METHOD FOR PRODUCING A PLASTIC FRAME FOR A TWO-WHEEL VEHICLE

Description

[0001] The invention relates to a method for producing a plastic frame for a two-wheeler having at least one hollow space in its interior, as described in the preamble of claim 1.

[0002] It is already known to manufacture bicycle frames from plastic. This is typically done using a resin injection process known as "Resin Transfer Molding" (RTM). In this process, glass and / or carbon fiber fabric is inserted into a mold. With the mold closed, the fabric is impregnated with a thermosetting matrix material, such as an epoxy resin or polyurethane, which is injected into the mold. Thermosetting matrix materials usually consist of two basic substances that must be thoroughly mixed before being introduced into the mold. After mixing and injection into the mold, a chemical reaction occurs. Once the reactants have been converted accordingly, the component can be demolded.

[0003] The glass or carbon fiber fabrics are typically inserted into the mold in a three-dimensional woven state. An inflatable tube is usually inserted inside the fabric. After resin injection, the tube can be inflated with a fluid inside the component, creating the desired cavity. Once the reactants have completed their reaction, the pressurized fluid is released. The cured component can then be removed.

[0004] Bicycle frames made of thermoset matrix material have the major disadvantage that they cannot be effectively recycled due to the material used. Apart from thermal recycling through incineration, there is no reasonable recycling option for the components manufactured in this way.

[0005] A bicycle frame has a complex geometry, which makes manufacturing using an injection molding process complicated. In particular, the frame comprises several long, hollow tubes arranged at an angle to each other and with different cross-sections. Furthermore, various attachments must be accommodated on the frame. The document CN 103 552 220 A discloses the basic idea of ​​creating the cavities in the tubes by displacing the still-liquid plastic in the core of the rod-like plastic structures in the cavity.

[0006] The object of the present invention is to provide a method for producing a plastic frame for a two-wheeler, in which a plastic can be used that enables a sensible recycling of the two-wheeler frame.

[0007] According to the invention, to achieve this object, a method for producing a plastic frame for a two-wheeler having at least one cavity in the interior by means of plastic injection molding with the steps according to claim 1 is provided.

[0008] The method according to the invention comprises at least the following steps: Injecting a thermoplastic melt into a closed injection mold; injecting a fluid to displace the plastic core from the component cavity and maintaining the fluid pressure inside the component for at least a short time.

[0009] In the method according to the invention, the cavity of the closed injection mold forms the geometry of a two-wheeler frame, for example a bicycle frame, wherein the tool is equipped with at least one injector for the introduction of a fluid. The fluid is capable of displacing the plastic core and thus achieving a tubular cross-section. The fluid is injected via a preset profile in a volume flow- or pressure / time-controlled manner. Due to the tubular cross-section, the cooling phase of the hot plastic melt can be significantly shortened due to the comparatively thin remaining wall thickness. This means that only a comparatively short cooling time is required. Overall, a very significant reduction in cooling time can be expected compared to a frame made of solid material. Due to the faster cooling time, the total time required to manufacture a two-wheeler frame can be significantly reduced.This allows these components to be manufactured even more cost-efficiently. Furthermore, the internal cavity significantly reduces the mass of the entire bicycle frame, which not only provides a weight advantage but also, and more importantly, an economic advantage. A closed tubular cross-section can also be expected to provide greater rigidity. When referring to a tubular cross-section, it can, of course, be circular, oval, polygonal, or any other desired shape.

[0010] Advantageously, the fluid is blown out and / or sucked out after at least a short period of maintaining the fluid pressure.

[0011] Accordingly, the fluid can, for example, press the plastic core into a secondary cavity provided in the injection mold.

[0012] According to an alternative embodiment of the invention, the fluid can press the plastic core into the screw antechamber via a mass push-back process through the heating channel or partial hot runner or cold runner of the plastic injection molding machine located in the injection molding tool.

[0013] According to another advantageous embodiment of the method according to the invention, the injection molding tool can be only partially filled with the preferably thermoplastic molten plastic, whereby the plastic core is displaced by inflating the preferably thermoplastic molten plastic in such a way that it adheres to the wall of the injection molding tool, forming a cavity. This process variant, known as the inflation process, enables very economical use of the plastic required to form the frame.

