METHOD AND APPARATUS FOR PRODUCING METAL LATTICE GIRDERS AND LATTICE GIRDER

Technical Field

[01] The present invention relates to a method and an apparatus for producing metal lattice girders, in particular suitable for use as reinforcements of prefabricated elements for construction.

Prior art

[02] Apparatuses that manufacture lattice girders, in particular made of metal, which can be used, for example, for the reinforcement of prefabricated elements for construction, for example modular floors, are known in the art.

[03] As is known, metal lattice girders are structures preferably consisting of at least a first, usually bottom, longitudinal chord, hereinafter referred as bottom chord for brevity, preferably a pair of bottom chords, and of a second, generally top, longitudinal chord, hereinafter top chord for brevity, arranged at a certain height with respect to the at least one bottom chord. The top chord and the at least one bottom chord are respectively joined, in particular by electrowelding, by at least one zigzag-shaped diagonal element or by a plurality of diagonal elements arranged or folded to form an inverted V, arranged in succession.

[04] Apparatuses known in the art allow the feeding of the at least one bottom chord and of the top chord, as well as the creation of the diagonal element by bending a respective metal wire suitably fed, and its suitable welding by means of a welding assembly, at the bent portions and the ends, respectively to the top chord and to the at least one bottom chord, to produce the metal lattice girder in a continuous manner.

[05] Finally, the known apparatuses allow the finished lattice girder to be separated from a new lattice girder to be made, using special cutting devices.

[06] In particular, the known apparatuses usually comprise a cutting device, arranged downstream of the welding assembly, comprising at least one bottom cutting device, adapted to separate the bottom chords, and possibly a top cutting device, adapted to separate the top longitudinal chord.

[07] Patent EP2726230 discloses a process and a device for continuously producing a meshtype support or lattice girder. The method involves, in particular, modifying during the continuous production of the mesh-type support the height of the top chord with respect to the bottom chords system, shearing the top chord before changing its height with respect to the bottom chords system. In particular, by arranging a cutting device for the top chord upstream of the welding station, it is possible to separate the top chord only and to modify the height of the lattice girder to be made during the manufacturing process.

[08] Patent EP3141314 discloses a further example of a method and an apparatus for producing metal lattice girders.

[09] Usually the diagonal chord, in the case of a single zigzag-shaped element and in the case of a succession of V-folded elements, is welded to the top chord at a folded portion, which results to be longitudinally interposed, when it is viewed from the top, for example in a substantially central position, with respect to the portions in which the branches converging to the same bent portion are joined to the respective bottom chord.

[10] Consequently, when the lattice girder is separated from the bottom chords and the top chord by the cutting devices arranged downstream and upstream of the welding station, the top chord has, both forward and rearward, a final section protruding with respect to the area of junction with the diagonal chord.

[11] These protruding sections are useless from a structural point of view, and therefore represent a waste, and, moreover, can represent a danger for operators who, on site, have to handle them. Sometimes, however, it may be useful, in order to facilitate assembly, to be able to adjust the length of the aforementioned protruding sections as desired.

Disclosure

[12] The aim of the present invention is to solve the aforementioned problems, by devising a method and an apparatus for producing metal lattice girders that maximizes productivity, operating in an effective and versatile way.

[13] In particular, it is an object of the present invention to devise a method and an apparatus that optimally carry out, in relation to the production needs, the production of metal lattice girders.

[14] Within this aim, it is a further object of the present invention to provide an apparatus of simple constructive and functional design, which is safe and reliable in operation, as well as relatively inexpensive.

[15] The cited objects are achieved, according to the present invention, by the method for producing metal lattice girders according to claim 1 and by the apparatus of claim 9.

[16] According to the invention, a method is proposed for producing metal lattice girders, made by joining, respectively, at least a first longitudinal chord, preferably a pair of first chords, and at least a second longitudinal chord, arranged at a specific distance or height with respect to the at least one first chord, to at least one diagonal element, preferably a pair of diagonal elements, having an alternating zigzag pattern between the at least one first chord and the second chord. The diagonal element can have a continuous developement or can be made up of a plurality of individual V-shaped or inverted V-shaped profiles, arranged in longitudinal succession.

