Die surface lubrication modeling and analysis method for reducing friction coefficient of injection friction pair

Abstract

The application discloses a punch surface lubrication modeling and analysis method for reducing friction coefficient of a plunger friction pair, relates to the technical field of tribology control and surface engineering in die casting forming process, and comprises the following steps: S1, constructing a multi-physical field geometry interaction model; S2, calculating a thermal time-varying viscosity field; S3, establishing a lubrication failure benchmark matrix; S4, constructing a non-uniform texture surface model to be evaluated; and S5, performing matrix difference value quantitative evaluation. The punch surface lubrication modeling and analysis method for reducing friction coefficient of the plunger friction pair establishes a punch and plunger chamber geometry interaction model, sets a molten metal heat input thermal boundary, analyzes space-time temperature distribution during plunger injection, calculates a thermal dynamic viscosity field in combination with a pressure-temperature coupling model, substitutes the thermal dynamic viscosity field into a transient Reynolds equation, solves an untextured benchmark friction coefficient matrix, identifies an inflection point to lock a key lubrication area, constructs a non-uniform micro-texture model, arranges high dynamic pressure micro-texture in the key area, and then solves the model to obtain an evaluation matrix, and performs difference operation to quantitatively evaluate lubrication improvement effect.

Description

Technical Field

[0001] This invention relates to the field of tribological control and surface engineering technology in die casting molding process, specifically to a method for modeling and analyzing the lubrication of the punch surface to reduce the friction coefficient of the injection friction pair. Background Technology

[0002] High-pressure die casting, as a highly efficient near-net-shape forming technology, places extremely high demands on the stability of the injection system during its production process. The die-casting punch, as the core actuator of the injection system, forms a critical friction pair with the inner wall of the pressure chamber during operation. It must withstand the high-temperature thermal shock of the molten metal, typically above 600°C, and reciprocate under extreme conditions during high-speed, fast-injection and high-pressure boosting stages. The lubrication state of this friction pair directly determines the energy loss, sealing performance, and operational reliability of the injection process. Poor lubrication can lead to drastic fluctuations in the friction coefficient, punch jamming, or premature wear failure, subsequently causing quality defects such as internal porosity and cold shuts in the casting.

[0003] To improve the friction and wear performance of the punch surface, traditional solutions mainly focus on improving the physical structure or optimizing the external lubrication method. For example, patent CN211176249U discloses a lubrication system for a die-casting machine injection punch. By axially spaced multiple circumferential grooves on the outer circumferential surface of the punch and using the axial straight groove of the feed cylinder to guide the flow of lubricating oil, it attempts to achieve full coverage of lubricating oil. However, this experience-based physical grooving method does not take into account the micro-hydrodynamic effects, and its macro-groove shape is difficult to generate sufficient hydrodynamic pressure effect to bear high loads under micron-level oil film thickness.

[0004] In recent years, surface texturing technology has become a research hotspot for improving the performance of friction pairs, and related numerical simulation design methods have emerged continuously. For example, the flat-wall surface drag reduction functional microtexturing design method proposed in patent CN111460699B combines boundary layer theory and flow field simulation software to determine the height and arrangement area of ​​microtexture by calculating the thickness of the viscous sublayer and the turbulence critical point, thereby achieving fluid drag reduction optimization. However, this model is based on a simplified flat-wall flow field construction and focuses on fluid drag reduction rather than heavy-load lubrication scenarios. It cannot be directly applied to complex friction pair systems such as die-casting punches that involve multiphase flow of oil, melt, and gas and have strong transient effects.

[0005] In the field of reciprocating motion components such as internal combustion engine cylinder liners, there have been attempts at related texture optimization technologies. For example, patent CN114483568A discloses a cylinder liner surface texture optimization method based on hydrodynamic pressure effect, which uses the Reynolds equation to solve for oil film pressure distribution and screen texture parameters. However, when applying existing surface texture-related technologies to specific scenarios of die-casting punches, there are still significant limitations, specifically: 1. There is a lack of a key lubrication area identification mechanism based on multi-physics coupling. Existing methods mostly involve uniformly distributing texture on the punch surface or simply dividing the texture area based on geometric position. They do not consider the significant differences in thermal and mechanical loads in different parts of the die-casting punch, and cannot accurately locate key areas with high risk of lubrication failure based on thermo-mechanical coupling analysis. 2. Poor adaptability to working conditions: Existing simulation methods are mostly based on steady-state assumptions or single speed conditions for analysis, which do not adapt to the transient change characteristics of the three stages of slow injection, fast injection and pressurization in the die casting process. Furthermore, they lack a hybrid lubrication model that integrates the statistical effect of surface roughness, the micro-protrusion contact model and the variable viscosity characteristics of lubricating oil, making it difficult to accurately predict the dynamic response of texture in the transient injection process. 3. The texture design strategy is too simple. Existing technologies mostly adopt a uniform array texture distribution and do not design a non-uniform gradient distribution scheme for different thermal states along the punch axis. This can easily lead to waste of processing resources in non-critical areas, while the critical harsh working conditions of high temperature and high pressure still have insufficient lubrication capacity.

[0006] In summary, there is an urgent need for a punch surface lubrication analysis method that is adapted to the actual dynamic working conditions of the die-casting process. This method should be able to accurately identify the key lubrication areas of the punch through thermo-mechanical coupling analysis, and carry out non-uniform micro-texture modeling and performance quantitative evaluation based on these areas, so as to achieve accurate prediction of the punch surface lubrication performance and optimized design of the texture scheme. Summary of the Invention

[0007] The purpose of this invention is to provide a modeling and analysis method for lubrication of the punch surface that reduces the friction coefficient of the injection friction pair, so as to solve the problems mentioned in the background art that the existing die-casting punch surface design lacks accurate response to the transient thermo-mechanical coupling conditions of the injection process, and cannot be specifically designed for the wear differences in different areas of the punch surface.

[0008] To achieve the above objectives, this invention provides a method for modeling and analyzing the lubrication of a punch surface to reduce the friction coefficient of the injection friction pair, comprising the following steps: S1. Construct a multiphysics geometric interaction model: Establish a geometric model of the die-casting punch and the pressure chamber, and define the physical boundary of the fluid dynamics computational domain; set thermal boundary conditions that include heat input, which includes the heat flux conducted by the contact interface between the molten metal and the punch, as well as the transient heat conduction inside the punch material.

[0009] In this embodiment, the actual geometric parameters of the punch and the dynamic working condition parameters of the injection process are extracted as follows: First, the actual geometric parameters of the die-casting punch are extracted as the geometric boundary conditions for subsequent numerical calculations; at the same time, based on the process curve of the injection process, the dynamic working condition parameters that change with time are extracted as the physical boundary conditions for lubrication analysis. The actual geometric parameters specifically include the punch diameter. Effective contact length Surface roughness of punch and the surface roughness of the inner wall of the pressure chamber The roughness parameter is used to calculate the overall roughness in the subsequent hybrid lubrication model; Dynamic operating parameters specifically include injection speed. Lubricant dynamic viscosity External load Film thickness ratio characterizing lubrication state and the temperature of the friction pair between the punch and the pressure chamber These parameters together determine the instantaneous lubrication state of the friction pair at different injection stages: slow injection, fast injection, and pressurization. Based on the extracted dynamic operating parameters, the axial section of the punch that is close to the molten metal section in the pressure chamber and bears higher thermal and mechanical loads is identified and defined as the critical lubrication area, so as to provide a positional basis for the non-uniform arrangement of subsequent textures. Furthermore, the dynamic operating parameters extracted in S1 include feature information for identifying differences in the axial lubrication state of the friction pair in the punch chamber, wherein the feature information is the transient temperature distribution of the friction pair along the axial direction. With pressure distribution ; Accordingly, the method also includes S1a before S2: identification of critical lubrication areas, which aims to quantify the failure risk of different parts of the punch through physical field analysis; Specifically, S1a involves establishing an axial one-dimensional heat conduction-convective heat transfer coupled numerical model of the punch chamber system during the injection process. This model can simulate the heat transfer and accumulation process along the axial direction of the punch.

