Method of welding a receptacle to a metal sheet and welding system performing said welding method

Abstract

A method for welding the outer perimeter edge (2) of a tank (1) to the inner perimeter edge (4) of a through-hole (5) formed in a metal sheet (6) comprising a preparation step comprising inserting the tank (1) into a welding jig (8), placing the metal sheet (6) on the outer perimeter edge (2) of the tank (1) and securing the metal sheet (6) and the tank (1) to the perimeter edge (8a) of the welding jig (8), followed by a step of detecting the position of the through-hole (5) of the metal sheet (6) in relation to a reference coordinate system comprising a first sub-step of checking the approximate position of the through-hole (5) and a second sub-step wherein the precision position of the through-hole (5) is checked. If the approximate and precision positions coincide, the welding executive step takes place in a system (100) comprising a movable base (25) supporting the welding jig (8), clamping means (23) for clamping the metal sheet (6) and the tank (1) to the welding jig (8) and a robotic arm (22) with associated a welding torch (7) and a laser pointer (21).

Description

[0001] METHOD OF WELDING A RECEPTACLE TO A METAL SHEET AND WELDING SYSTEM PERFORMING SAID WELDING METHOD.

[0002] DESCRIPTION

[0003] The invention relates to a method for welding a receptacle coaxially to a through-hole formed in a metal sheet.

[0004] The invention relates, in particular, to a method for welding the perimeter edge delimiting the outside of a tank to the inner perimeter edge of a through-hole made in a metal sheet.

[0005] The invention also relates to a welding system that carries out the aforesaid welding method.

[0006] It is well known that in order to produce sinks for kitchens or similar equipment, such as washtubs, they are used tanks made by folding or deep moulding, which are welded to the inner perimeter edge of a through-hole made in a metal sheet that, once welded, will form the work surface of the sink or washtub.

[0007] In particular, according to a preferred but not exclusive embodiment, the tank herein described has a square shape with substantially rectilinear sides with a slight concavity directed towards the inside of the tank itself and connected at the comers, and the hole, made in the metal sheet, also square-shaped, is delimited by sides connected with each other at the comers.

[0008] Obviously, sinks and washtubs can be made from a single metal sheet in which several through-holes are formed, into each of which a tank is welded.

[0009] According to a well-known embodiment, the tank has the opening mouth delimited by a perimeter edge folded outwards, which is configured to receive the metal sheet whose through-hole is placed coaxial to the opening mouth of the tank and whose inner perimeter edge is welded to the outer perimeter edge of the tank.

[0010] In order to obtain a quality product, it is important that the welding is carried out in a workmanlike manner, and to this end, it is essential that the preparatory operations for the mutual positioning of the metal sheet and the tank that have been described are also carried out in a workmanlike manner.

[0011] For this purpose, according to the prior art, special welding jigs are used, each having a profile adapted to receive the insertion of the tank body and keep it fixed in position while performing the subsequent sheet positioning and hole centring operations, which are performed manually by the operator. Then, the operator clamps the metal sheet and tank to the perimeter edge of the welding jig to keep them mutually fixed during the following welding operation, which can be performed either manually or automatically in a specific welding system.

[0012] A first recognised drawback of the prior art that has been briefly described is that the manufacturer must have a large number of welding jigs of different sizes, each suitable for a respective tank, and must also bear the associated costs for manufacturing them.

[0013] In addition, the manufacturer will also have to bear all the costs for their maintenance, which will become necessary over time.

[0014] Another recognised drawback is that the welding jigs have to be repeatedly changed both in case of a manual welding and of a welding performed with an automatic system every time the size of the tanks to be welded changes, and performing these operations involves downtime, which increases production costs and reduces productivity.

[0015] A further recognised drawback of the prior art is that checking the correct positioning of the metal sheet and of the tank, and particularly their centring before welding, is done visually directly by the operator without the aid of specialised instruments, and this does not guarantee that positioning and centring are always carried out in a workmanlike manner.

[0016] In fact, any operator, even an experienced one, may commit unintentional errors of judgement, and furthermore, different operators have different skills, which does not guarantee the qualitative repeatability of the work being performed.

[0017] It is obvious that, if this happens, the tank is welded off-centre in relation to the hole in the metal sheet and the resulting product after welding is unacceptable in terms of quality.

[0018] The present invention intends to overcome the drawbacks that have been set forth.

[0019] In particular, an object of the invention is to realise a method that allows tanks of different sizes to be welded using a single welding jig capable of accommodating tanks of different sizes.

[0020] Another object is that the method of the invention ensures the centring of the tank in the correct welding position.

[0021] A further object is that the method of the invention ensures that welding is always made within predetermined tolerances.

