Lathe turning is a type of lathe processing, and lathe machining is a part of the machining process.
The turning machine primarily uses a turning tool to shape a rotating workpiece. Additionally, other tools such as drills, reamers, taps, threading dies, and knurling tools can also be used on the lathe for machining purposes.
Lathes are commonly utilized to machine shafts, discs, sleeves, and other workpieces with a rotating surface.
This type of machine tool is the most widely used in machinery manufacturing and repair facilities.
Working principle
Turning is a machining process that involves rotating a workpiece while a turning tool moves in a straight or curved path along the surface of the workpiece. The process is usually carried out on a lathe, which is one of the most widely used machine tools in the manufacturing and repair of machinery.
Turning can be used to produce a variety of shapes and finishes on the workpiece, including inner and outer cylindrical faces, end faces, conical faces, forming faces, and threads. The turning tool moves parallel to the axis of rotation of the workpiece when machining cylindrical faces, and moves horizontally in a direction perpendicular to the axis of rotation when machining end faces or cutting the workpiece. When the trajectory of the turning tool is at an oblique angle to the axis of rotation, a conical surface can be machined.
The speed of the workpiece is controlled by the spindle of the machine tool, while the tool is held by a tool holder and moves in a feed direction. The cutting speed is determined by the linear velocity at the point of contact between the rotating workpiece and the turning tool. The depth of cut is the vertical distance between the surface being machined and the machined surface, while the feed amount is the amount of displacement of the turning tool in the feed direction per revolution of the workpiece.
The cutting speed for different materials and cutting tools can vary widely. For example, when cutting ordinary steel with high-speed steel turning tools, the cutting speed is typically between 25-60 m/min. With cemented carbide turning tools, the cutting speed can reach 80-200 m/min, and with coated hard-metal turning tools, it can be as high as 300 m/min or more.
Turning is usually divided into two categories: rough turning and finishing (including semi-finishing).
Rough turning aims to increase the efficiency of turning by using a large cutting depth and high feed rate while maintaining the cutting speed, but the accuracy of machining is limited to IT11 and the surface roughness is Rα 20-10 μm.
Finishing and semi-finishing turning use high speed and as small feed and cutting depth as possible to achieve high accuracy of machining. The accuracy of machining can reach IT10-7 and the surface roughness is Rα10-0.16μm.
High-precision metal parts can achieve a high level of precision with the use of high-precision diamond turning tools on high-precision lathes. The machining accuracy can reach IT7-5 and the surface roughness is Rα0.04-0.01μm. This type of turning is known as “mirror turning”.
If the cutting edge of the diamond turning tool is polished with a concave and convex shape of 0.1-0.2 μm, the surface of the turning will have extremely fine and irregular stripes that have a damask-like luster under the diffraction of light. This decorative surface is known as “rainbow turning”.
In turning machining, if the turning tool rotates at the same time, the turning speed of the tool (which is generally several times the speed of the workpiece) rotates in the same direction as the workpiece, allowing the relative movement trajectory of the turning tool and the workpiece with a polygonal cross section (such as triangle, square, prism, hexagon, etc.) to be processed.
By adding a longitudinal radial reciprocating motion to the tool holder for each revolution of the tool while the turning tool is fed in the longitudinal direction, the surface of a cam or other non-circular cross section can be machined.
On the shaper lathe, the flank of some multi-tooth tools, such as forming cutters and gear hobs, can be machined using a similar working principle, known as “shaping back”.
