System and method for cavitation abrasive finishing of interior surfaces

Abstract

To provide systems, apparatus and methods relating to smoothing interior surfaces using cavitation abrasive surface finishing.SOLUTION: A method includes immersing a workpiece 136 in slurry 126 that is a mixture of a liquid and an abrasive 150, inserting a cavitation peening nozzle 142 into a cavity 138 of the workpiece 136, and injecting a cavitating jet from the cavitation peening nozzle 142 into the cavity 138, thereby smoothing an inner surface 144.SELECTED DRAWING: Figure 1

Description

[Background technology]

[0001] Additive manufacturing has enabled the efficient production of new components with complex shapes and features that were impractical or impossible to produce by previous methods. However, the resulting surface finish is typically significantly rougher than parts produced by traditional manufacturing methods. Cavitational Abrasive Surfacing (CASF) is a promising new method for mechanically smoothing such surface roughness. Cavitation bubbles are generated by a gas-phase transition resulting from an increase in flow velocity and internal energy, and then collapse and implode as the flow velocity and pressure surrounding the bubbles dissipate. When the cavitation bubbles collapse, they generate microjets that can energize particles of abrasive material. However, generating a cloud of abrasive cavitation bubbles close enough to the interior surfaces of channels and other structures is not feasible with current CASF equipment. Summary of the Invention

[0002] The present disclosure provides systems, apparatus, and methods related to smoothing interior surfaces using cavitation abrasive surfacing. In some embodiments, a method for smoothing an interior surface of a tubular wall of a workpiece may include immersing the workpiece in a liquid and abrasive mixture and inserting a cavitation peening nozzle into a cavity in the workpiece. The method may further include injecting a cavitation jet from the cavitation peening nozzle into the cavity.

[0003] In some examples, an apparatus for smoothing a surface may include a first fluid source, a cavitation peening nozzle, a conduit connecting the first fluid source to the cavitation peening nozzle, and a pump configured to pump fluid from the first fluid source through the conduit to the cavitation peening nozzle. The cavitation peening nozzle may include an exterior and a spacer extending outwardly from the exterior and may be configured to generate a cloud of cavitation bubbles to smooth the interior surface of the tubular wall of the workpiece.

[0004] In some embodiments, an apparatus for smoothing a surface may include a fluid source and a cavitation peening nozzle configured to generate a cloud of cavitation bubbles to smooth the inner surface of a tubular wall of a workpiece. The apparatus may further include a conduit connecting the fluid source to the cavitation peening nozzle, a pump configured to pump high-pressure fluid from the fluid source through the conduit to the cavitation peening nozzle, and a slurry of liquid and abrasive inside the tubular wall of the workpiece.

[0005] The features, functions, and advantages may be realized individually in various embodiments of the present disclosure or may be combined in yet further embodiments, further details of which can be seen with reference to the following description and drawings. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic diagram of an exemplary abrasive cavitation system for an interior surface, according to aspects of the present disclosure. [Figure 2] FIG. 1 is an isometric view of another exemplary abrasive cavitation system for an interior surface. [Figure 3] 3 is an isometric view of the nozzle assembly of FIG. 2 finishing the interior surface of the pipe, with the side of the pipe wall cut away to show the nozzle. [Figure 4] FIG. 3 is an axial view of the nozzle assembly of FIG. 2 in a pipe with a guide vane attachment. [Figure 5] FIG. 1 is an isometric view of an additively manufactured part with two curved interior channels. [Figure 6] 6 is an isometric view of the nozzle assembly of FIG. 2 used in a system with an additional nozzle assembly finishing the interior surfaces of the two curved interior channels of the part of FIG. 5. A section of the part has been cut away to show the nozzles. [Figure 7] 1 is a flowchart depicting steps of an exemplary method for cavitation abrasive surfacing of an interior surface in accordance with the present teachings. DETAILED DESCRIPTION OF THE INVENTION

[0007] Various aspects and embodiments of systems and apparatuses for cavitation abrasive finishing of interior surfaces, and related methods, are described below and illustrated in the associated drawings. Unless otherwise specified, an abrasive cavitation system and / or its various components according to the present teachings may, but need not, include at least one of the structures, components, functions, and / or variations described, illustrated, and / or incorporated herein. Furthermore, unless specifically excluded, process steps, structures, components, functions, and / or variations described, illustrated, and / or incorporated herein in connection with the present teachings may be included in other similar devices and methods, including interchangeability among the disclosed embodiments. The following description of various embodiments is merely exemplary in nature and is not intended to limit the present disclosure, its applications, or uses. Additionally, the advantages provided by the embodiments described below are exemplary in nature, and not all embodiments provide the same or the same degree of advantages.

[0008] This detailed description includes the following immediately following sections: (1) Overview, (2) Examples, Components, and Alternatives, (3) Exemplary Combinations and Further Examples, (4) Advantages, Features, and Benefits, and (5) Conclusion. The Examples, Components, and Alternatives section is further divided into subsections A through C, each of which is labeled accordingly.

[0009] overview Generally, a system for cavitation abrasive finishing of interior surfaces according to the present teachings may include a nozzle assembly having a cavitation peening nozzle, a spacer, and a flexible fluid supply conduit, as well as a container filled with a liquid. A component having an interior surface to be polished may be submerged in the fluid filling the container, thereby filling the interior space defined by the interior surface. The fluid may include a suspended abrasive particle material, and / or the abrasive particles may be introduced into the interior space in other ways. The nozzle assembly may be inserted into the interior space and used to generate a cloud of cavitation bubbles to energize the abrasive particles, thereby smoothing the interior surface and removing any manufacturing process material.

[0010] Examples, Components, and Alternatives The following sections describe selected aspects of exemplary cavitational abrasive surface finishing apparatus and related systems and / or methods. The examples in these sections are for illustrative purposes and should not be construed as limiting the overall scope of the present disclosure. Each section may include one or more individual inventions and / or information, functionality, and / or structures derived from or related to the context.

