A design method for viscoelastic medium abrasive with controllable material removal

Abstract

The application provides a controllable material removal viscoelastic medium abrasive design method, relates to the abrasive flow finishing process technical field, and is based on the material performance and size precision requirement of a target part processing surface, the processing allowance of a previous process, a preset extrusion pressure and a processing time length, the rheological property, the flow rate and the active abrasive particle concentration of the expected abrasive medium with an ideal processing efficiency generated by theoretical calculation of a material removal model, the flow behavior of the medium in a channel with different structure sizes through fluid simulation analysis, the channel structure size with uniform flow effect of the medium, the design of a matched clamp, the proportion relationship of each component in the abrasive medium determined by the rheological property and the active abrasive particle concentration, the controllable material removal viscoelastic abrasive medium, the precise and efficient finishing of a complex target structure, and the reduction of the dependence on personal experience in the design, the selection of the abrasive medium and the designation of the processing parameters.

Description

Technical Field

[0001] This invention belongs to the field of abrasive finishing technology, and more specifically, it relates to a viscoelastic abrasive design method for controllable material removal. Background Technology

[0002] Currently, complex structural components are widely used in aerospace, automotive, and medical device fields, such as turbine blades and their film cooling holes, engine fuel nozzles and high-pressure common rail pipes, and microneedle arrays. Due to the limitations of their complex shapes, defects such as burrs and cracks, which seriously affect the safety and precision of the components, are inevitably produced when using mechanical removal (precision milling, precision grinding, etc.) and material melting removal (EDM, laser processing, etc.) to prepare these structures. Although traditional finishing processes such as precision grinding, electrolytic machining, and magnetic abrasive polishing are widely used to remove these defects in simple structures, they cannot effectively remove these defects in complex structures, or the processing efficiency is low and the removal cost is high. Therefore, it is urgent to explore a special finishing process for the efficient processing of these micro-complex structures and precision complex surfaces.

[0003] Leveraging the high accessibility of fluids, abrasive flow machining technology has gradually gained attention and is widely used in the finishing of irregularly shaped surfaces and complex pipes. Under extrusion pressure, an abrasive medium containing mixed hard abrasive particles can reciprocate within a defined channel formed by a fixture and workpiece, thereby producing the desired machining effect. The core component responsible for this machining effect is a viscoelastic abrasive medium composed of hard abrasive particles, a polymer matrix, and additives. The elastic component within the medium applies a normal force to the abrasive particles, forcing them to embed into the machined surface and inducing surface plastic deformation. The viscous component, under external extrusion pressure, drives the movement of the abrasive particles, causing the plastic deformation to extend across the entire surface, thus producing the desired material removal effect. For the finishing of precision parts, strict control of material removal is necessary. Although many studies have established material removal models for abrasive flows, most are based on surface deformation and cannot accurately describe the material removal performance of specific abrasive media.

[0004] To ensure uniform machining results on the workpiece surface, the primary prerequisite is to ensure that the abrasive medium completely fills the space defined by the fixture and workpiece. For workpieces with different structures and feature sizes, such as large sleeves, high-precision gears, and small valve assembly channels and micro-injection holes in fuel nozzles, the proportions of each component in the abrasive medium need to be adjusted to fill the entire machining space and flow smoothly within the machining area, thereby meeting the finishing requirements of parts with specific structures and sizes. Therefore, the overall flow behavior of the medium directly affects the machining effect and uniformity. Due to the limitations of the machining structure's integrity, it is currently impossible to directly monitor the flow behavior of the medium within the fixture-workpiece channel. Therefore, CFD simulation is often used for intuitive visualization. However, because the abrasive medium is a special viscoelastic fluid containing continuous and discrete two-phase components, its calculation is extremely complex and divergent, failing to obtain the expected results. Therefore, it is often simplified as a Newtonian fluid for simulation analysis to reduce computational difficulty, but the simulation accuracy is low and cannot accurately describe the flow behavior of the medium within different feature sizes and structures.

[0005] In summary, for precision finishing of parts with different feature sizes and structures, the processing performance and flow properties of abrasive media must be adapted to the structure and size to meet the processing accuracy and efficiency requirements of the parts. A literature search has revealed no design method for abrasive media composition based on non-Newtonian fluid flow and its own material removal properties. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for designing viscoelastic abrasive media with controllable material removal.

[0007] A method for designing viscoelastic abrasive media with controllable material removal includes the following steps:

[0008] S1: Pre-treatment testing and parameter selection of the parts to be processed. Test the surface material properties of the parts to be processed using a microhardness tester and a tensile testing machine. Test the characteristic structural dimensions using a laser diameter gauge or a coordinate measuring machine. Determine the processing accuracy requirements based on the part design drawings. Select the appropriate type and size of hard abrasive based on the above test results.

