RTM tool to prevent fiber leaching in the RTM process through optimized flow channel cross-sections

Abstract

RTM tool (1) for producing a fiber composite component using an RTM process by injecting a resin into a fiber semi-finished product (2) formed from at least one fiber layer (3) consisting of a plurality of parallel fibers (4) running in a fiber direction (X), wherein the RTM tool (1) forms a mold cavity, a surface (5) of the mold cavity comprises a resin distribution groove (6) with a resin distribution groove cross-section which has a greater cross-sectional height H than a cross-sectional width B orthogonal to a longitudinal axis (Y) of the resin distribution groove (6) and the resin distribution groove cross-section is at least partially circular, characterized in thatthat at least one fixing agent for fixing the fiber semi-finished product (2) to the mold cavity is formed on the surface (5) of the mold cavity adjacent to the resin distribution groove (6) or alternatively is arranged via a connecting agent on the surface (5) of the mold cavity adjacent to the resin distribution groove (6).

Description

The invention relates to an RTM tool for producing a fiber composite component using an RTM process by impregnating a fiber semi-finished product with a resin through resin distribution grooves. Resin Transfer Molding (RTM), also known as resin injection molding, is a process for manufacturing long or continuous fiber-reinforced composite components in small, medium, and sometimes large production runs. This process allows for the production of hollow fiber-reinforced profiles, shell components, and flat composite components by impregnating a fiber preform through the injection of a matrix material, such as resin. For this purpose, the fiber preform, in a near-net-shape preform, is placed into a mold cavity, which is formed by a tool typically consisting of two parts. The resin is injected into the fiber preform or the mold cavity through channels in the RTM tool at a constant flow rate and pressure. During injection or impregnation, the resin flows through the fiber layers of the composite component and, after permeation, can exit through risers.The filling of the mold cavity is followed by resin curing, if necessary under the influence of temperature and / or overpressure relative to ambient pressure. After the fiber composite component has cured, it can be removed from the mold. Due to the flow within the channels running along the mold cavity, individual fibers of the fiber semi-finished product, especially fibers of the fiber layer of the fiber semi-finished product that are directly adjacent to the RTM mold, can be carried along by the flow. The fibers washed into the channel disrupt the flow and hinder the uniform distribution of the resin into the fiber composite semi-finished product due to turbulence on the washed-in filaments, unwanted cross-sectional constrictions in the channels, increased shear forces and the resulting pressure differences. Various designs of RTM tools are already known from the prior art. For example, DE 10 2007 013 987 A1 discloses a tool for the RTM process. Grooves formed in the surface of the tool are used to distribute the matrix material. However, particularly with non-woven fabrics as fiber semi-finished products, individual filaments or fibers can easily become washed into the matrix, causing fibers from the layer directly adjacent to the grooves to be carried along by the matrix and sucked into the groove. The teaching described in DE 10 2013 003 940 B4 attempts to achieve a rapid distribution of the matrix material over the surface of the fiber semi-finished product by means of flow aids. However, this usually does not provide a solution for the incorporation of fibers, especially since these can interfere with the effect of the flow aids, potentially creating an additional pressure difference along the flow aids. US Patent 4,740,346 discloses a process in which resin is injected into a fiber semi-finished product through a multitude of injection points. Due to the large number of injection points leading directly into the fiber semi-finished product, there is no seepage into the channel; however, the resin is not distributed evenly over the entire surface of the fiber semi-finished product, but rather injected only at specific points. Further prior art in the present technical field is disclosed in documents DE 10 2013 226 827 A1 , DE 199 22 850 C1 , DE 38 79 704 T2 , DE 10 2011 087 622 A1 and DE 10 2012 215 189 A1. The invention is therefore based on the objective of overcoming the aforementioned disadvantages and providing an inexpensive, easy-to-manufacture tool for the RTM process that prevents filaments or fibers from the fiber semi-finished product from being washed into the channels that serve to distribute the matrix material and enables a uniform distribution of the matrix material over an area of ​​the component with the most constant pressure possible. This problem is solved by the combination of features according to claim 1. For this purpose, an RTM tool is proposed for the production of a fiber composite component using an RTM process by injecting a resin into a fiber semi-finished product. The fiber semi-finished product can be a non-woven fabric or a woven fabric and is formed from at least one fiber layer consisting of a multitude of parallel fibers running in one fiber direction. The RTM tool forms a mold cavity that represents a negative shape of the fiber composite component to be produced and defines a hollow space within the tool. The preform or fiber semi-finished product and, optionally, a fiber composite core are placed in this cavity for manufacturing. The surface of the mold cavity facing the hollow space includes at least one resin distribution groove, which serves to distribute the incoming matrix over an area of ​​the fiber semi-finished product adjacent to the