Patent Description:
The term "tubular product" used in the description and in the following claims is intended to refer to any product obtained from a tube (the cross section of which may have different shapes, in particular circular) or to an analogous elongated semi-finished product, such as a bar or a profile.

Various methods are known for obtaining tubular products by performing bending operations on metal tubes. Generally, depending on the geometries to be obtained and the material of the initial tube, the bending operations may be performed using, for example, roller-type or form bound bending devices.

In bending by means of a roller-type bending device, an initially straight metal tube is fed in the direction of its longitudinal axis and passed between at least three rollers arranged alternately on opposite sides with respect to the tube, one of which is transversely movable, i.e., substantially orthogonal to the longitudinal axis of the tube. While the tube is made to advance in the direction of its own longitudinal axis, the more the movable roller is pressed against the tube towards the longitudinal axis of said tube, the smaller the bending radius of the tube obtained. By changing the relative orientation of the tube with respect to the bending device, that is, with respect to the three rollers of the bending device, it is possible to change the orientation of the bending plane of the tube in space.

With roller-type bending devices, despite having the advantage of ensuring high dimensional and geometric precision, it is practically impossible to obtain complex-curvature tubular products by performing in sequence the various bends on immediately adjacent tube portions. In effect, a roller-type bending device plastically deforms the tube at the intermediate roller, while the other rollers must rest on curved or straight portions of tube lying on the plane of the tube. In particular, the problem of making immediately adjacent curved portions with curvatures lying on different bending planes is particularly difficult to deal with if, considering two adjacent curves, the first one to be made also has a particularly small bending radius.

From publication <CIT> of the same Applicant, a method is known which solves the problem described above, conceived in particular for the manufacturing of so-called ELM coils for nuclear fusion reactors, i.e., coils for controlling the instabilities located at the edge of the plasma (ELM - Edge Localized Mode). It concerns tubular products that have a particularly complex geometry, with a succession of immediately adjacent curved portions, and which must be made with very tight tolerances. The known method provides for subjecting the tube to a first bending operation with a first bending device, whereby a plurality of first curved portions separated with second straight portions is made. The tube is then subjected to a second bending operation with a second bending device, through which second curved portions are made in the intervals between the first curved portions. These second curved portions may have a reduced bending radius. <CIT> does not deal with making curved portions with a reduced bending radius and having a three-dimensional development.

In the manufacturing of the aforesaid ELM coils, the need is recognized to make corner portions in which, in addition to the curvature necessary to make the corner of a substantially rectangular coil, there is an additional curvature in different planes, superimposed and/or adjacent to the "main" one, with the primary object of obtaining a predetermined distance of the corner of the coil from the mounting surface thereof.

<CIT> discloses a method having the features of the preamble of claim <NUM>. Further methods are disclosed by <CIT>, <CIT>, <CIT> and <CIT>.

An object of this invention is therefore to provide a solution for making the aforesaid corner portions, with a reduced bending radius, so that these curved portions have a three-dimensional development.

More generally, another object of the invention is to provide a solution for making curves having a three-dimensional development in a tubular product.

Therefore, the invention is not intended to be limited to the manufacturing of ELM coils, but may be applied to the manufacture of other types of complex-curvature tubular products.

The aforesaid objects are fully achieved according to an aspect of this invention by a method as defined in the attached independent claim <NUM>.

Advantageous embodiments of the invention are specified in the dependent claims, the content of which is to be understood as an integral part of the description that follows.

In short, the invention is based on the idea of performing a method for making a three-dimensional curve in a tubular product starting with a tube extending along a rectilinear longitudinal axis, comprising the steps of.

wherein said step a) comprises
performing the first bending operation in such a way that the curved portion of the tube leaving said first bending device comprises a first curve and a second curve lying in said bending plane, wherein an inflection point is interposed between said first curve and second curve.

