EP1192016B1 - Method for assembling at least two component metal elements for producing a structure - Google Patents

Abstract

The invention concerns a method for assembling at least two simple sheet metal elements (1, 2, 3,; 11, 12, 21, 21', 22, 22') for producing a structural part with open section, preferably U-shaped, or closed section, at least one of the metal elements having a high or very high yield strength and low deformability. The invention is characterised in that the metal elements are formed by at least a folding process; the metal elements are arranged relative to each other along a junction section; the metal elements are assembled by a crimped lap-joint (4) along the junction section of said elements.

Description

Subject of the invention

The present invention relates to a method of assembling at least two metallic elements in order to create a structure, at least one of the two elements with a very high yield strength and its application to realize (beam) structures of complex form from simple elements, not requiring no significant deformations.

Technological background and state of the art

In the field of mechanical engineering and in particular of the automobile, the objective is to significantly reduce the weight of structures by using as little metal as possible. These structures, the chassis of motor vehicle for example are obtained by often complex parts assembled by stamping.

In order to reduce the thickness of the metal used to build these structures while retaining their mechanical properties, steels must be used with high mechanical characteristics. of the grades of low alloy carbon steels with high mechanical characteristics, but often associated to a capacity for shaping by deformation very limited, are available today.

• aciers doux : LE < 250 MPa ;
• aciers à haute limite d'élasticité (HLE) : 250 MPa < LE < 600 MPa ;
• aciers à très haute limite d'élasticité (THLE) : 600 MPa < LE < 1000 MPa ;
• aciers à ultra-haute limite d'élasticité (UHLE) : 1000 MPa < LE < 1500 MPa.

To fix the ideas, we will make the distinction, in the following description, between these steels on the basis of their elastic limit (LE):

• mild steels: LE <250 MPa;
• high yield strength steels (HLE): 250 MPa <LE <600 MPa;
• steels with very high yield strength (THLE): 600 MPa <LE <1000 MPa;
• ultra-high yield strength steels (UHLE): 1000 MPa <LE <1500 MPa.

Typically, the steels affected by this patent application, have a yield strength located between 400 and 1500 MPa. These steels are produced by mass steel processes known per se, which allow to offer steels whose cost price is close to that of conventional carbon steels. The interest then lies in the fact that one can obtain significant reduction in structure. However, due to their low formatting capacity and sometimes poor weldability, these steels pose specific implementation problems, and in particular assembly.

More specifically, the elements constitutive of the same structure often have complex shapes obtained by stamping processes involving significant deformations and therefore incompatible with poor formatting capabilities of these steels.

The mechanical hem crimping process or the like is well known, for example for assembly items such as ladders, in metal carpentry. Thus, document US-A-4 356 888 describes a seal structural of two elements, preferably made of malleable and deformable metal, such as aluminum. according to a particular form of execution, the first element has an elongated tongue and a short tongue. These two tabs define a cavity capable of receiving the second element at the level of a curved leg on a support such as a wire. When the two elements are pressed together, using a suitable tool, the tabs and the tab deform and interpenetrate. The elongated tongue forms at least partially a circular loop around the tab, then making any subsequent loosening impossible.

Document US-A-3 854 185 proposes, in the same area of application, a process for forming a joint structural between two rigid elements, one presenting on one side a flange with one projecting end and the other an essentially circular groove. By applying the two pieces with enough force one against the other, the flange enters the throat while deforming. More precisely, the assembly is done by joining of the flange with the groove, the flange forming a winding in said throat.

Document DE-C-385 642 proposes a machine for the assembly by crimping of two sheet metal elements to form a hollow body.

Document FR-A-2 321 962 proposes a process assembly by crimping a zinc element and a lead element to solve problems in the field of building cover.

Aims of the invention

The present invention aims to provide a method of assembling at least two metallic elements or component parts of which at least one of the two is made of steel with a very high limit of elasticity associated with a weak capacity of setting shape in order to make shaped structural parts complex, from simpler parts achievable at using formatting operations basically of folding type, not involving significant deformations in the plane of the sheet, and therefore compatible with steels with high mechanical characteristics.

Indeed, within an alloy family given, for example steels, or alloys aluminum, the higher the elastic limit, the more ductility is reduced. The yield strength level associated with this low formatting capacity depends on the alloy family considered; so for steels this limit can be located from 600 to 800 MPa depending on the nuance considered. Beyond this limit, steels do not can be very difficult to be shaped by stamping: deformations in the plane of the sheet in wide or expanding traction will quickly lead to breaking. The elastic return also makes it very difficult to respect the geometry of the part. Through against these steels keep a capacity of deformation by folding. However, the bending limit radius is several times the thickness, the assembly by crimping is practically impossible.

