Patent Description:
Additive layer manufacturing (ALM) has been proposed for the manufacture of components having complex geometries, including complex internal structures or channels. However, ALM can produce a component with a surface that is rough and/or has suboptimal hydrophobic surface characteristics and requires finishing to ensure good fluid flow characteristics.

<CIT> discloses a method of removing material from a surface of a workpiece via the discharging of a flow of fluid towards a workpiece, the formation of cavitation bubbles and the introduction of abrasive media. The method includes exciting the abrasive media with the cavitation bubbles, removing material from the workpiece by an interaction between the cavitation bubbles, the abrasive media and the surface of the workpiece.

In particular, internal channels can be finished by abrasive flow machining (AFM), but this method is slow, and can result in accumulation of abrasive particles at bends and narrow passages, or contamination of the component with abrasive particles.

There is a need to develop a surface finishing method to alleviate at least some of the aforementioned problems.

According to a first aspect of the invention, there is provided a method for finishing a surface (for example smoothing or enhancing the surface wettability of the surface) of a component according to claim <NUM>.

The flow of abrasives may be a flow of slurry or a flow of dry abrasives.

The cavitation generator may comprise an ultrasonic generator configured to generate cavitation bubbles in the liquid contacting the surface by ultrasonic excitation in the liquid. The method may comprise controlling an amplitude and/or a frequency of the ultrasonic vibrations to control the generation of cavitation bubbles.

The cavitation generator may comprise a laser configured to generate cavitation bubbles in the liquid contacting the surface by laser excitation in the liquid. The method may comprise controlling a frequency, wavelength and/or an exposure time of the laser to control the generation of cavitation bubbles.

The cavitation generator may be configured to deliver a flow of liquid to the surface to generate cavitation bubbles.

The method may comprise controlling the flow of liquid and the flow of abrasives independently of one another.

The method may further comprise pressurising the flow of liquid before delivering the flow of liquid along the surface. The method may also comprise pressurising the flow of abrasives before delivering the flow of abrasives along the surface.

The pressure and/or flow rate of the flow of liquid may be controlled to control an intensity of cavitation bubble generation and/or cavitation bubble implosion. The pressure and/or flow rate of the flow of abrasives may be controlled to control a degree of abrasion.

The flow of liquid and the flow of abrasives are mixed at the surface. The mixed flow is controlled to flow through a filtration system to separate the mixed flow into the liquid and the abrasives.

The separated liquid and abrasives may be recirculated to the apparatus for delivery.

According to a second aspect of the invention, there is provided an apparatus according to claim <NUM>.

The cavitation generator may comprise an ultrasonic generator configured to generate cavitation bubbles in the liquid contacting the surface by ultrasonic excitation in the liquid.

The cavitation generator may comprise a laser configured to generate cavitation bubbles in the liquid contacting the surface by laser excitation in the liquid.

The controller may be configured to control the flow of liquid and the flow of abrasives independently of one another.

The liquid supply line may comprise a supply of liquid, a liquid pump and liquid pressure regulating means. The liquid pump and liquid pressure regulating means may be configured to pressurise the flow of liquid.

The abrasive supply line may comprise a supply of slurry, a slurry pump and slurry pressure regulating means. The slurry pump and slurry pressure regulating means may be configured to pressurise the flow of slurry.

The controller may be configured to control the pressure and/or flow rate of the flow of liquid to control an intensity of cavitation bubble generation and/or cavitation bubble implosion. The controller may be configured to control the pressure and/or flow rate of the flow of abrasives to control a degree of abrasion.

The liquid may comprise water. The slurry may comprise a suspended mixture of abrasive particles.

The apparatus may comprise a first passageway to deliver the flow of liquid to the surface, and a second passageway to deliver the flow of slurry to the surface.

The apparatus may comprise a nozzle, wherein the nozzle may comprise the first passageway and the second passageway.

The first passageway may be located at a central region of the nozzle and the second passageway may surround the first passageway.

The apparatus comprises a cavitation chamber in which the component is installed. The cavitation chamber comprises a discharge line exiting from the cavitation chamber, wherein the discharge line carries a mixed flow of liquid and abrasives.

The discharge line may comprise a discharge pressure regulator configured to regulate a back pressure in the cavitation chamber.

The controller may be configured to control the discharge pressure regulator to regulate the back pressure in the cavitation chamber.

The apparatus includes a filtration system configured to receive the mixed flow from the discharge line and separate the mixed flow into the liquid and the abrasives.

The filtration system may comprise a filtration tank having at least one filter. The filtration tank may be configured to receive the mixed flow of liquid and abrasives. In use, the filter may at least partially restrict the flow of abrasives within the filtration tank to separate the mixed flow into the liquid and the abrasives.

The filtration system may comprise a plurality of filters, each of the plurality of filters having different pore sizes.

The controller may be configured to recirculate the separated liquid to the liquid supply line and recirculate the separated abrasives to the abrasives supply line.

The surface may comprise a surface of an internal channel of the component.

The invention may comprise any combination of the features and/or limitations referred to herein, except combinations of such features as are mutually exclusive.

