Patent Grant
10421113
This application is a 35 U.S.C. 371 National Phase Entry Application from PCT/JP2014/078212, filed Oct. 23, 2014, which claims the benefit of Japanese Patent Application No. 2013-260072 filed Dec. 17, 2013, the disclosure of which are incorporated by reference in their entirety.
Present invention relates to a formed material manufacturing method in which ironing is performed on a formed portion, and a surface treated metal plate used therein.
A convex formed portion is typically formed by performing a pushing process such as drawing using a surface treated metal plate such as a coated steel plate as a raw material. When the formed portion requires a particularly high degree of dimensional precision, ironing is implemented on the formed portion after the formed portion is formed. Ironing is a processing method of setting a clearance between a punch and a die to be narrower than a plate thickness of the formed portion prior to ironing, and then ironing a plate surface of the formed portion using the punch and the die so that the plate thickness of the formed portion matches the clearance between the punch and the die.
A configuration disclosed in Patent Document 1 and so on, shown below, for example, may be employed as a mold used during ironing. Specifically, the conventional mold includes a punch and a die. The punch is a columnar member having an outer peripheral surface that extends rectilinearly parallel to a pushing direction into a pushing hole, and is inserted into a formed portion. The die includes the pushing hole into which the formed portion is pushed together with the punch. The pushing hole has a shoulder portion disposed on an outer edge of an inlet of the pushing hole and constituted by a curved surface having a predetermined curvature radius, and an inner peripheral surface that extends rectilinearly from a radius end of the shoulder portion parallel to the pushing direction. When the formed portion is pushed into the pushing hole, the plate surface thereof is ironed by the shoulder portion so as to decrease gradually in thickness to a width of a clearance between the outer peripheral surface of the punch and the inner peripheral surface of the pushing hole.
[PTL 1]
The plate thickness of the formed portion prior to ironing is uneven in the pushing direction. More specifically, the plate thickness of a rear end side of the formed portion in the pushing direction is often thicker than the plate thickness of a tip end side of the formed portion. The reason why the rear end side is thicker is that when the formed portion is formed, the tip end side is stretched to a greater extent than the rear end side.
In the conventional mold described above, the outer peripheral surface of the punch and the inner peripheral surface of the pushing hole extend parallel to each other. Accordingly, the clearance between the outer peripheral surface of the punch and the inner peripheral surface of the pushing hole is uniform in the pushing direction, and therefore the part of the formed portion having the increased plate thickness is subjected to a larger amount of ironing. Hence, a surface treated layer of the part having the increased plate thickness is shaved, and as a result, a powder form residue may be generated. The powder form residue causes problems such as formation of minute pockmarks (dents) in the surface of the ironed formed portion and deterioration of the performance of a product manufactured using the formed material.
Present invention has been designed to solve the problem described above, and an object thereof is to provide a formed material manufacturing method and a surface treated metal plate used therein, with which generation of a large load on a part of a surface can be avoided so that an amount of generated powder form residue can be reduced.
A formed material manufacturing method according to present invention includes the steps of: forming a convex formed portion by performing at least one forming process on a surface treated metal plate; and performing ironing on the formed portion using an ironing mold after forming the formed portion. The surface treated metal plate includes a surface treated layer provided on a surface of the metal plate, and a lubricating film provided on a surface of the surface treated layer. The ironing mold includes a punch that is inserted into the formed portion, and a die having a pushing hole into which the formed portion is pushed together with the punch. The pushing hole includes a shoulder portion disposed on an outer edge of an inlet of the pushing hole and constituted by a curved surface having a predetermined curvature radius, and an inner peripheral surface which extends from a radius end of the shoulder portion in a pushing direction of the formed portion, and along which an outer surface of the formed portion slides in response to relative displacement between the punch and the die. The inner peripheral surface extends non-parallel to an outer peripheral surface of the punch, and the inner peripheral surface is provided with a clearance that corresponds to an uneven plate thickness distribution, in the pushing direction, of the formed portion prior to the ironing relative to the outer peripheral surface to ensure that an amount of ironing applied to the formed portion remains constant in the pushing direction.
Further, a surface treated metal plate according to present invention is used in a formed material manufacturing method including the steps of forming a convex formed portion by performing at least one forming process on the surface treated metal plate, and performing ironing on the formed portion using an ironing mold after forming the formed portion, and includes a surface treated layer provided on a surface of the metal plate and a lubricating film provided on a surface of the surface treated layer.
