METHOD FOR THE MANUFACTURE OF A COMPOSITE PRODUCT AND PRESS MOULD FOR CARRYING OUT THE METHOD

Abstract: Method for the manufacture of a composite product comprising a core of foamed material and at least one enveloping material comprising a thermoplastic material with a reinforcement, and where a significant step is to shape the product in a press shape mould. The enveloping material and the core material is introduced into the press shape mould while the core material and the enveloping material is still in a plastic, non-consolidated state. At least one moveable component of the press shape mould is then moved to inflict a first, relatively high pressure on the product blank, giving the product blank a temporarily compressed shape while the core is still plastic. Thereafter at least one moveable component of the press shape mould is withdrawn, allowing the product blank to expand and find its final shape and to consolidate. The invention also relates to a press shape mould for conducting the method.

Description: Method for the manufacture of a composite product and press mould for carrying out the method . The present invention relates to a method for the manufacture of composite products More particularly the invention relates to a method for the manufacture of composite products comprising an outer cover layer comprising a thermoplastic mateπal and a fibrous reinforcement, and a core of extruded, foamed polymer, wherein the core mateπal is still soft and not completely cures when the product is given its final shape in a press shape mould. The invention further relates to a press shape mould (tool) for conducting the method. Background Composite products are used in an increasing vaπety of applications due to their combination of high strength and low weight. With a suitable choice of materials, such products also represent environmentally friendly alternatives, where a high degree of recycling is possible. The products are competitive also in other respects, e.g. with respect to resistance against degradation inflicted by chemicals, temperature etc. A mam challenge has until now been to develop quick and convenient methods for the manufacture of such products in order to make them competitive with products in more traditional materials also with respect to pπce. Composite products typically comprise several layers of reinforcement in a polymer matrix, envelops a foamed core with a very low weight. The reinforcement layers provide strength to the product, and may additionally provide a desired surface finish. The method mostly used till now has been to prefabricate the core, and by means of suitable fixture, to arrange the core in a mould tool in a completely cured and cold state, whereafter one or more layers including reinforcement and possible a surface layer have been added to the mould tool in a preheated condition, and there given its final shape under cooling Particular surface layers may e g consist of felt or PMMA foil In Applicants own Norwegian patent applications Nos 19992654 and 19993471 there is suggested to manufacture such products with a core that is not prefabπcated but which is extruded simultaneously with the shaping of the product This may be beneficial with respect to manufacturing routines, but also represents [side 2J challenges with respect to obtaining products with sufficiently high end even quality It is thus a considerable challenge at the manufacture to according to these applications to ensure that a sufficiently good contact is obtained between the cavity of the press shape mould and the outer layer of the product This problem is particularly accentuated due to the fact that the core is still soft and do not provide a good basis for the required pressure between the press shape mould and the product Objective It is thus an objective with the present invention to provide a method for the manufacture of composite products of the kind descπbed heπnabove, where a sufficiently high pressure is obtained between the press shape mould and the product, and good contact between the two It is further an objective with the present invention to provide a method for the manufacture of such products, which method is quick and labour saving and well suited for mass production It is still further an objective to be able to do this with simple means to a very high quality and accuracy, satisfying the high quality requirements associated e g with the car industry These objectives are achieved with the method and device according to the invention The invention The invention is characterized by the features discloses by the characterizing part of claim 1. The press shape mould (tool) for conducting the method is characterized by the features disclosed by claim 7. Preferred embodiments of the invention are defined by the dependent claims. Drawings Figure la is a highly simplified, schematic view of an embodiment of a press shape mould tool according to the invention, in a state of a first work phase of the method, Figure lb shows the embodiment of figure la in a second work phase of the method. Figure lc shows the embodiment of figure la and lb in a third work phase of the method, Figure Id shows the embodiment of figure la - lc in a fourth work phase of the method, and Figure 2a-2d shows the work phases of figures la- Id with a slightly modified press shape mould. The press shape mould tool 1 (for simplification hereinafter usually referred to as press tool 1 ), which is illustrated highly simplified, generally comprises two tool halves 2 and 3. In one of the tool halves 2 is arranged a piston shaped member 4 which is arranged moveably back and forth (or up and down dependent on the orientation of the press tool) by means of any suitable mechanism 5 that may be influenced by an external force from an attachment not shown. The press tool 1 has internal surfaces 6a, 6b mainly located to the piston member 4 and to the tool half 3, forming the cavity of the tool, i.e. the shape is substantially complementary to the desired shape of the product, as these parts of the tool will bear directly against the product blanks during the press and shape procedure. The internal shape of a horizontal section of the press tool 1 in and of the piston member 4 is decided by the shape of the products. Thus, this shape may be of any regular or irregular kind. Along the circumference of the piston member 4, there is for practical reasons arranged a material 1 1 with a significantly lower heat conductance than that of the piston member itself. Between the tool halves 2 and 