EP4667128A1

EP4667128A1 - Counterforce unit

Info

Publication number: EP4667128A1
Application number: EP25184331.4A
Authority: EP
Inventors: Paolo BALZARIN
Original assignee: Balzarin Srl
Current assignee: Balzarin Srl
Priority date: 2024-06-20
Filing date: 2025-06-20
Publication date: 2025-12-24

Abstract

A counterforce unit (1;100;200;300;400) for a press comprises a support frame (2;102;202), at least one counteracting element (3;103;203,203';303,303";403,403',403") connected to the support frame (2;102;202) and movable with respect to it along a first direction (4;104;204;304) between a rest position and a working position, at least one connecting rod mechanism (5;105;205) which connects the at least one counteracting element (3;103;203,203';303,303";403,403',403") to elastic members (6;106;206) which are configured to maintain or return the at least one counteracting element (3;103;203,203';303,303";403,403',403") to the rest position, wherein the at least one connecting rod mechanism (5;105;205) comprises at least one connecting rod (7;107;207) which is curved and is connected to the at least one counteracting element (3;103;203,203';303,303";403,403',403") and to the elastic members (6;106;206) through respective hinge connections, in such a way that, following a displacement of the at least one counteracting element (3;103;203,203';303,303";403,403',403") along the first direction (4;104;204;304), the at least one connecting rod (7;107;207) imposes on the elastic members (6;106;206) a displacement along a second direction (8;108) with a different amplitude.

Description

FIELD OF THE ART

The present invention relates to a counterforce unit, usable in a press, for example for deep drawing and/or blanking, to control the movement of a counteracting element, such as a blank holder.

STATE OF THE ART

In the following description, explicit reference will be made to a counterforce unit usable in a press, with the understanding that the same can also be employed in other machinery, for example a deep drawing and/or blanking press, or in a hydraulic press in general, where it is necessary to apply a predetermined resisting force capable of opposing the movement of a movable element.
With reference to a deep drawing process, it is performed by means of a press comprising a movable crosshead approaching or distancing itself relative to a fixed base.
The press further includes a die for cold forming a metal sheet, operationally connected to the movable crosshead and the fixed base.
Generally, the die comprises a die matrix, a punch, and a blank holder, all operatively connected to a die holder.
The punch acts against a metal sheet, pushing it into a cavity defined in the matrix, thereby deforming it to obtain a hollow body.
The cavity of the matrix is shaped to correspond to the outer form of the hollow body to be made. The punch, on the other hand, is configured to engage the cavity of the matrix and has a shape corresponding to the internal cavity of the body to be produced.
The blank holder serves to press the sheet metal against the matrix and hold it in place during the deep drawing process. The blank holder prevents the formation of wrinkles and folds in the sheet during drawing.
The blank holder and the punch are configured to move relative to each other. In this regard, the blank holder defines a through-opening which the punch can engage to push the sheet into the cavity of the matrix.
Depending on the configuration of the press, the blank holder can be movably connected to an upper portion (crosshead) or lower portion (base) of the press to exert a retaining action on the sheet during die closure.
In particular, during the deep drawing process, the blank holder presses against the sheet and then, as a result of the clamping action between the crosshead and the base of the press, retreats inside the die.
The blank holder is connected to a portion of the die by means of elastic members, which are configured to exert a resisting force suitable for maintaining the blank holder in position and opposing its retraction inside the die.
According to one embodiment, the blank holder and the elastic members are connected to the movable crosshead (upper portion of the die) of a press.
In particular, the elastic members extend along a vertical direction of movement of the crosshead.
A drawback affecting traditional-type presses concerns the thinning of the sheet due to the excessive clamping force exerted by the blank holder during deep drawing.
An excessive clamping force prevents correct sliding of the sheet within the cavity of the matrix, causing tears and lacerations in the sheet itself near the cavity of the die.
This drawback, in particular, limits the possibility of performing deep drawing operations of significant depth.
The amount of pressure that the blank holder exerts on the sheet to keep it in position affects the ability of the sheet to slide and elongate.
The clamping force initially exerted by the blank holder on the sheet depends on the preload applied to the elastic members. Subsequently, following the closing of the press, the blank holder continues its stroke against the sheet, retreating inside the crosshead. The elastic members, being compressed by the blank holder, exert an increasing force against it, thus increasing the clamping force on the sheet.
An increase in the clamping force also corresponds to a reduction in the load-bearing section of the sheet, which the blank holder acts upon, resulting in the sheet material being unable to withstand further stress, thereby getting damaged.
Document US1519333A describes a press comprising a counteracting element connected through an articulated linkage to an elastic member. The articulated linkage includes a three-point hinged bracket, in which a portion of the bracket is connected to a connecting rod which, in turn, acts on the elastic member. The three-point hinged bracket allows for varying the motion transmitted from the blank holder to the connecting rod.
However, this solution also does not overcome the previously described drawbacks.
There is a need in the field to improve the performance of a traditional blank holder concerning the ability to control the force exerted during the deep drawing process, to prevent breakages or tears in the sheet.

