Method for producing a plastic component

Abstract

The invention relates to a method for manufacturing a plastic part (1) comprising an insert (13) surrounded by a hollow body (11), the method comprising: (a) placing the insert (13) in a mould such that a gap is formed between the insert (13) and the mould; (b) feeding a polymer melt into the gap, thereby forming the hollow body (11) surrounding the insert (13); (c) removing the plastic part (1) from the mould; wherein in order to form the gap, a projection (17) is formed on the insert (13), or wherein the mould comprises a pin (25) on which the insert is placed, or wherein the gap is a recess in the insert (13).

Description

[0001] The present invention relates to a method for manufacturing a plastic part, the plastic part comprising an insert surrounded by a hollow body, the method comprising:

[0002] (a) placing the insert into a mold such that a gap is formed between the insert and the mold;

[0003] (b) feeding a polymer melt into the gap, thereby forming the hollow body surrounding the insert;

[0004] (c) removing the plastic part from the mold.

[0005] Plastic parts manufactured by injection molding must be adapted to the limitations and boundary conditions given by the injection molding process and must be designed accordingly. The limitations of the injection molding process are usually due to mass accumulation and the demolding of the injection-molded plastic part by opening the mold.

[0006] Mass accumulation usually results in a higher cycle time because the plastic part requires a longer cooling time. In addition, mass accumulation also increases the risk of internal voids accumulating. Therefore, plastic parts manufactured by the injection molding process should have a small wall thickness.

[0007] For the plastic part to be demolded, it is necessary that each internal core, insert, or geometric design that reduces mass accumulation must have a shape that allows the mold to be opened and the plastic part to be withdrawn. This results in constraints on the geometry of the plastic part and requires a mold with complex movable cores and complex kinematics for opening and closing.

[0008] Currently, there are several non-standard injection molding processes by which hollow parts can be manufactured to avoid such mass accumulation. Such non-standard injection molding processes are, for example, gas-assisted injection molding (GAIM) or water-assisted injection molding technology (WIT) or fusible core technology.

[0009] In GAIM / WIT, the mold is completely filled with the polymer melt, and then a part of the hot polymer melt is pushed out of the mold by injecting a liquid (usually water) or a gas. By this liquid or gas injection, the polymer melt in contact with the wall of the mold remains in the mold and forms a hollow part. In the fusible core technology, a metal core is inserted into the mold, which then has to be melted to produce a hollow segment.

[0010] The disadvantages of the GAIM / WIT process are that complex injection machines are required to inject the liquid or gas; and further, due to the high pressure and speed of the liquid or gas, the wall thickness of the hollow part or the plastic part may be uneven. In the fusible core technology, removing the metal core results in additional process steps.

[0011] Accordingly, an object of the present invention is to provide a method for manufacturing a plastic part, which method has no mass accumulation and does not have the disadvantages of known GAIM / WIT processes or fusible core techniques.

[0012] This object is achieved by a method for manufacturing a plastic part, the plastic part comprising an insert surrounded by a hollow body, the method comprising:

[0013] (a) placing the insert in a mold such that a gap is formed between the insert and the mold;

[0014] (b) feeding a polymer melt into the gap so as to form the hollow body surrounding the insert;

[0015] (c) removing the plastic part from the mold,

[0016] wherein in order to form the gap, a protrusion is formed on the insert, or wherein the mold comprises pins on which the insert is placed, or wherein the gap is a recess in the insert.

[0017] By using an insert and retaining the insert in the plastic part, a plastic part comprising segments with different wall thicknesses can be manufactured without the disadvantages of known processes. In particular, if an insert with a low weight is used, a plastic part with a lower weight than a plastic part having walls made of solid material can be manufactured. Further, if the gap is a recess in the insert, the distribution point of the polymer melt can be positioned at a location that cannot be achieved by the injection point in the mold (e.g., on the lower side of the insert), and through this location, balanced filling and an undisturbed fiber orientation for utilizing anisotropic material behavior, as well as a reduction in warping of the plastic part, can be achieved.

[0018] In addition, by using a protrusion formed on the insert or using pins in the mold on which the insert is placed to form the gap, or the gap is a recess in the insert, the insert forms part of the mold. Accordingly, the walls of the hollow body of the plastic part have a defined thickness and shape different from those of the walls manufactured by known GAIM / WIT processes. Different from fusible core techniques, the insert remains in the plastic part and does not melt, making the method much simpler. To manufacture a plastic part by the method of the present invention, a standard injection molding process can be used, which also simplifies the method for manufacturing the plastic part. Other liquid plastic molding processes (e.g., casting processes (e.g., RIM)) are also suitable.

[0019] For the production of lightweight components, it is preferred to use inserts made of foam and / or as a second hollow body. In particular, the insert is made of foam. Since the gas forms the bubbles of the foam, the foam has a much lower density than a solid insert, enabling the production of components that are lighter in weight than comparable components with solid walls.

[0020] Since the insert forms part of the mold during the feeding of the polymer melt, it is necessary to use a material or construction for the insert that can withstand the loads and temperatures during the feeding of the polymer melt.

[0021] If the insert is a second hollow body, it is preferred to manufacture at least two parts of the second hollow body and then connect these parts to form the second hollow body. This connection can be achieved by welding, brazing or gluing. Alternatively, the parts can also be simply placed together without any fixation, since the parts are fixed in the mold by means of projections or pins and after being surrounded by the polymer melt from the polymer forming the hollow body. However, in order to avoid displacement of these parts, it is preferred to provide grooves and tongues or recesses on the edges that come into contact when the parts are connected. If the second hollow body is formed by connecting at least two parts, it is particularly advantageous that these parts can be manufactured by standard processes (such as by standard injection molding).