Embodiments will now be described, by way of example, with reference to the accompanying figures, in which:.

With reference to <FIG>, a gas turbine engine is generally indicated at <NUM>, having a principal and rotational axis <NUM>. The engine <NUM> comprises, in axial flow series, an air intake <NUM>, a propulsive fan <NUM>, an intermediate pressure compressor <NUM>, a high-pressure compressor <NUM>, combustion equipment <NUM>, a high-pressure turbine <NUM>, an intermediate pressure turbine <NUM>, a low-pressure turbine <NUM> and an exhaust nozzle <NUM>. A nacelle <NUM> generally surrounds the engine <NUM> and defines both the intake <NUM> and the exhaust nozzle <NUM>.

The gas turbine engine <NUM> works in the conventional manner so that air entering the intake <NUM> is accelerated by the fan <NUM> to produce two air flows: a first air flow into the intermediate pressure compressor <NUM> and a second air flow which passes through a bypass duct <NUM> to provide propulsive thrust. The intermediate pressure compressor <NUM> compresses the air flow directed into it before delivering that air to the high pressure compressor <NUM> where further compression takes place.

The compressed air exhausted from the high-pressure compressor <NUM> is directed into the combustion equipment <NUM> where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines <NUM>, <NUM>, <NUM> before being exhausted through the nozzle <NUM> to provide additional propulsive thrust. The high <NUM>, intermediate <NUM> and low <NUM> pressure turbines drive respectively the high pressure compressor <NUM>, intermediate pressure compressor <NUM> and fan <NUM>, each by suitable interconnecting shaft.

Other gas turbine engines to which the present invention may be applied may have alternative configurations. By way of example such engines may have an alternative number of interconnecting shafts (e.g. two) and/or an alternative number of compressors and/or turbines. Further the engine may comprise a gearbox provided in the drive train from a turbine to a compressor and/or fan.

Some components in a gas turbine engine may include complex internal channels with bends and narrow passages, such as pipes for conveying fuel from one location to another. Such components may be manufactured by a number of manufacturing techniques, and some of those techniques may result in rough surfaces or surfaces with poor surface wettability characteristics that may be surface finished to improve performance and/or geometric compliance. For example, such components may be manufactured by additive layering manufacturing (ALM). It may be advantageous to smooth an external surface or an internal surface of a component or to enhance its surface wettability. For example, in the case of a pipe, the internal surfaces may advantageously be smoothed to ensure that fuel can be efficiently and reliably conveyed to the required location.

<FIG> shows an example apparatus for finishing a surface of a component <NUM>. In this example, the surface is a surface of an internal channel of a component <NUM>. The apparatus comprises a liquid pressurisation system <NUM>, a slurry pressurisation system <NUM>, a cavitation chamber <NUM>, a filtration system <NUM>, and a controller <NUM>. The liquid pressurisation system <NUM> is configured to pressurise a supply of liquid and deliver the liquid to the cavitation chamber <NUM>. The slurry pressurisation system <NUM> is configured to pressurise a supply of slurry and deliver the slurry to the cavitation chamber <NUM>. The cavitation chamber <NUM> comprises an inner passageway <NUM>, which receives the liquid, and an outer passageway <NUM>, which receives the slurry.

In this example, the component <NUM> is manufactured by ALM, and therefore may comprise surface irregularities caused by randomly distributed balling melts throughout the surface. The surface may further comprise stepping or staircase effects caused by inconsistencies in layer thickness. In other examples, the component <NUM> may be manufactured using any suitable manufacturing method.

In order to provide surface finishing (for example smoothing or wettability enhancement) to a surface, in particular, the internal channel of the component <NUM>, the component <NUM> is installed in the cavitation chamber <NUM>, such that the internal channel <NUM> of the component <NUM> is fluidically connected to receive liquid from the inner passageway <NUM> and receive slurry from the outer passageway <NUM>. The controller <NUM> is configured to control the flow of liquid through the internal channel to generate cavitation bubbles and erode or plastically deform the surface of the internal channel by implosion of the cavitation bubbles.

Cavitation in the liquid is caused in particular due to a drop in hydrostatic pressure below the vapour pressure of the liquid at a given temperature. Without wishing to be bound by theory, the cavitation bubbles are thought to implode to generate shock waves which in turn generate micro jets. The micro jets are thought to cause micro pits or cracks on the surface of the internal channel, and thereby remove loosely bonded particles on the internal surface, erode or remove balling melts from the internal surface of a component <NUM> made by ALM, or plastically deform the surface, creating a micro-texture that increases the surface energy and enhances its surface wettability.

The controller <NUM> is further configured to control the flow of slurry through the internal channel of the component <NUM>, to abrade the surface of the internal channel. The slurry comprises abrasive particles which abrade or remove balling melts from the surface of the internal channel.

A mixed flow of liquid and slurry exits the internal channel to a discharge line <NUM>. The discharge line <NUM> carries the mixed flow of liquid and slurry to the filtration system <NUM>.

The filtration system <NUM> is configured to separate the mixed flow to produce a liquid and a slurry. The separated liquid and slurry are recirculated to the liquid pressurisation system <NUM> and the slurry pressurisation system <NUM>, respectively.

