WO2009006689A1

WO2009006689A1 - Process for manufacturing a component for a fluid dynamic device

Info

Publication number: WO2009006689A1
Application number: PCT/AU2008/001006
Authority: WO
Inventors: Eric Metrot
Original assignee: Entecho Pty Ltd
Priority date: 2007-07-09
Filing date: 2008-07-09
Publication date: 2009-01-15

Abstract

A process for manufacturing a component (20) comprises: a) forming a core (305) of the component (20) from a blank material; b) applying a skin (310) of material to said core (305) to form a component (20) such component (20) having an upper surface portion (304) and a lower surface portion (303); c) inserting the component (20) into a mold (320), such mold (320) comprising an upper mold surface (321 ) for molding a lower surface portion (303) of the component (20) and an intensifier (325), said intensifier (325) comprising at least a portion (330) of an interstitial mold surface disposed between said upper and lower component surface portions (303, 304); and d) subjecting the intensifier (325) to a pressure for a period of time during a curing process so as to bring the intensifier (325) into intimate contact with the component (20).

Description

PROCESS FOR MANUFACTURING A COMPONENT FOR A FLUID DYNAMIC

DEVICE

This invention relates to a process for manufacturing components from composite materials. The invention can be applied to the manufacture of a blade, or other component, for a fluid dynamic device. The invention is particularly useful for constructing rotor blades for use in aerodynamic propulsive devices using drum rotor type fans used for airborne craft thrust generation.

The applicant has developed a new type of airborne craft capable of vertical take-off and landing, hovering and flight. The craft utilises a drum rotor type fan to generate airflow which is used to generate a lifting/propulsive thrust to enable the aircraft to become airborne.

In a drum rotor fan for use in an airborne craft, it is desirable to make the rotor, including the rotor blades (which would typically number about 20 or 30 blades), of a durable, low weight, high strength material. This will not only improve the performance of the craft but will also reduce the gyroscopic effects generated by the rotor. Further, it is important that the blades be manufactured or constructed through a process which produces a reliable component that will not fail easily in use. Given that a multiple number of blades is required, it is desirable to use a low cost and efficient manufacturing process. An important aspect of a rotor blade, such as would be used in the drum rotor of the airborne craft described above, is its performance as a fluid dynamic device. As such, the geometry and tolerance control of the leading edge, that is, that portion of the blade at which the airflow is first separated to either side of the blade, is very important. A high level of surface finish of the blade is also highly desirable. Typically, the leading edge will be required to have a certain radius of curvature (for instance, in some of the blades being developed by the applicant, this radius is approximately 1.00 mm, and in others the radius is approximately 8.00 mm). Non conformance or variations to this radius will cause performance losses and potentially other undesirable effects. Similarly a smooth surface is required to ensure the optimal fluid dynamic performance. Being a device intended for airborne operation, weight is a crucial parameter for all parts, including the blades. For this reason the use of composite parts, typically carbon fibre composites, becomes highly desirable. The manufacture of composite parts, particularly carbon fibre parts, typically involves the application of a fabric material (e.g. carbon fibre matting) to a shaped core. This fabric material would, upon the application and curing of a resin, form a structural skin of the component as is well known in the art. Prior art manufacturing processes would typically require the use of an upper and lower mold tool. Such a mold is split along a part line (also referred to as a split line) to allow the component to be removed from the mold and it is known that there can be difficulties in the tolerance and finish of the surface, particularly at the part line. In particular, excess resin tends to accumulate at this part line and result in a compromised component. The issue becomes acute in the case of a blade for an fluid dynamic device as the leading edge of the blade would be at this part line. In addition, in such prior art systems, the surface of the blade may also require further working to attain the required surface finish as a result of any non-even distribution of resin on the surface (a task that may be difficult to achieve in the case that the structural skin is relatively thin - as is particularly desirable in the case of blades intended for airborne craft).. There is also an additional tooling cost associated with such prior art type split molds.

It is therefore an object of the present invention to overcome at least some of the limitations of existing processes for manufacturing blades and other components, particularly for aerodynamic or fluid dynamic devices, or at least provide a useful alternative.