[0022] Depending on the size of the insert and the pressure acting on the insert, if the insert is a second hollow body, it may be necessary to reinforce it. To reinforce the second hollow body, it can for example include columns or walls connecting the opposite inner walls of the second hollow body. The columns or walls connecting the opposite inner walls of the second hollow body can be separate parts placed in one part before connection to the second part, or can be formed integrally with at least one part. If the columns or walls are formed integrally with a part, they preferably have such a height that the parts forming the opposite inner walls contact the upper ends of the columns or walls after being connected to the part with the integrally formed columns or walls. In addition, a part of the columns or walls can also be formed integrally on those parts (which are placed such that they form the opposite inner walls of the second hollow body), and after connecting these parts of the hollow body, the walls or the parts of the columns of the parts forming the opposite inner walls of the hollow body also contact and thus form the columns or walls.

[0023] In addition to or as an alternative to the columns or walls, the inner or outer walls of the second hollow body can be reinforced by ribs or other suitable geometric shape reinforcements formed on the walls of the parts used to manufacture the second hollow body.

[0024] If the insert is made of foam, it is necessary to use a foam that substantially maintains its shape when the polymer melt is fed into the mold. For this purpose, the insert is preferably made of a foam with a high compression stiffness.

[0025] To further reduce the weight of the plastic part, it is further possible that the insert is a second hollow body made of foam. If such a second hollow body made of foam has too little stability, the hollow body can be filled with a lighter material. In the case of polyamide foam with foam made of, for example, thermoplastic polyurethane (TPU), expandable polyamide (EPA), or polystyrene (PS). By changing the material, the stiffness and weight can be adapted to the requirements of the plastic part.

[0026] If higher stiffness is required or parts must have a greater mass due to noise, vibration, and harshness requirements, or if the plastic part has electrical, magnetic, or other functions that require a higher weight, the insert can include a dense and heavy material, such as a non-foam polymer or metal.

[0027] Suitable materials for making the insert are all materials from which the insert can be formed and which substantially maintain their shape when the polymer melt is fed into the mold. Such materials can be, for example, polymer materials such as thermoplastics or thermosets, ceramics, or metals. Particularly preferably, the insert is made of a polymeric material.

[0028] If the insert is made of a polymeric material, it is preferably a polymeric material that forms a uniform connection with the polymer fed into the gap between the insert and the wall of the mold. In this context, a uniform connection means that the insert and the hollow body surrounding the insert are in contact over the entire surface, and in particular, the polymer melt fed into the gap between the mold and the insert melts the outer surface of the insert and welds to the outer surface of the insert, such that an inseparable form-fit connection is formed between the insert and the hollow body.

[0029] Furthermore, to achieve a stable insert, it may be advantageous to strengthen the insert. If a polymeric material is used to manufacture the insert, the polymeric material can be strengthened by adding short fibers, long fibers, or powdered reinforcing materials such as talc. In addition, continuous fibers can also be used to strengthen the insert. Regardless of whether short fibers, long fibers, or continuous fibers are used to strengthen the insert, the fibers can be glass fibers, carbon fibers, aramid fibers, or natural fibers such as twine or wool. If the insert is made of foam and continuous fibers are used to strengthen the insert, all known techniques for connecting the foam and the fibers can be used, such as overfoaming the fibers or placing prefabricated fiber parts into / onto the foam, which establishes the desired load path.

[0030] To be able to recycle plastic parts manufactured by the method of the present invention without complex separation steps for separating different materials used to form the plastic part, it is particularly preferred to use the same polymer to form the insert and the hollow body.

[0031] Suitable polymers for forming inserts and / or hollow bodies for plastic parts are preferably polyamide (PA), polyethylene (PE), polybutylene terephthalate (PBT), polyester, polyoxymethylene (POM) or polypropylene (PP). Due to the high compressive strength of polyamide foam, polyamide-based materials that can be reinforced are preferred. Thus, if the polymer forming the hollow body is, for example, polypropylene, the insert is preferably made of polypropylene or expanded polypropylene. If polyamide is used as the polymer of the hollow body, the insert is also made of a polymer and in particular of the same type of polymer as the hollow body.

[0032] In addition to inserts, reinforcing polymers can also be used to form hollow bodies. In this case, for forming the hollow body, the polymer melt can contain short fibers or long fibers or powdered reinforcing materials. The material made into fibers or the powdered material can be any material known to those skilled in the art for use as fibers or as a powdered reinforcing material, and preferably, the materials described above for inserts are used.

[0033] In addition to the reinforcing material, the polymer material for manufacturing the insert and the polymer material for manufacturing the hollow body can contain additives commonly used in polymer materials. Such additives are, for example, plasticizers, impact modifiers, dyes or any other type of additive known to those skilled in the art.

[0034] It is possible to use a polymer as an insert and in particular to use a foam or a second hollow body as an insert because, under mechanical loading, the highest stresses are usually located in the outer region of the hollow body surrounding the insert. Thus, no high stresses act on the insert, and thus the insert can be made of a material with lower mechanical properties.

[0035] To manufacture a plastic part, in a first step, the insert is placed in a mold. Thereby, the insert is placed in the mold in such a way that a gap is formed between the inner wall of the mold and the insert. This gap defines a cavity for the filling process by which the hollow body is formed. According to the invention, in order to form the gap, protrusions are formed on the insert or the mold includes pins on which the insert is placed.

[0036] If the protrusions are formed on the insert, the protrusions can be integrally formed on the insert or can be separate parts connected to the insert.

[0037] When forming the insert, a raised portion integrally formed on the insert is preferably formed. If the insert is made of foam, in this case, the raised portion is usually also made of foam. If the insert is a second hollow body, in this case, the raised portion is formed on the outer surface of the second hollow body and is usually also formed when forming the part that makes up the second hollow body. If the part used to form the second hollow body is made by injection molding, recesses are provided in the mold for the part used to manufacture the second hollow body at those positions where the raised portion should be located.