In this example, the controller <NUM> is used to control the operation of the apparatus, in particular the liquid pressurisation system <NUM>, the slurry pressurisation system <NUM>, the cavitation chamber <NUM> and the filtration system <NUM>. In other example embodiments, multiple controllers may be used to control the apparatus.

The operation of each system of the apparatus will be described in further detail with reference to <FIG>.

<FIG> shows a schematic diagram of an example liquid pressurisation system <NUM>. The liquid pressurisation system <NUM> comprises a supply of liquid <NUM>. In an example, the liquid <NUM> may be water. The liquid <NUM> may be provided in a liquid tank <NUM>. The liquid tank comprises a heater <NUM> and a temperature sensor <NUM>, which can be used to heat the liquid <NUM> and monitor its temperature. Increasing the temperature of the liquid <NUM> is thought to increase the cavitation intensity by increasing the generation of cavitation bubbles and increasing the intensity of the cavitation implosion.

There may also be a liquid level sensor <NUM> which is used to monitor the level of liquid <NUM> in the liquid tank. A liquid drainage valve <NUM> is provided in the liquid tank to remove liquid <NUM> from the liquid tank. The liquid pressurisation system <NUM> further comprises a liquid pump <NUM>. In this example, the liquid pump <NUM> may be a positive displacement pump e.g. a piston pump. However, any other suitable pump can be used. The liquid pump <NUM> is used to draw liquid <NUM> from the liquid tank and pressurise the liquid <NUM>. In an example, the liquid <NUM> is pressurised to around <NUM>-<NUM> bar, although it may pressurised as high as <NUM>,<NUM> bar in some examples. The liquid pump <NUM> is switched on or off according to the liquid level detected by the liquid level sensor. The liquid pressurisation system <NUM> may comprise a pressure relief valve <NUM> to relieve excess pressure in the flow line and return liquid <NUM> to the liquid tank.

The liquid pump <NUM> is configured to pump the liquid <NUM> to the cavitation chamber <NUM>. The liquid pressurisation system <NUM> also comprises a liquid flow control device <NUM> to control the flow rate of the liquid <NUM>. In an example, the liquid flow control device <NUM> may be a variable frequency drive. A liquid accumulator <NUM> is used to smooth out the pulsations in the flow of liquid <NUM> caused by the liquid pump <NUM>. A liquid pressure regulator <NUM> is provided to control the pressure in the flow of liquid <NUM>. In order to monitor the flow rate and the pressure of the liquid <NUM> flow, a liquid flow meter <NUM> and a liquid pressure sensor <NUM> are provided. A liquid valve <NUM> is provided to control the flow of liquid <NUM> to the cavitation chamber <NUM>. In examples, the liquid valve <NUM> may be a check valve or a non-return valve.

The controller <NUM> is configured to receive data from the liquid flow meter <NUM>, the liquid pressure sensor <NUM>, the liquid level sensor and the liquid temperature sensor. The controller <NUM> is configured to control any or all of the liquid pump <NUM>, the liquid heater <NUM> and the liquid flow control device <NUM> to regulate a cavitation intensity of the flow of liquid based on data received from the liquid flow meter <NUM>, the liquid pressure sensor <NUM> and the liquid temperature sensor. In other examples, the controller <NUM> may be configured to display the data from the liquid flow meter <NUM>, the liquid pressure sensor <NUM>, the liquid level sensor and the liquid temperature sensor, to a user to permit manual control and variation of the liquid pump <NUM> and/or liquid valve <NUM> by user input.

<FIG> shows a schematic of an example slurry pressurisation system <NUM>. The slurry pressurisation system <NUM> comprises a supply of slurry <NUM>. The slurry <NUM> comprises a suspended mixture of abrasive particles. The slurry <NUM> may comprise a concentration of up to <NUM>% (by wt. ) of abrasive particles suspended in a liquid. The abrasive particles may have a mean particle size of between <NUM> and <NUM>. The particle size may also be greater than <NUM>. The abrasive particles may be formed from any suitable abrasive material such as, for example, silicon carbide, cubic boron nitride, alumina, hematite, quartz, and apatite.

The slurry pressurisation system <NUM> comprises a slurry tank <NUM> which contains the slurry <NUM>. The slurry tank <NUM> comprises a slurry stirrer <NUM>, which mixes and agitates the slurry <NUM> in the tank and maintains homogeneity of the slurry <NUM>. The stirrer <NUM> may be powered by an electric motor. The slurry tank <NUM> may also comprise suitable temperature control equipment to control the temperature of the slurry <NUM>. There is also provided a slurry level sensor <NUM> which is used to monitor the level of slurry <NUM> in the slurry tank <NUM>. A slurry drainage valve <NUM> is provided in the slurry tank <NUM> to remove slurry <NUM> from the slurry tank <NUM>.

