Technical field of the invention

The present invention relates generally to the field of cold forming of sheet metal for household appliance components, such as drums for washing machines or tumble dryers.

More specifically, the present invention relates to a device for making, by plastic deformation, a circumferential groove on a hollow cylindrical sheet metal part, for example a sheet metal part designed to form the body of a drum for a washing machine or tumble dryer, as well as to an apparatus for processing a drum for a washing machine or tumble dryer provided with a first device of this type configured to make a circumferential groove in a first area of the sheet metal part, in particular an area close to an upper edge of the sheet metal part, and a second device of this type configured to make a circumferential groove in a second area of the sheet metal part, in particular an area close to a lower edge of the sheet metal part.

State of the art

With reference to Figure 1 of the accompanying drawings, a washing machine drum 10 typically comprises a hollow cylindrical sheet metal part 12 (hereinafter simply referred to, for the sake of convenience, as "sheet metal part") defining the body of the drum and a pair of plastic parts 14 and 16 assembled to the sheet metal part 12, namely a first plastic part 14 forming the mouth of the drum, which is mounted at the upper end of the sheet metal part 12, and a second plastic part 16 forming the bottom of the drum, which is mounted at the lower end of the sheet metal part 12.

The sheet metal part 12 is obtained by joining the two short sides S1 and S2 of a rectangular sheet S, shown in Figure 2. Joining of the two short sides S1 and S2 is typically carried out by crimping, i.e., by overlapping and folding, of these sides. Such an operation inevitably causes a thickening of the sheet metal part 12 in the area of the joint between the two short sides S1 and S2, indicated by J in Figure 3, and therefore a discontinuity in the external circumferential profile in any cross-sectional plane of the sheet metal part 12, i.e., in any cross-sectional plane oriented perpendicular to the longitudinal axis of the sheet metal part 12.

Typically, the first plastic part 14 and the second plastic part 16 are assembled onto the sheet metal part 12 by plastic deformation of an end region of the sheet metal part 12 (upper end region, in the case of the first plastic part 14 forming the mouth of the drum, and lower end region, in the case of the second plastic part 16 forming the bottom of the drum) on the respective plastic part. In order to enable the preliminary mounting of the two plastic parts 14 and 16 onto the sheet metal part 12, which is necessary before proceeding with the assembly of said pieces, a first circumferential groove G1 and a second circumferential groove G2 are made on the sheet metal part 12, namely in the area close to the upper edge and in the area close to the lower edge of the sheet metal part 12, respectively, as shown in Figure 4.

The first circumferential groove G1 and the second circumferential groove G2 are obtained by plastic deformation using respective groove forming devices, each comprising a pair of rollers, namely, an inner roller (i.e., a roller which, during processing, is arranged inside the sheet metal part 12 to operate on the inner surface of said part) and an outer roller (i.e., a roller which, during processing, is arranged outside the sheet metal part 12 to operate on the outer surface of said part), as well as a driving mechanism arranged to urge said rollers towards each other to deform the sheet metal part 12 while the latter is being rotated about its longitudinal axis. The inner roller has on its cylindrical lateral surface a circumferential groove, whose shape corresponds to that of the circumferential groove to be formed in the sheet metal part 12, while the outer roller has on its cylindrical lateral surface an annular protrusion arranged to act as a punch to press the material of the sheet metal part 12 towards the circumferential groove provided on the cylindrical lateral surface of the inner roller.

The fact that, as explained above, the sheet metal part 12 has a thickening in the joint area of the joint J between the two short sides S1 and S2 of the rectangular sheet S implies that, during the phase of deformation of the upper and lower end regions of the sheet metal part 12 for forming the circumferential grooves G1 and G2, the rollers of the groove forming device used to perform such processing are subjected to impulsive load stresses whenever, as a result of the rotation of the sheet metal part 12 around its axis, the rollers come into contact with such thickening. Such stresses may lead to wear and fatigue failure of the components of the processing apparatus over time.

