FR2793433A1 - METHOD OF ASSEMBLING BY WELDING A HOLLOW ELEMENT IN AUTOMOTIVE BODY ALUMINUM, AND HOLLOW ELEMENT ASSEMBLED ACCORDING TO THE PROCESS - Google Patents

Abstract

The invention provides a method for assembling a hollow element (10) of an aluminum automobile body which comprises a planar outer panel (12) to which an inner box (14) is assembled, which comprises a first step of positioning the edges horizontal (22) of the inner box (14) between the vertical edges (20) of the outer panel (12), a second step of folding the vertical edges (20) on the horizontal edges (22), a third step of crimping the edges (20) folded (12) around the horizontal edges (22), and a fourth step of welding the folded edges (20) on the horizontal edges (22), characterized in that, in the fourth step of welding, at least one resistance welding point is made in line with an electrode of a pair of welding electrodes (24, 25) (26) at least one of which is applied to the crimped edges (20), between which the current flows (J) welding.

Description

"Method of assembling by welding a hollow aluminum element of a motor vehicle body, and hollow element assembled according to the method" The invention relates to a hollow element of aluminum of a motor vehicle body and a method for assembling a such a hollow element.

The invention relates more particularly to a method of assembling a hollow element of an aluminum motor vehicle body which comprises an outer panel substantially in the form of a plate to which an inner lining box is assembled, of the type in which the method comprises first step during which vertical edges of a periphery of the outer panel receive with a horizontal clearance peripheral horizontal edges of the inner lining box which is precisely positioned relative to the outer panel, a second step during which the edges vertical of the outer panel are then folded horizontally over the horizontal edges of the inner lining box, a third step in which the folded edges of the outer panel are crimped around the horizontal edges of the lining box, and a fourth step during which the edges folded back from the panel outside are welded to the horizontal edges of the lining box.

Conventionally, the hollow aluminum elements of motor vehicle bodywork, and in particular the opening parts, result from the assembly of an inner lining box to an outer panel substantially in the form of a plate. The outer panel is generally formed by stamping a horizontal aluminum sheet, and thus forms a bowl which is delimited by a substantially flat and horizontal bottom and by vertical walls, resulting from the stamping, which form vertical edges of the exterior panel. The lining box has a similar shape, but it is smaller in size so that the horizontal edges of the lining box are internally complementary to a periphery of the outer panel delimited by the connection line between the bottom and the vertical edges of the panel. outside.

During assembly, the outer panel is placed horizontally on a mounting support, then the periphery of the outer panel is previously glued before the lining box is lowered vertically inside the outer panel. The edges of the outer panel are then folded and crimped onto the edges of the lining box. The entire hollow element can then be moved from one station to another to be treated by a cataphoresis process, which also allows the glue to be baked.

The drawback of such an assembly method lies in the fact that, when moving from the crimping station to the cataphoresis processing station, the lining box, which is mounted with play in the outer panel, is liable to move away from the ideal position it should occupy, the adhesive is not yet set. This can lead to significant appearance defects of the finished hollow element, and consequently considerably increase the costs for the mass production of hollow elements of adequate quality.

To remedy this drawback, it has been proposed, prior to the displacement of the hollow element towards the cataphoresis station, to weld the lining box to the external panel by a laser, TIG or MIG welding process. These methods make it possible to maintain the lining box in position relative to the exterior panel in an adequate manner, but they are very expensive and also have the drawback of requiring the application of the bead of adhesive which links the lining box to the exterior panel in an area remote from the welding area so that the temperature rise resulting from the welding does not degrade the adhesive.

This necessarily leads to a widening of the contact edges of the lining box, which makes it a deep-drawn or molded part which is difficult to manufacture.

To overcome this drawback, it has been proposed to apply to the assembly of a hollow aluminum body element the known methods of spot resistance welding which are conventionally used for the assembly of hollow steel elements.

