WO2024180340A1

WO2024180340A1 - Precision manufacture of hydraulic and pneumatic components

Info

Publication number: WO2024180340A1
Application number: PCT/GB2024/050549
Authority: WO
Inventors: Dan BURDEN; Steve Smith; Fred BUNCE; Phil ELLIOTT
Original assignee: Moog Controls Limited
Priority date: 2023-03-01
Filing date: 2024-02-29
Publication date: 2024-09-06
Also published as: GB202302979D0

Abstract

A method of manufacturing a hydraulic or pneumatic component is provided, the method comprising: providing a blank having a first surface and a second surface; applying laser radiation to the blank, thereby removing material from the blank by photoablation so as to form: a first aperture in the first surface; a second aperture in the second surface; a passage between the first aperture and the second aperture, wherein the passage is configured to provide a fluid flow path in use; and optionally a plurality of indents on an internal surface of the passage.

Description

Precision Manufacture of Hydraulic And Pneumatic Components

Field of invention

[0001] The present invention relates to hydraulic and pneumatic components, for example flow restrictions, nozzles, flow passages, orifices and other components used in hydraulic or pneumatic control systems.

Background

[0002] Hydraulic and pneumatic components have various geometries depending on the function they are to perform. Often, particularly when employed in control systems, such components require precise geometry to maintain, modify or otherwise affect the flow of fluid (be it hydraulic fluid or gas) through them. For instance, in some components it is necessary to modify fluid flow in a predictable way, with little energy loss, and/or without introducing turbulence.

[0003] The manufacture of such components must be to a high tolerance, and is generally a complex, multi-stage process. Each component must then be carefully characterised, with any that do not meet the required precise geometries and/or flow properties being discarded. Traditional manufacturing techniques often have a relatively low yield, with many components being discarded.

[0004] One example of such a component is a jet-pipe nozzle, of the type used in jet-pipe servo valves. A schematic cross section of an exemplary jet-pipe nozzle 100 as known in the prior art is shown in figure 1. The jet-pipe nozzle 100 has a body 102, and a narrowing passage 104 leading to an exit aperture 106. In use, hydraulic fluid flows from right to left (in the orientation shown in figure 1) through the nozzle 100 and out of the exit aperture 106, the pressure of the fluid being reduced as it does so. The diameter of the exit aperture 106, the profile of the passage 104, and the sharpness of the exit aperture (that is, the radius of the transition between the passage 104 and a surface 108 at the exit aperture 106) all have an impact of the flow characteristics and performance of the nozzle 100.

[0005] Traditionally, jet-pipe nozzle fabrication involves drilling a hole in a material blank substantially corresponding to, or slightly smaller than the exit aperture diameter. A stamp having an outside profile broadly corresponding to the desired inside profile of the passage 104 is then applied against the drilled hole to create the passage 104 the desired internal geometry. The drilling operation can introduce circular machining markings, which remain on the inside surface of the passage 104 even after the stamping operation. These marking run substantially orthogonal to the direction of fluid flow, and can affect flow properties through the nozzle, if not removed by an additional lapping or deburring operation. Additionally, the stamping operation typically results in at least some deformation of the surface 108, which must be removed using further lapping and deburring operations. The more deburring and lapping operations that are needed, the greater the risk that the sharpness of the exit aperture 106 will be reduced or its size increased, e.g., through successive deburring operations. After machining and smoothing operations have been completed, the nozzle may be hardened, which may change the dimensions of the nozzle from the desired profile. It will be appreciated that the geometry shown in figure 1 is schematic only.

[0006] As another example, ports in sliding spool valves are machined, with a grinding process often leaving a variable burr on the metering edge, making flow characteristics less predictable.

[0007] Therefore, there is a need for improved methods of manufacture for hydraulic and pneumatic components. It is further desired to improve the flow characteristics of such components.

Summary of invention

[0008] In order to mitigate at least some of the issues above, in a first aspect of the invention there is provided a method of manufacturing a hydraulic or pneumatic component, the method comprising: providing a blank having a first surface and a second surface; applying laser radiation to the blank, thereby removing material from the blank by photoablation so as to form (for example define/create the profile of): a first aperture in the first surface (for example having a width of 2mm or less, for example 1mm or less); a second aperture in the second surface (for example having a width of 2mm or less, for example 1mm or less); a passage between the first aperture and the second aperture, wherein the passage is configured to provide a fluid flow path in use.

[0009] Preferably the laser radiation is pulsed, having a pulse duration of 500 femtoseconds or less (also referred to as femtosecond laser radiation). [0010] Advantageously, this method produces hydraulic and pneumatic components to high tolerances and in a fast and repeatable manner. No subsequent lapping, deburring, etc. processes are required. In addition, high uniformity between components can be achieved using this method, providing predictable flow characteristics in use, high manufacturing yield and reduced requirement for testing/characterising individual components. Further, the method enables the use of component geometries that are difficult/impossible to make via traditional techniques, allowing for modified/improved performance. Using femtosecond laser radiation in particular further enhances ablation resolution without causing “re-cast melt”.

[0011] Optionally, applying laser radiation thereby removing material from the blank by photoablation further includes forming a plurality of indents on an internal surface of the passage. Preferably, a diameter of each of the plurality of indents is 10 microns or less, and optionally 5 microns or less. Advantageously, such indents (or “micro-pitting”) provide a turbulent boundary layer proximate the surface of the passage, promoting improved laminar flow in the bulk of the fluid flowing through the passage in use.

[0012] Preferably, an arithmetical mean roughness of the ablated internal surface of the passage is in the range 0.5 to 5 microns. This further improves flow properties in use and is difficult to achieve without a sequence of time intensive refining steps using traditional means. The plurality of indents are optionally such that: the internal surface has a maximum profile peak height, Rz, in the range 5 to 25 microns; and/or the internal surface has a mean width of profile elements, RSm, in the range 5 to 25 microns.

