ITTO970924A1 - METHOD FOR THE MANUFACTURE OF LIGHT STRUCTURAL ELEMENTS IN METALLIC SHEET WITH INTEGRATED STRENGTH CELLULAR CORE AND RELATIVE STRUCTURAL ELEMENTS. - Google Patents

Description

Description of the industrial invention entitled:

"Method for manufacturing lightweight structural elements in sheet metal with integrated stiffening cell core and related structural elements",

TEXT OF THE DESCRIPTION

Technological area of the invention - The method according to the invention can be used for the manufacture of mechanical parts with structural functions, having a high degree of torsional and fissional rigidity coupled with a low weight, made from metal sheets.

Technical assumptions - Mechanical parts are known which have the. characteristics described above, typically made by casting or hammering in light metal alloys, for example, but not limited to, aluminum alloys.

However, the parts thus made are expensive, both for the intrinsic cost of the materials and for that of the production process; the latter, then, also has problems of an ecological nature that are difficult to solve.

Mechanical parts are also known which have the characteristics described above, typically made by using semi-finished products consisting of sheets or stratified panels of the cellular sandwich type in metal alloys, for example thin honeycomb metal sheets or cellular sandwich sheets of the type described in Italian Patent Application N ° T096A000696 and in the corresponding International Patent Applications N ° PCT / IT97 / 000164 and N ° PCT / IT97 / 000165, both owned by the applicant; these semi-finished products, however, have limitations in their workability which prevent their use to create complex shapes or particular applications.

Therefore, the problem of manufacturing mechanical parts with structural functions, without limitations of shape and application, having a high degree of torsional and flexural rigidity coupled with a low weight, with low cost materials and through a simple, economical and of reduced environmental impact.

Summary of the invention - The purpose of the present invention is to define a method for manufacturing lightweight structural elements, even of complex three-dimensional shapes, in sheet metal with integrated stiffening cell core, using low cost materials, for example, but not only, steel sheets, and economic and non-polluting manufacturing processes such as, for example, press molding and laser welding.

The method consists in combining an external boxed element formed by two half-shells of sheet metal suitably shaped according to a perimeter, with an internal cellular core consisting of a three-dimensional corrugated structure of suitable shape and size, all made integral by welding the two half-shells together. along the perimeter and by welding the tops of the ridges and depressions of the internal cell core with respect to the two half-shells. ".

To give further rigidity to the structural element without significantly increasing its weight, it is also possible to fill the area inside the boxed element with material, typically resin, rigid with low density or foam.

Another purpose of the invention is to define light structural elements, including complex three-dimensional shapes, in metal sheet with integrated stiffening cell core, obtained by the manufacturing method previously described.

. The aforesaid objects are achieved by means of a method for manufacturing lightweight structural elements in metal sheet with integrated stiffening cellular core and the related structural elements, characterized as defined in the main claims.

These and other objects, characteristics and advantages of the invention will become evident on the basis of the following description of a preferred embodiment thereof, given by way of non-limiting example, with reference to the attached drawings.

LIST OF FIGURES

Fig. 1 - Schematically represents a sectional view of the pair of half-shells making up the box of the structural element according to the invention.

Fig. 2- Schematically represents a sectional view of the structural element according to a first embodiment of the invention.

Fig. 3- It schematically represents a sectional view of the structural element according to a variant of the first embodiment of the invention, in which the element is obtained from a semi-finished product of cellular sandwich metal sheet.

Fig. 4- Schematically represents a sectional view of the structural element according to the invention in the case where it includes a functional element.

Fig. 5- Schematically represents a sectional view of the structural element according to the invention in the case in which the two half-shells have an inconsistent thickness.

Fig. 6- Schematically represents a sectional view of the structural element according to the invention in the case where the cell core is composed of two sheets.

Fig. 7- Schematically represents a sectional view of the structural element according to the invention in the case in which the cells of the cell core have an inconsistent height.

Fig. 8- Schematically represents a sectional view of the structural element according to the invention in the case in which the cells of the cell core are obtained by hydroforming.

Fig. 9- Schematically represents a sectional view of the structural element according to a second embodiment of the invention, in which the two half-shells are made up of cellular sandwich sheets.

Fig. 10- Schematically represents a partial sectional view of the structural element according to the second embodiment of the invention, in the case in which the two half-shells are micro-drawn.

