Water-based two-phase flow polishing medium, polishing method and shear thinning characteristic determination method

Abstract

The invention provides a water-based two-phase flow polishing medium, a polishing method and a shear thinning characteristic determination method, and belongs to the technical field of metal part precision machining.The water-based two-phase flow polishing medium is prepared from, by weight, 89.1%-94% of deionized water, 2%-6% of silicon carbide abrasive particles and 2.4%-3.3% of dispersing agent. By improving the shear thinning characteristic of the water-based two-phase flow polishing medium, compared with the prior art, the surface roughness of a molded inner flow channel after polishing can reach Ra1.6 mu m or below; after the upper and lower surfaces of the inner runner are polished, the upper and lower surface roughness difference is reduced by 60% compared with the original upper and lower surface roughness difference, and after the inner and outer sides of a turn are polished, the inner and outer side roughness difference is reduced by 60% compared with the original inner and outer side roughness difference.

Description

Technical Field

[0001] This specification relates to the technical field of precision machining of metal parts, and particularly relates to an aqueous two-phase flow polishing medium, a polishing method, and a method for measuring shear thinning characteristics. Background Art

[0002] Parts with microscopically complex internal flow channel structures have extremely wide applications in the industrial field. In particular, components related to fluid power systems often have complex internal cavity structures such as microchannels, deep small holes, and the connection of microchannels and deep small holes, which play functions such as fluid transportation, exchange, or application of hydraulic pressure. Examples include various engine fuel nozzles, heat exchangers, hydraulic components, oil circuit control throttle valves, etc. The processing technologies that can machine microscopically complex internal flow channels include precision machining, femtosecond / water-jet / long-pulse laser machining, electrical discharge machining, and additive manufacturing (3D printing), etc. Except for additive manufacturing technology, the microscopically complex internal flow channel structures machined by other single processes are relatively simple and have a small length-to-diameter ratio, and other combined processes such as welding need to be combined to machine microscopically complex internal flow channels. Problems such as burrs, sharp corners at inflection points, or tool-changing steps will occur in the microscopically complex internal flow channels machined by precision machining; adhered residue particles and surface "step" effects will occur on the surface of the internal flow channels machined by femtosecond laser; remelted layers will occur on the surface of the internal flow channels machined by water-jet / long-pulse laser and electrical discharge machining; additive manufacturing (3D printing) is a technology that discretizes the model of a part with a complex three-dimensional structure into a two-dimensional structure and stacks it layer by layer for forming, which makes it possible to integrally form parts with complex microscopically complex internal flow channels, and thus its application in the industrial field is increasing day by day. However, due to its own process characteristics such as temperature gradient and layer-by-layer forming during the process of forming parts by additive manufacturing technology, there are semi-sintered or adhered powder particles and surface "step" effects on the surface of the internal flow channels of the parts.

[0003] Machine - processed burrs, sintered particles adhering to the internal flow channels during femtosecond laser processing, and bonded powders on the surface of the internal flow channels in additive manufacturing can all affect the service performance and safety of parts: When the fluid flowing through the internal flow channels causes burrs, adhered residue particles, or bonded powders to fall off due to high - speed friction with the surface layer, they will become foreign substances and spread everywhere with the fluid, either blocking the oil circuit or causing mechanical wear failures, thus resulting in major safety accidents; The rough inner surface is likely to become a fatigue crack source during long - term use. In the case of a high - temperature oil circuit system, carbon deposition is also likely to occur; The tool marks, inflection sharp corners, or tool - changing steps on the surface of the machined flow channels, and the "step" phenomenon on the surface of the internal flow channels processed by femtosecond laser and additive manufacturing will all cause turbulence, eddy currents, and a sharp increase in the fluid frictional resistance during the fluid movement process, even causing the fluid to get out of control, generating vibrations and reducing the service life of the parts. The rough surface will also cause a large number of cavitation bubbles to be generated in the fluid, affecting combustion and hydraulic power, and even causing cavitation corrosion; The remelted layer generated on the surface of the internal flow channels processed by water - jet / long - pulse laser and electric discharge machining is prone to micro - cracks, leading to premature failure of parts under complex working conditions. Therefore, appropriate surface finishing techniques need to be adopted to eliminate these adverse effects before the performance requirements of the product can be met. Summary of the Invention

[0004] In view of this, the embodiments of this specification provide a water - based two - phase flow polishing medium, a polishing method, and a shear - thinning property measurement method to solve the problem of non - uniform polishing that is likely to occur at the turning points of the flow channels and on the upper and lower surfaces with large initial roughness differences during the finishing of micro - fine and complex internal flow channels, and even problems such as dimensional tolerance exceeding and damage.

