Field of the invention The present invention relates to systems and methods for assembling supporting structures of dish-washing machines, of the type comprising a hemming operation of metal sheet elements forming part of said supporting structure, said hemming operation including:

- a first hemming step wherein at least one first flange of a first metal sheet element is bent around a second flange of a second metal sheet element and

- a second pressing step, wherein the hemmed joint obtained with the first hemming step is bent to a final position lying adjacent to one of said metal sheet elements,

Prior art

A method of the type indicated above is, for example, described and illustrated in document CN 104259329 A. Systems of this type produced to date, however, have the drawback of involving relatively high costs and of having a low level of flexibility, so that each new model of dish-washing machine to be introduced into production in practice requires almost complete renewal of the assembly line.

Document US 2008/134495 A1 discloses a method of the type indicated above, in which in addition the first hemming step is performed by rolling, with the aid of a roller hemming head, and in which, during this first hemming step, the geometry of said metal sheet elements is kept substantially unchanged with the aid of at least one inner containment support and at least one outer containment support which are applied to opposite faces of the metal sheet elements.

Object of the invention

Therefore, one object of the present invention is to provide a method and a system for assembling supporting structures of dish washing machines, which is characterized by a high production efficiency and - at the same time - by a high flexibility, such as to drastically simplify the necessary modifications to adapt it to each new application and each new machine model.

An additional object of the invention is to provide a method and a system of the type specified above that are relatively simple and of low cost.

Another object of the invention is to provide a method and a system of the type specified above wherein the means used to carry out the hemming operation are able to ensure the reliable execution of this operation without the need to apply extremely strong forces and, therefore, with the possibility of reducing the energy consumption of the system.

Yet another object of the invention is to provide a method and a system of the type specified above wherein the entire operating cycle can be carried out in a relatively short time and wherein it is also possible to minimize the productivity losses due to system maintenance interventions.

Summary of the invention

In view of achieving one or more of the aforesaid objects, the invention relates to a method of the type indicated at the beginning of the present description, also characterized in that:

- the first hemming step is performed by rolling, with the aid of a roller hemming head carried by a manipulator robot,

- during this first hemming step the geometry of the metal sheet elements to be assembled together is maintained substantially unchanged with the aid of containment supports applied to opposite faces of said metal sheet elements, and

- the second pressing step is performed either by rolling again, with the aid of a roller hemming head (H) carried by a manipulator robot (R), or by using at least one of the aforesaid containment supports as a pressing tool, which is moved with respect to said metal sheet elements in such a way as to engage and bend the hemmed joint formed in the aforesaid first step up to its final position,

- said second pressing step comprises a final pressing operation on the bent hemmed joint, wherein at least one of said containment supports (A2M) is used as a pressing tool, which is moved over the bent hemmed joint, to press it into its final position. The method of the invention is also characterized in that the containment support, which is used as a tool to perform the bending and/or final pressing of the hemmed joint in the said second pressing step is in the form of a beam arranged adjacent to the hemmed joint and configured to be pushed, in the second pressing step, in a direction orthogonal to the longitudinal direction of the joint, so as to engage the joint and bend it into the aforesaid final position.

Preferably, the beam constituting the bending and/or final pressing tool is oriented according to a slightly inclined direction, preferably by an angle not exceeding 5°, and even more preferably by an angle equal to about 3°, with respect to the longitudinal direction of the joint, so that when in the second pressing step, the tool is pushed in the direction orthogonal to the longitudinal direction of the joint, the tool progressively engages an increasing portion of the joint, starting from its first end towards its second end.

Before the hemming operation the first flange and the second flange are adjacent to each other and extend in a common longitudinal direction, and the first flange has a protruding portion, which extends over the second flange orthogonally to the second flange. In said first step, the manipulator robot moves the roller hemming head along said protruding portion of the first flange, bending this protruding portion - partially in a first pass and then completely in a second pass - around said second flange, until said hemmed joint is formed.

Preferably, the manipulator robot presses a hemming roller of said roller hemming head against said protruding portion of the first flange in one of said first pass and second pass, according to a push-like mode, and pulls the hemming roller of said hemming head against said protruding portion of the first flange in the other of said first pass and second pass, according to a pull-like mode.

