Technical field of the invention

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

More specifically, the present invention relates to an assembling apparatus for assembling a drum for a washing machine or tumble dryer, comprising:

- a first device configured to make by plastic deformation a joint between a hollow cylindrical sheet metal part defining the body of the drum and a first plastic part forming the mouth of the drum, and

- a second device configured to make by plastic deformation a joint between the sheet metal part and a second plastic part forming the bottom of the drum.

State of the art

With reference to Figure 1 of the appended drawings, a drum 10 for a washing machine or tumble dryer typically comprises a hollow cylindrical sheet metal part 12 defining the drum body and a pair of plastic parts 14 and 16 assembled to the sheet metal part 12, namely a first plastic part 14 forming the drum mouth, which is mounted at the upper end of the sheet metal part 12, and a second plastic part 16 forming the drum bottom, 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, having in particular a thickness between 0.4 and 0.8 mm. The two short sides S1 and S2 are typically joined by crimping, i.e., by overlapping and folding, of these sides. Such an operation inevitably produces a thickening of the sheet metal part 12 at the joint area between the two short sides S1 and S2, and therefore a discontinuity in the outer 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.

The assembly of the first plastic part 14 and the second plastic part 16 onto the sheet metal part 12 is normally carried out 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 drum mouth, and lower end region, in the case of the second plastic part 16 forming the drum bottom) onto the respective plastic part.

Referring now to Figure 3 of the attached drawings, where 18 indicates a flange of the first plastic part 14 and 20 indicates a flange of the second plastic part 16, the assembly of the first plastic part 14 with the sheet metal part 12 normally consists in the following two operations:

- a so-called riveting operation, consisting in bending at 90 degrees an upper end edge 12a of the sheet metal part 12 onto an axially outer face (upper face) 18a of the flange 18 of the plastic part 14, and

- a so-called crimping operation, consisting in pressing a portion 12c of the sheet metal part 12 close to the upper end edge 12a, so as to form a groove adjacent to an axially inner face (lower face) 18b of the flange 18 of the plastic part 14.

Likewise, the assembly of the second plastic part 16 with the sheet metal part 12 consists in the same two operations, except that in this case the riveting operation is performed on a lower end edge 12b of the sheet metal part 12 on an axially outer face (lower face) 20a of the flange 20 of the plastic part 16, and the crimping operation is performed by pressing a portion 12d of the sheet metal part 12 close to the lower end edge 12b, so as to form a groove adjacent to an axially inner face (upper face) 20b of the flange 20 of the plastic part 16.

Both the riveting operation and the crimping operation are performed, for each of the two plastic parts 14 and 16 to be assembled to the sheet metal part 12, by means of a machine comprising a pair of rollers, namely an upper roller and a lower roller, respectively, having a suitably shaped outer working surface. Each roller is urged radially against the sheet metal part 12, while the latter is set into rotation about its axis of symmetry, so as to plastically deform the upper end region and the lower end region of the sheet metal part 12 in order to cause these regions to take the desired geometry.

The fact that, as explained above, the sheet metal part 12 has a thickening at the joint area between the two short sides S1 and S2 means that, during the deformation of the end regions of the sheet metal part 12 for joining the two plastic parts 14 and 16, the rollers used for deforming the upper and lower end regions of the sheet metal part 12 are subjected to impulsive load stresses whenever, as a result of the rotation of the sheet metal part 12 about its axis, the rollers come into contact with this thickening. These stresses may lead to wear and fatigue failure of the components of the assembling apparatus over time. Furthermore, at the thickening of the sheet metal part 12 the rollers tend to press this thickening 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 to provide a joining device which allows a joint to be made between a sheet metal part, in particular a drum body for a washing machine or tumble dryer, and a plastic part, in particular a mouth or a bottom of a drum for a washing machine or tumble dryer, by riveting and crimping of an end region of the sheet metal part, without being affected by the disadvantages of the prior art illustrated above.

This and other objects are fully achieved according to the present invention by means of a joining device as defined in the annexed independent claim 1.

