MACHINING METHOD FOR BURRED FLAT HOLES IN METAL PLATES

Abstract

A machining method for a burred flat hole includes first an overhang portion is formed in a flat hole-forming region in a metal plate in a first step, subsequently a fiat hole portion is formed in the overhang portion in a second step, and finally burring is formed on the peripheral edge portion of the hole portion in a third step. Accordingly, when burring is to be formed, overhanging machining and perforating machining have been substantially completed, and therefore pressing force of a punch for burring machining can be set to the minimum value necessary for burring formation.

Claims

1. A machining method for a burred flat hole in a metal plate, comprising: a first step of pressing an overhanging punch having a flat cross-section orthogonal to a pressing direction onto a surface of a metal plate to form an overhang portion that is flat in the cross-section; a second step of pressing a perforating punch having a flat cross-section orthogonal to the pressing direction onto a bottom surface of the formed overhang portion to form a planar flat hole portion in the portion; and a third step of pressing a burring punch onto a peripheral edge portion of the formed hole portion to form a burring by pulling up the portion, wherein: each of the overhanging punch and the perforating punch has a pair of side surfaces that are parallel to the pressing direction and are positioned at both ends in a longitudinal direction (hereinafter, referred to as a major axis direction) of the cross-section and a pair of side surfaces that are positioned at both ends in a width direction (hereinafter, referred to as a minor axis direction) of the cross-section; and difference (7n2n) between the side surface gap 7n at both ends in the major axis direction of the cross-section of the burring punch and the side surface gap 2n at both ends in the major axis direction of the cross-section of the overhanging punch is set to be smaller than difference (7m2m) between the side surface gap 7m at both ends in the minor axis direction of the cross-section of the burring punch and the side surface gap (2m) in the minor axis direction of the cross-section of the overhanging punch, that is, (7n2n)<(7m2m).

2. The machining method for a burred flat hole in a metal plate according to claim 1, wherein the metal plate is a header plate for a heat exchanger.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0024] FIG. 1 illustrates a partial perspective view showing respective shapes of a metal plate formed by three steps in the present invention.

[0025] FIG. 2 illustrates a partial cross-section view explaining a machining method by three steps in the present invention.

[0026] FIG. 3 illustrates a partial perspective view of a header plate in which a burred flat hole is formed by the machining method in FIG. 2.

[0027] FIG. 4 illustrates a cross-section view along IV-IV in FIG. 3.

[0028] FIG. 5 illustrates a horizontal cross-section view in a second Example of the present invention, seen from the same direction as in FIG. 4.

[0029] FIG. 6 illustrates an explanation view of a conventional type burring-machined portion.

DESCRIPTION OF EMBODIMENTS

[0030] Next, on the basis of the drawings, embodiments of the present invention will be explained. FIG. 1 illustrates a partial perspective view showing respective shapes of a metal plate formed by three steps that are characteristics of a machining method of the present invention. That is, FIG. 1(A) shows a shape of a metal plate machined in a first step, FIG. 1(B) shows a shape of the metal plate machined in a second step, and FIG. 1(C) shows a shape of the metal plate machined in a third step. Meanwhile, respective views in FIG. 1 are views seen from a rear surface side (surface on a inverse direction side relative to a pressing direction of a punch) of the metal plate.

[0031] FIG. 2 illustrates partial cross-section views for explaining a machining method by three steps in the present invention, in which FIGS. 2(A1) and 2(A2) show the first step, FIGS. 2(B1) and 2(B2) show the second step, and FIGS. 2(C1) and 2(C2) show the third step. In these drawings, (A1), (B1) and (C1) are cross-section views of a cross-section parallel to a pressing direction F of respective overhanging punch 2, perforating punch 4 and burring punch 7 and a cross-section on the major axis of a cross-section orthogonal to the pressing direction F. (A2), (B2) and (C2) are cross-section views of a cross-section parallel to the pressing direction F of respective overhanging punch 2, perforating punch 4 and burring punch 7 and a cross-section seen on a minor axis of a cross-section orthogonal to the pressing direction F. Here, a major axis includes one whose cross-section orthogonal to the pressing direction F is flat ellipsoid shape (note that the ellipsoid shape is a race track shape (including a pair of parallel portions facing each other and a pair of arc portions linking both ends thereof)), and means the major axis of the ellipsoid. A minor axis means the minor axis of the ellipsoid.

[0032] FIGS. 2(A1) and 2(A2) in the first step show a state in which the overhanging punch 2, in which a horizontal cross-section orthogonal to the pressing direction F thereof is a flat ellipsoid, is pressed in the pressing direction F shown by an arrow onto a metal plate 1 to form an overhang portion 3 having a horizontal cross-section of ellipsoid in the metal plate 1. The flat overhanging punch 2 having an ellipsoidal horizontal cross-section has a pair of side surfaces 2b positioned at both ends in a major axis direction of an ellipsoidal horizontal cross-section and a pair of side surfaces 2a positioned at both ends in a minor axis direction, which are made of a hard metal for press and extend parallel to the pressing direction F. Meanwhile, in order to form this overhang portion 3, it is sufficient to place a metal plate on a not illustrated die in which a concave portion larger than the outer circumference of the overhang portion 3, and then to press the overhanging punch 2 into the die.