[0022] Not least, an object is that the method of the invention enables to obtain the repeatability of the quality of the welding that is performed.

[0023] The objects set forth above are achieved by the welding method of the invention and the system implementing it, both of which are the subject matter of the invention, the fundamental features of which correspond to those described in the main claim and in the dependent claims to which reference will be made.

[0024] Advantageously, the use of a single welding jig avoids the need to alternate welding jigs of different sizes as the dimensions of the tanks to be welded change.

[0025] This simplifies the work of the operators and eliminates welding downtime required, in the described prior art, to rotate the welding jigs as the dimensions of the tanks to be welded change.

[0026] In addition, production and productivity are also advantageously increased.

[0027] The foregoing objects and advantages shall be better highlighted below during the description of a preferred but not exclusive embodiment of the method and system of the invention, which are provided herein below by way of nonlimiting example, with reference to the appended drawings in which:

[0028] - Figure 1 represents an axonometric view of the welding system of the invention;

[0029] - Figures 2 and 3 represent the side and plan views respectively of the welding system of Figure 1 ;

[0030] - Figures 4 and 5 represent the side and plan views respectively of the welding system of Figures 2 and 3 in an operating step;

[0031] - Figures 6 and 7 represent views from above of two different operating positions of a detail of Figure 4;

[0032] - Figures 8 and 9 represent two side views of the welding system of Figure 4 in two different operating steps;

[0033] - Figure 10 represents the side view of the welding system of Figure 9 in another operating step;

[0034] - Figure 11 represents the plan view of the lower part of the welding system of Figure 10;

[0035] - Figures 12 and 13 represent two partial views of the invention system represented in Figure 1 in two different operating positions; - Figures 14 and 15 represent, in a schematic side view, two details of Figures 12 and 13 respectively in two different operating positions;

[0036] - Figures 16 and 17 represent, in a schematic side view, two details of Figure 15;

[0037] - Figure 18 represents the schematic plan view of Figure 16 or 17.

[0038] The invention relates to a method and a system for performing the welding of the outer perimeter edge 2 of a tank 1 to the inner perimeter edge 4 of a through-hole 5 made in a metal sheet 6 which are represented in Figures 1 to 18.

[0039] In particular, the method of the invention refers to a square-shaped tank 1 which is welded at a through-hole 5, also square-shaped, as it can be observed in Figures 11 to 13 where each square shape is defined by four substantially rectilinear sides with a slight concavity facing the inside of the tank, connected at the comers.

[0040] According to the invention, the method comprises a preparation step during which a plurality of welding preparatory operations are carried out, which first involve providing a welding jig 8, which can be observed in Figures 1 to 13, into which the tank 1 to be welded is inserted as represented, in particular, in Figures 8 to 15.

[0041] In particular, it can be observed in Figure 14 that the outer perimeter edge 2 of the tank 1 is placed against the perimeter edge 8a of the welding jig 8 and the metal sheet 6 is placed against the outer perimeter edge 2 of the tank 1 taking care that the through-hole 5 of the metal sheet 6 is centred above the opening mouth 3 of the tank 1.

[0042] Finally, the metal sheet 6 and the tank 1 are fixed above and against the perimeter edge 8a of the welding jig 8, as represented in Figure 15, by clamping means 23 which will be described hereinafter in detail.

[0043] Once the preparation step has been completed, the step of detecting the position of the through-hole 5 of the metal sheet 6 in relation to a reference system takes place, which comprises: a first sub-step wherein the approximate position of the through-hole 5 is checked and a second sub-step wherein the precision position of the same through-hole 5 is checked in relation to the reference system, which is preferably, but not necessarily, of the Cartesian type.

[0044] In the first sub-step, a set of operations are performed, which, with reference to schematic Figure 18, comprise:

[0045] - the definition of two approximate centring points A, B each positioned on one of two consecutive sides 5a, 5b of the through-hole 5;

[0046] - the detection and storage, in relation to the aforesaid reference system, of the coordinates of both of the aforesaid approximate centring points A, B;

[0047] - the calculation of the length and inclination of the segment 9 connecting the approximate centring points A, B.

[0048] Once these operations have been completed, the approximate position of the through-hole 5 is checked, if the length and inclination of the segment 9 are within the tolerances set by the operator.