[0014] According to the invention, a correspondingly shaped core is inserted during the injection molding process in the area of ​​at least one part to be integrated into the plastic frame, such as a motor or a battery, so that this area is hollow after the component is removed from the mold. The respective component, such as the motor or the battery, can then be inserted into this recess during final assembly.

[0015] According to a further embodiment of the invention, a design and / or functional film and / or a tape made of carbon or glass fiber fabric can be inserted into the mold before the plastic melt is injected and back-injected with the plastic melt. This film can, of course, also be used as a combination film that has a specific desired design and also a specific functionality. Such functionality could, for example, be a capacitive sensor that turns the motorcycle's lights on or off.

[0016] Yet another advantageous embodiment of the invention provides that parts of the two-wheel frame, such as the center strut, are inserted into the injection mold as a finished part made of plastic, aluminum or another material and are connected to the advantageously thermoplastic plastic during the injection molding process.

[0017] Although the fluid primarily serves to form the cavity in the plastic frame, it can be given a secondary use by being guided in a circulating flow after the cavity has been formed, so that it now serves to cool the plastic material, which is still very hot immediately after the injection process.

[0018] Advantageously, a plastic selected from the following group can be used in the process according to the invention: polyamide, preferably polyamide 12, polyamide 6 or polyamide 6.6, polypropylene, polyethylene, polyethersulfone, polyetherimide, polyetherketone, polyphenylene sulfide, polyvinyl chloride, polyester, acrylonitrile butadiene styrene (ABS), polycarbonate / acrylonitrile butadiene styrene (ABC / PC), polycarbonate (PC) and particularly preferably polybutylene terephthalate or polyterephthalateethylene.

[0019] These materials can also be selected and used individually or in combination. The selected plastics can also be reinforced with short and / or long fibers made of glass, carbon, and / or natural fibers.

[0020] Alternatively, the plastic can also be injected as caprolactam with an associated activator into the injection mold and polymerized in the heated mold.

[0021] The injected fluid can advantageously be water and / or a gas. This fluid is introduced via at least one injector arranged in the tool.

[0022] Further features, details and advantages are explained in more detail with reference to embodiments shown in the drawing, some of which are shown in the figures.

[0023] They show: Figures 1 to 5: the plastic frame of a women's bicycle according to a first embodiment of the invention in different schematically illustrated process stages; Figures 6 to 10: a plastic frame of a men's bicycle according to a second embodiment of the invention in different schematically illustrated process stages; and Figures 11 to 15: the plastic frame of a scooter according to a method not encompassed by the invention in different schematically illustrated process stages.

[0024] The basic process sequence of the method according to the invention for producing a two-wheeled plastic frame can be explained using the first embodiment of the present invention according to Figures 1 to 5.

[0025] So in Figure 1 The frame 10 of a ladies' bicycle is shown schematically. The rear wheel 12, which is later arranged in the rear part of the frame, is shown schematically. Figure 1 The thermoplastic melt has just been injected into the closed molding tool (not shown in detail here). At the same time, slides or cores 14, 16, and 18 have been inserted into the molding tool in the direction of the arrows, preventing the injected plastic melt from penetrating this area. Slides 14 and 16 form cavities for the steering head bearing, slide 18 forms a cavity for accommodating the seat tube to be attached later, and an inserted slide 20, perpendicular to the plane of the drawing, forms the cavity in which the bottom bracket will later be arranged. Figure 2 A fluid 22 is now injected in the direction of arrow A through an injector (not shown here in detail), which displaces the so-called plastic core from the interior of the component. Figure 2Here, a portion of the core has already been displaced. In this embodiment, the excess plastic material is pressed into a secondary cavity 24. The secondary or overflow cavity 24 can be opened and closed hydraulically, pneumatically, and / or electrically via a slide valve.

[0026] In Figure 3 a larger part of the frame 10 is already filled with the injected fluid. In Figure 4 The fluid injection and the displacement of the plastic core from the frame area are now complete. According to the illustration according to Figure 5 After the plastic material has cooled down, the slides 14, 16, 18 and 20 are pulled out in the direction of the arrow and the secondary cavity 22 is separated.