[0038] An insert made of foam can be manufactured by cutting the insert out of the foam or by forming a foamed insert in a mold. If the foamed insert is formed in a mold, in this case as well, recesses are provided at those positions where the raised portion should be located. When forming the foamed insert, the raised portion is also formed, where the raised portion is also made of foam. Similarly, if the insert is cut from a foamed raw material, the raised portion can be formed on or made of the foam.

[0039] If the raised portions are separate components, they can be connected to the insert by any suitable method known to those skilled in the art. For example, the raised portions can be glued to the insert using an adhesive or welded to the insert. In addition, in order to connect the raised portions to the insert, they can be partially surrounded by the insert. In order to partially surround the raised portions by the insert, it is preferred to place the raised portions in the mold and then form the insert by injecting the material for forming the foamed insert or injecting a polymer melt to form the parts of the second hollow body.

[0040] In addition, if the raised portions are separate components, they can be made of a material different from or the same as the material used to make the insert. However, if the insert and the hollow body forming the plastic part are made of different materials, it is particularly preferred that the raised portions are made of the same material as the hollow body forming the plastic part.

[0041] The raised portion can have any suitable form, such as a conical shape or a cylindrical shape. In addition to a conical shape or a cylindrical shape, any other shape is also possible. Preferably, the raised portion has a conical shape and is connected to the insert in such a way that the tip of the raised portion contacts the mold when the insert is placed in the mold. If the raised portion is made of a material different from the polymer of which the hollow body is made or is made of foam, such a conical shape is particularly preferred. Due to the conical shape and the orientation such that the tip of the conical raised portion contacts the mold, the contact with the surface of the mold is minimized, and the raised portion remains invisible in the plastic part after demolding.

[0042] If the projection is made of solid material and made of the same polymer as the hollow body of the plastic part, the projection generally also remains invisible in the case where the projection has a different shape (such as a cylindrical shape) and a larger contact area with the surface of the mold. Due to the use of the same material, during the feeding of the polymer melt, at least the surface of the projection melts, and the polymer melt forms an integral connection with the projection.

[0043] To minimize the contact area with the surface of the mold, alternatively, a convex curved surface can also be provided for the projection on the side facing away from the insert.

[0044] However, particularly preferably, the projection has a conical shape.

[0045] If, in order to form a gap between the inner surface of the mold and the insert and the mold includes pins, the pins can be fixed or retractable. In order to achieve a closed hollow body that surrounds the insert without openings after the plastic part is deformed, it is preferred that the pins are retractable. In order to avoid the displacement of the insert during the feeding of the mold, it is further preferred that during the feeding, the pins continuously retract when the polymer reaches them.

[0046] Since the insert remains in the plastic part manufactured by the method of the present invention, the insert forms part of the mold when feeding the polymer melt to form the hollow body. This has the advantage that the inner surface of the hollow body can have any possible shape. For example, the insert can be equipped with a structured surface.

[0047] To form a structured surface, the insert can, for example, include recesses such that during the feeding, the polymer melt fills the recesses. Since the insert remains in the plastic part, protrusions with undercuts can also be formed on the inner surface of the hollow body of the plastic part.

[0048] The structure of the surface can be such that the protrusions and recesses are smaller than the average wall thickness of the hollow body. Such a structure of the surface can contribute to defining better load transfer between the rigid polymer material of the hollow body and the insert. In addition, micro-treatment of the surface (such as small textures or plasma treatment) can be advantageous because it enables the insert to be better connected to the hollow body.

[0049] In addition to small protrusions and recesses, in a preferred embodiment, the recesses are such that the protrusions formed on the inner surface of the hollow body form, for example, the form of reinforcing ribs. Such rib-like protrusions allow the hollow body to be strengthened without changing the outer surface of the hollow body. Therefore, even if the hollow body has a smooth surface, reinforcing ribs can be provided.

[0050] In addition, for reinforcement, it is also suitable to form connecting rods that connect the opposite inner surfaces of the hollow body. To this end, openings are formed in the insert, and during the feeding of the polymer melt, the openings are filled with the polymer melt, thereby forming connecting rods between the opposite inner surfaces of the hollow body. In this case, the design of the core forms defined cavities for the polymer melt. After the filling process, these cavities act as well-defined load paths in the plastic part, and these well-defined load paths improve the mechanical behavior.

[0051] After placing the insert in the mold, the mold is closed and the polymer melt is fed into the mold. To feed the polymer melt into the mold, any suitable method known to those skilled in the art can be used. The polymer melt can be fed, for example, by an injection molding process. In this case, the mold in which the insert is placed before feeding the polymer melt is the mold of an injection molding machine. In addition to feeding the polymer melt by using an injection molding process, a casting process or a centrifugal casting process can also be used to feed the polymer melt into the mold. In these cases, the mold is the mold of a casting machine or a centrifugal casting machine, respectively. However, preferably, an injection molding process is used to feed the polymer melt into the mold.

[0052] To manufacture long plastic parts (especially long closed profiles that can be used, for example, in bending load or axial collision situations), the polymer melt can be injected into a mold with sequential gates. In this case, the insert is placed in the mold such that a gap is formed between the mold and the insert, and then the polymer melt is injected into the mold in a sequential manner: the first gate through which the polymer melt is injected into the mold is opened, the first gate is closed and the second gate is opened after injecting a limited amount of the polymer melt into the mold, and the injection of the polymer melt through the second gate is continued. After injecting a limited amount of the polymer melt, the second gate is closed and another gate is opened. This operation is continued until the polymer melt has been injected into the mold sequentially through all the gates. A good way to control the opening of the gates is to open each gate immediately after the melt has reached the position in the mold while closing the previous gate. By feeding the polymer melt into the mold in this way, the polymer can be injected into the mold with a much lower injection pressure than in the case of injecting the polymer melt into the mold via only one injection point. Due to the lower injection pressure, the clamping pressure of the mold can also be reduced, and very long profiles can be manufactured without the need for a large machine with a high clamping pressure and a strong injection unit.

