FR3076244A1 - PROCESS FOR THE PRODUCTION OF A PLASTIC MOLDED PART WITH SCREW BOSSING - Google Patents

Abstract

A method for manufacturing a plastic molded part comprises the following steps: a) preparing an injection molding mold, which comprises at least a first molding tool and a second molding tool which, together define a cavity for the molded part, wherein the second mold tool has a recess, in which a piston is disposed, wherein the piston is movable between a first position and a second position, wherein the piston and the recess define a partial cavity, when the piston is in the second position, for the formation of a screw boss, and in which the piston closes, in the first position, the partial cavity for the formation of a screw boss; b) the displacement of the piston in the first position; c) filling the cavity with a plastic material; and d) after the cavity has been filled, the displacement of the piston in the second position, so that the plastic material under pressure in the cavity can flow into the partial cavity, to form the screw boss.

Description

The invention relates to a method for manufacturing a plastic molded part with a screw boss, as well as a plastic molded part produced in this way.

In order to create a direct connection between a plastic molded part and a component to be fixed to the latter, a screw boss is frequently provided at the level of the plastic molded part, which makes it possible to fix the component to the molded plastic part. plastic material by means of a screw. A corresponding example is known from document US 2013/330149.

In the context of the manufacture of a screw boss, the method generally consists of designing the injection molding mold, by means of which the molded part is produced, with a corresponding cavity which forms the screw boss, as well as projecting a bolt-shaped molding member, which extends through the entire cavity, in order to produce, during the injection molding process, a corresponding recess in the form of a blind hole. In this way, the screw boss can be designed integrally with the molded part in a way that is both simple and inexpensive.

There is, however, a drawback in this case, since the plastic material injected there into the injection molding mold must be able to flow with high speed and high pressure around the forming element, so that that a weld line forms on the face of the molding element located opposite the inlet channel into the mold, which weld line remains clearly visible to the naked eye, that even a painting process, for example, can only conceal insufficiently, so that the optical appearance and / or mechanical properties, including resistance in particular, may be degraded.

Air inclusions can also occur, when the injected plastic is not able to completely expel the air that is inside when it flows into the cavity for the screw boss. This problem can be partially solved by providing additional ventilation for the cavity of the screw boss and / or by providing a modified geometry of this same cavity, so that the air present in the cavity of the screw boss can suddenly sure, be completely expelled or repressed and so that the plastic can, for sure, completely fill said cavity; this method however induces a significant corresponding additional cost with a view to corresponding injection molding and / or restricts design freedom in an undesired manner when designing a molded part.

An objective of the present invention therefore consists in specifying an improved process, intended for the manufacture of a plastic molded part with at least one screw boss, which plastic molded part overcomes the above-mentioned drawbacks.

Another objective of the invention consists in specifying a method intended for the manufacture of a plastic molded part with at least one screw boss, which plastic molded part avoids the appearance of air inclusions and / or the formation of weld lines.

ABSTRACT

The above-mentioned objectives as well as others are achieved by means of a process intended for the manufacture of a plastic molded part, comprising the following steps:

a) the preparation of an injection molding mold, which comprises at least a first molding tool and a second molding tool which together define a cavity for the molded part;

in which the second molding tool has a recess, in which a piston is arranged, in which the piston can be moved between a first position and a second position, in which the piston and the recess define a partial cavity, when the piston is is in the second position, for the formation of a screw boss, and in which the piston closes in the first position the partial cavity for the formation of a screw boss;

b) moving the piston to the first position;

c) filling the cavity with a plastic material;

d) after the cavity has been filled, moving the piston into the second position, so that the plastic material under pressure in the cavity can flow into the partial cavity, in order to form the screw boss;

e) the application of pressure maintenance; and

f) opening the injection molding mold and extracting the molded part.

The aforementioned objectives as well as others are also achieved by means of a plastic molded part produced according to the method according to the invention. Preferred embodiments are shown in the dependent claims.

