1 Introduction With the rapid development of precision, ultra-precision and nano-scale processing technologies, advanced control systems, laser measurement technologies, scanning probe microscopes and other related technologies, research on ultra-precision machining surfaces continues to make new progress, and its machining accuracy is gradually improving. From submicron to nanoscale, it has become possible to obtain ultra-smooth surfaces through superfinishing. However, these ultra-smooth surfaces are usually obtained on the basis of repeated processing and testing. How to obtain a high-quality surface stably and reproducibly, and realize the design function of the surface, is still a difficult point in the research of ultra-precision surface processing. At present, an important research direction for ultra-precision machining of surfaces is to study the formation mechanism of the surface, and according to the different uses of the surface and the corresponding functional requirements, to design and predict the surface before processing, so as to achieve a stable function surface To meet the actual application needs. To this end, a thorough and in-depth study of the processing, characterization, and function of super-precision component surfaces must be conducted. 2 Ultra-precision machining of surfaces and their characteristics The relevant definition of a machined surface is the peripheral surface of an object separated from other objects or spaces. In order to facilitate the research and analysis, the definition of the nominal surface, the actual surface and the measured surface is given in American National Standard ASME B46.1-1995, ie: 1 Nominal surface: The expected surface interface (excluding any surface roughness), Shapes and ranges are usually shown and labeled or detailed in the illustration. 2 Actual surface: The actual boundary surface of the object. The deviation from the nominal surface comes from the surface forming process. 3 Measuring surface: Based on the description of the actual surface obtained by the measuring instrument. Characteristics of the machined surface The difference between the actual surface and the nominal surface of the ultra-precision machining is that it can show surface features, defects, and shape errors. Among them, the surface features are the main contents of controlling the surface quality of industrial products. It is a combination of some typical deviations on the actual surface, mainly including roughness and waviness. Roughness refers to the fine irregularities of the surface characteristics, which are usually derived from the intrinsic effects or material conditions of the machining process. These may be characteristic marks left on the surface during processing. Waviness is a spatial composition with a wider range of surface features, resulting from deviations or vibrations in machine tools or workpieces. Roughness can be considered as a superposition on a fluctuating surface. As a physical entity, the surface has many features. The geometric shape of a surface is one of its important features. Its natural state is three-dimensional (3D), and its characteristic details are called topography. In many applications, the topography represents the main external features of the surface. 3 The processing, characterization and function of the surface of ultra-precision components The workpiece surface is produced in a large number of machining processes. Once the machining process is completed, the surface features reflecting the machining process will be reflected on the surface. Therefore, the surface features of the machining components are the reproduction of the entire machining process. (Fingerprint), any change in processing variables and machining tool errors will be reflected in the surface features. At the same time, these surface features determine the final function of the machined component surface. That is, a specific surface feature produces the corresponding surface function. Therefore, the surface is the link of its process control and function design, and the surface characterization is to obtain the surface information. The important means. It can be seen that the processing, characterization and function of the surface are related to each other: On the one hand, each processing stage and process of surface formation determines the macroscopic and microscopic geometric characteristics of the surface; on the other hand, the geometric characteristics and physics of the surface of the workpiece The chemical properties, etc., to a large extent determine the final function of the product surface. The relationship between surface processing, characterization, and functionality can be illustrated in Figure 1. For specific application functions, the geometric, physical, and chemical properties of the corresponding surface should be considered, and the desired surface design function can only be achieved through appropriate process control and quality control.
Sz—surface ten point height
Ssk - Skewness of surface height distribution
Sku - kurtosis of surface height distribution Sal - fastest decaying autocorrelation function
Sds—surface peak density
Str-surface structure shape ratio
Std—the texture direction of the surface S∆q—the root mean square slope of the surface
Ssc—surface arithmetic mean-vertex curvature
Sdr—surface area ratio of unfolded surface Sbi—surface support index
Sci-Center Liquid Retention Index
The Svi-Liquid retention index is a quantitative analysis of the surface and can also be characterized by MOTIF parameters and fractal functions. The MOTIF parameter characterization uses a full description of the surface roughness and waviness using seven parameters. The method is to decompose the unfiltered contour into a geometric feature characterized by a peak, and the peak of the profile disappears or remains unchanged according to the relative amplitude. Fractal is a continuous but not-differentiable function. In a certain range of observational dimensions, fractals exhibit self-similarity/relevance. Experiments show that many engineering surfaces have fractal features. Fractal function characterization can describe complex geometries using only one surface fractal dimension D (D is a fraction between 2 and 3). The most important feature of 3D analysis is that it can perform intuitive image characterization. The proper image characterization can provide enough surface micro-topography information. The commonly