[0009] S2: Based on the machining allowance of the preceding process in the component processing flow, which is the casting, forging or cutting process of the component, a general abrasive media material removal model is used. The model is based on the flow interaction between the continuous polymer matrix phase and the hard abrasive particles in the abrasive media, combined with the storage modulus, shear thinning characteristics and flow channel extrusion pressure difference to calculate the processing efficiency and obtain the storage modulus, flow rate and active abrasive particle concentration parameters of the abrasive media under the optimal processing efficiency.

[0010] S3: By utilizing the variation law of the energy storage modulus in the abrasive medium with the mass fraction of polymer melt, the mass ratio of polymer melt in the abrasive medium is determined, and the mass ratio of hard abrasive particles in the medium is obtained by using the number of active abrasive particles and the processing allowance of the previous process.

[0011] S4: Select a suitable polymer melt, wherein the suitable polymer melt is a polyurethane-based melt or an epoxy resin-based melt with a viscosity of 500-5000 mPa·s and no chemical reaction with the component material. Mix the selected type, particle size and mass ratio of hard abrasive particles evenly in it, add the remaining mass fraction of additives, stir evenly at a temperature of 60-120℃, and after standing for 12 hours, obtain a viscoelastic abrasive for the finishing of the target component.

[0012] S5: The properties of the prepared abrasive media are analyzed using a rheometer to detect the creep properties, stress relaxation behavior, dynamic viscoelastic properties and shear thinning characteristics of the media, and obtain the corresponding curves to comprehensively characterize the processing performance and flow properties of the abrasive media.

[0013] S6: The flow behavior of abrasive media is simulated and analyzed using existing non-Newtonian viscous fluid constitutive models and differential viscoelastic models. The pressure distribution, velocity distribution, shear rate distribution and wall shear rate distribution of abrasive media in the processing channel are quantitatively displayed, further reflecting the flow performance and processing performance of abrasive media.

[0014] S7: Analyze the law of medium flow behavior with the change of channel structure and size, determine the channel structure parameters that can produce uniform flow, including channel inner diameter, length, inlet and outlet angles and size range. Based on the determined channel structure parameters (including channel inner diameter, length, inlet and outlet angles and size range), guide the design of matching processing fixtures to achieve precision finishing of target parts.

[0015] Preferably, the surface material properties of the parts to be processed include surface hardness and tensile strength, and the processing accuracy requirements include the shape accuracy and dimensional accuracy of the channel structure, with surface roughness as the core control indicator.

[0016] Preferably, the material properties of the target component are tested using a microhardness tester and a tensile testing machine.

[0017] Preferably, for materials with a Rockwell hardness below 60 HRC, silicon carbide abrasives are used for processing; for materials with a Rockwell hardness above 60 HRC, diamond abrasives or cubic boron nitride abrasives are used.

[0018] Preferably, the general abrasive media material removal model is based on the interaction between the continuous polymer matrix phase and the hard abrasive particles in the abrasive media during the flow process. It combines the storage modulus of the abrasive media, the shear thinning characteristics and the extrusion pressure difference in the flow channel to construct a mechanical theoretical model of the hard abrasive particles. It also fully considers the number of active abrasive particles participating in the wall processing at the wall surface to construct the abrasive media material removal model.

[0019] Preferably, the abrasive media mainly consists of polymer melt, hard abrasive particles and additives, wherein the additives are mainly small molecule plasticizers, which have a monomer structure similar to that of the polymer melt, and are used to reduce the overall viscosity of the media and improve the overall fluidity of the abrasive media.

[0020] Preferably, the constitutive models for non-Newtonian viscous fluids include the PowerLaw constitutive model, the Bird-Carreau constitutive model, the Bingham constitutive model, the Herschel-Bulkley constitutive model, the Cross constitutive model, and the Carreau-Yasuda constitutive model; the differential viscoelastic constitutive models include the Maxwell constitutive model, the Oldroyd-B constitutive model, the White-Metzner constitutive model, the PhanThien-Tanner constitutive model, the Giesekus constitutive model, the FENE-P constitutive model, and the Leonov constitutive model.

[0021] Preferably, for pore structures at the millimeter level and below or slit structures at the micrometer level and below, a non-Newtonian fluid constitutive model is selected for flow behavior simulation, with the Bird-Carreau constitutive model or the Carreau-Yasuda constitutive model being preferred; for pore structures at the tens of millimeters level and above or slit structures at the millimeter level, the Giesekus constitutive model or the Leonov constitutive model in the differential viscoelastic constitutive model are selected.