[17] The method involves preparing a first advance assembly suitable for engaging the at least one first chord so as to advance a girder in formation and a second advance assembly suitable for engaging the second chord so as to advance the second chord. [18] The method also provides for pitch feeding the at least one first chord and the at least one second chord along a direction of advance by means of the first advance assembly and/or the second advance assembly.

[19] Furthermore, the method provides for forming, by a forming assembly, along the direction of advance, and pitch feeding at least one diagonal element.

[20] In an appropriate temporal relation, with respect to the steps of feeding and forming, the method provides for cyclically joining, at each pitch, at a welding station, a portion of the at least one first chord to a base portion of the diagonal element and a portion of the at least one second chord to a vertex portion of the diagonal element, to form a lattice girder.

[21] According to the method, the second chord is sheared by means of a cutting device arranged upstream of the welding station, determining a separation zone between a final section of the second chord of the lattice girder in formation and an initial section of the second current intended to be part of a girder to be started.

[22] This shearing is carried out in a controlled manner, to adjust a projection of the final section of the second chord with respect to the diagonal element to which it is already attached in the girder to be made.

[23] Advantageously, the method provides for operating in a controlled manner a retraction, advance or stop of the second chord of the girder to be started, with respect to the first chord, by engaging the initial section of the second chord by means of the second advance assembly, operated independently of the first advance assembly, to adjust a projection of the aforementioned initial section with respect to the diagonal element to which it is intended to be joined in the girder to be started.

[24] In order to finish the lattice girder to be started and the lattice girder being formed, the aforementioned feeding, forming and joining steps are repeated in an appropriate temporal relation.

[25] The method may provide that the step of shearing the second chord occurs by stopping the advance of the lattice girder being formed, in an intermediate time for an additional stop, between two consecutive stops of the pitch advance.

[26] The method may provide, alternatively or in addition, that the step of shearing the second chord takes place at a stop of the pitch advance of the lattice girder being formed.

[27] The method can also provide for the further step of moving the cutting device according to an adjustment motion in the direction of advance until reaching the separation zone between the initial section and the final section, to be separated.

[28] The method may provide, after the step of shearing the second chord, for moving at least the second advance assembly in a direction transverse, in particular perpendicular, to the longitudinal direction, to adjust the height of the girder to be started. Preferably, the second advance assembly is moved together with the cutting device. [29] The method can usefully provide for controlling the steps of shearing the second chord and/or activating in a controlled manner a respective advance, retraction or stopping of the second chord, by means of a control unit, to regulate the initial section and/or the final section of the second chord.

[30] Advantageously, the method can provide for sending to the aforementioned control unit as input data a measurement of a desired longitudinal extension for the second chord and/or of a desired projection for the final section, with respect to a vertex portion of the diagonal element joined thereto, for the girder being formed, so as to correspondingly activate the step of shearing the second chord by the cutting device.

[31] The method can include the step of sending to the aforementioned control unit as input data a measurement of a desired projection for the initial section of the second chord, with respect to a vertex portion of the diagonal element to which it is intended to be joined, in the lattice girder to be started, so as to correspondingly activate the step of activating in a controlled manner the retraction, advance or stopping of the second chord of the lattice girder to be started.

[32] The apparatus according to the invention, for producing the aforementioned metal lattice girders, comprises a first advance assembly for feeding in a direction of advance at least a first chord, a second advance assembly for feeding at least a second chord in the direction of advance, spaced out by a distance, in particular a height, with respect to the first advance assembly.

[33] The first and second advance assembly can usefully be operated independently, in order to be able to carry out the advance of the first and second chord in a different way.

[34] The apparatus also comprises a forming assembly configured to form and feed the diagonal element in the direction of advance.

[35] The apparatus further comprises a welding station for joining the diagonal element to the at least one first chord and to the second chord.

[36] The first advance assembly is arranged downstream and the second advance assembly upstream, with respect to the welding station.

[37] The apparatus also includes a cutting assembly, which in turn includes at least one cutting device for the second chord, arranged upstream of the welding station with respect to the direction of advance, and a control unit configured to command a retraction in a controlled manner, an advance or a stop of an initial section of the second chord with respect to the first chord, by means of the second advance assembly, operated independently from the first advance assembly, to correspondingly adjust a projection of the initial section of the second chord with respect to the diagonal element which is intended to be joined in the lattice girder to be formed.