However, these steels have potential interesting improvement of metallic structures and in particular of automobile structures. They allow to reduce weight for equal performance or improve performance at equal weight.

It is therefore crucial to be able to carry out parts of complex shapes from these metals to high mechanical properties, which is the subject of the present invention.

Main characteristic features of the invention

• les éléments métalliques sont mis en forme par au moins un procédé de pliage ;
• les éléments métalliques sont disposés l'un par rapport à l'autre suivant une section de jonction ;
• les éléments métalliques sont assemblés par sertissage par ourlet (4) le long de la section de jonction desdits éléments.

The present invention relates to a method of assembling at least two simple metal elements in sheet form, in order to create a structural part of open section, preferably in the shape of a "U", or closed, at least one of said metallic elements having a high or very high elastic limit LE greater than 250 MPa and a low deformation capacity, characterized in that:

• the metal elements are shaped by at least one folding process;
• the metal elements are arranged relative to each other along a joining section;
• the metal elements are assembled by hemming (4) along the joining section of said elements.

At least one of the elements is made of preferably in steel with yield strength greater than 400 MPa or in an aluminum alloy with a yield strength greater than 200 MPa.

Advantageously, the ratio of the radius of the hem to the sum of the thicknesses of the different elements that we want to assemble along the junction section is between 2 and 10.

In addition, the ratio of the difference between the radius of hem and outermost metal thickness with the innermost metal thickness is, advantageously greater than 2.

The nature or thickness of the different elements may not be the same for all elements.

The process is also characterized by the fact that the junction is not necessarily straight but may have local curvature, the radius of curvature preferably being greater than five radii hem exteriors.

The assembly method according to the invention is further characterized by the fact that after the operation of hem crimping, blocking said hem vis-à-vis the sliding of its elements along the section of junction, is obtained by gluing, indentation or nesting.

The present invention also relates to the product obtained by the assembly process described above, which is defined in claim 9.

In a first preferred form of the invention, the product is in the form of a double-core "I" beam, obtained by assembling four components connected by four hems the along the junction section of the four elements taken two by two.

In a second preferred form of the invention, the product results from the assembly of two elements by two hems so as to form a section closed, at least one of the two elements having a "U" section.

The process of the invention therefore allows to obtain structural parts of complex shape to from sheet metal materials presenting, on the one hand, a high to very high elastic limit, and on the other hand, a limited forming capacity. This last is not binding at the level of operations preparatory to the assembly process, such as the folding, involving little deformation in the plane of the sheet. This process thus makes it possible to obtain pieces of geometry equivalent to that obtained by stamping. Of plus, hem assembly is compatible with low formability of these steels, the working radius being several times the thickness, which is not the case for Simple crimping for example.

Another advantage of the invention lies in the fact that the assembly process or crimping by purely mechanical hem allows you to get rid of possible weldability problems of high steels mechanical characteristics.

An additional advantage of the invention is to propose a process for the production of pieces of reinforced structure, especially in industry automobile.

Finally, the method of the invention, which uses a simple press for assembly is a good process market.

Brief description of the drawings

Figures 1 describe a structure carried out in a conventional manner having a geometry in "U".

Figures 2 show the elements simple constituents in order to create the same kind of structure as that shown in FIGS. 1 according to the assembly method of the present invention.

Figures 3 show a tool allowing the realization of a structure as described in Figure 2.

Figure 4 shows variants assembly orientation for a U-shaped structure.

Figures 5 show a shape more complex execution of a structure with a closed section obtained by the assembly process of the present invention.

Figure 6 shows the tool used to make a closed structure as shown in Figures 5.

Figure 7 shows another form execution of a structure having the form of a double-core "I" beam.

Figure 8 shows the tool for realization and assembly of an "I" beam with core double.

FIG. 9 represents a part of the type shield crosspiece.

FIG. 10 represents a part of the type middle foot.

Figure 11 represents a part presenting tabs at the ends to facilitate assembly.

Figures 12 illustrate the principle of blocking of the relative sliding of the core with respect to the sole in hem assembly, by interlocking using a cut of alternating slots. Figures 12a and 12b present the two sheets just before production hem.

Detailed description of several embodiments of the invention

The idea behind the invention is to decompose a structure element of complex shape, usually achieved by shaping operations by stamping not very compatible with high steels mechanical characteristics, in simple sub-elements, performed using folding type forming operations, and hemmed together.

The present invention will be described in more detail details using the attached figures.