[0010] The governing equations for the heat conduction-convective heat transfer coupled model are:

[0011] In the formula, For transient terms; For thermal conductivity; This refers to the convective heat transfer term caused by the motion of the punch. The volumetric heat source term, which is converted from frictional power density, reflects the effect of frictional heat generation. This represents the equivalent heat flux load on the punch surface in the region near the molten metal, reflecting the thermal shock of the high-temperature molten metal.

[0012] By solving the heat conduction-convection-heat coupling model, the temperature field evolution along the axial direction of the punch surface can be obtained, thereby understanding the temperature change history of each part of the punch during the entire injection cycle.

[0013] Will satisfy And axial gradient A significant continuous axial section, combined with the fact that this section bears higher mechanical loads during the injection process, was identified as a critical lubrication area; this area is the danger zone where the lubricating oil viscosity decreases the fastest and the oil film is most prone to rupture.

[0014] S2. Calculation of the thermally induced time-varying viscosity field: Based on the transient heat conduction control equation, solve for the spatiotemporal temperature distribution of the punch during the injection cycle, including the slow injection, fast injection, and pressurization phases. Using a rheological constitutive model that includes pressure-temperature coupling terms, the temperature distribution and fluid pressure distribution are mapped to a dynamic viscosity field that evolves with time and space. To characterize the viscosity decay and compressive viscosity enhancement effect of lubricants under high temperature and high pressure.

[0015] In this embodiment, the calculation of the dynamic viscosity field in S2 uses the modified Roelands constitutive equation and introduces the following spatial distribution assumptions:

[0016] in The initial viscosity at room temperature and pressure. Temperature viscosity index (TVI) characterizes the viscosity evolution of lubricants under high temperature and high pressure coupling, and the dynamic viscosity field. The fluid film thickness is set to be uniformly distributed in the Z-direction and the punch circumferential direction in the Y-direction, depending only on the axial coordinate. and time change.

[0017] In this embodiment, the hybrid lubrication model is coupled with the texture: based on the parameters extracted by S1, a two-dimensional hybrid lubrication numerical model describing the lubrication state of the punch-chamber friction pair is established. This model can simultaneously calculate the hydrodynamic pressure effect and the micro-protrusion contact effect. The governing equations of the model are modified Reynolds equations that take into account the statistical effects of surface roughness, in order to correct the flow deviation caused by surface roughness hindering or promoting fluid flow, thereby more accurately describing the oil film pressure distribution under mixed lubrication conditions. Define a set of characteristic parameters for microtexture, including texture type, axial distribution position, distribution uniformity, and characteristic size. ,depth and area occupancy rate These parameters are design variables that affect the oil film's load-bearing capacity and friction coefficient; By constructing the film thickness equation The texture geometry is coupled into the two-dimensional hybrid lubrication numerical model, enabling the model to reflect the influence of local clearance changes caused by microtexture on the flow field; Furthermore, the governing equations of the two-dimensional hybrid lubrication numerical model described in S2 are transient Reynolds equations, the specific form of which is:

[0018] in , For pressure-flow factor, Shear flow factor These are contact factors; they are introduced to correct the effect of surface roughness on fluid flow and make the model applicable to mixed lubrication conditions.

[0019] The film thickness equation By matrix film thickness Surface roughness distribution The contribution of texture depth is composed of three superimposed components, and its mathematical expression is:

[0020] Among them, the contribution of texture depth is through texture depth Its corresponding geometric indicator function It is represented by the sum of the products; It is a switch function, when the coordinate point is located at the th The value is 1 when the texture unit is within a certain range, and 0 otherwise, thus precisely defining the geometric boundary of the texture.

[0021] Furthermore, the model described in S2 uses a rheological constitutive equation to describe the nonlinear changes in lubricating oil properties with pressure and temperature.

[0022] Specifically, this includes the viscosity-pressure and viscosity-temperature equations, such as the Roelands equation, which describes viscosity changes to reflect the exponential increase in viscosity of lubricating oil under high injection pressure and the sharp decrease in viscosity at high temperatures; and the density-pressure and density-temperature equations, such as the Dowson-Higginson equation, which describes density changes to reflect the compressibility and thermal expansion effect of lubricating oil, ensuring the accuracy of flow rate calculations under high-pressure conditions.

[0023] Furthermore, the axial distribution of the microtexture described in S2 is set according to the key lubrication area identified in step S1a, so as to achieve a differentiated design that is allocated on demand.

[0024] Specifically, the axial coordinate range of the key lubrication area identified by S1a is defined as the texture reinforcement interval. .

[0025] Within the texture enhancement zone, the area occupancy rate of the texture is set. follow ,in This serves as the baseline area occupancy rate for other regions along the axis. The area occupancy increment, determined based on the higher thermal-dynamic load level calculated within this range, aims to enhance the dynamic pressure bearing capacity and oil storage capacity of the region by increasing texture density.

[0026] The uniformity of the microtexture distribution is set to a non-uniform distribution that matches the difference in axial lubrication state, that is, a high-density distribution is used in critical areas and a low-density baseline distribution is used in non-critical areas.

[0027] S3. Establish the lubrication failure baseline matrix: This involves using the dynamic viscosity field... Substituting into the transient Reynolds equation with the introduction of the average flow factor, we solve for the spatiotemporal distribution matrix of the reference friction coefficient for the untextured smooth surface. Based on the gradient characteristics of the friction coefficient with axial position or the inflection point characteristics of the Stribeck curve, the key lubrication regions and their axial distribution boundaries that transition from fluid lubrication to mixed / boundary lubrication are identified. .

[0028] In this embodiment, the numerical solution process described in S3 further includes the following steps to ensure the convergence and efficiency of the solution: The rectangular computational domain is uniformly discretized into grid nodes, and the modified Reynolds equations are discretized using a central difference scheme, resulting in a system of linear equations in a five-point difference scheme. The discrete equations are then solved using the successive over-relaxation iterative method (SOR), with a relaxation factor introduced into the iterative scheme. The value is 1.0-1.5 to adjust the iteration step size.

[0029] use The cyclic multigrid strategy performs multiple bidirectional iterations between adjacent grid levels. By eliminating low-frequency errors on the coarse grid and high-frequency errors on the fine grid, this strategy can effectively solve the high-frequency oscillation problem caused by high-density microtexture and significantly accelerate convergence.

[0030] A convergence criterion is set: when the relative error of the pressure field between two adjacent iterations is less than the set convergence tolerance, such as... Stop iterating when the time comes and output the final pressure field.

[0031] Furthermore, the micro-protrusion contact model described in step S3 adopts a statistical contact model based on GW theory. This model calculates the film thickness ratio through numerical integration or approximate formulas. Related and In numerical computation, statistical functions can be solved using numerical integration or approximate fitting formulas, such as polynomial fitting or exponential fitting.

[0032] Specifically, the statistical function The mathematical definition of is as follows:

[0033] in, The rough peak height is a dimensionless value. For height, The root mean square roughness; This refers to the film thickness ratio.

[0034] Let be the probability density function of the rough peak height, which is assumed in this invention to follow a standard normal distribution:

[0035] In the hybrid lubrication model of this invention, the actual contact area... The calculation corresponds to Statistical functions of time Contact load The calculation corresponds to Statistical functions of time .

