FR2768360A1 - Method of opening mold to clear projecting section - Google Patents

Abstract

In opening the mold (17, 19) to release a projection (23) and extract the entire molding, motions of two mold sections (25, 27) take place in one of the following modes: two motions involve translation and rotation; or double translation takes place on two different axes; or a rotation frees the first section projection (37) from the recess (23) of the other. An Independent claim is included for the corresponding mold. Preferred features: The second section (25) is driven by a translation movement following one axis, causing mold opening, while the first element (27) is driven in two translations: one following the axis of motion of the second section; the other being secant to this axis, the second movement clearing the projection (37) of the first section from the gap of the recess (39) of the second. Further variations are described, based on the foregoing principles.

Description

 The invention relates to a method and a device for manufacturing a part in a mold, as well as to a molded part.

 Among the methods of manufacturing a molded part, it is already known that provide for the use of a mold comprising at least two parts, reserving between them a molding cavity for the part, at least one of these parts comprising at least first and second members which are movable relative to one another, between a molding position and a release (demolding) position, and which each have a molding surface defining a portion of the molding cavity, the first element having a protrusion engaged, in the molding position, in a recess in the second element, set back from the molding surface, the projection then filling only part of the recess, to provide between these elements a protrusion of the mold cavity having a shape having at least one undercut.

Such characteristics are found when, for example, a molded part with a protruding area, such as the clip holder of Figure 1, is to be realized. In this case, according to a known conventional molding method:
a) a molding material, such as a plastic material, is introduced into the mold,
b) the piece is molded into the mold cavity, by moving the material therein, including in the protuberance of the cavity, the parts and elements of the mold then being in the molding position,
c) then, the mold is opened by disengaging the projection of the first element away from the hollow of the second (release position), so as to extract the piece out of the mold, with the form undercut integrated in it.

 Some technicians in the field call mobile wedges the parts used to clear the protrusion of said first element.

 These shims are typically bonded to the mold ejection plate, at least in the pressurized injection molds used to make plastic parts.

However, the principle of such wedges requires a minimum stroke of the ejection (to clear the projection), therefore requires a consistent thickness of the mold, which in some cases generates a significant additional tooling cost
An example of such a part can be found in FR-A-2 726 874.

 Furthermore, in the case of tooling for molding a locally overmolded part (as for example in EP 97 400 879.9), for which a movable element is used, in the overmoulded portion that you can hardly put a mobile hold in this area. In addition, outside the zone defined by said element, the use of a movable wedge demolding a protrusion protruding may cause difficulties for the establishment of the decor sheet to overmold, in particular because of the size of the hold and precautions to take to avoid damaging the decor sheet.

 The object of the invention is to propose a solution that solves, or at least mitigates, at least some of the aforementioned disadvantages, by proposing a reliable, mechanically appropriate solution and an interesting cost price.

A solution proposed for this by the invention provides, in step c) above, to impose on at least one of the two elements of the mold:
two movements comprising a translation and a rotation, or a double translation along two different axes,
- Or a rotation, to clear, in one case as in the other, the projection of the first element away from the hollow of the second.

 On the basis of this general solution, several particular solutions are proposed.

 Firstly, during said step c), the second element can be driven by a translation movement along an axis generating the opening of the mold, while the first element is driven by two translational movements, one substantially following the axis of displacement of the second element, the other secant to this axis, this second movement being able to separate the projection of the first element away from the hollow of the second.

 The advantage of this solution lies particularly in its reliability, its simplicity and the efficiency of the oblique guidance that can be obtained, in particular by a finger inside a slide.

 According to another arrangement, still during the above-mentioned step c), the first and the second elements can first be driven by the same translational movement, along said opening axis of the mold, in order to clear a space of one side of the first element, then, possibly from a predetermined stroke (or at the same time), this same first element can be driven by a rotational movement capable of disengaging its projection away from the hollow of the second element element.

 This solution is particularly suitable when the part to be manufactured is a part locally molded by a decor sheet and the undercut projection is located outside the overmolded area.

 This solution is mechanically efficient and reliable.

