FR2790689A1 - Welding procedure for assembling overlapping zones of two components, e.g. of thin sheet metal, involves applying sufficient heat to vaporize coatings on components - Google Patents

Abstract

Two components (1, 2) are contacted for at least part of their overlapping zone and sufficient heat (3) is applied locally to component (1) to vaporize coatings (1', 2') on components in contact zone while retaining facing component surfaces solid. Same face of component (1) is then subjected to energy flow (4) to weld components over at least part of zone (3') in which first heat was applied. The two heat applications are repeated as necessary, either continuously or at intervals, to complete the required welding area. The welding energy flow is preferably provided by a focussed laser beam. An Independent claim is given for a device used to implement the above procedure.

Description

DESCRIPTION

  The present invention relates to the field of assembly of elements, parts or pieces by welding, in particular in the field of bodywork or articles or structures formed from sheets, in particular thin, and relates to a method and a device for assembling by welding two pieces. The assembly by welding, in particular by laser beam, of two coated parts, in particular of a sheet on any piece or of two sheets between them, poses the problem of the presence of said coating layers at the contact areas between parts to assemble and the effects they

induce upon welding.

  Partial fusion welding of materials, in particular by laser beam, of parts, in particular coated thin sheets, is a subject mastered in edge-to-edge configuration, but which remains difficult and delicate to implement in transparency configuration (partial overlap parts) due to

  effects of evaporation of coatings at the interface.

  Indeed, the non-metallic or metallic coatings (in particular zinc-based) deposited on the faces of the parts to be assembled are generally vaporized at temperatures equivalent to or lower than the melting temperatures of the materials of said parts and which are rapidly

  reached during welding, in particular by laser beam.

  The coating located on the external parts is vaporized by the supply of welding energy, for example by a focused laser beam, and disperses

  freely in the surrounding air, without affecting welding.

  However, the coating layers located at the interface also vaporize under the action of the laser beam and the fusion bath (steel melting temperature = 1500 C) and the vapors thus formed exert high local pressures, in particular on the molten bath, and escape by projecting the liquid metal from the molten bath to the outside, or remain trapped

  in this bath by constituting weakening cavities.

  Many techniques have been implemented to avoid this

harmful phenomenon.

  The simplest, used in an industrial way, consists in separating the two sheets by a given value, depending on the thickness of the coating and the sheet

  upper, to allow vapors to escape freely at the interface.

  2- However, this process requires precise control of the game at the interface, requires the implementation of specific tools and does not lead to a

  intimate surface contact between the two parts to be assembled.

  Furthermore, it is also known to produce assemblies of parts by electric welding. When such a welding process is applied to parts provided with a coating, it is known to achieve at least partial elimination of the latter by delivering several consecutive welding current pulses. However, this welding technique does not make it possible to obtain a controlled and total evacuation of said coating, necessarily requires two opposite accesses to the welding zone, does not make it possible to produce a continuous and thin welding bead and is difficult to apply when the coating at

  eliminating is electrically non-conductive.

  The present invention aims in particular to overcome the

aforementioned drawbacks.

  To this end, it relates to a method of assembling by welding two parts at an overlap zone, the surface of at least one of the two parts being at least partially covered with a coating layer at the level of said overlapping zone, characterized in that it consists in bringing the two parts into contact at least at a part of said overlapping zone, intended to constitute the future assembly zone, then to apply locally to the apparent or external face of a first of said parts to be assembled a quantity of heat energy adjusted to generate a temperature sufficient to vaporize said coating layer (s) at least in line with the area of application of said heat energy, while allowing to keep facing surfaces at the level of the interface in the solid state, to then apply, on the same face of said first part, a flow of energy capable of reacting read the assembly by welding of the two parts on at least part of said anterior zone of heat energy application and, finally, if necessary repeat these last two operations, continuously or discontinuously, simultaneously or offset in the time, by moving the areas of application of heat energy and of welding, in such a way that the area of application of welding energy progresses in the trace of the area

  application of heat energy.