It is also an object of the present invention to provide an assembling apparatus, in particular for assembling a mouth and/or a bottom of a drum for a washing machine or a tumble dryer, both made of plastic material, onto a body of a drum for a washing machine or tumble dryer made of sheet metal, which assembling apparatus comprises at least one joining device of that type.

Further advantageous aspects of the invention are set forth 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 which can be assembled by means of a joining device according to the present invention;

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

- Figure 3 is an axial sectional view showing in detail the joint area between the upper end region of the body and the mouth of the drum of Figure 1 , as well as the joint area between the lower end region of the body and the bottom of the drum of Figure 1 ; - Figure 4 is a front view of an assembling apparatus for assembling the mouth and the bottom to the body of the drum of Figure 1 , comprising a first and a second joining device, that is to say, a top joining device and a bottom joining device, respectively, according to an embodiment of the present invention;

- Figures 5, 6 and 7 are a side view, an axonometric view and an axial sectional view, respectively, of the bottom joining device of the assembling apparatus of Figure 4; and

- Figure 8 is an axial sectional view of a joining device according to a further embodiment of the present invention.

Detailed description

With initial reference to Figure 4, numeral 100 generally indicates an assembling apparatus arranged to assemble a first plastic part, in particular a mouth of a drum for a washing machine or tumble dryer, to the upper end of a hollow cylindrical sheet metal part, in particular a body of a drum for a washing machine or tumble dryer, and at the same time to assemble a second plastic part, in particular a bottom of a drum for a washing machine or tumble dryer, to the lower end of the aforementioned sheet metal part. In the present description, reference will be made, for the sake of convenience, to the use of the assembling apparatus for assembling a mouth and a bottom of a drum for a washing machine or tumble dryer to a drum body for a washing machine or tumble dryer, it being understood that the assembling apparatus is not limited to this specific application but may be used to assemble together parts of different types, provided that they have a rotationally symmetrical geometry.

The assembling apparatus 100 comprises a base structure 102 on which a turntable 104 is mounted, in a substantially central position, the turntable being drivable into rotation about a vertically oriented axis of rotation z by means of suitable driving means, comprising for example an electric motor 106. The turntable 104 is intended to receive the assembly formed by the drum body, the mouth and the bottom, which is prepared by an operator outside the apparatus and is then arranged on the turntable 104 for performing the joining between the mouth and the drum body and between the bottom and the drum body.

The assembling apparatus 100 further comprises a turret 108 arranged next to the turntable 104 and a pair of joining devices 110 and 112, that is, an upper joining device and a lower joining device, respectively, which are mounted on the turret 108 so as to be able to translate along a direction of translation oriented parallel to the axis of rotation z, in the present case in a vertical direction. The upper joining device 110 is intended to make the joint between the mouth and the body of the drum, while the lower joining device 112 is intended to make the joint between the bottom and the body of the drum. To each joining device 110, 112 respective driving means are associated for controlling the movement of the joining device in the vertical direction (or, more generally, in the aforementioned direction of translation) along the turret 108 so as to position the joining device at the desired height with respect to the drum body positioned on the turntable 104.

With reference now to Figures 5 to 7, the structure and operation of the lower joining device 112 will be described in detail, it being understood that what will be illustrated below with regard to the lower joining device 112 is substantially valid for the upper joining device 110 as well.

The lower joining device 112 comprises first of all a support structure 114, which is mounted on vertical guides 116 of the turret 108 (which can be seen in Figure 4) so as to allow movement of the joining device 112 in the vertical direction.

The lower joining device 112 further comprises a first sliding body 118, which is supported by the support structure 114 so as to be movable along a horizontal direction of advancement x (or, more generally, a direction of advancement perpendicular to the aforementioned axis of rotation z). Driving means are associated to the first sliding body 118 for controlling the movement of the first sliding body 118 along the direction of advancement x. In the example proposed herein, said driving means comprise an electric motor 120, carried by the support structure 114, and a motion conversion mechanism for converting the rotational motion of an output shaft of the electric motor 120 into a translational motion of the first sliding body 118. In particular, the motion conversion mechanism comprises a screw 122, which is rotatably supported by the support structure 114 for rotation about its axis and is drivable into rotation by the electric motor 120, and a nut screw 124, which is mounted on the first sliding body 118 and engages with the screw 122.

