DE19922799B4 - Process for producing a plastic molding - Google Patents

Abstract

Method for producing a plastic molded part, in particular a bottom shell of a motor vehicle, with the following steps: - making a preform (2) from reinforcement material (12); - Inserting the preform (2) into a tool; - closing the tool; - Injecting a matrix material; - Curing and removal of the molded part, the reinforcing material (12) for forming the preform (2) being formed by a fiber structure and being prestressed by means of a clamping frame (20) and preformed in a draping tool (6) while maintaining the clamping force, characterized in that, that the tensioning force along the edge area of the draping tool (6) is set in sections in order to control the pulling of the fiber layer into the draping tool through the different tensioning forces over the circumference of the molding, so that the warping or displacement of the layer during preforming is prevented.

Description

The invention relates to a method for producing a plastic molding according to the preamble of patent claim 1 and an apparatus for carrying out the method.

For the production of flat plastic molded parts with complex three-dimensional extent on a large industrial scale, for example, the resin injection process (Reaction Transfer Molding, RTM method) offers.

This method has been known since the fifties. It allows an economical production of fiber composite parts, which can be produced by the selection, type and arrangement of reinforcing materials and by the choice of the matrix system moldings, which are ideally adapted to the stresses occurring. According to the RTM process, composites with a high fiber content can be produced. The peculiarity of the method is that the fibrous materials, cores, nonwovens serving for reinforcement are first placed in the mold and then the matrix material is injected. In other words, the essential difference to press molding and injection molding is that the matrix material and the reinforcing / core material only come into contact with one another in the closed RTM tool.

This method is quite suitable for the production of simpler covers in mass production. However, it has been found that this method is limited on an industrial scale in the production of large-area plastic parts with complex part geometry, since the molded parts do not meet the requirements with regard to surface quality or dimensional accuracy.

From the DE 40 35 224 A1 , which forms the closest prior art for the invention, a method for producing a plastic molded part by means of a tool is known in which a reinforcing material for forming a preform is inserted into a clamping frame provided on the tool.

Furthermore, the describes DE 196 08 127 A1 a method for producing a spatially shaped fiber composite component, in particular a motor vehicle floor group.

In contrast, the invention has for its object to provide a method for producing a plastic molding, in particular a bottom shell of a motor vehicle and a device suitable for carrying out this method, with which even complex molding geometries can be produced with improved reproducibility.

This object is achieved with respect to the method by the combination of features of claim 1 and with respect to the device by the features of claim 11. The inventive method also makes it possible to produce a floor assembly of a motor vehicle made of fiber-reinforced plastic.

According to the invention, the preform is produced in a draping tool, the relative position of the layer with respect to the draping tool being determined during preforming by a tenter.

In this way, the layers are guided at lowering positive stamp of Drapierwerkzeuges on the clamping frame, so that discarding or shifting is almost impossible.

This method makes it possible for the first time to produce molded parts with extremely complex geometry, such as a bottom shell of a motor vehicle made of fiber-reinforced plastic, wherein the reinforcing material is continuous, d. H. is processed without incisions and not by joining partial areas, so that the fiber structure is preserved throughout. The weight of an underbody of a motor vehicle can be significantly reduced by using this provided with reinforcements bottom shell over conventional solutions in which the vehicle floor assembly consists essentially of sheet steel at least the same strength.

Another advantage of a base shell produced in this way is the simplification of the production process, since the entire base shell can be produced in one piece in one operation.

In order to be able to control the drawing of the fiber layer into the draping tool so that the warping or displacement of the layer during preforming is prevented, according to the invention the clamping force to be applied by the clamping frame is differently adjustable in sections.

It is preferred if the preform is made of several layers of fiber material, wherein the layers are preferably connected to one another via a binder.

In the case of particularly complex shaped parts, for example the aforementioned bottom shell, it is advantageous if the individual layers are preformed one after the other in the draping tool, so that after the insertion and preforming of the last layer the preform is made. In this case, a suitable binder can be used to connect the layers together.

To increase the strength and rigidity of the plastic molded part, preference is given to using fiber webs with different orientations instead of mats.

