GB2320216A - A flanged product,method of pressing a blank into same , and a reinforced planar blank for use in the method - Google Patents

Abstract

A method of pressing a planar blank into a flanged product having at least one reduced thickness wall portion, comprises the steps of preforming at least two weld beads 12 in the blank which extend over the respective reduced thickness wall portion of the product along metal flow of the reduced thickness wall portion and terminate before the periphery of the blank, placing the blank with the weld beads on a die opposed to a punch, in a predetermined position, pressing a blank holder against the blank placed on the die to clamp the periphery of the blank, and moving the punch into the cavity of the die to draw the blank along the surface of the punch and form a flange along the periphery of the blank, while keeping the blank clamped at the periphery.

Description

A FLANGED PRODUCT, METHOD OF PRESSING A BLANK INTO SAME, AND A REINFORCED PLANAR BLANK FOR USE IN THE METHOD The contents of Application No. 8-336103, with a filing date of December 16, 1996 in Japan, are hereby incorporated by reference.

The present invention relates to a method of pressing a planar blank of metal into a flanged product, and more specifically to a method of deep drawing of a planar metal sheet blank.

In press working, it is well known to arrange weld beads in a planar blank of metal by means of laser beam irradiation in order to reinforce the planar blank of metal.

Japanese Patent Application First Publication No. 61-60222 discloses a vehicular front side member as a completed finished product which has a plurality of high-hardness linear weld beads. The weld beads are arranged parallel to each other in a predetermined portion of the front side member for providing a local buckling area buckleable when a buckling load is applied thereto.

In the technique as described above, the mutually parallel weld beads are arranged regardless of metal flow of the blank which is caused when the blank is subject to press working. It is likely that deep drawablity is lowered with such arrangement of the weld beads as described in the conventional art when the blank is subject to deep drawing in which shrink flanging occurs.

A technical report "SOLEI TO KAKO, vol. 16 no.

169 (1975-2), p.148" discusses local quenching in a metal sheet blank by induction hardening for the purpose of improving strength of a portion of the blank which is easy to crack in deep drawing.

In the case of pressing the blank into a finished product having a complicated configuration, for instance, vehicle body components, it is manufacturally difficult that, before draw-pressing, the blank is subject to heat treatment in a large region thereof and then local heat treatment in a limited area thereof by induction hardening as discussed in the report.

It would be desirable to be able to provide a method of pressing a planar blank into a product, which is capable of improving performance of the pressing work by preforming weld beads in the blank in consideration of metal flow in the blank which occurs in the pressing process.

It would also be desirableto be able to provide a method of pressing a planar blank into a product, which is capable of restricting reduction of blank-thickness which is caused in deep drawing, by changing strain distribution occurring near weld beads in the pressing process, serving for improving deep drawability.

It would also be desirable to be able to provide a reinforced planar blank suitable for drawpressing which is increased in hardness and strength and capable of restraining reduction of a thickness thereof which is caused in the drawing process, by arranging weld beads in the blank.

It would also be desirable to be able to to provide a product formed by draw-pressing a planar blank, which has a good appearance without cracks and less reduced thickness.

According to one aspect of the present invention, there is provided a method of pressing a planar blank into a flanged product having at least one reduced thickness wall portion, comprising the steps of: preforming at least two weld beads in the blank which extend over the respective reduced thickness wall portion of the product along a metal flow of the reduced thickness wall portion and terminate before the periphery of the blank; placing the blank with the weld beads on a die opposed to a punch, in a predetermined position; pressing a blank holder against the blank placed on the die to clamp the periphery of the blank: and moving the punch into the cavity of the die to draw the blank along the surface of the punch and form a flange along the periphery of the blank, while keeping the blank clamped at the periphery According to another aspect of the present invention, there is provided a flanged product having at least one reduced thickness wall portion, formed by a method comprising the steps of: preforming at least two weld beads in the blank which extend over the respective reduced thickness wall portion of the product along a metal flow of the reduced thickness wall portion and terminate before the periphery of the blank: placing the blank with the weld beads on a die opposed to a punch, in a predetermined position; pressing a blank holder against the blank placed on the die to clamp the periphery of the blank; and moving the punch into the cavity of the die to draw the blank along the surface of the punch and form a flange along the periphery of the blank, while keeping the blank clamped at the periphery.

According to further aspect of the present invention, there is provided a planar blank having at least one reinforced portion, comprising at least two weld beads penetrating into the blank, said at least two weld beads being positioned over the respective reinforced portion of the blank and terminating before the periphery of the blank, said at least two weld beads being positioned along lines extending radially from a predetermined point in the blank.

According to still further aspect of the present invention, there is provided a product formed by draw-pressing a planar blank, comprising: a bottom wall having a curved periphery; a side wall connected with the bottom wall; at least one curved wall extending from the curved periphery of the bottom wall and connected with the side wall; a flange angularly extending from the side wall; and at least two weld beads positioned along lines extending radially from a predetermined point in the bottom wall through the respective curved wall and the side wall, said at least two weld beads terminating before the peripheral edge of the flange, said at least two weld beads penetrating into the blank.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view of a planar blank used in a first embodiment according to the present invention: Fig. 2 is a schematic section of apparatus for cupping deep drawing of the blank of Fig. 1, showing a die, a punch, a blank holder together with the blank; Fig. 3 is an enlarged section taken along line 3-3 of Fig. 1: Fig. 4 is a graph showing a relationship between a position of outer ends of weld beads and a limiting drawing ratio of the blank; Fig. 5 is a view similar to Fig. 1, but showing a planar blank used in a second embodiment according to the present invention; Fig. 6 is a graph showing a relationship between a distance between weld beads and a limiting drawing ratio of the blank; Fig. 7 is an explanatory diagram of a third embodiment according to the present invention, showing a planar blank and apparatus for deep drawing of the blank; Fig. 8 is a schematic fragmentary plan view of a die used in a fourth embodiment according to the present invention; Fig. 9 is a schematic fragmentary plan view of a blank used in the fourth embodiment: Fig. 10 is a graph showing a relationship between a distance between weld beads and a ratio of a thickness of a side wall of a completed product to an initial thickness of the blank; Fig. 11 is a graph showing a relationship between a length of weld beads and a ratio of a thickness of a side wall of a completed product to an initial thickness of the blank; Fig. 12 is a fragmentary enlarged section of the apparatus and the blank of the third embodiment, taken along the weld bead formed in the blank; Fig. 13 is a graph showing a relationship between a width of weld beads and a ratio of tensile strength of the weld beads relative to a base metal of the blank; Fig. 14 is a graph showing a relationship between a penetration depth of weld beads and a ratio of tensile strength of the weld beads relative to a base metal of the blank; and Fig. 15 is a bottom plan view of a completed finished product formed by the first embodiment of the method according to the present invention; Fig. 16 is a section taken along line 16-16 of Fig. 15; Fig. 17 is a fragmentary bottom plan view of a completed finished product formed by the third embodiment of the method according to the present invention; and Fig. 18 is a fragmentary section taken along line 18-18 of Fig. 17.