[0011] Exemplary System for Smoothing a Surface 1, this section describes an exemplary system 110 for smoothing interior surfaces. As mentioned above, system 110 is one example of a system for cavitation abrasive surfacing of interior surfaces.

[0012] 1 is a schematic diagram of system 110. A supply reservoir system 113, including a high-pressure pump 112, supplies pressurized water 114 along a conduit 116. A control valve 120 may allow precise control of the pressure and flow rate of water supplied along conduit 116 to a nozzle assembly 122. In some embodiments, system 110 may include multiple nozzle assemblies, which may be matched or different in size and / or shape. In such embodiments, the multiple nozzle assemblies may all be supplied by high-pressure pump 112 along conduit 116, or may have separate, dedicated sources of precisely controlled high-pressure water.

[0013] The nozzle assembly 122 is disposed within a pressurized tank 124 filled with a slurry 126 of abrasive particulate material 150 mixed with water. A lid 128 of the tank 124 may be opened to allow overflow from the tank into a collection container 130. To maintain pressure within the tank, the lid may be coupled to the tank 124 by a spring, controlled by a relief valve, or restrained by weight. The abrasive slurry 126 may also be drained from the tank 124 along a conduit 132 controlled by a control valve 134.

[0014] The nozzle assembly 122 includes a flexible conduit 140 and a cavitation peening nozzle 142. The flexible conduit 140 may include any structure suitable for carrying high-pressure fluid. The flexible conduit 140 may be repeatedly flexed, bent, twisted, and / or otherwise reconfigured. The conduit may include one or more flexible materials and / or mechanisms that allow for flexing, such as hinges or joints. The nozzle assembly 122 may include materials suitable for withstanding sustained exposure to cavitation and high-energy abrasive particles, particularly on the exterior surfaces of the assembly. In some embodiments, the flexible conduit 140 may be connected to the cavitation nozzle 142 by a section of rigid piping, and / or the assembly may be otherwise configured to achieve abrasion resistance or other desired structural characteristics.

[0015] The nozzle 142 of the assembly 122 is inserted into a cavity 138 of a workpiece 136 submerged in the tank 124 to smooth the inner surface 144. More specifically, the surface 144 is the inner surface of the tubular wall of the workpiece 136. For example, the nozzle may be inserted into a tubular workpiece, such as a channel, hole, chamber, recess, bore, orifice, aperture, and / or any channel-like feature. In the depicted embodiment, the workpiece 136 is a cylindrical pipe with a straight, circular central channel. The flexible conduit 140 of the nozzle assembly 122 may also facilitate cleaning of non-linear or curved channel-like features. The system 110 may be custom-configured to smooth the inner surface 144 of the workpiece 136, may be configured for use with a range of similar workpieces, or may be configured for use with a wide variety of workpieces.

[0016] High-pressure water 114 is injected as a cavitation jet by a nozzle 142 into the abrasive slurry 126 in the tank 124. The interaction between the cavitation jet and the abrasive slurry creates a cloud 146 of cavitation bubbles and abrasive particles. As the bubbles in the cloud 146 collapse, particles 150 of the abrasive material can be excited and energized. Microjets created by the collapsing bubbles can collectively accelerate the particle motion. When the mixture of bubbles and particles contacts the surface 144 of the workpiece 136, the particles can impact the surface and remove material. That is, the abrasive particles can be acted upon by the high force of the cavitation cloud to smooth the inner surface 144.

[0017] Conventional cavitation peening may also occur when cavitation bubbles directly interact with the surface 144 of the workpiece 136, thereby peening the surface 144, improving residual stress and fatigue strength, cleaning, painting, or preparing it for use.

[0018] The collapsing impact force of the cavitation bubbles is determined in part by the pressure of the injected water 114, the pressure of the slurry 126 in the tank 124, the ratio of these two pressures, and the temperatures of the water 114 and slurry 126 in the tank 124. To optimize these parameters, pressure, flow, or temperature sensors may be included in the tank 124 and / or in the conduits 116 or 132. The high-pressure water 114 may be between 50 and 20,000 pounds per square inch, or any effective pressure. The suitable pressure for the water 114 may depend on the pressure of the slurry 126 in the tank 124, the diameter of the surface 144 of the workpiece 136, and / or the size of the cavitation nozzle 142. The suitable pressure may also be related to the design, geometry, and / or other characteristics of the cavitation nozzle.

[0019] To optimize these parameters, pressure and temperature sensors may be included in tank 124 or in any of conduits 116 or 132. Control valves 120, 134 and lid 128, as well as reservoir supply system 113 and temperature control system, may be interfaced with an electronic controller or other such components to enable precise and coordinated control of pressure, flow, and temperature conditions throughout system 110.

[0020] In one depicted embodiment, the cavitation fluid is water; however, any desired fluid may be used. Properties such as viscosity of the fluid used can affect the collapse force of the cavitation bubbles, and the fluid may be selected to improve impact or to reduce the pressure required for a desired impact level. The fluid may also be selected according to the properties of the abrasive material used and / or to achieve the desired properties of the slurry 126. Any effective fluid flow device may be used to pump the pressurized flow rate through the nozzle assembly 122.

[0021] When high-pressure water 114 is sprayed into tank 124 by nozzle assembly 122, the ratio of water to abrasive particles in slurry 126 is affected. To maintain a desired ratio in slurry 126, abrasive material 150 may be added from source 152. Source 152 may be controlled by an electronic controller configured to regulate the introduction of water, the introduction of abrasive material, the overflow of slurry 126, and the outflow of slurry through conduit 132.