Fig. 11- Schematically represents a partial sectional view of the structural element according to the second embodiment of the invention in the case in which the cell core is also micro-drawn. Fig. 12- Schematically represents a sectional view of the structural element according to a third embodiment of the invention.

Fig. 13-. It schematically represents a partial sectional view of the structural element according to a variant of the third embodiment of the invention.

DESCRIPTION OF THE PREFERRED FORM

The method for manufacturing lightweight structural elements in sheet metal with cellular core with integrated stiffening according to a first embodiment of the invention will be described below, for the sake of simplicity, with reference to a substantially flat element or element with reduced curvature and shape in plan delimited by a continuous perimeter, within said perimeter, possibly but not necessarily, there may be one or more openings or holes, this in no case representing a limitation of the invention, as will become clear later.

A first step of the method consists in the manufacture of a box 10 consisting of two half-shells, an upper half-shell 11 and a lower half-shell 12, of compact metal sheet having a first thickness Si, of which a cross section is shown in Fig. 1. The sections of the two half-shells 11, 12 have specular shapes with each other and comprise an area 13, respectively 13 ', substantially flat and connected along its entire perimeter to a wall 14 substantially arranged at right angles with respect to the flat areas 13, 13' ; the wall 14 ends with an edge 15 in turn arranged substantially at right angles to the wall 14.

In the case of small and medium-sized structural elements, the two half-shells 11, 12 are obtained, for example, by molding with mechanical presses known per se; in the case of large dimensions, they are preferably obtained by rolling machines, also known in themselves.

A second step of the method consists in the manufacture of an internal element or cellular core 16 (see Fig. 2), obtained from a compact sheet having a second thickness S2, forming by plastic deformation on its surface a multiplicity of three-dimensional cells having reliefs 17 and depressions 18.

The cell core 16, for example, has a multiplicity of three-dimensional cells of small dimensions, with a total height h between 0.1 and 5 mm, preferably between 0.5 and 3 mm, distributed in a plane with a constant pitch p according to two directions substantially perpendicular to each other such that the ratio w / h between the pitch and the total height is equal to or greater than 1, preferably equal to or greater than 2, according to what is described in the Italian Patent Application N ° T096A000696 and in the corresponding International Patent Application N ° PCT / IT97 / 000165, previously cited, to which reference should be made for a more complete illustration of the characteristics.

According to another example, the cell core 16 has a multiplicity of three-dimensional cells with a total height h between 0.1 and 60 mm, preferably between 0.5 and 50 mm, distributed in a plane with a constant pitch p in two directions between of them substantially perpendicular such that the ratio w / h between the step and the total height is equal to or greater than 1, preferably equal to or greater than 2, as described in the International Patent Application No. PCT / IT97 / 000164, previously cited, to which reference should also be made for a more complete illustration of the characteristics.

The overall surface of the cellular core 16 has a substantially flat shape or with reduced curvature, corresponding exactly to the shape of the areas 13, 13 'of the half-shells 11, 12, and is contoured, by means of a per se known contouring process, so as to fit exactly inside the perimeter of the two half-shells 11, 12, placing themselves with the reliefs 17 and the depressions 18 in contact with the areas 13, 13 'respectively of the upper half-shell 11 and lower 12, being at the same time the edges 15 of the half-shells 11, 12 in contact with each other.

A third step of the method consists in joining and making rigidly and permanently integral with each other the upper half-shell 11, the lower half-shell 12 and the cell core 16 inside the two half-shells 11, 12, by means of a joining process , for example welding, in particular continuous laser welding, of the edges 15 to each other, and welding, for example laser spot welding, of the projections 17 of the cell core 16 with the area 13 of the upper half-shell 11 and of the depressions 18 of the cellular core 16 with the region 13 'of the lower half-shell 12; during the joining operation, the correct contact between the elements to be joined is ensured by appropriate locking jigs equipped with mechanical elastic systems or oleopneumatic pressers, known in the art.

Of course, it is possible to make changes to the invention described above, without thereby departing from its scope.

For example, a modification of the method of the invention is possible, particularly useful in the case in which the structural element has a substantially flat shape or with a slight curvature, consisting in making the structural element starting from a semi-finished product represented by a sandwich sheet. cell with cells of suitable total height h and appropriate pitch p, described in the International Patent Applications N ° PCT / IT97 / 000164 and N ° PCT / IT97 / 000165, previously cited, (see Fig 3) in which the second and third phase of the method are already implemented, since the two half-shells 11, 12 are already aggregated with the cellular core 16, and the first phase of manufacturing the rigid box is substantially carried out by carrying out an impact deep drawing along the perimeter of the element to create the edges 15 subsequently welded, for example by continuous laser welding.