One of the solutions is a method for manufacturing a plastic molded part which comprises the following steps: a) the preparation of an injection molding mold which comprises at least a first molding tool and a second molding tool, which together define a cavity for the molded part, in which the second molding tool has a recess, in which a piston is arranged, in which the piston can be moved between a first position and a second position, in which the piston and the recess define a partial cavity intended for the formation of a screw boss, when the piston is in the second position, and in which the piston closes the partial cavity for the purpose of forming a boss screw, when the piston is in the first position, b) moving the piston into the first position, c) filling the cavity with the a plastic material, d) after the cavity has been filled, the displacement of the piston in the second position, so that the plastic material under pressure in the cavity can flow in the partial cavity, in order to form the boss screw, e) applying pressure maintenance, and f) opening the injection molding mold and extracting the molded part.

It is therefore proposed that the partial cavity intended for the formation of the screw boss is first closed, at the start of the injection process. Thus, the plastic material first flows only through the cavity, which forms the main body of the molded part, and expels the air contained in the cavity. It is only when the cavity is filled and there is no more air in it that the partial cavity intended for the formation of the screw boss is opened. The plastic under pressure in the cavity, and still in a viscous state, can thus flow into the partial cavity which is now open and fill it completely without the risk of air inclusions.

In a preferred configuration, a spring element disposed in the second molding tool can also be provided, which subjects the piston to an initial stress in the first position, in particular so that the spring element allows movement of the piston from the first position to the second position, when the pressure of the plastic in the cavity exceeds a predetermined pressure value, preferably a pressure value greater than or equal to 70 bar.

In this way, it is possible to create a particularly constructive simple mechanism, intended for moving the piston from the first position to the second position and vice versa. For this purpose, it should be noted that it is particularly advantageous to obtain a rapid increase in the pressure in the cavity after the cavity has been filled with the plastic. In the case of a corresponding design of the return constants, the strongly increasing pressure in the cavity means that the piston is compressed in the second position and that the partial cavity is open.

As a variant or in addition, it is also possible to provide an actuator, which is arranged in the second molding tool and is used to move the piston and / or to subject it to an initial stress. In particular, hydraulic cylinders, pneumatic cylinders, electromagnetic actuators or actuators controlled by an electric motor may prove to be suitable actuators. These actuators can for example be operated in a mode of control and / or pressure or force regulation in order to somehow exert a predetermined force on the piston, in order to subject the piston to a stress initial in the first position and to compensate, in whole or in part, for the pressure prevailing in the cavity during filling or in the filled state. These actuators can, as a variant, serve as positioning elements, which directly determine the position of the piston by a corresponding actuation.

More preferably, a rod is disposed in the first molding tool, which can be moved outside and into the interior of the partial cavity and / or the cavity; wherein the rod has a cross section which corresponds to the cross section of a clearance hole or a blind hole to be formed in the screw boss; in which the method further comprises: - before step c): b1): displacement of the rod outside the cavity; and- after step c): c1): the displacement of the rod up to the interior of the cavity, in order to form the clearance hole or the blind hole.

It is therefore expected that the blind hole or the clearance hole is designed with a movable element, in which the movable element is not placed in the cavity until after the filling step. During the filling step, there is therefore no obstacle in the cavity which is likely to disturb the flow of the plastic material, which therefore prevents the formation of a weld line.

Preferably the rod is again moved outside the cavity only after step e) and before step f).

Suitably, the rod can be designed as a piston rod of a hydraulic cylinder, or the rod is actuated via an electromagnetic actuator or an actuator controlled by an electric motor. Likewise, provision can also be made for designing a rod in the form of a punching machine or a punching machine.

In the method, it may further preferably be provided that the rod in the cavity is moved to the interior of the cavity in step c1), until the rod is pressed against the piston and comes compress the piston to the second position.

The movement of the piston can thus be actively assisted by means of the rod actuated by the actuator, which makes it possible to track the movement of the piston in a defined manner by means of a control program.

After step c1), the rod can be partially released to a position, in order to form the blind hole.

The piston may furthermore be designed, preferably, in the form of a hollow cylinder, which comprises a hollow zone in which a fixed rod or a movable rod is further provided in the second molding tool. The rod or rod extends into the hollow zone of the piston and has a cross section which corresponds to the cross section of a clearance hole or a blind hole which must be formed in the screw boss. For the movable rod, the method can further comprise: - before step c): b2): displacement of the rod outside the partial cavity; and - after step c): c2): displacement of the rod up to the interior of the partial cavity and, if necessary, up to the interior of the cavity, in order to form the clearance hole or the blind hole.

