Surface roughness inspection
Surface roughness, defined as the unevenness of a part’s surface, with its small peaks and valleys, is a key indicator of surface quality. Surface roughness significantly impacts part performance, such as fit, wear resistance, sealing, and corrosion resistance. Therefore, accurate surface roughness testing is crucial for ensuring product quality. Surface roughness testing methods vary, and different methods are suitable for different applications and requirements, requiring careful consideration.
The comparison method is a simple and intuitive surface roughness testing method. It compares the surface of the part being tested with a standard sample with known roughness parameters, and determines the surface roughness level by visual inspection or feel. The comparison method is easy to use and does not require complex instrumentation, making it suitable for rapid inspections on-site. The standard sample is typically made of the same material and processed using the same method as the part being tested, resulting in high accuracy and reliability. When using the comparison method, attention should be paid to lighting conditions to avoid inaccuracies caused by excessively strong or weak light. Furthermore, the inspector should possess sufficient experience and skills to ensure the reliability of the test results. While simple and easy to use, the comparison method suffers from low accuracy and is therefore suitable for applications where surface roughness requirements are less stringent.
The light section method uses the principle of light sectioning to measure surface roughness. Using a microscope, a beam of parallel light is projected onto the surface being measured. The light is reflected by the peaks and valleys of the surface, forming alternating light and dark fringes. By measuring the width and height of the fringes, surface roughness parameters can be calculated. The light section method is suitable for measuring surface roughness with medium precision, generally ranging from Ra0.8 to Ra6.3μm. The light section method offers high accuracy, is relatively simple to operate, and can directly measure the actual surface roughness profile, making it a commonly used surface roughness inspection method. When using the light section method, care should be taken to adjust the microscope’s focal length and light source intensity to obtain a clear fringe image. Furthermore, the appropriate measurement direction and position should be selected to ensure representative results.
Interferometry is a method of measuring surface roughness using the principle of light interference. It splits a beam of light into two beams, one of which is projected onto the surface being measured, and the other onto a standard reflective surface. When the two reflected beams meet, interference fringes are generated. By measuring the shape and spacing of the interference fringes, the surface roughness parameters can be calculated. The interferometry method has very high measurement accuracy and is suitable for measuring high-precision surface roughness. The measurement range is generally Ra0.025~Ra0.8μm. The interferometry method can measure the microscopic profile of surface roughness and is an advanced surface roughness inspection method. However, the interferometry method has high requirements for the measurement environment and needs to be carried out in a constant temperature, constant humidity, and vibration-free environment. The instruments and equipment are expensive and complex to operate. It is only suitable for laboratories or the inspection of high-precision parts.
The stylus method is a contact measurement method for obtaining surface roughness parameters. It uses a diamond stylus to glide across the surface being measured, converting microscopic surface fluctuations into electrical signals. After processing, the surface roughness parameters are obtained. The stylus method is suitable for measuring various types of surface roughness, with a wide measurement range, from Ra 0.025μm to Ra 100μm. The stylus method offers high measurement accuracy and can accurately measure various surface roughness parameters such as Ra, Rz, and Ry. The stylus method is simple to operate, and the instrumentation is relatively inexpensive, making it suitable for both on-site inspections in the workshop and in the laboratory. When using the stylus method, careful attention should be paid to the stylus pressure and sliding speed to avoid damage to the surface being measured or loss of measurement accuracy due to excessive pressure or high speed. The stylus should also be calibrated and replaced regularly to ensure accurate measurement results.
With the development of science and technology, surface roughness inspection technology is also constantly improving. In recent years, non-contact measurement methods such as laser scanning and optical profilometry have gradually been applied. These methods have the advantages of fast measurement speed, high accuracy, and no damage to the measured surface. They are suitable for surface roughness inspection of parts with complex shapes and large parts. The laser scanning method scans the measured surface with a laser beam and uses the intensity change of the reflected light to obtain the microscopic contour information of the surface; the optical profilometry method uses an optical system to image the measured surface and uses image processing technology to calculate the surface roughness parameters. Non-contact measurement methods provide a new means for surface roughness inspection, improving inspection efficiency and quality. In the future, with the continuous development of computer technology and image processing technology, surface roughness inspection technology will develop in the direction of automation, intelligence, and high precision, providing a stronger guarantee for product quality control.
