The working principle of turning

The workpiece rotates, and the turning tool performs cutting processing with linear or curved movement in the plane. Turning is generally carried out on a lathe to process the inner and outer cylindrical surfaces, end surfaces, conical surfaces, forming surfaces and threads of the workpiece.

When turning the inner and outer cylindrical surfaces, the turning tool moves in a direction parallel to the axis of rotation of the workpiece. When turning the end face or cutting the workpiece, the turning tool moves horizontally in the direction perpendicular to the axis of rotation of the workpiece. If the moving track of the turning tool is at an oblique angle to the axis of rotation of the workpiece, a conical surface can be machined. The surface of the turning body formed by turning can adopt the forming tool method or the tool tip trajectory method. During turning, the workpiece is driven by the main shaft of the machine tool to rotate for the main movement; the turning tool clamped on the tool holder is for the feed movement. Cutting speed v is the linear speed (m/min) at the point of contact between the machined surface of the rotating workpiece and the turning tool; the depth of cut is the vertical distance (mm) between the machined surface and the machined surface of the workpiece during each cutting stroke. When cutting and forming turning, it is the contact length (mm) between the turning tool and the workpiece perpendicular to the feed direction. The feed represents the displacement (mm/revolution) of the turning tool in the feed direction per revolution of the workpiece, and it can also be expressed as the feed per minute (mm/min) of the turning tool. When turning ordinary steel with a high-speed steel turning tool, the cutting speed is generally 25-60 m/min, and the hard alloy turning tool can reach 80-200 m/min; the maximum cutting speed can reach 300 when the coated carbide turning tool is used. M/min or more.

Turning is generally divided into rough turning and finishing turning (including semi-finishing turning). Rough turning strives to use large cutting depth and large feed rate to improve turning efficiency without reducing the cutting speed, but the machining accuracy can only reach IT11, and the surface roughness is Rα20-10 microns; semi-finished turning and finishing turning Try to use high-speed and small feed and cutting depth, the machining accuracy can reach IT10~7, and the surface roughness is Rα10~0.16 microns. High-speed precision turning of non-ferrous metal parts with a finely-refined diamond turning tool on a high-precision lathe can make the machining accuracy reach IT7~5, and the surface roughness is Rα0.04~0.01 microns. This kind of turning is called "mirror turning". If the concave and convex shapes of 0.1 to 0.2 microns are re-ground on the cutting edge of the diamond turning tool, the surface of the turning will produce very small irregularities and neatly arranged stripes, which will show a brocade-like luster under the action of light diffraction. As a decorative surface, this kind of turning is called "Rainbow Turning".

During turning, if the turning tool rotates in the same direction with the workpiece at the corresponding speed ratio (the tool speed is generally several times the workpiece speed) while the workpiece is rotating, the relative motion trajectory of the turning tool and the workpiece can be changed. Workpieces with polygonal cross-sections (triangular, square, prismatic, hexagonal, etc.). If you add a periodic radial reciprocating motion to the tool holder for each revolution of the workpiece while the turning tool is longitudinally feeding, you can machine the surface of cams or other non-circular cross-sections. On a tooth shovel lathe, the flank face of certain multi-tooth tools (such as forming milling cutters, gear hobs) can be processed according to a similar working principle, which is called "shovel back".

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