[0053] After feeding the polymer melt into the mold, the polymer cures in the mold, and then the plastic part is removed from the mold.

[0054] The components that can be manufactured by the method of the present invention can be any components having a thicker region, in which inserts can be placed to reduce the risk of internal void accumulation and provide a uniform wall thickness, or in which the hollow part can be filled with foamed inserts, so that the components can be manufactured by a less complex method. In addition, by using foam as the insert, the dynamic behavior of the plastic component can be improved, and thus the dynamic response can be improved to obtain better acoustic and NVH (Noise, Vibration, Harshness) behavior.

[0055] The plastic components manufactured by the method of the present invention can be, for example, structural parts for fixing or supporting other components (such as, for example, an electric motor or a combustion engine), a support structure for a rotating machine, a structural mechanical load component, especially a part that may break due to impact (for example, in a vehicle) or a component in which other parts can be embedded. Such plastic components are, for example, roof rails, door handles, pedals, chairs, protective undercoats (especially for highway stones), bicycle frames, seat frames or rims.

[0056] Generally speaking, injection-molded plastic components used as structural mechanical load components are made of fiber-reinforced polymers and show complex geometric structures due to high loads and necessary designs.

[0057] In many cases, the injection point cannot be placed at the ideal position in the mold (i.e., the position where balanced filling can be achieved, undisturbed fiber orientation for utilizing the anisotropic material behavior, and warpage reduction of the plastic component) to achieve the best filling process. To optimally fill the cavity, an insert is used, which includes a recess that serves as a flow channel and connects the injection point to the optimal filling point for filling the cavity, so as to improve the quality and mechanical behavior of the plastic component.

[0058] The components for fixing or supporting other parts have a dynamic natural frequency behavior, which depends on the geometric structure, material and mechanical boundary conditions of the component. If the natural frequency of the component is close to the critical frequency of the main structure (for example, an electric motor or a combustion engine), this effect will cause an undesirable resonance effect. If the damping contribution of the component within the resonant frequency range is not high enough, the oscillation may cause breakage of the part or undesirable air noise and poor acoustic behavior.

[0059] Co-molding the foam as an insert allows for a new design of the plastic component, so that the resonance behavior and the damping behavior can be actively controlled by the material, geometric structure and placement of the foam insert. This method of co-molding a suitable foam insert allows for an intelligent modification of the dynamic behavior to actively control and improve the dynamic response in the system.

[0060] The advantage of surrounding an insert made of foam with a polymer is that the injection-molded polymer is placed on the outer skin of the available space. Here, the load is transferred more efficiently. Due to the necessary demolding direction in injection molding, there is no need to design a complex geometry for moving metal tool segments or make compromises in some performance aspects.

[0061] This effect becomes obvious when torsional loads have to be transferred. A torsionally loaded closed cross-section is always advantageous compared to an open segment. Due to demolding, open segments usually have to be used in standard injection molding. When designing a component with a foam insert with overmolding, closed segments can be easily used.

[0062] The plastic part that defines the visible outer skin of the component may have requirements regarding collisions, impact situations, or misuse. Drop tests of consumer machines are examples of such requirements.

[0063] Depending on the material chosen for the covering part, a collision situation may lead to brittle failure of the outer skin, where debris is generated due to the fracturing nature of the failure. Many small failure particles may cause undesired behavior when they break down and penetrate the environment.

[0064] By using an insert, the type of failure can be changed. On the one hand, the foamed insert distributes energy more evenly in the component and thus reduces local stress. On the other hand, the tight connection established between the foamed insert and the polymer melt can prevent the part from breaking down into many small particles.

[0065] If the plastic part needs to be connected to other parts and / or other parts have to be incorporated into the injection-molded component, these additional parts can be incorporated by including them in the insert before or after overmolding. These parts can be joined by any known connection technique (such as gluing, threading, snap-fitting, etc.). Parts to be incorporated into the plastic part are, for example, sensors, electrical devices, electronic circuit boards, metal reinforcements, inserts with and / or without threads.

[0066] To incorporate additional parts, the insert can contain cavities in which the parts to be incorporated into the plastic part are placed. After the additional parts are placed in the cavities, the openings in the foam can be closed and then overmolded with the polymer melt. In this case, the additional parts are safe and secure in the insert and will not be damaged by the polymer melt.

[0067] The possible connections of the additional parts to the outside (such as cables) can also be incorporated through the defined boundaries of the foamed insert with the polymer melt.

[0068] If additional parts, which are rather soft and cannot withstand the filling pressure of the polymer melt in an injection molding process, have to be incorporated into a plastic part under significant deformation, these additional parts can be incorporated into a foamed insert and fixed relative to each other such that no relative deformation occurs during the injection molding process. Such soft additional parts can be, for example, wires and rods used as electrical conductors. Deformation during the injection process such that they come into contact with each other may cause a short circuit in the electrical circuit. In this case, the part does not work and is useless. If the additional parts are used as a mechanical structure, the deformation will mean that the desired mechanical function is at least weakened or even destroyed. By incorporating the additional parts into an insert of the plastic part, the part still has the same external shape, but the tendency for core shift during the filling process is minimized.

[0069] To incorporate the additional parts into the foam, the additional parts can be placed in the foam tool before the start of the foaming process and thus embedded in the foamed insert. Alternatively, the foamed insert can be manufactured separately, and the additional parts can be incorporated into the foamed insert after the foaming process.

[0070] Embodiments of the invention are shown in the drawings and described in more detail in the following description.

