART

Steel members for automobiles and buildings are usually manufactured by press working. To produce a steel member required to have corrosion resistance, material in the form of cold-rolled steel sheet or hot-rolled steel sheet is pressed and then provided with paint and/or plating. Having painting and/or plating steps after pressing increases work time and/or costs.

To solve this problem, material in the form of plated steel sheet may be pressed. However, if a plated steel sheet is subjected to a press-working process involving cutting, such as stamping, the plating layer is severed at the cut edge surface, exposing base steel. If base steel at the cut edge surface remains exposed, corrosion initiates at the cut edge surface. Addressing this requires an additional step for plating the cut edge surface at which base steel is exposed, increasing work time and costs.

JP 2017-87294 A discloses a cutting method for cutting a surface-treated steel sheet using a die assembly in which the clearance between the die and punch is 1 to 20% of the sheet thickness and the shoulder of at least one of the die or punch has a radius curvature 0.12 times the sheet thickness of the surface-treated steel sheet or larger.

JP 2009-287082 A discloses a cutting method for cutting a zinc-based plated steel sheet using a die assembly composed of a die, a punch and a die holder, where that one of the die and punch which corresponds to the product steel sheet has a rounded shoulder with a radius of curvature 0.10 to 0.50 times the sheet thickness of the steel sheet, whereas the shoulder of the other one and the shoulder of the die holder each form a right angle, and where the cutting is performed with the side surfaces of the die and die holder aligned and with a clearance between the die and punch is not larger than 1.0% of the sheet thickness of the steel sheet.

PRIOR ART DOCUMENTS

Patent Documents

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

The processing conditions of JP 2017-87294 A reduce the fracture surface produced and increase the length of the shear surface when the die is conditioned to have a small clearance; however, the plating layer on the resulting shear surface is limited to a narrow area. On the other hand, when the die is conditioned to have a large clearance, the length of the shear surface is larger than with conventional conditions but a certain amount of fracture surface is produced. Thus, corrosion may occur in non-plated portions of the shear surface and the fracture surface.

The processing conditions of JP 2009-287082 A reduce the fracture surface produced and increase the length of the shear surface; however, the plating layer on the resulting shear surface is limited to a narrow area.

An object of the present invention is to provide a processing apparatus capable of manufacturing a metallic member with improved corrosion resistance at its cut edge surface, a method of manufacturing a metallic member with improved corrosion resistance at its cut edge surface, and a metallic member with improved corrosion resistance at its cut edge surface.

Means for Solving the Problems

A processing apparatus according to an embodiment of the present invention is a processing apparatus including a punch and a die to be positioned on one side and another side of a workpiece constituted by a metal sheet, the one and the other sides being arranged in a sheet-thickness direction, the processing apparatus adapted to shear the metal sheet by moving at least one of the punch and the die in the sheet-thickness direction such that the punch and the die are located closer to each other, wherein: each of the punch and the die includes an end face and a side face; the punch and the die are positioned such that the end face of the punch and the end face of the die do not overlap in plan view; at least one of the side face of the punch and the side face of the die includes an inclined portion providing a surface inclined to face the metal sheet and shaped to overlap the other one of the punch and the die in plan view; and the surface provided by the inclined portion and the sheet-thickness direction form an angle not smaller than 15°.

A method of manufacturing a metallic member according to an embodiment of the present invention includes using the above-described processing apparatus to shear a metal sheet having a plating layer on a surface.

A metallic member according to an embodiment of the present invention is a metallic member formed from a metal sheet having a plating layer on a surface, wherein an edge surface includes one inclined surface having a dimension in a sheet-thickness direction not smaller than 60% of a sheet thickness, the inclined surface and the sheet-thickness direction forming an angle not smaller than 15°, at least a portion of the inclined surface being covered with the plating layer.

Effects of the Invention

The present invention provides a metallic member with improved corrosion resistance at its cut edge surface.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Now, embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding components in the drawings are labeled with the same reference numerals, and their description will not be repeated. The size ratios between the components shown in the drawings do not necessary represent the actual size ratios.

First Embodiment

FIG.1is a cross-sectional view of a processing apparatus20according to a first embodiment of the present invention, schematically showing its construction. The processing apparatus20is a die assembly used to shear a metal sheet. Although not limiting, the processing apparatus20may be particularly suitably used to shear a metal sheet having a plating layer on its surface (hereinafter sometimes referred to as “surface-plated metal sheet”). Although not limiting, the shearing includes hole making, stamping and cutting.