A further modification of the method of the invention, useful in the case in which the structural element has a complex three-dimensional shape, consists, for example, in carrying out on the cellular core 16, in addition and superimposed on the forming of the multiplicity of three-dimensional cells of small dimensions having the reliefs 17 and depressions 18, a forming on a larger scale, corresponding to the same complex three-dimensional shape assumed by the union of the two half-shells 11, 12 along the edge 15. Said forming on a larger scale is obtained by means of a process of forming with a mechanical mold known per se, or, alternatively, by means of a hydroforming process, also known in the art.

For forms of particular complexity (for example, with accentuated bending or drawing radii), a further modification of the method of the invention consists in carrying out, as the first operation after the contouring, using a compact flat sheet as a semi-finished product, the forming on a larger scale , again by means of a forming process with a mechanical mold, or, alternatively, by means of a hydroforming process; and subsequently forming the plurality of smaller three-dimensional cells having the reliefs 17 and depressions 18 on the already formed sheet at a larger scale, again by means of a forming process with a mechanical mold, or, alternatively, by means of a hydroforming process.

Among the examples of complex three-dimensional shapes to which it is possible to apply the method modifications previously described, in particular, it is possible to cite as examples both tubes of any section (circular, elliptical, rectangular, etc.), and closed or open profiles.

Or it is possible to apply the method of the invention also in the case in which the two half-shells 11, 12 are given a shape capable of containing within itself not only the cellular core 16, but also a functional component, meaning by this term to indicate generically a component by which the structural element of the invention can functionally cooperate with another element; in Fig. 4 said functional component is represented by way of example by a bushing 20 made integral with the two half-shells 11, 12 by welding or other joining process known in the art, but other examples are pins, hubs, shafts, bearings, etc.

It is also possible to make another modification to the method of the invention, consisting in using the two half-shells 11, 12 in which the first thickness YES is not constant, but one or both of the two half-shells 11, 12 have zones 22, respectively 23 (see Fig. 5), having a different thickness, for example greater as in the figure, than the other zones; said areas 22, 23 of greater thickness can be obtained, for example, by superimposing in a suitable position, both externally as shown in the figure, and internally, a compact sheet of a specific shape having a third thickness S3 and making it integral with the sheet of thickness s1 of the two half-shells 11, 12 by continuous laser welding 0 by 0 points by brazing, so as to create areas of different stiffness.

A further modification of the method of the invention consists in the use of a cellular core 16 consisting of a simple corrugated sheet, with only unidirectional corrugations, of the type known in the art; or even in the use of a cellular core 16 consisting of more than one sheet, for example two as in Fig. 6, an upper corrugated sheet 24 and a lower corrugated sheet 25 joined together stiffly by laser spot welding or by brazing; or even in the use of a cellular core 16 consisting of a compact sheet metal in which discrete reliefs are obtained, for example by drawing, which project in a substantially perpendicular direction with respect to a first face and alternatively with respect to a second face, opposite on the first face, of the sheet itself, the shape of said reliefs being preferably, but not exclusively, of the spherical cap, truncated cone or truncated pyramid type.

Another modification to the method of the invention still consists in using a cell core 16 in which the total height h of the multiplicity of cells constituting the three-dimensional forming of small dimensions is not constant, but is variable from area to area for make the cell core 16 itself coherent with the two half-shells 11, 12 constituting the box 10, as shown in Fig. 7, in which the total height h varies from a minimum value hm to a maximum value hM depending on the analogue variation of the distance between the two half-shells 11, 12.

Still, a further modification of the method of the invention consists in using a cellular core 16 consisting of a multiplicity of three-dimensional "hollow elements 26 (see Fig. 8) obtained with the hydroforming technique, known per se, starting from a pair of compact flat sheets 27, 28 welded together at points 29; the shape of the hollow elements 26 can be any of those obtainable with the hydroforming technique: in the example shown in Fig. 8, the hollow elements 26 have a substantially circular section of diameter d.

A second embodiment of the method for manufacturing light structural elements in sheet metal with integrated stiffening cellular core according to the invention will now be illustrated, capable of giving the elements themselves a higher lightness with the same flexural and torsional rigidity.

