Surface finishing method for fine internal flow passages, fine internal flow passage workpiece and finishing medium

Abstract

The present invention relates to a surface finishing method for a fine internal flow passage, a fine internal flow passage workpiece, and a finishing medium. Here, the diameter of the fine internal flow passage is 3 mm or less, the length-to-diameter ratio is 50:1 or more, the finishing method uses a liquid-solid two-phase flow finishing medium, the liquid phase viscosity of the finishing medium is less than 1000 cP, and the solid phase of the finishing medium is abrasive grains (1), a predetermined pressure is applied to the finishing medium so that the finishing medium flows through the fine internal flow passage at a flow rate of more than 5 m / s, and the flow rate of the finishing medium flowing into the fine internal flow passage from one end thereof reaches a saturation value of the flow rate that can be accommodated by the diameter of the fine internal flow passage so that the liquid pressure inside the internal flow passage is in a pressure-trapping state. The surface finishing method for the fine internal flow passage realizes target processing of rough surface convex points, and can obtain a super-mirror quality in which the optimal roughness of the surface coincides with the average cutting edge contact length range of the abrasive grains without being limited by the material of the fine internal flow passage.

Description

[Technical Field]

[0001] The present invention relates to the field of precision machining of internal flow passages, and more particularly to a surface finishing method for fine internal flow passages, a workpiece with a fine internal flow passage, and a finishing medium. [Background technology]

[0002] Components with fine and complex internal flow path structures are widely used in industrial fields such as aerospace, ships, nuclear, automobiles, and molds. In particular, components related to fluid power systems often have complex internal bore structures such as fine flow paths, small-diameter deep holes, and connections between fine flow paths and small-diameter deep holes, and perform functions such as transporting, exchanging, or applying hydraulic pressure to fluids, such as fuel nozzles, heat exchangers, hydraulic modules, and oil passage control throttles in various engines for aerospace, ships, and automobiles.

[0003] Process technologies capable of fabricating fine and complex internal flow channels include precision machining, femtosecond / water jet guided / long pulse laser processing, spark machining, and additive manufacturing (3D printing), etc. Except for additive manufacturing technology, the fine and complex internal flow channel structures fabricated by other single processes are relatively simple and have a small length-to-diameter ratio, so they need to be combined with other combined processes such as welding to fabricate fine and complex internal flow channels. Precision machining can produce fine, complex internal flow passages with problems such as burrs, sharp corners, and uneven joints. Femtosecond laser machining can produce adhered residual particles and a "step" effect on the surface of internal flow passages. Guided water jet / long-pulse laser and spark machining can produce a remelted layer on the surface of internal flow passages. Additive manufacturing (3D printing) is a technology that separates complex 3D structured part models into 2D structures and then layers them together to form them. It enables the integrated molding of complex, fine, and intricate internal flow passage parts, and is therefore increasingly being applied in industrial fields such as aerospace, automotive, and molds. However, additive manufacturing technology has its own process characteristics, such as temperature gradients and layer-by-layer molding, which can cause semi-sintered or adhered powder particles and a "step" effect on the surface of the internal flow passages of parts.

[0004] Burrs during machining, particles sintered into internal flow passages during femtosecond laser processing, and adhesive powder on the surface of internal flow passages during additive manufacturing affect the performance and safety of components. When burrs, attached residual particles, or adhesive powder fall off due to high-speed friction between the fluid flowing into the internal flow passage and the surface, they become redundant and spread with the fluid, block the oil passage, or cause mechanical wear failure, resulting in serious safety hazards. Highly rough inner surfaces are prone to fatigue cracks during long-term use, and carbon accumulation is also likely to occur in high-temperature oil passage systems. Cutting edge marks on the flow passage surface during machining, sharp corners or steps at machined joints, and "step" phenomena on the surface of internal flow passages during femtosecond laser and additive manufacturing processes can cause turbulence, vortices, and a sudden increase in fluid frictional drag during fluid movement, leading to fluid runaway and vibration, shortening the service life of components. Rough surfaces can generate a large number of cavitation bubbles in the fluid, affecting combustion and hydraulic power, and can also cause cavitation corrosion. For internal flow channels and small connecting holes in parts made of specific materials, such as hollow blades, microcracks are likely to occur on the surface of the remelted layer, leading to early failure of the part. Therefore, it is necessary to reduce the thickness of the remelted layer or to prevent its appearance.

[0005] Therefore, when processing the internal flow passage surfaces of fluid power components using technologies such as precision machining, femtosecond / water jet guided / long pulse laser machining, spark machining, and additive manufacturing (3D printing), adverse issues such as burrs, adhesive powder, sintered particle residues, rough surfaces, and remelted layers can occur. Appropriate surface finishing techniques must be used to remove these adverse effects and meet the performance requirements of the product.

[0006] However, currently, there is no technology that can effectively finish the surfaces of fine and complex internal flow passages. Therefore, the roughness of the inner surface of fine and complex internal flow passage workpieces made by additive manufacturing generally only has an initial average roughness Ra of 6.3 μm or more after additive manufacturing. There are no products with an optimal surface roughness Ra of 1.6 μm or less for internal flow passages, and there are no products with an optimal surface roughness Ra of 0.8 μm or less for fine and complex internal flow passage workpieces made by laser processing or spark processing. In addition, with regard to machined workpieces with fine and complex internal flow paths, there are no products with an optimal surface roughness Ra of 0.4 μm or less for the internal flow paths. However, currently, when fine and complex internal flow paths have complex, irregularly shaped flow paths such as S-shaped, L-shaped, U-shaped, or O-shaped bends, this cannot be achieved with machining, which only allows for linear feed, and can only be achieved with methods such as additive manufacturing. Therefore, at present, there are no products with an optimal surface roughness Ra of 1.6 μm or less for fine, irregular, and complex internal flow paths produced by additive manufacturing. Summary of the Invention

[0007] An object of the present application is to provide a surface finishing method for a fine internal flow passage, a fine internal flow passage workpiece, and a finishing medium.

[0008] In a first aspect, the present application provides a surface finishing method for a fine internal flow passage, the fine internal flow passage having a diameter of 3 mm or less and a length-to-diameter ratio of 50:1 or more, the finishing method using a liquid-solid two-phase flow finishing medium, the liquid phase viscosity of the finishing medium being less than 1000 cP, and the solid phase of the finishing medium being abrasive grains, a predetermined pressure is applied to the finishing medium so that the finishing medium flows through the fine internal flow passage at a flow rate of more than 5 m / s, and the flow rate of the finishing medium flowing into the interior of the fine internal flow passage from one end thereof reaches a saturation value of the flow rate that can be accommodated by the diameter of the fine internal flow passage so that the liquid pressure inside the internal flow passage becomes a pressure-trapping state.

[0009] In the technical solution of the embodiment of this application, the viscosity of the liquid phase of the finishing medium is less than 1000 cP, the flow rate of the two-phase finishing medium within the fine internal flow passage is greater than 5 m / s, and the flow rate flowing into one end of the fine internal flow passage reaches the saturation value of the flow rate that can be accommodated within the diameter of the fine internal flow passage, creating a state in which the liquid pressure within the internal flow passage is trapped, thereby forming a means for efficiently polishing the fine internal flow passage using liquid-carrying abrasive grains. In other words, the synergistic effects of the low-viscosity liquid phase, fluid flow rate, and saturation flow rate solve the difficult problem of finishing the fine internal flow passage. The principle is as follows: First, the synergistic action of the low-viscosity liquid phase, the flow rate of the finishing medium, and the saturation flow rate allows the finishing medium to smoothly enter the fine internal passages and form a state similar to a non-Newtonian fluid within the fine internal passages. The fluid boundary layer is parallel to the surface of the internal passages, and the abrasive grains in the hard, "blade-like" non-Newtonian fluid use shear friction to machine the rough surface and convex points of the target. Furthermore, the synergistic action of these three factors generates a frictional, micro-cutting force between the abrasive grains in the finishing medium and the surface of the fine internal passages. This allows for an ultra-mirror quality finish in which the optimal surface roughness and the average cutting edge contact length range of the abrasive grains match, regardless of the material of the fine internal passages.

[0010] In some embodiments, the liquid phase of the finishing medium is an aqueous liquid.

[0011] In some embodiments, the abrasive grains have a surface structure with sharp corners, and the average cutting depth of the cutting edge of the abrasive grains is 1.4 nm to 14 nm, and the average contact length of the cutting edge of the abrasive grains is 50 nm to 1000 nm.

[0012] In some embodiments, the finishing medium finishes the fine internal passages in a reference period until an optimum surface roughness of the fine internal passages reaches a target value, the reference period being obtained by the following steps: the finishing medium finishes the fine internal passages in an initial period, detects the optimum surface roughness of the fine internal passages, and if the optimum surface roughness matches the target value, the initial period is the reference period; if the optimum surface roughness does not reach the target value, sequentially increase a step period until the optimum surface roughness reaches the target value, the corresponding total period being the reference period, wherein the initial period and the step period are obtained based on a one-side thinning rate corresponding to the abrasive grain and an initial average surface roughness of the fine internal passages.

[0013] In some embodiments, the predetermined pressure P satisfies the following equation:

number

[0014] where Ra0 is the initial average surface roughness of the micro-channel, Ra is the target value of the optimal surface roughness of the micro-channel after finishing, t is the initial period, L is the average cutting depth of the abrasive cutting edge, b is the average contact length of the abrasive cutting edge, ρl is the aqueous liquid phase density, ρp is the solid phase density of the abrasive, σw is the yield limit of the workpiece material, χ is the pressure increase ratio at which the saturated flow rate is reached, Re is the Reynolds number of the liquid phase, l is the length of the internal channel, D is the diameter of the internal channel, d is the abrasive grain diameter, and k is the asperity grinding ratio coefficient.

[0015] In some embodiments, the finishing method further includes, after finishing the internal flow passage, an optimum surface roughness corresponding to a diameter expansion value of the internal flow passage satisfies the following formula:

number

[0016] where Ra* is the optimum surface roughness after the internal flow passage is finished and the port diameter is enlarged, Ra0 is the initial average surface roughness of the fine internal flow passage, δ is the port diameter enlargement value, and k is the asperity grinding ratio coefficient.

[0017] In some embodiments, the finishing method further includes injecting a cleaning medium into the fine internal flow passages at the predetermined pressure after the optimal surface roughness of the fine internal flow passages reaches a target value, and the liquid phases of the cleaning medium and the finishing medium dissolve in each other until the Tyndall effect appears in the cleaning medium flowing out of the fine internal flow passages.

[0018] In some embodiments, the finishing method further includes gradually increasing the liquid-phase viscosity, solid-phase abrasive particle size, and solid-phase abrasive particle mass concentration of the finishing medium based on lower limit values ​​of the liquid-phase viscosity, solid-phase abrasive particle size, and solid-phase abrasive particle mass concentration until the flow rate or flow rate of the two-phase finishing medium is 1 to 5% lower than the flow rate or flow rate corresponding to the lower limit values, thereby obtaining optimal value ranges for the viscosity, solid-phase abrasive particle size, and solid-phase abrasive particle mass concentration.

[0019] In some embodiments, the finishing medium finishes the fine internal flow passages for a reference period, and a flow rate or rate of the finishing medium in the fine internal flow passages is determined, and when the flow rate or rate reaches a predetermined value, the optimal surface roughness reaches the target value.

[0020] In some embodiments, the fine internal channels are three-dimensionally elongated and comprise bent structures, including S-shaped bends, L-shaped bends, U-shaped bends, O-shaped bends, spiral bends, and the liquid phase of the finishing medium contains a polymeric thickener.

[0021] In a second aspect, the present application provides a fine internal channel workpiece obtained via the finishing method described in the first aspect above.

[0022] In some embodiments, the fine internal flow passage workpiece has a fine internal flow passage with a diameter of 3 mm or less and a length-to-diameter ratio of 50:1 or more, and the fine internal flow passage workpiece is obtained by additive manufacturing, casting, laser machining, spark machining, etc., and the fine internal flow passage has an inner surface with an optimum surface roughness Ra of 1.6 μm or less after finishing.

[0023] In some embodiments, the fine internal flow passage workpiece has a fine internal flow passage with a diameter of 3 mm or less and a length-to-diameter ratio of 50:1 or more, the fine internal flow passage workpiece is obtained by precision machining, and the fine internal flow passage has an inner surface with an optimum surface roughness Ra of 0.4 μm or less after finishing.