[0071] In the drawings:

[0072] Figure 1 a plastic part manufactured by the GAIM / WIT process according to the prior art is shown;

[0073] Figure 2 a plastic part manufactured by the method of the invention is shown;

[0074] Figure 3 a plastic part with a raised portion of conical shape on the insert is shown;

[0075] Figure 4 a plastic part with a raised portion of conical shape on the insert in a second embodiment is shown;

[0076] Figure 5 a plastic part with a raised portion in the form of a cylindrical pin on the insert is shown;

[0077] Figure 6 the fixing of an insert with a retractable pin is schematically shown;

[0078] Figure 7 a plastic part with an insert having a structured surface is shown;

[0079] Figure 8 an insert with a recess and an opening for forming an additional cavity to be filled is shown;

[0080] Figure 9 shows an insert in the form of a hollow body;

[0081] Figure 10a shows an insert with recesses as flow channels;

[0082] Figure 10b shows the plastic part injected into the insert of Figure 10a;

[0083] Figure 11 shows a bracket with a foamed insert for improving NVH;

[0084] Figure 12 shows an engine mount for an electric motor;

[0085] Figure 13 shows an engine mount for a combustion engine;

[0086] Figure 14 shows a plastic part with a foamed insert for preventing detachment in case of a collision;

[0087] Figure 15 shows a plastic part with an insert having a cavity for attaching additional parts;

[0088] Figure 16 shows an insert with bonded soft parts; and

[0089] Figure 17 shows a plastic part with an insert having bonded different materials.

[0090] In the drawings, exemplary plastic parts are shown for illustrative purposes. The plastic parts manufactured by the method of the present invention can have any geometric structure that can be manufactured by injection molding or casting processes, and can have, for example, more or less segments with different wall thicknesses, as shown herein. The plastic parts manufactured by the method of the present invention can, for example, have a simple geometric structure (such as a cylinder, a cone, or a sphere), or can have any other geometric shape. In addition, the plastic parts can have a much more complex structure, as shown herein.

[0091] Figure 1 shows an exemplary plastic part manufactured by the GAIM / WIT process according to the prior art.

[0092] The plastic part 1 includes several segments with different thicknesses. A first segment 3 with a small wall thickness, a second segment 5 with a medium wall thickness, and a third segment 7 with a large wall thickness. To avoid material accumulation in the second segment 5 and the third segment 7, the plastic part includes a cavity 9 surrounded by a polymer material that forms a hollow body 11.

[0093] According to the prior art, after a mold has been filled with a polymer melt, a cavity 9 is formed by injecting a gas or a liquid. The gas or liquid displaces the polymer melt and forms the cavity 9. By this process, material accumulation is avoided and a hollow body 11 is manufactured.

[0094] However, due to this process, variations in the wall thickness of the hollow body and non-uniform walls are inevitable. Further minor variations in the pressure or velocity of the gas or liquid used to displace the polymer melt may result in differences in the geometry of the hollow body.

[0095] To avoid these drawbacks, a plastic part is manufactured by the method of the present invention, which plastic part includes an insert surrounded by a hollow body. Figure 2 An example of such a plastic part is shown in.

[0096] Figure 2 The plastic part 1 has the same external geometry as Figure 1 the plastic part 1 shown in. However, unlike the plastic part 1 manufactured by the method according to the prior art, the plastic part 1 manufactured by the method of the present invention includes an insert 13 that completely fills the cavity 9 of the hollow body 11.

[0097] By using the insert 13, a hollow body 11 with a defined wall thickness can be manufactured and unintended different wall thicknesses can be avoided. The insert 13 can be, for example, a foam or a second hollow body, which second hollow body can be made of metal, ceramic or optionally reinforced polymer.

[0098] To manufacture the plastic part 1, the insert 13 is placed in the mold, thereby forming a gap between the insert 13 and the inner wall of the mold. Subsequently, the polymer melt is fed into the gap, thereby forming the hollow body 11.

[0099] To form the gap, projections can be provided on the insert or pins can be used in the mold on which the insert is placed.

[0100] Figures 3 to 5 Different embodiments of the projections on the insert are shown in.

[0101] Figure 3 A plastic part with a conical-shaped projection on the insert is shown in.

[0102] In order to achieve a hollow body 11 with a desired wall thickness, a mold into which a polymer melt is fed must be provided, the mold having a cavity corresponding to the desired shape of the hollow body. According to the method of the present invention, the cavity is defined by the inner wall of the mold and the surface 15 of the insert 13. Since the surface 15 of the insert is opposite to the inner wall of the mold, the cavity into which the polymer melt for forming the hollow body 11 flows has the form of a gap. The distance between the surface 15 of the insert 13 and the inner wall of the mold and thus the thickness of the wall of the hollow body 11 is defined by the projections 17 on the insert 13.

[0103] When the insert is placed in the mold, the projections 17 contact the inner wall of the mold, and the insert 13 together with the projections 17 rests on the inner wall of the mold. Thereby, a gap is formed into which the polymer melt for forming the hollow body 11 flows.

[0104] In Figure 3 the illustrated embodiment, the projections are placed on top of the surface 15 of the insert 13. This can be achieved by providing the projections and connecting them to the surface 15 of the insert, for example, by gluing or welding. In this case, the projections 17 can be made of the same material as the insert 13 or of a different material that can be fixed to the surface 15 of the insert 13. If the insert 13 and the hollow body 11 are made of different materials and the projections are made of a material different from the material of the insert, it is particularly preferred that the projections 17 are made of the same material as the hollow body 11. If the insert 13 and the hollow body 11 are made of the same material, it is preferred that the projections 17 are also made of the same material.

[0105] In addition to manufacturing the projections 17 separately from the insert 13 and fixing them to the surface 15 of the insert 13, the projections 17 can also be and preferably are manufactured integrally with the insert 13.

[0106] Particularly, if the projections 13 and the hollow body 11 are made of different materials or the projections 17 are made integrally with the insert 13, the conical shape of the projections 17 as Figure 3 shown is preferred to minimize the contact area of the projections 17 on the inner wall of the mold. This is particularly preferred if the projections 17 are manufactured integrally with the insert 13 and the insert is a foam, since in this case the projections 17 are also made of foam.