[0022] Preferably, uniform medium flow means that the pressure, velocity, and wall shear stress of the medium are uniformly distributed in the workpiece-fixture flow channel, and the flow velocity is uniformly distributed at any position on the entire machining surface, so as to reduce the risk of uneven machining.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] In this invention, based on the material properties, structural dimensions, and machining accuracy requirements of the target component, the type and size of hard abrasive grains can be precisely selected, and the proportions of each component within the abrasive medium can be determined. This makes the abrasive medium highly compatible with the machining requirements of specific components. Compared to the traditional method of selecting abrasive media based solely on personal experience, this greatly improves the targeting and effectiveness of the machining process, ensuring that precise and efficient finishing of complex target structures is achieved while maintaining the original dimensional and shape accuracy.

[0025] In this invention, a general abrasive media material removal model is used to theoretically calculate key parameters of the media under optimal processing efficiency, such as storage modulus, flow rate, and concentration of active abrasive particles. This not only allows for theoretical optimization of the set equipment process parameters, reducing the cost and time of process parameter optimization experiments, but also enables real-time prediction of the unit material removal rate of the abrasive media, allowing for precise adjustment of the material removal amount. Comparative experimental measurements have verified that the error is within 5%, effectively avoiding over-processing, meeting the requirements for high-precision surface quality processing, and improving production efficiency.

[0026] In this invention, a comprehensive analysis of the abrasive media's properties is conducted using a rheometer, and its flow behavior is simulated using a non-Newtonian viscous fluid constitutive model and a differential viscoelastic model. This allows for a deep understanding of the distribution of pressure, velocity, and shear rate of the abrasive media within the processing channel. Based on this, the channel structure and dimensions that enable uniform media flow can be designed according to the variation of media flow behavior with channel structure and dimensions, thereby guiding the design of matching fixtures. This ensures the uniformity of the abrasive media during processing, effectively improving processing quality and reducing processing defects caused by uneven media flow. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall process of the present invention;

[0028] Figure 2 This is a schematic diagram of the mechanical theoretical model of the hard abrasive grains in this invention;

[0029] Figure 3 This is a schematic diagram of the process of embedding abrasive tips into the machined surface in this invention. Detailed Implementation

[0030] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0031] Please see Figures 1-3 This invention provides a method for designing viscoelastic abrasive media with controllable material removal, comprising the following steps:

[0032] The first step is to test the surface material properties (surface hardness, tensile strength), characteristic structural dimensions, and machining accuracy requirements (shape accuracy and dimensional accuracy) of the parts to be processed, and then select the appropriate type and size of hard abrasive grains. Generally, for materials with a Rockwell hardness below 60 HRC, silicon carbide abrasive grains are usually selected for processing. For materials with a Rockwell hardness above 60 HRC, diamond abrasive grains or cubic boron nitride abrasive grains are generally selected.

[0033] The second step involves calculating the processing efficiency based on the machining allowance of the preceding process in the component processing flow, which is the casting, forging, or cutting process of the component. This process is based on the flow interaction between the continuous polymer matrix phase and the hard abrasive particles in the abrasive medium, combined with the storage modulus, shear thinning characteristics, and flow channel extrusion pressure difference. The result is the optimal processing efficiency parameters for the storage modulus, flow rate, and active abrasive particle concentration of the abrasive medium.

[0034] The general abrasive media material removal model is based on the interaction between the continuous polymer matrix phase and the hard abrasive particles in the abrasive media during the flow process. It combines the storage modulus of the abrasive media, shear thinning characteristics, and extrusion pressure difference within the flow channel to construct a mechanical theoretical model of the hard abrasive particles, as shown in equations (1) and (2). Figure 2 As shown in the figure. Then, taking into full account the number of active abrasive particles participating in the wall surface processing (as shown in equation (3)), an abrasive media material removal model is constructed, as shown in equation (4).

[0035] The above mechanical model is shown below (including the force expressions for normal and tangential forces):

[0036] Tangential force: (1)

[0037] Normal force: (2)

[0038] Among them, F pg For pressure gradient force, ;

[0039] F τw The shear stress experienced by the abrasive grains. ;

[0040] F d For drag force, ;

[0041] F f The friction force experienced by the abrasive grains. ;

[0042] F ps F is the average normal pressure exerted on the abrasive grains. ps =P i ×A grain ;

[0043] F e The elastic force of the medium acting on the abrasive grains. ;

[0044] F s For Saffman lift, .

[0045] Number of active abrasive particles: (3)

[0046] in, C s This represents the volume fraction of abrasive particles within the medium. V ag This represents the volume fraction of active abrasive particles at the wall surface. V sg This represents the volume fraction of a single abrasive grain.

[0047] The calculation model for the above material removal is shown below:

[0048] (4)

[0049] Where Nag is the number of active abrasive grains; θ is the average angle of the abrasive grain tip, which can be obtained by observing the morphology of hard abrasive grains using an optical microscope or an electron microscope; σs is the yield strength of the material to be processed; H is the average height of the abrasive grain; Agrain is the maximum projected area of ​​the abrasive grain; and uz is the average flow velocity of the medium.