[0013] In some embodiments, the passage comprises a length along an axis, and an inner surface having a diameter, wherein the diameter varies along the length such that the inner surface has a varying radius of curvature in a plane including the axis. Optionally, the radius of curvature has a peak value at a first position along the length, and decreases away from the first position along the length. Put differently, the rate of change of diameter of the passage has a maximum value at a certain point along the passage, and the rate of change of diameter decreases away from that point. Beneficially, this reduces/avoids imparting peaks in acceleration of hydraulic fluid/pneumatic gas passing through the passage, thus reducing wear. [0014] Optionally, the second aperture is non-circular, for example oval/elliptical or rectangular. This is difficult to accurately achieve through conventional manufacturing techniques, particularly when an aperture has a largest dimension of around 2mm or less. Advantageously, such aperture geometry can be used to tailor flow properties of the fluid exiting the component in use, and for tailoring interaction with other components (for example tailoring flow gain across a nozzle and receiver orifice in a jet-pipe servo valve).

[0015] Optionally providing the blank comprises smoothing the second surface and applying laser radiation comprises applying laser radiation to the first surface. This advantageously results in the second aperture exhibiting a high edge sharpness (that is, a small radius - for example less than 5 microns - transition between the passage and the second surface) without the need for deburring/smoothing operations that would otherwise be required when using traditional techniques. Accordingly, the method optionally further comprises forgoing deburring of the second aperture.

[0016] Optionally the blank comprises one or more of: 250 maraging steel; 350 maraging steel, 440C CRES steel; tungsten carbide; Stellite™. Advantageously, photoablation is able to remove material from relatively hard metals such as these. Accordingly, the method optionally comprises forgoing hardening of the blank after the passage has been formed. This beneficially removes a risk of altering the component dimensions during hardening.

[0017] Optionally, prior to forming the passage, photoablation is used to form a pilot hole. In this case a gas is preferably passed through the pilot hole (e.g., while forming/finishing the passage), thereby transporting material removed from the blank by photoablation through the pilot hole.

[0018] In a second aspect of the present invention, there is provided a hydraulic or pneumatic component manufactured using the method above.

[0019] In another aspect of the present invention, there is provided a hydraulic or pneumatic component, comprising: a first surface having a first aperture; a second surface having a second aperture; a passage between the first aperture and the second aperture, wherein the passage is configured to provide a fluid flow path in use; and, optionally, a plurality of indents on an internal surface of the passage. The optional plurality of indents are such that: the internal surface has an arithmetical mean height, Ra, in the range 0.5 to 5 microns; the internal surface has a maximum profile peak height, Rz, in the range 5 to 25 microns; and/or the internal surface has a mean width of profile elements, RSm, in the range 5 to 25 microns. In a preferred embodiment, the profiles (the final shapes/the geometries) of the first aperture, the second aperture, the passage and the optional plurality of indents are formed by photoablation, for example using femtosecond laser radiation.

[0020] Optionally, a diameter of each of the plurality of indents is 10 microns or less, and optionally 5 microns or less.

[0021] In some embodiments, the passage comprises a length along an axis, and an inner surface having a diameter, wherein the diameter varies along the length such that the inner surface has a varying radius of curvature in a plane including the axis. Optionally, the radius of curvature has a peak value at a first position along the length, and decreases away from the first position along the length.

[0022] Optionally, the second aperture is non-circular, for example oval/elliptical or rectangular.

[0023] In some embodiments, a transition between the passage and the second surface at the second aperture has a radius of curvature of 5 microns or less.

[0024] Optionally the hydraulic or pneumatic component is a jet-pipe nozzle; and the passage has a diameter that decreases towards the second aperture so as to define a horn shape. In some embodiments, the rate of change of the diameter of the passage with distance along the passage towards the second aperture varies, such that hydraulic fluid flowing through the passage towards the second aperture exhibits a substantially flat acceleration profile.

[0025] In a further aspect of the present invention, there is provided a jet-pipe servo valve comprising the jet-pipe nozzle above.

[0026] In a further aspect of the present invention, there is provided an aircraft comprising the jet-pipe servo valve above (for example as part of a control system).

[0027] Within the scope of this application, it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible.

Brief description of the drawings

[0028] Embodiments of the present invention will now be described, by way of example only, with reference to the following figures in which:

[0029] Figure 1 shows a schematic partial cross section of an exemplary jet-pipe nozzle known in the art.

[0030] Figure 2 shows a flow chart of a method of manufacturing hydraulic and pneumatic components in accordance with embodiments of the present invention.

[0031] Figures 3 A to 3D show schematic cross sections of a hydraulic or pneumatic component at various stages of fabrication according to the method of figure 2.

[0032] Figure 4A and 4B show partial cross sections of a jet-pipe nozzle design for fabrication using the method of figure 2 in accordance with an embodiment of the invention.

[0033] Figure 4C shown an SEM image of a jet-pipe nozzle according to figures 4A and 4B and fabricated according to the method of figure 2.

[0034] Figure 4D shows a graph of the measured flow rate through a jet-pipe nozzle having the profile shown in figure 4 A.

[0035] Figure 4E shows of the measured flow rate through a jet-pipe nozzle fabricated using first prior art methods.

[0036] Figure 4F shows of the measured flow rate through a jet-pipe nozzle fabricated using second prior art methods.

[0037] Figure 5A shows a graph detailing a jet-pipe nozzle geometry for fabrication via the method of figure 2 in accordance with an embodiment of the invention.