DETAILED DESCRIPTION Referring to Figs. 1-18, preferred embodiments of a method of pressing a planar blank into a flanged product, a completed finished product formed by the method, and a reinforced planar blank prepared for draw-pressing, according to the present invention, will be explained hereinafter.

As illustrated in Figs. 15 and 16, the completed product 400 has a cup-like shape. The completed product 400 is made from a planar metal blank. The completed product 400 includes a circular bottom wall 402, a cylindrical side wall 404 connected with the bottom wall 402, and a curved wall 406 extending between the bottom wall 402 and the side wall 404.

The side wall 404 extends substantially vertically relative to the bottom wall 402. The curved wall 406 extends angularly and radially outward from a curved periphery of the bottom wall 402, interconnecting the bottom wall 402 and the side wall 404. An annular flange 408 extends angularly and radially outward from the side wall 404. At least two linear weld beads, indicated at 12 in Figs. 15 and 16, are provided for reinforcing a reduced thickness portion of the completed product 400 which extends over the entire curved wall 406, the side wall 404 and the bottom wall 402. The reduced thickness portion is caused by being exposed to a tensile force applied to the planar blank in deep drawing process of the planar blank. The curved wall 406 is most influenced by the tensile force in deep drawing process. Each of the weld beads 12 is formed by using a suitable heat source having high energy density, for instance, laser beam, electron beam, or the like. Namely, a portion of the blank which is subject to irradiation of such beam, is melted by heat and then self-cooled to be hardened to form the weld bead 12 having hardness greater than the remaining portion 18 as base metal. Thus, the weld beads 12 penetrate into the blank.

The at least two weld beads extend through the curved wall 406 and the side wall 404 and terminate before the peripheral edge of the flange 408. The at least two weld beads 12 are positioned along lines extending radially from a predetermined point disposed in the bottom wall 402. The at least two weld beads 12 are extend through a sectorial region of the bottom wall 402 which has a central angle of 180 degrees at the predetermined point in the bottom wall 402. The at least two weld beads 12 are arranged in circumferentially equidistantly spaced relation to each other and prevented from intersecting at other point than the predetermined point in the bottom wall 402. Each of the at least two weld beads 12 has one end positioned within a region extending over the side wall 404 and distant radially inward from the peripheral edge of the flange 408 and the flange 408, and an opposite end positioned within the bottom wall 402.

Specifically, in this embodiment as shown in Figs. 15 and 16, eight linear weld beads 12 extend radially from the center of the bottom wall 402 along the curved wall 406 and the side wall 404. Each of the eight weld beads 12 has one end in the flange 408 and the opposite end in the bottom wall 402. These weld beads 12 thoroughly penetrate into the blank1 extending from one face of the blank to an opposite face thereof as shown in Fig. 16. The weld beads 12 are not limited to such through type as shown in this embodiment but may be of a non-through type having a depth of penetration sufficient for reinforcing the reduced thickness portion of the completed product.

The arrangement of the weld beads as explained above serves for preventing the completed product from cracking which is caused at the wall portion having a reduced thickness, and providing the completed product with a good appearance.

Referring to Figs. 1-3, the method of pressing a planar blank into the completed product 400 as shown in Figs. 15 and 16, is now explained.

Fig. 1 shows the planar blank 10 having a disk shape and made of sheet metal. At the first step in the method, at least two weld beads 12 are preformed in the blank 10 in such a manner as to extend over the above-described reduced thickness wall portion of the product along a metal flow of the reduced thickness wall portion and terminate before the periphery 16 of the blank 10. The metal flow is caused in a radial direction of the blank 10 when the blank 10 is plastically deformed in the drawing step as explained later, in the method. In the preforming step, predetermined blank portions of the blank 10 are exposed to the above-described high energy density heat source, such as laser beam, electron beam or the like. The predetermined blank portions of the blank 10 are heatedly melted and rapidly cooled by themselves to form the weld beads 12 which penetrate into the blank 10 and have more increased hardness than the remaining blank portion 18 of the blank 10. The high energy density heat source is more desirable and effective to rapidly cool the melted predetermined blank portions of the blank 10.

Particularly, in the case of hardening the blank made of steel plate less containing additional elements such as carbon, by heat treatment, it is required to cool the blank at higher cooling rate. Therefore, the above-described high energy density heat source is preferably useable in this case.

In the preforming step in the method, the at least two weld beads 12 are positioned along lines extending radially from a predetermined point disposed in the blank 10 and terminate before the periphery 16 of the blank 10. Namely, the at least two weld beads 12 are positioned within a region radially extending from the predetermined point of the blank 10 to a predetermined portion of the blank 10 which is spaced radially inward from the periphery 16.

Specifically, in this embodiment as shown in Fig. 1, eight linear weld beads 12 are positioned so as to extend radially outward from the center 14 of the blank 10 and terminate before the periphery 16 of the blank 10. In the preforming step, the at least two weld beads 12 are arranged in circumferentially equidistantly spaced relation to each other and within a sectorial region of the blank 10 which has a central angle of 180 degrees at the predetermined point as the center.

In the preforming step, the weld beads 12 are so arranged as to be prevented from intersecting at other point than the predetermined point, i.e., the center 14 of the blank 10. The weld beads 12 are prevented from intersecting within first and second predetermined portions 22 and 24 of the blank 10.

