Research On The Contact Characteristics Of Oil-bearing Joint Surfaces

The contact characteristics between the bonding surfaces are an important factor that affects the performance of the machine tool.There will be oil films on the surfaces of current mechanical equipment and parts,and there will also be oil films between the mechanically fixed joint surfaces.In this case,partial film contact,and the stiffness of the oil film between the joint surfaces will also have a certain impact on the contact stiffness of the joint surfaces.However,the existing literature basically studies the pure oil-free surface,which is inconsistent with the actual situation,so the results obtained will be different from the actual results.In this paper,the influence of lubricating oil is considered in the research on the contact characteristics of the bonding surface,and the contact characteristics are mainly studied from the following aspects:(1)The statistical characteristics and fractal characteristics of the real machined surface profile data are studied.The state of the oil-bearing joint surface under different film thicknesses is mainly studied,and the distribution method of the contact stiffness of the joint surface under different conditions is analyzed.The real machining surface contours corresponding to different machining methods are completely different,so the characteristics of the bonding surface are also completely different.This paper uses non-contact measurement method to obtain real grinding sample surface data,and then uses Matlab to establish three-dimensional models at different sampling intervals,and calculates the three-dimensional surface statistical parameter values,mainly height parameters and some functional parameters.The analysis shows that the ground surface heights at different resolutions are in accordance with the normal distribution and the function parameter values are obtained.Then,two-dimensional contour maps and spectrum curves are obtained by Fast Fourier Transform(fft)on the two surfaces.According to the WM function and the power spectral density method Power Spectral Density(PSD),the fractal dimension D and the fractal roughness G,which are characterized in double logarithmic coordinates,are obtained.The analysis shows that under the grinding process,the fractal and statistical characteristics on different sample surfaces are consistent,which lays the foundation for the subsequent contact theory modeling research.(2)Two different models of fractal theory,asperity continuous deformation theory and oil film are applied to establish the normal contact stiffness model of the oil-bearing joint.The contact characteristics of the bonding surface in this state are analyzed,and the analysis shows that in this state,the contact stiffness of the bonding surface is shared by the solid and the oil film,and it is connected in parallel.Applying the theory of continuous deformation of the asperity,a model including the elastic,elastoplastic and plastic stages is established for the asperity and extended to the entire joint surface to obtain the contact stiffness of the solid part.Then,the oil film resonance model and spring model are used to model the oil film,and the contact stiffness of this part is obtained.After the two parts are coupled,numerical simulation analysis is performed to obtain the relationship between the total stiffness and the fractal parameters,different media and other influencing factors.(3)The improved fractal theory and the average Reynolds equation were applied to model the joint surface.On the basis of the previous article,the fractal theory is improved,and the solid part is modeled.Since viscosity is a very important parameter of lubricating oil,the application of the average Reynolds equation to model the oil film can better predict the dynamic characteristics of the machine tool.The stiffness distribution idea of,obtains the total stiffness of the joint surface,and analyzes the influence law of fluid viscosity and other factors on the total stiffness.(4)The model was verified by comparison between experiments and finite element methods.Through an experimental device containing a joint,the vibration mode and natural frequency are obtained by the hammering method.The virtual material method is used to model the test device model,and the first three-order natural frequencies are obtained,which are in good agreement with the test results.From the comparison results,it can be seen that the natural frequency of the lubricating oil-containing joint surface under different tightening torques is greater than that of the non-lubricating joint surface.This also reflects from the side that the lubricating oil between the joint surfaces can improve the contact stiffness of the joint surfaces,which shows the correctness of the model in this paper.