DE102011006819A1 - Producing a three dimensional contoured sandwich structure including first thermoplastic covering layer, second thermoplastic covering layer and core material, comprises e.g. machining or carrying out separate processing of core material - Google Patents

Abstract

Producing a three dimensional contoured sandwich structure consisting of a first thermoplastic covering layer, a second thermoplastic covering layer and a core material with a honeycomb structure, arranged between the covering layers, comprises (a) machining and/or carrying out separate processing of the core material until the desired three-dimensional contour is obtained, (b) sequentially or parallely cutting the covering layers of the three-dimensional contour, and (c) applying thermoplastic covering layers onto the processed core material and cohesively connecting by hot pressing. Producing a three dimensional contoured sandwich structure consisting of a first thermoplastic covering layer, a second thermoplastic covering layer and a core material with a honeycomb structure, arranged between the covering layers, comprises (a) machining and/or carrying out separate processing of the core material (contouring process) until the desired three-dimensional contour is obtained, (b) sequentially or parallely cutting the covering layers of the three-dimensional contour obtained in the step (a), and (c) applying thermoplastic covering layers onto the processed core material and cohesively connecting by hot pressing.

Description

The present invention relates to a method for producing a three-dimensionally contoured sandwich structure of thermoplastic fiber-reinforced cover layers and thermoplastic honeycomb core material.

Sandwich structures consist of at least two cover layers and a core material lying between these cover layers. They are characterized on the one hand by their high bending and twisting stiffness and on the other hand by the low structural weight. The core material has cavity structures and is therefore particularly light. Frequently, the cavity structures have a uniform orientation perpendicular to the cover layers. The core material often consists of foamed components. However, bundles of tubular slats are used which have a round or hexagonal cross-section. There are a variety of other embodiments. For the cover layers, a variety of materials is used. In addition to continuous fiber reinforced plastics and metals, wood and paper are also used.

Continuous fiber-reinforced sandwich structures are mainly produced in the form of fiber-plastic composites (FRP) with thermosetting matrix. Currently there are essentially two technologies for the production of continuous fiber reinforced sandwich structures, which are realized by a thermoset and a planar thermoplastic process. A disadvantage of the classical thermoset structures are the time-consuming curing processes of the matrix systems and the associated long cycle times, which stand in the way of efficient mass-produced production. Furthermore, these impact-sensitive thermoset FRP components are only chemically or endothermically decomposable at the end of their product life cycle and emit climate-damaging CO ₂ . For highly complex components, it is also necessary to attach various load introduction and connection elements. For this purpose, currently classical thermoset sandwich structures are encapsulated in a further process step with a thermoplastic, wherein the connection between thermosetting insert and thermoplastic usually can only be realized on the basis of a complex form-fitting geometry.

It is therefore of particular interest to use thermoplastics instead of the thermoset matrix systems. Currently, honeycomb core thermoplastic sandwich structures are predominantly used for planar components such as floor panels. For many applications, however, a three-dimensional contouring of the sandwich structures is required, which is currently realized by mechanical forming processes. However, this can lead to damage to the core and the applied cover layers, which has a negative impact on the strength, rigidity and durability of the sandwich structures.

In the following, when the term "equal" is used, it is identical to the one ("equal"), d. H. chemically identical thermoplastic types. On the other hand ("similar") also those which, for example, contain additional modifiers, so that, for example, the thermoplastic matrix material can be extruded as a film or spun as a yarn.

The DE 196 04 613 A1 refers to the production of sandwich structures whose core and outer layers are made of the same or similar thermoplastic and to the mechanical deformation of the sandwich in the hot forming process. By forming the honeycomb structure is compressed, ie the length of the honeycomb is shortened, and there is a function of the degree of compression of a thermoplastic collection, which causes adverse local density increase of the sandwich structure.

The DE 196 04 611 also includes the production of contoured thermoplastic sandwich structures from the same or similar thermoplastic. The processing is again carried out by a forming process, in comparison to DE 196 04 613 not the finished sandwich structure, but the individual components, cover shells and core, are brought separately in their final form. The core consists of parallel tubes that slide along each other during hot forming, thus maintaining their parallel alignment without structural interference. Subsequently, the formed components are connected to form a sandwich component.

The development of manufacturing processes for the continuous production of planar thermoplastic sandwich structures or thermoplastic honeycomb cores has created the basis for high volume applications. The further processing of these structures to three-dimensionally contoured components by means of forming processes, however, involves various difficulties. Due to the introduced heat there is a risk that the core will collapse during the forming process. In general, it is disadvantageous in mechanical deformation that the compression of the core causes damage to the load-bearing honeycomb structure and, moreover, results in a local accumulation of thermoplastic. In addition, the heating of the matrix material of the cover layers in combination with the honeycomb structure results in a strongly heterogeneous one Surface image, which is called telegraphing or golf ball effect.