OBJECTS OF THE INVENTION

The object of the present invention is to control in a predetermined, efficient, and repeatable manner the clamping force exerted by a counteracting element, such as a blank holder, on a sheet during the deep drawing process.
A further object of the present invention is to achieve a high degree of deep drawing depth without tears or rips along the sheet.
Another object of the present invention is to reduce work hardening of a drawn sheet and obtain a final product with constant and uniform thickness.
Additionally, another object of the invention is to optimize the spatial footprint of a counterforce unit compared to traditional solutions.
These and other objects are achieved by a counterforce unit according to claim 1. The dependent claims specify further advantages of the counterforce unit according to the invention.
The advantages offered by the counterforce unit according to the invention are evident.
Indeed, the counterforce unit according to the invention comprises a connecting rod mechanism that connects a counteracting element with elastic members and is configured to vary, in a non-linear manner, the retaining force exerted by the counteracting element when it is pressed, for example, against a sheet during a deep drawing process.
By non-linearly increasing the retaining force, tears or breakages of the sheet are avoided, and a substantially uniform thickness is ensured along various portions of the drawn piece.
The connecting rod mechanism comprises at least one connecting rod operatively connected to the counteracting element, which transmits its motion to elastic members that determine the counteraction exerted by the counteracting element on an object against which it is pressed, such as a sheet.
It is noted that the at least one connecting rod allows varying the direction along which the force from the counteracting element is transmitted to the elastic members. In particular, the at least one connecting rod deviates the pushing direction (drawing direction) along a transverse direction relative to the movement direction of the at least one counteracting element.
In this way, besides varying the displacement value of the elastic members relative to the movement of the counteracting element, it is possible to position the elastic members orthogonally to the drawing direction, thereby reducing the overall footprint of a press comprising such a counterforce unit.
In particular, the counterforce unit according to the invention comprises a support frame, at least one counteracting element operatively connected to the support frame so as to face outward from it, wherein the at least one counteracting element is movable relative to the support frame along a first direction between a rest position, in which it is free, and a working position, in which it is at least partially retracted inside the support frame, wherein the counterforce unit comprises at least one connecting rod mechanism that connects the at least one counteracting element to elastic members, which are in turn configured to maintain or return the at least one counteracting element to the rest position, the at least one connecting rod mechanism is inside the support frame and comprises at least one connecting rod operatively connected to the at least one counteracting element and the elastic members, interposed between them, through respective hinge connections, in such a way that following a displacement of the at least one counteracting element along the first direction, the at least one connecting rod imposes on the elastic members a movement along a second direction, transverse to the first direction, with a different displacement value.
Compared to traditional-type presses, a press comprising at least one such counterforce unit has a reduced footprint along the drawing direction.

DESCRIPTION OF THE FIGURES

The present invention will now be described, by way of illustration but not limitation, according to its preferred embodiments, with particular reference to the Figures of the attached drawings, in which:

Figure 1 shows a partial lateral sectional view of a press comprising a counterforce unit according to the invention, in which the counterforce unit is in a rest configuration;
Figure 2 shows the press of Figure 1 in an operational configuration, where the counterforce unit is in a working configuration;
Figure 3 is a partially exploded perspective view of some components of a counterforce unit according to the invention;
Figure 4 is a schematic lateral sectional view of a further press comprising a counterforce unit according to the invention;
Figure 5 is a schematic lateral sectional view of another press comprising two counterforce units according to the invention, where the press is closed and both counterforce units are in a working configuration;
Figure 6 is a schematic lateral sectional view of the press of Figure 5, in which the press is open and the counterforce units are in a rest configuration;
Figure 7 is a schematic lateral sectional view of another press comprising three counterforce units according to the invention, all in a working configuration;
Figure 8 is a schematic lateral sectional view of a further press comprising three counterforce units according to the invention, all in a working configuration.