A slurry pump <NUM> is configured to pump the slurry <NUM> to the cavitation chamber <NUM>. In an example, the slurry pump <NUM> may be a positive displacement pump. The slurry pump <NUM> is configured to pressurise the slurry <NUM>. In an example, the slurry <NUM> may be pressurised to around <NUM> bar. The slurry pump <NUM> is switched on or off according to the slurry level detected by the slurry level sensor <NUM>. The slurry pressurisation system <NUM> may comprise a pressure relief valve (not shown) to relieve excess pressure in the slurry flow line and return slurry <NUM> to the slurry tank <NUM>.

The slurry pressurisation system <NUM> also comprises a slurry flow control device <NUM> to control the flow rate of the slurry <NUM>. In an example, the slurry flow control device <NUM> may be a variable frequency drive. A slurry accumulator <NUM> is used to smooth out the pulsations in the slurry flow caused by the slurry pump <NUM>. A slurry pressure regulator <NUM> is provided to control the pressure in the slurry flow. In order to monitor the flow rate and the pressure of the slurry flow, a slurry flow meter <NUM> and a slurry pressure sensor <NUM> are provided. A slurry valve <NUM> is provided to control the slurry flow to the cavitation chamber <NUM>. In examples, the slurry valve <NUM> may be a check valve or a non-return valve.

The controller <NUM> is configured to receive data from the slurry flow meter <NUM>, the slurry pressure sensor <NUM>, the slurry level sensor <NUM> and the slurry temperature sensor. The controller <NUM> is configured to control one or both of the slurry pump <NUM> and the slurry flow control device <NUM> based on the received data, to adjust the pressure, flow rate and temperature of the slurry <NUM>. In other examples, the controller <NUM> may be configured to display data from the slurry flow meter <NUM>, the slurry pressure sensor <NUM>, the slurry level sensor <NUM> and the slurry temperature sensor, to a user to permit manual control and variation of the slurry pump <NUM> and/or slurry valve <NUM> by user input.

<FIG> shows a detailed representation of an example arrangement of a cavitation chamber <NUM>. In this example, the component <NUM> is shown as a simple tube having an internal channel <NUM>. In other examples, the component <NUM> may be any shape and may have any number of complex channels for surface finishing. As discussed previously, the component <NUM> may be manufactured using ALM, and the internal channel may have a rough surface, for example caused by balling melts, or suboptimal surface wettability.

The pressurised liquid <NUM> delivered from the liquid pressurisation system <NUM> is received in the inner passageway <NUM>. The slurry <NUM> delivered from the slurry pressurisation system <NUM> is received in the outer passageway <NUM>. In this example, the inner passageway <NUM> and outer passageway <NUM> are present in a nozzle <NUM>. The nozzle <NUM> comprises an outer tube <NUM> and an inner tube <NUM> disposed within the outer tube <NUM>. The space within the inner tube <NUM> comprises the inner passageway <NUM> and the space between the outer tube <NUM> and the inner tube <NUM> comprises the outer passageway <NUM>. The inner passageway <NUM> and the outer passageway <NUM> are thus concentrically arranged. The inner tube <NUM> is located at a central region of the nozzle <NUM>, in particular along its central axis. The inner tube <NUM> comprises an inner outlet <NUM> and the outer tube <NUM> comprises an outer outlet <NUM>. In this example, the outer tube <NUM> surrounds the inner tube <NUM>. In this example the inner outlet <NUM> is offset from the outer outlet <NUM>, such that the inner outlet <NUM> is within the end of the nozzle <NUM>. The offset is referred to as stand-off distance of the nozzle. The stand-off distance affects the surface finish required and the effective length of cavitation stream inside the workpiece. However, in other examples, the inner outlet <NUM> may be placed within the end of the nozzle <NUM>. In other examples, the inner outlet <NUM> may protrude out of the nozzle outlet <NUM>. The nozzle <NUM> can be manufactured from any suitable wear resistant material.

In an example, the cavitation chamber <NUM> may comprise an enclosed space containing the component <NUM> and the nozzle <NUM>. The component <NUM> is installed in the cavitation chamber <NUM>, such that an entrance of the internal channel <NUM> is fluidically connected to the inner and outer outlets of the nozzle <NUM>, to receive the flow of liquid <NUM> and the flow of slurry <NUM> from the inner passageway <NUM> and outer passageway <NUM>, respectively. An exit of the internal channel, downstream of the entrance of the internal channel <NUM>, is also fluidically connected to the discharge line <NUM> to discharge the mixed flow of liquid <NUM> and slurry <NUM> to the filtration system <NUM>. The component <NUM> may be retained in the chamber with the use of any suitable securing means, such as by clamping, by a frictional fit or by fasteners.

In this example, cavitation in the liquid <NUM> occurs due to the change in pressure from the high pressure within the inner passageway <NUM> to the lower pressure outside the inner outlet <NUM>. In particular cavitation is caused by a drop in hydrostatic pressure below the vapour pressure of the liquid <NUM> at a given temperature. The diameter of the inner outlet <NUM> is selected such that cavitation bubbles <NUM> are generated in the liquid <NUM>. The diameter of the inner passageway <NUM> tapers down to the inner outlet <NUM>, such that the inner passageway <NUM> is narrowest at the inner outlet <NUM>. The flow of liquid <NUM> is partially restricted by the inner outlet <NUM>. By partially restricting the flow of liquid <NUM> as it passes through the inner outlet <NUM>, cavitation bubbles <NUM> may be generated in the liquid <NUM> by a hydrodynamic effect.