[0024] In some embodiments, the fine internal passage workpiece is an additively manufactured high-temperature alloy fuel nozzle for an aircraft engine, the fuel nozzle having the fine internal passage structure, the diameter of the fine internal passage being less than 2.5 mm, the structure including straight, L-shaped, and O-shaped bends, and the optimum surface roughness Ra of the fine internal passage being 1.6 μm or less. Alternatively, the fine internal passage workpiece is an additively manufactured aluminum alloy heat exchanger, the heat exchanger having a fine internal passage structure, the diameter of the passage being less than 3 mm, and the fine internal passage structure including straight, L-shaped, S-shaped, and U-shaped bends, and the optimum surface roughness Ra of the fine internal passage being 1.6 μm or less. Alternatively, the fine internal passage workpiece is a titanium alloy hydraulic module manufactured by additive manufacturing, the hydraulic module having a fine internal passage structure with a diameter of 3 mm, the fine internal passage structure having straight, S-shaped, or L-shaped bends, and the optimum surface roughness Ra of the fine internal passage is 1.6 μm or less. Alternatively, the fine internal passage workpiece is a stainless steel throttle manufactured by additive manufacturing, the throttle having a fine internal passage structure with a diameter of less than 1 mm, the fine internal passage structure having a spiral bend, and the optimum surface roughness Ra of the fine internal passage is 0.8 μm or less.

[0025] In some embodiments, the fine internal passage workpiece is a hollow blade made of a high-temperature alloy cast for an aircraft engine, and the hollow blade has an inner cavity structure in which the fine internal passage communicates with small holes, and the optimum roughness Ra of the inner surface of the small holes after finishing is 0.8 μm or less, there is no remelted layer, and the chamfer radius of the holes is greater than 0.1 mm.

[0026] In a third aspect, the present application provides a finishing medium for use in the finishing method of the first aspect, the finishing medium comprising a liquid phase and a solid phase, the liquid phase having a viscosity of less than 1000 cP, and the solid phase being an abrasive grain.

[0027] In some embodiments, the liquid phase of the finishing medium is added with a polymeric thickener.

[0028] In some embodiments, the liquid phase further contains an antifoaming agent, and during the process of machining fine internal channels using the finishing method, the volume ratio of the surface foam slurry of the finishing medium to the liquid phase does not exceed 0.3:1.

[0029] In some embodiments, the liquid phase of the finishing medium also includes a lubricant, which may include one or more combinations of inorganic compounds, elementary compounds, and polymeric compounds. [Brief explanation of the drawings]

[0030] The above and other features, properties and advantages of the present invention will become more apparent from the following description in conjunction with the accompanying drawings and embodiments, which should be noted that the accompanying drawings are illustrative only and are not drawn to scale, and should not be considered as limiting the scope of protection actually claimed by the present invention.

[0031] [Figure 1] 1 is a flowchart of a finishing method according to some embodiments of the present application. [Figure 2] Schematic diagram of the principle of micro-cutting force in the finishing method according to some embodiments of the present application [Figure 3]1 is a flowchart of a finishing method according to another embodiment of the present application. [Figure 4] 1 is a flowchart of a finishing method according to yet another embodiment of the present application. [Figure 5] 1 is a flowchart of a finishing method according to a further embodiment of the present application; [Figure 6A] Component image to be finished by the finishing method according to the first embodiment of the present application [Figure 6B] Component image to be finished by the finishing method according to the first embodiment of the present application [Figure 6C] Component image to be finished by the finishing method according to the first embodiment of the present application [Figure 7A] Component image to be finished by the finishing method according to the second embodiment of the present application [Figure 7B] Component image to be finished by the finishing method according to the second embodiment of the present application [Figure 7C] Component image to be finished by the finishing method according to the second embodiment of the present application [Figure 8A] Component image to be finished by a finishing method according to a third embodiment of the present application [Figure 8B] Component image to be finished by a finishing method according to a third embodiment of the present application [Figure 8C] Component image to be finished by a finishing method according to a third embodiment of the present application [Figure 9A] Component image to be finished by a finishing method according to a fourth embodiment of the present application [Figure 9B] Component image to be finished by a finishing method according to a fourth embodiment of the present application [Figure 10A] Component image to be finished by a finishing method according to a fifth embodiment of the present application [Figure 10B] Component image to be finished by a finishing method according to a fifth embodiment of the present application [Figure 11A] Component image to be finished by a finishing method according to a sixth embodiment of the present application [Figure 11B] Component image to be finished by a finishing method according to a sixth embodiment of the present application [Figure 12A]10 is a part image to be finished by a finishing method according to a comparative example corresponding to the finishing method according to the second embodiment of the present application. [Figure 12B] 10 is a part image to be finished by a finishing method according to a comparative example corresponding to the finishing method according to the second embodiment of the present application. [Figure 13] Schematic diagram of the bending structure of the fine internal flow channel DETAILED DESCRIPTION OF THE INVENTION

[0032] Various embodiments or examples of implementing the above-mentioned technical proposal are disclosed below. To simplify the disclosure, specific examples of each element and arrangement are described below, but these are merely examples and do not limit the scope of protection of the present invention. The terms "one embodiment," "one embodiment," and / or "several embodiments" refer to features, structures, or special features associated with at least one embodiment of the present application. Therefore, it should be emphasized and noted that "one embodiment," "an embodiment," or "alternative embodiments" mentioned more than once in different places in this specification do not necessarily refer to the same embodiment. Furthermore, some features, structures, or special features in expressions such as "several embodiments," "other embodiments," and "still other embodiments" of the present application may be appropriately combined.

[0033] Flowcharts are used herein to explain the operations performed by the system according to the embodiments of the present application. It should be understood that the preceding or following operations are not necessarily performed in precise order. Other operations may be added to these processes, or certain step or step operations may be removed from these processes.

[0034] Furthermore, the average roughness described below refers to the case where multiple areas on the surface to be measured are selected, measured, and the average value is taken to obtain the average roughness of the measured surface. The optimum roughness described below refers to the case where multiple areas on the surface to be measured are selected, measured, and the minimum value is taken to obtain the optimum roughness of the measured surface. For example, when performing roughness measurement, the area to be roughened is a pipe segment with a length of 8 mm, and multiple 8 mm pipe segments are selected and measured in the pipe to be measured, and the minimum value can be obtained.

[0035] Components with intricate and detailed internal flow passage structures are widely used in industries such as aerospace, marine, nuclear, automotive, and mold manufacturing. However, current machining processes, such as precision machining, femtosecond / waterjet guided / long-pulse laser machining, spark machining, and additive manufacturing (3D printing), can result in undesirable problems such as burrs, adhesive powder, sintered particle residues, rough surfaces, and remelted layers. Appropriate surface finishing techniques are required to eliminate these undesirable effects and ensure the product meets its performance requirements.

[0036] Currently, there are no additively manufactured products with fine internal passages having an optimum surface roughness Ra of 1.6 μm or less, no laser or spark machining products with fine internal passages having an optimum surface roughness Ra of 0.8 μm or less, and no mechanically manufactured products with fine internal passages having an optimum surface roughness Ra of 0.4 μm or less. However, when a fine internal passage has an irregular flow path structure such as an S-shaped, L-shaped, U-shaped, or O-shaped bend, this cannot be achieved by linear feed machining and can only be achieved by additive manufacturing, etc., and therefore there are no additively manufactured products with fine internal passages having an optimum surface roughness Ra of 1.6 μm or less. The inventor conducted in-depth research and tried and compared various internal passage surface finishing methods, and discovered the following: When the internal flow passages of a part are large in diameter (>3mm), have a small length-to-diameter ratio (<50:1), and are generally linear, they can be finished using common methods such as manual polishing, chemical, electrochemical, plasma, magnetic, magnetorheological, abrasive flow, water jet, and ultrasonic. However, for fine internal flow passages with small diameters (<3mm) and large length-to-diameter ratios (>50:1), (1) Abrasive flow technology was employed, using a semi-solid ointment finishing medium with high rigidity to finish the inner cavity through a pressure grinding mechanism. However, the inventors discovered that this creep fluid, with its extremely low Reynolds number, makes it difficult to achieve uniform processing through complex, long-distance microchannels. It is prone to blockages at bends and dead corners, and forcing its passage through can cause the channel to deform or tear. Even if the fluid barely passes through an internal channel with a length-to-diameter ratio of 50:1 or more, the pressure and flow rate rapidly decrease with increasing fluid stroke, resulting in "excessive grinding" at the ports of the internal channel, while the pressure and flow rate loss is so great that the interior becomes "under-ground." Furthermore, the water-insoluble colloidal abrasive flow medium tends to remain in the curves and dead corners of the internal channel, making it difficult or impossible to completely remove after processing. (2) Abrasive water jet technology, also known as fine abrasive slurry jet, high-velocity flow, or high-velocity water particle finishing, is used. By applying hydraulic pressure to the water jet nozzle, a water jet containing abrasive particles is ejected from the nozzle, and the impact kinetic energy washes away the surface material of the workpiece. However, because the distance between the water jet nozzle and the part surface is short, abrasive water jet technology is not effective on fine internal flow passages with small internal flow passage diameters (less than 3 mm) and large length-to-diameter ratios (more than 50:1). (3) Magnetic finishing technology can only produce a slight polishing effect on the surface of internal flow passages larger than 3 mm that extend in a roughly linear fashion. It cannot produce an effective surface finish on intricate, three-dimensional internal flow passages with diameters of 3 mm or less, such as S-, L-, U-, O-, or spiral bends. The reasons for this are as follows: Magnetic finishing is a flexible process that uses relatively large magnetic needle abrasive grains. It is based on the principle that convex and concave points on the surface are simultaneously processed under the action of an applied magnetic field. Therefore, these flexible processing methods can only produce a slight polishing effect on the surface. Even with a large amount of material removal, it cannot significantly improve the "step" effect on the surface, reduce surface roughness, significantly remove powder and particles adhering to the surface, or reduce burrs. Furthermore, because this method is limited by the movement of the magnetic field, it cannot be used to finish complex internal flow passages that extend in three dimensions in parts. (4) Although the chemical finishing method was adopted, the small diameter of the internal flow passages meant that only a small amount of corrosive solution could be accommodated, making the efficiency of the chemical finishing method extremely low, and even preventing finishing due to local accumulation of reactive bubbles. (5) Electrochemical, plasma finishing, and ultrasonic methods have been adopted, but they are unable to finish fine and complex internal flow paths because it is difficult to place tracing electrodes within the narrow, three-dimensionally stretched flow paths, including S-shaped bends, L-shaped bends, U-shaped bends, O-shaped bends, and spiral bends.

[0037] Furthermore, with regard to (4) and (5), methods such as chemical, electrochemical, and plasma finishing can cause various corrosion and altered layer defects in the microstructure of the flow path substrate, and the corrosive liquid and reactive gases have adverse effects on the environment and equipment. At the same time, (4) and (5) are also flexible processing methods, and similarly have drawbacks to (3), in that they can only achieve a slight polishing improvement on the surface, and even if a large amount of material is removed, they cannot significantly improve the surface "step" effect, reduce surface roughness, or significantly remove powder, particles, and burrs adhering to the surface.

[0038] Based on the above, the inventor has conducted extensive research and discovered that the above-mentioned processing methods are not suitable for finishing fine internal flow paths because they all face problems such as difficulty in finishing the deep parts of the fine internal flow paths and / or the finishing quality is not ideal.

[0039] Based on the above, the inventor further researched and invented a surface finishing method for fine internal passages. This method uses a two-phase liquid finishing medium with a viscosity of less than 1000 cP, and the flow rate of the two-phase finishing medium within the fine internal passages is set to be greater than 5 m / s. The flow rate of the two-phase finishing medium at one end of the fine internal passages is set to the saturation value that the diameter of the fine internal passage can accommodate. This creates a pressure-blocking state within the internal passages, thereby creating a means for the liquid to reach a saturation flow rate within the fine internal passages. In other words, the synergistic effects of the low-viscosity liquid phase, the fluid flow rate of the finishing medium, and the saturation flow rate have solved the difficult problem of finishing fine internal passages. The principle behind this method is as follows. First, the synergistic effects of the low-viscosity liquid phase, fluid flow rate, and saturation flow rate allow the finishing medium to smoothly penetrate into the microscopic, complex internal flow channels and form a non-Newtonian-like state within the channel. The fluid boundary layer is parallel to the surface of the channel, and the abrasive grains in the "knife-like" hard non-Newtonian fluid achieve target machining of surface convexities through shear friction. Furthermore, the synergistic effects of these three factors create a micro-cutting force between the abrasive grains in the finishing medium and the surface of the microscopic, complex internal flow channels. This allows the optimal surface roughness to match the average contact length of the abrasive grain cutting edge, regardless of the material of the microscopic, complex internal flow channel. This enables the optimal surface roughness to be achieved within the range of the average contact length of the abrasive grain cutting edge, even achieving an ultra-mirror quality surface roughness of 0.05 μm, breaking through the limitations of abrasive flow and waterjet technologies. The cutting mechanism of abrasive flow technology relies on volume forces generated by the abrasive grains pressing against the surface, which can easily result in pits or indentations (Ra > 0.8 μm) when machining low-hardness metals and flexible polymer materials. The cutting force in abrasive waterjet technology is the erosion force caused by the impact of abrasive grains on the surface, and when machining soft metals, the surface is prone to roughening (Ra>0.8μm).

