EP3178580A1

EP3178580A1 - Progressive die that allows to localize and control of the stretching of a sheet steel during forming of a brake plate

Info

Publication number: EP3178580A1
Application number: EP16202736.1A
Authority: EP
Inventors: Elio Bora
Original assignee: BORA Srl
Current assignee: Bora SpA
Priority date: 2015-12-11
Filing date: 2016-12-07
Publication date: 2017-06-14
Anticipated expiration: 2036-12-07
Also published as: IT201600124471A1; EP3178580B1

Abstract

A progressive die (100) that allows to localize and control the stretching of the sheet steel during forming of a brake plate, comprising: a central punch (2) fastened on a lower base of the die, in a way to be adjusted in height with shims; peripheral punches (3, 4) mounted on the lower base of the die, in a way to be individually adjusted in height with shims; and lateral punches (5, 6, 7, 8) mounted on the central punch (2) in a way to be individually adjusted in height with shims, regardless of the adjustment of the peripheral punches (3, 4).

Description

The present patent application relates to a progressive die, in particular to a stretching die, for making a brake plate.
Brake plates are characterized by relatively flat areas, which are quite easy to form, and high-deformation critical areas.
Fig. 1 shows a brake plate (P). The critical areas of the brake plate (P) are:

areas (A) with clews for fairlead holes (Fig.1-2);
areas (B) with a surface for fixing cylinders (Fig.1-3);
areas (C) with support feet (Fig.1-4).

These areas (A, B, C) of the brake plate (P) have strict dimensional and geometrical tolerances in order to ensure a correct mounting of the brake plate (P) in the braking system and ensure a minimum thickness to guarantee fatigue strength of the brake plate.
The forming method of brake plates provides for the following operations: shearing of a sheet steel; stretching of the sheet steel; deep drawing; adjustment; vertical drilling; drilling of fairlead holes by means of cams; edge trimming and part detachment.
These operations are generally made with a transfer press or progressive press provided with progressive dies for each working station.
The stretching operation is made with a die provided with a single punch with substantially hemispheric shape. In this way a practically uniform stretching is obtained on the sheet steel.
Fig. 2 shows a stretching die according to the prior art, indicated with reference numeral (200). The stretching die (200) comprises an upper base (201) connected to a ram of the press and a lower base, not shown. An upper sheet-presser (13) is fastened to the upper base (201). The upper sheet-presser has a central hole (13a).
A lower sheet-presser (14) is movably mounted on the lower base. A punch (15) passing through the lower sheet-presser (14) is fastened on the lower base. The punch (15) has a substantially hemispheric head and engages in the central hole (13a) of the upper sheet-presser to stretch the sheet steel.
With reference to Figs. 3 and 4, two punches (15) are generally provided in order to work two brake plates. When it comes down, the upper sheet-presser (13) first compresses the sheet steel (L) on the lower sheet-presser (14), which is lowered, and then stretches the sheet steel (L) on the approximately hemispheric punch (15). Fig. 2 shows the die in closed position (with the ram of the press in the lower dead center position).
Fig. 2A shows the sheet steel coming out of the stretching die (200). Using only one punch (15) the sheet steel is curved with a small radius of curvature that corresponds to the radius of curvature of the head of the punch. Moreover a uniform stretching of the material of the sheet steel (L) is obtained with such a die.
However the uniform stretching of the material of the sheet steel does not solve the problems of brake plates because the stretching should be higher in some areas of the brake plate with respect to other areas.
The uniform stretching, with only one almost hemispheric punch, requires the material to flow from one area to the other area of the brake plate during the subsequent deep drawing operation. Practically, however, the small radiuses of the punches used for deep drawing do not allow the sheet steel to flow from one area to the other area during deep drawing, thus generating localized defects, such as for example folding caused by excess material or excessive stretching caused by lack of material. As a consequence, difficulties are encountered in complying with the tolerance values required by the technical drawing of the brake plate.
Moreover, being made in only one piece, the punch (15) creates problems when setting up the die. To correct the defects found on the sheet steel, it is necessary to rework the entire surface of the punch, and not only the areas where defects are found. Even using computerized simulation methods and graphic measurements of the deformation of the sheet steel, numerous attempts must be made with multiple reworking operations of the almost hemispheric punch before an ideal solution is found for the optimal operation of the die.
US2689539 discloses a die for stretching a sheet steel comprising a plurality of punches mounted on a lower base and one punch mounted on an upper base of the die.
The purpose of the present invention is to eliminate the drawbacks of the prior art by disclosing a die, which can be part of a progressive forming system, able to stretch the sheet steel locally, or make the sheet steel slide to obtain a semi-finished part that is suitable for being worked in the subsequent stations in an effective, versatile and practical way.
This purpose has been achieved according to the present invention with the characteristics described in the independent claim 1.
Advantageous embodiments of the invention appear from the dependent claims.
In order to remedy the problems generated by the stretching die of the prior art, which is used in the stretching operation of the progressive forming method of the brake plate, a progressive die according to the present invention has been studied, which allows to localize and control the stretching of the sheet steel during forming of a brake plate.
Additional features of the invention will appear clearer from the detailed description below, which refers to a merely illustrative, not limiting embodiment, which is shown in the attached drawings, wherein:

Fig. 1 is a plan view of a brake plate;
Figs. 1-1, 1-2, 1-3 and 1-4 are section views of the brake plate respectively taken along the section planes I-I, II-II, III-III and IV-IV of Fig. 1;
Fig. 2 is a section view of a stretching die according to the prior art;
Fig. 2A is a perspective view showing the sheet steel coming out of the stretching die of Fig. 2;
Fig. 3 is a perspective view of a lower sheet-presser with single punches of the stretching die of Fig. 2;
Fig. 4 is a plan view of the lower sheet-presser of Fig. 3;
Fig. 4-1 is a section view taken along the section plane I-I of Fig. 4;
Fig. 5 is a block diagram of a transfer press for making a brake plate according to the invention and a perspective view showing a sheet steel coming out of the various stations of the transfer press;
Fig. 6 shows sections of a part coming out of a stretching die of the prior art; of a stretching die according to the present invention and of a deep drawing die, respectively taken along the section planes I-I, II-II, III-III and IV-IV of Fig. 1;
Fig. 7 is a section view of a stretching die according to the invention;
Fig. 8 is a perspective view of a lower sheet-presser and of the punches of the die of Fig. 7;
Fig. 9 is a plan view of the lower sheet-presser of the die of Fig. 7;
Figs. 9-1, 9-2, 9-3 and 9-4 are section views of the lower sheet-presser respectively taken along the section planes I-I, II-II, III-III and IV-IV of Fig. 9.