In order to facilitate the introduction of the layers into the negative form of the draping tool and the application of curvatures, etc., the layers of a layer should be fixed such that the fibers or fiber bundles (rovings) can still move independently of one another to some extent.

In the case of the multi-layer structure, in the case of complex geometries, the previously preformed layer may be displaced during preforming of the next layer. In order to prevent this, the already preformed layers can be fixed in the draping tool via suitable means. This fixation can be done for example via the binder, with which the layers are soaked and is melted before inserting into the draping tool. The curing of the binder can then be done by cooling the draping tool. Alternatively, the binder can also be applied to the preformed layer after preforming and then melted.

One aspect of the invention is that for the first time it is possible to form complex molded parts with the required strength and rigidity by using continuous layers instead of assembled mats. That is to say, the manufacture of an underbody of a motor vehicle using mats instead of mats as the reinforcing material, in itself, should already meet the requirements of patentability, since it is unprecedented in the prior art.

According to the invention, a clamping frame is used to carry out the method, over which the pre-formed layer of fiber material is biased against one half of the tool, so that when closing the Drapierwerkzeuges the fiber layer against the biasing force of the clamping frame inwardly drawn into the cavity or pulled around the punch becomes. In order to ensure a predetermined clamping force, the clamping frame should be at least partially adapted to the contours of the Drapierwerkzeuges, so that a flat support of the clamping frame is ensured on the fiber layer. It is essential here that the clamping force to be applied by the clamping frame is partially adjustable in sections. These different clamping forces over the circumference of the molding, the retraction of the fiber layer can be controlled in the Drapierwerkzeug, so that the discarding or displacement of the layer is prevented during preforming.

Other advantageous developments of the invention are the subject of the other dependent claims.

In the following a preferred embodiment of the invention will be explained in more detail with reference to schematic drawings. Show it:

1 a schematic representation of an apparatus for preforming a plastic molding;

2 a with the device according to 1 manufactured plastic molding;

3 a detailed view of a tenter 1 and

4 a bottom shell of a motor vehicle produced by the method according to the invention.

The moldings described in the following figures are produced by the RTM process. As mentioned above, the matrix material and the reinforcing material are first brought together in the cavity of an RTM tool. The matrix material consists of at least two components which are withdrawn from storage via metering devices and homogenized in a mixing head. The mixed matrix components are then injected via a nozzle device, either transversely to the parting plane or parallel to the parting plane. In the former case, one or more nozzle means are provided perpendicular to the parting plane in a tool plate of the RTM tool, while in the latter case, d. H. in the lateral injection, only a nozzle device is arranged laterally on the side circumference of the tool. The injected matrix material wets the reinforcing material, the composite cures relatively quickly due to heating of the RTM tool and the finished molded part can be removed.

According to the invention, the reinforcing material is not inserted directly into the RTM tool but first preformed in a separate process step.

The 1 shows the device 1 to form a preform 2 which is shown schematically in FIG 2 is shown.

The device 1 consists essentially of a draping tool 6 with a lower, fixed mold half, which is the negative mold 8th forms and a movable, the positive mold forming mold half 10 , In the illustration according to 1 the components of the device are shown approximately in the manner of an exploded view. In reality, the positive form becomes 10 only so far from the negative form 8th lifted off that one the reinforcing material 12 can be inserted. With lowered positive shape 10 dives a stamp 14 in a mold 16 the negative form 8th one, so that the the geometry of the preform 2 pre-existing cavity through the gap between the stamp 14 and die 16 as well as the contour of the mold halves 8th . 10 in the face area (parting plane) 18 is formed.

The reinforcing material 12 is withdrawn as a roll material in the direction of arrow X of roles not shown, the side of the device 1 are arranged.

The draping tool 6 is a tenter 20 assigned over which the reinforcing material 12 on the face 18 the negative form 8th clamped flat.

The clamping frame 20 can be from the in 1 indicated off-hook position in which the reinforcing material 12 can be fed, lower it until it is on the contour end face 18 the negative form 8th flat rests.