The aim is therefore to present a method for the production of three-dimensionally contoured thermoplastic sandwich structures, in which damage to the components during manufacture is avoided and a component surface quality is achieved, which meets the requirements in the field of vision, eg. In the automotive interior.

According to the invention, this object is achieved by the method according to claim 1. Advantageous embodiments are disclosed in the dependent claims.

The method provides that the three-dimensionally contoured sandwich structure, consisting of a first thermoplastic cover layer, a second thermoplastic cover layer and a honeycomb core material arranged between the cover layers, is produced by machining and / or separating the core material until it reaches the desired one three-dimensional contour takes place. Before, after or parallel to this processing of the core material, the cutting of the cover layers takes place. Thereafter, the cover layers are applied to the processed core material and a cohesive connection between the core material and cover layers by the action of pressure and heat (heat conduction, heat radiation), such as produced by hot pressing. Subsequently, the component is overmolded with an identical or similar plastic melt. This melt can be reinforced both by short fibers which are preferably up to 1 mm long and by long fibers which preferably have a length of between 1 mm and 50 mm.

The core material used is preferably a thermoplastic material with a honeycomb structure. Polypropylene PP, polycarbonate PC, polyvinyl chloride PVC, polyamide PA, polyethylene terephthalate PET, polybutylene terephthalate PBT, polyether ether ketone PEEK, polyetherimide PEI, polyphenylene sulfide PPS and / or biopolymers such as cellulose acetate and polylactic acid (PLA) are preferably used as the plastic.

In a preferred embodiment, the outer layers consist of individual layers and preferably have textile reinforcing structures that are surrounded with a thermoplastic matrix material, for example as a film or yarn. The reinforcing structures preferably consist of glass fiber material, aramid fiber material, carbon fiber material, basalt fiber material, ceramic fiber material and / or of natural fiber material, such as flax fiber material and hemp fiber material. Preferably, the plastic of the core material and the matrix material are the same or the same. In a preferred embodiment, reinforcing structures made of different materials are used.

By machining and / or separating the honeycomb core, prior to joining with the cover layers, it is advantageously possible to produce thermoplastic, three-dimensionally contoured sandwich structures (t3S) in the so-called t3S process. The three-dimensional processing of the honeycomb core advantageously allows a load-oriented contouring. Preferably, in this way, the core height is reduced in lightly loaded areas and thus further minimizes the weight of the component. It is advantageous that no further mechanical deformation of the core is required by the prior contouring of the honeycomb core and damage to the load-bearing honeycomb structure or a local thermoplastic accumulation of the molten core material is avoided.

Only after the honeycomb core has been processed is the integral joining of the core with the thermoplastic outer layers to the sandwich structure by means of hot pressing. In this way, wrinkling in the material of the cover layers is advantageously prevented and good optical properties of the visible surfaces of the cover layers are achieved. In the case of the thermoplastic outer layers, preference is given to various semi-finished products available on the market. In this case, different types of tissue are preferably used in addition to various combinations of matrix materials and reinforcing fibers. Depending on the required mechanical properties and depending on availability, the respective suitable semifinished product is preferably used.

• • Zellformen (Tubuswaben, Hexagonalwaben),
• • Thermoplasten (Polypropylen, Polycarbonat, etc.) und
• • Zellweiten sowie -höhen

zur Verfügung. Während der Konturierung werden vorteilhaft zusätzlich Aussparungen für die anschließende Integration von Krafteinleitungs- Lasteinleitungs- oder Verbindungselementen, sogenannte Inserts, erzeugt.In the following, the process of the t3S process for producing contoured thermoplastic sandwich structures is explained in more detail. At the beginning of the process chain, a separate, serial or parallel processing of the honeycomb core and the outer layers takes place. For the load-oriented contouring of the core, a machining and / or separating machining is preferably provided which preferably takes place by means of Computer Aided Design (CAD) data on computerized numerical control (CNC) systems. As core material are preferably honeycomb cores with different

• Cell shapes (tube honeycombs, hexagonal honeycombs),
• • thermoplastics (polypropylene, polycarbonate, etc.) and
• • Cell widths and heights

to disposal. During the contouring, recesses are additionally advantageously produced for the subsequent integration of force introduction load introduction or connection elements, so-called inserts.

The inserts are inserted in the recesses after contouring. The fixation of the inserts within the honeycomb structure is preferably carried out by the introduction of extrudate, which is preferably obtained by the melting of the material obtained in the contouring process. In this way, recycling already takes place within the process (s. ).

