Factors affecting surface roughness of workpiece
1.1 Residual area
The area of the uncut portion left by the two cutting edges on the machined surface is called the residual area. The larger the residual area and the higher the height, the greater the surface roughness value.
1.2Built-up edge
After the built-up edge is produced when cutting plastic metals at constant speed, the built-up edge is irregular and unstable. Therefore, on the one hand, the irregular part replaces the cutting edge for cutting, leaving traces of varying depths; on the other hand, part of the The fallen built-up edge is embedded in the machined surface of the workpiece, causing hard points and burrs to form, and the surface roughness value increases.
1.3 Vibration
The periodic vibration of the tool, workpiece or lathe components will cause periodic ripples on the machined surface and the roughness will increase significantly.
Methods to reduce surface roughness of workpiece
If it is found during production that the surface roughness of the workpiece does not meet the technical requirements, you should first observe the phenomenon of increased surface roughness, analyze the causes, find out the main factors affecting the surface roughness, and then propose solutions. Introducing several common phenomena of increased surface roughness and their solutions.
2.1 Increase in surface roughness caused by the height of the residual area
The main declination angle and secondary declination angle of the tool should be reduced (generally reducing the declination angle has a significant effect on reducing surface roughness), increase the tool tip arc radius, and reduce the feed amount.
2.2 Burrs are generated on the surface of the workpiece, causing the surface roughness to increase.
Burrs on the surface of the workpiece are generally caused by built-up edge. At this time, the cutting speed can be changed to inhibit the generation and growth of built-up edge. For example, when using high-speed steel turning tools, the cutting speed should be reduced to less than 5m. /min, and add cutting fluid; when using carbide turning tools, the cutting speed should be increased to avoid the medium speed range (15-30-m/min) where built-up edge is most likely to occur. Therefore, the surface roughness of the front and flank surfaces should be minimized, the tool should be regrinded or replaced in time, and the tool should always be kept sharp.
2.3 Chips rub the surface of the workpiece
The surface of the workpiece with chip wiping usually has irregular and shallow scratches. In this case, a turning tool with a negative blade inclination angle should be used to make the chips flow to the surface of the workpiece to be processed, and chip breaking or chip curling measures should be adopted.
2.4 Vibration causes the surface roughness of the workpiece to increase
The solutions required to increase the surface roughness of the workpiece caused by vibration are as follows:
(1) Adjust the spindle clearance, improve the bearing accuracy, adjust the large, medium and small slide plate plugs to make the clearance less than 0.04mm; (2) Reasonably select the tool geometric parameters, always keep the cutting edge clean and sharp, and increase the installation stiffness of the tool; (3) Increase the installation stiffness of the workpiece. When clamping the workpiece, the overhang should not be too long, and a center frame should be used when clamping a slender shaft; (4) Choose a smaller back engagement amount and feed amount, or reduce the cutting speed.
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2.5 Improve the performance of workpiece materials
The use of heat treatment process to improve the properties of the workpiece material is an effective measure to reduce its surface roughness value. For example, the more uniform the grains of the metal structure of the workpiece material are and the finer the particle size, the smaller the surface roughness value can be obtained during processing. For this reason, normalizing or tempering the workpiece before processing can significantly reduce the roughness value of the processed surface.
2.6 Choose the appropriate cutting fluid
The cooling and lubrication effects of cutting fluid are beneficial to reducing the roughness value of the machined surface. The more direct one is the lubrication effect. When the cutting lubricating fluid contains surface active substances such as sulfur, chlorine and other compounds, the lubrication performance is enhanced, which can make The degree of plastic deformation of the metal material in the cutting area decreases, thereby reducing the roughness value of the machined surface.
2.7 Choose the right tool material
Different tool materials have different chemical compositions, the maintenance of the tool surface hardness and surface roughness during processing, the affinity between the tool material and the metal molecules of the processed material, and the relationship between the front and rear blade surfaces of the tool, the chips and the machined surface. The coefficient of friction, etc. are different.
2.8 Prevent or reduce process system vibration
The low-frequency vibration of the process system generally produces surface waviness on the processed surface of the workpiece, while the high-frequency vibration of the process system will affect the processed surface roughness. In order to reduce the surface roughness value of processing, corresponding measures must be taken to prevent the occurrence of high-frequency vibration during processing.