[0107] Figure 4 illustrates an alternative for fixing the projections 17 to the insert 13.

[0108] Figure 4 The projections shown also have a conical shape. However, different from the Figure 3 illustrated embodiment,Figure 4 The projections 17 shown are not fixed to the surface 15 of the insert 13, but are partially surrounded by the material of the insert 13. This design of the insert 13 has the advantage that, in order to fix the projections 17 to the insert 13, no adhesive for gluing or additional steps for fixing them to the surface 15 of the insert 13 (for example by welding) are required.

[0109] If the projection 17 is made of solid material and the insert 13 is made of foam, such a design of the insert 13 with a partially enclosed projection 17 is particularly preferred. Also in this case, the projection 17 is preferably made of the same material as the hollow body 11.

[0110] To produce the insert 13 with the partially enclosed projection 17 , for example, the projection 17 is placed in a mold for producing the insert 13 , and the material for forming the insert 13 is subsequently fed into the mold.

[0111] Figure 5 A further alternative of a projection 17 at least partially surrounded by the material of the insert 13 is shown in FIG.

[0112] Figure 5 The embodiment shown is similar to Figure 4 The embodiment shown differs only in the shape of the projection 17. Figure 4 The implementation schemes are different. Figure 5 The projection 17 of the embodiment shown has a cylindrical shape.

[0113] Apart from Figure 5 The cylindrical shape of the raised portion 17 shown or Figure 3 or Figure 4 Besides the conical shape of the raised portion 17 shown, the raised portion 17 may have any other shape, such as a pyramid, a sphere or a hemisphere, or a cube.

[0114] like Figures 3 to 5 As shown, as an alternative to the raised portion 17 for forming the gap into which the polymer melt for forming the hollow body 11 flows, a pin in the mold can be used to form the gap. Figure 6 It is shown as an example in FIG.

[0115] For illustrative purposes, Figure 6Shows a section of a mold, which includes a first part 19 and a second part 21. To form the hollow body 11 of the plastic part 1, the first part 19 and the second part 21 are closed to form the mold. Each part 19, 21 of the mold includes an opening 23 in which a pin 25 is received. The pin 25 can be fixed or preferably retractable. If the pin is retractable, then to place the insert 13 into the mold, the mold is opened and the pin 25 is moved to a first position protruding into the mold. The length by which the pin protrudes into the mold corresponds to the width of the gap into which the polymer melt is injected to form the hollow body. Subsequently, the insert 13 is placed on the pin and the mold is closed. Alternatively, the insert can also be placed on the inner surface of the first part 19 or the second part 21, the mold is closed, and then the pin 25 is moved to the protruding position to form the gap.

[0116] To form the hollow body, the pin 25 can be in the protruding position during the feeding of the polymer melt. However, this has the disadvantage that there will be holes after the hollow body is removed from the mold. Therefore, it is preferred to use a retractable pin 25, and during the filling of the mold, when the polymer melt reaches the corresponding pin 25, the pin 25 is continuously retracted into its opening 23. By continuously retracting the pin 25 during the filling of the gap, the gap upstream of the melt front is filled with the polymer melt, and thus the insert 13 remains in its position.

[0117] Figure 7 Shows a plastic part with an insert having a structured surface.

[0118] In addition to the smooth surface as Figures 2 to 6 shown, the surface 15 of the insert 13 can have a structure 27. Depending on the intended function of the structure 27, the insert 13 can have a structure 27 with small surface variations or large surface variations. Small surface variations mean that the distance between the highest point of the protrusion of the structure and the lowest point of the depression is less than half of the average wall thickness of the hollow body. For example, small surface variations can help to define better load transfer between the material of the hollow body 11 and the material of the insert 13. In addition, particularly when a torsional load acts on the plastic part, small surface variations better connect the insert 13 to the hollow body 11, and thus when a torsional load acts on the plastic part and the relative position of the contact surface between the insert 13 and the hollow body 11 remains constant, the insert 13 does not slide within the hollow body 11 but deforms.

[0119] The structure 27 can have any suitable geometric structure, such as wavy, serrated, triangular or grooved. In addition, the surface can have protrusions of any possible shape (such as pyramids, cones, hemispheres, cylinders or any other shape).

[0120] In addition to small surface variations, the structure may also include large surface variations, which means that the distance between the lowest point of the recess and the highest point of the protrusion is greater than half of the average wall thickness of the hollow body. Such large surface variations may include, for example, reinforcing ribs. In addition to structures with small surface variations or large surface variations, combinations of small and large surface variations are also possible.

[0121] Figure 8 An example of an insert with a structure having large surface variations is shown.

[0122] The insert 13 includes a recess 29 and a hole 31. When the gap is filled with a polymer melt to form a hollow body, the polymer melt flows into the recess 29 and the hole 31. After curing, the polymer filling the recess 29 forms ribs on the inner surface of the hollow body. The polymer filling the hole 31 forms a connection between two opposite inner surfaces of the hollow body, thereby strengthening the polymer component.

[0123] In addition to including the recess 29 and the hole 31 as shown here, the insert 13 may also include only at least one hole 31 or only the recess 29 for forming reinforcing ribs on the inner surface of the hollow body 11. Thus, the geometry of the recess depends on the intended form of the reinforcing ribs. In addition to the cross-grooves shown here as the recess 29, the recess 29 may also be grooves of any shape arranged in parallel. Furthermore, the recess 29 may be provided not only on the thickest part 33 of the insert 13 as shown here, but also on other surfaces (such as the inclined surface 35 connecting the thinner part 37 to the thickest part 33 and / or connecting to the thinner part 37). In addition, the groove 29 may also be provided on any other surface of the insert 13.