[0050] The third step involves determining the mass percentage of polymer melt within the abrasive medium by utilizing the variation of the storage modulus within the abrasive medium with the mass fraction of polymer melt. Then, using the number of active abrasive particles and the machining allowance from the previous process, the mass percentage of hard abrasive particles within the medium is calculated.

[0051] The abrasive medium mainly consists of polymer melt, hard abrasive particles, and additives.

[0052] The storage modulus of the abrasive medium is a direct parameter characterizing the overall elastic strength of the medium. The overall elasticity of the medium comes directly from the polymer melt. Therefore, the mass ratio of the polymer melt in the medium directly determines the overall elastic strength of the medium, that is, the size of the storage modulus. There is a certain proportional relationship between the mass ratio of the polymer melt and the overall storage modulus of the medium. Therefore, the mass ratio of the polymer melt in the medium can be obtained by calculating the storage modulus of the medium.

[0053] The number of active abrasive particles refers to the number of abrasive particles that participate in the removal of the target part surface. It is directly related to the machining allowance of the previous process, and the relationship between the two is shown in equation (5).

[0054] (5)

[0055] Where Vag is the volume of active abrasive particles, and Vsg is the volume of a single abrasive particle. Figure 3 Taking the slit channel shown as an example, the calculation model of the active abrasive particle concentration volume Vag is shown in equation (6).

[0056] (6)

[0057] Where h is the embedding depth of the abrasive grains on the machined surface.

[0058] Therefore, the mass ratio of hard abrasive particles in the medium is as described in equation (7).

[0059] (7)

[0060] The fifth step involves selecting a suitable polymer melt, which is a polyurethane-based melt or an epoxy resin-based melt with a viscosity of 500-5000 mPa·s that does not chemically react with the component material. The selected type, particle size, and mass ratio of hard abrasive particles are uniformly mixed into the melt, and the remaining mass fraction of additives is added. The mixture is stirred evenly at a temperature of 60-120℃ and allowed to stand for 12 hours to obtain a viscoelastic abrasive for the finishing of the target component.

[0061] Its additives are mainly small-molecule plasticizers, which are similar to the monomer structure of polymer melt. This similar structure is conducive to the additives penetrating into the interior of polymer melt, dispersing polymer molecular chains, thereby reducing the overall viscosity of the medium and improving the overall fluidity of the abrasive medium.

[0062] The sixth step involves using a rheometer to analyze the properties of the prepared abrasive media, detecting its creep properties, stress relaxation behavior, dynamic viscoelastic properties, and shear thinning characteristics. This yields the corresponding creep, relaxation, storage modulus, dissipation modulus, and shear viscosity curves, comprehensively characterizing the processing and flow properties of the abrasive media.

[0063] The creep curve can quantitatively obtain the proportion of elastic and viscous components in the abrasive medium, thereby providing a preliminary qualitative characterization of the processing and flow properties of the abrasive medium.

[0064] The stress relaxation behavior is the ability of an abrasive medium to recover from a non-equilibrium state to an equilibrium state after being subjected to external disturbances. It can gradually release the stress generated by external strain, and the time to recover equilibrium is the relaxation time of the medium.

[0065] The dynamic viscoelastic properties are mainly characterized by the storage modulus and the dissipation modulus. The storage modulus reflects the elasticity of the medium and can quantitatively characterize the elastic force that the medium can exert on hard abrasive grains. The viscous component can quantitatively reflect the flow properties of the medium within a certain angular frequency range to a certain extent.

[0066] The shear thinning characteristic quantitatively characterizes the viscosity change of abrasive media under the action of external shear rate, and can reflect the potential of the flow performance of abrasive media to a certain extent. As a typical non-Newtonian fluid, the shear viscosity curve of abrasive media shows an exponential decreasing trend with increasing shear rate.

[0067] The seventh step involves using existing constitutive models of non-Newtonian viscous fluids and differential viscoelastic models to simulate and analyze the flow behavior of abrasive media. This quantitatively demonstrates the pressure distribution, velocity distribution, shear rate distribution, and wall shear rate distribution of the abrasive media within the processing channel, further reflecting the flow properties and processing performance of the abrasive media.

[0068] The constitutive models for non-Newtonian viscous fluids mainly include the Power Law constitutive model, the Bird-Carreau constitutive model, the Bingham constitutive model, the Herschel-Bulkley constitutive model, the Cross constitutive model, and the Carreau-Yasuda constitutive model. The non-Newtonian fluid exponents, zero-shear viscosity, and infinite-shear viscosity of each of these models can be obtained by fitting the shear viscosity curve of the abrasive medium using the corresponding model. The relaxation time corresponds to the time it takes for the relaxation modulus of the medium to stabilize.

