EP0695592A1 - Method and apparatus for making a metallic ondulated tube - Google Patents

Abstract

The method for shaping a metal tube by electromagnetism is characterised by: (a) a section of a metal tube (2) being placed between a means (1) capable of producing a magnetic field and a means (4) with required surface shape; (b) the device (1) being electrically activated to produce a force which deforms the tube wall and presses it against the means (4); (c) the means (1) and (4) being displaced longitudinally into another position along the length of the tube for continuation of the shaping process. The appts. incorporates means for longitudinal displacement of the tube relative to the means (1, 4) for step-by-step shaping of the tube (2).

Description

The present invention relates to a method and the means of implementing the method for manufacturing by magnetoforming elements of tubes with corrugated walls from metal tubes whose generatrices are substantially rectilinear and parallel to the longitudinal axis. Preferably, the basic metal tubes are cylindrical.

In industry, there is often a need to use fluid and / or gas tight pipes while having a certain flexibility. In some cases, the sealing problem can be solved by using tubes made of flexible material, for example plastic, elastomer or equivalent, but very often these materials have a certain gas permeability which may not be acceptable. It is also possible to use sections of rigid metal tube linked together by flexible joints. The difficulty in sealing is then transferred to the joints of the connection.

Corrugated metal tubes can be used made from metal strips formed by rollers, spiraled on a mandrel and continuously welded in order to form a sealed tube having corrugations, therefore increased flexibility by the shape of the corrugations. Thus, if the weld bead remains watertight, the problem has been resolved in order to manufacture a metal tube, therefore perfectly gas-tight in particular, and flexible thanks to the more or less corrugated shape of the generators. However, this manufacturing is slow and requires a fairly heavy manufacturing installation and welding is a technical solution for implementation and delicate control. In addition, the resistance to bending fatigue is often reduced due to welding and this type of manufacturing gives good results only for certain types of metals.

One can also form by rollers a cylindrical tube threaded on a mandrel of corrugated outer shape. However, this cold deformation notably has the drawback of being fairly slow and also of using fairly large machines, in particular when the tube has a diameter of the order of ten centimeters or more. This production is generally limited to relatively short sections.

The magnetoforming method is already used on elementary parts to carry out deformations or assemblies by crimping, welding, or plating. This method can be done by compression of the metal or on the contrary by expansion, according to the degree of deformation. However, no solution is provided in the case of the forming of the surface of a metal tube several meters long.

The magnetoforming process is well known and will therefore not be described here. It will be recalled that it consists in sending an electric pulse of very short duration in an electromagnetic coil arranged near the walls of the part to be formed. The variation of the electromagnetic field produced by the coil creates in the walls of the conductive metal tube an induced current which, by interaction with the current circulating in the coil (Laplace law) exerts on the walls of the tube forces equivalent to an electromagnetic pressure , said pressure deforming the tube by plating the walls on a form matrix.

• on place une portion de longueur d'un tube métallique entre des moyens de création d'un champ magnétique et des moyens de formage,
• on active électriquement les moyens de création d'un champ magnétique pour créer une énergie de déformation de ladite portion qui plaque les parois dudit tube sur lesdits moyens de formage,
• on déplace longitudinalement lesdits moyens de création d'un champ magnétique et lesdits moyens de formage pour les placer sur une autre portion de longueur du tube non déformée.

Thus, the present invention relates to a method of forming a metal tube by electromagnetism. The method includes the following steps:

• a length portion of a metal tube is placed between means for creating a magnetic field and means for forming,
• the means for creating a magnetic field are electrically activated to create a deformation energy of said portion which plates the walls of said tube on said forming means,
• said means for creating a magnetic field and said forming means are moved longitudinally to place them on another portion of the length of the non-deformed tube.

The forming means can be placed inside said tube portion, said means for creating a magnetic field surrounding the outside surface of the tube.

The tube can be deformed in a single activation according to a groove or a circular boss, the width of deformation being at most about one step.

The tube can be deformed in a groove or a helical boss around the axis of the tube.

The forming means can be moved longitudinally relative to the tube by a rotation of said forming means around the axis of the tube.

