FR2622490A1 - Method and device for welding two workpieces using an electron beam - Google Patents

Abstract

The subject of the present invention is a method and a device for the welding of two metal sheets 10, 12 along a seam 14 with the aid of an electron beam 16 when the metal sheets 10, 12 exhibit a magnetic field residual (remanence) . This magnetic field residual (remanence) is measured and a substantially equal field is applied, but of the opposite direction, so that the resultant field is as weak as possible. This opposing field is applied with the aid of two coils 24, 28 connected via a soft-iron connection bar 32. The latter may have a slot 34 through which the electron beam 16 passes. The assembly constituted by the coils 24, 28 and the bar 32 may be fixed either to one of the workpieces 10, 12 or to the electron gun. Application to the welding of thick metal sheets.

Description

METHOD AND DEVICE FOR WELDING TWO WORKPIECES USING
OF AN ELECTRON BEAM
DESCRIPTION
The present invention relates to a method and a device allowing the welding of two parts by electron beam which eliminate the drawbacks due to the residual magnetic field in the parts to be welded, this magnetic field can be of ferromagnetic or thermoelectric origin. .

 Electron beam welding is widely used at the present time and in particular in the nuclear field or in elements such as tanks require edge-to-edge welding of thick sheets, that is to say having a thickness of The order of 100 mm or even more. The operation is carried out in a known manner in a sealed chamber in which a vacuum is created relative to atmospheric pressure. The welding of two metallic elements is carried out by the fusion of the metal on either side of the contact zone between the two parts, this contact zone being called "joint line" or "weld joint". The operation is generally carried out without filler metal, the heat of fusion being supplied by the electron beam produced by an electron gun.

 Document FR-A-1 141 535 describes a process of this type.

However, the welding chamber being sealed and placed under vacuum, it is not easy to closely monitor the welding operations. In most cases, the relative displacement between
The harness and the parts to be welded is automated and can be controlled # n microprocessor. For the welding between two ferrous metals o # same nature, called "homogeneous welding", there remains a problem of residual magnetic field. Indeed, parts made of magnetic material, such as ferrous metals, are the seat of a residual magnetic field called "residual magnetic field and the latter has an influence on the trajectory of the electron beam, which does not allow d '' get a perfect solder joint.

Figure 1 attached illustrates this defect. It can be seen that the two parts to be welded 10 and 12, having a thickness e of the order of 100 mm or more, are brought into contact with one
The other along an edge, which defines the joint line 14.

The welding is carried out using an electron beam 16 produced by an electron gun, which is not shown in FIG. 1. The beam 16 falls vertically on the upper face of the parts 10 and 12 exactly at level of the joint line 14. Known devices make it possible to naftriser the path of the beam 16, for example the use of a shield surrounding the beam between the exit of the electron gun and the upper face of the parts 10 and 12.

 If there was no remanent magnetic field inside the latter, the beam would remain vertical (that is to say follow the path 16a) and the welding would be carried out exactly along the joint line 14. However, in the case of ferrous metals, there always remains a remanent magnetic field symbolically represented in FIG. 1 by the lines in dashed lines 18. This magnetic field has the effect of deflecting the beam 16 inside the mass of the parts 10 and 12 and the beam takes the path represented by the curve 16b. We therefore see that, on the underside of parts 10 and 12, the beam 16 is deflected by a distance d relative to the ideal path 16a corresponding to your joint line 14. This value b depends on the one hand on the value of the residual field and, on the other hand, the thickness e of the parts to be welded.

If this thickness is only a few millimeters, the beam is practically not deflected and its trajectory is practically coincident with the joint line 14. The melting of the metal will therefore be perfectly distributed over the entire thickness of the parts.