[0049] Then, in the second sub-step, another set of operations is performed, comprising:

[0050] - the definition on each side 5a, 5b, 5c, 5d of the inner perimeter edge 4 of the through-hole 5 of two precision centring points 5’a, 5”a; 5’b, 5”b; 5’c, 5”c; 5’d, 5”d which can be observed in Figure 18;

[0051] - the detection and storage, at each of the precision centring points 5’a, 5”a, 5’b, 5”b, 5’c, 5”c, 5’d, 5”d, of the coordinates which, in relation to the aforesaid reference system, define:

[0052] - the position of each side 5a, 5b, 5c, 5d of the through-hole 5 on the Cartesian plane X, Y as can be observed in Figure 18;

[0053] - the position of the upper surface 6a of the metal sheet 6 according to the direction Z orthogonal to the Cartesian plane X, Y that can be observed in Figures 16 and 17;

[0054] - the dimensions of the through-hole 5.

[0055] Once these further operations have been completed, the precision position of the through-hole 5 is checked if the data of the positions of the upper surface 6a of the metal sheet 6 and of each of the sides 5a, 5b, 5c, 5d of the through- hole 5 correspond to the data and dimensions of the through-hole 5 entered by the operator.

[0056] Specifically, measurements and positions are referred to a Cartesian tern consisting of the axes X and Y belonging to the upper surface 6a of the metal sheet 6 and the axis Z orthogonal to the same upper surface 6a.

[0057] The purpose of these measurements is to check the position of the through- hole 5 in space and to calculate the protrusion of the electrode from the welding torch, as discussed below. If the checks of both the approximate and precision positions of the through- hole 5 respectively give negative results and therefore do not coincide, the system stops and the operator intervenes, performs a new check and, based on the error found, carries out a new positioning.

[0058] If, on the other hand, the checks are positive, the execution step takes place during which the following operations are carried out:

[0059] - welding the outer perimeter edge 2 of the tank 1 to the inner perimeter edge 4 of the through-hole 5 of the metal sheet 6;

[0060] - removing from the welding jig 8 the assembled unit comprising the metal sheet 6 and the tank 1 welded together.

[0061] The method now described is implemented by the use of processing means involving at least the following steps:

[0062] - storing the coordinates of the approximate centring points A, B;

[0063] - calculating the length and inclination of the segment 9;

[0064] - checking whether the aforesaid length and inclination are within the tolerances set by the operator;

[0065] - storing the coordinates defining the position of the upper surface 6a of the metal sheet 6 and of each of the sides 5a, 5b, 5c, 5d of the hole 5;

[0066] - using the coordinate values to check whether the positions of the metal sheet 6 and each of the sides 5a, 5b, 5c, 5d of the through-hole 5 correspond to the data and dimensions of the through-hole 5 entered by the operator and to define the protrusion of the welding electrode from the welding torch;

[0067] - defining the welding trajectory by means of algorithms that use geometric parameters and electrode-to-metal sheet distances set by the operator.

[0068] According to the method of the invention, the origin of the reference coordinate system is preferably but not necessarily located at the welding jig 8.

[0069] Regarding the two approximate centring points A, B, preferably but not necessarily, each of them is positioned on the centreline Ma; Mb of the respective side 5a, 5b of the through-hole 5, as observed in Figure 18, and preferably but not necessarily both are marked on the metal sheet 6 while making the through-hole 5.

[0070] The detection of the coordinates of both approximate centring points A, B, is carried out by means of detection means which, preferably but not necessarily, consist of a laser pointer 21 which will be discussed in greater detail later in the description.

[0071] The two precision centring points 5’a, 5”a; 5’b, 5”b; 5’c, 5”c; 5’d, 5”d that are present on each side 5a, 5b, 5c, 5d of the through-hole 5, are arranged on opposite sides of the centreline Ma; Mb; Me; Md of the respective side 5a, 5b, 5c, 5d, each at a distance from the aforesaid centreline equal to of the length of said side.

[0072] The detection and storage of the coordinates defining the positions of the upper surface 6a of the metal sheet 6 and each of the sides 5a, 5b, 5c, 5d of the hole 5 are made by a welding electrode 7a associated with a welding torch 7 operatively connected to an electric welding machine when, at each of the aforesaid precision centring points 5’a, 5”a; 5’b, 5”b; 5’c, 5”c; 5’d, 5”d, the welding electrode 7a comes into contact with the metal sheet 6, alternately on the upper surface 6a of the metal sheet 6 and with the sides 5a, 5b, 5c, 5d defining the inner perimeter edge 4 of the through-hole 5.

[0073] With each contact, the welding electrode 7a closes the electrical circuit of the welding machine and sends an electrical signal to the processing means, which define the position of the through-hole 5.

[0074] More precisely, at each of the precision centring points 5’a, 5”a; 5’b, 5”b; 5’c, 5”c; 5’d, 5”d the welding electrode 7a makes a first contact with the upper surface 6a of the metal sheet 6, as observed in Figure 16, and a second contact with the inner perimeter edge 4 of the through-hole 5 in a position immediately below the upper surface 6a of the metal sheet 6, as shown in Figure 17.