Therefore, in one form, the invention resides in a process for manufacturing a component, the process comprising: a) forming a core of the component from a blank material,; b) applying a skin of material to said core to form a component such component having an upper surface portion and a lower surface portion; c) inserting the component into a mold, said mold comprising an upper mold surface for molding a lower surface portion of the component and an intensifier, said intensifier comprising at least a portion of an interstitial mold surface disposed between said upper and lower component surface portions; and d) subjecting the intensifier to a pressure for a period of time during a curing process so as to bring the intensifier into intimate contact with the

* component. By using this method, a component can be produced with high dimensional accuracy and surface finish without a mold part line or split line affecting a critical surface location which would have otherwise resulted using conventional manufacturing techniques. Preferably, the intensifier - an item directed to the application of pressure to the component to ensure the skin of the component conforms accurately to the component blank during the curing process - is of a semi-rigid material that is sufficiently flexible to conform to the contour of the component (so as to assume the outer shape of the component), whilst providing sufficient rigidity so that, when pressure is applied to the intensifier during the curing process, the intensifier itself does not wrinkle or crease and/or allow the skin to wrinkle or crease and/or the inner core material is not deformed in localized areas so as to produce an inaccurate or uneven surface. Thus, the intensifier acts as a pressure spreader, which prevents creasing of the skin of the component, and which prevents the uneven distribution of resin on the component surface and/or collapse of local regions of the surface of the item, especially in the event of the core material being crushable/deformable. Use of an intensifier in this way ensures an accurate surface geometry and high surface finish, which is highly desirable particularly in the case of the component being a rotor blade for a fluid dynamic device.

Conveniently, the intensifier covers or forms at least part of the upper mold surface so that the component is in effect loaded into the intensifier. In some cases, it may be possible to use the intensifier itself as the mold so that no separate rigid mold is used in the process, thus providing tooling cost savings. The intensifier may form a flexible joint between the upper mold surface and a lower mold surface so as to allow the mold to be opened and closed for allowing insertion and removal of the component.

In the case of the component being a rotor blade for a fluid dynamic device, the applicant has found that the use of a polypropylene material of approximately 1.0 to 1.5 mm thickness provides suitable properties for use in the manufacture of such rotor blades. However, the required properties of the intensifier will be dependent on the shape of the component itself. In the example of a rotor blade, the curvature of the leading edge of the blade is a particularly important functional area. The intensifier is therefore used to apply pressure to the leading edge of the blade. If the intensifier is too rigid, it will not properly allow pressure to be applied during the curing process to the leading edge of the blade to form the desired radius of curvature on the blade. Conversely, if the intensifier is too flexible then it may result in the intensifier becoming wrinkled (and thereby form crevices in which resin may accumulate) or allow the composite skin to crease or wrinkle (in either case resulting in an inaccurate or rough surface) and/or in excessive localized pressure being applied to the leading edge of the blade resulting in a curvature which is too sharp and therefore not according to the required design. Silicone material may also be adapted for use as an intensifier.

In a particularly advantageous arrangement, the intensifier used to manufacture a blade is attached to the upper surface of the lower mold, and has a permanent pre-set shape, or crease, corresponding to the position of the leading edge of the rotor blade. In this way the raw rotor blade (ie the uncured component or core assembly of the blade) can be loaded into the intensifier with the leading edge abutting against the crease to provide accuracy and repeatability and ensuring that the component is properly positioned during the curing process. Conveniently, the composite material may comprise of a fibre material, such as carbon fibre. The carbon fibre may be pre-impregnated with resin (known as pre-preg). Alternatively a resin material may be applied to the fibre material as part of step (2) in the above described process with the resulting resin impregnated fibre material may be applied to the inner core of the component to form the component.

In order to further improve the quality of the surface finish of the component, an intermediate step (2a) can be used comprising the application of a thin film covering the component once the composite skin has been applied. Such film provides for a high quality smooth surface finish and acts as a release agent to release the component from the mold and/or intensifier in that it prevents the resin from contact with the mold or the intensifier. The applicant has used Tedlar™ (Dupont) film with success, but acknowledges that other films may be used. This film is removed from the final product to leave a high quality surface finish on the blade. Alternatively, the applicant has also used Mylar™ film with an adhesive backing which remains permanently adhered to the final blade. However to save weight, it is preferred to remove the film from the final product.