[0022] The abrasive material 150 may comprise particles of any effective material of any grain size, or may comprise a mixture of materials. For example, the abrasive material may comprise particles of metal, glass, ceramic, silica oxide, aluminum oxide, pumice, nut shells, corn cob, and / or plastic. In another embodiment, the abrasive material may comprise particles of natural or synthetic rubber, silicone, fluoropolymer, elastomer, Viton, Teflon, and / or fullerene-based carbon nanomaterial. All particles may preferably be within the grain size range of approximately 16 to 1200 ANSI. In this embodiment, the abrasive material is garnet grains 150 of a grain size.

[0023] In this embodiment, the slurry 126 is preferably about one-third abrasive material and about two-thirds water. The appropriate ratio may be selected according to the abrasive material and / or cavitation fluid used. The density or concentration of the abrasive material in the slurry may be selected to achieve a desired material removal rate (MRR).

[0024] Particles of abrasive material 150 may tend to fall out of suspension within slurry 126 over time under the action of gravity. To maintain the suspension of slurry 126, a mixing device 154 is disposed within tank 124. In this embodiment, mixing device 154 is a mechanical agitator, such as a rotating propeller, and is disposed at the bottom of tank 124. Generally, any effective means for stirring, mixing, agitating, or otherwise maintaining the suspension of abrasive particles within slurry 126 may be used. For example, an ultrasonic agitator may be used, the agitator may be disposed at the top or side of tank 124, and / or multiple agitators may be disposed at multiple locations throughout the tank.

[0025] Exemplary Apparatus for Smoothing a Surface 2-6, this section describes an exemplary nozzle assembly 210 for smoothing the interior surface of a workpiece. As mentioned above, assembly 210 is one example of nozzle assembly 122 or a cavitation nozzle assembly. Assembly 210 may be used as part of a system such as abrasive cavitation system 110 described above, and / or may be used in a method such as interior surface finishing method 300 described below.

[0026] 2 is an isometric view of a nozzle assembly 210, including a cavitation peening nozzle 212 and a flexible conduit 214. The flexible conduit includes a metal-shielded outer hose 218 and a polymeric high-pressure supply inner hose 220. The nozzle 212 is coupled to the outer hose 218 and the inner hose 220 by a short section of rigid piping 216, which may also be described as a metal shield.

[0027] The outer hose 218 may comprise a metallic material or metal alloy, a braided material, a pleated material, bonded rigid sections, and / or any material that provides resistance to cavitation peening and impact from high-energy abrasive particles. The outer hose may be resistant throughout to protect the inner hose 220 from exposure to peening and abrasive impact. In some embodiments, the nozzle assembly 210 may be configured to allow replacement of the outer hose 218 or flexible conduit 214 once wear on the outer hose 218 reaches a level sufficient to compromise the protection of the inner hose 220.

[0028] The inner hose 220 may comprise a flexible polymer or plastic and may be rated for high pressure. The inner hose may be sized to provide a desired flow rate at the pressure supplied by the selected pump or compressor and / or to provide a desired pressure at the supplied flow rate. The inner hose 220 may also be appropriate for the temperature and / or chemical properties of the liquid used for cavitation.

[0029] The nozzle 212 is depicted as a cylinder with a circular orifice. Generally, the nozzle may have any geometry or configuration effective for generating a cavitation jet. That is, the nozzle is configured to dispense or inject a cavitation jet of fluid to generate a cloud of cavitation bubbles. For example, nozzles such as those disclosed in U.S. Pat. No. 6,855,208 or those specified in the American Society for Testing and Materials (ASTM) G134-95 standard may be used. As further described with reference to FIG. 4 below, the nozzle 212 may be sized to allow insertion into one or more target workpieces without clogging features, such as passages or channels, to be finished. For example, the nozzle 212 may have a diameter between one-quarter and three-quarters the diameter of the passage to be finished.

[0030] FIG. 3 illustrates a nozzle assembly 210 used. The nozzle 212 is inserted into a first end of a pipe 224 to smooth an interior surface 222. A flexible conduit 214 is connected to a source of high-pressure water, and the pipe 224 is submerged in a slurry 226 of water and abrasive particles 228. The nozzle 212 emits a cavitation jet 230 into an inner passage 232 of the pipe 224, generating a cloud 234 of cavitation bubbles. The abrasive particles 228 of the slurry 226 are drawn into the inner passage 232, where they are energized by the cavitation of the cloud 234. A portion of the energized abrasive particles impact an area of ​​the interior surface 222 near the cloud 234, thereby smoothing that area of ​​the surface.

[0031] In this embodiment, a pipe 224 is submerged in a slurry 226, and abrasive particles 228 are fed into a cloud 234 by the negative pressure effect created by the injection of high-pressure water through the nozzle 212, which pulls the surrounding slurry into and downstream of the pipe's inner passage 232. Sufficient clearance and optional guide structure around the nozzle 212 is required for the slurry to reach the cloud of cavitation bubbles created by the nozzle 212. As explained further below, the nozzle and guide structure(s) may be appropriately sized and / or configured.

[0032] In some examples, abrasive particles 228 may be supplied by other mechanisms. For example, a nozzle assembly used to lubricate a closed-ended bore may include an abrasive supply hose in flexible conduit 214 and an abrasive supply opening in nozzle 212. In another embodiment, a variable flow rate supply of slurry may allow for active control of the material removal rate. In such examples, nozzle 212 may be larger relative to the diameter of the passage to be finished and / or clearance requirements around the nozzle may differ from this example.

[0033] The nozzle assembly 210 is advanced slowly and smoothly along the pipe 224 to achieve a uniform and consistent smooth finish on the interior surface 222. In one embodiment depicted, the inner passageway 232 has a constant diameter, and therefore the nozzle assembly may be advanced at a constant speed. In embodiments where the interior space has a variable geometry, a variable speed of advancement may be calculated for the nozzle assembly to achieve a consistent smooth finish. In other words, the reduced smoothing effect caused by the increased distance from the surface to the cavitation cloud may be counteracted by increasing the exposure time. For example, in a variable diameter pipe, the nozzle assembly 210 may be advanced more slowly when passing through sections of larger diameter.