[0036] This leads to the micro-convexity contact load. and actual contact area This allows for a quantitative assessment of the contribution of direct contact between rough peaks to frictional resistance and load-bearing capacity under mixed lubrication conditions. The S3 step, identifying the key lubrication area and constructing the reference matrix, includes the following numerical calculation steps: S3-1, Calculation of hydrodynamic bearing capacity: Calculate the dynamic viscosity field obtained in S2. Substituting into the two-dimensional transient Reynolds equation, the fluid membrane pressure field distribution is solved and integrated to obtain the hydrodynamic bearing capacity. ; S3-2, Inverse solution of load balance: Based on the total external load conservation equation The nominal oil film thickness is adjusted using an iterative algorithm. Until the fluid bearing capacity and the micro-protrusion contact bearing capacity are met. The sum equals the external load. ; S3-3. Constructing the All-Time-Space Matrix: Integrating the contributions of fluid shear stress and micro-convex body contact shear stress, calculate the instantaneous total friction coefficient at all axial positions and throughout the entire time step, and construct a two-dimensional matrix. ; S3-4, Criterion for locking regional boundaries: [The text abruptly ends here, likely due to an incomplete sentence or a missing section.] Perform axial differential analysis to identify coordinates that satisfy the following conditions as the boundary of the critical region. :

[0037] in The preset gradient sensitivity threshold is used to capture the inflection point of the lubrication state transition.

[0038] In this embodiment, the micro-protrusion contact load in S3 and S3-2 Calculations were performed using the GW statistical contact model:

[0039] in For the equivalent elastic modulus, For the surface density of a microconvex body, The radius of curvature of the peak of the micro-convex body. The root mean square of the surface roughness; The model represents the probability distribution of rough peaks penetrating the oil film, using a parabolic cylindrical function or a Gaussian integral function; the model can respond to the nominal oil film thickness in S3-2. Tiny changes in the contact force produce nonlinear contact reaction forces.

[0040] In this embodiment, the elements of the friction coefficient matrix in 3, S3-3 Calculate the weighted sum including fluid shear and micro-assurance contact shear:

[0041] in , , This is the shear stress correction factor. The boundary membrane shear strength, It is the coefficient of dry friction.

[0042] In this embodiment, the numerical solution and friction coefficient calculation are performed as follows: the finite difference method is used to spatially discretize the governing equations, transforming the partial differential equations into a system of algebraic equations; and an iterative algorithm accelerated by multigrid processing is used to solve the pressure field. This addresses the problem of slow convergence caused by high mesh density due to microtexture. Based on the iteratively convergent pressure field, the fluid dynamic pressure load is calculated integrally. and fluid friction This part represents the load-bearing and friction-reducing effects of the lubricating oil film; Calculation of micro-convexity contact load using a micro-convexity contact model and friction This part represents the supporting force and frictional resistance generated by the direct contact of the rough peaks when the oil film breaks or becomes too thin; Ultimately based on the formula Calculate the total friction coefficient, which comprehensively reflects the overall lubrication performance under the current operating conditions and texture design.

[0043] S4. Construct a non-uniform textured surface model to be evaluated: Based on the key lubrication area determined in S3, map the non-uniform microtexture distribution scheme to be evaluated onto the punch surface geometry model: configure microtextures with the first hydrodynamic characteristic parameter in the key lubrication area, and configure microtextures with the second hydrodynamic characteristic parameter or keep the surface smooth in the area outside the key lubrication area.

[0044] In this embodiment, S4, the non-uniform microtexture distribution scheme, is specifically manifested as follows: From the contact surface to In the key lubrication area, microtextures with first hydrodynamic characteristic parameters are set to enhance the hydrodynamic pressure effect and lubricating oil retention capacity under high temperature and low viscosity conditions; exist In the region leading to the tail of the punch, a microtexture with a second hydrodynamic characteristic parameter is set, the second characteristic parameter being configured to generate less fluid resistance.

[0045] In this embodiment, the influence of texture parameters is analyzed and the performance is evaluated: the characteristic parameters of the microtexture are adjusted, S3 is repeated, and the friction coefficient under different combinations of texture parameters is calculated, in order to explore the sensitivity of each parameter to lubrication performance. Adjusting the characteristic parameters of microtexture includes changing the texture type, such as circular or elliptical; adjusting the distribution uniformity, such as gradient distribution, setting different axial positions, and changing the geometric dimensions, depth, and area occupancy. By comparing the calculation results under different parameter combinations, we analyze the influence of microtexture parameters and their distribution on the lubrication performance of the punch surface, and thus select the preferred texture design direction that can significantly reduce the friction coefficient and improve wear resistance. S5. Perform matrix difference quantitative evaluation: For the surface model containing microtexture features established in S4, solve the above fluid dynamics and contact model again, and output the spatiotemporal distribution matrix of friction coefficient for evaluation; perform matrix difference operation, and quantitatively evaluate the improvement performance of the texture scheme on thermally induced lubrication failure by calculating the local friction peak suppression rate and the failure area reduction rate in the key lubrication area.

[0046] In this embodiment, the calculation logic for the specific indicators of the quantitative evaluation in step S5 is as follows: Constructing a matrix difference model: Establishing the spatiotemporal matrix of the baseline friction coefficient With the evaluation friction coefficient spacetime matrix Calculate the difference matrix ; Local peak suppression rate Extracting key lubrication areas Maximum element value and Element value at the corresponding spatiotemporal location ,calculate:

[0047] Failure area shrinkage rate :statistics The median value exceeds the preset failure threshold. Total number of spatiotemporal points ,and The total number of spatiotemporal points exceeding the same threshold Compare and calculate: .

[0048] Compared with the prior art, the beneficial effects of the present invention are: This method for modeling and analyzing the lubrication of a punch surface to reduce the friction coefficient of the injection friction pair constructs a multi-physics geometric interaction model of the punch and the pressure chamber. It calculates the thermally induced time-varying viscosity field by combining the transient heat conduction equation and the pressure-temperature coupled rheological constitutive model, and then substitutes it into the transient Reynolds equation containing the average flow factor to solve the spatiotemporal matrix of the reference friction coefficient of the untextured surface. Through axial differential analysis, it accurately identifies the key areas of lubrication failure under thermo-mechanical coupling. Based on these areas, it constructs a non-uniform microtextured surface model, configuring high dynamic pressure effect microtextures in key areas and adapting low resistance parameters or keeping non-key areas smooth. Finally, through matrix difference operations, it quantitatively evaluates the friction reduction effect of the texture scheme by the local friction peak suppression rate and the shrinkage rate of the failure area. The entire process uses efficient algorithms such as the finite difference method and the multigrid method for solution, and integrates the GW / GT micro-convexity contact model to restore the mixed lubrication state.

[0049] 1. Furthermore, this invention introduces an axial one-dimensional heat conduction-convection heat transfer coupling model, which innovatively realizes the identification of key lubrication areas based on the characteristics of thermo-mechanical coupling. It can accurately locate the sections on the punch surface where the lubrication film is prone to rupture due to high temperature melt and high mechanical load, avoiding the waste of resources or local failure caused by blindly arranging textures uniformly in traditional designs, and providing a scientific basis for non-uniform texture design.

[0050] 2. Furthermore, this invention establishes a hybrid lubrication numerical model that includes the modified Reynolds equation, the GW micro-convexity contact model, and the rheological properties of lubricating oil. The model fully considers the interaction of multiple physical field factors such as surface roughness, microtexture morphology, and variable viscosity of oil under die-casting conditions. It can realistically reproduce the hybrid lubrication state of the die-casting punch under transient and complex working conditions, and significantly improve the consistency between the simulation analysis results and engineering reality.

[0051] 3. Furthermore, this invention proposes a non-uniform texture distribution strategy based on critical regions. In areas with poor lubrication, the dynamic pressure effect and oil storage capacity are enhanced by increasing the texture area occupancy rate, while a low-density distribution is maintained in non-critical regions. This differentiated design effectively balances the improvement of lubrication performance with the control of processing costs, and has extremely high engineering application value.