 According to another arrangement, rather than performing a rotation after the first translational stroke, it may be provided that the first element is driven by a second translational movement, transversely to the aforementioned axis of opening of the mold, always in order to separate the protrusion out of the hollow of the second element, the two translations being able to operate at the same time.

 The foregoing solutions, however, are not necessarily perfectly suited especially when the undercut protrusion to be demolded is located on an overmolded part of part.

 In this case, especially to promote the establishment of the decor sheet facing the mobile bezel typically used in a local overmolding operation, the second aforementioned element of the mold can be animated, in step c) already presented , of a translation movement, substantially along an axis generating the opening of the mold, while the first element is then advantageously driven by a rotational movement relative to the second element, this rotational movement being suitable for placing the against dewatering away from said protrusion of the first element of the mold, this preferably without this first element being driven by any translation relative to the second, with, furthermore, as a complementary feature that the rotation is first carried out of the first element before the movement of movement of the second element, thus releasing the undercut area of the workpiece, before ejecting it.

 An advantage of this solution is that the second element of the mold can then never protrude in an area that could hinder the establishment of the decor sheet, always remaining camouflaged.

Translated into tooling or mold, the foregoing features may be presented as follows:
the first element may first be slidably mounted along an oblique slide with respect to the opening axis of the mold and may furthermore have an arm transverse to this axis, this arm being slidably mounted in an opening of the second element,
the first element may be interposed between the second element and a guide piece, the first element being mounted sliding substantially along the axis of opening of the mold, relative to a wall of the guide piece in contact with which it comes into contact; molding position and which extends substantially along said opening axis and ends with an oblique slope relative to this axis, to clear a space of at least one side of said first element, in the mold release position, this first element being further pivotally mounted relative to the second element and the two movements of relative sliding and rotation of the first element operating under the control of a double slope slide,
- Or again, the first element of the mold is rotatably mounted in a slide, while being arranged fixed in translation in the corresponding part of said mold,
and, in particular in this case, a part of the first element which has said molding surface defines a door which, according to the position of this first element, allows or prohibits access to the protuberance of the molding cavity at the filling material of the mold.

This last feature is particularly useful for producing a rigid protrusion on a piece with softer outer skin, especially as mentioned in DE-A-37 11 079.

 With regard to the characteristics of the molded part, the main one of them relates to the presence of curved zones on at least part of the inner wall surfaces of this undercut piece, the presence of these zones being related to the intended movement of rotation of said first mold member.

A more detailed description of the invention will now be provided with reference to the accompanying drawings in which:
FIG. 1 is a view of an undercut shape projecting from a piece of molded plastic material, as found in the prior art or as can be obtained with one of the devices shown schematically in FIGS. at 9,
FIG. 2 is a cross-sectional view along line II - II of FIG. 1,
- Figures 3 to 6 show schematically, in cross-sectional local section, different possibilities for unmolding the undercut form of Figures 1 and 2,
FIGS. 7, 8 and 9 show two other devices for producing an undercut shape very close to that of FIGS. 1 and 2 (see FIG. 10),
FIG. 10 thus shows, in section, the appearance of the part of FIG. 2 when the device of FIGS. 7, 8 or that of FIG. 9 has been used, in order to produce the undercut shape,
FIG. 11 shows, according to the same view as FIG. 9, the same undercut shape with the demolding device of FIG. 9 still in the advanced position,
FIG. 12 shows the possible use as "gate" of the protrusion of the first element (section along XII - XII of FIG. 13), and
- Figure 13 is a sectional view along the line XIII - XIII of Figure 12.

 FIG. 1 or 2 firstly shows a partial view of a piece 1 made of plastic (one or more plastics, such as polypropylene) having on its lower surface 3 a projecting shape 5, such as that in this case a clip holder.

The part 5 has, along an axis 5a perpendicular to the surface 3, a through opening 7 opening towards the inside of the part 5, on a peripheral shoulder 9, defining a flange. For the engagement of a staple (known and not shown), the part 5 is open laterally, on one side, so as to have an internal cavity 11, so that in section as in FIG. protruding protrusion 5 has a form with undercut, such that in this case a substantially
Laterally, access to the axial orifice 7 is restricted by a neck 13.