[0075] The welding method of the invention described herein is realised by the welding system, which is also an object of the invention, shown in the appended figures, particularly in Figures 1 to 5 and 8 to 13, in which it is globally indicated by 100.

[0076] It can be observed that, according to the invention, the system 100 comprises a frame 20 associated, at the top, to a robotic arm 22, preferably but not exclusively of the Cartesian type, supporting a welding torch 7 operatively connected to an electric welding machine and provided with the corresponding welding electrode 7a.

[0077] The electric welding machine is not shown and described because it is an electric welding machine of the known type, well known to the person skilled in the art, that can be any type, but preferably, though not necessarily, a TIG welding machine.

[0078] The laser pointer 21 which, as mentioned above, is for detecting the coordinates of the approximate centring points A, B is attached to the welding torch 7.

[0079] In the lower part of the frame 20 there is a movable base 25 which supports the welding jig 8 whose perimeter edge 8a comprises removable inserts 24 which are made of conductive material, preferably but not exclusively of copper, which, as will be better described below, cooperate with special clamping means 23 to constrain the metal sheet 6 and the tank 1 to the welding jig 8 during welding and during the operating steps preceding it.

[0080] The system 100 further comprises computer means, which in turn comprise: memory means, wherein at least one computer product is stored, and at least one microprocessor configured to execute the computer product.

[0081] When the computer product is being processed, it performs a plurality of operations including moving the clamping means 23 in a vertical direction Z orthogonal to the metal sheet 6 according to both directions of the arrow in Figure 14 and moving the robotic arm 22 to move the laser pointer 21 and the welding torch 7, the latter according to the predefined welding trajectory T schematically shown in Figure 11 .

[0082] In the embodiment of the welding system described herein, the movement of the movable base 25 is carried out manually in the horizontal direction according to both directions of the arrow in Figure 5, but in a different embodiment this movement may be carried out by means of motorisation means controlled by the above-mentioned computer product when it is being processed.

[0083] Obviously, other movements that have not been mentioned herein can also be mechanised and controlled by the aforesaid computer means.

[0084] Regarding the frame 20, with particular reference to Figure 1 , it can be observed that it comprises a pair of columns 26 surmounted by a crosspiece 27 supporting the robotic arm 22 and an intermediate structure 28, fixed orthogonally and cantilevered to the pair of columns 26, which supports the clamping means 23.

[0085] Below the intermediate structure 28 there is a base structure 29, also visible in Figures 2 to 5, which comprises the movable base 25 supported by sliding guides 31 to move closer to and away from the frame 20, on which the welding jig 8 rests with its removable conductive inserts 24 forming its perimeter edge 8a.

[0086] There are also motorisation means for moving the robotic arm 22, the clamping means 23 and the movable base 25, which are not shown in the drawings as they are components well known to persons skilled in the art.

[0087] Regarding the aforementioned intermediate structure 28, it comprises a pair of sideboards 32 which are parallel to each other and are fixed orthogonally and cantilevered to the columns 26 and a pair of crosspieces, comprising a fixed front crosspiece 33 and a movable rear crosspiece 34, which are parallel to each other, spaced apart and orthogonal to the sideboards 32.

[0088] In particular, the fixed front crosspiece 33 has its ends 33a attached to the projecting ends 32a of the sideboards 32 and the movable rear crosspiece 34 has its ends 34a slidably associated with the sideboards 32 and movable along the sideboards 32 themselves.

[0089] The intermediate structure 28 is completed by a first movable bracket 35 and a second movable bracket 36 that are placed between the sideboards 32, are parallel to each other and to the same sideboards 32 and are both slidably associated as cantilevered to a longitudinal guide 37 supported by the columns 26 and parallel to both the fixed front crosspiece 33 and movable rear crosspiece 34.

[0090] The intermediate structure 28, as it can be observed in the figures, thus takes on the configuration of a substantially rectangular frame delimited by the sideboards 32 and by the crosspieces 33 and 34, within which the first movable bracket 35 and the second movable bracket 36 are arranged.

[0091] In addition, in the intermediate structure 28 the movable rear crosspiece 34 can be moved closer to and away from the fixed front crosspiece 33 while remaining parallel thereto, and both movable brackets 35 and 36 can be moved closer to and away from each other while remaining parallel and orthogonal to the crosspieces 33 and 34.

[0092] The intermediate structure 28 structured in this way is adapted to support the clamping means 23 mentioned above and arrange them aligned with the underlying removable conductive inserts 24, which define the perimeter edge 8a of the welding jig 8 to constrain the metal sheet 6 and the tank 1 before and during welding operations.

