Method For Producing a Moldable, Thermoplastic, Continuous Fiber Reinforced Composite Structure, Moldable Composite Structure, and Device For Producing Same

Abstract

The invention is characterized by a semifinished composite structure product with the at least two layers, of which the at least one layer, in which the continuous fibers are contained, is heated such that the matrix of thermoplastic material is heated within at least one first surface region to or above a melting temperature that can be assigned to the thermoplastic material, and the matrix of thermoplastic material is kept to a temperature below the melting temperature within a second surface region directly adjoining the first surface region. The semifinished composite structure product is heated in this way so that the moldable thermoplastic, continuous fiber-reinforced composite structure in which the continuous fibers within the first surface region are movable relative to each other and those within the second surface region are spatially fixed relative to each other.

Claims

1-19. (canceled)

20. A method for producing a moldable thermoplastic, continuous fiber-reinforced composite structure that has at least two layers with continuous fibers embedded in a matrix of the thermoplastic material in at least one layer thereof, comprising: providing a semifinished composite structure product with the at least two layers, heating the at least one layer of the semifinished composite structure product in which the continuous fibers are embedded so that the matrix of thermoplastic material within at least one first surface region is heated to or above a melting temperature of thermoplastic material and maintaining the matrix of thermoplastic material within a second surface region directly adjoining the first surface region at a temperature below the melting temperature; and providing the semifinished composite structure product, being heated in the before manner, as the moldable thermoplastic, continuous fiber-reinforced composite structure containing the continuous fibers are moved relative to each other within the at least one first surface region and spatially fixed relative to each other within the second surface region.

21. A method for producing a moldable thermoplastic, fiber-reinforced composite structure having at least two layers with continuous fibers embedded in a matrix of thermoplastic material in at least one layer thereof, comprising: providing a semifinished composite structure product with the at least two layers. heating the at least one layer of the semifinished composite structure product in which the continuous fibers are contained so that the matrix of thermoplastic material within at least a first surface region is heated to a first temperature T1 above a melting temperature of the thermoplastic material and heating the matrix of thermoplastic material within a second surface region directly adjoining the first surface region to a second temperature T2 which is at least equal to the melting temperature of the thermoplastic matrix and is lower than the first temperature T1; and providing the semifinished composite structure product, being heated in the before manner, as the moldable thermoplastic, continuous fiber-reinforced composite structure which continuous fibers within the first surface region are more readily movable than the continuous fibers within the second surface region.

22. The method according to claim 20, comprising: a flat solid multilayer structure or a flat solid sandwich structure with at least one core layer structure at least partly filled with air or gas, and at least one cover layer in which the continuous fibers are embedded in a matrix of thermoplastic material.

23. The method according to claim 21, comprising: a flat compact, solid multilayer structure or a flat solid sandwich structure with at least one core layer structure at least partly filled with air or gas, with at least one cover layer in which the continuous fibers are embedded in the matrix of thermoplastic material.

24. The method according to claim 20, comprising: heating of the composite structure product with at least one infrared radiation field so that the infrared radiation field is directed homogeneously towards the at least one layer in which the continuous fibers are embedded in the matrix of thermoplastic material.

25. The method according to claim 21, comprising: heating of the composite structure product with at least one infrared radiation field so that the infrared radiation field is directed homogeneously towards the at least one layer in which the continuous fibers are embedded in the matrix of thermoplastic material.

26. The method according to claim 20, comprising: heating at least the layer of the matrix of the thermoplastic composite structure product containing the continuous fibers homogeneously to a preheat temperature below the melting temperature, and heating only the at least first surface region of the composite structure product above the melting temperature.

27. The method according to claim 21, wherein: heating at least the layer of the composite structure containing the continuous fibers homogeneously to the second temperature T2 and heating only the at least first surface region of the composite structure to temperature T1.

28. The method according to claim 26, comprising: heating the composite structure t with at least one infrared radiation field while introducing an element between an infrared radiation source emitting the at least one infrared radiation field and at least a second surface region so that at least one second surface region is shielded from the at least one infrared radiation field.

29. The method according to claim 28, comprising: using a screen or mask as the element to at least one of absorbing and reflecting the infrared radiation.

30. The method according to claim 27, comprising: generating a forced air flow at least intermittently between the at least one infrared radiation source and the composite structure at least one of before, during, and after heating of the composite structure.

