DE102010006407A1 - Method for manufacturing plastic construction part, involves injecting plastic component into cavity of injection molding tool and injecting another plastic component into cavity - Google Patents

Abstract

The method involves injecting plastic component (4) into a cavity (6) of an injection molding tool (8) and injecting another plastic component into the cavity, where the latter plastic component is provided with a blowing agent. The method involves magnifying cavity before solidifying the latter plastic component, where an internal tool pressure is lowered and the latter plastic component expands by the blowing agent driven into the supplementary cavity. Independent claims are also included for the following: (1) a plastic construction part for use in hybrid construction; and (2) an injection molding tool.

Description

The invention relates to a method for producing a plastic component and an injection mold for carrying out said method.

In the case of plastic structural components, such as those used in modern vehicles, great importance is placed on high rigidity on the one hand, whereby the plastic components may at the same time have only a low weight. For this purpose, so-called multi-component injection molding has been developed in the past, in which various plastics are injected into an injection mold. Some plastics can be provided with propellants, so that they can be foamed. The foaming of a plastic component by a blowing agent reduces the weight of the entire component with the same volume. However, conventional foaming processes do not allow components with high functional integration, i. H. Integration of functional components in the foam body, with a good surface quality and minimal weight represent. It is particularly troublesome that components integrated in the foam can be marked off or on the surface of the component. Further, in such prior art components, it has not yet been possible to produce the component to be foamed with a very low density. This is due to the fact that the foam in the region of the component surface is very dense due to the production process, or no longer has any pores at all. The pores typically disintegrate into the forming tool during production in the skin layer to form a dense plastic layer. Thicker boundary layers result in higher component weights.

For this on the documents DE 10 2008 022 246 A1 and on the DE 199 44 352 C2 directed.

The object of the invention is to produce a multi-component injection-molded component which, compared to the prior art, has a lower weight, allows greater functional integration and has high surface quality.

The solution of the problem consists in a method for producing a plastic component according to claim 1 and in an injection mold for carrying out this method according to claim. 9

The inventive method according to claim 1 for the production of a plastic component comprises the following steps:
First, a first plastic component is injected into a cavity (also called mold cavity) of an injection molding tool. Subsequently, a further, second plastic component is injected into the same cavity. The second plastic component is provided with a blowing agent, by which the second plastic component is foamed and expanded to a foam structure. The propellant may be a propellant that acts chemically or physically.

In a next step, the cavity of the injection mold is even before the solidification of the second plastic component, or the two plastic components, increased, a cavity pressure is lowered and the second plastic component driven by the propellant, can expand into the additionally available cavity. The enlargement of the cavity can be done either by a targeted opening of the injection mold or it can be provided a slide, which increases portions of the cavity by moving the Kavitätswand. The opening of the injection mold can be done, inter alia, by an embossing stroke, or a negative embossing stroke, the injection molding machine.

In a preferred embodiment, the first plastic component is not completely solidified during injection and foaming of the second plastic component, so that the second plastic component can enter into a solid material connection with the first component at least during foaming. On the other hand, the strength of the first not completely solidified plastic component is already so high that the foaming of the second component can not push them aside.

In this case, a hybrid component is produced, which is composed of unfoamed surface layer and foamed core region. In this case, the unfoamed plastic on a very smooth and uninfluenced by the foamed area surface. The foamed and the unfoamed area are very firmly connected to each other in a cohesive connection.

The thickness of the non-foamed and smooth plastic layer can be comparatively thin compared to the thickness of the entire hybrid component. The non-foamed plastic layer can wrap the entire foamed core area or close to the outside. But it is also possible that the foamed plastic partially forms the component surface. Particularly preferably, at least the field of view of the component is completed in its intended arrangement with the non-foamed plastic layer.

It is of particular importance that almost the entire core area is interspersed with the pores of the foam and only a very thin boundary layer at the transition from the foamed core area to the first plastic component has almost no pores. The thickness of the non-pervaded edge layer of the foamed plastic component at the transition to the unfoamed plastic component is preferably below 10% of the total thickness of the foamed plastic component. Particularly preferably, the thickness is less than 2 mm.

By selectively enlarging the cavity during injection or after injection of the second plastic component, the second plastic component, driven by the blowing agent, expand more than is possible in a closed, volume unchanged cavity of an injection mold.