In one embodiment, the supporting structure to be assembled comprises:

- a main element of sheet metal, folded in a C-configuration, with a central wall and two side walls perpendicular to the central wall, to define the vertical rear wall and the vertical side walls of the supporting structure of a dishwasher, - two metal sheet covers to be assembled on opposite ends of the main C-shaped element, to define the upper and lower walls of the supporting structure of the dishwasher,

- each of said covers having a first flange along three sides of its perimeter, which is hemmed onto a second flange extending along the corresponding three sides of the main C-shaped element, so as to form a hemmed joint.

In the aforesaid embodiment, the main C-shaped element is positioned, to perform the hemming operation, with its central wall arranged horizontally, and with the two side walls extending downwards from the central wall, Inside the main C-shaped element, inner containment supports are arranged to maintain the geometry unchanged of the main C-shaped element and of the two covers during the hemming operation. Outside the main C-shaped element, outer containment supports are arranged adjacent to the three sides of each end of the main C-shaped element, to maintain the geometry unchanged of the main C- shaped element and of the covers during the hemming operation, During the second pressing step, one or more of the outer containment supports are used as a bending and/or final pressing tool, translating them in a horizontal direction against the hemming joint.

In one example, the aforesaid inner containment supports, once introduced into the main C-shaped element, are expanded outwards, against the inner surface of the main C-shaped element.

The invention also relates to a system configured to execute the above described method.

Detailed description of the invention

Further characteristics and advantages of the invention will become apparent from the description that follows with reference to the attached drawings, provided purely by way of non-limiting example, wherein:

- Figure 1 is an exploded perspective view of the metal sheet elements constituting a supporting structure of a dish-washing machine, which can be assembled with the method system according to the invention,

- Figures 2A, 2B and 2C schematically show three successive steps of the hemming method according to the invention,

- Figure 3 is a perspective view of a structure to be assembled with the method according to the invention, mounted on a transport pallet in a production plant and engaged by outer and inner containment supports configured to maintain the geometry unchanged of the metal sheet elements during the execution of the hemming operation.

- Figures 4-7 schematically illustrate successive stages of the first hemming step envisaged in the method according to the invention,

- Figure 8 schematically illustrates the second pressing step envisaged in the method according to the invention,

- Figure 9 is a perspective view of a structure to be assembled with the method according to the invention, engaged by outer containment supports, which are then used as pressing tools in the second pressing step of the method according to the invention,

- Figures 10, 11 schematically illustrate two successive steps of the second pressing step of the method according to the invention,

- Figures 12A, 12B show the configuration of the hemmed and bent joint, respectively, immediately after the hemming and bending operation and in a subsequent step, after an elastic return of the bent joint,

- Figures 13, 14 are perspective views, which schematically show the outer containment supports which are used as pressing tools in the pressing step, as well as the auxiliary tools used for pressing the hemmed joint at the corners of the structure to be assembled, in the case of an embodiment example of the method of the invention.

- Figure 15 is a perspective view of an example of a production line arranged to carry out the method according to the invention,

- Figure 16 is a side view of a station of the production line, and

- Figures 17, 18 are a side view and a front view of an apparatus arranged in the station of Figure 16.

Figure 1 illustrates an exploded perspective view of a supporting structure 1 for a dish-washing machine, which can be assembled by means of the method of the invention.

It should be noted that the structure 1 described and illustrated here constitutes only one example of a supporting structure of a dish-washing machine to which the invention is applicable. In the example illustrated, the structure 1 comprises a main element 2 made of steel sheet, having a general C-shaped configuration, with a central wall 3 and two side walls 4 intended to define, respectively, the vertical rear wall and the vertical side walls of a dish-washing machine structure.

The structure 1 also comprises an upper cover 5 and a lower cover 6, made of steel sheet, intended to define the upper wall and the lower wall of the structure of the dish-washing machine.

The upper cover 5 is intended to be assembled on the upper end of the main element 2 by means of a hemming operation of a first flange F1 arranged along three sides of the cover 5 on a second flange F2 arranged along the three sides of the upper end of the main element 2. Similarly, the cover 6 is intended to be assembled on the lower end of the main element 2 by means of a hemming operation of a first flange F1 arranged on three sides of the lower cover 6 on a second flange F2 arranged along the three sides of the lower end of the main element 2.