Preferably at the same time as contouring the core, the blanking of the cover layers takes place in accordance with the component geometry. Depending on the complexity, this can be done manually or preferably computer-aided. After the processing of the individual components, these are joined by means of hot pressing process to form a sandwich structure. For this purpose, the fiber-reinforced cover layers are preferably laid down selectively, in accordance with the load, so that the fiber course of the cover layer material is oriented in the direction of force flow.

For hot pressing, the first cover layer is preferably inserted together with the core material, which has been contoured three-dimensionally in a preceding process step, and with the second cover layer is inserted into a multi-part pressing tool which has the desired contour. In the subsequent pressing process, the shape of the sandwich material is formed by the shaping contour of the pressing tool. Here, the lower mold of the sandwich construction is molded by the contour of the lower mold. At the same time, the upper contour is imaged by a second, upper mold half during the pressing process. Both the upper and the lower pressing tool are heated to a temperature above the melting temperature of the thermoplastic material, so that a material-locking connection between the material of the outer layers and the core takes place.

If inserts have been inserted, they are preferably exposed after the pressing process by means of machining and / or cutting operations.

In a preferred embodiment, the cover layers consist of individual layers, which are connected to one another during the hot pressing process, and the layer closest to the core material is bonded to the core material. By the optional insertion of a honeycomb material and the matrix of the cover layer material same or similar film of small thickness can be reduced on the one hand, the telegraphing effect and on the other hand, the connection of the individual components of the sandwich structure can be improved.

In a particularly preferred embodiment, the additional insertion of a decorative film as the uppermost layer of the cover layer, a high-quality, so-called. Class A surface is achieved. Class-A reflects the special character or the high quality of the surface. The term is used in connection with surfaces that are visible to the user, and therefore must have a special quality. In further preferred embodiments, further surface designs are possible by various other films such as color, mirror, profile, luminescent or luminescent films.

For the production of complex components, it is also necessary that various force introduction, load introduction and connection elements are integrated into the components. By using thermoplastic cover layers, this can preferably be realized by means of extrusion coating of the structure. As a spray material is preferably the same or a similar thermoplastic used, as in the thermoplastic outer layers. This offers the advantage that a cohesive connection between the insert (t3S structure) and the injected plastic melt can be achieved. For this reason, the geometry of the insert or the core material need not be adjusted with respect to the realization of a positive connection.

The extension of the process (t3S-PI) by the injection molding process (t3S-PII) is preferably as follows. The three-dimensionally contoured sandwich structures are inserted into an injection mold after the pressing process. The positioning of the insert within the tool preferably takes place via the already integrated inserts. In this way, advantageously in the injection molding process, a functional integration, for. B. in the form of clips, as well as a post-processing high-quality Class-A surface are produced. The possibility of customizable surface design can by applying the in-mold labeling process, here the printed decorative film is inserted into the injection mold and materially joined to the sandwich component or by the in-mold decoration process, this is the decor of a carrier film applied to the component can be realized.

embodiment

The following application example describes the manufacture of a dashboard made of fiber-reinforced thermoplastics and structured core material. The listed process parameters refer to the processing of cover layers with polypropylene matrix as well as a core which also consists of polypropylene (PP). The core is in its macroscopic Structure of tubular lamellae, which have a hexagonal cross-section, together.

In a first step, the cutting takes place with regard to the required length and width of the core material, the thickness being constant in the longitudinal and transverse directions. For this purpose, a cutter knife is used. Subsequently, the cut sheet semifinished product is placed in a mold, similar to a frame, and removed by means of hot wire method core material according to the desired contour. For this purpose, the wire (diameter 0.5 mm) is heated by applying a voltage of 12 V and a current of 3 A and moved by means of a guide on the frame. Through this step, the core receives the desired three-dimensional contouring. The realization of local recesses is implemented by the method of the hot wire method. The removed material is fed to the material cycle and reused as an extrudate for fixing the force introduction elements.

The cutting of the continuous fiber-reinforced thermoplastic cover layers takes place parallel to the contouring of the core. As cover layers, the semifinished product Tepex dynalite 104-Glass / PP from Bond-Laminates GmbH is used for this application example. This material is based on polypropylene as a matrix material with roving glass as a fiber at a fiber volume content of 45%.

Processing temperature: 190 ° C The required geometry for the cutting of the 1 mm thick cover layers results, on the one hand, from the component geometry to be realized and, on the other hand, from the core height in the forming areas. This is taken into account, so that the core material is completely enclosed by the cover layer material. The lamination of the lateral edges or the completion of the honeycomb is done by bending the overhanging cover layer material during the pressing process.

