WO2000035612A2

WO2000035612A2 - Method for manufacturing three-dimensional, cellular structure components consisting of two metal sheets, and associated components

Info

Publication number: WO2000035612A2
Application number: PCT/IT1999/000406
Authority: WO
Inventors: Dario Amidei
Original assignee: Delta Di Amidei Dario & C., S.A.S.
Priority date: 1998-12-14
Filing date: 1999-12-09
Publication date: 2000-06-22
Also published as: ITTO981044A0; ITTO981044A1; WO2000035612A3; IT1303583B1

Abstract

A method for manufacturing three-dimensional, cellular structure components consisting of two metal sheets, comprising a starting step of separately pressing a first (22) and a second (23) metal sheet so that they assume respective three-dimensional shapes (R1, R2) compatible with each other, wherein at least one (23) of the sheets is provided along its surface with a cellular structure defining a plurality of depressions (26) and protrusions (27) reciprocally spaced and continuously distributed along the surface, and a successive step of joining the two previously pressed sheets (22, 23) together rigidly and permanently in a joining process, so as to constitute a cellular component (21) having a three-dimensional shape (R3). Preferably the cellular structure is produced at the same time as the three-dimensional shape (R2) by pressing the corresponding sheet (23), using the same mould. The method considerably extends the current possibilities of producing components made of two sheets, having a three-dimensional, even complex, shape together with good rigidity and at low cost, such as for example the engine bonnet (101) and other parts, external or internal, of a motor vehicle.

Description

METHOD FOR MANUFACTURING THREE-DIMENSIONAL, CELLULAR STRUCTURE COMPONENTS CONSISTING OF TWO METAL SHEETS, AND ASSOCIATED COMPONENTS

FIELD OF THE INVENTION The method according to the invention relates to the manufacture of components having a three-dimensional shape, made from two metal sheets, and provided with considerable torsional and fiexural rigidity and low weight, enabling them to be used to advantage in numerous applications requiring these characteristics.

TECHNICAL BACKGROUND In the current art, and in particular in the transport vehicles manufacturing sector, there is widespread use of components consisting of two or more metal sheets joined solidly together, to produce three-dimensional parts, complex ones included, and designed to have either a structural function, such as for example the chassis of a car, or even just a covering and/or both structural and aesthetic, or primarily aesthetic, function such as for example the engine bonnet or door of a car.

In particular these components, for the purposes of acquiring the rigidity necessary for the application for which they are designed while at the same time remaining low weight, are provided with ribs extending along the surface of the sheets comprising them. In particular, in the case of external parts, as for example in the case referred to above of an engine bonnet, the latter generally comprises an outer sheet, 0.8 mm thick for example, defining the outer style profile of the bonnet and which usually has a fairly regular convex shape, and a frame of sheet metal having a series of extensive ribs, which is connected by means of structural adhesives to the side not in view of the outer sheet, and/or seamed to the edges of the latter.

On the other hand, parts not in view, such as the floor of a car, are made typically of a sheet of suitable thickness, for example 1.2 mm, stiffened by means of ribs of elongated shape and extending in the most favourable direction to give good rigidity. A semi-processed material, also called "bubble steel", produced by the Thyssen company is known. Described in particular in the international patent application No. PCT/EP95/04813, this material is offered as the basic element for producing a wide range of parts, intended for the car industry in particular. In detail, this semi-processed material consists of a flat composite strip made from two sheets of galvanized steel 0.3 mm thick, which are joined together through electric welding spots made at a constant pitch of about 20 mm along the surface of the material, in correspondence with embossments of about 10 mm in diameter drawn on one or both the sheets. This semi-processed material is made in two versions, either with an overall thickness of 1.8 mm by joining a flat sheet and an embossed sheet, or with a thickness of 3.4 mm by joining two, mirror-image embossed sheets.

However, this bubble steel, though it can be machined conventionally by shearing and pressing in order to produce sheet components for the car industry and suitable for substituting traditional components made of compact steel, entails a number of significant limitations in the radii of curvature of the shapes of the components that can be made from it, and in particular does not permit bettering of the stiffness gain limits and the three-dimensional modelling possibilities imposed by the heights of 1.8 mm and 3.4 mm that the bubble steel is supplied in. Semi-finished or flat panels of the "cellular sandwich" type, as described in the

International Patent applications No. PCT/IT97/000164 and No. PCT/IT97/000165, both filed by this Applicant, are also known. These are made of at least three metal sheets overlaid and secured permanently together, where the inner one has a cellular structure consisting of a plurality of protrusions and depressions reciprocally spaced and continuously distributed over its surface.

These panels, however, have in reality a number of significant limitations or drawbacks, in particular with regard to their workability, which prevent or at least discourage their use in particular applications, and/or for the production of three- dimensional shapes of a certain complexity.

Beside, on account of their fairly complex sandwich structure comprising at least three sheets, these panels have an industrial manufacturing cost that renders them often not sufficiently economical for some applications, though they possess the required technical characteristics.

Therefore, generally speaking, the known solutions are not always capable of satisfying the modern requirements for the production of composite sheet components having ever more complex three-dimensional shapes, and especially not subject to particular limits with regard to their spatial progression and associated radius of curvature.

Finally it should be said that, in those cases where the current art does not permit the use of composite sheet components to obtain the desired shapes, traditional manufacturing processes such as smelting, forging, and other processes are still used, even though it is known that these processes often have drawbacks, including with regard to their consequences on the environment.

However the problem remains unsolved of manufacturing mechanical parts with structural and/or even only aesthetic functions, without limitations of shape and application, having a high degree of torsional and fiexural rigidity combined with low weight, using low cost materials in a manufacturing process that is simple, economical and with a low environmental impact.

