Patent Application
20160339498
The present invention relates to an ironing mold used to perform ironing on a folded and drawn formed portion, and a formed material manufacturing method.
A ring-shaped folded and drawn formed portion is typically formed by press forming such as drawing using a surface treated metal plate such as a coated steel plate as a raw material. For example, in PTL 1, a ring-shaped oil groove 17 is formed by a folding and drawing process in a portion of a housing 1 of an electric motor. The folded and drawn formed portion is a portion which is formed by folding a single sheet member, and includes an inner peripheral wall, an outer peripheral wall, and a fold portion which links the front ends of the inner peripheral wall and the outer peripheral wall. When the folded and drawn formed portion requires particularly high dimensional precision, ironing is implemented on the folded and drawn formed portion after the folded and drawn formed portion has been formed. Ironing is a process in which a clearance between a punch and a die is set to be narrower than a thickness of the folded and drawn formed portion prior to ironing, and the folded and drawn formed portion is then ironed using the punch and the die so that the thickness of the folded and drawn formed portion matches the clearance between the punch and the die. Ironing for a folded and drawn formed portion of this kind is also known as a “restrike”.
The folded and drawn formed portion is formed by a mold which is generally configured in the following manner. In other words, a conventional mold is provided with a punch, a die, and a counter pad part. The punch is configured as a columnar member, and the die is configured as a ring-shaped member which is disposed on the outer periphery of the punch. A pushing hole into which the folded and drawn formed portion is pushed is formed between the punch and the die. The die 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 which extends linearly parallel to the pushing direction from a radius end of the shoulder portion. The outer peripheral surface of the punch and the inner peripheral surface of the pushing hole extend mutually in parallel along the pushing direction of the folded and drawn formed portion.
The counter pad part is a member which is arranged facing the punch and the die in such a manner that the folded and drawn formed portion is positioned between the punch and the die, and the counter pad part pushes the folded and drawn formed portion into the pushing hole by relative displacement of the counter pad part with respect to the punch and the die. The wall surface of the outer peripheral wall of the folded and drawn formed portion is ironed by the shoulder portion when pushed into the pushing hole, and the whole folded and drawn formed portion is gradually thinned until coinciding with the width of the clearance between the outer peripheral surface of the punch and the inner peripheral surface of the pushing hole.
Japanese Patent Application Publication No. 2012-167818
In general, when the folded and drawn formed portion is pushed into the pushing hole, the folded and drawn formed portion is ironed and thinned by the shoulder portion of the die, from the fold portion on the front end side towards the counter pad side. In this case, since the thinned material is pushed towards the counter pad side, then the material plate thickness is greater towards the counter pad side, and the thick portion of the folded and drawn formed portion is subjected to a greater amount of ironing. Therefore, a surface treated layer of the portion of increased thickness is shaved, and therefore a powdery residue may be generated. The powdery residue causes problems such as formation of minute pockmarks (dents) in the surface of the formed portion after ironing, and deterioration of the performance of a product made using the formed material. Furthermore, when the radius of the shoulder portion of the die is small, then at the bottom dead center of the pressing action, the material which has been pushed by the ironing is crushed between the counter pad and the punch and the die, and generates a large residual compressive stress. This residual compressive stress is a cause of dimensional variation due to elastic deformation, in the product when released from the mold after forming.
The present invention was devised in order to resolve the problems described above, an object thereof being to provide an ironing mold and a formed material manufacturing method whereby the generation of a large load on a part of a surface treated layer can be avoided, an amount of generated powdery residue can be reduced, and deterioration in the dimensional precision of the folded and drawn formed portion after ironing can be prevented.