[0124] The optimal position and shape of the recess depend on the intended shape of the reinforcing ribs for optimal mechanical properties and can be determined by simulation calculations. This also applies to the hole 31 through which the polymer melt flows to form a connection between the two inner surfaces of the hollow body.

[0125] The hole 31 may have any cross-sectional area, such as circular as shown here. However, in addition to the circular shape, the cross-sectional area may be, for example, oval, square, triangular, cross-shaped, or in the form of any polygon. Furthermore, the cross-sectional area of the hole may be constant or variable along the entire length of the hole 31. The cross-sectional area may, for example, decrease or increase, or first decrease and then increase, or first increase and then decrease. In addition, the hole 31 may change the shape of the cross-sectional area along its length.

[0126] As Figures 2 to 8 shown, the insert 13 is preferably made of foam. As an alternative, the insert 13 may also be a second hollow body. This is, for example, inFigure 9 is shown in

[0127] If the insert 13 is the second hollow body, it is preferred that the insert 13 comprises at least a first part 39 and a second part 41, wherein the first part 39 and the second part 41 are connected and thereby form the insert 13. However, in addition to only two parts 39, 41 as shown herein, depending on the shape of the insert 13, the insert 13 may also be made of more than just two parts.

[0128] In order to stably connect the parts 39, 41 forming the insert, it is preferred if the connecting edges 43 of the parts 39, 41 are configured, for example, as shown herein with tongues and grooves. When connecting these parts, the tongue slides into the groove, so that these parts cannot move relative to each other. As an alternative to the tongues and grooves shown herein, projections may also be provided for each of the connecting edges, with the projection of one part on the outer surface and the projection of the other part on the inner surface, such that the part having the projection on the inner surface can slide into the part having the projection on the outer surface, thereby forming a stable connection.

[0129] Additionally, these parts can be fixed, for example, by gluing or welding.

[0130] In order to strengthen the insert 13 forming the second hollow body, columns or walls 45 may be provided, by which two opposite inner surfaces of the hollow body are connected. Thereby, the columns and / or walls can be manufactured on a part of the insert 13 or partly on two parts, wherein the contact parts of the partly formed columns and / or walls form the connecting columns or walls inside the second hollow body, as shown herein.

[0131] As an alternative or supplement to connecting the walls or columns on two opposite sides, reinforcing ribs may also be formed on a part of the inner surface or the entire inner surface of the second hollow body.

[0132] Figure 10a shows an example of an insert 13 with a recess 47 as a flow channel. The recess 47 connects the injection point 49, at which the polymer melt is injected into the mold, with the distribution point for distributing the polymer melt into the cavity 51 in the insert 13. The injection point 49 is located in the mold at a position where it can be easily positioned, and the distribution point for distributing the polymer melt is located at a position allowing an optimal filling (i.e., balanced filling) of the cavity 51, a reduction in the warping of the plastic part 1, and an undisturbed fiber orientation for achieving anisotropic material behavior (if the polymer melt contains fibers). Furthermore, by placing the injection point at a position where it can be easily positioned and the distribution point at a position for an optimal filling of the cavity, an improved quality and mechanical behavior of the resulting plastic part are achieved.

[0133] The plastic part after injecting the polymer melt into the cavity of the insert 13 in Fig. 10a is shown in Fig. 10b. The plastic part includes a sprue 53 at the injection point 49, a rod 54 formed in the flow channel and connecting the injection point 49 and the distribution point 55, and ribs 57 formed in the cavity 51 of the insert.

[0134] Figure 11 A bracket with a foamed insert for improving NVH (Noise, Vibration, Harshness) is schematically shown.

[0135] The bracket 59 with improved NVH may include a first bracket part 61 and a second bracket part 63. The insert 13 is placed between the first bracket part 59 and the second bracket part 61 and may additionally be surrounded by a connecting part 65 connecting the first bracket part 61 and the second bracket part 63. Due to its position, geometry and material, the insert 13 effectively changes the dynamic behavior of the bracket 59 and thus improves the dynamic response to obtain better acoustic and NVH behavior.

[0136] The insert 13 may completely or partially fill the cavity 9 between the first bracket part 61 and the second bracket part 63. If the insert 13 only partially fills the cavity 9, for example, it may be possible to position the insert 13 in the mold by means of a projection on the insert 13 or a pin in the mold during the injection of the polymer melt for the first bracket part 61 and the second bracket part 63, and the remaining hollow part is filled by the corresponding part of the mold.

[0137] Depending on the oscillation, it may be advantageous to use and position the insert 13 in different directions according to a given main load of shear, tension and / or compression. The insert 13, preferably made of polymer foam, itself can be the main component in which energy is dissipated or operates as a regulator or an enabler so that the rest of the entire plastic part behaves in a desired manner.

[0138] Examples of plastic parts with improved NVH that can be manufactured by the method of the present invention are, for example, engine mounts for electric engines or for combustion engines, as Figure 12 and Figure 13 exemplarily shown.

[0139] The engine mount 67 for an electric engine comprises a space for accommodating an electric motor. For vibration damping, the engine mount 67 has a cavity 9 which is filled with an insert 13 made of foam. The cavity 9 filled with the insert 13 has the additional advantage that the engine mount 67 can be designed with a substantially constant wall thickness. Furthermore, the heavy plastic part forms the outer skin of the engine mount 67 and the loads are therefore transmitted more efficiently. Due to the necessary demoulding direction in injection molding, there is no need to design complex geometries of moving metal tool segments or to compromise on some performance aspects.

[0140] This effect becomes evident when torsional loads have to be transferred. A closed cross section subjected to torsion is always advantageous compared to an open segment. Normally, open segments have to be used in standard injection molding due to demoulding. When designing the parts using the inventive manufacturing method for overmolded inserts, closed segments can easily be used.