SUMMARY OF THE INVENTION

Accordingly the object of this invention is to define a method for manufacturing three-dimensional components, of even highly complex shape, made from two metal sheets, that overcomes the limitations of the known systems, so as to considerably extend the application possibilities of components of this type, in particular in the transport vehicles manufacturing sector.

This object is achieved by the method defined in the main claim.

Another object of the invention is that of defining components, of any three- dimensional shape, including extremely complex, made from two sheets, which augment the solutions currently available, thus offering designers the possibility of extending the application of composite components made of two metal sheets to new fields.

A further object of the invention is that of defining a method for manufacturing components of lesser thickness and having three-dimensional shapes made by overlaying two metal sheets, which offer uniform and high resistance to fiexural and torsional stresses over their spatial surface combined with a low weight, making such components particularly suitable for applications requiring elevated structural characteristics in combination with as low a weight as possible. BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, characteristics and advantages of this invention will become apparent upon consideration of the following description of a preferred embodiment, provided by way of a non-exhaustive example, in conjunction with the accompanying drawings, wherein: Fig. 1 is a schematic representation of a sectional view of a first sheet of metal, having a substantially smooth surface free of corrugations, used in the method according to the invention;

Fig. 2 is a schematic representation of a sectional view of a second sheet of metal, having a cellular structure, used in the method according to the invention; Fig. 3a is a plan view of the second sheet of Fig. 2, provided with a cellular structure;

Fig. 3b is a plan view of a variant of the second sheet of Fig. 3a;

Fig. 4 is a schematic and sectional representation of a three-dimensional cellular component consisting of two metal sheets according to a first version of the method of the invention, in which only one of the two sheets has a cellular structure;

Fig. 5 is a perspective representation, with some parts removed, of the cellular component of Fig. 4;

Fig. 6 is a sectional view in enlarged scale of a portion of the cellular component of Fig. 4;

Fig. 7 is a sectional view of a three-dimensional cellular component according to the invention consisting of two sheets and having an intermediate cellular structure made from a plurality of modular elements solidly attached to the two sheets; Fig. 8 is a schematic representation of a variant of the first sheet of Fig. 1 , in which the latter also has a cellular structure;

Fig. 9 is a sectional representation of a cellular component consisting of two metal sheets according to a second version of the method of the invention, in which both sheets have a cellular structure; Fig. 10 is a schematic representation of a sectional view of a three-dimensional cellular structure component produced according to the method of the invention, illustrating the case where the component incorporates a functional element;

Fig. 11 represents a first variant of a three-dimensional cellular component consisting of two metal sheets obtained according to the method of the invention, in which the edges of the two metal sheets are joined together along a portion of the perimeter of the component;

Fig. 12 represents a second variant of the three-dimensional cellular component of the invention, in which the edges of the two metal sheets are joined together along the entire perimeter of the component; Fig. 13 represents a third variant of the three-dimensional cellular component of the invention, in which the relative cellular structure is reinforced in given areas of the component, in particular along the edge of the latter;

Fig. 14 is a schematic representation of other embodiments and applications of the three-dimensional cellular component manufactured according to the method of the invention, in which in particular the component is interfaced on the left with another composite cellular plate component, and on the right with a traditional compact plate component;

Fig. 15 is a schematic plan view from the inside of an engine bonnet manufactured according to the method of the invention; and

Fig. 16 is a sectional longitudinal view of the engine bonnet of Fig. 15. Description of a first embodiment of the method according to the invention The method according to the invention for manufacturing three-dimensional cellular structure components consisting of two metal sheets will be described, for simplicity's sake, with reference to two sheets of metal shaped according to a generic three-dimensional shape, as outlined in the drawings though the outlines should not in any case be construed as representing a limitation of the invention, as will be apparent in the following. With reference to Figs. 1 -6, a first version of the method of the invention has the object of producing a three-dimensional component, indicated generically with the numeral 21 , made from two sheets of metal 22 and 23, of which only the sheet 23 has a cellular structure.

In particular, to begin with, the two sheets 22 and 23 are supplied separately, in a substantially flat or similar configuration. Each sheet 22, 23 consists of a plate of a given thickness which is produced from a metallic material, such as for example iron, or steel, or aluminium, or any metal alloy, etc. The steel may be of various types, either normal or special, for example stainless steel. The material must however be provided with suitable properties to permit good deformation workability of the sheets 22 and 23. The sheets 22 and 23 may be of equal or different thickness, in relation to the characteristics required of the manufactured three-dimensional component.

In addition the sheets 22 and 23 may be made from metal sheets that have already had a preliminary treatment, painting for example, and/or a rustproofing surface treatment, such as nickel-plating, galvanizing, aluminization, passivation, etc. Again the geometric profile with which the sheets 22 and 23 are supplied to begin with must be considered in as broad a sense as possible, so that for example each sheet of metal 22 and 23 may possibly comprise one or more apertures or holes, or even discontinuities, within its perimeter, without departing from the scope of the invention.

Subsequently the two sheets of metal 22 and 23 undergo deformation, each one distinctly from the other, so that each sheet 22 and 23 acquires a given three- dimensional shape, defined respectively by a radius of curvature R1 and a radius of curvature R2.

These shapes are made separately for each sheet 22 and 23, for example by pressing in one or more passes or by folding, using known techniques.

The three-dimensional shapes assumed by the sheets 22 and 23 after deformation machining, and consequently the respective radii of curvature R1 and R2, are reciprocally compatible, in the sense that they are such as to permit a correct coupling between the sheets 22 and 23 in order to make, as described later, the three- dimensional component 21 according to the method of the invention, and accordingly to define its final shape.

