Method for obtaining a joint between elements of different materials

Abstract

A joint between at least one element of metal material and at least one element of plastic material is obtained by pressing these elements in contact against each other, with a simultaneous application of heat. A cladding of metal material and/or of plastic material is applied above the joint by additive manufacturing technology.

Claims

1. Method for obtaining a joint between elements of different materials in which the joint comprises at least one element of metal material and at least one element of plastic material, having respective contact surfaces, the method comprising: pressing said contact surfaces of said at least one element of metal material and said at least one element of plastic material against each other with a simultaneous application of heat, and applying a cladding of metal material and/or plastic material above said joint, by additive manufacturing technology.

2. Method according to claim 1, wherein the applying the cladding by additive manufacturing technology comprises a step of applying a cladding made with powders and/or wire of metal material and/or a step of applying a cladding made with powders and/or wire of plastic material.

3. Method according to claim 1, wherein the applying the cladding by additive manufacturing technology comprises a first step of applying a coarse base cladding and a second step of applying a fine cladding, including a distribution of strengthening micro-ribs above the base cladding.

4. Method according to claim 1, further comprising obtaining a local quenching step obtained by feeding a cold fluid above the cladding layer immediately after the step of applying the cladding.

5. Method according to claim 1, further comprising feeding a hot fluid immediately before or after the step of applying the cladding for local heating.

6. Method according to claim 1, wherein before joining the metal element and the element of plastic material with each other, further comprising forming on the contact surface of the metal element, with the aid of a laser, an uneven surface portion, having a distribution of asperities, the application of heat being such as to generate a softening of the plastic material, so that said material fills the spaces between the asperities of said uneven surface portion and keeps this configuration after a subsequent cooling.

7. Method according to claim 1, further comprising applying a layer of adhesive before the joining between the metal element and the element of plastic material on the contact surface of the metal element.

8. Method according to claim 1, wherein before joining the metal element and the element of plastic material with each other on the contact surface of the metal element, forming an uneven surface portion having a distribution of asperities, and applying a layer of adhesive before said joining above said contact surface having said uneven surface portion, the layer of adhesive filling the spaces between the asperities of said uneven surface portion.

Description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(1) Further features and advantages of the invention will become apparent from the description which follows with reference to the annexed drawings, given purely by way of non-limiting example, in which:

(2) FIGS. 1, 2, 4, 5, 6, 7 show subsequent steps of one embodiment of the method according to the invention,

(3) FIG. 3 is a perspective view of an element of metal material after the method step which is shown in FIG. 2,

(4) FIG. 8 shows a variant of FIG. 7,

(5) FIG. 9 is a diagrammatic view of an operating unit which can be used in implementing the method according to the invention, and

(6) FIG. 10 is a perspective view of one example of an upper cladding layer which is formed with micro-ribs.

(7) In the example shown in the drawings, the method of the invention includes a preliminary step in which a panel 1 of metal material, for example of steel, is subjected to a heating operation by means of a laser beam B emitted from a laser focusing head H which is displaced (for example by means of a robot) above, and at a distance from, the panel 1, so as to move the focusing spot of the laser beam P along a surface 1A of the panel.

(8) In the illustrated example, the method comprises a subsequent step in which on the surface 1A of the metal panel 1 an uneven surface portion 1B is formed, having a distribution of asperities. The uneven surface portion 1B can be for example a knurled surface, as shown in FIG. 3. In the case of the example of FIG. 2, the knurled surface 1B is obtained by means of a laser beam B projected against the surface 1A by a laser head H, which is moved above, and spaced apart from, surface 1A, for example with the aid of a robot. However, the uneven surface portion 1B could be obtained by any other suitable technique, for example by sand-blasting or by an etching operation.

(9) In the example illustrated herein, the method according to the invention includes a following step, shown in FIG. 4, in which above the surface 1A there is applied a layer of adhesive 1A, for example by means of a nozzle N for dispensing adhesive material, moved by means of a robot. The use of the adhesive material is required in the case in which the element of plastic material which is to be joined to the panel of sheet metal 1 is constituted by a thermosetting plastic material, whereas the use of adhesive can be useful, but can also be avoided if the plastic material of the panel which is to be joined to the panel of the sheet metal 1 is a thermoplastic material.