DESCRIPTION OF THE INVENTION

With reference to a first embodiment shown in the attached Figures 1-3, a counterforce unit according to the invention is globally indicated by reference number 1.
In the following description, reference will be made to a counterforce unit 1 used in a press, with the understanding that it may also be employed in other types of presses, for example, a deep drawing and blanking press.
A press comprising such a counterforce unit 1 is also an object of the present invention.
The counterforce unit 1 according to the invention comprises a support frame 2 to which a counteracting element 3 is operatively and movably connected.
By way of example, the support frame 2 may correspond to a crosshead or a base of a press.
The counteracting element 3 is slidingly movable relative to the support frame 2 along a first direction 4, between a rest position, in which it is free and extended relative to the support frame 2, and a working position, in which it presses against a sheet metal or similar, not shown in the attached Figures, and is at least partially retracted into the support frame 2.
With reference, by way of example, to the use of a counterforce unit 1 in a press, the counteracting element 3 corresponds to a blank holder, and the first direction 4 is the drawing direction.
The counteracting element 3 is positioned along the support frame 2 so as to face outward from it, for example, to selectively press against a sheet metal.
The counterforce unit 1 comprises a connecting rod mechanism 5, which is itself enclosed within the support frame 2.
The connecting rod mechanism 5 is configured to operatively connect the counteracting element 3 to elastic members 6. These, in turn, are housed within the support frame 2 and are configured to oppose the advancement of the counteracting element 3 into the support frame 2 as well as to maintain or return the counteracting element 3 to the rest position.
It is understood that alternative embodiments of a counterforce unit 1, with respect to what is shown in Figures 1-3, may include more than one connecting rod mechanism 5 and possibly more than one counteracting element 3 housed within the support frame 2. In the following description, therefore, reference will be made to the counteracting element 3 and the connecting rod mechanism 5 by introducing them with the expression "at least one".
The at least one connecting rod mechanism 5 comprises at least one connecting rod 7 operatively connected to the at least one counteracting element 3 and to the elastic members 6, in an interposed position between them.
As will be better described later, the at least one connecting rod 7 is connected to the at least one counteracting element 3 and to the elastic members 6 through respective hinge connections.
The at least one connecting rod 7 transmits the motion originating from the at least one counteracting element 3 along the first direction 4, deviating it towards a second direction 8, which is oriented transversely relative to the first direction 4, against the elastic members 6.
In particular, the displacement experienced by the elastic members 6 along the second direction 8 has a different value compared to the displacement of the at least one counteracting element 3 along the first direction 4.
The elastic members 6 are deformable along a line of action parallel to the second direction 8.
Preferably, the second direction 8 is perpendicular or substantially perpendicular to the first direction 4.
With reference to the at least one connecting rod mechanism 5, it comprises at least one first slide 9 connected to the at least one counteracting element 3 and at least one second slide 10 connected to the elastic members 6.
The at least one first slide 9 slides within the support frame 2 along a first sliding direction, which is parallel to the first direction 4, while the at least one second slide 10 slides within the support frame 2 along a second sliding direction that is parallel to the second direction 8.
The at least one first slide 9 and the at least one second slide 10 are connected to each other through the at least one connecting rod 7.
In particular, the at least one connecting rod 7 has a first end 11 hinged to the at least one first slide 9 and a second end 12 hinged to the at least one second slide 10 (see Figure 3).
Specifically, the at least one connecting rod 7 is hinged directly to the at least one first slide 9 at the first end 11 and directly to the at least one second slide 10 at its second end 12. The expression "directly hinged" means that there are no intermediate connection elements interposed between the first end 11 and the at least one first slide 9, and between the second end 12 and the at least one second slide 10.
According to a preferred embodiment, the at least one connecting rod 7 is configured as curved and has a concavity facing towards the at least one counteracting element 3.
According to an alternative embodiment, not shown in the attached Figures, the at least one connecting rod 7 is configured straight.
As a result of a displacement of the at least one counteracting element 3 towards the inside of the support frame 2, the at least one first slide 9 is moved along the first direction 4, pushing against the at least one connecting rod 7. The latter, in turn, during the advancement of the at least one counteracting element 3 into the support frame 2, rotates and exerts a pushing action on the at least one second slide 10, moving it along the second direction 8 away from the at least one counteracting element 3.
In particular, the at least one connecting rod mechanism 5 allows to vary the amplitude of the displacement transmitted to the at least one second slide 10 and, consequently, to the elastic members 6, with respect to the displacement performed by the at least one first slide 9.
As is known, according to Hooke's law, a spring opposes a restoring force to its compression which is proportional to the displacement (in this case, shortening) to which the spring itself is subjected: $F_{e} = - k * x$ where "k" is the spring constant and "x" corresponds to the elongation, meaning the difference between the spring's free length and its deformed length.
In practice, the counterforce unit 1 of the invention makes it possible to vary the displacement to which the at least one second slide 10 is subjected, relative to the displacement of the at least one first slide 9, thereby varying the force opposed by the at least one counteracting element 3 during its movement towards the inside of the support frame 2.
With reference to the embodiment shown in the attached Figures, the configuration of the at least one connecting rod 7 imposes that a reduced initial displacement of the counteracting element 3, and thus of the first slide 9 connected to it, corresponds to a greater displacement of the second slides 10 along the second direction 8. Subsequently, as the first slide 9 moves inwardly with respect to the support frame 2, the displacement of the second slides 10 moving apart from each other becomes more limited.
This variation between the stroke of the first slide 9 and the at least one second slide 10 results in a change in the progression of the counteracting force exerted by the elastic members 6 against the at least one second slide 10 and, consequently, in the clamping force exerted by the counteracting element 3 against a sheet metal during the movement of the support frame 2 along the first direction 4.
The elastic members 6 are configured to exert an elastic thrust force against each of the second slides 10 along the second direction 8, pushing them towards each other.
The elastic members 6 extend along the second direction 8, along which they are elastically deformable. This positioning of the elastic members 6 helps minimize the encumbrance of the counterforce unit1 along the first direction 4.
The elastic members 6 act by pushing against the second slides 10 and oppose the advancement of the at least one first slide 9 and of the at least one counteracting element 3 connected to it, along the first direction 4, from the rest position towards the working position.
In this way, it is possible to overcome a drawback typical of traditional solutions, where elastic members are connected to a blank holder in such a way that they are subjected to the same displacement performed by the blank holder.
According to an embodiment of the invention, the elastic members 6 can be configured as a gas spring.
In this embodiment, the elastic members 6 comprise a fixed element 13, at least one movable element 14, which is movable relative to the fixed element 13, and at least one spring interposed between the fixed element 13 and the movable element 14, designed to oppose the advancement of the movable element 14 approaching the fixed element 13 (see Figure 3).
By way of example but not limited thereto, the at least one spring is a gas spring, preferably nitrogen-based. It is understood that alternative types of gas other than nitrogen may also be used.
Furthermore, as an alternative to using a gas spring, a helical spring or an elastomer (e.g., in the form of a bumper) or, more generally, an elastically behaving element may be employed.