The first predetermined portion 22 is brought into contact with a curved surface portion PR of a cylindrical punch P as shown in Fig. 2, in the subsequent step of moving the punch P as explained later. The curved surface portion PR is disposed between a bottom surface portion PB and a vertical surface portion PW of the punch P. The second predetermined portion 24 is brought into contact with the vertical surface portion PW of the punch P in the step of moving the punch P. Disposed between the first and second predetermined portions 22 and 24 is an outer shoulder-end contact portion 30 of the blank 10 which is brought into contact with one shoulder end RW of the punch P at which the vertical surface portion PW and the curved surface portion PR are connected together, in the step of moving the punch P.

Further, in the preforming step, each of the weld beads 12 is so disposed as to have one end positioned radially inward the periphery 16 and within the second predetermined portion 24, and an opposite end positioned in a third predetermined portion 20 of the blank 10 which is brought into contact with the bottom surface portion PB of the punch P in the step of moving the punch P. Disposed between the first and third portions 22 and 20 is an inner shoulder-end contact portion 28 of the blank 1C which is brought into contact with the other shoulder end RB of the punch P at which the bottom surface portion PB and the curved surface portion PR are connected together, in the step of moving the punch P.

These weld beads 12 thoroughly penetrates into the blank 10 as shown in Fig. 3. The weld beads 12 each have a length L as shown in Fig. 1, and a width W and a depth T of penetration, as illustrated in Fig. 3. The length L of the weld beads 12 is variably adjusted such that the inner ends of the weld beads 12 are positioned in the third predetermined portion 20 of the blank 10 and the outer ends thereof are positioned in the second predetermined portion 24 and retracted radially inward from the periphery 16 of the blank 10.

Preferably, the width of the weld beads 12 is in a range of 0.5mm to 2.0mm and the depth T of penetration is determined larger than half the thickness of the blank 10.

Upon finishing the preforming step, the planar blank 10 having the reinforced portion formed with the at least two weld beads 12 is prepared for the following steps in the method. With the arrangement of the weld beads 12, strain distribution in the blank 10 is changed near the weld beads 12 in deep drawing. Thus, the planar blank 10 has an increased hardness and strength against the reduction of thickness thereof which is caused in the drawing step subsequent to the preforming step.

Referring to Fig. 2, the step subsequent to the above-described preforming step is explained. Fig. 2 illustrates apparatus for draw-pressing the blank 10 into the completed flanged product 400 as shown in Figs. 15 and 16. The apparatus includes a die D opposed to the punch P, and a blank holder H interposed therebetween. The punch P is of a cylindrical shape having the center axis X and adapted to be movable in the axial direction. The die D has a cylindrical cavity DC configured so as to receive the punch P. The blank holder H has a center hole HB for permitting movement of the punch P into and out of the cavity DC of the die D. In this step, the blank 10 with the weld beads 12 is placed on a die face DF of the die D in a predetermined position in which the center 14 of the blank 10 is aligned with the center axis X of the punch P.

In the step subsequent to the step of placing the blank 10 on the die D, the blank holder H is pressed against the blank 10 placed on the die D, clamping the periphery 16 of the blank 10.

Then, in the step subsequent to the step of pressing the blank holder H against the blank 10, the punch P is moved into the cavity DC of the die D to draw the blank 10 along the surface of the punch P and form an annular flange along the periphery 16 of the blank 10, while keeping the blank 10 clamped at the periphery 16. In this step, as the punch P moves into the cavity DC of the die D, the blank 10 is forced by the punch P to be shaped into a configuration of a portion of the punch P which contacts the blank 10. At this time, the blank 10 is subject to the tensile force causing the metal flow in the radial direction of the blank 10. Then, the blank 10 having the at least two weld beads 12 is less influenced by the metal flow and thus the blank 10 less suffers thickness reduction caused by the metal flow. When this step of moving the punch P is finished, the completed flanged product 400 as shown in Figs. 15 and 16 is produced.

Referring to Fig. 5, there is shown a second embodiment of the planar blank 110 according to the present invention, which differs in circumferential distance between the weld beads 12 from the first embodiment. Like reference numerals denote like parts and therefore detailed explanations therefor are omitted.

As illustrated in Fig. 5, the disk-shaped planar blank 110 made of sheet metal has six linear weld beads 12 preformed. These weld beads 12 are circumferentially spaced apart from each other by a predetermined distance as indicated at Q in Fig. 5 at the outer shoulder-end contact portion 30, which is larger than the distance in the first embodiment as shown in Fig. 1. The predetermined distance is in a range of 5mm to 30mm. The planar blank 110 having the preformed weld beads 12 is useable in the same steps in the method as explained in the first embodiment.

The methods of the first and second embodiments serve for improving performance of the pressing work. Further, according to the methods as embodied, the reduction of thickness of the blank which is caused in deep drawing, can be restricted. This serves for improving deep drawability of the blank.

Referring to Figs. 17 and 18, a third embodiment of the completed finished product 500, according to the present invention, is explained hereinafter.

The completed product 500 is made from a planar blank made of a high-tensile steel plate. As illustrated in Figs. 17 and 18, the completed product 500 includes a bottom wall 502 having a curved periphery. The bottom wall 502 is formed of a shape having at least one corner portion forming the curved periphery. The bottom wall 502 may be of a generally polygonal shape having corner portions, for instance, a rectangular shape or the like. The completed product 500 also includes a side wall 504 connected with the bottom wall 502, and at least one curved wall 506 extending angularly and outwardly from the corner portion of the bottom wall 502 along the curved periphery and then connected with the side wall 504. The side wall 504 extends substantially vertically relative to the bottom wall 502. The respective curved wall 506 is joined with the respective corner portion of the bottom wall 502 and connected with the side wall 504. A flange 508 extends angularly and outward from the side wall 504.

At least two linear weld beads 212 extend outward along the bottom wall 502, the respective curved wall 506 and the side wall 504 toward the flange 508 and terminate before the peripheral edge of the flange 508. The at least two weld beads 212 penetrate into the blank. Specifically, the at least two weld beads 212 extend radially from a predetermined point disposed inside the respective corner portion of the bottom wall 502. The at least two weld beads 212 are equidistantly spaced from each other and prevented from intersecting at other point than the predetermined point in the bottom wall 502. Each of the weld beads 212 has one end positioned within a region extending over the side wall 504 and the flange 508 and distant radially inward from the peripheral edge of the flange 508, and an opposite end positioned within the bottom wall 502. In this embodiment, the one end of each weld bead 212 is disposed within the flange 508. The at least two weld beads 212 extend through a sectorial region of the bottom wall 502 which has a central angle of 180 degrees at the predetermined point as the center.