According to a not-claimed embodiment, a method for manufacturing a complex-curvature tubular product starting with a tube extending along a rectilinear longitudinal axis, comprises the steps of.

wherein said step a) comprises
performing the first bending operations in such a way that each second curved portion of the tube leaving said first bending device comprises a first curve and a second curve lying in said bending plane, wherein an inflection point is interposed between said first curve and second curve.

Using such a method, it is possible to manufacture complex-curvature tubular products, i.e., products with immediately adjacent curved portions or with three-dimensional curvature, such as for example ELM coils.

Further features and advantages of this invention will be clarified by the detailed description that follows, given purely by way of non-limiting example in reference to the accompanying drawings, wherein:.

With initial reference to <FIG>, a tubular product obtainable by means of a method according to the invention is generally indicated with <NUM>'. The tubular product <NUM>' comprises first curved portions 10a' and second bent curved portions (in particular, corner portions) 10b" alternating with each other and immediately adjacent. In particular, the second bent curved portions or corner portions 10b" have a bending radius smaller than that of the first curved portions 10a'. As an example of a tubular product <NUM>' obtainable with the method of the invention, <FIG> shows an ELM coil, which comprises a plurality of turns <NUM> each having a plurality of curved sides, corresponding to the first curved portions 10a', and, between each pair of consecutive curved sides, a connecting portion, corresponding to a corner portion 10b", with a bending radius smaller than the bending radius of the curved sides. For example, the coil <NUM>' may have six turns <NUM>, each with four sides 10a', joined to each other by corner portions 10b". Obviously, the number of turns and sides may be chosen at will, depending on the requirements that the coil must meet. With reference to <FIG>, specifically a single second bent curved portion or corner portion 10b" of the tubular product or coil <NUM>' is shown, in particular a corner portion arranged at one of the lower corners or at the upper right corner of the coil of <FIG>. The central axis of the tubular product <NUM>' is indicated with x. As may be seen in <FIG>, the corner portion 10b" has a three-dimensional development; in other words, the central axis x does not lie in a plane. In the corner portion 10b" opposite ends 11b" and 12b" may be identified, at which the corner portion 10b" is joined to respective first curved portions 10a'.

This invention arises from the general observation that, for two straight skew lines in space, there are two mutually parallel planes, each containing one of these straight lines; these planes-which will be referred to in the following as A1 and A2-are placed at a distance d from each other. The tangents t1, t2 to the corner portion 10b" (more precisely, the tangents t1, t2 to the central axis x of the corner portion 10b") at the opposite ends 11b" and 12b" of the angle portion 10b" thus lie on two respective planes A1 and A2 parallel to each other and placed at a distance d from each other.

In the illustrated example, the corner portion 10b" is formed by the superposition or combination of a smooth double S-curve and a sharp curve. In particular, the tangent t1 to the corner portion 10b" at the first end 11b" lies on a first plane A1, and the tangent t2 to the corner portion 10b" at the second end 12b" lies on a second plane A2, parallel to the first plane A1. The distance between the two planes A1 and A2 is indicated with d in <FIG>. The central axis x at the corner portion 10b" is shaped as a double S-curve lying on a cylindrical surface, the generatrices of which are orthogonal to the A1 and A2 planes. More generally, the central axis x at the corner portion 10b" is shaped as a double S-curve, the tangents of which to the ends of the double curve lie on a cylindrical surface, the generatrices of which are orthogonal to the A1 and A2 planes.

With reference now to <FIG>, the manufacturing method of the tubular product <NUM>' starting with a tube <NUM> made of metal material will be described.

The tube <NUM> is represented in the drawings as a tube with a circular cross section, but it may have a cross section with a different shape than circular.

The longitudinal axis x, initially rectilinear, of the tube <NUM> is indicated with x. 10a indicates first straight portions of the tube <NUM> corresponding, in the final tubular product <NUM>', to the aforesaid first curved portions 10a', while 10b indicates second straight portions of the tube <NUM> corresponding, in the final tubular product <NUM>', to the aforesaid second bent curved portions or corner portions 10b". As shown in <FIG>, the first straight portions 10a alternate with the second straight portions 10b and extend immediately adjacent to the second straight portions 10b.