[0033] In the above-described overhanging punch 2, the apical portion (bottom portion 3a) in the pressing direction F shown in FIG. 2(A1) is flat, small arc portions are formed at both end portions in the major axis direction of the bottom portion, and the apical portion (bottom portion 3a) in the minor axis direction is formed in an arc shape as a whole, as shown in FIG. 2(A2). In other words, the major axis direction of the ellipsoid of the bottom portion 3a of the overhang portion 3 formed in the metal plate 1 is substantially flat, and the minor axis direction of the ellipsoid of the bottom portion 3a is formed in an arc shape. Meanwhile, the pressing force of the overhanging punch 2 is set within a range necessary for forming the overhang portion 3 in the metal plate 1. The shape of the overhang portion 3 formed in the first step is shown in FIG. 1(A).

[0034] FIGS. 2(B1) and 2(B2) of the second step show a state where the perforating punch 4 having a flat ellipsoidal cross-section is pressed in the pressing direction F shown by an arrow onto the bottom surface 3a of the overhang portion 3 formed in the first step to form a flat ellipsoidal hole portion 5 in the portion. The perforating punch 4, whose horizontal cross-section orthogonal to the pressing direction is a flat ellipsoid, has a pair of side surfaces 4b positioned at both ends in the major axis direction of the ellipsoid and a pair of side surfaces 4a at both end positions in the minor axis direction of the ellipsoid orthogonal to these, which are made of a hard metal for press and extend parallel to the pressing direction. This perforating step can be performed by arranging a not illustrated die for the outer circumference of the overhang portion 3 except for a perforating portion.

[0035] In the perforating punch 4, as shown in FIGS. 2(B1) and 2(B2), the apical portion (bottom portion) in the pressing direction F is formed evenly. Meanwhile, the pressing force of the perforating punch 4 is set within a range necessary for forming the hole portion 5 in the metal plate 1.

[0036] In the present embodiment, a side surface gap 4n of a pair of side surfaces 4b at both ends in the major axis direction of the horizontal cross-section in the perforating punch 4 is substantially identical to the side surface gap 2n of a pair of side surfaces 2b at both ends in the major axis direction of the horizontal cross-section in the overhanging punch 2, but a side surface gap 4m of a pair of side surfaces 4a at both ends in the minor axis direction in the perforating punch 4 is set to be smaller than the side surface gap 2m of a pair of side surfaces 2a in the minor axis direction in the overhanging punch 2.

[0037] Therefore, as in FIG. 2(B1), width 3n in the major axis direction of the hole portion 5 is substantially identical to the width in the major axis direction of the overhang portion 3, but the width in the minor axis direction of the hole portion 5 is, as in FIG. 2(B2), smaller than the width in the minor axis direction of the overhang portion 3. As a result, at the apical portion of the side surface 4a in the minor axis direction of the overhang portion 3, there remains an overhang zone 3b (FIG. 2(B2)) that is elongated and has an arc cross-section curved toward the inside of the minor axis direction. Meanwhile, in FIGS. 2(B1) and 2(B2), there is shown for reference the shape of a side cross-section of a metal piece 6 cut off when the hole portion 5 has been perforated. The shape of the overhang portion 3 with the hole portion 5 formed in the second step through the first step is shown in FIG. 1(B).

[0038] In FIGS. 2(C1) and 2(C2) of the third step, a state, where the burring punch 7 is pressed in the pressing direction F shown by an arrow onto the peripheral edge portion of the hole portion 5 formed in the second step and the portion is pulled up to form the burring 8 on the peripheral edge portion, is shown. The burring punch 7 has a pair of side surfaces 7b at both ends in the major axis direction and a pair of side surfaces 7a at both ends in the minor axis direction, which are made of a hard metal for press, extend parallel in the pressing direction F and are parallel to each other.

[0039] The difference 7n2n between the side surface gap 7n of a pair of side surfaces 7b at both ends in the major axis direction of a flat ellipsoid in a horizontal cross-section orthogonal to the pressing direction F in the burring punch 7 and the side surface gap 2n of a pair of side surfaces 2b at both ends in the major axis direction of a flat ellipsoid in the horizontal cross-section of the overhanging punch 2 in the first step is set to be smaller than the difference 7m2m between the side surface gap 7m of a pair of side surfaces 7a at both ends in the minor axis direction of the burring punch 7 and the side surface gap 2m of a pair of side surfaces 2a at both ends in the minor axis direction of the horizontal cross-section of the overhanging punch 2 (7n2n<7m2m).