The clamping frame 20 consists essentially of a support frame 22 that has a variety of clamping devices 24 with a support frame 26 connected is.

As a reinforcing material 12 In principle, it is possible to use textile fabrics, for example nonwovens, woven fabrics, scrims, braids, knitted fabrics, knitted fabrics, etc.

The use of layers makes it possible to carry out the molding with the required strength and rigidity in lightweight construction.

Layers are sheets in which, for example, unidirectional fibers are connected by sewing threads to a substrate. Such scrims can be produced, for example, in 0 °, + 45 °, -45 ° orientation. The scrim can also be connected in a spider-web fashion, whereby the bonding structure melts on heating and bonds the fibers.

According to the invention, the preform consists of a plurality of unidirectional layers or layers, ie of layers in which the fibers lie in one direction only. Particularly in the case of complex geometries and high basis weights, it is preferred according to the invention if the individual layers are successively introduced into the device, preformed and together to form the preform 2 get connected. Of course, all or several layers can be preformed simultaneously.

Preferably, the preforming step is carried out separately for each individual layer. In this way it is ensured that the layers in the predetermined orientation to each other in the preform 2 are arranged. The individual layers may differ from each other, for example, in the orientation of the fibers, so that the preform may consist, for example, of 6 layers, the lowest layer being a 0 ° layer, the middle 4 layers + 45 ° and -45 ° layers and the top cover layer is again a 0 ° layer. Instead of the structures mentioned, other orientations can also be used.

So that the previously formed layer is not displaced during the shaping of the subsequent layer, the individual layers of the reinforcing material ( 12a . 12b . 12c ) impregnated with a thermoplastic fixative. Before inserting into the device 1 become the individual layers of the reinforcing material 12 ( 12a . 12b ...) heated by a heat source, such as an infrared radiator or hot air, so that the binder melts. The layer with the molten binder is then applied to the negative mold 8th Already applying a pre-adaptation to the shape of the die 16 he follows.

After this situation 12 on the face 18 the negative form 8th rests, is the tenter 20 lowered so that the support frame 26 with its lower bearing surfaces in contact with the situation 12 on the negative mold 8th arrives.

As mentioned above, the bearing surface of the support frame 26 to the contour of the negative mold 8th adjusted so that the support frame 26 the location 12 flat against the face 18 the negative form 8th biases.

As in 1 indicated by dashed lines, is the support frame 26 only at the edge area 28 on the negative mold 8th so that, accordingly, the location 12 only in this border area 28 is curious. For more complex geometries, the clamping force should be individual along the edge area 28 be adjustable. At the in 1 illustrated embodiment, this is achieved in which the clamping devices 24 are formed by spring elements whose biasing force is adjustable.

3 shows a detailed view of the tenter 20 out 1 , Accordingly, the support frame 22 of threaded rods 30 interspersed, on the support frame 26 are attached. This support frame 26 exists at the in 3 illustrated embodiment of a sandwich component, with a PUR core 32 and two CFRP laminate cover layers 34 ,

In order to ensure a flat surface, this sandwich structure is produced directly on the face during production 18 the negative form 8th laminated so that the support frame 26 flat follows the tool contour.

To compensate for minor errors and the coefficient of friction between the reinforcing material 12 and the support frame 26 can be minimized at the bottom ( 3 ) of the support frame 26 a suitable cushioning material 38 be applied.

The threaded rod 30 is in threaded engagement with a nut 40 , so that by the axial displacement along the threaded rod 30 the bias of a biasing spring 42 changeable at the bottom (view after 3 ) of the support frame 22 is supported. That is, the compression spring 42 holds the two frames 22 . 26 in the distance, whereby the maximum distance by a stop screw 44 is given, which at the in 3 upper surface of the support frame 22 is applied.

As in particular from 1 can be found, the support frame 26 into several segments 26a to 26e be divided, each segment 26a ... a separate clamping device 24 is assigned, so that the contact pressure of the individual segments 26a ... is individually adjustable. In this way, in areas with a complex, three-dimensional geometry, a different clamping force can be selected than is the case in areas with flat surface sections.

