EP3052257B1 - Device for forming a workpiece made of sheet metal - Google Patents

Description

The invention relates to the field of machining workpieces of metal, for example of steel or other metals. It relates to a device for forming a workpiece, in particular a sheet metal blank.

The machining of a workpiece may include any operations such as cutting, pressing, drawing, forming.

The workpieces are often cup-shaped components. Pot-shaped components include a bottom, a pot wall and a drawing edge. Such a component is often used as a spring cup to accommodate the ends of a coil spring. They find particular use in the automotive industry in many ways.

Problematic in the production of such spring pots are high-strength steels. Although these have the advantage that they have extremely high tensile strengths, and therefore steels smaller thickness can be used, and thus also lower weight. However, such steels are relatively brittle and tend to crack. This occurs especially when forming on the highly stressed transition areas. The tearing occurs in particular in the transition region between the bottom of the pot and the pot wall and between the pot wall and the drawing edge.

DE 102 54 103 B3 describes a thermoforming tool for deep drawing of molded parts. This comprises an annular clamping device for clamping a circuit board. The clamping device encloses a space in which a bottom former and a frame former can be moved in the pulling direction. These two can have different speeds. As a result, a higher dimensional accuracy is to be achieved.

DE 27 27 174 C2 describes a method and apparatus for deep-drawing an aluminum container. Two parts are movable against each other, namely a punch and a die. The speed of the upwardly moving punch can be greater than the speed of the moving down die. As a result, a large thermoforming ratio is to be achieved.

DE 10 2007 050 581 A1 describes a method for influencing the thickness of sheet metal during deep drawing of hollow bodies. It is about a multiple buckling (deforming) and back buckling (reforming) of a workpiece. During the reforming phase, the relative speed between the punch and die is increased from the speed during the deforming phase. The punch performs a movement against the phase of deforming during the reforming phase. The speeds of the punch during these phases are unequal.

WO 2006/000187 A1 describes a forming press for regulating a sheet holding force between the tool lower part and the tool top. In this case, electric drives are used, comprising a linear or rotary direct drive for applying a pressure to the blank holder.

DE 10 2012 005 635 B3 describes a system and method for forming a sheet metal blank. However, the system shown operates without pneumatic or hydraulic cushions or pressure bolts.

DE 10 2007 033 943 A1 describes a press for forming workpieces. The aim is to compensate for unwanted deformations of the tool in the press.

In all known devices there is a risk of tearing the workpiece during the forming process. Such tearing occurs especially in the edge regions of the workpiece and at larger drawing depths.

In the prior art, one or more die cushions are provided which move during the drawing process in displacement mode as fast as the press ram. Also during the operation, the plunger cushion is displaced with ram speed.

The invention has for its object to make a device, a system, a method and a workpiece such that high-strength steels are deformable without tearing occurs in the edge regions, and that a greater draw depth than previously achieved.

This object is achieved by means of a device according to claim 1.

• Der Ziehprozess selbst wird gesteuert, nicht etwas anderes.
• Die im Patentanspruch 1 genannten Antriebe wirken auf das betreffende Werkzeugteil unmittelbar, das heißt ohne Zwischenschalten von funktionalen Teilen. Teile, die allein dem Übertragen der Kräfte dienen, zum Beispiel die Bolzen, können dabei verwendet werden. Jedoch ist auch eine mittelbare Einwirkung möglich.

The invention has numerous advantages:

• The drawing process itself is controlled, not something else.
• The drives mentioned in claim 1 act directly on the relevant tool part, that is, without interposition of functional parts. Parts that serve only to transmit the forces, such as the bolts, can be used. However, an indirect action is possible.

It has been shown that by interposing one or more servo units, the abovementioned bolts are not impacted abruptly, but more gently than before. The loading process and thus the action of the bolt on the workpiece takes place within a period of time that lasts only a few milliseconds longer than in known devices. This minimizes the risk of cracking and results in workpieces of high quality and strength.

According to a further aspect of the invention, the device is designed such that the inner die and the outer die can be moved at different speeds in the drawing direction during the forming process. For this purpose, the inner die and the outer die - optionally together with the blank holder - each associated with a special drive, which moves these two during the forming process at different speeds in the drawing direction - hereinafter called "Variotempo unit". In a press with a variotempo unit, the servo unit moves at a faster speed than the plunger of the press in the pulling direction, thus in the direction of the plunger.

Several variotempo units can be provided, distributed over the effective area of the press. This can be important in large components, for example, in fenders for automobiles. In such components, the load on the workpiece - during forming or in operation - be particularly high, so it is recommended to provide a Variotempo unit at the corresponding points of the workpiece during forming.

A variotempo unit can be arranged in the press table or in the press ram or in these two.

It can be arranged on or in a floating plate, this is a plate that distributes the pressing force on a surface.

Variotempo units can also be retrofitted to existing press systems.

Figur 1

zeigt schematisch eine Presse mit integrierter Servo-Einheit. Dabei ist die Servo-Einheit dem Pressentisch zugeordnet.