It is clear, as already underlined at the beginning of the description, that the curved shape defined by the radii of curvature R1 and R2 represents purely a schematization, so that the three-dimensional shape of the two sheets of metal 22 and 23 that is to be described herein, must be understood according to a general meaning, where it may be much more complex than the one shown and comprise in particular, for each sheet 22 and 23, a curved surface defined by a variable radius of curvature along the surface in question.

The sheet 22, after the deformation machining wherein it assumes the three- dimensional shape desired, is ready for coupling with the sheet 23, with a substantially smooth surface, namely without the corrugations associated with a cellular structure.

On the other hand the sheet 23, after the deformation machining and therefore after assuming its respective three-dimensional shape, is ready for coupling with the sheet 22, provided with a cellular structure or, in other words, with a continuous, distributed rib.

This cellular structure is preferably obtained from a deformation of the sheet of metal 23 that is somehow associated with the machining step, described earlier, designed to confer the three-dimensional shape on the sheet 23.

The cellular structure of the sheet of metal 23 is defined by a series of depressions 26 and protrusions 27, the latter also called "hills" or protuberances or embossments, disposed reciprocally spaced and continuously distributed over the surface of the sheet 23.

In particular, with reference to Figs. 3a and 3b which depict in plan view two possible arrangements of the cellular structure of the sheet 23, the protrusions 27 and the corresponding depressions 26 are disposed in rows, and can be reciprocally aligned or staggered from one row to the next.

For example Fig. 3a depicts a cellular structure in which the protrusions 27 are disposed in correspondence with the nodes of a triangular grid defined by a plurality of substantially equilateral triangles set side by side, whereas Fig. 3b depicts a cellular structure in which the protrusions 27 are disposed according to a substantially square grid.

In addition, the rows in which the protrusions 27 and the depressions 26 are disposed may be aligned or variously inclined with respect to any portion of the perimeter edge of the sheet 23.

The protrusions 27 and the depressions 26 follow one another in accordance with a first pitch P1 in a first direction, and in accordance with a pitch P2 in a second direction, not always perpendicular to the first.

The two pitches P1 and P2 are preferably equal, but may also be different, without this meaning that the sheet loses its cellular structure.

In this way the surface of the sheet of metal 23 is, by virtue of its cellular structure, divided into a multiplicity of three-dimensional cells 25, adjacent to each other, which give rise to an alternation of protrusions and depressions along the surface of the sheet 22.

The protrusions 27 may assume any shape whatsoever, even different from one protrusion to the next. For example, with reference to the mode of production described and illustrated here, the protrusions are all extending from the same side of the sheet 23, and have each a truncated cone shape, defined by a lower cylindrical base and by an upper cylindrical base disposed at a certain distance from each other, corresponding to the height of the sheet 23.

This does not mean however that the protrusions 27 may not extend from both sides of the sheet 23 and be spherical cap shaped, or truncated pyramid shaped.

The density of the protrusions 27, and correspondingly of the cells 25, in relation to a unit area of the sheet 23, may also vary from zone to zone of the sheet 23, without in this way prejudicing the relative cellular structure.

To go back to production of the cellular structure of the sheet 23, it is - as already said - preferably obtained in the production cycle together with the three-dimensional shape, defined by the radius of curvature R2 of the sheet 23 in question.

In particular this cellular structure is obtained by deformation or pressing of the sheet 23 with two different techniques, of which the first is generally applicable when the curved shape of the sheet 23 and correspondingly of the three-dimensional composite component to be made is less accentuated, namely is defined by radii of curvature of a fairly high value, and also the embossments of the cellular structure are of a height and shape that do not create problems or situations of undercut. In the first case the pressing of the sheet 23 with the relative cellular structure is produced in a single step, either on mechanical or hydraulic presses, by way of mechanical drawing of the flat starting sheet with a traditional type mould having both its male part and female part shaped according to the profile of the curved shape of the sheet 23 and of the relative truncated cone embossments. The second technique is, on the other hand, generally applicable when the sheet

23 and therefore the composite cellular component to be made have a more accentuated curved shape, i.e. defined by low radii of curvature, and further the truncated cone shaped embossments are of a height and shape such as to create situations of undercut.

In this second case the pressing of the sheet 23 takes place in two distinct steps and exclusively on hydraulic presses by means of a drawing mould not provided with protrusions on the male part but having hollows in the female part. Two different forming techniques are used, that is to say a mechanical drawing to produce the three- dimensional curved shape of the sheet 23 and a hydro-forming drawing to produce the truncated cone-shape embossments.

In particular in the first step, pressing with mechanical drawing of the flat starting sheet is performed in order to give the sheet 23 its three-dimensional curved shape. In the subsequent second step, with the mould closed at the end of stroke and acting as a sheet-press along the entire surface of the sheet 23, pressing is performed with drawing by hydro-forming of the truncated cone-shape embossments using the hollows made in the female part of the mould.

Subsequently the two sheets 22 and 23 thus formed are joined rigidly and permanently together in a joining process, in correspondence with the tips of the various protrusions 27 to give the three-dimensional component 21.