used image characterization methods include contour maps, grayscale maps, and projection maps. The contour map can help to recognize the directional characteristics of the surface. It uses a straight line or curve to connect points with the same height, and uses the linear interpolation method to find the rest of the intersection points, drawing the surface topography accordingly. Each point on the gray scale may represent a gray level that is highly correlated with it. In a projection map, a valid representation of a data point is based on an isometric or frontal projection. Surface functions In engineering applications, the surface of certain components is required to have certain special functional properties, such as high bearing capacity, sealing ability, lubricating oil retention capacity, and the like. In order to achieve these functional requirements, it is necessary to design the functional surface to a special appearance that can produce corresponding functions. The range of surface functions is very wide. For contact elements, common application functions require wear, friction, lubrication, fatigue, sealing, contact stiffness, contact stress, load bearing area, thermal conductivity, etc.; for non-contact components, the commonly used functional requirements are mainly There are optical focal length, reflection, surface protection, surface spraying and so on. There is no well-defined characterization method for surface functions. Some surface parameters can be used to predict the functional properties of the workpiece. For example, since the Rz value of the profile peak height of the roughness is always smaller than the coating thickness, the roughness parameter has the dual function of controlling the quality of the machined surface and ensuring the surface function. Some features of the surface are very important for realizing its special application functions, so sometimes it is necessary to describe the corresponding features of the surface with specially defined functional parameters. For example, the surface bearing index Sbi is used to indicate the bearing performance of the surface, and the Sbi value is large, indicating that the surface bearing performance is good; the central liquid retention index Sci can reflect the property of liquid retention in the central region of the surface, and the Sci value is large, indicating the central area of ​​the surface The liquid retention performance is good; the liquid retention index Svi in ​​the valley region indicates the liquid retention performance in the surface valley region, and the Svi value is large, indicating that the retention ability of the liquid in the surface valley region is strong. However, a set of functional parameters can only describe a limited number of types of application functions. Therefore, it is impossible to use a set of functional parameters to characterize all functional requirements. It is also not practical to establish corresponding functional parameters for each application function. . Since surface characteristic parameters (such as surface roughness) are sensitive to changes in processing and are a key factor in reflecting surface function under contact or flow conditions, they can be used to predict surface functional properties. In addition to surface roughness, physical properties such as geometric parameters, roundness or cylindricity parameters, and residual stresses can also be used to predict surface functional properties. DJ Whitehouse et al. recently proposed a new method to evaluate the functional characteristics of the workpiece surface—functional diagrams. This method attempts to clearly characterize surface functional properties and effectively control surface roughness and other influencing factors during the design phase. Because there is no boundary condition, the traditional surface parameters still apply to the function map. Functional diagrams represent the surface functional properties (it is also the simulation of the process map) graphically rather than literally. It is mainly composed of two Cartesian axes: the axis of ordinates represents the spacing between surfaces, if between surfaces Separated from each other, the interval value is positive; if the surfaces are in contact with each other, the interval value is negative (for example, if the surfaces are elastically or plastically deformed due to mutual embedding, a negative interval value is exhibited). The surface separation characteristics are mainly influenced by the process (especially when the surface spacing is small). The axis of abscissas represents the relative lateral movement between the surfaces. The number and distribution of contact points depends on the local geometry (derived from the profile information), and the relative velocity is affected by the overall shape of the surface and the zone layer (mainly affected by the tool space trajectory). The abscissa also needs to consider the lateral influence factors such as the shear stress and the contact kinetic energy of the surface motion. The scope of application of functional diagrams is not limited to dual surfaces. When the surface separation value is large (relative roughness value), it can be considered as an optically reflective single surface. However, when the function map is used to evaluate the function of the workpiece surface, some of the functional characteristics (such as bearing characteristics, etc.) cannot be expressed. The difficulty in achieving a stable and reproducible quality surface is not only the need to have a thorough and deep understanding of processing conditions, processability, and process control, but also how to make the component surface according to the designer's goals and specific requirements. To achieve the corresponding surface features. Therefore, it is necessary to have an accurate understanding of the surface processing process, surface features, and surface functions so that the desired functional surface can be obtained through continuous monitoring of the process. 4 Conclusion The surface is the link between machining control and function design. The surface features are generated in a large number of machining processes and at the same time determine the final function of the workpiece surface. A thorough understanding of the surface processing, characterization, function, and their interrelationships is the basis for the study of the mechanism of surface formation of ultra-precision components.