surface of the mold cavity. The matrix, which consists, for example, of a resin such as epoxy, polyester, or urea resin, can be introduced into the mold cavity from outside the RTM tool through channels opening into a resin distribution groove. The resin distribution grooves can be arranged independently of these channels, either alternatively or additionally, so that the matrix from the fiber semi-finished product enters a resin distribution groove and is distributed over an area of ​​the fiber semi-finished product.To enable a shape-appropriate distribution of the matrix on the surface of the fiber semi-finished product, further resin distribution grooves branch off from a resin distribution groove in a shape-appropriate manner. To prevent individual fibers of the fiber preform, especially fibers from non-woven fabrics, from being washed into the resin distribution grooves, each resin distribution groove has a cross-section that is orthogonal to a longitudinal axis of the resin distribution groove, with the cross-sectional height H being greater than its cross-sectional width B. The matrix, through its flow in the resin distribution groove, forms a main flow channel in which a strong suction effect is generated by the Bernoulli effect, which acts on the surrounding areas. Due to the shape of the resin distribution groove cross-section with a greater cross-sectional height H than cross-sectional width B, the main flow channel in the resin distribution groove is spaced away from the fibers of the fiber preform and does not directly border them. Furthermore, the resin distribution groove cross-section is at least partially circular.This minimizes shear forces between the matrix and the main flow channel in the area of ​​the resin distribution groove where the main flow channel of the matrix is ​​located. The inner surface of the resin distribution groove is designed to withstand shear forces, so that the shape and surface finish of the inner surfaces facing the resin distribution groove minimize friction, shear forces, turbulence, and pressure losses. To prevent fibers from being washed into the resin distribution groove, according to the invention, at least one fixing element is formed on the surface of the mold cavity facing the cavity and adjacent to the resin distribution groove, or alternatively, a connecting element is arranged on the surface of the mold cavity adjacent to the resin distribution groove. A screw, for example, serves as the connecting element. The fixing element serves to fix the fiber semi-finished product or the individual fibers of the fiber semi-finished product in the area adjacent to the resin distribution groove relative to the mold cavity, so that the freedom of movement of the fiber semi-finished product or the individual fibers is restricted at least along the surface of the mold cavity.To fix the fiber preform to the resin, when the preform is applied to the resin, an area of ​​the preform under and directly adjacent to the resin is compacted, and the individual fibers in this area are compressed. The limited movement of the fiber preform, caused by the resin, prevents it from being washed into the resin distribution groove. In an advantageous design, the fixing element is formed by a projection extending into the mold cavity. In a fixative cross-section parallel and / or orthogonal to the resin distribution groove cross-section, the projection can be at least partially trapezoidal, semicircular, or rectangular. The projection extends over at least a portion of the total length of the resin distribution groove. The length and arrangement of the projection are designed to conform to the shape of the fiber semi-finished product.An advantageous design is one in which the fixing element is formed by a multitude of projections. These fixing elements are arranged at regular intervals along the resin distribution groove, each extending over at least a portion of the groove's total length. The projections of this multitude can be at least partially trapezoidal, semicircular, or rectangular in cross-section parallel to and / or orthogonal to the resin distribution groove's cross-section. Each projection extends over at least a portion of the resin distribution groove's total length. The extent and arrangement of each projection within this multitude, as well as the multitude itself, are designed to conform to the shape of the fiber semi-finished product.that the protrusions and their arrangement depend on the shape of the fiber semi-finished product and follow a geometry of the fiber semi-finished product in order to ensure optimal fixation along the resin distribution groove and to maintain a target contour of the fiber composite component through shape-appropriate fixation even during the impregnation and curing process. In an advantageous further development variant, a first group and a second group each comprise a multitude of projections. The projections of the first and second groups are arranged at regular intervals along the resin distribution groove, and the projections of the multitude of projections in the first group are offset relative to the projections of the multitude of projections in the second group along the longitudinal axis, such that a projection of the first group follows a projection of the second group along the longitudinal axis of the resin distribution groove, and vice versa. This alternating arrangement of the projections of the first and second groups ensures that the fibers of the fiber layer are fixed in accordance with their fiber orientation. In an advantageous embodiment, a ratio H / B of the cross-sectional height H to the cross-sectional width B of the resin distribution groove cross-section is defined such that H / B ≥ 1.5. The cross-sectional height H of the resin distribution groove cross-section extends from a foot plane corresponding to the surface of the mold cavity directly