In particular the latter has a three-dimensional configuration corresponding to that of the sheets 22 and 23 and which is symbolized by way of example in Figs. 4 and 5 with a radius of curvature R3. The process of joining the two sheets 22 and 23 can be effected in any known way, obviously taking into consideration the materials and thicknesses of the plates the sheets are made from, for instance by welding, brazing, gluing with structural adhesives compatible with the metallic alloys of the plates and with their thickness (sometimes they are very thin), etc. In particular the joint can be made using the structural and semi-structural adhesives already normally used for the components and chassis parts defining the appearance of a motor vehicle, or by way of laser or electrical ring-type projection welding . In general the object of the process of joining the sheets 22 and 23 is to connect the protrusions 27 of the cellular structure of the sheet 23 with the sheet 22, in order to obtain a complete and effective structural cooperation between the two sheets 22 and 23. Fig. 6 illustrates in detail the fundamental characteristic parameters of the overall structure of the three-dimensional component 21, in particular the thicknesses S1 and S2 respectively of the plates that the sheets 22 and 23 are made from; the pitch P at which the protrusions or depressions of the cellular structure of sheet 23 are reciprocally placed apart; the bottom D1 and top D2 diameters of each truncated cone-shaped protrusion 27 of the cellular structure sheet 23; and the total height H of the three- dimensional component 21 determined by the overlaying of the two sheets 22 and 23.

Preferably, the three-dimensional component 21 made according to the method of the invention has a total height H, substantially conferred on it by the cellular structure of the sheet 23, of between 2 and 50 mm; in addition, the two metal sheets 22 and 23 are of thickness S1 and S2 of between 0.05 and 10 mm; whereas the ratio P/H of the pitch P of the protrusions 27 or the depressions 26 to the total height H is between 2 and 14.

More preferably the thicknesses of the metal sheets 22 and 23 have a range of values, located inside the previous one, of between 0.1 and 2 mm; and similarly the ratio P/H is inside a range of values, to be preferred with respect to the previous one, between 6 and 12.

Furthermore, and preferably, the drawn area on the sheet 23 and corresponding to the protrusions 27 of the relative cellular structure is between 20% and 40% of the total area of the sheet 23. The mechanical characteristics, in particular rigidity and fiexural and/or torsional resistance of the three-dimensional component 21 are considerably greater than those of the single sheets 22 and 23 when considered separately, so that the three- dimensional component 21 is suitable for application in a variety of practical cases, where elevated mechanical characteristics are required in conjunction with a certain lightness.

In addition, the cellular structure or continuous ribbing distributed through the three-dimensional component 21 renders the latter considerably more advantageous in a very wide range of cases than the solutions based on elongated ribs, or stiffening ribs not provided with a cellular structure.

In particular, thanks to the cellular structure, the component 21 acquires over its surface a substantially uniform resistance to the fiexural and torsional stresses, that is a characteristic which is not normally found in components stiffened by means of traditional type ribs. What is more, the three-dimensional component 21, for like weights, has a higher value of resistance to the fiexural and torsional stresses than traditional components.

Obviously changes may be made to the first version of the method of the invention. For example, the cellular structure may already be present in the metal sheet 23 before the machine deformation step designed to give it the desired spatial shape. It follows that, in this case, the cellular structure of the sheet 23 is to be referred to the starting supply condition of the sheet 23 in question and also that this cellular structure is maintained in the sheet 23 while the latter is being deformed, by pressing or bending, in order to assume the relative spatial shape. Furthermore, the three-dimensional shape of the two sheets 22 and 23, like the cellular structure of the latter sheet, may be obtained separately for each sheet in any machining process, smelting for example, other than pressing, or in general by a work process based on the deformation of a starting sheet.

Again, the cellular structure may be produced by attaching on one of the two sheets a plurality of protruding elements, suitably disposed in such a way as to define a plurality of protrusions and depressions coming one after the other continuously along the surface of the sheet.

As illustrated in Fig. 7, a three-dimensional cellular component 41 according to this solution consists of two sheets 42 and 43 and has a cellular structure that is made from a plurality of additional modular elements 44 of tubular section arranged between the two sheets 42 and 43 and attached rigidly thereto.

In particular during a starting work step, the modular elements 44 are surfaced and attached at one end to a first of the two sheets, for example the sheet 42, by way of a known joining technique, such as welding or gluing or other techniques, so as to define a continuous succession of depressions and protrusions over the surface of the first sheet 42.

The first sheet 42 to which the modular elements are initially attached may already possess a three-dimensional shape to begin with, obtained in a known way, or be initially supplied flat and be shaped so as to assume the desired three-dimensional shape only after the attachment thereto of the tubular modular elements 44.

Subsequently the first sheet 42, thus prepared with the cellular structure, is joined rigidly by way of known techniques to the second sheet 43, which in turn is already formed with a three-dimensional shape compatible with that of the first sheet 42. For instance, the second sheet 43 is welded or glued on the opposite ends of the tubular modular elements 44, in this way constituting the three-dimensional cellular component 41.

Indicatively only, in this variant the modular elements 44 forming the cellular structure of the three-dimensional component 41 have an inner diameter 0 of approximately 50 mm, a height H2 of between 30 and 100 mm, and a thickness S3 of approximately 1 mm, and are placed apart in the two directions over the surface of the component 41 at a pitch P3 of between 60 and 200 mm.

Description of an engine bonnet manufactured according to the method of the invention

The first version described above of the method of the invention may be applied to the production of a vast range of parts. As concrete examples of components made with this first version, it is possible to quote merely for guidance the outer parts of the chassis of a motor vehicle having a typically aesthetic function, such as for example an engine bonnet, or the roof, or the outside of a door.

In particular, an engine bonnet produced by using the method of the invention is made from two sheets of highly mouldable, galvanized steel, and has a final structure consisting of an outer sheet, generally slightly convex and free of corrugations, which defines the visible aesthetic shape or style of the bonnet, and an inner sheet, attached to the side of the style sheet not in view and having a cellular structure, endowing the bonnet with considerably enhanced mechanical characteristics.

The cellular structure in particular confers good rigidity to the bonnet, and dampens the possible vibrations during use of the motor vehicle.