[0040] It can be understood that the surface finishing method for an internal flow passage disclosed in the embodiments of the present application solves the problem of being unable to finish the surface of fine, complex internal flow passages with small internal flow passage diameters (3 mm or less) and large length-to-diameter ratios (50:1 or more), thereby producing fine internal flow passage workpieces with an optimal inner surface roughness Ra of 1.6 μm or less, and the workpieces can have fine, complex internal flow passage workpieces that are three-dimensionally stretched and have S-shaped, L-shaped, U-shaped, O-shaped, or spiral bends, such as various engine fuel nozzles, heat exchangers, hydraulic units, and oil passage control throttles for aviation, spacecraft, marine, and automobiles. It can also be understood that the surface finishing method for an internal flow passage disclosed in the embodiments of the present application is not limited to use for workpieces with fine, complex internal flow passages, but can also be used to process internal flow passage materials of other dimensions.

[0041] It is important to clarify that the terms "diameter" and "length" in this context refer to equivalent diameter and equivalent length, and the ratio of length to diameter is the ratio of equivalent length to equivalent diameter. Regarding the equivalent diameter, the cross-sectional shape of the internal flow passage may be a circle, an ellipse, or the like, whose cross-sectional contour is formed by a closed curve (non-broken line). The cross-sectional shape of the internal flow passage may be a rectangle, a triangle, or the like, whose cross-sectional contour is formed by a closed broken line. Since the cross-sectional contour is formed by any closed curve (non-broken line) or a closed broken line, and the cross-sectional contour is an irregular shape, an equivalent diameter is introduced and defined as follows: For any cross-sectional shape, an ideal circle is taken to be equal to the actual cross-sectional area of ​​the cross-sectional shape, and the diameter of this ideal circle is the equivalent diameter. The equivalent length refers to the total distance that the fluid in the internal flow passage actually flows between the two ports of the internal flow passage.

[0042] According to some embodiments of the present application, and referring to FIG. 1 , the present application provides a method for surface finishing an internal flow passage, the method comprising: Using a liquid-solid two-phase flow finishing medium in which the viscosity of the liquid phase is less than 1000 cP and the solid phase is an abrasive; A predetermined pressure is applied to the finishing medium so that the finishing medium flows through the fine internal flow passage at a flow rate of greater than 5 m / s, the flow rate of the finishing medium flowing into the fine internal flow passage from one end thereof reaches the saturation value of the flow rate that can be accommodated by the diameter of the fine internal flow passage, and the liquid pressure inside the internal flow passage is in a pressure-trapping state.

[0043] The liquid herein has a viscosity of less than 1000 cP. All references to viscosity values ​​in this application refer to the Ubbelohde viscosity at room temperature (approximately 25°C). The optimal viscosity of the liquid phase for a finishing method for microscopic internal channels with different materials, dimensions, and initial average roughness can be achieved by continuously increasing the viscosity based on a lower limit. Currently, the lower limit of viscosity in the examples is approximately 50 cP. Through extensive testing, the inventors have determined that for microscopic internal channels made of common materials such as titanium alloys, high-temperature alloys, steel, ceramics, aluminum alloys, and polymeric materials, the viscosity of the liquid phase must be at least 50 cP to achieve the target roughness after finishing. A specific method for achieving the optimal viscosity will be described in the examples below. The critical value of 1000 cP is not a general optimal value, but rather a limit value at which the finishing medium can flow continuously, smoothly, and stably through the microscopic internal channels.

[0044] The liquid phase described in the examples is, for example, an aqueous liquid phase, in which a certain thickener is added to deionized water so that the aqueous liquid has a certain viscosity. Benefits of using an aqueous liquid include low cost, easy availability, environmental friendliness, and ease of cleaning of the finishing medium after finishing is completed. However, it is understood that the liquid phase here is not limited to an aqueous liquid as long as it has a viscosity μ of less than 1000 cP.

[0045] The material of the solid-phase abrasive grains may be a common abrasive material, such as carbide ceramics including silicon carbide, tungsten carbide, etc., oxide ceramics including aluminum oxide, zirconium oxide, cerium oxide, etc., nitride ceramics including boron nitride, chromium nitride, etc., or natural minerals including diamond / sand, mica, quartz, olivine, etc. Preferably, the abrasive grains may be a combination of one or more of diamond / sand and oxide ceramics.

[0046] When selecting the grain size and mass concentration of abrasive grains, it is common to gradually increase them based on the lower limit to obtain an optimal range. If the grain size and mass concentration are below the lower limit, the expected finishing effect will not be achieved; that is, the fine internal flow passages will not achieve the target surface roughness. The principle is that if the grain size is too small, the mass of the abrasive grains themselves will be too low to generate enough kinetic energy to achieve effective polishing; if the mass concentration is too low, the grinding probability of the surface processing point will be reduced, making effective polishing impossible. The selection of the lower limit is generally conservative; for example, any lower limit can be selected conservatively, provided that it does not exceed the upper limit of the grain size. The lower limit for the ratio of the internal flow passage diameter to the abrasive grain size is usually 20. That is, the diameter of the internal flow passage must ensure that at least 20 abrasive grains can pass through in parallel without clogging. That is, the upper limit of the abrasive grain size is usually 1 / 20 of the internal flow passage diameter, and the lower limit of the abrasive grain size is generally 1 / 5 of the upper limit. The lower limit of the abrasive mass concentration is generally 10 g / L, and the selection of the lower limit is generally relatively conservative because the system pressure is relatively high, and clogging of the abrasive may result in the scrapping of the workpiece and the system, or even cracking and explosion. Therefore, the abrasive particle size and mass concentration are gradually increased based on the specified lower limit until the abrasive particle size or mass concentration is too large, causing significant flow resistance and reducing the flow rate, and mutual collisions between abrasive particles affect the flow rate, reducing the flow rate and grinding effect. That is, the optimal value can be obtained by testing based on the lower limit, and specific methods are described in the examples below.

[0047] A predetermined pressure is applied to the finishing medium so that the finishing medium flows through the fine internal passages at a flow rate greater than 5 m / s. The "predetermined pressure" here refers to a pressure that allows the finishing medium to flow through the fine internal passages at a flow rate greater than 5 m / s even at the initial stage of the finishing process. As the finishing process progresses, the surface roughness of the internal passages decreases, and under the same pressure conditions, the flow rate of the finishing medium within the fine internal passages becomes increasingly faster. It should be noted that the realized flow rate is within a certain range, so the "predetermined pressure" here is a concept of a range, rather than a specific value that can only be applied to the finishing medium. To measure the flow rate of the finishing medium within the fine internal passages, immersion measurement cannot be used, otherwise abrasive particles may damage the sensor probe. Ultrasonic velocity measurement can be used, or indirect measurement can be performed using the Hagen-Poiseuille law of viscous fluids (see equation below). In the formula, D is the internal flow passage diameter, l is the length of the fine internal flow passage, p is the pressure difference acting on both ends of the fine internal flow passage, i.e., the hydraulic pressure p, Re is the Reynolds number, um is the flow velocity of the liquid phase in the aqueous two-phase flow, ρl is the density of the liquid phase, and the flow velocity of the liquid phase is approximately equal to the flow velocity of the finishing medium.

number

[0048] The flow velocity of the finishing medium is greater than 5 m / s, based on the theoretical critical conditions for forming non-Newtonian fluids and the critical value obtained by the inventors through long-term practice. According to engineering fluid mechanics data (e.g., Yang Shuren, Wang Zhiming, He Guangyu, et al., Engineering Fluid Mechanics [M]. Petroleum Industry Press, 2006), when pure water has a viscosity of 1 cP, the critical flow velocity of non-Newtonian fluids is greater than 16.6 m / s. However, the lower limit of the viscosity of the liquid phase in this embodiment is 50 cP, which is greater than 1 cP, so the critical flow velocity of non-Newtonian fluids is less than 16.6 m / s. At the same time, based on practical results, the inventors have found that ideal processing results cannot be achieved at a flow velocity less than 5 m / s, so the critical value is set to 5 m / s.

[0049] The flow rate at which the finishing medium flows into one end of the fine internal flow passage reaches a saturation value of the flow rate that can be accommodated by the diameter of the fine internal flow passage, and the liquid pressure inside the internal flow passage becomes high, that is, it is in a state of what is known in this field as a saturated flow rate.

[0050] The saturated value of the flow rate and the state of saturated flow rate here mean that when a fluid flows into a pipe, the cross section of the pipe is filled and the cross section of the pipe can accommodate the maximum number of fluid molecules in parallel.

[0051] It can be seen that the beneficial effects of the finishing method of the above embodiment are as follows:

[0052] The viscosity of the liquid phase of the finishing medium is less than 1000 cP, and the flow rate of the two-phase finishing medium within the fine internal passages is greater than 5 m / s, so that the flow rate at one end of the fine internal passages reaches the saturation value that the diameter of the fine internal passages can accommodate. This creates a pressure-filled state within the internal passages, providing a means for the liquid to reach a saturation flow rate within the fine internal passages. In other words, the synergistic effects of the low-viscosity liquid phase, fluid flow rate, and saturation flow rate solve the difficult problem of finishing fine internal passages. The principle behind this is as follows. First, the synergistic effects of the low-viscosity liquid phase, fluid flow rate, and saturation flow rate create a low-viscosity, high-flow state for the finishing medium, allowing it to smoothly penetrate the microscopic internal channels and form a non-Newtonian fluid within the microscopic internal channels. The fluid boundary layer is parallel to the internal channel surface, and the abrasive grains in the "blade-like" hard liquid phase achieve targeted machining of convex surfaces through shear friction. This principle overcomes the problem of simultaneous machining of convex and concave surfaces during flexible machining, resulting in only a slight polish. At the same time, the small cutting force generated by friction between the abrasive grains in the finishing medium and the microscopic internal channel surface enables optimal surface roughness that matches the average contact length range of the abrasive cutting edge, regardless of the material of the microscopic internal channel. This breaks through the limitations of abrasive flow and waterjet technologies. The cutting mechanism of abrasive flow technology relies on volume forces generated by the pressure of the abrasive grains against the surface, which can easily result in pits (Ra > 0.8 μm) when machining low-hardness metals and flexible polymer materials. The cutting force in abrasive waterjet technology is the erosive force caused by the impact of abrasive particles on the surface. When machining soft metals, this can easily result in surface roughening (Ra > 0.8 μm). Furthermore, the low-viscosity, high-flow-rate, fluid-dynamic conformal machining method effectively polishes irregularities on the internal flow channel surface, such as steps, sharp corners, and geometric contour curvatures. This geometric streamlining of corners, sharp edges, internal flow channel contour curvatures, and hole shapes further improves the fluid dynamics of the internal flow channel. Furthermore, the above example proposed a critical flow velocity of 5 m / s for achieving a blade-like hard non-Newtonian fluid and target machining of convex surfaces through the shear friction of the abrasive particles.

[0053] Regarding the machining time of the finishing medium in the microscopic internal passage, the finishing medium may finish the microscopic internal passage during a reference period until the optimal surface roughness of the microscopic internal passage reaches a target value. The reference period may be a predetermined continuous period or a plurality of intermittent periods. The finishing process may automatically stop after a non-predetermined continuous period after starting, when it is detected that the flow rate of the finishing medium reaches a flow rate corresponding to the target value of the optimal surface roughness of the microscopic internal passage. For example, as described above, in some embodiments, after starting machining, the optimal surface roughness is indirectly characterized by measuring the flow rate or flow rate of the finishing medium in the microscopic internal passage. When the flow rate or flow rate reaches a predetermined value, the corresponding optimal surface roughness reaches the target value, and the finishing process is stopped manually or automatically. The term "optimum surface roughness is a target value" here does not necessarily mean that the optimal surface roughness does not necessarily need to be measured directly, but may be characterized indirectly, such as by characterizing the flow rate or flow rate of the finishing medium within the microscopic internal passage, as described above. The above target values ​​refer to the set optimum surface roughness values, and generally refer to the requirements for the final optimum surface roughness of the fine internal flow passages, but it is not excluded that further finishing may be carried out after the above finishing step, and what is set at this time is not the requirement for the final optimum surface roughness.