Figur 2

zeigt schematisch eine Presse mit integrierter Servo-Einheit. Dabei ist die Servo-Einheit dem Stößel der Presse zugeordnet.

Figur 3

zeigt in schematischer Darstellung eine Servo-Einheit.

Figur 4

zeigt in schematischer Darstellung und im Aufriss eine Ziehvorrichtung mit bereits vorgeformtem Werkstück in erster Umformphase des Umformhubes; hierbei ist die Servo-Einheit weggelassen.

Figur 5

zeigt das Werkstück kurz vor Ende der zweiten Umformphase.

Figur 6

zeigt das Werkstück am Ende des Umformvorganges.

Figuren 7 bis 12

veranschaulichen den Umformvorgang in sechs verschiedenen Umformstationen.

The invention is explained in more detail with reference to the drawing. It details the following:

FIG. 1

schematically shows a press with integrated servo unit. The servo unit is assigned to the press table.

FIG. 2

schematically shows a press with integrated servo unit. The servo unit is assigned to the plunger of the press.

FIG. 3

shows a schematic representation of a servo unit.

FIG. 4

shows a schematic representation and in elevation a drawing device with already preformed workpiece in the first forming phase of Umformhubes; Here, the servo unit is omitted.

FIG. 5

shows the workpiece shortly before the end of the second forming phase.

FIG. 6

shows the workpiece at the end of the forming process.

FIGS. 7 to 12

illustrate the forming process in six different forming stations.

The press includes u. a. a press table 1, 2 columns and a plunger 3. Between the press table 1 and the plunger 3, a die, not shown, and an unrepresented punch are arranged, the tool shells or a lower tool part wear.

The servo unit comprises two servo pillows 4 in the form of hydraulic chambers, further comprising a servo pump 5 and a servomotor 6. In the press table. 1 bolts 7 are arranged. These are acted upon by the respective servo pad 4, so that they go up and down vertically.

Each servo pad 4 may be associated with a different number of pins 7. So each servo pad can be assigned a single bolt. But it is also possible to assign two or more bolts a cushion.

The operating medium of the servo unit is in this case a liquid. It could also be a pneumatic system.

In FIG. 2 the servo unit is assigned to the plunger 3. Only pump 5 is indicated.

In the two embodiments according to the Figures 1 and 2 the servo unit is structurally integrated in the press table or in the ram.

The servo unit is in FIG. 3 shown in more detail, again schematically. It is integrated in a stamp 8. Instead of the punch, the servo unit could also be integrated into a die.

It can be seen three servo units 4. Each servo unit 4 acts on two bolts 7. Each servo chamber 4 is acted upon by a servo pump 5, which is driven by a servo motor. 6

In this case, each servo unit 4 can be assigned its own servo motor pump set. But it can also be applied to a plurality of servo units 4 by a single servo motor pump set. In this case, a control valve (not shown here) is connected in front of each servo unit 4.

In general, the control of the press or of the forming process will be linked to the control of the servo unit or units.

In the FIG. 4 The drawing device shown comprises a punch 8 and a sheet holder 9. The punch 8 is of slightly conical shape. It has a bottom mold surface 8.1 and a wall mold surface 8.2. The in the FIGS. 1 to 3 illustrated thought, including servo unit and bolt, is in FIG. 4 not shown. However, it should be understood that the thought of the pulling device according to FIG. 4 is realized.

Stamp 8 is surrounded by the sheet holder 9. Sheet metal holder 9 has a support surface 9.1. Sheet holder 9 is annular.

Above the punch 8 is an inner die 10. It is at least approximately cylindrical. It is surrounded by an outer die 11. This is ring-shaped.

The inner die 10 in turn has a bottom mold surface 10.1. The outer die 11 is annular. It has a wall molding surface 11.1, further a clamping surface 11.2 for clamping the drawing edge 12.3 of a workpiece 12 on the support surface 9.1 of the sheet holder 9. The workpiece 12 has emerged from a circular disk-shaped board. It comprises a bottom 12.1, a wall 12.2 and the said drawing edge 12.3.

It is initially open, that is, the clamping surface 11.2 of the outer die 11 is located approximately at the height of the bottom mold surface 10.1 of the inner die 10. At about the same height or higher is the support surface 9.1 of the sheet holder 9, sufficient for insertion of the workpiece 12th

In this phase, a workpiece 12 is inserted into the pulling device and clamped between the support surface 9.1 and the clamping surface 11.2. Now begins the actual work phase of the pulling device. In this case, the inner die 10 and the outer die 11 move together with the preformed workpiece 12, as well as with the sheet holder 9 down. The said parts (inner die 10, outer die 11, plate holder 9 and preformed workpiece) have the same speed.

This changes according to the invention in a subsequent phase. In this case, the inner die 10 overtakes the outer die 11.

In a further, subsequent phase, on the other hand, the outer die 11 overtakes the inner die 10.