[0027] In the aforementioned embodiment, the cavity of the closed injection mold forms the geometry of the bicycle frame in a manner not shown in detail. The mold, not shown here, is equipped with at least one injector for introducing the fluid 22, which can consist of gas, water, or a mixture of gases, or of water with gas or gases. The fluid for displacing the plastic core can be injected using volume flow control or pressure / time control via a preset profile. Due to the tubular cross-section, the cooling phase of the hot plastic melt relates only to the remaining wall thickness. This means that a huge reduction in cooling time is achieved compared to the cooling time of a full frame. The faster cooling time correspondingly shortens the overall cycle time, and the components can therefore be manufactured extremely cost-efficiently.The internal cavity reduces the mass of the entire bicycle frame, which offers not only a weight saving but also an economic advantage. A closed tubular cross-section also generally creates greater rigidity than a solid frame.

[0028] The complete process for manufacturing the bicycle frame is outlined below in the form of the required process steps. The sequence of steps is advantageously as follows: 1. Closing the injection mold; 2. Closing force build-up; 3. Injection of the thermoplastic melt; 4. Optionally only a short holding time of approx. two seconds; 5. Opening at least one injector in the tool and starting fluid injection; 6. Displacement of the plastic core from the component cavity by means of the fluid; 7. Maintaining fluid pressure inside the component for a short time (effect like a holding pressure); 8. Optional flushing process inside the component using the same fluid or a different fluid to achieve a better cooling effect; 9. Blowing out the fluid (or sucking it out using a vacuum); 10. Open the tool and 11. Ejecting the component.

[0029] With this sequence of steps, it should be noted that step 9 is not mandatory. If gas is used as the injected fluid, it can also remain in the component. The fluid used can consist of water or gas. However, it can also consist of both media, as, for example, an air bubble is often pushed ahead of the water, or nitrogen is used first to create the cavity and then CO2 is used to cool the component.

[0030] In the illustrated embodiment, polyamide or a polyolefin reinforced with glass fibers and / or carbon fibers and / or natural fibers is preferably used as the thermoplastic material.

[0031] In order to make the frame 10 as stiff as possible, so-called tapes or organic sheets, i.e. glass, natural or carbon fiber fabrics, can be inserted into the tool in certain areas. These can be back-injected with the plastic melt. The tapes can be placed and held in the tool by a special device. The targeted fiber orientation of the tapes / organic sheet tapes gives the frame greater stiffness in critical areas, such as the pedal or steering head bearings. In order to achieve the best possible bond between the tapes and the thermoplastic melt, the tapes can be preheated to a certain temperature before being inserted into the tool, with this specific temperature being selected depending on the matrix material of the tape.

[0032] To avoid the additional effort required for installing and fitting additional components for the finished bicycle frame after injection molding, the required components, such as pedal and / or steering head bearings, threaded sleeves for water bottle cages, the battery holder for an electric bicycle, or, for example, the holder for a conventional motor when the invention is used in motor-driven two-wheelers such as motorcycles, can be inserted directly into the injection mold and overmolded. This can significantly simplify the production process, since this process step allows the bicycle frame to be removed from the injection mold immediately with the required components.

[0033] To create a beautiful and individual design, the frame can be printed with a design using foils. These are inserted into the mold and back-injected. This is also known as "in-mold labeling" or "in-mold decoration." Instead of using purely design foils, functionalities can also be achieved using functionalized foils. These functionalized foils are also inserted into the mold and back-injected with the plastic material. The functionalized foils can, for example, be printed circuit boards or capacitive sensors with, if necessary, an attached microcontroller. They can also contain transponder properties. Furthermore, the foil could be functionalized with a GPS signal, which could then be used for theft protection.

[0034] Due to the positive property that the frame is made of plastic and is therefore non-conductive, signals, data, and / or energy can be transmitted seamlessly via the integrated and / or applied functionality. Additional cabling to conduct the generated energy from an energy-generating unit, such as a dynamo, to the consumer, such as a bicycle light, could also be replaced with a suitably functionalized film.