The ironing mold according to the present invention is an ironing mold for performing ironing on a folded and drawn formed portion which is formed using a surface treated metal plate as a raw material and which has an inner peripheral wall, an outer peripheral wall and a fold portion linking front ends of the inner peripheral wall and the outer peripheral wall, including: a punch; a die which is disposed on the outer periphery of the punch and which forms, with respect to the punch, a pushing hole into which the folded and drawn formed portion is pushed with the fold portion to the front; and a counter pad part which is disposed facing the punch and the die in such a manner that the folded and drawn formed portion is positioned between the punch and the die, and which pushes the folded and drawn formed portion into the pushing hole by relative displacement of the counter pad part with respect to the punch and the die, wherein the die 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 folded and drawn formed portion, and along which a surface of the outer peripheral wall of the folded and drawn formed portion slides in response to the pushing of the folded and drawn formed portion; a skewness Rsk of the surface treated metal plate is less than −0.6 and no less than −1.3; the curvature radius of the shoulder portion and the clearance between the radius end and the punch are determined such that, when the curvature radius of the shoulder portion is represented by r, the clearance between the radius end and the punch is represented by cre, a thickness of the folded and drawn formed portion prior to the ironing at a position that is sandwiched between the radius end and the punch upon completion of the ironing is represented by tre and a height of the folded and drawn formed portion is represented by h, then Y, which is expressed by {(tre−cre)/tre}×100, and X, which is expressed by r/tre, satisfy 0<Y≦18.7X−6.1, X satisfies X≧0.6, and r satisfies r≦0.5 h.
Furthermore, the ironing mold according to the present invention is an ironing mold for performing ironing on a folded and drawn formed portion which is formed using a surface treated metal plate as a raw material and which has an inner peripheral wall, an outer peripheral wall and a fold portion linking front ends of the inner peripheral wall and the outer peripheral wall, including: a punch; a die which is disposed on the outer periphery of the punch and which forms, with respect to the punch, a pushing hole into which the folded and drawn formed portion is pushed with the fold portion to the front; and a counter pad part which is disposed facing the punch and the die in such a manner that the folded and drawn formed portion is positioned between the punch and the die, and which pushes the folded and drawn formed portion into the pushing hole by relative displacement of the counter pad part with respect to the punch and the die, wherein the die 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 folded and drawn formed portion, and along which a surface of the outer peripheral wall of the folded and drawn formed portion slides in response to the pushing of the folded and drawn formed portion; a skewness Rsk of the surface treated metal plate is no less than −0.6 and no more than 0; the curvature radius of the shoulder portion and the clearance between the radius end and the punch are determined such that, when the curvature radius of the shoulder portion is represented by r, the clearance between the radius end and the punch is represented by cre, a thickness of the folded and drawn formed portion prior to the ironing at a position that is sandwiched between the radius end and the punch upon completion of the ironing is represented by tre and a height of the folded and drawn formed portion is represented by h, then Y, which is expressed by {(tre−cre)/tre}×100, and X, which is expressed by r/tre, satisfy 0<Y≦14.4X−6.4, X satisfies X≧0.8, and r satisfies r≦0.5 h.
The formed material manufacturing method according to the present invention is a formed material manufacturing method including the steps of: forming a ring-shaped folded and drawn formed portion having an inner peripheral wall, an outer peripheral wall and a fold portion linking front ends of the inner peripheral wall and the outer peripheral wall, by performing at least one forming process on a surface treated metal plate; and performing ironing on the folded and drawn formed portion using an ironing mold after forming the folded and drawn formed portion, wherein the ironing mold includes: a punch; a die which is disposed on the outer periphery of the punch and which forms, with respect to the punch, a pushing hole into which the folded and drawn formed portion is pushed with the fold portion to the front; and a counter pad part which is disposed facing the punch and the die in such a manner that the folded and drawn formed portion is positioned between the punch and the die, and which pushes the folded and drawn formed portion into the pushing hole by relative displacement of the counter pad part with respect to the punch and the die, the die 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 folded and drawn formed portion, and along which a surface of the outer peripheral wall of the folded and drawn formed portion slides in response to the pushing of the folded and drawn formed portion; a skewness Rsk of the surface treated metal plate is less than −0.6 and no less than −1.3; and the curvature radius of the shoulder portion and the clearance between the radius end and the punch are determined such that, when the curvature radius of the shoulder portion is represented by r, the clearance between the radius end and the punch is represented by cre, a thickness of the folded and drawn formed portion prior to the ironing at a position that is sandwiched between the radius end and the punch upon completion of the ironing is represented by tre and a height of the folded and drawn formed portion is represented by h, then Y, which is expressed by {(tre−cre)/tre}×100, and X, which is expressed by r/tre, satisfy 0<Y≦18.7X—6.1, X satisfies X≧0.6, and r satisfies r≦0.5 h.
