Technical field of the invention

The present invention relates to an apparatus and a method for making a Z-shaped profile on a sheet metal part, and more particularly to an apparatus and a method which, in order to make the Z-shaped profile, make use of mould elements which are movable with respect to each other, under the control of a suitable control system, in particular a hydraulically-operated one, so as to cold deform the sheet metal to the desired shape of the profile.

For the purposes of the present invention, by sheet metal part it is meant a steel product having a reduced thickness, in particular less than 1 mm, more preferably between 0,4 mm and 0,8 mm.

State of the art

It is known to make Z-shaped profiles on sheet metal parts, for example on home appliance parts such as kitchen oven casings, to allow two sheet metal parts to be coupled together.

Figure 1 of the enclosed drawings shows an example of a Z-shaped profile made on a first sheet metal part P1 of thickness s1 intended to be coupled with a second sheet metal part P2 of thickness s2. The Z-shaped profile is formed by a pair of flat flaps A and B, substantially parallel to each other, and by a connecting flap C, substantially perpendicular to the two flat flaps A and B, wherein the two flat flaps A and B extend from opposite sides to the connecting flap C. In other words, the Z-shaped profile is formed by a pair of bends, wherein the first bend (characterized by a bend angle of 90°) is formed between the first flat flap A and the connecting flap C and the second bend (characterized by a bend angle of 90°) is formed between the second flat flap B and the connecting flap C.

The first bend has a sharp edge both at its extrados, denoted E1 , and at its intrados, denoted 11. Likewise, the second bend has a sharp edge both at its extrados, denoted by E2, and at its intrados, denoted by I2. A sharp edge at the extrados and at the intrados of each of the two bends means that the bend radii at the extrados and at the intrados are very small: typically, the bend radius at the extrados must be less than, or at most equal to, 0,2 mm, while the bend radius at the intrados must be less than, or at most equal to, 0,1 mm. In addition, it is typically required that the sheet thickness at the connection flap is not greater than the sheet thickness at the two flat flaps.

The Z-shaped profile thus allows to make a pair of steps in the first sheet metal part P1 , at one of which (in the example illustrated, the step formed by the second bend, i.e., the bend between the second flat flap B and the connection flap C) the second sheet metal part P2 can be arranged and firmly secured. The height of this step, in this case the distance between the extrados E1 of the first bend and the intrados I2 of the second bend, will preferably be slightly greater, for example by 0,2 mm, than the thickness s2 of the second sheet metal part P2.

An example of a system for making a Z-shaped profile on a sheet metal is known from Italian Patent No. 1415950. According to this known solution, firstly two 90-degree bends are made on the sheet metal and then, in order to obtain a sharp edge at the extrados of each of the two bends, the two flat flaps are urged towards each other in a direction parallel to the connecting flap, while the two flat flaps are respectively clamped between a first and second pair of clamping elements, wherein an element of the first pair of clamping elements and an adjacent element of the second pair of clamping elements are configured to form the sharp edge at the extrados of the first bend, while the other element of the first pair of clamping elements and the other element of the second pair of clamping elements are configured to form the sharp edge at the extrados of the second bend.

A further example of a system for making a Z-shaped profile on a sheet metal is known from Italian Patent No. 102016000051587. According to this known solution, the Z- shaped profile is obtained by performing first a bending operation and then a pressing operation, wherein the pressing operation is obtained by applying a force directed perpendicular to the plane of the connecting flap of the Z-shaped profile, i.e., parallel to the two flat flaps of the Z-shaped profile. In the bending operation, with the first flat flap of the sheet metal clamped between a first pair of clamping elements and with the second flat flap (which at this stage is still coplanar with the first flat flap) of the sheet metal clamped between a second pair of clamping elements, the two pairs of clamping elements are moved perpendicular to the flat flaps so as to obtain a pair of bends, which at this stage have a bend angle of less than 90°. In the subsequent pressing operation, the first pair of clamping elements and the second pair of clamping elements are moved relative to each other in a direction parallel to the flat flaps until the bend angles of the two bends are brought to 90°.