In a bonnet made in this way the parameters defined above, preferably though not exclusively, assume the following values:

51 = thickness of the in-view or style sheet = 0.5 mm;

52 = thickness of the cellular structure sheet = 0.3 mm; H = total height = 5.5 mm;

D1 = 25 mm; D2 = 10 mm; P = pitch between the protrusions of the cellular structure = 40 mm.

In the manufacturing cycle, as first step, the two metal sheets constituting the bonnet are pressed. Then they are prepared to be assembled by distributing a semi- structural adhesive on the top surface of the various truncated cone-shaped embossments of the inner cellular structure sheet, in particular using robots, in order to produce a multiplicity of points of union formed by circular areas of the semi-structural adhesive. Successively the two metal sheets are urged and connected stably together, before being seamed along the edges.

It is underlined in particular that, as the stiffness of the outer style sheet alone is considerably greater than that of the cellular structure inner sheet alone, the style sheet acts during the joining process as a reference shape for the complete component, thus obliging the less stiff, cellular structure sheet to adapt to this shape.

Various embodiments of the engine bonnet are possible, without departing from the protective scope of this invention. For example, with reference to Figs. 15 and 16, an engine bonnet 101 according to the invention may comprise an outer or external style metal sheet 102, and an inner or internal metal sheet 103, provided with a cellular structure 108, in which the inner metal sheet 103 is made from an original metal sheet of a type called "tailored blank". As is known, a sheet of this type consists of various portions of metal sheet of differing thickness which are welded along the edge by means of, for instance, laser technology in order to constitute a continuous metal sheet having areas of different thickness.

In particular, this inner metal sheet 103 consists of a front portion 104, a rear portion 106, and an intermediate portion 107, the latter being the prevalent area, arranged between the front portion 104 and the rear portion 106, wherein the thickness of the two front and rear portions is notably greater than that of the intermediate portion

107.

The front portion 104 corresponds to the area of the bonnet 101 bearing the fasteners 111 to attach the bonnet to the body of the car on which the bonnet is or will ultimately be fitted, the rear portion 106 corresponds to the area bearing the pivots 112 to hinge the bonnet 101 to the car body, and the intermediate portion 107 corresponds to the central part, the most extensive longitudinally, of the bonnet 101.

Indicatively, the two front and rear portions 104, 106 have a thickness S10 of between 0,5 and 0.7 mm, while the intermediate portion 107 has a thickness S11 approximately of 0.3 mm.

In accordance with what was said earlier, the original tailored blank sheet is pressed in such a way as to assume globally a three-dimensional shape compatible with that of the external style sheet 102 of the bonnet, and moreover to acquire a specific cellular structure distributed all over the intermediate portion 107.

Furthermore, in the same pressing operation, the front and rear portions 104, 106 are appropriately shaped and/or machined depending on how these portions are to be used for fastening and hinging the bonnet.

It is stressed that, in this way, the front and rear portions 104, 106 take on a shape which, though possibly having ribbings or other corrugations, is still not such as to define a cellular type structure, as on the other hand is the case of the intermediate portion 107. For guidance, the global height H10 of the cellular structure 108 obtained by pressing along the intermediate portion 107 is approximately 5 mm.

Then the pressed inner sheet 103 is joined with the external style sheet 102, already shaped, in order to produce the bonnet 101, in accordance with the methods already described above, namely by bonding by means of an adhesive the tops of the protrusions of the cellular structure 108 with the external style sheet 102.

Also the front and rear portions 104, 106 are bonded by means of the same adhesive with the external style sheet 102

Accordingly in this way it is possible to make an engine bonnet which, though being relatively light and having a low overall thickness, possesses good rigidity, as already said, thanks to the cellular structure arranged over its inner surface, and which in addition is advantageously prepared to be completed, in correspondence with the front and rear edges, with the necessary hinging and fastening devices, so that it may be fitted on the car which will receive ultimately the engine bonnet.

Description of a second embodiment of the method according to the invention A second version of the method of the invention for manufacturing three- dimensional cellular components consists in stably joining two sheets of metal, both having a cellular structure or distributed ribbing, after having pressed them before so that each of them assumes a respective three-dimensional shape corresponding to the final shape of the component desired.

In particular the two cellular structure sheets are made respectively of a first sheet 32, shown in Fig. 8, having, after the initial pressing, a curved configuration defined by a radius of curvature R5 and also having a plurality of protrusions 37 and depressions 36, and a second sheet 33, also provided with a cellular structure, substantially equal to the sheet 23 shown in Fig. 1.

The cellular structure of each sheet 32, 33 is obtained by pressing, in ways not described here as they are similar to those of the previous first version of the method.

The joining of the two cellular structure sheets 32 and 33 is effected by uniting, in correspondence with the tops, the protrusions of the respective cellular structures, through a joining process of known characteristics and of the type indicated above with reference to the said first version of the method of the invention.

In this way a three-dimensional component 31 is obtained, such as the one shown in Fig. 9, having a radius of curvature R6. Changes and variants are also possible in relation to this second version of the method of the invention. For example, the cellular structure of each of the two sheets constituting the three-dimensional component may be made by pressing in conjunction, or otherwise, with the respective three-dimensional shape.

In particular, this cellular structure may exist prior to the process conferring the three-dimensional shape on each sheet 32 and 33 and therefore be referred to the tetter's initial supply condition.

Similarly the three-dimensional shapes of the two sheets and the relative cellular structures may be obtained separately for each sheet through a process other than pressing, for instance by smelting. Or the cellular structures of the two sheets may be produced by attaching to each thereof a plurality of protruding elements, suitably placed apart so as to define a typically cellular structure along the surface of the two sheets.