[0005] The technical solution of the present invention is specifically as follows: A water - based two - phase flow polishing medium, by weight, the water - based two - phase flow polishing medium includes 89.1% - 94% deionized water, 2% - 6% silicon carbide abrasive grains, and 2.4% - 3.3% dispersant.

[0006] Further, the dispersant includes one or a combination of polyvinyl alcohol, sodium silicate, and polystyrene.

[0007] Further, the dispersant includes polyvinyl alcohol, sodium silicate, and polystyrene, where polyvinyl alcohol is 0.7% - 1%, sodium silicate is 1.2% - 1.5%, and polystyrene is 0.5% - 0.8%.

[0008] Further, the water - based two - phase flow polishing medium further includes 0.2% - 0.3% thickener, 0.05% - 0.1% rust inhibitor, 0.4% - 0.5% defoamer, 0.4% - 0.5% lubricant, and 0.1% - 0.2% antifreeze.

[0009] The present invention also includes a polishing method, using the above - mentioned water - based two - phase flow polishing medium, and the polishing method includes:

[0010] Step 1: Configure the water-based two-phase flow polishing medium;

[0011] Step 2: Place the prepared water-based two-phase flow polishing medium in the material cylinder, adjust the pressure to the first set value and start the plunger pump to polish the workpiece;

[0012] Step 3: Stop the processing when the flow rate increase during the polishing operation reaches the second set value;

[0013] Step 4: Clean and dry the polished workpiece.

[0014] Further, Step 1: Configuring the water-based two-phase flow polishing medium specifically means that the addition order of each component in the water-based two-phase flow polishing medium is as follows: deionized water, silicon carbide abrasive grains, dispersant, thickener, rust inhibitor, defoamer, lubricant, and antifreeze.

[0015] Further, the first set value is 45 - 55 Mpa; the second set value is 45% - 55%.

[0016] Further, Step 4: Cleaning and drying the polished workpiece specifically means:

[0017] Blow out the water-based two-phase flow polishing medium inside the micro-channel of the polished workpiece with a high-pressure air gun, then soak and clean it using ultrasonic waves, and then rinse it several times with pure water and dry it.

[0018] The present invention also provides a method for measuring the shear-thinning property, which measures the shear-thinning property of the above-mentioned water-based two-phase flow polishing medium. The method for measuring the shear-thinning property includes the following steps:

[0019] Measure the pressure value p of the water-based two-phase flow polishing medium at the center of the inner flow channel of the workpiece 1 and the pressure value p of the water-based two-phase flow polishing medium near the wall surface of the inner flow channel 2 ;

[0020] According to the formula (p 1 - p 2 ) / r, calculate the numerical value of the flow field pressure gradient from the center to the near wall surface of the inner flow channel, where r is the radius of the inner flow channel;

[0021] When the numerical value of the flow field pressure gradient is greater than the first set threshold, it is determined that the shear-thinning property of the water-based two-phase flow polishing medium is significant.

[0022] Further, use a piezoelectric sensor probe to measure the pressure value p of the water-based two-phase flow polishing medium at the center of the inner flow channel 1 ;

[0023] Further, use a piezoelectric sensor chip to closely adhere to the outer wall surface of the inner flow channel to measure the pressure value p of the water-based two-phase flow polishing medium near the wall surface of the inner flow channel of the workpiece2 。

[0024] The present invention also provides a method for measuring the shear-thinning property, which is used to measure the shear-thinning property of the above water-based two-phase flow polishing medium. The method for measuring the shear-thinning property includes the following steps:

[0025] Measure the current surface roughness R of the inner side of the flow path turning in the workpiece, a1 and the original surface roughness Ra of the inner side of the flow path turning 1 and the current surface roughness R of the outer side of the flow path turning in the workpiece, a2 and the original surface roughness Ra of the outer side of the flow path turning in the workpiece 2 ;

[0026] Calculate the percentage reduction of the difference in roughness between the inner and outer sides of the turning after polishing compared to the difference in roughness between the inner and outer sides of the original turning through a formula

[0027] When the percentage reduction of the difference in roughness between the inner and outer sides of the turning after polishing compared to the difference in roughness between the inner and outer sides of the original turning is greater than the second threshold value, it is determined that the shear-thinning property of the water-based two-phase flow polishing medium is significant.

[0028] The present invention also provides a method for measuring the shear-thinning property, which is used to measure the shear-thinning property of the above water-based two-phase flow polishing medium. The method for measuring the shear-thinning property includes the following steps:

[0029] Select the sheared water-based two-phase flow polishing medium and the unsheared water-based two-phase flow polishing medium to perform polishing operations respectively. Under the same polishing time and the same polishing effect, obtain the reduction ratio of the first driving pressure difference and the reduction ratio of the second driving pressure difference;

[0030] Compare the reduction ratio of the first driving pressure difference with the reduction ratio of the second driving pressure difference. When the reduction ratio of the first driving pressure difference is greater than the reduction ratio of the second driving pressure difference, it is determined that the shear-thinning property of the sheared water-based two-phase flow polishing medium is more significant than that of the unsheared water-based two-phase flow polishing medium.