According to this second embodiment, the method comprises a first step consisting in the manufacture of a box 60 (see Fig. 9) consisting of two half-shells, an upper half-shell 61 and a lower half-shell 62, of bendable cellular sandwich metal sheet and drawing having an overall thickness sc, of which a cross section is shown in Fig. 9.

A second step of the method consists in the manufacture of the internal element or cellular core 16, and is substantially identical to the second step of the method described as the first embodiment of the invention.

A third step of the method consists in making the upper half-shell 61, the lower half-shell 62 and the cell core 16 rigidly and permanently integral with each other by continuous laser welding of the edges 65 to each other, after having been impacted. compressing the space inside the cellular sandwich sheets; and by laser spot welding of the projections 17 of the cell core 16 with the lower outer face 63 of the upper half shell 61, and of the depressions 18 of the cell core 16 with the upper outer face 64 of the lower half shell 62. During the operation correct contact between the elements to be welded is ensured by suitable locking jigs equipped with mechanical elastic systems or with oleo-pneumatic pressers, known in the art.

Of course, it is possible to make changes to this second embodiment of the invention described above, without thereby departing from the scope of the same.

In addition to all the modifications previously described and illustrated with reference to the first embodiment of the invention, which apply substantially also to this second embodiment of the invention, it is possible to make a further specific modification consisting in preceding the laser welding between the reliefs 17 and the depressions 18 of the cell core 16 and, respectively, the half-shells 61, 62, provided in the third phase of the method according to this second embodiment, by a micro-drawing operation of the cellular sandwich sheet constituting the two half-shells 61, 62 in correspondence only with the contact points 66 (see Fig. 10) between the reliefs 17 and the depressions 18 of the cell core 16 and, respectively, the half-shells 61, 62, by means of which the cellular sandwich sheet of the upper half-shell 61 is compacted towards the lower outer face 63 and the cellular sandwich sheet of the lower half-shell 62 is compacted towards the upper outer face 64, thus allowing the creation of stronger welding points.

A further modification of the method of the invention, useful for improving the aesthetic appearance of the finished structural element, consists in introducing a variant to this latter operation of micro-drawing, illustrated in Fig. 11, consisting in the fact that, while nothing changes for the contact points 66 of the lower half-shell 62, the micro-drawing of the superine half-shell 61 is performed by compacting the cellular sandwich sheet towards its upper external face 67 at the contact points 68 between the reliefs 17 of the cellular core 16 , in turn homologously drawn substantially with the same shape, to make the contact between the different sheets in the points 68 themselves more reliable and therefore the subsequent welding.

A third embodiment of the method for manufacturing light structural elements in sheet metal with integrated stiffening cellular core according to the invention, capable of giving the elements themselves a higher torsional rigidity, will now be illustrated.

According to this third embodiment, the method comprises, in addition to the three steps described above with reference to both the first and the second embodiment, a fourth step consisting in filling the empty space 19 (see Fig. 12) comprised between upper half-shell 11 and lower half-shell 12 by injecting a synthetic resin through suitable openings (not shown in the figure) made in one or both of the two half-shells 11, 12; the filling can be suitably facilitated, as is known in the art, by the simultaneous application of a pneumatic suction to evacuate the air present in the space 19.

Said synthetic resin is preferably a rigid thermoplastic resin, whose stiffness characteristics are increased by the presence of suitable mineral fillers and / or glass fibers; or a thermosetting resin, or even a rigid foam resin, all synthetic resins widely known to those skilled in the art.

Of course, it is also possible to make changes to this third embodiment of the invention described above, without thereby departing from the scope of the same; for example, if the two half-shells 61, 62 are made of cellular sandwich sheet, it is also possible to fill the empty spaces 69, included inside the upper half-shell 61, and / or 70, included inside the half-shell lower 62 (see Fig. 13), by injecting a synthetic resin through suitable openings (not shown in the figure) obtained in the two half-shells 61, 62, to give the finished structural element greater torsional rigidity.

In short, without prejudice to the principle of the present invention, the construction details and the embodiments may be widely varied with respect to what is described and illustrated, without thereby departing from the scope of the invention itself.