The processing apparatus20includes a punch21, a die22, and a sheet holder23. The punch21and die22are positioned on one side and the other side of a workpiece constituted by a metal sheet10, the one and the other sides being arranged in the sheet-thickness direction. The processing apparatus20uses a press, not shown, to shear the metal sheet10by moving at least one of the punch21and die22in the sheet-thickness direction such that the punch21and die22are located closer to each other. The sheet holder23is positioned to face the die22, with the metal sheet10sandwiched in between, and prevents the metal sheet10from warping during shearing of the metal sheet10and from clinging to the punch21during removal of the punch21.

The direction represented by the sheet-thickness direction will hereinafter sometimes be referred to as z-direction, while a plane perpendicular to the z-direction will sometimes be referred to as xy-plane. The dimension in the sheet-thickness direction will sometimes be referred to as “height”.

The punch21includes an end face211and a side face212contiguous with the end face. Similarly, the die22includes an end face221and a side face222contiguous with the end face. The end face211contacts the metal sheet10earlier during processing than the side face212does, and the end face221contacts the metal sheet10earlier during processing than the side face222does.

The end face211and the end face221are preferably perpendicular to the sheet-thickness direction. In other words, the end faces211and221are preferably parallel to the metal sheet10.

A clearance CL of a predetermined size in plan view is provided between the contour of the end face211and the contour of the end face221. Thus, the punch21and die22are positioned such that the end face211and the end face221do not overlap in plan view. As used herein, “in plan view” means looking at an object exactly in one sheet-thickness direction. The end face211and the end face221“not overlapping in plan view” means that the end faces211and221do not overlap when the end faces211and221are projected onto a plane perpendicular to the sheet-thickness direction (i.e., an xy-plane).

In this arrangement, the punch21and die22may be moved closer to each other until the distance between the end faces211and221in the sheet-thickness direction is zero or less. This enables severing the metal sheet10in a more reliable manner. It also prevents the punch21and die22from hitting each other when the metal sheet10is severed.

Each of the end faces211and221may have any shape as long as they do not overlap in plan view. The planar shape of the end face211(i.e., shape in an xy-plane) may be, for example, circular, elliptical, or rectangular. The planar shape of the end face221may be, for example, a shape with a circular hole formed therein, a shape with an elliptical hole formed therein, or a shape with a rectangular hole formed therein. The planar shape of the end face221is preferably such that the clearance CL is constant.

The planar shape of the end face211is preferably circular. The planar shape of the end face221is preferably a shape with a circular hole formed therein. If a circular shape is used, the end faces constrains the material circumferentially, which can achieve uniform deformation. Thus, when a surface-plated metal sheet is sheared, good corrosion resistance is provided to the edge surface.

The end face211is not limited to any particular size (i.e., surface area). However, if the end face211is too small, it may be unable to withstand the load during processing, and thus be damaged. The size of the end face211is preferably equivalent to a circle with a diameter of 10 mm (i.e., area of about 78 mm2) is larger. On the other hand, if the end face211is too large, this increases the load required to push the metal sheet10with an inclined portion212a, described further below, which may require use of a press with higher performance.

The punch21and die22may be solid or may be hollow. The punch21and die22are preferably solid. The punch21and die22receive compressive stress during a push of the metal sheet10by the inclined portion212a, discussed further below. Accordingly, the punch21and die22preferably have sufficient strengths for withstanding such stress.

The side face212of the punch21includes an inclined portion212aproviding a surface inclined to face the metal sheet10and shaped to overlap the die22in plan view.

As used herein, “providing a surface inclined to face the metal sheet10” means that a normal to the surface provided by the inclined portion212athat extends outwardly from the surface is directed toward the metal sheet10. More specifically, it means that, where the positive z-direction is defined as the direction from the metal sheet10toward the position of the punch21and the negative z-direction is defined as the direction toward the position of the die22, the component in the z-direction of the normal to the surface provided by the inclined portion212aextending outwardly from the surface is negative.

As used herein, the inclined portion212aand die22“overlapping in plan view” means that the inclined portion212aand die22overlap when the inclined portion212aand die22are projected onto a plane perpendicular to the sheet-thickness direction (i.e., an xy-plane). For the purposes of this definition, it is not necessary that the entire inclined portion212aoverlap the die22; it is sufficient if at least a portion of the inclined portion212aoverlaps the die22.

In this arrangement, when the punch21and die22are moved closer to each other, the metal sheet10is sandwiched by the inclined portion212aand die22such that compressive stress is applied to the metal sheet10. This compressive stress deforms the metal sheet10into a specific shape. Such shapes will be discussed further below.

The angle formed by the surface provided by the inclined portion212aand the sheet-thickness direction, θ, is not smaller than 15°. Preferable ranges of the angle θ will be specified further below.

Relative to the sheet thickness of the metal sheet10, the height of the inclined portion212a, HT, is preferably not smaller than 60% of the sheet thickness of the metal sheet10. The height HT of the inclined portion212ais preferably not smaller than 1 mm, more preferably not smaller than 3 mm, and yet more preferably not smaller than 5 mm.