With reference to the exploded view shown in the attached Figure 3, the fixed element 13 is configured to be connected to the support frame 2, while the movable element 14 is connected to the second slide 10.
The embodiment of the counterforce unit 1 shown in the attached Figures 1-3 comprises a connecting rod mechanism 5 operatively connected to a counteracting element 3, wherein the connecting rod mechanism 5 comprises two connecting rods 7, opposed to each other, both connected to a first slide 9 and each connected to a respective second slide 10, which in turn is connected to respective elastic members 6.
In other words, the connecting rod mechanism 5 shown in Figures 1-3 comprises a first slide 9, two connecting rods 7, two second slides 10, and two elastic members 6, wherein each elastic member is connected to a respective second slide 12.
The second slides 10 are positioned on opposite sides of the first slide 9, arranged symmetrically to one another.
By way of example but not limited thereto, the first slide 9 is configured as a quadrangular prism or substantially as a quadrangular prism, although alternative embodiments are possible wherein the first slide 9 may have a different configuration.
The first slide 9 is connected to the counteracting element 3 through column elements 15 or similar members extending through a wall or transverse portion 16 of the support frame 2 (see Figures 1 and 2), optionally provided in the support frame 2.
With reference to the exemplary shown in the attached Figure 3, the connecting rod mechanism 5 includes four column elements 15.
It is understood that alternative embodiments of the invention, not illustrated, may include a different number of column elements 15 for the mutual connection between the first slide 9 and the counteracting element 3, within a solution wherein the first slide 9 and the counteracting element 3 are mutually constrained in such a way as to prevent relative rotation.
The wall or transverse portion 16 of the support frame 2 may serve as a support to which a punch 17 is connected.
The punch 17 is fixed relative to the support frame 2. The at least one counteracting element 3, instead, is movable relative to the support frame 2, in order to perform the function of a blank holder.
In this regard, the support frame 2 features a seat 18 that extends internally along the first direction 4, in which the at least one counteracting element 3 is at least partially housed and movable.
Furthermore, the support frame 2 defines at least one internal cavity 19 in which the at least one connecting rod mechanism 5 is housed (see, for example, Figure 1).
The seat 18 and the internal cavity 19 are separated by the wall or transverse portion 16, if present.
The at least one internal cavity 19 defines a first portion 20, engaged by the at least one first slide 9, and a second portion 21, engaged by the at least one second slide 10 (see Figure 2).
The first portion 20 extends along the first direction 4, while the second portion 21 extends along the second direction 8. Both portions are in mutual communication to allow the movement of the at least one connecting rod 7 along the internal cavity 19.
The at least one internal cavity 19 is also configured to house the elastic members 6 within it.
In practice, the support frame 2 functions as the structure to which the components of the counterforce unit1 are connected.
As mentioned, the counterforce unit1 may comprise at least one punch 17 rigidly connected to the support frame 2.
The at least one punch 17 extends outwardly from the support frame 2, starting from the wall or transverse portion 16, along the first direction 4.
With reference to the embodiment illustrated in the attached Figures 1 and 2, the punch 17 extends through the at least one counteracting element 3. The punch 17 has an enlarged portion 22 which serves as a stop for a corresponding stop portion 23 protruding from the counteracting element 3.
The contact between the enlarged portion 22 of the punch 17 and the stop portion 23 of the at least one counteracting element 3 defines an end-of-stroke stop for the movement of the at least one counteracting element 3 relative to the punch 17, from the working position towards the rest position. In other words, the enlarged portion 22 acts as an abutment to stop the advancement of the at least one counteracting element 3 moving away from the support frame 2.
The exploded view in Figure 3 shows, by way of example but not limitation, a possible embodiment of certain components of the counterforce unit1, with reference to the counteracting element 3 and the connecting rod mechanism 5.
In particular, each connecting rod 7 has a width dimension, intended as the dimension extending along a direction perpendicular to both the first direction 4 and the second direction 8, which is comparable or substantially similar to that of the respective second slider 10 to which it is hinged.
A connecting rod 7 configured in this manner exhibits high resistance to the mechanical stresses encountered during use, with particular reference to bending stresses.
The first end 11 and the second end 12 of each connecting rod among the connecting rods 7 are rounded and engage a rounded seat defined, respectively, in the first slider 9 and in the second slider 10.
With reference to the embodiment illustrated in the attached Figures 1-3, where the connecting rod mechanism 5 comprises two connecting rods 7, the first slider 9 defines two first rounded seats 24, spaced apart and parallel to each other.
In particular, the first rounded seats 24 extend along an internal portion of the first slider 9 opposite to the portion connected to the at least one counteracting element 3.
Each connecting rod 7, therefore, rotates relative to the first slider 9 around a first axis of rotation 25.
Similarly to what has been described regarding the first end 11 of each connecting rod 7, the second end 12 of each connecting rod 7 is rounded and rotatably housed within a corresponding second rounded seat 26 defined in each of the second sliders 10.
Each second rounded seat 26 is defined along a respective one of the second sliders 10 on the side opposite to that where the elastic members 6 are connected to the same second sliders 10.
Each connecting rod 7, therefore, is rotatable relative to the second slider 10 around a second axis of rotation 27.
The first axis of rotation 25 and the second axis of rotation 27 are parallel to each other.
The counterforce unit 1 comprises a pair of side plates 28 for hinging each of the connecting rods 7 to the first slider 9.
In particular, the side plates 28 are hinged to the first end 11 of each connecting rod 7 and removably secured to opposite sides of the first slider 9, for example using screws or similar fastening means.
For instance, each connecting rod 7 defines a through-opening 29 at its first end 11, which can be engaged by a screw, a pin, or a similar element (not illustrated in the attached Figures), which in turn engages a corresponding through-hole 30 defined in each of the side plates 28.
The side plates 28 are connected to the first slider 9 in such a way that they do not obstruct its movement within the support frame 2.
To this end, the first slider 9 defines lateral seats in which a respective one of the side plates 28 is housed, such that they do not protrude beyond the footprint of the first slider 9 itself.
These lateral seats promote the positioning and connection of the side plates 28 to the sides of the first slider 9, in addition to the connection between the side plates 28 and the connecting rods 7.
Each of the connecting rods 7 is hinged to a respective one of the second sliders 10 in a manner analogous to that previously described regarding the connection between the connecting rods 7 and the first slider 9.
The counterforce unit 1 includes connecting plates 31 for connecting each of the connecting rods 7 to a respective one of the second sliders 10.
The connecting plates 31 are hinged to the second end 12 of a respective connecting rod 7.
For this purpose, each connecting rod 7 defines an additional through-opening 32 at its second end 12, which can be engaged by a screw, a pin, or a similar element (not illustrated in the attached Figures), which in turn engages a corresponding through-hole 33 defined in each of the connecting plates 31.
In other words, each of the connecting rods 7 is hinged to a respective one of the second sliders 10 by the retaining action exerted by a pair of connecting plates 31 and their corresponding hinge pin.
The connecting plates 31 are removably connected to opposite sides of each of the second sliders 10, for example using screws or similar fastening means.
Similarly to the connection between the side plates 28 and the first slider 9, each of the second sliders 10 defines shaped seats 34 designed to house the connecting plates 31 and retain them within the footprint of each of the second sliders 10.
The shaped seats 34 are defined on opposite sides of each of the second sliders 10, where the expression "opposite sides" refers to the sides parallel to the second direction 8.
