GB2124954A

GB2124954A - Apparatus for making drawn holes in workpieces on a piercing press

Info

Publication number: GB2124954A
Application number: GB08308879A
Authority: GB
Inventors: Walter Bredow
Original assignee: C Behrens AG
Current assignee: C Behrens AG
Priority date: 1982-07-31
Filing date: 1983-03-30
Publication date: 1984-02-29
Also published as: DE3228734C1; GB8308879D0; GB2124954B; CH659407A5

Abstract

An apparatus for forming flanges around holes in workpieces (13) on a piercing press having a numerically- controlled co-ordinate table comprises a die (12) and a lower tool incorporating a punch (10). The punch is movable by an actuating bolt (24) forced upwards against spring pressure. The punch (10) is also guided within a workpiece support (8). The workpiece support (8) is movable in the lower tool between stops, and the underside (31) of the workpiece support (8) bears against a piston (2) guided for sliding movement in a cylindrical chamber (1a). This piston (2) is spring-loaded (7) and its movement is limited by a stop (4). Within the annular piston (2), a driving piston (3) carrying the actuating bolt (24) for the punch (10) is guided. The cylindrical chamber (5) is filled with an incompressible medium. <IMAGE>

Description

SPECIFICATION Application for making drawn holes in workpieces on a piercing press This invention relates to apparatus for making drawn holes in flat or sheet-like workpieces on a piercing press equipped with a numerically-controlled coordinate table, the apparatus comprising a matrix die which can be lowered towards the workpiece top surface and a lower tool carrying an associated punch which is movable in the lower tool, by means of an actuating bolt forced upwards from below, from a rest position lying below the workpiece surface to a working position projecting above this workpiece surface, the punch also being guided in a workpiece support.

Such an apparatus enables one to manufacture drawn holes on a piercing press with a numericallycontrolled co-ordinate table and can therefore find a use in the conventional tool magazines, such as turret plates or the like, so that, without hindrance, besides the normal perforations and piercings, one can also produce drawn holes, particularly drawn holes for the reception of threads, on the same machine.

In one known apparatus of the aforementioned type, as described in our published British patent application 2086786A, the workpiece support is mounted fixedly on a lower tool carrier. The punch is driven from below by means of a separate actuating bolt, and this actuating bolt for its part is moved by a separate lifting device which is arranged beneath the actuating bolt on the piercing press. Besides the disadvantage of the structural cost and spatial requirements of a separate lifting device and the necessary transmission elements there is also the disadvantage that an additional pressure-generating unit is necessary for the lifting device, and this makes the apparatus as a whole more expensive.

Additionally, there arises a disadvantage in respect of the mode of operation. It is necessary to maintain the matrix die, and consequentially the associated upper tool, lowered on to the workpiece top surface against the stationary workpiece support at the lower dead point, before one can thereafter actuate the punch by means of the separate lifting device.

This considerably lengthens the operating cycle of the known apparatus.

It is an object of the present invention to provide an apparatus of the type first mentioned above by means of which the manufacture of drawn holes can be accomplished with the same speed as the normal perforating processes on the piercing press, thus avoiding additional working time due to the actuation of the punch of the apparatus. For this purpose the apparatus, and particularly the means for actuating the punch, should be simplified and the space requirements should be reduced as compared with the aforesaid known apparatus.

This is achieved according to the invention by apparatus for making drawn holes in flat or sheetlike workpieces on a piercing press having a numerically-controlled co-ordinate table, the apparatus comprising a matrix die which can be lowered towards the workpiece top surface and a lower tool carrying an associated punch which is movable within the lower tool from a rest position in which it lies below the workpiece surface to a working position in which it projects above this workpiece surface, this movement being effected by an actuat ing bolt forced upwards from below, and the punch being guided within a workpiece support, in which the workpiece support is guided for movement perpendicular to the workpiece surface in both directions and with its movement limited by stops in the lower tool, the underside of the workpiece support bears against an annular piston which is guided for coaxial sliding movement in a cylindrical chamber of the lower tool, the lower annular surface of the annular piston is spring-loaded and is limited by a stop in its movement in the direction towards the workpiece support, the annular piston is provided with a downwardly open cylindrical bore in which is arranged a coaxial driving piston carrying the actuating bolt for the punch, the punch is spring-biassed in the return direction, the driving piston is guided for sliding movement and is limited in its movement in the direction towards the workpiece support by stop means, and the cylindrical chamber remaining below the annular piston and the driving piston is filled with an incompressible medium.