[0035] A bicycle frame 10, as shown in the first embodiment using the Figures 1 to 5As explained, it can be manufactured from a single polymer or a mixture of several. Polyamides or polyolefins are generally particularly recommended for the frame. TPE or TPU can also be injected into the mold as additional components. These do not necessarily require a cavity, but are often used to overmold or encase the first component.

[0036] Based on the Figures 6 to 10 A further embodiment of the invention is shown schematically. Here, the method for manufacturing a men's bicycle is shown. The bicycle frame 10 thus has a Figures 1 to 5 different shape, as is typical for a men's bicycle. Essentially, the same components are designated with the same reference numerals. The sequence of steps in the manufacturing process, as described in the Figures 6 to 10is essentially the same as that according to the Figures 1 to 5 of the first embodiment. However, in this example, a center strut 26 made of aluminum or another material is inserted into the injection mold, so that it bonds with the thermoplastic during the injection molding process. This center strut 26 also has the receiving opening for the seat post to be inserted later and can also be filled with a different material, preferably polyurethane, for process-related or other reasons.

[0037] In the embodiment shown here, the fluid 22 is injected in the direction of arrow B to displace the plastic core. Figures 6 to 10 the respective progress of the displacement of the soul is shown, whereby here too the plastic soul is displaced into a secondary cavity 24.

[0038] For comparison, Figures 11 to 15The manufacture of a frame for a scooter (motor scooter) is shown schematically, which is not covered by the invention. This is a motor-driven two-wheeler. The somewhat more stable and complex frame of the scooter 10 results from the illustration according to the Figure 11 As with the bicycle frame, only the plastic material is shown here and not the closed injection mold.

[0039] According to the Figure 12 The fluid is injected in the direction of arrow C. This increasingly displaces the plastic soul, whereby the respective progress of the displacement of the soul in the Figures 13 to 15are shown. Not shown in detail in this exemplary embodiment is the secondary cavity, which connects behind the frame or accommodates the injection molding tool with a hot, semi-hot, or cold runner (for the mass compression molding process) and the displaced plastic material. This more complex example demonstrates that the simple and rapid manufacturing process for the two-wheeler frame can also be used for motor-driven two-wheelers with more complex frame structures. The tool is inserted in such a way that the fabric inserted in the tool is flooded. Increasing the temperature and pressure inside the mold, thereby polymerizing the injected plastic. The bicycle frame is removed from the mold after polymerization is complete.

[0040] The frame, made of thermoplastic matrix material, can be recycled at any time and is therefore reusable.

[0041] In this process, the injected fluid inside the frame should not come into contact with the plastic melt. Therefore, during in-situ polymerization, a tube is inserted into the mold. The tube serves as the core and can be inflated using the fluid pressure in the cavity. During polymerization, the fluid in the tube is pressurized. This pressure leads to better part quality during the process, although the pressure can vary over time (pressure / time profile). The inflated tube forms the cavity.

[0042] A bicycle frame 10, as shown in the first embodiment using the Figures 1 to 5As explained, it can be manufactured from a single polymer or a mixture of several. Polyamides or polyolefins are generally particularly recommended for the frame. TPE or TPU can also be injected into the mold as additional components. These do not necessarily require a cavity, but are often used to overmold or encase the first component.

[0043] Based on the Figures 6 to 10 A further embodiment of the invention is shown schematically. Here, the method for manufacturing a men's bicycle is shown. The bicycle frame 10 thus has a Figures 1 to 5 different shape, as is typical for a men's bicycle. Essentially, the same components are designated with the same reference numerals. The sequence of steps in the manufacturing process, as described in the Figures 6 to 10is essentially the same as that according to the Figures 1 to 5 of the first embodiment. However, in this example, a center strut 26 made of aluminum or another material is inserted into the injection mold, so that it bonds with the thermoplastic during the injection molding process. This center strut 26 also has the receiving opening for the seat post to be inserted later and can also be filled with a different material, preferably polyurethane, for process-related or other reasons.

[0044] In the embodiment shown here, the fluid 22 is injected in the direction of arrow B to displace the plastic core. Figures 6 to 10 the respective progress of the displacement of the soul is shown, whereby here too the plastic soul is displaced into a secondary cavity 24.