[0031] The present invention also provides a method for measuring the shear-thinning property, which is used to measure the shear-thinning property of the above water-based two-phase flow polishing medium. The method for measuring the shear-thinning property includes the following steps:

[0032] Select the sheared water-based two-phase flow polishing medium and the unsheared water-based two-phase flow polishing medium to perform polishing operations respectively. Under the same polishing effect, obtain the first processing time and the second processing time;

[0033] Compare the first processing time with the second processing time. When the first processing time is less than the second processing time, it is determined that the shear-thinning characteristic of the shear-thinned water-based two-phase flow polishing medium is more significant than that of the non-shear-thinned water-based two-phase flow polishing medium.

[0034] Compared with the prior art, the beneficial effects that can be achieved by at least one of the above technical solutions adopted in the embodiments of the present specification at least include: By improving the shear-thinning characteristic of the water-based two-phase flow polishing medium, the present invention can achieve a surface roughness of Ra 1.6 μm or less on the inner flow channel surface after polishing, compared with the prior art. The percentage reduction in the difference in surface roughness between the upper and lower surfaces of the inner flow channel after polishing and the original difference in surface roughness between the upper and lower surfaces, and the percentage reduction in the difference in roughness between the inner and outer sides after polishing and the original difference in roughness between the inner and outer sides at the turning are both greater than 60%. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 It is a comparison diagram of the shear-thinning effect principle diagram between the present invention and the prior art;

[0037] Figure 2 It is a schematic flowchart of an embodiment of the present invention;

[0038] Figure 3 It is a physical diagram of the workpiece after polishing in Embodiment 1 of the present invention;

[0039] Figure 4 It is a comparison diagram of the upper and lower surfaces of the workpiece in Embodiment 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The embodiments of the present application will be described in detail below with reference to the drawings.

[0041] The following describes the implementation manners of the present application through specific specific examples. Those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope protected by the present application.

[0042] The present invention provides an aqueous two-phase flow polishing medium. In terms of parts by weight, the aqueous two-phase flow polishing medium includes 89.1% - 94% deionized water, 2% - 6% silicon carbide abrasive grains, and 2.4% - 3.3% dispersant.

[0043] The dispersant in the embodiments of the present invention can significantly improve the shear thinning property, and can achieve that the surface roughness of the formed internal flow channel after polishing reaches Ra1.6μm or less. The percentage reduction of the roughness difference between the upper and lower surfaces of the additive manufacturing formed internal flow channel after polishing compared to the original roughness difference between the upper and lower surfaces and the percentage reduction of the roughness difference between the inner and outer sides of the turning after polishing compared to the original roughness difference between the inner and outer sides are both greater than 60%.

[0044] Specifically, the dispersant includes one or a combination of polyvinyl alcohol, sodium silicate, and polystyrene.

[0045] By detecting the rheological properties of the original polishing medium with a rheometer, it is found that its viscosity does not show obvious shear thinning with the increase of the shear rate, and its viscosity attenuation rate (the viscosity attenuation amount corresponding to each unit increase in the shear rate) is 0.035 - 0.2 dB / dec. When using polyvinyl alcohol, sodium silicate, and polystyrene as the dispersant, its viscosity attenuation rate is about 20 - 50 dB / dec. Since the viscosity attenuation rate is considered to have significant shear characteristics when it exceeds 20 dB / dec, it can be concluded that polyvinyl alcohol, sodium silicate, and polystyrene all have significant shear thinning effects as the dispersant.

[0046] The magnitude of the shear thinning property can be characterized by the flow field pressure gradient from the center to the near-wall surface of the internal flow channel when the shear thinning fluid flows through the internal flow channel, that is, the pressure difference between the flow field at the center of the internal flow channel and the near-wall surface flow field per unit distance along the normal direction of the pipeline. The larger the numerical value of the flow field pressure gradient from the center to the near-wall surface of the internal flow channel, the more significant the shear thinning effect. Refer to Figure 1 as shown (the left side is the prior art, and the right side is the present invention). The pressure gradient expression is (p 1 -p2 ) / r, where p 2 is the pressure value of the water-based two-phase flow polishing medium near the inner channel wall surface, and p 1 is the pressure value of the water-based two-phase flow polishing medium at the center of the inner channel, and r is the radius of the inner channel.