The rod can be designed in the form of a piston rod of a hydraulic cylinder or can be actuated by means of or by an actuator controlled by electric motor or electromag netic.

Another solution may consist of a molded plastic part, which is manufactured according to the method described in this specification.

BRIEF DESCRIPTION OF THE FIGURES

The invention is described below using embodiments produced by way of example in relation to the drawings:

Fig. 1 schematically shows an injection molding mold comprising a first molding tool and a second molding tool, according to a preferred embodiment;

Figs. 2A to 2E are used to explain the steps of a process intended for the production of a plastic molded part with a screw boss, using the injection molding mold of FIG. 1, according to a preferred embodiment;

Figs. 3A to 3C are used to explain the steps of a process intended for the manufacture of a plastic molded part with a screw boss, using the injection molding mold of FIG. 1, according to another preferred embodiment;

Fig. 4 schematically shows an injection molding mold comprising a first molding tool and a second molding tool, according to another preferred embodiment;

Figs. 5A to 5D are used to explain the steps of a process for manufacturing a plastic molded part with a screw boss, using the injection molding mold of FIG. 4, once again according to another preferred embodiment;

Fig. 6 schematically shows an alternative design of a second molding tool;

Fig. 7 schematically shows another alternative design of a second molding tool; and Fig. 8 schematically shows an alternative design of a first molding tool.

DETAILED DESCRIPTION

Fig. 1 schematically shows an injection molding mold according to a preferred embodiment. As shown in FIG. 1, the injection molding mold comprises a first molding tool 10 and a second molding tool 20. The second molding tool 20 is for example formed by a core, while the first molding tool 10 is for example formed by a molding plate. The first molding tool 10 and the second molding tool 20 together define a cavity 30 which has the shape of the molded part 50 to be manufactured (see Fig. 2E). The first molding tool 10 in this example defines a front face or a visible face of the molded part 50 and the second molding tool 20 defines a rear face of the molded part 50.

As further indicated, a recess 24 is formed in the second molding tool 20, in which recess 24 is provided a piston 22. The piston 22 is guided movably in the recess 24, as shown by the double arrow , so that the piston 22 can be moved between a first position, in which the piston 22 closes the region of the recess 24 relative to the cavity 30, and a second position, in which the piston 22 is positioned inside of the recess 24 and in which the piston 22 defines, in common with the cleared section of the recess 24, a partial cavity 32, with a view to the formation of the screw boss 52 (see FIG. 2E). The recess 24 may also have an abutment surface 26 which can ensure a defined position of the piston 22 in the second position.

As indicated, a spring element 28, such as for example a spiral spring, can be arranged on the rear face of the piston 22, which spring is pressed against the piston 22 and subjects the piston 22 to an initial stress. in the first position.

A rod 14 can be placed in the first molding tool 10, as further indicated in FIG. 1, which rod 14 is for example formed by a piston rod of a hydraulic cylinder 12. The rod 14 can be moved outside the cavity 30 and up to the inside of the cavity 30, depending on the order of the hydraulic cylinder 12, as shown by the double arrow. The rod 14 has a cross section which corresponds to the cross section of a clearance hole 54 (see Fig. 2E) or a blind hole 56 (see Fig. 3C) which must be formed in the screw boss 50.

An embodiment of a method for manufacturing a molded part 50 with a screw boss 52 which uses the injection molding mold of FIG. 1, is now described with reference to Figs. 2A to 2E.

As shown in FIG. 2A, the injection molding mold is first prepared, in which the piston 22 is in the first position, so that the cavity 32 is closed. Likewise, the rod 14 is moved outside the cavity 30. The plastic material 40 is then injected in this state into the cavity 30, until the cavity 30 is filled.

After filling the cavity 30 with the plastic 40, the rod 14 is compressed to the inside of the cavity 30 due to the discharge of the plastic 40, for example by actuation of the hydraulic cylinder 12, until 'that the rod 14 abuts against the piston 22 which is always in the first position. The rod 14 is further moved to the interior of the partial cavity 32, in which it slides the piston 22 in front of it <see FIG. 2B) and thus displaces the piston 22 in the second position, in which the partial cavity 32 is entirely released. Since the plastic material 40 which is in the cavity 30 is always present in the viscous state as well as under pressure, the plastic material 40 can flow into the partial cavity 32 in the process of opening and completely filling it , as shown in Fig. 2C.