[0045] However, the method according to the invention can be used to manufacture more than just bicycle frames. Based on the third embodiment according to the Figures 11 to 15 The manufacturing of a frame for a scooter is shown schematically. This is a motor-driven two-wheeler. The somewhat more stable and complex frame of the scooter 10 results from the illustration according to the Figure 11 As with the bicycle frame, only the plastic material is shown here and not the closed injection mold.

[0046] According to the Figure 12 The fluid is injected in the direction of arrow C. This increasingly displaces the plastic soul, whereby the respective progress of the displacement of the soul in the Figures 13 to 15are shown. Not shown in detail in this exemplary embodiment is the secondary cavity, which connects behind the frame or accommodates the injection molding tool with a hot, semi-hot, or cold runner (for the mass compression molding process) and the displaced plastic material. This more complex example demonstrates that the simple and rapid manufacturing process for the two-wheeler frame can also be used for motor-driven two-wheelers with more complex frame structures.

Claims

1. Method of manufacturing a plastic frame for a two-wheeler having at least one hollow space in the interior by means of plastic injection molding, said method comprising the following steps: - injecting a thermoplastic plastic melt into a closed injection molding tool; - injecting at least one fluid to displace the plastic core from the component cavity; and - at least briefly maintaining the fluid pressure in the component interior, characterized in that a plurality of fluids are injected into the injection molding tool and their individual fluid volume flows or pressure / time profiles are regulated separately from one another; a correspondingly shaped core is inserted during the injection molding process in the region of at least one part to be integrated into the plastic frame such as a motor and / or a storage battery such that this region is hollow after the component demolding; and at least one part to be integrated into the plastic frame, such as a steering head bearing and / or a bottom bracket bearing, are inserted into the injection molding tool, are held in the injection molding tool by means of an apparatus and are overmolded with plastic.

2. Method in accordance with claim 1, characterized in that the fluid is blown out and / or sucked out after a brief maintenance of the fluid pressure in the component interior.

3. Method in accordance with claim 1 or claim 2, characterized in that the fluid presses the plastic core into a secondary cavity provided in the injection molding tool.

4. Method in accordance with claim 1 or claim 2, characterized in that the fluid presses the plastic core via a mass back pressure process through a passage, for example a hot passage, a partly hot passage, or a cold passage, into the screw antechamber of the injection molding machine.

5. Method in accordance with claim 1 or claim 2, characterized in that at least one shaping cavity of the injection molding tool is only partially filled with the thermoplastic plastic melt; and in that the plastic core is displaced by the injection of the fluid so that the thermoplastic plastic melt is inflated such that it contacts the wall of the injection molding tool while forming a hollow space and the shaping cavity is then completely filled.

6. Method in accordance with one of the preceding claims, characterized in that a design and / or functional film and / or a tape or an organic sheet of fabric of carbon fibers, glass fibers and / or natural fibers is placed into the tool before the injection of the plastic melt and is back-injection molded or overmolded with the plastic melt.

7. Method in accordance with one of the preceding claims, characterized in that at least one part of the bicycle frame such as the middle strut are placed in as a finished part composed of plastic, aluminum, or of another material and are bonded to the thermoplastic during the injection molding process.

8. Method in accordance with one of the preceding claims, characterized in that the fluid is circulated after the hollow space formation to promote the cooling of the plastic.

9. Method in accordance with one of the preceding claims, characterized in that the plastic is a polyamide, preferably polyamide 12, polyamide 6 or polyamide 6.6, polypropylene or polyethylene, polyether sulfone, polyetherimide, polyetherketone, polyphenylene sulfide, polyvinyl chloride, a polyester, acrylonitrile butadiene styrene (ABS), polycarbonate / acrylonitrile butadiene styrene (ABC / PC), polycarbonate (PC), polybutylene terephthalate or polyterephthalate ethylene, preferably a polybutylene terephthalate or polyterephthalate ethylene.

10. Method in accordance with one of the preceding claims, characterized in that the injected fluids comprise water and / or one or multiple gases.