[38] The cutting device can be movable, on command of the control unit, in the direction of advance, to "chase" a portion of separation of the second chord, in which to separate a final section from the aforementioned initial section.

[39] This chasing can serve to coincide a stop in the pitch advance of the chords with the moment when the aforementioned separation portion reaches the drawing device, thus avoiding an additional stop to carry out the separation only.

[40] The aforementioned control unit can be configured to receive as input data a measure of a desired longitudinal extension of the second chord in the lattice girder being made and/or of a desired projection for a final section of the second chord with respect to a vertex portion of the diagonal element joined thereto, so as to correspondingly activate the cutting device.

[41] The control unit can be configured to receive as input data a measure of a desired projection for an initial section of the second chord with respect to a vertex portion of the diagonal element in the lattice girder, so as to correspondingly activate the retraction, advance or stop of the second chord.

[42] The second advance assembly and the cutting device can be usefully movable in a direction transverse to the direction of advance, in particular perpendicular, to vary the height of said lattice girder to be made.

[43] The lattice girder according to the invention comprises at least one first longitudinal chord, preferably a pair of first chords, a second longitudinal chord, spaced out at certain distance or height from the at least one first chord, at least one diagonal element, preferably a pair of diagonal elements, joined to the first chord and to the second chord arranged spaced. The diagonal element has an alternating zigzag pattern between the at least one first chord and the second chord.

[44] The first chord and the second chord have a differentiated longitudinal extension. This allows, in particular, to adjust the projection of the second chord with respect to the diagonal element to which it is attached, according to the needs of use.

[45] For example, it is possible to reduce this projection and, with it, the use of material.

[46] A reduction of this projection can also serve to make the lattice girder safer and easier to handle.

[47] Preferably, the second chord substantially does not protrude from the diagonal element attached thereto, maximizing in this way the advantages mentioned above.

[48] Preferably, at the opposite longitudinal ends of the lattice girder, the second chord protrudes from the diagonal element attached thereto, for longitudinal portions protruding in the same way, or protruding in a differentiated way, or not protruding.

Description of drawings

[49] The details of the invention will be more apparent from the detailed description of a preferred embodiment of the apparatus for producing metal lattice girders according to the invention, illustrated by way of example in the accompanying drawings, in which: Figures 1 to 8 are respectively a side view of the apparatus according to the invention, in subsequent operational steps;

Figure 7a is an enlarged detail of the apparatus shown in Figure 7;

Figures 9, 10 and 11 are respectively a perspective view, a side view and a front view of a lattice girder that can be produced by using the apparatus according to the invention.

Description of embodiments of the invention

[50] With reference to Figures 1 - 10, the apparatus according to the invention, for producing metal lattice girders 10 by joining at least one first longitudinal chord 11 , preferably a pair of first chords 11 , and at least one second longitudinal chord 12, arranged at a certain distance or height H from the at least one first chord 11 , to at least one diagonal element 13 or fret having an alternating zigzag pattern between the at least one first bottom chord 11 and the at least one top chord 12, has been indicated with the reference number 1.

[51] In particular, the case where the lattice girder comprises a plurality, for example a pair, of second elements 12 shall be meant included.

[52] Usually, the first chord 11 is arranged at the bottom in operation, while the second chord 12 is arranged at the top in operation. Therefore, it can generally be understood that the first chord 11 is the bottom chord and the second chord 12 is the top chord.

[53] The diagonal element 13 can be continuously developed, as illustrated by way of example in Figures 9 and 10, or can be made of a plurality of individual repeated profiles, each being substantially shaped like a triangle without a base, in particular like an inverted V, and arranged in a longitudinal succession between the at least one first chord 11 and the second chord 12.

[54] More precisely, the diagonal element 13, with single or continuous profiles, preferably has, in the assembled condition, a succession of pairs of branches, a first branch 13a and a second branch 13b, converging at a vertex portion 13c, arranged at the apex of a triangular, in particular V-shaped or inverted V-shaped, profile joined to the second chord 12. In the presence of a continuous diagonal element 13, the aforementioned triangular profiles are also mutually joined through folded base portions 13d, intended to be joined, for example inside the lattice girder 10, to a respective first chord 11 . In the case of a diagonal element 13 with single profiles, on the contrary, the base portions 13d are separated, but joined in a completely similar way to the respective first chord 11 .