In the case of the component being a rotor blade for a fluid dynamic device, preferably the core defines the shape of the blade. The blade cross- section may be of an airfoil shape having a leading edge, a camber and a chord length, all of which terms are to be understood as having their normal meaning to those skilled in the art of airfoil design

In the case of the blade being for a drum rotor, such as used in the applicant's airborne craft or industrial fans, the blade core may conveniently be of a constant cross-section along its length.

Preferably, the composite skin to be applied to the blade is of a unidirectional carbon fibre material.

Use of unidirectional carbon fibre is particularly advantageous from a cost point of view and is well suited to the blades for drum rotor fans which are primarily loaded in a bending mode across the length of the blade. In some cases the unidirectional carbon fibre can be very thin and therefore crease or wrinkle very easily during the manufacturing process, especially in the case of conventional vacuum bagging techniques being used wherein both the vacuum bag and the skin may wrinkle to give a poor surface finish that may require further finishing (normally involving an abrasive) - which itself may be difficult to achieve without damaging the thin composite skin. The present invention improves the ability to effectively use such thin materials without adverse creasing occurring during the manufacturing process and thus avoid the need for additional surface finishing steps to be taken

Preferably, the core of the blade is made from a blank of light weight, rigid material, such as polystyrene foam.

Advantageously, the core may be of polystyrene thermal insulation material. Such material is relatively inexpensive and readily available. The applicant has used Styrofoam™ HD300 having a compressive strength of approximately 0.7 Mpa successfully for the cores of its blades.

Advantageously, the core may be formed by a thermo-wire cutting process wherein a heated thin wire is moved through the foam to form the blade core. This process lends itself to forming multiple blades from a single action in that multiple hot wires may act in parallel through a single block of foam.

Preferably, the curing process for the blade is conducted at pressures above 200 kPa, and more preferably above 300 kPa. The use of these high pressures ensures that a minimum amount of resin remains in the blade with excess resin being squeezed out of the intensifier towards the trailing edge of the blade. This is done in order to maintain a low weight for the final blade.

Preferably, the curing temperature is held below 100 degrees Celsius or lower in order to avoid loss of strength of the foam used for the blade core. Advantageously, water pressure may be used to provide the required curing pressure.

In another form, the invention resides in a component which has been manufactured by use of the above identified manufacturing process.

By way of further background, the most common and widely employed free flying vertical takeoff and landing (VTOL) craft that operates at higher altitudes is the helicopter.

The rotor blades of a helicopter develop lift by accelerating air downward and parallel to the axis of its rotation (axially). The velocity of the tip of the rotor blade is typically set to a maximum that is close to sonic conditions on the advancing blade when the helicopter is at maximum forward speed. The remainder of the blade must operate at a lower velocity proportional to its distance from the axis of the rotor. Unfortunately, this non-uniform velocity along the blade means that significant blade length is underutilized despite varying the angle of attack and changing the aerodynamic profile along the length of the rotor blade because lift is proportional to the velocity squared. To compound the problems of the rotor, because the highest lift is generated at the highest velocity region, at the tip a very high bending moment is generated on this cantilevered structure. Further, to get the maximum lift from the rotor, the blade tip must operate at the highest permissible velocity close to sonic conditions, which means that considerable noise is generated. Correspondingly, the rotor diameter cannot be reduced because to generate the same lift, the velocity would have to increase beyond sonic conditions or some part of the operating envelope would have to be compromised. The applicant has therefore developed a new aerodynamic lifting device which uses a drum fan type rotor in an airborne craft capable of performance characteristics superior to helicopters by generating superior lift capability and/or a reduced horsepower requirement from a lifting device with a smaller footprint. The fan may be described as a radial drum fan which may be defined as a fan of which the blades have a radial depth that is less than 25% of the radial pitch of the blades. Since the radial dimension of the fan blades is small compared to the radius at which the blade operate, effectively the entire blade is operating at the same, optimum, speed. The drum fan type rotor generates air flow in a radial direction. In order to generate lifting thrust this air flow is re-directed, by means of a shroud that surrounds the rotor, from the radial out flow direction as provided by the rotor to a downward direction.

