WO1999036250A1

WO1999036250A1 - Method for producing a tubular support structure

Info

Publication number: WO1999036250A1
Application number: PCT/DE1999/000040
Authority: WO
Inventors: Jörg PAULY
Original assignee: M 1 - Sporttechnik Gmbh
Priority date: 1998-01-13
Filing date: 1999-01-13
Publication date: 1999-07-22

Abstract

Disclosed is a method for producing a tubular support structure, especially a bicycle frame, comprising at least one plastic strut which has a foamed core (2) with reinforcing members (4), is covered with an outer skin (8) and joined thereto by means of a resin. In order to improve the stability of the support structure, it is possible to provide the core with a layer of fibre material before the outer skin is applied or to use the separating edge (obtained when the supporting structure is pressed) as a functional device acting as a highly resistant structure with or without the addition of reinforcing members.

Description

description

Method of manufacturing a tubular support structure

The invention relates to a method for producing a tubular support structure according to the preamble of claim 1 and support structures which are manufactured in particular by this method.

Such a method is used in particular for the production of two-wheel frames. However, this method can also be used in other areas of technology and products in which a high-strength supporting structure with a low weight is desired.

Although the history of the bicycle is long and successful, hardly any other branch of industry has done as little for the safety of the user as in bicycle construction. At present, it is estimated that around ten percent of all bicycle accidents are due to technical errors, although those without the involvement of other road users are rarely recorded. Above all, the large mechanical loads on the bicycle components, such as the frame, fork, handlebars or seat post, or the frequent occurrence of these loads, can lead to cracks or fatigue fractures in the material of the components.

In order for a bicycle component to be considered operational, its functionality must be designed for a time that corresponds to its expected service life, on average ten years. The following calculation example is given here to illustrate the loads acting on a two-wheeler. Assuming that the owner of a two-year-old two-wheeler Travel time to work every day (212 days a year, twice ten minutes each) and 100 shopping trips of ten minutes each, results in a required total service life of 52,400 minutes. Studies have shown that during this time, around 250,000 loads in the area of fatigue strength, ie the stress to which a component may be exposed as often as required, and those with half the fatigue strength occur more than a million times during this time. Extreme situations, such as driving in a rocking step, through potholes or when braking hard, are not yet recorded.

In order to construct a high-quality or safe bicycle, it is important that the object to be manufactured is carefully planned and developed and that high-quality materials are used and these are assembled according to the most modern technical criteria. For economic reasons, it is not possible to take these criteria into account to a sufficient extent with conventional, inexpensive two-wheelers.

One area where high-quality two-wheelers are needed is cycling. In order to be able to achieve good results here, it is important that the sports equipment is manufactured under the three aspects of aerodynamics, rigidity and weight, whereby these aspects are given different importance depending on the application. The frame type mainly used here is the so-called monocoque frame, which is not only made entirely of plastic, but is also made from one piece. Compared to metal and plastic frames made from individual components, it is stiffer and therefore less dampens the driving force. In addition, it can be made more aerodynamic by using fiber composite technology in contrast to classic metal processing. Such a method for producing a high-quality two-wheel frame is described for example in DE 43 08 370 C2. Here, a solid fusible core is first formed in an auxiliary mold with the shape of the inner surface of the desired shaped body. Subsequently, a core body provided with a jacket is formed by completely enveloping the core with an elastic, gas-tight jacket material. From this, a molded body blank is then created by wrapping the core body with a fiber material, which blank is impregnated with reactive plastic either before or after the wrapping. The molded body blank is inserted into a divisible mold and a pressure medium is fed directly into the gap between the surface of the solid core and the inner surface of the shell via the shell opening, so that the impregnated fiber material is pressed against the inner wall of the mold. The shaped body blank is then cured by the action of pressure and heat and then the core is melted and let out of the now finished shaped body.

However, this method has some disadvantages. It was developed from the point of view that it can be used to produce shaped bodies with a complex shape and minimized weight. However, as can be seen from the above explanations, it is very intensive in terms of the process and device-technical outlay, since on the one hand several molding tools are required and on the other hand the shaping by means of the fusible core requires many work steps. This inevitably leads to high cycle times. Another aspect is the high energy requirement during production, since the heat curing and the melting of the wax during molding and demolding must be added. Such methods are very cost-intensive and are more suitable for the production of smaller series, which are manufactured according to customer requirements, than for large-scale use.