Figure 1 Relationship between surface processing, characterization, and function
Sz—surface ten point height
Ssk - Skewness of surface height distribution
Sku - kurtosis of surface height distribution Sal - fastest decaying autocorrelation function
Sds—surface peak density
Str-surface structure shape ratio
Std—the texture direction of the surface S∆q—the root mean square slope of the surface
Ssc—surface arithmetic mean-vertex curvature
Sdr—surface area ratio of unfolded surface Sbi—surface support index
Sci-Center Liquid Retention Index
The Svi-Liquid retention index is a quantitative analysis of the surface and can also be characterized by MOTIF parameters and fractal functions. The MOTIF parameter characterization uses a full description of the surface roughness and waviness using seven parameters. The method is to decompose the unfiltered contour into a geometric feature characterized by a peak, and the peak of the profile disappears or remains unchanged according to the relative amplitude. Fractal is a continuous but not-differentiable function. In a certain range of observational dimensions, fractals exhibit self-similarity/relevance. Experiments show that many engineering surfaces have fractal features. Fractal function characterization can describe complex geometries using only one surface fractal dimension D (D is a fraction between 2 and 3). The most important feature of 3D analysis is that it can perform intuitive image characterization. The proper image characterization can provide enough surface micro-topography information. The commonly used image characterization methods include contour maps, grayscale maps, and projection maps. The contour map can help to recognize the directional characteristics of the surface. It uses a straight line or curve to connect points with the same height, and uses the linear interpolation method to find the rest of the intersection points, drawing the surface topography accordingly. Each point on the gray scale may represent a gray level that is highly correlated with it. In a projection map, a valid representation of a data point is based on an isometric or frontal projection. Surface functions In engineering applications, the surface of certain components is required to have certain special functional properties, such as high bearing capacity, sealing ability, lubricating oil retention capacity, and the like. In order to achieve these functional requirements, it is necessary to design the functional surface to a special appearance that can produce corresponding functions. The range of surface functions is very wide. For contact elements, common application functions require wear, friction, lubrication, fatigue, sealing, contact stiffness, contact stress, load bearing area, thermal conductivity, etc.; for non-contact components, the commonly used functional requirements are mainly There are optical focal length, reflection, surface protection, surface spraying and so on. There is no well-defined characterization method for surface functions. Some surface parameters can be used to predict the functional properties of the workpiece. For example, since the Rz value of the profile peak height of the roughness is always smaller than the coating thickness, the roughness parameter has the dual function of controlling the quality of the machined surface and ensuring the surface function. Some features of the surface are very important for realizing its special application functions, so sometimes it is necessary to describe the corresponding features of the surface with specially defined functional parameters. For example, the surface bearing index Sbi is used to indicate the bearing performance of the surface, and the Sbi value is large, indicating that the surface bearing performance is good; the central liquid retention index Sci can reflect the property of liquid retention in the central region of the surface, and the Sci value is large, indicating the central area of ​​the surface The liquid retention performance is good; the liquid retention index Svi in ​​the valley region indicates the liquid retention performance in the surface valley region, and the Svi value is large, indicating that the retention ability of the liquid in the surface valley region is strong. However, a set of functional parameters can only describe a limited number of types of application functions. Therefore, it is impossible to use a set of functional parameters to characterize all functional requirements. It is also not practical to establish corresponding functional parameters for each application function. . Since surface characteristic parameters (such as surface roughness) are sensitive to changes in processing and are a key factor in reflecting surface function under contact or flow conditions, they can be used to predict surface functional properties. In addition to surface roughness, physical properties such as geometric parameters, roundness or cylindricity parameters, and residual stresses can also be used to predict surface functional properties. DJ Whitehouse et al. recently proposed a new method to evaluate the functional characteristics of the workpiece surface—functional diagrams. This method attempts to clearly characterize surface functional properties and effectively control surface roughness and other influencing factors during the design phase. Because there is no boundary condition, the traditional surface parameters still apply to the function map. Functional diagrams represent the surface functional properties (it is also the simulation of the process map) graphically rather than literally. It is mainly composed of two Cartesian axes: the axis of ordinates represents the spacing between surfaces, if between surfaces Separated from each other, the interval value is positive; if the surfaces are in contact with each other, the interval value is negative (for example, if the surfaces are elastically or plastically deformed due to mutual embedding, a negative interval value is exhibited). The surface separation characteristics are mainly influenced by the process (especially when the surface spacing is small). The axis of abscissas represents the relative lateral movement between the surfaces. The number and distribution of contact points depends on the local geometry (derived from the profile information), and the relative velocity is affected by the overall shape of the surface and the zone layer (mainly affected by the tool space trajectory). The abscissa also needs to consider the lateral influence factors such as the shear stress and the contact kinetic energy of the surface motion. The scope of application of functional diagrams is not limited to dual surfaces. When the surface separation value is large (relative roughness value), it can be considered as an optically reflective single surface. However, when the function map is used to evaluate the function of the workpiece surface, some of the functional characteristics (such as bearing characteristics, etc.) cannot be expressed. The difficulty in achieving a stable and reproducible quality surface is not only the need to have a thorough and deep understanding of processing conditions, processability, and process control, but also how to make the component surface according to the designer's goals and specific requirements. To achieve the corresponding surface features. Therefore, it is necessary to have an accurate understanding of the surface processing process, surface features, and surface functions so that the desired functional surface can be obtained through continuous monitoring of the process. 4 Conclusion The surface is the link between machining control and function design. The surface features are generated in a large number of machining processes and at the same time determine the final function of the workpiece surface. A thorough understanding of the surface processing, characterization, function, and their interrelationships is the basis for the study of the mechanism of surface formation of ultra-precision components.
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