[55] In the case shown for merely illustrative purposes, the lattice girder 10 comprises a pair of first chords 11 , joined to a second chord 12 by a pair of continuous diagonal elements 13, arranged on one side and on the opposite side with respect to the second chord 12, in turn arranged substantially centrally with respect to the first chords 11. In particular, the first chords 11 and the second chord 12 can be arranged in such a way that the lattice girder 10 shapes, in the assembled configuration, a substantially triangular, for example isosceles or equilateral, section. Alternatively, different conformations of the lattice girder 10 can be provided, which is made by the combination of at least a first chord 11 , a second chord 12 and a diagonal or fret 13.

[56] Hereinbelow, reference will be made to the illustrated example, with a pair of first chords 11 ; however, embodiments in which the lattice girder 10 to be made comprises a different number of first chords 11 , in particular only one first chord 11 , are intended to be included within the scope of protection of the present invention.

[57] The second chord 12 has, in the completed lattice girder 10, an initial section 12a and a final section 12b. The initial section 12a and the final section 12b are respectively joined to the vertex portion 13c of the initial pattern or fret and the final pattern or fret of each diagonal element 13 (see Figure 10). According to the invention, these sections can be protruding as desired or matching, therefore substantially not protruding, with respect to such junctions.

[58] In particular, according to the invention, the longitudinal extension L _s of the second chord 12 in the finished lattice girder 10 can be made as desired, in particular equal to, greater or smaller than the longitudinal extension Li of the first chord 11 , thus determining a projection that can be determined as desired, correspondingly, of the initial section 12a and/or of the final section 12b of the second chord 12, with respect to the vertex portion 13c of each diagonal element 13 to which the respective section is joined.

[59] Essentially, according to the invention, the extension of these projections can be adjusted in a range that extends, in absolute terms, from a substantially zero value to any value.

[60] The apparatus 1 includes a first advance assembly 2 for the first chords 11 , a second advance assembly 3 for the second chord 12, a forming assembly 4 to form and feed the diagonal chord 4 and a welding station 5 comprising at least a first welding assembly 51 of the first chord 11 and a second welding assembly 52 of the second chord 12.

[61] The apparatus also includes a cutting assembly 6, divided into different devices, to cut the first chords 11 , the second chord 12 and the diagonal element 13, in order to then unload the finished metal girders 10.

[62] More precisely, the apparatus 1 includes a frame 7 intended to support the operating assemblies and, in operation, the components intended to form the lattice girders 10.

[63] The frame 7, in particular, defines a support plane 70 for the components of the lattice girder 10 during processing.

[64] It is possible to provide that, preferably, a succession of lattice girders 10 is produced continuously, and that from time to time a finished lattice girder 10 is separated from the girders 10 being made, present at the end of the line on the support plane 70.

[65] At any time, for example, the frame 7 can support along its respective longitudinal extension the components of a lattice girder 10 being made and possibly an at least one partially already made lattice girder 10'.

[66] Finally, the apparatus 1 comprises a control unit adapted to control the operating members of the apparatus 1 , in particular the advance of the components of the lattice girder 10 and/or the activation of the cutting assembly 6.

[67] The apparatus is associated with unwinding and/or drawing means of the type known in the art to receive each metal wire intended to become the components of the lattice girder 10.

[68] More precisely, the apparatus 1 receives each first chord 11 along a feed line A, the second chord 12 along a spaced out feed line B, in particular spaced above each feed line A, and the diagonal elements 13.

[69] The first advance assembly 2 is preferably operatively arranged downstream of the welding station 5, to engage components of the lattice girder 10 being made that are already mutually joined by welding and therefore to be able to drag them integrally in advance, preferably via pitch feeding. More precisely, the first advance assembly 2 is arranged downstream of the welding station 5, with respect to a way of advance of the lattice girder in a direction of advance C, from an input station 8 to an output station 9 of the apparatus 1. This way of advance is shown in the figure by the arrow representing the direction of advance C.