In addition, at the thickening in the area of the joint J of the sheet metal part 12 the rollers tend to urge the material inwards during processing, thereby deforming the inner surface of the sheet metal part.

Summary of the invention

It is therefore an object of the present invention is to provide a groove forming device that allows to make by plastic deformation a circumferential groove in a hollow cylindrical sheet metal part, such as, in particular, a drum body for a washing machine or tumble dryer, without being affected by the drawbacks of the prior art discussed above.

This and other objects are fully achieved according to the present invention by a groove forming device as defined in the enclosed independent claim 1.

The present invention also relates to a processing apparatus comprising a pair of groove forming devices of the type specified above, namely a first device arranged to form a first circumferential groove in a first area of the sheet metal part, in particular an area close to an upper edge of the sheet metal part, and a second device arranged to form a circumferential groove in a second area of the sheet metal part, in particular an area close to a lower edge of the sheet metal part.

Further advantageous aspects of the invention are defined in the dependent claims, the subject-matter of which is to be understood as forming an integral part of the present description.

Brief description of the drawings

The 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, in which:

- Figure 1 is a front view of a drum for a washing machine or tumble dryer comprising a hollow cylindrical body having a pair of circumferential grooves obtainable with a groove forming device according to the present invention;

- Figure 2 is a plan view of a rectangular sheet from which the drum body of Figure 1 can be made;

- Figure 3 is a front view of the drum body of Figure 1 after the operation of joining of the two short sides of the rectangular sheet of Figure 2, but before the operation of forming the pair of circumferential grooves;

- Figure 4 is a front view of the drum body of Figure 1 ;

- Figure 5 is a front view of a processing apparatus for processing a drum for a washing machine or tumble dryer comprising a first groove forming device and a second groove forming device for forming an upper circumferential groove and a lower circumferential groove, respectively, according to an embodiment of the present invention;

- Figures 6 and 7 are an axonometric view and an axial sectional view, respectively, of one of the two groove forming devices of the apparatus of Figure 5;

- Figures 8 to 11 are side views showing in sequence some steps of the operation of forming of the upper and lower circumferential grooves in a drum body for a washing machine or tumble dryer by means of the processing apparatus of Figure 5;

- Figure 12 is an axial sectional view showing in detail the interaction between the inner and outer rollers of each of the two groove forming devices of the processing apparatus of Figure 5 during the operation of forming of the upper and lower circumferential grooves in a drum body for a washing machine or tumble dryer; and

- Figure 13 is an axial sectional view of a groove forming device according to a further embodiment of the present invention.

Detailed description

With reference first to Figure 5, numeral 100 generally indicates a processing apparatus arranged to form a pair of circumferential grooves in a hollow cylindrical sheet metal part, namely a first circumferential groove in a first area of the sheet metal part, in particular an area close to an upper edge of the sheet metal part, and a second circumferential groove in a second area of the sheet metal part, in particular an area close to a lower edge of the sheet metal part. In the present description, reference will be made for the sake of convenience to the use of the processing apparatus for forming a pair of circumferential grooves in the body of a drum for a washing machine or tumble dryer, it being understood that the processing apparatus is not limited to this specific application but can also be used form circumferential grooves on sheet metal parts of a different type, provided they are characterised by a rotationally symmetrical geometry.

The processing apparatus 100 comprises first of all a base structure 102 on which a workpiece-carrying drum 104 is rotatably mounted about an axis of rotation z oriented vertically. Suitable driving means (not shown in detail, but anyway of a per-se-known type) are associated with the workpiece-carrying drum 104 to drive the workpiececarrying drum 104 into rotation about the axis of rotation z.

