The invention concerns a pressure distributor for metal forming, particularly suited to be used in dies for forming sheet metal and especially for deep-drawing according to the preamble of claim 1.

Forming processes, as is known, are used to make objects by deforming a material using pieces of equipment called "dies".

As regards in particular sheet metal forming, a die, in its basic configuration, comprises a punch that forces the metal sheet inside a matrix so as to obtain a concave configuration of the metal sheet reproducing the outline of the matrix in plan view.

The forming operation in this case is called "drawing", and if the depth of the item that is being formed exceeds its larger dimension in plan view, the drawing process is called "deep drawing".

During the drawing process, sheet metal is deformed as a consequence of the stresses to which it is subjected and which can be summed up as follows:

• radial tensile stress produced by the action exerted by the punch that moves into the matrix in order to form the object;
• circumferential compressive stress produced by the progressive adaptation of the external perimeter of the metal sheet to the shape of the matrix.

These stresses are exerted simultaneously with variable intensity in the different areas of the metal sheet which, at the level of its edge, tends to corrugate and thicken, and thus to become thicker in the areas with limited sliding movements.

In order to avoid these drawbacks, the edges of the metal sheet are maintained adherent to the matrix by means of a sheet pressing device that, applying pressure at right angles to the edge of the metal sheet and distributing said pressure on the surface of the edge itself, prevents the metal sheet from corrugating and controls its sliding movements.

From a practical point of view, the efforts to which the metal sheet is subjected during the forming process generate compressive stresses at the level of corners and curves and compressive stresses generated by the sheet pressing device, which tend to press the metal sheet against the matrix in such a way as to avoid the formation of wrinkles and thicker portions.

However, it is known to the experts in the art that, notwithstanding the presence of the sheet pressing device, in some areas of the die, between the matrix and the sheet pressing device, the metal sheet becomes thicker and this causes the localized deformation of the sheet pressing device.

As a consequence of the above, the sheet pressing device is raised in the areas surrounding the deformed area, where the metal sheet, being subjected to a reduced holding action, slides more.

All this means that, notwithstanding the presence of the sheet pressing device, it is not possible to achieve total control of the sliding movements of the metal sheet and this causes the appearance of distortions, cracks, streaks and wrinkles in the formed object, thus negatively affecting the quality of the product.

In the worst cases, the formed object may even break.

In the attempt to eliminate the drawbacks described above, mechanical and/or hydraulic thrusting units are used which apply to the dies compensation forces that tend to deform them in the areas where the sheet pressing device tends to be raised, in such a way as to maintain the metal sheet as uniformly pressed as possible at the level of the edge and to control its sliding movements during the forming process.

The use of said units, however, poses some recognized drawbacks.

A first drawback lies in that the above mentioned mechanical-hydraulic thrusting units involve purchase and installation costs that must be added to the already high costs borne by the user for the purchase and installation of the presses.

Another drawback is represented by the further additional cost to be borne for the operation of said mechanical-hydraulic thrusting units.

A further drawback is represented by the fact that said mechanical-hydraulic thrusting units are characterized by a recognized lack of flexibility of use, as the same thrusting unit can be used only for dies suited to produce formed objects having geometrically similar shapes.

This means that the user needs to replace the thrusting units if there are significant differences in the shape and outline of the formed objects to be produced.

Another drawback is represented by the fact that said mechanical-hydraulic thrusting units are difficult to adjust, because of the required adjusting time and also because the adjustments must be carried out by expert personnel and adapted to each single die.

Another, yet not the least important drawback lies in that often the use of said mechanical-hydraulic thrusting units does not allow the desired results to be achieved, meaning uniform control of the sliding movements of the metal sheet during the forming process.

The patent document EP 0 808 224 B1 is also known, which describes a drawing die provided with pressing devices that are fixed to the punch and made of an elastomeric material.

The pressure devices are arranged at the periphery of the punch, are spaced from one another and each one of them is provided with a braking pad suited to come into contact with the edge of the metal sheet to be drawn during the drawing process.

During the drawing process, the elastic thrust exerted by the pressing device against the edge of the metal sheet controls the deformation to which the metal sheet is subjected when the punch forces it inside the matrix.

The patent document FR 884 771 A, on which the preamble of claim 1 is based, is also known, which describes a drawing process and a device suited to implement said process, wherein the edge of the metal sheet to be drawn is pressed against the surface of the matrix of the die by a sheet pressing device.

The latter is made elastic thanks to the presence of a yielding element that in the case described in the patent document is constituted by a rubber block included between the sheet pressing device and a holding plate which are both fixed by means of screws to a movable element of the press that is coaxial and external to the punch.

Even the devices described in the above mentioned patent documents pose the drawback that they do not ensure optimal control of the sliding movements of the metal sheet during the forming process.

In particular, none of the devices described above improves the absorption of the variable forces that develop in the areas where the thickness of the metal sheet is increased during the forming process.

The present invention intends to overcome all of the drawbacks described above.

