A process for co-molding a metal insert

Abstract: A process for co-molding a metal insert (2) forming a plurality of electrical circuits (4) in a synthetic plastics member (3), including the following steps: arranging the metal insert (2) inside respective cavities (7) of a mold (6); cutting respective junction regions (14) between the electrical circuits (4) of the insert (2) to obtain a mechanical and electrical separation of the circuits (4) themselves; injecting a fluid plastics material (33) into the mold (6) to mold the plastics member (3) and encapsulate the metal insert (2) therein; in the injection phase, the insert (2) is held at different regions (42) from the junction regions (14) and the means for cutting the junction regions (14) are withdrawn from the cavities (7) to allow the cut parts (15) of these regions to be encapsulated in the plastic.

Description: The present invention relates to a process for co-molding an insert forming a plurality of electrical circuits in a member of synthetic plastics material. The insert may be metallic. The present invention also relates to equipment for carrying out the above co-molding process. The preambles of claims 1 and 3 are based on US-A-4 965 933. A process is known from Italian Patent No. TO91A000275 of 12.4.1991 for co-molding electrical circuits with members of plastics material, in which the operation of separating the electrical circuits, formed as a single metal insert, is carried out by cutting the metal insert inside the injection mold. A blank holder associated with a cutting die and a punch cut the metal insert and also cooperate to hold it in a predetermined position during the injection of the fluid plastics material so as to avoid any movement of the insert. However, the above process is not without disadvantages: the use of the blank holder, the punch and the cutting die to hold the insert in position during the injection phase means that the cut regions are not encapsulated in the synthetic plastics material, with the result that the cut edge portions of the metal insert are left exposed; this means that, if the co-molded electrical circuit is used, for example, in a situation with a high degree of humidity or in a very dusty situation, the cut metal parts could accidentally be short-circuited by water droplets or dust. The process of US-A-4 965 933 does not provide cut regions that are fully encapsulated. The object of the present invention is to provide a process and equipment for manufacturing an insert forming a plurality of electrical circuits in a member of synthetic plastics material which overcomes the disadvantages described above. On this basis, the present invention according to claim 1 provides a process for co-molding an insert forming a plurality of electrical circuits in a synthetic plastics member. The invention according to claim 3 also provides equipment for the co-molding of a metal insert forming a plurality of electrical circuits in a synthetic plastics member. In order to provide a better understanding of the invention, there follows a description, given purely by way of a non-limitative example, with reference to the appended drawings, in which: Figure 1 is a partial, schematic view of equipment for carrying out the process of the invention at a first step in production; Figure 2 shows the equipment of Figure 1 on an enlarged scale and at a subsequent step in the process; Figure 3 is a section taken on the line III-III of the equipment of Figure 2; Figure 4 shows an enlarged detail of Figure 2; Figure 5 shows the equipment of Figure 2 in a later step in the process of the invention; Figure 6 shows an enlarged detail of the equipment of Figure 5 at a subsequent step; and Figure 7 schematically illustrates a metal insert used in the process according to the invention. With reference to Figures 1 to 7, equipment is indicated 1 for co-molding an insert 2 in a member 3 of synthetic plastics material; the insert 2 forms a plurality (for example two) of electrical circuits 4 (Figure 7). The equipment 1 comprises essentially a pair of half-molds 5a and 5b, constituting an injection mold 6, provided with respective cavities 7a and 7b for molding the member 3 while the metal insert 2 is clamped in a predetermined position 8 inside the cavities 7 by at least one tubular die 11 and a blank holder 12. The equipment 1 is also provided with a punch 13 slidable within the blank holder 12 and cooperating with the die 11 to cut the insert 2 at a junction region 14 between the electrical circuits 4 so as to obtain respective cut metal parts 15, thereby separating the circuits 4 both mechanically and electrically. According to the invention, the blank holder 12, the die 11 and the punch 13 are axially slidable inside the half-molds 5 in respective fluid-tight through-seats 16 and 18 formed in the half-molds and opening into the respective cavities 7. The equipment 1 is in fact provided with two carriages 21 and 22 which effect the controlled axial displacement of the blank holder 12, of the die 11 and of the punch 13. The die 11, which is provided with a preloaded spring 23, cooperates with the first carriage 21 which is movable perpendicular to the direction of movement of the die 11 itself; at one end 24, opposite a second end 25 facing the insert 2, the die 11 is rounded and cooperates slidingly with an inclined plane 26 formed on the carriage 21; in this way, the translational movement of the carriage 21 causes an associated movement of the die 11 in the seat 16 due to the action of the spring 23. The punch 13 and the blank holder 12 are supported by a support frame 31 of the respective half-mold 5a and are slidably mounted, the former within the latter, and fixed