The shaped seats 34 facilitate the positioning of the connecting plates 31 along the second sliders 10.
Preferably, the shaped seats 34 have a depth at least equal to the thickness of the connecting plates 31, so that the latter remain within the footprint of each of the second sliders 10 to which they are connected and do not interfere with their sliding within the support frame 2.
According to one aspect of the invention, the counterforce unit 1 includes internal channels for lubricating the at least one connecting rod mechanism 5, in order to prevent excessive stress and wear as well as potential seizing.
In this regard, in one embodiment, each connecting rod 7 defines at least one internal through-channel 35 that fluidly connects the first end 11 to the second end 12 (see, for example, Figure 2).
Each of the second sliders 10, in turn, defines at least one lubrication channel 36 that fluidly connects a top portion of each second slider 10 to the inside of the second rounded seat 26 in which the second end 12 is housed (see, for example, Figure 3, where the lubrication channels 36 are visible at the top portion of the second sliders 10).
In turn, the top portion of each of the second sliders 10 is fluidly connected to a lubricant reservoir or to elements designed to selectively supply lubricant into the at least one lubrication channel 36, which are not shown in detail in the attached Figures.
The support frame 2 defines an access opening 37 to allow access to the at least one connecting rod mechanism 5.
With reference to the embodiment illustrated in the attached Figures 1 and 2, the access opening 37 is defined along the support frame 2 on the side opposite to that of the counteracting element 3.
It is understood that alternative embodiments are possible, in which the support frame 2 defines an access opening 37 in a different position or a greater number of access openings, to promote access to the at least one connecting rod mechanism 5.
The counterforce unit 1 comprises at least one cover element 38 for the selective closure of the access opening 37, which is removably connected to the support frame 2.
Additionally, the at least one cover element 38 may function as an abutment for guiding a respective one of the second sliders 10 along the second direction 8.
By way of example but not limitation, in the case where the counterforce unit 1 includes a connecting rod mechanism 5 comprising two second sliders 10, the support frame 2 may define two access openings 37, each corresponding to a respective one of the second sliders 10, and two cover elements 38 (see, for example, Figure 1).
As previously mentioned, a press comprising a counterforce unit 1 also forms an object of the invention.
In the attached Figures 1 and 2, a stamping press 50 comprising a die, in turn comprising a crossbeam 51, a base 52, and a counterforce unit 1 housed within the crossbeam 51, is illustrated in an extremely schematic manner.
The crossbeam 51 corresponds to the previously described support frame 2.
The crossbeam 51 is movable in a reciprocating motion, approaching or moving away from the base 52 along the first direction 4, while the base 52 remains stationary.
In Figures 1 and 2, the mechanisms for moving the support frame 2 relative to the base 52 have been intentionally omitted, as they do not form part of the present invention.
Furthermore, all components responsible for the operation of a stamping press are not illustrated in detail, as they are considered well-known to those skilled in the art and are not a specific object of the invention.
Below is a brief description of the operation of the counterforce unit 1 according to the invention, with reference to its use in a stamping press.
With the mold in the open configuration (see Figure 1), the counteracting element 3 is kept in an extracted position by the thrust exerted by the elastic members 6.
The latter, in fact, push the second slides 10 towards each other, causing the rotation of the connecting rods 7 which, in turn, act in thrust against the first slide 9.
During the closing of the mold and the subsequent deep drawing phase of a sheet metal, not shown, the counteracting element 3 is brought into abutment against a sheet metal and pressed against it due to the advancement of the support frame 2 (crosshead 51) along the first direction 4, approaching the base 52.
The approach of the crosshead 51 towards the base 52 is necessary to advance the punch 17 with respect to a sheet metal to be drawn, positioned on the base 52.
As mentioned, the counteracting element 3 is connected to the support frame 2 by means of the connecting rod mechanism 5 and, for this reason, is movable relative to the punch 17 along the first direction 4.
During the lowering of the support frame 2 along the first direction 4, following an initial contact between the counteracting element 3 and the sheet metal on the base 52, the counteracting element 3 retracts inside the support frame 2, counteracting the thrust exerted by the elastic members 6.
When the counteracting element 3 is initially placed in abutment against a sheet metal, that is, during the initial movement of the counteracting element 3 from the rest position to the working position, the connecting rod mechanism 5 imposes on the second slides 10 a displacement along the second direction 8 greater than that performed by the first slide 9 along the first direction 4. Therefore, the retaining force that the counteracting element 3 is able to apply is high.
Subsequently, during the advancement of the deep drawing phase, up to the final stroke phase of the first slide 9 towards the inside of the support frame 2, the stroke performed by the second slides 10 along the second direction 8 is less than that performed by the first slide 9 along the first direction 4.
As a result, the elastic force opposed by the elastic members 6 during the advancement of the support frame 2 towards the base 52 is reduced, because the displacement of the second slides 10, which causes the compression of the elastic members 6, is less than the displacement of the support frame 2.
Furthermore, the use of a connecting rod mechanism 5 comprising two connecting rods 7 opposed to each other makes it possible to reduce the lateral stresses exerted by the first slide 9 along the internal walls of the support frame 2, resulting in greater mechanical efficiency and energy savings.
Moreover, such a solution is balanced and prevents jamming of the first slide 9 or the second slides 10 inside the support frame 2.
The counterforce unit 1 according to the invention allows to vary the clamping force exerted by the counteracting element 3 against the sheet metal during its deep drawing, in particular by reducing the clamping force in the final phase of the stroke of the support frame 2. During this phase, in fact, the surface of the sheet metal to be retained is reduced, and in traditional solutions, this limits the achievable drawing depth.
It is understood that a further embodiment of the counterforce unit 1 is possible, not shown in the accompanying Figures, in which the connecting rod mechanism 5 comprises a pair of first slides 9, each operatively connected to a respective second slide 10 via a respective connecting rod 7. Both first slides 9 are connected to a common counteracting element 3 in a manner analogous to that previously described.
Figure 4 shows a further embodiment of a press according to the invention, indicated overall with 150.
Hereinafter, to indicate components corresponding to those described for the previous embodiment, the same reference numbers increased by one hundred units will be used.
Compared to the previous embodiment, the press 150 comprises a counterforce unit 100 positioned in the base 152, instead of in the crosshead 151.
The configuration of the counterforce unit 100 is substantially the same as that described for the previous embodiment, to which reference is made.
The counterforce unit 100, in fact, comprises a support frame 102, which corresponds to the base 152, a counteracting element 103 movable along a first direction 104, and a connecting rod mechanism 105 which operatively connects the counteracting element 103 to elastic members 106 which, in turn, are oriented along a second direction 108.
The connecting rod mechanism 105 comprises a first slide 109 connected to the counteracting element 103, a pair of connecting rods 107, opposed to each other, each hinged at a respective first end 111 to a first slide 109 and at a second end 112 to a respective second slide 110. The first slide 109 slidably engages the support frame 102 (and therefore the base 152) along a first direction 104. Each second slide 110, on the other hand, slidably engages the support frame 102 along a second direction 108, transverse to the first direction 104, and is connected to elastic members 106.
The counterforce unit 100 comprises a punch 117 which extends from the support frame 102, passing through the counteracting element 103.
The punch 117 is fixed to the support frame 102.
The press 150 further comprises an additional punch 160, connected to the crosshead 151 and fixed relative thereto.
