Study On The Friction And Wear Characteristics Of Machine Tool Guide Based On Fractal Theory

The integration of machine tool guide is one of the most important structure in a machine tool system. The phenomenon of friction and wear will happen in the actual work due to the sliding characteristics,causing loss of the materials,affecting the manufacturing precision of the machine and service life. So how to improve the wear resistance of machine tool guide is important to the overall performance of machine tool.In order to seek the law of contact area, friction force, oil film force changing with the fractal parameters,this paper has done the ANSYS contact analysis and MATLAB oil film analysis based on the fractal theory, and apply the law in the digit control machine tool guideway.(1) Based on fractal theory, a 2D rough profile and a 3D fractal surface are established, respectively with MATLAB.The influence of fractal dimension and fractal roughness on the the ratio of surface roughness is studied. Come to a conclusion:with the increase of fractal roughness, the ratio of surface roughness is also increased but slowly.However,with the increase of fractal dimension, the ratio of surface roughness is decreased but fastly.So the influence of fractal dimension is greater than fractal roughness.(2) Extracting the keypoints from the fractal surface which is based on the 3D W-M function.Then the keypoints were imported into ANSYS and has done two contact analysis such as,smooth and rough,rough and rough. Come to a conclusion:with the increase of fractal dimension,the ratio of contact area is also increased under the same loading. The higher shearing strength of the materials are better than the common one on wear resistance under the same exposure conditions and always be used to improve the accuracy stable of machine tool.(3) Convertion the 3D fractal surface to another surface which had the same roughness and establishs a new calculation model of oil film pressure which combines with the hydrodynamic pressure lubrication theory.Then deduced the relationship between the fractal dimension and oil film pressure with the new lubrication theory.Through the numerical calculation,this paper came up with a relationship between fractal parameters and oil pressure.Come to a conclusion:with the increase of fractal dimension, the oil film pressure and friction force were decreased. Fluid produced by friction is far less than dry friction.(4) This paper characterize HMC500 based on a fractal surface under D=2.35 and Ra=1.3μm.Then based on the law how the wear and lubrication were influenced with the fractal dimension. The oil film bearing capacity is calculated about 1120 kg, far less than the rated loads 2000 kg with the law above.Conclusions conform to the actual working condition which are predicted by lubrication and friction and wear of the machine tool guideway based on the fractal theory.So the conclusions lay a solid foundation for the application of fractal theory in other areas.