Additive Carbon Fibre Molding Process

Abstract

The invention relates to a process for preparing a wheelchair frame (7) comprising: a) preparing parts or segments (4) of the wheelchair frame from a sacrificial material; b) applying a curable lightweight material to the parts or segments (4) obtained in step a); c) curing the parts or segments (4) obtained in step b); d) removing the sacrificial material in order to obtain hollow frame parts or hollow frame segments of the wheelchair made from the curable lightweight material.

Claims

1.-10. (canceled)

11. A process for forming a wheelchair frame comprising the steps of: a) preparing at least one of parts or segments of the wheelchair frame; b) applying a curable lightweight material to the at least one of parts or segments obtained in step a); c) curing the at least one of parts or segments obtained in step b); d) applying a secondary aesthetic layer of lightweight material; and e) curing the at least one of parts or segments obtained in step d); wherein in step a) the at least one of parts or segments of the wheelchair frame are formed from a sacrificial material, wherein the overall structure of the at least one of parts or segments has one of a porous or mesh-like structure, and in a removing step between the curing step c) and the applying step d) the sacrificial material is removed in order to obtain hollow frame parts or hollow frame segments of the wheelchair made from the curable lightweight material, wherein dissolving liquid removes the sacrificial material in the removing step.

12. The process of claim 11, wherein the at least one of parts or segments of the wheelchair are prepared by three dimensional (3D) printing techniques.

13. The process of claim 11, wherein the at least one of parts or segments of the wheelchair are a plurality of parts or segments that are fitted together before step b).

14. The process of claim 11, wherein step d) comprises placing the at least one parts or segments covered with the curable lightweight material into a solvent, developer solution, or etching solution which is capable of dissolving, developing, or etching the sacrificial layer.

15. The process of claim 11, wherein the sacrificial material is dissolved in an alkaline solution or an acid solution.

16. The process of claim 11, wherein the curable lightweight material is carbon fiber.

17. The process of claim 11, wherein one or more further layers of at least one curable lightweight material is applied to the at least one of parts or segments of the wheelchair frame after step c) and cured.

18. The process of claim 17, wherein the one or more further layers of at least one curable lightweight material are formed from one or more of a carbon fiber, an aramid fiber, a glass fiber, or a carbon fiber plant based alternative material.

19. A wheelchair comprising a frame prepared by the process of claim 11.

20. A process for forming a wheelchair frame comprising the steps of: a) preparing and assembling a plurality of parts or segments of the wheelchair frame, the plurality of parts or segments being formed from a sacrificial material having a porous or mesh structure; b) applying a curable lightweight material to the assembled parts or segments formed in step a); c) curing the curable lightweight material applied in step b); d) applying a further layer of curable lightweight material and curing the further layer; e) removing the sacrificial material from within the cured curable lightweight material of step c) to obtain hollow frame parts or hollow frame segments of the wheelchair made from the curable lightweight material, wherein a solution removes the sacrificial material; f) applying a secondary aesthetic layer of lightweight material; and g) curing the at least one of parts or segments obtained in step f);

21. The process of claim 20, wherein the solution is an alkaline solution or an acid solution.

22. The process of claim 20, wherein the curable lightweight material of step b) is formed from one or more of a carbon fiber, an aramid fiber, a glass fiber, or a carbon fiber plant based alternative material.

23. The process of claim 22, wherein the further layer of curable lightweight material of step d) is formed from a different material than the curable lightweight material of step b).

24. The process of claim 22, wherein the further layer of curable lightweight material of step d) is formed from the same material as the curable lightweight material of step b).

25. The process of claim 20, wherein removing the sacrificial material from within the cured curable lightweight material in step e) is conducted before the further layer of curable lightweight material is applied and cured in step d).