[0069] The differential viscoelastic constitutive models mainly include the Maxwell constitutive model, the Oldroyd-B constitutive model, the White-Metzner constitutive model, the Phan Thien-Tanner constitutive model, the Giesekus constitutive model, the FENE-P constitutive model, and the Leonov constitutive model. The parameters of each of these constitutive models can be obtained by fitting the storage modulus and dissipation modulus of the abrasive medium using the Polyflow software's built-in Polymat data analysis module.

[0070] The key parameters of the constitutive model can be obtained by fitting the shear viscosity curve or the storage modulus and dissipation modulus.

[0071] The eighth step is to analyze the law of change of medium flow behavior with the structure and size of the flow channel, and determine the flow channel structure parameters that can produce uniform flow, including the inner diameter, length, inlet and outlet angles and size range of the flow channel. Based on these parameters, the design of matching machining fixtures is guided to achieve precision finishing of the target parts.

[0072] Uniform flow of the medium refers to the uniform distribution of pressure, velocity, and wall shear stress of the medium within the workpiece-fixture flow channel. In particular, the velocity must be uniformly distributed at any position on the entire machining surface; otherwise, the risk of uneven machining may increase.

[0073] This method, based on the material properties, structural dimensions, and machining accuracy requirements of the target component, utilizes a general abrasive media material removal model for optimal calculation. This yields the optimal storage modulus, flow rate, and number of active abrasive particles for optimal efficiency. By leveraging the ratio of storage modulus to polymer melt mass fraction, the polymer melt mass fraction within the media is determined. The mass fraction of hard abrasive particles is then calculated using the number of active abrasive particles. This allows for the preparation of an abrasive media suitable for the target component's structure and accuracy requirements. The rheological properties of the abrasive media are characterized, and fluid simulation analysis is used to analyze its flow behavior within the workpiece-fixture channel. This analysis guides the design of the matching fixture, achieving an ideal high-precision surface while maintaining the original dimensional and shape accuracy. In existing technologies, abrasive media selection relies almost entirely on personal experience and intuition, making it impossible to accurately determine the media material removal rate. This can easily lead to over-machining of the structure being processed, or even damage to its original dimensional accuracy and tolerances. This method can predict the unit material removal rate of abrasive media in real time. Comparative experimental measurements show that its error is within 5%. By adjusting the processing time, the amount of material removed can be precisely adjusted to meet the requirements of high-precision surface quality processing.

[0074] The present invention will now be described in detail with reference to specific embodiments. The following examples are implemented under the premise of the technical solution of the present invention, providing detailed implementation methods and specific operating procedures, which will help those skilled in the art to further understand the present invention. It should be noted that the scope of protection of the present invention is not limited to the following embodiments; any adjustments and improvements made under the concept of the present invention are all within the scope of protection of the present invention.

[0075] Example 1:

[0076] For the micro-injection orifices of fuel nozzles in high-pressure common rail fuel injection systems, the micro-ignition process used in preparing these orifices can cause a remelted layer on the inner surface due to the limitations of their micro-size. Furthermore, the orifice shape and injection flow rate of the prepared orifices cannot meet the current enterprise's requirements. Therefore, an abrasive finishing process is needed to reshape the dimensions to meet these requirements. The abrasive media preparation and testing methods are as follows:

[0077] Step 1: Requirements for fuel nozzle orifice material properties, structural dimensions, and machining precision.

[0078] The fuel nozzle is made entirely of SUS304 stainless steel, which has a hardness of 90 HRB (much less than 60 HRC) and a yield strength of 310 MPa. Seven channels with an outlet diameter of approximately 130 μm and a channel length of approximately 1 mm are fabricated at the nozzle tip using micro-electrical discharge machining (EDM). However, because the EDM process involves machining from the nozzle outlet and then penetrating the nozzle wall to create the nozzle inlet, the overall nozzle shape is a truncated cone with a larger outlet and a smaller inlet. Therefore, the fuel injection flow rate is directly determined by the nozzle inlet diameter. Based on the required fuel injection flow rate, the finished fuel nozzle must have a flow rate in the range of 0.81~0.85 L / min. Test conditions: The flow rate of the calibration pump fuel at the fuel nozzle outlet was tested at 10 MPa pressure and 40℃. By measuring the initial flow rate (0.74 L / min ~ 0.78 L / min), the inlet channel diameter range of 120.7 μm~123.9 μm can be calculated using Bernoulli's equation. To achieve the specified flow rate (0.81~0.85 L / min), the inlet orifice diameter must range from 126.3 to 129.3 μm, with an average diameter of 127.8 μm. Therefore, the inlet diameter can be obtained by measuring the initial flow rate of the nozzle to be processed. The difference between the expected average inlet diameter and the initial diameter can then be calculated, which represents the machining allowance for each orifice, typically within the range of 2.4~8.6 μm.