[0093] Regarding the clamping means 23, it can be observed in the figures, particularly in Figures 3, 5 and 11 , that they comprise:

[0094] - first clamping means 23a that are associated with the fixed front crosspiece 33;

[0095] - second clamping means 23b that are associated with the movable rear crosspiece 34;

[0096] - third clamping means 23c that are associated with the first movable bracket 35;

[0097] - fourth clamping means 23d that are associated with the second movable bracket 36.

[0098] Each of the clamping means 23, as it can be observed in particular in Figure 8, comprises a pressor 38 made of conductive material, preferably but not necessarily copper, which is associated with an actuator 39 configured to move the pressor 38 relative to the underlying removable conductive insert 24. All of the clamping means 23 may be moved according to their alignment direction and in particular the first clamping means 23a may be moved along the fixed front crosspiece 33 and the second clamping means 23b, the third clamping means 23c and the fourth clamping means 23d may be moved along the movable rear crosspiece 34, the first movable bracket 35 and the second movable bracket 36 respectively.

[0099] It should be noted that the movements of the clamping means 23 according to the horizontal plane X, Y and along the respective crosspieces are carried out manually by the operator who places them in the desired positions.

[0100] Vice versa, for each of the clamping means 23 the movement of the respective pressor 38 against the underlying removable conductive insert 24 according to the direction Z orthogonal to the horizontal plane X, Y is carried out by a respective actuator 39 commanded by the aforementioned computer means. Therefore, the clamping means 23 may be arranged vertically aligned with the underlying removable conductive inserts 24 of the welding jig 8 whichever prismatic configuration it assumes depending on the dimensions of the tank 1 it is to accommodate.

[0101] In fact, it can be observed in Figure 1 and in particular in Figures 3, 5, 11 and in the schematic Figures 6 and 7 that the welding jig 8 comprises four plane vertical walls 40, 41, 42, 43 orthogonal to each other delimiting it by defining the lateral surface of a right prism, within which a housing 44 is defined also having the shape of a right prism configured to accommodate the insertion of the tank 1.

[0102] In particular, the four plane vertical walls 40, 41, 42, 43 can take on different mutual positions, as observed in Figures 6 and 7, so as to define housings 44 in the shape of a right prism of different sizes to accommodate different sizes of tanks 1.

[0103] The four plane vertical walls 40, 41, 42, 43 comprise: a first wall 40 attached to the movable base 25; a second wall 41 and a third wall 42 facing and spaced apart from each other and slidably restrained to the movable base 25 by means of guiding means of a known type and between which the first wall 40 and a third wall 43, slidably resting against the movable base 25, parallel to the first wall 40 and included respectively between the second and third wall 41 and 42, are included.

[0104] Furthermore, with reference to Figures 6 and 7, each of the walls 40, 41, 42, 43 is delimited by a free vertical edge 40b, 41b, 42b, 43b and on the opposite side by a vertical edge 40c, 41c, 42c, 43c each constrained to the respective face 42d, 40d, 43d, 41 d of the adjacent wall 42, 40, 43, 41 by means of sliding constraining means 40e, 41 e, 42e, 43e allowing the mutual movement of the walls while maintaining their orthogonality.

[0105] In this way, the constrained edge of each wall can slide with respect to the face of the adjacent wall and thus each movable wall can be moved slidably on the movable base 25 while maintaining the orthogonality of all the walls to each other.

[0106] It is therefore possible to give the welding jig 8 different configurations adapted to define housings 44 in the shape of a right prism of different sizes to accommodate tanks 1 of different sizes and / or shapes, as it can be observed in Figures 6 and 7.

[0107] This makes it possible to use a single welding jig that can be configured to weld tanks of different sizes.

[0108] The handling of the four plane vertical walls 40, 41, 42, 43 is carried out manually by the operator, but in another embodiment the handling can be motorised and controlled by computer means.

[0109] It should be noted that, as the first clamping means 23a are associated with the fixed front crosspiece 33, when the movable base 25 positions the welding jig 8 below the intermediate structure 28, the first wall 40 that is attached to the same movable base 25 will always be arranged so as to be always vertically aligned with the overlying first clamping means 23a that are associated with the fixed front crosspiece 33.

[0110] Regarding the other clamping means 23b, 23c and 23d, they may always be aligned vertically with the walls below 41, 42 and 43 by appropriately and respectively moving the movable rear crosspiece 34, the first movable bracket 35 and the second movable bracket 36 with which they are associated.

[0111] Operationally, in order to carry out the welding, the system 100 is set up in the configuration shown in Figures 4 and 5 in which the movable base 25 with the welding jig 8 are moved away from the frame 20.