However, if the thickness e is large, (of the order of 100 or 200 mm or even more), the trajectory can be strongly deviated. In the most unfavorable cases, the metal can melt outside the joint on a certain portion of it (especially near the underside of parts 10 and 12) and can be unevenly distributed on another corresponding portion where the beam begins to move away from the joint line 14. Thus, the metal is well fused on the joint at the leading edge (upper face of the parts to be welded) but, as it follows the path of the beam, for a very thick joint, it can, on the opposite face of the parts to be welded, be made at a certain distance from the joint line. Consequently, the weld will be unevenly distributed in the joint plane.

 Various methods have been proposed to eliminate this drawback.

THE ARTICLE PUBLISHED BY THE INTERNATIONAL INSTITUTE OF
WELDING, reference 11W Doc. IV -324-82, Study on High Power
Electron Beam Welding (Report 3) Development of the method for eliminating beam deflection caused by the residual magnetism of heavy thick plates (Hiroshi KIHARA, Setuji MINEHISA, Nobuharu
SAKABATA, Yoshiaki SHIBUYA, 1982, Hitachi Zosen Corporation,
Technical Research Institute) describes three solutions to cancel
The effects of magnetism remain on the path of the electron beam. These three solutions are as follows: - Demagnetization of the parts before carrying out the
welding; - Correction of beam path or magnetic field
during welding; and - Total shielding of the beam from the electron gun
to the parts to be welded.

 However, these solutions are not entirely satisfactory. First of all, demagnetization of parts is a difficult operation, especially for large and thick parts. The authors of the article even specify that, for thicknesses greater than 100 mm, we are at the limit of the possibilities of demagnetization techniques. Indeed, If the parts are large, it requires significant handling means and demagnetization facilities in relation to the dimensions of the parts. In addition, the time devoted to demagnetization and to the manipulations thus rendered necessary is relatively long, which increases the total duration of the welding operations.

 As for the correction of the beam trajectory or of the distribution of magnetism around it, The authors point out that this method is difficult to apply due in particular to the ignorance of the deflection of the beam and the distribution of the remanent magnetic fields . In addition, it gives no indication of the process for implementing this method. Finally, although not knowing the path of the beam, the authors also specify that the third method is practically the one used with demagnetization.

The article published in the Soviet Journal "Automatic
Welding "in July 1985" Narrow-gap Welding magnetized products without demagnetising them "describes a device used to keep an electric arc stable in an arc welding process which can be used in particular in a narrow joint. The authors describe a device comprising two coils so as to create a magnetic field which cancels the residual magnetism. In the case of an arc welding installation, it is perfectly possible for the operator to monitor the arc and act on the intensity of the direct current of supply of the coils as well as the polarity of the latter across the coils. However, in the case of a narrow joint weld, there are thin and simple-shaped parts. electron beam, the lack of space around the parts to be welded, and above all the lack of visibility of the weld joint, make it practically impossible to modify the opposing field during operation (i.e. say The field applies to oppose the residual field).

 The object of the present invention is to remedy the above drawbacks by proposing a method and a device for welding two parts by electron beam which makes it possible to considerably reduce the effects due to the remanent magnetic field, even if it acts of pieces of significant thickness.

 The process which is the subject of the invention is applied to the welding of two parts, one to the other using an electron beam produced by an electron gun, the two parts being in contact with one another. with the other along a Joint line Along which the welding must be carried out, a residual magnetic field remaining in the parts at the joint line.

According to the invention, this method comprises the following steps consisting in (a) - determining the value of the remanent magnetic field; and (b) - apply, where the welding is to be carried out,
a magnetic field of value substantially equal to that of
residual field, but in the opposite direction, so that you field
magnetic result has a value less than 2 gauss,
preferably less than 1 gauss.

 In the present invention, it is not a question of producing an antagonistic field which is, at the place of the weld, strictly equal and opposite to the residual field in order to obtain a zero resulting field. On the contrary, we measure beforehand the value of the remanent field in various places along the joint line and we determine a fixed value of the opposing field so that the resulting field is, if not zero, at least has a value low enough for La deflection of the electron beam is minimal.