By means of this apparatus it is possible to produce the necessary driving force for the punch movement just by the lowering movement of the matrix die with the help of the upper tool, so that a separately controlled and separately driven lifting device can be completely dispensed with. When a working stroke is initiated for the matrix die by the upper tool, then the workpiece support is moved downwards until it contacts its lower stop. In doing this it forces the annular piston downwards against the force of the springs. The lower annular surface of the annular piston displaces the enclosed incompressible medium which for its part pushes against the lower piston surface of the driving piston and moves this with the actuating bolt from below against the punch which consequently is forced up through the workpiece and forms the drawn hole by cooperation with the matrix die.When the matrix die with the upper tool is then lifted away from the workpiece surface, then the annular piston returns with the workpiece support to its starting position because of its spring loading. By means of the incompressible medium the driving piston with the actuating bolt is thus withdrawn, while the punch is returned to the rest position by means of a return spring. The whole apparatus is composed of simple, substantially coaxially arranged components and is compact and space-saving. Moreover, it is possible to convert the apparatus to produce drawn holes of different diameters just by exchanging a few components, namely the workpiece support, the punch and the matrix die.It has also been shown that by appropriate dimensioning of the effective piston surfaces the downward movement of the workpiece support necessary for the punch movement can be kept extraordinarily small, with the result that the course of the work on the piercing press, and especially on a turret piercing press, is in no way impaired.

The path or stroke of the workpiece support can be kept particularly small if the area of the lower annular surface of the annular piston is dimensioned to be greater than that of the lower end face of the driving piston.

It has been shown to be particularly reliable and effective if the lower annular surface of the annular piston is subjected to the force of cup springs located at the bottom of the cylindrical chamber. In order to achieve a trouble-free removal of air from the cylindrical chamber containing the incompressible medium it is desirable for the annular lower surface of the annular piston and for the bottom of the cylindrical chamber each to be formed as frusto-conical surfaces tapering in opposite directions with respect to the longitudinal axis of the apparatus.A particularly advantageous structural form is achieved in a further embodiment of the invention if the lower tool, with the help of a cup-shaped component forming the cylindrical chamber and receiving the movable workpiece support, is held in a matrix die support collar of the piercing press, and the workpiece support is movable between annular stop surfaces formed at the end of the cylindrical chamber on the one hand and at the lower end face of an annular screw fitting holding the workpiece support in the matrix die support collar on the other hand, with the diameter of the cylindrical chamber and consequently of the annular piston being smaller than that of the workpiece support.

The apparatus according to the invention is particularly suitable for turret piercing presses equipped with a numerically-controlled co-ordinate table, in which the advantage of the very short length of time necessary for producing the drawn holes is of particular importance, since the drawn holes can consequently be produced in the same working rhythm and with the same speed as the usual perforations or punctures.

Further features, advantages and details of the invention will appear from the following description of a preferred embodiment of the invention which is given with reference to the drawing. In the drawing there is shown only that part of the apparatus which is necessary for understanding the invention. The matrix die of the upper tool which is shown by itself is held in the upper tool in a suitable tool carrier. The remainder of the apparatus, including the matrix die support collar which holds it, is mounted on a lower tool carrier, particularly on a tool magazine, such as a turret plate of a turret piercing press.In the drawing: Figure 7 is a longitudinal sectional view through an apparatus according to the invention, in its rest position; Figure 2 is a view of part of the apparatus of Figure 1 showing the workpiece support, the matrix die and the punch in their working positions.

On an upper tool carrier, which is not shown, there is mounted a matrix die 12 which can be lowered from above towards a flat or sheet-like workpiece 13 which is to be processed.