[0141] like Figure 13 The engine mount 71 for a combustion engine shown by way of example comprises a cavity 9 which is filled with an insert 13 and damps the vibrations of the combustion engine. Furthermore, for mounting the combustion engine, the engine mount 71 comprises a blind hole 73 incorporating a metal insert 75 for accommodating a fixing element of the combustion engine.

[0142] The method according to the invention also allows the production of plastic parts with foamed inserts to avoid disassembly in the event of a crash. Examples of such plastic parts are Figure 14 Shown in cross-sectional view.

[0143] The component that is not disassembled in the event of a collision and that reduces the number of small particles that penetrate into the environment after a collision comprises an outer part 77, which usually forms an outer wall and can be a visible part of a component, such as the outer skin of a bumper. The insert is fixed to the inner surface 79 of the outer part 77 and is therefore not visible after installation. The tight connection of the insert 13 and the outer part 77 holds the parts together in the event of an impact or collision. In addition, the insert 13 (especially when made of foam) enhances the bending of the outer part 77, thereby increasing the overall strength.

[0144] The use of an insert 13 surrounded by a hollow body 11 has the additional advantage that additional parts can be incorporated into the plastic component 1. For this purpose, Figure 16 As shown, a cavity 81 is formed in the insert 13 .

[0145] Additional parts not shown here are placed in the cavity 81 of the insert 13. Depending on the shape of the parts to be incorporated into the insert 13 and thus the shape of the cavity 81, it may be necessary to use inserts made of several pieces, which are assembled before placing the insert 13 made of several pieces in the mold for overmolding with polymer melt.

[0146] Parts to be incorporated into the cavity 81 are, for example, sensors, electrical devices, electronic circuit boards, metal reinforcements, inserts with or without threads, or any other parts known to those skilled in the art that can be incorporated into the plastic part 1.

[0147] If the additional parts (such as wires or rods used as electrical conductors) are soft and may deform during the injection molding process, the insert 13 can be used to fix the additional parts. Figure 16 An example of the insert 13 with a conductor 83 as a bonded soft part is shown.

[0148] Soft additional parts (such as the conductor 83) can be embedded in the foam of the insert by placing them in the tool for manufacturing the foamed insert before filling the components for forming the foam into the tool. On the other hand, the insert can also be first formed from foam, and then the soft insert can be placed in the foam after the foaming process.

[0149] After the insert with the additional parts is completed, the insert 13 is placed in the mold, and polymer melt is injected into the gap between the insert 13 and the inner wall of the mold.

[0150] In addition to using the hollow insert 13, in order to reduce the weight of the plastic part 1, the cavity in the insert 13 can also be filled with a lighter material (such as foam with a lower density).

[0151] On the other hand, if a higher-quality plastic part 1 is required (such as to provide higher stiffness, to improve noise, vibration, harshness) or if the plastic part 1 should have electrical, magnetic, or other functions, a dense and heavier material can be incorporated into the insert 13. The material incorporated into the insert 13 depends on the intended function and can be, for example, a conductive material or a magnetic material, such as a metal. In addition, in order to increase stability or weight, a polymer with a higher density than the material of the foam of the insert can also be incorporated into the insert 13, for example, bonded to a non-foam polymer.

[0152] Figure 17 An example of the plastic part 1 with the insert 13 having additional different materials 85 is shown.

Claims

1. A method for manufacturing a plastic part (1), the plastic part comprising an insert (13) surrounded by a hollow body (11), the method comprising: (a) placing the insert (13) into a mold such that a gap is formed between the insert (13) and the mold; (b) feeding a polymer melt into the gap, thereby forming the hollow body (11) surrounding the insert (13); (c) removing the plastic part (1) from the mold; wherein in order to form the gap, a protrusion (17) is formed on the insert (13), or wherein the mold comprises pins (25) on which the insert is placed, or wherein the gap is a recess in the insert (13).

2. The method according to claim 1, wherein the insert (13) is made of foam or is a second hollow body.

3. The method according to claim 2, wherein the second hollow body comprises columns or walls (45) that connect opposite inner walls of the second hollow body for strengthening the second hollow body.

4. The method according to any one of claims 1 to 3, wherein the insert (13) is made of metal, ceramic or polymer.

5. The method according to any one of claims 1 to 3, wherein the insert (13) is made of a polymeric material that forms a homogeneous connection with the polymer fed into the gap.

6. The method according to any one of claims 1 to 5, wherein the polymer forming the insert (13) and the polymer forming the hollow body (11) are polyamide, polyethylene or polypropylene.

7. The method according to any one of claims 1 to 6, wherein the polymer inserted into the gap is the same as the polymer forming the insert (13).

8. The method according to any one of claims 1 to 7, wherein the protrusion (17) is made of the same material as the insert (13).

9. The method according to any one of claims 1 to 8, wherein the protrusion (17) is integrally formed on the insert (13).

10. The method according to any one of claims 1 to 7, wherein the protrusion (17) is a separate part and is connected to the insert (13).

11. The method according to any one of claims 1 to 10, wherein the protrusion (17) has a conical shape, and the protrusion (17) is connected to the insert in such a way that the tip of the protrusion (17) contacts the mold when the insert (13) is placed in the mold.

12. The method according to any one of claims 1 to 7, wherein the pins (25) of the mold are retractable, and during feeding of the polymer melt, the pins (25) preferably retract continuously as the polymer melt reaches them.

13. The method according to any one of claims 1 to 12, wherein the insert (13) has a structured surface (27).

14. The method according to any one of claims 1 to 13, wherein the surface of the insert (13) comprises recesses (29) such that during feeding of the polymer melt, the polymer melt fills the recesses (29), which preferably have a form such that reinforcing ribs are formed on the inner surface of the hollow body (11).

15. The method according to any one of claims 1 to 14, wherein an opening (31) is formed in the insert (13), which is filled by the polymer melt during the feeding step, thereby forming a connecting rod between two opposite inner surfaces of the hollow body (11).

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