Under certain processing conditions, corresponding surface features can be formed. If the machining control parameters (cutting speed, feed rate, depth of cut, etc.) are changed, the corresponding geometrical shape changes will inevitably occur. Due to many random factors such as vibration, thermal instability, processing environment changes, etc., some uncertain factors appear in the process control and surface formation, which hinders the engineering technicians to obtain the ideal surface by precisely controlling the processing conditions. Based on the analysis of machine tool kinematics and cutting theory, appropriate reasonable assumptions are made, and the relationship between machining control parameters and surface feature characterization parameters is modeled by mathematical transformation to realize surface quality before machining. It is an ultra-precision machining surface research. An important direction.
Surface characterization
As a link between process control and functional design, surface characterization provides valuable morphological and characterization information, so it is a key issue in surface research. There are many existing surface characterization methods, such as statistical analysis, spectral analysis, autocorrelation analysis, time series analysis, fractal and function description. But no matter what kind of technology is adopted, from the engineering point of view, the characterization of the surface topography is ultimately characterized by relevant parameters and supplemented by general vision technology, that is, the surface topography is based on visual image and surface parameter values. Conduct an evaluation.Due to the inherent three-dimensional state of the surface topography, it is difficult to provide sufficient and reliable information for analysis using two-dimensional parameters and contour maps, so 3D parameters and 3D images have become practical methods for evaluating surface topography. The 3D parameters characterize and quantify the microscopic geometry of the surface, and the 3D data is obtained by the meter. Visual and image processing techniques provide an intuitive, realistic description of the surface. Images can convey a large amount of easily interpretable information and are an effective way to characterize surfaces. Since a single parameter is difficult to fully describe a complex actual surface, it is necessary to use a comprehensive set of parameters for parameter characterization, each of which can only provide certain specific features of the microscopic geometry, which can be measured and quantified. Due to the complexity and comprehensiveness of the three-dimensional shape information of the engineering surface, it is difficult to fully describe the three-dimensional surface features with only a few parameters. KJ Stout et al. proposed to divide the parameters into four categories (a total of 14 parameters) according to different characterization characteristics. The categories and definitions of each parameter are shown in Table 2.
| Amplitude parameter | Spatial parameter | Comprehensive parameter | Function parameter |
|---|---|---|---|
| S q — root mean square deviation of surface topography S z — surface height of ten points S sk — the skewness of the surface height distribution S ku — the kurtosis of the surface height distribution | S al — the fastest decay autocorrelation function S ds — surface peak density S tr — the structural shape ratio of the surface S td — the texture direction of the surface | S ∆q — the root mean square slope of the surface S sc — surface arithmetic mean vertex curvature S dr — surface expansion interface area ratio | S bi — surface support index S ci — central liquid retention index S vi — Valley liquid retention index |
The most important feature of 3D analysis is that it can perform intuitive image characterization, and proper image characterization can give enough surface topography information. Commonly used image representation methods include contour maps, gray scale maps, and projection maps. The contour map helps to identify the directional characteristics of the surface. It uses straight lines or curves to connect points with the same height, and uses linear interpolation to find the remaining intersections, and draws the surface topography. Each point on the grayscale image can represent a gray level associated with its height. In the projected image, the effective representation of the data points is based on an isometric or frontal projection.
Surface functionIn engineering applications, the surface of certain components is required to have certain special functional properties, such as high support capacity, sealing ability, lubricating oil retention capacity, and the like. To achieve these functional requirements, the functional surface needs to be designed to produce a special shape for the corresponding function. The range of surface functions is very wide. For contact components, common application functions require wear, friction, lubrication, fatigue, sealing, contact stiffness, contact stress, bearing area, thermal conductivity, etc. For non-contact components, common functional requirements are mainly Optical focus, reflection, surface protection, surface coating, etc.