Preferably, the three-dimensional component 31 made with this second version of the method of the invention has a total height h, conferred to it substantially by the cellular structure of the two sheets 32 and 33, of between 2 and 100 mm; in addition the two metal sheets 32 and 33 have a thickness of between 0.05 and 10 mm; whereas the ratio P/h between the pitch P of the protrusions or the depressions of the cellular structure of each sheet 32 and 33 to the total height h, is between 1 and 7.

The thicknesses of the metal plates of the sheets 32 and 33 have a range of values, located inside and more preferably with respect to the previous one, of between 0.1 and 2 mm; and similarly the ratio P/h is inside a range of values, more preferably with respect to the previous one, of between 3 and 6. In addition, the drawn area on the sheets 32 and 33 and corresponding to the protrusions of the relative cellular structure, is preferably between 20% and 40% of the total area of each sheet 32 and 33.

Again this second version of the method of the invention may be applied to the production of a vast range of three-dimensional parts and/or components having a uniform and high resistance to fiexural and torsional stresses on their surface, combined with low weight.

As a concrete example of a component made with this second version, a floor provided with tunnel for a motor vehicle may be quoted merely for guidance.

In particular such a floor is made from two sheets of galvanized steel of high mouldability, which are joined stably together by electric spot welds produced by robots. In addition the floor has an overall structure wherein the relative parameters assume preferably, though not exclusively, the following values: thickness of the first and second sheet of metal = 0.5 mm; cellular structure defined by a plurality of truncated cone-shaped protrusions each having a bottom diameter = 25 mm, a top diameter = 10 mm, and a height = 10 mm; total height of the cellular floor = 11 mm; and pitch between the protrusions of the cellular structures of the two sheets = 40 mm.

Variants, modifications, improvements and additions may be made to the two versions of the method of the invention described above.

For example, the space formed between the two metal sheets in the three- dimensional component, thanks to the cellular structure of at least one of the two, may be used to allow the passage of a fluid, in turn brought in and let out through suitable holes made in the sheets of metal.

Or again, the space between the two metal sheets may be filled with low density resin or foam, in order to improve the rigidity of the three-dimensional component and/or confer thermo-acoustic insulation properties thereon.

In addition, the three-dimensional component made with the method of the invention, by virtue of its layered structure, can easily incorporate and/or support inserts, or other functional elements, enabling the component to be interfaced with other parts.

For example, with reference to Fig. 10, a three-dimensional component 51 made according to the method of the invention and consisting of two cellular structure sheets 52 and 53 of metal can incorporate a plate 54 having a threaded hole. Again the two sheets of metal comprising the three-dimensional cellular component may be seamed along the edges, partially or along the whole perimeter.

For example, Fig. 11 shows a first variant, indicated with the numeral 61, of a cellular component made according to the method of the invention, which has a structure similar to that of the component 21 described previously, and in particular is made of a first, substantially smooth sheet 62 and a second sheet 63 provided with a cellular structure, in which the two sheets 62 and 63 are reciprocally seamed by folding back one edge 64 of the sheet 62 on that of the sheet 63, along a portion of the perimeter of the three-dimensional component 61.

Similarly Fig. 12 shows a second variant, indicated with the numeral 71 , of the component of the invention, which is of the same type as the component 31 described before, and is made of two sheets 72 and 73 both provided with a cellular structure, wherein the two sheets 72 and 73 are joined along the entire perimeter 74, so as to produce a box-like structure for the three-dimensional component 71. Fig. 13 depicts a third variant, indicated with the numeral 81 and made of two sheets 82 and 83, of the component produced according to the method of the invention, wherein the sheet 82 is substantially smooth, the sheet 83 is provided with a cellular structure having a series of protrusions 87 extending from the two faces of the sheet 83, and the component 81 is reinforced in given areas along its surface.

Purely by way of example, the reinforcing area is disposed along the edge of the component 81 and takes the form of a substantially smooth sheet of metal 88, of lesser extent than the total extent of the component 81, and attached in a known way, for example by gluing, to the cellular structure sheet 83 on the side opposite that of the smooth sheet 82.

Furthermore the sheet 88, the sheet 82 and the sheet 83 are reciprocally joined at one end along the edge of the component 81 , so as to close each slot laterally and produce a box-type, sandwich reinforcing structure disposed adjacently to the edge of the component 81. Finally Fig. 14 shows a number of examples of the way in which a three- dimensional component 91 produced according to the method of the invention and made of two metal sheets 92 and 93 can interface laterally with external parts. In particular the component 91 on the left-hand side is inserted between the two sheets 97 and 98 of another three-dimensional component 96, to which it may be attached in a known way.

On the right, on the other hand, the component 91 accommodates internally between its respective two sheets 92 and 93 the edge of a plate 94, on which the two sheets 92 and 93 can rest, or can be attached stably, for example by welding.

In short, without prejudice to the principle of this invention, the manufacturing details and the embodiments may be widely varied with respect to what has been described and illustrated, without departing from the scope of the invention.

Claims

1 - Method for manufacturing three-dimensional cellular components (21 ; 31; 41" 51; 61; 71; 81; 91 ; 101) consisting of two metal sheets, characterized by the fact of comprising the following steps: manufacturing a first sheet (22; 32; 42; 52; 62; 72; 82; 92; 102) of metal having a respective three-dimensional shape (R1 ; R5), manufacturing a second sheet (23; 33; 43; 53; 63; 73; 83; 93; 103) of metal having a respective three-dimensional shape (R2) compatible with that of said first sheet (22; 32; 52; 62; 72; 82; 92), at least one (23; 32,33; 42,43; 52,53; 63; 72,73; 83; 92,93; 103) of said first and said second sheet of metal being provided, over all or part of its surface, with a cellular structure defining a plurality of depressions (26; 36) and protrusions (27; 37; 87) reciprocally spaced and continuously distributed over said surface, and subsequently joining rigidly and permanently, in a joining process, said first sheet (22; 32; 42; 52; 62; 72; 82; 92; 102) and said second sheet (23; 33; 43; 53; 63; 73; 83; 93; 103) of metal together.

