Surface roughness is one of the important indicators for evaluating the quality of parts. It is closely related to the matching properties, wear resistance, fatigue strength, contact stiffness, vibration and noise of mechanical parts, and has a great impact on the service life and reliability of mechanical products. have an important impact. The working performance, reliability and life of the product depend to a large extent on the surface quality of the main parts. Therefore, in order to ensure that the processing quality of the parts is qualified, the surface roughness of the workpiece must be inspected.

As for how to measure surface roughness, there are common comparison method and stylus method (contour method), in addition to impression method, interferometry and light section method.

Comparative method

The comparison method is usually used in workshop on-site measurement, mainly for medium or rough surface measurement. The specific method is to compare the measured surface with a roughness sample marked with a certain value to determine the measured surface roughness value.

Stylus method

The stylus method is to use a diamond stylus with a tip curvature radius of about 2 microns to slide slowly along the surface to be measured. The up and down displacement of the diamond stylus is converted into an electrical signal by an electrical length sensor, which is amplified, filtered, and calculated by the display instrument. The surface roughness value is indicated, and the recorder can also be used to record the profile curve of the measured section.

Generally, the measurement tool that can only display the surface roughness value is called a surface roughness measuring instrument, and the one that can record the surface profile curve is called a surface roughness profiler.

These two measurement tools have electronic calculation circuits or electronic computers, which can automatically calculate the arithmetic mean deviation Ra of the contour, the ten-point height Rz of the microscopic unevenness, the maximum height Ry of the contour and other evaluation parameters, with high measurement efficiency and suitable for The surface roughness of Ra is 0.025-6.3 microns is measured.

Impression method

In addition, in actual measurement, deep holes, blind holes, grooves, internal threads, etc. can neither be directly measured by instruments nor compared with samples. At this time, the impression method is commonly used. The impression method is to use some Non-flowing and elastic plastic materials (such as paraffin, etc.) are attached to the surface to be tested. The profile of the surface to be tested is copied into a mold. Then the impression is measured to evaluate the roughness of the surface to be tested.

Intervention

The interference law is to use the principle of light wave interference (see flat crystal, laser length measurement technology) to display the shape error of the measured surface as an interference fringe pattern, and use a microscope with a high magnification (up to 500 times) to visualize the microscopic appearance of these interference fringes. Partially magnified and measured to obtain the measured surface roughness. The surface roughness measurement tool using this method is called an interference microscope. This method is suitable for measuring surface roughness with Rz and Ry ranging from 0.025 to 0.8 microns.

light section method

The light section method is to project the light band formed by the light passing through the slit onto the measured surface, and measure the surface roughness with the contour curve formed by the intersection line between it and the measured surface. After the light emitted by the light source passes through the condenser lens, slit and objective lens 1, the slit is projected onto the measured surface at an inclination angle of 45° to form a cross-sectional profile figure of the measured surface, and then the figure is enlarged by the objective lens 2 and projected onto reticle. Use the micrometer eyepiece and the reading drum (not shown in Figure 1) to read the h value first, and then calculate the H value. The surface roughness measurement tool using this method is called optical section microscope. It is suitable for measuring the surface roughness of RZ and Ry ranging from 0.8 to 100 microns, and it needs to take points manually, and the measurement efficiency is low.

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