[0052] 4. Furthermore, this invention employs a W-cycle multigrid acceleration algorithm to solve the strongly nonlinear hybrid lubrication model. Compared with the traditional single-grid iterative method, this algorithm can effectively smooth the numerical oscillations caused by microtexture, significantly improve the convergence speed and computational stability of the pressure field, and make it possible to quickly analyze and evaluate a large number of texture parameter combinations. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the overall process flow of the present invention; Figure 2 This is a schematic diagram illustrating the principle of identifying key lubrication areas based on thermo-mechanical-motion coupling analysis of the present invention. Figure 3 This is a schematic diagram illustrating the punch-pressure chamber structure and key lubrication areas of the present invention. Figure 4 This is a schematic diagram of the injection mechanism model of the die-casting equipment of the present invention; Figure 5 This is a schematic diagram of the axial non-uniform distribution scheme of the microtexture on the punch surface of the present invention; Figure 6 This is a schematic diagram of the computational domain mesh generation and boundary condition settings for the two-dimensional hybrid lubrication numerical model of the present invention; Figure 7 This is a flowchart of the iterative calculation process for pressure and friction in this invention; Figure 8 This is a comparison curve of the friction coefficients of the axial non-uniform texture scheme of the present invention with those of the traditional uniform texture scheme and the no-texture scheme. Detailed Implementation

[0054] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] This invention provides a method for modeling and analyzing the surface lubrication of a die-casting punch to reduce the friction coefficient of the injection friction pair. The core of this method lies in constructing a multi-physics geometric interaction model: establishing a geometric model of the die-casting punch and the pressure chamber, defining the physical boundaries of the fluid dynamics computational domain; setting thermal boundary conditions that include heat input, which encompasses the heat flux conducted from the interface between the molten metal and the punch, as well as the transient heat conduction within the punch material; and calculating the thermally induced time-varying viscosity field: based on the transient heat conduction control equations, solving for the spatiotemporal temperature distribution of the punch during the injection cycle, including slow injection, fast injection, and pressurization stages. Using a rheological constitutive model that includes pressure-temperature coupling terms, the temperature distribution and fluid pressure distribution are mapped to a dynamic viscosity field that evolves with time and space. To characterize the viscosity decay and compressive adhesion enhancement effect of lubricants under high temperature and high pressure; to establish a lubrication failure benchmark matrix: to integrate the dynamic viscosity field Substituting into the transient Reynolds equation with the introduction of the average flow factor, we solve for the spatiotemporal distribution matrix of the reference friction coefficient for the untextured smooth surface. Based on the gradient characteristics of the friction coefficient with axial position or the inflection point characteristics of the Stribeck curve, the key lubrication region and its axial distribution boundary for the transition from fluid lubrication to mixed / boundary lubrication are identified. ; Construct a non-uniform textured surface model to be evaluated: Based on the key lubrication area determined in step S3, map the non-uniform microtexture distribution scheme to be evaluated onto the punch surface geometry model: configure microtextures with the first hydrodynamic characteristic parameter in the key lubrication area, and configure microtextures with the second hydrodynamic characteristic parameter or keep the surface smooth in areas outside the key lubrication area; Perform matrix difference quantization evaluation: For the surface model containing microtexture features established in S4, solve the above hydrodynamic and contact models again, and output the spatiotemporal distribution matrix of friction coefficient for evaluation. Perform matrix difference operations This study quantitatively evaluates the performance of texture schemes in improving thermally induced lubrication failure by calculating the local friction peak suppression rate and failure area reduction rate within key lubrication areas. The scheme is based on intelligent identification of key lubrication areas with thermo-mechanical coupling characteristics, overcoming the blindness of traditional uniform texture design and providing a scientific basis for differentiated texture layout. It establishes a multi-physics hybrid lubrication numerical model integrating the modified Reynolds equation, lubricating oil rheological properties, and micro-protrusion contact model, accurately reproducing the lubrication state under complex transient high-temperature and high-pressure conditions in die casting, improving the consistency between simulation and engineering reality. A non-uniform micro-texture distribution strategy is proposed, strengthening key areas and simplifying non-key areas, balancing lubrication performance improvement and processing cost control, demonstrating high engineering application value. The W-cycle multigrid acceleration algorithm is used to solve the strongly nonlinear model, effectively solving the numerical oscillation problem caused by micro-texture, significantly improving computational convergence speed and stability, and enabling rapid analysis and evaluation of a large number of texture parameter combinations.

[0056] like Figure 1 The diagram shown is an overall process flow chart of the present invention, illustrating the entire process from working condition extraction and area identification to fabric modeling and evaluation. It can be applied to the injection mechanism of a high-performance cold chamber die-casting machine. The injection mechanism employs hydrodynamic lubrication and transmission, specifically including a punch assembly and a pressure chamber assembly. The punch assembly includes a punch body, cooling pipes, and a connecting rod. The punch body is coaxially mounted on the front end of the connecting rod. During injection, the punch body performs reciprocating linear motion within the pressure chamber assembly. The contact interface structure between the punch and the pressure chamber is as follows: Figure 4 As shown, Figure 4 This is a schematic diagram of the injection mechanism model of the die-casting equipment in this invention, showing the geometric structure of the contact pair between the cylindrical surface of the punch with textured features and the inner wall of the pressure chamber; as shown... Figure 4 As shown, the cylindrical surface of the punch's outer periphery has micro-roughness characteristics, containing countless micro-protrusions at the micro-scale. Preferably, these micro-protrusions are provided on the cylindrical surface of the punch. Figure 5 The microtexture shown Figure 5 This is a schematic diagram of an axially non-uniform distribution scheme of microtextures on the punch surface, used in S2 of the present invention. It shows the design details of high-density texture reinforcement in critical lubrication areas, and the microtextures are divided into high-density distribution areas and low-density distribution areas according to different lubrication states; in addition, as Figure 3 As shown, Figure 3 A schematic diagram of the punch-pressure chamber structure and key lubrication areas is provided, which intuitively shows the temperature distribution cloud map of the punch in the pressure chamber and the location of the key lubrication areas. The front end face of the punch body is in direct contact with the high-temperature molten metal. Considering the thermal erosion of the punch material by the high-temperature molten metal and the frictional heat generated by high-speed movement, an extremely thin lubricating oil film is formed between the front end of the punch and the inner wall of the pressure chamber. The thickness of this oil film is affected by both the temperature field and the pressure field. Figure 2 This is a schematic diagram of the principle of identifying key lubrication areas based on thermo-mechanical-motion coupling analysis, which is applied to S1 and S1a of the present invention and corresponds to the multi-physics coupling identification logic in claim 2. Figure 6 A schematic diagram of the computational domain mesh generation and boundary condition setting for a two-dimensional hybrid lubrication numerical model, which is applied in S3 of this invention; Figure 7 This is a flowchart of the iterative calculation of pressure and friction, applied in S3 of this invention, illustrating the core steps of model solving and performance evaluation, including the specific processes of finite difference solution and multigrid acceleration; simultaneously Figure 8 This is a comparison curve of the friction coefficients between the axial non-uniform texture scheme, the traditional uniform texture scheme, and the no-texture scheme.