These solutions require the clamping elements to be moved in several directions, in particular both vertically and horizontally, which makes the machines used to produce the Z-shaped profiles particularly complex and expensive. Summary of the invention

It is therefore an object of the present invention to allow to make a Z-shaped profile on a sheet metal part in a simpler and less expansive manner than in the state of the art discussed above.

This object is fully achieved, according to a first aspect of the present invention, by an apparatus having the features defined in the appended independent claim 1 and, according to a further aspect of the present invention, by a method comprising the steps defined in the appended independent claim 8.

Further advantageous aspects of the apparatus and the method according to the invention are defined in the dependent claims, the subject matter of which is to be regarded as forming an integral part of the present description.

In summary, the invention is based on the idea of using, in order to make a Z-shaped profile on a sheet metal part, an apparatus comprising a first mould element acting as a punch, a second mould element acting as a die, and a third mould element acting as a sheet pressing element, wherein the second mould element and the third mould element have respective flat clamping surfaces, which extend parallel to each other, and are movable with respect to each other between an open position, wherein said clamping surfaces are spaced apart from each other to allow insertion of the sheet metal part to be worked, and a closed position, wherein said clamping surfaces are in contact with opposite sides of the sheet metal part to clamp said part, wherein the first mould element is movable along a working direction inclined to a direction perpendicular to said clamping surfaces, once the second mould element and the third mould element are in the above-mentioned closed position with the sheet metal part clamped between their respective clamping surfaces, towards a final working position in which the first mould element presses the sheet metal part against the second mould element, and wherein the first mould element and the second mould element have respective working surfaces which are shaped in such a manner as to define, when said mould elements are in the final working position, the geometry of the first bend and the geometry of the second bend of the Z-shaped profile to be formed.

Thus, according to the invention, the deformation of the sheet metal to make the Z- shaped profile is achieved in a single operation, due to the movement of the first mould element towards the second mould element along a single working direction, once the sheet metal is clamped between the second mould element and the third mould element. This makes it possible to simplify the apparatus and thus reduce its costs (both manufacturing and maintenance costs), compared to the known apparatuses, as well as to reduce production costs and time compared to the known methods. Furthermore, the present invention guarantees a high level of precision, resulting in a reduction in production waste.

Brief description of the drawings

Further features and advantages of the present invention will become clearer from the following detailed description, given purely by way of non-limiting example with reference to the accompanying drawings, wherein:

- Figure 1 shows a first sheet metal part having a Z-shaped profile obtainable with an apparatus and a method according to the present invention, coupled with a second sheet metal part;

- Figure 2 schematically shows the mould elements forming part of the apparatus of the present invention, in the initial operating condition;

- Figures 3 to 9 are schematic views showing in sequence the movements of the mould elements of Figure 2, from the initial operating condition of said figure up to the final operating condition in which the first sheet metal part has been deformed to form the desired Z-shaped profile;

- Figure 10 is a side view of a sheet metal part on which a Z-shaped profile has been formed with the apparatus of the present invention;

- Figure 11 is a perspective view of only the lower block of the apparatus of the present invention;

- Figure 12 is a perspective view of only the upper block of the apparatus of the present invention, arranged in an upside-down position with respect to the normal operating position;

- Figure 13 is a sectional view of the apparatus of the present invention, in its initial operating condition;

- Figure 14 is a sectional view showing a detail of the apparatus of the present invention, in its final operating condition;

- Figure 15 is a sectional view of a group of corner mould elements of the apparatus of the present invention; and

- Figure 16 is a perspective view of part of the group of mould elements of Figure 15.

RECTIFIED SHEET (RULE 91) ISA/EP Detailed description

With reference first to Figures 2 to 9, an apparatus for making a Z-shaped profile on a sheet metal part P basically comprises a first mould element 10 acting as a punch, a second mould element 12 acting as a die, and a third mould element 14 acting as a sheet pressing element.