3 a product blank 7 is shown, which product blank comprises one or more enveloping materials 8a, 8b and at least one core material 9. Figure 1 a shows a situation where enveloping material 8a, 8b and freshly extruded core material 9 have been introduced into or preferably through the openings betwween the press tool halves 2, 3 that eventually decides the outer dimensions of the finished product. The assembly is shown with a horizontal input of material, but the invention works independently of this orientation. It may preferably have a vertical orientation as described in Applicant's Norwegian patent application No. 19993471. It is, however, essential that both the enveloping materials 8a, 8b and the core 9 are introduced in a heated but not yet consolidated state. Figure lb shows the next phase or step of the process. Here the press tool halves 2, 3 have been moved together and close the void in which the product is formed, defined mainly by the surfaces 6a, 6b. At the same time the piston member 4 of the press tool 1 has been moved forward to a position h,, where it bear against the outer surface of the product blank 7 that still is in a plastic non-consolidated state. Figure lc shows the next step of the method according to the invention, which is the step constituting the most significant feature. Here the piston member 4 has been moved further forward against the product blank to a level h 2 where the product blank 7 is compressed to a state far more than corresponding to its desired final shape. In this state the locked up air or gas in the freshly extruded core 9, which is still not consolidated, is highly compressed. It cannot, however, escape and will therefore remain in the structure of the product. The position shown in fig. lc is maintained for a little while, the length of which depends a.o. of the size of the product, so that consolidation is initiated in this state. The material resting against the press tool, i.e. the enveloping material 8a, 8b will commence consolidation first, while the core 9 needs some additional time to be cooled and therefore will consolidate a little later. During this phase there is a very good contact between the internal surfaces 6a, 6b of the tool and the enveloping material 8a, 8b of the product blank 7, and the outer surface of the product therefore receives the shape and firmness desired, while the product's internal volume is still compressed beyond the desired volume and shape. Due to material 11 with low heat conductance in the region of the circumference, the enveloping material 8a in this region remains flexible for a longer period of time than the other parts of the enveloping material 8a, 8b. As soon as the enveloping material 8a, 8b has cured sufficiently (has "settled"), and well before the core 9 of the product is consolidated, the piston member 4 is drawn back as shown on figure Id to a level h3 so that the pressure is reduced. More precisely the piston member is withdrawn to an extent where the cavity of the press tool, defined mainly by surfaces 6a and 6b, corresponds precisely to the desired volume of the finished product. The gas pressure in the core 9, which has barely begun to consolidate, will during this phase "blow up" the core again , ensuring that the core fills the entire internal void of the product in the way intended. The part of the enveloping material 8a, 8b that is in the region of the circumference of the product, will due to the material with low heat conductance remain its flexibility to this stage, and therefore allow the core to blow up so the product finds its final shape. The product is maintained in this position for a period of time sufficiently to allow the entire product to consolidate, i.e. until the core 9 has settled to a degree where it no longer changes its shape when the product is removed from the press tool 1. At this time the press tool is opened for removal of the finished product (for storage or secondary treatment), and the tool is again ready to receive a fresh product blank 7 for the same treatment. Figure 2a-2d principally illustrates steps similar to figure la- Id. Here, however, a press shape mould tool comprising a groove 10 in the surface of the piston member 4, so that the surface 8a of the product blank 7 will penetrate the groove and receive a corresponding shape. Also the core material 9 will to some extent enter into and be shaped by the groove 10 if the groove has a sufficient size. While figure 2 depicts only one groove it is evident that several grooves may be applied or an entire pattern of grooves and recesses, in order to provide the surface of the product with certain functional or visual structures. The grooves may be minute grooves or deep recesses, dependent on their objectives. Similar grooves and recesses may off course also be arranged in tool half 3 as in the piston member 4. In the description above we have referred only to one moveable piston member 4 in the press tool 1. Depending somewhat on the shape of the product, it is evident that more than one piston member may be applied, to one or more sides of the product blank. In such cases the product blank may be compressed by moving forward two or more such piston members, while not necessary all of them need to be withdrawn when the pressure subsequently is to be reduced. It is actually possible that entirely different piston members are used to reduce the pressure during step Id compared to the piston members used to compress the product blank during the preceding step lc. The press shape mould tool 1 is depicted as an assembly of two approximately even halves 2 and 3. It is, however, also possible that the press shape mould comprises more than two parts, and the different parts need not be approximately evenly sized. The variations in the tool design is mainly influenced by the shape of the products, so that products with a simple geometry is preferably made in correspondingly simple tool shapes, while products of more complex geometry may require more complicated press shape moulds. As indicated the internal cavity 6a, 6b of the press shape mould 1 may have very different and more complicated shapes than the one depicted, depending upon the shape desired for the finished product. For particularly complex product surfaces, it may furthermore be required to provide special types of reinforcement in order to obtain the required flexibility of the product blank, e.g. fibre reinforcements with very short fibre fragments or the like. This is, however, conditions that are outside the frame of the