In addition to the inclined portion212a, the side face212of the punch21includes an extreme end portion212bcontiguous with the inclined portion212aand located at an end adjacent to the metal sheet10as determined along the sheet-thickness direction and providing a surface generally parallel to the sheet-thickness direction. The angle formed by the surface provided by the extreme end portion212band the sheet-thickness direction is preferably not larger than 5.0°, more preferably not larger than 3.0°, yet more preferably not larger than 1.0°, and still more preferably not larger than 0.5°.

The extreme end portion212benables applying large shearing stress to the metal sheet10. This further ensures that the metal sheet10is severed. However, depending on the size of the clearance CL and the material of the metal sheet10, the metal sheet10may be severed with no extreme end portion212. Accordingly, it is not essential that the side face212include an extreme end portion212b; the side face212need not include an extreme end portion212b.

Furthermore, the presence of the extreme end portion212bmakes the size of the clearance CL clearer, which further ensures that the punch21and die22are properly positioned. This effect is produced if an extreme end portion212bis present, even if the height H of the extreme end portion212bis small. Relative to the sheet thickness of the metal sheet10, a lower limit of the height H is preferably 1% of the sheet thickness of the metal sheet10, more preferably 2%, and yet more preferably 3%. A lower limit of the height H is preferably 0.03 mm, more preferably 0.06 mm, and yet more preferably 0.09 mm.

On the other hand, if the height H of the extreme end portion212bis too large, the metal sheet10may be severed before the inclined portion212acontacts the metal sheet10. Further, there is a tendency that the smaller the height H, the later the time at which the metal sheet10is severed. If a surface-plated metal sheet is sheared, the later the time at which the metal sheet10is severed, the better corrosion resistance is provided to the edge surface, as discussed in more detail further below.

Thus, to provide good corrosion resistance to a produced metallic member, the smaller the height H of the extreme end portion212b, the better. Relative to the sheet thickness of the metal sheet10, an upper limit of the height H is preferably 50% of the sheet thickness of the metal sheet10, more preferably 40%, and yet more preferably 30%. An upper limit of the height H is preferably 1.6 mm, more preferably 1.2 mm, and yet more preferably 0.8 mm.

The side face222of the die22is generally parallel to the sheet-thickness direction. The side face222of the die22does not include an inclined portion like the inclined portion212aof the side face212of the punch21.

[Method of Manufacturing Metallic Member]

Next, a method of manufacturing a metallic member will be described. A method of manufacturing a metallic member according to the present embodiment includes the step of shearing a surface-plated metal sheet using the processing apparatus20.

Although not limiting, the base material of the surface-plated metal sheet may be steel, copper, a copper alloy, aluminum, or an aluminum alloy, for example. The manufacturing method according to the present embodiment is particularly suitable in implementations where the base material of the surface-plated metal sheet is steel, i.e., the surface-plated metal sheet is a plated steel sheet, because steel is prone to rust and, as such, providing corrosion resistance to steel according to the present embodiment has significant advantages. The plated steel sheet may be, for example, a Zn-based plated steel sheet or an Al-based plated steel sheet.

More preferably, the surface-plated metal sheet is a Zn-based plated steel sheet. A Zn-based plating acts as a sacrificial corrosion protection for the steel sheet, i.e., base material. This prevents corrosion initiating at exposed base material at the cut edge surface resulting from the shearing, thereby further increasing the corrosion resistance of the produced metallic member. Although not limiting, the Zn-based plating may be hot-dip galvanizing, galvannealing, Zn—Ni-based plating, Zn—Al-based plating, Zn—Mg-based plating, or Zn—Al—Mg-based plating, for example.

The sheet thickness of the surface-plated metal sheet is preferably 0.2 to 9 mm. If the sheet thickness is too large, the proportion of the fracture surface after shearing may be larger, reducing the effect of improving corrosion resistance. An upper limit of the sheet thickness of the surface-plated steel sheet is more preferably 6 mm. On the other hand, if the sheet thickness is sufficiently small, any rust developed on the edge surface will not be noticeable and, as such, the benefit of improved corrosion resistance will be small. A lower limit of the sheet thickness of the surface-plated steel sheet is more preferably 1.0 mm.

The thickness of the plating layer of the surface-plated metal sheet is preferably not smaller than 15 μm. If the plating layer is too small, the plating layer may be insufficient for covering the edge surface such that corrosion resistance may not be provided to the edge surface. A lower limit of the thickness of the plating layer of the surface-plated metal sheet is more preferably 30 μm. Although not limiting, an upper limit of the thickness of the plating layer of the surface-plated metal sheet is 150 μm, for example.