The second mould element 12 and the third mould element 14 have respective flat clamping surfaces 12a and 14a, which extend parallel to each other. In particular, the clamping surfaces 12a and 14a extend vertically. The second mould element 12 and the third mould element 14 are movable relative to each other between an open position (shown in Figure 2), in which they allow insertion of the sheet metal part P to be worked, and a closed position (shown in Figure 4), in which they clamp the sheet metal part P from opposite sides, with the respective clamping surfaces 12a and 14a, so as to lock the sheet metal part P in position during the subsequent working steps. More precisely, according to the proposed embodiment, the second mould element 12 is translatable in a direction perpendicular to the respective clamping surface 12a, thus in particular in a horizontal direction (as indicated with double arrows F2), while the third mould element 14 is translatable along a direction (as indicated with double arrows F3) inclined by a certain angle a (preferably included in the range from 15° to 40°) with respect to a direction perpendicular to the respective clamping surface 14a, thus in particular with respect to the horizontal.

The first mould element 10 is translatable along a working direction (as indicated by double arrows F1) parallel to the direction of translation (double arrows F3) of the third mould element 14. In this regard, the third mould element 14 has a flat guide surface 14b, which extends along the aforementioned working direction, and the first mould element 10 has a corresponding flat guide surface 10b, which extends parallel to the guide surface 14b and is kept in contact with the latter.

The first mould element 10 and the second mould element 12 also have respective working surfaces configured to act on the sheet metal part P, as a result of the movement of the first mould element 10 towards the second mould element 12 along the aforementioned working direction, so as to deform the sheet metal part P until it takes the desired Z-shaped profile, as shown in Figures 8 and 9.

More specifically, with reference in particular to Figures 8 and 9, the first mould element 10 has a first flat working surface 10a, extending parallel to the clamping surfaces 12a and 14a of the second mould element 12 and of the third mould element 14, and a second flat working surface 10c, extending perpendicular to the first working surface 10a, joining the latter with the guide surface 10b. On the other hand, the second mould element 12 has a first flat working surface 12b, extending parallel to the clamping surfaces 12a and 14a of the second mould element 12 and of the third mould element 14, and a second flat working surface 12c, extending perpendicular to the first working surface 12b, joining the latter with the clamping surface 12a.

In this way, when the first mould element 10 is in the final working position (Figures 8 and 9), with the second mould element 12 and the third mould element 14 placed in the closed position to clamp the sheet metal part P between the respective clamping surfaces 12a and 14a, and with the edge joining the guide surface 10b and the second working surface 10c aligned with the clamping surface 14a of the third mould element 14, the clamping surface 14a of the third mould element 14 forms with the second working surface 10c of the first mould element 10 the extrados E1 of the first bend of the Z-shaped profile, the second working surface 10c of the first mould element 10 forms with the first working surface 10a of said element the intrados I2 of the second bend of the Z-shaped profile, the clamping surface 12a of the second mould element 12 forms with the second working surface 12c of said element the intrados 11 of the first bend of the Z-shaped profile, and finally the second working surface 12c of the second mould element 12 forms with the first working surface 12b of said element the extrados E2 of the second bend of the Z-shaped profile.

The method for making the Z-shaped profile on the sheet metal part P provides therefore for the execution in sequence of the following movements of the three mould elements 10, 12 and 14, as shown in Figures 2 to 9.