The processing apparatus 100 further comprises a turret 106 arranged next to the workpiece-carrying drum 104 and a pair of groove forming devices 108 and 110, namely, an upper groove forming device and a lower groove forming device, respectively, which are mounted on the turret 106 so as to be able to translate along a first direction of translation parallel to the axis of rotation z, in the present case a vertical direction. The upper groove forming device 108 is intended to form the aforementioned first circumferential groove G1 in the drum body 12, while the lower groove forming device 110 is intended to form the aforementioned second circumferential groove G2 in the drum body 12. Respective driving means (comprising, for example, a pair of electric motors 112 and 114, one for each device) are associated to each groove forming device 108, 110 for controlling the movement of the groove forming device in a vertical direction (or, more generally, in the aforementioned first direction of translation) along the turret 106 so as to position the groove forming device at the desired height with respect to the drum body 12 mounted on the workpiece-carrying drum 104. Furthermore, the turret 106 is mounted on the base structure 102 in a translatable manner along a second direction of translation (in the present case a horizontal direction) passing through the axis of rotation z and perpendicular to said axis, and driving means (generally referred to as 116) are associated to the turret 106 for controlling the movement of the turret 106 along said second direction of translation.

With reference now to Figures 6 and 7, the structure and operation of the lower groove forming device 110 will be described in detail, it being understood that what will be illustrated below with regard to the lower groove forming device 110 is substantially valid also for the upper groove forming device 108. The two groove forming devices 108 and 110 have, in fact, substantially the same structure and are simply mounted on the turret 106 in a mirror-image manner with respect to each other, namely one (the upper one) with the rollers facing downwards and the other (the lower one) with the rollers facing upwards.

The groove forming device 110 comprises first of all a support body 118, which is fixed to a carriage 120 mounted on vertical guides 122 of the turret 106 (which guides can be seen in Figure 5) so as to allow the movement of the device in a vertical direction (or, more generally, along the aforementioned first direction of translation).

The groove forming device 110 further comprises a pair of rollers 124 and 126 configured to cooperate with each other for forming the aforementioned second circumferential groove G2 in the drum body 12. The rollers 124 and 126 are mounted on respective pins 128 and 130, in particular at the upper ends of said pins so as to protrude upwards from the support body 118, in such a manner as to be freely rotatable about respective axes of rotation z1 and z2, coinciding with the axes of said pins. The pins 128 and 130 are positioned in such a manner that the axes of rotation z1 and z2 are oriented parallel to each other, as well as parallel to the axis of rotation z of the workpiece-carrying drum 104 (thus, in the present case, oriented vertically). Furthermore, the pins 128 and 130 are positioned in such a manner that the axes of rotation z1 and z2 are aligned along the aforementioned second direction of translation (indicated x in Figures 6 and 7), i.e., the plane passing through the axes of rotation z1 and z2 also passes through the axis of rotation z of the workpiece-carrying drum 104. The roller 124 is arranged closer to the axis of rotation z of the workpiece-carrying drum 104 than the roller 126 and will hereinafter be referred to as the inner roller, as it is intended to operate on the inner lateral surface of the drum body 12, while the roller 126 will hereinafter be referred to as the outer roller, as it is intended to operate on the outer lateral surface of the drum body 12. The inner roller 124 has on its cylindrical lateral surface a circumferential groove 124a having a shape corresponding to that of the circumferential groove G2 to be made in the drum body 12, while the outer roller 126 is provided with an annular protrusion 126a configured to act as a punch to urge the material of the drum body 12 towards the bottom of the circumferential groove 124a of the inner roller 124 so that the circumferential groove G2 made in the drum body 12 has a shape corresponding to that of the circumferential groove 124a of the inner roller 124.

The pin 128 on which the inner roller 124 is mounted is carried by the support body 118 of the groove forming device 110, while the pin 130 on which the outer roller 126 is mounted is carried by a first sliding body 132, which is supported by the support body 118 so as to be translatable along the second direction of translation x. Driving means are associated to the first sliding body 132 for driving the movement of the first sliding body 132 along the second direction of translation x. In the example proposed herein, said driving means comprise an electric motor 134, carried by the support body 118, and a motion conversion mechanism for converting the rotational movement of an output shaft of the electric motor 134 into a translation movement of the first sliding body 132. In particular, the motion conversion mechanism comprises a screw 136, which is supported by the support body 118 in a rotatable manner about its axis (directed along the second direction of translation x) and is drivable into rotation by the electric motor 134, and a nut screw 138, which is mounted on the first sliding body 132 and engages with the screw 136.