[70] Preferably, the first advance assembly 2 is configured to engage the first chords 11 and feed them on the support plane 70 in a pitch advance motion along the direction of advance C (see Figure 1 ).

[71] The first advance assembly 2 may for example comprise a clamp drawing device, preferably configured to engage the first chords 11 when they are downstream of the welding station 5, that is at a part of the lattice girder 10 where the first chords 11 are already welded to the diagonal elements 13 and the latter to the second chord 12, so as to be able to drag forward along the direction of advance C also everything that is joined to the first chords 11. The clamp drawing device, whose actuating means 20 are shown in Figures 1 - 8, is for example mounted on a respective carriage 21 movable on respective guides by a reciprocating motion, first in one way and then in the opposite way, along the direction of advance C, to achieve said pitch advance.

[72] For example, said reciprocating motion is created for example by means of a crankshaft device.

[73] More precisely, the aforementioned pitch of advance corresponds to the pitch P of the profile of the diagonal chord 13 of the girder 10 to be made (see Figure 9).

[74] The second advance assembly 3 is operatively arranged upstream, according to the aforementioned way of advance, of the welding station 5 and is configured to move forward the second chord 12 along the spaced out feed line B, in particular arranged above each base feed line A, spaced out by a height substantially equal to the height H of the girder 10 to be formed.

[75] The second advance assembly 3 can be made by means of a so-called "pinch roll" device adapted to engage and drag the second chord 12 forward. This advance can be usefully performed in a controlled manner, for example by means of the control operated by the aforementioned control unit of the apparatus 1.

[76] The second advance assembly 3 can alternatively be arranged in an active configuration, in which it engages the second chord 12 to hold it stationary or to perform a controlled movement thereof along the direction of advance C, for example of advance or retraction, and in an inactive configuration, in which it does not engage the second chord 12.

[77] Advantageously, the second advance assembly 3 is mounted on a movable, in particular sliding, slide 30 along guides 71 , which are preferably at least one pair, fixed to the frame 7 of the apparatus 1 . More precisely, the slide 30 is associated with drive means 31 , adapted to command a transverse, in particular perpendicular, movement with respect to the direction of advance C, in order to adjust the distance between each feed line A and the spaced out feed line B. In this way it is possible to adjust, in particular modify, according to the production needs, the height H of the girder 10 to be made.

[78] The second advance assembly 3, in particular the slide 30, can carry a guide channel 32, arranged along the spaced out feed line B, adapted to slidably house the second chord 12, to facilitate its advance to the welding station 5, as described in detail heareafter. Preferably, the guide channel 32 extends, continuously or discontinuously, between the second advance assembly 3 and the operating members of the welding station 5, intended to act on the second chord 12 (see Figure 7a).

[79] Like the second advance assembly 3, the forming assembly 4 is also operatively arranged upstream of the welding station 5. It serves to form the fret-shaped or substantially triangular profile of each diagonal element 13 on the support plane 70 and to arrange it in the correct position for welding to the first chords 11 and to the second chord 12. For this purpose, the forming assembly 4 may comprise a "Z-shaping" machine of the type known in the art. In particular, at each forming cycle, the forming assembly 4 arranges a base portion 13d of each formed pattern at a forming plane D perpendicular to the direction of advance C and to the support plane 70, arranged upstream of the welding station 5, in particular upstream of the second welding assembly 52 of the second chord 12, with respect to the aforementioned way of advance along the direction of advance C.

[80] The welding station 5, which is interposed between the first advance assembly 2 and the second advance assembly 3, comprises the first welding assembly 51 , adapted to join on the support plane 70 each first chord 11 to the respective diagonal element 13, and the second welding assembly 52, arranged upstream of the first welding assembly 51 with respect to the way of advance of the girder 10. The second welding assembly 52 is adapted to join the second chord 12 to each diagonal element 13, in particular on opposite sides of the second chord 12 itself. More precisely, at each welding cycle, the second welding assembly 52 joins the vertex portions 13c of the diagonal elements 13 to the second chord 12 at a welding plane E of the second chord, perpendicular to the direction of advance C and to the support plane 70.