In contrast, the invention has the object of providing a support structure and process for producing ^'a supporting structure such to provide, in which the method and apparatus technical effort is reduced to a minimum.

This object is achieved with regard to the method by the features of patent claim 1 and with regard to the supporting structure, in particular the two-wheel frame, by the features of patent claim 10.

In the method according to the invention for producing a tubular support structure, in particular a two-wheel frame, the foam core has several advantageous properties. On the one hand, it serves as a positioning element in the gluing or pressing and additionally, as will be explained later, during the pressing step takes over the function of the pressure generator from the inside, which means the complex and complicated use of a fusible core and a gas-tight jacket or its Applying pressure to the fiber material for shaping. The foam core also serves as a support for the reinforcing elements, which can be attached both to and in the core. This enables high-strength, but also space-saving support structures to be produced.

On the one hand, the use of an outer skin, which is manufactured using the deep-drawing process, offers the advantage of a freer design of the geometric shape than, for example, in classic metal processing, and on the other hand you get surfaces that no longer need to be reworked. In addition, there is no decorative work, such as painting, since the entire decor is preferably already applied to or under the outer skin.

The method on which the invention is based allows fasteners or inserts to be anchored therein via undercuts even while the outer skin is being deep drawn. This prevents destruction of the support structure when such inserts are retrofitted.

Furthermore, prefabrication of the outer skin in the deep-drawing process offers the possibility of adapting it to recesses preformed in the core, so that three-dimensional structures, such as e.g. Names, logos, images, embossments and hollows can be formed on the surface of the supporting structure.

If the core is covered with a layer of fiber material before the outer skin is connected to the foam core covered with reinforcing elements, an improvement in the strength of the construction of the supporting structure according to the invention is achieved with only a slight increase in weight.

It is also possible to at least partially form the outer skin of the two-wheel frame from a layer of damping material. This measure has the advantage that the frame structure is protected when it collides with a solid body. An advantageous embodiment of the present invention results from the fact that the separating edge formed during the pressing is removed in a further process step. On the one hand this results in a reduction in the frame weight and on the other hand you get smooth or round surfaces, which takes into account the aesthetic aspect.

In a further advantageous embodiment, the separating edge formed during the pressing is brought into a predetermined shape with predetermined dimensions in an additional method step. This separating edge offers several advantages. By precisely matching the number of reinforcing fibers pressed in the separating edge, the separating edge can be used as a highly stable load-bearing element. The geometry of the separating edge, which is preferably rounded off in the transition to the actual frame, prevents indentations and also achieves technical advantages such as an optimized flow of force. Fastenings, for example for containers, can also be attached to the separating edge. It is also possible to integrate components, such as metal holders for fasteners, in the separating edge.

If, in a further training, the separating edge is covered with padding, the cyclist receives optimal protection when it hits the frame, especially in the event of a fall. Furthermore, despite the aesthetic aspect, the covering edge of the separating edge does not dispense with the stabilizing properties of the separating edge.

Other advantageous developments of the invention are the subject of the further subclaims. Preferred embodiments of the invention are explained in more detail below with the aid of schematic drawings. Show it:

Figure 1 is a schematic plan view of a two-wheel frame according to a support structure of the present invention;

FIG. 2 shows a cross section along the axis X-X 'indicated in FIG. 1 of a two-wheel frame according to an embodiment of the present invention;

3 shows a cross section along the axis X-X 'indicated in FIG. 1 of a two-wheel frame according to a further embodiment of the present invention;

FIG. 4 shows a cross section along the axis X-X 'indicated in FIG. 1 of a two-wheel frame according to the invention with a further development on the separating edge;

5 shows a cross section along the axis X-X 'of a two-wheeled frame indicated in FIG. 1, in which recesses are provided or inserts are anchored in the outer skin via undercuts.