[0079] The second step is to select the appropriate type and size of hard abrasive grains.

[0080] Based on the material properties, hardness, and tensile strength obtained in the first step, and taking into account processing efficiency, silicon carbide (SiC) was selected as the hard abrasive. Based on the nozzle inlet diameter calculated in step one and the abrasive selection criteria, a hard abrasive particle size of 25 μm was chosen.

[0081] The third step is to use a material removal model to calculate the medium storage modulus, flow rate, and concentration of active abrasive particles.

[0082] Based on the processing allowance of the previous process, determine the amount of material to be removed within the expected time. Since the medium flow rate is directly related to the medium viscosity (i.e., flowability), and the medium viscosity is inversely proportional to the medium elasticity, the two are mutually exclusive. Therefore, the storage modulus, which characterizes the medium elasticity, and the concentration of active abrasive particles, which is directly affected by elasticity, are both inversely proportional to the medium flow rate. Based on the above relationship that "storage modulus, active abrasive particle concentration, and flow rate are inversely proportional," when the processing efficiency is the objective function, there must exist an optimal matching value for flow rate, storage modulus, and active abrasive particle concentration, i.e., the efficiency peak point of the flow rate-storage modulus and flow rate-active abrasive particle concentration curves, which maximizes the processing efficiency. Based on this, the specific values ​​of the medium storage modulus, flow rate, and active abrasive particle concentration under the optimal processing efficiency can be calculated. Based on the material performance parameters and values ​​in step two, the medium storage modulus is calculated to be approximately 10 kPa, the medium flow rate is approximately 12.3 mm / s, and the number of active abrasive particles participating in the micro-jet nozzle processing is approximately 41.

[0083] The fourth step is to calculate the mass fraction of polymer melt and hard abrasive particles within the medium.

[0084] Since the storage modulus of a medium is an important indicator characterizing its elasticity, and the elasticity of a medium originates from the polymer melt within it, there must be a specific proportional relationship between the storage modulus of the medium and the mass fraction of the polymer melt. Extensive previous experimental results show that when using highly elastic polydimethylsiloxane as the polymer melt, the storage modulus G' of the medium and the mass fraction P of the polymer melt have the following relationship. Substituting the storage modulus obtained in step three, we can see that the mass fraction of highly elastic polydimethylsiloxane within the medium is approximately 15.7%.

[0085] (8)

[0086] Based on equation (5), the mass fraction of media hard abrasive particles can be calculated to be approximately 57% based on the number of active abrasive particles obtained in step three.

[0087] The fifth step involves configuring the abrasive media suitable for the finishing of the micro-aperture nozzles described above.

[0088] Based on the polymer melt type and mass fraction described in the preceding steps, and the type, particle size, and mass fraction of the hard abrasive particles, a mixture is prepared and placed in a mixer. The mixture is then thoroughly stirred at a specific temperature. The remaining mass fraction of additives (mainly plasticizing oil) is added to ensure complete mixing of the three components. After complete stirring, the mixture is allowed to stand for 12 hours to remove internal air bubbles, increase the bonding strength between the hard abrasive particles and the polymer melt, and further improve the stability of the abrasive media.

[0089] Step 6: Testing the rheological properties of the abrasive media.

[0090] The rheological properties of abrasive media at room temperature were tested using an MCR302 rotational rheometer. The testing method is as follows:

[0091] Select a 25mm test rod, lay the medium flat on the test platform, with a gap of 0.5mm between the test rod and the test platform. Then scrape off the excess medium.

[0092] First, the linear viscoelastic range of the abrasive medium was determined. The LVE mode was selected, and the changes in storage modulus and dissipation modulus within the strain range of 0.01% to 50% were measured. The median values ​​of strain and stress in the range where the storage modulus and dissipation modulus were constant were selected as the strain and stress required for creep recovery and stress relaxation testing of the abrasive medium.

[0093] Select the stress relaxation mode, set the strain to the median strain value in the linear viscoelastic range mentioned above, and measure the relaxation modulus change curve of the medium within a 500s range. When it tends to stabilize, this time point is the relaxation time of the abrasive medium.

[0094] Select the creep recovery mode, set the stress to the median stress within the aforementioned linear viscoelastic range, and measure the creep compliance value change curve over 300 seconds. Then, set the stress to 0 and continue recording the creep compliance change over 100 seconds. Finally, calculate the ratio of the decreased creep compliance value to the remaining value.

[0095] Select the frequency sweep mode, set the strain to the median strain in the linear viscoelastic range mentioned above, and measure the storage modulus, dissipation modulus, complex viscosity and loss tangent curves in the range of 0.01~200 rad / s.