The tubular product <NUM>' is obtained according to the invention with a manufacturing method essentially comprising the steps of:.

In particular, <FIG> shows the aforesaid step a), wherein the tube <NUM> is fed, by means of a feeding device <NUM> (of a type known per se and therefore shown only very schematically in the drawings), to the first bending device <NUM> for performing the aforesaid first bending operations.

The first bending operations are each performed on a respective first straight portion 10a of the tube <NUM> and on a respective second straight portion 10b, and each on a bending plane passing through the longitudinal axis x of the tube, in such a way that the tube <NUM> leaving the first bending device <NUM> comprises a corresponding plurality of first curved portions 10a' which are separated by second curved portions 10b'. The first curved portions 10a' and the second curved portions 10b' may lie on the same bending planes or on different bending planes. The curvature of the second curved portions 10b' is slight and therefore imperceptible in the representation of <FIG>. Each of these second curved portions 10b' corresponds to the aforesaid double S-curve, lying however on a plane passing through the longitudinal axis x of the tube. One of these second curved portions 10b' is specifically represented in <FIG>. In this figure, it should be noted that the curvatures of the second curved portion 10b' are shown exaggerated for reasons of clarity. The second curved portion 10b' comprises a first curve 11b' and a second curve 12b' lying on the same bending plane. This first curve 11b' and this second curve 12b' have respective bending radii R1 and R2 (referring more precisely to the central axis x), which in <FIG> are represented as if they were the same value; however, this condition is not required. An inflection point 13b' is interposed between the first curve 11b' and the second curve 12b'. By way of reference, <FIG> also shows the ends 11b" and 12b" which, differently from what is shown in <FIG>, still lie in the same plane, i.e., the plane of the first curve 11b' and of the second curve 12b'. <FIG> also shows the tangents t1 and t2 and the distance d between the planes A1 and A2.

Preferably, the first bending device <NUM> is a free-form bending device, in which the desired bend is imparted to the tube by means of a movable part of the device which exerts a deformation force on the advancing tube. An example of a bending device of this type is a roller-type bending machine.

A roller bending machine is generally capable of bending the tube only in a certain bending plane passing through the longitudinal axis of the tube. In order to change the bending plane, it is possible to change the relative orientation of the rollers with respect to the tube.

Another example of a free-form bending device is the so-called penetration bending machine, such as described in <CIT>. With such machines it is easier to change the plane of curvature of the tube.

<FIG> also shows the aforesaid step b) of the method according to the invention, wherein the tube <NUM> leaving the first bending device <NUM> is subjected to the aforesaid second bending operations by means of a second bending device <NUM> located downstream of the first bending device <NUM>.

The second bending operations are each performed on a respective second curved portion 10b' of the tube <NUM>, in such a way that the tubular product <NUM>' leaving the second bending device <NUM> comprises, between each pair of first consecutive curved portions 10a', a respective second bent curved portion or corner portion 10b".

With reference in particular to <FIG>, the second bending device <NUM> is preferably a form bound bending device, comprising, in a manner known per se, a mold or die <NUM>, having a groove 28a, and at least one shoe or clamping vise <NUM> with a respective groove 28b. The clamping shoe or vise <NUM> is provided to act on the tube <NUM>, in cooperation with the die <NUM>, to bend the tube <NUM> according to a given curve. The second bending device <NUM> is configured to execute a corner curve superimposed on the second curved portion 10b' and lying on a cylindrical surface having generatrices orthogonal to the planes A1 and A2 shown in <FIG>. More generally, the second bending device <NUM> is configured to execute a corner curve superimposed on the second curved portion 10b', so that the resulting three-dimensional curve has tangents to the opposite ends of the curve lying on a cylindrical surface having generatrices orthogonal to the A1 and A2 planes shown in <FIG>. In the illustrated example, the grooves 28a and 28b are shaped to receive the double S-curve, and the groove 28a of the die <NUM> extends along a surface 28c of the die <NUM> which may be at least partly cylindrical. In particular, the grooves 28a and 28b may be dimensioned in such a way that the corner curve has a bending radius R3 (more precisely, a bending radius R3 at the central axis x) which is smaller than the bending radius R1 and R2 of the first curve 11b' and 12b'. The corner portion 10b" shown in <FIG> is thus obtained.

