A method of connecting a pair of elements of a structure by gluing and a plant for implementing the method

Abstract: A method of connecting a pair of elements of a structure by gluing comprises the following steps: forming, in a single press (3), first and second elements (12a, 12b) to be connected to one another by gluing along their coupling surfaces; interposing an adhesive material (23) between the coupling surfaces; and coupling the elements (12a, 12b), by subjecting them to compression in the press (3). A backing sheet (13) is provided near the press (3) and an adhesive material (23) is spread thereon at least along a predetermined outline (25) corresponding to the coupling surfaces of the elements (12a, 12b). The backing sheet (13) is fed between the two elements (12a, 12b) so that the adhesive material (23) is deposited on the coupling surfaces. The elements (12a, 12b) are coupled with the backing sheet (13) interposed.

Description: The present invention relates to a method of connecting a pair of elements of a structure by gluing, comprising the following steps: forming, in a single press and in mutually facing positions, first and second elements which can be connected by gluing along their coupling surfaces, interposing an adhesive material between the coupling surfaces of the elements, and coupling the elements by subjecting them to compression in the press. A method of the type indicated above is known from the Applicant's European patent application EP-A-336 906. In this method, the adhesive material is spread, in conventional manner, on the coupling surfaces of at least one of the elements to be glued together, for example, manually by an operator when the dies of the press are in the open condition. To allow the operator to spread the adhesive, the press has to be kept in its open configuration for a predetermined period of time, which adversely affects the overall duration of the production cycle of the structure as a whole. Moreover, the operator entrusted with the spreading of the adhesive has to work under extremely unpleasant environmental conditions since he is subjected directly both to the heat necessary for the moulding process and to the vapours of the adhesive material which often have an unpleasant smell. Since the manual spreading of the adhesive material takes a considerable time, the adhesive is subject to different temperatures on different portions of the coupling surface because it is spread at different moments onto regions having different amounts of residual heat, so that its characteristics may not be uniform along the coupling surfaces of the elements to be connected. In order to prevent the aforementioned problems, the subject of the present invention is a method of the type specified above, which also comprises the steps of: providing a backing sheet, spreading the adhesive material on the backing sheet, at least along a predetermined outline corresponding to the coupling surfaces of the elements, feeding the backing sheet between the two elements so that the adhesive material is disposed at least along said coupling surfaces, and coupling the elements with the interposition of the backing sheet bearing the adhesive material. By virtue of these characteristics, the method according to the invention optimizes the times taken by the production cycles of the structure since the spreading of the adhesive material is carried out outside the press and does not therefore affect these times. Moreover, the adhesive material is applied simultaneously over the whole extent the coupling surfaces of the elements so as not to give rise to non-uniform characteristics, and use can advantageously be made of the residual heat stored in the moulded elements to bring about prepolymerization of the adhesive material. A further subject of the invention is a plant for producing a shell-like structure including a pair of half-shells of plastics material which can be connected by gluing, comprising in combination: a press having a pair of parallel main dies movable relative to one another along a common axis of movement between a position in which they are spaced apart and a position in which they are close together, and an intermediate die movable transverse the axis of movement of the two main dies, in which the dies can adopt a closed moulding configuration in which both of the main dies are brought close to the intermediate die so that respective cavities defining the shapes of the half-shells are defined between the main dies and the intermediate die, and an open configuration in which the main dies are spaced apart and the intermediate die is moved away from the common axis of movement of the main dies, characterised in that it further comprises: a backing sheet disposed close to the press, supply means for spreading an adhesive material on the backing sheet at least along a predetermined outline corresponding to the coupling surfaces of the half-shells, transfer means for the backing sheet, for feeding it between the two main dies in their open configuration, adjacent the coupling surfaces of the elements. Further characteristics and advantages of the present invention will become clearer from the following detailed description, given with reference to the appended drawings, provided purely by way of non-limiting