The process of the present invention is well suited to the manufacture of rotor blades for the drum rotor used in the applicant's airborne craft. However, it is to be appreciated that the process lends itself to the economical manufacture of other components and should not be limited to blades for airborne craft. For example, the process can be used to manufacture stator blades (ie the stationary blades that are also used in the applicant's airborne craft) or fins for surfboards/windsurfers or spoilers for automobiles. The method of the present invention may be more fully understood from the following non-limiting description of preferred embodiments thereof made with reference to the accompanying drawings in which:

FIG. 1 is a schematic drawing of an airborne craft which uses a drum rotor fan whose rotor blades may be manufactured using the present invention.

FIG. 2 is an isometric view of the drum rotor of the airborne craft shown in Fig 1.

FIG. 3 shows a isometric view of a rotor blade of the drum rotor shown in Fig 2. FIG. 4 shows a schematic cross-section of the rotor blade shown in Fig 3.

FIG. 5 shows a partially exploded view illustrating the system for manufacturing a component in accordance with the invention. Referring to Fig. 1 , there is shown an airborne craft 100, which can be used in a wide variety of applications. Fig. 1 indicates the use of a shape for the central load carrying space 120 that provides a cockpit operating area 140 for an operator or other payload (not shown) while maximizing the area available for airflow into the drum rotor fan 9. In particular, the horizontal annular area defined by the cockpit 140 and the upper annular retaining ring for the stator 36 is held to the maximum and the volume available for the operator is allowed to grow vertically and radially above this plane to provide more load space without compromising airflow into the fan 9. The flexible shroud 15, which is used as a thrust vectoring means, is shown in a forward deflected position as may be used to effect a braking or reversing maneuver. The air flow to the drum rotor fan 120 flows via the central area of the craft and is expelled radially by the rotor fan 120 and redirected downwardly by the flow vectoring skirt, or shroud, 15. Referring to Fig. 2, there is shown the drum rotor fan 9 of the airborne craft 100 of Fig 1. The drum rotor fan 9 comprises a plurality of vertically disposed rotor blades 20 supported at one end by an upper rotor blade retaining ring 18 and at the other end by a lower rotor blade retaining ring 19. The drum rotor fan 9 creates an airflow as it rotates about its central vertical axis. In the case of the airborne craft 100 shown in Fig 1 , this airflow is radially outwards. Referring to Fig. 3, there is shown one of the plurality of rotor blades 20, of the drum rotor fan 9. The illustrated rotor blade 20 comprises a leading edge 301 , trailing edge 302, and surfaces 303 and 304 disposed on either side of the blade. The blade is wrapped in a composite skin 310, of unidirectional carbon fibre, the fibers being orientated in the longitudinal direction (i.e vertical direction per Fig 3).

Referring to Fig 4, there is shown a cross-section of the blade 20 of Fig 3 wherein the reference numbers correspond to the same features as per Fig 3. The inner core of the blade 305 comprises of a polystyrene material commercially known as Styrofoam™ HD300. The applicant has found that this material provides very desirable properties for a rotor blade in that it has a low density, of approximately 42 kg per cubic meter (leading to a low weight component), relatively high compressive modulus of 0.7 Mpa and can be readily shaped using thermo wire processes (also known as hot wire cutting). This inner part 305 forms the core for the molding system which is shown in Fig 5 and which will now be described. An important feature of the blade 20 is the radius of the fillet at the leading edge 301 of the blade 20 and the smooth surface finish of the surfaces 303 and 304 which is required for acceptable performance of blade 20 in service of the airborne craft 100.