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  The invention will be better understood from the following description, which

  relates to a preferred embodiment, given by way of nonlimiting example, and explained with reference to the appended schematic drawings, in which: Figure I is a side elevation view in section showing the progress of the assembly process by welding according to the invention in continuous operation applied to two coated sheets, and, Figure 2 is a sectional view along AA of the object shown in the

figure 1.

  The present invention therefore relates to a method of assembling by welding two parts I and 2 at an overlap zone, in particular when the surface 1 ", 2" of at least one of the two parts I and / or 2 is at least partially covered with a coating layer 1 ′, 2 ′ at the level

of said overlapping area.

  This method mainly consists in bringing the two parts 1 and 2 into contact at least at a part of said overlapping zone intended to constitute the future assembly zone, then to apply locally to the visible or external face of a first 1 of said parts I and 2 to assemble a quantity of heat energy 3 adjusted to generate a temperature sufficient to vaporize said coating layer (s) 1 ′, 2 ′ at least in line with the application area 3 ′ of said energy calorific 3, while making it possible to keep surfaces 1 "and 2" facing each other at the interface in the solid state to then apply, on the same face of said first part 1, a flow of energy 4 capable of perform the assembly by welding of the two parts I and 2 on at least a part 4 'of said zone 3' of previous application of heat energy 3 and, finally, if necessary repeat these last two operations, so as to continuous or discontinuous, simultaneously or offset in time, by moving the areas of application 3 'and 4' of heat energy and welding, in such a way that the

  application zone 4 'progresses in the trace of the application zone 3'.

  The aforementioned method does not therefore require access to the other face of the first part 1, or to the second part 2, only access to the visible or external face 1 "'of the part 1, that is to say, the face opposite to the surface 1 ",

  at the welding assembly areas being required.

  The implementation of the above method is preferred when the first part I at least has a relatively small thickness, at least at the level

  overlapping area or welding assembly must be performed.

  The aforementioned method makes it possible either to produce continuous or split weld beads 8, of small width, or spaced local weld points. As shown in Figures 1 and 2 of the accompanying drawings, the density of heat energy 3 applied is advantageously adjusted to produce a local fusion bath 5 in the first part 1, not opening onto the interface between the two parts I and 2 , so as to keep a thin solid layer 6 of said first part 1 in line with said bath 5, the thickness of said solid layer 6 being, on the one hand, sufficiently low that the temperature reached at the interface opposite the application area 3 'of the heat energy 3 to allow the vaporization of the coating layer (s) 1', 2 'at this location and, on the other hand, strong enough to constitute a solid material barrier preventing passage vapors resulting from the vaporization of the layer (s) of

  coating 1 ', 2', towards said melt 5.

  According to a characteristic of the invention, represented in FIG. 1 of the accompanying drawings, the flux of welding energy 4, preferably in the form of a focused laser beam, is applied at the level of a part 4 ′ of the zone of application 3 'of heat energy 3 after stopping the application of heat energy 3 at the latter or displacement of the application area 3', with sufficient time to allow the evacuation of the vapors layer (s) of

  coating 1 ', at least 2' of the interface region in line with said zone 3 '.

  In accordance with a preferred variant embodiment of the invention, the means for applying the heat energy 3 and the means for applying the flux of welding energy 4 are moved synchronously, the application zones 3 ' and 4 ′ of the two types of energy being constantly separated by a given distance, a function in particular of the characteristics of the first part I and

movement speed.

  However, provision can therefore be made for moving the parts to be assembled 1 and 2, in front of the energy application means, which may

  possibly use the same source.

  In addition, according to another alternative embodiment of the invention, the flux of welding energy 4 can also be applied, for a given assembly zone, after the calorific energy 3, in a second operating phase of the process. , distinct and consecutive to the first consisting of

  the application of heat energy 3.