For a better understanding of the support structure 1 according to the invention, the description of the figures describes the manufacture of a support structure according to the first embodiment.

Figure 1 shows a preferred embodiment in which the support structure is designed as a two-wheel frame 1.

This has a curved central region (central support), at the end sections of the steering head with a receptacle for the steering head tube 32 and a receptacle 26 are designed for the bottom bracket. A freely projecting seat post support with a receptacle 34 for the seat tube is formed approximately in the central region of the central body. To stabilize the frame structure 1, a circumferential separating edge 10 is formed, which is covered with padding 12 in the section between the control head tube 32 and the seat tube 34. Furthermore, special fixing or reinforcement elements 24, a ^'front cover 30 and a contour provided with a logo 20 can be seen on the bicycle frame. 1 To increase the torsional rigidity, the frame is designed as a closed profile, for example with an oval cross section.

Figures 3, 4 and 5 shown below are cross sections taken along the axis X-X 'of a frame strut. The cross sections of the two-wheel frames 1 according to the preferred embodiments have an approximately elliptical or oval shape, the straight line containing the focal points representing the axis of symmetry or vertical axis V of the shape and lying within the frame plane. The separating edge 10 is also aligned along this vertical axis V. A step is formed at approximately a quarter of the total height of the mold in the vertical direction from above, in which a lower section with a larger radius of curvature merges into an upper section with a smaller radius of curvature. The reinforcement elements 4 attached to or in the foam core 2 are arranged approximately symmetrically with respect to the vertical axis V both in the upper and in the lower section and thereby extend the separating edge 10.

FIG. 2 shows a cross section of a two-wheeled frame 1, which is produced according to the first embodiment of the method according to the invention. The two-wheeled frame 1 produced according to the method described below has a core 2, which is not necessarily designed with the comparatively simple cross-section shown in FIG. 2, but in which three-dimensional structures can also be incorporated (see FIG. 5). The core 2, for example, (expandable polystyrene) of an EPS, PU (polyurethane) foam or similar materials loading ^'is, is usually supplied by suppliers in the desired configuration, and has already been provided with recesses 20 for receiving further Provide components (for inserts, brackets, etc.).

When the core 2 is formed, reinforcement elements 4, which consist, for example, of metal, injection molding or carbon, can be foamed directly or subsequently introduced into the core 2. Furthermore, the reinforcing elements 4 and inserts or holders can be attached to the core outer surface 2 subsequently. Aluminum, for example, can be used as the metal for the reinforcing elements. The positioning or fastening is carried out by means of special adhesives or adhesive tapes or by mechanical connections, such as for example plug-in or press connections in prefabricated or foamed placeholders or clamps or the like. A combination of several variants is also conceivable.

The core 2 provided with reinforcing elements 4 is covered according to a specially developed and tested occupancy plan with an intermediate layer of fiber material 8, which consists for example of glass, aramite, polyamide, carbon fibers or carbon fibers etc. or their mixed materials. It is also conceivable to use a so-called "sandwich" structure instead of the simple layer of fiber material 8, in which rigid foam plates are inserted between two layers of fiber material. However, it is important to align the assignment according to whether a separating edge 10 that is created during pressing should be retained as a stabilizing element on the finished two-wheeled frame 1, or whether it is cut off during post-processing. So that the separating edge 10 receives its high-strength structure, part of the assignment must be integrated in it. The molded part or core 2, which is made of fiber material 8, is also called "mummy".

If it is primarily a matter of a low weight and less of a high-strength construction of the support structure 1, the step of covering the core 2 with an intermediate layer of fiber material 8 can be omitted.

Resin (matrix), which consists, for example, of epoxy or PU resin, is applied in defined amounts to the mummy or core 2 created in this way. The addition of blowing agents in the synthetic resin, especially in the case of epoxy resin, can be advantageous. The resin can be applied automatically by a computer-controlled spraying system, by a bar caster or manually by spreading the amount of resin with a brush or doctor blade.