[0040] As a consequence of this setting, upon burring machining, at rim portions of the hole portion 5 at both ends in the major axis direction with small gap difference, a low major axis direction burring 8b is formed while expanding smaller, and at rim portions of the hole portion 5 in the minor axis direction with large gap difference, a high minor axis direction burring 8a is formed while expanding more largely.

[0041] On the other hand, in the second step of the embodiment, it is machined so that a rectilinear remaining portion 3c is formed at apical portions of side surfaces at both ends in the major axis direction of the horizontal cross-section of the overhang portion 3 as described above, and that the overhang zone 3b that is elongated and has an arc cross-section curved toward the inside of the minor axis direction of the overhang portion 3 remains (see FIG. 2(B2)). Upon burring machining, this arc overhang zone 3b is pulled up with plastic deformation in the vertical direction by pressing force of the burring punch 7, and therefore burring can be formed by furthermore low pressing force as compared with a case where it is vertical from the beginning.

[0042] As the synergistic result of above-described plurality of effects, upon burring machining, at both ends in the major axis direction of the horizontal cross-section, the burring 8b in the major axis direction is low, and therefore stress generated in that is reduced and occurrence of a crack phenomenon in a part of the portion is surely avoided.

[0043] By the third step, as the burring 8, a low burring 8b in the major axis direction and a high burring 8a in the minor axis direction are formed on the peripheral edge portion of a flat hole 9, and in FIG. 1(C) the flat hole 9 with the the burring 8 machined in this way is shown.

[0044] FIG. 3 illustrates a partial perspective view of a header plate in which a burred flat hole is formed by the machining method in FIG. 2, and FIG. 4 illustrates a cross-section view along IV-IV in FIG. 3. In a header plate 10 that is the metal plate 1, plural flat holes 9 with the burring 8 are formed in parallel to each other, and each of flat holes 9 and an end portion, inserted therein, of a flat tube 11 shown with a flat tube 11 in FIG. 4 are brazed and fixed each other in the state.

[0045] The contact area between the outer circumference surface of the flat tube 11 and the inner circumference surface of the flat hole 9 is increased by the burring 8, and therefore fixing strength of the brazing can be maintained sufficiently. Meanwhile, in FIG. 4, a tank main body 12 shown with a dashed one-dotted line is fixed to both of the curved rim portions in the header plate 10 to form a tank 13 on an inlet side or an outlet side of fluid.

[0046] Note that fins (not illustrated) are arranged between a plurality of flat tubes 11 stacked with each other, and a core portion is formed with these plurality of flat tubes 11 and fins.

[0047] Moreover, in the above example, the plane of the header plate 10 is formed flatly, but it may be formed so as to have an arc cross-section. In this case, a burring portion is formed along the arc, and burring portions at both ends in the major axis direction is formed lower than that in the minor axis direction.

[0048] In FIG. 5, a schematic view of the horizontal cross-section is shown. In the example, the horizontal cross-section of the header plate 10 is formed in an arc shape. To the header plate 10, the tank main body 12 having an arc horizontal cross-section is fixed to form the tank 13, and the core portion is formed with a stacked plurality of flat tubes 11 and fins (not illustrated) arranged therebetween. Further, in the header plate 10 having an arc cross-section, the burring 8 is formed. The height of the burring 8 is low at both ends in the major axis direction of an ellipsoidal hole, and is high at the center in the major axis direction thereof. The burring 8 like this may be formed by forming the burring punch 7 so as to have a shape in which a plan cross-section is flat and an outer circumference of a longitudinal cross-section in the major axis direction is formed in an arc, and setting the cross-section at the center in the major axis direction of the burring punch 7 to be higher than both ends in the major axis direction. Then, a heat exchanger is configured by these respective members.

INDUSTRIAL APPLICABILITY

[0049] A machining method for a burred flat hole in metal plates of the present invention can be utilized for burring machining metal plates such as a header plate for a heat exchanger in vehicles and the like.

REFERENCE SIGNS LIST

[0050] 1 metal plate

[0051] 2 overhanging punch

[0052] 2a side surface

[0053] 2b side surface

[0054] 2c bottom surface

[0055] 2n side surface gap

[0056] 2m side surface gap

[0057] 3 overhang portion

[0058] 3a bottom surface

[0059] 3b overhang zone

[0060] 3c remaining portion

[0061] 3n width

[0062] 4 perforating punch

[0063] 4a side surface

[0064] 4b side surface

[0065] 4n side surface gap

[0066] 4m side surface gap

[0067] 5 hole portion

[0068] 6 metal piece

[0069] 7 burring punch

[0070] 7a side surface

[0071] 7b side surface

[0072] 7n side surface gap

[0073] 7m

[0074] side surface gap

[0075] 8 burring

[0076] 8a minor axis direction burring

[0077] 8b major axis direction burring

[0078] 9 flat hole

[0079] 10 header plate

[0080] 11 flat tube

[0081] 12 tank main body

[0082] 13 tank

[0083] 14 crack portion

[0084] F pressing direction