In Fig 5, there is shown a schematic exploded view of the system used to manufacture a rotor blade, 20. Fig 5 shows a core 305 in the shape of a rotor blade having a lower surface portion 303 and an upper surface portion 304. A mold 320 is provided which has an upper mold surface 321 which corresponds to the lower surface portion 303 of the blade 20. A semi-rigid intensifier 325 which surrounds the core assembly is provided. The intensifier 325 is flexible enough to conform to the final shape of the blade 20, whilst being stiff enough to avoid collapse of localized regions (for example, the leading edge 301 of the blade). Intensifier 325 acts as a pressure spreader to avoid such collapse. Although shown as being separated from the upper mold surface 321 , the intensifier 325 may be permanently attached and form part of the upper mold surface 321. Alternatively, the intensifier may be formed integrally with and effectively become part of the lower mold 320.

Before the core 305 is inserted into the intensifier 325, a carbon fibre skin (and liquid resin) 310 is applied to the core 305. This skin will, in its final form provide the structural strength to the blade. The amount of resin is kept to a minimum to ensure the lowest possible weight of the blade.

Once the carbon fibre skin 310 and liquid resin have been applied to the core 305, the entire component is wrapped in a thin film 311 to form a "raw blade". The applicant has used a Tedlar™ (Dupont) film which is a clear, thin film. This film helps to provide a high gloss, smooth surface finish to the final blade, but the film does not form part of the final blade in order to keep the weight of the blade to a minimum. It also acts as a release agent to prevent the core assembly from binding to the intensifier 325 and/or mold 320. During the manufacturing process, the raw blade is loaded into the intensifier 325, with the lower surface portion 303 of the raw blade placed upon the upper mold surface 321. The intensifier 325 is then brought to bear against the upper surface portion of the raw blade and a controlled pressure is applied to the intensifier 325. This pressure may be applied in the form of water pressure which may be most conveniently supplied in a water tank adapted for such purposes. To ensure a high surface finish and proper dispersion of the resin, a pressure of approximately 300 kPa is applied. Conveniently, any excess resin is squeezed out towards the trailing edge of the blade 20 into the region 350 where it may be ready removed in a final cutting operation (described further below).

The intensifier 325 conveniently comprises or includes a permanent crease 330 which conforms to the radius of the blade at the leading edge 301. Importantly, this crease is located at the intermediate region of the blade 20 which defines the leading edge 301 between the upper surface portion 304 and the lower surface portion 303 of the blade. Advantageously, the crease 330 acts as an interstitial surface portion of the mold 320 - whilst also functioning as a flexible hinge for the mold - which allows for convenient ingress and egress of blade 20. By loading the raw blade with the leading edge 310 abutting against the crease 330 of the intensifier 325, a positive stop is provided. This improves the robustness of the manufacturing process by eliminating any misalignment of the raw blade and the mold which would otherwise cause an imperfect blade, particularly along the leading edge 301.

In use, the forces on the rotor blade 20 are mostly transverse bending forces (resulting from the aerodynamic loads on the surfaces 304 and 305), and therefore the carbon fibre skin may conveniently be of a unidirectional carbon fibre orientated in the longitudinal direction of the blade 20. This skin is relatively thin.

It will be appreciated that the leading edge 301 of the blade 20 falls at a location that would have otherwise been a part-line in a conventional molding process. Being of a relatively shallow cross-section there would then arise the possibility of the raw blade not being perfectly positioned within the mold. This would then lead to the leading edge 301 of the blade 20 either being crushed by the mold 320, or not being supported properly within the mold and potentially causing the composite material to "wrinkle" thereby producing an imperfect leading edge 301. This is further exacerbated in the case that the composite material is relatively thin since it can more easily wrinkle and any final sanding process used to remove such wrinkle would result in the composite skin being breached.

Once the raw blade has been cured for a sufficient period, the intensifier 325 is released and the rotor blade 20 is removed. Any excess material in the region of the trailing edge 302 may then be cut off from the blade 20. A final cutting process may be performed on the upper edge 331 and lower edge 332 of the blade to conform to the lower side of the upper ring 18 and the upper side of the lower ring 19 respectively, of the rotor 9 (shown in Fig 2). Although not shown in the figures, the lower surface of the upper ring 18 and the upper surface of the lower ring 19 of the rotor form a converging duct as the air flows radially outwards through the rotor 9. In addition to this converging duct shape, the chord of the blades 20 are not aligned radially along the rotor, so that the edges 331 and 332 are required to be of a complex shape to properly conform to the upper and lower rotor rings. Alternatively, the composite skin may overlap the core and thereby completely seal the core at either edge 331 and 332 and be trimmed after removal from the mold.