Furthermore, the formed material manufacturing method according to the present invention is a formed material manufacturing method including the steps of: forming a ring-shaped folded and drawn formed portion having an inner peripheral wall, an outer peripheral wall and a fold portion linking front ends of the inner peripheral wall and the outer peripheral wall, by performing at least one forming process on a surface treated metal plate; and performing ironing on the folded and drawn formed portion using an ironing mold after forming the folded and drawn formed portion, wherein the ironing mold includes: a punch; a die which is disposed on the outer periphery of the punch and which forms, with respect to the punch, a pushing hole into which the folded and drawn formed portion is pushed with the fold portion to the front; a counter pad part which is disposed facing the punch and the die in such a manner that the folded and drawn formed portion is positioned between the punch and the die, and which pushes the folded and drawn formed portion into the pushing hole by relative displacement of the counter pad part with respect to the punch and the die, the die 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 folded and drawn formed portion, and along which a surface of the outer peripheral wall of the folded and drawn formed portion slides in response to the pushing of the folded and drawn formed portion; a skewness Rsk of the surface treated metal plate is no less than −0.6 and no more than 0; and the curvature radius of the shoulder portion and the clearance between the radius end and the punch are determined such that, when the curvature radius of the shoulder portion is represented by r, the clearance between the radius end and the punch is represented by cre, a thickness of the folded and drawn formed portion prior to the ironing at a position that is sandwiched between the radius end and the punch upon completion of the ironing is represented by tre and a height of the folded and drawn formed portion is represented by h, then Y, which is expressed by {(tre−cre)/tre}×100, and X, which is expressed by r/tre, satisfy 0<Y≦14.4X−6.4, X satisfies X≧0.8, and r satisfies r≦0.5 h.
According to the ironing mold and the formed material manufacturing method of the present invention, since the pushing hole is configured in such a manner that the material pushed by the ironing of the folded and drawn formed portion is not crushed excessively between the punch and the die and the counter pad, at the bottom dead center of the pressing action, then the generation of a large load on a part of the surface treated layer can be avoided, and deformation after separation from the mold can also be reduced. Consequently, the amount of generated powdery residue can be reduced, and deterioration in the dimensional precision of the folded and drawn formed portion after ironing can be prevented.
Below, an embodiment of this invention is described with reference to the drawings.
As shown in
As shown in
The ironing process S2 is a process for performing ironing on the folded and drawn formed portion 1 by using the ironing mold described below. Ironing is a process in which a clearance between a punch and a die of an ironing mold is set to be narrower than a thickness of the folded and drawn formed portion 1 prior to ironing, and the folded and drawn formed portion 1 is then ironed using the punch and the die so that the thickness of the folded and drawn formed portion 1 matches the clearance between the punch and the die. In other words, the thickness of the folded and drawn formed portion 1 after ironing is less than the thickness of the folded and drawn formed portion 1 prior to ironing. Ironing for a folded and drawn formed portion 1 of this kind is also known as a “restrike”.
As indicated in
Next,
Normally, the front end-side curved surface portion of the outer peripheral wall 11 and the curved surface portion of the die shoulder make contact so as to form an acute angle mutually with respect to the direction of travel. Due to the presence of the gap, however, the shoulder portion of the die contacts the portion of the outer peripheral wall 11 nearer to the punch, and the front end-side curved surface portion of the outer peripheral wall 11 and the curved surface portion of the die shoulder make contact at an obtuse angle.