Figure 1 shows the usual mode of production of a "U" shaped part. classically this type of part is obtained by stamping from a flat sheet as shown schematically in Figure la. As part steels with very high yield strength, stamping of such a room poses severe problems of control of the elastic return: the shape obtained deviates appreciably of the ideal shape as shown in Figure 1b. of the critical problems due to low formability of this type occur, for example when the height of the "U" section varies significantly as shown in figure 1c or when the height of the section remains constant, the curvature of the "U" beam varies locally so sensitive (Figure 1d).

The principle according to the present invention proposed to make this type of part is illustrated in figures 2. The part is broken down into simple elements, the sides 1 and 2, the bottom 3 which are joined by a hem 4.

Parts 1, 2 and 3 can be obtained by folding or lifting the edge. These bet techniques in shape only involve small deformations in the sheet plane and are compatible with steels with very high yield strength with low capacity forming.

Figure 3 shows a typical tool allowing the realization of this type of part using of a press. The side elements 1 or 2 and the bottom 3 are prepared for hemming as shown in 5. These parts produced using press operations are presented in the tool described in Figure 3.

The left half-view shows the closed tool, before the hem, the right half view presents the tool when the hem is finished. Elements 7, 7 'and 9 are supported on the upper slide of the press by means of springs not shown and whose crushing stroke is greater than the stroke of tools 8, 8 'forming the hem. In the situation presented in FIG. 3, the springs are compressed and press, by through parts 7 and 9, parts 1, 2 and 3 against part 10 which follows their shape and rests on the press table. When the press slide ends its course, the element 8 'which is directly to it bound forms the hem as shown on the right side of Figure 3.

Parts 1, 2 and 3 are not necessarily all high-limit steel elasticity: for example, depending on the function of the part, only part 3 can be made of very high limit steel of elasticity, steel parts 1 and 2 having a better formability and better weldability, making it easy to assemble the part to the rest of the structure with assembly processes such as spot welding. The process allows also to adapt thicknesses to requirements structural parts: the three parts 1, 2 and 3 may have different thicknesses, the process hem assembly accepting thicknesses significantly different, with a ratio greater than of them.

Variations of hemming orientation are shown in Figure 4.

The method also makes it possible to carry out closed sections as shown in Figure 5. According to the FIG. 5, the part 11 can be obtained by simple folding, a variation of the closed section being obtained by varying the height of the folded edges. Exhibit 12 which closes the section is even simpler in shape. As a variant of in this case, the part 11 can also be produced by deep drawing of steel with lower yield strength, less than 400 MPa for example, part 12 being in very high yield strength steel and playing the role of reinforcement.

A typical tool allowing to realize this type of part is presented in figure 6. The principle is close to that described in FIG. 3. Elements 14, 14 'and 15 are supported on the upper slide of the press by means of springs not shown.

Element 15 holds parts 10 and 11 against the 17-17 'element which rests on the lower table of the press.

In the left part of the figure, the situation before hem formation is shown: the press slide brought elements 14 and 15 into contact, the springs being slightly compressed. The view of right presents the situation at the end of the formation of the hem: the press slide continued to run and the element 16 ', which is directly connected to it, has formed hem.

Another possible embodiment of closed structure is based on the assembly of parts by four hems. A typical section corresponding to this application is shown in Figure 7. Parts 22, 22 'are assembled by hem with the parts 21 and 21'.

Figure 8 presents a tool allowing hem this section to the hurry. Exhibits 21 and 22 are prepared for the hem formation as shown in 23: they received a preform which initiates the hem. The pieces are then placed in the tooling which is composed of the elements mobile 20 and 20 ', 19 and 19'. These elements are first apart, horizontally for 20 and 20 ', vertically for 19 and 19 '. The pieces 21 and 21 'are deposited on 19 and 19' respectively and maintained by means not shown, a magnetic system for example. Likewise, parts 22 and 22 'are deposited on elements 20 and 20 'and maintained in the same way. All type 18 tools (18 ', 18 '', 18 '') are then in the position indicated for the tool 18. The tools 18 are then moved, successively or simultaneously to form the hem and find in the position indicated by 18 ', 18' ', 18' ''. This type of tool can be mounted on a press, elements 19, 18 and 18 'being implemented by the slide upper of the press: 19 is mounted on springs and its stroke is limited by a stop not shown. The element 19 'rests on the press table and is therefore fixed, the 18 '' and 18 '' tools being activated by the slide bottom of the press. This type of assembly method by press tool makes it possible to produce shapes whose section is not constant: the distance between the pieces 21 and 21 'as well as the distance between parts 22 and 22' may vary.