[0054] In summary, the finishing method introduced in the above examples solves the long-standing industry challenge of finishing fine internal passages with diameters of 3 mm or less and length-to-diameter ratios of 50:1 or more by combining measures such as establishing a hydraulic system at both ends of the internal passage to be machined, utilizing a low-viscosity, high-speed solid-liquid two-phase fluid, achieving a saturation flow rate in the internal passage to be machined, and utilizing a fine cutting mechanism generated by the high-speed friction of abrasive grains in the two-phase flow against the surface of the internal passage.

[0055] In some embodiments, as shown in Figure 2, the abrasive grains 1 of the two-phase flow finishing media may have a surface cusp structure 2 to facilitate fine cutting. The grain structure parameters may be an average cutting depth L of 1.4 nm to 14 nm and an average contact length b of 50 nm to 1000 nm. It is understandable that, because the particle size of individual abrasive grains is generally small, localized agglomeration of abrasive grains occurs in practice. The abrasive grain structure model shown in Figure 2 is not a physical representation of the atoms or molecules of a single abrasive grain, but rather an equivalent abrasive grain group in which localized agglomeration occurs. That is, the aforementioned average cutting depth of the abrasive grains is the average cutting depth of the cutting edge of the equivalent abrasive grain group, and the average contact length of the abrasive grains is the average contact length of the cutting edge of the equivalent abrasive grain group. Furthermore, Figure 2 is not drawn to scale to clearly show the average cutting depth L and the average contact length b of the cutting edge. Furthermore, the average cutting depth L of the abrasive cutting edge, 1.4 nm to 14 nm, and the average contact length b of the abrasive cutting edge, 50 nm to 1000 nm, were determined not by direct observation using an electron microscope but by statistical calculations based on data acquired by the inventors through long-term practice. The inventors discovered that when using the finishing method described above, the side thinning rate relative to the diameter of the internal flow passage is 5 μm / h to 50 μm / h, and the corresponding side thinning rate per second is 1.4 nm / s to 14 nm / s. This means that the average cutting depth L of the abrasive cutting edge where the equivalent abrasive grain group contacts the fine internal flow passage surface per second is 1.4 nm / s to 14 nm / s. This not only ensures the finishing effect, but also prevents excessive polishing and grinding due to excessively fast fine cutting speeds, thereby meeting the dimensional accuracy requirements of the finishing process and avoiding deviations from tolerances. The inventors also found that when using the finishing method described above, the optimum surface roughness Ra can be achieved in the range of 0.05 μm to 1 μm. Because the average contact length of the abrasive grain edges determines the final optimum roughness, the corresponding average contact length of the abrasive grain edges is 50 nm to 1000 nm. Obtaining the structural parameters of the equivalent abrasive grain group through extensive practice can play an important role in calculating parameters such as the specified pressure.The specific value of the average cutting depth of the abrasive cutting edge that contacts the fine internal flow channel surface in one second, between 1.4nm and 14nm, and the specific value of the average contact length of the abrasive cutting edge, between 50nm and 1000nm, can be obtained correspondingly based on the specific particle size approximation of the abrasive grains. The larger the particle size of the abrasive grains, the greater the average cutting depth and average contact length of the abrasive cutting edge that contacts the fine internal flow channel surface in one second. The specific corresponding values ​​are obtained from long-term experimental data of the single-side thinning speed corresponding to the abrasive grain size, i.e., the average cutting depth and average contact length of the abrasive cutting edge that contacts the fine internal flow channel surface in one second, i.e., the optimal roughness after finishing.

[0056] In another embodiment, as shown in Figure 3, the finishing medium finishes the fine internal flow passages for a reference period, and the specific value of this reference period may be a reference period obtained by a preliminary test or a reference period obtained by a field test. The procedure for obtaining this reference period is as follows.

[0057] The finishing medium finishes the microscopic internal passages during an initial period, and detects the optimum surface roughness of the microscopic internal passages. If the optimum surface roughness matches the target value, the initial period is the reference period. If not, the step period is successively increased until the optimum surface roughness reaches the target value, and the corresponding total period is the reference period. Here, the initial period and step period are obtained from the one-side thinning rate of the abrasive grinding and the initial average surface roughness of the microscopic internal passages.

[0058] The initial period is generally calculated based on the initial average surface roughness of the microscopic internal passage and the average cutting depth of the abrasive cutting edge that contacts the microscopic internal passage surface in 1 second. For example, if the initial average surface roughness Ra of the internal passage of a part is 10 μm, the average height difference between the surface convex and concave points is approximately 10 μm, and the average cutting depth of the abrasive cutting edge that contacts the microscopic internal passage surface in 1 second is 1.4 nm to 14 nm, the single-side thinning speed is 5 μm / h to 50 μm / h. If the lower limit is 5 μm / h, the reference period is at least 2 hours, so the initial period is set to 2 hours. The step period is generally selected based on the part's dimensional tolerance requirements and the single-side thinning speed. For example, if the tolerance is plus or minus 5 μm, the single-side thinning speed is 5 μm / h to 50 μm / h, and the lower limit is 5 μm / h, the step time is correspondingly 1 hour, preventing the time step from being too large and resulting in tolerance deviation.

[0059] It can be understood that the above process can be obtained by on-site testing during the finishing process. That is, if it is necessary to determine the initial period corresponding to a certain fine internal flow path, a reference period can be obtained by finishing the initial period and step period according to the above method, and at the same time, the processing of the fine internal flow path of this structure is also completed. After that, when this kind of fine internal flow path is finished, the total processing time can be directly obtained from the reference period. There is no need to test the initial period and step period.

[0060] In some embodiments, a method for detecting the optimum surface roughness of the fine internal flow passage after the finishing medium finishes the fine internal flow passage in the initial period may be to indirectly detect the optimum surface roughness of the fine internal flow passage by using the optimum surface roughness value corresponding to the diameter expansion value, which satisfies the following formula:

number

[0061] Here, Ra* is the optimum surface roughness after diameter expansion, Ra0 is the initial average surface roughness, δ is the port diameter expansion value, which is generally 0.01 mm to 0.5 mm, and k is the asperity grinding ratio coefficient, which is generally 0.2 to 0.4.

[0062] The asperity grinding ratio coefficient k indicates the distribution probability ratio of abrasive grains located at the peaks to the valleys, and can be measured as the ratio of grinding thinning at the valleys to the peaks. In the case of cutting tools used in machining, the cutting tool performs directional grinding only on the peaks using rigid positioning, resulting in k ≒ 0. In the case of abrasive flow, both the peaks and valleys are pressed against the abrasive grains and grinded by contact, resulting in k ≒ 0.6–0.8. Flexible methods such as chemical, electrochemical, magnetic, and ultrasonic + abrasive grinding are isotropic to the peaks and valleys, resulting in k ≒ 0.9–1. This means that even if the grinding takes a long time and the average surface thinning is large, the surface roughness is not significantly improved, and only a polished, orange-peel-like surface morphology remains. In the case of the two-phase flow finishing method introduced in the above examples, non-Newtonian fluids have a higher directional grinding effect on the peaks due to the high-speed shear motion of the surface caused by the rigid cutting tool, resulting in k ≒ 0.2–0.4. Generally, first calculate the target diameter expansion value corresponding to the target value of the optimum surface roughness, and then compare the actual diameter expansion value with this initial period. If the actual diameter expansion value is 90% or more of the target diameter expansion value, it means that the optimum surface roughness Ra* after expansion corresponding to this diameter expansion value matches the target value, so this initial period is the reference period. However, if it does not match the target value, the step period is gradually increased until the optimum surface roughness reaches a predetermined value.

[0063] When the optimum surface roughness of the fine internal flow passage is indirectly detected by the optimum surface roughness corresponding to the diameter enlargement value, the detection process is convenient and can be directly detected on site.

[0064] In yet another embodiment, as shown in FIG. 4, the finishing method further includes cleaning the finished fine internal flow path after the optimal surface roughness of the fine internal flow path is set as the target value, and specifically includes the following steps:

[0065] A cleaning medium is injected into the fine internal flow passages through the ports at a predetermined pressure, and the cleaning medium dissolves in the aqueous liquid of the finishing medium until the Tyndall effect appears in the cleaning medium flowing out of the fine internal flow passages.

[0066] The cleaning medium and the aqueous liquid are mutually soluble. For example, when the finishing medium is an aqueous two-phase flow, the cleaning medium is correspondingly deionized water. This allows the aqueous liquid phase of the finishing medium to be thoroughly cleaned, avoiding defects such as bent internal flow paths and residues in dead corners caused by abrasive flow technology, which are difficult or impossible to completely remove after processing is completed. Meanwhile, the pressure of the cleaning medium is the same as a predetermined pressure, allowing the cleaning medium to remove the solid phase of the finishing medium. The inventors discovered that the residual location of the solid phase is generally related to the applied pressure, so by applying the same pressure, the cleaning medium can "find" and remove the residual solid phase.

[0067] To determine whether cleaning is complete, the workpiece does not need to be disassembled for observation; instead, the cleaning agent can be characterized by the Tyndall phenomenon occurring in the cleaning agent flowing out of the fine internal channels after cleaning. For example, the cleaning agent can be placed in a transparent drainage container and then drained from the container. During this process, the deionized water in the drainage container is constantly illuminated by a spotlight. If the light beam in the deionized water after cleaning is turbid and the Tyndall effect, which is a linear milky white beam, does not occur, cleaning is not yet complete. Continue adding deionized water until the light beam in the deionized water in the drainage container becomes a linear milky white beam, i.e., the Tyndall effect, appears. It is understood that ultrasonic cleaning and drying in a drying box can be performed sequentially after the above cleaning process.

[0068] In some embodiments, referring to FIG. 5 , in order to obtain optimal values ​​for the viscosity of the aqueous liquid phase of the finishing medium, and the abrasive grain size and abrasive grain mass concentration of the solid phase, the viscosity of the liquid phase, the abrasive grain size and abrasive grain mass concentration of the solid phase of the finishing medium may be gradually increased based on the lower limit values ​​of the viscosity of the liquid phase, the abrasive grain size and the abrasive grain mass concentration of the solid phase until the flow rate or flow rate of the two-phase finishing medium is 1% to 5% lower than the flow rate or flow rate corresponding to the lower limit values.

[0069] For example, the viscosity of the liquid phase is tested using an Ubbelohde viscometer with pure water, gradually increasing the amount of thickener to adjust the aqueous viscosity to a minimum of 50 cP. Then, test machining is performed on the internal flow channel of the fine internal flow channel workpiece to be machined. The initial flow rate or flow rate data corresponding to the finishing medium is read as the reference value, and the thickener is increased by 1 g / L, corresponding to a viscosity increase of approximately 10 cP. Test machining of the internal flow channel to be machined is continued, repeating the increase step until the initial flow rate or flow rate data is less than 1-5% of the reference flow rate or flow rate. At this point, the thickener concentration is optimal, and the viscosity of the corresponding finishing medium is optimal. Table 1 shows the optimal viscosity ranges for different diameters of fine internal flow channels. Table 1: Optimal viscosity ranges of the liquid phase of the finishing medium for different diameters of the fine internal channels [Table 1]

[0070] For example, for the solid-phase abrasive grain size, a conservative lower limit is selected, provided that the upper limit is not exceeded. The lower limit of the ratio of the internal flow passage diameter to the abrasive grain size is typically 20, i.e., the internal flow passage diameter must be large enough to prevent clogging when at least 20 abrasive grains pass through it in parallel. Therefore, a lower limit of the abrasive grain size corresponding to a different internal flow passage diameter is determined. For example, if the corresponding internal flow passage diameter is 3 mm, the corresponding upper limit of the abrasive grain size is 3 / 20 mm, or 150 μm. Based on this upper limit, to ensure test safety, the lower limit is generally set to 1 / 5 of the upper limit, i.e., the abrasive grain size is increased based on the lower limit of 30 μm. The inventors discovered that if the abrasive grain size is smaller than the lower limit, the mass of the abrasive grain itself is too low to generate sufficient kinetic energy for high-efficiency polishing. After selecting the minimum abrasive grain size, test machining is performed, and the initial flow rate or flow rate data corresponding to the finishing medium is taken as the reference value. Then, based on the minimum abrasive grain size, the grain size is increased by 1 to 10 μm. Test machining of the internal passage to be machined is continued until the initial flow rate or flow rate data is less than 1 to 5% of the reference flow rate or flow rate, at which point the abrasive grain size is at the optimum value. Table 2 shows the abrasive grain size ranges corresponding to different diameters of the fine internal passage. Table 2: Optimal range of abrasive grain size for finishing media corresponding to different diameters of fine internal channels [Table 2]

[0071] Furthermore, for example, the lower limit of the abrasive mass concentration in the solid phase is selected based on a mass concentration of 10 g / L. The inventors discovered that if the mass concentration is below this lower limit, the grinding effect will be insufficient due to a decrease in the probability of grinding points on the abrasive surface. After selecting the lower limit of the mass concentration, a test machining is performed, and the initial flow rate or flow rate data corresponding to the finishing medium is read as a reference value. Then, based on the lower limit of the mass concentration, the abrasive mass concentration is increased by 2 g / L to 5 g / L and test machining of the internal flow path to be machined is continued. This increase step is repeated until the initial flow rate or flow rate data is less than 1 to 5% of the reference flow rate or flow rate value, at which point the abrasive mass concentration reaches the optimal value. Table 3 shows the optimal values ​​for the mass concentration range corresponding to different diameters of the fine internal flow path. As shown in Table 3, the inventors found that for fine internal flow passages with a diameter of 0.5 mm to 1 mm, the optimal abrasive mass concentration is correspondingly low, at 10 g / L to 15 g / L, whereas for fine internal flow passages with a diameter of more than 1 mm, the abrasive mass concentration has a low correlation with the diameter dimension, at 10 g / L to 35 g / L. Table 3: Optimal range of abrasive mass concentration in finishing media for different diameters of fine internal channels [Table 3]

[0072] It is understood that the above optimal values ​​can be obtained by on-site machining tests, i.e., if it is necessary to determine the optimal values ​​of the viscosity, abrasive grain size, and abrasive grain mass concentration of the finishing medium corresponding to a certain fine internal passage, they can be obtained by test machining based on the above method. When finishing such a fine internal passage, these optimal values ​​can be directly applied, and no test machining is required.