[0047] When polyvinyl alcohol, sodium silicate or polystyrene is added alone to the polishing medium, good shear thinning effects can be obtained. When the addition amount of polyvinyl alcohol alone is 7 - 10 g / L, the shear thinning effect is relatively significant, and its pressure gradient value is 0.66 - 0.71 Mpa / mm; when the addition amount of sodium silicate alone is 12 - 15 g / L, the shear thinning effect is relatively significant, and its pressure gradient value is 0.63 - 0.69 Mpa / mm; when the addition amount of polystyrene alone is 5 - 8 g / L, the shear thinning effect is relatively significant, and its pressure gradient value is 0.7 - 0.73 Mpa / mm.

[0048] When any two of polyvinyl alcohol, sodium silicate or polystyrene are added to the polishing medium, good shear thinning effects can be obtained, and the combination of the two substances has a better shear thinning effect than the addition of a single substance. When polyvinyl alcohol and sodium silicate are mixed and added, when the addition amount of polyvinyl alcohol is 7 - 10 g / L and the addition amount of sodium silicate is 12 - 15 g / L, the shear thinning effect is better than that of the single addition of the two, and its pressure gradient value is 0.75 - 0.79 Mpa / mm; when polyvinyl alcohol and polystyrene are mixed and added, when the addition amount of polyvinyl alcohol is 7 - 10 g / L and the addition amount of polystyrene is 5 - 8 g / L, its pressure gradient value is 0.81 - 0.83 Mpa / mm; when sodium silicate and polystyrene are mixed and added, when the addition amount of sodium silicate is 12 - 15 g / L and the addition amount of polystyrene is 5 - 8 g / L, its pressure gradient value is 0.83 - 0.85 Mpa / mm.

[0049] When the three combinations of polyvinyl alcohol, sodium silicate or polystyrene are added to the polishing medium, the best shear thinning effect can be obtained. When polyvinyl alcohol, sodium silicate and polystyrene are mixed and added, when the addition amount of polyvinyl alcohol is 7 - 10 g / L (0.7% - 1% by weight fraction), the addition amount of sodium silicate is 12 - 15 g / L (1.2% - 1.5% by weight fraction), and the addition amount of polystyrene is 5 - 8 g / L (0.5% - 0.8% by weight fraction), its pressure gradient value is 0.88 - 0.91 Mpa / mm, and the shear thinning effect is the best. In addition, this dispersant combination can effectively maintain the suspension of abrasive particles in the water-based two-phase flow polishing medium.

[0050] Preferably, the water-based two-phase flow polishing medium further includes 0.2% - 0.3% of a thickener, 0.05% - 0.1% of a rust inhibitor, 0.4% - 0.5% of an antifoaming agent, 0.4% - 0.5% of a lubricant, and 0.1% - 0.2% of an antifreeze agent. It should be noted that the sum of the above components should be 100%.

[0051] As Figure 2 shown, the present invention also provides a polishing method, which uses the above-mentioned water-based two-phase flow polishing medium. The polishing method includes:

[0052] Step 1: Prepare the water-based two-phase flow polishing medium;

[0053] Step 2: Place the prepared water-based two-phase flow polishing medium in the material cylinder, adjust the pressure to the first set value, and start the plunger pump to polish the workpiece;

[0054] Step 3: Stop the processing when the flow rate increase during the polishing operation reaches the second set value;

[0055] Step 4: Clean and dry the polished workpiece.

[0056] Among them, it should be noted that the first set value is 45 - 55 Mpa; the second set value is 45% - 55%.

[0057] The following lists two specific embodiments for illustration.

[0058] Embodiment 1: This embodiment is a two-dimensional internal flow channel specimen with a turn. The internal flow channel to be finished is manufactured by laser additive manufacturing technology. The structure is a micro internal flow channel with a diameter D = 1.5 mm, a total flow channel length of about 80 mm, a length-diameter ratio of about more than 50:1. The flow channel contains two turn structures, the material is a superalloy, the original roughness on the outer side of the internal flow channel turn is Ra7.8 μm, and the original roughness on the inner side of the turn is Ra10.2 μm. The specific processing method is as follows:

[0059] The first step: Prepare a shear-thinning water-based two-phase flow polishing medium. The addition sequence and addition amount of each substance are as follows: deionized water, silicon carbide abrasive grains (50 g / L), dispersants (the addition amount of polyvinyl alcohol is 7 - 10 g / L, the addition amount of sodium silicate is 12 - 15 g / L, the addition amount of polystyrene is 5 - 8 g / L), thickener (3 g / L), rust inhibitor (1 g / L), antifoaming agent (5 g / L), lubricant (5 g / L), and antifreeze agent (2 g / L).

[0060] The second step: Place the shear-thinning polishing medium prepared in the first step in the material cylinder, and set the plunger pump pressure to 51 Mpa.

[0061] The third step: Stop the processing when the flow rate increase reaches 50%.