With the second mould element 12 and the third mould element 14 initially in the open position, the sheet metal part P to be worked is inserted into the free space between the clamping surfaces 12a and 14a of said elements, as shown in Figure 2. Subsequently, as shown in Figures 3 and 4, the second mould element 12 and the third mould element 14 are moved towards each other until they clamp the sheet metal part P from opposite sides with the respective clamping surfaces 12a and 14a. In the example proposed herein, first the second mould element 12 is moved (in the direction indicated by the double arrows F2) towards the sheet metal part P until the respective clamping surface 12a comes into contact with said part and, at that point, the third mould element 14 is also moved (in the direction indicated by the double arrows F3) towards the sheet metal part P until the respective clamping surface 14a comes into contact with said part. The first working surface 10a of the first mould element 10 remains in a position further back than the clamping surface 14a of the third mould element 14, so that at this stage only the clamping surface 14a comes into contact with the sheet metal part P. However, it can be envisaged that the movements of the second mould element 12 and the third mould element 14 occur simultaneously, or at least partially simultaneously, with respect to each other, instead of one after the other.

Starting from the condition in which the sheet metal part P is clamped between the clamping surfaces 12a and 14a of the second mould element 12 and the third mould element 14, with said mould elements held stationary in the closed position, the first mould element 10 is moved along the aforementioned working direction (identified by the double arrows F1), sliding with its guide surface 10b along the corresponding guide surface 14b of the third mould element 14, towards the second mould element 12. As a result of this movement, as shown in Figure 5, initially the first working surface 10a of the first mould element 10 comes to a position where it is substantially aligned with the clamping surface 14a of the third mould element 14 and is thus in contact with the sheet metal part P.

Further movement of the first mould element 10 along the aforementioned working direction towards the second mould element 12 leads to a deformation of the sheet metal part P, as shown in Figures 6 and 7. This movement is stopped when the edge joining the second working surface 10c and the guide surface 10b of the first mould element 10 is aligned with the clamping surface 14a of the third mould element 14, or in any case does not protrude beyond the clamping surface 14a of the third mould element 14 towards the second mould element 12, as shown in Figures 8 and 9. In this regard, the mould elements 10 and 12 will be suitably configured so that in the final working position of Figures 8 and 9 the space between the working surfaces 10a and 10c of the first mould element 10 and the working surfaces 12b and 12c of the second mould element 12 corresponds to the geometry of the Z-shaped profile to be made on the sheet metal part P. This means that the distance between the first working surface 10a of the first mould element 10 and the clamping surface 14a of the third mould element 14, when the first mould element 10 is in the final working position, will have to correspond to the distance between the extrados E1 of the first bend and the intrados I2 of the second bend of the Z-shaped profile, while the distance between the clamping surface 12a and the first working surface 12b of the second mould element 12 will have to correspond to the distance between the intrados 11 of the first bend and the extrados E2 of the second bend of the Z-shaped profile.

As is apparent from the above explanations, the deformation of the sheet metal part P to form the Z-shaped profile is obtained by movement of the first mould element 10 along only one direction, namely the aforementioned working direction inclined by the angle a with respect to a direction perpendicular to the clamping surfaces 12a and 14a of the second mould element 12 and of the third mould element 14.

Figure 10 shows an example of a sheet metal part P having a Z-shaped profile which can be obtained with an apparatus according to the present invention. According to this example, the sheet metal part P is a kitchen oven casing, thus a sheet metal part having a bottom wall BW and four side walls SW extending from the bottom wall BW and defining a cavity with the latter. The side walls SW are substantially flat, or at least mainly flat, and are joined to each other by means of arcuated corner portions AW. As shown in the detail A of said figure, the Z-shaped profile is made on the side walls SW, in particular in an end zone thereof opposite the bottom wall BW, as well as on the corner portions AW, in such a way as to extend along the entire perimeter of the sheet metal part P.

Furthermore, according to the example shown in Figure 10, in the corner portions AW the wall below the Z-shaped profile is bent outwards, as indicated with arrow F in the detail A of said figure, in such a way as to give greater rigidity to the sheet metal part at these portions. This additional bend may have a straight or at least partially curved shape. Moreover, this additional bend may be made not only in the corner portions AW, but also in the side walls SW, so as to extend along the entire perimeter of the sheet metal part P.