As the slurry <NUM> flows through the outer outlet <NUM> and into the internal channel <NUM> of the component <NUM>, the abrasive particles <NUM> in the slurry <NUM> strike the surface of the internal channel <NUM> and remove surface irregularities by abrading the surface. By directing the slurry <NUM> into the internal channel via the outer outlet <NUM>, the slurry <NUM> can flow adjacent to the surface of the internal channel <NUM> and therefore the abrasive particles <NUM> can have a high level of interaction with the surface. The liquid <NUM> and the slurry <NUM> may be controlled to flow simultaneously through the internal channel <NUM>. In this example, the implosion or collapse of the cavitation bubbles <NUM> in the liquid <NUM> may generate shock waves, which cause the abrasive particles <NUM> in the adjacent slurry <NUM> to accelerate. Accelerating the abrasive particles <NUM> can cause the abrasive particles <NUM> to strike the surface of the internal channel <NUM> at a faster rate and therefore result in a faster rate of abrasion.

It is thought that the abrasive particles <NUM> in the slurry <NUM> may have surface imperfections which trap gases while travelling at high speeds, resulting in a local pressure drop, and thereby generate more cavitation bubbles <NUM> to accelerate the abrasive particles <NUM> and enhance the finishing.

It is thought that whilst cavitation bubbles <NUM> may be effective in removing relatively large imperfections in the surface of the internal channel, such as loosely bonded particles and balling melts, they may be less effective (at least without abrasive particles <NUM>) in smoothing or removing the bulk material of the component <NUM>. The abrasive particles <NUM> in the slurry <NUM> abrade the surface of the internal channel, and may smooth it to a finer finish (e.g. a relatively lower roughness) than the cavitation bubbles <NUM> alone.

The slurry <NUM> comprises abrasive particles <NUM> suspended in a low viscosity liquid, therefore the risk of abrasive particle accumulation at narrow portions or complex bends in the component <NUM> is reduced when compared to methods relying on a higher viscosity liquid.

The cavitation intensity relates to the amount of cavitation bubbles <NUM> which are generated in the liquid <NUM> and/or to the intensity of implosion of the cavitation bubbles <NUM>. The cavitation chamber <NUM> may comprise sensors <NUM> (<FIG>) which monitor the cavitation intensity of the liquid <NUM>, which send data to the controller <NUM>. The controller <NUM> may use this data to control the pressure, flow rate and temperature of the liquid <NUM> to control the level of erosion of the surface of the component <NUM>. Similarly, the controller <NUM> may control the pressure, flow rate and temperature of the slurry <NUM> to control the level of abrasion of the surface of the component <NUM>. Different values of surface roughness can be achieved by controlling the respective parameters of the liquid <NUM> and the slurry <NUM>.

The size of the abrasive particles <NUM> in the slurry <NUM> can be varied to produce different levels of surface finishing in the internal channel of the component <NUM>. Large abrasive particles, for example in the order of <NUM> or greater, may be used in the slurry <NUM>. The large abrasive particles can cause a high degree of abrasion in the internal channel and can be used to achieve a relatively rough surface finish, or to remove large amounts of material to achieve the required surface finish. Small abrasive particles, for example in the order of <NUM>-<NUM>, may be used in the slurry <NUM>. The small abrasive particles cause a low degree of abrasion in the internal channel and can be used to achieve a finer surface finish. In another example, the slurry <NUM> may comprise a mixture of large and small abrasive particles, in relative concentrations selected to achieve the required surface finish.

Whilst in this example, the liquid <NUM> and slurry <NUM> are controlled to flow simultaneously through the internal channel, the apparatus is configured to control the flow of liquid <NUM> independently of the flow of slurry <NUM>.

The slurry valve <NUM> may be closed and the liquid valve <NUM> may be opened to only allow the liquid <NUM> to flow to the inner passageway <NUM>. In this configuration, only the liquid <NUM> is controlled to flow through the internal channel of the component <NUM> such that cavitation bubbles <NUM> are generated to erode the internal channel. Often in components manufactured by ALM, the internal channels may have large surface irregularities, such as balling melts or stepping effects on the surface. The internal channel of the component <NUM> may be blocked as a result. The high pressure flow of liquid and cavitation of the liquid <NUM> to generate cavitation bubbles <NUM> can help to clear the blocked internal channel before performing further surface finishing with a combination of liquid flow to generate cavitation bubbles <NUM> and the flow of slurry <NUM>, or a flow of slurry <NUM> alone.

Likewise, the slurry valve <NUM> may be opened and the liquid valve <NUM> may be closed to only allow the slurry <NUM> to flow to the outer passageway <NUM> and then to the internal channel of the component <NUM>. The flow of slurry <NUM> allows the surface of the internal channel to be finished to a finer finish by the abrasive particles <NUM>. This may be advantageous as a secondary finishing process used after a primary finishing process of the flow of liquid and generation of cavitation bubbles <NUM>. Alternatively, if the component <NUM> has low wall thickness, the level of surface finishing required may be low to prevent excess removal of material from the internal channel and subsequent weakening of the component <NUM>. In such an example, the apparatus can be controlled to only allow a flow of slurry <NUM> through the internal channel to achieve the required surface finish.