[0038] Figure 5B shows a graph illustrating the acceleration of profile of hydraulic fluid passing through a jet-pipe nozzle having the profile described in figure 5A. [0039] Figure 6A shows a schematic partial cross section of a jet-pipe servo valve as known in the prior art.

[0040] Figure 6B shows a schematic cross section illustrating the overlap of apertures in the jet-pipe servo valve of figure 6A.

[0041] Figure 7 illustrates an exemplary alternative aperture geometry achievable using the method of figure 2 for use in a jet-pipe servo valve in accordance with an embodiment of the invention.

[0042] Figure 8 illustrates a further exemplary alternative aperture geometry achievable using the method of figure 2 for use in a jet-pipe servo valve in accordance with an embodiment of the invention.

[0043] Figure 9 shows a schematic top-down view of an aircraft employing jet-pipe servo valves in accordance with an embodiment of the invention.

Detailed description

[0044] Some of the following examples discuss components for use in hydraulic jet-pipe servo valves. However, it will be readily appreciated by a person skilled in the art that the techniques, geometries, and surface characteristics discussed below may be applied to other hydraulic and pneumatic components including, but not limited to, nozzles, restrictions, fluid flow passages, and/or apertures, for example as used in sliding spool valves, check valves and other control valves, actuators, etc. Such components are used in a wide variety of contexts, for example in aircraft flight control systems.

[0045] Figure 2 shows a flow chart of an improved method 200 for manufacturing hydraulic and pneumatic components via photoablation (particularly those where precise geometry and dimensions are important) in accordance with the present invention. Figures 3A to 3D show schematic cross sectional representations of hydraulic or pneumatic component 300 at various stages of manufacture in accordance with the method of figure 2. It will be appreciated that the precise geometries of the component 300 will vary according to its intended end purpose.

[0046] At step S202, a blank 302 formed of suitable material is provided. The blank has a first surface 304 and a second surface 306. Advantageously and in contrast to known machining/stamping techniques, the photoablation steps described below can be performed on materials having a high hardness, reducing wear on the component 300 when in use and/or avoiding the need to perform a hardening step after the geometry of the component 300 has been established. Preferably, the blank 302 comprises material having a hardness of 45 HRC or higher, such as 55 HRC or higher, or 65 HRC or higher. Optionally the blank 302 comprises one or more of 250 maraging steel, 350 maraging steel, 440C CRES steel, tungsten carbide, and Stellite™.

[0047] Depending on the desired geometry of the component, some features can be machined into the blank using traditional techniques prior to the photoablation discussed below. Thus the coarse geometry is optionally defined using known machining processes, with refining of those features/creating of further features performed by photoablation as discussed below.

[0048] Optionally, providing the blank includes measuring the external dimensions of the blank.

[0049] Optionally, the second surface 306 (and or the first surface 304) is smoothed (e.g., lapped) in step S204 prior to any photoablation. Beneficially, this avoids the need for performing lapping of the second surface following photoablation as discussed in more detail below.

[0050] At step S206, a photoablation laser 350 is used to apply laser radiation 352 to the blank. As used herein, photoablation (or “laser ablation”) refers to the process of using laser radiation (generally from a pulsed laser) to remove material from an object. In the preferred embodiment, the photoablation technique used involves applying femtosecond laser pulses to an object to remove material without causing any significant heating of the object, particularly when using the relatively hard blank materials mentioned above. For example, some “cold” laser ablation techniques make use of the photoelectric effect to eject electrons from a small region of a metal surface, which momentarily leaves a region of positively charged material on the metal - the remaining positive charges repel each other causing a small quantity of the material to be ejected from the surface. The photoablation processes discussed herein may be performed using an ML-5 laser ablation machine produced by Georg Fischer Eimited. Alternatively other photoablation techniques can be employed. In less preferred embodiments, techniques involving using a laser to locally heat an object over a very small area, causing material in that area to evaporate/sublimate, can be used. [0051] Applying laser radiation 352 optionally includes applying femtosecond (or shorter) laser pulses to the blank. Each laser pulse has a duration - for example as measured at the full width (time) at half maximum (intensity) of the pulse - of several hundred femtoseconds or less. Use of femtosecond (or faster) laser pulses for this purpose is particularly advantageous. Using femtosecond lasers, the ablation process is initiated via coulomb explosion with minimal heating of the remaining material, as opposed to thermal vaporisation. This enables material to be removed in smaller quantities than, for example, nanosecond laser pulses, allowing finer resolution in form. Femtosecond laser pulses thus provide sub-micron ablation resolution without causing “re-cast melt”. This is discussed for example in Ch 6. Femtosecond laser ablation: Fundamentals and applications, Sivanandan S. Harilal et al, in S. Musazzi and U. Perini (eds.), Laser-Induced Breakdown Spectroscopy, Springer Series in Optical Sciences 182, DOI: 10.1007/978-3-642-45085-3_6, Springer- Verlag Berlin Heidelberg 2014. In the context of the present embodiment, use of femtosecond laser radiation beneficially allows a both a smooth contour with a uniform surface texture to be created in the blank (for example the passage 308 discussed below), and also a burr-free, sharp exit edge to any apertures created in the blank (for example the aperture 312 discussed below). Both these characteristics enable improved flow properties in the resulting hydraulic and pneumatic components, without having to employ further surface refinement operations (e.g. electro-polishing). In some examples, the pulse duration is 500 fs or less, 350 fs or less, lOOfs or less, 50fs or less, or 10 fs or less. The wavelength of the laser radiation preferably falls in the ultraviolet, visible or infrared ranges. For example, the use of 280 fs pulses of infrared laser radiation has been found by the inventors to provide excellent flow properties in hydraulic components fabricated using the techniques described herein.