Between the pin 130 on which the outer roller 126 is mounted and the first sliding body 132 there is a second sliding body 140 supported by the first sliding body 132 in a translatable manner along a third direction of translation x', which is preferably inclined by a certain angle with respect to the second direction of translation x (therefore, in the proposed example, by a certain angle with respect to the horizontal). The angle of inclination of the third direction of translation x' is appropriately chosen depending on the geometry of the circumferential groove to be made, but will generally be in the range of 10° to 50°. In the example proposed herein, the angle of inclination of the third direction of translation x' is 20°. In other words, the pin 130 on which the outer roller 126 is mounted is thus carried by the second sliding body 140, which is translatable along the third direction of translation x' with respect to the first sliding body 132, which in turn is translatable along the second direction of translation x.

A spring member 142 is associated to the second sliding body 140 and has the function of allowing, during processing, a certain displacement of the second sliding body 140, and therefore of the pin 130 with the associated outer roller 126, along the third direction of translation x' with respect to the first sliding body 132 in the direction away from the drum body (i.e. , towards the right, with respect to the point of view of a person looking at Figures 6 and 7), in case of impulsive loads acting on the outer roller 126 in a direction opposite to the direction of the force with which said roller is pressed against the drum body. In this way, during processing, whenever the outer roller 126 comes into contact with the thickening of the drum body at the aforementioned joint area J, and is therefore subjected to an impulsive load in the opposite direction to that with which said roller is pressed against the drum body, the spring member 142 allows a certain displacement (typically in the order of a few millimetres) of the second sliding body 140 carrying the outer roller 126 along the third direction of translation x' in the same direction as the impulsive load in order to absorb that load. By appropriately calibrating the spring member 142 (in terms of preload and stiffness), it is possible to adjust the intensity of the force required to cause a displacement of the second sliding body 140, as well as the magnitude of such displacement. Naturally, the spring member 142 exerts on the second sliding body 140 a biasing force tending to urge the second sliding body 140, and therefore also the pin 130 with the outer roller 126, towards the drum body 12, i.e., towards the left with respect to the point of view of a person looking at Figures 6 and 7.

The spring member 142 is mounted on the first sliding body 132, in particular on an inclined surface 132a of that slide, in such a manner that the biasing force exerted by that member is directed along the third direction of translation x', and thus has not only a component along the second direction of translation x (horizontal component) but also a component along the axis of rotation z2 of the outer roller 126 (vertical component).

For example, the spring member 142 is formed, as in the embodiment proposed herein, by an elastomer spring with a plurality of elastomeric elements 144 arranged one behind the other. In this case, the stiffness of the spring member 142 may be adjusted by inserting or removing the elastomeric elements 144. However, the spring member might be of a type different from the one illustrated herein, for example being formed by a gas spring.

With regard to the upper groove forming device 108, what has been illustrated above with regard to the lower groove forming device 110 still applies. As can be seen from Figure 5, the upper groove forming device 108 has the same structure as the lower groove forming device 110, but is mounted in an inverted position, i.e. so that the rollers 124 and 126 protrude downwards, rather than upwards, from the support body 118.

With reference now to Figures 8 to 12, the operation of the processing apparatus 100 will be described.

Once the drum body 12 (or, more generally, the hollow cylindrical sheet metal part) to be worked has been positioned on the workpiece-carrying drum 104, the groove forming devices 108 and 110 are moved along the first direction of translation z and the second direction of translation x so as to bring the rollers 124 and 126 of each device astride the respective area of the drum body 12 in which to make the respective circumferential groove.

More particularly, first the groove forming devices 108 and 110 are moved along the first direction of translation (vertical direction) away from each other, so as to bring the rollers 124 and 126 of the upper groove forming device 108 above the upper edge of the drum body 12 and the rollers 124 and 126 of the lower groove forming device 110 below the lower edge of the drum body 12, as shown in Figure 8.