The at least two weld beads 212 are formed by the high energy density heat source and each have an increased hardness larger than the remaining portion 18, as explained in the first embodiment. The respective curved wall 506 is reduced in thickness by being most exposed to a tensile force caused in the deep drawing process. The side wall 504 and the bottom wall 502 are also reduced in thickness but less influenced by the tensile force than the curved wall 506. Thus arranged weld beads 212 reinforce the reduced thickness wall portion of the product 500.

Further, with the arrangement of the weld beads 212, the side wall 504 can be prevented from suffering from cracks in such a case where the blank is exposed to an increased tensile force in draw-pressing in order to eliminate wrinkles. The wrinkles tend to be caused in draw-pressing due to the plastic strain ratio of the high-tensile steel plate forming the blank which is lower than the plastic strain ratio of an ordinary steel plate. Thus, the arrangement of the weld beads 212 also serves for restraining wrinkling occurring in draw-pressing.

Referring back to Figs. 7 and 12, the method of pressing a planar blank 210 into the third embodiment of the above-described completed product 500, is now explained. Figs. 7 and 12 shows the planar blank 210 and apparatus for producing the third embodiment. In Fig. 7, for better understanding of the method, the blank holder in the apparatus is not shown and the planar blank 210 is illustrated as viewed from the upper side thereof.

As illustrated in Fig. 7, the planar blank 210 is of a shape having at least one corner. The planar blank 210 is made of the high-tensile steel plate as explained above. The punch P is of a column-like shape having the bottom surface portion PB formed with at least one curved corner. The punch P may be of a generally prismatic shape having the bottom surface portion PB formed with a plurality of curved corners. The curved surface portion PR of the punch P is joined with the curved corner. The cavity DC of the die D is configured similar to the punch P.

Similar to the first embodiment, this embodiment of the method starts from the step of preforming at least two weld beads 212 in the blank 210. In the preforming step, first an image point is fixed as a predetermined point C2 in the blank 210 by projecting a center C1 of curvature of the curved surface portion PR of the punch P in the axial direction of the punch P. The predetermined point C2 is disposed at the inside of the respective corner of the planar blank 210 and within the third predetermined portion 20 of the blank 210. And then, in the preforming step, the at least two weld beads 212 are positioned along lines extending radially outward from the predetermined point C2 and terminate before the periphery 216 of the planar blank 210. Namely, the at least two weld beads 212 are positioned within a region extending from the predetermined point C2 to a predetermined portion retracted from the periphery 216 of the planar blank 210.

In the preforming step, each of the at least two weld beads 212 is so arranged as to have one end disposed between an outer shoulder-end contact portion 230 of the blank 210 which is brought into contact with the one shoulder end RW of the punch P when the punch P is moved into the cavity DC of the die D, and a clamped portion 232 of the blank 210 which is clamped by the blank holder and a draw bead DB formed on the die face DF of the die D when the blank holder pressed against the blank 210 placed on the die D. In the preforming step, each of the at least two weld beads 212 is positioned so as to have an opposite end disposed in the third predetermined portion 20 of the blank 210. Further, in the preforming step, the at least two weld beads 212 are positioned so as to have the distance therebetween in the range of 5mm to 30mm at the outer shoulder-end contact portion 230 of the blank 210 which is brought into contact with the one shoulder end RW of the punch P when the punch P is moved into the cavity DC of the die D. Reference numeral 228 denotes an inner shoulder-end contact portion of the blank 210 which forms the boundary between the third predetermined portion 20 and the first predetermined portion 22.

At the inner shoulder-end contact portion 228, the blank 210 is brought into contact with the other shoulder end RB of the punch P when the punch P is moved into the cavity DC of the die D in the direction as indicated by arrow F. Furthermore, in the preforming step, the at least two weld beads 212 are arranged within a sectorial region of the blank 210 which has a central angle of 180 degrees at the predetermined point C2 as the center.

The preforming step in this embodiment is similar to that in the first embodiment except features discussed above.

In the step of placing the blank 210 on the die D, the predetermined point C2 is aligned with the center of curvature of the curved surface portion PR of the punch P.

The steps subsequent to the above-described placing step are similar to the steps conducted after the placing step as explained in the above-described first embodiment.

With the arrangement of the weld beads 212, the completed product is prevented from cracking at the shoulder-end contact portion 230. Further, in this embodiment, a tensile force can be increased for eliminating wrinkles occurring in deep drawing. This serves for restraining wrinkling in deep drawing.

Referring to Figs. 8 and 9, a fourth embodiment of the method of the invention will be explained hereinafter, which differs from the third embodiment in that a planar blank 300 is composed of two kinds of steel plates 302 and 304, which are different in strength and/or thickness, welded together by means of laser beam.

Fig. 8 shows a die D for use in deep drawing of such welded blank 300. The die D has a die face DF having an inclination determined depending on material characteristic of one of the steel plates 302 and 304 which has drawability lower than that of the other.

As illustrated in Fig. 9, there is shown the welded planar blank 300 composed of the ordinary steel plate 302 having good deep-drawability and the high-strength steel plate 304 having deep-drawability inferior to that of the ordinary steel plate 302. In the method of this embodiment, the step of preforming at least two linear weld beads 312 in the blank 300 is similar to the third embodiment except that the at least two weld beads 312 are arranged in the hightensile steel plate 304 along lines extending radially from the predetermined point in the blank 300 and have a length of one-t of the axial movement and the bottom surface portion PB thereof when the punch P is positioned at the bottom dead center in the stroke. Similar to the third embodiment, in the preforming step in the method of this embodiment, the at least two weld beads 312 are positioned so as to have the distance therebetween in the range of 5mm to 30mm at an outer shoulder-end contact portion 330 of the blank 300 which is brought into contact with the one shoulder end RW of the punch P when the punch P is moved into the cavity DC of the die D.

With the arrangement of the weld beads 312, the difference between deep drawabilities of the steel plates 302 and 304 of the blank 300 decreases, serving for improving formability of the completed product without reducing stock utilization. Further, even when a tensile force required for eliminating wrinkles caused by the difference in deep drawability is applied to the blank 300 in the drawing process, the blank 300 is formed into the completed product without cracks. Thus, this serves for restraining wrinkling in deep drawing.

The present invention is described in more detail by way of example by referring to the accompanying drawings. However, these examples are only illustrative and not intended to limitthescope of the present invention.