2 - Method according to claim 1 , characterized by the fact that the step of manufacturing said first sheet (22; 32; 52; 62; 72; 82; 92; 102) of metal is effected by pressing, in such a way as to have said first sheet assume the respective three-dimensional shape (R1 ; R5), and the step of manufacturing said second sheet (23; 33; 53; 63; 73; 83; 93; 103) of metal is effected by pressing, in such a way as to have said second sheet assume the respective three-dimensional shape (R2).

3 - Method according to claims 1 or 2, characterized by the fact that the cellular structure of said at least one (23; 32,33; 52,53; 63; 72,73; 83; 92,93; 103) of said sheets is obtained by pressing.

4 - Method according to claims 1 or 2, characterized by the fact that said cellular structure is obtained by attaching to the surface of said at least one of said sheets (42, 43) a plurality of protruding and reciprocally spaced modular elements (44) so as to define said cellular structure.

5 - Method according to claim 4, characterized by the fact that said modular elements are tubular shape and have a height of between 10 and 100 mm, an inner diameter of between 10 and 100 mm, and a thickness of between 0.2 and 2 mm.

6 - Method according to claim 1 or 2, characterized by the fact that both said first sheet (32; 52; 72; 92) and said second (33; 53; 73; 93) sheet of metal are provided with a respective cellular structure extending, at least partially, over their surfaces, and defining a plurality of depressions (36) and protrusions (37) reciprocally spaced and continuously distributed over the surfaces.

7 - Method according to claim 6, characterized by the fact that the cellular structure of each of said first sheet (32; 52; 72; 92) and said second sheet (33; 53; 73; 93) is obtained by pressing.

8 - Method according to any of the previous claims, characterized by the fact that the plates from which are obtained said first (22; 32; 42; 52; 62; 72; 82; 92) and said second

(23; 33; 43; 53; 63; 73; 83; 93) sheets are made of a material selectable from a group comprising normal steels and special alloyed steels, such as for example stainless steel, and soft iron, aluminium, metal alloys.

9 - Method according to claim 8, characterized by the fact that said plates have undergone a protective treatment selectable from a group comprising galvanizing, nickel-plating, painting, aluminization, passivation.

10 - Method according to any of the claims from 1 to 3, characterized by the fact that said three-dimensional cellular component (21; 61; 81) has a total height H, conferred substantially thereon by the cellular structure of said at least one sheet (23; 63; 83), which is between 2 and 50 mm; that the metal plates from which said first (22; 62; 82) and said second (23; 63; 83) sheets are made have a thickness (S1 , S2) of between 0.05 and 10 mm; and that the ratio P/H between the pitch according to which said protrusions (27; 87) or depressions (26) of said cellular structure are spaced apart and said total height H is included in a range from 2 to 14.

11 - Method according to claim 10, characterized by the fact that the metal plates of said first (22; 62; 82) and of said second (23; 63; 83) sheets have a thickness (S1 , S2) of between 0.1 and 2 mm, and that the ratio P/H is between 6 and 12.

12 - Method according to claims 10 or 11 , characterized by the fact that the drawn area on said at least one sheet (23; 63; 83) and corresponding to the protrusions (27; 87) of the relative cellular structure is between 20% and 40% of the total area of said at least one sheet (23; 63; 83).

13 - Method according to the claims 6 or 7, characterized by the fact that said three- dimensional cellular component (31; 51 ; 71 ; 91) has a total height h, conferred substantially thereon by the joined cellular structures of both said sheets (32,33; 52,53; 72,73; 92,93), which is between 4 and 100 mm; that the metal plates from which said first (32; 52; 72; 92) and said second (33; 53; 73; 93) sheet are made have a thickness of between 0.05 and 10 mm; and that the ratio between the pitch according to which said protrusions (37) or depressions (36) are spaced apart and said total height h is included in a range from 1 to 7.

14 - Method according to claim 13, characterized by the fact that the metal plates of said first (32; 52; 72; 92) and said second (33; 53; 73; 93) sheets have a thickness of between 0.1 and 2 mm, and that said ratio is between 3 and 6.

15 - Method according to claims 13 or 14, characterized by the fact that the drawn area on each of said sheets (32,33; 52,53; 72,73; 92,93) of metal and corresponding to the protrusions (27) of the respective cellular structure is between 20% and 40% of the total area of each sheet.

16 - Method according to any of the previous claims, characterized by the fact that a generic one of said protrusions (27; 37; 87) has a shape selected from a group comprising spherical cap shape, truncated cone shape and truncated pyramid shape.

17 - Method according to any of the previous claims, wherein the spatial shape of said three-dimensional cellular component (21 ; 31 ; 51 ; 61 ; 71 ; 81 ; 91 ) follows, at least in a circumscribed area, a curved pattern defined by a radius of curvature (R3; R6), characterized by the fact that said radius of curvature (R3; R6) is a value of between 1 cm and 10 metres.

18 - Method according to claim 3 or 7characterized by the fact that the pressing of said cellular structure is obtained by mechanical drawing simultaneously with the pressing of the corresponding sheet (23; 32,33; 52,53; 63; 72,73; 83; 92,93) to have it assume the respective three-dimensional shape, and furthermore using the same mould.

19 - Method according to claim 3 or 7 characterized by the fact that the pressing of said cellular structure is obtained by hydro-forming, with a mould provided only at one end with a shape copying that of said cellular structure, said end having in particular a plurality of hollows corresponding to the protrusions of said cellular structure.