adjacent to the resin distribution groove, in an orthogonal direction to the section of the summit area furthest from the foot plane in an orthogonal direction. The cross-sectional width B of the resin distribution groove cross-section extends from the transition area of ​​one side to the transition area of ​​the other side and is to be measured in the plane of half the cross-sectional height H. An advantageous design is one in which the cross-sectional height H lies within a range of 1–5 mm, preferably within a range of 1–3 mm. A cross-sectional height H of 2.5 mm is particularly advantageous. The cross-sectional width B relative to the respective cross-sectional height H is determined by the ratio H / B. In an advantageous further development, the resin distribution groove cross-section forms a base region, a transition region, and a common summit region on each of its two sides bordering the surface of the mold cavity. Each base region forms a first transition from the surface of the mold cavity to the respective transition region. This first transition is either abrupt, for example, with a sharp bend in its contour within the resin distribution groove cross-section, or smooth, for example, with a quarter-circle contour within the resin distribution groove cross-section. Each transition region forms a second transition from its respective base region to the summit region, the second transition being linear or semicircular.The second transition is formed in the resin distribution groove cross-section with an angle β designed to accommodate resin flow relative to the surface of the mold cavity facing the cavity. The angle β between the surface of the mold cavity and the transition area lies within a range of 90° ≤ β ≤ 135°. The summit area is semicircular and connects the transition areas located on either side. The transitions between the respective base areas and the respective transition areas, as well as the transitions between the respective transition areas and the summit area, are smooth. In an advantageous further development, the longitudinal axis of the resin distribution groove and the fiber direction of the multitude of parallel fibers form an angle α between them in the range of 70° ≤ α ≤ 110°, preferably 80° ≤ α ≤ 100°, and more preferably α = 90°. Due to the angle α between the resin distribution groove and the fiber direction of the individual fibers, the cross-sectional area of ​​a resin distribution groove with a single fiber is minimal, and suction forces act on a smaller area than would be the case with a larger cross-sectional area. The minimized suction forces in the cross-sectional area prevent fibers from being washed into or carried along by the suction forces within the resin distribution groove. In a preferred embodiment, the RTM tool comprises a tool half that forms the resin distribution groove. Alternatively or additionally, the RTM tool comprises the mold cavity, which defines a hollow space within the RTM tool and in which a fiber composite component core forming a resin distribution groove is arranged. To optimize the suction forces acting in a resin distribution groove, the pressure of the matrix within the groove, and the resin flow-optimized design of the resin distribution groove, in an advantageous further development, the cross-sectional height H and / or the cross-sectional width B of the resin distribution groove are greater in a first region of the groove than in a second region of the groove, which is spaced apart from the first region in a resin flow direction along the longitudinal axis. The transition between the first region and the second region can be gradual or abrupt with respect to the height H and the width B, preferably linear. The resin distribution groove can be formed by machining or forming processes, whereas the fixing elements can also be produced by additive manufacturing processes. The resin distribution groove and / or the fixing elements are formed by a tool half and / or the fiber composite component core, or alternatively by a support element that is arranged on the tool half or the fiber composite component core. The cross-sectional height H and the cross-sectional width B can each be measured with a suitable measuring instrument, such as a caliper, or checked with a suitable gauge. The features disclosed above can be combined in any way as far as is technically possible and provided they do not contradict each other. Other advantageous embodiments of the invention are characterized in the dependent claims or are described in more detail below together with the description of the preferred embodiment of the invention with reference to the figures. Figure 1 shows a sectional view through the fiber semi-finished product and the RTM tool with a resin distribution groove and two fixing agents; Figure 2 shows a sectional view through the RTM tool with a resin distribution groove and two fixing agents; Figure 3 shows a sectional view through the RTM tool with a resin distribution groove and through a fixing agent; Figure 4 shows a schematic top view of a fiber semi-finished product and four resin distribution grooves with fixing agents arranged thereon; The figures are schematic examples. Identical reference symbols in the figures indicate identical functional and / or structural features. Fig. 1 shows a section of a sectional view through the RTM tool 1 and through a fiber semi-finished product 2 with the fiber layer 3, such that a resin distribution groove 6 and the fixing elements formed as projections 7 are visible on the two sides of the resin distribution groove 6 bordering the surface 5 of the mold cavity. The resin distribution groove 6 forms a base region 61 on each of the two sides bordering the surface 5, creating a smooth transition from the projection 7 of the respective side to the transition region 62 of the respective side. The transition region 62 of the respective