It was then found that the use of a welding tool which comprises, in a known manner, a welding clamp comprising two aligned electrodes mounted at the ends of two opposite jaws, was unsuitable. Indeed, in a process using such a welding tool to weld the folded edges of the outer panel to the horizontal edges of the lining box, the electrodes are applied on either side of the outer panel, which leads to the production of '' a welding point which links together three thicknesses of the element, i.e. respectively the thickness of the bottom of the outer panel, the thickness of the edge of the lining box, and the thickness of the folded edge of the panel outside.

The welding point thus produced on a material such as aluminum cannot be obtained without the appearance of a thermal concentration zone or "hot spot" located in the vicinity of the welding point, which leads to significant deformation of the panel. exterior and interior lining box in this area.

To remedy this drawback, the invention provides an assembly method allowing resistance resistance spot welding deforming neither the lining box nor the outer panel, and a hollow aluminum body element produced according to such a method.

For this purpose, the invention provides a method of the type described above, characterized in that the fourth welding step is a step of resistance spot welding, during which each welding point is produced by means of a pair of '' parallel electrodes of a welding tool, at least a first of which is applied to the crimped edges of the outer panel and a second of which is applied to the element so that a welding current flows transversely, in the thickness of the inner box lining, from the first electrode to the second electrode, to produce at least one welding point in line with at least one of the two electrodes.

According to other characteristics of the invention - the welding points are produced on the tongues of the crimped edges of the outer panel through two thicknesses of aluminum sheet, respectively a thickness of the crimped edges of the outer panel, and a thickness of the edges horizontal of the inner box; the first and the second electrode are applied to two tongues adjacent to the crimped edges of the outer panel in order to produce a spot of welding at the level of each electrode; - The first electrode is applied to a tongue of the crimped edges of the outer panel and the second electrode is applied to the horizontal edge of the inner box near the tongue to achieve a single spot of welding in line with the first electrode.

The invention further provides a hollow aluminum element forming an opening for a motor vehicle body, of the type which comprises an outer panel in the form of a substantially horizontal plate to which an inner lining box is assembled, of the type in which a periphery of the panel has vertical edges which receive horizontal clearance from the horizontal edges of the inner lining box on which they are folded horizontally then crimped, and of the type in which the edges of the outer panel have tabs which extend in the plane of the edges of the external panel and on which at least one resistance welding point is produced, characterized in that the horizontal edges of the lining box have, facing each tab, a boss for concentrating the flow of welding current in contact with each tab.

According to other characteristics of the hollow element - each boss is a substantially hemispherical boss of a determined diameter which is intended to melt when it is crossed by a flux of welding current to form a welding point of determined diameter; the tongues extend over a great length along the edges of the outer panel, and include cutouts in the shape of an arc of a circle which are centered around the bosses which are intended to concentrate the current flow in the vicinity of each boss and compensating for the deformation of the tongues when, during welding, the boss melts to form the welding point; - The tabs extend over a short length along the edges of the outer panel and the edges of the outer panel are of reduced width between each tab to concentrate the flow of current in the vicinity of the boss and compensate for the deformation of the tabs when, during welding, the boss melts to form the welding point; - The tongues came integrally with the outer panel and are produced during a step of cutting the outer panel; - the tabs are distributed at regular intervals along the periphery of the edges of the outer panel; - The tongues have a substantially trapezoidal shape.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows for the understanding of which reference will be made to the appended drawings in which - Figure 1 is an exploded perspective view of a plate intended to form an outer panel and an associated lining box intended to form a hollow bodywork element according to the invention; - Figure 2 is a perspective view according to Figure 1 illustrating the positioning of the inner lining box between the vertical edges of the glued outer panel; - Figure 3 is a view according to Figure 1, illustrating an embodiment of the operations of folding, welding, and crimping of the edges of the outer panel on the edges of the lining box; - Figure 4 is a detail view according to Figure 1 of a first embodiment of the invention in which the first and second electrodes are applied to an edge of the outer panel; - Figure 5 is a sectional view through the plane 5-5 of Figure 4 illustrating the application of an electrode and the welding operation according to the first embodiment of the invention; - Figure 6 is a detail view according to Figure 1 of a second embodiment of the invention in which the first electrode is applied to an edge of the outer panel and in which the second electrode is applied to an edge of the box lining; - Figure 7 is a sectional view through the plane 7-7 of Figure 6 illustrating the application of the first electrode and the welding operation according to the second embodiment of the invention; - Figure 8 is a sectional view through the plane 8-8 of Figure 6 illustrating the application of the second electrode according to the second embodiment of the invention; - Figure 9 is a detail view according to Figure 1 of a third embodiment of the invention in which the first and second electrodes are applied to an edge of the outer panel having lunules; and - Figure 10 is a sectional view through the plane 10-10 of Figure 9 illustrating the application of an electrode and the welding operation according to the third embodiment of the invention.