[0057] Example 1: To better understand the above technical solution, the following will provide a detailed description of the technical solution in conjunction with the accompanying drawings and specific implementation methods. (Refer to...) Figure 1As shown in the figure, this is an overall process flow diagram. The method for modeling and analyzing the lubrication of the punch surface to reduce the friction coefficient of the injection friction pair includes the following steps: Step S1: Construct a multiphysics geometric interaction model: Establish a geometric model of the die-casting punch and the pressure chamber, and define the physical boundary of the fluid dynamics calculation domain; set thermal boundary conditions that include heat input, which includes the heat flux conducted by the contact interface between the molten metal and the punch, as well as the transient heat conduction inside the punch material. Specifically, the extraction of actual geometric parameters of the punch and dynamic working condition parameters of the injection process: First, the actual geometric parameters of the die-casting punch are extracted as the geometric boundary conditions for subsequent numerical calculations; at the same time, based on the process curve of the injection process, the dynamic working condition parameters that change with time are extracted as the physical boundary conditions for lubrication analysis. The actual geometric parameters specifically include the punch diameter. Effective contact length Surface roughness of punch and the surface roughness of the inner wall of the pressure chamber The roughness parameter is used to calculate the overall roughness in the subsequent hybrid lubrication model; Dynamic operating parameters specifically include injection speed. Lubricant dynamic viscosity External load Film thickness ratio characterizing lubrication state and the temperature of the friction pair between the punch and the pressure chamber These parameters together determine the instantaneous lubrication state of the friction pair at different injection stages: slow injection, fast injection, and pressurization. Based on the extracted dynamic operating parameters, the axial section of the punch that is close to the molten metal section in the pressure chamber and bears higher thermal and mechanical loads is identified and defined as the critical lubrication area, so as to provide a positional basis for the non-uniform arrangement of subsequent textures. Dynamic operating parameters include feature information used to identify differences in the axial lubrication state of the friction pair in the punch chamber; the feature information is the transient temperature distribution of the friction pair along the axial direction. With pressure distribution ; Accordingly, the method also includes S1a before S2: identification of critical lubrication areas, which aims to quantify the failure risk of different parts of the punch through physical field analysis; Specifically, S1a involves establishing an axial one-dimensional heat conduction-convective heat transfer coupled numerical model of the punch chamber system during the injection process. This model can simulate the heat transfer and accumulation process along the axial direction of the punch.

[0058] The governing equations for the heat conduction-convective heat transfer coupled model are:

[0059] In the formula, For transient terms; For thermal conductivity; This refers to the convective heat transfer term caused by the motion of the punch. The volumetric heat source term, which is converted from frictional power density, reflects the effect of frictional heat generation. This represents the equivalent heat flux load on the punch surface in the region near the molten metal, reflecting the thermal shock of the high-temperature molten metal.

[0060] By solving the heat conduction-convection-heat coupling model, the temperature field evolution along the axial direction of the punch surface can be obtained, thereby understanding the temperature change history of each part of the punch during the entire injection cycle.

[0061] Will satisfy And axial gradient A significant continuous axial section, combined with the fact that this section bears higher mechanical loads during the injection process, was identified as a critical lubrication area; this area is the danger zone where the lubricating oil viscosity decreases the fastest and the oil film is most prone to rupture.

[0062] Step S2: Calculate the thermally induced time-varying viscosity field: Based on the transient heat conduction control equation, solve the spatiotemporal temperature distribution of the punch during the injection cycle, including slow injection, fast injection and pressurization stages; using a rheological constitutive model that includes pressure-temperature coupling terms, map the temperature distribution and fluid pressure distribution into a dynamic viscosity field that evolves with time and space, so as to characterize the viscosity decay and compressive viscosity enhancement effect of the lubricant under high temperature and high pressure.

[0063] Specifically, the dynamic viscosity field is calculated using the modified Roelands constitutive equation, and the following spatial distribution assumptions are introduced:

[0064] in The initial viscosity at room temperature and pressure. Temperature viscosity index (TVI) characterizes the viscosity evolution of lubricants under high temperature and high pressure coupling, and the dynamic viscosity field. The fluid film thickness is set to be uniformly distributed in the Z-direction and the punch circumferential direction in the Y-direction, depending only on the axial coordinate. and time change; Hybrid lubrication model establishment and texture coupling: Based on the parameters extracted by S1, a two-dimensional hybrid lubrication numerical model describing the lubrication state of the punch-pressure chamber friction pair is established. This model can simultaneously calculate the hydrodynamic pressure effect and the micro-protrusion contact effect. The governing equations of the model are modified Reynolds equations that take into account the statistical effects of surface roughness, in order to correct the flow deviation caused by surface roughness hindering or promoting fluid flow, thereby more accurately describing the oil film pressure distribution under mixed lubrication conditions. The axial distribution of the microtexture described in S2 is set according to the key lubrication areas identified in step S1a, so as to achieve a differentiated design that is allocated as needed.

[0065] Specifically, the axial coordinate range of the key lubrication area identified by S1a is defined as the texture reinforcement interval. .

[0066] Within the texture enhancement zone, the area occupancy rate of the texture is set. follow ,in This serves as the baseline area occupancy rate for other regions along the axis. The area occupancy increment, determined based on the higher thermal-dynamic load level calculated within this range, aims to enhance the dynamic pressure bearing capacity and oil storage capacity of the region by increasing texture density.

[0067] The uniformity of the microtexture distribution is set to a non-uniform distribution that matches the difference in axial lubrication state, that is, a high-density distribution is used in critical areas and a low-density baseline distribution is used in non-critical areas. The model employs the rheological constitutive equations of lubricating oil to describe the nonlinear changes in lubricating oil properties with pressure and temperature. Specifically, it includes the viscosity-pressure and viscosity-temperature equations, the Roelands equation, which describes viscosity changes to reflect the exponential increase in viscosity of lubricating oil under high injection pressure and the sharp decrease in viscosity at high temperature, as well as the density-pressure and density-temperature equations, the Dowson-Higginson equation, which describes density changes to reflect the compressibility and thermal expansion effect of lubricating oil, ensuring the accuracy of flow rate calculation under high pressure conditions. Define a set of characteristic parameters for microtexture, including texture type, axial distribution position, distribution uniformity, and characteristic size. ,depth and area occupancy rate These parameters are design variables that affect the oil film's load-bearing capacity and friction coefficient; By constructing the film thickness equation The texture geometry is coupled into the two-dimensional hybrid lubrication numerical model, enabling the model to reflect the influence of local clearance changes caused by microtexture on the flow field; film thickness equation By matrix film thickness Surface roughness distribution The contribution of texture depth is composed of three superimposed components, and its mathematical expression is:

[0068] Among them, the contribution of texture depth is through texture depth Its corresponding geometric indicator function It is represented by the sum of the products; It is a switch function, when the coordinate point is located at the th The value is 1 when the texture unit is within a certain range, and 0 otherwise, thus precisely defining the geometric boundary of the texture.

[0069] Step S3: Establish the lubrication failure baseline matrix: This involves using the dynamic viscosity field... Substituting into the transient Reynolds equation with the introduction of the average flow factor, we solve for the spatiotemporal distribution matrix of the reference friction coefficient for the untextured smooth surface. Based on the gradient characteristics of the friction coefficient with axial position or the inflection point characteristics of the Stribeck curve, the key lubrication regions and their axial distribution boundaries that transition from fluid lubrication to mixed / boundary lubrication are identified. ; Specifically, the transient Reynolds equations are in the following form:

[0070] in , For pressure-flow factor, Shear flow factor These are contact factors; they are introduced to correct the effect of surface roughness on fluid flow, making the model applicable to mixed lubrication conditions. The identification of critical lubrication areas and the construction of the baseline matrix include the following numerical calculation steps: S3-1, Calculation of hydrodynamic bearing capacity: Calculate the dynamic viscosity field obtained in S2. Substituting into the two-dimensional transient Reynolds equation, the fluid membrane pressure field distribution is solved and integrated to obtain the hydrodynamic bearing capacity. ; S3-2, Inverse solution of load balance: Based on the total external load conservation equation The nominal oil film thickness is adjusted using an iterative algorithm. Until the fluid bearing capacity and the micro-protrusion contact bearing capacity are met. The sum equals the external load. ; Micro-protrusion contact load Calculations were performed using the GW statistical contact model:

[0071] in For the equivalent elastic modulus, For the surface density of a microconvex body, The radius of curvature of the peak of the micro-convex body. The root mean square of the surface roughness; The model represents the probability distribution of rough peaks penetrating the oil film, using a parabolic cylindrical function or a Gaussian integral function; the model can respond to the nominal oil film thickness in S3-2. Tiny changes in these parameters generate nonlinear contact reactions. S3-3. Constructing the All-Time-Space Matrix: Integrating the contributions of fluid shear stress and micro-convex body contact shear stress, calculate the instantaneous total friction coefficient at all axial positions and throughout the entire time step, and construct a two-dimensional matrix. ; Elements of the friction coefficient matrix Calculate the weighted sum including fluid shear and micro-assurance contact shear:

[0072] in , , This is the shear stress correction factor. The boundary membrane shear strength, The coefficient of dry friction; Numerical solution and friction coefficient calculation: The finite difference method is used to spatially discretize the governing equations, transforming the partial differential equations into a system of algebraic equations; the pressure field is solved using an iterative algorithm accelerated by multigrids to address the problem of slow convergence caused by the high mesh density due to microtexture. The numerical solution process includes the following steps to ensure convergence and efficiency: The rectangular computational domain is uniformly discretized into grid nodes, and the modified Reynolds equations are discretized using a central difference scheme, resulting in a system of linear equations in a five-point difference scheme. The discrete equations are then solved using the successive over-relaxation iterative method (SOR), with a relaxation factor introduced into the iterative scheme. The value is 1.0-1.5 to adjust the iteration step size.

[0073] use The cyclic multigrid strategy performs multiple bidirectional iterations between adjacent grid levels. By eliminating low-frequency errors on the coarse grid and high-frequency errors on the fine grid, this strategy can effectively solve the high-frequency oscillation problem caused by high-density microtexture and significantly accelerate convergence.

[0074] Within each time step, the discretized pressure equations are solved by error smoothing on the coarse grid and solution correction on the fine grid; in particular, for complex surfaces containing texture, a high-density computational grid is used to analyze the pressure distribution inside the texture. A convergence criterion is set: when the relative error of the pressure field between two adjacent iterations is less than the set convergence tolerance, such as... Stop iteration when the time is up and output the final pressure field; The micro-protrusion contact model adopts a statistical contact model based on GW theory. This model calculates the statistical function related to the film thickness ratio through numerical integration or approximate formulas. In numerical calculation, the above statistical function can be solved by numerical integration or approximate fitting formulas, such as polynomial fitting or exponential fitting.

[0075] Specifically, the statistical function The mathematical definition of is as follows:

[0076] in, The rough peak height is a dimensionless value. For height, The root mean square roughness; This refers to the film thickness ratio.

[0077] Let be the probability density function of the rough peak height, which is assumed in this invention to follow a standard normal distribution:

[0078] In the hybrid lubrication model, the actual contact area The calculation corresponds to Statistical functions of time Contact load The calculation corresponds to Statistical functions of time .

[0079] This leads to the micro-convexity contact load. and actual contact area This allows for a quantitative assessment of the contribution of direct contact between rough peaks and the load-bearing capacity under mixed lubrication conditions.

[0080] Based on the iteratively converged pressure field, the fluid dynamic pressure load and fluid friction force are calculated by integration, which represents the load-bearing and friction-reducing effects of the lubricating oil film. The contact load and friction force of the micro-protrusions are calculated by combining the micro-protrusion contact model. This part represents the supporting force and frictional resistance generated by the direct contact of the rough peaks when the oil film is broken or too thin. Finally, the total friction coefficient is calculated based on the formula. This coefficient comprehensively reflects the overall lubrication performance under the current working conditions and texture design. S3-4, Criterion for locking regional boundaries: [The text abruptly ends here, likely due to an incomplete sentence or a missing section.] Perform axial differential analysis to identify coordinates that satisfy the following conditions as the boundary of the critical region. :

[0081] in A preset gradient sensitivity threshold is used to capture the inflection point of lubrication state transition; The numerical solution boundary condition model uses a cavitation boundary condition model, which includes: Axial inlet boundary: Set pressure boundary conditions ,in The fluid pressure given at the inlet; Axial outlet boundary: Reynolds free boundary conditions are used to dynamically locate the oil film rupture position. That is, at the oil film rupture boundary The pressure is zero at the same time. And the pressure gradient along the axial direction is zero. The conditions are used to simulate cavitation and oil film discontinuity at the punch exit position. Circumferential boundary: in and Set periodic boundary conditions at the location, satisfying This is to simulate the geometric continuity of the punch cylindrical surface.

[0082] Step S4: Construct a non-uniform textured surface model to be evaluated: Based on the key lubrication area determined in step S3, map the non-uniform micro-texture distribution scheme to be evaluated onto the punch surface geometry model: configure micro-textures with the first hydrodynamic characteristic parameter in the key lubrication area, and configure micro-textures with the second hydrodynamic characteristic parameter or keep the surface smooth in the area outside the key lubrication area. Specifically, the non-uniform microtexture distribution scheme is manifested as follows: From the contact surface to In the key lubrication area, microtextures with first hydrodynamic characteristic parameters are set to enhance the hydrodynamic pressure effect and lubricating oil retention capacity under high temperature and low viscosity conditions; exist In the region extending to the tail of the punch, a microtexture with a second hydrodynamic characteristic parameter is set, the second characteristic parameter being configured to generate less fluid resistance; Analysis of the influence of texture parameters and performance evaluation: The characteristic parameters of the microtexture were adjusted systematically, and S3 was repeated to calculate the friction coefficient under different combinations of texture parameters, in order to explore the sensitivity of each parameter to lubrication performance; Adjusting the characteristic parameters of microtexture includes changing the texture type, such as circular or elliptical; adjusting the distribution uniformity, such as gradient distribution, setting different axial positions, and changing the geometric dimensions, depth, and area occupancy. By comparing the calculation results under different parameter combinations, we can analyze the influence of microtexture parameters and their distribution on the lubrication performance of the punch surface, and thus select the preferred texture design direction that can significantly reduce the friction coefficient and improve wear resistance.

[0083] Step S5: Perform matrix difference quantization evaluation: For the surface model containing microtexture features established in S4, solve the above fluid dynamics and contact model again, and output the spatiotemporal distribution matrix of friction coefficient for evaluation. Perform matrix difference operations By calculating the local friction peak suppression rate and failure area reduction rate in the key lubrication area, the improvement performance of the texture scheme on thermally induced lubrication failure is quantitatively evaluated. The specific calculation logic for the quantitative assessment indicators is as follows: Constructing a matrix difference model: Establishing the spatiotemporal matrix of the baseline friction coefficient With the evaluation friction coefficient spacetime matrix Calculate the difference matrix ; Local peak suppression rate Extracting key lubrication areas Maximum element value and Element value at the corresponding spatiotemporal location ,calculate:

[0084] Failure area shrinkage rate :statistics The median value exceeds the preset failure threshold. Total number of spatiotemporal points ,and The total number of spatiotemporal points exceeding the same threshold Compare and calculate: .

[0085] Example 2, a specific data example is as follows: Step 1: Extraction of actual geometric parameters of the punch and dynamic operating parameters of the injection process: Extract the physical boundary parameters between the punch and the pressure chamber through sensor monitoring or design drawings, and pass the extraction results to the numerical calculation module. Specifically: A. Extract the actual geometric parameters of the die-casting punch, including the punch diameter. Effective contact length In this embodiment, the punch diameter Effective contact length .