[0112] In this configuration, the operator begins the welding preparation step by mutually moving the walls 40, 41, 42 and 43 of the welding jig 8 until they are arranged in the position suitable to accommodate the tank 1 , as it can be seen in Figure 9 and in the schematic Figure 14 in which the outer perimeter edge 2 of the tank 1 rests on the removable conductive inserts 24 that form the perimeter edge 8a of the welding jig 8 and the metal sheet 6 rests on the outer perimeter edge 2 of the tank 1.

[0113] Care must be taken to ensure that the inner perimeter edge 4 of the through- hole 5 of the metal sheet 6 is centred in relation to the opening mouth 3 of the tank 1.

[0114] Once these operations have been carried out, the movable base 25 is moved closer to the frame 20 and the welding jig 8 is placed underneath the intermediate structure 28 and the clamping means 23 are aligned vertically with the underlying removable conductive inserts 24 of the welding jig 8, as observed in Figures 10 to 12.

[0115] The clamping means 23 are lowered, as it can be observed in Figure 13, to block the metal sheet 6 and the tank 1 against the removable conductive inserts 24, as is also well represented in the schematic Figure 15.

[0116] When the metal sheet 6 and the tank 1 are blocked, the step of detecting the position of the through-hole 5 of the metal sheet 6 begins, which, as has been described, comprises the first sub-step wherein the approximate position of the through-hole 5 in relation to the reference coordinate system is verified, and the second sub-step wherein the precision position of the same through-hole 5 is verified.

[0117] While performing the aforesaid sub-steps, all the detection and control operations are carried out in relation to the approximate centring points A and B and the precision centring points 5’a, 5”a; 5’b, 5”b; 5’c, 5”c; 5’d, 5”d in the manner previously described.

[0118] If the detection and control operations reveal that the through-hole 5 is not correctly positioned in relation to the reference system, the metal sheet 6 and the tank 1 are released from the pressure exerted by the clamping means 23 which are lifted, allowing the operator to reposition the metal sheet 6 by re-centring the through-hole 5 and to repeat the checks until the correct positioning in relation to the reference system is achieved.

[0119] Conversely, if the detection and control operations show that the through-hole 5 is correctly positioned in relation to the reference system, the execution step is performed during which the robotic arm 22 moves the welding torch 7 according to the trajectory T shown in Figure 11 and makes the welding seam S between the tank 1 and the metal sheet 6.

[0120] Once welding is complete, the movable base 25 is moved away from the frame 20 and returned to the same initial position as shown in Figure 4, and the assembled unit, comprising the metal sheet 6 and the tank 1 welded together, is removed from the welding jig 8.

[0121] The system 100 is then ready to carry out a new welding.

[0122] Based on what has been described, it is understood that the welding method and the system implementing it, both of which are the subject matter of the invention, achieve the intended purposes and benefits.

[0123] First of all, it has been shown that the method of the invention employs a single welding jig 8 of variable shape that allows welding tanks 1 of different sizes.

[0124] Advantageously, by employing a single welding jig, it is not necessary to rotate different sized jigs as the size of the tanks to be welded changes, and this, compared to the prior art, reduces downtime and increases the production and productivity of the welding operation, whether it is performed manually or by a system.

[0125] The purpose to carry out the instrumental control that allows, prior to welding, to check the correct position in space of the through-hole 5 formed in the metal sheet 6 is also achieved.

[0126] Consequently, this control reduces the possibility of out-of-tolerance welding and thus the probability of producing defective semi-finished products or even scrap.

[0127] Finally, this control also improves the quality repeatability of the semi-finished products that are produced.

[0128] In the execution step, changes and variations may be made to the method and to the system of the invention that have not been described and are not represented in the attached figures.

[0129] It is understood, however, that such changes and variations, should they fall within the scope of the following claims, shall all be deemed to be protected by this patent.