31. The method according to claim 20, comprising: ending heating of the composite structure product as soon as the matrix of thermoplastic material within the first surface region is melted uniformly at a predefined temperature.

32. The method according to claim 21, wherein: ending heating of the semifinished composite structure as soon as the matrix of thermoplastic material within the first surface region is melted uniformly at the first temperature T1.

33. A moldable thermoplastic, continuous fiber-reinforced composite structure including at least two layers, in which continuous fibers are embedded in a matrix of thermoplastic material, comprising: melting the matrix of the thermoplastic material within at least a first surface region so that the continuous fibers within the first surface region are moveable relative to each other; and the matrix of the thermoplastic material is solid within a second surface region adjacent to the first surface region and the continuous fibers within the second surface region are spatially fixed relative to each other.

34. A moldable thermoplastic, continuous fiber-reinforced composite structure that has at least two layers, in which continuous fibers are embedded in a matrix of thermoplastic material, comprising: melting the matrix of the thermoplastic material within at least a first surface region so that the molten thermoplastic material within the first surface region has a first viscosity; and heating the matrix of the thermoplastic material within a second surface region adjoining the first surface region so that the molten thermoplastic material within the second surface region has a second viscosity which is greater than the first viscosity.

35. The composite structure according to claim 34, wherein: the at least one layer in which the continuous fibers are embedded in the matrix of thermoplastic material includes a cover layer and the at least one layer is part of a multilayer laminate or a sandwich structure.

36. A use of the composite structure according to claim 35, comprising shaping the composite structure after the structure cools.

37. A use of the composite structure according to claim 36, wherein: the shaping operation is a thermoforming process, in which the composite structure is shaped by at least one shaping tool.

38. A use of the composite structure according to claim 36, wherein: shaping of the composite structure is a thermally assisted joining process for attaching at least one thermoplastic component to the at least one first surface region of the composite structure.

39. A device for producing the fiber-reinforced composite structure according to claim 33, comprising: at least one radiation source generating a homogeneous infrared radiation field which during heating of the fiber is positioned at least one of above or below a flat, horizontally mounted support grid, and the infrared radiation field is directed toward the support grid with a top side supporting the composite structure, and with at least one screen positioned between the at least one radiation source and the support which is movable relative to the support in a direction parallel to the top side.

40. The device according to claim 39, wherein: the screen is arranged with a vertical separation from the support grid at a distance ranging from 0.5 mm to 3 cm between the screen and the composite structure supported on the top side of the support grid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The invention will now be described for exemplary purposes without limitation of the general inventive thought on the basis of embodiments thereof and with reference to the drawing. In the drawing:

[0042] FIG. 1 is a schematic representation of a semifinished composite structure product;

[0043] FIGS. 2a, b and c show the sequence of process steps for heating and softening the semifinished composite structure product according to the invention; and

[0044] FIG. 3 is a representation of a preferred variant of a moldable, thermoplastic continuous fiber-reinforced composite structure.

DETAILED DESCRIPTION OF THE INVENTION

[0045] FIG. 1 shows a schematic longitudinal cross-section through a flat semifinished composite structure product 1, which is constructed as a multilayer structure having three layers, with a top cover layer 2 made from a thermoplastic material in which continuous fibers 3 are embedded. A core layer 4 is located immediately adjacent to the top cover layer 3, and is constructed either from further continuous fiber-reinforced thermoplastic individual layers or a structured thermoplastic layer, in the form of a honeycomb structure for example. A bottom thermoplastic cover layer 5 is located immediately below the core layer 4; continuous fibers 3 are also embedded in the thermoplastic matrix of the bottom cover layer. The thermoplastic materials of at least the top and bottom cover layers 2, 5 are preferably identical. The flat semifinished composite structure product initially has a solid consistency.

[0046] In order to heat the respective top and bottom cover layers 2, 5, the semifinished composite structure product 1 illustrated in FIG. 1 is positioned between two infrared radiation fields 6, which are each emitted by a plurality of radiation sources 7 mounted on support structures 8, as shown in FIG. 2a. Both infrared radiation fields 6 have a homogeneous radiation intensity, with which the semifinished composite structure product 1, mounted on a support grid structure 13, is irradiated uniformly. The support grid structure 13 preferably is a metal grating which is transparent to infrared radiation but has no or negligibly weak infrared shading properties.