[0052] The laser radiation 352 is focussed on the blank. Where the dimensions of the blank are measured in step S202, this information is optionally used when positioning the blank relative to the laser 350 to ensure accurate focussing. In the arrangement shown in figures 3A and 3B, laser radiation 352 is applied to the first surface 304, though it will be appreciated that the laser radiation 352 can be applied to any surface of the blank 302 and at any angle depending on the type of component 300 being made and the required geometry. The laser radiation 352 incident on the first surface 304 begins to ablate the blank 302 as shown by ablated portion 305 shown in figure 3B. [0053] Optionally, performing photoablation includes forming a pilot hole 307 through the blank 302 in step S208, and as shown in figure 3C. Advantageously, this provides a passage through which further material removed from the blank 302 during photoablation can be removed from the blank. In this arrangement, a suitable stream of gas is preferably directed towards the pilot hole 307 during photoablation (e.g., from the first surface 304 to the second surface 302) to encourage removed material out of, and away from, the ablated parts of the blank 302. The stream of gas is optionally only provided during final contouring of the passage 308. In other embodiments, a pilot hole or other opening may be drilled/machined using other techniques in step S202 above, and photoablation is used to refine the profile of the component 300 thereafter.

[0054] The photoablation process includes forming a first aperture 310 in the first surface at step S210, forming a passage 308 at step S212 and forming a second aperture 312 at step S214. Optionally, these steps respectively involve creating/defining/refining the profile of the first aperture 310, passage 308 and second aperture 312 following the creation of a pilot hole/other opening (for example a port in a sliding spool valve) by other means such as machining. It will be appreciated that steps S210, S212 and S214 may be performed in a different order, as a single continuous activity, etc. As shown in figures 3A to 3D, laser radiation 352 is applied towards a single side of the blank 302. Alternatively, the laser radiation 352 can be applied from a different or a variety of sides of the blank at various stages of photoablation, depending on the geometry required for the component 300.

[0055] Advantageously, photoablation allows the geometry of the passage 308, the geometry of the first aperture 310 and the geometry of the second aperture 312 to be attained to a high degree of precision and in a repeatable manner. Thus components 300 can be made more quickly, to higher tolerances with lower variation in flow properties, and hence at a higher yield than traditional techniques. Because successive components 300 manufactured using this method 200 are highly similar, the method further reduces the need for hydraulic/pneumatic testing to characterise the components 300 on a part-by-part basis.

[0056] Further, photoablation allows the passage 308 to be formed with a high smoothness, without the need for subsequent smoothing/lapping/deburring operations. Preferably the arithmetical mean roughness (Ra) of the internal surface of the passage 308 is 5 microns or less, 3 microns or less, or 2 microns or less. In some examples, Ra may be 2.5 microns, 1.6 microns, or less. [0057] As noted above, where the second surface 306 is smoothed prior to photoablation, no subsequent lapping of the second surface 306 is required. This means that the second aperture 212 can be formed with high sharpness (i.e., a very low radius transition between the passage 308 and the second surface 306 can be achieved). In some embodiments, the transition between the passage 308 and the second surface 306 at the second aperture 312 has a radius of curvature of 5 microns or less. Similar sharpness is optionally achieved in respect of the first aperture 304. Since a sharp edge provides beneficial flow properties in many components 300, the use of photoablation leads to improvements in component performance.

[0058] At step S216, a plurality of indents 314 or “micro-pits” are preferably formed via photo ablation on at least a portion of an internal surface of the passage 308 as shown in figure 3D. Step S216 may be performed concurrently with step S212. Each indent 314 is preferably less than around 10 microns in diameter, for example around 5 microns in diameter. Such “micro-pitting” 314 provides for improved fluid flow characteristics through the passage 308 in use. It is known that turbulence leads to incoherent flow patterns, energy losses and promotes cavitation in hydraulic/pneumatic components. This in turn leads to fluctuations in flow pattern over time and with changes in pressure conditions. Conventional hydraulic component design focusses on providing a surface finish that is as smooth as possible to prevent turbulence, particularly in regions that will experience high fluid velocities/high Reynolds numbers in use. In contrast, the plurality of indents 314 (micropitting) introduced in step S216 provide a controlled degree of surface roughness to deliberately create a thin, turbulent boundary layer at the surface of the passage 308 in use (for example a boundary layer having a thickness on the order of 10 microns, such as between 5 and 20 microns). This boundary layer delays the onset of large-scale turbulence and thus promotes laminar flow in the bulk of the surrounding fluid. This in turn leads to an increase in the critical cavitation number and thus avoids cavitation in components in which fluid experiences large pressure drops in use. Beneficially, photoablation provides a convenient means by which to create the desired indents 314 with no significant increase in operation time or cost.

[0059] The introduction of such indents 314 also allows for improved hydraulic/pneumatic component 300 design. The indents allow laminar flow to be maintained over more steeply curved (i.e., smaller radius) internal passage 308 geometries. Accordingly, components 300 can be designed to have such steeper curvatures, which in turn can allow for less material to be removed during manufacture and thus a shortened fabrication time, or indeed entirely new geometries.

[0060] The indents 314 optionally have a range of sizes, as opposed to uniform dimensions. In some embodiments the arithmetical mean height/roughness (Ra) of the internal surface of the passage 308 comprising the indents 314 is in the range 0.5-5 microns, for example 1-3 microns, for example 2-2.5 microns. In one example, Ra is 2.5 microns. In another example, Ra is 1.6 microns. In such embodiment, the maximum profile peak height (Rz) is in the range 5-25 microns, for example 10-20 microns, for example 12-17 microns. In one example, Rz is 15.3 microns. In such embodiments, the mean width of profile elements (RSm) is in the range 5-25 microns, for example 10-20 microns, for example 15-18 microns. In one example, RSm is 17.0 microns. Optionally, the range in dimensions of the indents 314 is such that the surface profile of the passage 308 with indents 314 follows an approximately Gaussian probability density function. In other words, the depth of the indents 314 and/or the width of the indents 314 have a Gaussian or roughly Gaussian distribution about a mean value, with indents 314 more likely to have a depth/width close to the mean depth/width.