[0073] In some embodiments, the value of the predetermined pressure P can be calculated according to the following formula:

number

[0074] where Ra0 is the initial average surface roughness of the internal channel, Ra is the target value for the optimal roughness of the internal channel surface after machining, L is the average cutting depth of the abrasive cutting edge, b is the average contact length of the abrasive cutting edge, ρl is the liquid phase density, ρp is the solid phase density of the abrasive, σw is the yield limit of the workpiece material, t is the initial period mentioned above, which can generally be calculated from the initial average surface roughness of the internal channel and the average cutting depth of the abrasive cutting edge contacting the fine internal channel surface in 1 second, χ is the pressure increase ratio when the internal channel reaches saturation flow rate, Re is the Reynolds number of the liquid phase, l is the length of the internal channel, D is the diameter of the internal channel, d is the grain size of the abrasive, and k is the asperity grinding ratio coefficient.

[0075] Regarding the meaning and specific values ​​of the above parameters, the initial surface average roughness Ra0 is generally determined by taking the average roughness of each area of ​​the internal flow path, as the surface roughness of each area is not completely consistent initially after the internal flow path is manufactured. Typical Ra0 values ​​are as follows: 6.3 μm to 30 μm for 3D printing, 3.2 μm to 6.4 μm for precision casting, 0.8 μm to 1.6 μm for machining, and 1.6 μm to 3.2 μm for laser machining and wire cutting. The target value Ra for the optimal surface roughness after finishing (the initial roughness of each area after polishing is not completely consistent, so the optimal value for the roughness of each area of ​​the internal flow path is taken) is typically as follows: 1.6 μm or less for 3D printing and precision casting, 0.4 μm or less for machining, and 0.8 μm or less for laser machining and wire cutting. The length of the fine internal flow passage is l, the diameter D is 3 mm or less, the length-to-diameter ratio l / D is 50 or more, the Reynolds number Re is 20 to 200, which can be obtained by calculating the viscosity and flow rate of the liquid phase, the uneven grinding ratio coefficient k is 0.2 to 0.4, the abrasive grain diameter D is 5 μm to 150 μm, and the average cutting depth L of the abrasive grain cutting edge is 1.4 nm to 14 nm. The average cutting depth L of the abrasive grain cutting edge can be measured in terms of the amount of thinning per unit time, and the thinning speed of one side of the internal flow passage in aqueous two-phase flow finishing technology is 5 μm / h to 50 μm / h. The average contact length b of the abrasive cutting edge is 50-1000 nm. This can be measured at the final limit scratch and the corresponding optimum roughness. The optimum roughness Ra after abrasive grinding in aqueous two-phase flow finishing is 0.05-1 μm, so the contact length b of the abrasive cutting edge is 50-1000 nm. The liquid phase density ρl is 1200-1500 kg / m³, typically 1500 kg / m³ for aqueous liquid phases. The solid phase density ρp of the abrasive is 2200-3300 kg / m³, with specific values ​​varying depending on the solid abrasive. The yield limit σw of the workpiece material can be obtained by looking up the table, where t is the initial period, i.e., calculated from the initial average roughness and the average cutting depth of the abrasive cutting edge. The intensification ratio χ at the saturated flow rate must be greater than 1 and is generally between 50 and 400.The saturated flow rate boost ratio here refers to the ratio of the inner diameter of the inner passage at the tip of the inner passage to the cross-sectional area of ​​the inner passage when the fluid enters the inner passage from the tip of the inner passage. For example, if the cylinder that propels the polishing medium is at the tip and the inner passage is at the rear, the ratio of the cross-sectional area of ​​the cylinder to the cross-sectional area of ​​the inner passage of the workpiece to be machined is 50 to 400. The specific value will vary depending on the actual situation.

[0076] This method solves the problem of pre-setting the fine internal channel processing parameters, making the finishing method efficient, safe, and reliable. It can be understood that the predetermined pressure P can be determined by trial and error, provided that the finishing medium flows through the fine internal channel at a flow rate greater than 5 m / s. For example, a small lower limit can be estimated based on experience, and then trials can be continued until the required flow rate is met. However, this method is inefficient. A data table can be created based on this formula or test data, and then the finishing process can be performed simply by consulting the table. After long-term testing, the inventors have obtained the process parameters for the finishing method corresponding to titanium alloys, high-temperature alloys, and steels, as shown in Table 4 below. Table 4: Process parameters for finishing methods for titanium alloys, high-temperature alloys, and steels [Table 4]

[0077] For the ceramic / aluminum alloy / polymer material, the corresponding predetermined pressure is 50% to 70% lower than the predetermined pressure P corresponding to the titanium alloy / high temperature alloy / steel material in Table 4.

[0078] In some embodiments, the thickener used to provide the aqueous liquid phase with a certain viscosity for the finishing medium described above may include a polymeric thickener, preferably a combination of one or more long-chain flexible polymers such as polyoxyethylene and polyacrylamide. The inventors discovered that using a polymeric thickener can actually result in a nearly uniform flow rate and a uniform polishing effect in each region of the internal flow path as the viscosity increases within a certain range. This is likely due to the long chains of the polymer providing a turbulent drag reduction effect, reducing frictional resistance in the liquid flow path, thereby achieving a nearly uniform flow rate and a uniform polishing effect in each region of the internal flow path and avoiding differences in polishing effect between the port and the interior. The inventors also discovered that using a non-polymeric thickener increases the viscosity of the liquid phase, but the difference in polishing effect between the flow port and the interior begins to increase, resulting in a higher polishing effect in the flow port than the interior. The use of polymeric thickeners is particularly suitable for structures with fine internal flow channels that are three-dimensional and include S-, L-, U-, O-, and spiral bends. The turbulent resistance reduction effect of the polymeric thickener prevents the liquid from significantly decreasing its flow rate due to increased frictional resistance during the finishing process of these three-dimensional structures. This ensures that the difference between the worst and optimal roughness of each region is within 30%, achieving a uniform finish. It is also understood that polymeric thickeners are not necessary for relatively simple structures, such as linear internal flow channels.

[0079] In some embodiments, a thickener and an antifoaming agent may be added to the aqueous liquid phase of the finishing medium so that the volume ratio of the foam slurry on the surface of the two-phase flow polishing medium to the liquid phase during the finishing process does not exceed 0.3:1. This prevents bubbles from interfering with the fine cutting process of the finishing medium and the flow rate and pressure detection system. Non-silicon-based antifoaming agents may be selected, including organic compounds such as alcohols, fatty acids, fatty acid esters, phosphate esters, mineral oils, and amides. Polyether-based agents include copolymers of ethylene oxide and propylene oxide. Silicone-based agents include polydimethylsiloxane and dimethylsilicone oil. Preferably, the antifoaming agent is a combination of one or more of lauric acid, polymerized propylene oxide, etc., and the mass concentration of the antifoaming agent is 1 g / L to 5 g / L.

[0080] In some embodiments, a lubricant may be added to the finishing medium, with the mass concentration of the lubricant ranging from 1 g / L to 10 g / L. The lubricant may be an element or an inorganic substance such as MoS2, graphite powder, talc powder, tetraboron mononitride, calcium fluoride, barium fluoride, or lead oxide, or an organic polymer such as polytetrafluoroethylene or polyimide. Preferably, a combination of one or more of MoS2 and graphite powder is used. The lubricant should ensure that the flow rate and pressure of the finishing medium during finishing do not suddenly decrease by more than 5% due to possible clogging of the abrasive grains, thereby ensuring the reliability of the finishing process.

[0081] In some embodiments, the liquid phase of the finishing medium may contain additives at the following mass concentrations: 1 g / L to 5 g / L of a rust inhibitor to prevent corrosion of the aqueous liquid phase against the part to be processed; 20 g / L to 30 g / L of a dispersant to ensure that the solid-phase abrasive grains and various additives in the finishing medium are well dispersed in the liquid phase, especially in aqueous systems; and 1 g / L to 2 g / L of an antifreeze agent to prevent freezing of the finishing medium due to low temperatures and, therefore, the impact of a decrease in flow rate or volume on the finishing process.

[0082] Based on the above, the finishing method described in the above example allows for the production of fine internal channel workpieces with diameters of 3mm or less, length-to-diameter ratios of 50:1 or greater, and an optimal surface roughness Ra of 0.05μm. This extremely low surface roughness avoids the problem of burrs, adhered particles, or adhesive powder shedding caused by high-speed friction between the fluid flowing into the internal channel and the surface, which can disperse and block the channel. It also avoids the problem of rough internal surfaces becoming a source of fatigue cracks during long-term use and carbon buildup in high-temperature oil channel systems. Furthermore, it also avoids the "step" phenomenon on the internal channel surface, which can cause turbulence and vortices in the fluid flow process, rapidly increasing fluid friction resistance, further causing fluid runaway and vibration, shortening the service life of components. It also avoids the generation of large amounts of cavitation bubbles in the fluid in the fine internal channels, which can affect combustion and hydraulic power and lead to cavitation corrosion. For example, in some examples, the fine internal passage workpieces obtained using the finishing method described above were additively manufactured high-temperature alloy fuel nozzles for aircraft engines. The oil passages were fine internal passages with diameters less than 2.5 mm, length-to-diameter ratios greater than 50:1, and optimal surface roughnesses (Ra) of 1.6 μm or less. The achievement of such low optimal surface roughness after finishing indicates that the finishing process removed semi-sintered or adhered powder particles from the internal passage surface of the part. Compared to unfinished additively manufactured fuel nozzles, this method avoids the risk of burrs, adhered particles, or adhered powder falling off due to high-speed friction between the fuel entering the internal passage and the surface, which can then disperse into the fluid, block the oil passage, cause mechanical wear failures, and lead to serious safety hazards. Furthermore, the roughness of the internal surface, which is prone to fatigue cracking during long-term use, and the tendency for carbon accumulation to occur in high-temperature oil passage systems, are avoided. In addition, the "step" phenomenon on the surface of the internal flow path prevents turbulence and vortices from occurring in the fluid movement process, causing a sudden increase in fluid friction resistance, and further causing the fluid to run out of control, resulting in vibration and shortening the lifespan of parts.In addition, the rough surface prevents the generation of a large number of cavitation bubbles in the fluid, which affects combustion and hydraulic power, and ultimately prevents cavitation corrosion.

[0083] For example, in some embodiments, the fine internal flow passage workpiece obtained by the finishing method introduced in the above embodiments is a hollow blade cast for an aircraft engine, and the cooling holes connected to the pores on the blade surface are fine internal flow passages, with a length-to-diameter ratio of greater than 50:1, the pore diameters on the blade surface are 0.3 mm to 0.6 mm, the inner wall roughness Ra is 0.8 μm or less, there is no remelt layer, and the hole chamfer is greater than 0.1 mm, which avoids premature failure of the part due to the tendency for microcracks to occur on the surface of the remelt layer, extends the life of the hollow blade, and improves its aerodynamic performance.