The lower joining device 112 further comprises a pair of rollers 126 and 128 arranged one above the other. The roller 126 has the function of performing the aforementioned riveting operation, or 90-degree bending, and will hereinafter be referred to as the riveting roller, while the roller 128 has the function of performing the aforementioned crimping operation and will hereinafter be referred to as the crimping roller. In the lower joining device 112 the riveting roller 126 is arranged below the crimping roller 128, while in the upper joining device 110 (not illustrated in detail herein) the riveting roller is arranged above the crimping roller.

The riveting roller 126 is mounted on a pin 130 in a freely rotatable manner about a respective vertical axis of rotation z1 , or, more generally, an axis of rotation perpendicular to the direction of advancement x. Likewise, the crimping roller 128 is mounted on a pin 132 in a freely rotatable manner about a respective vertical axis of rotation z2, or, more generally, an axis of rotation perpendicular to the direction of advancement x and parallel to the axis of rotation z1 of the riveting roller 126.

The pin 130 of the riveting roller 126 is fixed to the first sliding body 118, and is therefore drivingly connected therewith in the translational movement along the direction of advancement x controlled by the electric motor 120. The pin 132 of the crimping roller 128 is fixed to a second sliding body 134 which is supported by the first sliding body 118 so as to be able to translate along a direction x'. Preferably, the direction x' is inclined by a certain angle with respect to the horizontal, or, more generally, with respect to the direction of advancement x, and will therefore be referred to hereinafter as the inclined direction. This angle of inclination is appropriately chosen depending on the desired geometry of the coupling surface between the sheet metal body and the bottom of the drum (or the mouth of the drum, in the case of the upper joining device 110), but will generally be in the range between 10° and 50°. In the example proposed herein, the angle of inclination of the inclined direction x' is 20°.

A spring member 136 is associated to the second sliding body 134 and has the function to allow, during processing, a certain displacement of the second sliding body 134, and therefore of the pin 132 with the associated crimping roller 128, along the inclined direction x' with respect to the first sliding body 118 away from the drum body (i.e., towards the left, with respect to the point of view of a person looking at Figures 5 and 7), in case of impulsive loads acting on the crimping roller 128 in the direction opposite to that of the force with which said roller is pressed against the drum body. In this way, during processing, whenever the crimping roller 128 comes into contact with the aforementioned thickening of the drum body, and is therefore subjected to an impulsive load in the direction opposite to that with which said roller is pressed against the drum body, the spring member 136 allows a certain displacement (typically in the order of a few millimetres) of the second sliding body 134 which carries the crimping roller 128 in the same direction as that of the impulsive load in order to absorb said load. The spring member 136 is for example formed by a gas spring, as in the embodiment illustrated herein, but might also be formed by an elastomer spring. By appropriately calibrating the spring member 136 (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 134, as well as the magnitude of such displacement. Naturally, the spring member 136 exerts on the second sliding body 134 a biasing force tending to urge the second sliding body 134, and hence the crimping roller 128 with it, towards the drum body, i.e. , towards the right with respect to the point of view of a person looking at Figure 7. The spring member 136 is mounted on a support body 138 of the first sliding body 118 in such a manner that the longitudinal axis of the spring member 136 is directed along the inclined direction x'. In particular, the spring member 136 is mounted on a surface 138a of the support body 138 which is inclined with respect to the horizontal, or, more generally, with respect to the direction of advancement x, by the same angle as the inclined direction x'.

Furthermore, as shown in Figure 7, according to the embodiment illustrated herein, the support body 138 is in turn mounted on the first sliding body 118 so as to be able to translate in a horizontal direction, and between the support body 138 and the first sliding body 118 a further spring member 140 is mounted, which is capable of allowing a certain displacement of the support body 138 with respect to the first sliding body 118 along the direction of advancement x, also in this case away from the drum body (i.e., to the left, with respect to the point of view of a person looking at Figures 5 and 7). The spring member 140, like the spring member 136, can also be suitably calibrated (in terms of preload and stiffness) to adjust the intensity of the force required to cause a displacement of the support body 138, as well as the magnitude of such displacement. Furthermore, also the spring member 140, like the spring member 136, is for example formed by a gas spring, but might also be formed by an elastomer spring.