[0061] Beneficially, photoablation does not form a burr on the first and second apertures 310, 312, therefore subsequent deburring can optionally be forgone in step S218, for example if one or both of the first and second surfaces 304, 306 are smoothed prior to photoablation.

[0062] As noted above, the blank 302 preferably comprises a material having a hardness of at least 45 HRC, in which case hardening of the component 300 after the apertures 310, 312 and passage 308 have been formed is optionally forgone at step S220.

[0063] Figures 4A and 4B show cross sections of a hydraulic jet-pipe nozzle 400 having a horn-shaped passage, suitable and intended for use in a jet-pipe servo valve, fabricated in line with the method 200 described above, and having a passage 408 extending between an entrance aperture 410 and an exit aperture. Figure 4C shows an SEM image of a passage 408 within the jet-pipe nozzle 400.

[0064] In this example, the passage 408 comprises a number of sections 408a, 408b, 408c, 408d, all with different geometries. The use of photoablation enables the accurate fabrication of these geometries to a higher tolerance than could be achieved using traditional fabrication techniques. Additionally, these differing geometries can be produced during a single manufacturing step, avoiding the need to perform multiple processes using different tools. [0065] A first portion 408a of the passage 408 adjacent to the exit aperture 412 is cylindrical about an axis 422, and has an inside diameter of 0.183 ± 0.010 mm and a length of 0.31 mm. The nozzle 400 has an exit surface 406 (corresponding to the second surface 306 described in relation to figures 3 A to 3D above). The point at which the first portion 408a meets the exit surface 406 defines an exit aperture 412. At the exit aperture, the exit surface 406 lies orthogonal to the axis 422. The transition 420 between the inside surface of the first portion 408a and the exit surface is defined by a radius of 0.005 mm or less. The arithmetical mean roughness of the inside surface of the first portion 408a is 0.8 microns.

[0066] Adjacent to the first portion 408a, at the opposite end to the exit aperture 412, is a second portion 408b of passage 408. The second portion 408b is rotationally symmetric about the axis 422. The radius of the second portion 408b about the axis 422 is the same as that of the first portion 408a at the point the second portion 408b meets the first portion 408b, and increases with axial distance away from the first portion 408a, such that the inside surface of the second portion 408b exhibits curvature in a plane including the axis 422. The radius of curvature of the inside surface of the second portion 408b in said plane is 0.45 ± 0.005 mm. The arithmetical mean roughness of the inside surface of the second portion 408b is 1.6 microns.

[0067] Adjacent to the second portion 408b, at the opposite end to the first portion 408a, is a third portion 408c of passage 408. The third portion 408c is rotationally symmetric about the axis 422. The radius of the third portion 408c about the axis 422 is the same as that of the second portion 408b at the point the third portion 408c meets the second portion 408b, and increases linearly with axial distance away from the second portion 408b. The third portion 408c provides a tangential lead-in to the second portion 408b.

[0068] Adjacent to the third portion 408c, at the opposite end to the second portion 408b, is a fourth portion 408d of passage 408. The fourth portion 408d is rotationally symmetric about the axis 422. The radius of the fourth portion 408d about the axis 422 is constant and equal to that of the third portion 408c at the point the fourth portion 408d meets the third portion 408c. The angle between the inside surface of the fourth portion 408d and the inside surface of the third portion 408c in a plane including the axis 422 is 120 ± 1 degree. Optionally, the fourth portion 408d can be created by traditional drilling/boring/machining techniques (for example using a flat bottom cutter) prior to photoablation taking place, and subsequently the first, second and third portions 408a, 408b, 408c are created by photoablation (in this case the junction between the third portion 408c and fourth portion 408d corresponds to the first aperture described above in relation to figures 2 to 3D).

[0069] In use, hydraulic fluid passes through the nozzle 400 from the entrance aperture 410, through the passage 408 and out of the exit aperture 412 (i.e., from right to left as shown in figures 4A to 4B). The geometry of the passage 408 allows the pressure of the hydraulic fluid to be reduced from a value of around 5000 psi (3.5 xlO⁷ Pa) in the fourth portion 408d of the passage 408 to around 50 psi (3.5 xlO⁵ Pa) when leaving the exit aperture 412.

[0070] As best shown in figure 4C, the passage 408 includes a plurality of indents 414 having an average diameter of around 5 microns, created during the photoablation process. As described above, in use the indents 414 create a thin, turbulent boundary layer in the hydraulic fluid at the surface of the passage 408, thereby delaying the onset of large-scale turbulence and promoting laminar flow in the bulk of the surrounding hydraulic fluid.

