Method for producing a sandwich composite component with pressed two or three-dimensional shape and such a composite component

Abstract

Described is a method for producing a sandwich composite component and a sandwich composite component with a pressed two- or three-dimensional shape, having at least one structured core layer made of thermoplastic material which has two opposite core layer surfaces, each bonded to a thermoplastic cover layer. A sandwich composite component is also described.

Claims

1-21: (canceled)

22. A method for producing a sandwich composite component with a pressed two- or three-dimensional shape, having at least one structured core layer made of a thermoplastic material which has two opposite core layer surfaces, and with thermoplastic cover layers cohesively bonded with each of the two core layer surfaces, comprising: heating a flatly shaped sandwich semi-finished product which includes the at least one structured core layer with the cover layers bonded to each side of the core layer surfaces thereof by infrared radiation heating, so that the structured core layer has a temperature below a melting temperature associated with the thermoplastic material of the core layer, and at least parts of the two cover layers have a temperature equal to or above a melting temperature associated with the thermoplastic material of the cover layers; transferring the heated, flat sandwich semi-finished product into a pressing tool comprising at least two pressing mold halves which are mounted in a linearly movable manner relative to each other along a spatial direction with at least one first pressing mold half including at least two pressing mold segments which are mounted in a linearly movable manner relative to each other along the spatial direction so at least regions of the sandwich semi-finished product come into surface contact with at least one of the two pressing mold halves; moving the pressing mold halves towards each other along the spatial direction so that at least some regions of the sandwich semi-finished product are brought into surface contact with the at least two pressing mold halves so that a first pressing mold segment runs ahead of the respective other pressing mold segment of the first pressing mold half in the direction of movement, a region thereof coming into contact with one of the two cover surfaces, and together with the other pressing mold half pre-presses the sandwich semi-finished product in two or three dimensions, until a first minimum spacing corresponding to a greatest thickness assignable to the pre-pressed sandwich semi-finished product is reached between the first pressing mold segment and the other pressing mold half; stabilizing the pre-shaped sandwich semi-finished product within the regions contacted by at least one of the first pressing mold segment and the other pressing mold half by a contact cooling process; and deflecting the other pressing mold segment of the first pressing mold half in the spatial direction onto the other pressing mold half, while the first pressing mold segment rests relative to the other pressing mold half, and contacting some regions of the pre-pressed sandwich semi-finished product and completing molding until a second minimum spacing is reached between the other pressing mold segment and the other pressing mold half, with spacing being selected to be smaller than the first minimum spacing to obtain the sandwich composite component pressed into a two- or three-dimensional shape.

23. A method according to claim 22, wherein: the flat sandwich semi-finished product has one of a honeycombed or cylindrically structured core layer.

24. A method according to claim 23, wherein: the cover layers are each a thermoplastic material, from which the core layer is also produced, and to which structure-reinforcing fiber components have also been added.

25. A method according to claim 24, wherein: the structure-reinforcing fiber components are endless fibers, wherein individual fibers pass completely through the sandwich semi-finished product once and are arranged approximately and unidirectionally in at least one layer or on a woven structure.

26. A method according to claim 22, wherein: the heating of the flat sandwich semi-finished product is performed contactlessly by an infrared radiation heating process.

27. A method according to claim 22, the contacting of the sandwich semi-finished product with at least one pressing mold half and the first pressing mold segment is supported by application of a negative pressure to contact regions between the sandwich semi-finished product and the pressing mold halves, and the sandwich semi-finished product is cooled in the contact region with the pressing mold tool by a contact cooling process.

28. A method according to claim 22, wherein: the movement of the two pressing mold halves and the two- or three-dimensional pressing associated therewith toward each other to obtain the pre-pressed sandwich semi-finished product which is carried out with the structured core layer being retained in a pre-shaped sandwich semi-finished product which preserves the structure.