[0096] Select the flow field mode to measure the shear viscosity curve and shear stress curve in the range of 0.01~200 s⁻¹.

[0097] Step 7: Simulation analysis of the flow behavior of abrasive media in the machining channel.

[0098] To truly demonstrate the flow behavior of the medium within a microstructure, computational fluid dynamics (CFD) simulation was used for the study. The specific operational steps are as follows:

[0099] Based on the target component structure, construct the actual flow channel of the medium within the target structure, and define the inlet and outlet and the wall surface;

[0100] The three-dimensional flow channel structure is meshed, and the mesh is refined at the wall surface;

[0101] Import the mesh file into Fluent or Polyflow and set the boundary conditions;

[0102] The shear viscosity curve is fitted using the Bird-Carreau (BC) or Yasuda-Carrreau (YC) equations to obtain parameters such as the annual viscosity at zero shear, the viscosity at infinite shear, coefficients, and the non-Newtonian fluid index.

[0103] Then, the above parameters and the relaxation time obtained in the second step are substituted into the BC model or YC model selected in Fluent or Polyflow for calculation.

[0104] Analysis yields information on medium pressure distribution, flow velocity distribution, wall shear stress distribution, and shear rate distribution.

[0105] Step 8: Design a matching fixture to produce a uniform machining effect.

[0106] The calculation process in step three above is based on the assumption that the medium produces a uniform processing effect on the surface to be processed. Since the flow behavior of the medium directly affects its processing effect, a matching fixture needs to be designed to ensure that the medium produces a uniform processing effect within the workpiece-fixture flow channel. Based on the pressure, velocity, and shear stress distribution of the medium within the processing channel in step seven, the channel structure and dimensions are adjusted to ensure a uniform distribution of the medium flow behavior parameters, further guiding the design of the matching fixture.

[0107] Example 2:

[0108] This embodiment focuses on the finishing of gears widely used in automotive transmissions to eliminate vibrations and high-frequency noise caused by high surface roughness and grinding marks during high-speed gear meshing. Abrasive flow machining is employed for this finishing process. The gear material is bearing steel with a hardness of approximately 55 HRC, a yield strength of approximately 518 MPa, an initial roughness Ra of approximately 1.83 μm, and a tooth pitch of approximately 4.838 mm. To reduce the roughness to below 0.5 μm, based on material properties and structural dimensions, SiC abrasive grains with a particle size of 212 μm are selected as the hard abrasive phase for this abrasive flow machining. Similar to steps three and four in Embodiment 1, the polymer melt mass fraction in the medium is calculated to be approximately 35% wt, and the hard abrasive grain mass fraction is approximately 55% wt. Then, based on the above parameters, the corresponding abrasive medium is configured according to step five, and the rheology, flow, and matching fixtures of the medium are designed according to steps six, seven, and eight in Embodiment 1 to achieve efficient finishing of the gear tooth surface.

[0109] Example 3:

[0110] This embodiment focuses on the tailstock sleeve component, made of 45 steel with an inner diameter of approximately 65 mm. After heat treatment, its hardness is around HRC20~HRC30, its yield strength is approximately 355 MPa, and its initial roughness is approximately 0.3 μm, which needs to be reduced to below 0.1 μm after machining. Therefore, SiC hard abrasive with a particle size of 65 μm is selected. Following the calculation process in steps three and four of Example 1, the polymer melt mass fraction in the medium is approximately 37%, the hard abrasive mass fraction is approximately 50%, and the plasticizer oil ratio is approximately 13%. Then, based on the above parameters, the corresponding abrasive medium is configured according to step five, and the rheology, flow, and matching fixture of the medium are designed according to steps six, seven, and eight of Example 1 to perform efficient finishing on the gear tooth surface.

[0111] The embodiments of the present invention are given for illustrative and descriptive purposes only, and are not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described in order to better illustrate the principles and practical application of the invention, and to enable those skilled in the art to understand the invention and to design various embodiments with various modifications suitable for a particular purpose.