[81] Both the first welding assembly 51 and the second welding assembly 52 preferably comprise at least one electro-welding device known in the art, suitable for the mutual joining of metal, in particular iron, wires.

[82] The cutting assembly 6 advantageously comprises at least one cutting device 61 for cutting the second chord 12 at a cutting plane F perpendicular to the direction of advance C and to the support plane 70 (see Figure 1 ).

[83] The cutting device 61 is preferably adjustable in a transverse, in particular perpendicular, direction to the direction of advance C, therefore in a substantially vertical direction, if the first chords 11 and the second chord 12 are fed in a substantially horizontal direction. The cutting device 61 is thus configured to adapt its positioning, in the aforementioned transverse direction, to the height H of the girder 10 being formed.

[84] For example, the cutting device 61 can be carried by the same slide 30 that carries the first advance assembly 3, being so movable integrally therewith.

[85] The cutting device 61 can for example be of the electric shears type.

[86] The cutting assembly 6 also includes a separation device 62, aligned with each feed line A, preferably arranged downstream of the first advance assembly 2, according to the aforementioned way of advance, to separate, for example by shearing, the first chords 11 and diagonal elements 13 and thus make it possible to separate and unload the girder 10' when it is already formed. The separation device 62 operates at a separation plane G transverse to the direction of advance and substantially perpendicular to the support plane 70.

[87] Preferably, the separation device 62 includes a pair of shears, each on a respective feed line A, to cut both the first chords 11 and the diagonal elements 13 at a respective final section.

[88] The cutting assembly 6 can also include an auxiliary separation device 63, aligned with the spaced out feed line B, possibly intended to carry out the separation, for example by shearing, of the second chord 12 in cases where it is not cut by the cutting device 61.

[89] Preferably the auxiliary separation device 63 is arranged substantially at the same longitudinal position as the separation device 62 along the way of advance, to operate on the same separation plane G (see for example Figure 1 ). The auxiliary cutting device 63 is used, for example, to produce a girder 10 whose longitudinal extension L _s of the second chord 12 is equal to that of the first chords 11 . [90] In particular, the separation device 62 and the auxiliary separation device 63, if provided, can be mounted at a fixed longitudinal distance with respect to the welding station 5, in correspondence with the output station 9 of the apparatus 1 .

[91] For example, the separation device 62 and the further separation device 63 can be mounted on a single structure 64 secured to the frame 7 of the apparatus 1 .

[92] Preferably the auxiliary separation device 63 is fixed in the longitudinal direction, while it is movable, in particular adjustable, in the direction transverse to the direction of advance C, to vary its height according to the height H of the girder 10 to be made.

[93] The operation of the apparatus for producing metal lattice girders according to the invention is understandable from the foregoing description.

[94] In an initial preparation phase, the drawing and/or unwinding means associated with the apparatus 1 is activated, to feed thereto the metal wires intended to become the first chords 11 , the second chord 12 and the diagonal elements 13 of the girder 10 being formed. The metal wires involved are therefore inserted at the input 8 of the apparatus 1 .

[95] The forming assembly 4 is then activated to begin forming the first fret of the girder 10 to be made and the first chords 11 are fed along the feed lines A and the spaced out feed line B, in an appropriate phase relationship, on support plane 70 and, respectively, the second chord 12, at a distance corresponding to the height H of the girder to be formed.

[96] The production cycle of the girder 10 is therefore started, through the repetition of advance steps, alternating with the steps, in particular of stopping, for welding the different wires involved.

[97] Figure 1 shows, in particular, an already late production step, in which a partially formed girder 10' is already inside the apparatus 1 on the support plane 70 and a girder 10 instead starts to be formed. In particular, the trailing fret of the at least partially formed girder 10' is already welded to the respective second chord 12, therefore it is arranged downstream, according to the way of advance, of the second welding assembly 52.

[98] More precisely, at the trailing end of the at least partially formed girder 10' the second chord 12 has a final section 12b already separated from the initial section 12a of the second chord 12 of the girder 10 to be formed.

[99] Instead, at the same trailing end, the first chords 11 may be continuous, therefore not yet separated from the sections which are intended to constitute the first chords 11 of the girder 10 to be formed. This is determined by the fact that the trailing end of the at least partially formed girder 10' is disposed upstream, with respect to the way of advance, of the separation plane G where the described means operates, specifically adapted to separate the first chords 11 .