<FIG> shows an example arrangement of the filtration system <NUM>. The filtration system <NUM> comprises a filtration tank <NUM>, which is configured to receive the mixed flow of liquid <NUM> and slurry <NUM> from the discharge line <NUM>. The discharge line <NUM> delivers the mixed flow of liquid <NUM> and slurry <NUM> towards the bottom of the filtration tank <NUM>. The filtration system <NUM> also comprises a mixer <NUM> which agitates the mixed liquid <NUM> and slurry <NUM> within the tank.

The filtration system <NUM> comprises at least one filter, the filter extending across the width of the filtration tank <NUM>. In this example, two filters, a fine filter <NUM> and a coarse filter <NUM>, are present in the filtration tank <NUM>. The fine filter <NUM> has a smaller pore size than the coarse filter <NUM>, preventing particles larger than the pore size from passing through the fine filter <NUM>. In this example, the fine filter <NUM> and the coarse filter <NUM> are wire mesh filters; however in other examples, other types of filter may be used. The pore size can be varied by selecting different mesh sizes in the wire mesh filters.

The filtration system <NUM> further comprises a filtration level sensor <NUM>, which monitors the level of the mixed liquid <NUM> and slurry <NUM> within the filtration tank <NUM>. A filtration tank drainage valve <NUM> is included to remove liquid <NUM> and slurry <NUM> from the filtration tank <NUM>.

In operation, the controller <NUM> operates the stirrer to circulate the mixed liquid <NUM> and slurry <NUM> within the filtration tank <NUM> and prevents the abrasive particles in the slurry <NUM> from settling at the bottom of the filtration tank <NUM>. The liquid <NUM> rises towards the top of the filtration tank <NUM> and passes through both the coarse filter <NUM> and the fine filter <NUM>. The flow of the abrasive particles in the slurry <NUM> is restricted by the filters. In particular, the fine filter <NUM> restricts the flow of small particles present in the mixed liquid and slurry, which may include debris which was eroded or abraded from the component. The coarse filter <NUM> restricts the flow of the abrasive particles in the slurry. The mixed liquid <NUM> and slurry <NUM> is separated, with the liquid <NUM> at the top of the filtration tank <NUM>, the slurry comprising abrasive particles <NUM> at the bottom of the filtration tank <NUM>, and a mixture of small particles <NUM> between the fine and coarse filters. The mixture of small particles <NUM> may be removed from the filtration tank as a waste product.

The separated liquid <NUM> at the top of the tank is collected from the filtration tank <NUM> to a collection tank <NUM>. The collection tank <NUM> comprises a collection level sensor <NUM> and a collection tank drainage valve <NUM>. A liquid transfer pump <NUM> is used to pump the liquid <NUM> from the collection tank <NUM> to the liquid tank of the liquid pressurisation system <NUM>. The liquid <NUM> is pressurised in the liquid pressurisation system <NUM> and re-used for surface finishing the internal channel of the component <NUM>.

Liquid <NUM> collected in the collection tank <NUM> from the filtration tank <NUM> may contain particulates, which may include particles smaller than the pore size of the fine filter <NUM>, or debris from the internal channel of the component <NUM>, which was eroded or abraded away during the surface finishing. To remove the particulates, the liquid <NUM> is pumped through a micro-filter <NUM>. The micro-filter <NUM> has a very fine pore size, which is smaller than the fine filter <NUM>. In this example, a single micro-filter <NUM> is shown; however, in other examples, multiple micro-filters may be used, each with different pore sizes.

The slurry <NUM> collected at the bottom of the filtration tank <NUM> is pumped to the slurry tank <NUM> in the slurry pressurisation system <NUM> by a slurry transfer pump <NUM>. The slurry <NUM> can be pressurised in the slurry pressurisation system <NUM> and re-used for surface finishing the internal channel of the component <NUM> by abrasion.

<FIG> shows a detailed schematic of an example apparatus for finishing a surface of a component <NUM> according to the present invention. The apparatus comprises the liquid pressurisation system <NUM>, the slurry pressurisation system <NUM>, the cavitation chamber <NUM>, the filtration system <NUM> and the controller <NUM>.

As shown, a discharge pressure gauge <NUM> and a discharge pressure regulator <NUM> are provided in the discharge line <NUM>. The discharge pressure gauge <NUM> is used to monitor the pressure of the flow exiting the cavitation chamber <NUM>. The discharge pressure regulator <NUM> can be used to control the pressure of the liquid and the slurry within the cavitation chamber <NUM>. In particular, the discharge pressure regulator <NUM> can be used to regulate a back pressure in the cavitation chamber <NUM>. The controller <NUM> can control the operation of the discharge pressure regulator <NUM>. By controlling the back pressure, a level of surface finishing of the surface can be altered.