  - In what follows, the invention will be described more precisely in the context of an application where the first part I at least is a coated metal sheet. Initially, a source generating a medium density energy flow, for example in the form of a laser beam (for example of the CO2, Nd-Yag type, with diodes or the like) defocused or of an electrical process conventional (for example of the type known under the designation MIG, under the designation TIG, plasma or the like) is used to generate a fusion bath 5 in a sheet 1, this bath not completely opening at the interface, so as to keep at the root a thin solid layer 6 of the material of said sheet 1, close

of the interface.

  The use of an energy source of medium density makes it possible to create a large fusion bath 5 by conduction and to control the depth of it.

penetration into the sheet 1.

  Thanks to the thinness of the layer 6 which has remained in the solid state, and to the local heating induced by the proximity of the liquid melting bath 5, the temperature reached at the interface of the sheet I and of the piece 2 (this the latter possibly also being a sheet, the two sheets I and 2 being able to be provided with coating layers 1 ′ and 2 ′ at least at their surfaces 1 "and 2" facing each other), will exceed the vaporization temperature of the or some

  coating layer (s) 1 'and / or 2', and thus cause its or their vaporization.

  Said vapors being enclosed between two solid walls defining the interface, they can only escape by sliding along said interface, between the two parts 1 and 2 (for example coated thin sheets) and a large part of the material coating present at the interface zone located under the melt 5 is discharged in this way in gaseous form. In addition, it should be noted that when the first part I consists of a metal sheet provided, at least at its surface 1 "facing the part 2, with a coating layer 1 ', it can advantageously be provided that said sheet I is maintained so as to be authorized to locally undergo a slight angular deformation following the cessation of the application of heat energy 3 or the displacement of the application area 3 ′, due to the stresses induced by shrinkage during rapid cooling of the melt 5

  room after moving away from the energy application area 3.

  This results in an opening or spacing of the interface and the creation of a slight clearance between the sheets 1 and 2 on either side of the fusion bead, favoring the escape of the vapors of layer material. (s) of coating 1 '

and / or 2 '.

  In order to allow efficient conduction heating between the two coating layers 1 'and 2' possibly present (or between the uncoated surface 1 "of part I and the coating layer 2 'of part 2), allowing evacuation important of the coating material, care should be taken to make an intimate contact at the interface between the two parts I and 2 to be assembled, in particular at the level of the zone of application 3 ′ of the energy flow

calorific 3.

  It should also be noted that the maximum thickness of the thin solid layer 6 kept in the first part or sheet I will depend on the thermophysical characteristics of the material constituting the latter and of the

  material of the coating layer (s) 1 'and / or 2'.

  In any event, this remaining solid layer 6 must be thin enough to obtain a thermal gradient enabling the vaporization temperature of the coating material to be reached at the interface, while remaining thick enough to be able to withstand the pressure of the vapors. generated

in the interface.

  Following the passage of the heat energy flow 3, a welding energy flow 4, preferably in the form of a focused laser beam and centered on the trace of the first bead, is used to weld the two parts 1 and 2 together, crossing the thickness of the first piece or sheet I and entering

  completely or partially the second 2.

  During this welding operation, the small quantity or the absence of coating material at the interface makes it possible to overcome the harmful effects resulting from the vaporization of the latter at the time of carrying out the welding. In addition, the angular deformation resulting from the prior passage of the flow of heat energy 3 contributes to further reducing said effects.

  harmful by promoting the evacuation of residual coating vapors.

  As shown schematically in Figure I of the accompanying drawings (the relationships between dimensions and distances not being observed), the focused laser beam 4 is advantageously applied immediately after the flow of heat energy 3, at a sufficient distance authorizing the evacuation of

  coating material vapors.

  This close application over time, for a given area, of the flow of welding energy 4 following the flow of heat energy 3 -7 can be advantageously exploited in terms of energy balance and power required for welding, since the preheating of the parts or sheets I and 2 makes it possible to significantly reduce the amount of energy to be transmitted by

  the welding energy flow 4 in order to be able to carry out the assembly by welding.