Consequently, since the deformation resistance which causes the outer peripheral wall 11 to make tight contact with the inner peripheral wall 10 increases, then a large load is generated on a part of the surface treated layer, leading to the generation of powdery residue.
Furthermore, as the radius of the shoulder portion of the die decreases, the portion on the outer peripheral wall 11 that is contacted by the die shoulder portion becomes nearer to the punch, and therefore the die shoulder portion and the outer peripheral wall 11 make contact at an obtuse angle, thus leading to increase in the deformation resistance giving rise to powdery residue.
Next,
A pushing hole 210 into which the folded and drawn formed portion 1 is pushed is formed between the die 21 and the punch 20. As shown in
The cushion pad part 22 is made from carbon tool steel, or alloy tool steel, for example, and is arranged to face the punch 20 and die 21. The cushion pad part 22 is provided so as to be displaceable relatively with respect to the punch 20 and die 21. In the present embodiment, the cushion pad part 22 is provided so as to be displaceable in a direction towards the punch 20 and die 21, and a direction away from the punch 20 and die 21. The folded and drawn formed portion 1 is disposed between the cushion pad part 22 and the punch 20 and die 21. The folded and drawn formed portion 1 is pushed into the pushing hole 210, by displacement of the cushion pad part 22 in a direction towards the punch 20 and die 21.
When the folded and drawn formed portion 1 is pushed into the pushing hole 210, the wall surface of the outer peripheral wall 11 of the folded and drawn formed portion 1 is ironed by the shoulder portion 211, as shown in
In order to prevent the occurrence of powdery coating residue when the outer wall 11 of the folded and drawn formed portion 1 contacts the shoulder portion 211 of the die 21, the radius r of the shoulder portion 211 of the die 21 must be set to a large value so as to contact the outer wall 11 of the folded and drawn formed portion 1 at an acute angle.
Furthermore, the surface of the outer peripheral wall 11 of the folded and drawn formed portion 1 slides along the inner peripheral surface 212 due to being pushed into the pushing hole 210. The outer wall 11 of the folded and drawn formed portion 1 is thinned as the ironing advances, and surplus material is pushed towards the counter pad side. In this case, the material which has been thinned is pushed towards the counter pad side, and therefore the material plate thickness becomes larger towards the counter pad side. Consequently, nearer to the counter pad side, the amount of ironing becomes greater and the surface treated layer is shaved more readily. Therefore, by increasing the radius r of the shoulder portion 211 of the die 21, the gap between the punch 20 and the die 21 at the position corresponding to r is increased, and increase in the amount of ironing is suppressed.
Moreover, the material that is thinned and pushed by the ironing is then crushed between the die 21 and punch 20, and the counter pad 22, at the bottom dead center of the pressing action. In this case, the volume of the pushed material increases as the clearance becomes smaller, and therefore, as the clearance becomes smaller, the extent of crushing at the bottom dead center of the press increases, leading to dimensional variations after separation from the mold due to increase in the residual compressive stress. In this respect also, by increasing the radius r of the shoulder portion 211, it is possible to ensure a large space between the punch 20 and the counter pad 22 at the bottom dead center of the press, and therefore it is possible to prevent dimensional variations after separation from the mold.
As described above, the smaller the clearance between the punch 20 and the die 21, the greater the increase in the volume of the pushed material, and therefore in order to prevent the generation of coating residue and to improve dimensional precision, it is necessary to increase the radius r of the shoulder portion 211. However, when the radius r of the shoulder portion 211 is too large, then the gap between the punch 20 and the die 21 becomes too large, which leads conversely to deterioration in the dimensional precision. In other words, if the radius r of the shoulder portion 211 is too large, then the inner peripheral wall 10 and the outer peripheral wall 11 deform greatly along the curved surface of the shoulder portion 211. The magnitude of the deformation of the inner peripheral wall 10 and the outer peripheral wall 11 along the curved surface of the shoulder portion 211 has a correlation with the length of the inner peripheral wall 10 and the outer peripheral wall 11 which is processed by the shoulder portion 211, in other words, the height h of the folded and drawn formed portion 1 (see
Next, a mechanism by which coating residue is generated due to the ironing by the shoulder portion 211 will be described with reference to
The amount of generated coating residue has a correlation with a ratio r/t between the curvature radius r of the shoulder portion 211 and the thickness t of the folded and drawn formed portion 1. 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 13 and the shoulder portion 211, and therefore the amount of generated coating residue increases. Furthermore, as the thickness t of the folded and drawn formed portion 1 increases, an amount of thinning by the shoulder portion 211 increases, leading to an increase in a load applied to the surface of the Zn coated steel plate, and consequently the amount of generated coating residue increases. In other words, the amount of generated coating residue increases, the smaller the ratio r/t, and the amount of generated coating residue decreases, the greater the ratio r/t.
