| The machining of microstructure arrays with tiny dimensions,controllable morphologies,and orderly arrangement on the surface of mechanical parts can adjust the surface friction,wear,hydrophilicity,and hydrophobicity,meeting the surface’s needs for special working conditions and enhancing the service performance of the part’s surface.However,processing methods for surface microstructure arrays,such as laser processing,reactive ion etching,electric spark machining,and high-precision machining,are costly and inefficient,limiting their large-scale industrial applications.This paper proposes a new method of fabricating microstructure arrays on the surface of soft metal friction pairs through cold press forming,and investigates key scientific and technological issues such as mold manufacturing,morphology control,and performance adjustment in the cold press forming of surface microstructure arrays,aiming to improve the processing efficiency and reduce the cost of surface microstructure arrays.This will promote the transformation of theoretical and experimental research on surface microstructure arrays into industrial applications,effectively enhancing the friction and wear performance of friction pairs,reducing energy consumption,and prolonging the service life of mechanical parts.This paper explored the processing method of surface microstructure array molds using mask electrochemical etching.It utilized Python for secondary development of Abaqus to reconstruct the surface morphology after forming through simulation analysis,data extraction,and function fitting analysis.Additionally,the cold press forming process and material deformation mechanism were analyzed using the crystal plasticity finite element method.Initial results were obtained regarding the technological process and parameter adjustment methods for cold press forming of surface microstructure arrays.The main research contents of this paper are as follows:(1)This paper investigates different preparation methods for molds used in the cold press forming of surface microstructure arrays.The electrochemical etching process with masks was applied to 42Cr Mo alloy steel.The processing steps include coating,pre-baking,photolithography,intermediate baking,developing,post-baking,electrochemical etching,and subsequent treatments.Among these steps,photolithography parameters and electrochemical etching parameters have a significant impact on the mold morphology and quality.By enhancing the UV light source and adjusting the photolithography time,the size of the glued spots on the mold can be made consistent with the mask size.A self-made electrochemical etching equipment was used to test the electrochemical etching system by outputting positive pulses and bidirectional pulses.The experiments showed that using a positive pulse with a voltage of 14V,a frequency of 20 KHz,and a duty cycle of 75%for etching can achieve good etching results.Additionally,using a bidirectional pulse with a voltage of 14 V,a frequency of 20 KHz,and a duty cycle of 50%for finishing the etched surface can further enhance the surface quality.After cold press testing,the mold fulfills the usage requirements.(2)This paper proposes the use of the chi-squared distribution’s probability density function to fit the surface profile curve during the cold press forming process.The fitted parameters are then employed as characteristic parameters to represent the surface morphology.The relationship between the surface morphology and processing parameters is investigated,and the forming laws are analyzed.Through numerous fitting attempts,it is found that using a scaled chi-squared function to fit the base surface morphology results in smaller errors.Only one scaling parameter _kh and one degree of freedom parameter n are required to describe a curve,and rotating this curve once around its axis would represent the base surface morphology surrounding a single microstructure after pressing.Unlike parameters such as surface roughness and flatness,which merely provide statistical analysis of surface data,this morphology description method allows for the reconstruction and reproduction of complex surfaces,resulting in a higher level of descriptive accuracy.The material properties of the pressed material and the cold pressing depth are correlated with the value of n in the fitted chi-squared function,providing a foundation for establishing the relationship between the processing parameters and the resulting morphology in the cold press forming of microstructure arrays.(3)The influence range of a single microstructure on the base surface is relatively small,and the distance between two microstructures in the surface microstructure array is relatively large.Simulation analysis has found that the material flow and Mises stress in the middle region between two microstructures are both low,satisfying the superposition principle.Therefore,the overall morphology of the base surface can be calculated by mutually superimposing the scaled chi-squared functions,which reconstructs the overall morphology of the base surface after forming.Simulation and calculation results indicate that when the spacing between microstructures is large,the influence ranges of the base surface are independent of each other.As the spacing between microstructures decreases,the bulges on the base surface start to overlap.When the spacing falls within a certain range,the impact of cold press forming of the microstructure array on the base surface is minimal due to the superposition effect.Using the scaled chi-squared function to fit the base surface,information such as the height,position,and curvature of the high points of surface fluctuations can be calculated,providing a foundation for calculating the surface contact of friction pairs with microstructure arrays.(4)The impact of cold press forming on material properties was studied using the crystal plasticity finite element method(CPFEM).By utilizing Abaqus to call Python scripts,the drawing of grains with different sizes was achieved,and the crystal plasticity finite element simulation of microstructure cold press forming was implemented by calling the constitutive function from a for file.Due to the different orientations and strengthening degrees of various grains,the randomness of material stress and flow during the cold press process increases.As a result,slip strengthening and grain refinement occur in the material surrounding the microstructures.After cold pressing,the material strength around the microstructures increases,contributing to the improvement of the material’s friction-reducing and wear-resistant properties.Experimental results indicate that the surface hardness of T2 copper with a microstructure array was strengthened from 39.9 HRB to 42.7 HRB after cold pressing.(5)Surface microstructure arrays with different parameters were cold-pressed on various metal surfaces.The results showed that due to the influence of surface errors,when the forming pressure is small,microstructures are only produced in local areas;when the pressure exceeds a certain value,the microstructures basically cover the entire surface of the workpiece;when the pressure continues to increase,the entire pressed surface yields,and the depth of the microstructures rapidly increases with the pressure,and the parameters of the microstructures gradually converge.The cold pressing process exhibits strong robustness.The impact of various processes,including mold preparation,workpiece material preparation,cold pressing and demolding,and post-processing,on the forming quality of the surface microstructure array was analyzed,and methods for adjusting parameters such as the spacing,depth,final morphology,and hardening layer properties of the surface microstructure array were obtained.Compared to surface microstructure array processing methods such as laser etching and mask electrochemical etching,cold pressing offers higher efficiency and can meet the demand for mass production of surface microstructure arrays. |
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