A method of moulding plastic bumpers for motor vehicles and a die for implementing the method

Abstract: A die constituted by a female die (3) and a male die (4) comprising a matrix (5) and a pair of curved blocks (6, 6') is used to form a plastics bumper (1') by injection. The female die has undercut portions (20, 20') in contact with the bumper (1'). In order to open the die, the female die (3) and the blocks (6, 6') are moved away from the matrix (5) of the male die (4) along respective translation axes at substantially the same speed so that the blocks (6, 6') move the bumper (1') away from the female die (3), enabling the undercut portions (20, 20') to be disengaged from the bumper (1').

Description: The present invention relates to a method of moulding plastics bumpers for motor vehicles and to a die for implementing the method. US-A- 4 854 849 is directed to such technology. Figure 1 is an axonometric view of a typical plastics bumper for motor vehicles, indicated 1; Figure 2 is a section of the bumper of Figure 1 taken in the plane II-II indicated in that drawing. Plastics bumpers of the type illustrated in Figures 1 and 2 are produced, according to the prior art, by means of dies of the type shown in partial schematic section in Figure 3. In this drawing, a female matrix is indicated 3 and a male die is generally indicated 4; the male die 4 comprises a male matrix 5 and a pair of curved blocks 6, 6'; between the female matrix 3 and the male die 4, is a cavity 7 with a shape corresponding to that of the bumper 1 to be produced, shown in Figures 1 and 2. Stripping plates, indicated 9, can be translated parallel to their starting positions guided by plate-guide pins perpendicular thereto and not shown, for simplicity. Inclined pins 11, 11' which converge towards the female matrix 3 and are fixed to the stripping plates 9, 9' carry, at their free ends, the curved blocks 6,6' which are fixed firmly to the inclined pins 11, 11'. The curved blocks 6,6' are in contact with the curved end surface of the bumper 1, the undercut portions 14, 14' of which bear partially against the flat portions of the blocks 6, 6'. Adjacent the undercut portions 14, 14' of the bumper, there are stripping members 15, 15', the function of which will be explained below. Reference will now be made to Figures 4 and 5 which show the portion indicated IV in Figure 3, in section and more completely, on an enlarged scale, in two different operative positions, the following applying in exactly the same way to the portion which is symmetrical to that indicated IV in Figure 3; in Figures 4 and 5, the parts corresponding to or the same as those shown in Figure 3 are indicated by the same reference numerals. It is assumed that the bumper 1 (see Figures 1 and 2) has been formed and is to be removed from the die. In order to remove the bumper 1 from the cavity 7, the female matrix 3 is raised (by known means, not shown for simplicity) and the plates 9 are moved upwardly (see Figure 3) parallel to their starting positions, guided by the plate-guides mentioned above; the inclined pin 11 correspondingly moves along its own inclined axis and gradually brings the stripping member 15 into contact with an inclined plane 17 which gradually urges the stripping member 15 in a direction such as to move the bumper away from the curved block 6 until it is slid off the flat portion of the curved block 6 (Figure 5) so that the bumper is released from the die and can thus be removed therefrom. Bumpers manufactured as described above have the disadvantage of having a flash-line in the region of the join between the female matrix and the male matrix (indicated A in Figures 1 to 4), which is visible once the bumper 1 is mounted on the car for which it is intended. This flash-line has an unacceptable appearance, particularly for bumpers which are to be painted, such that, before being painted, bumpers produced by the method just described have to be sanded in the region mentioned above in order to eliminate the flash-line. This involves considerable costs in terms of labour and times for handling the bumpers, with non-homogeneous results amongst the various bumpers after sanding. The object of the present invention is to produce a bumper which avoids the aforementioned problems by having the join line between the male and female matrices in a region of the bumper which is not visible once it is mounted on the car for which it is intended. The present invention achieves this and other advantages by means of a method of moulding bumpers for motor vehicles having the specific characteristics recited in claim 1. The invention also comprises a die for implementing the method mentioned above as defined in claim 2. The invention will now be described purely by way of non-limiting example, with reference to the appended drawings, in which: Figures 1 to 5 (which have already been described) show a plastics bumper produced according to the prior art and the various stages of the moulding of the bumper and its removal from the die, Figure 6 is a perspective view of a plastics bumper produced according to the invention, Figure 7 shows the bumper of Figure 6 sectioned in the plane VII-VII of that drawing, Figure 8 shows a die for producing a bumper according to the invention, in partial schematic section, Figure 9 shows the portion indicated IX in Figure 8 more completely and on an enlarged scale, and Figures 10 to 13 show the various stages of the removal, according to the invention, of the plastics bumper, after moulding, with reference to the portion indicated IX in Figure 8. With reference to Figures 6 and 7, a plastics bumper, similar to that shown in Figures 1 and 2 but with the join line between the female matrix and the male die formed along a line B which is not visible once the bumper is mounted on the car for which it is intended, is indicated 1'. Reference will now be made to Figures 8 to 13, in which parts the same as or corresponding to those already described with reference to Figures 3 to 7 are indicated by the same reference numerals. A die for plastics bumpers according to the invention is shown schematically in partial section in Figure 8, the join line between the female matrix 3 and the male die 4 being indicated B. The join line B, as can better be seen in Figure 9, which shows the part of the die indicated IX in Figure 8 more completely and on an enlarged scale, is in a position such as to prevent the female matrix 3 from being raised directly without damaging the bumper 1', because of the presence of the undercut 20 of the female matrix which would interfere with the undercut portion 14 of the bumper 1' if the female matrix 3 were raised vertically. In order to open the die without damaging the bumper 1', it is necessary to proceed as shown in Figures 10 to 13 which show the portion of the die which is shown with the die in the closed condition in Figure 9, in the various configurations of the opening of the die. Figures 9 to 13 show only the left-hand portion of the die of Figure 8 and, more precisely, as already stated, the portion indicated IX in that drawing, the following applying in exactly the same way to the right-hand portion. It is assumed that the bumper 1' has been moulded and the die is closed as shown in Figure 9 and the bumper is to be removed from the die. With reference to Figures 10 to 13, the female matrix 3 and the block 6 are moved away from the male matrix 5 along respective translation axes, the matrix 3 being moved by known means, not shown, and the block 6 being urged by the inclined pin 11 which is moved by the translation plates 9 of Figure 8 which are not shown in Figures 9 to 13, for simplicity. The female matrix 3 and the block 6 are moved away from the male matrix 5 substantially at the same speed so that the block 6 moves the bumper 1' away from the female matrix 3 and is spaced from the surface of the female matrix 3 in a transverse direction relative to the direction of movement of the matrix, thus enabling the undercut portion 20 of the female matrix 3 to be disengaged from the bumper 1' (Figure 10). At this point, the removal continues as already explained above, the female die 3 being moved away and the block 6 sliding upwards, bringing the stripping member 15 into contact with the inclined plane 17 until the bumper is detached from the male matrix 5 (Figures 11, 12, 13). Naturally, the principle of the invention remaining the same, wide variations may be applied to the embodiment described and illustrated without, however, departing from the scope of the invention as defined in claims 1 and 2.