Claims

CLAIMS1 ) Method for welding the outer perimeter edge (2) of a tank (1 ) to the inner perimeter edge (4) of a square-shaped through-hole (5) made in a metal sheet (6), said method being characterised in that it comprises:- a preparation step comprising the following operations:- providing a welding jig (8);- inserting said tank (1 ) into said welding jig (8);- placing said outer perimeter edge (2) of said tank (1 ) against the perimeter edge (8a) of said welding jig (8);- placing said metal sheet (6) against said outer perimeter edge (2) of said tank (1 );- arranging said through-hole (5) of said metal sheet (6) above the opening (3) of said tank (1 );- fixing said metal sheet (6) and said tank (1 ) to said perimeter edge (8a) of said welding jig (8);- a step of detecting the position of said through-hole (5) of said metal sheet (6) in relation to a reference coordinate system, said detection step comprising:- a first sub-step wherein, in relation to said reference coordinate system, the approximate position of said through-hole (5) is checked referring to the coordinates of the approximate centring points (A, B) positioned on the edge of said through-hole (5);- a second sub-step wherein, in relation to said reference coordinate system, the precision position of said through-hole (5) is checked referring to the coordinates of the precision centring points (5’a, 5”a; 5’b, 5”b; 5’c, 5”c; 5’d, 5”d) also positioned on the inner perimeter edge (4) of said through- hole (5);- if said approximate and precision positions do not coincide, a new approximate positioning of said through-hole (5) is performed and a new check is carried out;- if, on the other hand, said approximate and precision positions coincide, the following step is taken:- an execution step that comprises the following operations:- welding said outer perimeter edge (2) of said tank (1 ) to said inner perimeter edge (4) of said through-hole (5) of said metal sheet (6);- removing from said welding jig (8) the assembled unit comprising said metal sheet (6) and said tank (1 ) welded together; said first sub-step comprising the following operations:- defining said two approximate centring points (A, B), each of which is positioned on one of two consecutive sides (5a, 5b) of said through-hole (5);- detecting and storing the coordinates of both said approximate centring points (A, B);- calculating the length and inclination of the segment (9) connecting said approximate centring points (A, B), said approximate position of said through-hole (5) being checked if the length and inclination of said segment (9) are within the tolerances set by the operator, and said second sub-step comprising the following operations:- defining on each side (5a, 5b, 5c, 5d) of the inner perimeter edge (4) of said through-hole (5) two of said precision centring points (5’a, 5”a; 5’b, 5”b; 5’c, 5”c; 5’d, 5”d);- at each of said precision centring points (5’a, 5”a; 5’b, 5”b; 5’c, 5”c; 5’d, 5”d) detecting and storing the coordinates that define:- the position of each side (5a, 5b, 5c, 5d) of said through-hole (5) on a Cartesian plane (X, Y);- the position of the upper surface (6a) of said metal sheet (6) according to the direction (Z) orthogonal to said Cartesian plane (X, Y);- the dimensions of said through-hole (5), said precision position of said through-hole (5) being verified if said positions of said upper surface (6a) of said metal sheet (6) and of each of said sides (5a, 5b, 5c, 5d) of said through-hole (5) correspond to the data and dimensions of said through-hole (5) entered by the operator, each side (5a, 5b, 5c, 5d) of said through-hole (5) of said two precision centring points (5’a, 5”a; 5’b, 5”b; 5’c, 5”c; 5’d, 5”d) being arranged on opposite sides of the centreline (Ma; Mb; Me; Md) of said side (5a, 5b, 5c, 5d), each at a distance from said centreline equal to of the length of the side.2) Method according to claim 1 , characterised in that each of said two approximate centring points (A, B) is positioned on the centreline (Ma; Mb) on one of said two consecutive sides (5a, 5b) of said through-hole (5).3) Method according to any one of the preceding claims, characterised in that it is implemented by the use of processing means which are configuredto perform at least the following operations:- storing said coordinates of said approximate centring points (A, B);- calculating the length and inclination of said segment (9);- checking whether said length and said inclination are within the tolerances set by the operator;- storing said coordinates defining said position of said upper surface (6a) of said metal sheet (6) and of each of said sides (5a, 5b, 5c, 5d) of said through-hole (5);- using the values of said coordinates to check whether said positions of said metal sheet (6) and of each of said sides (5a, 5b, 5c, 5d) of said through- hole (5) correspond to the data and dimensions of said through-hole (5) entered by the operator, and to define the protrusion of the welding electrode;- defining the welding trajectory by means of algorithms that use geometric parameters and electrode-to-metal sheet distances set by the operator.4) Method according to any one of the preceding claims, characterised in that the detection and storage of said coordinates defining the positions of said upper surface (6a) of said metal sheet (6) and of each of said sides (5a, 5b, 5c, 5d) of said through-hole (5) are made by a welding electrode (7a) associated with a welding torch (7) of an electric welding machine when, at each of said precision centring points (5’a, 5”a; 5’b, 5”b; 5’c, 5”c; 5’d, 5”d), said welding electrode (7a) comes into contact with said metal sheet (6) alternately on the upper surface (6a) of said metal sheet (6) and with said sides (5a, 5b, 5c, 5d) of said through-hole (5), and at each contact said welding electrode (7a) closes the