A first activation of the means for creating a magnetic field can partially deform the tube over a portion of the circumference of the tube relative to the desired final deformation, and after having moved the forming means by rotation, a second activation can complete the deformation on at least part of said partially deformed portion.

The metal tube can comprise at least one tube made of material that cannot be deformed by magnetoforming and a tube adapted to be deformed by magnetoforming, said tube that can be deformed by magnetoforming being interposed between the tube that cannot be deformed by magnetoforming and the means for creating a magnetic field.

The invention also relates to a device for forming a metal tube by electromagnetism comprising means for creating an electromagnetic field and means for forming. The tube is placed between the means for creating an electromagnetic field and the forming means, and the device comprises means for moving the tube relative to the means for creating an electromagnetic field and the means for forming longitudinally along the axis. of the tube in order to deform the tube step by step.

The forming means may include a mandrel whose outside diameter is slightly less than the inside diameter of said tube, and the mandrel may have a groove on its outer surface.

The throat can be helical.

The device may comprise means for moving the tube longitudinally relative to the mandrel comprising means for rotating said mandrel relative to the tube and the means for creating an electromagnetic field may include means for connecting with the mandrel so that their respective positions remain fixed transversely to the tube.

The groove may have a depth of zero at its starting point and may deepen substantially regularly over a portion of helix length less than the length corresponding to about one step until reaching the depth corresponding to the constant shape of said groove which continues in a helix.

On the side of the origin of the groove, the cylindrical surface of the mandrel may have a determined length in order to center the tube properly on the mandrel while not blocking the tube when it is subjected to differential axial deformations resulting from the rates different radial deformations.

The end of the mandrel, on the origin side of the groove, can be chamfered or has a fillet with a large radius.

• La figure 1 représente une demi-coupe d'un tube en cours de formage,
• La figure 2 montre une perspective du mandrin,
• La figure 3 montre un exemple schématique des dimensions d'une ondulation,
• La figure 4 montre une vue de dessus du mandrin,
• Les figures 5 et 6 montrent une coupe du mandrin suivant deux plans différents.

The present invention will be better understood and its advantages will become more clearly apparent from the following description of specific, non-limiting examples, illustrated by the appended figures, among which:

• FIG. 1 represents a half-section of a tube during forming,
• FIG. 2 shows a perspective of the mandrel,
• FIG. 3 shows a schematic example of the dimensions of a corrugation,
• FIG. 4 shows a top view of the mandrel,
• Figures 5 and 6 show a section of the mandrel along two different planes.

Figure 1 shows schematically a preferred embodiment of the method and the device according to the invention. The reference 1 identifies the electromagnetic coil of substantially annular shape and placed around a tube 2 whose part located to the right of the coil is not yet formed, while the part of the tube located to the left of the coil has been formed and comprises corrugations 3. Forming means or mandrel 4 are placed inside the tube. The shape of the mandrel 4 in the zone 5 serves as a support and a matrix for the deformation of the tube 2 when the coil 1 is activated by an electric current.

• La déformation du métal dans le sens radial et circonférentiel doit se faire préférentiellement par raccourcissement du tube plutôt que par allongement du métal. En effet, si au cours du formage, le tube ne peut effectuer des déplacements longitudinaux pour suivre le pliage ondulé dont la trace est plus longue par rapport à la génératrice rectiligne de l'origine, le métal ne peut se former en ondulation qu'avec des allongements de la matière elle même. Ces allongements peuvent former des strictions importantes et parfois des fissures. Dans un tel cas de formage, les parois auront obligatoirement des zones d'épaisseur réduite qui diminueront la résistance mécanique du tube ondulé.
• Dans le cas de formage d'un tube ondulé, si on déforme les parois sur plusieurs ondulations en même temps, de part et d'autre d'un sommet de l'ondulation, il y a blocage du déplacement longitudinal de la matière du tube puisque de part et d'autre du sommet la matière subit des tensions opposées. La forme en creux entre deux sommets se fait par allongement de la matière puisque les deux sommets bloquent la matière entre eux, cela n'est pas le cas lorsqu'un creux comporte latéralement, sur au moins un côté, une partie cylindrique.