In the following description, identical reference numerals designate identical parts or have similar functions, and the terms "horizontal", "vertical", "lower", "upper", etc. are used, without limitation, with reference to the figures.

There is shown in Figure 1 an outer panel and a lining box of a hollow bodywork element implemented in an assembly process according to the invention. In a known manner, a hollow bodywork element 10 comprises an exterior panel 12 and an interior box 14 of lining which are intended to be assembled together so as to form the hollow bodywork element 10.

The inner lining box 14 and the outer panel 12 are made from aluminum sheets which are cut and stamped according to complementary dimensions so that, as illustrated in FIG. 2, the inner lining box 14 can be received "inside" from the outside panel 12.

To this end, the outer panel 12 is a panel substantially in the form of a plate which is stamped in the form of a "bowl" delimited by edges 20 and a bottom 16, the edges 20 which extend vertically from a periphery 18 of the bottom 16, as illustrated in FIG. 2.

During the assembly of the element 10, in a first step of the assembly method according to the invention, this bowl is arranged horizontally bearing on an assembly support 28, via its bottom 16, for receiving with clearance between the vertical edges 20, at the limit of the periphery 18 of the bottom 16, complementary horizontal edges 22 of the inner lining box 14.

A bead of glue 23 is then unrolled on the upper face of the bottom 16 of the panel 12, slightly set back from the vertical edges 20 and the periphery 18 of the outer panel 12, towards the inside of the bowl. Then the lining box 14 is lowered, vertically along the arrow in FIG. 2, inside the bowl so that its horizontal edges 22 adhere to the bead of glue 23.

As illustrated in FIG. 3, in a second step of the assembly method according to the invention, the edges 20 of the outer panel 12 are folded over by a folding tool (not shown), then crimped by a crimping tool 29 during a third crimping step, and finally welded by at least one welding tool 26 to the horizontal edges 22 of the lining box 14 during a fourth welding step which will be described more explicitly later.

In known manner, the lining box 14 was, during the first step, received with the above-mentioned horizontal clearance between the vertical edges 20 of the outer panel 12. Because of this clearance, as long as the adhesive of the cord 23 is not not hardened, the lining box 14 is liable to deviate from the position in which it has been placed relative to the outer panel 12 by sliding horizontally relative to the latter, which can for example occur during the movement of the 'hollow element 10 of bodywork from one workstation to another. The vertical edges 20 are then folded back in the second step, then, during the third step of the assembly method according to the invention, the crimping tool 29 is lowered vertically, as indicated by the corresponding arrow in FIG. 3 , on the folded edges 20 of the outer panel 12, then pressed on them so that crimping sleeves 31 of the crimping tool 29 descend to crimp the folded edges 20 of the outer panel 12 on the edges 22 of the inner box lining 14 by plastically deforming the sheet of the outer panel 12 and the lining box 14.

This arrangement is not limiting of the invention and the crimping sleeves 31 can be advantageously replaced by any other crimping method, in particular a crimping bar (not shown) ensuring in the same way the crimping of the folded edges 20 of the panel exterior 12. A fourth step of welding the crimped edges 20 of the exterior panel 12 to the horizontal edges 22 of the lining box 14 makes it possible to immobilize them relative to one another.