[0034] 4 is an end view of the nozzle assembly 210 within another pipe 236. The nozzle 212 is positioned within the pipe 236 by a guide attachment 240. The guide attachment 240 may also be described as a spacer. The guide attachment is configured to space the outer surface 239 of the nozzle 212 from the inner surface 238 of the pipe 236 while allowing the flow of water and abrasive particles past the nozzle and down the pipe.

[0035] In this embodiment, guide attachment 240 maintains nozzle 212 in a central or substantially central position within pipe 236 and guides the nozzle along a generally central path through the pipe. Such placement can help achieve a uniformly smooth interior surface 238 and avoid removing too much material or leaving roughness. The tolerance for deviation from a strictly central path can depend on the desired uniformity of the resulting smoothness. That is, the more uniformly smooth the surface desired, the more precisely the nozzle may be required to be positioned. In embodiments where only an overall average reduction in roughness is required, the nozzle may follow a roughly central path and / or a path that is generally approximately central. For example, the nozzle may be manually guided through the pipe without using guide attachment 240.

[0036] Nozzle 212 has an outer diameter 247, measured in cross section and perpendicular to the direction of fluid flow through the nozzle. In this embodiment, nozzle 212 has a constant outer diameter. In some embodiments, outer diameter 247 may vary along the nozzle. Both the constant outer diameter and / or the maximum value of outer diameter 247 may be less than the inner diameter of pipe 236. In other words, nozzle 212 may be sized to allow a sufficient flow rate of water and abrasive particles through the nozzle to create a cavitation cloud. Preferably, outer diameter 247 may be less than about 75% of inner diameter 248.

[0037] The guide attachment 240 may include a plurality of protrusions extending outward from the outer surface 239 of the nozzle 212. Each protrusion may have a major axis perpendicular to the direction of fluid flow through the nozzle 212 and / or perpendicular to the direction of the cavitation jet generated by the nozzle. The protrusions may be equal in length to match the circular cross section of the pipe, or may vary according to the interior geometry of the pipe.

[0038] In the disclosed embodiment, guide attachment 240 includes four equally sized, triangular-shaped vanes 242 equally spaced around a ring 244 that engage the nozzle 212. The vanes may be described as arranged as two pairs of inverted vanes. The distal end of each vane 242 contacts the inner surface 238. Guide attachment 240 may be described as having a span 246 between the distal ends of each pair of inverted vanes. Span 246 matches the inner diameter 248 of the pipe 236.

[0039] The triangular shape of the vanes 242 reduces the cross-sectional area of ​​the pipe 236 obstructed by the guide attachment, which can maximize the flow rate of water and abrasive particles into the cavitation cloud created by the nozzle 212. Any shape and / or number of vanes 242 may be included in the guide attachment 240 that allows for sufficient flow rate and provides effective placement of the nozzle 212.

[0040] In some embodiments, guide attachment 240 may be configured to accommodate varying geometries and / or inner surfaces 238 of pipe 236. For example, vanes 242 may each be collapsible, but spring-biased to extend outward from ring 244, such that span 246 changes to accommodate variations in inner diameter 248. Guide attachment 240 may thereby maintain nozzle 212 in a centered position within pipe 236. In another example, vanes 242 may include a flexible material configured to plastically deform in response to changes in the cross-sectional shape of pipe 236.

[0041] Guide attachment 240 may be part of a set of guide attachments, allowing for the configuration of nozzle assembly 210 for use with various sizes of pipes and / or other channel-like features. A guide attachment having a span that matches the inner diameter of the workpiece may be selected and installed on nozzle 212 prior to surfacing. Ring 244 and nozzle 212 may include corresponding features that allow for a snap-fit ​​or other easy connection and disconnection of the guide attachment.

[0042] In the present disclosure, the guide attachment 240 is constructed from a Teflon material and is designed to be replaced periodically. In some embodiments, the attachment is disposable and / or easily disposable. Other materials that are vulnerable to damage over time when exposed to energized abrasive particles for cavitation peening and surface preparation may be used for attachments with limited such use. In some embodiments, the guide attachment may comprise a metal or other material that can withstand such exposure and may be suitable for extended and / or long-term use.

[0043] FIG. 5 depicts an additively manufactured (AM) part 260 having a first channel 262 and a second channel 264. The channels 262, 264 are manufactured along with the part 260, rather than being machined or drilled from the AM part. Thus, the channels can have more complex and curved shapes, as well as the same surface roughness characteristics of AM. Cavitation abrasive surface finishing may be performed on the exterior surface 266 of the AM part 260 using either the nozzle assembly 210 or a larger, rigid nozzle assembly. However, as depicted in FIG. 6, the nozzle assembly 210 may also be required to finish the interior surfaces of the curved channels 262, 264.

[0044] In some embodiments, two channels can be completed sequentially using nozzle assembly 210. In Figure 6, nozzle assembly 210 is shown being used in conjunction with a second nozzle assembly 211. The two assemblies can be matched and each can have a separate high-pressure water supply, or both can be fed by a single high-pressure pump.

[0045] The AM part 260 is submerged in a slurry 270 of water and abrasive particles. Each of the nozzle assemblies 210, 211 is inserted into the upper opening 272 of a respective channel 262, 264. Water is pumped through the nozzle assemblies to generate a cavitation jet, which in turn generates a cloud 274 of cavitation bubbles and energized abrasive particles when injected into the slurry 270. The interior surface is thereby smoothed, finished, and peened.

[0046] The cavitation jet also forces the water and slurry 270 down the channels 262, 264 and out the lower openings (not shown). As a result, the slurry 270 is drawn into the upper opening 272, down the channels, and through the nozzle assembly, delivering abrasive particles into a cloud 274.