The step of shearing the metal sheet10(i.e., surface-plated metal sheet) using the processing apparatus20will be described referring toFIGS.1and2. As mentioned in the description of the construction of the processing apparatus20, the punch21and die22are positioned on one side and the other side, arranged in the sheet-thickness direction, of the metal sheet10. At least one of the punch21and die22is moved in the sheet-thickness direction by a press, not shown, such that the punch21and die22are located closer to each other. During this, an inclined surface111is formed in the metal sheet10by the inclined portion212aof the punch21, as shown inFIG.2.

Thereafter, the punch21and die22are moved even closer to each other such that the metal sheet10is severed into a first portion11and a second portion12. At this time, a cut surface112is formed in the edge surface of the first portion11, contiguous with the inclined surface111. The cut surface112includes a shear surface and a fracture surface. However, depending on the processing conditions, the cut surface112may be constituted by only one of a shear surface and a fracture surface, or no cut surface112may be formed at all.

According to the present embodiment, the first portion11including the inclined surface111provides a product (i.e., metallic member). The inclined surface111is formed through deformation of the surface of the metal sheet10, which is a surface-plated metal sheet, and thus has a plating layer at least in some portions. The inclined surface111may have some of its plating layer peeled off by sliding against the punch21, for example, but still is more likely to be covered with a plating layer than the shear surface and fracture surface. Further, the thickness of the plating layer covering the inclined surface111does not significantly decrease from the amount of thickness of the plating layer of the surface-plated metal sheet.

The shear surface may be covered with a plating layer originating from the plating layer on the surface of the metal sheet10that has detoured and entered, or may not be covered with a plating layer. The fracture surface is usually not covered with a plating layer.

With the processing apparatus20according to the present embodiment and the method of manufacturing a metallic member according to the present embodiment, the edge surface of a produced metallic member includes an inclined surface, thereby increasing the proportion of the edge surface covered with a plating layer. This provides a metallic member with improved corrosion resistance at its cut edge surface.

The angle θ (FIG.1) formed by the surface provided by the inclined portion212aof the punch21and the sheet-thickness direction is not smaller than 15°. There is a tendency that the larger the angle θ, the later the time at which the metal sheet10is severed. “Later the time at which the metal sheet10is severed” means that the metal sheet10is not severed until the punch21and die22are moved even closer to each other. The later the time at which the metal sheet10is severed, the smaller the height of the cut surface112and the higher the proportion of the height of the inclined surface111in the sheet thickness of the metal sheet10. Thus, the larger the angle θ, the higher the proportion of the edge surface covered with a plating layer. A lower limit of the angle θ is preferably 20°, and more preferably 30°.

On the other hand, the larger the angle θ, the larger the load required to form the inclined surface111. The angle θ is equal to the angle of inclination of the inclined surface111; as such, a larger angle θ means a larger projection area of the formed inclined surface111in an xy-plane. An upper limit of the angle θ is preferably 60°, more preferably 50°, and yet more preferably 45°.

As mentioned in the description of the construction of the processing apparatus20, there is a tendency that the smaller the height H of the extreme end portion212bof the punch21, the later the time at which the metal sheet10is severed. The later the time at which the metal sheet10is severed, the smaller the height of the cut surface112and the higher the proportion of the height of the inclined surface111in the sheet thickness of the metal sheet10. Thus, the smaller the height H, the higher the proportion of the edge surface covered with a plating layer.

As mentioned above, with the method of manufacturing a metallic member according to the present embodiment, the first portion11inFIG.2provides a product (i.e., metallic member). After the second portion12is stamped out of the metal sheet10, the remaining portion constitutes the first portion11. The first portion11will be hereinafter referred to as metallic member11.

FIG.3is a perspective view of the metallic member11, andFIG.4is a cross-sectional view taken on line IV-IV inFIG.3. AlthoughFIG.3shows an implementation where the hole in the metallic member11has a circular contour, this is merely illustrative. As mentioned in the description of the construction of the processing apparatus20, each of the end face211of the punch21and the end face221of the die22may have any planar shape. Accordingly, the contour of the hole in the metallic member11may have any shape.

The metallic member11includes one inclined surface111in its edge surface. The metallic member11further includes a cut surface112contiguous with the inclined surface111and located at that one of the ends of the metallic member11as determined along the sheet-thickness direction at which the size of the member is increased by the inclined surface111. As show inFIG.4, the cut surface112includes a shear surface112aproviding a surface generally parallel to the sheet-thickness direction, and a fracture surface112b. The shear surface112aand the fracture surface112bare formed in this order, beginning at the one adjacent to the inclined surface111.