The invention also relates to a device for implementing this method. According to the main characteristic of this device, it comprises
- a first electromagnetic coil having a first end and a second end
- a second electromagnetic coil having a first end and a second end; and
- A connecting bar of magnetic material having two ends which can be fixed to said second ends of the electromagnetic coils, the electrical supply of the coils being such that when their first ends are in the immediate vicinity of one of the parts to be welded, the magnetic field created goes from the first coil to the second through said part, and from the second coil to the first through the connecting bar.

 Preferably, at least one of the coils comprises a core of magnetic material disposed substantially along its axis, this core having a first end which can be placed in the immediate vicinity of one of the parts to be welded and a second end to which can be fixed One end of the link bar.

 The expression "in the immediate vicinity of one of the parts to be welded" means that the first end of the coil or of its core is either in contact with this part, or at an extremely short distance from it, so that the magnetic field created enters this room. In the general case, the length of the core is slightly greater than that of the coil and the latter has its first end in contact with the part. Anyway, even in this case, it can be considered that the first end of the coil is in the immediate vicinity of the part.

Still in the case where a magnetic core is used, the second end of it slightly protrudes from the second end of the coil and is fixed to the connecting bar.

However, it can still be considered that the connecting bar is fixed to the second end of the coil via the core.

 In a first embodiment, your connecting bar has, between its two ends, a groove allowing the passage of the electron beam.

 This arrangement is preferably used when the joint line is a straight line. In this case, the device consists of the two coils and the connecting bar is fixed and the beam # of electrons moves along the groove.

 In this case, the device further comprises means for fixing the assembly constituted by the two coils and the connecting bar on at least one of the parts to be welded.

In another embodiment, the device further comprises means for fixing the assembly consisting of two coils and the connecting bar on the gun with electr # - #
This arrangement is especially used in the case where the joint line is not straight but has for example a circular shape or any shape. In this case, it is
The assembly constituted by the electron gun and the device object of the invention which moves by following the joint line.

The invention will be better understood on reading the description which follows, given by way of purely illustrative and in no way limitative example, with reference to the appended drawings, in which:
FIG. t is a schematic view in vertical section of two parts to be welded showing the deflection of the electron beam under the effect of the remanent magnetic field,
FIG. 2 is a top view of an electromagnet placed on a support and used to create a magnetic field,
FIG. 3 is a set of curves giving the value of the magnetic field measured on the pole line of the electromagnet of FIG. 2 for different intensities of the current,
- Figure 4 is a view similar to Figure 3, but giving the magnetic field measured on a circle of larger radius than the Polar Line,
FIG. 5 is a schematic perspective view of a first embodiment of the device object of the; nvenx "n, the parts to be welded being shown partially cut, and
- Figure 6 is a schematic profile view of another embodiment of this device.

 As indicated above, the invention consists in measuring the remanent magnetic field at different places along the joint line and in creating an antagonistic field of constant value, but opposite to the remanent field, so that the resulting field has a value null or weak enough not to be annoying.

 Figure 2 shows, seen from above, an experimental device used to create an opposing magnetic field when the joint line is circular.

 This device consists of an electromagnet 20 placed on a horizontal support 22. The electromagnet 20 consists of a coil 21 surrounding a core 23 which may for example be made of soft iron. The pole line of the electromagnet 20 is the circle C1 shown schematically in phantom in the drawing. There is also shown on this a system of axes Ox, Oy in the plane of the support 22, the center of which is coincident with the center of the circle Cl. The two axes are perpendicular and the axis Oy is coincident with that of coil 21.