present invention. The method may be modified in different ways without departing from the scope of the invention. For instance it is possible that several similar or non-similar products 7,, 7 2 , „..7 n is shaped side-by -side in one press tool that comprises several similar or non-similar cavities, each receiving a core material and an enveloping material. For instance, for relatively small products, it would be convenient to manufacture them in matrixes of e.g. 2x2, 2x4 or 4x4 products at the time. It is not a requirement that the enveloping material constitutes one material only. It may e.g. be one material 8a on one side of the product and two or more - similar or different - layers 8 bl , 8 b2 on the other side of the core, all depending on the requirements to the product. It is furthermore possible to conduct the phase comprising withdrawal of the piston member 4 in several steps, or in a continuous, very slow backward movement. The time period before starting withdrawal and the way it is conducted, are mainly deciding for the density and the possible variations in density in the finished core. The time aspect off course also relates to the size of the product, as it takes a longer period of time to cool a large product than to cool a small product. If the foaming core material has a particularly high viscosity, it is not strictly necessary to close the tool halves 2, 3 along their circumference prior to compressing the product blank 7 with the piston member 4. High viscosity of the core material 9 will contribute to hold the gas locked up for the time required by the method. Other alternatives are that the tool halves 2, 3 are closed only along parts of their circumference, or that closing occurs subsequent to initiated compression. The spirit of the invention still remains the same, that in a limited period of time the product blank 7 is exposed to a pressure that compresses the blank in excess of what is required to give it the desired final shape in order to ensure a best possible consolidated surface, and that the pressure is thereafter reduced, allowing the product to find its final, desired shape. Additional required elements of such manufacturing processes are like the ones previously known, e.g. with respect to extruding, preheating etc. As mentioned the orientation of the tool may be either horizontally, vertically or any other orientation. Examples of products suited for manufacture by the method according to the present invention are interior and exterior details of cars, like seat backs, door sides, details of the front and/ or rear, hereunder bumpers etc., as well as other products where lightweight and strong, shock absorbing components are required. For many products, it is desirable or required to be able to attach reinforcements, grommets (eyes, ears, loops), attachments for bolts or for headrests on a car seat. This is easily combinable with the method according to the invention, e.g. by prior to the described steps introducing the requested detail/ attachment between the tool halves by means of suitable fixtures. For the purpose of best possible environmental manufacture, it is often convenient to use the same polymer for the core as for the enveloping material, but this is not a requirement according to the invention. Regarding the reinforcement, which itself constitutes an option, it may be of any convenient kind for the relevant products.

Claims: Claims 1 Method for the manufacture of a composite product comprising a core of foamed mateπal and at least one enveloping mateπal comprising a thermoplastic mateπal with a reinforcement, and where a significant step is to shape the product in a press shape mould, characterized in that the enveloping material and the core mateπal is introduced into the press shape mould while the core material and the enveloping mateπal is still in a plastic, non-consolidated state, and that at least one moveable component of the press shape mould then is moved to inflict a first, relatively high pressure on the product blank, giving the product blank a temporarily compressed shape while the core is still plastic, whereafter at least one moveable component of the press shape mould is withdrawn, allowing the product blank to expand and find its final shape and to consolidate. 2 Method according to claim 1, characterized in that the press shape mould is completely or partly closed along whole or part of its circumference after the materials are introduced into the press shape mould but prior to pressure being inflicted on the materials, effectively avoiding any parts of the foamed material from escaping from the press shape mould. 3. Method according to claim 1, characterized in that parts of the press shape mould are designed with recesses into which enveloping material and core material are allowed to move during shaping, for the formation of desired surface patterns on the product. 4. Method according to claim 1, characterized in that prior to the shaping process at least one solid or pre-conso dated core element, forming at least one element of the product, is introduced into and fixed in the press shape mould. 5. Method according to claim 1 , characterized in that an additional top layer like felt, PMMA-foil or the like is introduced into the press shape mould to provide the product with a particular surface finish. 6. Method according to claim 1 , characterized in that the enveloping material is pre-heated to a temperature where the thermoplastic component of the material is fluid or close to fluid, prior to introducing it into the press shape mould. 7. Press shape mould for shaping and pressing composite products comprising a core of foamed material and at least one enveloping material comprising a thermoplastic and a fibre reinforcement, and where a significant step consists in shaping the product in a press shape mould, which press shape mould (1) comprises at least two complementary parts (2, 3) arranged to be moved against each other to form a cavity (61, 6b) able to shape the product thereinbetween characterized in that at least one of the press shape mould parts (2, 3) contains a moveable piston member (4) carrying part of the surface (6a) arranged to shape the product, which piston member (4) is arranged to expose the product blank with a varying degree of pressure over time by externally controlled means.

Inventors: NORDLI BJARNE, NORDLI, BJARNE
Applicants: NORDLI BJARNE, SPILKA IND AS, NORDLI, BJARNE, SPILKA INDUSTRI AS
Application year: 2000
Main classification: B29C43
IPC codes: B29C43, B29C70