[0047] The surfaces of the top and bottom cover layers 2, 5 of the semifinished composite structure product 1 are irradiated completely and uniformly in a preheating process until both cover layers 2, 5 reach a temperature just below the melting point of the thermoplastic material. The melting temperature is defined as the crystallite melting point for semicrystalline thermoplastics and as the glass transition temperature for amorphous thermoplastics.

[0048] After reaching a predetermined target temperature just below the melting temperature, typically 3 to 20 K below the melting temperature, screens 9, preferably made from a metallic material, are placed close to the surface of the cover layers 2, 5 between the IR radiation sources 7 and the semifinished composite structure product 1, preferably each at a distance between 0.5 and 3 cm above or below the surface of the cover layer. The screens shield the top and bottom cover layers 2, 5 from infrared radiation 6 for the purpose of further heating of the respective second surface region 10, with the result that further heat input by the infrared radiation 6 in these respective second surface regions is prevented. The screens 9 are preferably arranged to be movable relative to the support grid structure 13, so the screens 9 are each slidable above or below the top or bottom cover layer 2, 5 respectively for purposes of shielding them from infrared radiation.

[0049] In the subsequent phase of the process, the regions that are not shielded by the screens 9, referred to as the first surface regions 11, are heated further until the thermoplastic material within the first surface regions 11 of the top and bottom cover layers 2, 5 is completely and uniformly molten.

[0050] Since the coefficient of thermal conductivity of the thermoplastic material in the top and bottom cover layers 2, 5 is only small, and due to the colder air temperature in the atmosphere surrounding the semifinished composite structure product 1—compared with the temperature of the semifinished composite structure product—little or only a negligible quantity of heat is input into the respective shielded second surface regions 10. This enables a highly effective isolation of the respective solid thermoplastic matrix within the second surface regions 10 from the respective, molten first surface regions 11 which are directly adjacent thereto. The melting process according to the invention can be interrupted or ended instantaneously as shown in FIG. 2c to prevent undesirable overheating and the associated material degradations within the softened thermoplastic material matrix.

[0051] The shape, number and size of each of the second surface regions 10 that remain in the solid aggregate state may be selected individually using individually configured and arranged screens 9.

[0052] As the outcome, a moldable thermoplastic continuous fiber-reinforced composite structure 12 as illustrated in FIG. 3 is obtained, whose top and bottom cover layers 2, 5 have first surface regions 11, in which the continuous fibers 3 embedded in the locally melted thermoplastic matrix are movable relative to each other, whereas within the second surface regions 10 immediately adjoining the first surface regions 11 the continuous fibers 3 embedded in the respective solid thermoplastic matrix are joined fixedly. The fixed attachment of the continuous fibers within the second surface region 10 is ensures that the continuous fibers 3 within the first surface regions 11 can be re-orientated correctly in the course of subsequent reshaping process. The stabilization of the continuous fibers with each of the second surface regions 10 makes it possible to obtain more complex component geometries when producing continuous fiber-reinforced thermoplastic components with reversibly definable material properties.

[0053] The moldable, thermoplastic, continuous fiber-reinforced composite structure 12 can be removed from the infrared heater with the aid of a suitable gripping and transporting apparatus, which grips and handles the composite structure 12 only by the unmelted second surface regions 10, and these leave no handling marks of any kind on the surfaces of the respective second surface regions 10.

[0054] The screens 9 explained previously lend themselves to use in the case of the alternative method variants, in which the second surface regions 10 are also heated to a temperature T2 above the melting temperature but below the temperature T1 prevailing in the respective first surface regions 11. Contrary to the previous explanations, both cover layers 2, 5 are preheated completely and uniformly to temperature T1, preferably just above the melting point of the thermoplastic material. The further heating is carried out as described earlier, using screens 9 that shield the respective second surface regions 10 contactlessly.

LIST OF REFERENCE NUMERALS

[0055] 1 Semifinished composite structure product

[0056] 2 Top cover layer

[0057] 3 Continuous fibers

[0058] 4 Core layer

[0059] 5 Bottom cover layer

[0060] 6 Infrared radiation field

[0061] 7 Infrared radiation source

[0062] 8 Support structure

[0063] 9 Screen

[0064] 10 Second surface region

[0065] 11 First surface region

[0066] 12 Composite structure

[0067] 13 Support grid structure