Reference Example 1 Five planar blank samples were tested in the following manners to examine the change in ratio of the tensile strength of the weld beads formed therein relative to that of the base metal having no weld beads when the width of the weld beads was variously changed.

Each of the blank samples was prepared according to the following procedures. Linear weld beads were formed in an ordinary steel plate made of SPCC, by irradiating CO2 gas laser beam at 3kW. The width of the weld beads was altered in the range of 0.4mm to 1.5mm every plate. The thus-prepared planar blank samples were subject to measurement of the tensile strength of the weld beads. Further, the ratio of the measured tensile strength to that of the base metal was obtained every blank sample. The test results are shown in Fig. 13. Subsequently, the planar blank samples were subject to deep drawing to produce the completed products. The appearances of the thus-produced completed products were visually observed.

Reference Example 2 Five planar blank samples were tested in the following manners to examine the change in ratio of the tensile strength of the weld beads formed therein relative to that of the base metal having no weld beads when the depth of penetration of the weld beads into the blank samples was variously changed.

Each of the blank samples was prepared in the same manner as in Reference Example 1 except that weld beads had a constant width of 0.7mm but were different in depth of penetration into the plate every plate. The thus-prepared planar blank samples were subject to the same measurement of the tensile strength of the weld beads. The test results are shown in Fig. 14. Then, these planar blank samples were subject to deep drawing to produce the completed products. The appearances of the thus-produced completed products were visually observed.

As a result, it was found that, when the ratio of the tensile strength of the weld beads to that of the base metal was not less than 5%, the crack resistance and suitability for deep drawing of the planar blank were considerably improved.

Further, as seen from Figs. 13 and 14, it can be appreciated that the tensile strength ratio of not less than 5% was achieved when the weld beads had the width ranging from 0.5mm to 2.0mum and the penetration depth was not less than a half of a thickness of the blank.

Example 1 A planar blank of the first embodiment as shown in Fig. 1 was prepared according to the following procedures. A disk plate had a diameter of 92mm and a thickness of l.Omm and was made from an ordinary steel plate, i.e., cold rolling steel sheet SPCC.

Eight linear weld beads were formed by irradiating CO2 gas laser beam at 3kW to thoroughly penetrate into the disk plate. The weld beads extended radially from the center of the disk plate and terminated at a portion of the disk plate which was distant radially inward by 5mm from the periphery.

The weld beads were spaced in circumferentially equidistant relation to each other. The weld beads each had a width of 1.0mm.

Next, the thus-prepared planar blank was subject to deep drawing by using the same apparatus as shown in Fig. 2. The apparatus had the punch having a diameter of 40mm and a punch radius of 8mm, the die having a cavity of 44mm in diameter and a die radius of 10mm, and the blank holder operative to clamp the blank at a blank-holding pressure of 1.0 t. The completed product was produced under the abovedescribed deep drawing conditions. The appearance of the thus-produced completed product was visually observed.

As a result, it was recognized that the completed product had the good appearance without cracks.

Comparative Example 1 A planar blank was prepared in the same manner as described in Example 1 except that no weld bead was formed therein. The thus-prepared planar blank was subject to deep drawing under the same conditions as described in Example 1 to produce the completed product. The appearance of the thus-produced completed product was visually observed.

As a result, the completed product failed to have a good appearance.

Example 2 A planar blank of the first embodiment was prepared in the same manner as described in Example 1 except that the disk plate had a diameter of 96mm and a thickness of 0.7mm and was made from a high-tensile steel plate, i.e., cold rolling steel sheet SAFC 38R, having a tensile strength of 38kgf/mm2, and that the weld beads extended radially from the center 14 of the disk plate to a portion of the disk plate which was distant radially outward by 5.0mum from the outer shoulder-end contact portion. The thus-prepared planar blank was subject to deep drawing under the same conditions as described in Example 1 except that the blank-holding pressure was 0.8 t. The completed product was produced in the above-described deep drawing condition and the appearance thereof was visually observed.

As a result, it was recognized that the thusproduced completed product had a good appearance without cracks.

Example 3 A planar blank of the first embodiment as shown in Fig. 1 was prepared in the same manner as described in Example 2 except that the disk plate had a diameter of 94mum and that the weld beads radially extended from the center of the disk plate to the position distant radially inward by 5.0mum from the periphery of the disk plate. The thus-prepared planar blank was subject to deep drawing under the same conditions as described in Example 2 to produce the completed product. The appearance of the thusproduced completed product was visually observed.

As a result, it was recognized that the completed product had a good appearance without cracks.

Example 4 The same procedure as described in Example 3 was repeated except that the length of the weld beads formed in each blank was changed variously such that the outer ends thereof were displaced radially inwardly every blank by lmm from the periphery to the position slightly radially inward the inner shoulderend contact portion of the blank. Further, the thusprepared planar blanks were subject to deep drawing under the same conditions as described in Example 3 to produce the completed product, and subject to measurement of the limiting drawing ratios of the blanks. Two measurements were conducted each blank, and the average thereof was regarded as the limiting drawing ratio of the blank. The test results are shown in Fig. 4. In Fig. 4, first shoulder-end contact portion indicates the inner shoulder-end contact portion of the blank and second shoulder-end contact portion indicates the outer shoulder-end contact portion of the blank.

As shown in Fig. 4, when the outer ends of the weld beads were positioned at the second shoulder-end contact portion of the blank, the limiting drawing ratio was 2.375. When the outer ends of the weld beads were located at the position radially inward distant by 5.0mum from the periphery of the blank, the limiting drawing ratio was also 2.375. Further, when the outer ends of the weld beads were positioned at the periphery of the blank, the limiting drawing ratio was 2.35.

It was found that, when the outer ends of the weld beads were positioned within the region between 5.0mum inward from the periphery and the second shoulder-end contact portion, the limiting drawing ratio of the planar blank was as high as not less than 2.375 and the planar blank had a good deep drawability.

Comparative Example 2 A planar blank was prepared in the same manner as described in Example 3 except that no weld bead was formed therein. The thus-prepared planar blank was subject to deep drawing under the same conditions as described in Example 3 to produce the completed product. The appearance of the thus-produced completed product was visually observed.

As a result, the completed product failed to have the good appearance.