29. A method according to claim 22, wherein: the movement towards each other of the two pressing mold halves and the two- or three-dimensional pre-pressing to obtain the pre-pressed sandwich semi-finished product constitutes a first pressing process step which is followed by a second pressing process step, in which the respective other pressing mold segment of the first pressing mold half is deflected in spatial direction onto the other pressing mold half, and the pre-pressed sandwich semi-finished product is contacted directly or indirectly adjacent in a region excluded from the pre-pressing, and the pre-pressed sandwich semi-finished product is compacted in this region by the application of a pressing force to a thickness which corresponds to the second minimum spacing.

30. A method according to claim 22, wherein: the second minimum spacing is selected so that the thermoplastic material of the cover layers and the core layer is formed of a compacted material composite in a region of the sandwich composite component which was finally molded by the pressing mold segment.

31. A method according to claim 22, wherein: the deflection of the respective the other pressing mold segment of the first pressing mold half is performed so that a geometrically definable three-dimensional transition contour is formed with either a constant or an inclined transition between a region of the pre-pressed sandwich semi-finished product created with the first pressing mold segment and a region of the sandwich composite component which was finally molded by respective other pressing mold segment.

32. A method according to claim 29, wherein: after the first pressing process step the pre-shaped sandwich semi-finished product is cooled inside regions contacted with at least one of the first pressing mold segment and the other pressing mold half.

33. A method according to claim 32, wherein: during the cooling and a solidification of the thermoplastic material resulting therefrom, the pre-shaped sandwich semi-finished product is fixed on the contact regions to the first pressing mold segment and to the other pressing mold half by means of negative pressure.

34. A method according to claim 22, wherein: the stabilization is carried out free from molding forces acting on the pre-shaped sandwich semi-finished product for a period of at least 1 second.

35. A sandwich composite component with a pressed two- or three-dimensional shape, which has at least one structured core layer made of thermoplastic material with two opposite core layer surfaces, and with thermoplastic cover layers which are each bonded with the two core layer surfaces, wherein at least one three-dimensional transition contour is provided, which connects a first region of the sandwich composite component, in which the structured core layer separates the two cover layers from each other, with an adjacent second region of the sandwich composite component has a single part, in which the structured core layer and both cover layers are compacted and welded with a material bond to form a multilayer laminate.

36. A sandwich composite component according to claim 35, wherein: the three-dimensional transition contour is positioned on at least one of an edge, along a peripheral circumferential border of the sandwich composite component and an inside the sandwich composite component so that the first region at least partially encloses the second region.

37. A sandwich composite component according to claim 35, wherein: cover layers are each a thermoplastic material, from which the thermoplastic material core layer is also made, and to which additional structure-reinforcing fiber components are added.

38. A sandwich composite component according to claim 37, wherein: the structure-reinforcing fiber components include endless fibers, with individual fibers passing completely through the sandwich semi-finished product once and are arranged unidirectionally at least in one layer or are present in a woven structure.

39. A sandwich composite component according to claim 35, wherein: the structured core layer of the flat sandwich semi-finished product has structure walls with opposite structure wall edges bonded with one of the two cover layers; and a weld bead of thermoplastic material is on each side of each of the structure wall edges bonded to a cover layer, which is bonded integrally both with the cover layer and with the structure wall.

40. A sandwich composite component according to claim 39; wherein: in regions of the sandwich composite component with a pressed two- or three-dimensional shape where a shape has been changed, the weld bead of thermoplastic material accumulates which has a shear force induced deformation extending unidirectionally with an adjacent cover layer.

41. A sandwich composite component according to claim 39, wherein: in regions of decreasing structure wall height of the sandwich composite component having a pressed two- or three-dimensional shape where shape has been changed, the structure walls have curved sections adjacent to structure wall edges.

42. A method of use of the sandwich composite component according to claim 22 as a flat, load-bearing component or a load-bearing structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In the following text, the invention will be described for exemplary purposes without limitation of the general inventive thought, on the basis of exemplary embodiments, with reference to the drawing. In the drawing:

[0034] FIGS. 1a)-c) Show sequence images illustrating the shaping of a sandwich composite component with structure-receiving core layer and fluid-tight component periphery according to the invention;

[0035] FIG. 2 Represents a sandwich semi-finished product with flat construction;

[0036] FIG. 3a) Shows a longitudinal section through a finished sandwich composite component, and

[0037] FIGS. 3b)-g) Show detail views of longitudinal sections.