The "wet" mummy provided with the fresh resin application or the resin-coated core 2 is then brought to the press system, which usually has a press mold with two movable mold halves. Before inserting the mummy or the core 2 into the mold, an outer skin 6 made of a thermoplastic film 6 or a layer 6 of shock-absorbing material is introduced into the mold surfaces of the two mold halves in each case using the vacuum deep-drawing method. The thermoplastic film 6 consists, for example, of ABS (acrylonitrile-butadiene-styrene), ASA (acrylic rubber-styrene-acrylonitrile), PC (polycarbonate) or PMMA (polymethylmedacrylate) and the layer 6 damping material, for example made of EVA (ethylene-vinyl acetate copolymer) or foamed PE (polyethylene) plates.

In each case, one film web is aligned with respect to the lower or upper mold half, heated and a vacuum is applied so that the film webs lie completely over the mold surfaces of the respective mold halves. This negative pressure is maintained until the "wet" mummy or core 2 is inserted into the mold. After pressing in the mold, the thermoplastic film 6 or the layer 6 of damping material form the outer skin 6 of the supporting structure 1. This process is known in the technical literature as the "double deep-drawing process".

Instead of prefabricating the outer skin 6 of the support structure 1 or the two-wheel frame 1 in the movable mold halves of the press mold, it is also possible to preform the surface layer 6 or outer skin 6 in special separate deep-drawing molds. It is also conceivable to produce the outer skin 6 separately instead of using the deep-drawing process in other processes, such as, for example, the RTM (resin transfer molding) process. In this variant, the solidified outer skin 6, which already has the relevant contours, is inserted into the production mold in a further operation. This separate preforming of the outer skin 6 makes it possible to achieve short cycle times.

The "wet" mummy or core 2 is in one of the

Molded halves of the production mold are inserted, the position being fixed with reference to the prefabricated outer skin element 6 via components which were inserted in the mold half in an initial process step. The mold is then closed after a predetermined time or pressure curve. If the mold halves have been moved towards one another or pressed to a distance of approximately 1 to 2 mm, the complete closing takes place only after a certain period of time in order to ensure that the excess resin required for the process is driven off. The foam core 2 is dimensioned such that it has a local oversize together with the fiber covering 8 in the press mold, which means that a press pressure can be built up from the inside. This pressing pressure distributes the resin on the surface and presses it through the fiber layers 8 so that they are all sufficiently impregnated with synthetic resin.

In this context, the separating edge 10 that arises during pressing deserves special attention. In the area in which the two outer skin halves 6 adjoin one another, due to the geometry, only a little pressing pressure can be generated, since this primarily acts in the pressing direction, but not perpendicular to it. For this reason, in the case in which it is desirable, the occupancy with fiber material 8 is made more generous in order to ensure that a high-strength separating edge 10 is formed during pressing with part of the occupancy. The press edge gap, which can be designed differently, is dimensioned so that an optimal resin content is achieved. A particular advantage of the separating edge 10 lies in the fact that, on the one hand, special reinforcing elements 24, especially for reinforcement in the tension / compression area, and on the other hand components 24, such as metal receptacles for fastenings, can be integrated into it.

The two-wheel frame 1 is finally cured at the pressure and the temperature required for the method, depending on the requirement, for about 30 minutes. It is particularly important here that a stabilized state of hardening is ensured in order to ensure that to avoid borrowing of frame 1. To optimize the cycle time, it is also possible to subsequently temper the two-wheeled frame 1 in special holders.

The pressing process is understood not only as the pressure / temperature application in a pressing tool, but also any pressure increase, for example by chemical reactions (cf. RIM (Reaction Injection Molding) process) or others.

The product obtained after the pressing process is distinguished by an excellent surface quality, so that the subsequent finishing of the supporting structure 1 essentially consists of the finishing of the separating edge 10 in order to remove possible sharp corners or edges. Furthermore, any openings that may be provided, such as for bottom bracket 26 or headset, must be drilled out or milled.

In a further embodiment, the separating edge 10 is cut off with special tools, such as milling devices, in order to obtain an aesthetic shape with the additional effect of a lower weight.

It is obvious that a very high degree of automation can be achieved by the procedure according to the invention, whereby an inexpensive production and thus also feasible in high-wage countries is possible.