Below the workpiece 13 a matrix die support collar 14 is held in a lower tool carrier of the piercing press, this lower tool carrier also not being shown. A cup-shaped component 1 is set into this matrix die support collar 14 and has a flange resting upon an annular surface 16 of the matrix die support collar 14. In the lower portion of the component 1 there is formed a cylindrical chamber la in which an annular piston 2 is guided for sliding movement. The annular piston 2 is limited in its movement in the direction towards the workpiece 13 by a retaining ring 4. At its lower annular surface 20 the annular piston 2 is spring-loaded upwards in the direction towards the workpiece 13, by cup springs 7, these cup springs being seated at their lower end on the bottom 19 of the cylindrical chamber 1 a.The annular piston 2, in its rest position, is therefore always urged into contact with the retaining ring 4 by the cup springs 7.

In the cylindrical bore 18 of the annular piston 2, which is open in the downward direction, a driving piston 3 is guided for coaxial sliding movement. This driving piston 3 carries an actuating bolt 24 at its upper end. The motion of the driving piston 3 in the direction towards the workpiece 13 is limited by a stop, in that the piston has an annular surface 25 which can come into contact with an annular upper end surface 26 which closes the top of the cylindrical bore 18 of the annular piston 2.

The generally cylindrical chamber 5 remaining below the annular piston 2 and the driving piston 3 is filled with an incompressible medium, for example with oil or a permanently plastic mass. In order to be able to exclude air from this filling, the upper and the lower limit surfaces of the cylindrical chamber 5, namely the annular surface 20 at the bottom of the annular piston 2, and the cylindrical chamber base 19, are formed as frusto-conical surfaces inclined in respectively opposite directions with respect to the longitudinal axis of the cup-shaped component 1 and consequently the apparatus. In order to remove air there is provided, in the centre of the cylindrical chamber base 19, a vent hole 22 which is closed by a closure screw 6.In order that no closed spaces which cannot easily be vented can be formed between the cup springs 7, reamed passages 21 are included at the periphery 23 of the cylindrical chamber base 19, there where the cup springs rest against the peripheral surface.

A workpiece support 8 is guided for movement perpendicular to the workpiece surface in the upper portion of the cup-shaped component 1. The workpiece support 8 is limited in both directions of movement by stops. For this, the workpiece support 8 includes an annular collar 28. The workpiece support 8 is held in the cup-shaped component 1 by an annular screw fitting 9 whose lower end face forms an annular abutment which constitutes the upper limiting stop for the workpiece support 8.

Downwardly the movement of the workpiece support 8 is limited by the contact of its lower end face with an annular surface 1 bat the top of the cylindrical chamber 1 a. The workpiece support 8 is guided by the internal bore 27 of the annular screw fitting 9.

A punch 10 is arranged coaxially within the workpiece support 8 and is guided for longitudinal movement therein. The punch 10, in its rest position, is urged against the actuating bolt 24 by a coil spring 11 which is seated at its lower end on a collar 29 at the bottom of the punch. Consequently, the punch 10 is spring-loaded in the return direction. In its rest position the punch is additionally supported by contact against the upper end face of the annular piston 2.

The mode of operation of the apparatus is as follows. When a working stroke is initiated at the upper tool and thus at the matrix die 12, the matrix die 12 moves downwards until its lower surface 30 contacts the workpiece 13. Since the working stroke is not yet terminated at this point, the workpiece 13 is pressed by the matrix die 12 against the workpiece support 8 and the annular underside 31 of the workpiece support is pressed down against the top of the annular piston 2. The lower annular surface 20 of the annular piston 2 exerts a pressure on the medium which is within the cylindrical chamber 5, in opposition to the effect of the cup springs 7. Since the medium is incompressible and its volume is therefore constant, the medium is forced up in the direction of the arrow 33 and thus forces the driving piston 3 upwards.The driving piston 3 for its part, and by way of the actuating bolt 24, forces the punch 10 upwards from its rest position shown in Figure 1 to its working position projecting above the workpiece surface. By this means the material of the workpiece is drawn up around a small pre-existing hole 34 into the receiving socket 15 of the matrix die, this position being shown in Figure 2. When the workpiece cycle is terminated, then the matrix die 12 with the upper tool moves upwards again and releases the workpiece 13. This causes the incompressible medium in the cylindrical chamber 5 to be relieved of pressure and the cup springs 7 then urge the annular piston 2 back into the starting position as shown in Figure 1.The coil spring 11 draws the punch 10 back from the now drawn hole 40 in the workpiece 13 into its rest position shown in Figure 1, in which the punch is positioned below the workpiece surface.