[0062] Step 4: First use a high-pressure air gun to blow out the high-speed water-based two-phase flow polishing medium inside the fine inner flow channel, then use ultrasonic immersion cleaning, and then rinse with pure water several times and then dry.

[0063] like Figure 3 As shown, the two-dimensional inner flow channel sample with a turn after finishing is cut, and the inner surface of the flow channel can clearly see the flattening close to the machined surface and the significant finishing effect, and the surface is smooth and bright. Metallographic detection shows that there is no residual, embedded and semi-sintered additive manufacturing powder. The roughness test shows that the outer side of the inner flow channel turn is Ra1.1μm, and the inner side of the turn is Ra1.5μm, reaching the target requirement of roughness Ra<3.2μm after polishing and the difference in roughness between the inner and outer sides of the turn is greater than 60%.

[0064] Example 2: This example is the finishing of a two-dimensional O-shaped inner flow channel sample. The inner flow channel to be finished is manufactured using laser additive manufacturing technology. The structure is a fine inner flow channel with a diameter D = 1.5 mm, a total flow channel length = 160 mm, an aspect ratio of about greater than 100:1, an O-shaped bend structure, and a material of high-temperature alloy. The original roughness Ra of the inner flow channel is about 7.4 (non-overhanging surface) ~ 11.3 μm (overhanging surface). The specific processing method is as follows:

[0065] Step 1: Prepare shear-thinning water-based two-phase flow polishing media. The order and amount of adding each substance are as follows: deionized water, silicon carbide abrasive (50 g / L), dispersant (polyvinyl alcohol addition is 7-10 g / L, sodium silicate addition is 12-15 g / L, polystyrene addition is 5-8 g / L), viscosity enhancer (3 g / L), rust inhibitor (1 g / L), defoamer (5 g / L), lubricant (5 g / L) and antifreeze (2 g / L).

[0066] Step 2: Place the shear-thinning polishing medium prepared in the first step into the material cylinder and set the plunger pump pressure to 51Mpa.

[0067] Step 3: Stop processing when the flow rate reaches 50%.

[0068] Step 4: First use a high-pressure air gun to blow out the high-speed water-based two-phase flow polishing medium inside the fine inner flow channel, then use ultrasonic immersion cleaning, and then rinse with pure water several times and then dry.

[0069] like Figure 4As shown (the left figure in the drawing is the upper surface and the right figure is the lower surface), the machined two-dimensional O-shaped internal flow channel specimen is sectioned, and the flattening close to the machined surface and the significant finishing effect can be clearly seen on the inner surface of the flow channel, and the surface is smooth and bright. After metallographic inspection, there is no residual, inlaid or semi-sintered additive manufacturing powder. After roughness inspection, the roughness Ra of the overhanging surface of the O-shaped internal flow channel is 3.1 μm, and the roughness Ra of the non-overhanging surface is 1.8 μm, meeting the target requirements of roughness Ra < 3.2 μm and the roughness difference between the polished upper and lower surfaces with a large original difference being greater than 60%. In the substance addition sequence, the dispersant should be added after deionized water and abrasive grains and before other additives. The reason is that the dispersant belongs to a surfactant, and most of the subsequent additives are organic substances. Adding the surfactant first and then other additives can significantly increase the dissolution rate of the subsequent organic additives.

[0070] The present invention also provides a method for measuring the shear-thinning property, which measures the shear-thinning property of the above water-based two-phase flow polishing medium. The method for measuring the shear-thinning property includes the following steps:

[0071] Measure the pressure value p of the water-based two-phase flow polishing medium at the near-wall surface of the internal flow channel of the workpiece 2 and the pressure value p of the water-based two-phase flow polishing medium at the center of the internal flow channel 1 ;

[0072] According to the formula (p 1 - p 2 ) / r, calculate the numerical value of the flow field pressure gradient from the center to the near-wall surface of the internal flow channel, where r is the radius of the internal flow channel;

[0073] When the numerical value of the flow field pressure gradient is greater than the first set threshold value, it is determined that the shear-thinning property of the water-based two-phase flow polishing medium is significant. The first set threshold value can be 0.5 Mpa / mm. Of course, the first set threshold value in this embodiment can be adjusted according to different requirements.

[0074] Specifically, a piezoelectric sensor contact piece is used to closely adhere to the outer wall surface of the internal flow channel to measure the pressure value p of the water-based two-phase flow polishing medium at the near-wall surface of the internal flow channel of the workpiece 2 . A piezoelectric sensor probe is used to measure the pressure value p of the water-based two-phase flow polishing medium at the center of the internal flow channel 1 .

