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

Abstract

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

Claims

1. A method for producing a sandwich composite load-bearing component product comprising a pressed shape having a structured core with two opposed core surfaces and cover layers each respectively being cohesively bonded to one of the two opposed core surfaces, and the structured core and the cover layers are made of the same thermoplastic material, the method comprising steps in order as presented below: contactlessly heating with infrared radiation a flat semi-finished sandwich product including the structured core and the cover layers being respectively joined to the two opposed core surfaces of the structured core, the structured core during the heating attaining a temperature below a melting temperature of the thermoplastic material, while at least parts of the opposed cover layers have a temperature equal to or above the melting temperature; transferring the heated flat semi-finished sandwich product into a pressing tool comprising a first pressing mold halve and a second pressing mold halve, each of the pressing mold halves being linearly movable relative to each other in a spatial direction, the first pressing mold halve including at least two pressing molding segments, each of the pressing molding segments being movable linearly in the spatial direction so that at least regions of the semi-finished sandwich product move into surface contact with at least one of the first and the second pressing mold halves; moving the first and the second pressing mold halves in the spatial direction towards each other to cause at least one region of the semi-finished sandwich product to make surface contact with at least one of the first and the second pressing mold halves so that one of the at least two pressing mold segments moves spatially ahead of the other of the at least two pressing mold segments to cause the at least one region to come into contact with one of the two cover layers, together with the first and the second pressing mold halves pressing the semi-finished sandwich product in two or three dimensions to reach a first minimum thickness corresponding to a greatest thickness of the pre-pressed semi-finished sandwich product between the one of the at least two pressing mold segments and the second pressing mold halve; stabilizing the pre-pressed semi-finished sandwich product in the at least one region contacted by the one of the at least two pressing mold segments and the second pressing mold halve by cooling the one of the at least two pressing mold segments by contact with the second pressing mold halve; deflecting the other of the at least two pressing mold segments in the spatial direction to contact the second pressing mold halve, while the one of the at least two pressing mold segments rests relative to the second pressing mold halve; and contacting some regions of the pre-pressed semi-finished sandwich product with the other of the at least two pressing mold segments and completing pressing of the semi-finished sandwich product by moving the other of the at least two pressing mold segments in the spatial direction until a second minimum spacing is reached between the other of the at least two pressing mold segments and the second mold halve in the spatial direction to produce the second minimum spacing of the semi-finished sandwich product which is smaller than the first minimum spacing to produce the sandwich composite component product which has been pressed in two or three dimensions; and wherein the structured core comprises side by side honeycombs or cylinders, and wherein height of walls of the structured core is reduced by melting into a weld bead which accumulates in a region of the sandwich composite component product, where the structured core and the cover layers are cohesively bonded together.

2. A method according to claim 1, comprising: retaining the semi-finished sandwich product in at least one of the two pressing mold halves and one of the at least two pressing mold segments by application of a negative pressure to cause suction in at least one of the regions between the semi-finished sandwich product and the pressing mold halves, and cooling the semi-finished sandwich product in at least one region by contact with the second pressing mold halve.

3. A method according to claim 1, comprising: moving the first and the second pressing mold halves in the spatial direction towards each other to finish the pre-pressed semi-finished sandwich product and then moving the other of the at least two pressing mold segments in the spatial direction toward the second pressing mold halve, and contacting the pre-pressed semi-finished sandwich product adjacent to at least one region which is not pre-pressed, and then compacting the pre-pressed semi-finished sandwich product in the at least one region by application of a pressing force to reduce a thickness to the second minimum spacing.

4. A method according to claim 3, comprising: providing endless fibers passing completely through the semi-finished sandwich product which are arranged unidirectionally in at least one layer or in a woven structure.

5. A method according to claim 1, comprising: a composite material within a region which is finally molded by one of the pressing mold halves.

6. A method according to claim 1, comprising: moving the at least two pressing mold segments to form a three-dimensional transition contour having either a constant or an inclined transition between at least one region of the pre-pressed semi-finished sandwich product and another region of the sandwich composite component product which is finally molded.

7. A method according to claim 6, comprising: during the stabilization, the pre-pressed semi-finished sandwich product is cooled by contact between one of the at least two pressing mold segments and the second pressing mold halve.

8. A method according to claim 1, wherein: cooling of the semi-finished sandwich product provides a solidification of the thermoplastic material while the pre-pressed semi-finished sandwich product is retained by negative pressure in regions of contact with the one of the at least two pressing mold segments and the second of the pressing mold halves.

9. A method according to claim 1, comprising: stabilizing the pre-pressed semi-finished sandwich product without molding forces acting on the pre-pressed semi-finished sandwich product for a period of at least 1 second.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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:

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

(3) FIG. 2 Represents a sandwich semi-finished product with a flat construction;

(4) FIG. 3a) Shows a longitudinal section through a finished sandwich composite component; and

(5) FIGS. 3b)-g) Show detail views of longitudinal sections.

DETAILED DESCRIPTION OF THE INVENTION

(6) 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 of mold halves. 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).

(7) 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 mold halves 2, 3, which in the closed state enclose a cavity, inside of which the sandwich composite component 4 to be produced is ultimately formed as illustrated in FIG. 1c).

(8) 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 halve 2 as shown comprises two pressing mold segments 5, 6 which are mounted in a linearly movable manner relative to each other along the spatial direction R. The second pressing mold halve 3 is positioned opposite the first pressing mold halve 2 and is constructed as a single part in this case.

(9) 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 x 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.

(10) 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 halve 3, and are connected to a corresponding negative pressure source provided on the tool side.

(11) In the situation shown in FIG. 1a), a flat sandwich semi-finished product 4 is lying on the surface of the lower pressing mold halve 3.

(12) 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 which 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 as a woven structure.

(13) 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 of 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.

(14) The two-stage pressing process begins with a closing movement of the pressing tool 1, in which the first pressing mold halve 2 is deflected relative to the second pressing mold halve 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.

(15) FIG. 1b) represents the situation in which the upper pressing mold halve 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.

(16) 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 mold segment 6 which is in contact with the sandwich semi-finished product 4 and the pressing mold halve 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.

(17) 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 halve 3, while the first pressing mold segment 6 rests relative to the second pressing mold halve 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).

(18) 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.

(19) 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.

(20) 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).

(21) 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.

(22) 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. 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.

(23) 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.

(24) 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.

(25) The transition region B1 is illustrated in detail in FIGS. 3b) and 3c), of which FIG. 3b) is a photographic detailed 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.

(26) 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 similar to a weld bead is provided on each side of the structure wall borders are joined to a cover layer 9, 10. The accumulation is bonded integrally with both the cover layer 9, 10 and the structure wall 15.

(27) 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.

(28) 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.

(29) 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, then 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

(30) 1 Pressing tool 2 First pressing mold half 3 Second pressing mold half 4 Sandwich composite component 4 Flat sandwich semi-finished product 4 Pre-pressed sandwich semi-finished product 5 Respective other pressing mold segment 6 First pressing mold segment 7 Flat sandwich semi-finished product 8 Core layer 9, 10 Cover layer 11 First minimum spacing 12 Compacted layer composite 13 Transition 14 Second minimum spacing 15 Structure wall 16 Material accumulation 16 Single-sided material accumulation B1 Transition region B2 Unshaped region B3 Shaped region