20 - Method according to claim 19 characterized by the fact that said mould is the same as is used to have the sheet provided with said cellular structure assume the relative three-dimensional shape.

21- Method according to any of the previous claims, characterized by the fact that said joining process is effected in such a way as to connect said first (22; 32; 52; 62; 72; 82; 92) and said second (23; 33; 53; 63; 73; 83; 93) sheets in correspondence with the tips of the protrusions (27; 37; 87) of said cellular structure.

22- Method according to any of the previous claims, characterized by the fact that said joining process is selected from a group comprising brazing, normal and laser welding, and gluing with structural or semi-structural adhesives.

23- Method according to any of the previous claims, characterized by the fact that it further comprises a step of integrating a functional element (54) inside said three- dimensional cellular component (51 ), by stably connecting it to at least one of said first (52) and said second (53) sheets.

24- Method according to any of the previous claims, characterized by the fact that it further comprises a step of injecting a filling material in the spaces formed in said three- dimensional cellular component by said cellular structure between said first and said second sheets, so as to fill at least partially said spaces.

25- Method according to any of the previous claims, characterized by the fact that it further comprises a step of continuously joining the edges of said first (62; 72) and said second (63; 73) sheets at least along a portion of the perimeter (74) of said three- dimensional cellular component (61 ; 71 ).

26 - Method according to claim 25 characterized by the fact that said joining step is effected by stapling, folding one edge (64) of one sheet (62) back on that of the other sheet (63).

27 - Method according to any of the previous claims, characterized by the fact that it further comprises a step of attaching to at least one of said sheets (83), and in particular to that provided with said cellular structure, a reinforcing sheet (88) having a lesser area than the overall area of said three-dimensional cellular component (81), in such a way as to structurally reinforce said component in a circumscribed area corresponding to the area of said reinforcing sheet (88).

28 - Method according to claim 27, characterized by the fact that said reinforcing sheet is attached along a perimeter edge of said three-dimensional cellular component (81 ).

29 - Three-dimensional, cellular type component (21; 31; 41; 51 ; 61; 71 ; 81; 91) comprising two metal sheets, characterized by the fact that it is produced according to the method defined by one of the previous claims.

30 - Component according to claim 29, in that it is dependant on one of the claims from 1 to 3, characterized by the fact that it is an engine bonnet (101) for a motor vehicle, wherein a first external sheet (102), substantially free of corrugations, defines the style profile of said bonnet (101), and a second internal sheet (103) provided with said cellular structure (108) is attached to the side not in view of said first external sheet (102).

31 - Engine bonnet according to claim 30, characterized by the fact that the external style sheet has a thickness greater than that of said internal sheet provided with said cellular structure.

32 - Engine bonnet according to claim 30 or 31 , characterized by the fact that the external style sheet has a thickness of between 0.3 and 1.5 mm, and the internal sheet provided with said cellular structure has a thickness of between 0.1 and 0.5 mm, with said cellular structure having a height of between 2 and 15 mm.

33 - Engine bonnet according to claim 32, characterized by the fact that the external style sheet has a thickness of approximately 0.5 mm, and the internal sheet provided with said cellular structure has a thickness of approximately 0.3 mm, with said cellular structure having a height of approximately 5 mm, so that said engine bonnet assumes a total height of approximately 5.5 mm.

34 - Engine bonnet according to claim 30, characterized by the fact that the protrusions of said cellular structure are truncated cone shape, wherein each of said protrusions has a bottom diameter of approximately 25 mm, and a top diameter of approximately 10 mm, and wherein furthermore said protrusions are spaced apart according to a pitch of 40 mm.

35 - Engine bonnet according to claim 30 or 31, characterized by the fact that said external sheet and said internal sheet are seamed at least partially along their perimeter.

36. - Engine bonnet (101) according to claim 30, characterized by the fact that said second internal sheet (103) provided with said cellular structure (108) is made using a tailored blank type sheet consisting of a plurality of portions (104, 106, 107) of differing thickness.

37. Engine bonnet (101) for a car according to claim 36, characterized by the fact that said second internal sheet (103) consists of a front portion (104) and a rear portion (106), arranged respectively in the area where said bonnet is fastened and in the area where said bonnet is hinged to the body of said car, and an intermediate portion (107), arranged between said front portion and said rear portion and extending longitudinally along the central part of said bonnet, wherein said intermediate portion (107) is of lesser thickness than the other two portions (104, 106) and has a shape, obtained by pressing, such as to define said cellular structure (108), and wherein the other two portions (104, 106), front and rear, have respective shapes not comparable to said cellular structure.

38. Engine bonnet (101 ) according to claim 37, characterized by the fact that, in said internal sheet (103), said front portion (104) and said rear portion (106) have a thickness (S10) of between 0.5 and 0.7 mm, and said intermediate portion (107) has a thickness (S11) approximately of 0.3 mm, and in that said external sheet (102) has a thickness approximately of 0.5 mm, whereas the cellular structure (108) defined by said intermediate portion (107) has a global height (H10) of approximately 5 mm.

39 - Component according to claim 29, in that it is dependant on one of the claims from 1 to 3, or on one of the claims 6 or 7, characterized by the fact that it is a floor for a motor vehicle.

40 - Floor for a motor vehicle according to claim 39, characterized by the fact that each of the two sheets comprising said floor has a thickness of approximately 0.5 mm, and is provided with a cellular structure having a height of approximately 5.5 mm, so that the floor thus composed assumes a total height of approximately 11 mm; that the protrusions of said cellular structure are truncated cone shape and each has a bottom diameter of approximately 25 mm, a top diameter of 10 mm; and that said protrusions are spaced apart according to a pitch of 40 mm.