It may be appreciated from the test results of Examples 1 to 4 and Comparative Example 2 that, when the outer ends of the weld beads were positioned within the region extending radially outward from the second shoulder-end contact portion to a portion retarded inward from the periphery, the limiting drawing ratio of the planar blank was in the relatively high range and the planar blank was permitted to exhibit a good suitability for deep drawing in which the completed product had a good appearance.

Example 5 The same procedure as described in Example 3 was repeated except that the distance between the weld beads formed in each blank was variously changed at the outer shoulder-end contact portion of the planar blank. The distance between the weld beads was altered by a certain value every blank up to the maximum value of 70mm. The thus-prepared planar blanks were subject to deep drawing under the same conditions as described in Example 3 to produce the completed products, and subject to measurement of the limiting drawing ratios of the blanks. Two measurements were conducted each blank, and the average thereof was regarded as the limiting drawing ratio of the blank. The results are shown in Fig. 6.

Further, the appearances of the thus-produced completed products were visually observed.

As seen from Fig. 6, when the distance between the weld beads was 30mm, the limiting drawing ratio of the blank was 2.25. When the distance between the weld beads was 16mm, the limiting drawing ratio of the blank was 2.35. When the distance between the weld beads was less than 5mm or more than 30mm, the limiting drawing ratio of the blank was lower and the completed product had crack. It was found that, when the distance between the weld beads was within the range of Smm to 30mm, the limiting drawing ratio of the blank was relatively high and the completed product had a good appearance.

Comparative Example 3 A planar blank was prepared in the same manner as described in Example 3 except that the weld beads intersected at the position displaced radially outward beyond the outer shoulder-end contact portion. The thus-prepared planar blank was subject to deep drawing under the same conditions as described in Example 3 to produce the completed product, and subject to measurement of the limiting drawing ratio of the blank.

As a result, the limiting drawing ratio of the blank was lowered and the completed product failed to have an improved deep drawability thereof.

Comparative Example 4 A planar blank was prepared in the same manner as described in Example 3 except that no weld bead was formed therein. The thus-prepared planar blank was subject to deep drawing under the same conditions as described in Example 3 to produce the completed product, and subject to measurement of the limiting drawing ratio of the blank.

As a result, the limiting drawing ratio of the blank was 2.15.

It was recognized from the test results of Example 5 and Comparative Examples 3 and 4 that, when the weld beads had the distance therebetween within the range of 5mm to 30mm, the crack resistance and suitability for deep drawing of the planar blank were desirably improved.

Example 6 A planar blank of the third embodiment as shown in Fig. 7 was prepared according to the following procedures. A plate had a thickness of 0.7mm and was made from a high-tensile steel plate, i.e., cold rolling steel sheet SAFC 38R. Weld beads were formed in the plate by irradiating CO2 gas laser beam at 3kW to thoroughly penetrate into the plate. The weld beads extended radially from the predetermined point of the plate and terminated at the clamped portion of the plate, as explained in the above-mentioned third embodiment. The weld beads each had a width of l.Omm. The weld beads were prevented from intersecting at other point than the predetermined point. The distance between the weld beads at the outer shoulder-end contact portion was within a range of 5mm to 30mm.

The thus-prepared planar blank was subject to deep drawing by using the same apparatus as described in the above-mentioned third embodiment. The apparatus had the punch having a punch radius of loom, the die having a die radius of 10mm, and the blank holder operative to clamp the planar blank at a blank-holding pressure of 1.5 t. The completed product was produced under the above-described deep drawing conditions. The appearance of the thusproduced completed product was visually observed.

As a result, it was found that the completed product had a good appearance and was prevented from cracking at the curved portion which was contacted with the shoulder of the punch in the deep drawing process. It may be appreciated that the completed product can be prevented from wrinkling at the curved portion in the deep drawing process.

Example 7 A planar-blank of the fourth embodiment as shown in Fig. 9 was prepared according to the following procedures. A plate was formed by welding two different kinds of ordinary steel plates together by using laser beam. One of the plates was cold rolling steel sheet SPHC having a thickness of 1.4mm. The other of the plates was cold rolling steel sheet SPCC having a thickness of 0.7mm.

The thus-prepared planar blank was subject to deep drawing under the same condition as described in Example 6 except that the punch had a punch radius of 12mm and the blank holder had the blank-holding pressure of 60 t. The completed product was produced under the above-described deep drawing conditions. The appearance of the thus-produced completed product was visually observed.

As a result, the completed product had a good appearance without cracks. It can be appreciated that, when the weld beads are arranged as described above in the planar blank composed of the different kinds of steel plates, the difference between deep drawabilities of the different kinds of ordinary steel plates composing the planar blank becomes smaller and the completed product is produced without reducing stock utilization. Further, it may be appreciated that the blank can be prevented from cracking and wrinkling even if a greater tensile force is applied to the blank in order to eliminate wrinkles occurring due to the difference in drawablity in the deep drawing process.

Example 8 The same procedure as described in Example 1 was repeated except that the distance between the weld beads formed in each blank was variously changed at the outer shoulder-end contact portion of the planar blank in the same manner as described in Example 5.

The thus-prepared planar blanks were subject to deep drawing under the same conditions as described in Example 1 to produce the completed products. Then, the thus-produced completed products were subject to measurement of a ratio of a thickness of the side wall thereof subjected to deep drawing to an initial thickness of the blank before conducting the deep drawing. The ratio is hereinafter referred to as thickness reduction ratio. Two measurements were conducted each completed product, and the average thereof was regarded as the thickness reduction ratio.

Comparative Example 5 A planar blank was prepared in the same manner as described in Example 1 except that no weld bead was formed therein. The thus-prepared planar blank was subject to deep drawing under the same conditions as described in Example 1 to produce the completed product. Then, the thus-produced completed product was subject to measurement of the thickness reduction ratio in the same manner as described in Example 8.

The test results of Example 8 and Comparative Example 5 are indicated at El and E2 in Fig. 10, respectively.

As shown in Fig. 10, when the distance between the weld beads was 30mm, the thickness reduction ratio was 0.93. When the distance between the weld beads was 16mm, the thickness reduction ratio was 0.935. In the case of the planar blank having no weld bead, the thickness reduction ratio was 0.928.

It was found that, the planar blank having the weld beads had the thickness reduction ratio larger than that of the planar blank having no weld bead. It was recognized that when the weld beads had the distance therebetween of not more than 30mm, the side wall of the completed product was effectively prevented from decreasing in thickness in the deep drawing process.