DETAILED DESCRIPTION OF THE INVENTION

[0038] The method according to the invention enables production of a two- or three-dimensionally shaped sandwich composite component 4 in two consecutive process steps using a pressing tool 1 from a flat sandwich semi-finished product 4′ with a structured core layer 8 and two cover layers 9 which cover it on both sides within a cycle time from one to a few minutes. The two consecutive process steps for the shaping are initiated during a linear tool closing movement. The linear closing movement is performed with the aid of a vertically or horizontally closing pressing tool which will be explained below with reference to FIGS. 1a) to c).

[0039] FIGS. 1a) to c) each illustrate a cross-sectional representation through a pressing tool 1 in chronologically successive method situations. The pressing tool 1 has two preferably metal pressing mould halves 2, 3, which in the closed state enclose a cavity, inside which the sandwich composite component 4 to be produced is ultimately formed as illustrated in FIG. 1c).

[0040] The pressing tool 1 is equipped with two deflectable pressing mold halves 2, 3 which are linearly movable along a spatial direction R, preferably vertically as shown, or horizontally, of which the upper, first pressing mould half 2 as shown comprises two pressing mould segments 5, 6 which are mounted in a linearly movable manner relative to each other along the spatial direction R. The second pressing mold half 3 which is positioned opposite the first pressing mould half 2 and is constructed as a single part in this case.

[0041] In the starting situation represented in FIG. 1a), the first pressing mold segment 6 is deflected relative to the respective other pressing mold segment 5 by a distance Δx and protrudes downwards with respect to the respective other pressing mold segment 5. Such a configuration enables a two-stage pressing process with interim stabilization of the initially reshaped geometry.

[0042] Vacuum cups, which are preferably made from air-permeable materials such as porous aluminium, metal foams or sintered metals, are integrated in the pressing mold segments 5, 6 and on the surface of the lower pressing mold half 3, and are connected to a corresponding negative pressure source provided on the tool side.

[0043] In the situation shown in FIG. 1a), a flat sandwich semi-finished product 4′ is lying on the surface of the lower pressing mold half 3.

[0044] FIG. 2 represents a flat sandwich semi-finished product 4′ of such kind, which has a structured core layer 8 and two cover layers 9, 10 are each made from the same thermoplastic material. The core layer 8 has a structured construction in the form of honeycombs or cylinders arranged side by side. The cover layers 9, 10 contain endless fibers for the purpose of reinforcement, wherein the individual fibers ideally pass entirely through the semi-finished product once and are arranged unidirectionally in at least one layer or are provided in the form of a woven structure.

[0045] The sandwich semi-finished product 4′ represented in FIG. 2 is brought to a certain thermal state before or while it is placed in the pressing tool 1. The defining feature this thermal state is that the thermoplastic material of the cover layers 9 and 10 reaches temperatures above its melting temperature, and the thermoplastic material of the core layer 8 reaches temperatures equal to or below its melting temperature. Heating of the sandwich semi-finished product 4′ preferably takes place immediately before the shaping with the aid of infrared radiation warming applied to both sides.

[0046] The two-stage pressing process begins with a closing movement of the pressing tool 1, in which the first pressing mould half 2 is deflected relative to the second pressing mould half 3, in the present case vertically downwards. The sandwich semi-finished product 4′ is attached at least to the underside thereof before and during the shaping by vacuum cups.