For this purpose, it is presumed that the spring element 28 subjects the piston 22 to an initial stress, with such a force that the piston 22 does not move only under the pressure of the plastic material 40, but does not move, from the first position in the second position, only as a result of the additional force exerted by the rod 14. This is however not restrictive and it can also be provided that the spring element 28 subjects the piston 22 at an initial stress with less force, in particular so that the piston 22 moves, from the first position to the second position, only under the effect of the pressure of the plastic material 40. In this case, the rod 14 only "follows" the movement of the piston 22, without actively sliding it in front of it. Likewise, mixed forms of these two variants are also possible, in which the pressure of the plastic material 40 is sufficient to compress the piston 22 in part, but remains however insufficient to completely move the piston 22 to the second position. In this case, the force exerted by the rod 14 causes the piston 22 to be fully displaced up to the abutment surface 26 and, therefore, in the second position.

After the partial cavity 32 has thus been completely filled with the plastic material 40, the step of maintaining pressure can take place in order to compensate for the thermal reduction and, if necessary, also to compensate for a reduction in volume due to the Crystallization of the plastic 40. It turns out here to be particularly advantageous for the piston 22 to continue to compress, by means of a force defined under the action of the spring element 28 on the screw boss 52, of so that the piston 22 can take care of a particularly suitable pressure maintenance on the screw boss 52, in order to compensate in a particularly adequate manner for the thermal reduction and / or the reduction in volume in this zone, which zone can be distinguish, in general, from the thermal reduction and / or the reduction in volume of the molded part 50.

Then, the rod 14 is again moved outside the cavity 30, as shown in FIG. 2D, and the injection molding mold can be opened and the molded part 50 extracted, as shown in FIG. 2E.

In this way, it is possible to manufacture a molded part 50 which has a screw boss 52 with a clearance hole 54.

In order to manufacture a molded part 50 with a screw boss 52, which molded part 50 has a blind hole 56 which opens towards the visible face, it is possible to deviate slightly from the process described with reference to Figs. 2A to 2E, as well as this slightly divergent process is described with reference to Figs. 3A to 3C.

To this end, the same steps are first performed again as described with reference to Figs. 2A to 2C, that is to say that the rod 14 is moved into the interior of the cavity 30 and the partial cavity 32, until the piston 22 has been moved into the second position.

The rod 14 is then partially released again, as shown in FIG. 3A, until said rod 14 penetrates inside the cavity 30 and the partial cavity 32, depending on the length of the blind hole 56 which must be formed. The plastic 40, which is still in the viscous state and under pressure, can now flow in the area released by the rod 14 and close off the screw boss which is on the side of the piston 22.

Then follows again the application of a pressure maintenance, then the release of the rod 14, in its entirety, outside the cavity 30 (see Fig. 3B), as well as the opening of the mold. injection molding with a view to extracting the molded part 50 produced therefrom (see FIG. 3C).

While in the example above, it is again assumed that the rod 14 actively slides the piston 22 into the second position, this process is also not restrictive. When the spring element 28 is designed so that the piston 22 is only compressed in the second position due to the pressure of the plastic material 40 in the cavity 30, it is therefore also possible to move the rod 14, to from the position released outside the cavity 30, only until it is moved into the interior of the cavity 30 and the partial cavity 32, in order to form the blind hole 56, without however that the rod 14 is fully displaced up to the piston 22.

While the above example describes the fabrication of a molded part 50 with a screw boss 52 with reference to Figs. 3A to 3C, which screw boss 52 has a blind hole 56 which opens towards the visible face, it is also possible to manufacture a molded part 50 comprising a screw boss 52, which has a blind hole 58 which s opens towards the rear panel, as described below.

To this end, it is possible to prepare an injection molding mold according to another embodiment, as shown in Figs. 4 and 5A to 5C.

Since in this embodiment, no opening opening towards the visible face (side of the first molding tool 10) is created, it is not necessary to provide a rod 14 in the first tool molding 10, as shown in FIG. 1. Consequently, the first molding tool 10 of this embodiment has neither rod 14 nor hydraulic cylinder 12.