Example 9 The same procedure as described in Example 2 was repeated except that the length of the weld beads formed in each blank was variously changed such that the outer ends thereof were displaced radially outwardly every blank by 10mm to the periphery of the blank. The thus-prepared planar blanks were subject to deep drawing under the same conditions as described in Example 2 to produce the completed products. Then, each of the thus-produced completed products was subject to measurement of the thickness reduction ratio in the same manner as described in Example 8. The test results are shown in Fig. 11.

In Fig. 4, first shoulder-end contact portion indicates the inner shoulder-end contact portion of the blank and second shoulder-end contact portion indicates the outer shoulder-end contact portion of the blank. As seen from Fig. 11, when the outer ends of the weld beads were positioned at the first shoulder-end contact portion, the thickness reduction ratio was 0.901. When the outer ends of the weld beads were positioned at the second shoulder-end contact portion, the thickness reduction ratio was 0.904. When the outer ends of the weld beads were positioned at the position distant radially outward by 30mm from the center of the blank, the thickness reduction ratio was 0.915.

It-was found that, when the outer ends of the weld beads were positioned within the region extending from the second shoulder-end contact portion to the periphery of the blank, the thickness reduction ratio was relatively high. It was appreciated that, when the weld beads had the outer ends within the region between the outer shoulder-end contact portion and the periphery of the blank, the side wall of the completed product less suffered from reduction of thickness in the deep drawing process.

Claims (52)

CLAINS:

1. A method of pressing a planar blank into a flanged product having at least one reduced thickness wall portion, comprising the steps of: preforming at least two weld beads in the blank which extend over the respective reduced thickness wall portion of the product along metal flow of the reduced thickness wall portion and terminate before the peiphery of the blank: placing the blank with the weld beads on a die opposed to a punch, in a predetermined position; pressing a blank holder against the blank placed on the die to clamp the periphery of the blank: and moving the punch into the cavity of the die to draw the blank along the surface of the punch and form a flange along the periphery of the blank, while keeping the blank clamped at the periphery.

2. A method as claimed in claim 1, wherein the step of preforming the at least two weld beads in the blank includes causing predetermined portions of the blank to penetrate into the blank by using a heat source having high energy density.

3. A method as claimed in claim 2, wherein the step of preforming the at least two weld beads in the blank includes preventing the weld beads from intersecting within a first portion of the blank brought into contact with the curved surface portion of the punch which extends between the bottom surface portion and the vertical surface portion thereof when the punch is moved into the cavity of the die, and a second portion of the blank which is brought into contact with the vertical surface portion of the punch when the punch is moved into the cavity of the die.

4. A method as claimed in claim 3, wherein the step of preforming the at least two weld beads in the blank includes positioning one end of each of the weld beads in the second portion of the blank

5. A method as claimed in claim 4, wherein the step of preforming the at least two weld beads in the blank includes positioning an opposite end of each of the weld beads in a third portion of the blank which is brought into contact with the bottom surface portion of the punch when the punch is moved into the cavity of the die.

6. A method as claimed in claim 3, wherein the step of preforming the at least two weld beads in the blank includes positioning the weld beads equidistantly spaced from each other.

7. A method as claimed in claim 6, wherein the step of preforming the at least two weld beads in the blank includes positioning the weld beads such that the distance therebetween is in a range of 5mm to 30mum at a shoulder-end contact portion of the blank which is brought into contact with one shoulder end of the punch at which the vertical surface portion thereof and the curved surface portion thereof are connected together when the punch is moved into the cavity of the die.

8. A method as claimed in claim 5, wherein the step of preforming the at least two weld beads in the blank includes positioning the one end of each weld bead between a shoulder-end contact portion of the blank which is brought into contact with one shoulder end of the punch at which the vertical surface portion thereof and the curved surface portion thereof are connected together when the punch is moved into the cavity of the die, and a clamped portion of the blank which is clamped by the blank holder and a draw bead formed on the die when the blank holder is pressed against the blank on the die.

9. A method as claimed in claim 3, wherein the step of preforming the at least two weld beads in the blank includes forming the weld beads each having a width of 0.5mm to 2.0mum.

10. A method as claimed in claim 3, wherein the step of preforming the at least two weld beads in the blank includes forming the weld beads each having a depth of penetration into the blank which is larger than half the thickness of the blank.

11. A method as claimed in claim 5, wherein the step of preforming the at least two weld beads in the blank includes positioning the weld beads along lines extending radially from the center of the blank, the blank having a disk shape.

12. A method as claimed in claim 11, wherein the step of preforming the at least two weld beads in the blank includes arranging the at least two weld beads within a sectorial region of the blank which has a central angle of 180 degrees at the center of the blank.

13. A method as claimed in claim 11, wherein the step of placing the blank on the die includes aligning the center of the blank with the center axis of the punch having a cylindrical shape.

14. A method as claimed in claim 5, wherein the step of preforming the at least two weld beads in the blank includes fixing an image point in the blank by projecting a center of curvature of the curved surface portion of the punch having the bottom surface portion of a shape having at least one corner portion which forms a curved periphery, and positioning the weld beads along lines extending radially from the image point.

15. A method as claimed in claim 14, wherein the step of preforming the at least two weld beads in the blank includes arranging the at least two weld beads within a sectorial region of the blank which has a central angle of 180 degrees at the image point as the center.

16. A method as claimed in claim 14, wherein the step of placing the blank on the die includes aligning the image point of the blank with the center of curvature of the curved surface portion of the punch.

17. A flanged product having at least one reduced thickness wall portion, formed by a method comprising the steps of: preforming at least two weld beads in the blank which extend over the respective reduced thickness wall portion of the product along metal flow of the reduced thickness wall portion and terminate before the periphery of the blank: placing the blank with the weld beads on a die opposed to a punch, in a predetermined position; pressing a blank holder against the blank placed on the die to clamp the periphery of the blank: and moving the punch into the cavity of the die to draw the blank along the surface of the punch and form a flange along the periphery of the blank, while keeping the blank clamped at the periphery.

18. A flanged product as claimed in claim 17, wherein the step of preforming the at least two weld beads in the blank includes causing predetermined portions of the blank to penetrate into the blank by using a heat source having high energy density.

