On The Generation Mechanism Of Checkerboard Texture And Surface Stress Concentration Feedback Controlling In Machining Curved Surface With Variable Curvatures

With the development and progress of society,more and more families have their own cars.Cars play an important role in today's society.It facilitates people's travel and gradually becomes a rigid demand goods in people's lives.In the processing and forming of the car top cover,most of them are formed by stamping,which requires a stamping die.There are a large number of curved surfaces with variable curvature in the automobile panel mold.In the 3-axis CNC milling of the variable-curvature surface mold,the tool path is composed of tiny straight segments.After the variable-curvature surface mold is processed by CNC milling,a checkerboard texture of light and dark will often appear on the processed surface.The checkerboard texture leads to an increase in roughness and a decrease in processing accuracy.Stress concentration is an important indicator to evaluate the quality of the surface.When the tool path is formed by the interpolation line fitting surface curve,the sharp Angle of different degrees will be formed at the connection point of the interpolation line.The presence of sharp corners leads to an increase in the stress concentration factor.Associate the stress concentration with the surface checkerboard pattern.The checkerboard texture can be alleviated by the feedback of stress concentration factor to the checkerboard texture.This paper takes the tool path of the curved surface as the research object,and uses the three-axis CNC machining center to process the curved surface.The checkerboard texture on the machined surface was geometrically characterized,and the generation mechanism of the checkerboard texture in the automobile panel mold was analyzed.The surface topography model of ball-end milling surface based on acceleration and deceleration control is established,and the generation of checkerboard texture is predicted through simulation.This paper studies the influence of checkerboard pattern on surface stress concentration based on the surface topography model.A method for controlling the length of the interpolation line based on stress concentration is proposed through the study of surface stress concentration.This method can reduce the checkerboard pattern,improve the quality of the processed surface,and is suitable for curved surfaces with variable curvatures.This method is of great significance to the programming of curved surfaces and the processing of high-quality molds.First,a surface topography model of ball-end milling cutter was established with the control of machine acceleration and deceleration.The surface topography model not only has a certain predictive effect on the generation of checkerboard patterns,but also provides surface topography data for subsequent research.Through the CNC programming of the UG software,the cubic spheroidal graphite cast iron is processed into a curved surface using a 3-axis CNC machining center.Find the area where the checkerboard texture appears,and measure the geometric characteristics of the checkerboard texture.Through the measurement of the geometric characteristics of the checkerboard texture,the mechanism of the checkerboard texture is analyzed.The results show that the checkerboard texture is caused by the interpolation line.The sharp angle formed at the joint of the interpolation line and the fluctuation of the feed per tooth will affect the appearance of the checkerboard texture.Secondly,through the surface topography model,the surface statics analysis is carried out.The influence of the checkerboard texture on the surface stress concentration is studied.The results show that when the radius of curvature and central angle are constant,the stress concentration factor increases with the increase of the length of the interpolation line.When the radius of curvature and the length of the interpolation line are constant,the stress concentration factor decreases with the increase of the central angle.When the central angle and the length of the interpolation line are constant,the stress concentration factor decreases with the increase of the radius of curvature.According to the above research.A method for selecting the length of the interpolation line is proposed.This method needs to consider the stress concentration factor.Finally,the proposed new method and the traditional method of selecting the length of the interpolation line are used to process the curved surface with variable curvature.Analyze and compare the surfaces obtained by these two methods.The results show that the new method of selecting the length of the interpolation line takes slightly more time than the traditional method to process the same workpiece.However,the surface roughness after processing by the new method is smaller.The surface checkerboard texture will be less obvious.