[0047] Channels 262, 264 are matched in cross-sectional area and curvature, and nozzle assemblies 210, 211 are advanced down the channels in unison. In embodiments with different channels, the nozzles are independently controlled and advanced along the channels. As each nozzle assembly advances along its respective channel, flexible conduit 214 flexes to follow the curvature of the channel, allowing nozzle 212 to remain centered within the channel. Flexible conduit 214 may also allow nozzle 212 to reach portions of the channel that are inaccessible to rigid tools.

[0048] Exemplary methods for smoothing inner surfaces This section describes steps of an exemplary method 300 for smoothing the inner surface of a tubular wall of a workpiece with reference to FIG. 7. Aspects of the abrasive cavitation system and / or nozzle assembly described above may be utilized in the method steps described below. Where appropriate, references may be made to components and systems that may be used in performing each step. These references are for illustrative purposes and are not intended to limit the possible ways in which any particular step of the method may be performed.

[0049] 7 is a flowchart illustrating steps performed in an exemplary method, but does not list the complete process or every step of the method. Although various steps of method 300 are described below and illustrated in FIG. 7, the steps do not necessarily have to be performed all together, and in some cases, may be performed simultaneously or in a different order than that illustrated.

[0050] In step 310, the method includes immersing the workpiece in a slurry of liquid and abrasive. The slurry may be contained in a tank and maintained at a constant pressure and abrasive concentration. In some embodiments, the tank may include a mixing device, such as a mechanical agitator, to maintain the suspension of the abrasive within the liquid. In such embodiments, an optional step 311 may be performed of mixing the slurry to maintain the suspension of the abrasive within the liquid. Additional abrasive may also be added as needed to maintain the desired concentration.

[0051] The abrasive may include particles of one or more of metal, glass, ceramic, silica oxide, aluminum oxide, pumice, nut shells, corn cob, plastic, natural or synthetic rubber, silicone, fluoropolymer elastomer, Viton, Teflon, and carbon nanomaterial abrasives. Preferably, the included particles may be within a size range of about 16 to 1200 ANSI grit size. Any effective abrasive media, combination of media, or mixture of media or particles may be used.

[0052] For example, an additively manufactured part with through channels may be submerged in a mixture of garnet grains 150 and water in a 1:2 ratio, which may fill the channels when the part is submerged.

[0053] Step 312 involves inserting a cavitation peening nozzle into a cavity in the workpiece. The nozzle may be connected to a conduit supplying a high-pressure fluid, such as water. Preferably, the supplied fluid may be consistent with the liquid of the slurry. Both the nozzle and a section of the conduit proximate to the nozzle may be configured to withstand exposure to cavitation and energetic abrasive particles. For example, the nozzle and / or the conduit may have an outermost structure comprising a metal or metallic material.

[0054] The workpiece may be any part having an open-ended cavity or a cavity with first and second openings. The cavity may include a tubular wall or a tubular section having a circumferential wall. Method 300 may be used to smooth the inner surface of the wall portion or circumferential wall.

[0055] Step 314 includes injecting a cavitation jet from the nozzle into the cavity to generate a cloud of cavitation bubbles. The cavitation jet may include a high-pressure fluid supplied to the nozzle and projected at a pressure and flow rate through the nozzle geometry to generate the cloud of cavitation bubbles. The fluid may be projected at a high pressure, preferably between 50 and 20,000 pounds per square inch.

[0056] The cavitation jet may be injected into the liquid-abrasive slurry filling the cavity, generating a mixture of cavitation bubbles and abrasive particles. The generated bubble cloud may have a swirling vortex motion that imparts velocity, momentum, and kinetic energy to the abrasive. The collapse of the cavitation bubbles also collectively accelerates the motion of the abrasive particles to smooth the surface of the workpiece, which achieves high velocity and sufficient kinetic energy to remove material from the surface of the workpiece upon impact, thereby facilitating material removal from the inner surface of the workpiece. The cavitation bubbles may further perform cavitation peening and cleaning of the inner surface of the workpiece.

[0057] Step 316 includes moving the nozzle through the tubular section of the cavity. The nozzle may advance along the tubular section while continuing to eject a cavitation jet from the nozzle. In this manner, a cloud of cavitation bubbles and abrasive particles may be moved through the tubular section to smooth the inner surface of the tubular section. The nozzle may be advanced slowly to allow the cavitation bubbles and abrasive particles to act on the inner surface and perform the desired smoothing and peening.

[0058] Substep 318 of step 316 includes varying the speed of movement of the nozzle through the tubular section according to the inner diameter of the tubular section. When the inner diameter of the tubular section remains constant, the nozzle may be moved at a constant speed, and the speed of movement may be increased for areas of the tubular section having a smaller inner diameter and decreased for areas having a larger inner diameter. Such control of the speed of movement may facilitate a uniform smooth finish of the inner surface of the tubular section when the distance between the inner surface and the cloud of cavitation bubbles generated by the nozzle changes. In other words, when the cloud is farther away from the surface to be smoothed, a uniform smooth finish may require more exposure time.

[0059] In some examples, the speed of nozzle movement may be calculated according to the geometry of the tubular section. For example, the nozzle movement may be computer controlled according to a three-dimensional model of the tubular section. In some examples, an operator may assess the smoothness and move the nozzle when the desired smoothness is achieved.

[0060] Step 320 includes maintaining a space between the nozzle and the inner wall of the tubular section using a spacer. Sub-step 322 includes guiding the nozzle along a central path, which in some embodiments may also be performed using a spacer. Step 320 and sub-step 322 may be performed throughout step 316 as the nozzle is moved through the tubular section of the workpiece cavity.

[0061] The nozzle may be sized to allow space between the outside of the nozzle and the inner wall of the tubular section; for example, the outer diameter of the nozzle may be less than half the inner diameter at its narrowest point within the tubular section. A spacer may be removably or fixedly attached to the nozzle and may extend radially outward from the nozzle relative to the direction of fluid flow through the nozzle. The spacer may include a plurality of protrusions that may contact the inner wall of the tubular section to prevent the nozzle from approaching the inner wall less than a selected spacing distance.