side transitions smoothly into the summit region 63 of the resin distribution groove 6, with the respective transition region 62 being elliptically and concavely shaped relative to the resin distribution groove 6.The cross-sectional height H of the resin distribution groove extends from a base plane corresponding to the plane of the surface 5 of the mold cavity directly adjacent to the resin distribution groove 6, in an orthogonal direction to the section of the summit region 63 furthest from the base plane in an orthogonal direction. The cross-sectional width B of the resin distribution groove extends from the transition region 62 of one side to the transition region 62 of the opposite side and is defined in the plane of half the cross-sectional height H. A projection 7 is arranged or formed on each of the two sides of the resin distribution groove 6 adjacent to the surface 5. The projections 7 have a semicircular cross-section, are arranged directly adjacent to the resin distribution groove 6, and each transitions into one of the base regions 61.The projections 7 each extend only over a part of the total length of the resin distribution groove 6 in the direction of the longitudinal axis of the resin distribution groove 6. Fig. 2 shows, with the exception of the fiber semi-finished product 2 with the fiber layer 3, elements that are equivalent to those shown in Fig. 1. However, the transition areas 62 are formed orthogonally to the surface 5 of the mold cavity or at an angle β of 90° to it. In the respective base areas 61, the resin distribution groove transitions abruptly to the surface 5 of the mold cavity via a kink with an internal angle of 90°. The fixing elements, designed as a plurality of projections 7', are spaced apart from the resin distribution groove 6 and are formed by dowel pins located in blind holes provided for this purpose, which are produced, for example, by drilling and subsequent honing. Due to the shape of the dowel pins, the fixing elements 7 form a trapezoidal cross-section and a round cross-section orthogonal to it.The projections 7' in the form of dowel pins are arranged uniformly over the entire length of the resin distribution groove 6 in the direction of its longitudinal axis. Fig. 3 shows, with the exception of the fiber semi-finished product 2 with the fiber layer 3, elements that are equivalent to those shown in Fig. 1. However, the transition areas 62 are linear and each creates a seamless transition from the radius of the respective base area 61 to the radius of the top area 63. In the respective base areas 61, the resin distribution groove transitions smoothly to the surface 5 of the mold cavity via a semi-circular or nearly quarter-circular shape. The fixing elements, designed as a multitude of projections 7', are spaced apart from the resin distribution groove 6 and are formed by the surface 5 of the mold cavity.The projections 7' each have a trapezoidal cross-section and a length in the direction of the longitudinal axis of the resin distribution groove 6, wherein the length in the direction of the longitudinal axis of the resin distribution groove 6 is greater than a width of the projections measured at their base in the plane of the surface 5 of the mold cavity and orthogonal to the direction of the longitudinal axis of the resin distribution groove 6. A projection 7' ​​on one of the sides of the resin distribution groove 6 that adjoin the surface 5 of the mold cavity is arranged along the longitudinal axis of the resin distribution groove 6 alternating with a projection 7' ​​on the other side of the resin distribution groove 6. Figure 4 shows a schematic top view of the fiber semi-finished product 2 with the fiber layer 3 directly adjacent to the RTM tool 1. The plurality of fibers 4 of the fiber layer 3, running parallel in the fiber direction X, lie at an angle α to the resin distribution grooves 6, which extend in the direction of their longitudinal axis Y. Fixing elements are arranged on both sides of each resin distribution groove 6. The fixing elements of the first resin distribution groove 6 (counting from the left) are formed by two groups, each consisting of a plurality of projections 7'. The first plurality has an oval shape, and the second plurality has a rectangular shape with rounded corners. The projections 7' of the second plurality are each spaced at a different distance from the resin distribution groove 6 in the longitudinal direction Y compared to the preceding projection 7'.The fixing means of the second resin distribution groove 6, counting from the left, are formed by a projection 7 on each of the two sides of the resin distribution groove 6, the projections 7 each extending over the entire length of the resin distribution groove 6 in the direction of the longitudinal axis Y of the resin distribution groove 6. The fixing means of the third resin distribution groove 6, counted from the left, are formed by two groups of a plurality of projections 7' each, wherein the projections 7' have a round basic shape and a first projection 7' ​​of one group of the two groups is opposite a second projection 7' ​​of the other group of the two groups. The fixing means of the fourth resin distribution groove 6, counted from the left, are formed by two groups of a plurality of projections 7' each, wherein the projections 7' have a round basic shape and the projections 7' of the two groups are arranged alternately to each other, so that in the direction of the longitudinal axis Y a projection 7' ​​of one group is followed by a projection 7' ​​of the other group. The invention is not limited in its implementation to the preferred embodiments specified above. Rather, a number of variants are conceivable, which utilize the illustrated solution even in fundamentally different designs. For example, multiple fixing areas with fixing agents on both sides of the resin distribution groove can also be used.