According to the invention, the fourth welding step is a spot resistance welding step, in which each welding point is produced by a pair of parallel electrodes of at least one welding tool 26, in particular at least a pair which comprises a first electrode 24 and a second electrode 25 of opposite polarities, which are represented in FIG. 3 by the signs "+" and "_", FIG. 3 shows two welding tools 26 which each comprise a pair of electrodes, each pair of electrodes comprising an electrode 24 and an electrode 25. During the fourth welding step, for a given welding tool 26, at least the first electrode 24 is applied to the edges 20 of the panel exterior 12. The second electrode 25 is applied to a determined location of the element 10 so that a welding current J travels transversely through the thickness of the housing its lining interior 14, from the first electrode 24 to the second electrode 25, for producing at least one welding point in line with at least one of the two electrodes 24 and 25.

According to the invention, the welding points of the crimped edges 20 of the outer panel on the horizontal edges 22 of the inner lining box 14 can be produced in accordance with different embodiments of the invention.

Thus, according to a first embodiment of the invention illustrated in Figures 4 and 5, the edges 20 of the outer panel 12 have tabs 30 in the form of trapezoids which extend in the plane of the edges 20 of the outer panel 12 and which , when they are folded in accordance with FIG. 5, each delimits a pointing surface 32 which extends inwards in the direction of the lining box 14 by providing sufficient surface for the production of a welding point.

Advantageously, the tongues 30 have come in one piece with the outer panel 12 and are produced by cutting the latter when it is initially plane as shown in FIG. 1. The tongues 30 are distributed at regular intervals around the periphery 18 of the outer panel 12 so that they make it possible to offer a plurality of pointing zones 32 which thus perfectly immobilize the lining box 14 relative to the outer panel 12.

Welding is obtained by the welding current J which is supplied by a current generator (not shown) to one of the electrodes 24 or 25, for example to the electrode 24, according to the arrow in FIG. 4. As illustrated In FIG. 5, this welding current J crosses the folded edge 20 of the outer panel 12 and enters the thickness of the horizontal edge 22 of the lining box 14.

The penetration of the welding current J into the thickness of the horizontal edge 22 of the lining box 14 is notably facilitated by a boss 34 of the horizontal edge 22 of the lining box 14 which is intended to concentrate the flow of welding current J in contact of each tab 30.

The horizontal edges 22 of the lining box 14 comprise several bosses 34 which are distributed at regular intervals, each boss 34 being arranged opposite a pointing surface 32 of a tongue 30, as shown in FIG. 2. Between two tongues 30 of the crimped edges 20 of the outer panel 12, the crimped edges 20 are of a width I reduced so as to concentrate the current flow J in the vicinity of the boss 34 by allowing it to flow preferentially in the thickness of the edge horizontal 22 of the lining box 14 adjacent to the electrodes rather than in the folded edge 20 of the outer panel 12.

In addition, the reduced thickness I of the crimped edges 20 between two tongues 30 makes it possible to compensate for the deformation of the tongues 30 which would be liable to be deformed due to the rise in temperature of the aluminum.

Thus, a flow of current J is established between the "input" electrode 24 to which the current J is supplied and the other electrode, or "output" electrode 25, which is applied to the pointing zone 32 of the tab 30 "output" adjacent to the tab 30 "input" at the same time as the input electrode 24.

In a similar manner to the electrode 24, the outlet electrode 25 is in fact in contact with the pointing zone 32 of the outlet tongue 30, itself in contact with a boss 34 of the horizontal edge 22 of the inner lining box.

The current flow J circulates between the two electrodes 24 and 25 along the dotted line in FIG. 4 and causes the aluminum of the horizontal edges 22 and the edges 20 to melt at the point where the concentration of the current flow J of welding is maximum, that is to say at the level of the bosses 34. Then, the current J again crosses the folded edge 20 of the outer panel 12 to exit by the output electrode 25. For this reason, this welding process is called "series" resistance spot welding.