The additional punch 160 is configured to abut against the counteracting element 103 and push it along the first direction 104 towards the base 152, following a mutual approach between the base 152 itself and the crosshead 151.
The press 150 further comprises a movable stop 161, movably connected to the crosshead 151 along the first direction 104, so as to be selectively movable between an extracted position and a partially retracted position within the crosshead 151 itself.
The press 150 comprises at least one spring or elastic element 162 interposed between the movable stop 161 and the crosshead 151, to maintain the movable stop 161 in the extracted position relative to the crosshead 151 itself.
The movable stop 161 acts as a stop for the punch 117 and defines a movable bottom for the forming cavity during deep drawing.
The additional punch 160, instead, laterally delimits the forming cavity.
Compared to what has been described regarding the previous embodiment of the counterforce unit, it is noted that the counterforce unit 100 is configured in such a way that when the counteracting element 103 reaches the end-of-stroke position inside the support frame 102 (working position), the position of the first end 111 of each of the connecting rods 107 is at a lower point compared to the position of a respective second end 112 of each of the connecting rods 107.
In other words, with the counteracting element 103 in the end-of-stroke position inside the support frame 102, the point where each connecting rod 107 is hinged to the first slide 109 is positioned at a lower height along the first direction 104, compared to the point where each connecting rod 107 is hinged to a respective second slide 110.
The expression "at a lower height" is intended to indicate that the first end 111 of each connecting rod 107 is closer to a bottom portion of the base 152 compared to the distance between the second end 112 of each connecting rod 107 and said bottom portion of the base 152 (support frame 102).
The bottom portion of the base 152 is the portion opposite to a top portion of the base 152 itself, from which the counteracting element 103 and the punch 117 extend.
It is noted that when the counteracting element 103 reaches the end-of-stroke position inside the base 152, the connecting rod mechanism 105 reaches a locking position, in which the connecting rod 107 remains in position despite the thrust action exerted by the elastic members 106 near the second end 112.
This locking position, in fact, is determined by the position reached by the first end 111 of the connecting rod 107 relative to the second end 112.
The locking position of the connecting rod 107 and, consequently, of the connecting rod mechanism 105, remains even when the crosshead 151 is raised and moved away relative to the base 152, mutually distancing the additional punch 160 from the counteracting element 103.
The counteracting element 103, despite no longer being held in the retracted position by the additional punch 160, remains in the partially retracted position in the base 152 due to the locking in position of the connecting rod mechanism 105 as previously described.
The counterforce unit 100 comprises thrust members, collectively indicated with 180, which are operatively connected to the connecting rod mechanism 105 or to the counteracting element 103 and are configured to act in thrust to unlock the connecting rod mechanism 105 and allow the extraction of the counteracting element 103 again.
In the attached Figure 4, the thrust members 180 are depicted in an extremely schematic manner to promote the intelligibility of the structure of the counterforce unit 100 and to show a possible positioning and operation thereof.
With reference to the embodiment shown by way of example in the attached Figure 4, the counterforce unit 100 comprises two thrust members 180, each configured to exert a thrusting action against a respective connecting rod 107.
According to an embodiment, the thrust members 180 are configured as a piston comprising a movable element adapted to selectively engage against a connecting rod 107 and to push it upwards, causing its rotation in such a way as to bring the first end 111 to a position higher than that of the second end 112 along the first direction 104.
As soon as the first end 111 of the connecting rod 107 exceeds the position (elevation) of the second end 112, the thrusting action exerted by the elastic members 106 determines the subsequent movement of the connecting rod 107, causing the extraction of the counteracting element 103.
It is understood that alternative embodiments of the thrust members 180 are possible, not illustrated, configured to selectively command the unlocking of the connecting rod mechanism 105. For example, it is possible to provide the use of pneumatic members positioned at the base 152 and configured to emit jets of pressurized air against the counteracting element 103 to cause a first extraction movement thereof relative to the base 152, thereby moving the first end 111 of the connecting rod 103 to a position higher than the second end 112 of said connecting rod 103 itself, unlocking the connecting rod mechanism 105.
A counterforce unit 100 thus configured, comprising thrust members 180, allows achieving a positional locking of the connecting rod mechanism 105 when the counteracting element 103 reaches the end-of-stroke position and is at least partially retracted inside the support frame 102.
Through the thrust members 180, it is also possible to unlock the connecting rod mechanism 105, thereby allowing its movement once again and, consequently, the extraction of the counteracting element 103 from the working position towards the rest position.
More specifically, at the end of the deep-drawing process, to release the drawn part from the press 150, the crossbeam 151 and the base 152 are moved away from each other, thereby moving the further punch 160 away from the counteracting element 103, with which it is no longer in abutment.
Due to the locking position reached by the connecting rods 107, a positional locking of the counteracting element 103 occurs and, consequently, a delay in the extraction of the drawn sheet metal.
The extraction of the counteracting element 103 is commanded by the thrust members 180 and delayed with respect to the opening of the mold.
This delay makes it possible to prevent the drawn part from undergoing an axial load during extraction, since the drawn part, during the opening of the mold, remains in proximity to the lower portion of the same, that is, in the base 152.
The counterforce unit 100, in addition to achieving the same advantages described in relation to the previous embodiment, allows to selectively obtain a delayed extraction of a drawn part through a mechanical solution, easy to implement and less complex compared to traditional solutions that involve hydraulic movement of the individual press components.
Figures 5 and 6 illustrate a further embodiment of a press comprising two abutment groups according to the invention.
The press is generally indicated by 250, while the abutment groups are indicated by 200 and 200'.
Hereinafter, to describe components corresponding to those disclosed in the previous embodiments, the same reference numbers will be used, increased by one hundred units compared to the press 150 and counterforce unit 100, by two hundred units compared to the press 50 and counterforce unit 1.
The press 250 comprises a mold which in turn comprises a crossbeam 251 and a base 252, reciprocally movable in approaching or distancing along the first direction 204.
The press 250 comprises an abutment group 200 positioned inside the crossbeam 251 and a further abutment group 200' positioned inside the base 252.
The crossbeam 251 and the base 252 perform the same function as the support frame 2, 102 described in relation to the previous embodiments, to which reference is made.
The counterforce unit 200 substantially corresponds to the counterforce unit 1.
Indeed, the counterforce unit 200 comprises a connecting rod mechanism 205 which in turn comprises a first slider 209 connected to two second sliders 210 via two connecting rods 207. Each of the second sliders 210 is then operatively connected to respective elastic members 206.
The at least one first slider 209 may be configured as an annular or frame-shaped element sliding along a vertical portion of the crossbeam 251, to which the two connecting rods 207 are connected, opposed to each other.
The first slider 209 is connected to a counteracting element 203 movable along the first direction 204 relative to a punch 217 which, in turn, is constrained to the movable crossbeam 251, so as to protrude from it towards the base 252.
The counterforce unit 200 allows achieving the same purposes described in relation to the abutment group 1, to which reference is made.
The further counterforce unit 200', on the other hand, corresponds to the counterforce unit 100 previously described, differing in the mutual positioning between the respective counteracting element 203' and the respective punch 217'.
In the further counterforce unit 200', in fact, the respective counteracting element 203' is placed internally with respect to the respective punch 217' which externally surrounds the respective counteracting element 203'.