Note that this may be the other way around.

In the FIG. 4 The drawing apparatus shown is only one station of a series of drawing stations. These are not shown here. In practice, they are connected in series in a workshop.

It only needs a single drawing station designed according to the invention, that is provided with drives that can give the inner die 10 on the one hand, the outer die 11 and the sheet holder 9 on the other hand, different speeds during the drawing process.

How the workpiece looks after leaving the various drawing stations can be seen from the FIGS. 7 to 12 ,

• der Umformvorgang verläuft optimal und führt zu qualitativ hochwertigen Werkstücken
• die Erfindung ist besonders erfolgreich anwendbar bei großflächigen Werkstücken wie Kotflügel. Diese können an verschiedenen Stellen unterschiedlichen Umformvorgängen unterworfen werden, mit entsprechend unterschiedlichen Materialbeanspruchungen. Werden mehrere Variotempo-Einheiten eingesetzt, über die gesamte Werkstückfläche verteilt, so kann dem Rechnung getragen werden, indem das Verhältnis der Geschwindigkeiten von Innenmatrize und Außenmatrize beim Umformvorgang entsprechend bemessen wird.
• eine Gesamtregelung ist relativ einfach durchführbar, wobei das Regeln der Bewegungen der Bolzen einerseits und der gesamten Presse andererseits leicht aufeinander abgestimmt werden können
• das System lässt sich ohne weiteres in existierende Anlagen verwirklichen.

The advantages of the invention can be summarized as follows:

• The forming process is optimal and leads to high-quality workpieces
• The invention is particularly successfully applicable to large workpieces such as fenders. These can be subjected to different forming processes at different points, with correspondingly different material stresses. If several Variotempo units are used, distributed over the entire workpiece surface, so can be taken into account by the ratio of the speeds of inner die and outer die during the forming process is sized accordingly.
• an overall control is relatively easy to carry out, the rules of the movements of the bolts on the one hand and the entire press on the other hand can be easily matched
• The system can be easily implemented in existing plants.

LIST OF REFERENCE NUMBERS

1

press table

2

pillar

3

tappet

4

Servo unit in the form of hydraulic chambers

5

power steering pump

6

servomotor

7

bolt

8th

stamp

8.1

Floor molding surface

8.2

Wall molding surface

9

blankholder

9.1

support surface

10

inner matrix

10.1

Floor molding surface

11

outer die

11.1

Wall molding surface

11.2

chucking

12

workpiece

12.1

Workpiece ground

12.2

Workpiece wall

12.3

drawing border

Claims (6)

1. A device for forming a sheet-metal blank, comprising the following features:

   1.1. a press frame having a pressing table (1), vertical columns (2), a cross head and a ram (3);

   1.2. a tool top part, comprising an outer and an inner dye (11, 10) as well as a tool base part, comprising a punch (8) and a sheet-metal holder (9);

   1.3. at least one drive, which is assigned to at least one of the two tool parts;

   characterized by the following features:

   1.4. the drive comprises:

   - a plurality of bolts (7), which are arranged vertically slideable in the pressing direction in the press table (1) and/or in the ram (3) and which act upon the respective tool part;

   - a plurality of pneumatic or hydraulic servo cushions, acting upon individual or groups of bolts (7) in the pressing direction;

   - a servo pump (5) loading the servo cushions, which are driven by a servomotor (6);

   1.5 the punch (8) comprises a base forming face (8.1) and a wall forming face (8.2);

   1.6 a annular sheet-metal holder (9) surrounding the punch (8) and having a support face (9.1);

   1.7 an inner die (10) having a base forming face (10.1);

   1.8 an outer die (11) having a wall forming face (11.1) and a clamping face (11.2) for gripping the peripheral surface of the emerging workpiece (12);

   1.9 one drive is in each case assigned to the inner die (10) on the one hand, and to the outer die (11) as well as to the sheet metal holder (9) on the other hand, which drive displaces the said two at different speeds in the drawing direction.
2. The device according to claim 1, characterized in that one single servomotor - pump set is assigned to one hydraulic servo cushion.
3. The device according to claim 1 or 2, characterized in that one single servomotor - pump set is assigned to one or multiple hydraulic servo cushions, and in that a control valve for controlling the pressure and/or the amount of the medium supplied to the servo cushion is assigned to the servomotor - pump set.
4. The device according to any one of the claims 1 to 3, characterized in that an overall control is provided, which adjusts the control of the press and the control of the servo unit to one other.
5. The device according to claim 4, characterized by a multitude of inner dies, which act upon the workpiece at different locations.
6. A method for operating a device according to any one of the claims 1 to 5, characterized by one or more of the following method steps:

   I. during a starting period, both dies (10, 11) move in the same direction at equal speed;

   II. during an intermediate phase, both dies (10,11), in turn, move in the same direction, but the inner die (10) at a higher speed than the outer one (11);

   III. in a final phase, the inner die (10) stands still while the outer die (11) moves on at constant speed.

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