It is also possible to inject the foamed plastic in a further process step by further opening the tool and filling the new cavity with additional plastic. In principle, here again the first plastic component, foamable plastic or other plastic material can be used.

The inventive method, in particular a lower density of the entire plastic component is achieved.

Furthermore, it is also possible to integrate several functional components in the component during the production process. For this purpose, the functional components are introduced into the injection mold as inserts. The functional components can be completely, partially or not at all arranged in the foamed plastic. They can also partially form the surface of the component. The functional components may be, for example, metallic joining or fastening parts or reinforcing ribs.

In a further embodiment of the invention, a temperature of the injection mold during the injection of the first plastic component to a temperature which is at most 20 ° C below the melting point of the first plastic component. This means that the injection molding process per se takes place at tool temperatures that are relatively close to the melting point of the plastic component used, in contrast to conventional mold temperatures for compact injection molding. As a result, the wall thicknesses, which are generated by the first plastic component can be kept as low as possible, which in turn leads to a lower component density.

It may be expedient to temper special regions of the injection mold more warmly than others in order to allow subsequent flow of the first plastic component in enlarging the cavity in these regions. As a result, for example, it is possible to achieve a full-surface lining of the injection molding tool with the first plastic component, or to achieve complete envelopment of the foamed plastic component with the first plastic component.

In this case, the temperature of the injection molding tool is understood to be the temperature in the immediate vicinity of tempering channels in the tool. This temperature, in turn, can be realized relatively accurately by setting a temperature control medium on a tempering device. The actual temperature at individual sections of the tool surface in the area of the cavity differs from the set tempering temperature and depends on the geometry of the cavity surface (implicitly of the component geometry) and the time available for heat compensation (process cycle).

In a further embodiment of the invention, the first plastic component is injected in a partial filling in the cavity. The second plastic component is injected in a second step after the first plastic component. This is a sequential injection method. In principle, it is also possible to inject both components together through a split spray nozzle during a process step into the cavity.

It has also been found to be advantageous to apply different temperatures to the injection mold during the entire injection molding cycle. In this case, the temperature is maintained by a temperature at a relatively high temperature during injection, as mentioned above, possibly about 20 degrees below the melting point of the first plastic component. When removing the molded plastic component, the temperature is lowered by cooling. By this measure, on the one hand, the thin wall thickness of the first plastic component can be achieved and, secondly, the shaping of the plastic component can be optimized.

In a further advantageous embodiment of the invention, a gate of the injection molding tool is located at a region of the cavity which is filled with the first plastic component. As a result, sink marks or other surface defects in the area of the foamed second plastic component are avoided. Furthermore, it may be expedient to have a separate To provide temperature control for a portion of the injection mold, in which the gate is arranged.

Also, to increase the surface quality of the finished plastic component, it may be expedient to cool in areas of the injection mold in which component edges of the plastic component, by insulation slower than other areas of the plastic component. As a result, the plastic of the first plastic component can flow when enlarging the cavity and an uninterrupted component edge is formed.

It is also expedient that component edges or component surfaces, which are visible in the intended installation state of the plastic component, are represented by the first plastic component. The first plastic component can be a fiber-reinforced polypropylene in an advantageous embodiment of the invention.

Both plastic components can be used both fiber reinforced, as well as without fiber reinforcement.

As already stated, the ejection of the plastic component at a relatively high temperature is a sensitive process step, which is why ejectors that are as large as possible are used or so-called air ejectors are used.

Another object of the invention is an injection molding tool for performing a method according to any one of the preceding claims. The injection molding tool according to claim 9 is characterized in that a slide is provided by its movement during injection of the second plastic component, an enlargement of the cavity he follows.

Further advantageous embodiments and further features of the invention will be explained in more detail with reference to the following description of the figures. Showing:

1 a schematic cross-sectional view of an injection mold with a cavity and an insulation at specific edge regions of the cavity,

2 another injection mold with a cavity and a slide,

3 the injection mold 2 with the slider moved down to increase the cavity,

4 Section of a cut surface through a plastic component ( 2 ) with unfoamed plastic component ( 4 ), foamed plastic component ( 10 ) and component edge ( 7 )

5 Section of a cut surface through a plastic component ( 2 ) with unfoamed plastic component ( 4 ), foamed plastic component ( 10 ), Pores ( 11 ) and non-pervious edge layer ( 9 )

6 a plastic component with unfoamed plastic component ( 4 ), Functional component ( 5 ) and foamed plastic component ( 10 ).