There are several difficulties to be solved in order to obtain a good quality corrugated tube while resulting from an economical manufacturing process:

• The deformation of the metal in the radial and circumferential direction should preferably be done by shortening the tube rather than by lengthening the metal. Indeed, if during the forming, the tube cannot make longitudinal displacements to follow the corrugated folding whose trace is longer compared to the rectilinear generator of the origin, the metal can only form in corrugation with lengthening of the material itself. These elongations can form significant necks and sometimes cracks. In such a forming case, the walls will necessarily have zones of reduced thickness which will reduce the mechanical resistance of the corrugated tube.
• In the case of forming a corrugated tube, if the walls are deformed on several corrugations at the same time, on either side of a top of the corrugation, the longitudinal movement of the material of the tube is blocked since on both sides of the summit the material undergoes opposite tensions. The hollow shape between two vertices is done by elongation of the material since the two vertices block the material between them, this is not the case when a hollow comprises laterally, on at least one side, a cylindrical part.

Also, the present invention recommends a method and a device for avoiding these drawbacks.

In the case of circular ripples, the width of the coil must be such that the electroforming is carried out at the first electrical pulse on only one hollow so that the material which forms the hollow can at best come from a displacement of the tube in the direction of a shortening. After this first deformation, the mandrel and the coil are moved the length of a recess to be able to form a second recess following the previous one. The deformation over the entire tube thus continues step by step. In the case of a circular wave, the mandrel must be designed in a retractable manner so that it can be released from the already formed recesses.

When the forming is done by expansion instead of compression, it is clear that the disadvantages are comparable and therefore that identical solutions can be provided. In this case, it is the coil which is inside the tube and the mandrel outside. It is simpler in this latter configuration to design a matrix which opens in at least two parts to be disengaged from the formed tube and to be displaced in line with a portion of unformed tube.

The present invention is preferably applied to undulations arising from a groove or a boss, not circular (that is to say in a ring around the tube) but helical.

The advantage of such preforming is twofold:
- As will be described later, a mandrel inside or outside the tube having the shape corresponding to the corrugation in a helical groove can be moved relative to the tube by rotation about the axis of the mandrel. Indeed, the system is comparable to a screw (mandrel) in a corresponding female part (tube). A rotation of the screw makes it move longitudinally relative to the female part. The mandrel, whether external or internal to the tube, does not need to be highly retractable or removable to allow deformations of the tube by successive activations of the coil.

Figures 2 and 4 illustrate a mandrel 6, seen in perspective in Figure 2 and in top view in Figure 4 according to arrow 7 (Figure 2). It should be noted that a certain number of lines or dotted lines, helically or longitudinally have no geometric meaning but that they result from the CAD drawing mode and that they have been kept only for better readability of surfaces and volumes.

A trihedron Ox, y, z identifies the mandrel 6 of axis Ox. The mandrel 6 comprises a cylindrical part 8 whose diameter is close to the internal diameter of the tube 2 (Figure 1). The groove 11 originates from the line 10 and has a little more than two helix pitches on the mandrel. The end of the cylindrical part 8 is machined according to a leave 9 so that this part which penetrates into the tube not yet formed is in contact with the internal surface of the tube while providing the least possible friction. Indeed, the part 8 serves as axial guide of the tube on the mandrel and vice versa, but the tube shortens substantially as a result of the radial deformations provided by the electromagnetic field of the coil. It can be assumed that such a shortening is not uniformly regular over the circumference if the rate of radial deformation is distributed differently over the circumference. The tube can then shorten while offsetting slightly. The rounded shape 9 of the cylinder 8 can limit possible blockages of the tube on the mandrel when the tube thus offsets.

Figure 3 shows an example of a wave trace defined by a step p = 37.2 mm, a height h of the wave h = 11.8 mm, the hollow having a radius rb = 13 mm, the vertex having a radius ra = 7.5 mm, the connection of the hollows and vertices being made tangentially, the orthogonal to the tangent of the two circles of radius ra and rb making an angle of 25 ° relative to the axis of the tube.

Such an example of ripple was determined in such a way that the deformation rate would theoretically be 25%, if the tube did not shorten.

Of course the present invention is not limited to this profile, equivalent profiles for other corrugated tubes can be obtained with the method and the device described here.