[0075] In a specific embodiment, the internal flow channel specimen selects a CoCrMo superalloy internal flow channel with a diameter of 3 mm and a length-diameter ratio of 100:1. The hydraulic drive pressure of the water-based two-phase flow device is 50 Mpa, and the hydraulic drive mode is a constant pressure mode. The water-based two-phase flow polishing medium is selected as a dispersant without abrasive grains and with different mass concentrations. The reason for the two-phase flow polishing medium to be measured without abrasive grains is that adding abrasive grains will cause abrasive erosion damage to the piezoelectric sensor contact piece and the piezoelectric sensor probe.

[0076] The present invention also provides a method for measuring the shear thinning property, which measures the shear thinning property of the above water-based two-phase flow polishing medium. The method for measuring the shear thinning property includes the following steps:

[0077] Measure the current surface roughness R of the inner side of the inner flow path bend of the workpiece, a1 , the original surface roughness Ra of the inner side of the inner flow path bend 1 , the current surface roughness R of the outer side of the inner flow path bend of the workpiece, a2 and the original surface roughness Ra of the outer side of the inner flow path bend of the workpiece 2 ;

[0078] Calculate the percentage reduction of the difference in roughness between the inner and outer sides of the inner flow path bend after polishing compared to the difference in roughness between the inner and outer sides of the original bend through a formula, that is

[0079] When this percentage is greater than the second threshold, it is determined that the shear thinning property of the water-based two-phase flow polishing medium is significant.

[0080] The shear thinning effect can be characterized by the percentage reduction of the difference in roughness between the upper and lower surfaces after polishing of the inner flow path formed by additive manufacturing compared to the difference in roughness between the original upper and lower surfaces, and the percentage reduction of the difference in roughness between the inner and outer sides after polishing of the inner and outer sides of the bend compared to the difference in roughness between the original inner and outer sides, and it can be achieved that this percentage is greater than the second threshold (generally selected as 60%). The larger this percentage, the more significant the shear thinning property.

[0081] Specifically, when the pressure gradient value is 0.63 - 0.91 Mpa / mm, the percentage reduction in the roughness difference between the upper and lower surfaces of the additive manufacturing inner flow channel after polishing compared to the original roughness difference between the upper and lower surfaces, and the percentage reduction in the roughness difference between the inner and outer sides of the turn after polishing compared to the original roughness difference between the inner and outer sides are both greater than 60%, and this percentage value increases with the increase in the pressure gradient value; when the pressure gradient value < 0.63, the percentage reduction in the roughness difference between the upper and lower surfaces of the additive manufacturing inner flow channel after polishing compared to the original roughness difference between the upper and lower surfaces, and the percentage reduction in the roughness difference between the inner and outer sides of the turn after polishing compared to the original roughness difference between the inner and outer sides are both less than 60%, and this percentage value decreases with the decrease in the pressure gradient value. The reason is that the shear-thinning non-Newtonian fluid has the characteristics that the pressure in the central flow field region of the inner flow channel is relatively high, and the flow field pressure gradually decreases from the central region along the vertical direction near the wall surface. The particle velocity near the wall surface of the inner flow channel moves faster, and the particle velocity in the center of the inner flow channel moves slower. It is equivalent to the central flow field of the inner flow channel continuously applying a thrust of abrasive particles to both sides through the pressure gradient and the difference in abrasive particle concentration distribution in the vertical direction, causing the abrasive particles to migrate and accumulate from the center of the inner flow channel to the near-wall surfaces on both sides, which is conducive to increasing the thrust generated by the shear-thinning of the abrasive particles at the turn of the inner flow channel and pushing and accumulating them on the inner and outer side walls. It can overcome the problem that the abrasive particles are mainly distributed on the outer side wall of the turn due to the differences in mass density and inertia between the solid phase of the abrasive particles and the water-based liquid phase, increase the distribution of the abrasive particles on the inner side of the turning region of the micro-inner flow channel, and improve and reduce the difference in the polishing effect between the outer side wall and the inner side wall of the turning region of the inner flow channel. In addition, since there are more abrasive particles distributed on the lower surface of the inner flow channel and the outer side of the turn, the abrasive particles are more likely to diffuse from the region with a higher concentration gradient to the region with fewer abrasive particles on the upper surface of the inner flow channel and the inner side of the turn, enhancing the polishing effect on the upper surface of the inner flow channel and the inner side of the turn, and improving and reducing the difference in roughness after polishing between the upper and lower surfaces of the inner flow channel and between the inner and outer sides of the turn.

[0082] The present invention further provides a method for measuring the shear-thinning characteristics to measure the shear-thinning characteristics of the above water-based two-phase flow polishing medium. The method for measuring the shear-thinning characteristics includes the following steps:

[0083] Select the sheared water-based two-phase flow polishing medium and the unsheared water-based two-phase flow polishing medium respectively for polishing operations, and obtain the reduction ratio of the first driving pressure difference and the reduction ratio of the second driving pressure difference under the same polishing time and the same polishing effect;

[0084] Compare the reduction ratio of the first driving pressure difference with the reduction ratio of the second driving pressure difference. When the reduction ratio of the first driving pressure difference is greater than the reduction ratio of the second driving pressure difference, it is determined that the shear-thinning characteristics of the sheared water-based two-phase flow polishing medium are more significant than those of the unsheared water-based two-phase flow polishing medium.

