1. Surface roughness theory
The proposal and development of surface roughness standards are closely related to the development of industrial production technology. It has gone through two stages from qualitative assessment to quantitative assessment. The effect of surface roughness on the surface performance of machine parts has been the first to be noticed since 1918. In the design of aircraft and aircraft engines, due to the requirement of using the least material to achieve maximum strength, people began to treat the surface of the tool marks and scratches on the fatigue strength Study the impact. However, due to the difficulty of measurement, there was no quantitative evaluation requirement at that time, which was only determined based on visual perception. In the 1920s and 30s of the 20th century, many industrial countries in the world widely used a combination of triangular symbols (â–½) to represent processed surfaces with different precisions.
In order to study the effect of surface roughness on the performance of parts and the need to measure the microscopic unevenness of the surface, from the late 1920s to the 1930s, some experts in Germany, the United States and the United Kingdom designed and produced profile recorders and profilers, which also produced Instruments such as light-cutting microscopes and interference microscopes are used to measure the microscopic unevenness of the surface by optical methods, which creates conditions for quantitatively evaluating the surface roughness numerically. Since the 1930s, quantitative evaluation parameters for surface roughness have been studied. For example, Abbott in the United States has proposed to use the depth from the surface profile peak and the support length rate curve to characterize the surface roughness. In 1936, Schmaltz published a monograph on surface roughness, and proposed suggestions for the standardization of surface roughness evaluation parameters and values. However, the use of roughness evaluation parameters and their values ​​has truly become a widely accepted standard since the corresponding national standards of various countries were released in the 1940s.
The first is that the United States issued the ASAB46.1 national standard in 1940, after which it has been revised several times to become the current standard ANSI / ASMEB46.1-1988 "Surface Structure Surface Roughness, Surface Waviness, and Processed Texture", which uses a midline System, and Ra as the main parameter; then the former Soviet Union issued the national standard GOCT2789-1945 "Surface Finish, Surface Microgeometry, Grading and Representation" in 1945, and after 3 revisions became GOCT2789-1973 "Surface Roughness" Degree parameters and characteristics ", the standard also uses the midline system, and specifies six evaluation parameters including the root mean square deviation of the profile (now Rq) and their corresponding parameter values. In addition, most of the standards of other industrially developed countries were formulated in the 1950s. For example, the Federal Republic of Germany issued DIN4760 and DIN4762 standards for surface roughness evaluation parameters and terms in February 1952.
The national standards of the above countries all use the midline as the calculation system for the surface roughness parameters. The specific parameters vary widely, but the main parameter defined is still Ra (or Rq), which is also the most widely used international exchange. parameter.
2. Definition of basic parameters in surface roughness standards
With the development of industry and the need for opening to the outside world and technical cooperation, China's research and standardization of surface roughness is increasingly valued by the scientific and technological and industrial circles. And to achieve the role of international unification, China equivalently adopts the international standards of the International Organization for Standardization (ISO) to formulate GB3505-1983 "Surface Roughness Surface and Its Parameters". GB3505 specifically stipulates terms related to surface roughness and its parameters, among which there are three parts with a total of 27 parameter terms: a. Surface roughness parameter terms related to microscopic unevenness height characteristics. The commonly used terms defined in it are: 11 parameters such as the arithmetic mean deviation Ra of the contour, the root mean square deviation Rq of the contour, the maximum height Ry of the contour and the ten-point height Rz of micro unevenness. b. Terminology of surface roughness parameters related to the microscopic unevenness spacing characteristics. There are a total of 9 parameters including the average spacing Sm of the contour micro-unevenness, the peak density D of the contour, the root mean square wavelength lq of the contour, and the average single-peak spacing S of the contour. c. Terminology of surface roughness parameters related to the shape characteristics of micro unevenness. There are 5 parameters including contour skewness Sk, contour root mean square slope Dq and contour support length ratio tp.
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