A recess 24 is again provided on the sides of the second molding tool 20, like the embodiment of FIG. 1, in which recess 24 a piston 22 is guided in a movable manner and subjected to an initial stress by means of a spring element

28. Unlike the embodiment of FIG. 1, it is here however provided that the piston 22 is designed in the form of a hollow cylinder, which comprises a hollow zone, inside which a rod 23 is again provided, which is preferably designed d 'in one piece with the second molding tool 20. The rod 23 has a cross section and an extension as far as the interior of the partial cavity 32 and, where appropriate, as far as the interior of the cavity 30, which correspond to the blind hole 58 which must be formed.

In order to manufacture the molded part 50, plastic material 40 is again injected into the cavity 30 until the latter is filled (see FIG. 5A) and until the pressure of the plastic material 40 compresses the piston 22 to the second position. For this purpose, the piston 22 moves beyond the fixed rod 23, in order to release it (see the

Fig. 5B). The plastic material 40 which flows in then fills the zone defined by the partial cavity 32 and that defined by the rod 23, with a view to forming the screw boss 52 with the blind hole 58 which opens in the direction of the rear face (see Fig. 5C). It is then possible to reapply the pressure maintenance, then to extract the molded part outside the injection molding mold (see Fig. 5D).

Although various preferred embodiments have been described above, the preceding description is not limited to it and it is possible to provide numerous modifications and variants, without however renouncing the lessons learned from this specification.

In place of the spring element 28 which acts passively, it is thus for example possible to provide an actuator, which allows an active stress on the piston 22 with a predefined force and / or which allows a displacement and / or active positioning of the piston 22. This embodiment is for example indicated in FIG. 6, on which the second molding tool 20 has a hydraulic cylinder 60, with a piston rod 61 at the end of which the piston 22 is located and, preferably, is fixed. If the hydraulic cylinder 60 is stressed with a constant pressure, the piston 22 can be subjected to an initial stress with a predetermined and well defined force which, in particular, does not depend on the position of the piston 22. The hydraulic cylinder 60 can also be operated in such a way as to actively move the piston 22, which offers the advantage that the movement of the piston 22 and, consequently, the moment and the evolution over time of the opening of the partial cavity 32 can be predetermined, preferably via a corresponding command program of a command (not shown).

Likewise, it is also possible to use a movable rod 71 in place of a fixed rod 23, as shown in FIG. 7, which movable rod 71 can, in particular, be produced in the form of a piston rod of a hydraulic cylinder 70. As in the case of the rod 14 of FIG. 1, the movable rod 71 can therefore be moved here also inside the partial cavity 32 and / or the cavity 30 and be moved outside the partial cavity 32 and / or the cavity 30.

In addition, other actuators can be used in place of the hydraulic cylinders, which actuators can move the piston 22, the rod 14 and / or the movable rod 71 such as, for example, pneumatic cylinders, actuators controlled by electric motor or electromagnetic actuators, which can also be set up to exert a defined force, much like controlling or regulating force or pressure in an operating mode , and / or in the form of positioning actuators, like a command and / or a regulation of the position in an operating mode.

What is more, it is also possible, in the case of the formation of clearance holes 54, to form the rod 14 and / or the movable rod 71 by means of a cutting blade 81, in particular a punching machine 81 of a hole punch 80. For this purpose, the punching machine 81 is molded according to the cross section of the blind hole 54 to be formed. The perforator 80 also has an actuating element 82 which is arranged inside the punching machine 82. The actuating element 82 is designed to be compressed in the cavity under the effect of the pressure of the material. plastic 40, thus triggering the actuation of the punching machine 81 of the punching machine 80. The punching machine 80 can in particular be designed as described in document WO 2016/050931 A1.