[0085] The shear thinning effect is characterized by the proportion of the reduction in the driving pressure difference under the same time and polishing effect, and a reduction of 16% - 23% in the driving pressure difference can be achieved. The more the driving pressure difference is reduced under the same time and polishing effect, the more significant the shear thinning property. Specifically, when the pressure gradient value is 0.63 - 0.91 Mpa / mm, under the same polishing effect, the driving pressure difference can be reduced by 16% - 23% compared with the water-based two-phase flow polishing medium without shear thinning. And without affecting the final polishing effect, the driving pressure difference decreases with the increase of the pressure gradient value; when the pressure gradient value < 0.63, the reduction in the driving pressure difference < 16%, and the driving pressure difference increases with the decrease of the pressure gradient value. The reduction in the feed driving pressure difference will reduce the flow rate of the water-based two-phase flow polishing medium and the inertia of the abrasive grains, thereby further alleviating the difference in surface roughness after polishing between the upper and lower sides of the inner flow channel and the inner and outer sides of the turning area.

[0086] The present invention also provides a method for measuring the shear thinning property, which measures the shear thinning property of the above-mentioned water-based two-phase flow polishing medium. The method for measuring the shear thinning property includes the following steps:

[0087] Select the sheared water-based two-phase flow polishing medium and the unsheared water-based two-phase flow polishing medium respectively for polishing operations, and under the same polishing effect, obtain the first processing time and the second processing time;

[0088] Compare the first processing time with the second processing time. When the first processing time is less than the second processing time, it is determined that the shear thinning property of the sheared water-based two-phase flow polishing medium is more significant than that of the unsheared water-based two-phase flow polishing medium.

[0089] The shear thinning effect can also be characterized by the reduction in the processing time under the same driving pressure difference and polishing effect, and a reduction of 80% to 270% in time can be achieved. The more the processing time is reduced under the same driving pressure difference and polishing effect, the more significant the shear thinning property. The reason is that for shear thinning non-Newtonian fluids, as the driving pressure and flow shear rate increase, the shear stress first increases rapidly, then increases slowly and tends to be stable. For non-shear thinning non-Newtonian fluids, as the driving pressure and flow shear rate increase, the shear stress shows a downward trend. Therefore, under high shear rate conditions, through the shear thinning rheological property, a relatively stable shear stress of the abrasive grains on the wall surface can be maintained, thereby improving the polishing efficiency of the water-based two-phase flow polishing medium on the inner flow channel wall surface; in addition, in the shear thinning non-Newtonian fluid, the central flow field of the inner flow channel continuously applies the abrasive grains to migrate and aggregate from the center of the inner flow channel to the side walls through the vertical pressure gradient, which will effectively increase the distribution probability and collision frequency of the abrasive grains on the inner flow channel wall surface, especially on the rough wall surface, further contributing to the efficient micro-cutting polishing of the flow channel wall surface, and the efficiency is significantly improved compared with the high-speed water-based two-phase flow polishing medium without shear thinning.

[0090] As described above, it is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A water-based two-phase flow polishing medium, characterized in that: In parts by weight, the water-based two-phase flow polishing medium comprises 89.1% to 94% of deionized water, 2% to 6% of silicon carbide abrasive grains, and 2.4% to 3.3% of a dispersant.

2. The water-based two-phase flow polishing medium according to claim 1, characterized in that: The dispersant includes one or a combination of polyvinyl alcohol, sodium silicate and polystyrene.

3. The water-based two-phase flow polishing medium according to claim 2, characterized in that: The dispersant comprises polyvinyl alcohol, sodium silicate and polystyrene, wherein the polyvinyl alcohol is 0.7% to 1%, the sodium silicate is 1.2% to 1.5%, and the polystyrene is 0.5% to 0.8%.

4. The water-based two-phase flow polishing medium according to claim 3, characterized in that: The water-based two-phase flow polishing medium also includes 0.2% to 0.3% of a viscosity enhancer, 0.05% to 0.1% of a rust preventer, 0.4% to 0.5% of a defoamer, 0.4% to 0.5% of a lubricant, and 0.1% to 0.2% of an antifreeze agent.

5. A polishing method, using the water-based two-phase flow polishing medium according to any one of claims 1 to 4, characterized in that: The polishing method comprises: Step 1: Prepare water-based two-phase flow polishing medium; Step 2: placing the prepared water-based two-phase flow polishing medium in a material cylinder, adjusting the pressure to a first set value and starting the plunger pump to perform a polishing operation on the workpiece; Step 3: When the flow rate of the polishing operation reaches the second set value, the processing is stopped; Step 4: Clean and dry the polished workpiece.