example, in which: Figure 1 is a schematic, perspective view of plant for implementing the method of the invention, Figure 2 is a side elevational view sectioned on the line II-II of Figure 1, Figure 3 is a view similar to Figure 1 of a different moment during the implementation of the method, Figure 4 is a side elevational view sectioned on the line IV-IV of Figure 3, Figure 5 is a view similar to Figure 3 of a stage of the coupling of the elements of the structure, Figure 6 is a side elevational view sectioned on the line VI-VI of Figure 5, Figure 7 is a schematic, perspective view corresponding to a final stage of the production cycle of the structure, Figure 8 is a perspective view of the structure which can be produced by means of the method according to the invention, sectioned on the line VIII-VIII of Figure 7, and Figure 9 is a view of a detail indicated by the arrow IX in Figure 8, on an enlarged scale. With reference to the drawings, a plant, generally indicated 1, is for producing a shell-like structure 10 of plastics material of the thermoplastic or thermosetting type, which is formed by the gluing of two half-shells 12a, 12b along their coupling surfaces, and which can be used, for example, as an auxiliary structure for supporting a propulsion unit of a motor vehicle. The plant 1 comprises a press 3 having a base 5 which supports a pair of main plate-shaped dies 7 and 9 which have respective mutually facing cavities 7a and 9a defining the external shapes of the half-shells 12a, and 12b. The dies 7 and 9 are movable relative to the base 5 along a common axis A which is normally oriented vertically, so that the press 3 is generally known as a vertical press. An intermediate die or punch 11, associated with the press 3, is movable relative to the dies 7 and 9 along an axis B transverse the axis A so that the punch 11 can be moved from a position in which it is disposed beside and outside the press 3 and another position in which it is interposed between the main dies 7 and 9. The opposed faces of the punch 11 are formed so as to have shaped projections 11a and 11b facing the cavities 9a and 7a, respectively, for defining the internal surfaces of the half-shells 12a, 12b. Near the press 3 is a backing sheet 13 made of a thin and porous material, for example, of fibres of plastics material arranged in a woven or non-woven fabric-like structure the purpose of which will be explained further in the following description. The sheet 13 is arranged with an end portion thereof on a table 14 adjacent the press 3 and can be unwound from a roll 15. Advantageously, means for cutting the sheet 13, constituted, for example, by a movable blade 17, are associated with the table 14. Beside the backing sheet 13, near the table 14, is an anthropomorphic robot 19, the arm of which supports a head 21 for supplying an adhesive material 23 in the fluid state. Both the movements of the robot 19 and the operation of the head 21 are advantageously subservient to electronic control means, for example, of the digital type, which also control the operation of the press 3. The half-shells 12a, 12b are formed separately and simultaneously in the course of a single hot-moulding operation in the press 3, inside a pair of moulding forms defined between the cavity 7a and the projection 11b and between the cavity 9a and the projection 11a, respectively. The adhesive material 23 which may, for example, be of the polyurethane or epoxy type, is spread on a single face of the backing sheet 13 by means of the supply head 21, simultaneously with the moulding of the half-shells 12a and 12b in the press 3. Owing to the type of material used for the sheet 13 which, as stated above, is thin and porous, the adhesive material 23 soaks into the sheet 13 from the face on which it is spread until it also reaches its opposite face. The supply head 21 is controlled so as to spread the adhesive material 23 along a predetermined outline 25 at least corresponding to the coupling surfaces of the half-shells 12a, 12b. The outline 25 is preferably wider than the coupling surfaces of the half-shells 12a, 12b, alone so as to compensate for any errors in the subsequent positioning of the sheet 13 between the main dies 7 and 9. Upon completion of the moulding of the half-shells 12a, 12b, the dies 7 and 9 are opened and they both move along the axis A away from the intermediate die 11, retaining the respective half-shells 12a, 12b. The die 11 is then moved away from the press 3 along the axis B and, almost simultaneously, the sheet 13 is fed between the dies 7 and 9 by means of a transfer device of known type, for example, a mechanical arm (not shown in the drawings), so that the outline 25 of the adhesive material 23 is disposed adjacent the coupling surfaces of the half shells 12a, 12b. The mechanical arm is also subservient to the electronic control means which govern the operation of the press 3 and of the robot 19. When the outline 25 is correctly positioned along the coupling surfaces of the half-shells 12a, 12b, the main dies 7, 9 are closed again, moving towards one another along the line defined by the axis A until they are brought into mutual contact. The sheet 13 bearing the adhesive material 23 is thus gripped between the dies 7 and 9 so that the adhesive material 23 is