To carry out the hemming operation of the flanges F1 of the upper cover 5 and of the lower cover 6 on the flanges F2 at the upper and lower ends of the main element 2, the two covers 5, 6 are firstly positioned adjacent to the respective ends of the main element 2.

Figure 2A illustrates in cross-section and on an enlarged scale the detail of the flanges F1 and F2 of the upper cover 5 and of one side of the upper end of the main element 2, in the juxtaposed condition, before the hemming operation.

The cross-section of Figure 2A corresponds to the cross-section plane illustrated with the line II in Figure 1. As can be seen, in the case of this example, the flange F2 projects outwards from the upper end of the side wall 4, in a plane orthogonal to the wall 4, and extends in the longitudinal direction of the upper edge of the wall 4, from one end of this upper edge to the other end. The flange F1 of the upper cover 5 projects outwards starting from a vertical peripheral wall 7 of the cover 5, and is positioned adjacent to the flange F2. The flange F1 also extends in the longitudinal direction of the corresponding side edge of the cover 5, from one end of this edge to the other.

Again with reference to Figure 2A, the flange F1 has a first portion 8A, parallel and adjacent to the flange F2, and a portion 8B that protrudes above the flange F2 and - in its initial configuration - is bent in a plane orthogonal to the plane of the portion 8A.

The method according to the invention comprises a first step of hemming the first flange F1 around the second flange F2. This first hemming step is carried out, according to the invention, by rolling the portion 8B of the first flange F1 with the aid of a manipulator robot R equipped with a roller hemming head FI, of the type illustrated, for example, in Figure 15 and described in more detail below.

In the embodiment example illustrated herein of the method according to the invention, a manipulator robot R moves a roller hemming head FI along the portion 8B of the first flange F1 , in such a way as to partially bend it in a first pass and then totally in a second pass until the portion 8B is brought to a final position adjacent to the flange F2, wherein the flange F2 is clamped between the portion 8A and the portion 8B of the first flange F1.

With the first pass of the head FI along the portion 8B of the flange F1 , the portion 8B is carried into the position illustrated with dashed lines and indicated with the reference 8B1 in Figure 2A. Again with reference to the specific illustrated example, the residual angle of inclination between the portion 8B1 and the flange F2 is equal to 45°.

With a second pass of the roller hemming head FI carried by the manipulator robot R, the portion 8B of the flange F1 is carried from the position 8B1 to the final position 8B2 illustrated in Figure 2B, wherein the angle formed between the portion 8B and the flange F2 is substantially equal to 0°.

With the aforesaid first hemming step, a hemmed joint J is thus obtained, defined by the first flange F1 wrapped around the second flange F2, and protruding from the walls 4, 7 substantially in a plane orthogonal to these walls.

The method according to the invention comprises a second pressing step by which the joint J obtained with the first hemming step is bent and brought adjacent to the wall 4 of the main metal sheet element 2, as illustrated with a dashed line in Figure 2C.

Figure 3 shows the structure 1 for assembling configured to be subjected to the hemming operation of the present invention. The main element 2 is positioned on top of a pallet 9, serving for the transport of the structure 1 through the production line, with the central wall 3 arranged horizontally and the side walls 4 extending downwards from the central wall 3, and which are supported on the pallet 9. The covers 5 and 6 are arranged adjacent to the opposite ends of the main element 2. The elements constituting the structure 1 to be assembled are kept in the assembly position by inner containment supports A1 and outer containment supports A2. In the illustrated example, two inner containment supports A1 projecting upwards from the ends of the pallet 9 adjacent to the two opposite ends of the main element 2 are provided. Similarly, two outer containment supports A2 are provided, which engage the main element 2 and the covers 5, 6 at the opposite ends of the structure.

Figure 3 shows a simplified case, wherein each of the inner containment supports A1 and each of the outer containment supports A2 consists of a single element, which develops along the three sides of each of the ends of the main C-shaped element 2. In a variant, each of the supports A1, A2 consists of separate elements, according to that described in detail below.