The curves in FIG. 3 correspond to measurements carried out on the circle C1 and those in FIG. 4 to measurements carried out on a circle C2 whose diameter is greater than that of the circle C1, the difference between the two diameters being for example of 40 mm. The curves of Figures 3 and 4 are obtained as follows
For a given value of the intensity of the current in the coil 21, the magnetic field is measured at different points on the polar line Ci. In FIG. 3, a line OAI is drawn whose angle with the axis Ox is identical to that of line OA in FIG. 2, the length of which is proportional to the intensity of the magnetic field measured (for the clarity of the drawing, the point O has not been indicated in FIG. 2). A polygon is thus obtained, such as the polygon P1 in FIG. 3. On this, the polygons P1, P2, P3 and P4 correspond respectively to values of current intensity in the coil 21 of O; 1.5; 3 and 5 amps.

 The curves of FIG. 4 are obtained in the same way but the measurements are carried out on the circle C2. - The polygons P51 P6, P7 and P8 correspond to current intensities in the coil 21 of O; 1.5; 3 and 5 amps respectively. The curves P1 and P5 are obtained for a zero intensity in the coil 21 and therefore represent the residual magnetic field. We see that the value of the magnetic field on the polar line (circle C1) is, at least along the x-axis, greater than the value of the remanent magnetic field.

However, at a slightly greater distance, of the order of 20 mm (corresponding to the difference of the radii of the circles C1 and
C2), the value of the magnetic field measured is practically equal to that of the remanent field. It can therefore be seen that, in the case of a circular joint, it is possible to use a device of the type of that illustrated in FIG. 2 arranged so that it has a pole line corresponding approximately to the joint line and passing through in the coil 21 a constant current whose value and direction are determined so that the resulting field is as small as possible.

 The perspective view of FIG. 5 illustrates a device making it possible to weld along a straight joint line.

 This figure shows the parts to be welded 10 and 12 in contact with each other along the joint line 14. The device object of the invention, bearing the general reference 36, comprises a first coil 24 equipped with a core 26 and a second coil 28 equipped with a core 30. The two coils are placed at a certain distance from each other and their cores are perpendicular to the upper surface of the parts 10 and 12. The cores 26 and 30 have a length greater than that of the coils 24 and 28 and have one of their ends in contact with the parts 10 and 12 at the joint line 14. The other ends of the cores 26 and 30 are fixed to the ends of a connecting bar 32, Which is made of a material with high magnetic permeability as well as the cores 26 and 30. The bar 32 has a longitudinal groove 34 whose length is practically equal to the distance between the coils-24 and 28 and whose width is sufficient to allow the passage of the electron beam 16. The assembly is placed so that the groove 34 is practically parallel to the joint line 14.

In the particular case described here, the device 36 constituted by the bar 32 and the two coils 24 and 28 is fixed relative to the parts to be welded and it is the beam 16 which moves inside the groove 34.

 The electrical supply of the coils is such that the magnetic field created closes on itself through the parts 10 and 12 and the bar 32. This is how, in the particular example illustrated in FIG. 5, the field magnetic goes from the coil 24 to the coil 28 passing inside the parts 10 and 12, as symbolized by the arrow F1, represented in dashed lines, and then the magnetic field goes from the coil 28 to the coil 24 passing along the bar 32, as is symbolized by the arrows F2 also in broken lines. In any case, the coils are placed and applied to the parts to be welded so as to maintain a good magnetic link with the flux lines.

 To carry out the welding in the vicinity of the edges of the parts 10 and 12, a metal part is placed in contact with the latter, which bridges the flux lines.

 As indicated above, The operation takes place inside a sealed enclosure and it is not possible to intervene during the operation to modify the current flowing in the coils. However, this is chosen once and for all before starting the welding operation, according to the measured values of the residual field. This value is such that the resulting magnetic field has a value which can possibly be zero in certain places, but which, elsewhere, has a value varying between certain limits sufficiently low so that the beam is practically not deflected inside the plane. seal.

 The profile view of FIG. 6 ilLutre another device which can be used in the case where the joint line is no longer straight. In Figure 6, we see only the part 12 because the joint plane is coincident with that of The figure, at least at the place where the welding is carried out.