disposed in contact with the coupling surfaces of the half-shells 12a, 12b and is spread thereon as a result of the compression effect exerted by the press 3. The blade 17 enables the portion of the sheet 13 with the adhesive material 23 to be separated from the rest of the sheet 13. As stated above, the dies 7 and 9 and the half-shells 12a and 12b store heat in the course of the moulding operation. Their temperature may be greater than 100°C upon completion of the moulding of the half-shells. Since the opening of the dies 7 and 9 lasts for the very short time necessary simply to feed the sheet 13 between them, a minimal portion of the heat stored by the dies 7 and 9 and by the half-shells 12a and 12b is dissipated to the atmosphere and their residual heat is thus used to bring about prepolymerization of the adhesive material 23 during the coupling of the half-shells 12a and 12b. Upon completion of the prepolymerization of the adhesive material 23, the dies 7 and 9 are opened so that the structure 10 can be removed therefrom. In this case, residual portions of the sheet 13 will project from the structure 10 and can be removed manually to finish the outer surface of the structure 10. Alternatively, the dies 7 and 9 may have cutting portions near the cavities 7a and 9a so that preliminary finishing of the outer surface of the structure 10 can be achieved during the coupling and gluing of the half-shells 12a, 12b. The method according to the invention thus considerably reduces the times taken by the production cycle of the shell-like structure 10, avoiding the use of operators, who would be forced to operate in extremely harsh environmental conditions, to spread the adhesive material along the coupling surfaces of the half-shells 12a, 12b, and, moreover, advantageously enables use to be made of the residual heat of the main dies 7 and 9. Some characteristics of a material usable to produce the half-shells 12a, 12b of the structure 10, of possible constituents of an adhesive material 23 usable in the method, and of a sheet 13 usable as a backing for the adhesive 23 are given below, purely by way of example, according to the results which emerged from experimental tests carried out by the Applicant. Both of the half-shells 12a, 12b were made of SMC (sheet moulding compound) composite material. The reinforcing fibre used was 30% by weight of a filler of E-type glass impregnated with a resin having the following characteristics: Parts by volume % by volume - polyester resin:OCF E-955 75 27.8 - thermoplastic additive:OCF E-571 25 9.3 - catalyst: tertiary butyl perbenzoate 1 9.3 - release agent:Zn stearate 4 1.5 - polyethylene powder 6 2.0 - calcium carbonate filler 150 55.6 - pigment paste 8 3.0 - thickener: Mg oxide 1 0.4 Total 270 100.0 in which OCF (Owens Corning Fibreglass) is an abbreviation identifying a manufacturer. After complete polymerization, the SMC had the following mechanical properties: - flexural strength 230 MPa - flexural modulus 14 GPa - tensile strength 137 MPa - tensile modulus 17 GPa - compressive strength 203 MPa - extensibility under tension 1.5 % - Izod impact strength (with notch) 117 J/M of notch x 10 - thermal conductivity 0.25W.m/m 2 .°C - specific heat 1.46 KJ/kg.°C - flammability (UL classification) Category 945V - Rockwell hardness 112 - dielectric strength 1800V/m x 10 4 - specific weight 2.1 - heat distortion point 260°C at 1.9 MPa - continuous service temperature 204°C - coefficient of thermal expansion 211/°C x 10 -6 in which the abbreviation UL indicates the firm Underwriters Laboratories Inc. The adhesive material used was a structural two-part polyurethane adhesive suitable for automatic supply which includes a resin A and a resin B. Resin A was a complex mixture made up as follows, in percentages by weight of the components: - glycols 50 % - calcium carbonate 40 % - amorphous silica 0.2 % - aliphatic amines 0.8 % - zeolite (silicates) 7 % - titanium oxide 2 %. Resin A had a viscosity of between 200,000 and 230,000 mPas and a specific weight of 1.4 ± 0.05 g/ml. Resin B was a complex mixture made up as follows in percentages by weight of the components: - MDI aromatic isocyanates 30 % - Al silicate 15 % - calcium carbonate 50 % - phthalic plasticizer 5 %. Resin B had a viscosity of between 100,000 and 140,000 mPas and had a specific weight of 1.7 ± 0.05 g/ml. The adhesive material was produced by mixing resins A and B with a mixing ratio of: - by weight part A: 100 part B: 130 - by volume part A: 100 part B: 100 and had a post-life of 8÷14 minutes, a slippage ≤ 2.5 mm and a resistance to separation under shear of 50 daN/cm 2 after a cycle of 10 minutes at 80°C plus 7 days at ambient temperature for two sheets of SMC free of powder and connected to one another. A polyester, polyamide or polypropylene fabric may be used for the backing sheet 13, in a woven or non-woven variant. A sheet used by the Applicant was non-woven polyester fabric having the following characteristics expressed in terms of quantities according to ASTM (American Society for Testing Materials) standards and physical quantities: ASTM test physical quantities - basic weight D-3776 20 g/m 2 - longitudinal/transverse tearing strength D-1682 60/60 N - extensibility upon longitudinal/transverse tearing D-1682 45/50 % - thickness D-1777 0.11 mm.