[0086] B. Extract surface morphology parameters, including punch surface roughness. and the surface roughness of the inner wall of the pressure chamber In this embodiment, , Calculate the overall roughness according to the formula. Its value is The square of and The arithmetic square root of the sum of squares, the result. Furthermore, fractal dimension is introduced. Spatial frequency of surface profile To characterize the microscopic contact properties.

[0087] C. Extract dynamic operating parameters of the injection process, including injection speed. Lubricant dynamic viscosity External load And ambient temperature. In this embodiment, the injection system temperature is 680℃, and the punch speed is... Inlet pressure Export pressure .

[0088] Step 2: Identification of key lubrication areas based on thermo-mechanical coupling analysis: The numerical calculation module constructs a thermo-mechanical coupling model based on the dynamic operating parameters extracted in Step 1 to identify areas on the punch surface that are prone to lubrication failure.

[0089] When the punch moves at high speed, its front end is heated by the high-temperature molten liquid, and its entire length is affected by frictional heat. Based on this characteristic, the temperature field distributed along the axial direction of the punch is detected. The numerical calculation module compares the relationship between the temperature of each node and the failure threshold, and outputs the side where the temperature exceeds the threshold as the high-risk side for thermal failure; it also detects the pressure field distributed along the axial direction of the punch. The numerical calculation module compares the relationship between the pressure of each node and the load threshold. The side with the higher output pressure is the side with a high risk of mechanical failure, and the location of the critical lubrication area is determined accordingly.

[0090] Let the inlet temperature extracted in step 1 be... The outlet temperature is Therefore, in step 2, the method for identifying the critical lubrication area is as follows: Figure 2 As shown, it includes the following steps: Step 2-1, Threshold Determination: Establish an axial one-dimensional heat conduction-convection heat transfer coupling model and calculate the threshold at any axial position. transient temperature at , temperature With respect to the set lubricating oil failure temperature threshold In this embodiment, the comparison is set at 220°C. If the condition is met, proceed to step 2-2; otherwise, it is determined to be a non-critical area.

[0091] Step 2-2: Determine the axial section to be strengthened: Let the total length of the punch be... If in the interval The internal temperature meets the above conditions and simultaneously withstands high mechanical loads and pressure. Therefore, the area requiring high-density texture reinforcement is identified as the critical lubrication area at the front end. In this embodiment, the identified critical area is... Located in the range of 0 to 0.025m.

[0092] Step 2-3: Determine the target texture area occupancy: Based on the overheating level and pressure value calculated in Step 2-1, determine the target area occupancy within the key areas. The specific design formula follows the principle of maximizing the dynamic pressure effect. In this embodiment, it is set as follows: Furthermore, the microtexture units in the key area are elliptical micro-pits, and the size combination with the most significant hydrodynamic effect is selected. Therefore, in steps 2-3, the sensitivity of the texture to oil film thickness enhancement is detected by setting the geometric parameters of the texture. The specific parameter settings are as follows: Step 2-3A, Define texture dimensions: Texture major axis diameter ; Texture minor axis diameter ; Texture depth .

[0093] Step 2-3B: Determine texture distribution: in key areas Inside, elliptical microtextures of the aforementioned dimensions are evenly distributed, occupying 33.33% of the area; in non-critical areas... Inside, the area occupancy rate is set to 5% or it is a smooth surface.

[0094] Steps 2-4: Determine the output friction coefficient: Based on the hybrid lubrication model, the numerical calculation module takes the aforementioned non-uniformly distributed texture parameters as input and converts them into the average friction coefficient of the entire punch. The core of solving the above hybrid lubrication model lies in the pressure distribution. The calculation is based on the modified Reynolds equation, where the dynamic viscosity of the lubricating oil is... Considering high-temperature dilution, the value is taken as follows: .

[0095] This invention utilizes the numerical computation toolbox in Matlab software, employing the finite difference method (FDM) combined with a multigrid algorithm to identify the unknown pressure field distribution in the equations. Specifically: Define the number of nodes in the X-axis direction. ; Define the number of nodes in the Y-direction. ; Each grid is subdivided into 10x10 subgrids to achieve precise capture of the flow field inside the microtexture.

[0096] Step 3: Repeat steps 1 and 2, adjusting the depth of the texture. or area occupancy rate This ensures that the calculated average friction coefficient and oil film thickness are both within the set optimization threshold range.

[0097] In this invention, the non-uniform texture controls the lubrication of different areas on the punch surface independently. When the punch undergoes thermal deformation, the contact state between critical and non-critical areas is different, the stress form of each area is different, and the film thickness distribution along the axial direction of each area is different. The microtexture at different positions on the punch surface can output different dynamic pressure bearing forces according to different thermo-mechanical coupling states, control the oil film pressure distribution on the punch surface, and achieve direct action on the punch surface to control friction and wear.

[0098] In this embodiment, the elliptical texture applies the same control method and principle to the fluid dynamic pressure on the punch surface, and the control of critical and non-critical areas is independent of each other. Therefore, taking the control of the friction coefficient in the critical area as an example, according to the GW contact model and fluid lubrication theory, the total friction force is equal to the sum of the fluid shear force and the micro-protrusion contact force.

[0099] This invention, through simulation calculations, detected the average coefficient of friction on a completely smooth surface without the application of non-uniform texture control. Approximately 0.35. After applying the non-uniform texture control of this invention, the high-density elliptical texture in key areas... Significant dynamic pressure is generated, and the calculated average coefficient of friction is obtained. It is approximately equal to 0.23.

[0100] The friction coefficient has a nonlinear relationship with the texture parameters. The input parameters can be represented in matrix form. This invention calls the solver in Matlab software and identifies the pressure field based on the W-cycle multigrid algorithm. The system is given a complex surface morphology input signal, including roughness and texture. The actual output signal and pressure distribution of the system are collected. The non-uniform texture parameters are input into the hybrid lubrication model. The output of the model is used as the dynamic response, which, together with the ideal lubrication state under actual working conditions, constitutes new identification data.

[0101] Numerical simulations were performed on the above model, using an over-relaxed iterative SOR solver combined with multi-grid acceleration. This yielded friction coefficient variation curves under different texture schemes, as shown below. Figure 8 As shown.

[0102] Depend on Figure 8It can be seen that after the injection is started, it enters a stable high-speed stage in about 0.02 seconds. The friction coefficient curve of the non-uniform elliptical texture scheme of the present invention drops rapidly and stabilizes at about 0.23. Compared with the no texture scheme, the black curve remains at a high level above 0.35, and the uniform long rectangular texture scheme, the green curve, and the uniform spiral rectangular texture scheme, the blue curve, the friction coefficient of the punch surface optimized by the method of the present invention is significantly reduced and the curve oscillation is smaller.

[0103] The non-uniform texture was compared with the uniform texture by 0.23 only to compare with the uniform texture of 0.28 and the no texture of 0.35. These values ​​were read from the friction coefficient variation curve. It shows that the non-uniform elliptical texture design based on key area identification can make the punch lubrication better and wear less. However, because there is a truncation error in the numerical calculation process, the output result can only approach the theoretical extreme value when the ideal working condition is input, whether it is optimized or not.

[0104] This invention employs a thermo-mechanical coupling model to monitor the temperature and pressure distribution along the axial direction of the punch in real time, and outputs the key area identification results to the texture design module, enabling the lubrication system to reduce the friction coefficient by about 25% under high temperature and high pressure conditions. It has the advantages of high identification accuracy and strong targeting. Through multi-grid algorithm cyclic solution, it can ensure that the pressure calculation value of each node is close to the real physical value.