Figure 4 schematically shows a cross-sectional view in the plane IV of Figure 3 of a detail of the cover 5, of the main element 2, of the inner containment support A1 and of the outer containment support A2, prior to the hemming operation. Figure 4 shows the condition corresponding to that illustrated in Figure 2A, wherein the flange F1 of the cover 5 has its protruding portion 8B extending orthogonally to the flange F2.

Figure 5 shows the first hemming step of the method of the invention, by which the protruding portion 8B of the flange F1 is made to wrap around the flange F2 (position 8B2 in Figure 2B). As already indicated, according to the invention, this operation is performed by rolling, with the aid of a manipulator robot R of any known type, carrying a roller hemming head FI of any known type, equipped with a hemming roller H 1.

As already indicated, in a preferred example, the portion 8B is brought into the final position 8B2 of Figure 2B in two successive passes of the roller hemming head FI. Figure 5 schematically shows the hemming roller H1 of the hemming head H during the first pass along the flange F2, necessary to bend the protruding portion 8B by 45°, up to the position 8B1.

Figure 6 shows the same detail of Figure 4 after the first pass of the roller hemming head H 1 with the portion 8B1 of the flange F1 bent by 45°. Starting from this condition, the roller hemming head FI performs the second pass over the flange F1 , bringing the protruding portion of the flange F1 into the final position 8B2 shown in Figure 7, so as to form the hemmed joint J, protruding orthogonally from the plane of wall 4 (condition also illustrated in Figure 2C).

In an actual exemplary embodiment, the roller hemming head FI is configured in such a way that during a rolling pass, the manipulator robot carrying the head can push the hemming roller against the workpiece ("push" mode) or it can pull the hemming roller against the workpiece ("pull" mode), which gives the manipulator robot greater operational flexibility, as it can arrange itself with respect to the workpiece and orient the hemming head with respect to the workpiece according to the available space, the width of the robot's working field, and also taking into account the need to avoid interfering with other robots that may be present in the working area. A rolling head having these features is known for example from document WO 2012/160512 A1.

Figure 8 schematically illustrates the second pressing step of the method according to the invention (also illustrated in Figure 2C) by which the hemmed joint J obtained in the first step is bent by 90°, resting it against the wall 4.

According to a first solution, this second step is performed again by rolling, with the aid of a roller hemming head FI carried by a manipulator robot R (which can be the same robot that performed the first hemming step or another robot dedicated solely to this second step). Preferably, in this case, the hemming head brings the hemmed joint J into its final position, illustrated with a dashed line in Figure 8 in two successive passes. In a first pass, the joint is bent by about 45°, while with the second pass the joint reaches its final position, in a manner similar to that indicated with reference to Figures 4-7. Also in this case, as in the case of Figures 4-7, the two passes may correspond to a back and forth movement of the head H, to save time. Of course, with reference to Figure 8, in the case of the first solution described here, the outer containment support A2 must be moved away from the position shown in Figure 8, to allow the engagement of the roller against the joint J.

As an alternative to the first solution described above, the invention envisages a second solution, which will be described with reference to Figures 9, 10 and 11, wherein the second pressing step is performed using an outer containment support as the pressing tool, which in the first rolling step is kept in a stationary position, having only the function of containment support in this step. In this case, with reference to Figure 8, the pressing operation is performed by moving the outer containment support A2, or a portion thereof, to the right, i.e. in the direction of the arrow P.

It is important to note that, in any case, that is, both in the case of the first solution wherein the hemmed joint J is bent into its final position with an additional rolling operation, and in the case of the second solution, wherein the hemmed joint J is bent into its final position using one of the outer containment supports as a movable tool, the method of the invention comprises a final pressing operation of the hemmed and bent joint J, wherein at least one of said outer containment supports is used as a tool, which is moved over the hemmed and bent joint J, in order to press it into its final position.

Returning to the description of the second solution mentioned above, wherein the joint J is bent using a pressing tool, Figure 9 illustrates, still in perspective view, the structure 1 to be assembled after the first hemming step, and configured to be subjected to the second pressing step.