In particular, the plate surface of the folded and drawn formed portion 1 prior to ironing in a position that is sandwiched between the radius end 211a and the punch 20 upon completion of the ironing is thinned to the greatest extent by the shoulder portion 211. Therefore, from the viewpoint of suppressing the amount of generated coating residue, the amount of generation coating residue has a strong correlation with a ratio r/tre between the curvature radius r of the shoulder portion 211 and a thickness tre of the folded and drawn formed portion 1 at the position sandwiched between the radius end 211a and the punch 20 upon completion of the ironing.
Furthermore, the amount of generated coating residue also has a correlation with the ironing rate by the shoulder portion 211. The ironing rate is expressed by {(tre cre)/tre}×100, when the clearance between the radius end 211a and the punch 20 is represented by cre, and the thickness of the folded and drawn formed portion 1 prior to ironing at the position sandwiched between the radius end 211a and the punch 20 upon completion of the ironing is represented by tre. The clearance cre corresponds to the thickness of the folded and drawn formed portion 1 after ironing at the position sandwiched between the radius end 211a and the punch 20. As the ironing rate increases, the load applied to the surface of the Zn coated steel plate increases, leading to an increase in the amount of generated coating residue.
Next,
Here, Rq is root mean square roughness (=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 the probability of the existence of projecting portions in the irregularities 13a on the coating layer 13 (see
As shown in
Next,
The ordinate in
As shown in
Next,
As shown in
In the ironing mold 2 and formed material manufacturing method of this kind, in the case of a material having a skewness Rsk of less than −0.6 and no less than −1.3, since the curvature radius r of the shoulder portion 211 and the clearance cre between the radius end 211a and the punch 20 are determined such that Y which is expressed by {(tre−cre)/tre}×100 and X which is expressed by r/tre satisfy 0<Y≦18.7X−6.1, and such that X satisfies X≧0.6, and r satisfies r≦0.5 h, then it is possible to avoid the generation of a large load on a part of the surface treated layer (coating layer 10), and the amount of generated powdery residue (coating residue) can be reduced. By reducing the amount of generated powdery residue, problems such as formation of minute pockmarks (dents) in the surface of the formed portion 1 after ironing, deterioration of the performance of a product manufactured using the formed material, and the need for an operation to remove the powdery residue, can be eliminated. This configuration is particularly effective when ironing is performed on a Zn coated steel plate.
Furthermore, in the case of a material having a skewness Rsk of no less than −0.6 and less than 0, since the curvature radius r of the shoulder portion 211 and the clearance cre between the radius end 211a and the punch 20 are determined such that Y which is expressed by {(tre−cre)/tre}×100 and X which is expressed by r/tre satisfy 0<Y≦14.4X−6.4, and such that X satisfies X≧0.8, and r satisfies r≦0.5 h, then it is possible to reduce the amount of powdery residue generated by the ironing by the shoulder portion 211, similarly to the case of a material where the skewness Rsk is less than −0.6 and no less than −1.3.
In the embodiment, the surface treated metal plate is described as a Zn coated steel plate, but the present invention may be applied to other surface treated metal plates such as an aluminum plate having a painted film on the surface thereof, for example.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-012290 | Jan 2014 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/060704 | 4/15/2014 | WO | 00 |