In the following, we will first discuss the procedure in general terms. This is exemplified by the 1 and 2 be explained.

In an injection mold 8th in which a plastic component 2 is produced and that a cavity 6 which is also referred to as a mold cavity, first becomes a first plastic component 4 injected. In this plastic component 4 this is a fiber-reinforced polypropylene in this embodiment. This polypropylene has a melting point of 167 ° C. The temperature of the injection mold 8th lies during the injection process of the first plastic component 4 only slightly below the melting point of the polypropylene. It has been found that, for example, a temperature in a range of 20 ° C below the melting point is suitable as a tool temperature. Strictly speaking, the temperature of the tool is that temperature which is provided by a tempering system not shown in the figures. In this case, by Temperierungskanäle the injection mold 8th a Temperierungsmedium, usually an oil, pumped, which has the appropriate temperature. Subareas of the injection mold 8th , in particular the surface of the cavity 6 have temperatures that are close to this tempering temperature, but can not be identical to this.

In the first injection process described thus becomes the first plastic component 4 in a partial filling in the cavity 6 of the injection mold 8th filled. This will, as in 2 schematically represented by small dots, a dense surface layer on a Kavitätsinnenwand by the first plastic component 4 educated. This is the functional layer, which is also the visible surface in the later installation position of the plastic component to be produced 2 represents. By filling the cavity 6 with the first plastic component 4 However, this is not quite filled.

In the second step, a further injection of a second plastic component takes place 10 . which in turn is provided with a chemical or physical blowing agent which generates gas at the applied mold temperature, through which the second plastic component 10 is foamed. In conventional prior art processes, the second plastic component remains 10 however, only the mold cavity available through the first plastic component 4 not yet filled.

In the present method, however, a further method step is used, in which the cavity 6 is selectively increased. It stands, as in 3 it can be seen, now an additional cavity 12 to disposal. This extra cavity 12 can on the one hand by a targeted opening of the tool on a parting plane 20 respectively. This will cause the internal pressure of the injection mold 8th So in the cavity 6 , lowered and there is a further expansion of the second plastic component 10 ,

On the other hand, as in 3 is shown, this enlargement of the cavity 6 around the additional cavity 12 through a slider 18 respectively. The expanding and foaming second plastic component 10 is in 3 represented by larger bubbles.

The enlargement of the cavity 6 around the additional cavity 12 occurs either during the injection of the second plastic component 10 or shortly after their injection.

It should be noted that in principle even more plastic layers can be injected during the injection molding process, which are not shown separately here.

The foamed foam structure is also called the core of the plastic component 2 denotes a density of the core structure of less than 0.8 g / cm ³ , preferably less than 0.2 g / cm ³ , achieved by the described method.

By the already described relatively high mold temperature during injection, in particular the first plastic component 4 It may happen that the cycle times for the production of the plastic component 2 are relatively high. Therefore, it is expedient to provide a variable mold temperature. In this case, the tempering system during the injection of the first plastic component 4 in the injection mold 8th a relatively high temperature applied, already during the injection of the second plastic component or at least after the injection of the second plastic component 10 becomes the temperature of the injection mold 8th lowered by a defined temperature. Subsequently, the injection mold 8th opened and the finished plastic component 2 formed.

When molding the still relatively warm plastic component 2 It is expedient to use with respect to its component geometry relatively large-area ejector.

On the other hand, it may also be appropriate, by special blowing devices in the injection mold 8th the plastic component 2 by demolding (air ejector).

The gate marks of the plastic component 2 are sensitive areas in the described method. It should be avoided that sink marks or marks occur in the gate area. For this purpose, special measures are advantageous. As low has been found, the gate, so the sprue in the compact component area, by the first plastic component 4 is formed to lay. Optionally, it is also expedient to set a targeted temperature in the region of the gate, which is tuned with the other process parameters.

In particular in the area of the component edges, surface defects or geometry errors can arise due to unfavorable cooling conditions. The unfavorable cooling conditions arise because areas with component edges, in which the surface-volume ratio of the plastic component 2 is greater than in volume areas of the plastic component 2 to cool faster than the volume areas inside the plastic part 2 lie. Therefore, it may be appropriate to the plastic component 2 designed so that critical component zones are laid in a non-visible area.