Claims (35)

CLAIMS 1. Method for manufacturing lightweight structural elements characterized in that it includes the following steps: manufacturing a boxed metal sheet comprising a first upper half-shell and a second lower half-shell, said box having a first perimeter and enclosing a first space inside, and said sheet having a determined thickness; fabricating a cellular core in metal sheet having a surface and a second perimeter, said surface having a plurality of three-dimensional cells having raised and depressions formed by a forming process, and said second perimeter being substantially equal to said first perimeter, making rigidly and permanently integral by means of a process of joining said cellular core inside said box with said first upper half-shell and with said second lower half-shell, and said first upper half-shell with said second lower half-shell. 2. Method according to claim 1, characterized in that it further comprises the step of filling said first space by injection of a rigid synthetic resin. 3. Method according to claim 1, characterized in that said first space inside said box is adapted to receive a functional component in addition to said cellular core. 4. Method according to claim 3, characterized in that said functional component is selected from the group consisting of bushings, pins, shafts, hubs and bearings. 5. Method according to claim 1, characterized in that said surface of said cellular core is a substantially flat surface. 6. Method according to claim 1, characterized in that said surface of said cellular core is a complex three-dimensional surface. 7. Method according to claim 6, characterized in that said complex three-dimensional surface is selected from the group consisting of open sections, closed sections and tubes. 8. Method according to claim 1, wherein said ridges and depressions have a total height h, characterized in that said total height h has a value comprised between 0.1 and 60 mm. Method according to claim 8, wherein said ridges and depressions have a total height h, characterized in that said total height h has a value comprised between 0.1 and 5 mm. 10. Method according to claim 8, characterized in that said total height h has a value comprised between 0.5 and 50 mm. 11. Method according to claim 9, characterized in that said total height h has a value comprised between 0.5 and 3 mm. Method according to claim 8, wherein said ridges and depressions have a uniform pitch p in two directions substantially perpendicular to each other, characterized in that a ratio p / h of said pitch p and said total height h is equal to or greater of 1. 13. Method according to claim 12, characterized in that a ratio p / h of said pitch p and said total height h is equal to or greater than 2. 14. Method according to claim 8, characterized in that said three-dimensional cells have a shape chosen from the group consisting of a spherical cap shape, a truncated cone shape and a truncated pyramid shape. 15. Method according to claim 1, wherein said ridges and depressions have a total height h, characterized in that said total height h has a constant value. 16. Method according to claim 1, wherein said ridges and depressions have a total height h, characterized in that said total height h has a variable value, comprised between a minimum value Hm and a maximum value hM. 17. Method according to claim 1, characterized in that said forming process comprises a drawing process. 18. Method according to claim 1, characterized in that said forming process comprises a hydroforming process. 19. Method according to claim 1, characterized in that said joining process comprises a laser welding process. 20. Method according to claim 19, characterized in that said laser welding process is of the continuous type. 21. Method according to claim 19, characterized in that said laser welding process is of the spot type. Method according to claim 1, characterized in that said joining process comprises a brazing process. 23. Method according to claim 1, characterized in that said joining process comprises a bonding process. 24. Method according to claim 1, characterized in that said determined thickness is constant. 25. Method according to claim 1, characterized in that said determined thickness is variable. 26. Method according to claim 25, characterized in that said variable thickness is obtained by means of a metal sheet of a given shape rigidly and permanently joined to at least one of said upper half-shell and said lower half-shell. Method according to any one of the preceding claims, characterized in that said metal sheet of said box is a bendable and drawable cellular sandwich sheet. Method according to claim 27, characterized in that said joining process comprises a micro-drawing process. 29. Method according to claim 28, characterized in that said micro-drawing process is carried out only on one of said first upper half-shell and said second lower half-shell. 30. Method according to claim 28, characterized in that said micro-drawing process is carried out on both said first upper half-shell and said second lower half-shell. 31. Method according to claim 29, characterized in that said micro-drawing process is also carried out on said cellular core. 32. Method according to claim 27, characterized in that said cellular sandwich sheet is filled by injection of a rigid synthetic resin. Method according to claims 2 or 32, characterized in that said rigid synthetic resin is of the type selected from the group consisting of filled thermoplastic resins, thermosetting resins and rigid foam resins. 34. Method according to claim 1, characterized in that said upper half-shell, said lower half-shell and said cellular core constitute a semi-finished product of cellular sandwich metal sheet, and said step of manufacturing a box-like structure comprises an impact drawing along said first perimeter. 35. Lightweight structural element in sheet metal with cellular core, characterized in that it is produced according to the method defined in any one of the preceding claims.