[0071] Advantageously, the jet-pipe nozzle 400 of figures 4A to 4C, fabricated via photoablation in the manner described above in relation to figures 2 to 3D, exhibits accurate geometry and very good flow properties that are difficult, if not impossible, to achieve through traditional manufacturing techniques. In particular, use of this method allows the nozzle 400 to have: a flat exit face 406 with no surface scratches; a sharp, burr-less exit aperture 412 of well-defined diameter; a parallel collimating section (the first portion 408a); a contoured inlet (the second portion 408b) with a well-defined radius of curvature; a tangential lead-in section (the third portion 408c); and all with a typical surface roughness of 1.6 microns or less. Together, these features provide a known exit flow area and known coefficient of discharge, meaning that the flow rate is not only highly reproducible between different nozzles 400 made in this way, but also precisely predictable. Further, this geometry promotes smooth acceleration of hydraulic fluid through the nozzle 400, avoiding flow separation from the walls or the introduction of turbulence. Indeed, when tested, the jet-pipe nozzle 400 exhibited a coefficient of discharge of 0.93, close to the theoretical maximum of 1.0. The nozzle 400 thus produces a collimated and coherent jet of hydraulic fluid at the exit aperture 412. The smooth hydraulic fluid acceleration profile provided by this geometry limits local fluid accelerations, and thereby reduces erosion of the passage 408 and improves nozzle longevity. [0072] The measured flow properties of a jet-pipe nozzle 400 in accordance with figures 4A to 4C, fabricated via photoablation in the manner described above in relation to figures 2 to 3D are shown in Figure 4D. Figure 4D shows a plot of the flow rate of hydraulic fluid through the jet-pipe nozzle 400 (y-axis) as a function of the difference between the supply pressure Ps and the return pressure (alternatively referred to as the exit pressure or downstream pressure) Pr (x-axis). A first line 450 corresponds to data measured at a value of Pr of 50 psi (344738 Pa), a second line 452 corresponds to data measured at a value of Pr of 250 psi (1.724xl0⁶ Pa). As can be seen in figure 4D, the two lines 450, 452 are coincident, exhibiting no cavitation. This measured jet-pipe nozzle 400 exhibited a coefficient of discharge Cd of 0.93.

[0073] For comparison, the measured flow properties of jet-pipe nozzles fabricated using prior art techniques are shown in figures 4E and 4F. Figure 4E shows measured properties of a jet-pipe nozzle fabricated by drilling, reaming and abrasive flow machining. Figure 4F shows measured properties of a jet-pipe nozzle fabricated by drilling and reaming. In both figures 4E and 4F the flow rate of hydraulic fluid through the respective jet-pipe nozzle (y- axis) is plotted as a function of the difference between the supply pressure Ps and the returnpressure Pr (x-axis). Lines 454 and 460 correspond to data for the respective jet pipe-nozzles measured at a value of Pr of 250 psi (1.724xl0⁶ Pa). Lines 456 and 462 correspond to data for the respective jet pipe-nozzles measured at a value of Pr of 50 psi (344738 Pa). In both figure 4E and figure 4F there is a difference between the data measured at Pr of 50 psi (344738 Pa) and data measured at 250 psi (1.724xl0⁶ Pa): lines 454 and 456 are not coincident in region 458, and lines 460 and 462 are no coincident in region 464. This is indicative of cavitation (the formation of bubbles in the hydraulic fluid) occurring in conditions corresponding to regions 458 and 464. The jet-pipe nozzle fabricated by drilling, reaming and abrasive flow machining of figure 4E was measured as having a value of Cd of 0.79. The jet-pipe nozzle fabricated by drilling and reaming of figure 4F was measured as having a value of Cd of 0.71. Accordingly, the jet-pipe nozzle 400 fabricated in accordance with an embodiment of the present invention exhibited improved flow characteristics.

[0074] In other examples, the geometry of the hydraulic/pneumatic part may be different. In particular, the use of the fabrication technique above allows for the use of new and more complex geometries, that cannot be reliably created using previously known fabrication techniques. [0075] Known jet-pipe nozzles typically impart a non-constant acceleration profile to hydraulic fluids passing through them. Erosion effects can manifest when the acceleration of hydraulic fluid reaches a peak at a certain point within the nozzle, increasing wear and reducing component lifetime. Similar is also true of other hydraulic/pneumatic components. The fabrication techniques of the present invention can be used to replicate complex curvilinear, mathematically derived geometry that smooths the acceleration profile of fluids when passing through such components.

[0076] An example is shown with respect to figures 5A and 5B. Figure 5A shows a graph 500 of a mathematically derived diameter profile for a jet-pipe nozzle. Diameter of a fluid flow passage (e.g., passage 308) is shown on the y-axis. Distance from an exit aperture (e.g., corresponding to the second aperture 312 discussed above) along an axis of the passage is shown on the x-axis, (with 0 corresponding to the position of the exit aperture). As can be seen, the diameter increases non-linearly with distance from the exit aperture, the rate of increase in diameter increasing with distance from the exit aperture. Further, the curve of the graph (and hence the curve of the inner surface of the passage in a plane including the axis of the passage) does not follow a fixed radius of curvature - instead the radius of curvature increases to a peak value and then decreases.

[0077] Figure 5B shows the acceleration profile 502 of hydraulic fluid passing through the passage described in figure 5A. Acceleration of the fluid flowing along the passage is shown on the y-axis. Distance from an exit aperture along an axis of the passage is shown on the x- axis (again, with 0 corresponding to the position of the exit aperture). Advantageously, the acceleration profile is approximately constant along the length of the passage. A jet-pipe nozzle made to this design can thus exhibit reduced erosion effects. Such a design can be achieved by the photoablation techniques discussed above, which allow tuning over very small length scales, but is not readily achievable via traditional techniques.

[0078] Similar applies to other hydraulic/pneumatic components. By locally increasing the radius of curvature of an inside surface of a passage at locations that would otherwise create a peak in fluid acceleration, erosion effects can be reduced. An additional benefit of a local increase in radius of curvature is that the component can also be made more compact, since the overall length of the passage is reduced. [0079] Known jet-pipe nozzles employ circular exit apertures, as do other hydraulic and pneumatic components (particularly those of relatively small dimensions, for example those between around 1 mm and 2 mm in diameter). Advantageously, use of the photoablation fabrication methodology described above allows for the use of precisely defined, non-circular shaped apertures that would be difficult if not impossible to accurately fabricate via other means.