electrical circuit of said welding machine and sends an electrical signal to said processing means which also define:- the position in space of said through-hole (5);- the length of said welding electrode (7a).5) Method according to claim 4, characterised in that at each of said precision centring points (5’a, 5”a; 5’b, 5”b; 5’c, 5”c; 5’d, 5”d) said welding electrode (7a) achieves:- a first contact with the upper surface (6a) of said metal sheet (6);- a second contact with the inner perimeter edge (4) of said through-hole (5) at a position immediately below said upper surface (6a) of said metal sheet (6).6) System (100) configured to weld the outer perimeter edge (2) of a tank (1 ) to the inner perimeter edge (4) of a square-shaped through-hole (5) made in a metal sheet (6), using the welding method according to any one of claims 1 to 5, characterised in that it comprises a frame (20) with which they are associated:- a robotic arm (22) to which said welding torch (7) and a laser pointer (21 ) are associated;- said welding jig (8);- clamping means (23) of said metal sheet (6) and of said tank (1 ) against said perimeter edge (8a) of said welding jig (8) comprising removable inserts (24) made of conductive material;- a movable base (25) supporting said welding jig (8), said system (100) further comprising computer means which in turn comprise:- storage means in which at least one computer product is stored;- at least one microprocessor configured to execute said computer product which, when in the processing step, performs at least the following operations:- commands the movement of said clamping means (23) in a direction (Z) orthogonal to the lying plane of said metal sheet (6);- commands the movement of said robotic arm (22) to move said laser pointer (21 );- commands the movement of said robotic arm (22) to move said welding torch (7) with said welding electrode (7a) according to said predefined welding trajectory.7) System (100) according to claim 6, characterised in that said frame (20) comprises:- a pair of columns (26) surmounted by a crosspiece (27) supporting said robotic arm (22);- an intermediate structure (28) fixed orthogonally and cantilevered to said pair of columns (26), which supports said clamping means (23);- a base structure (29) arranged below said intermediate structure (28) and comprising sliding guides (31 ) of said movable base (25) supporting said welding jig (8) with said removable conductive inserts (24);- motorisation means for moving said robotic arm (22) and said clamping means (23) according to said direction (Z).8) System (100) according to claim 7, characterised in that said intermediate structure (28) comprises:- a pair of sideboards (32) parallel to each other and fixed orthogonally and cantilevered to said columns (26);- a fixed front crosspiece (33) having its ends (33a) attached to the projecting ends of said sideboards (32);- a movable rear crosspiece (34) parallel to said fixed front crosspiece (33) and having its ends (34a) slidably associated with said sideboards (32) and movable along said sideboards (32);- a first movable bracket (35) and a second movable bracket (36) parallel to each other, opposite to each other and included between said pair of sideboards (32) parallel to each other, both said movable brackets (35, 36) being slidably associated as cantilevered to a longitudinal guide (37) supported by said pair of columns (26) and parallel to said fixed front (33) and movable rear (34) crosspieces, and is configured to support and arrange said clamping means (23) above said removable conductive inserts (24) of said welding jig (8).9) System (100) according to any one of claims 6 to 8, characterised in that said clamping means (23) comprise:- a first set (23a) of clamping means (23) associated with said fixed front crosspiece (33);- a second set (23b) of said clamping means (23) associated with said movable rear crosspiece (34);- a third set (23c) of said clamping means (23) associated with said first movable bracket (35);- a fourth set (23d) of said clamping means (23) associated with said second movable bracket (36), each of said clamping means (23) comprising a pressor (38) associated with an actuator (39) configured to move said pressor (38) relative to the removable conductive insert (24) opposite thereto.10) System (100) according to any one of the preceding claims 6 to 9 characterised in that said welding jig (8) comprises four plane vertical walls (40, 41 , 42, 43) orthogonal to each other forming the lateral surface of a right prism inside which a housing (44) is defined also having the shape of a right prism configured to accommodate the insertion of said tank (1 ), said fourplane vertical walls (40, 41 , 42, 43) being mutually movable and configured to assume different mutual positions to define housings (44) of different sizes.11 ) System (100) according to claim 10, characterised in that said four plane vertical walls (40, 41 , 42, 43) comprise:- a first wall (40) attached to said movable base (25);- a second wall (41 ) and a third wall (42) between which said first wall (40) is comprised, which are facing and spaced apart from each other and are slidably constrained to said movable base (25);- a fourth wall (43) facing and spaced apart from said first wall (40), comprised between said second wall (41 ) and said third wall (42) and slidably resting on said movable base (25), each of said walls (40, 41 , 42, 43) being delimited by a free vertical edge (40b, 41 b, 42b, 43b) and on the opposite side by a vertical edge (40c, 41c, 42c, 43c) each constrained to the face (42d, 40d, 43d, 41 d) of the adjacent wall (42, 40, 43, 41 ) by means of sliding constraining means (40e, 41 e, 42e, 43e) that allow the mutual sliding of said walls and keep them orthogonal to each other.

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