[0105] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

[0106] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for modeling and analyzing the lubrication of a punch surface to reduce the friction coefficient of the injection friction pair, characterized in that, Includes the following steps: S1. Construct a multiphysics geometric interaction model: Establish a geometric model of the die-casting punch and the pressure chamber, and define the physical boundary of the fluid dynamics computational domain; set thermal boundary conditions that include heat input, which includes the heat flux conducted by the contact interface between the molten metal and the punch, as well as the transient heat conduction inside the punch material. S2. Calculation of the thermally induced time-varying viscosity field: Based on the transient heat conduction control equation, solve for the spatiotemporal temperature distribution of the punch during the injection cycle, including the slow injection, fast injection, and pressurization phases. Using a rheological constitutive model that includes pressure-temperature coupling terms, the temperature distribution and fluid pressure distribution are mapped to a dynamic viscosity field that evolves with time and space. To characterize the viscosity decay and compressive viscosity enhancement effect of lubricants under high temperature and high pressure; S3. Establish the lubrication failure baseline matrix: This involves using the dynamic viscosity field... Substituting into the transient Reynolds equation with the introduction of the average flow factor, we solve for the spatiotemporal distribution matrix of the reference friction coefficient for the untextured smooth surface. Based on the gradient characteristics of the friction coefficient with axial position or the inflection point characteristics of the Stribeck curve, the key lubrication regions and their axial distribution boundaries that transition from fluid lubrication to mixed and boundary lubrication are identified. ; S4. Construct a non-uniform textured surface model to be evaluated: Based on the key lubrication area determined in step S3, map the non-uniform micro-texture distribution scheme to be evaluated onto the punch surface geometry model: configure micro-textures with the first hydrodynamic characteristic parameter in the key lubrication area, and configure micro-textures with the second hydrodynamic characteristic parameter or keep the surface smooth in the area outside the key lubrication area. S5. Perform matrix difference quantization evaluation: For the surface model containing microtexture features established in S4, solve the above fluid dynamics and contact model again, and output the spatiotemporal distribution matrix of friction coefficient for evaluation. Perform matrix difference operations By calculating the local friction peak suppression rate and the failure area reduction rate in the critical lubrication area, the improvement performance of the texture scheme on thermally induced lubrication failure is quantitatively evaluated.

2. The method for modeling and analyzing the lubrication of a punch surface to reduce the friction coefficient of the injection friction pair according to claim 1, characterized in that: S2, dynamic viscosity field The calculations employ the modified Roelands constitutive equation and introduce the following spatial distribution assumptions: ； in The initial viscosity at room temperature and pressure. Temperature viscosity index (TVI) characterizes the viscosity evolution of lubricants under high temperature and high pressure coupling, and the dynamic viscosity field. The fluid film thickness is set to be uniformly distributed in the Z-direction and the punch circumferential direction in the Y-direction, depending only on the axial coordinate. and time change.

3. The method for modeling and analyzing the lubrication of a punch surface to reduce the friction coefficient of the injection friction pair according to claim 2, characterized in that: The S3 step, identifying the key lubrication area and constructing the reference matrix, includes the following numerical calculation steps: S3-1, Calculation of hydrodynamic bearing capacity: Calculate the dynamic viscosity field obtained in S2. Substituting into the two-dimensional transient Reynolds equation, the fluid membrane pressure field distribution is solved and integrated to obtain the hydrodynamic bearing capacity. ; S3-2, Inverse solution of load balance: Based on the total external load conservation equation The nominal oil film thickness is adjusted using an iterative algorithm. Until the fluid bearing capacity and the micro-protrusion contact bearing capacity are met. The sum equals the external load. ; S3-3. Constructing the All-Time-Space Matrix: Integrating the contributions of fluid shear stress and micro-convex body contact shear stress, calculate the instantaneous total friction coefficient at all axial positions and throughout the entire time step, and construct a two-dimensional matrix. ; S3-4, Criterion for locking regional boundaries: [The text abruptly ends here, likely due to an incomplete sentence or a missing section.] Perform axial differential analysis to identify coordinates that satisfy the following conditions as the boundary of the critical region. : ； in The preset gradient sensitivity threshold is used to capture the inflection point of the lubrication state transition.

4. The method for modeling and analyzing the lubrication of a punch surface to reduce the friction coefficient of the injection friction pair according to claim 3, characterized in that: The micro-protrusion contact load in S3, S3-2 Calculations were performed using the GW statistical contact model: ； in For the equivalent elastic modulus, For the surface density of a microconvex body, The radius of curvature of the peak of the micro-convex body. The root mean square of the surface roughness; The model represents the probability distribution of rough peaks penetrating the oil film, using a parabolic cylindrical function or a Gaussian integral function; the model can respond to the nominal oil film thickness in S3-2. Tiny changes in the contact force produce nonlinear contact reaction forces.

5. The method for modeling and analyzing the lubrication of a punch surface to reduce the friction coefficient of the injection friction pair according to claim 3, characterized in that: The elements of the friction coefficient matrix in 3, S3-3 Calculate the weighted sum including fluid shear and micro-assurance contact shear: ； in , , This is the shear stress correction factor. The boundary membrane shear strength, It is the coefficient of dry friction.

6. The method for modeling and analyzing the lubrication of a punch surface to reduce the friction coefficient of the injection friction pair according to claim 5, characterized in that: The non-uniform microtexture distribution scheme in S4 is specifically manifested as follows: From the contact surface to In the key lubrication area, microtextures with first hydrodynamic characteristic parameters are set to enhance the hydrodynamic pressure effect and lubricating oil retention capacity under high temperature and low viscosity conditions; exist In the region leading to the tail of the punch, a microtexture with a second hydrodynamic characteristic parameter is set, the second characteristic parameter being configured to generate less fluid resistance.

7. The method for modeling and analyzing the lubrication of a punch surface to reduce the friction coefficient of the injection friction pair according to claim 6, characterized in that: The specific calculation logic for the quantitative evaluation indicators in S5 is as follows: Constructing a matrix difference model: Establishing the spatiotemporal matrix of the baseline friction coefficient With the evaluation friction coefficient spacetime matrix Calculate the difference matrix ; Local peak suppression rate Extracting key lubrication areas Maximum element value and Element value at the corresponding spatiotemporal location ,calculate: ； Failure area shrinkage rate :statistics The median value exceeds the preset failure threshold. Total number of spatiotemporal points ,and The total number of spatiotemporal points exceeding the same threshold Compare and calculate: 。 8. The method for modeling and analyzing the lubrication of a punch surface to reduce the friction coefficient of the injection friction pair according to claim 7, characterized in that: The fluid dynamics lubrication models in S3 and S5 employ two-dimensional transient Reynolds equations that incorporate an average flow factor: ； in , For pressure-flow factor, Shear flow factor For contact factor.

9. The method for modeling and analyzing the lubrication of a punch surface to reduce the friction coefficient of the injection friction pair according to claim 8, characterized in that: The numerical solution processes in S3 and S5 employ efficient iterative numerical algorithms, including the W-loop scheme of the multigrid method to accelerate convergence: Within each time step, the discretized pressure equations are solved by error smoothing on the coarse grid and solution correction on the fine grid; in particular, for complex surfaces containing texture, a high-density computational grid is used to analyze the pressure distribution inside the texture.

10. The method for modeling and analyzing the lubrication of a punch surface to reduce the friction coefficient of the injection friction pair according to claim 9, characterized in that: The numerical solution boundaries in S3 and S5 adopt the cavitation boundary condition model, which includes: Axial inlet boundary: in Set pressure boundary conditions ,in The fluid pressure given at the inlet; Axial outlet boundary: Reynolds free boundary conditions are used to dynamically locate the oil film rupture position. That is, at the oil film rupture boundary The pressure is zero at the same time. And the pressure gradient along the axial direction is zero. The conditions are used to simulate cavitation and oil film discontinuity at the punch exit position. Circumferential boundary: in and Set periodic boundary conditions at the location, satisfying This is to simulate the geometric continuity of the punch cylindrical surface.

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