Potential applications concern different types of automotive structural parts like cockpit reinforcement parts (shield cross member), feet midpoints, spar elements, engine cradle. Some of these applications are illustrated in FIGS. 8 to 10.

The technique allows for complex shaped structures with steels having a very low ductility taking advantage of the productivity of the hem assembly process and the reinforcement it brings to the structure. It also helps to spare at the ends of the pieces of the metal tabs making it easy to assemble these parts to the rest of the automotive structure (Figure 11).

The hem assembly guarantees a very good keeping metals in the plane perpendicular to the axis of hem. However, there is a significant risk of sliding of the assembled elements in the axis of the hem or at least in the longitudinal direction, if the hem is not not straight. We can easily remedy this disadvantage, for example by interposing an adhesive between the two sheets of metal at the hem, in performing local fusion welds or preferably by locally crushing the hem with a press comprising for example a punch in the shape of "V" terminated by a rounding and a flat anvil. This operation can be carried out with the press very productive: a tool can be designed to achieve simultaneously the indentations, the indentation step being on the order of 5 to 10 times the outside diameter of hem.

You can also make cuts serrated alternating in the two sheets of metal, in the area to be hemmed together, so as to guarantee longitudinal locking (Figures 12). These cuts are practiced during the manufacturing steps in the press of these parts. The teeth 20 have a lower height around the hem, for example a third of this circumference. The width of the teeth 20 is slightly less than that of the intervals 21 between the teeth. then of joining the two sheets of metal by hem, the sheet metal teeth closest to the axis of the hem fit into the space between the teeth of the exterior metal sheet thereby blocking along the axis of the hem.

Claims (13)

1. Process for assembling at least two simple sheet metal parts (1, 2, 3; 11, 12; 21, 21', 22, 22') in order to create a structural component of open cross section, which is preferably U-shaped, or of closed cross section, at least one of said metal parts having a high or very high elastic limit (EL of more than 250 MPa) and low deformability, characterised in that:

   the metal parts are formed by at least one bending process;

   the metal parts are arranged relative to each other in a junction section;

   the metal parts are assembled by crimping at the hem (4) along the junction section of said parts.
2. Assembly process according to Claim 1, characterised in that at least one of the parts is made of steel and has an elastic limit of more than 400 MPa.
3. Assembly process according to Claim 1, characterised in that at least one of the parts is made of aluminium alloy and has an elastic limit of more than 200 MPa.
4. Assembly process according to any one of Claims 1 to 3, characterised in that the ratio of the radius of the hem (4) to the sum of the thicknesses of the various parts one wishes to assemble along the junction section is between 2 and 10.
5. Assembly process according to any one of Claims 1 to 3, characterised in that the ratio of the difference between the radius of the hem (4) and the thickness of the outermost metal with the thickness of the innermost metal is more than 2.
6. Assembly process according to any one of the preceding claims, characterised in that the nature or the thickness of the various parts is not identical for all.
7. Assembly process according to any one of the preceding claims, characterised in that the junction is not rectilinear and has a local curvature, the radius of which is more than at least five times the external radius of the hem (4).
8. Assembly process according to any one of the preceding claims, characterised in that, after said hem crimping, a blocking of said hem with respect to the sliding of the assembled parts along the junction section is achieved by bonding, indentation or imbrication.
9. Product obtained by the assembly process described in any one of the preceding claims, characterised in that it has at least two simple sheet metal parts (1, 2, 3; 11, 12; 21, 21', 22, 22') in order to create a structural component of open cross section, which is preferably U-shaped, or of closed cross section, at least one of said metal part having a high or very high elastic limit (EL of more than 250 MPa) and low deformability, characterised in that the metal parts, which have been formed by at least one bending process and arranged relative to each other in a junction section, are assembled by means of a hem (4) along said junction section, said hem mechanically reinforcing the structure.
10. Product according to Claim 9, characterised in that the ratio of the radius of the hem (4) to the sum of the thicknesses of the various parts that are assembled along the junction section is between 2 and 10.
11. Product according to Claim 9 or 10, characterised in that the ratio of the difference between the radius of the hem (4) and the thickness of the outermost metal with the thickness of the innermost metal is more than 2.
12. Product according to any one of Claims 9 to 11, characterised in that it is in the form of a two-web I-shaped girder obtained by assembling four constituent parts (21, 21', 22, 22') connected by means of four hems (4) along the junction section of the four parts taken in pairs.
13. Product according to any one of Claims 9 to 11, characterised in that it results from the assembly of two parts (11, 12) by means of two hems (4) so as to form a closed cross section, at least one of the two parts having a U-shaped cross section.

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