[0062] Maintaining a space between the nozzle and the inner wall of the tubular section may allow the flow of slurry in which the workpiece is submerged to proceed through the nozzle and into the cavitation cloud. The pressure of the cavitation jet downstream of the tubular section may provide a negative pressure effect that pulls the slurry through the nozzle and downstream of the tubular section, thereby maintaining the flow of liquid and abrasive at the nozzle to generate a cloud of cavitation bubbles and energized abrasive particles.

[0063] The spacer may be configured to minimize blockage of flow through the nozzle. For example, the spacer may include perforations, may include a minimum number of protrusions necessary for effective spacing, and / or may have any shape suitable for promoting slurry flow. The spacer may also be configured to center the nozzle in the tubular section. For example, the protrusions on the spacer may be arranged in pairs of equal length on either side of the spacer.

[0064] Positioning the nozzle in the center of the tubular section and guiding the nozzle along a central or substantially central path through the tubular section may enable a uniformly smooth finish of the inner wall circumference. In some embodiments, substep 322 may be performed without spacers by an experienced operator and / or by computer control following a three-dimensional model of the tubular section. In some embodiments, characteristics of the tubular section, such as asymmetric geometry, may require a non-central path to achieve uniform smoothness. In that case, substep 322 may include guiding the nozzle along such a path.

[0065] Optional step 324 involves removing the spacer from the nozzle and installing a different size spacer. This optional step may be performed while smoothing separate cavities or tubular sections of a single workpiece and / or while smoothing areas of different diameters within a tubular section after the workpiece has been smoothed and before repeating method 300.

[0066] The spacer may be one of a set of spacers and / or may be described as a modular spacer. The spacer may be selectively attachable to the nozzle, for example, by a resilient or snap-fit ​​engagement. The nozzle may include a recess or other feature to facilitate attachment of the spacer.

[0067] Exemplary Combinations and Further Examples This section describes additional aspects and features of methods and apparatus for smoothing surfaces, presented non-limitingly as a series of paragraphs, some or all of which may be alphanumeric designated for clarity and efficiency. Each of these paragraphs may be combined in any suitable manner with one or more of the other paragraphs and / or with the disclosure of other parts of this application. Some of the following paragraphs explicitly refer to and further qualify other paragraphs, thereby providing non-limiting examples of some suitable combinations.