[100] During this step, the advance assemblies 2, 3 are stationary and it is possible to carry out a welding cycle. The second welding assembly 52 and the first welding assembly 51 are preferably operated substantially at the same time, to join, respectively, the vertex portion 13c of a first fret to the second chord 12 of the girder 10 being formed and a base portion 13d for each diagonal element 13 to the respective first chords 11 of the at least partially formed girder 10' (see Figure 1 ). In practice, to complete the formation of the girder 10', the first welding assembly 51 must be activated, preferably simultaneously with the second welding assembly 52, to weld the respective first chords 11 to the diagonal elements 13.

[101] Subsequently, the first advance assembly 2 is activated to advance the at least partially formed girder 10' at a pitch P and, together, the first chords 11 of the girder 10 being formed. This is made possible by the fact that the first chords 11 of the at least partially formed girder 10' and of the girder 10 being formed are without interruption, as noted above (see Figure 2).

[102] At the same time, the second advance assembly 3 is arranged in the inactive condition, of disengagement of the second chord 12. The latter is in fact dragged by the first advance assembly 2, due to the fact that it is integral with the first chords 11 because of the connection just carried out to the diagonal elements 13.

[103] Following this advance, the vertex portion 13c of a second formed fret, for each diagonal element 13, and an advanced portion of the second chord 12 of the girder 10 being formed arrive at the second welding assembly 52, while a correspondingly advanced base portion 13d of the diagonal elements 13 arrives, together with respective advanced portions of the first chords 11 , at the first welding assembly 51 .

[104] As previously described, at this point the welding assemblies 51 , 52 are activated to join, respectively, the aforementioned base portion 13d of each diagonal element 13 with each first chord 11 , in the at least partially formed girder 10', and the second fret of each diagonal element 13 to the second chord 12, in the girder 10 being formed.

[105] Then, there is an alternation of a cycle of advance carried out by the first advance assembly 2 and a stop to perform the welding by the welding assemblies 51 , 52, thereby joining further frets in the girder 10 being formed and, respectively, in the partially formed girder 10’ (see Figures 3 - 5). In particular, Figure 5 shows five frets formed and joined in the girder 10 being formed.

[106] When, after successive steps of advance, a portion of the second chord 12 intended to become the final section 12b in the girder 10 being formed reaches the cutting device 61 of the cutting assembly 6, i.e. when the section of the second chord 12 that has passed the cutting device 61 has reached the desired longitudinal extension L _s of the second chord 12, the apparatus 1 then cuts the second chord 12 at the cutting plane F. For this purpose, the advance of the girder 10 can be, if necessary, specifically suspended to allow the cutting device 61 to shear the second chord 12 (see Figure 6). In the step illustrated in Figure 6, by way of example, it is noted that the girder 10 being formed is sheared at the second chord 12 when it has eight formed and joined frets.

[107] As a consequence of the cutting, the final section 12b of the second chord 12 in the girder 10 being formed is separated from the initial section 12a of the second chord 12 of a subsequent girder 10 yet to be started.

[108] The second advance assembly 3 is therefore activated in the active configuration to engage the second sheared chord 12 and activate it in a controlled manner, preferably by said control unit, to produce an advance, a retraction or the stop of the initial section 12a of the same second chord 12. In this way, it is possible to adjust as desired the projection of the second chord 12 with respect to the vertex portion 13c of the first fret, in the leading part of the girder 10 to be started.

[109] An advance cycle is then resumed at pitch P, interrupted by the cutting cycle.

[110] In particular, the advance of the first chords 11 is operated by the first advance assembly 2.

[111] At the same time, the second advance assembly 3 in the active configuration carries out the advance of the portion of the second sheared chord 12, free from diagonal elements 13, until, after a subsequent stop through the welding station 5, it is indirectly joined to the first chord 11 by the diagonal elements 13. In this condition, of joining to the diagonal elements 13 and, indirectly, to the first chords 11 , the second chord 12 can then be dragged by the same first advance assembly 2.