 Such a piece can in particular be obtained by a tool of which a partial cross-sectional view appears in FIGS. 3 to 6.

 In FIG. 3, first of all, the tooling marked as a whole 15 and which is seen in an enlarged view in FIG. 4, for its detail marked W in FIG. 3, shows a mold comprising two parts, respectively a die 17 and a punch 19. These two parts 17, 19 define between them a molding cavity 21, adapted to manufacture the part 1, with, at 23, a protruding protrusion communicating with the cavity and of suitable shape to ensure the molding of the protrusion 5 shown in FIGS. 1 and 2.

 In Figure 3, the mark 15a designates the axis in which the relative displacement movement between the die and the punch is made, for the opening and closing of the mold.

 The punch 19 essentially comprises a telescope 25, movable along the axis 15a, surrounded, at least at the place where the protrusion of the part to be produced (sub-cavity 23) is to be formed, by a wedge 27, also movable .

 The wedge 27 externally has an oblique wall 29, able to slide opposite a complementary oblique wall 31 of an outer part 33, which can be fixed in position relative to the frame 35 of the mold 15, which can be a mold of injection under pressure of at least one plastic material.

 It will be noted that in the molding position, as in FIGS. 3 and 4, the bezel 25, the movable wedge 27 and the external guide piece 33 have, in FIG. 3 in particular, an upper surface which delimits locally the contour of the cavity 21 (respectively 25a, 27a and 33a).

 More particularly in FIG. 4, it may be noted that at the location of the molding cavity 23, the spacer 27 has a lug or projection 37 engaging in a recess or recess 39 formed in an upper corner of the bezel 25, in the molding position.

 Note that to achieve the shape of Figures 1 and 2, this bezel 25 has full volumes corresponding to the areas marked 7, 11 and 13 in Figures 1 and 2.

 It will also be noted that in FIG. 4, a cover sheet, or decor, 41, such as a sheet of fabric, pressed against the molding surface of the die 17 and marked in turn, is placed inside the mold. phantom in Figure 2, after this sheet has been overmolded by the plastic.

 To guide the movement of the wedge 27 during demolding of the part, this same piece 27 has a tenon 43, directed perpendicular to the axis 15a and slidably mounted inside a slide 45 formed laterally in the telescope 25.

 Another internal slide 47 has been formed inside the spacer 27, in a direction 49a oblique with respect to the direction 15a.

 A finger 51, fixedly mounted on the frame 35, passes through the corner piece 33 to penetrate tightly inside the slideway 37, providing its oblique guide in translation relative to the axis 15a, during the opening of the mold.

 Thus, if one starts from a closed mold, as in FIG. 3, the molding of the part partially seen in FIGS. 1 and 2 is carried out by injecting plastic into cavities 21 and 23. It is then allowed to cool. then we open the mold. This opening along the general axis 15a will generate, under the effect of the displacement of the telescope 25 along the same axis, an oblique displacement of the wedge 27 along the direction 49a, under the effect of the guide of the finger 51, the tenon 43 gradually emerging from the slide 45, in the direction of the arrow 53. This will of course gradually cause the displacement of the protrusion 37, in the direction of the same arrow 53, until this outgrowth allows to release freely outside the mold cavity, the undercut form occupying the cavity 23.

 Then, the parts 25 and 27 are moved in reverse translation until they return to their position in FIG.

 In FIG. 5, there are the same parts and shapes as in FIG. 3, with the exception of finger 51 and slide 47.

 In this case, the wedge piece 33 oblique ramp 31 is movable in translation parallel to the axis 15a, under the effect of an axial control rod 55 which, after a predetermined stroke, is blocked, while the bezel 25 and the movable wedge 27 continue their axial translation (for example, under the effect of one or more control rods of the telescope 25), until the inclined face 29 of the wedge 27 has sufficiently slid along the ramp 31 (vis-à-vis which it is held by a rail) so that it is operated the lateral clearance of the protrusion 37 necessary for demolding the cavity 23 corresponding to the form against undercut 5 The tenon 43 always operates.

 Thus, in this case, the lateral movement of the shim 27 is delayed with respect to the solution of FIG.