In the example of Figure 10, the Z-shaped profile has the function of accommodating an additional sheet metal part (not shown) and allowing it to be coupled with the sheet metal part P without creating discontinuity in feel, while the additional bend has the function of facilitating the insertion of the additional sheet metal part to be coupled with the sheet metal part P.

However, it is clear that the invention can also be applied to the working of sheet metal products having shapes other than the one of Figure 10.

An example of an apparatus according to the present invention will now be described with reference to Figures 11 to 14. According to this embodiment, the apparatus is arranged to make the Z-shaped profile on the sheet metal part P shown in Figure 10. Of course, depending on the specific shape of the sheet metal part P to be worked, the apparatus may be suitably modified with respect to the solution described and illustrated herein.

The apparatus, which is shown in its entirety in Figure 13 (where it is indicated with 100), is essentially configured as a press which, by means of a hydraulic drive, controls the movement of the mould elements described above, transmitting the force required to perform the forming operation on the sheet metal part P to be worked.

The apparatus 100 basically comprises a lower block 102 (shown in Figure 11), in which the mould elements 10, 12 and 14 described above are mounted, and an upper block 104 (shown in Figure 12).

With regard to the lower block 102, given the shape of the sheet metal part P (which, as mentioned, is in this case a kitchen oven casing) on which the apparatus is arranged to make the Z-shaped profile, there are in this case four groups of mould elements, one on each side of the perimeter edge of the sheet metal part, wherein each group of mould elements comprises the first mould element 10, the second mould element 12 and the third mould element 14 described above. Furthermore, since in the present case the Z- shaped profile is also to be made at the arcuate corner portions, each of which connects a pair of adjacent sides, four further groups of mould elements are provided, hereinafter referred to as corner mould element groups (while the four groups of mould elements operating on the four sides will be hereinafter referred to as main mould element groups). The sheet metal part to be worked is positioned on the lower block 102, resting on a plate 106 acting as a supporting and centring member, with the four sides of the perimeter edge extending vertically, and thus the arrangement of the mould elements of each main mould element group is similar to that illustrated above with reference to Figures 2 to 9, i.e., with the clamping surfaces 12a and 14a of the second mould element 12 and of the third mould element 14, respectively, extending vertically.

With reference not only to Figure 11 , but also to Figure 13, the lower block 102 basically comprises a support base 108 to which a plurality of guide bodies 110 are fixed, in the present case four guide bodies, each associated with a respective main mould element group, and each having a flat guide surface 110a, which is inclined by the aforementioned angle a to the horizontal and thus extends parallel to the working direction of the respective main mould element group.

In the sectional view of Figure 13 there are shown the guide bodies 110 associated with the main mould element groups operating on the two parallel short sides of the perimeter edge of the sheet metal part to be worked, but the same applies to the guide bodies associated with the main mould element groups operating on the parallel long sides of the perimeter edge of the sheet metal part to be worked.

As shown in Figure 13, a first carriage 112 is mounted on each guide body 110 and forms at its bottom a flat guide surface 112a adapted to slide on the guide surface 110a of the guide body 110. The first carriage 112 carries both the first mould element 10 and the third mould element 14. With reference also to Figure 14, according to the illustrated embodiment, the first carriage 112 forms at its top a first support surface 112b which extends parallel to the guide surface 112a and on which the first mould element 10 rests with a lower flat surface 10d thereof. In addition, the first carriage 112 forms, in a proximal portion thereof (i.e., in a portion thereof facing the centre of the lower block 102), a flat abutment surface 112c arranged adjacent to the first support surface 112b and extending perpendicular to the latter, so that the first mould element 10 is in abutment with its proximal side against the abutment surface 112c. The third mould element 14 is arranged on the first mould element 10, with its guide surface 14b in contact with the guide surface 10b of the first mould element 10, said guide surfaces 10b and 14b extending parallel to the guide surface 110a of the guide body 110, thus along the aforementioned working direction. The third mould element 14 further forms at its top a flat guide surface 14c, which extends parallel to the guide surface 14b of said mould element and runs along a corresponding flat guide surface 112d of the first carriage 112, which extends parallel to the guide surface 112a of said carriage.