[0080] Figure 6A shows a partial cross section of a known jet-pipe servo valve 600 fabricated using traditional techniques (drilling, stamping, lapping, etc.). Such a servo valve comprises a jet-pipe nozzle 602 movable relative to a pair of receiver orifices 604a, 604b, each of which has a substantially circular cross section relative to the direction of hydraulic fluid flow. The exit aperture 601 has a diameter di, and the receiver orifices 604a, 604b have diameters of ds and ds respectively (d and ds may be the same). In use, the nozzle 602 issues a coherent jet of hydraulic fluid from an exit aperture 601, that is then incident onto receiver orifices 604a, 604b. By moving the nozzle 602 in the x-direction (i.e., leftwards or rightwards as shown in figure 6A), the proportion of the hydraulic fluid output from the nozzle 602 received by each of the receivers 604a, 604b can be varied.

[0081] The quantity of flow received is roughly proportional to the area of overlap between the exit aperture 601 and the receiver 604a, 604b entrance. Thus, the flow gain (i.e., the flow change per unit of distance travelled by the nozzle 602 along the x-axis) at each receiver 604a, 604b depends on the width wi, at the intersection of the exit aperture 601 and receiver holes 604a, 604b in the y-direction, that is, perpendicular to the direction of movement of the nozzle 602. This overlap is illustrated in figure 6B, which shows the relative positions of the exit aperture 601 and receiver orifices 604a, 604b in a plane perpendicular to that shown in figure 6A (in this case when the exit aperture 601 is positioned roughly over the midpoint between the receiver orifices 604a, 604b).

[0082] Figure 7 illustrates an alternative jet-pipe servo valve geometry that can be accurately and reliably obtained using the photoablation processes described above. In this example, the jet-pipe servo valve is as described above in relation to figures 6A and 6B, with the exception that each of the jet-pipe nozzle exit aperture 701 and the receiver orifices 704a, 704b are fabricated using the photoablation method described above in relation to figures 2 to 3D, and have an oval cross section relative to the direction of fluid flow. Figure 7 shows the overlap between, and relative positions of, the exit aperture 701 and receiver orifices 704a, 704b from a viewpoint analogous to that of figure 6B (in this case when the exit aperture 701 is positioned roughly over the midpoint between the receiver orifices 704a, 704b). The width di of the exit aperture 701 and the widths ds, ds of the receiver orifices 704a, 704b in the x- direction (i.e., parallel to the direction of travel of the nozzle) is the same as for the arrangement in figures 6A and 6B, however the respective widths in the y-direction (i.e., perpendicular to the direction of movement of the nozzle) are greater, meaning that the width of the overlap W2 is greater than wi for the arrangement of figures 6A and 6B at a corresponding nozzle position. This allows the nozzle exit aperture 701 and receiver 704a, 704b areas to be extended in the y-direction (i.e., perpendicular to the direction of movement of the nozzle) relative to the arrangement of figures 6A and 6B, while maintaining the existing dimensions in the x-direction (i.e., parallel to the direction of movement of the nozzle). Advantageously, this geometry again allows for the nozzle to issue a coherent jet from the exit aperture 701, but additionally enables the flow gain to be chosen at will when designing the servo valve, with no need to modify the travel of the nozzle. Thus, use of photoablation allows the flow gain to be tailored to specific requirements for a particular application, without changing the overall package size of the servo valve.

[0083] Use of photoablation further enables use of rectilinear apertures. Figure 8 shows a further alternative jet-pipe servo valve geometry that can be accurately and reliably obtained using the photoablation processes described above. In this example, the jet-pipe servo valve is as described above in relation to figures 6A and 6B, with the exception that each of the jetpipe nozzle exit aperture 801 and the receiver orifices 804a, 804b are fabricated using the photoablation method described above in relation to figures 2 to 3D, and have a rectangular cross section relative to the direction of fluid flow. As with the arrangement of figure 7, The width di of the exit aperture 801 and the widths d , ds of the receiver orifices 804a, 804b in the x-direction is the same as for the arrangement in figures 6A and 6B, however the respective widths in the y-direction are greater, meaning that the width of the overlap ws is greater than wi for the arrangement of figures 6A and 6B at a corresponding nozzle position. Figure 8 shows the overlap between, and relative positions of, the exit aperture 801 and receiver orifices 804a, 804b from a viewpoint analogous to that of figure 6B (in this case when the exit aperture 801 is positioned roughly over the midpoint between the receiver orifices 804a, 804b). As with the example of figure 7, this allows the nozzle exit aperture 801 and receiver 804a, 804b areas to be extended in the y-direction relative to the arrangement of figures 6A and 6B, while maintaining the existing dimensions in the x-direction. Again, this enables flow gain to be tailored to a specific application without the need to modify the travel of the nozzle exit aperture 801 relative to the receiver orifices 804a, 804b.

[0084] It will be appreciated that by using photoablation in the manner described above in relation to figures 2 to 3D, apertures may be fabricated having any desired shape (curvilinear, rectilinear, polygonal, symmetric, asymmetric, and permutations thereof). Thus, the present fabrication technique permits a high degree of tailoring of fluid flow properties (for example by altering the shape of apertures in jet-pipe servo valves, by altering port dimensions/shapes in sliding spool valves, etc.).

[0085] It will further be appreciated that the non-circular aperture geometries discussed above may be combined with other aspects described above, for example the introduction of indents (micro-pitting) and the passage curvature profiles described in relation to figures 4A to 5B.

[0086] Figure 9 shows an aircraft 900 having one or more flight control systems 902a, 902b. The one or more flight control systems 902a, 902b comprise one or more jet-pipe servo valves 904a, 904b having jet-pipe nozzles and/or receiver orifices fabricated in line with the techniques described above in relation to any of figures 2 to 5B and/or 7 to 8. In one example, the one or more jet-pipe servo valves 904a, 904b are used in the actuation of flight control surfaces 906a, 906b (for example, the one or more jet-pipe servo valves 904a, 904b may be used as the first stage in a multistage servo valve).