Description

[0056] FIG. 1a shows a cross section view of part or segment prepared from a sacrificial material;

[0057] FIG. 1b shows another embodiment of a cross section view of part or segment prepared from the sacrificial material;

[0058] FIGS. 2a and 2b show a schematic view of a part or segment prepared from the sacrificial material into which threaded inserts have been added;

[0059] FIGS. 3a and 3b show a cross section view of part or segment prepared from the sacrificial material, wherein jigs have been fitted to the castor and footrest;

[0060] FIG. 4 shows the complete parts or segments of the wheelchair frame prepared from the sacrificial material;

[0061] FIG. 5 show an assembled part of the wheelchair frame with a carbon fibre wrapping;

[0062] FIG. 6 shows the part of the wheelchair of FIG. 3, after the (first) curing process and the application of the final (aesthetic) layer of carbon fibre;

[0063] FIG. 7 shows an assembled wheelchair frame prepared according to a process of the present invention; and

[0064] FIG. 8 shows an image of the finished wheelchair.

[0065] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.

[0066] FIGS. 1a and 1b are cross section views of different embodiments of a part or segment prepared from sacrificial material. The overall structure is porous (mesh like) so that the dissolving liquid can fully remove the sacrificial material in the removing step. In FIG. 1b a diamond shaped channel is formed that allows the solution to flow through the entire frame. The diamond shape gives suitable structural support. The solution can then eat through the thin wall section of the channel and into the infill and finally the outer wall thickness.

[0067] In one exemplary embodiment, the frame mandrel of the wheelchair is 3D printed to the respective customers dimensions. In this embodiment, the frame is printed in parts or segments (4). The Fused Deposition Modelling (FDM) technique is applied, wherein the material is the Stratasys SR-30 support material. Here, the wall thickness of the prepared parts or segments (4) is about 3 mm. FIG. 4 depicts the printed parts and segments of the wheelchair frame.

[0068] In the next step the parts or segments (4) are fitted together, for example with press fit joints, to make two halves of the wheelchair frame, the axle and the footrest. This allows an even better access for, for example, a dissolving solution later in the process.

[0069] FIGS. 2a and 2b show an alternative embodiment, wherein additional threaded inserts have been incorporated into the parts or segments (4). FIG. 2a shows that the threaded inserts are left partially exposed so that carbon fibre can be wrapped around and under the head of the insert to secure them in carbon frame when cured. FIG. 2b shows the part or segment (4) with threaded inserts after a carbon fibre material has been wrapped and cured.

[0070] Alternatively, FIGS. 3a and 3b show that aluminum jigs have been fitted to the castor and footrest of a printed part or segment (4) of the wheelchair frame (7). The aluminum machined jig has a tolerance on its external dimensions, the aluminum maintains its structural integrity better than the 3D printed material. This allows the inside of the wrapped and cured frame to have a tolerance internal dimension that will allow precision componentry to be assembled with ease.

[0071] The (part of the) assembled frame described above is wrapped with carbon fibre (FIG. 5). After laying the carbon fibre up to 90% of the desired material thickness, a first stage cure is applied in an autoclave or oven. In this embodiment a temperature of 80 C. is applied for a period of about 11 hours.

[0072] In the next step the cured frame is then trimmed to a smooth finish.

[0073] The cured frame is submerged in a caustic NaOH diluted solution in an appropriate container with good circulation at a temperature of 70 C. which will dissolve the SR-30 FDM mandrel from within the carbon fibre frame.

[0074] Further, a final aesthetic layer of carbon fibre is then applied to the frame (FIG. 6). The second cure prevents any finish issues created by submerging the frame in solution. The two stage cure process prevents any further sanding or trimming on the final layup which prevents imperfections in the final layer and finish. In this embodiment, the second cure is carried out at a temperature of 80 C. for about 8 hours.

[0075] In the final step the frame can be finished and assembled to the final wheelchair (7) (FIGS. 7 and 8).

[0076] The features disclosed in this specification, the claims and the figures may be important for the claimed invention, taken separately or in any combination, for the respective different embodiments.

REFERENCE SIGNS

[0077] 1 external wall [0078] 2 mesh structure/printed infill [0079] 3 diamond hollow channel [0080] 4 parts or segments of wheelchair frame [0081] 5 threaded inserts [0082] 6 jigs [0083] 7 wheelchair frame