On the other hand, it may be appropriate to isolations 16 to provide, as it is in 1 is sketched, in particular the component edges 7 the later plastic component 2 Insulate them so that they do not cool down so quickly. Thus, all component areas of the plastic component cool 2 - supported by the targeted temperature control of the injection mold 8th in itself - as evenly as possible. As a result, very high quality surfaces, even in the component edges 14 , scored.

The 4 and 5 represent sections of the plastic components produced by the method described. The figures show cutting surfaces through the component. In 4 is the foamed core portion of the component left, top and bottom completely closed by the first plastic components. The component edge ( 7 ) is thicker, or wider than the upper and lower bounding material layers of the first plastic component ( 4 ). The first Plastic passes directly and cohesively into the second plastic.

In 5 is a boundary layer ( 9 ) recognizable from the plastic of the foamed plastic component ( 10 ) and is characterized by having virtually no pores ( 11 ) reveals more. The core area, however, is uniform and with high density of deep black pores ( 11 ) interspersed. The foamed plastic ( 10 ) appears roughly structured by its fiber reinforcement.

6 1 schematically shows a cross section through a variant of a plastic component, in which the foamed plastic component (FIG. 10 ) only partially with the unfoamed plastic component ( 4 ) is completed. The functional component ( 5 ) may be, for example, a tubular reinforcing strut, a metallic flange or a cable channel.

LIST OF REFERENCE NUMBERS

2

Plastic component

4

first plastic component

5

functional component

6

cavity

7

component edge

8th

injection mold

9

boundary layer

10

second plastic component

11

pore

12

additional cavity

16

insulation

18

pusher

20

parting plane

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008022246 A1 [0003]
• DE 19944352 C2 [0003]

Claims (10)

Method for producing a plastic component ( 2 ), comprising the following steps: injection of a first plastic component ( 4 ) into a cavity ( 6 ) of an injection molding tool ( 8th ); Injection of a second plastic component ( 10 ) into the cavity ( 6 ), wherein the second plastic component ( 10 ) is provided with a propellant; - enlargement of the cavity ( 6 ) before solidification of the second plastic component ( 10 ), wherein a cavity pressure is lowered and the second plastic component ( 10 ) driven by the propellant in the additionally available cavity ( 12 ) expands. A method according to claim 1, characterized in that a temperature of the injection mold ( 8th ) during injection of the first plastic component ( 4 ) at most 20 ° C below the melting point of the first plastic component ( 4 ) is selected. Method according to claim 1 or 2, characterized in that by the first plastic component ( 4 ) only a partial filling of the cavity ( 6 ) is made. Method according to one of the preceding claims, characterized in that in a further process step after foaming of the plastic component ( 10 ) with propellant, the cavity ( 6 ) is enlarged and injected another plastic component. Method according to one of the preceding claims, characterized in that a separate temperature control for a region of the injection molding tool ( 8th ) is made, on which the gates or the component edges are arranged. Plastic component ( 2 ) in hybrid construction comprising a non-foamed plastic component ( 4 ) and arranged in the core region of the component foamed plastic component ( 10 ), characterized in that the unfoamed plastic component ( 4 ) the foamed plastic component ( 10 ) at least on the intended installation state of the plastic component ( 2 ) completely completes the visible surface. Plastic component according to claim 6, characterized in that the core region of the plastic component ( 2 ) made of foamed plastic component ( 10 ) completely from the unfoamed plastic component ( 4 ) is completed. Plastic component according to claim 6 or 7, characterized in that the thickness of the non-pervaded edge layer ( 9 ) of the foamed plastic component ( 10 ) at the transition to the unfoamed plastic component ( 4 ) is below 10% of the thickness of this plastic component and / or below 2 mm. Plastic component according to claim 6, 7 or 8, characterized in that the unfoamed and / or the foamed plastic component is fiber-reinforced. Injection mold for carrying out a method according to one of claims 1 to 5, characterized in that this a slide ( 18 ) by its movement during or after the injection of the second plastic component ( 10 ) an enlargement of the cavity ( 6 ) and / or that the injection mold an insulation ( 16 ) of areas in which component edges ( 7 ) of the plastic component to be molded ( 2 ) are present.

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