The lower annular surface 20 of the annular piston 2 is larger than the lower end face of the driving piston 3 and indeed is substantially larger. Both surfaces face towards the incompressible medium which is enclosed within the cylindrical chamber 5.

This sizing means that even a small downward movement of the annular piston 2 displaces the medium so much that the driving piston 3 for its part is lifted through a substantially greater distance. If one denotes the annular surface area 20 of the annular piston 2 facing the medium by F, the lower end face area of the driving piston 3 facing the medium by f, the downward movement of the workpiece support 8 and thus of the annular piston 2 by h1, and the upward movement of the driving piston 3 in the direction 33 and thus of the punch 10 by h2, then one has the relationship: F : f = h2: h. If the external diameter of the annular piston 2 is for example 30mm and that of the driving piston is 10mm, then this results in surface areas as follows: F = 706.6mm2 and f = 78.52.If the downward movement of the workpiece support 8 is taken to be 1 mm, then this results, according to the preceding equation, in an upward movement of the driving piston 3 and thus of the punch h2 = 9mm. In practice one generally needs a smaller stroke of the punch 10 than 9mm, so that the stroke of the workpiece support 8 can be set to an even smaller value than 1 mm. This relatively small stroke of less than 1 mm in no way inpairs for example the course of the working cycle on a turret piercing press. The aforesaid surface area and stroke relationships are chosen in accordance with the particular application and in accordance with the machine to be used. As the description and drawing show, the apparatus can be adapted very simply for the production of the drawn holes of different diameters. For this purpose it is only necessary to exchange the workpiece support 8, the punch 10 and the matrix die 12. All the other components of the apparatus can remain in the machine and be used again.

Claims

1. Apparatus for making drawn holes in flat or sheet-like workpieces on a piercing press having a numerically-controlled co-ordinate table, the apparatus comprising a matrix die which can be lowered towards the workpiece top surface and a lower tool carrying an associated punch which is movable within the lower tool from a rest position in which it lies below the workpiece surface to a working position in which it projects above this workpiece surface, this movement being effected by an actuating bolt forced upwards from below, and the punch being guided within a workpiece support, in which the workpiece support is guided for movement perpendicular to the workpiece surface in both directions and with its movement limited by stops in the lower tool, the underside of the workpiece support bears against an annular piston which is guided or coaxial sliding movement in a cylindrical chamber of the lower tool, the lower annular surface of the annular piston is spring-loaded and is limited by a stop in its movement in the direction towards the workpiece support, the annular piston is provided with a downwardly open cylindrical bore in which is arranged a coaxial driving piston carrying the actuating bolt for the punch, the punch is spring-biassed in the return direction, the driving piston is guided for sliding movement and is limited in its movement in the direction towards the workpiece support by stop means, and the cylindrical chamber remaining below the annular piston and the driving piston is filled with an incompressible medium.

2. Apparatus according to claim 1, in which the lower annular surface of the annular piston has a larger surface area than the lower end face of the driving piston.

3. Apparatus according to claim 1 or 2, in which the lower annular surface of the annular piston is subjected to the pressure of cup springs positioned at the base of the cylindrical chamber.

4. Apparatus according to any preceding claim, in which the lower annular surface of the annular piston on the one hand and the base of the cylindrical chamber on the other hand are each formed as frusto-conical surfaces inclined in respectively opposite directions with respect to the longitudinal axis of the apparatus.

5. Apparatus according to any preceding claim, in which the lower tool is held in a matrix die support collar of the piercing press by means of a cupshaped element which defines the cylindrical chamber and which receives the movable workpiece support, the workpiece support is movable between annular stop surfaces formed on the one hand by one end of the cylindrical chamber and on the other hand by the lower face of an annular screw fitting which holdes the workpiece support in the matrix die support collar, and the diameter of the cylindrical chamber and thus of the annular piston is smaller than that of the workpiece support.

6. Apparatus for making drawn holes in flat or sheet-like workpieces as claimed in claim 1, substantially as hereinbefore described with reference to the accompanying drawing.