In the case of the example illustrated in Figure 9, the portions of the outer containment supports A2, which were used in the first step of hemming by rolling (not illustrated in Figure 9) move to a position spaced apart from the structure to allow engagement and subsequent advancement of supports dedicated to the second pressing step, which include, at each end of the structure, a first element A2M, which is movable in the horizontal direction to perform the pressing operation, and a second element A2F, which remains in a fixed position, to contain the wall of the respective end cover. In the simplified and illustrated example, each of the elements A2M and A2F is in a single piece extending along the three sides of the main element 2 with a C-configuration.

Starting from the position illustrated in Figure 9, the two elements A2M are pushed horizontally towards each other, in the direction of the arrows P, to bend the hemmed joints J extending along the three sides of the main element 2, against the respective wall of the main element 2.

Figures 10, 11 schematically show the initial position and the final position of the outer containment support A2M, in which the hemmed joint J is bent over the wall 4.

Figures 12A, 12B show, respectively, the joint J at the end of the pressing operation. When the pressing tool A2M is in the final position illustrated in Figure 11, the joint J is in the condition illustrated in Figure 12A, wherein the total thickness of the joint has the value SO illustrated in Figure 12A. After removing the pressing tool, the joint normally has an elastic return, which brings the total thickness of the joint to the value S1 illustrated in Figure 12B, slightly greater than SO.

With reference again to Figures 10 and 11 , the movable support A2M, which is used as a pressing tool, has a flat and vertical front face, which is joined by a curved surface with a lower flat face. The curved surface portion is configured in such a way that when the support A2M advances against the joint J (Figure 10) it causes a progressive bending of the joint J towards its final position, by means of engaging the curved surface portion against the joint J. In the final part of the stroke of the support A2M it is, instead, the lower flat surface of the support A2M that engages the hemmed and bent joint J above, to press it into its final position.

The aforesaid final pressing operation, carried out using an outer containment support A2M, which in the first hemming step is in a stationary position, is - in any case - envisaged in the method of the invention, even in the case of the first solution described above, wherein the second bending step of the hemmed joint J into its final position is performed by rolling. Therefore, even if the bending of the joint J illustrated in Figure 8 is performed with one or more passes of a rolling head carried by a robot, a pressing operation of the joint J into its final position is in any case provided, carried out by moving the A2M support, as shown in Figures 10, 11.

With reference to Figure 13, in a preferred embodiment example, each of the outer containment supports A2M arranged at the two ends of the structure to be assembled is formed by three separate beams B1 , B2, B3 extending along the longitudinal direction of each of the three sides of the main metal sheet element 2 in a C-configuration.

As already indicated above, the central wall 3 and the two side walls 4 of the main element 2 have a flange at the upper and lower ends of the element 2 (with reference to Figure 13), said flange extending longitudinally from one end to the other end of the upper edge and lower edge of each wall. Similarly, the covers 5, 6 have, along the three sides to be assembled to the central wall 3 and to the side walls 4 of the main element 2, a flange extending longitudinally from one end to the other of each of these three sides.

The solution illustrated in Figure 13 envisages that each of the three beams B1 , B2, B3 arranged at each end of the structure and intended to act as pressing tools in the second pressing step of the method according to the invention are oriented in a slightly inclined direction (preferably by an angle not exceeding 5°, and even more preferably by an angle equal to about 3°) with respect to the longitudinal direction of the respective sides of the main element 2 and of the covers 5, 6.

In this way, during the second pressing step of the method according to the invention, when the beams B1 , B2, B3 are moved in the direction of the arrows P to engage the hemmed joint J obtained in the first hemmed step, each beam progressively engages an increasing portion of the respective hemmed joint, from a first end of the joint towards the second end of the joint. In this way, the force that must be applied to the beams B1 , B2, B3 to perform the pressing operation is drastically reduced.

Of course, it would also be possible - in any case - to envisage that each pressing tool is split into three separate beams B1 , B2, B3, keeping the beams parallel to the respective hemmed joints.

It should also be considered that the configuration of the structure to which the method according to the invention is applicable could also be different from that illustrated here by way of example. In general, the method of the invention is applicable, for example, to the joining of only two metal sheet elements that have two respective flanges extending in the same longitudinal direction.