In particular, it is one object of the invention to provide a pressure distributor that makes it possible to absorb the variable forces that during the forming process are exerted on the sheet pressing device at the level of the areas where the thickness of the metal sheet increases.

It is another object of the present invention to provide a pressure distributor that also allows said variable forces to be redistributed at the periphery of the areas where said increases in thickness take place.

It is another, yet not the least important object of the present invention to provide a pressure distributor that during the forming process allows better control of the sliding movements of the metal sheet compared to the sheet pressing devices known in the art.

The objects listed above are achieved by a pressure distributor having the features defined in independent claim 1, to which reference is made.

Preferred features are described in the dependent claims. Advantageously, compared to the known art, the use of the pressure distributor that is the subject of the invention improves the distribution of pressures on the metal sheet during the forming process and reduces the differences in thickness that are found on the formed product once the forming process has been completed.

To further advantage, the formation of wrinkles, cracks and streaks that affect the quality of the formed product is also reduced.

The objects and advantages listed above are highlighted in greater detail in the following description of the pressure distributor of the invention and of preferred construction variants of the same based on the same innovative concept that are illustrated by way of examples with reference to the attached drawings, wherein:

• Figure 1 shows an axonometric view of the pressure distributor according to a preferred embodiment of the invention applied to a die arranged in open configuration;
• Figure 2 shows the die of Figure 1 arranged in closed configuration;
• Figure 3 shows a sectional view of the die with an exploded view of the pressure distributor of Figure 2;
• Figure 4 shows the die of Figure 3 arranged in closed configuration;
• Figure 5 shows the die of Figure 4 during the forming process;
• Figures from 6 to 11 show enlarged details of further preferred embodiments of the pressure distributor of the invention;
• Figure 12 shows an enlarged view of a detail of the die of Figure 5, where it is possible to observe in detail how the metal sheet and the pressure distributor of the invention are deformed during the forming process.

A preferred embodiment of the pressure distributor that is the subject of the present invention is represented in axonometric view in Figure 1, where it is indicated as a whole by 1 and is associated with a die indicated as a whole by 10 and represented in open configuration in Figure 1 and in closed configuration in Figure 2.

The pressure distributor 1, in fact, is configured in such a way that it can be placed between the matrix 11 and the base 12 of the die 10 during the forming process carried out on a metal sheet A which, as can be observed in the Figures from 3 to 5, is interposed between the matrix 11 and the pressure distributor 1.

According to the invention the pressure distributor, which can be observed in greater detail in Figure 6, comprises a composite laminar structure 2 provided with a shaped opening 3 for the passage of the punch 13 of the die 10, wherein said composite laminar structure 2 comprises a sheet pressing plate 21 configured in such a way that it can be placed in contact with the metal sheet A and an elastically deformable plate 22 included between the sheet pressing plate 21 and the base 12 of the die 10.

Variant embodiments of the pressure distributor 1 of the invention are possible, some of which are represented in the figures from 7 to 11.

A first variant embodiment of the pressure distributor, indicated as a whole by 1a, is visible in Figure 7 and according to this embodiment the composite laminar structure 2a comprises a sheet pressing plate 21 configured in such a way that it can be placed in contact with the metal sheet A, an elastically deformable plate 22 resting on the base 12 of the die 10 and a first intermediate plate 24 included between the sheet pressing plate 21 and the elastically deformable plate 22.

Another variant embodiment of the pressure distributor, indicated as a whole by 1b, is visible in Figure 8 and according to this embodiment the composite laminar structure 2b comprises a sheet pressing plate 21 configured in such a way that it can be placed in contact with the metal sheet A, an elastically deformable plate 22 facing and placed against the sheet pressing plate 21 and a second intermediate plate 25 included between the elastically deformable plate 22 and the base 12 of the die 10.

Another variant embodiment of the pressure distributor, indicated as a whole by 1c, is visible in Figure 9 and according to this embodiment the composite laminar structure 2c comprises a sheet pressing plate 21 configured in such a way that it can be placed in contact with the metal sheet A, a first intermediate plate 24 included between the sheet pressing plate 21 and an elastically deformable plate 22 and a second intermediate plate 25 included between the elastically deformable plate 22 and the base 12 of the die 10.

Another, yet not the least important variant embodiment of the pressure distributor of the invention, indicated as a whole by 1d, is visible in Figure 10 and according to this embodiment the composite laminar structure 2d comprises a sheet pressing plate 21 configured in such a way that it can be placed in contact with the sheet A, an underlying elastically deformable plate 22 placed against the sheet pressing plate 21 and two second intermediate plates 25 facing each other and included between the elastically deformable plate 22 and the base 12 of the die 10.

Other variant embodiments of the invention are possible, which are neither described nor illustrated herein and in which a variable number of intermediate plates may be used, variously arranged between the sheet pressing plate 21 and the elastically deformable plate 22 and/or between the elastically deformable plate 22 and the base 12 of the die 10.

Furthermore, said intermediate plates may be made of metallic or non-metallic materials.