The surfaces of the metallic member11except for the edge surface are covered with the plating layer10a. In the edge surface of the metallic member11, at least a portion of the inclined surface111is covered with the plating layer10a. The shear surface112amay be covered, or may not be covered, with the plating layer10a. The fracture surface112bis usually not covered with the plating layer10a.FIG.4, by way of example, shows an implementation where the entire inclined surface111and a portion of the shear surface112aare covered with the plating layer10aand base material is exposed at the remainder of the shear surface112aand the fracture surface112b.

The height Ht of the inclined surface111is not smaller than 60% of the sheet thickness T. The higher the proportion of the height Ht in the sheet thickness T, the higher the corrosion resistance of the edge surface. A lower limit of the height Ht is preferably 70% of the sheet thickness T, more preferably 80%, and yet more preferably 90%. The height Ht of the inclined surface111may be increased by, for example, increasing the angle θ formed by the surface provided by the inclined portion212aof the punch21(FIG.1) and the sheet-thickness direction, or reducing the height H of the extreme end portion212bof the punch21.

The entire edge surface of the metallic member11may be constituted by the inclined surface111. In other words, the metallic member11need not include a cut surface112. On the other hand, if the metallic member11includes a cut surface112, the metallic member11can be manufactured in a more stable manner. A lower limit of the height of the cut surface112is preferably 3% of the sheet thickness T, and more preferably 5%.

Even if a portion of the cut surface112is not covered with the plating layer10a, the metallic member11has good corrosion resistance because at least a portion of the inclined surface111is covered with the plating layer10a. Particularly, if the surface-plated metal sheet is a Zn-based plated steel sheet, the Zn-based plating layer acts as a sacrificial corrosion protection for the base material, i.e., steel sheet, which provides a certain corrosion resistance even if the proportion of the surface at which base material is exposed is relatively large.

The angle θ formed by the inclined surface111and the sheet-thickness direction is not smaller than 15°. A lower limit of the angle θ is preferably 20°, and more preferably 30°. An upper limit of the angle θ is preferably 60°, more preferably 50°, and yet more preferably 45°.

The angle θ formed by the inclined surface111and the sheet-thickness direction may be controlled by adjusting the shape of the punch21(FIG.1). The angle θ formed by the inclined surface111and the sheet-thickness direction is equal to the angle θ formed by the inclined portion212aand the sheet-thickness direction.

The plating layer10acovering at least a portion of the inclined surface111is derived from the workpiece. Consequently, the plating layer10acovering at least a portion of the inclined surface111has completely the same composition as the plating layer10acovering the surfaces other than the edge surface.

The proportion of the surface region of the inclined surface111covered with the plating layer10ais preferably not lower than 60%. More preferably, the entire inclined surface111is covered with the plating layer10a.

The thickness of the portion of the plating layer10acovering the inclined surface111ais preferably 25 to 90% of the thickness of the portions of the plating layer10acovering the surfaces other than the edge surface.

AlthoughFIG.4shows an implementation where the inclined surface111and the cut surface112are formed in the edge surface of the metallic member and the cut surface112includes a shear surface112aand a fracture surface112b, the cut surface112may not include one of a shear surface112aand a fracture surface112b. Further, as mentioned above, the metallic member11may not have a cut surface112.

The processing apparatus20, the method of manufacturing a metallic member, and the metallic member11according to the first embodiment of the present invention have been described. The present embodiment provides a metallic member with improved corrosion resistance at the cut edge surface.

Second Embodiment

FIG.5is a cross-sectional view of a processing apparatus30according to a second embodiment of the present invention, schematically showing its construction. The processing apparatus30is different from the processing apparatus20according to the first embodiment (FIG.1) in the construction of the punch and die. The processing apparatus30includes a punch31replacing the punch21of the processing apparatus20, and a die32replacing the die22of the processing apparatus20.

The punch31includes an end face311and a side face312contiguous with the end face. Similarly, the die32includes an end face321and a side face322contiguous with the end face. According to the present embodiment, too, a clearance CL with a predetermined size in plan view is provided between the contour of the end face311and the contour of the end face321. Thus, the punch31and die32are positioned such that the end face311and the end face321do not overlap in plan view.

The side face312of the punch31is generally parallel to the sheet-thickness direction.

The side face322of the die32includes an inclined portion322aproviding a surface inclined to face the metal sheet10and shaped to overlap the punch31in plan view.

As used herein, “providing a surface inclined to face the metal sheet10” means that, more specifically, where the positive z-direction is defined as the direction from the metal sheet10toward the position of the punch31and the negative z-direction is defined as the direction toward the position of the die32, the component in the z-direction of the normal to the surface provided by the inclined portion322aextending outwardly from the surface is positive.