At present, there is no clear characterization method for surface function. Some surface parameters can be used to predict the functional characteristics of the workpiece. For example, since the height of the profile peak roughness R z value is always less than the thickness of the coating, thus having the dual role of controlling the roughness parameters of the surface quality and ensure that the surface functions. Certain features of the surface are important to achieve their particular application function, so it is sometimes necessary to describe the corresponding features of the surface with specially defined functional parameters. For example, the surface support index S bi is used to indicate the support performance of the surface, and the S bi value is large, indicating that the surface support performance is good; the central liquid retention index S ci can reflect the liquid retention property in the central region of the surface, and the S ci value is large, indicating The liquid retention property in the central region of the surface is good; the liquid retention index S vi in the valley region indicates the liquid retention property in the surface valley region, and the S vi value is large, indicating that the liquid retention property in the surface valley region is strong. However, a set of functional parameters can only describe a limited number of application functions, so it is impossible to use a set of functional parameters to characterize all functional requirements, and it is unrealistic to establish corresponding functional parameters for each application function. . Since surface characteristic parameters (such as surface roughness) are sensitive to changes in processing and it is a key factor in reflecting surface function under contact or flow conditions, it can be used to predict surface functional properties. In addition to surface roughness, physical properties such as geometrical parameters, roundness or cylindricity parameters, and residual stress can also be used to predict surface functional properties.DJ Whitehouse et al. recently proposed a new method for evaluating the functional properties of workpiece surfaces - functional diagrams. The method attempts to clearly characterize the surface functional properties and effectively control the influence factors such as surface roughness during the design phase. Since there are no boundaries, traditional surface parameters still apply to the function diagram. The function diagram is a graphical representation of the surface functional properties (which is also a simulation of the machining diagram) in a graphical rather than a textual manner. It consists mainly of two Cartesian axes: the ordinate axis represents the spacing between surfaces, if between surfaces When they are 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, they are represented as negative interval values). Surface spacing characteristics are primarily affected by the processing (especially when the surface spacing is small). The abscissa axis represents the relative lateral movement between the surfaces. The number and distribution of contact points depends on the local geometry (derived from the contour information), while the relative velocity is affected by the overall shape of the surface and the regional layer (mainly affected by the tool space trajectory). The horizontal axis also needs to consider the lateral influence factors such as shear stress and contact kinetic energy of surface motion. The application range of the function diagram is not limited to the double surface. When the surface spacing value is large (relative roughness value), it can be considered as an optically reflective single surface. However, when using the function chart to evaluate the surface function of the workpiece, some functional characteristics (such as load characteristics) cannot be expressed.
Achieving a stable, repeatable, high-quality surface is not only due to the need for a comprehensive and deep understanding of processing conditions, processability, and process control, but also how to make the surface of the component according to the designer's goals and specific requirements. Achieve the corresponding surface function. Therefore, it is necessary to have an accurate understanding and mastery of the surface processing, surface features and surface functions, so as to obtain the desired functional surface by continuous monitoring of the machining process.4 Conclusion
The surface is the connection between the machining control and the functional design. The surface features are generated by a large number of machining processes and at the same time determine the final function of the workpiece surface. A comprehensive understanding of the surface processing, characterization, function and their relationship is the basis for the study of the surface formation mechanism of ultra-precision components.Previous page
Steel bends and steel elbows are both very common pipe fittings which are used to change the flowing direction in a piping systems. In addition to pipe fittings for connecting , elbow pipe also refers to a processing method. It is to Bend the straight pipe through the processing method to achieve the purpose of changing the circulation direction of the pipeline. The manufacturing process and the finished product are called pipe bend.
In order to ensure that the wall thickness of the bending part is no less than that of the straight pipe part, the minimum radius of the pipe bending should be 3D( the D means nominal diameter of this bend). The specific size depends on the operating conditions. That is to say, radius is not restricted as long as it exceeds 3D, which can be 3D or 3.2D, even 4D, 5D, 6D and 8D are also acceptable. In addition, the angle of the bend can be in any degree, some times there are also custom-designed bends which are 22.5 °, 45 °, 90 °, 135 °, 180 °, 270 ° and so on.
ASTM A105,A234 WPB,Pipe Fitting Bend
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