Claims: A method of connecting a pair of elements of a structure by gluing, comprising the following steps: forming, in a single press (3) and in mutually facing positions, first and second elements (12a, 12b) which can be connected by gluing along their coupling surfaces, interposing an adhesive material (23) between the coupling surfaces of the elements (12a,12b), and coupling the elements (12a, 12b) by subjecting them to compression in the press (3), characterized in that it also comprises the steps of: providing a backing sheet (13), spreading the adhesive material (23) on the backing sheet (13) at least along a predetermined outline (25) corresponding to the coupling surfaces of the elements (12a, 12b), feeding the backing sheet (13) between the two elements (12a, 12b) so that the adhesive material (23) is disposed at least along said coupling surfaces, and coupling the elements (12a, 12b) with the interposition of the backing sheet (13) bearing the adhesive material (13). A method according to Claim 1, characterized in that the elements are two half-shells (12a, 12b) which are intended to form a shell-like structure (10) in their coupled condition, and in that both of the two half-shells (12a, 12b) are made of plastics material. A method according to Claim 2, characterized in that the adhesive material (23) is a polymerizable plastics adhesive which undergoes a prepolymerization process in the course of the coupling of the two half-shells (12a, 12b). A method according to any one of Claims 1 to 3, characterized in that the backing sheet (13) is thin and is made of a porous material so that the adhesive material applied to only one face of the backing sheet (13) soaks into it until it reaches the opposite face. A method according to any one of Claims 1 to 4, characterized in that the press (3) comprises a pair of parallel main dies (7, 9) movable relative to one another along a common axis of movement (A) between a position in which they are spaced apart and a position in which they are close together, and an intermediate die (11) movable transverse the axis of movement (A) of the two main dies (7, 9), the dies (7, 9, 11) being able to adopt a closed moulding configuration in which both of the main dies (7, 9) are brought close to the intermediate die (11) so that respective cavities (7a, 9a) defining the shapes of the half-shells (12a, 12b) are defined between the main dies (7, 9) and the intermediate die (11), and an open configuration in which the main dies (7, 9) are spaced apart and the intermediate die (11) is moved away from the common axis of movement (A) of the main dies (7, 9). A method according to Claim 5, characterized in that transfer means provided for the backing sheet (13) can feed it between the two main dies (7, 9) in their open configuration. A method according to Claim 6, characterized in that the transfer means comprise a mechanical arm. A method according to Claim 7, characterized in that there are supply means (21) for spreading the adhesive material (23) along the predetermined outline (25) on the backing sheet (13) and in that the supply means (21) are subservient to electronic control means. A method according to Claim 8, characterized in that the supply means (21) are associated with an anthropomorphic robot (19). A method according to any one of Claims 2 to 9, characterized in that the step of spreading the adhesive material (23) on the backing sheet (13) is carried out simultaneously with the step of moulding the half-shells (12a, 12b). A method according to Claim 10, characterized in that the step of feeding the backing sheet (13) between the two half-shells (12a, 12b) is carried substantially simultaneously with the movement of the intermediate die (11) away from the two main dies (7, 9). A plant for forming a shell-like structure including a pair of half-shells of plastics material which can be connected by gluing, comprising in combination: a press (3) having a pair of parallel main dies (7, 9) movable relative to one another along a common axis of movement (A) between a position in which they are spaced apart and a position in which they are close together, and an intermediate die (11) movable transverse the axis of movement (A) of the two main dies (7, 9), in which the dies (7, 9, 11) can adopt a closed moulding configuration in which both of the main dies (7, 9) are brought close to the intermediate die (11) so that respective cavities (7a, 9a) defining the shapes of the half-shells (12a, 12b) are defined between the main dies (7, 9) and the intermediate die (11) and an open configuration in which the main dies (7, 9) are spaced apart and the intermediate die (11) is moved away from the common axis of movement (A) of the main dies (7, 9), characterised in that it further comprises: a backing sheet (13) disposed close to the press (3), supply means (21) for spreading an adhesive material (23) on the backing sheet (13) at least along a predetermined outline (25) corresponding to the coupling surfaces of the half-shells (12a, 12b), transfer means for the backing sheet (13) for feeding it between the two main dies (7, 9) in their open configuration, adjacent the coupling surfaces of the elements (12a, 12b). A plant according to Claim 12, characterized in that it comprises electronic means for controlling the operation of the press (3), of the transfer means and of the supply means (21). A plant according to Claim 12 or Claim 13, characterized in that it comprises electronic control means for controlling the supply means (21) so as they spread the adhesive material (23) on the backing sheet (13) during the moulding of the half-shells (12a, 12b) in the press (3). A plant according to Claim 14, characterized in that the supply means (21) are associated with an anthropomorphic robot (19). A plant according to any one of Claims 12 to 15, characterized in that it comprises means for feeding the backing sheet (13) bearing the adhesive material (23) between the two half-shells (12a, 12b) and substantially simultaneously moving the intermediate die (11) away from the two main dies (7, 9). A plant according to any one of Claims 12 to 16, characterized in that the transfer means comprise a mechanical arm. A plant according to Claim 16 or Claim 17, characterized in that the backing sheet (13) is unwound from a roll onto a table (14) with which means (17) for cutting the backing sheet (13) are associated. A plant according to Claim 18, characterized in that members for cutting the backing sheet (13) in order to finish the outer surface of the shell-like structure (10) are associated with the main dies (7, 9).

Inventors: DA RE MARIO, DA RE', MARIO
Applicants: FIAT AUTO SPA, FIAT AUTO S.P.A.
Application year: 1995
Main classification: B29C69
IPC codes: B29C70, B29C65, B29C69