  The present invention also relates to a device for the

  implementation of the assembly process by welding as described above.

  As shown in particular schematically in Figure I of the accompanying drawings, this device essentially comprises, on the one hand, a means 7 for supporting, holding and / or pressing the two parts I and 2 to be assembled, on the other part, a means or source of local application of heat energy 3 on one of the two parts 1, 2, and, finally, a means or source of local application of a flux of welding energy 4, consecutively to the application of heat energy 3 for a given assembly area 4 ', the means or sources of local application of heat energy 3 and of welding 4 being able to be moved

  relative to parts I and 2 to be assembled or vice versa.

  According to a first alternative embodiment of the invention, the means or sources of application of heat energy 3 and of welding 4 are moved synchronously with respect to the parts, according to the desired welding path, the zones of application 3 'and 4' of the two types of energy being constantly separated by a predetermined distance, depending in particular on the characteristics of the parts 1 and 2 to be assembled and the speed of movement, and the application area 4 'of the welding energy 4 being smaller than the energy application area 3 '

calorific 3.

  The density of heat energy 3 delivered is then advantageously sufficient to generate a melt 5 adapted to the welding speed of the flux

welding energy 4.

  According to a second embodiment of the invention, the flux of welding energy 4 can also be applied after the energy

  calorific 3, in a consecutive operational phase.

  Preferably, the means of applying heat energy 3 consists of a defocused laser beam and the means of applying welding energy 4 of a focused laser beam, coming from the same source or from two.

different sources.

  Indeed, when the heat energy flow 3 and the welding energy flow 4 are applied in a single operation, synchronously, the corresponding beams, respectively defocused and focused, can be obtained by dividing an original beam unique and adapted optical treatment of each of the two secondary beams, or by the use of two different sources. Similarly, when the vaporization of the coating layers 1 ′ and / or 2 ′ and the assembly by welding are carried out consecutively and offset in time, the corresponding beams can be obtained either by means of a single source whose beam is treated each time in a suitable manner (focused or defocused), either by means of two different sources, including the

  have the desired characteristics.

  Practical tests were carried out by the inventor on 0.8 mm thick steel sheets coated on each side with a layer of zinc

  deposited in bath and having an average thickness of 10 prm.

  As part of these tests, use was made of a diode laser with a power of 1.5 kW, emitting at two wavelengths (808 nm and 940 nm), to carry out the first pass (flux of calorific energy 3), by creating a

  fusion with an average depth of 0.6 mm and an average width of 2 mm.

  The diode laser was preferred in this embodiment, because it allows, thanks to its excellent stability, to easily control the depth of penetration of the bath

of fusion.

  In a second step, a focused CO2 laser made it possible, by producing a weld bead centered on the zone pretreated thermally by the passage of the flow of heat energy 3, to carry out the assembly of the two sheets while completely eliminating the problems related to vaporization of the coating material. Of course, the invention is not limited to the embodiment described and shown in the accompanying drawings. Modifications remain possible, in particular from the point of view of the constitution of the various elements or by substitution of technical equivalents, without thereby departing from the scope of

protection of the invention.

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Claims (8)