After lowering the clamping frame 22 Thus, the respective position of the reinforcing material 12a , ... with a predetermined force on the edge area 28 the negative form 8th pressed.

Maintaining the bias then becomes the positive shape 10 lowered, leaving the stamp 14 into the matrix 16 dips. The outer circumference 46 the positive form 10 is there so formed that it is in the inner peripheral openings 48 . 50 of the support frame 22 or the support frame 26 can dive. That is, the positive form 10 does not come into contact with the tenter 20 ,

By the dipping stamp 14 becomes the location of the reinforcing material 12 into the interior of the matrix 16 pulled in, leaving the material under the tenter frame 20 through in the matrix 16 is moved in. The bias of the tenter 20 is accordingly chosen so that a uniform, warp-free material feed into the negative mold 8th is guaranteed.

In the negative form 8th is a heat exchanger 52 provided over which it is cooled to the thermoplastic binder of the reinforcing material 12 cure, so that the location of the reinforcing material 12a ... on the respective base, ie either on the negative form 8th or is fixed on the previously preformed reinforcing material layer.

After this preforming a layer become the positive shape 10 and the tenter 20 lifted off, so the next situation ( 12b . 12c , ...) over the face 18 the negative form 8th can be pulled. This location 12b , ... in turn contains a thermoplastic binder, which was melted before laying and hardens during the subsequent preforming and produces a bond with the underlying layer.

Of course, the invention is by no means limited to the use of thermoplastic binders / fixatives, but it could also be an adhesive material or a chemically reacting agent used to the layers 12a . 12b , ... to fix.

Fusible epoxy powder has proven to be a particularly suitable alternative to thermoplastic binders. Epoxy powder is characterized by rapid curing, so that the cycle times are short. In this process variant, the layer to be deformed 12 soaked in the draping tool 6 inserted, preformed and then applied the epoxy powder. At the same time the stamp 14 the positive form 10 over a heater 54 heated and lowered so that it is flat on the provided with epoxy powder layer 12 rests. The powder then melts due to the elevated stamping temperature. Subsequently, the stamp 14 cooled so that the epoxy powder hardens and the positive mold 10 reaches the temperature required for the next preforming operation. Curing can also be done with the draping tool open 6 respectively.

In a six layer reinforcing material construction, the above procedure is repeated almost six times until the final preform 2 with the in 2 shown form is obtained. This preform 2 then gets out of the opened draping tool 6 taken, the removal by heating the negative mold 8th is facilitated (loosening the fixative / binder from the negative mold 8th ).

It is essential in the above-described preforming that the clamping frame 20 circumferentially enough clamping force applied to the feeding of the reinforcing material 12 in the negative form 8th to perform without wrinkles. That is, the tenter frame 20 must be made very stable, the support frame must be made of steel for larger moldings usually.

To the reproducibility of the preform 2 To increase, it is advantageous if the geometry of the negative mold 8th the desired final contour of the molding corresponds, while the positive mold 10 has a predetermined distance to the negative mold on the inclined surfaces in the closed position. This distance can be in the range between 1 and 3 mm for large-area tools (with a component wall thickness of about 2 mm). It has proved to be favorable if the negative form on the horizontal surfaces (0 °) 8th and the postitive form 10 lie directly on each other (zero distance).

In large-scale moldings considerable closing forces must be applied to perform the above-described preforming can. It may therefore be necessary for the draping tool 6 Assign a hydraulic clamping unit over which the mold halves 8th . 10 can be closed without tilting etc. and the required closing pressure can be built up.

As the material for the fibers, for example, glass fibers, carbon fibers, aramid fibers or mixed layers of such components can be used.

The preform produced in this way 2 is then cut to size on the peripheral edge, possibly occupied with further reinforcements and further processed in the RTM tool in the manner described above. After curing of the composite of matrix system and reinforcing material, the finished plastic molded part is removed and fed to further production.

4 shows an embodiment of such a plastic molding, which can be used as a bottom shell for a motor vehicle. Such a component has a length of up to 5 m and furthermore has a pronounced three-dimensional geometry which places considerable demands on the production technology.