(10) FIG. 5 shows the following step of the method according to the invention, in which a panel of plastic material 2 is superimposed and pressed (by any suitable means of known type, not illustrated herein for greater clarity of the drawings). In particular, surface 2A of the panel of plastic material 2 which faces towards the panel 1 of metal material is pressed against surface 1A of the panel of metal material 1, with the interposition of the layer of adhesive A.

(11) FIG. 6 shows that, while the two panels 2 are still pressed against each other by forces F, the joint between the two panels is subjected to heating with the aid of a laser beam B focused by a laser head H, for example carried by a robot. This step involves a local softening of the plastic material constituting the panel 2 in case this plastic material is a thermoplastic material. Also in this case, the layer of adhesive A, as already indicated above, can be omitted, so that the softened thermoplastic material penetrates into the cavities between the asperities of the uneven surface portion 1B, and then hardens within the above mentioned cavities.

(12) According to a basic feature of the invention, above the joint of the two panels 1, 2 there is applied a cladding C, by additive manufacturing technology.

(13) FIG. 9 of the annexed drawings diagrammatically shows a head 3 for additive manufacturing, comprising a first dispensing nozzle 4, located at one end of a conduit (not shown) for supplying powders or wire of metal material or plastic material. The head 3 further comprises a laser head 5 for focusing a laser beam in the area of the position of the powders or wire of metal material or plastic material. Finally, in the embodiment illustrated herein, the head for additive manufacturing 3 also comprises a nozzle 6 for dispensing a cold or hot fluid, in order to cool or heat the area of the position of the cladding, right before or after the application of the cladding, as it will be described more in detail in the following.

(14) In the example illustrated in FIG. 7, the cladding C is applied so as to be superimposed both to the panel of metal material 1, and to the panel of plastic material 2, in the area of the joint. The result is a joint having improved strength characteristics, with no relevant increase in weight.

(15) In a preferred embodiment, the step of applying a cladding by additive manufacturing technology can comprise a first step of applying a coarse base cladding (thickness in the order of millimeters) and a second step of applying a fine cladding (thickness in the order of 100 microns) and/or a super-fine cladding (thickness in the order of tenths of micron or even less). The fine cladding superimposed to the base cladding preferably includes a distribution of micro-ribs having a strengthening function, above the base cladding, for example according to the configuration shown in FIG. 10, which includes a plurality of ribs 7 in the form of leafs orthogonal to the substructure so as to define a plurality of closed cells 8.

(16) FIG. 8 shows a variant of FIG. 7, in which a cladding of plastic material C1 is applied above the panel of plastic material 2, and a cladding of metal material C1 is applied above the panel of metal material 1. The cladding C1 adheres both to the surface 1A of the metal panel 1, and to the lateral edge 2L of the panel of plastic material 2.

(17) In one embodiment of the method according to the invention, a local quenching step is provided, which is obtained by feeding a cold fluid (for example through nozzle 6 visible in FIG. 9) above the cladding layer, immediately after the step of applying the cladding. In this manner, an increase of the mechanical characteristics of the joint is obtained.

(18) Also according to the invention, a local heating step can be provided, obtained by feeding a hot fluid (for example by means of the same nozzle 6 shown in FIG. 9) immediately before or after the step of applying the cladding, in order to release inner stresses induced in the material.

(19) Studies and tests conducted by the Applicant have shown that the method according to the invention dramatically improves the mechanical characteristics of the joint between an element of metal material and an element of plastic material, without involving at the same time any relevant increase in weight.

(20) Naturally, the invention is also applicable to a joint which includes more than one element of metal material or more than one element of plastic material.

(21) As also indicated, the element of plastic material can be constituted by thermoplastic material or thermosetting material, or also by a composite material including a synthetic matrix reinforced with fibers, such as carbon fibers.

(22) The method according to the invention is also adapted to be easily implemented in assembling processes of motor-vehicle bodies, wherever there is the need of the obtaining joints between metal elements and elements of plastic material for components which must have also a structural function.

(23) Naturally, while the principle of the invention remains the same, the details of construction and the embodiments may widely vary with respect to what has been described and illustrated purely by way of example, without departing from the scope of the present invention.