Method of manufacturing a two-wheeler frame

Abstract

The invention relates to an injection molding method of manufacturing a two-wheeler frame in which a melt of a thermoplastic is injected into a cavity of an injection molding tool before a portion of the plastic melt is displaced from the cavity again by a subsequent fluid injection to form the inner hollow space of the tubular frame, with the fluid flowing upward in the course of the displacement process.

Claims

1. A method of manufacturing a two-wheeler frame having tubular frame components comprising at least a steering tube, a down tube, and chain stays, the method comprising: injecting a plastic melt of a thermoplastic into a cavity of an injection molding tool through at least one plastic injection point; and subsequently injecting a fluid into the cavity through at least two different fluid injection points disposed in different regions of the cavity corresponding to different tubular frame components to displace a portion of the plastic melt from the cavity and urge the portion of the plastic melt that is displaced out of the cavity through at least one outlet of the cavity, to form an inner hollow space of the tubular frame components; wherein each of the at least two different fluid injection points is disposed at the injection molding tool below the at least one outlet and a shape of the cavity, a position of the at least one outlet, and a position of each of the at least two different fluid injection points are such that the fluid flows only in an upward direction in the cavity from each of the at least two different fluid injection points to the at least one outlet.

2. The method in accordance with claim 1, wherein injecting the fluid comprises sequentially injecting a gas and a liquid.

3. The method in accordance with claim 1, wherein also the at least one plastic injection point is disposed below the at least one outlet.

4. The method in accordance with claim 1, wherein the at least one outlet is at least two outlets, wherein one of the at least two different fluid injection points is disposed in a region of the cavity corresponding to the steering tube of the two-wheeler frame, wherein the cavity comprises the at least two outlets through each of which a part of the portion of the plastic melt that is displaced is urged out of the cavity, and wherein two of the at least two outlets are disposed in regions of the cavity corresponding to dropouts of the chain stays of the two-wheeler frame.

5. The method in accordance with claim 1, wherein the two-wheeler frame that is manufactured additionally comprises a seat tube and seat stays, wherein one of the at least two different fluid injection points is disposed in a region of the cavity corresponding to the steering tube of the two-wheeler frame, and wherein the at least one outlet through which the portion of the plastic melt that is displaced is urged out of the cavity is disposed in a region of the cavity corresponding to an upper end of the seat stays of the two-wheeler frame.

6. The method in accordance with claim 1, wherein the two-wheeler frame that is manufactured additionally comprises a bottom bracket mount or a motor mount arranged around the down tube and the chain stays, and wherein one of the at least two different fluid injection points is disposed in a region of the cavity that corresponds to the bottom bracket mount or the motor mount of the two-wheeler frame.

7. The method in accordance with claim 1, wherein the method further comprises: inserting a sleeve as an inserted part into a region of the cavity corresponding to the steering tube of the two-wheeler frame, and wherein injecting the plastic melt overmolds the sleeve with the plastic melt.

8. The method in accordance with claim 7, wherein the sleeve has an opening and inserting the sleeve includes placing the sleeve into the cavity with the opening facing a region of the cavity that corresponds to the down tube of the two-wheeler frame.

9. The method in accordance with claim 1, wherein the two-wheeler frame that is manufactured additionally comprises a seat tube, and wherein the method further comprises: inserting the seat tube as an inserted part into a region of the cavity corresponding to the seat tube of the two-wheeler frame, and wherein injecting the plastic melt at least partially overmolds the seat tube with the plastic melt.

10. The method in accordance with claim 9, wherein the seat tube has one or more openings in a radial peripheral jacket and is inserted into the region of the cavity corresponding to the seat tube of the two-wheeler frame such that the one or more openings face one or more of a region of the cavity that corresponds to the down tube of the two-wheeler frame or regions of the cavity that correspond to the chain stays of the two-wheeler frame.

11. The method in accordance with claim 10, wherein one of the at least two different fluid injection points is located in the region of the cavity corresponding to the seat tube of the two-wheeler frame.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further details and advantages of the invention result from the embodiments discussed in the following with reference to the Figures. There are shown in the Figures:

(2) FIGS. 1a and 1b illustrate a plan view and a perspective view of a half of an injection molding tool having a partly shown molded frame;

(3) FIG. 2 illustrates a representation of an insertion sleeve for the steering tube that has radial openings;

(4) FIG. 3 illustrates a representation of the direction of flow of the fluid in the variant of the invention shown in FIG. 1;

(5) FIG. 4 illustrates a representation of the direction of flow of the fluid in an expanded version of the variant of the invention shown in FIG. 1;

(6) FIG. 5 illustrates a schematic representation for a possible decoupling of a region of the injection molding cavity corresponding to the crossbar of a bicycle frame; and

(7) FIG. 6 illustrates a schematic representation for an alternative method management in the course of the invention.