The apparatus further comprises a first exit valve <NUM>, a second exit valve <NUM>, and a three-way valve <NUM>, downstream of the cavitation chamber <NUM> along the discharge line <NUM>. The first exit valve <NUM> can be opened to direct flow in the discharge line <NUM> to the filtration system <NUM>, in particular the filtration tank <NUM>. The second exit valve <NUM> can be opened to direct flow in the discharge line <NUM> to the three-way valve <NUM>. The three-way valve <NUM> can selectively control either liquid <NUM> to flow to the collection tank <NUM> or control slurry <NUM> to flow to the slurry tank <NUM>.

The apparatus can be operated in number of different configurations, depending on the surface finishing requirements of the component <NUM>. As described above, in one configuration, the apparatus can be operated such that the liquid pressurisation system <NUM> delivers a flow of liquid <NUM> to the cavitation chamber <NUM>, and the slurry pressurisation system <NUM> delivers a flow of slurry <NUM> to the cavitation chamber <NUM>. The controller <NUM> can control the flow of liquid <NUM> along the surface of the component <NUM> to generate cavitation bubbles to erode the surface by implosion of the cavitation bubbles and simultaneously control the flow of slurry <NUM> to abrade the surface. The mixed flow of liquid <NUM> and slurry <NUM> exiting the cavitation chamber <NUM> is carried via the discharge line <NUM>. In this configuration, the first exit valve <NUM> is opened and the second exit valve <NUM> remains closed, directing the mixed flow of liquid <NUM> and slurry <NUM> to the filtration system <NUM> to be separated.

In another configuration, only a flow of liquid <NUM> is directed from the liquid pressurisation circuit to the cavitation chamber <NUM>. The controller <NUM> can control the flow of liquid <NUM> to generate cavitation bubbles to erode the surface by implosion of the cavitation bubbles. This may be used for example, to clear a blocked internal channel of a component <NUM>. In this configuration, the discharge line <NUM> only carries a flow of liquid <NUM> away from the cavitation chamber <NUM>. When only a flow of liquid is used for surface finishing the component, the first exit valve <NUM> is closed and the second exit valve <NUM> is opened, and the three-way valve <NUM> is controlled to direct the flow of liquid <NUM> to the collection tank <NUM>. The liquid <NUM> may contain varying amounts of particle matter, which in examples, may include debris eroded away from the component <NUM> or abrasive particles remaining in the component <NUM> from a prior finishing process using slurry <NUM>. As described previously, the liquid transfer pump <NUM> is controlled to pump the liquid <NUM> from the collection tank <NUM> through the micro-filter <NUM> to remove the particle matter. The liquid <NUM> is pumped to the liquid tank, where it can be pressurised and reused for surface finishing in the cavitation chamber <NUM>.

In another configuration, only a flow of slurry <NUM> is directed from the slurry pressurisation system <NUM> to the cavitation chamber <NUM>, where the flow of slurry <NUM> is controlled to abrade the surface of the component <NUM>. This may be used when the level of surface finishing required is low, requiring only abrasion by slurry <NUM>. In this configuration, the discharge line <NUM> exiting the cavitation chamber <NUM> carries only a flow of slurry <NUM>. In this configuration where only a flow of slurry is used for surface finishing, the first exit valve <NUM> is closed and the second exit valve <NUM> is opened, and the three-way valve <NUM> is controlled to direct the flow of slurry <NUM> to the slurry tank <NUM>. In an example, this configuration may be used when a continuous flow of slurry <NUM> is required to flow through the cavitation chamber <NUM> to abrade the surface of the component <NUM>.

Whilst it has been described that the apparatus is used for finishing an internal surface of a component <NUM>, it will be appreciated that the apparatus can also be used for finishing an external surface of a component <NUM>. By controlling the flow parameters, i.e. the pressure, flow rate and temperature of the liquid <NUM> and the pressure, flow rate and particle size of the slurry <NUM>, the apparatus can be used for a number of different operations on the component <NUM>. For example, the surface of the component <NUM> may be cleaned by the generated cavitation bubbles in the liquid <NUM> and the subsequent collapse of the cavitation bubbles. In another example, the flow parameters can be controlled to perform surface treatment on the surface of the component <NUM> and modify its mechanical properties by inducing compressive residual stresses at the surface.

<FIG> shows an alternative embodiment of the present invention, in which the nozzle <NUM> is mounted to a robotic arm <NUM>. The robotic arm <NUM> may be used to manipulate the nozzle <NUM> to perform surface finishing on multiple areas of the component <NUM>. The nozzle <NUM> can be mounted to an end effector of the robotic arm <NUM>. The robotic arm <NUM> may be articulated and configured to move in six degrees of freedom. As described previously, the nozzle <NUM> is configured to receive a flow of liquid from the liquid pressurisation system <NUM> and a flow of slurry from the slurry pressurisation system <NUM>.