Again with reference to Figure 13, as well as to Figure 14, on each first carriage 112 a second carriage 114 is slidingly mounted in a horizontal direction and the second mould element 12 is fixed thereto. In this respect, the first carriage 112 forms at its top a second support surface 112e which extends horizontally and on which the second carriage 114 rests with a flat lower surface 114a thereof. The second carriage 114 can thus slide horizontally on the second support surface 112e of the first carriage 112, carrying with it the second mould element 12.

The second carriage 114 is arranged between a proximal protrusion 116 and a distal protrusion 118 of the first carriage 112. The proximal protrusion 116 of the first carriage 112 forms, on its side facing the second carriage 114, an abutment surface 112c, while the distal protrusion 118 forms, on its side facing the second carriage 114, a flat control surface 118a which is inclined to the vertical by the same angle a mentioned above.

In turn, as better shown in Figure 14, the second carriage 114 forms, on its side facing the distal protrusion 118 of the first carriage 112, a flat control surface 114b which is inclined to the vertical by a certain angle (in particular an angle between 20° and 60°). Depending on their length, the first carriages 112 may have a single control surface 118a, such as the first carriages 120 associated with the short sides of the perimeter edge of the sheet metal part to be worked, or a pair of control surfaces 118a arranged side by side at a certain distance from each other, such as the first carriages 112 associated with the long sides of the perimeter edge of the sheet metal part P to be worked. In the case of first carriages 112 having two control surfaces 118a, there will advantageously be provided, for each of said first carriages, a pair of second carriages 114, each arranged so that its control surface 114b faces one of the control surfaces 118a of the first carriage 112.

Referring now to Figures 12 and 13, the upper block 104 basically comprises a fixed plate 120, which is mounted on a plurality of support bodies 122 fixed to the support base 108 of the lower block 102, and a movable plate 124, which is arranged above the fixed plate 120 and is vertically movable relative to it by means of a hydraulic drive (which is neither shown nor described in detail, but nevertheless of a type per se known) between a lowered position, shown in Figure 12 (where, as indicated above, the upper block 104 is shown in an upside-down position), and a raised position, shown in Figure 13.

The upper block 104 further comprises, for each side of the perimeter edge of the sheet metal part P to be worked, thus for each main mould element group, at least one wedge- shaped control member 126, which is fixed to the lower face of the movable plate 124 and protrudes from it downwards, passing through a respective through opening 128 in the fixed plate 120. In particular, in the proposed embodiment there are one control member 126 for each of the two short sides of the perimeter edge of the sheet metal part P to be worked and two control members 126 for each of the two long sides of the perimeter edge of the sheet metal part P to be worked. Each control member 126 forms a first flat control surface 126a, which is adapted to cooperate with the control surface 118a of the respective first carriage 112 and has the same inclination to the vertical as the control surface 118a, and, on the opposite side with respect to the first flat control surface 126a, a second flat control surface 126b (which can be better observed in Figure 14), which is adapted to cooperate with the control surface 114b of the respective second carriage 114 and has the same inclination to the vertical as the control surface 114b.

The control surfaces 118a, 114b, 126a and 126b of the first carriage 112, of the second carriage 114 and of the control member 126, respectively, are configured in such a way that, as a result of the movement of the movable plate 124 from the raised position to the lowered position, and therefore as a result of the downward movement of the control member 126, first the second control surface 126b of the control member 126 comes into contact with the control surface 114b of the second carriage 114, causing the second carriage 114 to move horizontally inwardly (in a leftward direction, relative to the point of view of a person looking at Figure 13), and then the first control surface 126a of the control member 126 comes into contact with the control surface 118a of the first carriage 112, causing the first carriage 112 to move along the guide surface 110a of the guide body 110 upwardly and outwardly (in a rightward direction, relative to the point of view of a person looking at Figure 13).