Advantageously, the diameter of the welding points thus produced can be chosen according to the constraints that the element 10 is capable of withstanding, since each boss 34 is a substantially hemispherical boss of a determined diameter "d" which melts when it is crossed by the welding current flow J to form the welding point of determined diameter "d".

This fourth welding operation is particularly advantageous because it only performs the welding of the horizontal edges 20 of the inner lining box 14 on the crimped edges 20 of the outer panel 12, and not on the bottom 16 of the outer panel 12. In this way, the temperature of the bottom 16 rises only slightly during this third operation, and the adhesive bead 23 shown in Figures 1 and 5 is not likely to be degraded.

Figures 6 to 8 illustrate a second embodiment of the invention in which a single welding point is produced by the series welding process.

In fact, in this embodiment of the invention, the edges 20 of the outer panel 12 include tongues 30 in the form of trapezoids which are spaced apart by a spacing twice that of two consecutive electrodes 24 and 25.

The electrode 24 is intended to be applied to the folded edge 20 of the outer panel 12 while the electrode 25 is offset towards the inside of the element 10 so as to be applied directly to the horizontal edge 22 of the lining box 14 Thus, each tongue 30 delimits, similarly to the first embodiment of the invention, a pointing surface 32 which extends inwards in the direction of the lining box 14 by providing sufficient surface for the production of a welding point, while the lining box 14 has at least one pointing surface 33 which is intended to receive the electrode 25 and which is arranged for example in a recess 35 in the inner lining box 14. This recess 35 is by example obtained during stamping of the inner lining box 14.

Welding is obtained by the welding current J which is supplied by the current generator (not shown) to the electrode 24, according to the arrow in FIGS. 6 and 7. As illustrated in FIGS. 6 to 8, this current J of welding passes through the crimped edge 20 of the outer panel 12, a boss 34 similar to that previously described, and enters the thickness of the horizontal edge 22 of the lining box 14, then exits through the outlet electrode 25 which is directly at the contact of the horizontal edge 22 of the lining box 14.

In this embodiment, the flux of welding current J is concentrated only in each boss 34 in contact with each tab 30.

The horizontal edges 22 of the lining box 14 comprise several bosses 34 which are distributed at regular intervals, each boss 34 being arranged opposite a pointing surface 32 of a tongue 30.

Thus, the flow of current J is established between the "input" electrode 24 to which the current J is supplied and the other electrode, or "output" electrode 25, which is applied to the pointing zone 33 from the horizontal edge 22 of the inner lining box 14. The current flow J flows in the thickness of the horizontal edge 22 of the inner lining box 14, and a single welding point is produced in line with the electrode 24 due to melting the aluminum of the boss 34.

FIGS. 9 and 10 illustrate a third embodiment of the invention as a variant of the first embodiment of the invention, in which the tongues 30 have cutouts 38 in the form of an arc of a circle, also called "lunules", which are intended to circumvent the current of welding current J radially close to the axis of each electrode 24 and 25, on each pointing zone 32.

In fact, these lunules 38, obtained by cutting the outer panel 12 form areas of welding current J welding which prevent losses of welding current J in the aluminum from the crimped edges 20 of the outer panel 12.

Furthermore, these lunules 38 have the advantage of imparting elasticity relative to the crimped edges 20 of the outer panel 12, which makes it possible to compensate for possible deformations of these edges resulting from the temperature rise of these edges during the third welding operation.

Advantageously, the cutouts or lunules 38 of the outer edges 20 of the outer panel 12 are produced by punching with a punch when the latter has the planar shape which is shown in FIG. 1.

Advantageously, the method according to the invention makes it possible to obtain a hollow bodywork element which has an aspect of great geometric precision and which is free from any defect in alignment, which represents in terms of manufacture, in particular on a chain automotive manufacturing, a significant gain in quality, and therefore a reduction in production costs.