In the case of the example of Figure 14, the pressing operation is completed at the four corners of the central wall 3, by means of respective auxiliary pressing tools C. It is however possible to shape the beams B1 , B2 and B3 in such a way that they also include portions configured to engage the corners of the structure.

Figure 15 shows, purely by way of example, a production line for carrying out the method according to the invention. The drawing schematically shows a conveying line L along which pallets 9 advance, each carrying a structure 1 to be assembled consisting of the main C- shaped metal sheet element and the two end covers. Again in the case of this example, the line L has two stations arranged in series, each with two manipulator robots R for carrying out the first hemming step by rolling. In this example, in each station, two distinct robots simultaneously perform the rolling operation of the flanges arranged at the two ends of the structure. Again in the case of this specific example, two robots in a first station perform a first pass for the 45° bending of the flange F1 (Figure 2A and 2B), while in the following station, two additional robots perform the second rolling pass simultaneously on the two ends of the structure, necessary to obtain the hemmed joint J (Figure 2B).

Of course, the solution of Figure 15 is just an example. It allows considerable reduction of the cycle time but involves greater costs for arranging four manipulator robots. Flowever, it would be possible to provide a single hemming station arranged with two robots to perform both the first rolling pass and the second rolling pass simultaneously on the two ends of each structure 1. It would also be possible to provide a single robot in this single station, which first performs the two rolling passes at one end of the structure and then the other two rolling passes at the other end of the structure. Of course, in the case of the first solution described above, wherein the bending operation of the hemmed joint into its final position is also performed by rolling, the same robots that perform the first hemmed step can perform the second bending step of the hemmed joint obtained with the first step. Also in this case, the bending of the joint into the final position can be obtained in two successive passes, for example, with a back and forth movement of each rolling head.

More generally, the method according to the invention may be applied to a production plant that provides one or more hemming stations, arranged in series or parallel to each other, each comprising at least one manipulator robot equipped with a roller hemming head for carrying out the first hemming step, and one or more pressing stations, arranged in series or parallel to each other, as well as a conveying line for a plurality of pallets each carrying a structure to be assembled, said conveying line being configured to carry each pallet through one of the hemming stations and then through one of said pressing stations.

It is also possible to provide an installation comprising one or more assembling stations, arranged in parallel with each other, each comprising at least one manipulator robot equipped with a roller hemming head and configured to carry out both said first hemming step and said pressing step.

Figure 16 shows a side view of a station of a production line, equipped with an apparatus to insert inside the structure 1 for assembling the inner containment supports A1, which are used to maintain the geometry of the structure unchanged during the hemming operation.

To this end, below a conveyor line 11 , mounted on a stationary support structure 10, and provided with a chain conveyor 12 for the pallets 9, there is a lifting device 18 of any known type (shown only schematically in the Figure), which is used to introduce the inner containment supports A1 within the structure to be assembled 1 , making them pass through an opening W of the pallet 9. By means of the lifting device, it is possible to move a frame 19 vertically guided within vertical guides 20.

With reference in particular to Figures 17 and 18, the structure 19 comprises a base plate 20 from which four uprights 21 stiffened by connecting walls 22, 23 extend upwards. The uprights 21 carry two pairs of inner containment supports A1 , in the form of vertically extending beams. As can be seen in Figure 18, each of the two pairs of supports A1 can be expanded outwards by means of thrusting members 24 having outer ends in engagement with the respective supports A1 and inner ends carrying cam-follower rollers 25. The cam-follower rollers 25 are in engagement with conical portions 26 of a respective vertical actuator rod 27 (a rod 27 is provided for each pair of supports A1), which can be moved vertically by means of an actuator 28 of any known type.

With reference to Figure 18, the actuator rod 27 of a pair of supports A2 is illustrated in a raised position wherein the cam follower rollers 25 are in engagement with the larger diameter end of the respective conical portion 26. In this condition, the rod 27 keeps the supports A1 pressed against the inner surfaces of the structure 1 to be assembled (after the entire structure 19 has been raised inside the structure 1). Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to those described and illustrated purely by way of example, without departing from the scope of the present invention, as defined in the appended claims.