By the method according to the invention described above, it was possible for the first time to produce such a bottom shell 2 to produce fiber material, wherein by suitable combination of the different layers 12a . 12b , ... the required strength of the bottom shell and rigidity were achieved with maximum lightweight construction. A further stabilization of the bottom shell is made by retrofitting reinforcing parts, such as side rails, structural panels, reinforcements, seat attachments, etc., which are mounted after curing of the bottom shell or are already inserted in the RTM tool.

This complete new development of a bottom shell is characterized by extremely low weight with excellent strength, so that all strength requirements can be met. At the in 4 Longitudinal fibers are preferably used, wherein fiber contents of more than 40% by volume are required.

By means of the method according to the invention, the base shell with the required component quality (high reproducibility) can be produced at low cost and with minimal cycle times.

Disclosed is a method for producing a plastic molded article according to the resin injection method, in which a preform is made in a draping tool. This draping tool has a clamping frame, via which the fiber material forming the preform is prestressed, so that a distortion-free drawing of the fiber material into the cavity of the draping tool is possible. As a special feature here is the realization of a highly complex geometry using opportunities to see what was previously possible only with mats.

Claims (12)

Method for producing a plastic molding, in particular a base shell of a motor vehicle, comprising the steps of: - producing a preform ( 2 ) of reinforcing material ( 12 ); - inserting the preform ( 2 ) into a tool; - closing the tool; - injecting a matrix material; Hardening and removal of the molding, wherein the reinforcing material ( 12 ) for forming the preform ( 2 ) is formed by a fiber fabric and by means of a tenter frame ( 20 ) and in a draping tool ( 6 ) is preformed while maintaining the clamping force, characterized in that the clamping force along the edge region of the Drapierwerkzeugs ( 6 ) is adjusted in sections to control by the different clamping forces over the circumference of the molding, the retraction of the fiber layer in the Drapierwerkzeug so that the discarding or displacement of the layer is prevented during preforming. Method according to claim 1, characterized in that the reinforcing material in several layers ( 12 ) is formed. Method according to claim 1 or 2, characterized in that the reinforcing material consists of continuous fiber layers ( 12 ) preferably with different orientations. Method according to claim 2 or 3, characterized in that the layers ( 12 ) are made of fibrous webs with fibers or fiber bundles in 0 °, -45 °, + 45 °, and / or 0 ° orientation. Method according to one of the claims 2 to 4, characterized in that the fiber layers are fixed together so that the fibers or fiber bundles can move independently. Method according to one of the preceding claims, characterized in that the layers ( 12 ) are preformed one after the other. Method according to claim 6, characterized in that a preformed layer ( 12a ) before applying a next layer ( 12b ) is fixed. A method according to claim 7, characterized in that the fixation is flat, for example by melting a fixing agent. Method according to claim 7, characterized in that the layers ( 12 ) are impregnated by a thermoplastic fixing agent and before being introduced into the draping tool ( 6 ) and in the draping tool ( 6 ) are cooled to cure the fixing agent. Method according to one of the preceding claims, characterized in that the layers ( 12 ) of the reinforcing material are formed by band material. Device for carrying out the method according to one of the claims 1 to 10, with a draping tool ( 6 ) with a negative form ( 8th ) and a positive form ( 10 ) which together specify a molding geometry and with a tenter frame ( 20 ) for clamping on a mold half of the draping tool ( 6 ) laid on fiber material, wherein the tenter frame ( 20 ) according to the tool contour of the mold half ( 8th . 10 ) in the investment area to the location ( 12 ), characterized in that the clamping frame ( 20 ) a support frame ( 22 ) and a support frame ( 26 ), which has clamping devices ( 24 ) are connected to each other via which the clamping force of the support frame ( 26 ) is determined in sections. Device according to claim 11, characterized in that the support frame ( 26 ) into several subsegments ( 26a . 26b . 26c , ...) is divided, each of which at least one clamping device ( 24 ) is assigned, so that the clamping force of each sub-segment ( 12a . 12b , ...) is individually adjustable.

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