With the formed material manufacturing method according to the present invention, the inner peripheral surface of the pushing hole extends non-parallel to the outer peripheral surface of the punch, and the inner peripheral surface is provided with a clearance that corresponds to the uneven plate thickness distribution, in the pushing direction, of the formed portion prior to the ironing relative to the outer peripheral surface to ensure that the amount of ironing applied to the formed portion remains constant in the pushing direction. Therefore, generation of a large load on a part of the surface can be avoided, and as a result, an amount of generated powder form residue can be reduced. In particular, the surface treated metal plate includes the surface treated layer provided on the surface of the metal plate and the lubricating film provided on the surface of the surface treated layer, and therefore the amount of generated powder form residue can be reduced under a wider range of processing conditions.
Embodiments of the present invention will be described below with reference to the drawings.
First Embodiment
As shown in
As shown in
The ironing process S2 is a process for performing ironing on the formed portion 1 using the ironing mold to be described below. Ironing is a processing method of setting a clearance between a punch and a die of an ironing mold to be narrower than a plate thickness of a formed portion prior to ironing, and then ironing a plate surface of the formed portion using the punch and the die so that the plate thickness of the formed portion matches the clearance between the punch and the die. In other words, the thickness of the formed portion 1 following ironing is thinner than the thickness of the formed portion 1 prior to ironing.
As shown in
The die 21 is a member that includes the pushing hole 210 into which the formed portion 1 is pushed together with the punch 20. The pushing hole 210 includes the shoulder portion 211 and an inner peripheral surface 212. The shoulder portion 211 is disposed on an outer edge of an inlet of the pushing hole 210, and is constituted by a curved surface having a predetermined curvature radius. The inner peripheral surface 212 is a wall surface extending in the pushing direction 1c from a radius end 211a of the shoulder portion 211. The radius end 211a of the shoulder portion 211 is a terminal end of the curved surface constituting the shoulder portion 211 on an inner side of the pushing hole 210. The point that the inner peripheral surface 212 extends in the pushing direction 1c means that a component of the pushing direction 1c is included in an extension direction of the inner peripheral surface 212. As will be described in more detail below, the inner peripheral surface 212 of the pushing hole 210 extends non-parallel (does not extend parallel) to the outer peripheral surface 20a of the punch 20.
When the formed portion 1 is pushed into the pushing hole 210 together with the punch 20, as shown in
To ensure that an amount of ironing applied to the formed portion 1 remains constant in the pushing direction 1c, the inner peripheral surface 212 is provided with a clearance 212a that corresponds to the uneven plate thickness distribution, in the pushing direction 1c, of the formed portion 1 prior to ironing relative to the outer peripheral surface 20a of the punch 20. Here, as shown in
In other words, the inner peripheral surface 212 is provided such that the clearance 212a relative to the outer peripheral surface 20a in any position in the pushing direction 1c takes a value obtained by subtracting a fixed value (the required ironing amount) from the plate thickness of the formed portion 1 prior to ironing in an identical position. When the clearance 212a in any position in the pushing direction 1c is set as C (d), the plate thickness of the formed portion 1 prior to ironing in the same position is set as Tb (d), and the required ironing amount is set as A, the inner peripheral surface 212 is provided to satisfy C (d)=Tb (d)−A. Note that d is the distance from the base portion 1b of the formed portion 1 in the pushing direction 1c.
To put it another way, the inner peripheral surface 212 is provided such that the clearance 212a between the inner peripheral surface 212 and the outer peripheral surface 20a decreases in the pushing direction 1c at an identical rate to the reduction rate of the plate thickness of the formed portion 1 in the pushing direction 1c prior to ironing. When the reduction rate of the plate thickness of the formed portion 1 in the pushing direction 1c prior to ironing is constant, the inner peripheral surface 212 is constituted by a rectilinear tapered surface that extends at an angle corresponding to the reduction rate of the plate thickness of the formed portion 1. When the reduction rate of the plate thickness of the formed portion 1 in the pushing direction 1c prior to ironing is uneven, on the other hand, the reduction rate of the plate thickness of the formed portion 1 is approximated to a fixed value, and the inner peripheral surface 212 is formed as a tapered surface that extends at an angle corresponding to the approximated value.
By forming the inner peripheral surface 212 in this manner, a load exerted on the surface of the formed portion 1 by the ironing process can be made uniform in the pushing direction 1c even when the plate thickness distribution of the formed portion 1 in the pushing direction 1c is uneven. As a result, generation of a large load on a part of the surface can be avoided so that the amount of generated powder form residue (coating residue and the like) can be reduced.