6. The polishing method according to claim 5, characterized in that: The step 1: preparing a water-based two-phase flow polishing medium is specifically as follows: the order of adding the components in the water-based two-phase flow polishing medium is: deionized water, silicon carbide abrasive particles, dispersant, viscosity enhancer, rust inhibitor, defoamer, lubricant and antifreeze.

7. The polishing method according to claim 6, characterized in that: The first setting value is 45-55 MPa; the second setting value is 45%-55%.

8. The polishing method according to claim 6, characterized in that: The fourth step of cleaning and drying the polished workpiece is as follows: The water-based two-phase flow polishing medium inside the micro-channel of the polished workpiece is blown out with a high-pressure air gun, then cleaned by ultrasonic immersion, rinsed with pure water several times and then dried.

9. A method for measuring shear thinning characteristics, for measuring the shear thinning characteristics of the water-based two-phase flow polishing medium according to any one of claims 1 to 4, characterized in that: The shear thinning property determination method comprises the following steps: Measure the pressure value p1 of the water-based two-phase flow polishing medium at the center of the inner flow channel of the workpiece and the pressure value p2 of the water-based two-phase flow polishing medium near the wall of the inner flow channel; The flow field pressure gradient value from the center of the inner flow channel to the near wall is calculated according to the formula (p1-p2) / r, where r is the radius of the inner flow channel; When the flow field pressure gradient value is greater than the first set threshold value, it is determined that the shear thinning characteristic of the water-based two-phase flow polishing medium is significant.

10. The shear thinning property measurement method according to claim 9, characterized in that: The piezoelectric sensor probe is used to measure the pressure value p1 of the water-based two-phase flow polishing medium at the center of the inner flow channel.

11. The shear thinning property measurement method according to claim 9, characterized in that: A piezoelectric sensor contact piece is used to closely contact the outer wall of the inner flow channel to measure the pressure value p2 of the water-based two-phase flow polishing medium near the wall of the inner flow channel of the workpiece.

12. A method for measuring shear thinning characteristics, for measuring the shear thinning characteristics of the water-based two-phase flow polishing medium according to any one of claims 1 to 4, characterized in that: The shear thinning property determination method comprises the following steps: Measure the current surface roughness R on the inner side of the turning point of the flow channel in the workpiece. a1 , the original surface roughness Ra1 of the inner side of the inner flow channel bend, the current surface roughness R of the outer side of the inner flow channel bend of the workpiece, a2 and the original surface roughness Ra2 of the outer side of the turning point of the flow channel in the workpiece; The formula is used to calculate the percentage reduction of the difference in roughness between the inside and outside of the turn after polishing compared to the difference in roughness between the inside and outside of the original turn. When the percentage reduction of the difference in roughness between the inner and outer sides of the turn after polishing compared with the difference in roughness between the inner and outer sides of the original turn is greater than a second threshold, it is determined that the shear thinning property of the water-based two-phase flow polishing medium is significant.

13. A method for measuring shear thinning characteristics, for measuring the shear thinning characteristics of the water-based two-phase flow polishing medium according to any one of claims 1 to 4, characterized in that: The shear thinning property determination method comprises the following steps: Selecting a shear-thinned water-based two-phase flow polishing medium and a non-shear-thinned water-based two-phase flow polishing medium to perform polishing operations respectively, and obtaining a ratio of a first driving pressure difference reduction and a ratio of a second driving pressure difference reduction under the same polishing time and the same polishing effect; The ratio of the first driving pressure difference reduction is compared with the ratio of the second driving pressure difference reduction. When the ratio of the first driving pressure difference reduction is greater than the ratio of the second driving pressure difference reduction, the shear thinning characteristics of the shear-thinning water-based two-phase flow polishing medium are determined to be more significant than the shear thinning characteristics of the non-shear-thinning water-based two-phase flow polishing medium.

14. A method for measuring shear thinning characteristics, for measuring the shear thinning characteristics of the water-based two-phase flow polishing medium according to any one of claims 1 to 4, characterized in that: The shear thinning property determination method comprises the following steps: Selecting a shear-thinned water-based two-phase flow polishing medium and a non-shear-thinned water-based two-phase flow polishing medium to perform polishing operations respectively, and obtaining a first processing time and a second processing time under the same polishing effect; The first processing time is compared with the second processing time. When the first processing time is less than the second processing time, the shear thinning characteristics of the shear-thinned water-based two-phase flow polishing medium are determined to be more significant than the shear thinning characteristics of the non-shear-thinned water-based two-phase flow polishing medium.

Images