Claims

RTM tool (1) for producing a fiber composite component using an RTM process by injecting a resin into a fiber semi-finished product (2) formed from at least one fiber layer (3) consisting of a plurality of parallel fibers (4) running in a fiber direction (X), wherein the RTM tool (1) forms a mold cavity, a surface (5) of the mold cavity comprises a resin distribution groove (6) with a resin distribution groove cross-section having a greater cross-sectional height H than a cross-sectional width B orthogonal to a longitudinal axis (Y) of the resin distribution groove (6), and the resin distribution groove cross-section is at least partially circular, characterized in thatthat at least one fixing agent for fixing the fiber semi-finished product (2) to the mold cavity is formed on the surface (5) of the mold cavity adjacent to the resin distribution groove (6) or alternatively is arranged via a connecting agent on the surface (5) of the mold cavity adjacent to the resin distribution groove (6). RTM tool (1) according to claim 1, wherein the fixing means is formed by a projection (7) extending into the mold cavity, which extends at least over a part of the total length of the resin distribution groove (6). RTM tool (1) according to claim 1, wherein the fixing means is formed by a plurality of projections (7') and the projections (7') of the plurality of projections (7') are arranged at regular intervals along the resin distribution groove (6) and each extend over a part of a total length of the resin distribution groove (6). RTM tool (1) according to claim 1 or 2, comprising a first group of projections (7') and a second group of projections (7'), each having a plurality of projections (7'), the projections (7') of the first and second groups being arranged at regular intervals along the resin distribution groove (6), and the projections (7') of the plurality of projections (7') of the first group being offset to the projections (7') of the plurality of projections (7') of the second group in the direction of the longitudinal axis (Y). RTM tool (1) according to one of the preceding claims, wherein a ratio H / B of the cross-sectional height H to the cross-sectional width B of the resin distribution groove cross-section is specified such that H / B ≥ 1.5 and / or the cross-sectional height H is in a range of 1-5 mm. RTM tool (1) according to one of the preceding claims, wherein the resin distribution groove cross-section of the resin distribution groove (6) forms a foot region (61), a transition region (62) and a summit region (63) on each of its two sides bordering the surface (5) of the mold cavity, wherein the respective foot region (61) forms a first transition from the surface (5) of the mold cavity to the respective transition region (62) and the first transition is abrupt or continuous, the respective transition region (62) forms a second transition from the respective foot region (61) to the summit region (63) and the second transition follows a linear or semicircular course, the summit region (63) is semicircular and connects the transition regions (62). RTM tool (1) according to one of the preceding claims, wherein the longitudinal axis (Y) of the resin distribution groove (6) and the fiber direction (X) of the plurality of parallel fibers enclose an angle α between them in a range of 70° to 110°. RTM tool (1) according to one of the preceding claims, wherein the RTM tool (1) comprises a tool half through which the resin distribution groove (6) is formed. RTM tool (1) according to one of the preceding claims, wherein the mold cavity defines a cavity and the RTM tool (1) comprises a fiber composite component core arranged in the cavity, which forms the resin distribution groove (6). RTM tool (1) according to one of the preceding claims, wherein the cross-sectional height H and / or the cross-sectional width B of the resin distribution groove (6) is larger in a first region of the resin distribution groove (6) than in a second region of the resin distribution groove (6), which is spaced apart from the first region in a resin flow direction along the longitudinal axis (Y).

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