[112] When the terminal section 12b of the second chord 12 of the girder 10 being formed arrives at the second welding assembly 52, the junction of this chord with the diagonal elements 13 is performed, in particular with the last fret which, in the example illustrated, is the twelfth (see Figure 7). Preferably at the same time, the first welding device 51 is also activated, to join the first chords 11 to respective base sections 13d of the diagonal elements 13.

[113] The initial section 12a of the second chord 12 intended to be assembled in the next girder 10 can be retained stationary by the second advance assembly 3, for example at the cutting plane F, or retracted or advanced, so as to adjust its extension in the next production cycle, in particular to adjust, for example usefully reduce, the projection of this section in the girder 10 to be started. More precisely, the initial section 12a of the next girder 10 to be formed can stop upstream of the guide channel 32 (see Figure 7a).

[114] In the next step, after a further pitch advance P operated by the first feed assembly 2, and a controlled advance, operated by the second advance assembly 3 on the second chord 12, it is possible to start the formation of a further lattice girder. More precisely, the control unit independently controls the activation of the second advance assembly 3, so that the advance of the second chord 12 takes place in a controlled manner and therefore the initial section 12a of the new girder 10 reaches the second welding assembly 52 so as to protrude in a desired manner from the junction with the vertex portion 13c, possibly of a projection even substantially null, depending on the production needs.

[115] At the same time, in the girder 10, as previously described for the partially formed girder 10', the junction of the base portions 13d of the frets of the diagonal elements 13 to the first chords 11 continues via the first welding assembly 51 .

[116] When the now completed lattice girder 10' reaches the separation plane G at the output station 9, the separation device 63 cuts the first chords 11 and the diagonal elements 13 (see Figure 8) and the finished lattice girder 10' can be unloaded from the apparatus 1.

[117] The production cycle continues, repeating the steps as aforesaid for forming the new girder 10 and for finishing the girder 10 arranged in succession to the first, in the direction of advance C according to the way of advance.

[118] According to a different embodiment, not shown in the figures, it is possible to provide that the cutting device 61 is mounted and can move with a longitudinal adjustment motion in the direction of advance C.

[119] This longitudinal adjustment motion allows the cutting device 61 to reach the longitudinal position in which, in a given welding stop during a production cycle, the second chord section 12, intended to become the final section 12b, is interposed between the second advance assembly 3 and the second welding device 52. It is possible to provide that in this case the guide channel 32, if provided, has an adequate longitudinal development, for example it is suitably interrupted, so as to allow, without interference, an appropriate longitudinal adjustment stroke to the cutting device 61 .

[120] This adjustment motion therefore allows "chasing" a separation zone, at which the initial section 12a from the aforementioned final section 12b is separated in the second chord 12. Thanks to this "chasing" it is possible to obtain the advantageous result of avoiding an additional stop, in addition to the welding stops, which would only be necessary to cut the second chord 12 between one lattice girder and another. It is thus possible to carry out both the cutting operation of the second chord 12 in the desired separation zone and the welding operation in the same stop.

[121] In this case, the apparatus 1 can advantageously comprise drive means to correspondingly drive the cutting device 61 in the direction of advance C and, preferably, corresponding guide means.

[122] The control unit of the apparatus 1 can then control said actuation means to ensure that the shearing of the second chord 12 at the desired longitudinal extension L _s occurs precisely, in the same welding step.

[123] According to a further embodiment, not shown in the figures, the cutting assembly 6 can include, in addition to the separation device 62, only the cutting device for the second chord 12, arranged upstream of the welding station, in particular indicated with the reference number 61 in the embodiments described above, without using the auxiliary separation device 63.

[124] This solution therefore advantageously allows the overall cost of the apparatus 1 to be reduced, thanks to the elimination of a second device for separating the second chord 12.

[125] The method for producing metal lattice girders, as well as the apparatus capable of implementing it, according to the invention, therefore allow the production of metal lattice girders, even those having particular shapes, quickly and effectively.

[126] In the practical embodiment of the invention, the materials used, as well as the shape and the dimensions, may be modified depending on needs.

[127] Should the technical features mentioned in any claim be followed by reference signs, such reference signs were included strictly with the aim of enhancing the understanding of the claims and hence they shall not be deemed restrictive in any manner whatsoever on the scope of each element identified for exemplifying purposes by such reference signs.