[0084] To more clearly explain the effects of the present invention, six specific examples of fine internal flow path workpieces using the finishing method introduced in the above examples are shown below. Note that the structural schematic diagrams of parts shown in Figures 6A, 7A, 8A, 9A, 10A, and 11A are not drawn to scale.

[0085] (First Example) As shown in Figure 6A, the target product of this example is a fuel nozzle 100 for a certain type of aircraft engine. The internal flow passage to be finished is manufactured using laser additive manufacturing technology. The fine internal flow passage diameter D is 1.3mm to 1.4mm, the total length of the flow passage is 130mm to 140mm, the length-to-diameter ratio is 100, and the structure includes a straight line 101, an L-shaped bend 102, and an O-shaped bend 103. As shown in Figure 13, the parameters of the bend structure mainly include the bend radius and bend angle. The bend point is the point along the axis (straight line) where deflection first occurs. The bend angle is the central angle corresponding to the arc length between two adjacent bend points. The bend radius is defined as the radius of curvature corresponding to the arc length between two adjacent bend points. As shown in Figure 13, the first bending structure 11 has bending points 111 and 112, a bending radius of R1, and an acute bending angle a1. The second bending structure 12 has bending points 121 and 122, a bending radius of R2, and a bending angle a2, which is a right angle. The third bending structure has bending points 131 and 132, a bending radius of R3, and an obtuse bending angle a3. As shown in Figure 6A, the L-shaped bending 102 has a bending angle of approximately 90° and a bending radius of approximately 6 mm. The O-shaped bending 103 and the corner 104 of the straight line 101 have a bending angle of approximately 60° and a bending radius of approximately 8 mm. The O-shaped bending 103 has a bending angle of 180° and a bending radius of approximately 15 mm. The material is a high-temperature alloy. The specific finishing method is as follows:

[0086] The first step is to prepare the finishing medium. First, add antifreeze, antifoam, rust remover, dispersant and lubricant to deionized water in sequence, and test using an Ubbelohde viscometer. Slowly increase the amount of thickener to adjust the aqueous viscosity to 50 cP. Then, test the internal flow passage of the part to be processed. Take the flow rate or flow rate data as the reference value. Continue to increase the thickener by 1 g / L and the corresponding viscosity increase by about 10 cP. Continue test processing the internal flow passage of the part to be processed until the initial flow rate or flow rate data is 1% to 5% below the reference value. At this time, the thickener concentration is optimal and the corresponding viscosity of the finishing medium is optimal. Tests have shown that the optimal thickener addition amount for the fuel nozzle is 4 g / L to 5 g / L, which means the liquid phase viscosity of the finishing medium is 90 cP to 100 cP. Similarly, for the abrasive grain size, a conservative lower limit is selected, provided that it does not exceed the upper limit. The lower limit for the ratio of the internal flow passage diameter to the abrasive grain size is typically 20. This means that the internal flow passage diameter must be able to accommodate at least 20 abrasive grains passing through in parallel without clogging, resulting in an upper limit for grain size of 70 μm and a lower limit for grain size of 13 μm. Then, test machining of the internal flow passage of the part to be machined is performed based on the lower limit of grain size, and the flow rate or velocity data is taken as the reference value. The initial grain size is increased by 1 μm to 10 μm, and test machining of the internal flow passage of the part to be machined is continued until the initial flow rate or velocity data is less than 1% to 5% of the reference value. At this point, the abrasive grain size is considered optimal, and the test results show that the abrasive grain size d is 30 μm to 32 μm. Similarly, for the abrasive mass concentration, first select 10 g / L as the lower limit of the abrasive mass concentration and perform test processing on the internal flow passage of the part to be processed. Then, read the reference value for the flow rate or flow rate data and increase the abrasive mass concentration by 2 g / L to 5 g / L based on the 10 g / L abrasive mass concentration. Continue test processing of the internal flow passage of the part to be processed until the flow rate or flow rate data is less than 1% to 5% of the reference value. At this point, the abrasive mass concentration is optimal. Tests have shown that the optimal abrasive mass concentration is 20 to 22 g / L. After adding all of the above materials to the deionized water, the two-phase flow finishing medium is produced and added to the equipment cylinder.

[0087] Step 2: The specific characteristic parameters for this fuel nozzle are: pipe length l = 130mm~140mm, pipe diameter D = 1.3mm~1.4mm, length to diameter ratio l / D = 100, initial average roughness Ra0 = 10μm, target value of optimum roughness after finishing Ra = 1.6μm, Reynolds number Re = 120, uneven grinding ratio coefficient k = 0.3, average abrasive grain diameter d = 30μm, average cutting depth L of the abrasive grain cutting edge corresponding to this grain diameter = 3.3 nm, i.e., the thinning rate of one side during the machining process is approximately 12 μm / h, the abrasive cutting edge contact length b = 500 nm, i.e., the final limit scratch and the corresponding optimum roughness Ra are 0.5 μm, the aqueous liquid phase density ρl = 1500 kg / m3, the abrasive solid phase density ρp = 3300 kg / m3, the high-temperature alloy material yield limit σw = 300 MPa, the initial period machining time t = 1 h, and the pressure increase ratio χ = 145.These parameters are substituted into the following equation.

number

[0088] The calculated predetermined pressure P is 46.7 MPa.

[0089] Step 3: The specified pressure P = 46.7 MPa and processing time of 1 hour from Step 2 are input into the equipment to perform prototype processing. After the prototype processing is completed, the diameter of the internal flow passage port of the test piece is measured with a plug gauge, where δ is the port diameter expansion value. After measurement, δ = 0.04 mm is found, which does not reach the theoretical diameter expansion value δ = 0.096 mm calculated using the following formula with Ra = 1.6 μm. This means that the internal flow passage roughness does not reach the optimal roughness Ra = 1.6 μm after the above-mentioned finishing.

number

[0090] Step 4: The step time was increased by 1 hour each time, and finally the total processing time was 8 hours, after which the theoretical diameter enlargement value δ=0.096 mm was reached.

[0091] Step 5: Enter the 8-hour period and the specified pressure P = 46.7 MPa into the equipment and perform the formal processing. When the processing time reaches 8 hours, the equipment will automatically stop and the processing will end.

[0092] Step 6: After the processing is completed, the finishing medium in the cylinder is sucked out to clean the cylinder, and deionized water with a purity of 0.1μs / cm~10μs / cm is added to the cylinder as a cleaning medium. The pressure is set to P=46.7MPa, and the equipment is started to apply this pressure to the deionized water to perform deionized water processing and cleaning. The deionized water discharged through the internal flow path is irradiated with a spotlight beam, and the cleaning is completed when a linear milky white light beam appears, indicating the Tyndall effect.

[0093] Step 7: The parts are ultrasonically cleaned for 10 minutes, dried with an air gun, and finally dried in an oven to complete the final cleaning.

[0094] As shown in Figure 6B, the finished fuel nozzle was cut along the axis of the passage by wire cutting. Further magnification, as shown in Figure 6C, clearly shows the inner surface of the passage, with a flattened surface close to that of a machined surface and a remarkable finish. The surface is smooth and bright. Metallographic detection revealed no residual, inlaid, or semi-sintered additive manufacturing powder. Roughness detection revealed an optimal roughness Ra of 1.3 μm, achieving the target Ra<1.6 μm.

[0095] (Second Example) As shown in FIG. 7A, the target product in this example is an internal flow passage 200 of a certain type of heat exchanger. The internal flow passage to be finished is fabricated using laser additive manufacturing technology. The structural features are a fine internal flow passage diameter D of 2.3mm to 2.4mm, a total length l of 500mm, a length-to-diameter ratio l / D of 28, and a structure including a straight line 201, an L-shaped bend 202, an S-shaped bend 203, and a U-shaped bend 204. The bending angle of the S-shaped bend 203 is approximately 60°. That is, the first bending structure 2031 and the second bending structure 2032 of the S-shaped bend 203 shown in FIG. 7A have a bending angle of 60° and a bending radius of approximately 6mm. The bending angle of the L-shaped bend 202 is 90°. The U-shaped bend 204 is a structure including two consecutive symmetrical L-shaped bends 202. The material is an aluminum alloy. The specific processing method is as follows.

[0096] First step: As in the first example, no further explanation is given here. The viscosity of the liquid phase of the obtained two-phase flow finishing medium is 100-120 cP, the abrasive grain size is d = 50 μm-52 μm, and the optimal abrasive grain mass concentration is 30 g / L-35 g / L.

[0097] Step 2: The specific characteristic parameters of the internal flow path of this heat exchanger are "pipe length l = 500 mm, pipe diameter D = 2.3 mm ~ 2.4 mm, length to diameter ratio l / D = 208, initial average roughness Ra0 = 25 μm, target value of optimal roughness after finishing Ra = 1.6 μm, Reynolds number Re = 60, uneven grinding ratio coefficient k = 0.2, abrasive grain diameter d = 50 μm, average cutting depth L of the corresponding abrasive grain cutting edge = 10 nm, that is, the machining process The thinning rate per side is 35 μm / h, the average contact length of the abrasive cutting edge is b=800 nm, i.e., the final limit scratch and the corresponding optimum roughness Ra is 0.8 μm, the aqueous liquid phase density ρl=1500 kg / m3, the abrasive solid phase density ρp=3300 kg / m3, the aluminum alloy material yield limit σw=100 MPa, the initial processing time t=1 h, and the pressure increase ratio χ=87. Similarly, the above parameters are substituted into the following equation.

number

[0098] The calculated predetermined pressure P is 51.5 MPa.

[0099] Step 3: The specified pressure P = 51.5 MPa and initial period of 1 hour in Step 2 are input into the equipment to perform prototype processing. After the prototype processing is completed, the diameter of the internal flow passage port of the test piece is measured with a plug gauge, where δ is the port diameter expansion value. After measurement, δ = 0.22 mm is found, which is more than 90% of the theoretical diameter expansion value δ = 0.234 mm calculated using the following formula with Ra = 3.2 μm. This means that the desired optimal roughness target value Ra = 1.6 μm after the internal flow passage finishing processing for a total time of 1 hour has been achieved.

number

[0100] Step 4: Input the reference time of 1 hour and the specified pressure P = 51.5 MPa into the equipment and perform the formal processing. When the processing reaches the reference processing time, the equipment will automatically stop and the processing will end.

[0101] Step 5: After the processing is completed, the finishing medium in the cylinder is sucked out to clean the cylinder, and deionized water with a purity of 0.1μs / cm~10μs / cm is added to the cylinder as a cleaning medium. The pressure is set to P=51.5MPa, and the equipment is started to apply this pressure to the deionized water to perform deionized water processing and cleaning. The deionized water discharged through the internal flow path is irradiated with a spotlight beam, and the cleaning is completed when a linear milky white light beam appears, indicating the Tyndall effect.

[0102] Step 6: The parts are ultrasonically cleaned for 10 minutes, then dried with an air gun, and finally dried in an oven to complete the final cleaning.

[0103] As shown in Figure 7B, a finished heat exchanger was cut along the axis of the flow channel using a wire cutter. Further magnification, as shown in Figure 7C, clearly shows that the inner surface of the flow channel is flattened to a machined surface and has a remarkable finish, with a smooth and bright surface. Metallographic detection revealed no residual, inlaid, or semi-sintered additive manufacturing powder. Roughness detection revealed that the optimum roughness Ra was 1.08 μm, achieving the target Ra of 1.6 μm or less.

[0104] In one comparative example, the predetermined pressure for the internal flow path structure was 21.2 MPa, as in the second embodiment. As shown in Figures 12A and 12B, taking the area around the first bending structure 2031 of the S-bend of the U-bend 204 attachment as an example, a significant "orange peel effect" appeared on the machined surface, and the roughness improvement was not significant. The inventors subsequently calculated the reason for this: the flow velocity of the finishing medium was 4.2 m / s, which did not reach the critical flow velocity of non-Newtonian fluids > 5 m / s, so target grinding of only the convex points was not achieved, and both high and low points on the surface were ground together, leaving a significant "orange peel effect" on the surface and failing to achieve the processing effect achieved by target grinding of only the convex points at flow velocities > 5 m / s.