The insertion of the components in the pressing tool, which depicts the later component form, takes place manually. Already preconsolidated cover layers, such. For example, Tepex dynalite 104 and Twintex P PP with a thickness of 0.5 mm have a high inherent rigidity compared to the non-consolidated cover layers (eg Twintex T PP). For semi-finished semi-finished products a more complex handling is necessary in order not to move the reinforcing fibers from the defined position. However, due to the sluggish properties, unconsolidated topcoats can be draped into the lower die mold so that they rest against the tool wall. During positioning, it must be ensured that the fiber orientation is load-bearing.

The storage of the components is done here individually, but with regard to the mass production suitability for simultaneous storage appropriate. In this case, a sandwich of the machined cover layer and honeycomb core components and optional decorative films is then inserted as a package in the lower press tool and pressed into a dashboard.

The components are processed into a component in sandwich construction using the following process parameters. Basically, the variables temperature and heating time influence each other. The higher the tempering of the tool wall, the shorter the pressing time is. Due to the melting point, a processing temperature between 160 ° C and 200 ° C is required for the cohesive connection of the PP components. At a mold temperature of 175 ° C, for example, the pressing time is about 20 seconds. The combination of temperature, time and pressure ensures that the thermoplastic matrix material of the cover layers melts and bonds cohesively with both the honeycomb core and with an optionally integrable decorative film. During closing of the tool core and cover layers are melted and pressed together under the force of 100 kN.

• • Massetemperatur 200°C bis 280°C
• • Werkzeugwandtemperatur 20°C bis 80°C
• • Schneckenstaudruck 50 bar bis 200 bar
• • Schneckenumfangsgeschwindigkeit 1,2 m/Sek.

Within this process, the pressed component acts as a depositor and is hereinafter referred to as such. The transfer of the insert from the press or from a stack of stock in the injection mold is done manually. Within the injection mold of the insert is positioned by means of pins and realized in this way a defined distance between the tool wall and the insert. This space is filled during the injection of the plastic melt. For an optimal cohesive connection between the insert and the plastic melt, the use of the same or similar plastic in melt and layers is appropriate. Furthermore, with regard to the connection between the melt and the insert, preheating of the insert to 100 ° C. is beneficial. Analogous to the pressing process, the different parameters also influence one another within the injection molding process. Basically, the information recommended by the manufacturers for processing is oriented. For PP these are:

• • Melt temperature 200 ° C to 280 ° C
• • Tool wall temperature 20 ° C to 80 ° C
• • Screw back pressure 50 bar to 200 bar
• • Worm speed 1.2 m / sec.

In addition to the machine parameters, a modification of the material properties by means of fillers is also carried out. For improved flow properties or the realization of long flow paths, the modifier maleic anhydride (MSA) in a dosage of 2 vol .-% to add. Post-processing of the component is usually not required after removal from the mold.

characters

1 shows the flow of the t3S PI process.

2 shows the flow of the t3S PII process following the t3S PI process.

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 19604613 A1 [0006]
• DE 19604611 [0007]
• DE 19604613 [0007]

Claims (10)

Method for producing a three-dimensionally contoured sandwich structure, consisting of a first thermoplastic cover layer, a second thermoplastic cover layer and a honeycomb core material arranged between the cover layers, characterized by the steps: a. cutting and / or separating machining of the core material (contouring process) until reaching the desired three-dimensional contour, b. sequential or parallel to step a. Cutting the cover layers, c. Applying the thermoplastic cover layers on the processed core material and cohesive connection by hot pressing. A method according to claim 1, characterized in that during step a. recesses are produced according to claim 1, are then inserted and fixed in the inserts. A method according to claim 2, characterized in that the inserts are fixed by the introduction of extrudate, which is obtained by the melting of the material obtained in the contouring process. Method according to one of the preceding claims, characterized in that for carrying out the step c. the following sub-steps are executed: c1. Inserting the first cover layer into a contoured pressing tool, c2. Inserting the core material in the contoured pressing tool on the first cover layer c3. Insert the second cover layer onto the core material c4. Hot pressing the first cover layer, the core material and the second cover layer until cohesive connections between the first cover layer and core material and the second cover layer and core material are produced. A method according to claim 4, characterized in that the sub-step c4. a further sub-step c5. Exposing the inserts, follows. Method according to one of the preceding claims, characterized in that the first and / or the second cover layer consists of a plurality of individual layers, which are interconnected during the hot pressing. A method according to claim 6, characterized in that are achieved by the additional insertion of films such as decorative, color, mirror, profile, luminescent or phosphors as the top layer of the cover layer, high-quality, so-called. Class A surfaces with Oberflächendekoren , A method according to claim 4 or 5, characterized in that the inserts are encapsulated for functional extension, such as clips. A method according to claim 8, characterized in that the material for encapsulating the depositors is the same or similar thermoplastic material as in the thermoplastic outer layers. A method according to claim 9, characterized in that the material for encapsulating the deposit further contains short or long fiber material.

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