[0047] FIG. 1b) represents the situation in which the upper pressing mold half 2 has been lowered vertically, and the originally flat sandwich semi-finished product 4′ has been pre-shaped by contact with the leading first pressing mold segment 6 with the application of pressing force. Pre-pressing of the sandwich semi-finished product 4′ was carried out while preserving the structure of the core layer 8. This shaping process for obtaining the pre-shaped sandwich semi-finished product 4″ illustrated in FIG. 1b ends when a minimum spacing 11 between pre-shaped sandwich semi-finished product 4″ is reached. The first minimum spacing 11 corresponds to a maximum layer thickness of the pre-pressed sandwich semi-finished product 4′. Preferably, all contact regions close to the subsequent transition contour between the cover layers 9, 10 of the sandwich semi-finished product 4′ and the surfaces of the first pressing mold segment 6 as well as the second pressing mold half 3 are supplied with negative pressure during the pre-pressing, with the result that the effect of the negative pressure on the contact regions between sandwich semi-finished product 4″ and pressing mold tool 1 serves to prevent at least one of core failure and undesirable core height reduction of the core layer 8.

[0048] In the time before a second, subsequent pressing process step is carried out, the pre-shaped sandwich semi-finished product 4″ is stored and cooled inside the pressing mould segment 6 which is in contact with the sandwich semi-finished product 4″ and the pressing mould half 3 without any further molding forces that would modify the shape of the pre-shaped sandwich semi-finished product 4″. The sandwich semi-finished product is cooled by contact cooling through contact on both sides of the pre-pressed sandwich semi-finished product 4″ on the opposite contact regions. This brings about partial to total solidification of the thermoplastic material of the contacted cover layers at the previously melted cover layer surface regions. This targeted solidification and the adhesion of the sandwich semi-finished product 4″ to the leading pressing mold segment 6 is preferably due to negative pressure having the effect of stabilizing these sandwich regions. The stabilization reduces or entirely prevents undesirable deformations on the pre-pressed sandwich semi-finished product in the subsequent, second pressing process step. The duration of this stabilizing state is at least 1 second.

[0049] In a second pressing process step, the previously uncontacted sub-regions of the sandwich semi-finished product 4″ are reshaped and pressed by deflection of the respective other pressing mold segment 5 against the opposite second pressing mold half 3, while the first pressing mold segment 6 rests relative to the second pressing mold half 3. As the closing movement progresses, the sandwich core is compressed in the regions laterally outside the first pressing mold segment 6 until a second minimum spacing 14 is reached between the respective other pressing mold segment 5 and the second pressing mold half 2, thus forming a compacted laminate 12. These compacted component regions 12 may be molded to extend around the periphery of at least one of the component and in the interior of the sandwich component depending on the component shape and the design of the pressing mold segments (5, 6).

[0050] The transition 13 between the structurally preserved core layer regions and the peripheral compacted laminate region 12 may have a steep-flanked or be constant depending on the construction and shape of the pressing mold segments.

[0051] The pressing method explained here may be combined with other conventional processing steps according to the pressing tool used or even the injection molding machine used, such as for example a subsequent edge trimming with punches or further functionalization by injection molding.

[0052] The sandwich composite components produced with the method according to the invention may include both flat and curved sandwich regions with defined core height. The core height depends in each case on the gap width inside the cavity as illustrated in FIG. 1c).

[0053] The transition 13 between regions in which the sandwich composite component 4 is shaped with a core layer whose structure is preserved and the adjacent compacted laminate regions 12 may be shaped as a chamfer, for example.

[0054] After the pressing and before the final molding of the component, the shaped sandwich component dwells in the pressing tool for a few seconds longer in order to cool down. In this time, the thermoplastic matrix of all cover layer regions solidifies, and the component temperature generally cools down. In this situation, the remaining negative pressure may be used advantageously to reduce air inclusions and improve the surface quality.

[0055] The compacted laminate which extends circumferentially around the periphery of the component, may seal the interior of the sandwich against penetration by air and fluids, and at the same time may serve as a joint. It is also possible to create compact laminate regions as with corresponding transitions inside the finished sandwich composite component 4.

[0056] FIG. 3a) shows a longitudinal section through a finished sandwich composite component 4, which besides a peripheral compacting 12, in which both cover layers 9, 10 are pressed jointly with the core layer 8 to form an integral or practically integral material composite, contains the transition region B1, an unshaped region B2 adjacent thereto, and subsequently a 2D- and 3D-shaped region B3.