 As before, we find the coils 24 and 28 with the cores 26 and 30 connected by the connecting bar 32. As above, the magnetic field closes inside the circuit formed by the coils, parts 10 and 12 and the link bar 32 as indicated symbolically by the arrows F1 and F2 in FIG. 6.

However, in this variant, the bar 32 does not need to have a groove 34 because it is fixed directly to the electron gun 38. In fact, it can be fixed either directly to the latter, or to the armor tube 40 which surrounds the beam 16. In this variant, it is the whole assembly formed by the electron gun 38, the shielding tube 40 and
The device 36 which moves along the joint line 14.

In this case, the first ends of the cores 26 and 30 are not in close contact with the upper face of the parts 10 and 12, but at a very small distance therefrom, of the order of a millimeter. The operation is the same as previously, the intensity of the current in the coils being determined so as to have an antagonistic field of a value such that the resulting field is as small as possible.

 Thus, the method and the device which are the subject of the invention have particularly advantageous advantages since they allow parts of large dimensions and very thick to be welded without the electron beam being deflected excessively under the effect. of the resulting magnetic field. This is due to the fact that an antagonistic field is applied which is intended not to cancel the remanent field, but to obtain a field resulting from their value sufficiently low so that the deflection of the beam is minimal. In addition, the devices illustrated in Figures 5 and 6 are simple and can be made easily from commercially available elements.

 Finally, it is understood that the invention is not limited to the single embodiments which have just been described, but that many variants can be envisaged without departing from the scope of the invention. Thus the person skilled in the art can, according to each particular application envisaged, use any type of magnetic or electromagnetic device capable of creating an antagonistic field of value such that the value of the resulting field remains within given limits. In the case of the devices illustrated in FIGS. 5 and 6, it may vary the shape, the construction and the material of the coils and of the bar 32 as well as, in the case of FIG. 6, the means of fixing the latter. on the electron gun. Finally, if, in the above description, the sheets are placed horizontally, the electron beam striking their upper face, it would not go beyond the scope of the invention to place them in a different way, for example vertically.

Claims (6)

 preferably less than 1 gauss.  magnetic result has a value less than 2 gauss,  residual field, but in the opposite direction, so that the field  a magnetic field of value substantially equal to that of The other using an electron beam (16) produced by an electron gun (38), the two parts (10, 12) being in contact with each other along a joint line (14) Along which the welding must be carried out, a residual magnetic field remaining in the parts (10, 12) at the level of the joint line (14), characterized in that it comprises the following steps consisting in: (a) - determine the value of the remanent magnetic field; and (b) - apply, where the welding is to be carried out,  1. Method of welding two parts (10, 12) one to Said part, and from the second coil <28) to the first t24) through the connecting nar (32). When their first ends are in the immediate vicinity of one of the parts to be welded, the created magnetic field goes from the first coil (24) to the second (28) through The electrical supply of the coils (24, 28) being such that  - a connecting bar (32) made of magnetic material having two ends which can be fixed to said second ends of the electromagnetic coils (24, 28),  - a second electromagnetic coil (28) having a first end and a second end; and  - a first electromagnetic coil (24) having a first end and a second end; Claim 1, characterized in that it comprises  2. Device for implementing the method according to  3. Device according to claim 2, characterized in that at least one (24) of the coils comprises a core (26) of magnetic material arranged substantially along its axis, this core (26) having a first end which can be brought to immediate vicinity of one of the parts to be welded and a second end to which one of the ends of the connecting bar (32) can be fixed.  4. Device according to claim 2, characterized in that the connecting bar (32) has, between its two ends, a groove (34) allowing the passage of the electron beam (16).  5. Device according to claim 2, characterized in that it further comprises means for fixing the assembly consisting of the two coils (24, 28) and the connecting bar (32) on at least one of the parts to be welded.  6. Device according to claim 2, characterized in that it further comprises means for fixing the assembly constituted by the two coils (24, 28) and the connecting bar (32) on the electron gun (38 ).