Similarly to what has been described in relation to the counterforce unit 100, the further counterforce unit 200' is configured to determine a controlled or controllable delay in the extraction of the respective counteracting element 203' following the opening of the mold, that is, following the reciprocal distancing between the crossbeam 251 and the base 252.
Evidently, the reciprocal distancing between the crossbeam 251 and the base 252 determines the distancing and separation between the punch 217 connected to the crossbeam 251 and the respective counteracting element 203' connected to the base 252, as well as the distancing and separation between the counteracting element 203 connected to the crossbeam 251 and the respective punch 217' connected to the base 252.
Through the thrust members 280, it is possible to control the delay in the extraction of the respective counteracting element 203' following the opening of the mold, determining a delayed extraction of the drawn part, preventing a load from being applied to the same during the opening of the mold and avoiding that the stamped part remains accidentally attached to the counteracting element 203 connected to the crossbeam 251.
By way of example but not limitation, in the attached Figure 5, the press 250 is shown with the mold closed, in a configuration in which both the counteracting element 203 operatively connected to the crossbeam 251 and the respective counteracting element 203' operatively connected to the base 252 are in a working position, that is, partially inside the crossbeam 251 and the base 252, respectively.
In the attached Figure 6, on the other hand, the press 250 is shown with the mold open, that is, with the crossbeam 251 and the base 252 reciprocally distanced.
With the mold in the open configuration, both the counteracting element 203 and the respective counteracting element 203' are in a rest position, promoting the extraction of the drawn part.
Figure 7 shows a further embodiment of a press according to the invention, generally indicated with the number 350.
To describe components corresponding to those of the previous embodiments, the same reference numerals will be used, increased by one hundred units compared to press 250.
Unlike the previous embodiments, the press 350 is configured to perform both the drawing and shearing of a sheet metal.
The press 350 comprises a crosshead 351 and a base 352, reciprocally movable in alternating approach and separation along a first direction 304.
The crosshead 351 comprises a first counterforce unit 300 and a second counterforce unit 300', operatively connected, respectively, to a counteracting element 303 and to a punch 317.
The press 350 differs from the previous embodiments in that both the counteracting element 303 and the punch 317 are movable with respect to each other and with respect to the crosshead 351 along the first direction 304.
Moreover, the counteracting element 303 has a protruding portion 370 configured to cooperate with a respective seat defined in an abutment 371 fixed to the base 352, and to shear a sheet metal with which it comes into contact following the mutual approach between the crosshead 351 and the base 352.
The press 350 comprises a third counterforce unit 300" inside the base 352, operatively connected to a respective counteracting element 303".
The respective counteracting element 303" is designed to oppose the punch 317, which in turn is connected to the second abutment group 300' included in the crosshead 351.
The press 350 also comprises an inner punch 372, fixedly connected to the crosshead, which extends internally with respect to the punch 317.
The inner punch 372 extends beyond the punch 317 and is configured to perforate a central portion of a sheet metal drawn by the punch 317.
According to an alternative embodiment not shown in the attached Figures, the press 350 is devoid of the inner punch 372.
According to yet another alternative embodiment not shown in the attached Figures, the press 350 is devoid of the inner punch 372, and the punch 317 has a protruding portion, which extends externally from the punch 317 along the first direction 304, wherein said protruding portion performs the shearing function of the inner punch 372.
The press 350 allows achieving the same advantages previously described in relation to the press 50, with regard to the ability to adjust the clamping force applied by the counteracting element 303 and by the punch 317, as well as the ability to determine a delay in the extraction of the respective counteracting element 303" following the opening of the mold, thanks to the presence of thrust members 380.
Figure 8 illustrates a further embodiment of a press according to the invention, generally indicated with the number 450.
The press 450 differs from the previous embodiment of the press 350, with regard to the presence of a crossbeam 451 provided with a first counterforce unit 400 and a second counterforce unit 400', in which the first counterforce unit 400 comprises a first counteracting element 403 movable with respect to the crossbeam 451, the second counterforce unit 400' comprises a second counteracting element 403' movable with respect to the crossbeam 451 and positioned externally with respect to the first counteracting element 403, and the crossbeam 451 comprises a punch 417 that extends passing centrally through the first counteracting element 403 and the second counteracting element 403'. In particular, the punch 417 is positioned internally to the first counteracting element 403.
Moreover, the press 450 comprises a first abutment 471 connected to the base 452, and a second abutment 471', also connected to the base so as to surround the first abutment 471.
Both the first abutment 471 and the second abutment 471' extend outwardly from the base 452, towards the crossbeam 451.
The first abutment 471 is configured to interact with the counteracting element 403 and push it towards the inside of the crossbeam 451 following an approach between the crossbeam 451 itself and the base 452.
Similarly, the second abutment 471' is configured to interact with the second counteracting element 403' in the same manner previously described in relation to the first abutment 471 and the first counteracting element 403, to which reference is made.
The first abutment 471 and the second abutment 471' may have different heights between them (with reference to Figure 8, the first abutment 471 has a height greater than that of the second abutment 471') depending on specific usage needs, for example to allow the shearing of the metal sheet or the execution of specific deformations of the metal sheet.
The press 450 comprises a third counteracting group 400" inside the base 452.
The third counteracting group 400" substantially corresponds to the counteracting group 300' described in relation to the previous embodiment of the press 350, to which reference is made.
The third counteracting group 400" comprises pushing members 480 operatively connected to a third counteracting element 403".
These pushing members 480, similarly to what has been described in relation to the previous embodiments, allow to selectively control the extraction of the third counteracting element 403".
With reference to what has been previously described, it is evident that the counteracting group 1, 100, 200, 300, 300', 300", 400, 400', 400" according to the invention is capable of achieving the intended objectives with regard to the ability to vary the resisting force opposed by elastic members in a non-linear manner with respect to the deformation of said elastic members.
The use of at least one connecting rod mechanism 3, 103, 203, 303, 403 allows to define the law by which the resisting force opposed by the elastic members 6, 106, 206, 306, 406 varies, according to a mechanical solution that has a structure of practical use and easy maintenance compared to hydraulic solutions or those characterized by complex structures necessary to regulate the clamping force of an counteracting element.
Moreover, the counterforce unit 1, 100, 200, 300, 400 according to the invention allows to selectively control a delay in the movement of an counteracting element operatively connected to the elastic members with respect to when the counteracting element itself is no longer retained in the working position.
Such a delay is advantageous to promote an optimal extraction of a deep-drawn piece from a press, without the piece itself being subjected to loads that could deform or damage it.
The counteracting group 1, 100, 200, 300, 300', 300", 400, 400', 400" according to the invention is of practical use and flexible implementation in a press, whose configuration can be easily adapted, in the design phase, depending on specific usage requirements.
In the foregoing, some embodiments have been described and variants of the present invention have been suggested, but it is to be understood that those skilled in the art may make modifications and changes without thereby departing from the related scope of protection, as defined by the attached claims.