[0057] The transition region B1 is illustrated in detail in FIGS. 3b) and 3c), of which FIG. 3b) is a photographic detail representation showing both cover layers 9, 10 and the structure walls of the core layer 8 arranged between them, and FIG. 3c) shows a schematic partial longitudinal section in which the respective lower half of the longitudinal section is shown in the transition region B1. FIGS. 3d) and e) show corresponding illustrations for the unshaped region B2, and FIGS. 3f) and g) for the shaped region B3.

[0058] The preferably honeycomb-like core layer 8 includes structure walls 15, whose opposite structure wall edges are each cohesively joined to one of the two cover layers 9, 10 wherein a material accumulation 16 of thermoplastic material in similar to a weld bead is provided on each side of the structure wall borders, each of which is joined to a cover layer 9, 10, the accumulation being bonded integrally with both the cover layer 9, 10 and the structure wall 15.

[0059] In transition region B1, the structure wall height becomes lower, starting from the unshaped structure wall height h in region B2 and progressing downwards, forming a complete film structure with the cover layers 9, 10 in the edge region of the compacting 12. Due to the height reduction caused by pressing forces and the maximum temperatures in the structure walls 15 close to the cover layers 9, 10 and the cover layers 9, 10 themselves, which are hotter than the melting temperature of the thermoplastic matrix, the structure walls 15 begin to deform, at least in the region close to the cover layers 9, 10 and themselves melt into the weld-bead like material accumulation. This results in a stronger weld-bead like material accumulation with further reduction of the structure wall height h. Moreover, shearing forces lead to a deformation of the material accumulations 16 tangentially to the cover layers 9, 10 relative to the structure wall 15 in each case. Foot-like deformations 16′ are formed, from which the structure walls 15 extend.

[0060] The structure walls 15 extend substantially linearly between the two cover layers 9, 10 within the unshaped sandwich composite component region B2. Weld bead-like material accumulations 16 of thermoplastic material are located on both sides of each of their structure wall borders, and are each bonded monolithically in these regions with both the cover layers 9, 10 and the structure walls 15.

[0061] Inside the region B3 of the sandwich composite component 4 with a pressed two- or three-dimensional shape, the weld bead-like material accumulations 16 of thermoplastic material exhibit a shear force-induced deformation which extends unidirectionally with the adjacent cover layer such that an increasing material accumulation 16′ forms on one side of the structure wall borders depending on the curvature, as may be seen particularly clearly in the detail illustrations of FIGS. 3f) and g). Ideally, the structure walls 15 are largely unshaped, that is straight, in this region B3 as well. However, deviating structure wall deformations may occur, caused by excessively steep curvatures of the sandwich composite component 4, too rapid reduction of the structure wall height h in regions B2 and B3 and/or by the temperature being too low in the cover layers 9,10, which then results in blockage of the sliding motion from the cover layers 9,10 on the structure walls 15 and therefore results less in shear-induced deformation of the weld-bead like material accumulations 16, but instead to a shear-induced deformation of the structure walls 15 themselves. Insufficient high cover layer temperatures are attributable to inadequate thermal energy input during the heat treatment with at least one of IR radiation and excessively long transfer time from the time of completion of the IR radiation heat treatment to the start of the first pressing process step.

LIST OF REFERENCE NUMERALS

[0062] 1 Pressing tool [0063] 2 First pressing mould half [0064] 3 Other pressing mould half [0065] 4 Sandwich composite component [0066] 4′ Flat sandwich semi-finished product [0067] 4″ Pre-pressed sandwich semi-finished product [0068] 5 Respective other pressing mould segment [0069] 6 First pressing mould segment [0070] 7 Flat sandwich semi-finished product [0071] 8 Core layer [0072] 9, 10 Cover layer [0073] 11 First minimum spacing [0074] 12 Compacted layer composite [0075] 13 Transition [0076] 14 Second minimum spacing [0077] 15 Structure wall [0078] 16 Material accumulation [0079] 16′ Single-sided material accumulation [0080] B1 Transition region [0081] B2 Unshaped region [0082] B3 Shaped region