With reference to Fig. 5, a transfer press or progressive press for making a brake plate is diagrammatically shown.
Said transfer press comprises seven working stations: a shearing station (S1); a stretching station (S2); a deep drawing station (S3); an adjustment station (S4); a vertical drilling station (S5); a cam drilling station (S6); an edge trimming and part detachment station (S7).
A sheet steel is fed in the transfer press and suitably worked parts (P1, P2, P3, P4, P5, P6, P7) come out of each station (S1-S7).
Figs. 7 - 9 show the stretching die of the invention, which is generally indicated with reference numeral (100).
The die (100) comprises an upper base (101) connected to a ram of the press and a lower base, not shown. An upper sheet-presser (10) is fastened to the upper base (101). The upper sheet-presser has a central hole (10a). An upper punch (11) is fastened to the upper base and disposed in the central hole (10a) of the upper sheet-presser. The upper punch (11) has a substantially flat head with a curved edge. The diameter of the upper punch (11) is lower than the diameter of the central hole (10a) in a way to leave an annular space (10b).
A lower sheet-presser (9) is mounted on the lower base with possibility of moving vertically. The lower sheet-presser (9) is shaped as a plate. Grooves (12) are provided on the lower sheet-presser (9), where draw bead rods fastened to the upper base (101) operate.
A central punch (2) is fastened to the lower base and passes through the lower sheet-presser (9), in a way to be easily adjusted in height with shims or spacers not shown in the figure. The central punch (2) is shaped as a disc with rounded upper edges and a substantially flat head. The central punch (2) is disposed in correspondence of the central hole (10a) of the upper sheet-presser (10). The central punch (2) protrudes in upper position with respect to the lower sheet-presser (9).
Two peripheral punches (3, 4) are disposed in diametrally opposite position above the central punch (2) in a way to enter the annular space (10b) of the upper sheet-presser. The peripheral punches (3, 4) are fastened to the lower base with supports that pass through the central punch (2). In this way the peripheral punches (3, 4) can be easily adjusted in height with shims not shown in the figure. The adjustment of the peripheral punches (3, 4) is independent of the adjustment of the central punch (2).
Each peripheral punch (3, 4) has a substantially semi-cylindrical shape with axis parallel to the upper surface of the lower sheet-presser (9). The peripheral punches are disposed in parallel position in diametrally opposite positions with respect to the center of the central punch (2).
The first peripheral punch (3) is higher than the second peripheral punch (4). The peripheral punches (3, 4) are situated in correspondence of areas where reverse deep drawing will be made (for example in correspondence of area (B) of Fig. 1-3).
Lateral punches (5, 6, 7, 8) are fastened on the central punch (2) and disposed on the sides of the peripheral punches (3, 4) in such manner to enter the space (10b) of the upper sheet-presser. The lateral punches (5, 6, 7, 8) are four lateral punches disposed in diametrally opposite positions with respect to the center of the central punch (2) and spaced by 90°. Two lateral punches (7, 8) are disposed on the sides of the first peripheral punch (3) and other two lateral punches (5, 6) are disposed on the sides of the second peripheral punch (4). Each lateral punch (5, 6, 7, 8) has a shape with hemispheric head. The lateral punches (7, 8) beside the first peripheral punch (3) are higher than the lateral punches (5, 6) beside the second peripheral punch (4).
The lateral punches (5, 6, 7, 8) are positioned in the areas where the final shape is obtained with subsequent deep drawing operations (area A of Fig. 1-2). The adjustment of the lateral punches (5, 6, 7, 8) is independent of the adjustment of the peripheral punches (4). The adjustment of the lateral punches (5, 6, 7, 8) is made with shims or spacers, not shown in the figures. The arrangement of the upper punch (11) and of the central punch (2) in the area that corresponds to the central area of the brake plate, and the arrangement of the peripheral punches (3, 4) and of the lateral punches (5, 6, 7, 8) in peripheral position with respect to the center of the brake plate allow for the sliding of the sheet steel from the central area of the brake plate towards the peripheral punches (3, 4) and the lateral punches (5, 6, 7, 8).
Advantageously the die (100) comprises two central punches (2) to make two brake plates.
This description continues by illustrating the operation of the die (100).
The sheet steel, which is sheared in the first station (S1), is fed towards the die (100) of the second station (S2) that receives the sheet steel on the lower sheet-presser (9), with die open and lower sheet-presser (9) in high position. The high position of the lower sheet-presser (9) allows the sheet steel to slide on the central punch (2), on the peripheral punches (3, 4) and on the lateral punches (5, 6, 7, 8).
The upper base (101) comes down and the sheet steel (L) is compressed between the upper sheet-presser (10) and the lower sheet-presser (9).
Under the thrust of the upper sheet-presser (10), the lower sheet-presser (9) is lowered. The upper base (101) keeps coming down and the sheet steel (L), compressed between the two sheet-pressers (9, 10), is stretched on the punches (2-8). The draw bead rods acting on the sheet steel in correspondence of the slots (12) of the lower sheet-presser brake the sliding of the sheet steel compressed between the upper sheet-presser (10) and the lower sheet-presser (9). After a suitable travel of the upper base (101), the upper punch (11) comes in contact with the sheet steel (L) and starts deep drawing the sheet steel in correspondence of the central part of the brake plate.
At the end of the travel of the upper base (10), the upper punch (11) compresses the sheet steel on the central punch (2), then the upper base (101) rises towards the initial position.
Such a progressive die (100) allows to localize and control the stretching of the sheet steel during forming of a brake plate.
The novelty of the die (100) according to the present invention compared to the die of the prior art (200) consists in the replacement of the single central punch (15) with a plurality of punches (2, 3, 4, 5, 6, 7, 8) and in the addition of the upper punch (11).
With such a punch configuration, the die (100) allows to stretch the sheet steel because the lower punches (2, 3, 4, 5, 6, 7, 8) and the upper punch (11) keep having a contact surface with the sheet steel with a large radius of curvature.
The upper punch (11) adds a deep drawing part (sliding of the sheet steel in the central part of the brake plate) to the stretching of the sheet steel.
The lower punches (2-8) can be individually adjusted in height.
The reworking of the punches, for setting up the die, is only made on the punches that operate in the areas of the brake plate to be set up.
In this way it is easier to control the thickness of the material and obtain a surface morphology that is more suitable for the deep drawing of the subsequent operation. From the morphological viewpoint, this result appears evident in Fig. 6, which compares the results of the two forming systems, in the stretching operation, compared to the shape of the brake plate after deep drawing.
The sections on the brake plate correspond to the section planes (I-I. II-II, III-III and IV-IV) of Fig.1.
Figs. 6.1, 6A.1 and 6B.1 are sections of the disc along a section plane I-I of Fig. 1.
Fig. 6.1 shows the result of forming with the die (200) of the prior art.
Fig. 6A.1 shows the result of forming with the die (100) of the invention.
Fig. 6B.1 shows the result of forming after deep drawing.
Figs. 6.2, 6A.2 and 6B.2 are sections of the disc along the section plane II-II of Fig. 1.
Fig. 6.2 shows the result of forming with the die (200) of the prior art.
Fig. 6A.2 shows the result of forming with the die (100) of the invention.
Fig. 6B.2 shows the result of forming after deep drawing.
Figs. 6.3, 6A.3 and 6B.3 are sections of the disc along the section plane III-III of Fig. 1.
Fig. 6.3 shows the result of forming with the die (200) of the prior art.
Fig. 6A.3 shows the result of forming with the die (100) of the invention.
Fig. 6B.3 shows the result of forming after deep drawing.
Figs. 6.4, 6A.4 and 6B.4 are sections of the disc along the section plane IV-IV of Fig. 1.
Fig. 6.4 shows the result of forming with the die (200) of the prior art.
Fig. 6A.4 shows the result of forming with the die (100) of the invention.
Fig. 6B.4 shows the result of forming after deep drawing.
Compared to forming with only one punch, it can be seen that with the die (100) of the invention, the material is distributed in a better way to favor the deep drawing that is made with the subsequent operation.
The computerized calculation shows that in the area (A) of Fig.1-2, with the stretching made with the die (100) of the invention, after the deep drawing operation, the thickness of the material increases by 12% compared to the thickness of the material that would be measured in the same area if the deep drawing operation was preceded by a stretching operation made with the die (200) with almost hemispheric punch of the prior art.

