FR2475442A1 - BOSSAGE FOR SOLDERING TOLES, METHOD FOR CARRYING OUT SUCH BOSSING, AND USE THEREOF FOR RESISTANCE SOLDERING OF SHEETS - Google Patents

Abstract

BOSSING FOR SHEET WELDING, PROCESS FOR MAKING SUCH BOSSING, AND ITS USE FOR RESISTANCE WELDING OF SHEETS. BOSS FOR RESISTANCE WELDING OF SHEETS, CHARACTERIZED IN THAT THE SIDES 11, 12; 18, 19 OF BOSS 7, 16 FORM INTERNALLY AN ANGLE A FROM 45 TO 75 AND OUTSIDE AN ANGLE B OF 60 TO 100 AND IN THAT THE STRENGTH OF THE MATERIAL IN THE SIDE REGION IS ABOUT 50 GREATER THAN THE RESISTANCE OF THE BASIC MATERIAL 17 NEXT. THIS BOSS IS PARTICULARLY USED FOR WELDING ALUMINUM ALLOY SHEETS.

Description

The present invention relates to a boss for welding by

  sheet resistance, to a process for producing

  such bosses, and the use of said bosses.

  In the field of mass production of resistance welded objects, the boss welding of workpieces

  ferrous metals is one of the most popular welding processes

  for quality links. It is known that, unlike spot welding, in weld welding, the extent of the weld is not determined by the area of the electrode section, but by that of the section of the bosses. It thus becomes possible, on the one hand, to define

  the surface of the weld and, in part, the work

  jet, the density of the current and the superficial pressure

  and maintain these factors constant and, on the other hand, it becomes possible to weld simultaneously a number of bosses, exactly under the same conditions, in

  avoiding parasitic circuits in bypass.

  However, in the case of non-ferrous metals, and in particular in the case of aluminum and its alloys, this known method of boss welding can not be performed

  in safe conditions when it comes to thin sheets.

  This is due to the fact that, unlike iron, the alminium

  opposes to the welding current an electrical resistance

  weaker blow and, at the same time, offers a much better

  conductivity to heat generated by the electric current

  that, and as a result, this heat is spreading more

  weld point to the surrounding areas.

  To this is added another difficulty which is the fact that by applying the force necessary for the welding on the

  parts, that is to say on the bosses, by means of electro-

  -des, it is necessary to use a force much greater than in the case of iron, so that these bosses crash before we have time to turn on the current

  electric. If, on the other hand, we want to operate with a lower

  electrode pressure, the bosses may burn before the welding is done, because of the excessive

  contact resistance between the bosses and the plates.

  To remedy these drawbacks, it has been proposed to take steps to apply with extreme gentleness

2475442 -

  the electrodes on the parts and to allow the full force of the electrodes to be exerted immediately before

  welding current, thanks to a set timer

  corn. However, even with the numerical control machines intended to ensure the mutual synchronization of the variation of the current and the pressure, it has not been possible, by this known method, to obtain satisfactory boss welds and

  reproducible at will as required by mass production.

  Similarly, in the recent literature on this subject (for example in "Resistance Welding Manual", Vol 1, page 44, the aluminum manual 13, 1974 edition, page 58!) It is emphasized, repeatedly, that boss welding of aluminum can not be safely performed. he

  another book exists, notably that of

  entitled "Fachkunde des Widerstandsschweissens". where it is indi-

  page 44 that welding of light metals is possible with suitable machines. However, it is not at all

  explained how such welding can be achieved.

  Thus, the welding of aluminum with embossed bosses is known both in the literature and in practice and has given conclusive results. However, embossed bosses can only be produced on massive pieces, for example, on stanchion sleeves

  frying; on the other hand, on sheets or other

  thin massive bosses absolutely can not be

  produced under advantageous economic conditions.

  Accordingly, the present invention has

  purpose of bringing a boss by means of which aluminum sheets.

  and alloys of aluminum and others can be welded to

  safe way, and which allows, in particular, to produce simul-

  a number of the udings by the boss method.

  Another object of the invention is to provide a method for producing such bosses, which method is adapted for

mass production.

  The invention also aims to weld aluminum and

  aluminum alloys with a minimum of energy consumption

  electrical power, that is, by charging the network to the minimum.

  Another object of the invention is to ensure the production

  boss-welded connections to aluminum and its alloys

  which have a perfect metallurgical structure and

perfect reproducibility.