As used herein, the inclined portion322aand punch31“overlapping in plan view” means that the inclined portion322aand punch31overlap when the inclined portion322aand punch31are projected onto a plane perpendicular to the sheet-thickness direction (i.e., an xy-plane). For the purposes of this definition, it is not necessary that the entire inclined portion322aoverlap the punch31; it is sufficient if at least a portion of the inclined portion322aoverlaps the punch31.

In this arrangement, when the punch31and die32are moved closer to each other, the metal sheet10is sandwiched by the inclined portion322aand punch31such that compressive stress is applied to the metal sheet10. This compressive stress deforms the metal sheet10into a specific shape.

The angle θ formed by the surface provided by the inclined portion322aand the sheet-thickness direction and the height HT of the inclined portion322aare the same as in the first embodiment.

In addition to the inclined portion322a, the side face322of the die32includes an extreme end portion322bcontiguous with the inclined portion322aand located at an end adjacent to the metal sheet10as determined along the sheet-thickness direction and providing a surface generally parallel to the sheet-thickness direction. The height H of the extreme end portion322bis the same as in the first embodiment. Further, as is the case with the first embodiment, the side face322may not include an extreme end portion322b.

[Method of Manufacturing Metallic Member]

Next, a method of manufacturing a metallic member will be described. A method of manufacturing a metallic member according to the present embodiment includes the step of shearing a surface-plated metal sheet using the processing apparatus30.

The step of shearing the metal sheet10(i.e., surface-plated metal sheet) using the processing apparatus30will be described referring toFIGS.5and6. The punch31and die32are positioned on one side and the other side, arranged in the sheet-thickness direction, of the metal sheet10. At least one of the punch31and die32is moved in the sheet-thickness direction by a press, not shown, such that the punch31and die32are located closer to each other. During this, an inclined surface141is formed in the metal sheet10by the inclined portion322aof the die32, as shown inFIG.6.

Thereafter, the punch31and die32are moved even closer to each other such that the metal sheet10is severed into a first portion13and a second portion14. At this time, a cut surface142is formed in the edge surface of the second portion14, contiguous with the inclined surface141. The cut surface142includes a shear surface and a fracture surface. However, depending on the processing conditions, the cut surface142may be constituted by only one of a shear surface and a fracture surface, or no cut surface142may be formed at all.

According to the present embodiment, the second portion14provides a product (i.e., metallic member).

With the processing apparatus30according to the present embodiment and the method of manufacturing a metallic member according to the present embodiment, the edge surface of a produced metallic member includes an inclined surface141, thereby increasing the proportion of the edge surface covered with a plating layer. This provides a metallic member with improved corrosion resistance at its cut edge surface.

As mentioned above, with the method of manufacturing a metallic member according to the present embodiment, the second portion14inFIG.6provides a product (i.e., metallic member). The second portion14is stamped out of the metal sheet10. The second portion14will be hereinafter referred to as metallic member14.

FIG.7is a perspective view of the metallic member14, andFIG.8is a cross-sectional view taken on line VIII-VIII inFIG.7. AlthoughFIG.7shows an implementation where the metallic member14has a circular contour, this is merely illustrative. The contour of the metallic member14may have any shape.

The metallic member14includes one inclined surface141in its edge surface. The metallic member14further includes a cut surface142contiguous with the inclined surface141and located at that one of the ends of the metallic member14as determined along the sheet-thickness direction at which the size of the member is increased by the inclined surface141. As shown inFIG.8, the cut surface142includes a shear surface142aproviding a surface generally parallel to the sheet-thickness direction, and a fracture surface142b. The shear surface142aand the fracture surface142bare formed in this order, beginning at the one adjacent to the inclined surface141.

In the metallic member14, as is the case with the metallic member11(FIG.4), the surfaces except for the edge surface are covered with the plating layer10a. In the edge surface of the metallic member14, at least a portion of the inclined surface141is covered with the plating layer10a. The shear surface142amay be covered, or may not be covered, with the plating layer10a. The fracture surface142bis usually not covered with the plating layer10a.FIG.8, by way of example, shows an implementation where the entire inclined surface111and a portion of the shear surface142aare covered with the plating layer10aand base material is exposed at the remainder of the shear surface142aand the fracture surface142b.

The height Ht of the inclined surface141, the height of the cut surface142, the angle θ formed by the inclined surface141, the sheet-thickness direction, etc., are the same as in the first embodiment. The height Ht of the inclined surface141, the height of the cut surface142, and the angle θ formed by the inclined surface141and the sheet-thickness direction may be controlled by adjusting the shape of the die32(FIG.5). Further, as is the case with the first embodiment, the cut surface142may not include one of a shear surface142aand a fracture surface142b, and the metallic member14may not have a cut surface142.