 The solution of FIG. 6 is also similar to the solution of FIG. 3, with the exception of finger 51 and its associated slideway.

 In this case, during the axial translation of the telescope 25, bringing with it the wedge 27, in the direction of the axis 15a and the arrow 57, the same wedge 27 will gradually move away from the telescope, in the direction and the radial direction shown schematically by the arrow 53, under the effect of the spring or piston 59, thus plating the pan 29 of the wedge 27 against the ramp 31 of the corner piece 33, until sufficiently clear the outgrowth molding 37, as previously.

 Let us now look at FIGS. 7 to 9 to see illustrated a rotational demolding principle, in order to achieve the undercut shape 5 'of FIG. 10.

 This shape 5 'is identical to that shown in FIG. 2, except for the curved, substantially rounded shape that the rim 9' presents, this curvature which is refined to the free lateral end of the edge 13 '. being function, in particular for its slope, of the shape, the position and the angle of rotation of the demolding wedge 27 used.

 It is the same for the at least locally rounded surface 9 "facing, where we can note the presence of an end nozzle 10, in front of the edge 13 'of the neck.

 These roundings are, as understood, quite characteristic of the use of a pivoting part, to unmold this form having an undercut.

 In FIG. 7, the movable wedge 67, pivotally mounted about an axis 69, substantially aligned with the location where the shape 5 '(in a direction parallel to the demolding axis 15a) is to be formed, has a protrusion 71 cooperating with the shape 73 of the bezel 75, to achieve the desired protrusion 5 'which corresponds to the cavity 23'.

 As can be seen more clearly in FIG. 8, which shows the part 67 in the retracted or tilted position (allowing the form 5 'to be demolded), the protrusion 71 comprises rounded offsets, on both sides, towards its end. base, marked 77a and 77b in Figure 8, to achieve the shapes 9 'and 9 "(see Figure 10).

 In the molding position, the parts 67 and 75 are in their nested position of FIG. 7. The external oblique slope 79 of the pivoting wedge 67 is blocked by the adjacent oblique pan 81 of the outer corner wedge 83 fixed to the frame of FIG. punch 35 of the press. At the time of demolding, when the bezel 75 is moved along the axis 15a by the jacks of the press, it causes in its translational movement the pivoting wedge 67. When the race, along the axis 15a, has provided angular deflection sufficient to the shim 67, the effect of the pusher 85 causes a greater tilting of the piece 67, along the arrow 87, with an angle sufficient to clear the protrusion 71, the hollow 11 ', the shape 5', as it can be seen in Figure 8. The combined movement of translation and rotation of the wedge 67 is guided, preferably, by a slide 89 sliding in a slide 91 whose double slope shape ensures in this case a gradual tilting of the piece 67, as and when the opening movement of the mold.

 In FIG. 9, the previous shim 67 has been replaced by an exclusively pivoting shim 97, operable in rotation about a fixed axis 99 aligned, as in the previous figure, with the shape 5 'to be produced. The shim 97 is controlled by a rod linkage 101 and tie rod 103, the ball 101 being connected to a jack 105 mounted to move in translation on a frame 107, in a direction perpendicular to the opening / closing direction 15a of the mold.

 The wedge 97 is in the form of a substantially circular C-shaped piece terminated by a protrusion 110 shaped so that the recess 11 'of FIG. 10 is obtained.

 Note that the "deformation" 10 'is a possibility, it can generate a necking to avoid shrinkage.The curved area "recessed" 9' is needed.The zone 9a in the continuity (left of the axis) can be flat The 9 "curved area should exist, at least to the left of the axis; but is not essential to the right of this axis 15b. Zone 10 (outgrowth) is necessary.

 In FIG. 11, the curved surfaces 110a, 110b, junction between the portion 110 and the body 120 of the shim 97 which will allow demolding in particular zones 13 'and 10 of the form 5', without forgetting the 'rounded upper end, at the place of the rounded 10' where the protrusion 5 'is connected to the piece 1 (Figure 10).