Alternatively, however, it may be envisaged that the support body 138 is made in one piece with the first sliding body 118 or is formed as a separate piece from the first sliding body 118 but is rigidly connected thereto.

With regard to the upper joining device 110, what has been illustrated above with regard to the lower joining device 112 still applies. The only difference is that the crimping roller 128 is in this case arranged below the riveting roller 126, and therefore the second sliding body 134 carrying the crimping roller 128 is also arranged below the first sliding body 118.

The operation of the joining devices 110 and 112 is as follows.

Once the assembly formed by the drum body, the mouth and the bottom has been positioned on the turntable 104, the joining devices 110 and 112 are moved along the turret 104 to be positioned at the desired height, namely at the upper end region of the drum body, as regards the upper joining device 110, and at the lower end region of the drum body, as regards the lower joining device 112. The turntable 104 is then set into rotation about the axis of rotation z, and the riveting roller 126 and the crimping roller 128 of each of the two joining devices 110 and 112 are urged against the drum body to perform the respective riveting and crimping operations. In this regard, for each of the joining devices 110, 112 the driving means (i.e. , the electric motor 120) associated to the first sliding body 118 are driven to control the movement of the first sliding body 118, and hence of the second sliding body 134 with it, along the direction of advancement x towards the drum body. In the movement towards the drum body, the assembly formed by the first sliding body 118 and the second sliding body 134, with the associated rollers 126 and 128, behaves substantially as a rigid body. However, when during processing the crimping roller 128 comes into contact with the discontinuity on the outer surface of the drum body due to the thickening in the area of the joint between the two short sides of the rectangular sheet from which the drum body is made, the impulsive load generated by this discontinuity on the crimping roller 128 is absorbed by retraction of this roller, due to the fact that the spring member 136 allows a certain displacement of the second sliding body 134, on which the pin 132 carrying the crimping roller 128 is mounted, along the inclined direction x'. The biasing action exerted by the spring member 136 on the second sliding body 134 ensures that, during processing, the crimping roller 128 always remains in contact with the outer surface of the drum body.

By virtue of the fact that the crimping roller is a separate component with respect to the riveting roller and is displaceable with respect to the latter due to the yielding of the spring member, the joining device according to the invention is able to absorb the impulsive loads generated on the crimping roller as a result of the discontinuity present on the outer surface of the drum body and is therefore less prone to wear and fatigue failure than the prior art. Furthermore, the possibility of retraction of the crimping 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 therefore allows a more precise geometry of the inner surface of the drum body to be maintained. Preferably, the movement of the second sliding body, and hence of the crimping 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 axial (i.e. vertical) and radial (i.e. horizontal) forces generated due to the pressure of the roller on the drum body is a force inclined to the horizontal by an angle equal to that of said inclined direction. This allows to ensure a better tolerance than the prior art in the distance between the upper groove of the drum body, i.e., the groove adjacent to the drum mouth, and the lower groove of the drum body, i.e., the groove adjacent to the drum bottom.

Finally, with reference to Figure 8, where parts and elements identical or corresponding to those of the joining device of Figures 5 to 7 have been given the same reference numbers, according to a further embodiment of the present invention the lower joining device 112 (but the same also applies to the upper joining device 110) may further comprise an actuator 142 arranged in series with respect to the spring member 136 so as to be able to act on the second sliding body 134 via the spring member 136.

The actuator 142 may be, for example, a servo-controlled electric motor coupled to a mechanism for converting the rotary motion into linear motion, or a pneumatic or hydraulic linear actuator. The actuator 142 may, for example, be used to vary the preload of the spring member 136.

The same applies for the rest as explained above with reference to Figures 4 to 7.

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.