Claims

1. A method of designing a viscoelastic medium abrasive for controlled material removal, characterized in that, The method comprises the following steps: S1: Pre-treatment test and parameter selection are performed on the parts to be machined, the surface material performance of the parts to be machined is tested by a microhardness tester and a tensile testing machine, the size of the characteristic structure is tested by a laser diameter measuring instrument or a three-coordinate measuring machine, the machining precision requirement is determined according to the part design drawing, and the type and particle size of the hard abrasive particles are selected based on the test results; S2: Based on the machining allowance of the previous process before the viscoelastic medium abrasive machining process in the machining process of the part, the previous process is a casting, forging or cutting machining process of the part, a general abrasive medium material is used to remove the model, the model is constructed based on the flow interaction of the continuous polymer matrix phase and the flow phase of the hard abrasive particles in the abrasive medium, the storage modulus, the shear thinning characteristic and the flow channel extrusion pressure difference are combined to calculate the machining efficiency, and the storage modulus, the flow rate and the active abrasive particle concentration parameters of the abrasive medium under the optimal machining efficiency are obtained; S3: The mass proportion of the polymer melt in the abrasive medium is determined by using the change rule of the storage modulus of the abrasive medium with the mass fraction of the polymer melt, and the mass proportion of the hard abrasive particles in the medium is obtained by backstepping based on the number of active abrasive particles and the machining allowance of the previous process; S4: The appropriate polymer melt is selected, the appropriate polymer melt is a polyurethane-based melt or an epoxy resin-based melt with a viscosity of 500-5000 mPa·s and no chemical reaction with the material of the part, the hard abrasive particles of the selected type, particle size and mass proportion are uniformly mixed therein, the remaining mass fraction of the additive is added, and the mixture is uniformly stirred at a temperature of 60-120℃, and after standing for 12h, the viscoelastic medium abrasive for the finishing machining of the target part is obtained; S5: The performance of the prepared abrasive medium is analyzed by using a rheometer, the medium creep performance, stress relaxation behavior, dynamic viscoelastic performance and shear thinning characteristic are detected, the corresponding curves are obtained, and the machining performance and flow performance of the abrasive medium are comprehensively characterized; S6: The flow behavior of the abrasive medium is simulated and analyzed by using an existing non-Newtonian viscous fluid constitutive model and a differential viscoelastic model, the pressure distribution, the flow rate distribution, the shear rate distribution and the wall shear rate distribution of the abrasive medium in the machining channel are quantitatively displayed, and the flow performance and machining performance of the abrasive medium are further reflected; S7: The change rule of the medium flow behavior with the flow channel structure and size is analyzed, the flow channel structure parameters including the flow channel inner diameter, length, inlet and outlet angle and size range that can produce uniform flow of the medium are determined, the design of the matching machining clamp is guided based on the determined flow channel structure parameters, and the precision finishing machining for the target part is realized.

2. The method of claim 1, wherein the controllable material removal of the viscoelastic medium abrasive design is characterized by, The surface material performance of the part to be machined includes the material surface hardness and the tensile strength, the machining precision requirement includes the shape accuracy and size accuracy of the channel structure, and the surface roughness is taken as the core control index.

3. The method of claim 1, wherein the controllable material removal of the viscoelastic medium abrasive design is characterized by, The material performance of the target part is detected by using a microhardness tester and a tensile testing machine.

4. The method of claim 1, wherein the controllable material removal of the viscoelastic medium abrasive design is characterized by, For the material with a Rockwell hardness of 60HRC or less, silicon carbide abrasive particles are selected for machining; For the material with a Rockwell hardness of more than 60HRC, diamond abrasive particles or cubic boron nitride abrasive particles are selected.

5. The method of claim 1, wherein the controllable material removal of the viscoelastic medium abrasive design is characterized by, The general abrasive medium material removal model is based on the interaction between the continuous polymer matrix phase and the hard abrasive particles in the abrasive medium during flow, combines the storage modulus, shear thinning characteristics and extrusion pressure difference in the flow channel of the abrasive medium, constructs a mechanical theoretical model of the hard abrasive particles, and fully considers the number of active abrasive particles participating in wall machining at the wall surface to construct the abrasive medium material removal model.

6. The method of claim 1, wherein the controllable material removal of the viscoelastic medium abrasive design is characterized by, The abrasive medium is mainly composed of a polymer melt, hard abrasive particles and additives.

7. The method of claim 1, wherein the controllable material removal of the viscoelastic medium abrasive design is characterized by, The non-Newtonian viscous fluid constitutive model includes a PowerLaw constitutive model, a Bird-Carreau constitutive model, a Bingham constitutive model, a Herschel-Bulkley constitutive model, a Cross constitutive model and a Carreau-Yasuda constitutive model. The differential viscoelastic constitutive model includes a Maxwell constitutive model, an Oldroyd-B constitutive model, a White-Metzner constitutive model, a Phan Thien-Tanner constitutive model, a Giesekus constitutive model, a FENE-P constitutive model and a Leonov constitutive model.

8. The method of claim 7, wherein the controllable material removal of the viscoelastic medium abrasive design is characterized by, For millimeter-level and below hole structures or micron-level and below slit structures, a non-Newtonian fluid constitutive model is selected for flow behavior simulation, and the Bird-Carreau constitutive model or the Carreau-Yasuda constitutive model is preferentially selected.

9. The method of claim 8, wherein the controllable material removal of the viscoelastic medium abrasive design is characterized by, For tens of millimeter and above hole structures or millimeter-level slit structures, the Giesekus constitutive model or the Leonov constitutive model in the differential viscoelastic constitutive model is selected.

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