[0105] (Third Example) As shown in FIG. 8A, the target product of this embodiment is an internal flow passage 300 of a certain type of hydraulic module. The internal flow passage to be finished is manufactured using laser additive manufacturing technology. The structure has a fine internal flow passage diameter D of 3 mm, a total length l of 150 mm, and a length-to-diameter ratio l / D of 50. It includes a straight line 301, an S-shaped bend 302, and an L-shaped bend 303. Here, the S-shaped bend 302 refers to a stepped structure consisting of multiple consecutive L-shaped bends. The bending angle of the L-shaped bend 303 is approximately 90° for the inner bend and approximately 60° for the outer bend. Here, the terms "inner" and "outer" refer to the distance from the center of the bend area when the fluid moves in a bending direction. The bend closer to the center of the circle is the inner bend, and the bend further from the center of the circle is the outer bend. For example, as shown in Figure 8A, the first bending structure 3031 of the L-shaped bending member 303 has an inner bending angle 30311 of approximately 90° and an outer bending angle 30312 of approximately 60°, while the second bending structure 3032 of the L-shaped bending member 303 has an inner bending angle 30321 of approximately 90° and an outer bending angle 30322 of approximately 60°, with a bending radius of approximately 10 mm, and the material is a titanium alloy. The specific finishing method is as follows:

[0106] First step: As in the first example, no further explanation is given here. The viscosity of the liquid phase of the obtained two-phase flow finishing medium is 120 cP-150 cP, the abrasive grain size is d=100 μm-120 μm, and the optimal abrasive grain mass concentration is 30-35 g / L.

[0107] Step 2: The specific characteristic parameters of the internal flow path of this hydraulic module are: pipe length l = 150 mm, pipe diameter D = 3 mm, length-to-diameter ratio l / D = 50, initial average roughness Ra0 = 25 μm, desired optimal roughness target value Ra = 3.2 μm, Reynolds number Re = 50, asperity grinding ratio k = 0.1, abrasive grain diameter d = 100 μm, corresponding average cutting depth L = 14 nm, i.e., the side thinning rate during the machining process is 50 μm / h, average contact length b = 1000 nm, i.e., the final limit scratch and corresponding optimal roughness Ra is 1 μm, aqueous liquid phase density ρl = 1500 kg / m3, abrasive grain solid phase density ρp = 3300 kg / m3, titanium alloy material yield limit σw = 600 MPa, initial period t = 0.5 h, and pressure increase ratio χ = 65. These parameters are substituted into the following equation:

number

[0108] The calculated predetermined pressure P is 40.5 MPa.

[0109] Step 3: In Step 2, the predetermined pressure P = 40.5 MPa and initial period of 0.5 h are input into the equipment to perform prototype processing. After the prototype processing is completed, the diameter of the port in the internal flow path of the test piece is measured with a plug gauge, where δ is the port diameter expansion value. After measurement, δ = 0.2 mm is found, which reaches the theoretical diameter expansion value δ = 0.194 mm calculated using the following formula with Ra = 3.2 μm. This means that the internal flow path roughening processing time of 0.5 hours basically achieved the desired optimal roughness target value Ra = 3.2 μm after the above-mentioned finishing.

number

[0110] Step 4: Enter the reference time of 0.5 hours and the specified pressure P = 40 MPa into the equipment to perform the formal processing. When the processing reaches the reference processing time of 0.5 hours, the equipment will automatically stop and the processing will end.

[0111] Step 5: After the processing is completed, the finishing medium in the cylinder is sucked out to clean the cylinder, and deionized water with a purity of 0.1μs / cm~10μs / cm is added to the cylinder again. The pressure is set to P=40MPa, and the equipment is started to apply this pressure to the deionized water to perform deionized water processing and cleaning. The deionized water discharged through the internal flow path is irradiated with a spotlight beam, and the cleaning is completed when a linear milky white light beam appears, indicating the Tyndall effect.

[0112] Step 6: The parts are ultrasonically cleaned for 10 minutes, then dried with an air gun, and finally dried in an oven to complete the final cleaning.

[0113] As shown in Figure 8B, the inner surface of a hydraulic module internal flow passage after finishing was cut along the flow passage axis by wire cutting. Further magnification, as shown in Figure 8C, clearly shows a smooth, bright surface with a flat, nearly machined surface and a remarkable finish. Metallographic detection revealed no residual, inlaid, or semi-sintered additive manufacturing powder. Roughness detection revealed an optimal roughness Ra of 2.6 μm, achieving the target Ra of 3.2 μm or less.

[0114] (Fourth Example) As shown in Figure 9A, the target product in this example is a throttle internal flow passage 400. The internal flow passage to be finished is manufactured using laser additive manufacturing technology. The structure is a fine internal flow passage with a diameter D of 0.5 mm, a total flow passage length l of 200 mm, a length-to-diameter ratio l / D of 400, and a spiral bend 401 with a bend angle of 180° and a bend radius of 5.5 mm. The material is stainless steel. The specific processing method is as follows:

[0115] First step: As in the first example, no further explanation is given here. The viscosity of the liquid phase of the obtained two-phase flow finishing medium is 50 cP to 60 cP, the abrasive grain size is d = 5 μm to 6 μm, and the optimal abrasive grain mass concentration is 10 g / L to 12 g / L.

[0116] Step 2: The specific characteristic parameters of the internal flow path of this hydraulic module are: pipe length l = 200 mm, pipe diameter D = 0.5 mm, length-to-diameter ratio l / D = 400, initial average roughness Ra0 = 6.4 μm, target value of optimal roughness after finishing Ra = 0.8 μm, Reynolds number Re = 180, asperity grinding ratio k = 0.4, abrasive grain size d = 5 μm, corresponding average cutting depth L = 2 nm, i.e., the side thinning rate during the machining process is 7 μm / h, average contact length b = 100 nm, i.e., the final limit scratch and corresponding optimal roughness Ra are 0.1 μm, aqueous liquid phase density ρl = 1500 kg / m3, abrasive solid phase density ρp = 3300 kg / m3, stainless steel material yield limit σw = 170 MPa, initial period t = 1 h, and pressure increase ratio χ = 500. These parameters are substituted into the following equation:

number

[0117] The calculated predetermined pressure P is 55.5 MPa.

[0118] Step 3: The predetermined pressure P = 55.5 MPa in Step 2 and the initial period of 1 hour are input into the equipment to perform prototype processing. After the prototype processing is completed, the diameter of the internal flow passage port of the test piece is measured with a plug gauge, where δ is the port diameter expansion value. After the measurement, δ = 0.024 mm is found, which does not reach the theoretical diameter expansion value δ = 0.075 mm calculated using the following formula with Ra = 0.8 μm. This means that the internal flow passage roughness after the initial period of 1 hour does not reach the optimal roughness target value Ra = 0.8 μm after the above-mentioned finishing.

number

[0119] Step 4: The processing step was increased by 1 hour, and finally, the total accumulated processing time was 8 hours, and the theoretical diameter enlargement value δ=0.075 mm was reached.

[0120] Step 5: Input the reference period of 8 hours and the specified pressure P = 55 MPa into the equipment and perform the formal processing. When the processing reaches the reference processing time, the equipment will automatically stop and the processing will end.

[0121] Step 6: After the processing is completed, the finishing medium in the cylinder is sucked out to clean the cylinder, and deionized water with a purity of 0.1μs / cm~10μs / cm is added to the cylinder as a cleaning medium. The pressure is set to P=55MPa, and the equipment is started to apply this pressure to the deionized water to perform deionized water processing and cleaning. The deionized water discharged through the internal flow path is irradiated with a spotlight beam, and the cleaning is completed when a linear milky white light beam appears, indicating the Tyndall effect.

[0122] Step 7: The parts are ultrasonically cleaned for 10 minutes, dried with an air gun, and finally dried in an oven to complete the final cleaning.

[0123] The finished workpiece was then cut along axis X1 (Figure 9A) using wire cutting. Further magnification revealed the spiral-bent channel port cross section, as shown in Figure 9B, with a tilted arrangement of circular holes. Observing the inner surface of the channel through the holes clearly revealed a smooth, bright surface with a flat, nearly machined surface and outstanding finish. Metallographic detection revealed no residual, inlaid, or semi-sintered additive manufacturing powder. Roughness testing revealed an optimal roughness Ra of 0.7 μm, achieving the target Ra of 0.8 μm or less.

[0124] (Fifth Example) As shown in FIG. 10A, the target product of this embodiment is a high-temperature alloy hollow blade 500 for an aircraft engine. The blade is formed by precision casting, and the air film holes 501 are drilled by spark drilling. The diameter of the air film holes 501 is 0.3 mm to 0.6 mm, and the thickness of the remelted layer is 5 μm. The fine internal flow passages in the blade communicate with the surface air film holes 501. The hollow blade 500 has an internal cavity structure 502 in which the fine internal flow passages communicate with the air film holes 501. The fine internal flow passage structure is characterized by a diameter D of 3 mm or less, a total length of 300 mm, and a length-to-diameter ratio of 100 or more. It should be understood that FIG. 10A is an example, and the actual number of air film holes 501 is generally much greater than three. The specific finishing method for the air film holes 501 on the blade surface is as follows.

[0125] First step: As in the first example, no further explanation is given here. The viscosity of the liquid phase of the obtained two-phase flow finishing medium is 50 cP to 60 cP, the abrasive grain size is d = 5 μm to 6 μm, and the optimal abrasive grain mass concentration is 10 g / L to 12 g / L.

[0126] Step 2: The specific characteristic parameters of the internal flow passage of this hydraulic module are: "The diameter D of the internal flow passage of the blade is 3 mm, the pipe length l = 300 mm, the ratio of the pipe length to the diameter l / D = 100, the diameter of the air film hole D = 0.5 mm, the initial average roughness Ra0 = 1.6 μm, the target value of the optimum roughness after finishing Ra = 0.8 μm, the Reynolds number Re = 180, the unevenness grinding ratio k = 0.4, the abrasive grain diameter d = 5 μm, and the average cutting depth L of the corresponding abrasive grain cutting edge 2 nm, i.e., the edge thinning rate during the machining process is 7 μm / h, the average contact length b of the abrasive cutting edge is 50 nm, i.e., the final limit scratch and the corresponding optimum roughness Ra are 0.05 μm, the aqueous liquid phase density ρl is 1500 kg / m3, the abrasive solid phase density ρp is 3300 kg / m3, the stainless steel material yield limit σw is 170 MPa, the initial period t is 30 min, and the pressure increase ratio χ is 400.These parameters are substituted into the following equation.

number

[0127] The calculation yields the predetermined pressure P = 40 MPa.

[0128] Step 3: In Step 2, the specified pressure P = 40 MPa and initial period of 30 minutes were input into the equipment to perform a prototype. After the prototype was completed, the small hole port diameter of the test piece was measured with a plug gauge, where δ is the port diameter expansion value. After measurement, δ = 0.01 mm was found. The side thinning rate had already reached 5 μm, meeting the requirement for sufficient removal of the remelted layer. The roughness was more than 90% of the theoretical diameter expansion value δ = 0.011 mm calculated using the following formula: Ra = 0.8 μm. This means that the roughness of the small hole inner wall reached the target value Ra = 0.8 μm after the above-mentioned finishing.

number

[0129] Step 4: Enter the specified time of 30 min and the specified pressure P = 40 MPa into the equipment and perform the formal processing. When the processing reaches the standard processing time, the equipment will automatically stop and the processing will end.

[0130] Step 5: After the processing is completed, the polishing media in the cylinder is sucked out to clean the cylinder, and deionized water with a purity of 0.1μs / cm~10μs / cm is added to the cylinder again. The pressure is set to P=40MPa, and the equipment is started to perform deionized water processing and cleaning. The deionized water discharged from the internal flow path is irradiated with a spotlight beam. When a linear milky white beam appears, the cleaning is complete.

[0131] Step 6: The parts are ultrasonically cleaned for 10 minutes, then dried with an air gun, and finally dried in an oven to complete the final cleaning.

[0132] As shown in Figure 10B, a localized photograph of the small hole after polishing was taken. Microscopic observation of the small hole surface clearly showed a significant polishing effect, with the inner surface of the small hole being nearly as flat as a machined surface. The surface was smooth and bright, and the hole opening had significant halation. That is, the hole chamfer radius was greater than 0.1 mm, preventing microcracks from occurring at the edge of the hole due to fatigue corrosion when gas passes through. Roughness detection revealed an optimal roughness Ra of 0.8 μm, achieving the target Ra of 0.8 μm. Unlike Examples 1 to 4, Example 5 focuses on the surface air film pores 501 of the blade, rather than the fine internal flow passages. The inventors discovered that finishing the air film pores 501 of aircraft engines using a finishing method for fine internal flow passages can completely remove the remelted layer. Furthermore, using fluid processing allows the finishing medium to smoothly pass through the internal flow passages of the blade, achieving the final air film pore finish.