[0068] A0. 1. A method for smoothing an inner surface of a tubular wall of a workpiece, comprising: Immersing the workpiece in a mixture of liquid and abrasive; inserting a cavitation peening nozzle into a cavity in the workpiece; and injecting a cavitation jet from the cavitation peening nozzle into the cavity. A1. The method of A0, further comprising moving the cavitation peening nozzle through a tubular section of the cavity, the tubular section having a circumferential wall. A2. The method of any one of A0 to A1, further comprising maintaining a radial space between an outer surface of the cavitation peening nozzle and the circumferential wall of the tubular section during the moving step. A3. The method of any one of A1 to A2, wherein the moving step includes varying a speed of movement of the cavitation peening nozzle through the tubular section in relation to a change in an inner diameter of the circumferential wall. A4. The method of any one of A1 to A3, wherein the cavitation peening nozzle has a cylindrical outer surface with an outer diameter that is less than 90% of the inner diameter of the circumferential wall of the tubular section. A5. The method of A4, wherein the outer diameter is less than 75% of the inner diameter. A6. The method of any one of A0 to A5, wherein the mixture is contained in a tank, and the method further comprises mixing the mixture to maintain suspension of the abrasive within the liquid. A7. The method of any one of A0 to A6, further comprising supplying a pressurized fluid to the cavitation peening nozzle. A8. The method of any one of A0 to A7, further comprising guiding the cavitation peening nozzle along a substantially centrally located path through the tubular section of the cavity by using a spacer between an outer surface of the cavitation peening nozzle and an inner surface of the tubular section of the cavity. A9. The method of A8, wherein the spacer includes a plurality of protrusions extending outward from the outer surface of the cavitation peening nozzle. A10. The method of A9, wherein the plurality of protrusions comprises vanes uniformly distributed around the exterior surface of the cavitation peening nozzle. A11. The method of A10, wherein the plurality of protrusions are at least four vanes. A12. The method of any one of A9 to A11, wherein the plurality of protrusions includes at least one retractable protrusion, the protrusion being spring biased to extend outward from the outer surface of the cavitation peening nozzle. A13. The method of any one of A9 to A12, wherein the plurality of protrusions includes at least one protrusion comprising a flexible material. A14. The method of any one of A8 to A13, wherein the spacer is configured to change shape according to the changing geometry of the inner surface of the tubular section of the cavity. A15. The method of any one of A8 to A14, wherein the spacer has a variable diameter. A16. The method of any one of A8 to A15, further comprising removing the spacer and installing another spacer sized for a different tube shape. A17. The method of any one of A0 to A16, wherein the abrasive comprises garnet grains. B0. 1. An apparatus for smoothing a surface, comprising: a first fluid source; a cavitation peening nozzle having an outer surface and a spacer extending outwardly from the outer surface; a conduit connecting the first fluid source to the cavitation peening nozzle; and a pump configured to pump a first fluid from the first fluid source through the conduit to the cavitation peening nozzle; The apparatus, wherein the cavitation peening nozzle is configured to generate a cloud of cavitation bubbles to smooth an inner surface of a tubular wall of a workpiece. B1. The apparatus of B0, further comprising a tank containing a second fluid configured to contain a submerged workpiece, while the cavitation peening nozzle is used to smooth the inner surface of a tubular wall of the workpiece. B2. The apparatus of B1, wherein the tank includes a mixing device for maintaining a uniform concentration of abrasive particles within the second fluid. B3. The apparatus of B2, wherein the concentration maintained is between about one-quarter and about three-quarters. B4. The device of B2, wherein the maintained concentration is between about 10% and about 60%. B5. The apparatus of any one of B1 to B4, wherein the tank comprises a plurality of mixing devices. B6. The apparatus of any one of B1 to B5, wherein the second fluid comprises an abrasive. B7. The apparatus of B6, wherein the abrasive comprises garnet grains. B8. The apparatus of B6 or B7, wherein the abrasive material comprises one or more of: (a) natural or synthetic rubber, (b) silicone, (c) fluoropolymer elastomer, (d) Viton, (e) Teflon, and (f) fullerene-based carbon nanomaterial. B9. The apparatus of any one of B6 to B8, wherein the abrasive comprises a nanomaterial. B10. The apparatus of any one of B0 to B9, wherein the spacer is configured to maintain the cavitation peening nozzle in a substantially central position inside the tubular wall. B11. The apparatus of any one of B0 to B10, wherein the spacer includes a plurality of protrusions extending from the exterior configured to maintain substantially equal radial distances between the exterior of the cavitation peening nozzle and the inner surface of the tubular wall of the workpiece. B12. The apparatus of B11, wherein each of the plurality of protrusions has a major axis extending perpendicular to a direction of fluid flow through the cavitation peening nozzle. B13. The apparatus of B11 or B12, wherein the plurality of protrusions includes at least four protrusions. B14. The apparatus of any one of B0 to B13, wherein the cavitation peening nozzle has a cross-sectional diameter parallel to an inner diameter of the tubular wall, and the cross-sectional diameter of the cavitation peening nozzle is less than 90% of the inner diameter of the tubular wall. B15. The device of B14, wherein the cross-sectional diameter is less than 75% of the inner diameter. B16. The apparatus of any one of B0 to B15, wherein the cavitation peening nozzle has a proximal end and a distal end, the proximal end having a fitting for connecting the cavitation peening nozzle to a flexible tube portion of the conduit, and the distal end having an aperture for dispensing a cavitation jet of the first fluid. B17. The apparatus of B16, wherein the flexible tube portion has a metal guard over a section of the flexible tube portion adjacent the fixture of the cavitation peening nozzle. B18. The apparatus of B16 or B17, wherein the flexible tubing portion includes a metal-reinforced flexible outer hose and a polymeric flexible inner hose. B19. The apparatus of any one of B0 to B18, wherein the spacer is removable, allowing interchangeable spacers of different sizes to be used on the same cavitation peening nozzle to smooth different pipe shapes. B20. The apparatus of any one of B0 to B19, further comprising an abrasive material supply mechanism. B21. The apparatus of B20, wherein the abrasive material supply mechanism is integrated into the cavitation peening nozzle. B22. The apparatus of B21, wherein the abrasive material supply mechanism is configured to deliver a slurry of abrasive material and water. C0. 1. An apparatus for smoothing a surface, comprising: fluid source, Cavitation Peening Nozzle, a conduit connecting the fluid source to the cavitation peening nozzle; a pump configured to pump high-pressure fluid from the fluid source through the conduit to the cavitation peening nozzle, the cavitation peening nozzle configured to generate a cloud of cavitation bubbles to smooth an inner surface of a tubular wall of a workpiece; and An apparatus including a liquid and abrasive slurry inside the tubular wall of the workpiece. C1. The apparatus described in C0, wherein the cavitation peening nozzle has a circumferential outer surface and a spacer extending outward from the outer surface. C2. The apparatus of C1, wherein the spacer includes a plurality of vanes uniformly distributed around the exterior surface of the cavitation peening nozzle. C3. The apparatus of C1 or C2, wherein the spacer is removable, allowing interchangeable spacers having different sized vanes to be used on the same cavitation peening nozzle to smooth different pipe geometries.

[0069] Advantages, Features, and Benefits The various implementations of cavitation abrasive surface finishing described herein offer several advantages over known solutions for finishing rough surfaces. For example, exemplary embodiments of the methods described herein enable the finishing of interior surfaces and features such as channels, bores, tubes, and / or hollow structures.

[0070] Additionally, among other advantages, the exemplary embodiments described herein allow a surface to be smoothed, cleaned, and peened in one step.

[0071] Additionally, among other advantages, the exemplary embodiments described herein allow for surface finishing using safe and inexpensive materials such as water and ceramic abrasives.

[0072] Additionally, among other advantages, the exemplary embodiments described herein enable a consistent, uniform, smooth finish along the length of an elongated interior space, such as a channel.

[0073] No known system or device performs these functions, especially for those surfaces where access to such surfaces is difficult. Accordingly, the exemplary embodiments described herein are particularly useful for additively manufactured components having interior surfaces. However, not all embodiments described herein provide the same advantages or the same degree of advantages.

[0074] conclusion The above disclosure may encompass multiple individual embodiments with distinct utilities. While each of these inventions has been disclosed in its preferred form(s), numerous variations are possible and the specific embodiments disclosed and illustrated herein should not be construed in a limiting sense. As used within this disclosure, section headings are for organizational purposes only. The subject matter of this disclosure includes all novel and non-obvious combinations and subcombinations of the various elements, features, functions, and / or properties described herein. The following claims particularly point out certain combinations and subcombinations that are deemed novel and inventive. Other combinations and subcombinations of features, functions, elements, and / or properties may be claimed in applications claiming priority from this or a related application. Furthermore, such claims, whether broader, narrower, equal, or different in scope from the claims originally filed, are deemed to be within the scope of the subject matter of this disclosure.

