Turning cutting is lathe processing and lathe machining is part of machining. The Turning cutting machine mainly uses a Turning cutting tool to turn the rotating workpiece. On the lathe, drills, reamer, reamer, taps, dies and knurling tools can also be used for machining. Lathes are mainly used for machining shafts, discs, sleeves and other workpieces with a rotating surface. They are the most widely used type of machine tool in machine building and repair plants.
1. The working principle of Turning cutting
The workpiece is rotated, and the Turning cutting tool performs a straight or curved movement in the plane. Turning cutting is generally carried out on a lathe to machine the inner and outer cylindrical faces, end faces, conical faces, forming faces and threads of the workpiece.
When Turning cutting the inner and outer cylindrical faces, the Turning cutting tool moves in a direction parallel to the axis of rotation of the workpiece.
When Turning cutting the end face or cutting the workpiece, the Turning cutting tool moves horizontally in a direction perpendicular to the axis of rotation of the workpiece. If the trajectory of the Turning cutting tool is at an oblique angle to the axis of rotation of the workpiece, the conical surface can be machined. For the surface of the Turning cutting body formed by Turning cutting, a forming tool method or a tool tip trajectory method may be employed.
During Turning cutting, the workpiece is driven by the spindle of the machine tool for rotation; the tool held by the tool holder is used for feeding motion. The cutting speed v is the linear velocity (m/min) at the point of contact between the rotating workpiece machining surface and the Turning cutting tool; the cutting depth is the vertical distance (mm) between the workpiece to be machined surface and the machined surface for each cutting stroke, but The cutting and forming Turning cutting is the contact length (mm) of the Turning cutting tool perpendicular to the feeding direction.
The feed amount indicates the amount of displacement (mm/rev) of the Turning cutting tool in the feed direction per revolution of the workpiece, and can also be expressed by the feed per minute (mm/min) of the Turning cutting tool. When Turning cutting ordinary steel with high-speed steel Turning cutting tools, the cutting speed is generally 25-60 m/min, the carbide Turning cutting tool can reach 80-200 m/min; the highest cutting speed can reach 300 when using coated carbide Turning cutting tools. M/min or more.
Turning cutting is generally divided into two types: roughing and finishing (including semi-finishing). The rough car strives to increase the Turning cutting efficiency with a large cutting depth and large feed without reducing the cutting speed, but the machining accuracy can only reach IT11, the surface roughness is Rα20～10 microns; semi-finished and refined Try to use high speed and small feed rate and cutting depth, the processing precision can reach IT10~7, and the surface roughness is Rα10～0.16μ. High-precision fine-grained metal parts with high-precision diamond Turning cutting tools on high-precision lathes can achieve machining accuracy of IT7~5 and surface roughness of Rα0.04~0.01 microns. This Turning cutting is called "mirror Turning cutting".
If the concave and convex shape of 0.1 to 0.2 μm is repaired on the cutting edge of the diamond Turning cutting tool, the surface of the Turning cutting will produce extremely fine and irregularly arranged stripes, which will have a brocade-like luster under the diffraction of light. As a decorative surface, this Turning cutting is called "rain plane Turning cutting".
During Turning cutting machining, if the Turning cutting tool rotates at the same time and the corresponding speed ratio (the tool speed is generally several times the workpiece speed) rotates in the same direction as the workpiece, the relative movement trajectory of the Turning cutting tool and the workpiece can be changed and processed.
A workpiece whose cross section is a polygon (triangle, square, prism, hexagon, etc.). If a longitudinal radial reciprocating motion is added to the tool holder for each revolution of the tool while the longitudinal direction of the Turning cutting tool is being fed, the surface of the cam or other non-circular cross section can be machined. On the shovel lathe, the flank of some multi-tooth tools (such as forming cutters and gear hobs) can be machined according to a similar working principle, called "shovel back".
2. Processing method
(1) Rough Turning cutting is the most economical and effective method for roughing rough. Since the purpose of roughing is mainly to quickly remove excess metal from the blank, increasing productivity is its main task.
Rough cars typically use the largest amount of back-feeding and feed to increase productivity. In order to ensure the necessary tool life, the cutting speed is usually low. When roughing, the Turning cutting tool should select a larger lead angle to reduce the back force and prevent the bending deformation and vibration of the workpiece; select the smaller rake angle, back angle and negative edge angle to enhance the Turning cutting tool. The strength of the cutting portion. The machining accuracy that can be achieved by roughing is IT12 to IT11, and the surface roughness Ra is 50 to 12.5 μm.
(2) The main task of the fine car finishing car is to ensure the machining accuracy and surface quality required by the parts.
The outer surface of the finishing car is generally processed with a small amount of backing knife and feed and a high cutting speed. When machining the outer circumference of large shaft parts, the wide-blade Turning cuttingtool is often used. When Turning cutting the car, the cutter should use a larger rake angle, a back angle and a positive knife inclination to improve the surface quality. The finishing car can be used as a final machining of a higher precision outer circle or as a pre-processing of fine machining. The finishing precision of the finishing car can reach IT8~IT6, and the surface roughness Ra can reach 1.6~0.8μm.
(3) The characteristics of the fine car fine car are: the value of the back-feeding knife and the feed amount are extremely small, and the cutting speed is as high as 150-2000 m/min. Fine cars are generally processed with super-hard material tools such as cubic boron nitride (CBN) and diamond. The machine tools used must also be high-precision or precision machine tools with high-speed rotation and high rigidity. The precision and surface roughness of the fine car are roughly equivalent to ordinary cylindrical grinding. The machining accuracy can reach above IT6, and the surface roughness Ra can reach 0.4~0.005μm. It is often used for precision machining of non-ferrous metal workpieces with poor grinding workability. For aluminum and aluminum alloy workpieces that easily block the pores of the grinding wheel, fine cars are more effective. When machining large precision outer surfaces, fine cars can replace grinding.
3. Practical application
Different Turning cutting tools or other tools can be used on the lathe to process various rotary surfaces, such as inner and outer cylindrical surfaces, inner and outer conical surfaces, threads, groove Turning cutting grooves, end faces and forming surfaces, etc.
The machining precision can reach IT8-IT7, surface roughness. The Ra value is 1.6 to 0.8, and Turning cutting is often used to machine parts with a single axis, such as straight shafts and general discs, sleeve parts, and the like. Multi-axis parts (such as crankshafts, eccentrics, etc.) or disc cams can be machined if the position of the workpiece is changed or the lathe is properly modified. In the single-piece small batch production, various shafts, discs, sleeves and other parts are mostly processed by a wide-format horizontal lathe or CNC lathe; large parts with large diameter and short length (length to diameter ratio of 0.3 to 0.8) are used. Vertical lathe processing.
When the batch production is more complicated, and the small and medium-sized shafts and sleeve parts with inner holes and threads are used, the turret lathe should be used for processing. Large quantities and large quantities of small parts with less complicated shapes, such as screws, nuts, pipe joints, bushings, etc., are often processed using semi-automatic and automatic lathes. It has high productivity but low precision.