[0133] (Sixth Example) As shown in FIG. 11A , the target product of this embodiment is a valve 600 with intersecting deep holes. The internal flow passages require finishing, and machining is performed to remove burrs at the intersections of the deep holes. The valve 600 includes a first group of intersecting deep holes 601 and a second group of intersecting deep holes 602. The intersecting deep hole group 601 includes a first deep hole 6011. The second deep hole 6012 has a fine internal flow passage with a diameter D of 1.6 mm, a total length l of 100 mm, a length-to-diameter ratio l / D of 50, and a structure including a straight line 603 and an L-shaped bend 604. The L-shaped bend 604 has a bending angle of 90°. For example, the L-shaped bend 604 formed by the first deep hole 6011 and the second deep hole 6012 of the first intersecting deep hole group 601 has a bending radius of 0.2 mm. The material is an aluminum alloy. The specific processing method is as follows:

[0134] First step: As in the first example, no further description is given here. The viscosity of the liquid phase of the obtained two-phase flow finishing medium was 90 cP to 100 cP, the abrasive grain size d was 40 μm to 42 μm, and the optimal abrasive grain mass concentration was 20 to 22 g / L.

[0135] Step 2: The specific characteristic parameters of the internal flow path of this deep cross hole are: pipe length l = 100 mm, pipe diameter D = 1.5 mm ~ 2 mm, length to diameter ratio l / D = 50, initial average roughness Ra0 = 0.8 μm, target roughness after finishing Ra = 0.4 μm, burrs at the cross hole position are sufficiently removed under a 40x microscope, Reynolds number Re = 100, unevenness grinding ratio coefficient k = 0.3, abrasive grain diameter d = 40 μm, and the flatness of the abrasive grain tip contacting the fine internal flow path surface at each second. The average cutting depth L = 3 nm, i.e., the thinning rate of one side during the machining process is 11 μm / h, the contact length of the abrasive grain cutting edge b = 200 nm, i.e., the target value Ra of the final limit scratch and the corresponding optimum roughness is 0.2 μm, the aqueous liquid phase density ρl = 1500 kg / m3, the abrasive grain solid phase density ρp = 3300 kg / m3, the aluminum alloy material yield limit σw = 100 MPa, the initial period t = 30 min, and the pressure increase ratio χ = 125. Similarly, the above parameters are substituted into the following equation.

number

[0136] The calculated predetermined pressure P is 42 MPa.

[0137] Step 3: The predetermined pressure P = 42 MPa and initial period of 30 minutes in Step 2 were input into the equipment to perform prototype machining. After the prototype machining was completed, the diameter of the internal flow channel port of the test piece was measured with a plug gauge, where δ is the port diameter expansion value. After measurement, δ = 0.05 mm was found, which reached the theoretical diameter expansion value δ = 0.047 mm calculated using the following formula with Ra = 0.4 μm. By setting the actual machining time for the internal flow channel roughness of the intersecting deep hole to 30 minutes, this means that the desired optimal roughness target value Ra = 0.4 μm was achieved after the finishing process.

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[0138] Step 4: Enter the reference time of 30 min and the specified pressure P = 42 MPa into the equipment and perform the formal processing. When the processing reaches the reference processing time, the equipment will automatically stop and the processing will end.

[0139] Step 5: After the processing is completed, the finishing medium in the cylinder is sucked out to clean the cylinder, and deionized water with a purity of 0.1μs / cm~10μs / cm is added to the cylinder as a cleaning medium. The pressure is set to P=42MPa, and the equipment is started to apply this pressure to the deionized water to perform deionized water processing and cleaning. The deionized water discharged through the internal flow path is irradiated with a spotlight beam, and the cleaning is completed when a linear milky white light beam appears, indicating the Tyndall effect.

[0140] Step 6: The parts are ultrasonically cleaned for 10 minutes, then dried with an air gun, and finally dried in an oven to complete the final cleaning.

[0141] After finishing, the intersecting deep holes of valve 600 were cut along the axis of the passage using a wire cutter. Further magnification, as shown in Figure 11B, clearly shows the remarkable finish on the inner surface of the passage. The surface is smooth and bright, and under a 40x microscope, burrs at the intersection of the deep holes have been sufficiently removed. Roughness detection revealed that the optimum roughness Ra was 0.4 μm, achieving the target Ra of 0.4 μm or less.

[0142] Although the present invention has been disclosed in the above embodiments, the present invention is not limited to these embodiments, and those skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention and the content that does not deviate from the technical solution of the present invention fall within the scope of protection defined in the claims of the present invention.

Claims

1. A method for finishing a fine internal flow passage, wherein the diameter of the fine internal flow passage is 3 mm or less and the ratio of length to diameter is 50:1 or more; A liquid-solid two-phase flow finishing medium is used, the liquid phase viscosity of the finishing medium is less than 1000 cP, and the solid phase of the finishing medium is abrasive grains; a predetermined pressure is applied to the finishing medium so that the finishing medium flows through the fine internal flow passages at a flow velocity of greater than 5 m / s; A finishing method characterized by including: a flow rate at which the finishing medium flows into the fine internal flow passage from one end thereof being set to a critical flow rate permitted by the diameter of the fine internal flow passage so that the liquid pressure inside the internal flow passage is maintained at a pressure-maintaining state.

2. 2. The method of claim 1, wherein the liquid phase of the finishing medium is an aqueous liquid.

3. The finishing method according to claim 1, characterized in that the abrasive grains have a surface sharp-angle structure, the average cutting depth of the abrasive grain cutting edge is 1.4 nm to 14 nm, and the average contact length of the abrasive grain cutting edge is 50 nm to 1000 nm.

4. The finishing medium finishes the fine internal flow passages in a reference period until an optimum surface roughness of the fine internal flow passages reaches a target value, and the reference period is obtained by the following steps: The finishing method of claim 3, wherein the finishing medium finishes the fine internal passages in an initial period and detects the optimum surface roughness of the fine internal passages; if the optimum surface roughness matches the target value, the initial period is the reference period; if the optimum surface roughness does not reach the target value, the step period is successively increased until the optimum surface roughness reaches the target value, and the corresponding total period is the reference period; wherein the initial period and the step period are obtained based on the unidirectional thinning rate corresponding to the abrasive grain and the initial average surface roughness of the fine internal passages.

5. The predetermined pressure P satisfies the following formula: [Equation 1] Here, Ra0 is the initial average surface roughness of the fine internal flow passage, Ra is the target value of the optimal surface roughness of the fine internal flow passage after finishing, t is the initial period, L is the average cutting depth of the abrasive cutting edge, b is the average contact length of the abrasive cutting edge, ρl is the aqueous liquid phase density, ρp is the abrasive solid phase density, σw is the yield limit of the workpiece material, χ is the pressure increase ratio at which the saturation flow rate is reached, Re is the Reynolds number of the liquid phase, l is the length of the internal flow passage, D is the diameter of the internal flow passage, d is the abrasive grain diameter, and k is the uneven grinding ratio coefficient.

6. Further, after the internal flow passage is finished, the optimum surface roughness corresponding to the increase in the diameter of the internal flow passage due to the finishing satisfies the following formula: [Equation 2] Here, Ra* is the optimum surface roughness after the internal flow passage is finished and the port diameter at the end of the internal flow passage is enlarged, Ra0 is the initial average surface roughness of the fine internal flow passage, δ is the increase in the port diameter, and k is the asperity grinding ratio coefficient.

7. 2. The finishing method according to claim 1, further comprising injecting a cleaning medium into the fine internal passages at the predetermined pressure after the optimum surface roughness of the fine internal passages reaches a target value, and the liquid phases of the cleaning medium and the finishing medium dissolve in each other until the Tyndall effect appears in the cleaning medium flowing out of the fine internal passages.

8. The finishing method of claim 1, further comprising gradually increasing the viscosity of the liquid phase, the abrasive grain size in the solid phase, and the abrasive grain mass concentration of the finishing medium based on lower limit values ​​of the viscosity of the liquid phase, the abrasive grain size in the solid phase, and the abrasive grain mass concentration, until the flow rate or flow rate of the two-phase flow finishing medium is reduced by 1 to 5% below the flow rate or flow rate corresponding to the lower limit values, thereby obtaining optimal value ranges for the viscosity, abrasive grain size, and abrasive grain mass concentration.

9. The finishing method described in claim 1, characterized in that the finishing medium finishes the fine internal flow path during a reference period, detects the flow velocity or flow rate of the finishing medium in the fine internal flow path, and when the flow velocity or flow rate reaches a predetermined value, the optimal surface roughness reaches a target value.

10. The finishing method according to claim 1, characterized in that the fine internal flow passages are three-dimensionally extended and have a curved structure including an S-shaped curve, an L-shaped curve, a U-shaped curve, an O-shaped curve, and a spiral curve, and the liquid phase of the finishing medium contains a polymer thickener.

11. A finishing method as described in claim 1, wherein the fine internal flow passages are made from one of a high-temperature alloy, an aluminum alloy, a titanium alloy, or stainless steel.

12. A fine internal flow passage workpiece obtained by the finishing method according to any one of claims 1 to 11.

13. A fine internal flow path workpiece as described in Claim 12, characterized in that it has a fine internal flow path with a diameter of 3 mm or less and a length to diameter ratio of 50:1 or more, the fine internal flow path workpiece being obtained by additive manufacturing, casting, laser processing or spark processing, and the fine internal flow path has an inner surface with an optimum surface roughness Ra of 1.6 μm or less after finishing.

14. A fine internal flow path work as described in Claim 12, characterized in that it has a fine internal flow path with a diameter of 3 mm or less and a length to diameter ratio of 50:1 or more, the fine internal flow path work being obtained by precision machining, and the fine internal flow path having an inner surface with an optimal surface roughness Ra of 0.4 μm or less after finishing.

15. The fine internal passage workpiece is an additively manufactured high-temperature alloy fuel nozzle for an aircraft engine, the fuel nozzle has the fine internal passage structure, the diameter of the fine internal passage is less than 2.5 mm, the structure includes a straight line, an L-shaped bend, and an O-shaped bend, and the optimum surface roughness Ra of the fine internal passage is 1.6 μm or less; or The fine internal flow passage workpiece is an aluminum alloy heat exchanger manufactured by additive manufacturing, the heat exchanger has a fine internal flow passage structure, the diameter is less than 3 mm, and the fine internal flow passage structure has a straight line, an L-shaped bend, an S-shaped bend, and a U-shaped bend, and the optimum surface roughness Ra of the fine internal flow passage is 1.6 μm or less, or The fine internal flow path workpiece is a hydraulic module made of a titanium alloy by additive manufacturing, the hydraulic module has a fine internal flow path structure, a diameter of 3 mm, and the fine internal flow path structure has a straight line, an S-shaped bend, and an L-shaped bend, and the optimum surface roughness Ra of the fine internal flow path is 3.2 μm or less, or The fine internal flow path workpiece according to claim 12, characterized in that the fine internal flow path workpiece is a stainless steel throttle manufactured by additive manufacturing, the throttle has a fine internal flow path structure, a diameter of less than 1 mm, and the fine internal flow path structure has a spiral bend, and the optimum surface roughness Ra of the fine internal flow path is 0.8 μm or less.

16. The fine internal passage workpiece according to claim 12, characterized in that the fine internal passage workpiece is a hollow blade made of a high-temperature alloy cast for an aircraft engine, the hollow blade has an inner cavity structure in which the fine internal passage communicates with a small hole, and the optimum roughness Ra of the inner surface of the small hole after finishing is 0.8 μm or less, there is no remelted layer, and the chamfer radius of the hole is greater than 0.1 mm.

17. A finishing medium for use in the finishing method according to any one of claims 1 to 11, wherein the finishing medium comprises a liquid phase and a solid phase, the viscosity of the liquid phase being less than 1000 cP, the solid phase being an abrasive grain, and a polymeric thickener is added to the liquid phase of the finishing medium, and the step of obtaining the finishing medium comprises: A finishing medium comprising: gradually increasing the viscosity of the liquid phase, the abrasive grain size and the abrasive grain mass concentration of the solid phase of the finishing medium based on lower limit values ​​of the viscosity of the liquid phase, the abrasive grain size and the abrasive grain mass concentration of the solid phase until the flow rate or flow rate of the two-phase flow finishing medium is reduced by 1 to 5% below the flow rate or flow rate corresponding to the lower limit values, thereby obtaining an optimum value range for the viscosity, abrasive grain size and abrasive grain mass concentration.

18. The finishing medium of claim 17, wherein the liquid phase further contains an antifoaming agent, and the volume ratio of the surface foam slurry of the finishing medium to the liquid phase during the process of machining fine internal channels by the finishing method does not exceed 0.3:

1.

19. 20. The finishing medium of claim 17, wherein the liquid phase of the finishing medium also includes a lubricant comprising one or more combinations of inorganic compounds, elementary compounds, and polymeric compounds.

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