19. A flanged product as claimed in claim 18, wherein the step of preforming the at least two weld beads in the blank includes preventing the weld beads from intersecting within a first portion of the blank brought into contact with the curved surface portion of the punch which extends between the bottom surface portion and the vertical surface portion thereof when the punch is moved into the cavity of the die, and a second portion of the blank which is brought into contact with the vertical surface portion of the punch when the punch is moved into the cavity of the die.

20. A flanged product as claimed in claim 19, wherein the step of preforming the at least two weld beads in the blank includes positioning one end of each of the weld beads in the second portion of the blank.

21. A flanged product as claimed in claim 20, wherein the step of preforming the at least two weld beads in the blank includes positioning an opposite end of each of the weld beads in a third portion of the blank which is brought into contact with the bottom surface portion of the punch when the punch is moved into the cavity of the die.

22. A flanged product as claimed in claim 19, wherein the step of preforming the at least two weld beads in the blank includes positioning the weld beads equidistantly spaced from each other.

23. A flanged product as claimed in claim 22, wherein the step of preforming the at least two weld beads in the blank includes positioning the weld beads such that the distance therebetween is in a range of 5mm to 30mm at a shoulder-end contact portion of the blank which is brought into contact with one shoulder end of the punch at which the vertical surface portion thereof and the curved surface portion thereof are connected together when the punch is moved into the cavity of the die.

24. A flanged product as claimed in claim 23, wherein the step of preforming the at least two weld beads in the blank includes positioning one end of each weld bead between the shoulder-end contact portion of the blank and a clamped portion of the blank which is clamped by the blank holder and a draw bead formed on the die when the blank holder is pressed against the blank on the die.

25. A flanged product as claimed in claim 19, wherein the step of preforming the at least two weld beads in the blank includes forming the weld beads each having a width of 0.5mm to 2.0mum.

26. A flanged product as claimed in claim 19, wherein the step of preforming the at least two weld beads in the blank includes forming the weld beads each having a depth of penetration into the blank which is larger than half the thickness of the blank.

27. A flanged product as claimed in claim 21, wherein the step of preforming the at least two weld beads in the blank includes positioning the weld beads along lines extending radially from the center of the blank,having a disk shape.

28. A flanged product as claimed in claim 27, wherein the step of preforming the at least two weld beads in the blank includes arranging the weld beads within a sectorial region of the blank which has a central angle of 180 degrees at the center of the blank.

29. A flanged product as claimed in claim 27, wherein the step of placing the blank on the die includes aligning the center of the blank with the center axis of the punch having a cylindrical shape.

30. A flanged product as claimed in claim 21, wherein the step of preforming the at least two weld beads in the blank includes fixing an image point in the blank by projecting a center of curvature of the curved surface portion of the punch having the bottom surface portion of a generally polygonal shape, and positioning the weld beads along lines extending radially from the image point.

31. A flanged product as claimed in claim 30, wherein the step of preforming the at least two weld beads in the blank includes arranging the weld beads within a sectorial region of the blank which has a central angle of 180 degrees at the image point as the center.

32. A flanged product as claimed in claim 30, wherein the step of placing the blank on the die includes aligning the image point of the blank with the center of curvature of the curved surface portion of the punch.

33. A planar blank having at least one reinforced portion, comprising at least two weld beads penetrating into the blank, said at least two weld beads being positioned over the respective reinforced portion of the blank and terminating before the periphery of the blank, said at least two weld beads being positioned along lines extending radially from a predetermined point in the blank.

34. A planar blank as claimed in claim 33, wherein the at least two weld beads are prevented from intersecting at other point than the predetermined point.

35. A planar blank as claimed in claim 34, wherein the at least two weld beads are equidistantly spaced from each other.

36. A planar blank as claimed in claim 34, wherein the at least two weld beads each have a width of 0.5mm to 2.0mm.

37. A planar blank as claimed in claim 34, wherein the at least two weld beads each have a depth of penetration larger than half the thickness of the blank.

38. A planar blank as claimed in claim 33, wherein the blank has a disk shape and the predetermined point is at the center of the disk shape.

39. A planar blank as claimed in claim 33, wherein the blank has a shape having at least one corner and the predetermined point is disposed inside the respective corner of the blank.

40. A product formed by draw-pressing a planar blank, comprising: a bottom wall having a curved periphery; a side wall connected with the bottom wall; at least one curved wall extending from the curved periphery of the bottom wall and connected with the side wall: a flange angularly extending from the side wall; and at least two weld beads positioned along lines extending radially from a predetermined point in the bottom wall through the respective curved wall and the side wall, said at least two weld beads terminating before the peripheral edge of the flange, said at least two weld beads penetrating into the blank.

41. A product as claimed in claim 40, wherein the weld beads are prevented from intersecting at other point than the predetermined point.

42. A product as claimed in claim 41, wherein each of the weld beads has one end disposed within a region extending over the side wall and the flange and an opposite end disposed within the bottom wall.

43. A product as claimed in claim 42, wherein the one end of each of the weld beads is disposed in the flange.

44. A product as claimed in claim 41, wherein the weld beads are equidistantly spaced from each other.

45. A product as claimed in claim 41, wherein the bottom wall has a circular shape having a center and the predetermined point is at the center of the circular-shaped bottom wall.

46. A product as claimed in claim 45, wherein the at least two weld beads extend through a sectorial region of the bottom wall which has a central angle of 180 degrees at the center of the bottom wall.

47. A product as claimed in claim 41, wherein the bottom wall is of a shape having at least one corner portion forming the curved periphery, the respective curved wall is joined with the respective corner portion of the bottom wall, and the predetermined point is disposed inside the respective corner portion.

48. A product as claimed in claim 47, wherein the at least two weld beads extend through a sectorial region of the bottom wall which has a central angle of 180 degrees at the predetermined point as the center.

49. A method of pressing a planar blank, substantially as described with reference to Figures 1 to 4, Figures 5 and 6, Figure 7, or Figures 8 and 9 of the accompanying drawings.

50. A method of pressing a planar blank, substantially as described with reference to any of Examples 1 to 9.

51. A flanged product substantially as described with reference to, and as shown in, Figures 15 and 16 or Figures 17 and 18 of the accompanying drawings.

52. A planar blank substantially as described with reference to, and as shown in, Figure 1, Figure 5, Figure 7, or Figure 9 of the accompanying drawings.