 Note that the pivoting shim 97 is mounted inside a sealed slide 111, whose sectional shape corresponds closely to it, and whose length is adapted to enable it to reach the required molding and clearance positions. Around this slide, extends the bezel 115 whose translational movement in the demolding direction 15a will allow the release of the part 1, after rotation of the shim 97 to its release position of Figure 9. Peripherally, the axially movable bezel 115 is surrounded by a fixed peripheral piece 117, carried by the punch frame and from which, the bezel comes out, after retraction of the shim 97, to facilitate demolding of the piece 1.

 In Figure 12, there is shown a version in which the movable shim 117 provides as a complementary function the complete closure of the inlet zone 23a of the cavity 23 at the beginning of the molding operation.

 More specifically, in this variant embodiment, the protrusion 130 of the shim 117, which penetrates inside the crenelike corner clearance 121 of the bezel 125, is rotatably mounted, as in FIGS. , along the arrow 123, to occupy, during molding, successively three positions (A, B, C).

 In the first position A, the shim 117 is advanced, at the location of a frontal end bead 131, as far as the front wall 127 facing the telescope and then closes the inlet 23a of the cavity 23.

 While the piece 117 is in this advanced position, two plastics may be injected under pressure into the cavity 21, both of which comprise a relatively soft skin material in its cold state and a core material, more viscous and harder than the first material, also in its cold state.

 The skin material is injected first and in particular covers the area opposite the access 23a then closed.

 The core material is injected shortly thereafter, so that it penetrates the interior of the skin material.

 The shim 117 is then moved back to its position B, so that the core material pierces the skin material facing 23a and enters the cavity 23 until it completely fills.

 Once the cooling time has passed, the shim 117 is then again moved back to a "demolding" position (C) already presented, so that its protrusion 130 releases the central cavity 11 from the part of FIGS. 2 which was then formed.

 Thus, in this variant embodiment of which a schematic illustration is provided in FIGS. 12 and 13, the mobile wedge 117 acts as a selective closing gate for access to the cavity 23 reserved for molding the shaped protrusion. against clearance.

In Figure 13, the shim 117 is in the intermediate position "molding" (B). This view shows that the following rule must be respected for proper operation:

<tb> (Y <SEP> = <SEP> X <SEP> sina
<tb> I <SEP> X1 <SEP> = <SEP> X2
<Tb>
This makes it possible to reach the seal: X1 = X2 = 0.

 When the shim 117 is in the advanced position (A), it will be noted that X1 is the distance between the wall 127 and the bead 131, along the axis 15c (perpendicular to 15a); X2 is the always following distance 15c, but between the side wall 127a (which extends 127) and that 130 which forms one of the sides of the shim 117 (at the location of the outgrowth 130); a is the angle formed by the wall 130a (or 130b, on the other side of 130) with the axis 15c; Y is the distance between 130a and 127a (or 130b and 127b) along an axis perpendicular to 15c and 15a (Figure 12).

 It should also be noted that the side walls 127a, 130a; 127b, 130b could be curved, in correspondence.

Claims (11)