The processing apparatus30, the method for manufacturing a metallic member, and the metallic member14according to the second embodiment of the present invention have been described. While the processing apparatus20according to the first embodiment (FIG.1) provides an inclined portion212ain the side face212of the punch21, the processing apparatus30according to the second embodiment (FIG.5) provides an inclined portion322ain the side face322of the die32. While the first embodiment provides an inclined surface111in the first portion11(FIG.2), the second embodiment provides an inclined surface141in the second portion14(FIG.6). Both embodiments produce the same effects in terms of the corrosion resistance of the edge surface.

In other words, to produce a metallic member having an edge surface with improved corrosion resistance, it is sufficient if at least one of the side face of the punch and the side face of the die includes an inclined portion. The inclined portion is only required to provide a surface inclined to face the metal sheet and overlapping the other one of the punch and die in plan view.

Third Embodiment

FIG.9is a cross-sectional view of a processing apparatus40according to a third embodiment of the present invention, schematically showing its construction. The processing apparatus40is different from the processing apparatus20according to the first embodiment (FIG.1) in the construction of the die. The processing apparatus40includes a die32replacing the die22of the processing apparatus20. The die32is the same as in the processing apparatus30according to the second embodiment (FIG.5).

According to the present embodiment, too, a clearance CL of a predetermined size in plan view is provided between the contour of the end face of the punch21and the contour of the end face of the die32. Thus, the punch21and die32are positioned such that their end faces do not overlap each other in plan view.

According to the present embodiment, an inclined portion is provided in each of the side face of the punch21and the side face of the die32. As shown inFIG.10, the metal sheet10is severed into a first portion11including an inclined surface111and a second portion14including an inclined surface141. According to the present embodiment, each of the first and second portions11and14provides a product (i.e., metallic member).

The processing apparatus, the method for manufacturing a metallic member, and the metallic member according to the third embodiment of the present invention have been described. The present embodiment, too, provides a metallic member with improved corrosion resistance at its cut edge surface.

Fourth Embodiment

FIG.11is a cross-sectional view of a processing apparatus50according to a fourth embodiment of the present invention, schematically showing its construction. The processing apparatus50is different from the processing apparatus20according to the first embodiment (FIG.1) in the construction of the punch and die. The processing apparatus50includes a punch51replacing the punch21of the processing apparatus20, and includes a die52replacing the die22of the processing apparatus20.

The punch51includes an end face511and a side face512contiguous with the end face. Similarly, the die52includes an end face521and a side face522contiguous with the end face. A clearance CL of a predetermined size in plan view is provided between the contour of the end face511and the contour of the end face521. Thus, the punch51and die52are positioned such that their end faces do not overlap in plan view.

As is the case with the first embodiment, the side face512of the punch51includes an inclined portion521aand an extreme end portion512b. The side face522of the die52is generally parallel to the sheet-thickness direction.

The punch51and die52of the processing apparatus52are different from the punch51and die22of the processing apparatus20(FIG.1) in their planar shape.

FIG.12is a perspective view of a metallic member15produced by the processing apparatus50. The metallic member15is produced by cutting a metal sheet along one direction perpendicular to the sheet-thickness direction (i.e., y-direction). The metallic member15includes an inclined surface151and a cut surface152.

The inclined surface151and cut surface152are the same as the inclined surface111and cut surface112of the metallic member11(FIG.3) except that they are different in their planar shape (i.e., shape in an xy-plane). Thus, the present embodiment, too, provides a metallic member with improved corrosion resistance at its cut edge surface.

FIGS.3and7illustrate implementations where the metallic member produced is the remainder of the metal sheet after a predetermined shape has been stamped out (FIG.3), and where the metallic member is the portion stamped out of the metal sheet (FIG.7). In addition, the same effects produced by the previously discussed embodiments are produced by implementations where a metal sheet is cut into a metallic member, as according to the present embodiment. It will be understood that the line along which the metal sheet10is cut need not be a straight line.

The above embodiment illustrates an implementation where an inclined portion512ais provided in the side face512of the punch51; in other implementations, in lieu of the side face512of the punch51or in addition to the side face512of the punch51, the side face522of the die52may include an inclined portion.

Examples

Now, the present invention will be described more specifically with reference to examples. The present invention is not limited to these examples.

A processing apparatus representing the construction of the processing apparatus20(FIG.1) was used to perform stamping on a metal sheet. The end face211of the punch21had a circular shape with a diameter of 10.0 mm, and the clearance CL was 0.05 mm (the diameter of the hole in the die22being 10.1 mm). Trial production was performed while the angle θ was changed to 15°, 30° and 45° and the height H was changed to 0.1 mm, 0.4 mm and 0.8 mm. The workpiece was a Zn—Al—Mg-based plated steel sheet with a yield strength of 366 MPa, a tensile strength of 454 MPa, an elongation of 31%, a sheet thickness of 3.2 mm, and an amount of adherent plating of 275 g/m2.