The horizontal inwardly translational movement of the second carriage 114 causes the second mould element 12 to move against the sheet metal part P, as described above with reference to Figure 3. This movement is stopped when the second control surface 126b of the control member 126 is no longer in contact with the control surface 114b of the second carriage 114, but the control member 126 and the second carriage 114 are in contact with each other with respective vertical flat surfaces, as shown in Figure 14. Naturally, such surfaces will be designed to ensure that the travel of the second carriage 114 is sufficient to bring the second mould element 12 into contact with the sheet metal part P. In addition, suitable compensation systems may be provided to compensate for any overtravel of the second carriage 114.

On the other hand, the translational upwardly and outwardly movement of the first carriage 112 along the guide surface 110a of the guide body 110 causes the third mould element 14 and the first mould element 10 to move along the aforementioned working direction, as described above with reference to Figures 4 to 9. As shown in Figure 13, initially the third mould element 14 is positioned so that its clamping surface 14a is closer to the sheet metal part to be worked than the first working surface 10a of the first mould element 10, whereby as a result of the movement of the first carriage 112 there is first contact of the third mould element 14 with the sheet metal part P and then contact of the first mould element 10. Again, suitable compensation systems may be provided to compensate for any overtravel of the first carriage 112.

Referring now to Figures 15 and 16, as well as Figures 11 and 12, the corner mould element groups will also be briefly described, which groups are similar in configuration and operation to the main mould element groups described above. For ease of reference, the components of the corner mould element groups similar to those of the main groups are indicated in the figures by the same reference numbers, with the addition of the symbol «'».

As shown in Figure 11 , there are provided on the support base 108 a plurality of guide bodies 110', in the present case four guide bodies, each associated with a respective corner mould element group. In the present case, each guide body 110' is arranged at 45° to the two guide bodies 110 adjacent thereto.

With reference to Figure 15, each guide body 110' has a flat guide surface 110a' inclined to the horizontal, on which a carriage 112' is slidingly mounted and carries both the first corner mould element 10' acting as a punch and the third corner mould element 14' acting as a sheet pressing element. Also in this case, the movement of the carriage 112' along the flat guide surface 110a' of the guide body 110' is controlled by a wedge-shaped control member 126', which is fixed to the lower face of the movable plate 124 and protrudes from it downwards. In this regard, each control member 126' forms a flat control surface 126a' adapted to cooperate with a corresponding control surface 118a' of the respective carriage 112'.

As can be seen from Figure 6, in the case of the corner mould element groups, the working surfaces of the mould elements will not be flat surfaces, but arcuate surfaces, since these surfaces have to operate on arcuate corner portions of the sheet metal part P.

Finally, as shown in Figure 15, the first corner mould element 10' forms at its bottom, i.e. , below the first working surface 10a', a working surface 10d' arranged to make the outward bend in the corner portions of the sheet metal part P below the Z-shaped profile. As can be seen from the above description, the present invention makes it possible to realise a Z-shaped profile along the entire perimeter of a sheet metal part, such as, for example, a kitchen oven casing, with at least the following advantages over the state of the art:

- fewer directions of movement of the mould elements, since the first and third mould elements are both moved in the working direction and the second mould element is moved in the horizontal direction;

- single control system (movable plate of the upper block, with its control members, and first and second carriages of the lower block) which controls the movement of all the mould elements;

- simplicity of the apparatus, which basically consists of a hydraulic press and a mould;

- reduction in production costs and time;

- reduction in maintenance costs and time; and

- increase in efficiency and reduction in production waste.

Furthermore, an apparatus according to the present invention allows not only to make a Z-shaped profile, but also to form additional geometries on the sheet metal part during the same operation, i.e., without performing additional working operations at other working stations.

The present invention has been described with reference to a preferred embodiment or mode of implementation thereof. It is to be understood that other embodiments or modes of implementation may be envisaged, which share the same inventive core with those described herein, as defined by the appended claims.