 A method of manufacturing a workpiece in a mold comprising at least two parts (17, 19), reserving between them a cavity (21) for molding the workpiece, at least one (19) of said parts comprising a first and a second movable member (25, 27; 75, 67; 115, 97; 125, 117) between a molding position and a release position, each having a molding surface defining a portion of the molding cavity, the first element (27, 67, 97, 117) having a projection (37, 71, 110, 130) engaged, in the molding position, in a recess (39) formed in the second element (25, 75, 115, 125) recessed with respect to the molding surface, the projection then filling only a part of the hollow, to provide between these elements an outgrowth (23, 23 ') of the molding cavity, having a shape having at least one undercut, in which process:  a) a molding material, such as a plastic material, is introduced into the mold,  b) the workpiece (1, 5, 5 ') is molded into the mold cavity (21, 23, 23') by moving the material therein, including in the protrusion (23, 23 ') of the cavity, the mold parts and elements then being in the molding position,  - c) then, the mold is opened by releasing the projection (37, 71, 110, 130) of the first element away from the hollow of the second, so as to extract the piece out of the mold, with the form against body integrated therein, characterized in that, during step c), at least one of the two elements of the mold is imposed:  two movements comprising a translation and a rotation, or a double translation along two different axes (15a, 49a),  - Or a rotation, to clear, in one case as in the other, the projection of the first element away from the hollow of the second.  2. Method according to claim 1, characterized in that, in step c), the second element (25) is driven in a translation movement along an axis (15a) generating the opening of the mold, while the first element (27) is driven by two translational movements, one following substantially the axis of displacement of the second element, the other (49a) secant to this axis, this second movement being able to separate the projection (37 ) of the first element away from the hollow (39) of the second.  3. Method according to claim 1, characterized in that, in step c), the second element (75) is driven in a translation movement along an axis (15a) generating the opening of the mold and then drives along said axis, the first element (67) fixed thereto, which is furthermore rotated relative to the second element, capable of disengaging its projection (71) away from the hollow of the second element (75) .  4. Method according to claim 1, characterized in that, in step c), the first and the second elements (25, 27) are driven by the same translational movement along an axis (15a) generating the opening of the mold and the first element (27) is further animated by another translational movement (along 53), transversely to said opening axis, to disengage its projection (37) away from the hollow of the second element ( 25).  5. Method according to claim 1, characterized in that:  during step c), the second element (115) is driven by a translation movement substantially along an axis (15a) generating the opening of the mold, while the first element (97) is driven by a rotational movement relative to the second member, adapted to disengage its projection (110) away from the hollow of said second member, without translation of the first member relative to the second,  and, during this step c), the first element (97) is first rotated, before the axial translation of the second element (115).  A mold comprising at least two parts for reserving between them a mold cavity (21) for a workpiece, at least one (19) of said parts comprising a first and a second element (25, 27, 75, 67; 97; 125, 117) movable relative to each other between a molding position and a release position, and each having a molding surface defining a portion of the molding cavity, the first element (27, 67, 97, 117) having a protrusion (37, 71, 110, 130) engaged, in the molding position, in a recess (39) in the second element (25, 75, 115, 125), set back from at the molding surface, the projection then filling only part of the hollow, to provide between these elements an outgrowth (23, 23 ') of the molding cavity, having a shape having at least one undercut, the protrusion of the first element being disengaged from said hollow of the second, in release position, by movement between the two LEMENTS, so as to allow then to extract the shaped body against, characterized in that, to disengage the projection from said recess before extraction of the molded part, at least one of the two elements is movable:  or following two movements comprising a translation and a rotation, or a double translation along two different axes,  - or according to a rotation.  7. Mold according to claim 6, characterized in that the second element is slidably mounted along a translation axis (15a) generating an opening of the mold,  - And the first element (27) is slidably mounted relative to the second element (25), along a transverse axis vis-à-vis said mold opening axis (15a), said first element (27) being for this slidably mounted along a slide (31, 33) oblique with respect to said opening axis (15a) of the mold, this first element further having an arm (43) trans- sional to this axis and which is slidably mounted in an aperture (45) of the second element (25).  Mold according to claim 6, characterized in that:  the second element (75) is slidably mounted along a translational axis (15a) generating an opening of the mold,  the first element (67) is connected in translation with the second element (75) and is interposed between this second element and a guide piece (83) having a wall (81) oblique with respect to the said opening direction of the mold (15a)  said first element (67) is further pivotally mounted relative to the second element (75), to disengage its projection (71) away from the corresponding recess of said second element,  and the two movements of translation and rotation of the first element take place under the control of a slider (91) with a double slope.  Mold according to claim 6, characterized in that:  the first element (97) is rotatably mounted in a sealing slide (111),  - And this first element is further mounted fixed in translation in the corresponding part of the mold (19).  Mold according to any one of claims 6 to 9, characterized in that a portion (131) of the projection (130) of said first element (117) defines a door which, depending on the position of said first element relative to the second (125) allows or denies access to the protuberance (23 ') of the mold cavity (21) to the mold filler.  11. Part obtained by the implementation of the method according to any one of claims 1 to 5, wherein using the mold according to any one of claims 6 to 10, with a rotational movement of the first element (67, 110 ), characterized in that the protrusion (5 '), corresponding to that (23') of the molding cavity, has curved areas (9 ', 10, 10') on a part of its inner wall surfaces. undercut, in connection with the rotational movement of said first member (67,97).