The turret 106 is then moved along the second direction of translation towards the workpiece-carrying drum 104 so as to bring the inner roller 124 and the outer roller 126 of each of the two groove forming devices 108 and 110 to the inner side and the outer side of the cylindrical lateral wall of the drum body 12, respectively, as shown in Figure 9.

At that point, the two groove forming devices 108 and 110 are again moved along the first direction of translation (vertical direction), but in this case towards each other, so as to bring the rollers 124 and 126 of the upper groove forming device 108 below the upper edge of the drum body 12 and the rollers 124 and 126 of the lower groove forming device 110 above the lower edge of the drum body 12, as shown in Figure 10.

With the two groove forming devices 108 and 110 thus positioned, the actual forming of the two circumferential grooves in the drum body is performed, as shown in Figures 11 and 12. To this end, the workpiece-carrying drum 104, and with it the drum body 12, is set into rotation about the axis of rotation z and the outer roller 126 of each groove forming device 108, 110 is urged by the first sliding body 132 towards the inner roller 124, so that the annular protrusion 126a of the outer roller 126 deforms the sheet metal portion of the drum body 12 between the two rollers, thereby obtaining a circumferential groove of a shape corresponding to that of the circumferential groove 124a in the inner roller 124. In the movement towards the drum body 12, the assembly formed by the first sliding body 132, the second sliding body 140, the pin 130 and the outer roller 126 behaves substantially as a rigid body. However, when, during the circumferential groove forming operation, the outer roller 126 comes into contact with the discontinuity on the outer surface of the drum body 12 due to the thickening in the joint area J between the two short sides S1 and S2 of the rectangular sheet S from which the drum body 12 is made, the impulsive load generated by this discontinuity on the outer roller 126 is absorbed by means of the retraction of the roller itself, thanks to the fact that the spring member 142 allows the second sliding body 140, on which the pin 130 carrying the outer roller 126 is mounted, a certain movement along the third direction of translation x'. The biasing action exerted by the spring member 142 on the second sliding body 140 ensures that the outer roller 126 always remains in contact with the outer surface of the drum body 12 during processing.

Thanks to the fact that the outer roller of each of the groove forming devices is displaceable with respect to the first sliding body by virtue of to the yielding of the spring member, the groove forming device according to the invention is able to absorb the impulsive loads generated on said roller due to the discontinuity present on the outer surface of the drum body and is therefore less subject to wear and fatigue failure than the prior art. In addition, the possibility of retraction of the outer roller following contact with the discontinuity present on the outer surface of the drum body prevents the roller from tending to move this discontinuity towards the inside of the drum body and thus makes it possible to maintain a more precise geometry of the inner surface of the drum body.

Preferably, the movement of the second sliding body, and hence of the outer roller, with respect to the first sliding body is directed along a direction inclined to the horizontal, in such a manner that the resultant of the vertical and horizontal forces generated by the pressure of the outer roller on the drum body is a force inclined to the horizontal by an angle equal to that of this inclined direction. This allows to ensure a better tolerance than the prior art in the distance between the upper circumferential groove and the lower circumferential groove of the drum body.

Finally, with reference to Figure 13, in which parts and elements identical or corresponding to those of the groove forming device of Figures 6 and 7 have been assigned the same reference numbers, according to a further embodiment of the present invention the lower groove forming device 110 (but the same also applies to the upper groove forming device 108) may further comprise an actuator 146 arranged in series with respect to the spring member 142 so as to be capable of acting on the second sliding body 140 via the spring member 142.

The actuator 146 may be, for example, a servo-controlled electric motor coupled to a mechanism for converting the motion from a rotational one to a linear one, or a pneumatic or hydraulic linear actuator. The actuator 146 may, for example, be used to vary the preload of the spring member 142.

The same applies for the rest as explained above with reference to Figures 5 to 12. The present invention has been described herein with reference to a preferred embodiment thereof. It is to be understood that other embodiments may be envisaged which share the same inventive core with the one described herein, as defined by the appended claims.