For comparative examples, stamping was performed on a metal sheet using a columnar punch with a diameter of 10.0 mm and a die having a columnar hole with a diameter of 10.8 mm.

FIG.13shows contour diagrams each illustrating the stress distribution inside a metal sheet in the middle of the processing, calculated by the finite element method. As shown inFIG.13, with the processing apparatus for the inventive examples, the region pushed by the inclined portion was under high pressure, and a stress concentration zone was produced that extended from the shoulder of the die, parallel to the inclined portion.

FIG.14shows photographs each showing a cross section of a metal sheet immediately before fracture.FIG.14shows that, if processing was done by the processing apparatus for the inventive examples, the time at which cracking occurred was later than when processing was done by the processing apparatus for the comparative examples (i.e., cracking did not occur until the punch was pushed in deeper).

FIG.15is a graph showing the relationship between the angle θ and height H and the push-in limit during stamping. The push-in limit during stamping is the amount of push-in by the punch immediately before the metal sheet is fractured; a larger push-in limit during stamping means a later time at which the metal sheet is fractured.FIG.15shows that the larger the angle θ or the smaller the height H, the larger the push-in limit during stamping.

FIG.16shows photographs each showing a cross section of a metal sheet after processing, as well as results of element analysis of the edge surface. “Hp” inFIG.16means the height of the portion of the edge surface that has a remaining plating layer thereon (hereinafter referred to as “remaining plating height Hp”). The remaining plating height Hp was determined by measuring the edge surface of the metal sheet with energy-distribution X-ray analysis equipment (EDX) and determining the distributions of Zn and Fe on the edge surface. A metal sheet processed by a punch including an inclined portion with an angle θ of 30° had some of the plating layer peeled off near the lower end of the inclined surface. In a metal sheet processed by a punch including an inclined portion with an angle θ of 45°, the plating layer remained all the way to the lower end of the inclined surface, although intermittently.

FIG.17is a graph showing the relationship between the angle θ and height H and the persistence of plating. The persistence of plating is the remaining plating height Hp divided by the sheet thickness.FIG.17shows a tendency that the larger the angle θ or the smaller the height H, the higher the persistence of plating. It is to be noted that the persistence of plating on a metal sheet processed by the processing apparatus for the comparative examples was 20% at the maximum.

FIG.18shows photographs of metal sheets before and after atmospheric corrosion testing. The atmospheric corrosion testing was conducted by cutting a metal sheet in halves, applying a rust-preventive paint to the edge surfaces other than the surface to be evaluated (i.e., edge surface formed by stamping), and then placing the metal sheet outdoors. Each of the metal sheets processed by the processing apparatus for the comparative examples had large, conspicuous regions of red rust on the fracture surface three weeks after the initiation of exposure. In contrast, in the case of the metal sheets processed by the processing apparatus for the inventive examples, a small amount of red rust was produced three weeks after the initiation of exposure for an example with a height H of 0.4 mm and eight weeks after the initiation of exposure for an example with a height H of 0.1 mm, although in narrow regions and difficult to observe visually.

Next, a processing apparatus representing the construction of the processing apparatus50(FIG.11) was used to perform shearing to cut a metal sheet along a straight line. The clearance CL between the end face511of the punch51and the end face521of the die52was 0.05 mm. Trial production was performed while the angle θ was changed to 15°, 30° and 45° and the height H was changed to 0.1 mm, 0.4 mm and 0.8 mm. The workpiece used was a Zn—Al—Mg-based plated steel sheet identical with that for stamping. For comparative examples, a shearing die assembly with vertical side faces (with a clearance of 0.4 mm) was used to perform shearing to cut a metal sheet along a straight line.

FIG.19shows photographs each showing a cross section of a metal sheet after processing, as well as results of element analysis of the edge surface. In a metal sheet processed by a punch including an inclined portion with an angle θ of 45°, the plating layer remained all the way to the lower end of the inclined surface.

FIG.20is a graph showing the relationship between the angle θ and height H and the persistence of plating. It is to be noted that the persistence of plating of a metal sheet processed by the processing apparatus for the comparative examples was 18% at the maximum.

FIG.21shows photographs of metal sheets before and after atmospheric corrosion testing. Each of the metal sheets processed by the processing apparatus for the comparative examples had red rust on the fracture surface six weeks after the initiation of exposure. In contrast, in the metal sheets processed by the processing apparatus for the inventive examples, no red rust was produced as of six weeks after the initiation of exposure.

Embodiments of the present invention have been described. The above-described embodiments are merely illustrative examples useful for carrying out the present invention. Thus, the present invention is not limited to the above-described embodiments, and the above-described embodiments, when carried out, may be modified as appropriate within the scope of the invention.

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