[0087] The above embodiments are provided as examples only and the invention is not limited to the described embodiments. The scope of the invention is defined by the appended independent claims. The invention covers all variations and equivalents as fall within the scope of the appended independent claims.

Claims

1. A method of manufacturing a hydraulic or pneumatic component, the method comprising: providing a blank having a first surface and a second surface; applying pulsed laser radiation to the blank, the pulsed laser radiation having a pulse duration of 500 femtoseconds or less, thereby removing material from the blank by photoablation so as to form: a first aperture in the first surface; a second aperture in the second surface; a passage between the first aperture and the second aperture, wherein the passage is configured to provide a fluid flow path in use; wherein at least one of: applying pulsed laser radiation to the blank forms a plurality of indents on an internal surface of the passage; the passage formed by applying pulsed laser radiation to the blank comprises a length along an axis, and the internal surface has a diameter, wherein the diameter varies along the length such that the internal surface has a varying radius of curvature in a plane including the axis.

2. The method of claim 1, wherein a diameter of each of the plurality of indents is 10 microns or less, and optionally 5 microns or less.

3. The method of claim 1 or claim 2, wherein applying pulsed laser radiation to the blank forms the passage such that at least one of: the internal surface has an arithmetical mean height, Ra, in the range 0.5 to 5 microns; the internal surface has a maximum profile peak height, Rz, in the range 5 to 25 microns; the internal surface has a mean width of profile elements, RSm, in the range 5 to 25 microns.

4. The method of claim 1, wherein the passage comprises the length along the axis, and the internal surface has the diameter, wherein the diameter varies along the length such that the internal surface has the varying radius of curvature in the plane including the axis: wherein the radius of curvature has a peak value at a first position along the length, and decreases away from the first position along the length.

5. The method of any preceding claim, wherein the second aperture is non-circular.

6. The method of claim 5, wherein the second aperture is oval or rectangular.

7. The method of any preceding claim: wherein providing the blank comprises smoothing the second surface; wherein applying laser radiation comprises applying laser radiation to the first surface; and further comprising forgoing deburring of the second aperture.

8. The method of claim 7, wherein a transition between the passage and the second surface at the second aperture has a radius of curvature of 5 microns or less.

9. The method of any preceding claim, wherein the blank comprises one or more of: 250 maraging steel; 350 maraging steel, 440C CRES steel; tungsten carbide; Stellite™.

10. The method of claim 9 further comprising forgoing hardening of the blank after the passage has been formed.

11. The method of any preceding claim further comprising, prior to forming the passage, using photoablation to form a pilot hole; during forming the passage, passing a gas through the pilot hole, thereby transporting material removed from the blank by photoablation through the pilot hole.

12. A hydraulic or pneumatic component manufactured using the method of any preceding claim.

13. A hydraulic or pneumatic component, comprising: a first surface having a first aperture; a second surface having a second aperture; a passage between the first aperture and the second aperture, wherein the passage is configured to provide a fluid flow path in use; and a plurality of indents on an internal surface of the passage, such that at least one of: the internal surface has an arithmetical mean height, Ra, in the range

0.5 to 5 microns; the internal surface has a maximum profile peak height, Rz, in the range 5 to 25 microns; the internal surface has a mean width of profile elements, RSm, in the range 5 to 25 microns.

14. The hydraulic or pneumatic component of claim 13, wherein at least one of: the internal surface has an arithmetical mean height, Ra, that is: in the range 1 to 3 microns; optionally in the range 2 to 2.5 microns; optionally 2.5 microns; the internal surface has a maximum profile peak height, Rz, that is: in the range 10 to 20 microns; optionally 12-17 microns; optionally 15.3 microns; the internal surface has a mean width of profile elements, RSm, that is: in the range 10 to 20 microns; optionally in the range 15-18 microns; optionally 17.0 microns.

15. The hydraulic or pneumatic component of claim 13 or claim 14 wherein a diameter of each of the plurality of indents is 10 microns or less, and optionally 5 microns or less.

16. The hydraulic or pneumatic component of claim 13, claim 14 or claim 15 wherein profiles of the first aperture, the second aperture, the passage and the plurality of indents are formed by photoablation using pulsed laser radiation, the pulsed laser radiation having a pulse duration of 500 femtoseconds or less.

17. The hydraulic or pneumatic component of any of claims 14 to 16, wherein: the passage comprises a length along an axis, and an inner surface having a diameter and, the diameter varies along the length such that the inner surface has a varying radius of curvature in a plane including the axis.

18. The hydraulic or pneumatic component of claim 17, wherein the radius of curvature has a peak value at a first position along the length, and decreases away from the first position along the length.

19. The hydraulic or pneumatic component of any of claims 14 to 18 wherein the second aperture is non-circular.

20. The hydraulic or pneumatic component of claim 19 wherein the second aperture is oval or rectangular.

21. The hydraulic or pneumatic component of any of claims 14 to 20 comprising a transition between the passage and the second surface at the second aperture, wherein the transition has a radius of curvature of 5 microns or less.

22. The hydraulic or pneumatic component of any of claims 14 to 21 wherein: the hydraulic or pneumatic component is a jet-pipe nozzle; and the passage has a diameter that decreases towards the second aperture so as to define a horn shape.

23. The jet-pipe nozzle of claim 22, wherein the rate of change of the diameter of the passage with distance along the passage towards the second aperture varies, such that hydraulic fluid flowing through the passage towards the second aperture exhibits a substantially flat acceleration profile.

24. A jet-pipe servo valve comprising the jet pipe nozzle of claim 22 or 23.

25. An aircraft comprising the jet-pipe servo valve of claim 24.