After the actual support structure 1 is finished, the parts necessary for the operation of a two-wheeler, such as guides, headsets, bottom brackets, etc. are attached to the frame 1. In order to seal the core against water, for example in the bottom bracket receptacle 26, an insert can be integrated here or a seal can be created using a blowing agent-containing synthetic resin. If necessary, the relatively soft thermoplastic film 6 or layer 6 of damping material must be removed from the bottom bracket receptacle 26 in order to avoid any play that may subsequently occur. A metal O-ring on the headset can provide the necessary reinforcement.

In order to improve the optical effect, a front cover 30 (see FIG. 1), a so-called “front cover”, can be attached in the control head area, which consists, for example, of metal such as aluminum, injection molding, carbon, etc.

It is not necessary to paint the two-wheel frame 1 since the complete decor is already printed on or under the outer skin 6. If necessary, stickers can be used for additional decoration.

Figure 3 shows a cross section of a two-wheel frame 1, which is made according to another embodiment of the method according to the invention.

In this embodiment, the separating edge 10 formed during the pressing, which in this respect lies in the frame plane, is brought into a predetermined shape with predetermined dimensions in a further method step during the post-processing, for example by means of milling devices. In order to minimize the risk of injury in the case of undesired contact with the separating edge 10, this is rounded off and can have a dimension or width B of approximately 10 to 30 mm in a horizontal plane perpendicular to the frame plane V. As already mentioned above, the separating edge 10 not only has the advantage that it improves the stability of the two-wheel construction, but also that it can also be used to fasten components. Of- further, the geometry of the separating edge 10, which is preferably rounded in the transition to the actual frame, prevents indentations and also achieves technical advantages such as an optimized flow of force.

FIG. 4 shows a cross section along the axis X-X 'indicated in FIG. 1 of a two-wheel frame according to the invention with a development on the separating edge;

According to FIG. 4, the separating edge 10 is covered here with an elastic padding 12, which consists, for example, of EVA or foamed PE or PU panels. This not only gives the cyclist protection in the event of a rough impact on the frame, especially in the event of a fall, but the aesthetic aspect is also taken into account by hiding the separating edge 10 under the padding 12.

FIG. 5 shows a cross section along the axis X-X 'indicated in FIG. 1 of a two-wheel frame 1, which has the cross section shown in FIG. 4. In this embodiment, recesses 20 are provided or inserts 22 are anchored in the outer skin via undercuts. Possibilities for receiving peripheral components such as inserts 22, fastening elements 22 or cutouts 20 are illustrated below.

One measure consists in permanently anchoring inserts 22, such as fastening elements, in the outer skin 6 via undercuts. In the step of prefabricating the outer skin 6 before deep drawing, the inserts 22 to be anchored in the outer skin 6 are fixed in the upper mold half with pins etc. During the subsequent deep-drawing of the surface or outer skin 6 consisting of the thermoplastic film 6 or the layer 6 of damping material, through the thermal deformation of the outer skin suitably surrounds the inserts 22 inserted into the mold half. After the outer skin 6 thus formed has subsequently cooled, the inserts 22 are anchored stably and permanently in the outer skin 6 via undercuts.

Another measure consists in creating two- or three-dimensional structures 20, such as recesses 20 or elevations 20, on the frame 1. On the one hand, these structures 20 must be taken into account in or on the core 2 covered with fiber material 8 and on the other hand in the prefabricated outer skin 6. Here, in particular, the deep-drawing processes, in which the desired three-dimensional structure 20 only has to be formed in the corresponding mold half, offer a simple possibility of also producing complicated three-dimensional structured surface layers. It is conceivable to use the cutouts 20 thus created by subsequently gluing, gluing, screwing on or chemical or thermal welding of inserts, fastening elements, decorative elements etc. as functional devices or simply leaving them as an aesthetic feature.

An advantage of the frame construction according to the invention is that, for example, a full carbon frame can also be produced with the same molds or molds. Instead of the fiber layer 8 applied to the core 2 and the outer skin 6 surrounding this fiber layer 8, it is possible to use Prebreg (fiber material impregnated with reactive plastic) made of synthetic resin, Prebreg with thermoplastic or wet laminate. However, the mold halves must be heatable here.

