May 22, 2017
The size of the extrusion allowance determines the magnitude of the required extrusion force, and the magnitude of the extrusion force has a direct bearing on the extrusion effect.If the extrusion allowance is too large, the extrusion knife will wear rapidly, resulting in a lower surface quality; if the extrusion allowance is too small,it will not meet the expected processing goal. Therefore, the minimum extrusion allowance should be chosen as long as the extrusion accuracy is guaranteed. Generally, when extruding carbon steel and alloy steel material, the extrusion allowance can be selected from 0.025 to 0.04mm, and 0.03 to 0.05mm should be selected when squeezing the cast iron. When the workpiece material is soft (such as non-ferrous metal) can choose larger extrusion margin; workpiece size is small, should choose smaller extrusion margin, in order to prevent overall deformation. As the extrusion allowance is affected by extrusion, surface hardness, surface roughness of workpiece before extrusion and workpiece wall thickness, it is better to test extrusion before machining to determine the optimum extrusion parameters. High speed extrusion finishing can make extrusion cutter and workpiece surface contact zone temperature, workpiece surface yield strength decreased, the workpiece is easy to deformation and lower surface wave in the trough, thus improving the surface roughness of the workpiece. But if the extrusion speed is too high, it will destroy the lubricating oil film, which will easily cause burns or scratches on the surface of the workpiece. Therefore, there exists an optimum speed of light absorption (which can be obtained by experiment). When processing ferrous metal, the extrusion speed can be selected between 0.5 and 1m/ s, and the amount of the knife can be selected between 0.01 and 0.03mm/r. The bigger value is taken when machining the excircle, and the smaller value is selected when machining the inner hole. The following problems should be paid attention to in extrusion processfor carbide turning tools:
The working parts shall be the straight line of 3 to 5mm on the extrusion edge, and the tungsten carbide turning tools should be squeezed about 1mm higher than the center. Extrusion process should be adjusted according to the various phenomena produced by the workpiece surface. Such as the workpiece surface pitting or scratches, extrusion showed that blade surface roughness, burnishing speed; the surface peeling phenomenon indicates that the large amount of repeated extrusion, extrusion or workpiece material ductility. Lubrication and cooling in extrusion process are very important. Before extrusion workpiece surface does not allow the existence of rust, oil, iron, dust, lubricating and cooling fluid should be injected into the full extrusion process, to take the heat generated in the extrusion, prolong the service life of extrusion knife. Usually, the mixture of oleic acid and kerosene can be used to squeeze the cast iron. When it is used to squeeze carbon steel and alloy steel, oil can be used as a cooling lubricant.
The extrusion test and the processing practice show that the cold extrusion finishing of the workpiece with carbide turning toolson the surface has the advantages of reliable quality, simple operation, economical and practical, high efficiency and low cost. Before extrusion workpiece surface roughness is Ra3.2 ~ 1.6 m after extrusion surface roughness is Ra0.8 ~ 0.2 m, improve the rate of up to 70% ~ 90%; by extrusion can also reduce the size of the workpiece diameter tolerances; extruding after burnishing hardening layer of workpiece is 3mm, which can greatly improve the fatigue strength of the workpiece and anti corrosion ability. If the extrusion knife is mounted on a vertical lathe, extrusion of the oversize workpiece beyond the grinding range of the grinding machine can be carried out. The extrusion processing method has wide application range, and can be used for processing ferrous metal materials and processing non-ferrous metal materials.
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