Claims

Counterforce unit (1;100;200;300,300',300";400,400',400") for a press, wherein said counterforce unit (1;100;200;300,300',300";400,400',400") comprises:
a support frame (2;102;202),

at least one counteracting element (3;103;203,203';303,303";403,403',403") operatively connected to said support frame (2;102;202) so as to face outward from said support frame (2;102;202), wherein said at least one counteracting element (3;103;203,203';303,303";403,403',403") is movable relative to said support frame (2;102;202) along a first direction (4;104;204) between a rest position, in which it is free, and a working position, in which it is at least partially retracted within said support frame (2;102;202),

said counterforce unit (1;100;200;300,300',300";400,400',400") being characterized in that it comprises at least one connecting rod mechanism (5;105;205) that connects said at least one counteracting element (3;103;203,203';303,303";403,403',403") to elastic members (6;106;206) which, in turn, are configured to maintain or return said at least one counteracting element (3;103;203,203';303,303";403,403',403") in said rest position, wherein said at least one connecting rod mechanism (5;105;205) is within said support frame (2;102;202) and comprises at least one connecting rod (7;107;207), wherein said at least one connecting rod (7;107;207) is curved, presents a concavity facing towards said at least one counteracting element (3;103;203,203';303,303";403,403',403") and is operatively connected to said at least one counteracting element (3;103;203,203';303,303";403,403',403") and to said elastic members (6;106;206), in a position interposed therebetween, through respective hinge connections, such that following a movement of said at least one counteracting element (3;103;203,203';303,303";403,403',403") along said first direction (4;104;204), said at least one connecting rod (7;107;207) imposes on said elastic members (6;106;206) a movement along a second direction (8;108), transverse to said first direction (4;104;204), with a different amplitude.
Counterforce unit (1;100;200;300,300',300";400,400',400") according to claim 1, wherein said at least one connecting rod mechanism (5;105;205) comprises at least a first slider (9;109;209) connected to said at least one counteracting element (3;103;203,203';303,303";403,403',403") and hinged to a first end (11) of said at least one connecting rod (7;107;207), and at least a second slider (10;110;210) connected to said elastic members (6;106;206) and hinged to a second end (12) of said at least one connecting rod (7;107;207).
Counterforce unit (1;100;200;300,300',300";400,400',400") according to claim 2, wherein said at least one connecting rod (7;107;207) is hinged directly to said at least one first slider (9;109;209) and directly to said at least one second slider (10;110;210), wherein said direct connection provides for the absence of intermediate connecting elements interposed between said first end (11) and said at least one first slider (9;109;209) and between said second end (12) and said at least one second slider (10;110;210).
Counterforce unit (1;100;200;300,300',300";400,400',400") according to claim 2 or 3, wherein said at least one first slider (9;109;209) is slidably movable in said support frame (2;102;202) along said first direction (4;104;204), and wherein said at least one second slider (10;110;210) is slidably movable in said support frame (2;102;202) along said second direction (8;108).
Counterforce unit (1;100;200;300,300',300";400,400',400") according to any one of the preceding claims, wherein said elastic members (6;106;206) comprise a fixed element (13), at least one movable element (14) movable with respect to said fixed element (13), and at least one elastic element interposed between said fixed element (13) and said movable element (14) suitable for elastically opposing the advancement of said at least one movable element (14) towards said fixed element (13).
Counterforce unit (1;100;200;300,300',300";400,400',400") according to any one of claims 1 to 5, wherein said elastic members (6;106;206) are configured as a gas spring or a spring.
Counterforce unit (1;100;200;300,300',300";400,400',400") according to claim 2, wherein a displacement of said at least one first slider (9;109;209) along said first direction (4;104;204) determines a displacement of different amplitude of said at least one second slider (10;110;210) along said second direction (4;104;204).
Counterforce unit (1;100;200;300,300',300";400,400',400") according to any one of the preceding claims, comprising at least one punch (17) fixedly connected to said support frame (2;102;202), wherein said punch (17) extends from said support frame (2;102;202) along said first direction (4;104;204) and develops internally or externally with respect to said counteracting element (3;103;203,203';303,303";403,403',403").
Counterforce unit (1;100;200;300,300',300";400,400',400") according to claim 2, wherein said at least one connecting rod mechanism (5;105;205) comprises two connecting rods (7;107;207) arranged opposite each other, each connecting rod among said connecting rods (7;107;207) being hinged to a same first slider (9;109;209) at respective first ends (10), and each connecting rod among said connecting rods (7;107;207) being hinged to a respective second slider (10;110;210) at a respective second end (12).
Counterforce unit (1;100;200;300,300',300";400,400',400") according to any one of the preceding claims, wherein said support frame (2;102;202) delimits at least one access opening (37) for access to said at least one connecting rod mechanism (5;105;205), and at least one cover element (38) removably connected to said support frame (2;102;202) for the selective closure of said at least one access opening (37).
Counterforce unit (100;200';300";400") according to any one of the preceding claims, comprising pushing members (180;280;380;480) operatively connected to said connecting rod mechanism (105;205) to generate a push along said first direction (104;204;304) and to command the extraction of said counteracting element (203';303";403") operatively connected to said connecting rod mechanism (105;205).
Counterforce unit (1;100;200;300,300',300";400,400',400") according to claim 2, wherein said first ends (11) and second ends (12) of each connecting rod among said connecting rods (7;107;207) are rounded and engage respective rounded seats delimited, respectively, in said first slider (9) and in said second slider (10).
Press (50;150;250;350;450) for deep-drawing and/or blanking of sheet metal comprising a die which in turn comprises a crossbeam (51;151;251;351;451) and a base (52;152;252;352;452) movable towards and away from each other along a first direction (4;104;204;304;404), characterized in that it comprises at least one counterforce unit (1;100;200;300;400) according to any one of claims 1-12 operatively connected to at least one between said crossbeam (51;151;251;351;451) and said base (52;152;252;352;452).