DETAILED DESCRIPTION

(8) Views of a part of an injection molding tool 10 having a molded frame 20 that is only shown in part are shown in FIGS. 1a and 1b.

(9) The regions of the molded frame 20 shown comprise a steering tube 21, a down tube 22, and two chain stays 23. The part of the injection molding tool 10 shown comprises a cavity 11 for demolding the corresponding regions of the frame 20, a fluid injector 12 that is arranged in the region of the cavity 11 corresponding to the steering tube 21, and two overflow cavities 13 that are arranged in the regions of the cavity 11 corresponding to the rear ends of the chain stays 23.

(10) The positioning of the injection molding tool 10 in the course of the carrying out of the injection molding method of manufacturing the frame 20 is as it is shown in FIGS. 1a and 1b. The region of the cavity 11 corresponding to the steering tube 21 is therefore disposed at the lowest point and the regions of the cavity 11 corresponding to the rear ends of the chain stays 23 are disposed at the highest point. The fluid injector 12 is accordingly arranged below the overflow cavities 13.

(11) In the course of the method of manufacturing the frame 20, a melt of a thermoplastic, for example of a polyamide, is first injected into the cavity 11 by a plastic injector not shown in FIG. 1a or 1b, but likewise disposed in the region of the cavity 11 corresponding to the steering tube 21 until said cavity 11 is partially filled, for example up to and into the transition region between the down tube 22 and the chain stays 23. A fluid, for example water, is subsequently pressed into the cavity 11 by the fluid injector 12. The fluid displaces the plastic core of the initially solid plastic bar that has been produced in the region of the cavity 11 corresponding to the down tube 22 while the regions of the bar directly adjacent to the surface of the cavity 11 have already cooled down and hardened so much that a displacement no longer takes place there. The displaced plastic material initially fills the regions of the cavity 11 still remaining empty, inter alia the regions corresponding to the chain stays 23. Once these regions have also been completely filled, the displaced plastic material escapes through corresponding outlets into the overflow cavities 13. The injection of the fluid is continued for so long until all the frame regions shown, that is the down tube 22 and chain stays 23, are tubular due to the displacement of the plastic core out of the initially bar-shaped elements. The fluid injection subsequently ends and the fluid can be removed, for example sucked, out of the core of the frame 20 produced. In variants of the invention, the fluid can also remain in the tube for a specific time period before its removal and can also optionally be circulated therein to assist the cooling and hardening of the tube walls of the produced frame. The completed frame 20 is then demolded.

(12) A metal sleeve 30 as shown in FIG. 2 is inserted into the region of the cavity 11 corresponding to the steering tube 21 before the injection of the plastic melt. The metal sleeve 30 is overmolded with the plastic and reinforces the steering tube in the completed frame 20.

(13) As can be recognized in FIG. 2, the sleeve 30 has a radial opening 31. The sleeve 30 is positioned in the cavity 11 in the course of the method such that the opening 31 faces the region of the cavity 11 that corresponds to the down tube 22 of the frame 20. The flow of the plastic melt and the flow of the fluid are thus not impeded by the sleeve 30.

(14) The flow of the fluid in the course of the method management shown can be recognized with reference to the extent path V1 drawn in FIG. 3.

(15) An expansion of the just described method can be recognized in FIG. 4 in which a seat tube 24 composed of plastic is inserted as an inserted part into the regions of the cavity (not shown in FIG. 1a or 1b). Further injection nozzles for plastic and fluid are located at the upper end of the seat tube 24 and the seat tube has a radial opening that correspond to the regions of the cavity corresponding to seat stays 25 (not shown in FIG. 1a or 1b). Two separate fluid flows V1 and V2 result that are drawn in FIG. 4, with the fluid flow V1 corresponding to that one that has already been shown in the variant of FIG. 3. The seat tube 24 can also be completely overmolded with plastic in that a region of the cavity surrounds the plastic inserted part and plastic is injected into the gap between the walls of the cavity and the inserted part.

(16) FIG. 5 schematically illustrates the possibility of decoupling a region of the cavity 11 that corresponds to a crossbar 26 of the frame 20 in the course of a method in accordance with the invention by replaceable tool inserts. This variant of the invention makes it possible to produce both regular frames having a crossbar, which is, e.g., the diamond frames typical for sports bicycles and men's cycles, and step-throughs or wave frames typical with women's bicycles. The position of the crossbar can also be changed in this manner if the cavity has two regions corresponding to differently positioned crossbars of a frame.

(17) Finally, FIG. 6 shows an alternative method management using alternative flow paths for the plastic melt and the fluid. In this variant of the method, the rear region of the down tube 22 represents the lowest point of the molded frame 20 in the injection molding tool 10. The injection of the plastic and of the fluid accordingly also takes place there. The hollow spaces in the inserted parts, that is in the sleeve 30 and the seat tube 24, complement the flow paths for the plastic melt and the fluid in this variant, as can be recognized with reference to the flow arrows V3.