Other modifications and variations of the process of manufacture of the invention may be apparent to skilled readers of this disclosure. Such modifications and variations are deemed within the scope of the present invention

Claims

CLAIMS:

1. A process for manufacturing a component comprising: a) forming a core of the component from a blank material; b) applying a skin of material to said core to form a component such component having an upper surface portion and a lower surface portion; c) inserting the component into a mold, said mold comprising an upper mold surface for molding a lower surface portion of the component and an intensifier, said intensifier comprising at least a portion of an interstitial mold surface disposed between said upper and lower component surface portions; and d) subjecting the intensifier to a pressure for a period of time during a curing process so as to bring the intensifier into intimate contact with the component.

2. The process of claim 1 wherein the intensifier is of a semi-rigid material sufficiently flexible to conform to the contour of the component.

3. The process of claims 1 or 2 wherein the intensifier is a pressure spreader preventing the creasing of the skin of the component.

4. The process of claim 1 or 2 wherein the intensifier is a pressure spreader preventing the collapse of local regions of the surface of the component.

5. The process of any one of the preceding claims wherein the intensifier covers or forms at least part of the upper mold surface.

6. The process of claim 5 wherein the intensifier forms a flexible joint between the upper mold surface and a lower mold surface so as to allow the mold to be opened and closed for allowing insertion and removal of the component.

7. The process of any one of the preceding claims wherein the properties of the intensifier are dependent on the shape of the component.

8. The process of any one of the preceding claims wherein the component is a blade for a fluid dynamic device.

9. The process of claim 8 wherein the intensifier applies pressure to a leading edge of the blade.

10. The process of claim 5 wherein the intensifier is attached to the upper mold surface and has a permanent pre-set shape or crease corresponding to the position of the leading edge of the blade.

11. The process of claim 10 wherein the core assembly of the blade is loaded into the intensifier with the leading edge abutting against the crease to provide accuracy and repeatability and ensuring that the component is properly positioned during the curing process.

12. The process of any one of the preceding claims wherein the material is a fibre material.

13. The process of claim 12 wherein the fibre material is unidirectional carbon fibre.

14. The process of claim 12 or 13 wherein a resin material impregnates the fibre material.

15. The process of claim 14 wherein the resin impregnated fibre material is forms the skin which is applied to the core blank to form the component.

16. The process of any one of the preceding claims wherein a thin film is applied around the core once the skin has been applied.

17. The process of claim 16 wherein the thin film acts as a release agent to release the component from at least one of the mold and intensifier.

18. The process of claim 16 wherein the thin film is Tedlar film.

19. The process of claim 16 wherein the thin film is Mylar film with an adhesive backing.

20. The process of claim 8 wherein the core defines the shape of the blade.

21. The process of claim 20 wherein the blade cross-section is of airfoil shape having a leading edge and a camber.

22. The process of claim 1 wherein the component is a blade for a drum rotor fan and the core of the blade is of constant cross-section along its length.

23. The process of any one of claims 20 to 22 wherein the core of the blade is made from a blank of lightweight rigid material.

24. The process of claim 23 wherein the material is polystyrene foam or polystyrene thermal insulation material.

25. The process of claim 24 wherein the core is made by a thermo-wire cutting process with a heated thin wire moved through the foam to form the blade core.

26. The process of claim 25 wherein multiple thin wires are moved through a single block of foam to form a plurality of blades.

27. The process of any of the preceding claims wherein the curing process is conducted at controlled pressures preferably above 200 kPa.

28. The process of claim 27 wherein the curing process is conducted at pressures above 300 kPa.

29. The process of claim 27 or 28 wherein curing temperature is held below 100 degrees Celsius.

30. The process of claim 27 or 28 wherein the pressure is applied through hydraulic pressure.

31. A component manufactured by the process of any one of the preceding claims.

32. The component of claim 31 being a rotor for an airborne craft.