LIST OF REFERENCE ELEMENTS

Molding tool

Molding surface

Hydraulic cylinder

stem

Molding tool

Molding surface

Piston

Baguette

Recess

Stop surface

Hollow area

Spring element

Cavity

Partial cavity for screw boss

Plastic material

Molded part

Screw boss

Clearance hole

Blind hole

Blind hole

Hydraulic cylinder

Piston rod

Hydraulic cylinder

Movable rod

punch

Punching machine

Actuator

Claims (13)

1. A method for manufacturing a molded plastic part (50), comprising the following steps: a) preparing an injection molding mold, which comprises at least a first molding tool (10) and a second molding tool (20) which together define a cavity (30) for the molded part (50) ; in which the second molding tool (20) has a recess (24), in which a piston (22) is arranged, in which the piston (22) can be moved between a first position and a second position, in which the piston (22) and the recess (24) define a partial cavity (32), when the piston (22) is in the second position, for the formation of a screw boss (52), and in which the piston (22) closes in the first position the partial cavity (32) for the formation of a screw boss (52); b) moving the piston (22) to the first position; c) filling the cavity (30) with a plastic material (40); d) after the cavity (30) has been filled, moving the piston (22) to the second position, so that the plastic (40) under pressure in the cavity (30) can flow into the cavity partial (32), in order to form the screw boss (52); e) the application of pressure maintenance; and f) opening the injection molding mold and extracting the molded part (50). 2. Method according to claim 1, characterized in that a spring element (28) is further provided in the second molding tool (20), which spring element (28) is arranged and adjusted in order to subject the piston (22) at an initial stress in the first position. 3. Method according to claim 2, characterized in that the spring element (28) is adjusted in order to allow movement of the piston (22) from the first position to the second position, when the pressure of the plastic in the cavity (30) exceeds a predetermined pressure value, in particular a pressure value greater than or equal to 70 bar. 4. Method according to claim 1, characterized in that an actuator (60) is further provided in the second molding tool (20), in order to subject the piston (22) to an initial stress and / or in view displacement of the piston (22). 5. Method according to one of the preceding claims, characterized in that a rod (14) is arranged in the first molding tool (10), which can be moved outside and up to the inside of the partial cavity (32) and / or cavity (30), in which the rod (14) has a cross section which corresponds to the cross section of a clearance hole (54) or a blind hole (56) to be formed in the screw boss, wherein the method further comprises: - before step c): b1): the displacement of the rod (14) outside the cavity (30); and - after step c): c1): the displacement of the rod (14) up to the interior of the cavity (30), in order to form the clearance hole (54) or the blind hole (56). 6. Method according to claim 5, characterized in that the rod (14) is again displaced outside the cavity (30) after step e) and before step f). 20 7. Method according to one of claims 5 to 6, characterized in that the rod (14) is designed in the form of a piston rod of a hydraulic cylinder; or the rod (14) is actuated by means of an actuator controlled by an electric or electromagnetic motor; or the rod (14) is designed in the form of a punch (81) of a punch (80). 8. Method according to claim 7, characterized in that, in step c1), the rod (14) in the cavity (30) is moved inside the cavity (30) until the rod (14) is compressed against the piston (22) and comes to compress the piston (22) in the second position. 30 9. Method according to claim 8, characterized in that the rod (14) is partially released, after step c1), to a position in order to form the blind hole (56). 10. Method according to one of claims 1 to 9, wherein the piston (22) is designed in the form of a hollow cylinder which comprises a zone 35 hollow, in which a rod (23) is further provided in the second molding tool (20), which extends in the hollow area of the piston (22) and has a cross section which corresponds to the cross section of a clearance hole (54) or a blind hole (58) which must be formed in the screw boss (52). 11. Method according to one of claims 1 to 9, in which the piston (22) is designed in the form of a hollow cylinder which comprises a hollow zone, in which a rod (71) is further arranged in the second molding tool (20), which extends into the hollow zone of the piston (22) and has a cross section which corresponds to the cross section of a clearance hole (54) or a blind hole (58) which must be formed in the screw boss (52), wherein the method further comprises: - before step c): b2): the displacement of the rod (71) outside the partial cavity (32); and - after step c): c2): the displacement of the rod (71) up to the interior of the partial cavity (32) and, if necessary, up to the interior of the cavity (30), in order to form the clearance (54) or the blind hole (58). 12. Method according to claim 11, characterized in that the rod (71) is designed in the form of a piston rod of a hydraulic cylinder (70); or the rod (71) is actuated by means of an actuator controlled by an electric or electromagnetic motor. 13. Molded plastic part, produced according to the method according to one of the preceding claims.