However, as has already been indicated at the beginning, the invention is in no way related to the production of Two-wheel frame 1 limited, but also extends to other areas of application.

What is disclosed is a method for producing a support structure 1, in particular a two-wheeled frame 1, which has at least one strut made of plastic, the strut having a foam core 2 provided with reinforcing elements 4, which is surrounded by an outer skin 6 ^' and connected to it by means of a resin is. In order to improve the stability of the support structure 1, it is possible to provide the core with a layer of fiber material 8 before the outer skin 6 is applied, or to use the separating edge 10 obtained during the pressing of the support structure as a functional device, with and without special reinforcing elements 24 ensures a high-strength structure.

Claims

Expectations

1. A method for producing a tubular support structure (1), in particular a two-wheeled frame (1), with the steps:

Forming a foam core (2) provided with reinforcing elements (4)

Applying a resin layer to the core (2)

Manufacture of an outer skin (6) and

- Connect the outer skin (6) with the occupied foam core (2).

2. The method according to claim 1, characterized in that the outer skin (6) is prefabricated in the deep-drawing process.

3. The method according to claim 1 or 2, characterized by the further step that the foam core (2) before the outer skin (6) with the occupied foam core (2) is covered with a layer of fiber material (8).

4. The method according to any one of claims 1 to 3, characterized by the further step that the separating edge (10) formed during pressing is removed.

5. The method according to any one of claims 1 to 3, characterized by the further step that the separating edge (10) formed during pressing is brought into a predetermined shape with predetermined dimensions.

6. The method according to claim 5, characterized by the further step that the separating edge (10) with a padding (12) is covered.

7. The method according to any one of claims 1 to 6, characterized in that the outer skin (6) consists at least partially of a layer (6) made of damping material.

8. The method according to any one of claims 2 to 7, that inserts (22) during the deep-drawing process of the outer skin

(6) can be permanently anchored in this undercut.

9. The method according to any one of claims 1 to 8, characterized in that two or three-dimensional structures

(20) on the supporting structure (1), such as names, logos, images, embossings and hollows.

10. two-wheel frame (1) with at least one strut made of plastic, in particular manufactured according to a

Method according to claims 1 to 9, characterized in that the strut has a foam core (2) provided with reinforcing elements (4), which is surrounded by an outer skin (6) and is connected to it by means of a resin.

11. two-wheel frame (1) according to claim 10, characterized in that the outer skin (6) is made of a thermoplastic.

12. two-wheel frame (1) according to claim 10 or 11, characterized in that between the foam core (2) and the outer skin (6) a layer of fiber material (8) is formed.

13. Two-wheeled frame (1) according to one of claims 10 to 12, characterized in that the outer skin (6) consists of several parts, a separating edge (10) being formed on the adjacent peripheral edges of the parts.

14. Two-wheeled frame (1) according to claim 13, characterized in that the separating edge (10) lies in the frame plane (V) of the two-wheeled frame (1) and in a horizontal plane perpendicular thereto, a width (B) of approximately 10 to 30 mm.

15. Two-wheel frame (1) according to claim 13 or 14, characterized in that the separating edge (10) is surrounded by a padding (12).

16. two-wheeled frame (1) according to one of claims 13 to

15, characterized in that special reinforcing elements (24) are attached in the tension / compression area.

17. two-wheel frame (1) according to any one of claims 10 to

16, characterized in that the reinforcing elements (4,24) made of metal such as aluminum and / or the core (2) made of a PU or EPS foam and / or the outer skin (6) made of an ABS, ASA, PC - Or PMMA film and / or the padding (12) and the layer (6) made of damping material made of EVA or foamed PE material.

18. Two-wheel frame (1) according to one of claims 10 to 17, characterized in that a front on the control head

Cover (30) is attached.

19. Two-wheel frame (1) according to claim 18, characterized in that the front protective cover (30) consists of metal such as aluminum, injection molding or carbon.

20. Two-wheel frame (1) according to one of claims 10 to 19, characterized in that the fiber material (8) has carbon fibers.