  1) Method of assembling by welding two parts at the level of an overlapping zone, the surface of at least one of the two parts being at least partially covered with a coating layer at the level of said overlapping zone, characterized in that it consists in bringing the two parts (1I and 2) into contact at least at a part of said overlapping zone intended to constitute the future assembly zone, then to apply locally on the visible face or external of a first (1) of said parts (1 and 2) to assemble a quantity of heat energy (3) adjusted to generate a temperature sufficient to vaporize said at least one coating layer (1 ', 2') in line with the area of application (3 ') of said heat energy (3), while allowing surfaces (1 "and 2") to be kept opposite at the interface in the solid state, to be applied then, on the same face of said first part (1), a energy flow (4) able to carry out the assembly by welding of the two parts (1 and 2) on at least one part (4 ') of said zone (3') of prior application of heat energy (3) and finally, if necessary, repeating these last two operations, continuously or discontinuously, simultaneously or offset in time, by moving the application zones (3 ′ and 4 ′) of heat energy and welding, such that the application area (4 ') progresses   in the trace of the application area (3 ').   2) welding assembly method according to claim 1, characterized in that the calorific energy density (3) applied is adjusted to achieve a local melt (5) in the first part (1), not leading to the interface between the two parts (1 and 2), so as to keep a thin solid layer (6) of said first part (1) in line with said bath (5), the thickness of said solid layer (6) being on the one hand, sufficiently low for the temperature reached at the interface opposite the application area (3 ') of the heat energy (3) to allow the coating layer or layers (1 ', 2') at this point and, on the other hand, strong enough to constitute a solid material barrier preventing the passage of vapors resulting from the vaporization of   the coating layer (s) (1 ′, 2 ′), towards said melt (5).   3) Method of assembly by welding according to any one of   claims 1 and 2, characterized in that the welding energy flow (4),   preferably in the form of a focused laser beam, is applied to a part (4 ') of the application area (3') of the heat energy (3) -10- after application has stopped of heat energy (3) at the latter or displacement of the application zone (3 ') with sufficient time to allow the evacuation of the vapors from coating layer (s) (1', 2 ') at less of the region   interface to the right of the said zone (3 ').   4) Method of assembly by welding according to any one of   Claims I to 3, characterized in that the means for applying the energy   calorific (3), and the means for applying the welding energy flow (4) are moved synchronously, the application zones (3 'and 4') of the two types of energy being constantly separated from a given distance, a function in particular   characteristics of the first part (1) and the speed of movement.   ) Assembly method according to any one of claims I   and 2, characterized in that the energy flow (4) for welding is applied   after the heat energy (3), in a second operating phase.   6) Method of assembly by welding according to any one of   Claims I to 5, characterized in that at least the first part (1) consists   in a metal sheet provided with a coating layer (1 ') at least at its surface (1 ") facing the part (2), said sheet (1) being maintained so as to be authorized to undergo locally slight angular deformation following cessation of the application of heat energy (3) or displacement of the area of application (3 ').   7) Method of assembly by welding according to any one of   Claims 1 to 6, characterized in that the two parts (I and 2) to be assembled   consist of sheets, preferably thin, provided with coating layers (1 'and 2') at least at their surfaces (1 "and 2") mutually opposite.   8) Device for implementing the assembly process by   welding according to any one of claims I to 7, characterized in that it   essentially comprises, on the one hand, a means (7) for supporting, holding and / or pressing the two parts (I and 2) to be assembled, on the other hand, a means or source of local application of energy heat (3) on one of the two parts (1, 2), and, finally, a means or source of local application of a welding energy flow (4), following the application of energy heat (3) for a given assembly area (4 '), the means or sources of local application of heat energy (3) and welding (4) can be moved relative to the parts   (1 and 2) to assemble or vice versa.   9) Device according to claim 8, characterized in that the means or sources of application of heat energy (3) and welding (4) are -11- moved synchronously with respect to the parts, according to the desired welding path, the application areas (3 'and 4') of the two types of energy being constantly spaced by a predetermined distance, depending in particular on the characteristics of the parts (I and 2) to be assembled and the speed displacement, and the area of application (4 ') of the welding energy (4) being smaller than the area   application (3 ') of the heat energy (3).   ) Device according to claim 8, characterized in that the flux of welding energy (4) is applied after the heat energy (3),   in a consecutive operating phase.   I 1) Device according to claim 9 or 10, characterized in that the means for applying heat energy (3) consists of a defocused laser beam and in that the means for applying welding energy (4) consists of   a focused laser beam, coming from the same source or from two different sources.