Optionally, the method may also comprise the operations of measuring the extent of advancement of the tube <NUM> and/or of marking the tube <NUM> during the advancement, respectively by means of a measuring device (not shown, but in any case, of a type known per se) and a marking device (not shown, but in any case, of a type known per se), for example an ink or laser marking device.

The method according to the invention may be carried out, for example, by first performing all the first bending operations by means of the first bending device <NUM>, to obtain all the first curved portions 10a' and the second curved portions 10b' of the tubular product <NUM>', and then performing all the second bending operations by means of the second bending device <NUM>, to obtain all the second corner portions 10b" of the tubular product <NUM>'.

Alternatively, the method according to the invention may be carried out, for example, by performing in sequence the first and second bending operations by means of the first and second bending devices <NUM> and <NUM> respectively to obtain a portion of the tubular product <NUM>' each time comprising at least two first curved portions 10a' and, between each pair of first curved portions 10a', a second corner portion 10b".

In particular, when used for the manufacturing of an ELM coil having a plurality of turns <NUM>, the method according to the invention may be carried out either by making the turns all together, i.e. by first performing all the first bending operations and then all the second bending operations, or proceeding turn by turn, that is to say by first performing the first bending operations envisaged for a first coil and then the second bending operations envisaged for the first coil and then repeating these operations for the subsequent turns.

As already mentioned, a further aspect of the invention relates to an apparatus for manufacturing complex-curvature tubular products starting with a metal tube extending along a rectilinear longitudinal axis x. This apparatus comprises, in addition to the feeding device <NUM>, the first bending device <NUM> and the second bending device <NUM> described above, support means (not shown, but in any case, of a known type) arranged between the first bending device <NUM> and the second bending device <NUM> to support the tube <NUM> leaving the first bending device <NUM>.

The apparatus <NUM> may further comprise the measuring device and/or the marking device mentioned above.

In the preceding description, a method has been described for obtaining a three-dimensional curve in a tubular product <NUM>', applied to the manufacturing of a complex-curvature tubular product comprising first curved portions 10a' and second corner portions 10b". As may be appreciated, this specific method may find a more general application, if it is necessary to obtain a three-dimensional curve comprising a first curve component which has opposite ends extending on a plane, and a second curve component obtained by bending on a cylindrical surface the plane on which the ends of the first curve component lie.

Claim 1:
A method for forming a three-dimensional curve in a tubular product (<NUM>') starting from a tube (<NUM>) extending along a rectilinear longitudinal axis (x), comprising the steps of:
a) performing, by means of a first bending device (<NUM>), a first bending operation in a bending plane passing through said longitudinal axis (x), in such a way that the tube (<NUM>) leaving said first bending device (<NUM>) comprises a curved portion (10b') having opposite ends (11b", 12b"), wherein the tangents (t1, t2) to the curved portion (10b') at said ends, hereinafter first tangent and second tangent, lie in said bending plane; and
b) performing on the curved portion (10b') of the tube (<NUM>) leaving said first bending device (<NUM>), by means of a second bending device (<NUM>), a second bending operation, in such a way to obtain that a bent curved portion (10b") of the tube (<NUM>) having the tangents (t1, t2) at said ends lying in a cylindrical surface having generatrices orthogonal to a plane (A1) containing the first tangent (t1) and to a plane (A2) containing the second tangent (t2),
said method being characterized in that said step a) comprises
performing the first bending operation in such a way that the curved portion (10b') of the tube (<NUM>) leaving said first bending device (<NUM>) comprises a first curve (11b') and a second curve (12b') lying in said bending plane, wherein an inflection point (13b') is interposed between said first curve and second curve.