Figure 4 is a top view of the mandrel 6 according to arrow 7 (Figure 2), that is to say that the wavy contours shown in Figure 4 are those of the intersection of the Oxy plane with the mandrel. Line 11 is the starting point of the helical groove which here takes a little more than two steps to lead into zone 12 of the mandrel. Line 13, diametrically opposite to the point of origin 11 of the groove, represents the shape of the groove as it continues helically until 12. At 11, we note that the bottom of throat is cylindrical. The groove is deepened regularly on the half-circumference between 11 and 13. On the other hand, from 13, the groove has a constant profile up to the end of the mandrel. In Figure 4, there is shown the tube 2, not formed, positioned to the point referenced 14 of the mandrel. The coil 1 surrounds the end of the tube 2.

Figures 5 and 6 show the sections of the mandrel according to the Oxu and Oxv planes referenced in Figure 2. Figure 5 shows the section of the mandrel along the Oxu plane inclined at 60 ° to the Oxy plane. Line 15 shows the profile of the groove in this plane, a fairly shallow profile. FIG. 6 represents the section of the mandrel according to the Oxv plane inclined at 60 ° relative to the Oxu plane. Line 16 shows the profile of the groove in this plane, a profile less deep than the final profile, but nevertheless quite close. It should be noted that the profiles diametrically opposite to the groove of increasing depth are connected on the right on a cylindrical part of the mandrel. This shape is advantageous because it promotes the shortening of the tube. This function will be explained in more detail below.

Operations:

FIG. 4 represents the first step of electromagnetic forming on a fully cylindrical tube 2. The tube is brought in and positioned by conventional means. The coil 1 and the mandrel 6 are linked, for example by a frame and an axis which carries the mandrel, said axis having a certain length which will allow penetration or extraction of the mandrel relative to the tube as and when formed and the coil is thus linked to the mandrel so that it remains in the same radial plane.

The tube 2 brought to point 14 of the mandrel covers several zones, starting from the right of the mandrel: a cylindrical part, a half-step of the groove of increasing depth over a half-turn, a certain portion of groove having the final profile. At the first "shot" or activation of the coil, the tube 2 is pressed against the mandrel by taking its shape, that is to say: a groove with variable depth and a groove with a final profile. This first shot does not pose any problem of elongation of the material because no prior deformation blocks the possibility of displacement of the tube longitudinally, whether by the right or the left with reference to FIG. 4.

After this first shot, the mandrel can only be moved relative to the tube by rotation, according to the thread that represents the groove initiation. By rotating the mandrel, here anticlockwise since the propeller is on the right, while blocking the rotation of the tube around its axis, the mandrel is moved to the right by a distance directly related to the angle of rotation and the pitch of the propeller. For example, a rotation of half a turn will move the mandrel back half a step. It is assumed that in the example illustrated in FIG. 4, a half-turn of unscrewing is carried out from the right of the mandrel in the tube. This has the consequence that the previously partially formed part will be in front of a part of the groove with a final profile, that a cylindrical part of the tube will be in front of the groove with increasing depth and that the part of the tube formed according to the groove of final profile is moved into a groove portion of the same profile on the mandrel. This last part also serves as a guide for screwing the mandrel into the tube.

On the second shot, only two modes of deformation take place: the cylindrical part of the tube which is in front of the groove with increasing depth partially deforms and the part of the tube partially deformed beforehand forms after the second shot in the form final throat in front of which this part is located.

The deformation of the tube continues by repeating this second step.

• obtenir un procédé de fabrication le plus rapide,
• obtenir une friction minimale entre le mandrin et le tube formé,
• obtenir un formage avec diminution de l'épaisseur du tube la plus faible possible.

As described above, one of the objects of the invention is to avoid blocking the longitudinal displacements of the tube so that there is little or no elongation of the material as a result of the forming and that this is done by displacement of material and shortening of the tube. It is noted that during the second shot (and also following) the tube is cylindrical to the right of each formed part which leaves the tube free to match the shapes of the corresponding mandrel preferably by displacement rather than by elongation. To meet this condition, theoretically the second step before the second shot (and the following steps) must be done with a rotation of the mandrel by an angle at most equal to 360 ° -i, i being the angle corresponding to the length of the throat of increasing depth. The optimization of the invention may relate to the adaptation of said angle i, of the shape of the groove and of the part with increasing depth, of the angle of rotation of the mandrel so as in particular:

• get the fastest manufacturing process,
• obtain minimum friction between the mandrel and the formed tube,
• obtain a formation with reduction of the thickness of the tube as small as possible.