Claims: A method of producing a bumper (1') for motor vehicles by injection moulding, by means of a die including a male die (4) and a female die (3) which is mounted for translation relative to the male die (4) in a first predetermined direction, a cavity (7) with a shape corresponding to that of the bumper (1') to be moulded being defined between the male die (4) and the female die (3), the male die (4) comprising a stationary matrix (5) and a pair of curved side blocks (6, 6') each of which has a convex surface which corresponds to an end portion of the internal surface of the bumper (1') and which is connected to the recessed seat of the male die (4) to form a corresponding re-entrant edge of the bumper (1'), the blocks (6,6') being translatable relative to the matrix (5) along respective axes inclined at an angle to the first direction and converging towards the female die (3), characterized in that the surface of the cavity of the female die (3) having, at each end, an undercut portion (20, 20') which is connected to the corresponding recessed seat of the male die (4) to form one of the edges of the bumper and a portion of the re-entrant rim adjacent the edge, each end of the female die (3) being connected to the male die (4) along join lines which extend between the edge and the end of the corresponding re-entrant rim, wherein, after the injection-moulding of a bumper (1'), the female die (3) and the blocks (6, 6') are moved away from the matrix (5) of the male die (4) along the respective translation axes, at substantially the same speed, in the said first direction, in a banner such that the blocks (6, 6') move the bumper away from the matrix (5) and are spaced from the surface of the female die (3) in a direction transverse the first direction, enabling the undercut portions (20, 20') of the female die (3) to be disengaged from the bumper (1'). A die for motor-vehicle bumpers for implementing the method according to Claim 1, including a male die (4) and a female die (3) which is mounted for translation relative to the male die (4) in a first predetermined direction, a cavity (7) with a shape corresponding to that of the bumper (1') to be moulded being defined between the male die (4) and the female die (3), the male die (4) comprising a stationary matrix (5) and a pair of curved side blocks (6, 6'), each of which has a convex surface which corresponds to an end portion of the internal surface of the bumper (1') and which is connected to a recessed seat of the male die (4) to form a corresponding re-entrant edge of the bumper, the blocks (6, 6') being translatable relative to the matrix (5) along respective axes inclined at an angle to the first direction and converging towards the female die (3), characterized in that the surface of the cavity of the female die (3) has, at each end, an undercut portion (20, 20') which is connected to the corresponding recessed seat of the male die (4) to form one of the edges of the bumper and a portion of the re-entrant rim adjacent the edge, each end of the female die (3) being connected to the male die (4) along join lines which extend between the edge and the ends of the corresponding re-entrant rim, the arrangement being such that, after the injection-moulding of the bumper (1'), the female die (3) and the blocks (6, 6') are moved away from the matrix (5) of the male die (4) along the respective translation axes at substantially the same speed, in the first direction, in a manner such that the blocks (6, 6') move the bumper away from the matrix (5) and are spaced from the surface of the female die (3) in a direction transverse the first direction, enabling the undercut portions (20, 20') of the female die (3) to be disengaged from the bumper (1').

Inventors: CAVAGNERO GUIDO, CAVAGNERO, GUIDO
Applicants: FIAT AUTO SPA, FIAT AUTO S.P.A.
Application year: 1995
Main classification: B29C45
IPC codes: B29C45