  Other features and advantages of the invention

  will emerge from the description that follows, which did not

  Of course, no limiting character, with reference to the accompanying drawings in which: Figure 1 is a sectional view through a stamped boss; Figure 2 is a similar sectional view through a conventional round boss; Figure 3 is a sectional view through a linear boss;

  FIG. 4 is a sectional view of an annular boss.

  groove; Figures 5 and 6 are diagrams showing the

  curves of variation of the current and the force or pressure

  welding; Figure 7 is a sectional view through a conventional tool for producing bosses; Fig. 8 is a similar sectional view through a tool for producing bosses such as those shown in Figs. 3 and 4; and, Figure 9 is a sectional view through the lens

  metal welding of a piece of aluminum.

  Figure 1 shows a solid stamped boss, which can be formed on parts 2 of light metal, for example, by stamping or by a metal supply. Such bosses

  are able to withstand the pressure exerted by electro-

  to maintain a single interface electrical resistance

  form, on the one hand, between the surfaces 3 of the electrodes and the

  parts 2 and 4 to be welded and, on the other hand,

say parts 2 and 4.

  FIG. 2 shows a hollow hollow boss classically

  which is generally used for sheet metal welding

  of iron. When it comes to light metals, the boss 5 is

  melting or crushing generally before we have time to engage the welding current, and we do not get a

satisfactory welding.-

  Figure 3 is a sectional view of an elongate boss 16 for aluminum and aluminum alloys, which boss is used to weld narrow edges in the case where the place

  is insufficient for an annular boss. Because of the

  With the plastic deformation to which the base material 17 has been subjected in the forming tools, the sides 18 and 19 of the boss have a strength which is approximately greater than that of this base material 17. The flanks 18 and 19 embossed wedge 16 in the material (base plate 17) internally form an angle C <of about 60 and

  externally an angle θ of about 900.

  Figure 4 illustrates the structure of an annular boss.

  7, which has proved particularly advantageous for the welding of aluminum and its alloys. The boss 7 differs mainly from the usual annular bosses used for the steel by the relatively small ratio - 1.5 to 3 which, b in this case, if necessary, makes it possible to obtain a lens

welded through.

  Here too, we obtain an increase in the resistance

  base material of around 50% in the regions

  11 and 12 flanks during the shaping. At this increase

  The addition of the resistance of the flanks 11 and 12 of the boss is compounded by the fact that the central circular region 13, which remains locally unchanged compared with the surrounding material 10, makes it possible to transfer a large part of the pressure of the electrodes to the inner sidewall 12. boss, so

  that the total force of the electrodes is distributed in the boss

  ge 7 uniformly between its two flanks 11 and 12. Thus, the

  lines of force extend into boss 7 ,. Approximately

  vementen parallel and are only slightly inclined by

  relative to the perpendicular passing through the plane of welding.

  When boss 7, 16 starts to be crushed by the action of

  the force F of the electrodes and as a result of the resulting heating.

  as the passage of the welding current I, the inclination of these lines of force increases visibly. The superficial pressure

  specificity between the parts remains essentially maintained.

  It is obvious that the diameter of the disc 7 can not be chosen at will because the intensity-of the necessary welding current increases approximately as the square of the diameter d. However, satisfactory results have been obtained in the case of a sheet of 1.05 mm thick with a diameter d of 3 mm and a boss having a height h of 0.7 mm, using as material, for example , an alloy AlMg 0.4 Si 1.2. Compared with a round boss with a height h of 1.1 mm and the same diameter d, it has been found that

  under the action of a force F of 200 daN the boss of the fi

  Figure 4 shows only a permanent deformation of approximately 8% of the dimension h while in the case of a round boss

  -10 this deformation h is 54% .-

  Unlike the known methods for producing bosses of ferrous materials, which are generally produced by free plastic deformation (FIG.

  embossments according to the invention are pressed into a matrix (

  Figure 8). The geometric shape of the bosses, and in particular their flanks 11, 12; 18, 19, is the same for all bosses in a room. The plastic deformation of the material

  The basic form is produced by means of a cooperating form punch.

with a form-matrix 21.

  It should be noted that the stamping tools 20, 21 of FIG. 8 not only maintain the angles I and P, but are necessary to obtain them and, on the other hand, allow the shaping and the resulting consolidation of the material of the flanks 11, 12; 18, 19. It is important that,

  in the case of an annular boss, the central circular surface

  tral 13 retains, at least, the level of the initial surface

surrounding sheet metal.

  It is obvious to those skilled in the art that the good quality

  the weld does not depend solely on the shape of the boss, but that the nature of the welded material, as well as the pace of the variation in time of the pressure of the electrodes and, in particular, the pace of the variation of

  Welding current also play a very important role.

  The high thermal conductivity of aluminum and its alloys requires that the stripping energy, that is to say that the welding current, be applied for a very short time. In addition, all aluminum-based materials require, as is known, for the reasons stated (high electrical conductivity, low internal electrical resistance) welding currents higher than

ferrous materials.