Claims

1. A method (300) for smoothing the inner surface of a tubular wall of a workpiece, comprising: Immersing the workpiece in a mixture of liquid and abrasive (310); Inserting a cavitation peening nozzle into the cavity of the workpiece (312); injecting (314) a non-abrasive liquid pressurized by a pump from the cavitation peening nozzle into the tubular section of the cavity as a cavitation jet along an inner passage formed by a circumferential wall of the tubular section, whereby the abrasive particles are fed into a cloud of cavitation bubbles by a negative pressure effect due to the injection of the liquid through the cavitation peening nozzle; moving the cavitation peening nozzle through the tubular section (316); moving (316), including maintaining a radial space (320) between an outer surface of the cavitation peening nozzle and the circumferential wall of the tubular section; The method (300), wherein the maintaining (320) further includes guiding (322) the cavitation peening nozzle along a path through the tubular section of the cavity by using a spacer between an outer surface of the cavitation peening nozzle and an inner surface of the tubular section of the cavity.

2. 2. The method (300) of claim 1, wherein the moving (316) comprises varying a speed of movement of the cavitation peening nozzle through the tubular section (318) relative to a change in an inner diameter of the circumferential wall.

3. 3. The method (300) of claim 1 or 2, wherein the mixture is contained in a tank, and the method further comprises mixing (311) the mixture to maintain suspension of the abrasive within the liquid.

4. A method (300) according to any one of claims 1 to 3, wherein guiding (322) the cavitation peening nozzle along a path through the tubular section of the cavity further comprises guiding (322) the cavitation peening nozzle along a substantially centrally located path through the tubular section of the cavity.

5. The method (300) of any one of claims 1 to 4, further comprising removing (324) the spacer and installing another spacer sized for a different tube geometry.

6. A method (300) according to any one of claims 1 to 5, wherein the spacer includes a plurality of protrusions extending from the outside of the cavitation peening nozzle.

7. The method (300) of claim 6, wherein each of the protrusions has a long axis extending perpendicular to the direction of fluid flow through the cavitation peening nozzle.

8. A method (300) as described in claim 6 or 7, wherein the plurality of protrusions include vanes uniformly distributed around the outside of the cavitation peening nozzle.

9. A method (300) according to any one of claims 6 to 8, wherein each of the protrusions is configured to change shape in accordance with the changing geometric dimensions of the inner surface of the tubular section of the cavity.

10. A method (300) according to any one of claims 6 to 9, wherein the plurality of protrusions includes at least one retractable protrusion, the protrusion being spring-biased to extend outward from the exterior of the cavitation peening nozzle.

11. 1. A device (110) for smoothing a surface, comprising: a first fluid source (113); a cavitation peening nozzle (142, 212) having an outer surface (239) and a spacer (240) extending outwardly from the outer surface; a conduit (116, 140, 214, 216) connecting the first fluid source to the cavitation peening nozzle; a pump (112) configured to pump a non-abrasive first fluid (114) from the first fluid source through the conduit to the cavitation peening nozzle; a tank (124) configured to contain a submerged workpiece (136, 224, 236, 260) while the cavitation peening nozzle (142, 212) is used to smooth the inner surface (144, 238) of a tubular wall (232, 262, 264) of the workpiece (136, 224, 236, 260), the tank (124) containing a second fluid (126, 226, 270) including an abrasive; the cavitation peening nozzle (142, 212) is configured to generate a cloud of cavitation bubbles (146, 234, 274) by injecting the first fluid pressurized by the pump (112) as a cavitation jet along and into an inner passage formed by an inner surface (144, 238) of a tubular wall (232, 262, 264) of the workpiece (136, 224, 236, 260), whereby the abrasive particles are supplied to the cloud of cavitation bubbles by a negative pressure effect due to the injection of the first fluid through the cavitation peening nozzle; Apparatus (110).

12. The apparatus (110) of claim 11, wherein the tank (124) includes a mixing device (154) for maintaining a uniform concentration of abrasive particles (150, 228) within the second fluid (126, 226, 270).

13. 13. The apparatus (110) of claim 12, wherein the maintained concentration is between 10% and 60%.

14. The apparatus (110) of any one of claims 11 to 13, wherein the abrasive (150, 228) comprises garnet grains.

15. 15. The apparatus (110) of claim 11, wherein the spacer (240) includes a plurality of protrusions (242) extending from the outside configured to maintain an equal radial distance between the outside (239) of the cavitation peening nozzle (142, 212) and the inner surface (144, 238) of the tubular wall (232, 262, 264) of the workpiece (136, 224, 236, 260).

16. 16. The apparatus (110) of any one of claims 11 to 15, wherein the cavitation peening nozzle (142, 212) has a cross-sectional diameter (247) parallel to an inner diameter (248) of the tubular wall (232, 262, 264), the cross-sectional diameter of the cavitation peening nozzle being less than 75 percent of the inner diameter of the tubular wall.

17. An apparatus (110) as described in any one of claims 11 to 14, wherein the spacer (240) includes a plurality of protrusions (242) extending from the outside of the cavitation peening nozzle (142, 212).

18. An apparatus (110) as described in claim 17, wherein each of the protrusions (242) has a long axis extending perpendicular to the direction of fluid flow through the cavitation peening nozzle (142, 212).

19. An apparatus (110) as described in claim 17 or 18, wherein the plurality of protrusions (242) include vanes uniformly distributed around the outside of the cavitation peening nozzle (142, 212).

20. An apparatus (110) as described in any one of claims 17 to 19, wherein each of the protrusions (242) is configured to change shape in accordance with the changing geometric dimensions of the inner surface of the tubular wall.

21. An apparatus (110) as described in any one of claims 17 to 20, wherein the plurality of protrusions (242) include at least one retractable protrusion, the protrusion being spring-biased to extend outward from the outside of the cavitation peening nozzle (142, 212).

22. An apparatus (110) as described in any one of claims 11 to 21, further comprising an abrasive supply hose disposed within the conduit (214) and an abrasive supply opening within the cavitation peening nozzle (212), wherein the abrasive supply hose and the abrasive supply opening are configured to supply an abrasive.

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