In all of its variant embodiments described herein, the pressure distributor of the invention comprises also a frame 4 that delimits perimetrically the composite laminar structure, so that the pressure distributor of the invention constitutes an easily handled unit that can be rapidly and easily installed in and removed from the corresponding die.

For this purpose, as can be observed in the figures, in the base 12 of the die 10 there is a perimeter housing 15 that accommodates the frame 4 in order to stabilize the pressure distributor when it is installed in the die.

Regarding the elastically deformable plate 22, this is preferably but not exclusively made of an elastomer or an equivalent material and therefore it is characterized by reduced hardness and increased elasticity compared to the overlying sheet pressing plate 21, so that during the forming of the metal sheet A it serves the function of absorbing and distributing pressure, which is described in greater detail below.

The elastically deformable plate in turn has a variant embodiment illustrated in Figure 11 and indicated as a whole by 23, comprising a pair of parallel foils 23a, 23b spaced from each other through the interposition of two or more annular gaskets 23c, 23d, wherein the foils together with the gaskets define an annular chamber 23e containing a fluid 23f that can be a liquid or a gas.

In this way, the elasticity of the fluid 23f and of the annular gaskets 23c, 23d allows the foils 23a, 23b, which from a functional point of view behave as an elastomer, to be mutually moved towards and away from each other.

From an operational point of view, in order to form the metal sheet A, for example to carry out a deep drawing process and obtain a container as shown in Figure 5, the pressure distributor 1 is arranged in the operating position with the frame 4 housed in the annular cavity 15 provided in the base 12 of the die 10, after arranging the punch 13 so that it is completely recessed within the base 12 itself, as can be seen in Figure 4.

Then the metal sheet A is positioned on the pressure distributor 1 so that the metal sheet is included between the latter and the overlying matrix 11.

Obviously, any pressure distributor made according to any of the variant embodiments described above may be used, but for the sake of simplicity here below reference is made to the pressure distributor indicated as a whole by 1 and comprising the sheet pressing plate 21 and the underlying elastically deformable plate 22 made of an elastomer.

In order to proceed with the forming operation, the punch 13 is lifted and this penetrates the matrix 11 as shown in Figure 5 and thus deforms the metal sheet A, creating in the same a cavity with variable shape and depth that depend on the shape of the punch 13 and the depth of penetration of the same in the matrix 11 itself.

For the reasons already explained above, during the forming process the metal sheet A is deformed and in some of its perimeter areas, in particular in proximity to the angular areas of the matrix 11, during the bending operation it is subjected to a compression force that increases its thickness from value A1 to value A2, which is schematically represented in Figure 12, in which the deformation states are represented in a marked way on purpose, in order to make them more evident.

The increase in the thickness of the metal sheet generates a thrusting action F that deforms the underlying sheet pressing plate 21, which in turn deforms the underlying elastically deformable plate 22.

At the same time, the areas adjacent to the area where the sheet pressing plate 21 is deformed tend to become spaced from the metal sheet A that, being less controlled in those areas, shows an increased tendency to slide. Said uncontrolled sliding movement of the metal sheet, however, is counteracted by the elastically deformable plate 22, as the elastomer with which it is made substantially behaves as a fluid and transforms the localized deforming force F into a pressure P that acts on the sheet pressing plate 21 at the level of the areas around the deformation area, in the direction contrary to that of the force F, as schematically represented in Figure 12.

In substance, the elastomer with which the elastically deformable plate 22 is made absorbs the deforming force F and redistributes it on the overlying sheet pressing plate 21 in the form of a counter pressure P¹ with value equal to that of the pressure P that is distributed based on the well-known Pascal's law. Therefore, in the areas around the area where the sheet pressing plate 21 has been deformed said counter pressure P¹ tends to move the sheet pressing plate 21 back towards the metal sheet A that is thus held in a substantially uniform way along its entire perimeter edge for the whole duration of the forming process.

This leads to the advantage of obtaining an almost constant thickness of the metal sheet and eliminating the distortions, cracks, streaks and wrinkles that appear during the forming process carried out according to the known art and thus negatively affect the quality of the product once the forming process has been completed and that in the worst cases may even cause the metal sheet to break.

Experimental tests have made it possible to verify that by applying the pressure distributor of the invention to a die it is possible to reduce the thickness increases that take place on the metal sheet, and such increases are much smaller than those observed when the forming process is carried out using dies with sheet pressing devices of the known type.

The embodiment of the pressure distributor that, as explained above, is constituted by the composite laminar structure made up of a sheet pressing plate, an elastically deformable plate, intermediate plates in a variable number and the frame that delimits them, makes it possible to provide a unit that can be rapidly installed in and removed from a die with operations that can be carried out in a simple and safe manner also by inexpert personnel.

Furthermore, the use of the pressure distributor of the present invention makes it possible to eliminate the need to use the costly hydraulic equipment that according to the known art is presently used to control the sliding movements of the metal sheet during the forming process.

During the production stage, the pressure distributor of the invention may be subjected to modifications and variants that are neither illustrated in the drawings nor described herein but that must all be considered protected by the present patent, provided that they fall within the scope of the claims expressed below.