by a cam 32 to the second carriage 22 which is movable perpendicular to the direction of movement of the punch 13 and of the blank holder 12 and effects the controlled movement of these latter; the blank holder 12 includes an outer sleeve 34 in which a rod 35 which defines the punch 13 is slidable; a carrier sleeve 36 is connected to the cam 32 while a spring 37 is arranged between the outer sleeve 34 and the carrier sleeve 36 for providing resilient biasing for the blank holder 12. In order to hold the metal insert in the predetermined position 8, both before and during the injection of a fluid synthetic plastics material 33 into the cavities 7 when the blank holder 12, the die 11 and the punch 13 have been withdrawn by the carriages 21 and 22, the equipment 1 also includes a series of plungers 41 which act at restraining regions 42 of the metal insert 2 (Figure 3) which differ from the junction regions 14. The plungers 41 are provided with respective springs 43, appropriately calibrated to transmit a predetermined force, and with tips 44 for coupling with respective centering holes 45 formed in the restraining regions 42 of the metal insert 2 (Figure 7). With reference in particular to Figures 3 and 7, the plungers 41 have a active surfaces 46 which are substantially larger than the corresponding contact surfaces 47 of the corresponding restraining regions 42 so that they project beyond the edges of these latter within the cavities 7 and, during the injection step and after the cavities 7 have been filled with fluid plastics material 33, are acted upon by the hydrostatic pressure which is such as to overcome the action of the springs 43 and thus enables the cavities 7 to be completely filled with the plastics material 33, even around the restraining regions 42. The process for the co-molding of the insert 2 in a member 3 of synthetic plastics material consists essentially of the following steps: a first step (Figure 1) in which the insert 2 is arranged between the two half-molds 5 and, once the mold 6 is closed, the metal insert 2 is clamped in the predetermined position 8 both by the mutual cooperation of the blank holder 12 and the die 11 and by the plungers 41 which couple with the corresponding restraining regions 42; a second step (Figure 2) in which the insert 2 is cut by the punch 13 with the formation of the cut metal parts 15; and a third step (Figure 5) in which the punch 13, together with the blank holder 12 and the die 11, is moved away from the metal insert 2 which at this point is held in the predetermined position 8 by the plungers 41 alone. Next comes the injection step (Figure 6) during which a fluid synthetic plastics material 33 is injected into the cavities 7, totally encapsulating the metal insert 2; once the cavities 7 have been filled, the hydrostatic pressure of the fluid plastics material 33 forces the plungers back into respective chambers 48 formed in the half-molds 5 and thus allows the cavities 7 to be completely filled with the fluid plastics material 33. At the end of the injection step and after the member 3 has cooled, the latter is pushed out of the mold 6 by an ejector pin which is slidable in the die 11. The advantages of the present invention will be apparent from the above description; the co-molding process described enables the production, in a single operation and with the use of a single piece of equipment, of a synthetic plastics member which completely encapsulates an insert forming a plurality of circuits, even in those regions at the junctions between its electrical circuits (Figure 5) in which the insert is cut; this avoids the disadvantages of circuits in which the regions in which the inserts are cut are not suitably electrically insulated.

Claims: A process for co-molding a insert (2) forming a plurality of electrical circuits (4) in a synthetic plastics member (3), comprising the steps of: arranging the insert (2) inside respective cavities (7) of a mold (6) for the production of said synthetic plastics member (3); cutting respective junction regions (14) between said electrical circuits (4) of said insert (2) to obtain respective cut metal parts (15), so as to achieve the mechanical and electrical separation of the circuits (4) themselves; holding said electrical circuits (4) in said cavities (7) at regions (42) thereof other than said junction regions (14); withdrawn respective dies (11) and punches (13) for executing the step of cutting said junction regions (14) from said cavities (7) into respective seats (16, 18) in the mold (6); and injecting a fluid plastics material (33) into said mold (6) to mold the plastics member (3) and embed said insert (2) therein; characterized in that: said holding step is carried out both before and during said injection step, at respective restraining regions (42) of each of said electrical circuits (4) designed to be embedded too in said plastic member (3); said withdrawing step is carried out with said mold closed, keeping said dies (11) and punches (13) into said seats (16, 18) so as to delimit with said dies and punches (11, 13), and together with said seats (16, 18), respective portions of said cavities (7) in which said plastics member will be formed with respective solid portions which will completely encapsulate the metal parts (15) at the junction regions (14) and maintain them electrically separated; and said restraining regions (42) are held by means of pressure elements (41) movable against the action of biasing means (43) inside respective recesses (48) in the mold (6) facing said cavities (7), each pressure element (41) having an active surface (46) with an area substantially larger than that of a corresponding contact surface (47) of the