The adaptation must also take into account the geometry of the tube and its material.

To facilitate the displacement of the tube by screwing the mandrel, lubricant or equivalent products can be inserted between the tube and the mandrel, before firing. These products can be injected into the annular space by means of orifices opening out at the bottom of the groove of the mandrel.

The invention is not limited to the example described here, other applications can be implemented. In particular, in the case of a tube made from a poorly conductive material, the method of forming by electromagnetism may not apply. In this case, it will be possible to interpose between the tube which is a poor conductor of electricity and the coil, a tube which is a good conductor so that the deformation of this tube, called propellant in the profession, results in the deformation of the tube which is bad or not conductive.

The corrugated tube portions manufactured within the limit of the penetration of the mandrel into the tube, these can be welded together to form a continuous tube of greater length.

Claims (14)

1) Method of forming a metal tube by electromagnetism, characterized in that it comprises the following stages: a portion of the length of a metal tube is placed between means for creating a magnetic field and means for forming, the means for creating a magnetic field are electrically activated to create a deformation energy of said portion which presses the walls of said tube on said forming means, - Moving said means for creating a magnetic field and said forming means longitudinally to place them on another portion of length of the non-deformed tube. 2) Method according to claim 1, characterized in that the forming means are placed inside said tube portion, said means for creating a magnetic field surrounding the outer surface of the tube. 3) Method according to one of the preceding claims, characterized in that the tube is deformed in a single activation according to a groove or a circular boss, the width of deformation being at most about one pitch. 4) Method according to one of claims 1 or 2, characterized in that the tube is deformed according to a groove or a boss in the form of a helix around the axis of the tube. 5) Method according to claim 4, characterized in that said forming means are displaced longitudinally relative to the tube by a rotation of said forming means around the axis of the tube. 6) Method according to one of claims 4 or 5, characterized in that a first activation of the means for creating a magnetic field partially deforms the tube on a portion of the circumference of the tube relative to the desired final deformation, in that after having displaced the forming means by a rotation, a second activation ends the deformation on at least part of said partially deformed portion. 7) Method according to one of the preceding claims, characterized in that said metal tube comprises at least one tube made of non-deformable material by magnetoforming and a tube adapted to be deformed by magnetoforming, said deformable tube being interposed between the non-deformable tube and the means for creating a magnetic field. 8) Device for forming a metal tube by electromagnetism comprising means for creating an electromagnetic field and means for forming, characterized in that the tube is placed between the means for creating an electromagnetic field and the means for forming, and in that it comprises means for moving the tube relative to the means for creating an electromagnetic field and to the forming means longitudinally along the axis of the tube in order to deform the tube step by step. 9) Device according to claim 8, characterized in that the forming means comprise a mandrel whose outer diameter is slightly less than the inner diameter of said tube, and in that the mandrel has on its outer surface a groove. 10) Device according to one of claims 8 or 9, characterized in that said groove is helical. 11) Device according to claim 10, characterized in that it comprises means for moving the tube longitudinally relative to the mandrel comprising means for rotating said mandrel relative to the tube and in that the means for creating an electromagnetic field comprise means of connection with the mandrel so that their respective positions remain fixed transversely to the tube. 12) Device according to claim 11, characterized in that the groove has a zero depth at its starting point and deepens substantially regularly over a portion of helix length less than the length corresponding to about one pitch until reaching the depth corresponding to the constant shape of said groove which continues in a helix. 13) Device according to one of claims 8 to 12, characterized in that on the side of the origin of the groove, the cylindrical surface of the mandrel has a determined length in order to center the tube properly on the mandrel while not blocking the tube when it is subjected to differential axial deformations resulting from different radial deformation rates. 14) Device according to claim 13, characterized in that the end of the mandrel, on the origin side of the groove, is chamfered or has a leave of large radius.

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