  Using bosses with the structure

  3 and 4, together with a welding current and an electrode force having the appearance of FIGS. 5 and 6, it becomes possible to produce, in a surprising manner, very high quality, perfectly reproducible, consistent with the polished cut of

Figure 9.

  Figures 5 and 6 show the variation curve 14 of the current as a function of time t1 t2 and t1 t3; Figure 15

  represents the variation of the electrode drilled between.

  moments to and t4. The intensity curve 14 of FIG. 6 has, compared with FIG. 5, a so-called "post-heating" phase between times t2 t3. This phase:

  post-heating can be useful and is even necessary for -

  certain subjects, in order to extend the time of re-cooling

  (with a view to better reoristallisation):

  additional menta-ton of the presson of! oudage; part in -

  mixed lines of the curve 15 of the figurations at and 6) at the fir of the welding phase helps to avoid the formation of sinkholes and cracks in the lens-welding o

  Figure 9 is a sectional view through the lens -

  22 between two plates 23, 24 constituted by

  different aluminum bindings, and secured by welding annular bosses. On none of the surfaces of the two sheets 23, 24 was removed the oxide layer. Nevertheless, we get

  a symmetrical lens, perfectly homogeneous and without

  sions. Another factor to consider is the structure of the electrode, particularly its moving mass, upon which so-called "follow-on behavior" depends. Indeed, the electrode must, during the very good welding period t1 t2 be able to follow without delay the boss by train

  to melt, in order to avoid the projections of

fied.

  Preferably, the electrodes. have a relative surface

  large in order to reduce the current density between them

  and parts, thus reducing to a minimum the wear and tear of

  the latter. It is particularly advantageous to use a frequency converter welding machine for carrying out the described procedure. Using a single-pulse and DC welding procedure the welding energy can be transferred to the parts in a minimum amount of time. When simultaneously welding several bosses, it is advantageous for the electrodes to be movably mounted and spring-loaded so that the pressure of the electrodes and the welding current are applied exactly under the same conditions.

to all bosses.

  Compared with prior, relatively safe welding procedures for aluminum and its alloys, particularly with respect to spot welding, the welding method according to the invention has many advantages, in particular:

  It makes it possible to increase the pro-

  duction due to the possibility of simultaneously welding several bosses without resulting parasitic bypass circuits and without excessive welding currents are required, which has the following consequence: Uniform mechanical resistance welds;

  Uniform resistance despite variations in

  current tensity; A further increase in the production of

  relatively dirty and practically negligible

  electrodes and their wear due to the low current density at the contact points;

  Constant quality of the welds due to the

  pressure of alloy inputs to the electrodes; A correct position of the welds on the parts because of the presence of the bosses set up in advance; and, eliminating the need to clean surfaces

  oxidized sheets by kinetic etching, brushing, etc ...

before welding.

Claims (11)

  1. Boss for resistance welding of heads characterized in that the flanks (11, 12; 18, 19) of the boss   (7, 16) internally form an angle α of 45 to 750 and   an angle P of 60 to 1000 and that the resistance of the material in the flank region is approximately   50% to the strength of the adjacent base material (17).   2. Boss according to claim 1, characterized in that the boss (7) has an annular shape and in that its central circular region (13) is located in the same plane as the adjacent base material.   3. Boss according to claim 1, characterized in   the boss (16) has a linear shape.   4. Boss according to claim 2, characterized in that   that the central circular surface (13) rises slightly   above the plane of the neighboring basic material.   The boss of claim 1, characterized in that   that the angle i is 600 and the angle f is 90.   6. Boss according to claim 2, characterized in that the ratio between the average diameter d of the annular boss   (7) and the width b of the border is less than 3.   7. Boss according to claim 1, characterized in that.   the average resistance of the flanks (11, 12; 18, 19) is   approximately 50% higher than that of the base material.   8. A method for producing an annular boss or allon-   ge and in particular a boss on tales and thin pieces according to claim 1, characterized in that the boss (7, 16) is produced by imposing on the base material (10, 17) a plastic deformation and in that the shaping & said projection to the prescribed dimensions is obtained by making the metal under pressure between a punch (20) and a matrix (21) of a press tool.   9. Use of the boss according to one of the claims   1 to 7, for the welding of aluminum and alloy sheets aluminum alloys.   10. Use of the boss according to claim 9,   characterized in that it is not not necessary to do   the surfaces of aluminum sheets and aluminum alloys   before welding, a cleaning treatment by bros- wise other CU.   11. Use of the boss according to claim 9 or claim 10 for electrical resistance welding   of aluminum sheets consisting of forming on one side a reinforcement   cement and the other a relief, characterized in that during the implementation of a force of application of the electrodes reducing the contact resistances, the relief of the boss does not   hardly deforms and does not retract before closing of the welding current.