The component <NUM> may be installed in a chamber, such as tank <NUM>. In another example, the component <NUM> may be retained by a fixture. In this example, the tank <NUM> contains a bath of slurry <NUM>. The component <NUM> may be submerged within the bath of slurry <NUM>. The outlet of the nozzle <NUM> may also be submerged within the tank <NUM>. The flow of liquid can be controlled to generate cavitation bubbles to erode the surface of the component <NUM> by implosion of the cavitation bubbles. The flow of slurry can be controlled to abrade the surface of the component <NUM>. The surface of the component <NUM> may comprise an external surface or an internal surface. The robotic arm <NUM> can be controlled to vary the angle of the nozzle <NUM> to direct the flow of cavitation bubbles and the flow of slurry from the nozzle <NUM> to the component <NUM>. The surface finish achieved can be varied as a result of varying the angle of the nozzle <NUM>. The pressure and flow rate of the liquid and the slurry can be controlled to vary the degree of surface finishing. The liquid and slurry exiting the nozzle <NUM> may be collected by the tank <NUM>. The filtration system <NUM> may be used to separate the collected liquid and slurry.

<FIG> illustrates another alternative embodiment that is similar to the embodiment of <FIG> but with an alternative arrangement of the cavitation chamber <NUM>'. The cavitation chamber <NUM>' has the same nozzle arrangement <NUM> with inner and outer passageways <NUM>, <NUM> described above with reference to <FIG>. However, unlike the cavitation chamber <NUM> of <FIG>, the cavitation chamber <NUM> of <FIG> includes a tank <NUM> open to atmospheric pressure and filled with a liquid, in this case pure water.

The nozzle <NUM> and component <NUM> are immersed in the liquid in the tank <NUM>. Immersing the component <NUM> in the liquid conveniently allows for some cavitation and abrasion to occur adjacent an external surface of the component <NUM>, providing some finishing to the external surface. Although not illustrated in <FIG>, the filtration system <NUM> may be adapted to return liquid to the tank <NUM> to maintain the level of the tank <NUM>.

<FIG> illustrates another alternative embodiment in which the liquid pressurisation system <NUM> is replaced with a different source of cavitation generation <NUM>'.

In a first example according to <FIG>, cavitation bubbles are generated by ultrasonic excitation of the working fluid, which in <FIG> is the supply of slurry flowing through the outer passageway <NUM> of the nozzle <NUM> and into the internal channel of the component <NUM>. An ultrasonic generator <NUM>' generates ultrasonic vibrations which are then communicated to the working fluid via the nozzle <NUM>. In particular, the ultrasonic generator <NUM>' may be coupled to the inner tube <NUM> of the nozzle <NUM> so that the nozzle can transmit the vibrations into the fluid. In some cases the inner tube <NUM> may act as or be coupled to an ultrasonic horn that amplifies the vibrations.

The vibration frequency and amplitude of the nozzle or horn may be controlled by controller <NUM> in order to generate cavitation at different intensities. Suitable frequencies of the order <NUM> to <NUM> may be used, with vibration amplitudes of the ultrasonic horn of the order of <NUM> to <NUM>, though these will depend to some extent on the geometry of the arrangement. If the chamber is pressurised, its pressure, and indeed the slurry inlet pressure, may also be controlled to finish the surface of the component as desired.

In a second example according to <FIG>, cavitation bubbles are generated by laser excitation of the working fluid, which in this case is the supply of slurry flowing through the outer passageway <NUM> of the nozzle <NUM> and into the internal channel of the component <NUM>. In this case a laser <NUM>' is focussed on the component surface and concentrated to generate plasma in the fluid surrounding the component, resulting in cavitation.

The laser type, wavelength, frequency and exposure time may be selected and/or controlled by the controller <NUM> so as to generate cavitation effects at the desired intensity. Suitable laser wavelengths may be in the range of <NUM> to <NUM>,<NUM> nanometres, with exposure times of the order of <NUM> femtosecond to <NUM> second. If the chamber is pressurised, its pressure, and indeed the slurry inlet pressure, may also be controlled to finish the surface of the component as desired.

In both of these cases, the filtration system <NUM> of <FIG> and <FIG> may be replaced with a simpler system <NUM>'. Specifically, the system <NUM>' may not be required to filter the output received via the discharge line <NUM> or return liquid to a liquid pressurization system <NUM>, and may instead only return the slurry to the slurry pressurization system <NUM>. In some cases a combination of a liquid pressurisation system and an ultrasonic generator <NUM>' and/or laser <NUM>' may be used for cavitation, in which case a filtration system <NUM> may still be provided.

Claim 1:
A method for finishing a surface of a component (<NUM>), the method comprising the steps of:
installing the component (<NUM>) in an apparatus configured to deliver a flow of abrasives (<NUM>) to the surface and to generate cavitation bubbles (<NUM>) in a liquid (<NUM>) contacting the surface using a cavitation generator (<NUM>, <NUM>');
mixing the flow of liquid (<NUM>) and the flow of abrasives (<NUM>) at the surface;
controlling the mixed flow to flow through a filtration system (<NUM>, <NUM>') to separate the mixed flow into the liquid (<NUM>) and the abrasives (<NUM>);
controlling the cavitation generator (<NUM>, <NUM>') such that cavitation bubbles (<NUM>) are generated to finish the surface by implosion of the cavitation bubbles (<NUM>); and
controlling the flow of abrasives (<NUM>) to the surface so as to finish the surface by abrasion.