Next, referring to
The amount of generated coating residue correlates with a ratio r/t between a curvature radius r of the shoulder portion 211 and a plate thickness t of the Zn coated steel plate. As the curvature radius r of the shoulder portion 211 decreases, local skewness increases, leading to an increase in sliding resistance between the surface of the coating layer 10 and the shoulder portion 211, and as a result, the amount of generated coating residue increases. Further, as the plate thickness t of the Zn coated steel plate increases, an amount of thinning performed by the shoulder portion 211 increases, leading to an increase in a load exerted on the surface of the Zn coated steel plate, and as a result, the amount of generated coating residue increases. In other words, the amount of generated coating residue increases as the ratio r/t decreases and decreases as the ratio r/t increases. When the coating surface is covered by a lubricating film, on the other hand, sliding resistance between the surface of the coating layer 10 and the shoulder portion 211 decreases, and therefore the ratio r/t at which coating residue is generated takes a smaller value than in a condition where a lubricating film is not provided.
In particular, the plate surface of the pre-ironing formed portion 1 in a position sandwiched between the radius end 211a and the punch 20 upon completion of the ironing is thinned to the largest extent by the shoulder portion 211. From the viewpoint of suppressing the amount of generated coating residue, therefore, the amount of generated coating residue correlates strongly with a ratio r/tre between the curvature radius r of the shoulder portion 211 and a plate thickness tre of the pre-ironing formed portion 1 in the position sandwiched between the radius end 211a and the punch 20 upon completion of the ironing.
The amount of generated coating residue also correlates with an ironing rate applied by the shoulder portion 211. When a clearance between the radius end 211a and the punch 20 is set at cre and the plate thickness tre of the pre-ironing formed portion 1 in the position sandwiched between the radius end 211a and the punch 20 upon completion of the ironing is set at tre, the ironing rate is expressed by {(tre−cre)/tre}×100. The clearance cre corresponds to the plate thickness of the post-ironing formed portion 1 in the position sandwiched between the radius end 211a and the punch 20. As the ironing rate increases, the load exerted on the surface of the Zn coated steel plate increases, leading to an increase in the amount of generated coating residue.
Here, Rq is a root mean square roughness (=a square root of a second moment of an amplitude distribution curve), and
∫Z3 (x) dx is a third moment of the amplitude distribution curve.
The skewness Rsk represents an existence probability of projecting portions among the irregularities 10a (see
As shown in
Next, examples will be described. The inventors performed ironing on a Zn—Al—Mg alloy coated steel plate under following conditions while modifying the ironing rate and r/tre. A steel plate not having a lubricating film (a comparative example) and a steel plate having a lubricating film (an example of the invention) were both used as the Zn—Al—Mg alloy coated steel plate. Note that a plate thickness of the Zn—Al—Mg alloy coated steel plate was set at 1.8 mm, and a coating coverage was set at 90 g/m2.
As shown in
Next,
Next,
Next,
Next,
From the results shown in
Next,
As shown in
Hence, in the ironing mold 2 and the formed material manufacturing method described above, to ensure that the amount of ironing applied to the formed portion 1 remains constant in the pushing direction 1c, the inner peripheral surface 212 is provided with the clearance 212a that corresponds to the uneven plate thickness distribution, in the pushing direction 1c, of the formed portion 1 prior to ironing relative to the outer peripheral surface 20a of the punch 20, and therefore generation of a large load in a part of the surface can be avoided, with the result that the amount of generated powder form residue can be reduced. By reducing the amount of generated powder form residue, problems such as formation of minute pockmarks (dents) in the surface of the ironed formed portion 1, deterioration of the performance of a product manufactured using the formed material, and the need for an operation to remove the powder form residue can be eliminated. This configuration is particularly effective when ironing is performed on a Zn coated steel plate.
Further, the thickness of the lubricating film is set to be thicker than 0.2 μm and thinner than 1.8 μm, and therefore the amount of generated powder form residue can be reduced more reliably under a wider range of processing conditions.
Moreover, the thickness of the lubricating film is set to be no less than 0.5 μm and no more than 1.2 μm, and therefore the amount of generated powder form residue can be reduced even more reliably under an even wider range of processing conditions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-260072 | Dec 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/078212 | 10/23/2014 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2015/093145 | 6/25/2015 | WO | A |
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| Number | Date | Country | |
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| 20160311006 A1 | Oct 2016 | US |