restraining regions (42), said active surfaces projecting beyond the restraining regions (42) into said cavities (7) to receive, during the injection step and after the filling of said cavities (7) with said fluid plastics material (33), a hydrostatic thrust able to overcome the action of said biasing means (43). A process as claimed in Claim 1, characterized in that it comprises a first step during which said insert (2) is arranged between said two half-molds (5) and then, with the mold (6) closed, said insert (2) is clamped in a predetermined position (8) due to the cooperation of blank holder means (12) and die means (11); a second step in which said insert (2) is cut by means of said punch (13) with the consequent production of two cut metal parts (15); a third step in which the punch (13), the blank holder means (12) and the die means (11) are withdrawn while the insert (2) is restrained in said predetermined position (8) by the action of pressure means (41) on said respective restraining regions (42), the pressure means being acted upon by respective biasing means (43); and an injection step in which the fluid plastics material (33) is injected and fills said cavities (7) of the mold (6) and completely encapsulates the insert (2) within it; the static pressure of said fluid (33), after said cavities (7) have been filled, causing the pressure means (41) to return into respective recesses (48) to allow the complete filling of said cavities (7) with said fluid plastics material (33); after the completion of the injection step and the cooling of the plastics material (33), the co-molded member (3) being removed by respective removal means. Equipment (1) for the co-molding of a insert (2) forming a plurality of electrical circuits (4) in a synthetic plastics member (3), of the kind comprising a pair of half-molds (5) provided with respective cavities (7) for molding said member (3) from a plastics material, die means (11) and blank holder means (12) for clamping the insert (2) in said cavities (7) at respective junction regions (14) thereof between the electrical circuits (4), and punch means (13) for cutting said junction regions (14) to obtain cut metal parts (15) unconnected to each other due to the mechanical and electrical separation of said circuits (4); characterized in that (i)- said punch means (13), said die means (11) and said blank holder means (12) are mounted for axial sliding movement with substantially fluid-tight seals within respective through-seats (16,18) formed in said half-molds (5) and opening into said cavities (7); (ii)- said punch means (13), die means (11) and blank holder means (12) are so shaped and arranged that, when they are in a retracted position within said seats (16,18), they are able to define, together with said seat themselves, respective portions of said cavities (7) designed to form respective solid portions of said plastic member (3) which will completely encapsulate said cut metal parts (15) at the junction regions (14) and maintain them electrically separated; and (iii) said equipment (1) further includes: means (21, 22) for effecting the controlled displacement of said punch means (13), said die means (11) and said blank holder means (12); and restraining means (41) for holding the insert (2) at restraining regions (42) of each of said electrical circuits (4) designed to be embedded too in said plastic member (3) and other than said junction regions (14); said restraining means consisting of pressure elements (41) movable against the action of biasing means (43) inside respective recesses (48) in the mold (6) facing said cavities (7), each pressure element (41) having an active surface (41) with an area substantially larger than that of a corresponding contact surface (47) of the restraining regions (42), said active surfaces projecting beyond the restraining regions (42) into said cavities (7) to receive, during the injection step and alter the filling of said cavities (7) with said fluid plastics material (33), a hydrostatic thrust able to overcome the action of said biasing means (43). Equipment as claimed in Claim 3, characterized in that said restraining means (41) are constituted by plungers (41) provided with resilient biasing means (43) calibrated to transmit a predetermined force and having respective tips (44) for coupling with centering holes (45). Equipment as claimed in Claim 3 or Claim 4, characterized in that said die means (11) include a preloaded spring (23) and cooperate with a first carriage (21) movable perpendicular to the direction of movement of said die means (11); said die means (11) having a first end (24) opposite a second end (25) facing said insert (2), said first end having a rounded shape and cooperating with a respective inclined plane (26) formed on said first carriage (21); said punch means (13) and blank holder means (12) being supported by a respective support frame (31) of the respective half-mold (5a) and being slidably assembled the first within the second and connected by cam means (32) to a second carriage (22) movable perpendicular to the direction of movement of said punch means (13) and blank holder means (12). Equipment (1) as claimed in Claim 5, characterized in that said blank holder means (12) comprise an outer sleeve (34) housing a rod (35) defining said punch means (13) for sliding therein, a carrier sleeve (36) connected to said cam means (32) and respective spring means (37) for said blank holder means (12) arranged between said outer sleeve (34) and said carrier sleeve (36).

Inventors: CIBIN SILVANO, CIBIN, SILVANO
Applicants: ITW FASTEX ITALIA SPA, ITW FASTEX ITALIA S.P.A.
Application year: 1993
Main classification: B29C45
IPC codes: H05K3, B29C45