Claims

Progressive die (100) that allows to localize and control the stretching of the sheet steel during forming of the brake plate, said progressive die (100) comprising:
- a central punch (2) that is fastened on a lower base of the die, in a way to be adjusted in height with shims; and

- peripheral punches (3) that are mounted on the lower base of the die, in a way to be individually adjusted in height with shims;
characterized in that it comprises
- lateral punches (5, 6, 7, 8) that are mounted on the central punch (2) in a way to be individually adjusted in height, with shims, regardless of the adjustment of the peripheral punches (3, 4).
The progressive die (100) of claim 1, wherein the peripheral punches (3, 4) are disposed in peripheral position above the central punch (2).
The progressive die (100) of claim 1 or 2, wherein the central punch (2) has a disc-like shape with a flat upper surface.
The progressive die (100) of claim 3, wherein the peripheral punches (3, 4) are two peripheral punches disposed in diametrally opposite positions with respect to the center of the central punch (2).
The progressive die (100) of claim 4, wherein the peripheral punches (3, 4) comprise a first peripheral punch (3) that is higher than a second peripheral punch (4).
The progressive die (100) of any one of the preceding claims, wherein the peripheral punches (3, 4) have a substantially semi-cylindrical shape.
The progressive die (100) of any one of the preceding claims, wherein the lateral punches (5, 6, 7, 8) are peripherally fixed on the central punch (2) and are disposed laterally with respect to the peripheral punches (3, 4).
The progressive die (100) of any one of the preceding claims, wherein the lateral punches (5, 6, 7, 8) have a hemispheric head.
The progressive die (100) of any one of the preceding claims, wherein the peripheral punches (5, 6, 7, 8) are four lateral punches disposed in diametrally opposite positions with respect to the center of the central punch (2) and spaced by 90°.
The progressive die (100) of claim 9, comprising a first pair of lateral punches (7, 8) that is higher than a second pair of lateral punches (5, 6).
The progressive die (100) of any one of the preceding claims, comprising a lower sheet presser (9) mounted in a way to move vertically on said lower base, the central punch (2) passing through said lower sheet presser (9).
The progressive die (100) of any one of the preceding claims, comprising:
- an upper base (101) intended to be fastened to a ram of a press,

- an upper sheet presser (10) fastened to the upper base (101) and having a central hole (10a) and

- an upper punch (11) fastened to said upper base, in correspondence of said central punch (2), said upper punch (11) being disposed in the central hole (10a) of the upper base in a way to generate an annular space (10b) intended to receive said peripheral punches (3, 4) and said lateral punches (5, 6, 7 8).
The progressive die (100) of claim 12, wherein the head of said upper punch (11) is flat.
The progressive die (100) of claim 12, comprising draw bead rods fastened to the upper base (101) of the die and acting on the sheet steel (L) in correspondence of slots (12) obtained in the lower sheet-presser device (9).
The progressive die (100) of any one of the preceding claims, comprising two central punches (2) to make two brake plates.