Claims (11)

<U> CLAIMS </U> 1. A method of assembling a hollow element (10) of an aluminum motor vehicle body which comprises an outer panel (12) substantially in the form of a plate to which is assembled an inner box (14) of lining, of the type in which the method comprises a first step during which vertical edges (20) of a periphery (18) of the outer panel (12) receive with a horizontal clearance horizontal edges (22) peripheral of the inner casing (14) of lining is precisely positioned relative to the outer panel (12), a second step in which the vertical edges (20) of the outer panel (12) are then folded horizontally over the horizontal edges (22) of the inner box (14) of lining, a third step in which the folded edges (20) of the outer panel (12) are crimped around the horizontal edges (22) of the lining box (14), and a fourth step during which the crimped edges (20) of the outer panel (12) are welded to the horizontal edges (22) of the lining box (14), characterized in that the fourth welding step is a step resistance welding step, when from which each welding point is produced by means of a pair of parallel electrodes (24, 25) of a welding tool (26) of which at least one first (24) is applied to the edges (20) crimped with the outer panel (12) and a second (25) is applied to the element (10) so that a welding current (J) travels transversely, in the thickness of the inner lining box (14), from the first electrode (24) to the second electrode (25), to produce at least one welding point in line with at least one of the two electrodes (24, 25). 2. Method according to claim 1, characterized in that the welding points are produced on tongues (30) edges (20) crimped of the outer panel (12) through two thicknesses of aluminum sheet, respectively a thickness of edges (20) set with the outer panel (12), and a thickness of the edges (22) horizontal of the inner box. 3. Method according to claim 2, characterized in that the first (24) and the second (25) electrodes are applied to two adjacent tongues (30) of the edges (20) set with the outer panel (12) to achieve a point of solder to the right of each electrode (24, 25). 4. Method according to claim 2, characterized in that the first electrode (24) is applied to a tongue (30) of the edges (20) set with the outer panel (12), and in that the second electrode (25) is applied to the horizontal edge (22) of the inner box (14) near the tongue (30) to produce a single spot of welding in line with the first electrode (24). 5. Hollow aluminum element (10) forming an opening for a motor vehicle body, of the type which comprises an outer panel (12) in the form of a substantially horizontal plate to which an inner lining box (14) is assembled, of the type in which a periphery (18) of the panel (12) has vertical edges (20) which receive with horizontal clearance horizontal edges (22) of the box (14) of inner lining on which they are folded horizontally then crimped, and of the type in in which the edges (20) of the outer panel include tabs (30) which extend in the plane of the edges (20) of the outer panel and on which at least one resistance welding point is formed, characterized in that the edges (22) horizontal of the lining box (14) comprise, facing each tongue (30), a boss (34) for concentrating the current flow (J) of welding in contact with each tongue (30). 6. Element (10) according to the preceding claim, characterized in that each boss (34) is a substantially hemispherical boss of a determined diameter (d) which is intended to melt when it is traversed by a current flow (J ) welding to form a welding point of determined diameter (d). 7. Element (10) according to one of claims 5 or 6, characterized in that the tongues (30) extend over a long length along the edges (20) of the outer panel and include cutouts (38) in form of a circular arc which are centered around the bosses (34), which are intended to concentrate the flow of current (J) in the vicinity of each boss (34) and to compensate for the deformation of the tongues (30) when, during welding, the boss (34) melts to form the welding point. 8. Element (10) according to any one of claims 5 or 6, characterized in that the tongues (30) extend over a short length along the edges (20) of the outer panel, and in that the edges (20) of the outer panel (12) are of reduced width between each tab (30) to concentrate the flow of current (J) in the vicinity of the boss (34) and compensate for the deformation of the tabs (30) when, during welding , the boss (34) melts to form the welding point. 9. Element (10) according to any one of claims 5 to 8, characterized in that the tongues (30) came integrally with the panel (12) outside and are produced during a step of cutting the panel ( 12) exterior. 10. Element (10) according to any one of claims 5 to 9, characterized in that the tongues (30) are distributed at regular intervals along the periphery (18) of the edges (20) of the panel (12) outside. 11. Element (10) according to any one of claims 5 to 10, characterized in that the tongues (30) have a substantially trapezoidal shape.